Multilevel converter circuit and method

A power conversion system including a first converter configured to convert an input voltage into a plurality of discrete voltages. A second converter configured to convert the plurality of discrete voltages into a plurality of modulated voltages. Each modulated voltage of the plurality of modulated voltages comprises two voltage levels equal, respectively, to two of the discrete voltages of the plurality of discrete voltages. A selection unit configured to alternatively output each modulated voltage of the plurality of modulated voltages across a pair of output terminals.

BACKGROUND

Converters may be used for converting direct current (DC) voltage into another DC voltage and/or to an alternating current (AC) voltage. Converter construction may typically make use of power transistors and diodes. The power transistors and diodes may be operated as electronic switches. Certain converter designs may use “hard” switching, which may give rise to switching losses which, for high values of the switching frequency, may cause a reduction in energy conversion efficiency. Hard switching may be characterized by a total commutation voltage drop over the current-carrying switch at a current commutation time. In case of hard switching, the voltage may increase up to the value of the commutation voltage while the current continues flowing, before it drops, which may cause high power loss peaks in the switch. It may therefore be desirable to develop converter topologies and switching methods that enable “soft” switching, which may reduce total switching losses.

In attempts to improve converter efficiency and reduce costs, high-power converters may make use of a technique referred to as multi-level inversion. Multi-level converter design may reduce the occurrence of simultaneously high values of voltage and current, and hence high-power dissipation values, during the switching process. Additionally, multi-level converter topologies may provide multiple output voltage values, which may reduce the size of associated output filters. It may be desirable to develop converter topologies and efficient switching methodologies to improve the cost and/or efficiency of converters.

SUMMARY

The following summary briefly describes certain features and is not intended to be an extensive overview and is not intended to identify key or critical elements.

Systems, apparatuses, and methods are described for a multi-level converter configurable to convert a direct current (DC) voltage its input to an alternating current (AC) at its output. A first converter may be adapted to convert an input voltage to give multiple first discrete output voltages on respective first output terminals of the first converter. A second converter may be adapted to convert at least one of the first discrete output voltages to two discrete states of voltage. The two discrete states of voltage may be provided on multiple second output terminals of the second converter for each of the first discrete output voltages. A selection unit may be adapted to provide an output voltage on output terminals selected from the second output terminals responsive to sensed electrical parameters of the multi-level converter and/or a reference signal.

These and other features and advantages are described in greater detail in the Detailed Description below.

DETAILED DESCRIPTION

In the following description of various illustrative embodiments, 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.

By way of introduction, features may be directed in general to a converter topology that converts a direct current (DC) voltage at its input to an alternating current (AC) voltage at its output. The DC voltage at the input may be a single DC voltage that, for example, may be provided from various interconnections of DC power sources. The single DC voltage in a first conversion may be separated by the first conversion to give multiple DC outputs that then in a second conversion may provide multiple AC outputs. The AC outputs may then be selected and controlled responsive to a reference signal and/or electrical parameters sensed in the converter topology. The selection control may ensure correct levels of operating voltage, current, impedance, resistance, phase angle, power factor, level of harmonic distortion, frequency and/or power for example.

The term pulse width modulation (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 substantially open and closed circuit 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 the time period. During the time period, the switch remains substantially closed circuit for the 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. During the time period, the switch remains substantially open circuit for the time period.

The term “multiple” as used here in the detailed description indicates the property of having or involving two or more 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.

Reference is now made toFIG. 1A, which illustrates a block diagram of a power system100, according to illustrative aspects of the disclosure. Power system100may include multiple wiring configurations111. Each wiring configuration111may include one or more power sources101that may be connected to a respective power device103. Power sources101may be AC power sources (e.g., wind turbines) or sources of DC power derived from wind turbines, battery banks, photovoltaic solar panels, rectified alternating current (AC) or electrical power derived from petrol generators, for example. Each wiring configuration111may include output terminals A and B. The outputs on terminals A and B of the wiring configurations111may be connected in series to form a series connection of wiring configuration111outputs that may be connected to input terminals of a converter107. Each wiring configuration111may include output terminals A and B. The outputs on terminals A and B of the other wiring configurations111may be connected in parallel to form a parallel connection of wiring configuration111outputs. The parallel connection may be connected to input terminals of converter107with a voltage VDC. The output terminals converter107may be connected to load109and/or multiple loads109. According to illustrative aspects of the disclosure described below, converter107may be a DC to AC converter, and load109may be an AC utility grid, for example.

Reference is now made toFIG. 1B, which illustrates a block diagram of further details of converter107a, according to illustrative aspects of the disclosure. Converter107amay include single input multiple level output (SIMLO) converter10a, multiple input multiple output (MIMO) converter12aand selector unit16a. Converter107amay be considered as an example of a substantially symmetric converter topology. Connected to the input of SIMLO converter10aat terminals A and B is direct current (DC) voltage VDC. Voltage VDCmay be supplied from the DC output of power system100. The voltage VDCmay be another source of DC supply such as DC from a battery, DC generator, a photovoltaic panel or any other source of DC power that may be provided on terminals A and B. Included in SIMLO converter10amay be two DC to DC converters1000with two inputs connected in parallel to each other at terminals A and B.

Converters1000may have a series connection of switches S1a/S1band Sna/Snb connected respectively across the two outputs of converters1000. Switches S1a/S1band Sna/Snb may be included in MIMO converter12a. A series connection of capacitors C21-C2nmay connect between the two outputs of converters1000. At substantially in the middle of the series connection of capacitors C21-C2nmay be provided the neutral (N) connection point for converter107a. Two outputs of MIMO converter12amay be provided at the respective points where switch S1aconnects to switch S1band switch Sna connects to switch Snb. The two outputs of MIMO converter12aconnect to the two inputs of selector unit16arespectively to one side of each of switches S2aand S2b. The other side of switches S2aand S2bconnect together and to one side of inductor L2. The other side of L2and the middle of the series connection of capacitors C21-C2nmay provide respectively the live (L) and neutral (N) alternating current (AC) output of converter107a. Converters1000located and connected on either side of the middle of the series connection of capacitors C21-C2n. The other side of switches S2aand S2bconnecting together to one side of inductor L2provides the substantially symmetric topology of converter107a.

In operation, SIMLO converter10amay be configurable to convert voltage VDCto two discrete voltage levels of DC output voltage respectively as V1or V2and Vn−1 or Vn. DC output voltage V1or V2and Vn−1 or Vn may be provided on each of the two output terminals of SIMLO converter10awith respect to negative terminal V0. SIMLO converter may comprise switching circuitry as shown inFIG. 1Band other figures. The two discrete voltage levels of DC output voltage on each the two output terminals of SIMLO converter10amay provide two respective selectable current paths Pt1and Pt2. Paths Pt1and Pt2may be provided by selector unit16aso as to provide the live (L) and neutral (N) alternating current (AC) output of converter107a.

Reference is now made toFIG. 1C, which illustrates a block diagram of further details of converter1000, according to illustrative aspects of the disclosure. Converter1000is shown as a DC to DC boost converter with input at terminals A and B. One side of inductor L connects to terminal A. The other side of inductor L connects to the anode of diode D and on side of switch S. The cathode of diode D connects to one side of capacitor C. The other sides of capacitor C and switch S connect to terminal B. The output of converter1000is provided across capacitor C as output voltage Voutn. In the case of converter1000being a DC to DC boost converter output voltage Voutnmay be greater than the input voltage VDCapplied to the input of converter1000. Alternatively, or in addition, converter1000may be implemented as another DC to DC converter to give a buck, buck/boost and/or buck+boost operation on voltage VDC.

Reference is now made toFIG. 1D, which illustrates a block diagram of converter107b, according to illustrative aspects of the disclosure. Converter107bmay include single input multiple level output (SIMLO) converter10b, multiple input multiple output (MIMO) converter12band selector unit16b. Converter107bmay be considered as an example of a substantially asymmetric converter topology. Connected to the input of SIMLO converter10bat terminals A and B is direct current (DC) voltage VDC. Included in SIMLO converter10bmay be DC to DC converter1000providing voltage Voutnat its output. Converter1000may have a series connection of switches in a switch network Sn connected respectively across the output of converter1000. Switch network Sn may be included in MIMO converter12b. Further included in MIMO converter12bis a series string of capacitors C20-C2n-1connected between the lower switch of switch network Sn and terminal B. A possibility of connecting other switch networks Sn across other capacitors is shown with respect to capacitor C21.

