Patent Publication Number: US-2023163696-A1

Title: Coupled Inductors Inverter Topology

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of and claims priority to U.S. patent application Ser. No. 17/148,322, filed Jan. 13, 2021, which is a non-provisional of and claims priority to U.S. Provisional Patent Application No. 62/961,377, filed Jan. 15, 2020, each of which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     A multilevel inverter is a power electronic device that is capable of providing a desired alternating current (AC) voltage level at its output. The desired AC voltage output is output by conversion of one or more input direct current (DC) voltage levels at the multilevel inverter input. A multilevel inverter with three or more output voltage levels may provide a combined voltage (Vout) at its output. Compared to an inverter with two levels of voltage combined together at its output, the combined voltage (Vout) of the multilevel inverter may have a lower differential change in voltage with respect to time. The lower differential change in voltage may therefore provide a lower harmonic distortion of the combined voltage (Vout). The lower harmonic distortion of the combined voltage (Vout) may therefore provide an increased smoothness of the combined voltage (Vout). Increased smoothness of the combined voltage (Vout) may be proportional to the increase in the number of output voltage levels. However, the smoother combined voltage (Vout) of the multilevel inverter may demand a controller with increased complexity. The increased number of output voltage levels may also further demand an increased number of components for the realization of the multilevel inverter. The increased number of components may include more switches when compared to the inverter with two levels of voltage combined together at its output. The inverter with two levels of voltage combined together at its output may require a controller with less complexity. 
     SUMMARY 
     The following summary is a short summary of some of the inventive concepts for illustrative purposes only, and is not intended to limit or constrain the inventions and examples in the detailed description. 
     Illustrative embodiments disclosed herein may be with respect to power sources in a power system, which may include the interconnection of various groups of power sources. Each group of power sources may contain different types of power derived from renewable energy sources and non-renewable energy sources. The renewable energy sources may be provided from photovoltaic (PV) systems, wind or wave power. Examples of non-renewable energy sources may include fuel used to drive turbines or generators, for example. 
     Illustrative embodiments disclosed herein may include a power system utilized to supply power to a load and/or a storage device. The power system may include various inter connections of groups of direct current (DC) power sources that also may be connected in various series, parallel, series parallel and parallel series combinations, for example. Some illustrative embodiments may involve the connection of DC sources to a power converter circuit to provide an alternating current (AC) on its output. The power converter circuit may be a multi-level inverter topology, which may include a pair of input terminals and a first series connection of a first capacitor and a second capacitor. The first series connection may be connected across the pair of input terminals. A connection of the first capacitor to the second capacitor may be at a first terminal. A second series connection may include a first switch, a second switch, a third switch and a fourth switch connected in series. The second series connection may be connected across the pair of input terminals. A connection of the first switch to the second switch may be at a second terminal. And a connection of the second switch to the third switch may be at a third terminal. A connection of the third switch to the fourth switch may be at a fourth terminal. The first terminal may connect to the third terminal. 
     A plurality of other series connections of two or more switches may be connected across the second terminal and the fourth terminal. Each of the plurality of other series connections of two or more switches may comprise an intermediate (e.g., central) node. A respective inductor may be coupled to each of the intermediate (e.g., central) nodes, connected between the intermediate node and a (e.g., output) terminal, configured to combine the voltages of the intermediate (e.g., central) node. 
     The (e.g., output) terminal configured to combine the voltages of the intermediate (e.g., central) nodes may be a single-phase output with respect to at least one of a neutral potential, an earth potential, or another terminal of the power converter circuit. The output terminal of the power converter circuit may be powered by converting a DC input voltage connected to the pair of input terminals to an AC output voltage. 
     Each of the respective inductors may have mutual inductance with at least one of the other inductors. The power converter circuit may further include a controller operably attached and configured to control, by pulse width modulated (PWM) signals, each of the switches of the second series connection, and each of the plurality of other series connections of two or more switches, which may be connected across the second terminal and the fourth terminal. The controller may be operable to convert, using the second series connection, a DC input voltage connected to the pair of input terminals to provide multi-level AC voltages with DC offset (with respect to at least one of the pair of input terminals) across the second terminal and the fourth terminal. 
     The controller may measure/sense the current flowing through the coupled inductors and may control, by changing the PWM signals, switches (e.g., MOSFETs/IGBTs) to balance the currents flowing through the inductors/legs. 
     In some aspects, the coupled inductors may be coupled to the output terminal through relays. The controller may use relays for connecting the power converter circuit (e.g., an inverter) to a grid/load. The relays may also function as a circuit breaker and/or a protective mechanism to prevent high current/voltage or unintentional feeding of the electrical device into a sub grid or a stand-alone grid, often referred to as an anti-islanding operation. Based on an interruption (e.g., the grid “going down”) or a fault detection, the controller may operate the relays to disconnect the output terminal from the grid/load to ensure safety and to prevent damage to the electrical circuit or the grid. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present disclosure will become better understood with regard to the following description, claims, and drawings. The present disclosure is illustrated by way of example, and not limited by, the accompanying figures. 
         FIG.  1    illustrates a diagram of an electrical circuit according to aspects of the disclosure. 
         FIG.  2    illustrates a diagram of an electrical circuit according to aspects of the disclosure. 
         FIG.  3    illustrates a timing diagram of an electrical circuit according to aspects of the disclosure. 
         FIG.  4    illustrates a timing diagram of an electrical circuit according to aspects of the disclosure. 
         FIG.  5    illustrates a block diagram according to aspects of the disclosure. 
         FIG.  6    illustrates a diagram of an electrical circuit according to aspects of the disclosure. 
         FIG.  7    illustrates a timing diagram of an electrical circuit according to aspects of the disclosure. 
         FIG.  8    illustrates waveforms associated with electrical circuits according to aspects of the disclosure. 
         FIG.  9    illustrates a diagram of an electrical circuit according to aspects of the disclosure. 
         FIG.  10    illustrates a diagram of an electrical circuit according to aspects of the disclosure. 
         FIG.  11    illustrates a diagram of an electrical circuit according to aspects of the disclosure. 
         FIG.  12    illustrates a diagram of an electrical circuit according to aspects of the disclosure. 
         FIG.  13    illustrates a diagram of an electrical circuit according to aspects of the disclosure. 
         FIG.  14    illustrates a diagram of an electrical circuit according to aspects of the disclosure. 
         FIG.  15    illustrates a diagram of an electrical circuit according to aspects of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of various aspects of the disclosure, reference is made to the accompanying drawings, which form a part hereof, and in which is shown, by way of illustration, various embodiments in which aspects of the disclosure may be practiced. It is to be understood that other embodiments may be utilized and structural and functional modifications may be made, without departing from the scope of the present disclosure. 
     Features of one or more aspects disclosed herein may relate to a power converter circuit (e.g., multilevel inverter). The power converter circuit may be capable of providing a desired alternating current (AC) voltage level at its output from direct current (DC) voltage applied to its input. The power converter circuit may be realized by a multi-level inverter circuit topology. The desired AC voltage output is output from conversion of multiple DC voltage levels via an intermediate converter included in the multi-level inverter circuit topology. 
     The term “PWM” as used herein is with respect to the operation of switches described below. Unless otherwise stated, the term “PWM” refers to an active use of a switch for a period of time. The active use of the switch during the period of time may include the switch being opened and closed repeatedly during the time period. The term “ON” as used herein with respect to the operation of switches described below, refers to the active use of a switch during a time period. When a switch is “ON”, the switch remains substantially closed for an “ON” time period. The term “OFF” as used herein is with respect to the operation of switches described below and refers to active use of a switch during the time period. When a switch is “OFF”, the switch remains substantially open for an “OFF” time period. 
     The term “multiple” as used here in the detailed description indicates the property of having or involving several parts, elements, or members. The claim term “a plurality of” as used herein in the claims section finds support in the description with use of the term “multiple” and/or other plural forms. Other plural forms may include for example regular nouns that form their plurals by adding either the letter ‘s’ or ‘es’ so that the plural of converter is converters or the plural of switch is switches, for example. 
     The claim terms “comprise”, “comprises” and/or “comprising” as used herein in the claims section finds support in the description with use of the terms “may”, “include”, “includes” “including”, etc. 
     The terms, “substantially”, and, “about”, used herein include variations that are equivalent for an intended purpose or function (e.g., within a permissible variation range). Certain ranges are presented herein with numerical values being preceded by the terms “substantially” and “about”. The terms “substantially” and “about” are used herein to provide literal support for the exact number that it precedes, as well as a number that is near to or approximately the number that the term precedes. In determining whether a number is near to or approximately a specifically recited number, the near or approximating unrequited number may be a number, which, in the context in which it is presented, provides the substantial equivalent of the specifically recited number. 
     All values are examples, and are not meant to be taken as limiting. Also, all given values include values that are substantially equal to the given values. For example, a given value of 100 A can include any value that would be operationally equivalent, e.g., about 99.5 A, 101 A, 98.5 A, etc. 
     Reference is made to  FIG.  1   , which illustrates a circuit diagram of a power converter circuit  10  according to illustrative aspects of the disclosure.  FIG.  1    provides an example of a multi-level inverter circuit topology. Thus, in the example embodiment of  FIG.  1   , the power converter circuit  10  is an example of a multilevel inverter. A direct current (DC) input voltage Vin may be applied across input terminals A and B. Input voltage Vin may be a DC voltage received from one or more DC power sources, e.g. a battery, a photovoltaic panel, a rectified source of alternating current (AC) from an AC generator, etc. 
     In some aspects, power converter circuit  10  may comprise a controller  80 , for example: a digital signal processing (DSP) circuit, a field programmable gate array (FPGA) device, etc. Controller  80  may control power converter circuit  10  and its components (for example, switches, voltages, etc.) based on a predetermined algorithm, a measured parameter (e.g., a measurement collected by one or more sensors), a calculated parameter, determined or estimated (e.g., based on one or more measured parameters) parameter, any other appropriate data, etc. As an example, the electrical parameter may be: current, voltage, power, frequency, etc. In some aspects, controller  80  may comprise sensors to measure or sense one or more electrical parameters. 
     A series connection of capacitors C 1  and C 2  may be connected across input terminals A and B. In some aspects, capacitors C 1  and C 2  may be replaced by a plurality of series and/or parallel connected capacitors. Node E may be the point of connection between capacitors C 1  and C 2  (e.g., intermediate node). Node E may be coupled to neutral and/or earth potential. 
