Patent Publication Number: US-2023144906-A1

Title: Modular high power bi-directional half bridge buck/boost converter assembly

Description:
BACKGROUND 
     The present invention generally relates to a modular high power bi-directional half bridge buck/boost converter assembly and, in particular, to a system for converting power from one form of current (either AC or DC) to a differing level of voltage, either lower (buck) or higher (boost), to output a wave signal based on pulse width modulation (PWM) switching control by means of an external digital controller and methods of operation. 
     SUMMARY 
     In an aspect of the invention, an inverter-converter system includes at least one half bridge module including a plurality of circuit components; at least one inductor which is connected to the at least one half bridge module and a power supply; and a controller which is configured to receive and send instructions to the at least one half bridge module for converting an input voltage to an output voltage and dynamically tune switching frequencies based on a load of the inverter-converter system. 
     In further aspects of the invention, a bi directional modular half bridge converter circuit includes at least one half bridge module including a plurality of circuit components; an inductor on a circuit board; at least one current sensor on a circuit board which is a connection between the inductor and the at least one half bridge module; and a gate driver board being mounted directly to the at least one half bridge module. 
     In another aspect, a method includes receiving an input value based on a load of an inverter-converter system; and dynamically adjusting a switching frequency based on the received input vale such that the switching frequency is above a predetermined frequency based on the load being below a predetermined load and the switching frequency is below the predetermined frequency based on the load being above the predetermined load. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention. 
         FIG.  1 A  shows a block diagram of an inverter-converter consisting of two channels and an optional third channel in accordance with aspects of the invention. 
         FIG.  1 B  shows a basic-inverter converter circuit schematic diagram of a two channel inverter-converter with an optional third channel in accordance with aspects of the present invention. 
         FIG.  2 A  shows a single channel buck/boost block diagram of a bi-directional buck/boost DC converter in accordance with aspects of the present invention. 
         FIG.  2 B  shows a basic inverter-converter circuit schematic diagram of a single channel bi-directional buck/boost DC converter in accordance with aspects of the present invention. 
         FIG.  3    show a single channel bi directional modular half bridge buck/boost converter assembly in accordance with aspects of the present invention. 
         FIG.  4    shows a single channel bi directional modular half bridge buck/boost converter assembly exploded view in accordance with aspects of the present invention. 
         FIG.  5    shows a half bridge module assembly and gate driver board in accordance with aspects of the present invention. 
         FIG.  6 A  shows a DC source buck and boosting switches in accordance with aspects of the present invention. 
         FIG.  6 B  shows a DC source buck and boosting switches in a reverse current flow from  FIG.  6 A  in accordance with aspects of the present invention. 
         FIG.  6 C  shows an AC to DC and DC to AC switching in accordance with aspects of the present invention. 
         FIG.  7    shows a switching and sampling frequency graph in accordance with aspects of the present invention. 
         FIG.  8    shows dynamic tuning of switching frequencies in accordance with aspects of the present invention. 
         FIG.  9    shows a bi-directional inverter-converter assembly in accordance with aspects of the present invention. 
         FIG.  10    shows a top view of the bi-directional inverter-converter assembly in accordance with aspects of the present invention. 
         FIG.  11    shows an exploded view of the bi-directional inverter-converter assembly in accordance with aspects of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention generally relates to a modular high power bi-directional half bridge buck/boost converter assembly and, in particular, to a system for converting power from one form of current (either AC or DC) to a differing level of voltage, either lower (buck) or higher (boost), to output a wave signal based on pulse width modulation (PWM) switching control by means of an external digital controller and methods of operation. The wave signal can be a variety of different wave forms, including but not limited to a sine wave signal, a square wave signal, or a constant wave signal based on the PWM switching control. In addition, the system of the present disclosure can have energy travel in one direction or in a bi-directional capability. 