An output of converter12bis provided at the point where the two series switches of switch network Sn. The output provided by switch network Sn may connect to an input of selector unit16bto one side of inductor L2that may be included in selector unit16b. The other side of inductor L2connects to one side of capacitor Cm and to one side of switches SW1aand SW2a, which are connected together. The other side of capacitor Cm connects to the neutral (N) connection point inside multiplexor (MUX)88. The other sides of switches SW1aand SW2aprovide respectively the live (L) and neutral (N) outputs of converter107b. The live (L) and neutral (N) outputs of converter107bconnect respectively to switches SW1band SW2bthat may be included in MUX88. The other side of switches SW1band SW2bconnect together and provide the multiple live (L) and neutral (N) inputs to MUX88. The multiple inputs may be provided by an interconnection of multiple switches (not shown). The interconnection may allow the live (L) or neutral (N) inputs of MUX88to be selectively connected to terminals V1, V2, V2-V3, V3and V(n−1) via respective switches SW1band SW2b.

Reference is now made toFIG. 1E, which illustrates a block diagram of converter107c, according to illustrative aspects of the disclosure. Converter107cmay include multiple input multiple output (MIMO) converter12cand selector unit16c. Converter107cis the same as converter107bexcept that converter107cdoes not include SIMLO converter10b. Instead, with converter107c, voltage VDCprovided at terminals A and B may be connected across the input of MIMO converter12cat terminals Vn and V1. One converter1000(not shown inFIG. 1E) may be located and connected to one side above the middle of the series connection of capacitors C21-C2n. The difference between connections/operating frequencies PWM of switch network Sn and multiplexor88may provide the substantially asymmetric topology of converters107dand107e.

Reference is now made toFIG. 1F, which illustrates a partial view of a switch network Sna that may be included in a MIMO converter12, according to illustrative aspects of the disclosure. As withFIGS. 1D and 1E, the partial view shows two series connected switches connected across a capacitor that may be included in switch network Sn. The capacitor may be the output and/or the output capacitor C of converter1000or a capacitor of series string of capacitors C20-C2n-1. Another switch network Sn may be connected across another capacitor that may be next to the capacitor. Another switch network Sn may be separated a number of capacitors away from the capacitor in the series string of capacitors (C20-C2n-1for example). A further two switches Sn1and Sn2may be wired in series and wired across the two outputs of the two switch networks Sn. The point where switches Sn1and Sn2are connected together corresponds to the output of switch network Sna.

Reference is now made toFIG. 1G, which illustrates further details of multiplexor88, according to illustrative aspects of the disclosure. In descriptions that follow, multiple switches wired in series such as switches Q340c, Q330a, and Q310afor example may be implemented with a single switch. The source of switch SW1a(not shown) may provide the live (L) output terminal of converters107b/107cand is further connected to the drain of switch SW1b/Q320d. The source of switch SW2a(not shown) may provide the neutral (N) output terminal of converters107b/cand is further connected to the drain of switch SW2b/Q310b. Switch SW1bmay include switches Q320b, Q320cand Q320d. The source of switch Q320bconnects to the source of switch Q31. In general switches Q31-Q34may be included as part of a MIMO converter12and/or a selector unit16. The drain of switch Q320bconnects to the source of switch Q320cand the source of switch Q320a. The drain of switch Q320aconnects to the drain of switch Q32. The drain of switch Q320cconnects to the source of switch Q320dand to the source of switch Q340c. The drain of switch Q340cconnects to the drain of switch Q340band the source of switch Q340a. The drain of switch Q340aconnects to the drain of switch Q34. The source of switch Q340bconnects to the source of switch Q33. Switch SW2bmay include switches Q310awhere the drain of switch Q310awired in series with the source switch Q310b. The point at which the drain of switch Q310aconnects with the source switch Q310balso connects to the source of switch Q330a. The drain of switch Q330aconnects to the drain of switch Q32. The drain of switch Q310bmay provide the neutral (N) output terminal of converter107b/107c.

The neutral (N) point of converters107b/107cmay connect to voltage terminal V1via switches SW2a(not shown) and SW2band body diode of switch Q31and/or voltage terminal V2via switch SW2a, SW2band switch Q32. Further, the neutral (N) point of converter107b/107cmay connect to voltage terminal V3via the body diodes of switches Q310band Q330athen through and Q33and/or voltage terminal V4via the body diodes of switches Q310band Q330aand through switch Q34.

In a similar way, the live (L) point of converters107b/107cmay connect to voltage terminal V1via switches SW1a(not shown) and SW1band/or from voltage terminal V2via switch Q320a, switch Q320cand switch Q320d. Further, the live (L) point of converter107b/107cmay connect to voltage terminal V3via switches Q340b, Q340cand Q320dand/or voltage terminal V4via switches Q340a, Q340cand Q320d. In sum, MUX88may allow the live (L) or neutral (N) inputs of MUX88to be selectively connected to terminals V1, V2, V2-V3, V3and V(n−1) via respective switches SW1band SW2b.

Descriptions so far in general, and in greater detail in descriptions that follow, for converters may include cascade-able elements that are interchangeable in various combinations. For example, one or more outputs of one stage (e.g., a first converter) may be connected to one or more inputs of another stage (e.g., a second converter). Thus, for example, when A is cascaded with B, the outputs X and Y of A may be connected to the inputs of W and Z of B, respectively. The cascade-able elements may be configured for example to provide for the function of harmonic cancellation in a converter, reduce the occurrence of simultaneously high values of voltage and current. The reduction of simultaneously high values of voltage and current may therefore may reduce high-power dissipation values during the switching process. Additionally, the multi-level converter topologies described above and in descriptions that follow may provide multiple output voltage values. The multiple output voltage values may reduce the size of associated output filters, may minimize the number of switches utilized and enable the choice of switches that are cheaper.

Reference is now made toFIG. 1H, which illustrates a generalized block diagram of further details of converter107, according to illustrative aspects of the disclosure. The generalized block diagram also includes generalized SIMLO converter10, MIMO converter12and selector unit16. SIMLO converter10may be implemented as SIMLO converters10a,10b,10cdescribed above and below in the descriptions that follow. Similarly, MIMO converter12and selector unit16may be implemented respectively as MIMO converters12a,12b,12cand selector units16a,16b,16cdescribed above and below in the descriptions that follow. MIMO converter12may comprise switching circuitry as shown inFIG. 1Hand other figures. In general, reference to SIMLO converter10, MIMO converter12and selector unit16is intended to include all the other embodiments of SIMLO converters, MIMO converters and selector units described above and below. Further, the embodiments described above and below for SIMLO converter10, MIMO converter12and selector unit16may be cascaded together in a variety of combinations. For example, a cascade of SIMLO converter10b, MIMO converter12cand selector unit16amay be utilized in some embodiments.

As described above, voltage VDCon terminals A and B may be the DC output of power system100. Voltage VDCon terminals A and B may be another source of DC supply such as DC from a battery, DC generator, a photovoltaic panel or any other source of DC power. Voltage VDCmay have a negative terminal (V0) that may connect to neutral (N), earth or ground, or may not connect to neutral (N), earth or ground. In some aspects, negative terminal (V0) may be galvanically isolated from neutral (N) and/or earth. If the negative terminal of voltage VDCis not connected to ground, voltage VDCmay be referred to as a floating voltage. VDCas shown may be considered to be an example of a unipolar voltage. Voltage VDCmay also be a bipolar voltage so that the input to SIMLO converter10may have three inputs: VDC/2, 0 and −VDC/2 for example. Voltage VDCmay connect to the input of a single input multi-level output (SIMLO) converter10. The positive terminal of voltage VDCmay connect to the positive input of SIMLO converter10via inductor L1. SIMLO converter10may convert voltage VDCto eight discrete voltage levels of DC output voltage respectively on eight output terminals V1-V8with respect to negative terminal V0. Eight output terminals V1-V8with respect to negative terminal V0of SIMLO converter10may connect to respective input terminals of multi input multiple output (MIMO) converter12.

MIMO converter12may convert the discrete voltage levels (V1-V8) on its input to two discrete states of voltage level on each of seven outputs O/P1-O/P7. For example, the two discrete states of voltage provided on output O/P7may be voltages V7and V8, the two discrete states of voltage on output O/P6may be voltages V6and V7. The outputs O/P1-O/P7may be summarized in Table 1 below.

The two discrete values of voltage on each output (O/Pn, n=1-7) may alternate from one to each other by virtue of multiple pulse width modulation (PWM) signals from PWM unit14. The PWM signals may be applied to the control inputs of the switches (not shown) of MIMO converter12. The switches of MIMO converter12may provide two levels of voltage on each respective output O/P1-O/P7by virtue of the PWM applied by PWM unit14.