     A series connection of switches Sa 1 , Sa 2 , Sa 3  and Sa 4  may also be connected across input terminals A and B. A first terminal of switch Sal may be coupled to input terminal A and a second terminal of switch Sa 1  may be coupled to node C. A first terminal of switch Sa 2  may be coupled to node C and a second terminal of switch Sa 2  may be coupled to node F. Node F may be coupled to node E directly so that Nodes E and F have the same electric potential. A first terminal of switch Sa 3  may be coupled to node F and a second terminal of switch Sa 3  may be coupled to node D. A first terminal of switch Sa 4  may be coupled to node D and a second terminal of switch Sa 4  may be coupled to input terminal B. 
     A plurality of series connections of two or more switches may be connected across nodes C and D. For example, circuit  10  of  FIG.  1    comprises N (e.g., N≥2) series connections of two switches, such that each one the series connections are coupled in parallel with respect to each other. A series connection of switches Sb 1  and Sb 2  may be connected across nodes C and D. A terminal of Sb 1  and a terminal of Sb 2  may be coupled to intermediate (e.g., central) node IN 1 . As shown in  FIG.  1   , intermediate node IN 1  is a central node between two of the switches (Sb 1  and Sb 2 ) belonging to one of the series connections. If the series connection had three switches, intermediate node IN 1  could be the node between the first and second switches or between second and third switches. A series connection of switches Sb 3  and Sb 4  may also be connected across nodes C and D. A terminal of Sb 3  and a terminal of Sb 4  may be coupled to intermediate node IN 2 . A series connection of switches Sb 5  and Sb 6  may also be connected across nodes C and D. A terminal of Sb 5  and a terminal of Sb 6  may be coupled to intermediate node IN 3 . A series connection of switches Sb (2N−1)  and Sb 2N  may also be connected across nodes C and D. A terminal of Sb (2N−1)  and a terminal of Sb 2N  may be coupled to intermediate node IN N . 
     A corresponding first terminal of inductors L 1 , L 2 , L 3  . . . L N  may be coupled to node J (e.g., an output terminal) and a corresponding second terminal of inductors L 1 , L 2 , L 3  . . . L N  may be coupled respectively to terminals IN 1 , IN 2 , IN 3  . . . IN N . Terminal J may combine the voltages of the output legs. In some aspects, terminal J may be an output terminal of power converter circuit  10  that may output an AC sine wave (e.g., with DC offset). For example, terminal J may be an output terminal of one phase in a single-phase/three-phase/multi-phase converter. Inductors L 1 , L 2 , L 3  . . . L N  may be mutually coupled together. Inductors L 1 , L 2 , L 3  . . . L N  may be utilized to smooth a sine-wave of an AC output of power converter circuit  10 . 
     Controller  80  may control switches Sa 1 , Sa 2 , Sa 3  and Sa 4 . Switches Sa 1 , Sa 2 , Sa 3  and Sa 4  may be switched at a first frequency. The first frequency may be the output frequency (e.g., grid frequency, load frequency, utility frequency, (power) line frequency, 50 Hz-60 Hz, etc.). Switches Sa 1  and Sa 3  may be closed/turned ON/conducting substantially at the same time, and may be open/turned OFF/non-conducting substantially at the same time (e.g., switches Sa 1  and Sa 3  may be controlled in a corresponding manner, for example, based on a common control signal). Switches Sa 2  and Sa 4  may be closed/turned ON/conducting substantially at the same time, and may be open/turned OFF/non-conducting substantially at the same time (e.g., switches Sa 2  and Sa 4  may be controlled in a corresponding manner, for example based on a common signal) and in a complementary manner with regard to switches Sa 1  and Sa 3  (e.g., when switches Sa 1  and Sa 3  are closed, Sa 2  and Sa 4  may be open). 
     Controller  80  may control switches Sb 1 , Sb 2 , Sb 3 , Sb 4 , Sb 5 , Sb 6  . . . Sb (2N−1) , Sb 2N . Switches Sb 1 , Sb 2 , Sb 3 , Sb 4 , Sb 5 , Sb 6  . . . Sb (2N−1) , Sb 2N  may be switched at a second frequency. The second frequency may be higher than the first frequency. Switch Sb 1  may be switched in a complementary manner with regard to switch Sb 2 . For example, switch Sb 1  may be closed/turned ON/conducting when switch Sb 2  is open/turned OFF/non-conducting, and switch Sb 1  may be open/turned OFF/non-conducting when switch Sb 2  is closed/turned ON/conducting. Switch Sb 3  may be switched in a complementary manner with regard to switch Sb 4 . Switch Sb 5  may be switched in a complementary manner with regard to switch Sb 6 . Switch Sb (2N−1)  may be switched in a complementary manner with regard to switch Sb 2N . Also, in an embodiment with more than two switches in any one series connection, two or more of the switches may be switched (like Sb (2N−1) ) in a complementary manner with regard to the remaining switches of that series connection (like Sb 2N ). In some aspects, switches Sb 1 , Sb 3 , Sb 5  . . . Sb 2N  may be switched in a phase-shifted manner. For generalization, in a circuit comprising a plurality of N series connections of two or more switches, each series connection may be switched with phase-shift of 360°/N with respect to each other. For example, where N=3 the switches may be switched with phase-shift of 120°. 
     For example, the switches of power converter circuit  10  of  FIG.  1    (Sa 1 , Sa 2 , Sa 3 , Sa 4 , Sb 1 , Sb 2 , Sb 3 , Sb 4 , Sb 5 , Sb 6  . . . Sb (2N−1) , Sb 2N ) may be insulated gate bipolar transistors (IGBTs), metal oxide semiconductor field effect transistors (MOSFETs), bipolar junction transistors (BJTs), field effect transistors (FETs), silicone-controlled rectifiers (SCRs) or any known solid-state switch, or any combination of these components. 
     In some aspects, switches Sb 1 , Sb 2 , Sb 3 , Sb 4  Sb 5 , Sb 6  . . . Sb (2N−1) , Sb 2N  may be switched according to the duty cycle ratio (which may be changed according to a comparison between a reference voltage and the output voltage Vout), where each group (e.g., pair) of series-connected switches (e.g., where Sb 1 -Sb 2  is the first pair, Sb 3 -Sb 4  is the second pair, Sb 5 -Sb 6  is the third pair . . . and Sb (2N−1) -Sb 2N  is the n th  pair) is shifted sequentially by 1/N (where N is the number of series connections) of the switching period with respect to the other groups (e.g., pairs) of series-connected switches. The specific timing shown in  FIGS.  3 - 4    may be an example of the desired duty cycles, but a variety of different timings may be used that may have similar or different switching performance. 
     Reference is now made to  FIG.  2   , which illustrates a diagram of electrical circuit  20  (e.g., multilevel inverter), an example of power converter circuit  10  of  FIG.  1   , according to aspects of the disclosure. In  FIG.  2   , inductors L 1 , L 2 , L 3  of  FIG.  1    may be replaced by mutually coupled inductors L 4 , L 5 , L 6 . Controller  80  of  FIG.  1    may be replaced by controller  180 . 
     As shown in  FIG.  2   , in some aspects, switches Sa 1 , Sa 2 , Sa 3  and Sa 4  of  FIG.  1    are insulated gate bipolar transistors (IGBTs). 
     For example, electrical circuit  20  comprises IGBTs Sc 1 , Sc 2 , Sc 3  and Sc 4 . Controller  180  may control the gate (g) of IGBTs Sc 1 , Sc 2 , Sc 3  and Sc 4 . The collector (c) of IGBT Sc 1  may be coupled to input terminal A. At node C, the emitter (e) of IGBT Sc 1  may be coupled to the collector (c) of IGBT Sc 2 . At node F, the emitter (e) of IGBT Sc 2  may be coupled to the collector (c) of IGBT Sc 3 . Node F may be coupled to node E. At node D, the emitter (e) of IGBT Sc 3  may be coupled to the collector (c) of IGBT Sc 4 . The emitter of IGBT Sc 4  may be coupled to input terminal B. 
     As shown in  FIG.  2   , in some aspects, switches Sb 1 , Sb 2 , Sb 3 , Sb 4 , Sb 5 , Sb 6  of  FIG.  1    are metal oxide semiconductor field effect transistors (MOSFETs). 
       FIG.  2    also shows that the number N of series connections of two or more switches may be three (e.g., N=3). Accordingly, the three series connections including switches Sb 1 , Sb 2 , Sb 3 , Sb 4 , Sb 5 , Sb 6  in  FIG.  1    are replaced by six MOSFETs M 1 , M 2 , M 3 , M 4 , M 5  and M 6  in  FIG.  2   . Controller  180  may control each one of MOSFETs M 1 , M 2 , M 3 , M 4 , M 5  and M 6 . Each one of MOSFETs M 1 , M 2 , M 3 , M 4 , M 5  and M 6  may be an n-type enhancement metal-oxide-semiconductor field-effect transistor comprising drain, source and gate terminals (denoted D, S and G respectively). In this example, controller  180  may control the voltage difference between the source and gate terminals of MOSFETs M 1 , M 2 , M 3 , M 4 , M 5  and M 6 . 
     The source terminals (S) of MOSFETs M 1 , M 3  and M 5  may be coupled to node C. At node IN 1  the drain terminal (D) of MOSFET M 1  may be coupled to the source terminal (S) of MOSFET M 2 . At node IN 2  the drain terminal (D) of MOSFET M 3  may be coupled to the source terminal (S) of MOSFET M 4 . At node IN 3  the drain terminal (D) of MOSFET M 5  may be coupled to the source terminal (S) of MOSFET M 6 . The drain terminals (D) of MOSFETs M 2 , M 4  and M 6  may be coupled to node D. 
     In some aspects of the disclosure herein, controller  180  may operate MOSFETs M 1 , M 2 , M 3 , M 4 , M 5  and M 6  at a first frequency (e.g. high frequency), based on a modulation scheme that may include pulse width modulation (PWM), frequency modulation (FM), or a variable frequency plus variable pulse width modulation, for example. The modulation scheme may optimize spectrum and reduce ripple based on space vector (SV) modulation, types of phase disposition (PD) modulation, alternate phase opposition disposition (APOD) modulation, various multicarrier PWM strategies for multilevel inverters, etc. Controller  180  may operate IGBTs Sc 1 , Sc 2 , Sc 3  and Sc 4  at a second frequency (e.g. low frequency). The second frequency may be the load frequency, utility frequency, (power) line frequency, etc. In some aspects, the first frequency may be higher than the second frequency. For example, the first frequency may be 500 Hz, 1 kHz, 5 kHz, 25 kHz, 100 kHz, 500 kHz, 1 MHz, etc. and the second frequency may be 50 Hz, 60 Hz, 500 Hz, etc. 
     In some aspects of the disclosure herein, mutually coupled inductors L 4 , L 5 , L 6  may be coupled to terminal J optionally through additional circuit elements. Terminal J may combine the voltages at the output of the legs of (e.g., filter) inductors L 4 , L 5 , L 6 . For example, in  FIG.  2   , coupled inductors L 4 , L 5 , L 6  may be coupled to terminal J through relays R 1 , R 2  and R 3 , respectively. In some aspects, a (e.g., filter) capacitor may be coupled to one terminal of mutually coupled inductors L 4 , L 5 , L 6  (e.g., the terminal of the inductors L 4 , L 5 , and L 6  that is coupled with relays R 1 , R 2  and R 3 , respectively). For example, in  FIG.  2   , capacitor C 4  may be coupled between a terminal of inductor L 4  and node K, capacitor C 5  may be coupled between a terminal of inductor L 5  and node L, and capacitor C 6  may be coupled between a terminal of inductor L 6  and node M. Nodes K, L, M may be coupled to nodes having a different voltage levels or to one or more nodes having a same voltage level. Further, one or more of nodes K, L, M may be coupled to a node of electrical circuit  20  having a reference voltage (e.g., node E) or another node having another voltage reference, such as neutral and/or earth potential. In  FIG.  2   , inductor L 7  (e.g., differential filter) may be coupled/connected between terminal J and node N. A single-phase AC output/sine wave with DC offset of power converter circuit  10  may be provided across capacitors C 4 , C 5  and C 6 . An AC output voltage Vout may be applied across capacitors C 4 , C 5  and C 6 . AC output voltages Vout 1 , Vout 2 , and Vout 3  may be applied across capacitors C 4 , C 5 , and C 6 , respectively. AC output voltages Vout 1 , Vout 2 , and Vout 3  may be similar at the second frequency and phase shifted at the first frequency by 120°. 
     In some aspects, capacitors C 4 , C 5  and C 6  may be replaced by a capacitor (or a plurality of capacitors) connected between terminal J and a reference terminal (e.g., node E). 
     In aspects of the disclosure herein, one or more of relays R 1 , R 2  and R 3  may comprise two or more relay contacts that may be provided using a multi-pole relay module. A multi-pole relay module incorporates a plurality of relays in a single package. A multi-pole relay module may enable the use of a common control coil for more than one relay contact, thereby reducing the size and the costs of the system. For example, a dual-pole relay module may have two contacts controlled by a single control coil so that a second control coil is not required, thereby reducing the relay array size, the dissipated energy during operation, the manufacturing costs, and/or the like. 
     In aspects of the disclosure herein, one or more of relays R 1 , R 2  and R 3  may use a different electrical contact configuration (e.g., single-pole single-throw (SPST), single-pole double-throw (SPDT), double-pole single-throw (DPST)). For example, when the relay array comprises two or more relays, using a DPST relay (e.g., a pair of switches or relays actuated by a single coil) may reduce the consumed energy for driving the control coils of the relay. 