     In the system of the present disclosure, the modular high power bi-directional half bridge buck/boost converter assembly includes a half bridge module and an inductor module. The half bridge module and the inductor module are the main components of the modular high power bi-directional half bridge buck/boost converter assembly in which electrical energy flows through. These modules can be arranged in a specific configuration to optimize a desired application of energy conversion. The energy conversion can include bi-directional functionality from DC to DC, bi-directional functionality from DC to AC, and bi-directional functionality from AC to DC. Further, the unique form factor of each module allows for configurability in a multitude of ways, including scaling of power through paralleling or series without a need for a unique circuit board layout. The modules and external control board are capable of different configurations with adjustments to a control logic. 
     In two or three channels of the assembly of the present disclosure, alternating currents (AC) can be rectified to a wide range of DC voltage outputs, or generated (i.e., inverted) from a wide range of DC supply currents to form a desired AC output root mean squared (RMS) voltage (or other desired wave signal output). The assembly of the present disclosure has the ability to provide a wide range of voltages (e.g., 150-1,000 V DC, 120-600 V AC) with desired output frequencies (e.g., 50 Hz, 60 Hz, etc.) and high current capability rating in a compact package through the use of high frequency switching equipment (i.e., 100 kHz range). 
     Advantageously, the present disclosure uses an assembly and control methods to improve performance, packaging, efficiency, and power density of power converts and allows a greater range of application through a wide range of voltage as well as AC or DC current capabilities while maintaining a modular design capable of interleaving assemblies for easily scaled power levels. These advantages are achieved by the use of a half bridge circuit topology with input filtering and capacitance, and high frequency (i.e., 100 kHz range) switching of metal-oxide-semiconductor field-effect transistor (MOSFET) controlled by an external control board with a processing unit, to run through an inductor an output a signal with additional signal filtering and capacitance. In the present disclosure, the circuit with MOSFETs can be used for either active switching or an idle diode in a current path that allows for bi-directional capability. In this scenario, a high voltage rating of the assembly refers to 1,000 V DC and high power refers to a power rating of 50,000 watts (at 1,000 V DC) constant operating capacity on a single channel. 
     The assembly of the present disclosure has several means of a control loop function and signal interpretation to provide switching control of a MOSFET and a buck or boost state of the assembly. In particular, the assembly of the present disclosure contains mirrored filtering and capacitance on either end which serves several functions: 1) greater capacitance that can help smooth out fluctuations in voltage from a supply side or a load side; and 2) provides a passive filter for noise that may be induced upon a circuit through switching of MOSFETs of the assembly. Further, by tuning a circuit of the assembly, extremely high efficiency is achieved. For example, the efficiency of the assembly can be approximately 98% overall at peak efficiency. 
     A combination of different capacitors in the present disclosure can provide a balanced level to prevent a fluctuating of instantaneous power in/out as well as a “ripple” generated by a high frequency switching circuit. Ripple current/voltage is a total amount of a root mean square (RMS) alternating and correct current/voltage that a capacitor can withstand without failing. The ripple needs to be filtered out to the degree that the peak current/voltage does not exceed the operating limitations of the devices on the circuit. In relation to a MOSFET switching module, a smoother switch node ripple with lower peaks allows for greater use of a component based on a voltage or a current rating. Further, by using the smoother switch node ripple, less input/output capacitance is needed and a smaller packaging can be implemented for the assembly. A gate switching ripple is directly correlated to the time it takes to fully switch on a MOSFET, in addition to the smoothness of the signal directly correlating with efficiency (i.e., less heat loss). 
     In the present disclosure, short duration switching allows for a higher useable frequency of switching, which compliments a quality output voltage/current ripple. The inductor that flows an output switched voltage/current in the circuit opposes a rate of change of current that may be present in the circuit, which provides a high quality of current output. All components in the circuitry improve efficiency performance, voltage rating, current capacity, and size in comparison to conventional circuits. 
     In the present disclosure, an inverter-converter system can be used in an electric vehicle or an electric vehicle application, internal or external to the vehicle, and provides for charging a vehicle battery or other rechargeable energy storage device and also allows a battery to be connected to an electric power grid to deliver power to a grid or otherwise be a source of power. In charge mode, the inverter-converter system is coupled with an AC power source, and the AC power source is converted to DC for charging the battery coupled with the inverter-converter system. Charging is a term that describes when a system is configured to convert the AC from a line to DC to charge a battery pack. Inverting is a term that describes when the system is configured to convert the DC voltage from the battery to AC power for a grid. Also, the inverter-converter system can be configured to provide a power source. 