Controller18(e.g., control unit) may include two control line outputs and one input from reference waveform19. Control line output18aconnects to a control input of PWM unit14and control line output18bconnects to a control input of selector unit16. Control line output14aconnects to SIMLO convert10and control line14bconnects to MIMO converter12. Control lines18aand/or18bmay be provided respectively to PWM unit14and/or selector unit16, responsive to parameters of reference waveform19and/or sensed parameters of converter107. Controller18may additionally include a PWM unit similar to that of PWM unit14and supply a PWM control signal to selector unit16via control signal18b. In general, according to features described in greater detail below, the PWM supplied to SIMLO converter10and/or MIMO converter12may be at a higher frequency compared to the frequency of PWM that may be supplied to selector unit16.

Sensed parameters of converter107by sensors (not shown) may be included in control unit18or operatively connected to control unit18. Selector unit16may provide a single-phase output shown as terminals live (L) and neutral (N). Further details of converter107and its operation are shown in the descriptions that follow. In sum, converter107may include an input connected to DC voltage VDCthat may be converted by converter107to a single-phase AC output on terminals live (L) and neutral (N) for example. Additionally, the features described above and, in more detail, below for converter107may be repeatable and inter connected. Repeatable and interconnected features of converter107may provide, for example, a split phase and/or three phase AC output on output terminals of converter107.

Reference is now made toFIG. 1I, which shows a block diagram of further details of control unit18, according to illustrative aspects of the disclosure. A controller180may include a microprocessor, microcontroller and/or digital signal processor (DSP) that may connect to a memory189. Controller180may serve as a central controller to other controllers that may be included in power devices103for example. Communications interface182connected to controller180may provide communications between controller180and other controllers/communication interfaces included in power system100for example. The communications to and from communications interface182may be as a result of a control algorithm running on controller180. The communications may include control signals provided on control lines18aand18bto control PWM unit14and/or selector unit16. Communications in communications interface182may also include measured or sensed parameters via sensors/sensor interface184. Sensors/sensor interface184may be included in and/or operably connected to SIMLO converter10, MIMO converter12and selector unit16. The communications by communications interface182may be conveyed by use of WiFi, power line communications (PLC), near field communications or RS232/485 communication bus, for example. Communications interface182may communicate with a local area network or cellular network in order to establish an internet connection that, for example, may provide a feature of remote monitoring/or reconfiguration of converter107.

Display188connected to central controller180may be mounted on the surface of the housing of converter107for example. Display188may display, for example, the power produced from converter107that may be utilized by load109that may be measured by sensors/sensor interface184.

Connected to controller180may be connected to safety and remote shutdown unit186. Sensing by sensors/sensor interface184as well as sensed parameters communicated between controller180and sensors/sensor interfaces of SIMLO converter10, MIMO converter12and selector unit16may be indicative of a fault condition. Upon detection of a fault, remote shutdown unit186may be activated in order to isolate the fault condition and/or shutdown converter107, for example.

Reference now made toFIG. 1J, which shows a block diagram of further details of SIMLO converter10d, MIMO converter12dand selector unit16d, according to illustrative aspects of the disclosure. Switches shown in SIMLO converter10d, MIMO converter12dand selector unit16dare shown as metal oxide semiconductor field effect transistors (MOSFETs). Switches shown in SIMLO converter10dmay also include other solid-state semiconductor switches and/or electro-mechanical switches such as relays, for example. The cascaded series of stages in the processing chain of electrical powers and the further details SIMLO converter10d, MIMO converter12dand selector unit16dmay be utilized in converter107as shown inFIG. 1A.

Voltage VDCat nodes A and B connects to the input of a single input multi-level output (SIMLO) converter10dvia inductor L1. The other end of inductor L1connects to the point where two switches Q1and Q2are connected in series. The other ends of switches Q1and Q2connect respectively to terminal V8and one end of capacitor C1. The other end of capacitor C1connects to node B. Two series strings ST1and ST2of inductors connect between terminals V8and V1and/or node B. Using inductor L11as an example that may apply for each of the inductors in series strings ST1and ST2, inductor L11may include a switches Q11aand Q11bwired in series on either side of inductor L11. In a similar way, inductor L12may include a switches Q12aand Q12bwired in series on either side of inductor L1. Switch, Q11ais wired in series with switch Q13band switch Q12ais wired in series with switch Q14b. The point where Q11ais wired in series with switch Q13band switch Q12ais wired in series with switch Q14bmay be further connected together to provide terminal V6. In a similar way, the point where Q11bwired in series with switch Q9aand switch Q12bmay be wired in series with switch Q14band these two series connections may be further connected provides terminal V5. The gate of switch Q12aconnects to terminal V6in a similar way that the gate of switch Q10aconnects to terminal V5. The gates of switches Q11a, Q11band Q12bmay receive PWM from PWM unit14via control line output14a.

Inductor L11and inductor L12as with the other inductor pairs may be both electrically connected together and also electro-magnetically connected together by virtue of the mutual inductance between inductor pairs of inductors L11and L12, L15and L16etc., being wound on the same core CR1that may run throughout the length of strings ST1and ST2. Inductor pairs may have the same number of winding turns, and each inductor pair may form what may be referred to as auto transformer circuits with primary windings (e.g., L3, L5, to L15) and secondary windings (L4, L6, to L16). There can be a different number of turns to each of the inductor pairs. The different number of turns may allow an adjustment of the typical relative maximum power point (MPP) voltage of each of the voltages on terminals V1-V8, for example. Additionally, with respect to inductors L15and L16, terminal V7also connects to capacitor C1where capacitor C1connects to switch Q2.

SIMLO converter10dmay be provided with a circuit for a separating of direct current (DC) input power (VDC). The separating may provide multiple direct current (DC) voltage outputs on terminals V1-V8by use of multiple tapped inductors. Tapped inductors may include respective primary ends, secondary ends and taps connected to terminals V1-V8. The taps provided between a series connection of inductors (L13and L11, or L14and L12for example) and between two series connected switches (Q13band Q11a, or Q14band Q12afor example). The taps may be adapted for connecting individually to the DC voltage outputs (terminals V1-V8). Each tapped inductor may form a switched auto transformer circuit with both electrical and electro-magnetic connections. The electrical and electro-magnetic connections may be operated so that multiple direct current (DC) voltage outputs may be provided on terminals V1-V8. The multiple direct current (DC) voltage outputs may be derived from converting the input voltage (VDC) by SIMLO converter10d. Operation and control of the switched auto transformer circuits may include control signal14bfrom PWM unit14, for example.

The single input multi-level output SIMLO converter10dvia inductor L1, where L1connects to the point where two switches Q1and Q2may be connected in series. The other ends of switches Q1and Q2connected to the auto transformer circuits may provide a way of operation to the input of SIMLO converter10d. A central controller (not shown) such as controller180, for example, may sense electrical parameters in power system100and/or converter107dto operate switches Q1and Q2and/or the auto transformer circuits. The way of operation therefore may be to provide a buck, boost, buck/boost and/or buck+boost operation on voltage VDCthat may be the DC output of power system100for example. The electrical parameters sensed by sensors/sensor interface184for example may be voltage, current, impedance, resistance, phase angle, power factor, level of harmonic distortion, frequency or power. Control line output14amay be used send control signals to SIMLO converter10to provide appropriate control of SIMLO converter10responsive to the sensed electrical parameters.

Two switches Q8aand Q8bconnected in series across capacitor C8at nodes X and Y may present an input to a two-level inverter topology to the DC potential difference between terminals V8and V7applied to the input. The alternating current (AC) output O/P7of the two-level inverter topology may be derived from the mid-point connection between switches Q8aand Q8b. A three-level and/or multilevel inverter topology may be implemented to provide an input between nodes X and Y so that alternating current (AC) output O/P7may be a three-level and/or multilevel AC voltage.

Seven voltages or more may be output from SIMLO converter10dto the input of MIMO converter12d, i.e., the seventh voltage is the potential difference between output terminals V7and V8, the sixth voltage is the potential difference between output terminals V7and V8and so on.

Capacitor C2connects across terminals V1and V2and capacitors C3-C8connect across respective terminals, such that C3connects across terminals V2and V3and so on. By way of example using capacitor C8for all other capacitors C2-C7, two switches Q8aand Q8bconnect in series across capacitor C8. The mid-point connection between switches Q8aand Q8bprovides output O/P7of MIMO converter12d. The mid-point connection between switches Q5aand Q5bmay provide the neutral (N) connection point output of MIMO converter12dand the neutral (N) output terminal of converter107d/selection unit16d. Selection unit16dmay comprise a plurality of interconnected switches (e.g., Q9a, Q9b, Q10b, Q11a, Q11b, Q11c, etc.) configured to output an output voltage on a selected output terminal. The mid-point connection between switches Q5aand Q5bmay provide a symmetrical output of converter107/selection unit16that may provide for the function of harmonic cancellation in converter107. The other mid-point connections between the switches MIMO converter12din general also may serve to provide the neutral (N) connection point output of MIMO converter12dand the neutral (N) output terminal of converter107d/selection unit16d. The gates of switches Q8aand Q8bas with the gates of the other switches of MIMO converter12dmay receive PWM from PWM unit14via control line output14b.