     In some aspects of the disclosure, controller  180  may measure/sense or receive estimations and/or determinations (e.g., measurements collected by sensors) and/or data, of one or more electrical parameters of circuit  20 . For example, controller  180  may measure/sense the current flowing through each one of inductors L 4 , L 5 , L 6 . The current measurement/sensing of the current flowing through the coupled inductors L 4 , L 5 , L 6  may be used, by controller  180 , to balance the leg (e.g., inductors L 4 , L 5 , L 6 ) currents. The current balance may be achieved by changing the PWM signals that may control the switches/MOSFETs/IGBTs. Current balance between the legs (e.g., inductors L 4 , L 5 , L 6 ) may divide/split/control the output current of electrical circuit  20  in a substantially equal way between each of the output legs/inductors L 4 , L 5 , L 6 . By virtue of the current balance between the legs, each of relays R 1 , R 2  and R 3  may be configured to conduct a lower peak current than if the leg currents were not balanced, thereby reducing the size and the costs of the system. For example, in a case where the output current of electrical circuit  20  is rated to a current at level of  30 A, the current balance may ensure that a current of no more than  10 A is flowing through each of the relays R 1 , R 2  and R 3 . Thus, a configuration of the electrical circuit  20  using lower-rated relays may be enabled by virtue of the current balance. 
     In some aspects of the disclosure, controller  180  may measure the current flowing through coupled inductors L 4 , L 5 , L 6  (e.g., differential current) and L 7 , voltage across capacitors C 4 , C 5 , C 6 , C 1 , and C 2 , etc. Based on detection of a differential current above a predetermined level, controller  180  may vary its control to amend the differential current (e.g., by changing the PWM signals). 
     Controller  180  may use relays R 1 , R 2  and R 3  for connecting electrical circuit  20  (e.g., an inverter, a power converter) to a grid/load. The relays R 1 , R 2  and R 3  may also function as a circuit breaker and/or a protective mechanism to prevent high current/voltage or unintentional feeding of the electrical device into a sub grid or a stand-alone grid, often referred to as an anti-islanding operation. Based on an interruption (e.g., the grid “going down”) or a fault detection, relays R 1 , R 2  and R 3  may disconnect electrical circuit  20  from the grid/load to ensure safety and to prevent damage to electrical circuit  20  or the grid. Relays R 1 , R 2  and R 3  may be coupled with the outputs of or incorporated into electrical circuit  20 . 
     Reference is now made to  FIG.  3   , which illustrates timelines  30  showing waveforms that describe, according to some aspects of the disclosure, a possible control method of a power converter circuit (e.g., power converter circuit  10  and electrical circuit  20  of  FIGS.  1  and  2    respectively). The upper graph shows a waveform, in volts (V) versus time, for output voltage Vout. Output voltage Vout may be any one of AC output voltages Vout 1 , Vout 2 , and Vout 3  of  FIG.  2   , with respect to a reference voltage (e.g., node E, neutral potential terminal, an earth potential terminal). Output voltage Vout in  FIG.  3    may be the output power of power converter circuit  10  and electrical circuit  20  of  FIGS.  1  and  2   , respectively. In some aspects, Vout may be filtered by a filter circuit comprising a capacitor to generate a substantially AC sinusoidal voltage waveform at the output of the filter circuit. In the example shown in  FIG.  3   , output voltage Vout may be a 50 Hz sine-waveform of 230V RMS . Graphs PWM 1 , PWM 2 , PWM 3 , PWM 4  and PWM 5  may represent PWM control signals used to control switches of the power converter circuit. The PWM 1 , PWM 2 , PWM 3 , PWM 4  and PWM 5  signals may be generated by digital encoding component(s) (e.g., a microprocessor) and/or analog circuit(s) (e.g., using a comparator, oscillator, etc.). For example, PWM 1 , PWM 2 , PWM 3 , PWM 4  and PWM 5  signals may be generated by controller  80  of  FIG.  1    or controller  180  of  FIG.  2   . 
     In the example shown in  FIG.  3   , signals PWM 1  and PWM 2  may be relative to the frequency of output voltage Vout, e.g., 50 Hz. Signals PWM 1  and PWM 2  may be complementary with respect to each other. For example, signal PWM 1  may be applied to control switches Sa 1 /Sa 3  of  FIG.  1    and/or the gate terminals (g) of IGBTs Sc 1 /Sc 3  of  FIG.  2   . Signal PWM 2  may be applied to control switches Sa 2 /Sa 4  of  FIG.  1    and/or the gate terminals (g) of IGBTs Sc 1 /Sc 3  of  FIG.  2   . 
     In the example shown in  FIG.  3   , signals PWM 3 , PWM 4  and PWM 5  may be configured to control switches to be switched all during the same cycle. For example, signal PWM 3  may control the gate terminal (G) of MOSFET M 1  of  FIG.  2   , signal PWM 4  may control the gate terminal (G) of MOSFET M 3  of  FIG.  2   , and signal PWM 5  may control the gate terminal (G) of MOSFET M 5  of  FIG.  2   . A complementary PWM signal with respect to signal PWM 3  may control the gate terminal (G) of MOSFET M 2  of  FIG.  2   , a complementary PWM signal with respect to signal PWM 4  may control the gate terminal (G) of MOSFET M 4  of  FIG.  2   , and a complementary PWM signal of signal PWM 5  may control the gate terminal (G) of MOSFET M 6  of  FIG.  2   . 
     In the example, signals PWM 3 , PWM 4  and PWM 5  may control each of the switches/MOSFETs to be switched at 3 kHz. This allows each switch/MOSFET to turn ON for a period, according to the duty cycle ratio (which may be changed according to a comparison between a reference voltage and the output voltage Vout), where each of the signals PWM 3 , PWM 4  and PWM 5  may be shifted sequentially by 1/N (where N is the number of series connections of switches/MOSFETs (for example, MOSFETs M 1 -M 2 , MOSFETs M 3 -M 4 , MOSFETs M 5 -M 6 ), which in the example shown in  FIG.  3    is three (N=3)) of the switching period, such as ⅓ kHz or around 333.33 microseconds. During this time each switch turns ON and OFF. This may effectively increase the effective frequency to 3 times the switching period at the output terminal (e.g., terminal J of  FIG.  2   ) of the power converter circuit  10  or electrical circuit  20  of  FIGS.  1  and  2   , respectively, without actually increasing the switching frequency. However, in embodiments described herein, the MOSFETs may be switched at a much higher rate (e.g., 200 kHz). 
     Further, the design may be scalable in that the effective frequency can be increased more and more by increasing the number of series connections of switches; the multi-level switching in each series connections of switches allows the switching to increase an effective frequency (e.g., relative to the switching frequency) of the current flowing through the differential filter (e.g., inductor L 7  of  FIG.  2   ) without driving a single MOSFET faster. Signals PWM 1  and PWM 2  may be complementary with respect to each other. For example, signal PWM 1  may be applied to control switches Sa 1 /Sa 3  of  FIG.  1    and/or the gate terminals (g) of IGBTs Sc 1 /Sc 3  of  FIG.  2   . Signal PWM 2  may be applied to control switches Sa 2 /Sa 4  of  FIG.  1    and/or the gate terminals (g) of IGBTs Sc 2 /Sc 4  of  FIG.  2   . 
     Reference is now made to  FIG.  4   , which illustrates timelines showing waveforms that describe, according to some aspects of the disclosure, a possible method of generating a pulse width modulation (PWM). 
     The example shown in  FIG.  4   , illustrates timelines  40  describing a possible method of generating a pulse width modulation (PWM) signal PWM 3  of  FIG.  3   . 
     The upper graph shows a waveform, in volts (V) versus time, for output voltage Vout. Output voltage Vout may be any one of AC output voltages Vout 1 , Vout 2 , and Vout 3  of  FIG.  2   , with respect to a reference voltage (e.g., node E, neutral potential terminal, an earth potential terminal) and equivalent with Vout shown in  FIG.  3   . Output voltage Vout may be the output power of power converter circuit  10  and electrical circuit  20  of  FIGS.  1  and  2   , respectively. In some aspects, Vout may be filtered by a filter circuit comprising a capacitor to generate a substantially AC sinusoidal voltage waveform at the output of the filter circuit. In the example shown in  FIG.  4   , output voltage Vout may be a 50 Hz sine-waveform of 230V RMS . 
     The second graph from the top of  FIG.  4    may represent a reference signal COM corresponding to (e.g., related to) output voltage Vout. During the positive half of the sine-wave Vout, reference signal COM may be similar to output voltage Vout (e.g., a sine wave with substantially the same frequency but with a different amplitude). During the negative half of the sine-wave Vout, reference signal COM may be complementary to output voltage Vout. For example, reference signal COM may be equivalent with 1−(Vout/Vamp), where Vamp is the peak amplitude of sine-wave Vout. 
     The third graph from the top of  FIG.  4    may represent another reference signal REF 3  used to compare with the reference signal COM. In some aspects, REF 3  may be a saw tooth wave (or saw wave). In the example, the saw tooth wave REF 3  may have a frequency of 3 kHz. 
     The lower graph shows PWM control signal PWM 3  used to control a switch(s) of the power converter circuit. For example, signal PWM 3  may control switch Sb 1  of  FIG.  1    and/or the gate terminal (G) of MOSFET M 1  of  FIG.  2    and may be equivalent with control signal PWM 3  of  FIG.  3   . Control signal PWM 3  may be generated by digital encoding component(s) (e.g., a microprocessor) and/or analog circuit(s) (e.g., using a comparator, oscillator, etc.). In this example control signal PWM 3  may be generated by a comparator receiving reference signals COM and REF 3  as inputs. Where reference signal COM is larger than reference signal REF 3 , control signal PWM 3  may be ‘1’ indicating an ‘ON’ state. Where reference signal COM is smaller than reference signal REF 3 , control signal PWM 3  may be ‘0’ indicating an ‘OFF’ state. 
     The PWM control signal PWM 3  may be generated by digital encoding component(s) (e.g., a microprocessor) and/or analog circuit(s) (e.g., using a comparator, oscillator, etc.). For example, PWM control signal PWM 3  signals may be generated by controller  80  of  FIG.  1    or a similar one. 
     Reference is now made to  FIG.  5   , which illustrates a block diagram of a controller according to aspects of the disclosure herein. Controller  80  of  FIG.  1    and/or controller  180  of  FIG.  2    may be implemented with controller  280 . A controller  280  may include at least one of a microprocessor, microcontroller, digital signal processor (DSP), or the like. Controller  280  may be connected to a memory  289 . Controller  280  may serve as a central controller to other similar controllers as controller  280  which may be included to control multiple interconnected power converter circuits (e.g., a plurality of power converter circuits  10  for example). Communications interface  282  connected to controller  280  may provide communications between controller  280  and other controllers (and other communication interfaces) included generally in a power system, which includes power converter circuit  10 . The communications to and from communications interface  282  may be based on a control algorithm running on controller  280 . The communications may include control signals provided on control lines which operably connect to and control power converter circuit  10 . For example, controller  280  may generate control signals to control the switches of power converter circuit  10  of  FIG.  1    (Sa 1 , Sa 2 , Sa 3 , Sa 4 , Sb 1 , Sb 2 , Sb 3 , Sb 4 , Sb 5 , Sb 6  . . . Sb (2N−1) , Sb 2N ) and/or the IGBTs and MOSFETs of power converter circuit  10  of  FIG.  1    (IGBTs Sc 1 , Sc 2 , Sc 3  and Sc 4  and MOSFETs M 1 , M 2 , M 3 , M 4 , M 5  and M 6 ). 
     Communications through communications interface  282  may also include measured and/or sensed parameters via sensors/sensor interface  284  that, for example, may be included in power converter circuit  10  of  FIG.  1   . The communications by communications interface  282  may be conveyed using WiFi, power line communications (PLC), near field communications or a RS232/485 communication bus, for example. Communications interface  282  may communicate with a local area network or cellular network in order to establish an internet connection. For example, the internet connection may provide a feature of remote monitoring or reconfiguration of power converter circuit  10 . 
     A display  288  connected to central controller  280  may be mounted on the surface of the housing used to house power converter circuit  10  for example. Display  288  may display for example the power produced from power converter circuit  10 . Controller  280  may be connected to a shutdown device  286  (e.g., a safety and remote shutdown device). Sensing by sensor(s)/sensor interface  284  as well as sensed parameters communicated between controller  280  and sensor(s)/sensor interfaces of power converter circuit  10  may be indicative of a fault condition (e.g., overvoltage, overcurrent, ground fault, failure of components, input power or load disconnection). Upon detection of the fault condition, shutdown device  286  may be activated in order to isolate the fault condition and/or shutdown power converter circuit  10 . For example, in such a case, controller  180  of  FIG.  2    may turn OFF relays R 1 , R 2  and R 3 . 
     Control signals from controller  280  applied to the switches of power converter circuit  10  of  FIG.  1    (Sa 1 , Sa 2 , Sa 3 , Sa 4 , Sb 1 , Sb 2 , Sb 3 , Sb 4 , Sb 5 , Sb 6  . . . Sb (2N−1) , Sb 2N ) and/or the IGBTs and MOSFETs of electrical circuit  20  of  FIG.  2    (IGBTs Sc 1 , Sc 2 , Sc 3  and Sc 4  and MOSFETs M 1 , M 2 , M 3 , M 4 , M 5  and M 6 ) are generated using a modulation scheme. The modulation scheme may be responsive to the electrical parameters sensed in power converter circuit  10  when power converter circuit  10  may or might not be connected to a load. The load may be an AC motor or a utility grid supply for example. The modulation scheme may include pulse width modulation (PWM), frequency modulation (FM), or a variable frequency plus variable pulse width modulation, for example. An algorithm of controller  280  may allow application of control signals. The control signals may be applied responsive to a sensing step of an algorithm to sense the electrical parameters in power converter circuit  10  connected to a load and/or when power converter circuit  10  is not connected to a load. For example, sensor(s)/sensor interface  284  may sense/measure the current flowing through the output legs/mutually coupled inductors L 4 , L 5 , L 6 . The load may be a utility grid, for example. 