       FIG.  1 A  shows a block diagram of an inverter-converter consisting of two channels and an optional third channel in accordance with aspects of the invention. In  FIG.  1 A , an inverter-converter system  5  includes a controller  10 , a plurality of half bridge board modules  12 , a plurality of inductors  14 , and a plurality of AC power supplies  16 . In the inverter converter-system  5 , the dotted rectangular box  17  represents an optional third channel for a three phase power inversion. In another embodiment in which the dotted rectangular box  17  is not included, the inverter-converter system  5  can have two channels for a single phase AC, or a “split phase” sometimes referred to as “two phase” AC power inversion. 
     In  FIG.  1 A , each of the half bridge modules  12  can be connected to one of the inductors  14 . Further, each of the inductors  14  can be connected to one of the AC power supplies  16  or a DC power supply (represented as DC+). Further, the half bridge modules  12  in a first channel (i.e., the highest half bridge modules  12  in the inverter converter system  5 ) are connected to the half bridge modules  12  in the second channel (i.e., the half bridge modules  12  in between the first channel and the third channel) and the third channel (i.e., the lowest half bridge modules  12  in the dotted rectangular box  17 ). Each of the half bridge modules  12  in a second channel (i.e., the half bridge modules  12  in between the first channel and the second channel) are connected to each other. The controller  10  of the inverter converter system  5  can both send and receive instructions to each of the half bridge modules  12 . In an example, the controller  10  can adjust switching frequency of the inverter converter system  5 . 
       FIG.  1 B  shows a basic-inverter converter circuit schematic diagram of a two channel inverter-converter with an optional third channel in accordance with aspects of the present invention.  FIG.  1 B  is a detailed circuit diagram of the block diagram of the inverter-converter system  5  in  FIG.  1 A . Therefore, the inverter-converter  5  of  FIG.  1 B  is similar to  FIG.  1 A , with the exception of including the electrical circuit components of the half bridge modules  12 . In  FIG.  1 B , the half bridge modules  12  of the first channel (i.e., the highest half bridge modules  12  in the inverter converter system  5 ) include transistors T 1 , T 2 , T 3 , T 4 , T 5 , and T 6 , inductors  14 , AC power supply  16 , EMI inductors  18 , capacitors  20 , and a DC power supply (represented as DC+). Further, the half bridge modules  12  of the second channel (i.e., the half bridge modules  12  in between the first channel and the third channel) include transistors T 7 , T 8 , T 9 , T 10 , T 11 , and T 12 , inductors  14 , AC power supply  16 , EMI inductors  18 , capacitors  20 , and a DC power supply (represented as DC+). The half bridge modules  12  of the optional third channel shown as the dotted rectangular box  17  includes transistors T 13 , T 14 , T 15 , T 16 , T 17 , and T 18 , inductors  14 , AC power supply  16 , EMI inductors  18 , capacitors  20 , and a DC power supply (represented as DC+). 
     In the inverter-converter system  5  of  FIG.  1 B , a single phase AC input (e.g., 120V AC in North America) or “split phase” (e.g., 240V AC in North America) may be a load or source of energy, depending on an application. In an instance of power inversion, in which a source of energy is a DC power source which may be a static or variable voltage and a load is in a form of AC power, current will first pass through a set of inductors, then through a set of interleaving half bridge switches (i.e., one set of switches for each channel), which depends on a DC supply voltage, and will either buck or boost voltage to a desired static DC buss voltage. On each half bridge module  12 , a set of capacitors  20  helps sustain small variances in a voltage due to a variable power supply or load. Further, the inverter side of the inverter-converter system  5  can be split for each phase of AC power required, and each “channel” is response for a partial sine wave generation of two phases of AC power. Each of the channel&#39;s current can then pass through a final set of inductors, before making its way to a grid or load. An additional channel (e.g., a third channel) can be added to a pair, for an additional phase of power generation, and a fourth neutral channel can be added to a set of three for load balancing on a three phase circuit. 