The seven voltages output from MIMO converter12don outputs O/P1-O/P7may be input into respective inputs of selection unit16das shown. The switches of selection unit16dmay be connected and operated to provide two main paths P1and P2(shown by dotted line and arrow) that connect to the output of selector unit16via inductor L2. Inductor (filter) L2may provide a filtering of the AC voltages provided from paths P1and/or P2.

Path P1may be supplied from sub paths P1aand/or P1band path P2may be supplied by sub paths P2aand/or P2b. Selection by selection unit16dof the paths may be by the PWM supplied to selection unit16d. The PWM may be at a lower frequency compared to the frequency of PWM that may be supplied to SIMLO converter10dand/or MIMO converter12d. As mentioned previously, MIMO converter12dmay convert the discrete voltage levels (V1-V8) on its input to two discrete states of voltage level on seven outputs O/P1-O/P7.

By way of non-limiting example, reference is made to path P2, which may be supplied from outputs O/P7, O/P6, O/P5or O/P4. If output O/P7is required to appear on the output of selector unit16d, PWM may be applied to the gates of switches Q9a, Q10a, Q10bto provide sub path P2b. PWM applied to the gates of switches Q11a, Q11band Q11cto provide path P2while all other switches in selector unit16dare OFF. Similarly, if output O/P6is required to appear on the output of selector unit16d, PWM may be applied to the gates of switches Q9b, Q10a, Q10bto provide sub path P2b. PWM applied to switches Q11a, Q11band Q11cto provide path P2while all other switches in selector unit16dare OFF. Path P2may be supplied by sub path P2aby operation of switches connected to outputs O/P5and O/P4in a similar way as with respect to outputs O/P6and O/P7described above. Path P1may also supplied from outputs O/P3, O/P2and/or O/P1similar as that described with respect path P2described above.

Reference is now made toFIG. 2A, which shows a flow chart of an example method201for the operation of converter107d. The flow chart of method201may be used in general to describe the operation of interconnected and/or cascaded components of converter107. Steps202,204,206,208, and210of method201may be considered to be operating at substantially the same time by virtue of the cascaded stages in the processing chain of electrical powers converted by SIMLO converter10/MIMO converter12and selected by selector unit16.

Operation of SIMLO Converter10d

At step202, voltage VDCapplied at the input of SIMLO converter10dmay be converted to provide multiple direct current (DC) voltage outputs on terminals V1-V8. In other words, SIMLO converter10dmay be a circuit for separating a direct current (DC) input power (VDCfor example) to provide multiple direct current (DC) voltage outputs on its output terminals V1-V8.

As part of what may be included in step210, controller180as an example of a central controller may sense electrical parameters in power system100and/or converter107/107dat step208. Step210includes operation of switches Q1and Q2connected to inductor L1and capacitor C1and/or the auto transformer circuits. The auto transformer circuits may for example include inductor pairs of inductors such as L15and L16and four switches Q15a, Q15b, Q16aand Q16bto give a converter circuit function. The converter circuit provides may be a buck, boost, buck/boost and/or buck+boost operation on voltage VDC. Alternatively, converter1000may be utilized instead of or in addition to the auto transformer circuits to provide a buck, boost, buck/boost and/or buck+boost operation on voltage VDC. The electrical parameters sensed by sensors/sensor interface184, for example, may be voltage, current, impedance, resistance and/or power (P). Power P may be a calculation using sensed voltage (V) multiplied (x) by sensed current (I). The calculation performed by controller180, for example. Control line output14amay be used to send control signals to SIMLO converter10dfor appropriate control of SIMLO converter10dto provide a buck function on voltage VDC. The buck function on voltage VDCmay be to step down the voltage level of voltage VDCif too high whilst stepping up the input current from voltage VDCresponsive to the sensed electrical parameters. Whereas in contrast, a boost function on voltage VDCmay step up the voltage level if VDCis too low whilst stepping down the input current from voltage VDCresponsive to the sensed electrical parameters. Responsive to the electrical parameters sensed by sensors/sensor interface184, configuration of inductor pairs and switches may provide where appropriate the buck, boost, buck/boost and/or buck+boost operation on voltage VDC.

Control signals provided on control line output14amay also include control signals with respect to the operation of the auto transformer circuits. The operation may provide multiple direct current (DC) voltage outputs on the output terminals V1-V8of SIMO converter10d. Operation of the auto transformer circuits by use of multiple tapped inductors of the auto transformer circuits may include respective primary ends, secondary ends and taps connected to terminals V1-V8. The taps provided between a series connection of inductors may be L13and L11, or L14and L12and between two series connected switches may be switches Q13band Q11a, or Q14band Q12a, for example. The taps may be adapted for connecting individually to the DC voltage outputs (terminals V1-V8). Each tapped inductor therefore may form a switched auto transformer circuit with both electrical and electro-magnetic connections. The switched auto transformer circuit may be operated so that multiple direct current (DC) voltage outputs may be provided on terminals V1-V8. The voltage outputs may be derived from converting the input voltage (VDC) by SIMLO converter10d.

Control signals on control line output14amay be by a first modulation scheme responsive to the electrical parameters sensed at step208. The first modulation scheme may include pulse width modulation (PWM), frequency modulation (FM) or a variable frequency and variable pulse width. Control signals on control line output14amay include consideration of reference waveform19and the effect of a load connected to the output of selector unit16. The control signals may be responsive to sensing step208so that the DC voltage outputs on terminals V1-V8may be set and maintained at the required DC levels. PWM from PWM unit14may be applied to the gate connections of the switches of SIMLO converter10dvia control line output14a.

Operation of MIMO Converter12d

At step204, MIMO converter12dmay convert the discrete voltage levels (V1-V8) on its input to two discrete states of alternating current (AC) voltage level on each of seven outputs O/P1-O/P7. The switches of MIMO converter12dmay provide two levels of voltage on each respective output O/P1-O/P7. Two levels of voltage on each respective output O/P1-O/P7may be by virtue of the PWM applied by PWM unit14on control line output14bto the gates of the switches of MIMO converter12d. The PWM on control line output14bmay be provided by controller180(as part of control step210) responsive to sensed electrical parameters of converter107/107dat step208. The sensed electrical parameters of converter107may include the discrete voltage levels (V1-V8) and the effect of a load connected to the output of selector unit16. The sensed electrical parameters of converter107may further include consideration of reference waveform19.

For example, the two discrete states of voltage provided on output O/P7may be voltages V7and V8, the two discrete states of voltage on output O/P6may be voltages V6and V7. The outputs O/P1-O/P7may be summarized as shown in Table 1 above. By way of example, two switches Q8aand Q8bconnected in series across capacitor C8at nodes X and Y may present an input to a two-level inverter topology. The DC potential difference between terminals V8and V7applied to the input of the two-level inverter topology. The alternating current (AC) output O/P7of the two-level inverter topology may be derived from the mid-point connection between switches Q8aand Q8b. A three-level and/or multilevel inverter topology may be implemented to provide an input between nodes X and Y. Therefore, alternating current (AC) output O/P7may be a three-level and/or multilevel AC voltage.

Operation of Selection Unit16d

At step206, the seven voltages output from MIMO converter12don outputs O/P1-O/P7may be input into respective inputs of selection unit16d. Referring again toFIG. 1J, the switches of selection unit16dmay be connected and operated to provide two main paths P1and P2(shown by dotted line and arrow). Paths P1and P2connect to the output of selector unit16dvia inductor L2. Inductor (filter) L2may provide a filtering of the AC voltages provided from paths P1and/or P2. Path P1may be supplied from sub paths P1aand/or P1band path P2may be supplied by sub paths P2aand/or P2b. Selection by selection unit16of the paths may be the PWM supplied to selection unit16d. The PWM may be at a lower frequency compared to the frequency of PWM that may be supplied to SIMLO converter10dand/or MIMO converter12d.