     In some aspects of the disclosure herein, controller  280  of  FIG.  5    may be implemented as an independent circuit or component. The implementation may be digital (e.g. using a microprocessor), analog (e.g. using an integrator), or both (e.g., using a digital-analog converter). 
     Reference is made to  FIG.  6   , which illustrates a circuit diagram of a power converter circuit  30  according to illustrative aspects of the disclosure.  FIG.  6    provides an example of a multi-level inverter circuit topology. Thus, in the example embodiment of  FIG.  6   , the power converter circuit  30  is an example of a three-phase multilevel inverter. A direct current (DC) input voltage Vin may be applied across input terminals A and B. Input voltage Vin may be a DC voltage received from a DC power source, e.g. a battery, a photovoltaic panel, a rectified source of alternating current (AC) from an AC generator, etc. 
     A series connection of capacitors C 1  and C 2  may be connected across input terminals 
     A and B. In some aspects, capacitors C 1  and C 2  may be replaced by a plurality of series and/or parallel connected capacitors. Node E may be the point of connection between capacitors C 1  and C 2  (e.g., intermediate node). Node E may be coupled to neutral and/or earth potential. 
     In some aspects, power converter circuit  30  may comprise a plurality of single-phase power converter circuits. Thus, in the example embodiment of  FIG.  6   , the power converter circuit  30  comprises three single-phase converter circuits  11 ,  21  and  31 . In the example embodiment of  FIG.  6   , each of single-phase converter circuits  11 ,  21  and  31  are similar to power converter circuit  10  of  FIG.  1   . Each of the single-phase converter circuits  11 ,  21  and  31  may be connected across input terminals A and B and configured to receive direct current input voltage V in . Each of the single-phase converter circuits  11 ,  21  and  31  may be connected to node E. Each of the single-phase converter circuits  11 ,  21  and  31  may be configured to convert direct current input voltage V in  to an alternating current. 
     Power converter circuit  11  may comprise: a series connection of switches Sd 1 , Sd 2 , Sd 3  and Sd 4  (e.g., similar to switches Sa 1 , Sa 2 , Sa 3  and Sa 4  of  FIG.  1   ) that may also be connected across input terminals A and B, and a plurality of series connections of switches M 1 , M 2 , M 3 , M 4 , M 5  and M 6  (e.g., similar to switches Sb 1 , Sb 2 , Sb 3 , Sb 4 , Sb 5  and Sb 6  of  FIG.  1   ) that may be connected across nodes C and D. In the example embodiment of  FIG.  6   , switches Sd 1 , Sd 2 , Sd 3  and Sd 4  may be insulated gate bipolar transistors (IGBTs) and switches M 1 , M 2 , M 3 , M 4 , M 5  and M 6  may be MOSFETs (e.g., similar to  FIG.  2   ). Each series connection of switches M 1 , M 2 , M 3 , M 4 , M 5  and M 6  may comprise an intermediate node; the series connection of switches M 1 -M 2  may comprise intermediate node IN 11 , the series connection of switches M 3 -M 4  may comprise intermediate node IN 12 , and the series connection of switches M 5 -M 6  may comprise intermediate node IN 13 . Within power converter circuit  11 , a corresponding first terminal of inductors L 11 , L 12 , and L 13  may be coupled to node J 1  (e.g., an output terminal) and a corresponding second terminal of inductors L 11 , L 12 , and L 13  may be coupled respectively to terminals IN 11 , IN 12 , and IN 13 . Terminal J 1  may combine the voltages of the output legs. In some aspects, terminal J 1  may be an output terminal of power converter circuit  11  that may output an AC sine wave (e.g., with DC offset). For example, terminal J 1  may be an output terminal of one phase in a single-phase/three-phase/multi-phase converter. Inductors L 11 , L 12 , and L 13  may be mutually coupled together. Inductors L 11 , L 12 , and L 13  may be utilized to smooth a sine-wave of an AC output of power converter circuit  11 . In some embodiments, inductor L 111  (e.g., differential filter) may be coupled/connected between terminal J 1  and terminal P 1 . In such embodiment, terminal P 1  may be an output terminal of one phase in a single-phase/three-phase/multi-phase converter. In some aspects, a capacitor may be coupled between terminal J 1  and a reference terminal (e.g., node E). 
     Power converter circuit  21  may comprise: a series connection of switches Sd 5 , Sd 6 , Sd 7  and Sd 8  (e.g., similar to switches Sa 1 , Sa 2 , Sa 3  and Sa 4  of  FIG.  1   ) that may also be connected across input terminals A and B, and a plurality of series connections of switches M 11 , M 12 , M 13 , M 14 , M 15  and M 16  (e.g., similar to switches Sb 1 , Sb 2 , Sb 3 , Sb 4 , Sb 5  and Sb 6  of  FIG.  1   ) that may be connected across nodes C and D. In the example embodiment of  FIG.  6   , switches Sd 5 , Sd 6 , Sd 7  and Sd 8  may be insulated gate bipolar transistors (IGBTs) and switches M 11 , M 12 , M 13 , M 14 , M 15  and M 16  may be MOSFETs (e.g., similar to  FIG.  2   ). Each series connection of switches M 11 , M 12 , M 13 , M 14 , M 15  and M 16  may comprise an intermediate node; the series connection of switches M 11 -M 12  may comprise intermediate node IN 21 , the series connection of switches M 13 -M 14  may comprise intermediate node IN 22 , and the series connection of switches M 15 -M 16  may comprise intermediate node IN 23 . Within power converter circuit  21 , a corresponding first terminal of inductors L 21 , L 22 , and L 23  may be coupled to node J 2  (e.g., an output terminal) and a corresponding second terminal of inductors L 21 , L 22 , and L 23  may be coupled respectively to terminals IN 21 , IN 22 , and IN 23 . Terminal J 2  may combine the voltages of the output legs. In some aspects, terminal J 2  may be an output terminal of power converter circuit  21  that may output an AC sine wave (e.g., with DC offset). For example, terminal J 2  may be an output terminal of one phase in a single-phase/three-phase/multi-phase converter. Inductors L 21 , L 22 , and L 23  may be mutually coupled together. Inductors L 21 , L 22 , and L 23  may be utilized to smooth a sine-wave of an AC output of power converter circuit  21 . In some embodiments, inductor L 121  (e.g., differential filter) may be coupled/connected between terminal J 2  and terminal P 2 . In such embodiment, terminal P 2  may be an output terminal of one phase in a single-phase/three-phase/multi-phase converter. In some aspects, a capacitor may be coupled between terminal J 2  and a reference terminal (e.g., node E). 
     Power converter circuit  31  may comprise: a series connection of switches Sd 9 , Sd 10 , Sd 11  and Sd 12  (e.g., similar to switches Sa 1 , Sa 2 , Sa 3  and Sa 4  of  FIG.  1   ) that may also be connected across input terminals A and B, and a plurality of series connections of switches M 21 , M 22 , M 23 , M 24 , M 25  and M 26  (e.g., similar to switches Sb 1 , Sb 2 , Sb 3 , Sb 4 , Sb 5  and Sb 6  of  FIG.  1   ) that may be connected across nodes C and D. In the example embodiment of  FIG.  6   , switches Sd 9 , Sd 10 , Sd 11  and Sd 12  may be insulated gate bipolar transistors (IGBTs) and switches M 21 , M 22 , M 23 , M 24 , M 25  and M 26  may be MOSFETs (e.g., similar to  FIG.  2   ). Each series connection of switches M 21 , M 22 , M 23 , M 24 , M 25  and M 26  may comprise an intermediate node; the series connection of switches M 21 -M 22  may comprise intermediate node IN 31 , the series connection of switches M 23 -M 24  may comprise intermediate node IN 32 , and the series connection of switches M 25 -M 26  may comprise intermediate node IN 33 . Within power converter circuit  31 , a corresponding first terminal of inductors L 31 , L 32 , and L 33  may be coupled to node J 3  (e.g., an output terminal) and a corresponding second terminal of inductors L 31 , L 32 , and L 33  may be coupled respectively to terminals IN 31 , IN 32 , and IN 33 . Terminal J 3  may combine the voltages of the output legs. In some aspects, terminal J 3  may be an output terminal of power converter circuit  31  that may output an AC sine wave (e.g., with DC offset). For example, terminal J 3  may be an output terminal of one phase in a single-phase/three-phase/multi-phase converter. Inductors L 31 , L 32 , and L 33  may be mutually coupled together. Inductors L 31 , L 32 , and L 33  may be utilized to smooth a sine-wave of an AC output of power converter circuit  31 . In some embodiments, inductor L 131  (e.g., differential filter) may be coupled/connected between terminal J 3  and terminal P 3 . In such embodiment, terminal P 3  may be an output terminal of one phase in a single-phase/three-phase/multi-phase converter. In some aspects, a capacitor may be coupled between terminal J 3  and a reference terminal (e.g., node E). 
     Controller  380  may be: a digital signal processing (DSP) circuit, a field programmable gate array (FPGA) device, etc. Controller  380  may control power converter circuit  30  and its components (for example, switches, voltages, etc.) based on a predetermined algorithm, a measured parameter (e.g., a measurement collected by one or more sensors), a calculated parameter, determined or estimated (e.g., based on one or more measured parameters) parameter, any other appropriate data, etc. As an example, the electrical parameter may be: current, voltage, power, frequency, etc. In some aspects, controller  380  may comprise sensors to measure or sense one or more electrical parameters. 
     Controller  380  may control switches Sd 1 , Sd 2 , Sd 3 , Sd 4 , Sd 5 , Sd 6 , Sd 7 , Sd 8 , Sd 9 , Sd 10 , Sd 11 , Sd 12 , M 1 , M 2 , M 3 , M 4 , M 5 , M 6 , M 11 , M 12 , M 13 , M 14 , M 15 , M 16 , M 21 , M 22 , M 23 , M 24 , M 25  and M 26 . The switches M 1 , M 2 , M 3 , M 4 , M 5 , M 6 , M 11 , M 12 , M 13 , M 14 , M 15 , M 16 , M 21 , M 22 , M 23 , M 24 , M 25  and M 26  may be insulated gate bipolar transistors (IGBTs), metal oxide semiconductor field effect transistors (MOSFETs), bipolar junction transistors (BJTs), filed effect transistors (FETs), as silicone-controlled rectifiers (SCRs) or any known solid-state switch, or any combination of these components. 
     Switches Sd 1 , Sd 2 , Sd 3 , Sd 4 , Sd 5 , Sd 6 , Sd 7 , Sd 8 , Sd 9 , Sd 10 , Sd 11 , and Sd 12  may be switched at a first frequency. The first frequency may be the output frequency (e.g., grid frequency, load frequency, utility frequency, (power) line frequency, 50 Hz-60 Hz, etc.). Each switch in each pair of switches Sd 1 +Sd 3 , Sd 2 +Sd 4 , Sd 5 +Sd 7 , Sd 6 +Sd 8 , Sd 9 +Sd 11 , Sd 10 +Sd 12 , may be closed/turned ON/conducting substantially at the same time, and may be open/turned OFF/non-conducting substantially at the same time. Each pair of the pairs of switches Sd 1 +Sd 3 , Sd 5 +Sd 7 , and Sd 9 +Sd 11  may be switched at the same time and in a complementary manner with regard to the pairs of switches Sd 2 +Sd 4 , Sd 6 +Sd 8 , and Sd 10 +Sd 12  respectively (e.g., when pair of switches Sd 1 +Sd 3  are closed, the pair of switches Sd 2 +Sd 4  may be open). 
     The pairs of switches Sd 1 +Sd 3  and Sd 2 +Sd 4  may be switched in a 120° phase (of the first frequency) with respect to pairs of switches Sd 5 +Sd 7  and Sd 6 +Sd 8 , and may be switched in a 240° phase (of the first frequency) with respect to pairs of switches Sd 9 +Sd 11  and Sd 10 +Sd 12 . 
     Switches M 1 , M 2 , M 3 , M 4 , M 5 , M 6 , M 11 , M 12 , M 13 , M 14 , M 15 , M 16 , M 21 , M 22 , M 23 , M 24 , M 25  and M 26  may be switched at a second frequency. The second frequency may be higher than the first frequency. Each switch of switches M 1 , M 3 , M 5 , M 11 , M 13 , M 15 , M 21 , M 23 , and M 25  may be switched in a complementary manner with regard to switch M 2 , M 4 , M 6 , M 12 , M 14 , M 16 , M 22 , M 24 , and M 26  respectively. For example, switch M 1  may be closed/turned ON/conducting when switch M 2  is open/turned OFF/non-conducting, and switch M 1  may be open/turned OFF/non-conducting when switch M 2  is closed/turned ON/conducting. 
     For generalization, in a power converter circuit comprising a plurality of N series connections of two or more switches, each group (e.g., pair) of series-connected switches (e.g., where M 1 -M 2  is the first pair, M 3 -M 4  is the second pair, M 5 -M 6  is the third pair . . . and M (2N−1) -M 2N  is the n th  pair) is shifted sequentially by 1/N (where N is the number of series connections) of the switching period of the second frequency with respect to the other groups (e.g., pairs) of series-connected switches. For example, power converter circuits  11 ,  21  and  31  comprise three (N=3) series connections of switches, thus each series connection of switches may be switched with phase-shift of 120°. 
     In some aspects, each group (e.g., pair) of the groups (e.g., pairs) of series-connected switches of all power converter circuits may be shifted sequentially by 1/(P*N) (where P is the number of parallel connected power converters) of the switching period of the second frequency with respect to the other groups (e.g., pairs) of series-connected switches. 
     For example, in  FIG.  6    where P=N=3, the switches M 1 , M 2 , M 3 , M 4 , M 5 , M 6 , M 11 , M 12 , M 13 , M 14 , M 15 , M 16 , M 21 , M 22 , M 23 , M 24 , M 25  and M 26  may be switched according to following sequential phase-shifting of the second frequency (e.g., higher-frequency): 
     