     A path of current flow for converting AC to DC energy is the reverse of DC to AC with all of the same components. Each phase of the AC source passes through one of two channels of the inverter-converter system  5 , depending on a position of an AC wave. The AC wave form is actively rectified which also conditions power factor on the AC line, and a voltage is boosted (compared to AC RMS voltage) to a higher DC positive and negative voltage onto the DC buss. Interleaving half bridge modules  12  can then further boost or buck down DC voltage to a desired output, and through a final set of inductors which smooth out “ripple” in the DC current generated. 
       FIG.  2 A  shows a single channel buck/boost block diagram of a bi-directional buck/boost DC converter in accordance with aspects of the present invention. The single channel buck/boost system  22  includes the half bridge modules  12 , the inductors  14 , and capacitors  20 . The single channel in  FIG.  2 A  is represented by the dotted rectangular box  17  (i.e., an optional third channel). In this configuration of  FIG.  2 A , the single channel buck/boost system  22  allows for DC to DC power conversion with only two half bridge modules  12  and a single inductor  14  between the two half bridge modules  12 . 
       FIG.  2 B  shows a basic inverter-converter circuit schematic diagram of a single channel bi-directional buck/boost DC converter in accordance with aspects of the present invention.  FIG.  2 B  is a detailed circuit diagram of the single channel buck/boost system  22  in  FIG.  2 A . Therefore, the single channel buck/boost system  22  of  FIG.  2 B  is similar to  FIG.  2 A , with the exception of including the electrical circuit components of the half bridge modules  12 . 
     In  FIGS.  1 B and  2 B , the half bridge modules  12  of the single channel (i.e., an optional third channel as represented by the dotted rectangular box  17 ) include transistors T 13 , T 14 , T 15 , and T 16 , inductors  14 , EMI inductors  18 , and capacitors  20 . In  FIG.  2 B , a half bridge module  12  with the input capacitor  20  and the EMI inductor  18  is connected in series with an inductor  14 , which is then connected in series with another half bridge module  12 . In one direction of current flow, only one of the half bridge module  12  is actively switching while the another half bridge module  12  acts as a diode set. 
       FIG.  3    show a single channel bi directional modular half bridge buck/boost converter assembly in accordance with aspects of the present invention.  FIG.  4    shows a single channel bi directional modular half bridge buck/boost converter assembly exploded view in accordance with aspects of the present invention. In  FIGS.  3  and  4   , the single channel bi directional modular half bridge buck/boost converter  30  includes two half bridge modules  12 , an inductor  14 , a gate driver board  24 , a gate driver signal board  26 , current sensor boards  28 , and MOSFET spring clips  32 . 
     In particular, the single channel bi directional modular half bridge buck/boost converter  30  includes the gate driver signal board  26  which receives control means from an external unit (i.e., the external unit is not part of the single channel bi directional modular half bridge buck/boost converter  30 ) and provides switching control signals to each of the two gate driver boards  24 . The inductor  14  and the half bridge module  12  are fixed to a heat sink mechanically by threaded spacers, washers, nuts, and spring clips. 
     The single channel bi directional modular half bridge buck/boost converter  30  can be controlled based on several means of feedback, which allows for a multitude of operating configurations. In particular, the single channel bi directional modular half bridge buck/boost converter  30  provides the ability of a user to define a desired type of control means and with several feedback criteria provided on the circuit itself, a variable or fixed target output can be achieved from a variable or fixed input. One such example would be a DC to DC configuration, whereas a variable power supply (such as a battery where voltage decreases as power is consumed) can provide a steady DC output at a voltage different from that which is provided. For DC to DC power conversion, bucking or boosting voltage is achieved by a pulse width modulation (PWM) switching signal sent to an appropriate module (i.e., the single channel bi directional modular half bridge buck/boost converter  30 ) to a degree that modulates an output voltage to a desired target. A voltage sensing circuit on an output end of the circuit sends a reference signal to an intermediate board, which then relays this to a control board (i.e., an external control board) for a control function. 