By way of non-limiting example, reference is made to path P2that may be supplied from outputs O/P7, O/P6, O/P5or O/P4. If output O/P7is required to appear on the output of selector unit16d, PWM may be applied to switches Q9a, Q10a, Q10bto provide sub path P2b. PWM applied to switches Q11a, Q11band Q11cto provide path P2while all other switches in selector unit16dare OFF. Similarly, if O/P6is required to appear on the output of selector unit16d, PWM may be applied to switches Q9b, Q10a, Q10bto provide sub path P2b. PWM applied to switches Q11a, Q11band Q11cto provide path P2while all other switches in selector unit16dare OFF. Path P2may be supplied by sub path P2aby operation of switches connected to outputs O/P5and O/P4. In a similar way, P2may be supplied by sub path P2bby operation of switches connected to outputs O/P6and O/P7described above. Path P1may also supplied from outputs O/P3, O/P2and/or O/P1similar as that described with respect path P2described above.

Reference is now made toFIG. 2B, which shows graphical waveforms to illustrate the operation of converter107d, according to illustrative aspects of the disclosure. Waveforms are shown with horizontal axis of time (no numerical values specified) versus voltage on the vertical axis (no units specified). Reference waveform19is shown as a sinewave by dotted line. Reference waveform19may be a sinewave, triangular wave, square wave or any periodic waveform. Reference waveform19may be considered to be representative of the desired output of converter107d. Control signals on control lines18aand/or18bmay be provided respectively to PWM unit14and selector unit16d. Control signals on control lines14aand14bmay be provided respectively to SIMLO converter10dand MIMO converter12dresponsive to parameters of reference waveform19and/or sensed parameters of converter107d.

The parameters of reference waveform19may include the desired voltage amplitude and frequency of the output from converter107d. For example, where load109may be a utility grid or single-phase AC motor, the desired voltage and frequency may be 220 Volts (V) and 50 Hertz (Hz) respectively. Electrical parameters sensed by sensors/sensor interface184and appropriate signals on control lines18a,18b,14aand14bmay provide appropriate control of converter107d. Appropriate control of converter107dmay be to ensure correct levels of operating voltage, current, impedance, resistance, phase angle, power factor, level of harmonic distortion, frequency and/or power for example.

Referring back toFIG. 2A, at step202, voltage VDCapplied at the input of SIMLO converter10dmay be converted to provide multiple direct current (DC) voltage outputs on terminals V1-V8. Voltage outputs V1-V8may be shown by the horizontal lines of the shaded rectangles that represent the outputs from MIMO converter12don outputs O/P1-O/P7provided at step204. By way of example, referring to output O/P7, the two discrete states of voltage provided on output O/P7may be voltages V7and V8. Output O/P7being voltages V7and V8may be because MIMO converter12d, in general, may convert the discrete voltage levels (V1-V8) on its input to two discrete states of AC voltage. The two discrete states may be provided on each of seven outputs O/P1-O/P7. The PWM used to drive both converters10dand/or12din general may be much higher in frequency than PWM control signal20applied to selection unit16.

During time period T7of PWM control signal20, output O/P7switches between levels V8and V7many times during time period T7. During time period T7, referring again toFIG. 1J, PWM control signals20may be applied to switches Q9a, Q10a, Q10b. PWM control signals may provide sub path P2b. PWM control signal20applied to switches Q11a, Q11band Q11cto provide path P2while all other switches in selector unit16dare OFF. All other switches in selector unit16dOFF means that the two discrete states of AC voltage provided on output O/P7appears on the output of converter107d.

In a similar way, PWM control signals20may be applied to switches Q9b, Q10a, Q10bto provide sub path P2b. PWM control signal20applied to switches Q11a, Q11band Q11cto provide path P2while all other switches in selector unit16dare OFF. All other switches in selector unit16dare OFF so that the two discrete states of AC voltage provided on output O/P6appears on the output of converter107d. PWM control signal20may be the PWM signal applied to selector unit16dvia control line18b. PWM signal applied to selector unit16dmay be to select which outputs O/P1-O/P7appear on the output of converter107das part of step206. PWM control signal20may be applied to selection unit16dincluded in control step210responsive to reference signal19and/or sensed parameters of converter107dat step208.

Reference is now made toFIG. 2C, which illustrates a block diagram of a converter207, according to illustrative aspects of the disclosure. Converter207is the same as converter107shown inFIG. 1Hbut with the addition of a junction box25, generator20and rotary switch26. Further reference is also made toFIG. 2D, which shows a partial plan view of rotary switch26that includes some of poles P1-P7(poles not shown are represented by dashed line). Generator20may be rotated (shown by rotation24) by a turbine, for example, so that generator20generates electricity as a single-phase supply on live L20and neutral N20. Generator20may also generate a three-phase supply of electricity. The single-phase supply on live L20and neutral N20may connect to the single-phase supply provided on live L and neutral N of rotary switch26and/or the single-phase supply provided on live L and neutral N of selector unit16. Specifically, converter207according to descriptions below may provide a combined and synchronized single phase outputs from generator20and rotary switch26, when rotary switch26is used instead of selector unit16. The combined and synchronized single phase outputs may be by virtue of rotation24of the rotor of generator20to provide a way to synchronize the AC of converter207(at the output of MIMO converter12) to the AC generated by generator20.

In general, converter207may be operated to include the single-phase output of selector unit16as described above, the single-phase output of generator20or the combined and synchronized single phase outputs from generator20and rotary switch26.

A possible electro-mechanical implementation of selector unit16described above may be to use rotary switch26with terminals/poles P1-P7connectable to the output terminals of MIMO converter12by way of junction box25and multi-core cable27. A pole of rotary switch26may provide the AC output voltage similar to that of selector unit16responsive to the velocity of rotation24of a rotor/shaft of rotary switch26. The rotation24of a rotor of rotary switch26may be used to implement an electro-mechanical equivalent of PWM control signal20, where time T7and corresponding arc length for the pole of output O/P7is greater than the corresponding arc length for the pole of output O/P6for example. The physical arc length of poles P1-P7of rotary switch26may allow for more and/or less time for an output of the output terminals of MIMO converter12to be ON. Poles P1-P7of rotary switch26are connected to outputs of MIMO converter12on its outputs O/P1-O/P7in junction box25. Therefore, converter207may be operated to include the single-phase output of selector unit16as described above, the single-phase output of generator20or the combined and synchronized single phase outputs from generator20and rotary switch26.

The rotor of rotary switch26may be rotated so that rotation24may be at three thousand revs per minute (RPM), for example. Three thousand revolutions per minute (RPM) may be derived from the following equation for generator20with n=two poles at a frequency ƒ=50 Hz:

Speed of three thousand revolutions per minute (RPM) gives a frequency output of 50 Hertz (Hz) for the AC output voltage of rotary switch26. Rotation24of the rotor of generator20may provide a way to synchronize the AC of MIMO converter12to the AC generated by generator20on live Lao and neutral N20. Therefore, a combined and synchronized single phase outputs from generator20and rotary switch26may be achieved when rotary switch26is used instead of selector unit16to provide an electro-mechanical equivalent of PWM control signal20.

Reference now made toFIG. 3A, which shows a block diagram of further details of SIMLO converter10e, MIMO converter12eand selector unit16e, according to illustrative aspects of the disclosure. Switches shown in SIMLO converter10e, MIMO converter12eand selector unit16emay be shown as metal oxide semiconductor field effect transistors (MOSFETs). Switches may also include other solid-state semiconductor switches and/or mechanical switches. The cascaded connection of the further details SIMLO converter10e, MIMO converter12eand selector unit16emay be one of many implementations that may be utilized to implement converter107shown inFIG. 1A. The further details SIMLO converter10e, MIMO converter12eand selector unit16emay be considered to have both some similar and dissimilar component implementations and/or functions of respective SIMLO converter10, MIMO converter12and selector unit16shown inFIG. 1J. Similar components and are given the same reference number in the description below.

The positive terminal of voltage VDCmay connect to the positive input of SIMLO converter10evia inductor L1. SIMLO converter10emay convert voltage VDCto seven discrete voltage levels of DC output voltage respectively on eight output terminals V1-V8with respect to negative terminal V0. The other end of inductor L1connects to the point where two switches Q1and Q2are connected in series. The other ends of switches Q1and Q2connect respectively to terminal V8and one end of capacitor C1. The other end of capacitor C1connects to node B.

Series string ST1may include a series string of inductors connected between terminals V8and V1and/or node B. Using inductor L11as an example that may apply for each of the inductors in series string ST1, inductor L11may include switches Q11aand Q11bwired in series on either side of inductor L11. In a similar way, inductor L9may include switches Q9aand Q9bwired in series on either side of inductor L9. The inductors in series string ST1may be wound around core CR1. The connection between switches Q13band Q11aprovide voltage terminal V6and in a similar way the connection between switches Q11band Q9aprovide voltage terminal V5. A further feature similar to that shown inFIG. 1J, inductor L15is connected in parallel across inductor L16and via switches Q16aand Q16bwired in series with inductor L16. Inductor L15may also electromagnetically coupled to inductor L16by virtue of inductor L16also wound on core CR1. In sum, series string ST1forms an auto transformer between terminals V8and V1. The auto transformer may include an inductor pair of inductors L15and L16and four switches Q15a, Q15b, Q16aand Q16b. The auto transformer may provide a buck, boost, buck/boost and/or buck+boost operation on voltage VDC. Alternatively, converter1000may be utilized instead or in addition to the auto transformer circuits. Converter1000may therefore, provide a buck, boost, buck/boost and/or buck+boost operation on voltage VDC. Gates of switches Q15aand Q16amay be connected terminal V8and the gate of switch Q13aconnects to terminal V7. All other gates of the remaining switches of SIMLO converter10emay connect to control line14aof PWM unit14.