       
         
           
               
               
            
               
                   
                   
               
               
                   
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                 M3- 
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                 M2 
                 M4 
                 M6 
                 M12 
                 M14 
                 M16 
                 M22 
                 M24 
                 M26 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Phase- 
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                 shift 
               
               
                   
               
            
           
         
       
     
     The phase shifting between each pair of the pairs of series-connected switches of all single-phase power converter circuits (e.g., single-phase converter circuits  11 ,  21 , and  31 ) may enable a power converter (e.g., power converter circuit  30 ) to achieve lower ripple input current and lower voltage fluctuations over the input capacitance (e.g., capacitors C 1  and C 2  of  FIGS.  1 ,  2  and  6   ). 
     In some aspects, the sequential phase shifting at the second frequency of the switches may reduce the temporary and mean (e.g., average) input current drawn by the power converter circuit (for example, power converter circuit  30 ) according to illustrative aspects of the disclosure. Thus, the ripple voltage across the bulk/input capacitors (e.g., capacitors C 1  and C 2 ) may be reduced. The reduction of ripple voltage and/or current flowing through the bulk/input capacitors may reduce the cost and size of a power converter circuit. 
     Switches M 1 , M 2 , M 3 , M 4 , M 5 , M 6 , M 11 , M 12 , M 13 , M 14 , M 15 , M 16 , M 21 , M 22 , M 23 , M 24 , M 25  and M 26  may be switched according to the duty cycle ratio, which may be changed according to a comparison between a reference voltage and the output voltage at output terminals P 1 , P 2  and P 3 . In some aspects, the reference voltage of the switches of series connection of switches (e.g., Sd 1 , Sd 2 , Sd 3 , and Sd 4 ) may be similar to the reference voltage of the switches of the same power converter circuit (e.g., switches M 1 , M 2 , M 3 , M 4 , M 5 , and M 6 ). An example for the timing shown in  FIGS.  3 - 4    may be an example of the desired duty cycles, but a variety of different timings may be used that may have similar or different switching performance. 
     Reference is made to  FIG.  7   , which illustrates timelines  70  showing waveforms that describe, according to some aspects of the disclosure, a possible control method of a power converter circuit (e.g., power converter circuit  30  comprising three single-phase converter circuits  11 ,  21  and  31 ). The timelines show waveforms, in volts (V) versus time, and illustrate an example for possible control signals. A different graph is provided for each of the control signals PWM 11 , PWM 12 , PWM 13 , PWM 14  and PWM 15  used to control switches of the power converter circuit. The PWM 11 , PWM 12 , PWM 13 , PWM 14  and PWM 15  control signals may be generated by digital encoding component(s) (e.g., a microprocessor, general processor, etc.) and/or analog circuit(s) (e.g., using a comparator, oscillator, etc.). For example, PWM 11 , PWM 12 , PWM 13 , PWM 14  and PWM 15  control signals may be generated by controller  380  of  FIG.  6   . 
     In the example shown in  FIG.  7   , control signals PWM 11 , PWM 12 , PWM 13 , PWM 14  and PWM 15  may be generated at the second frequency of  FIG.  6   , which is relatively higher than the first frequency, the switching frequency of the switches of the series connection of switches (e.g., switches Sd 1 , Sd 2 , Sd 3  and Sd 4  of  FIG.  6   ), and the frequency of the output voltage at output terminals P 1 , P 2  and P 3 , e.g., 50 Hz. Control signals PWM 11 , PWM 12 , PWM 13 , PWM 14  and PWM 15  may be varied according to the duty cycle ratio, which may be changed according to a comparison between a reference voltage and the output voltage at output terminals P 1 , P 2  and P 3 . 
     Control signals PWM 11 , PWM 14  and PWM 15  may control switches of different series connections in a power converter, where all series connections may be connected in parallel with respect to each other. For example, control signals PWM 11 , PWM 14  and PWM 15  may control the gate terminal (G) of MOSFETs M 1 , M 3  and M 5  of power converter circuit  11  in  FIG.  6   , respectively (or M 11 , M 13  and M 15  of power converter circuit  21  in  FIG.  6   , respectively, or M 21 , M 23  and M 25  of power converter circuit  31  in  FIG.  6   , respectively). For instance, control signals PWM 11 , PWM 14  and PWM 15  may be similar to control signals PWM 3 , PWM 4  and PWM 5  of  FIG.  3   . 
     Control signals PWM 11 , PWM 14  and PWM 15  may be shifted sequentially by 1/(P) (where P is the number of parallel connected single-phase power converters) of the switching period of the second frequency with respect to each other. For example, in  FIG.  6   , where P=3, control signals PWM 11 , PWM 14  and PWM 15  may be shifted sequentially by 120°. 
     Control signals PWM 11 , PWM 14  and PWM 15  may be varied according to a common duty cycle ratio, which may be changed according to a comparison between a common reference voltage and the output voltage at the output terminal of the single-phase power converter (e.g., terminal P 1  of single-phase power converter  11 ). 
     In some aspects, controller  380  of  FIG.  6    may generate complementary PWM control signals with respect to PWM control signals PWM 11 , PWM 14  and PWM 15 . The complementary PWM control signals may control the corresponding and complementary switch(es) to the series connection. For example, complementary PWM control signals with respect to PWM control signals PWM 11 , PWM 14  and PWM 15  may control the gate terminal (G) of MOSFETs M 2 , M 4  and M 6  of  FIG.  6   , respectively. 
     Control signals PWM 11 , PWM 12  and PWM 13  may control each of the switches of different parallel-connected power converters. Following the above example, where control signal PWM 11  controls the gate terminal (G) of MOSFET M 1  of power converter circuit  11  in  FIG.  6   , control signals PWM 12  and PWM 13  may control the gate terminal (G) of MOSFETs M 1 l and M 21  of power converters  21  and  31  in  FIG.  6   , respectively. 
     Control signals PWM 11 , PWM 12  and PWM 13  may be shifted sequentially by 1/(P*N) (where P is the number of parallel connected power converters, and N is the number of parallel series connections in each power converter) of the switching period of the second frequency with respect to each other. For example, in  FIG.  6   , where P=N=3, control signals PWM 11 , PWM 12  and PWM 13  may be shifted sequentially by 40°. 
     Control signals PWM 11 , PWM 12  and PWM 13  may be varied according to a different duty cycle ratio, which may be changed according to a comparison between a common reference voltage and the output voltage at the output terminal of the corresponding single-phase power converter. For example, the duty cycle ratio of control signal PWM 11  may be changed according to a comparison between a common reference voltage and the output voltage at terminal P 1  of single-phase power converter  11 . The duty cycle ratio of control signal PWM 12  and PWM 13  may be changed according to a comparison between a common reference voltage and the output voltage at terminal P 2  of single-phase power converter  21  and P 3  of single-phase power converter  31 , respectively. The output voltages at each of terminals P 1 , P 2  and P 3  may be phase shifted by 120°, thus, the duty-cycle of each of control signals PWM 11 , PWM 12  and PWM 13  may vary. 
     Reference is made to  FIG.  8   , which illustrates timelines  80  and  81  showing waveforms that describe, according to some aspects of the disclosure, a current flowing through the bulk/input capacitors of a power converter circuit (e.g., capacitors C 1  and C 2  of  FIGS.  1 ,  2  and  6   ). The timelines show waveforms, in current (A) versus time. 
     Timeline  80  illustrates a current flowing through the bulk/input capacitors of a 3-phase power converter circuit using sequential phase shifting (for example, as depicted referring to  FIGS.  6  and  7   ) with respect to each of the switches (within each phase and between each phase). 
     Timeline  81  illustrates a current flowing through the bulk/input capacitors of a 3-phase power converter circuit with the same configuration of elements as the power converter circuit of timeline  80 . However, the current shown in timeline  81  illustrates an operation without the sequential phase-shifting at the high-frequency (e.g., second frequency of  FIGS.  1 ,  2 ,  3 ,  4  and  6   ) between different single-phase power converters; although a high-frequency phase-shift between different series connections within a single-phase power converter may exist, for example, as shown in  FIG.  3   . 
     It can be noted, based on the comparison between the currents illustrated in timelines  80  and  81 , that the sequential phase shifting may achieve lower ripple input current, and, thus, lower voltage fluctuations over the input capacitance (e.g., capacitors C 1  and C 2  of  FIGS.  1 ,  2  and  6   ). 
     In some aspects, the sequential phase shifting of the switches may reduce the temporary and mean (e.g., average) input current drawn by the power converter circuit (for example, power converter circuit  30 ) according to illustrative aspects of the disclosure. The reduction of ripple voltage and/or current flowing through the bulk/input capacitors may reduce cost and size. 
     Reference is made to  FIG.  9   , which illustrates a circuit diagram of a power converter circuit  95  according to illustrative aspects of the disclosure.  FIG.  9    provides a generalization of an (e.g., multi-level) inverter circuit topology according to illustrative aspects of the disclosure. In the example embodiment of  FIG.  9   , the power converter circuit  95  is an example of a three-phase multilevel inverter. A direct current (DC) input voltage Vin may be applied across input terminals A and B. Input voltage Vin may be a DC voltage received from a DC power source, e.g. a battery, a photovoltaic panel, a rectified source of alternating current (AC) from an AC generator, etc. 
     A series connection of capacitors C 1  and C 2  may be connected across input terminals A and B. In some aspects, capacitors C 1  and C 2  may be replaced by a plurality of series and/or parallel connected capacitors. Node E may be the point of connection between capacitors C 1  and C 2  (e.g., intermediate node). Node E may be coupled to neutral and/or earth potential. 
     In some aspects, power converter circuit  95  may comprise a plurality of single-phase power converter circuits. In the example embodiment of  FIG.  9   , the power converter circuit  95  comprises three single-phase converter circuits  96 ,  97  and  98 . Each of the single-phase converter circuits  96 ,  97  and  98  may be connected across input terminals A and B and configured to receive direct current input voltage V in . Each of the single-phase converter circuits  96 ,  97  and  98  may be connected to node E. Each of the single-phase converter circuits  96 ,  97  and  98  may be configured to convert direct current input voltage V in  to an alternating current at a first frequency. 
     In the example embodiment of  FIG.  9   , each of single-phase converter circuits  96 ,  97  and  98  may comprise a plurality of switches (e.g., switches Sa 1 -Sa 4  and Sb 1 -Sb 2N  of power converter circuit  10  of  FIG.  1   ). The plurality of switches may be coupled in different configurations, for example according to the following topologies: neutral-point clamped (NPC), T-type neutral-point clamped (TNPC), active neutral-point clamped (ANPC), half-bridge (HB), flying-capacitor (FC), etc. The switches may be insulated gate bipolar transistors (IGBTs), metal oxide semiconductor field effect transistors (MOSFETs), bipolar junction transistors (BJTs), field effect transistors (FETs), silicone-controlled rectifiers (SCRs) or any known solid-state switch, or any combination of these components. 
     Controller  990  may be: a digital signal processing (DSP) circuit, a field programmable gate array (FPGA) device, etc. Controller  990  may control power converter circuits  96 ,  97  and  98  and their components (for example, switches, voltages, etc.) based on a predetermined algorithm, a measured parameter (e.g., a measurement collected by one or more sensors), a calculated parameter, a determined or estimated (e.g., based on one or more measured parameters) parameter, any other appropriate data, etc. As an example, the electrical parameter may be: current, voltage, power, frequency, etc. In some aspects, controller  990  may comprise sensors to measure or sense one or more electrical parameters. 
     Power converter circuits  96 ,  97  and  98  may comprise an inductor or a plurality of inductors coupled to an output terminal. In some aspects, power converter circuits  96 ,  97  and  98  may output at a corresponding output terminal an AC sine wave (e.g., with DC offset). The inductor may be utilized to smooth a sine-wave of an AC output of a corresponding power converter circuit. In case of a plurality of inductors, the inductors may be mutually coupled together. 
     Power converter circuit  96  may comprise a plurality of circuits comprising N circuits: F 1 , F 2 , F 3  . . . and FN. The plurality of circuits F 1 , F 2 , F 3  . . . and FN may be connected across input terminals A and B and configured to receive direct current input voltage V in . Each of the plurality of circuits F 1 , F 2 , F 3  . . . and FN may be connected to node E. 
     Power converter circuit  97  may comprise a plurality of circuits comprising N circuits: G 1 , G 2 , G 3  . . . and GN. The plurality of circuits G 1 , G 2 , G 3  . . . and GN may be connected across input terminals A and B and configured to receive direct current input voltage V in . Each of the plurality of circuits G 1 , G 2 , G 3  . . . and GN may be connected to node E. 
     Power converter circuit  98  may comprise a plurality of circuits comprising N circuits: H 1 , H 2 , H 3  . . . and HN. The plurality of circuits H 1 , H 2 , H 3  . . . and HN may be connected across input terminals A and B and configured to receive direct current input voltage V in . Each of the plurality of circuits H 1 , H 2 , H 3  . . . and HN may be connected to node E. 
     Each circuit of the plurality of circuits F 1 , F 2 , F 3  . . . and FN, circuits G 1 , G 2 , G 3  . . . and GN, H 1 , H 2 , H 3  . . . and HN may comprise a similar configuration of elements (e.g., switches, capacitors, inductors, etc.). The configuration of elements may be according to one or more of the following topologies: neutral-point clamped (NPC), T-type neutral-point clamped (TNPC), active neutral-point clamped (ANPC), half-bridge (HB), flying-capacitor (FC), etc. Controller  990  may control the plurality of circuits F 1 , F 2 , F 3  . . . and FN, circuits G 1 , G 2 , G 3  . . . and GN, H 1 , H 2 , H 3  . . . and HN at a second frequency corresponding to the selected configuration. In some aspects, the second frequency may be similar to the first frequency. 
     Each circuit of the plurality of circuits of each power converter circuit (for example each circuit of the plurality of circuits F 1 , F 2 , F 3  . . . and FN) may be shifted sequentially by 1/N (where N is the number parallel-connected circuit) of the switching period (of the second frequency) with respect to the other circuits of the plurality of circuits. 
     The output voltage of power converter circuit  96  may be in a 120° phase with respect to the output voltage of power converter circuit  97 , and in a 240° phase (of the first frequency) with respect to output voltage of power converter circuit  98 . 
     For generalization, in an inverter circuit comprising P parallel connected power converters (e.g., power converters  96 ,  97  and  98 ) generating a sine-wave at a first frequency, where each power converter of the power converters comprises N circuits (e.g. F 1 , F 2 , F 3  . . . and FN) controlled at a second frequency, each circuit (e.g. F 1 , F 2 , F 3  . . . and FN) may be shifted sequentially by 1/(P*N) of the switching period of the second frequency with respect to the other circuits of power converters (e.g. circuits G 1 , G 2 , G 3  . . . and GN, H 1 , H 2 , H 3  . . . and HN). 
     For example, power converter circuit (e.g., inverter)  95  comprises three power converter circuits  96 ,  97  and  98 , and thus P=3. Each of the three power converter circuits  96 ,  97  and  98  comprises four (N=4) series connections of switches, thus controller  990  may control each circuit with phase-shift of 30°, according to following control scheme using a sequential phase-shifting (of the second frequency): 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
                   