       FIG.  5    shows a half bridge module assembly and gate driver board in accordance with aspects of the present invention. In  FIG.  5   , the half bridge module  12  includes the EMI inductor  18 , the capacitor  20 , a gate driver pin header  34 , a silicon high power MOSFET  36 , a printed circuit board  38 , and a power terminal (i.e., represented as DC+). In  FIG.  5   , a gate driver board  40  is connected to the half bridge module  12  through the gate driver pin header  34 . 
       FIG.  6 A  shows a DC source buck and boosting modes in accordance with aspects of the present invention.  FIG.  6 B  shows a DC source buck and boosting modes in a reverse current flow from  FIG.  6 A  in accordance with aspects of the present invention.  FIG.  6 C  shows an AC to DC and DC to AC switching in accordance with aspects of the present invention. In  FIGS.  6 A- 6 C , switches of transistors T 1 -T 6  will operate depending on a direction of current flow and a desired inverting or converting of current. Further, pre-established programs from an external digital controller (e.g., controller  10 ) will consider metered information such as voltage and current flow at multiple points in a circuit and adjust pulse width modulation (PWM) signals to maintain a desired output. The phase of interleaving channels for interleaving PWM switching is dependent on the number of channels in interleaving, and programming may be adjusted for any number of channels. 
     In particular,  FIG.  6 A  shows that in a buck (i.e., lowering) mode of the graph  50 , transistor T 1  of  FIG.  1 B  has a pulse width modulation (PWM) switching signal and transistor T 2  of  FIG.  1 B  has a pulse width modulation (PWM) inverted switching signal. Further, in a buck (i.e., lowering) mode of the graph  50  of  FIG.  6 A , transistor T 3  of  FIG.  1 B  receives a high switch constant on signal, which ensures that the transistor T 3  is always on. In a buck (i.e., lowering) mode of the graph  50  of  FIG.  6 A , transistor T 4  of  FIG.  1 B  receives a low switch constant on signal, which ensures that the transistor T 4  is always off. Further, the buck mode in  FIG.  6 A  lowers the output voltage of the inverter-converter system  5  and has a current flow towards the right (as indicated by the arrow pointing to the right). 
       FIG.  6 A  also shows that in a boost (i.e., higher) mode of the graph  50 , transistor T 1  receives a high switch constant on signal, which ensures that the transistor T 1  is always on. In the boost (i.e., higher) operating condition of the graph  50 , transistor T 2  receives a low switch constant off signal, which ensures that the transistor T 2  is always off. In the boost (i.e., higher) mode of the graph  50 , transistor T 3  receives a pulse width modulation (PWM) inverted switching signal and transistor T 4  receives the pulse width modulation (PWM) switching signal. Further, the boost mode in  FIG.  6 A  increases the output voltage of the inverter-converter system  5  and has a current flow towards the right (as indicated by the arrow pointing to the right). 
       FIG.  6 B  shows that in a buck (i.e., lowering) mode of the graph  60 , transistor T 1  of  FIG.  1 B  receives a high switch constant on signal, which ensures that the transistor T 1  is always on. In the buck (i.e., lowering) mode of the graph  60 , transistor T 2  of  FIG.  1 B  receives a low switch constant off signal, which ensures that the transistor T 2  is always off. In the buck (i.e., lowering) mode of the graph  60 , transistor T 3  receives a pulse width modulation (PWM) switching signal. In the buck (i.e., lowering) mode of the graph  60 , transistor T 4  receives a pulse width modulation (PWM) inverted switching signal. Further, the buck mode lowers the output voltage of the inverter-converter system  5  and has a current flow towards the left (as indicated by the arrow pointing to the left). 