In MIMO converter12e, capacitor C2connects across terminals V1and V2. Capacitors C3-C8connect across respective terminals, such that C3connects across terminals V2and V3, C4connects across terminals V3and V4and so on. Two switches Q8aand Q8bconnect in series across capacitor C8. The mid-point connection between switches Q8aand Q8bprovides output to inductor L2of selection unit16e. The switching of switches Q8aand Q8bat the point where switches connected together provides two discrete states of voltage level (V8and V7) to inductor L2of selection unit16e. Capacitors C7, C6and C5do not have two series connected switches across them.

The point at which the drain of switch Q34connects to the connection between capacitor C4and C5is also connected to the drain of switch Q340aof MIMO converter12e. The point may provide (depending of the switching of the switches in MIMO converter12eand selection unit16e) discrete voltages V4-V7. Switches Q340a, Q340cand Q340dmay be included in multiplexor88a. The source of switch Q34connects to the drain of switch Q33that further connects to the drain of switch Q330athat is included in selection unit16e. The point at which the source of switch Q33connects to the connection between capacitor C3and C4is also connected to the source of switch Q340bof MIMO converter12e. The point may provide (depending of the switching of the switches in MIMO converter12eand selection unit16e) discrete voltages V3-V4. The drain of switch Q33connects to the drain of switch Q330aof MIMO converter12e. The point at which the drain of switch Q32connects to the connection between capacitor C2and C3is also connected to the drain of switch Q320aof MIMO converter12e. The point may provide, depending of the switching of the switches in MIMO converter12eand selection unit16e, discrete voltages V2-V3. The source of switch Q32connects to the drain of switch Q31. The source of switch Q31connects to the source of switch of320bof MIMO converter12eto provide discrete voltages V1-V2. Provision of discrete voltages V1-V2may be dependent on the switching of the switches in MIMO converter12eand selection unit16e. The drain of switch Q31also connects to the source of switch Q310a.

In selection unit16e, the other end of inductor L2connects to the drains of switch SW1aand switch SW2a. Both switches SW1aand SW2ainclude multiple switches connected between respective sources and drains. In descriptions that follow, multiple switches wired in series such as switches Q340c, Q330a, and Q310afor example may be implemented with a single switch. The source of switch SW1aprovides the live (L) output terminal of converter107eand is further connected to the drain of switch SW1b/Q320d. The source of switch SW2aprovides the neutral (N) output terminal of converter107eand is further connected to the drain of switch SW2b/Q310b. Switch SW1bmay include switches Q320b, Q320cand Q320d. The source of switch Q320bconnects to the source of switch Q31of MIMO converter12e. The drain of switch Q320bconnects to the source of switch Q320cand the source of switch Q320a. The drain of switch Q320aconnects to the drain of switch Q32of MIMO converter12e. The drain of switch Q320cconnects to the source of switch Q320dand to the source of switch Q340c. The drain of switch Q340cconnects to the drain of switch Q340band the source of switch Q340a. The drain of switch Q340aconnects to the drain of switch Q34of MIMO converter12e. The source of switch Q340bconnects to the source of switch Q33of MIMO converter12e. Switch SW2bmay include switches Q310awhere the drain of switch Q310awired in series with the source switch Q310b. The point at which the drain of switch Q310aconnects with the source switch Q310balso connects to the source of switch Q330a. The drain of switch Q330aconnects to the drain of switch Q32of MIMO converter12e. The drain of switch Q310bmay provide the neutral (N) output terminal of converter107e/selection unit16e.

Operation of SIMLO Converter10e

Reference is now made again to method201, at step202voltage VDCapplied at the input of SIMLO converter10e. Voltage VDCmay be converted to provide multiple direct current (DC) voltage outputs on terminals V1-V8. In other words, SIMLO converter10may be a circuit for separating a direct current (DC) input power (VDCfor example) to provide multiple direct current (DC) voltage outputs on its output terminals V1-V8.

As part of what may be included in step210, controller180as an example of a central controller may sense electrical parameters in power system100and/or converter/107eat step208. Step210may operate switches Q1and Q2connected to inductor L1and capacitor C1and/or the auto transformer circuit included series string ST1. The auto transformer circuit may for example include an inductor pair of inductors such as L15and L16and four switches Q15a, Q15b, Q16aand Q16b. The auto transformer circuit may therefore, provide a buck, boost, buck/boost and/or buck+boost operation on voltage VDC. Alternatively, converter1000may be utilized instead or in addition to the auto transformer circuits to provide a buck, boost, buck/boost and/or buck+boost operation on voltage VDC. The electrical parameters sensed by sensors/sensor interface184for example may be voltage, current, impedance, resistance and/or power (P). The power P may be a calculation of sensed voltage (V) multiplied (x) by sensed current (I) performed by controller180. Control line output14amay be used to send control signals to SIMLO converter10efor appropriate control of SIMLO converter10eto provide a buck function on voltage VDC. The buck function on voltage VDCmay be to step down the voltage level of voltage VDCif too high whilst stepping up the input current from voltage VDCresponsive to the sensed electrical parameters. Whereas in contrast, a boost function on voltage VDCmay step up the voltage level if VDCis too low whilst stepping down the input current from voltage VDCresponsive to the sensed electrical parameters.

Control signals provided on control line output14amay also include control signals with respect to the operation of the auto transformer circuit. The auto transformer circuit may include inductors L3-L13to provide multiple direct current (DC) voltage outputs on the output terminals V1-V7of SIMO converter10e. Operation of the auto transformer circuit by use of multiple tapped inductors of the auto transformer circuit that may include switches Q3b-Q13a. The taps may be adapted for connecting individually to the DC voltage input to (terminals V1-V8). Each tapped inductor therefore may form a switched auto transformer circuit with both electrical and/or electro-magnetic connections (in the case of inductors L15and L16). The electrical and/or electro-magnetic connections may be operated so that multiple direct current (DC) voltage outputs derived from converting the input voltage (VDC) by SIMLO converter10eare provided on terminals V1-V8. The inductor pair of L15and L16may have the same number of winding turns. There may also be a different number of turns to the inductor pair of L15and L16. The different number of turns may provide a way to adjust the typical relative maximum power point (MPP) voltage of each of the voltages on terminals V1-V8.

Control signals on control line output14amay be by a first modulation scheme responsive to the electrical parameters sensed at step208. The first modulation scheme may include pulse width modulation (PWM), frequency modulation (FM) or a variable frequency and variable pulse width. Control signals on control line output14amay include consideration of reference waveform19and the effect of a load connected to the output of selector unit16e. The control signals may be responsive to sensing step208so that the DC voltage outputs on terminals V1-V8may be set and maintained at the required DC levels. PWM from PWM unit14may be applied to the gate connections of the switches of SIMLO converter10evia control line output14a.

Operation of MIMO Converter12eand Selection Unit16e

At step204, MIMO converter12emay convert some of the discrete voltage levels (V1-V8) on its input to two discrete states of alternating current (AC) voltage levels on the five outputs of MIMO converter12e(OP1a-OP5a). Unlike MIMO converter12d, the five outputs (OP1a-OP5a) of MIMO converter12emay have DC sources that have different potential difference values or unequal voltage amplitude values. For example, the potential difference of two discrete voltage levels between output OP4a(V4-V3) may be greater than the potential difference the two discrete voltage levels of output OP5a(V7-V8). When MIMO converter12eis used in conjunction with selection unit16ein steps204and206to choose unequal dc sources, some switching-state redundancies may be avoided. Consequently, different output-voltage levels may be generated with substantially the same number of switches and/or less switches.