               
               
                 Circuits 
                 F1 
                 F2 
                 F3 
                 F4 
                 G1 
                 G2 
                 G3 
                 G4 
                 H1 
                 H2 
                 H3 
                 H4 
               
               
                   
               
             
            
               
                 Phase-shift 
                 0° 
                 90° 
                 180° 
                 270° 
                 30° 
                 120° 
                 210° 
                 300° 
                 60° 
                 150° 
                 240° 
                 330° 
               
               
                   
               
            
           
         
       
     
     The phase shifting between each circuit of all power converter circuits may enable the power converter circuit  95  to achieve lower ripple input current and lower voltage fluctuations over the input capacitance (e.g., capacitors C 1  and C 2  of  FIGS.  1 ,  2 ,  6  and  9   ). 
     In some aspects, the sequential phase shifting of the switches may reduce the temporary and mean (e.g., average) input current drawn by the power converter circuit (for example, power converter circuit  95 ) according to illustrative aspects of the disclosure. Thus, the ripple voltage across the bulk/input capacitors (e.g., capacitors C 1  and C 2 ) may be reduced. The reduction of ripple voltage and/or current flowing through the bulk/input capacitors may reduce cost and size. 
     Reference is made to  FIG.  10   , which illustrates a circuit diagram of a power converter circuit  90  according to illustrative aspects of the disclosure.  FIG.  10    provides a generalization of an (e.g., multi-level) inverter circuit topology according to illustrative aspects of the disclosure.  FIG.  10    may be an example of circuit  95  of  FIG.  9   , according to aspects of the disclosure. As shown in  FIG.  10   , in some aspects of the disclosure, the circuits of each power converter circuit might not be coupled to the middle point of connection between capacitors C 1  and C 2  (e.g., intermediate node). Thus, in  FIG.  10   , the input capacitance is shown by a single capacitor Cin, which may comprise a capacitor or a plurality of capacitors. 
     In some aspects, power converter circuit  90  may comprise a plurality of single-phase power converter circuits. In the example embodiment of  FIG.  9   , the power converter circuit  90  comprises three single-phase converter circuits  96 ,  97  and  98 . Each of the single-phase converter circuits  91 ,  92  and  93  may be connected across input terminals A and B and configured to receive direct current input voltage V in . Each of the single-phase converter circuits  91 ,  92  and  93  may be configured to convert direct current input voltage V in  to an alternating current at a first frequency. 
     In the example embodiment of  FIG.  10   , each of single-phase converter circuits  91 ,  92  and  93  may comprise a plurality of switches (e.g., switches Sa 1 -Sa 4  and Sb 1 -Sb 2N  of power converter circuit  10  of  FIG.  1   ). The plurality of switches may be coupled in different configurations, for example according to the following topologies: neutral-point clamped (NPC), T-type neutral-point clamped (TNPC), active neutral-point clamped (ANPC), half-bridge (HB), flying-capacitor (FC), etc. The switches may be insulated gate bipolar transistors (IGBTs), metal oxide semiconductor field effect transistors (MOSFETs), bipolar junction transistors (BJTs), field effect transistors (FETs), silicone-controlled rectifiers (SCRs) or any known solid-state switch, or any combination of these components. 
     Power converter circuit  91  may comprise a plurality of circuits comprising N circuits: A 1 , A 2 , A 3  . . . and AN. The plurality of circuits A 1 , A 2 , A 3  . . . and AN may be connected across input terminals A and B and configured to receive direct current input voltage V in . 
     Power converter circuit  92  may comprise a plurality of circuits comprising N circuits: B 1 , B 2 , B 3  . . . and BN. The plurality of circuits B 1 , B 2 , B 3  . . . and BN may be connected across input terminals A and B and configured to receive direct current input voltage V in . 
     Power converter circuit  93  may comprise a plurality of circuits comprising N circuits: C 1 , C 2 , C 3  . . . and CN. The plurality of circuits C 1 , C 2 , C 3  . . . and CN may be connected across input terminals A and B and configured to receive direct current input voltage V in . 
     Controller  980  may be: a digital signal processing (DSP) circuit, a field programmable gate array (FPGA) device, etc. Controller  980  may control power converter circuits  91 ,  92  and  93  and their components (for example, switches, voltages, etc.) based on a predetermined algorithm, a measured parameter (e.g., a measurement collected by one or more sensors), a calculated parameter, a determined or estimated (e.g., based on one or more measured parameters) parameter, any other appropriate data, etc. As an example, the electrical parameter may be: current, voltage, power, frequency, etc. In some aspects, controller  980  may comprise sensors to measure or sense one or more electrical parameters (e.g., current, voltage, resistance). 
     Controller  980  may control each circuit of the power converters (e.g. circuits A 1 , A 2 , A 3  . . . and AN, B 1 , B 2 , B 3  . . . and BN, B 1 , B 2 , B 3  . . . and BN) according the control scheme depicted in reference to  FIG.  9    and controller  990 . 
     For generalization, in an inverter circuit comprising P parallel connected power converters (e.g., power converters  91 ,  92  and  93 ) generating a sine-wave at a first frequency, where each power converter of the power converters comprises N circuits (e.g. A 1 , A 2 , A 3  . . . and AN) controlled at a second frequency, each circuit (e.g. A 1 , A 2 , A 3  . . . and AN) may be shifted sequentially by 1/(P*N) of the switching period of the second frequency with respect to the other circuits of power converters (e.g. circuits B 1 , B 2 , B 3  . . . and BN, C 1 , C 2 , C 3  . . . and CN). 
     For example, inverter  90  comprises three power converter circuits  91 ,  92  and  93 , thus P=3. Each of the three power converter circuits  91 ,  92  and  93  comprises four (N=4) series connections of switches, thus controller  980  may control each circuit with phase-shift of 30°, according to following control scheme using a sequential phase-shifting (of the second frequency): 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
                   
               
               
                 Circuits 
                 A1 
                 A2 
                 A3 
                 A4 
                 B1 
                 B2 
                 B3 
                 B4 
                 C1 
                 C2 
                 C3 
                 C4 
               
               
                   
               
             
            
               
                 Phase-shift 
                 0° 
                 90° 
                 180° 
                 270° 
                 30° 
                 120° 
                 210° 
                 300° 
                 60° 
                 150° 
                 240° 
                 330° 
               
               
                   
               
            
           
         
       
     