       FIG.  6 B  also shows that in a boost (i.e., higher) mode of the graph  60 , transistor T 1  of  FIG.  1 B  receives a pulse width modulation (PWM) inverted switching signal. In the boost (i.e., higher) mode of the graph  60 , transistor T 2  receives a pulse width modulation (PWM) switching signal. In the boost (i.e., higher) mode of the graph  60 , transistor T 3  receives a high switch constant on signal, which ensures that the transistor T 3  is always on. In the boost (i.e., higher) mode of the graph  60 , transistor T 4  receives a low switch constant off signal, which ensures that the transistor T 4  is always off. Further, the boost mode in  FIG.  6 B  increases the output voltage of the inverter-converter system  5  and has a current flow towards the left (as indicated by the arrow pointing to the left). 
       FIG.  6 C  shows an AC to DC and DC to AC switching in accordance with aspects of the present invention. In an operating condition for converting AC to DC power in the graph  70  of  FIG.  6 C , transistors T 5  and T 6  of  FIG.  1 B  receive a power factor correction pulse width modulation (PFC PWM). In particular, the power factor correction (PFC) can correct a line current of a power supply by producing a sinusoidal input current waveform that is in phase with a line input voltage. In an operating condition for converting DC to AC power in  FIG.  6 C , transistors T 5  and T 6  of  FIG.  1 B  receive an alternating current pulse width modulation (AC PWM). 
     A field programmable gate array (FPGA) digital design 8-bit pulse width modulator controls a switching signal for each MOSFET in  FIG.  1 B  (e.g., transistors T 1 -T 18 ) proportional to a duty cycle given by an input value received from a microcontroller (e.g., controller  10 ). An input pulse width modulation (PWM) value can be static, which is set by a user for a constant duty cycle output, or a closed loop cycle that interprets output current and voltage and adjusts the duty cycle appropriately to match a desired output. The latter method is desirable in use cases where a source power, a power drain, or both the source power and the power drain are variable. 
     A high input/output pin density of an FPGA device allows for multiple PWM control channels. Depending on an application, a control board is designed for up to twelve channels of synchronous PWM control totaling twenty four high speed PWM outputs (although any amount of channels can be used). Of twelve channels, any amount can be in an interleaving set. Interleaving PWM is an ability to parallel operate a switching device (i.e., buck, boost, inverter) by creating equally spaced switching wave forms depending on a number of channels being used. In embodiments, the FPGA device and the pulse width modulator can be included in the controller  10  of  FIGS.  1 A and  1 B . In an alternative embodiment, the FPGA device and the pulse width modulator can be external to the inverter-converter system  5  and can interface (i.e., receive/send signals) to the inverter-converter system  5  through the controller  10 . 
       FIG.  7    shows a switching and sampling frequency graph  80  in accordance with aspects of the present invention. For example, the present disclosure uses three channels of an inverter control with an equal spacing of 120 degrees to generate a three phase AC output. Both AC and DC PWN modulators begin by dividing a 106.25 MHz external oscillator clock. A series of clock divider and counters are then used to create a base sampling frequency of 12970 Hz as shown in the graph  80  of  FIG.  7   . In a DC operation, the base sampling frequency is then multiplied by a default value of eight. In other words, eight times will switch per 12970 Hz cycle to generate a 103.680 kHz as shown in the graph  80  of  FIG.  7   . The switching rate is adjustable up or down from a default integer of 8, from 1 to 12. In an AC application, the PWM modulator further divides the 12970 Hz frequency by 60 (for 60 Hz sine wave) resulting into 216 which is a number of samples per 60 Hz cycle of a sine waveform as shown in the graph  80  of  FIG.  7   . An integer value from 0 to 15 (e.g., the default value being 8) will dictate a switching frequency of AC generation PWM. A benefit of variable integer values that change a switching frequency is so that efficiency can be enhanced by means of utilizing passive components characteristics through the load profile of a system. 
     In conventional circuits, a digitized version of a sine wave can be created using pulse width modulation (PWM) when generating AC power. Further, in conventional circuits, the digitized sine wave can be divided into twelve sample points. In contrast, the present disclosure can divide the sine wave into 216 sample points (as shown in the graph  80  of  FIG.  7   ). In each sample point, a duty cycle is calculated to generate a section of the sine wave. 