When MIMO converter12eis used in conjunction with selection unit16ein order to realize steps204and206, switches Q8aand Q8bconnect in series across capacitor C8at nodes X and Y. Nodes X and Y present an input to a two-level inverter topology to the DC potential difference between terminals V8and V7applied to the input. The alternating current (AC) output of the two-level inverter topology (V8-V7) may be derived from the mid-point connection between switches Q8aand Q8b. The mid-point connection connects to inductor L2of selection unit16e. Similar two-level inverter topologies may exist between the other switches of MIMO converter12e, for example between switches Q34and Q33, Q33and Q32, Q32and Q31. The switches of selection unit16emay be used to enable outputs of the two-level inverter topologies selectable by the switches of selection unit16e. For example, the live (L) connection point of converter107emay be provided from the mid-point connection between switches Q8aand Q8b. The mid-point connection connects to inductor L2of selection unit16e, through inductor L2and switch SW1ato the live (L) connection point of converter107eas discrete voltage levels V7and V8. The operation of the other switches in selection unit16emay also provide the live (L) connection point of converter107e. The live (L) connection point may be provided from discrete voltage levels V1-V2, V2-V3, V3-V4and/or V4-V7.

The neutral (N) point of converter107emay connect to voltage terminal V1via switches SW2aand SW2bof selection unit16eand body diode of switch Q31. The neutral (N) point of converter107emay connect to and/or voltage terminal V2via switch SW2aand SW2bof selection unit and switch Q32. Further, the neutral (N) point of converter107emay connect to voltage terminal V3via the body diodes of switches Q310band Q330athen through and Q33and/or voltage terminal V4via the body diodes of switches Q310band Q330aand through switch Q34. The PWM on control line output14bmay be provided by controller180(as part of control step210) responsive to sensed electrical parameters of converter107eat step208. The sensed electrical parameters of converter107emay include the discrete voltage levels (V1-V8). The effect of a load connected to the output of selector unit16eand may further include consideration of reference waveform19. In a similar way the live (L) point of converters107b/107cmay connect to voltage terminal V1via switches SW1a(not shown) and SW1band/or from voltage terminal V2via switch Q320a, switch Q320cand switch Q320d. Further, the live (L) point of converter107b/107cmay connect to voltage terminal V3via switches Q340b, Q340cand Q320dand/or voltage terminal V4via switches Q340a, Q340cand Q320d.

Reference is now made toFIG. 3B, which shows a possible waveform of the live (L) voltage output of selection unit16ewith respect to neutral (N), according to illustrative aspects of the disclosure. Waveforms may be shown with horizontal axis of time (no units specified) versus voltage on the vertical axis (no numerical values specified). Reference waveform19is shown as a sinewave by dotted line. Reference waveform19may be a sinewave, triangular wave, square wave or any periodic waveform. Reference waveform19may be considered to be representative of the desired output of converter107e/selection unit16e. Control signals on control lines18aand/or18bmay be provided respectively to PWM unit14and selector unit16e. Control signals on control lines14aand14bmay be provided respectively to SIMLO converter10eand MIMO converter12eresponsive to parameters of reference waveform19and/or sensed parameters of converter107e.

The parameters of reference waveform19may include the desired voltage amplitude and frequency of the output from converter107e. For example, where load109may be a utility grid or single-phase AC motor, the desired voltage and frequency may be 220 Volts (V) and 50 Hertz (Hz) respectively. Electrical parameters sensed by sensors/sensor interface184and appropriate signals on control lines18a,18b,14aand14bmay provide appropriate control of converter107erealized by SIMLO converter10e, MIMO converter12eand selection unit16e. Signals on control lines18a,18b,14aand14bmay ensure correct levels of operating voltage, current, impedance, resistance, phase angle, power factor, level of harmonic distortion, frequency and/or power.

By way of example, in general the two discrete states of AC voltage provided on outputs OP1a-OP5amay be driven with PWM used to drive both converters10eand/or12e. the PWM may be much higher in frequency than PWM control signal20aapplied to selection unit16efor example. The five outputs (OP1a-OP5a) may have different potential difference values or unequal voltage amplitude values of MIMO converter12. The output L of converter107e/selection unit16emay include PWM1in the positive half cycle and PWM5in the negative half cycle that may correspond with the selection of output OP5aby selection unit16e. Similarly, PWM2, PWM3and PWM4that may correspond with outputs OP2a, OP3aand OP4a. For example, PWM2may correspond with output OP4asuch that the potential difference of two discrete voltage levels between output OP4a(V4-V3) may be greater than the potential difference the two discrete voltage levels of output OP5a(V7-V8) as shown. However, the time periods by comparison withFIG. 2B, time T7aof PWM control signal20amay be greater than time period T7of PWM control signal20. In time period T7aapproximately fifty percent of the conversion energy provided by MIMO converter12emay reduce the effect of switching-state redundancy when compared to that of MIMO converter12dfor example. The fifty percent of the conversion energy may be by use of the inductor pair of L15and L16and four switches Q15a, Q15b, Q16aand Q16bto provide a buck, boost, buck/boost and/or buck+boost operation on voltage VDC. The buck, boost, buck/boost and/or buck+boost operation may be in in conjunction with switches Q8aand Q8bof MIMO converter12e. Alternatively, converter1000may be utilized instead or in addition to the auto transformer circuits to provide a buck, boost, buck/boost and/or buck+boost operation on voltage VDC. SIMLO converter10e, MIMO converter12eand selector unit16emay therefore be able to produce different output-voltage levels (V1-V8) with substantially the same amount or less switches as MIMO converter12dand selector unit16ddescribed above. The different output-voltage levels (V1-V8) with substantially the same amount or less switches may reduce the size and cost of converter107e. The reliability of converter107emay also be improved since less semiconductors and capacitors may be employed.

Reference now made toFIG. 4A, which shows a diagram of further details converter107fthat includes SIMLO converter10f, MIMO converter12fand selector unit16f, according to illustrative aspects of the disclosure. Converter107fis similar to converter107ein that SIMLO converter10eis the same as SIMLO converter10f. Common to the other MIMO converters described above, MIMO converter12fincludes capacitor C2that connects across terminals V1and V2and capacitors C3-C8that connect across respective terminals. Capacitor C3connects across terminals V2and V3, C4connects across terminals V3and V4and so on. Two switches Q8aand Q8bconnect in series across capacitor C8that is the same as switching network Sn described above. A further two switches Q7aand Q7bconnect in series across capacitor C7to provide a second switch network Sn. A further two switches Q9aand Q9bmay be wired in series and wired across the two outputs of the two switching networks Sn. The point where switches Q9aand Q9bare connected together gives an output of MIMO converter12fthat connects to one end of inductor L2that may be included in selector unit16f.

The other end of inductor L2connects to one end of capacitor C9and to one side of switches SW1aand SW2athat are connected together. The other side of capacitor C9connects to both the neutral (N) and live (L) via respective switches SW2band SW1b. The other sides of switches SW1aand SW2aprovide respectively the live (L) and neutral (N) outputs of converter107f. The live (L) and neutral (N) outputs of converter107fconnect respectively to switches SW1band SW2bthat may be included in MUX88b. The other side of switches SW1band SW2bconnect together and provide the multiple live (L) and neutral (N) inputs to MUX88b. Control of switches in MUX88ballow connection of neutral (N) to either terminal V1or V respectively via switch SW2bor a portion of switch SW2band switch Q440b. Similarly, live (L) may be connected to terminal V1or V3respectively via switch SW1bor a portion of switch SW1band switch Q440a. Alternatively switches Q440aand Q440bmay be located in MIMO converter12fso that the PWM supplied to SIMLO converter10fand/or MIMO converter12fmay be at a higher frequency compared to the frequency of PWM that may be supplied to selector unit16f.

Reference is now made toFIG. 4B, which shows a possible waveform of the live (L) voltage output of selection unit16fwith respect to neutral (N), according to illustrative aspects of the disclosure. Waveforms may be shown with horizontal axis of time (no units specified) versus voltage on the vertical axis (no numerical values specified). Reference waveform19is shown as a sinewave by dotted line. Reference waveform19may be a sinewave, triangular wave, square wave or any periodic waveform. Reference waveform19may be considered to be representative of the desired output of converter107f/selection unit16f. Control signals on control lines18aand/or18bmay be provided respectively to PWM unit14and selector unit16f. Control signals on control lines14aand14bmay be provided respectively to SIMLO converter10fand MIMO converter12fresponsive to parameters of reference waveform19and/or sensed parameters of converter107f.

The parameters of reference waveform19may include the desired voltage amplitude and frequency of the output from converter107f. For example, where load109may be a utility grid or single-phase AC motor, the desired voltage and frequency may be 220 Volts (V) and 50 Hertz (Hz) respectively. Electrical parameters sensed by sensors/sensor interface184and appropriate signals on control lines18a,18b,14aand14bmay provide appropriate control of converter107e. Signals on control lines18a,18b,14aand14bmay ensure correct levels of operating voltage, current, impedance, resistance, phase angle, power factor, level of harmonic distortion, frequency and/or power for example.