     Reference is made to  FIG.  11   , which illustrates a circuit diagram of an electrical circuit (e.g., power converter)  110 . Electrical circuit  110  comprises circuit  111 , which may be an example of each of circuits A 1 , A 2 , A 3  . . . and AN, B 1 , B 2 , B 3  . . . and BN, and C 1 , C 2 , C 3  . . . and CN of  FIG.  10   , according to aspects of the disclosure. In some aspects, circuit  111  may be a flying-capacitor converter or ANPC with flying-capacitors. 
     Circuit  110  includes electrical circuit (e.g., power converter)  111  and output inductor L 1 . Circuit  111  includes: a first plurality of switches Sw 1 , Sw 2 , Sw 3  and Sw 4 , a second plurality of switches S 1 , S 2 , S 3 , S 4  . . . S 2N−1 , S 2N , S 2N+1  and S 2N+2 , and a plurality of capacitors C 100 , C 101 , C 102  . . . and C 10 N. 
     Electrical circuit  111  may be connected across input terminals A and B. (e.g., similar to input terminals A and B of  FIG.  10   ). Electrical circuit  111  may convert the input direct-current (e.g., DC) voltage across input terminals A and B to an output alternating-current (e.g., AC) voltage at terminal OUT. Output inductor L 110  may be connected to terminal OUT. 
     The first plurality of switches may be connected across input terminals A and B. A first terminal of switch Sw 1  may be coupled to input terminal A and a second terminal of switch Sw 1  may be coupled to node C. A first terminal of switch Sw 2  may be coupled to node C and a second terminal of switch Sw 2  may be coupled to node F. A first terminal of switch Sw 3  may be coupled to node F and a second terminal of switch Sw 3  may be coupled to node D. A first terminal of switch Sw 4  may be coupled to node D and a second terminal of switch Sw 4  may be coupled to input terminal B. 
     The second plurality of switches S 1 , S 2 , S 3 , S 4  . . . S 2N−1 , S 2N , S 2N+1  and S 2N+2  may comprise pairs of switches S 1 -S 2 , S 3 -S 4  . . . S 2N−1 -S 2N , and S 2N+1 -S 2N+2 . Capacitor C 100  (or a plurality of capacitors) may be coupled to node C and node D, and between pairs of switches S 1 -S 2 . Another capacitor (or a plurality of capacitors) may be connected between two pairs of switches. For example, capacitor C 101  may be connected between pairs of switches S 1 -S 2  and S 3 -S 4 , capacitor C 102  may be connected between pairs of switches S 5 -S 6  (not shown), and capacitor C 10 N may be connected between pairs of switches S 2N−1 -S 2N , and S 2N+1 -S 2N+2 . Terminal OUT may be connected between pair of switches S 2N+1 -S 2N+2 . 
     The first plurality of switches may be switched by a controller (e.g., controller  980  of  FIG.  10   ) at a first frequency. The first frequency may be the output frequency of the voltage at terminal OUT. Switch Sw 1  may be switched and conduct simultaneously (e.g., at the same time) with switch Sw 3  during the positive half-cycle of the output voltage at terminal OUT. Switch Sw 2  may be switched and conduct simultaneously (e.g., at the same time) with switch Sw 4  during the negative half-cycle of the output voltage at terminal OUT. 
     The second plurality of switches may be switched by a controller (e.g., controller  980  of  FIG.  10   ) at a second frequency and according to a duty-cycle ratio of the output voltage at terminal OUT. The second frequency may be higher than the first frequency. Each two switches of the same pair of switches, may be switched (e.g., turned ON/conduct) in a complementary manner. For example, during the positive half-cycle of the output voltage at terminal OUT, switch S 1  may be switched at a duty-cycle ratio D of the output voltage at terminal OUT, while switch S 3  may be switched at 1-D. When switch S 1  is OFF, switch S 3  may be ON, and vice versa. During the negative half-cycle of the output voltage at terminal OUT, switch S 3  may be switched at the duty-cycle ratio D of the output voltage at terminal OUT, while switch S 1  may be switched at 1-D. 
     In some aspects of the disclosure, each pair of switches of the second plurality of switches may be shifted sequentially by 1/N (where N is the number of pair of switches of the second plurality) of the switching period of the second frequency. 
     In a case where circuit  111  is used for each of circuits A 1 , A 2 , A 3  . . . and AN, B 1 , B 2 , B 3  . . . and BN, and C 1 , C 2 , C 3  . . . and CN of  FIG.  10   , all output terminals OUT of each circuit of the same power converter (e.g., A 1 , A 2 , A 3  . . . and AN) may be coupled together, to the same node of the output inductor of the corresponding power converter (for example, output inductor L 110 ). In some aspects of the disclosure herein, all output terminals OUT of each circuit of the same power converter (e.g., A 1 , A 2 , A 3  . . . and AN) may be coupled to mutually coupled inductors (e.g., coupled inductors L 4 , L 5 , L 6  of  FIG.  2   ), each of which is connected to an output inductor (e.g., differential filter), similar to output inductor L 7  of  FIG.  2   . 
     In some aspects, circuit  111  may function as a single-phase power converter. For example, circuit  111  may replace each of the single-phase converter circuits  91 ,  92  and  93 . 
     Reference is made to  FIG.  12   , which illustrates a circuit diagram of an electrical circuit (e.g., power converter)  120 . Electrical circuit  120  comprises circuit  121 , which may be an example of circuits F 1 , F 2 , F 3  . . . and FN, circuits G 1 , G 2 , G 3  . . . and GN, H 1 , H 2 , H 3  . . . and HN of  FIG.  9   , according to aspects of the disclosure. In some aspects, circuit  121  may be a neutral-point-clamped (e.g. NPC) converter. 
     Circuit  120  includes electrical circuit (e.g., power converter)  121  and output inductor L 120 . Circuit  121  includes: a plurality of S 11 , S 12 , S 13 , and S 14 , and diodes D 1 , and D 2 . 
     Electrical circuit  121  may be connected across input terminals A and B. (e.g., similar to input terminals A and B of  FIG.  10   ). Electrical circuit  121  may be configured to connect to node E, which may be an intermediate node (e.g., the point of connection) between capacitors C 1  and C 2  of  FIG.  9   . In some embodiments, node E may be coupled to neutral and/or earth potential. 
     Electrical circuit  121  may convert the input direct-current (e.g., DC) voltage across input terminals A and B to an output alternating-current (e.g., AC) voltage at a first frequency (e.g., 50/60 Hz) at terminal OUT. Output inductor L 120  may be connected to terminal OUT. 
     The plurality of switches may be connected across input terminals A and B. A first terminal of switch S 11  may be coupled to input terminal A and a second terminal of switch S 11  may be coupled to node C. A first terminal of switch S 12  may be coupled to node C and a second terminal of switch S 12  may be coupled to node F. A first terminal of switch S 13  may be coupled to node F and a second terminal of switch S 13  may be coupled to node D. A first terminal of switch S 14  may be coupled to node D and a second terminal of switch S 14  may be coupled to input terminal B. 
     The anode of the first diode D 1  may be coupled to node E and the cathode of the first diode D 1  may be coupled to node C. The anode of the second diode D 2  may be coupled to node D, and the cathode of the second diode D 2  may be coupled to node E. 
     Switches S 12  and S 13  of the plurality of switches may be switched by a controller (e.g., controller  990  of  FIG.  9   ) at a first frequency. The first frequency may be the output frequency of the voltage at terminal OUT of electrical circuit  121  in  FIG.  12   . Switches S 12  and S 13  may be switched in a complementary manner. For example, during the positive half-cycle of the output voltage at terminal OUT, switch S 12  may be ON and switch S 13  may be OFF. During the negative half-cycle of the output voltage at terminal OUT, switch S 13  may be ON and switch S 12  may be OFF. 
     Switches S 11  and S 14  of the plurality of switches may be switched by a controller (e.g., controller  990  of  FIG.  9   ) at a second frequency. The second frequency may be higher than the output frequency of the voltage at terminal OUT of electrical circuit  121  in  FIG.  12   . 
     During the positive half-cycle of the output voltage at terminal OUT, switch S 11  may be switched according to the duty-cycle ratio D of the output voltage. During the positive half-cycle of the output voltage at terminal OUT, switch S 14  may be turned OFF. Thus, during the positive half-cycle, the first diode D 1  may conduct in a complementary manner with respect to switch S 11 , e.g., at 1-D. 
     During the negative half-cycle of the output voltage at terminal OUT, switch S 14  may be switched according to the duty-cycle ratio D of the output voltage. During the negative half-cycle of the output voltage at terminal OUT, switch S 11  may be turned OFF. Thus, during the negative half-cycle, the second diode D 2  may conduct in a complementary manner with respect to switch S 14 , e.g., at 1-D. 
     In a case where circuit  121  is used for each of circuits F 1 , F 2 , F 3  . . . and FN, circuits G 1 , G 2 , G 3  . . . and GN, H 1 , H 2 , H 3  . . . and HN of  FIG.  9   , all output terminals OUT of each circuit of the same power converter (e.g., F 1 , F 2 , F 3  . . . and FN of power converter  96 ) may be coupled together, to the same node of the output inductor of the corresponding power converter (for example, output inductor L 120 ). 
     In a case where circuit  121  is used for each of circuits F 1 , F 2 , F 3  . . . and FN, circuits G 1 , G 2 , G 3  . . . and GN, H 1 , H 2 , H 3  . . . and HN of  FIG.  9   , each circuit of the same power converter (e.g., F 1 , F 2 , F 3  . . . and FN of power converter  96 ) may be shifted sequentially by 1/N (where N is the number of circuits in the power converter) of the switching period of the second frequency. In addition, each circuit of each power converter may be shifted sequentially by 1/N*P (where P is the number of single-phase power converters, and N is the number of circuits in the power converter) of the switching period of the second frequency. 
     In some aspects of the disclosure herein, all output terminals OUT of each circuit of the same power converter (e.g., F 1 , F 2 , F 3  . . . and FN of power converter  96 ) may be coupled to mutually coupled inductors (e.g., coupled inductors L 4 , L 5 , L 6  of  FIG.  2   ), each of which is connected to an output inductor (e.g., differential filter), similar to output inductor L 7  of  FIG.  2   . 
     Reference is made to  FIG.  13   , which illustrates a circuit diagram of an electrical circuit (e.g., power converter)  130 . Electrical circuit  130  comprises circuit  131 , which may be an example of circuits F 1 , F 2 , F 3  . . . and FN, circuits G 1 , G 2 , G 3  . . . and GN, H 1 , H 2 , H 3  . . . and HN of  FIG.  9   , according to aspects of the disclosure. In some aspects, circuit  131  may be a T-type neutral-point-clamped (e.g. TNPC) converter. 
     Circuit  130  includes electrical circuit (e.g., power converter)  131  and output inductor L 130 . Circuit  131  includes: a plurality of switches S 21 , S 22 , S 23 , and S 24 , and two diodes D 11  and D 12 . 
     Electrical circuit  131  may be connected across input terminals A and B. (e.g., similar to input terminals A and B of  FIG.  10   ). Electrical circuit  131  may be configured to connect to node E, which may be an intermediate node (e.g., the point of connection) between capacitors C 1  and C 2  of  FIG.  9   . In some embodiments, node E may be coupled to neutral and/or earth potential. 
     Electrical circuit  131  may convert the input direct-current (e.g., DC) voltage across input terminals A and B to an output alternating-current (e.g., AC) voltage at a first frequency (e.g., 50/60 Hz) at terminal OUT. Output inductor L 130  may be connected to terminal OUT. 
     A first terminal of switch S 21  may be coupled to input terminal A and a second terminal of switch S 21  may be coupled to terminal OUT. A first terminal of switch S 22  may be coupled to node E and a second terminal of switch S 22  may be coupled to node F. A first terminal of switch S 23  may be coupled to node F and a second terminal of switch S 23  may be coupled to terminal OUT. A first terminal of switch S 24  may be coupled to terminal OUT and a second terminal of switch S 24  may be coupled to input terminal B. Diode D 11  may be coupled in parallel with switch S 22 , where the anode of D 11  may be coupled to node E, and the cathode of D 11  may be coupled to node F. Diode D 12  may be coupled in parallel with switch S 23 , where the anode of D 12  may be coupled to terminal OUT, and the cathode of D 12  may be coupled to node F. 
     Switches S 22  and S 23  of the plurality of switches may be switched by a controller (e.g., controller  990  of  FIG.  9   ) at a first frequency. The first frequency may be the output frequency of the voltage at terminal OUT. Switches S 22  and S 23  may be switched in a complementary manner. For example, during the positive half-cycle of the output voltage at terminal OUT, switch S 23  may be ON and switch S 22  may be OFF. During the negative half-cycle of the output voltage at terminal OUT, switch S 22  may be ON and switch S 23  may be OFF. 
     Switches S 21  and S 24  may be switched by a controller (e.g., controller  990  of  FIG.  9   ) at a second frequency. The second frequency may be higher than the output frequency of the voltage at terminal OUT. 
     During the positive half-cycle of the output voltage at terminal OUT, switch S 21  may be switched according to the duty-cycle ratio D of the output voltage. During the positive half-cycle of the output voltage at terminal OUT, switch S 24  may be turned OFF. Thus, during the positive half-cycle, diode D 11  may conduct in a complementary manner with respect to switch S 21 , e.g., at 1-D. 
     During the negative half-cycle of the output voltage at terminal OUT, switch S 24  may be switched according to the duty-cycle ratio D of the output voltage. During the negative half-cycle of the output voltage at terminal OUT, switch S 21  may be turned OFF. Thus, during the negative half-cycle, diode D 12  may conduct in a complementary manner with respect to switch S 24 , e.g., at 1-D. 
     In a case where circuit  131  is used for each of circuits F 1 , F 2 , F 3  . . . and FN, circuits G 1 , G 2 , G 3  . . . and GN, H 1 , H 2 , H 3  . . . and HN of  FIG.  9   , all output terminals OUT of each circuit of the same power converter (e.g., F 1 , F 2 , F 3  . . . and FN of power converter  96 ) may be coupled together, to the same node of the output inductor of the corresponding power converter (for example, output inductor L 130 ). 
     In a case where circuit  131  is used for each of circuits F 1 , F 2 , F 3  . . . and FN, circuits G 1 , G 2 , G 3  . . . and GN, H 1 , H 2 , H 3  . . . and HN of  FIG.  9   , each circuit of the same power converter (e.g., F 1 , F 2 , F 3  . . . and FN of power converter  96 ) may be shifted sequentially by 1/N (where N is the number of circuits in the power converter) of the switching period of the second frequency. In addition, each circuit of each power converter may be shifted sequentially by 1/N*P (where P is the number of single-phase power converters, and N is the number of circuits in the power converter) of the switching period of the second frequency. 
     In some aspects of the disclosure herein, all output terminals OUT of each circuit of the same power converter (e.g., F 1 , F 2 , F 3  . . . and FN of power converter  96 ) may be coupled to mutually coupled inductors (e.g., coupled inductors L 4 , L 5 , L 6  of  FIG.  2   ), each of which is connected to an output inductor (e.g., differential filter), similar to output inductor L 7  of  FIG.  2   . 
     Reference is made to  FIG.  14   , which illustrates a circuit diagram of an electrical circuit (e.g., power converter)  140 . Electrical circuit  140  comprises circuit  141 , which may be an example of circuits F 1 , F 2 , F 3  . . . and FN, circuits G 1 , G 2 , G 3  . . . and GN, H 1 , H 2 , H 3  . . . and HN of  FIG.  9   , according to aspects of the disclosure. In some aspects, circuit  141  may be an active neutral—point clamped (e.g., ANPC) converter. 
     Circuit  140  includes electrical circuit (e.g., power converter)  141  and output inductor L 140 . Circuit  141  includes: a first plurality of switches S 31 , S 32 , S 33 , and S 34 , and a second plurality of switches Ss 1  and Ss 2 . 
     Electrical circuit  141  may be connected across input terminals A and B. (e.g., similar to input terminals A and B of  FIG.  10   ). Electrical circuit  141  may be configured to connect to node E, which may be an intermediate node (e.g., the point of connection) between capacitors C 1  and C 2  of  FIG.  9   . In some embodiments, node E may be coupled to neutral and/or earth potential. 
     Electrical circuit  141  may convert the input direct-current (e.g., DC) voltage across input terminals A and B to an output alternating-current (e.g., AC) voltage at a first frequency (e.g., 50/60 Hz) at terminal OUT. Output inductor L 140  may be connected to terminal OUT. 
     A first terminal of switch S 31  may be coupled to input terminal A and a second terminal of switch S 31  may be coupled to node C. A first terminal of switch S 32  may be coupled to node E and a second terminal of switch S 32  may be coupled to node C. A first terminal of switch S 33  may be coupled to node E and a second terminal of switch S 33  may be coupled to node D. A first terminal of switch S 34  may be coupled to node D and a second terminal of switch S 34  may be coupled to input terminal B. 