       FIG.  8    shows dynamic tuning of switching frequencies in accordance with aspects of the present invention. In embodiments of the present disclosure, a higher frequency switching can be achieved in comparison to conventional circuits by using 216 sample points and multiplying the 216 sample points by an N integer, as shown in the table  90  of  FIG.  8   . In  FIG.  8   , the selected N integer can be an integer value, e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12, as shown in the table  90 . Further, the output frequency of the table  90  can correspond with the selected N integer values recited above, e.g., 25.920 kHz, 38.880 kHz, 51.840 kHz, 64.840 kHz, 77.76 kHz, 90.72 kHz, 103.680 kHz, 116.640 kHz, 129.60 kHz, 142.56 kHz, and 155.520 KHz. 
     As a result of multiplying the 216 sample points by an N integer, the sine wave is digitized in many steps as shown in the graph  80  of  FIG.  7   . Therefore, digitizing the sine wave in the graph  80  of  FIG.  7    has much more steps than the conventional circuits. For example, by default, each of the 216 samples for the PWM duty cycle will be executed eight times. Further, the present disclosure reduces the magnetics required to filter the squared switching waveforms and also results in a smooth 60 Hz sine wave. 
     A phase locked loop (PLL) frequency synthesizer consists of a circuit which has an ability to generate a range of frequencies derived from a single input reference frequency. Further, a power conversion system can be modified to allow an integer value from a control input of a microcontroller (e.g., the controller  10 ) to dictate an output frequency of the PWM signals. Therefore, combining a phase locked loop integrated circuit and logic within the FPGA device allows for an adjustable switching frequency. In contrast to conventional circuits, the present disclosure allowing for the adjustable switching frequency enables superior tuning and flexibility in the area of power conversion. 
     In the present disclosure, having the ability to adjust the frequency of PWM signals for DC and AC converters allows for a dynamic tuning of PWM switching frequency based on loads. For example, at a lower load of the inverter converter system  5 , it is preferable to switch at higher frequencies to allow operation of magnetics in continuous conduction mode. Further, at a high load of the inverter converter system  5 , it is preferable to switch at lower frequencies to allow operation of the magnetics to limit the amount of switching losses. 
       FIG.  9    shows a bi-directional inverter-converter assembly in accordance with aspects of the present invention.  FIG.  10    shows a top view of the bi-directional inverter-converter assembly in accordance with aspects of the present invention.  FIG.  11    shows an exploded view of the bi-directional inverter-converter assembly in accordance with aspects of the present invention. In  FIGS.  9 - 11   , the bi-directional inverter-converter assembly  100  includes the half bridge modules  12 , the inductors  14 , the gate driver signal boards  26 , the current sensors  28 , a control board  110 , buss bars  120 , a heat sink  130 , and a fan  140 . 
     In particular, the bi-directional inverter-converter assembly  100  is consistent electrically with the basic-inverter converter circuit schematic diagram of  FIG.  1 B . Therefore, each of the gate driver signal boards  26  in  FIGS.  9 - 11    are directly connected to the inductor  14  and the half bridge module  12 . Further, the half bridge modules  12  are connected to the control board  110 . In  FIGS.  9 - 11   , the fan may not be required in the bi-directional inverter-converter assembly  100 . Also, the heat sink  130  in the bi-directional inverter-converter assembly  100  can be replaced with any type of heat transferring component, e.g., heat pipe, liquid cooling cold plate, etc. The operation of the bi-direction inverter-converter assembly  100  is similar to the operation of basic-inverter converter circuit schematic diagram of  FIG.  1 B . 
     In embodiments, a service provider could offer to perform the processes described herein. In this case, the service provider can create, maintain, deploy, support, etc., the computer infrastructure that performs the process steps of the invention for one or more customers. These customers may be, for example, any business that uses technology. In return, the service provider can receive payment from the customer(s) under a subscription and/or fee agreement and/or the service provider can receive payment from the sale of advertising content to one or more third parties. 
     The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.