By way of example, in general the two discrete states of AC voltage provided on outputs OP1b-OP3bmay be driven with PWM used to drive both converters10fand/or12f. The PWM may be much higher in frequency than PWM control signal20bapplied to selection unit16ffor example. Three outputs (OP1b-OP3b) may have different potential difference values or unequal voltage amplitude values of MIMO converter12f. The output L of converter107fselection unit16fmay include PWM1in the positive half cycle and PWM3in the negative half cycle that may correspond with the selection of output OP3bby selection unit16f. Similarly, PWM1and PWM2may correspond with outputs OP1band OP2b. PWM2may correspond with output OP4asuch that the potential difference of two discrete voltage levels between output OP2b(V3-V1) may be greater than the potential difference the two discrete voltage levels of output OP3b(V8-V6) as shown. However, the time periods by comparison withFIG. 3B, time T7bof PWM control signal20bmay be greater than time period T7aof PWM control signal20a. Time period T7bmay be approximately more than fifty percent of the conversion energy provided by MIMO converter12f. The more than fifty percent of the conversion energy may reduce the effect of switching-state redundancy when compared to that of MIMO converter12e, for example.

The more than fifty percent of the conversion energy may be by use of the inductor pair of L15and L16and four switches Q15a, Q15b, Q16aand Q16bto provide a buck, boost, buck/boost and/or buck+boost operation on voltage VDC. The more than fifty percent of the conversion energy may be in conjunction with switches Q8a, Q8b, Q9aand Q9bof MIMO converter12f. Alternatively, converter1000may be utilized instead or in addition to the auto transformer circuits to provide a buck, boost, buck/boost and/or buck+boost operation on voltage VDC. SIMLO converter10f, MIMO converter12fand selector unit16fmay therefore be able to produce different output-voltage levels (V1-V8) with substantially the same amount or less switches as MIMO converter12eand selector unit16edescribed above. The different output-voltage levels (V1-V8) with substantially the same amount or less switches may reduce the size and cost of converter107f. The reliability of converter107fmay also be improved since less semiconductors and capacitors may be employed. In sum, converters107eand107fmay be considered as having asymmetric converter topologies. In general, a de-population of the number of switches used in MIMO converter12and selection unit16by use of multiplexor88may provide a way to reduce the size and cost of converter107. Whereas converter107dmay have more switches compared to converters107eand107f. Converter107dmay offer an improved reduction in total harmonic distortion (THD) by providing for the function of harmonic cancellation due to the symmetrical topology of converter107d.

Now referring to Table 2 below, Table 2 shows a comparison of the number of switches in each of MIMO converters12d,12e,12f, selection units16d,16e,16fshown in respectiveFIGS. 1J, 3A and 4A. Using selection unit16eas an example and applying the analysis to the other selection units16dand16f, multiple switches wired in series such as switches Q340c, Q330a, and Q310afor example may be implemented using a single switch.

From Table 2 it can be seen that the number of switches used is reduced when comparing converter107dwith converter107eand converter107ewhen compared to converter107f. However, the number of levels of current/voltage outputs also decreases when comparing converter107dwith converter107eand converter107ewhen compared to converter107f. Performance of when comparing converter107dwith converter107eand converter107ewhen compared to converter107fwith respect to root mean square (RMS) of the filtered outputs of each selection unit16is summarized in Table 3 below in greater detail in descriptions that follow.

In general, the root mean square (RMS) of a function g{x} may be given by the following formula:

Solving the above definite integral, where g(x) is an AC sine wave of frequency ƒ=50 Hz, peak current Im=50 A, ω=πƒ, the RMS output current (Irms) of selection units16may be calculated by the following formula derived from solving the above integral:

Now referring to Table 3 below, Table 3 shows a summary of RMS current (Irms) values for the output currents of each of converters107d,107eand107fshown in respective figuresFIGS. 1J, 3A and 4A. The outputs currents of converters107d,107eand107fare considered sinusoidal by virtue of filtering provided by inductors L2in each of converters107d,107eand107f. For each of the converters107d,107eand107f, the above equations with respect to RMS current (Irms) are calculated for a half cycle of AC output current. Times t1and t2for each output shown in each column of Table 3 correspond to the selection times of respective selection units16d,16eand16f. The selection times determined by respective PWM control signals20,20aand20b. The selection times in general have a lower frequency of PWM control signals compared to PWM control signals applied to respective MIMO converters12d,12eand12f. Output waveforms for each of converters107d,107eand107fmay be represented by graphs shown in respectiveFIGS. 2B, 3B and 4B.

Assuming the same switching frequency and capacitor values from Table 3, it can be seen that time T7(2.58 ms) of MIMO converter12dmay be less than time T7a(4.77 ms) of MIMO converter12eand time T7b(6.68 ms) may be greater than time period T7aof MIMO converter12f. However, the differences between each RMS current (Irms) for respective time periods T7(15.756 A), T7a(18.853 A) and T7b(20.709 A) are not so different compared to the time differences. Therefore, a benefit of using converter107fcompared to converters107eand107dmay be use of fewer switches with similar power loss in MIMO converter12fcompared to MIMO converters12dand12e. Whereas a benefit of MIMO converter12dcompared to the asymmetric topology of MIMO converters12eand12f, may offer an improved reduction in total harmonic distortion (THD). The improved reduction in THD may be provided by the symmetrical topology of converter107dthat may include more switches to provide symmetrical topology. The switches of converter107d, because of the lower values of rms current (Irms) compared to converters107eand107d, may be realized using cheaper MOSFETs within a single converter design. The cheaper MOSFETs may be cheaper because of higher drain to source (rds) resistance compared to MOSFETs of converters107eand107d. Compared to converter107d, the lower values of rms current (Irms) for converters107eand107dwith the higher drain to source (rds) resistance may give a substantially similar power loss to more expensive lower rds resistance of MOSFETs for converter107d.

More specifically, with respect to the switches in MIMO converters12d,12eand12f, the current in the switches may follow the substantially rectangular PWM applied to the switches of MIMO converters12d,12eand12f. Since the current may follow the substantially rectangular PWM, the RMS of a PWM current waveform (IRMS) is proportional to the square root of its duty cycle D.

Where A is the peak current value of the PWM current waveform in amperes, TONis the ON period of the PWM current waveform and TOFFis the OFF period of the PWM current waveform. The overall time period T of the PWM current waveform is the sum of TONand TOFF.

Both energy and power loss in MIMO converters12d,12eand12fmay therefore be inversely proportional to the capacitance values of the capacitors C2-C8in each of the MIMO converters12d,12eand12f, the switching frequency and duty cycle of the switches for each RMS output current (Irms) may be summarized in Table 4 below. A fixed duty cycle (D) of 50% is used in calculation for each respective output of the switches of MIMO converters12d,12eand12f.

The substantially symmetrical topology of converter107dis reflected in the substantially equal currents for each switch in MIMO converter12dof 6.35 amperes (A). Whereas the substantially asymmetrical topologies of converters107eand107fis reflected in different IRMScurrent values per switch since the number of levels of current/voltage outputs also decrease when comparing converter107dwith converter107eand converter107ewhen compared to converter107f. A benefit of using converter107fcompared to converters107eand107dis that it that may use fewer switches with similar power loss in MIMO converter12fcompared to MIMO converters12dand12e. Whereas a benefit of MIMO converter12dcompared to the asymmetric topology of MIMO converters12eand12f, may offer an improved reduction in total harmonic distortion (THD). The improved reduction in THD may be provided by the symmetrical topology of converter107dthat may include more switches to provide symmetrical topology.

Descriptions above have illustrated a single-phase converter but the same use of switches may be applied to similar three phase converter circuit implementations also. The same use of switches may be applied to other converter topologies for both three-phase and single-phase converters. The same use of switches may also be similarly applied to multi-level converters of various types.

All optional and preferred features and modifications of the described aspects and dependent claims are usable in all aspects taught herein. Furthermore, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described aspects are combinable and interchangeable with one another. In addition to descriptions forFIG. 1J,FIG. 3AandFIG. 4Athat describe the cascaded components for converter107, it may be possible by way of non-limiting example to have converter107as SIMLO converter10dcascaded with MIMO converter12eand selector unit16fand/or SIMLO converter10e, cascaded with MIMO converter12fand selector unit16eand so on. A person skilled in the art would make the appropriate selection of components of converter107and selection of the appropriate control signals (e.g. control outputs14a,14b,18aand18b). The appropriate selection of components and selection of appropriate control signals responsive to a desired reference waveform19and sensed electrical parameters of converter107. The sensed electrical parameters may include voltage, current, impedance, resistance, phase angle, power factor, level of harmonic distortion, frequency and/or power.