     The first plurality of switches S 31 , S 32 , S 33 , and S 34  may be switched by a controller (e.g., controller  990  of  FIG.  9   ) at a first frequency. The first frequency may be the output frequency of the voltage at terminal OUT. Switches S 31  and S 33  may be switched at the same time (e.g. simultaneously). Switches S 32  and S 34  may be switched in a complementary manner with respect to switches S 31  and S 33 . For example, during the positive half-cycle of the output voltage at terminal OUT, switches S 31  and S 33  may be ON and switches S 32  and S 34  may be OFF. During the negative half-cycle of the output voltage at terminal OUT, switches S 32  and S 34  may be ON and S 31  and S 33  may be OFF. 
     Switches Ss 1  and Ss 2  may be switched by a controller (e.g., controller  990  of  FIG.  9   ) at a second frequency. The second frequency may be higher than the output frequency of the voltage at terminal OUT. 
     During the positive half-cycle of the output voltage at terminal OUT, switch Ss 1  may be switched according to the duty-cycle ratio D of the output voltage. During the positive half-cycle of the output voltage at terminal OUT, switch Ss 2  may be switched in a complementary manner with respect to switch Ss 1 , e.g., at 1-D. 
     During the negative half-cycle of the output voltage at terminal OUT, switch Ss 2  may be switched according to the duty-cycle ratio D of the output voltage. During the negative half-cycle of the output voltage at terminal OUT, switch Ss 1  may be switched in a complementary manner with respect to switch Ss 2 , e.g., at 1-D. 
     In a case where circuit  141  is used for each of circuits F 1 , F 2 , F 3  . . . and FN, circuits G 1 , G 2 , G 3  . . . and GN, H 1 , H 2 , H 3  . . . and HN of  FIG.  9   , all output terminals OUT of each circuit of the same power converter (e.g., F 1 , F 2 , F 3  . . . and FN of power converter  96 ) may be coupled together, to the same node of the output inductor of the corresponding power converter (for example, output inductor L 140 ). 
     In a case where circuit  141  is used for each of circuits F 1 , F 2 , F 3  . . . and FN, circuits G 1 , G 2 , G 3  . . . and GN, H 1 , H 2 , H 3  . . . and HN of  FIG.  9   , each circuit of the same power converter (e.g., F 1 , F 2 , F 3  . . . and FN of power converter  96 ) may be shifted sequentially by 1/N (where N is the number of circuits in the power converter) of the switching period of the second frequency. In addition, each circuit of each power converter may be shifted sequentially by 1/N*P (where P is the number of single-phase power converters, and N is the number of circuits in the power converter) of the switching period of the second frequency. 
     In some aspects of the disclosure herein, all output terminals OUT of each circuit of the same power converter (e.g., F 1 , F 2 , F 3  . . . and FN of power converter  96 ) may be coupled to mutually coupled inductors (e.g., coupled inductors L 4 , L 5 , L 6  of  FIG.  2   ), each of which is connected to an output inductor (e.g., differential filter), similar to output inductor L 7  of  FIG.  2   . 
     In some aspects of the disclosure herein, in case where a power converter (e.g., power converter  96  comprising F 1 , F 2 , F 3  . . . and FN) comprises a plurality of parallel-connected circuits of circuit  141 , the first plurality of switches S 31 , S 32 , S 33 , and S 34  may be used for each of the parallel-connected circuits. For example, circuit  10  of  FIG.  1    is an example for a power converter comprising N parallel-connected circuits, similar to circuit  141 . The series connection of switches Sa 1 , Sa 2 , Sa 3  and Sa 4  may be common to each of the N parallel-connected circuits. The use of common switches, while achieving the same functionality, may reduce the size and cost of circuit  10 . 
     Reference is made to  FIG.  15   , which illustrates a circuit diagram of an electrical circuit (e.g., power converter)  150 . Electrical circuit  150  comprises circuit  151 , which is an example of each of circuits A 1 , A 2 , A 3  . . . and AN, B 1 , B 2 , B 3  . . . and BN, and C 1 , C 2 , C 3  . . . and CN of  FIG.  10   , according to aspects of the disclosure. In some aspects, circuit  151  may be a half-bridge converter. 
     Circuit  150  includes electrical circuit (e.g., power converter)  151  and output inductor L 150 . Circuit  151  includes: switches S 41  and S 42 . 
     Electrical circuit  151  may be connected across input terminals A and B. (e.g., similar to input terminals A and B of  FIG.  10   ). Electrical circuit  151  may convert the input direct-current (e.g., DC) voltage across input terminals A and B to an output alternating-current (e.g., AC) voltage at terminal OUT. Output inductor L 150  may be connected to terminal OUT. 
     Switches S 41  and S 42  may be series-connected across input terminals A and B. A first terminal of switch S 41  may be coupled to input terminal A and a second terminal of switch S 41  may be coupled to terminal OUT. A first terminal of switch S 42  may be coupled to terminal OUT and a second terminal of switch S 42  may be coupled to input terminal B. 
     Switches S 41  and S 42  may be switched by a controller (e.g., controller  980  of  FIG.  10   ) in a complementary manner at a second frequency and according to a duty-cycle ratio of the output voltage at terminal OUT. The second frequency may be higher than the first frequency. For example, during the positive half-cycle of the output voltage at terminal OUT, switch S 41  may be switched at a duty-cycle ratio D of the output voltage at terminal OUT, while switch S 42  may be switched at 1-D. When switch S 41  is OFF, switch S 42  may be ON, and vice versa. During the negative half-cycle of the output voltage at terminal OUT, switch S 42  may be switched at the duty-cycle ratio D of the output voltage at terminal OUT, while switch S 41  may be switched at 1-D. 
     In a case where circuit  151  is used for each of circuits A 1 , A 2 , A 3  . . . and AN, B 1 , B 2 , B 3  . . . and BN, and C 1 , C 2 , C 3  . . . and CN of  FIG.  10   , all output terminals OUT of each circuit of the same power converter (e.g., A 1 , A 2 , A 3  . . . and AN) may be coupled together, to the same node of the output inductor of the corresponding power converter (for example, output inductor L 150 ). In some aspects of the disclosure herein, all output terminals OUT of each circuit of the same power converter (e.g., A 1 , A 2 , A 3  . . . and AN) may be coupled to mutually coupled inductors (e.g., coupled inductors L 4 , L 5 , L 6  of  FIG.  2   ), each of which is connected to an output inductor (e.g., differential filter), similar to output inductor L 7  of  FIG.  2   . 
     In some aspects, circuit  151  may function as a single-phase power converter. For example, circuit  151  may replace each of the single-phase converter circuits  91 ,  92  and  93  in  FIG.  10   . 
     It is to be understood that the inventions are not limited in application to the details set forth in the description contained herein or illustrated in the drawings. Other examples of the inventions are contemplated and the inventions are capable of being practiced and carried out in various ways. Hence, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for designing other structures, methods, and systems for carrying out the several purposes of the presently disclosed subject matter. 
     Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are described as example implementations of the following claims. 
     Those skilled in the art will readily appreciate that various modifications and changes can be applied to the examples as hereinbefore described without departing from the scope, defined in and by the appended claims, of the disclosure. Further, various modifications should be readily appreciated from the following paragraphs describing various combinations of features set forth in numbered clauses. 
     Clause 1: A system comprising: 
     a direct current (DC) power source configured to supply a DC voltage across a pair of input terminals; and an apparatus comprising: 
     a first plurality of power converters comprising P power converters, wherein each power converter of the first plurality of power converters is coupled to the pair of input terminals and configured to convert the DC voltage to an alternating-current (AC) voltage at a first frequency at a respective output terminal; 
     wherein each power converter of the first plurality of power converters comprises a second plurality of electrical circuits comprising N electrical circuits; and 
     wherein each electrical circuit of the second plurality of electrical circuits is configured to switch based on one of a plurality of control signals having a second frequency, wherein each of the plurality of control signals is phase shifted, by 1/(N*P) of a switching period of the second frequency, with respect to another control signal of the plurality of control signals and phase shifted, by 1/N of the switching period of the second frequency, with respect to another control signal, of the plurality of control signals, for another electrical circuit of the same power converter. 
     Clause 2: A system comprising: 
     a direct current (DC) power source configured to supply a DC voltage across a pair of input terminals; and an apparatus comprising: 
     a first plurality of power converters comprising P power converters, wherein each power converter of the first plurality of power converters is coupled to the pair of input terminals and configured to convert the DC voltage to an alternating-current (AC) voltage at a first frequency at a respective output terminal; 
     wherein each power converter of the first plurality of power converters comprises a second plurality of electrical circuits comprising N electrical circuits; and 
     wherein each electrical circuit of the second plurality of electrical circuits is configured to switch based on one of a plurality of control signals having a second frequency, wherein each of the plurality of control signals is phase shifted, by 1/(N*P) of a switching period of the second frequency, with respect to another control signal of the plurality of control signals. 
     Clause 3: A system comprising: 
     a direct current (DC) power source configured to supply a DC voltage across a pair of input terminals; and an apparatus comprising: 
     a first plurality of power converters comprising P power converters, wherein each power converter of the first plurality of power converters is coupled to the pair of input terminals and configured to convert the DC voltage to an alternating-current (AC) voltage at a first frequency at a respective output terminal; 
     wherein each power converter of the first plurality of power converters comprises a second plurality of electrical circuits comprising N parallel-connected electrical circuits; and 
     wherein each parallel-connected electrical circuit of the second plurality of parallel-connected electrical circuits is configured to switch based on one of a plurality of control signals having a second frequency, wherein each of the plurality of control signals is phase shifted, by 1/(N*P) of a switching period of the second frequency, with respect to another control signal of the plurality of control signals. 
     Clause 4: The apparatus of any one of clauses 1 or 2 or 3, wherein each power converter of the first plurality of power converters is coupled a third input terminal. 
     Clause 5: The apparatus of clause 4, wherein the third input terminal is coupled to at least one of a neutral potential, an earth potential, or the first terminal. 
     Clause 6: The apparatus of any one of clauses 1 or 2 or 3, wherein a capacitor is coupled between the pair of input terminals. 
     Clause 7: The apparatus of any one of clauses 1 or 2 or 3, wherein a plurality of series-connected capacitors is connected across the pair of input terminals. 
     Clause 8: The apparatus of any one of clauses 1 or 2 or 3, further comprising one or more inductors coupled to a respective output terminal. 
     Clause 9: The apparatus of any one of clauses 1 or 2 or 3, wherein each power converter of the first plurality of power converters provides a single phase output with respect to at least one of a neutral potential, an earth potential, or the first terminal. 
     Clause 10: The apparatus of any one of clauses 1 or 2 or 3, wherein a first inductor for a first electrical circuit of the second plurality of electrical circuits is configured to have mutual inductance with at least a second inductor for a second electrical circuit of the second plurality of electrical circuits. 
     Clause 11: The apparatus of any one of clauses 1 or 2 or 3, wherein at least one electrical circuit of the second plurality of electrical circuits comprises a switch. 
     Clause 12: The apparatus of any one of clauses 1 or 2 or 3, wherein at least one electrical circuit of the second plurality of electrical circuits comprises two or more switches. 
     Clause 13: The apparatus of any one of clauses 1 or 2 or 3, wherein at least one electrical circuit of the second plurality of electrical circuits comprises a plurality of series-connected switches. 
     Clause 14: The apparatus of clause 11, further comprising a controller configured to control the switch. 
     Clause 15: The apparatus of clause 12, further comprising a controller configured to control the two or more switches. 
     Clause 16: The apparatus of clause 13, further comprising a controller configured to control plurality of series-connected switches. 
     Clause 17: The apparatus of any of clauses 14 or 15 or 16, wherein the controller is configured to switch a first switch in a complementary manner with respect to a second switch. 
     Clause 18: The apparatus of any of the preceding clauses, wherein the controller is configured to switch each parallel-connected electrical circuit of the second plurality of parallel-connected electrical circuits in a phase-shifted manner with respect to each other. 
     Clause 19: The apparatus of any of the preceding clauses, wherein the controller is configured to switch each electrical circuit of the second plurality of electrical circuits in a phase-shifted manner with respect to each other. 
     Clause 20: The apparatus of any of the preceding clauses, wherein the controller is configured to switch one of the switch, series-connected switches, or the two or more switches, based on a duty cycle ratio. 
     Clause 21: The apparatus of any of the preceding clauses, further comprising a relay connected between at least one of the one or more inductors and the output terminal. 
     Clause 22: A method comprising: 
     converting, by a power converter of a first plurality of P power converters, a DC voltage, received across a pair of input terminals, to an alternating-current (AC) voltage at a first frequency at a respective output terminal, wherein each power converter of the first plurality of the P power converters comprises a second plurality of electrical circuits comprising N electrical circuits; and 
     switching (e.g., sequentially shifting) the second plurality of electrical circuits based on a plurality of control signals having a second frequency, wherein each of the plurality of control signals is phase shifted, by 1/(N*P) of a switching period of the second frequency, with respect to another control signal of the plurality of control signals. 
     Clause 23: A method comprising: 
     converting, by a power converter of a first plurality of P power converters, each comprising a second plurality of electrical circuits comprising N electrical circuits, a DC voltage, received across a pair of input terminals, to an alternating-current (AC) voltage at a first frequency at a respective output terminal; and 
     controlling each electrical circuit of the second plurality of electrical circuits based on a plurality of signal having a second frequency, wherein each of the plurality of signals is phase shifted, by 1/(N*P) of a switching period of the second frequency, with respect to another signal of the plurality of signals and phase shifted, by 1/N of the switching period of the second frequency, with respect to another signal, of the plurality of signals, for another electrical circuit of the same power converter. 
     Clause 24: A method comprising: 
     converting, by a power converter of a first plurality of P power converters, each comprising a second plurality of series-connections of switches comprising N series-connections of switches, a DC voltage, received across a pair of input terminals, to an alternating-current (AC) voltage at a first frequency at a respective output terminal; and 
     controlling each of the series-connections of switches based on a plurality of signals having a second frequency, wherein each of the plurality of signals is phase shifted, by 1/(N*P) of a switching period of the second frequency, with respect to another signal of the plurality of signals and phase shifted, by 1/N of the switching period of the second frequency, with respect to another signal, of the plurality of signals, for another series-connection of switches of the same power converter. 
     The method of any one of clauses 22 or 23 or 24, further comprising one or more features of any of clauses 1-21.