Systems and methods for scalable power converters with reconfigurable architecture and model predictive control

Abstract

Disclosed are scalable power converter systems and methods. The scalable power converter system includes one or more power converter phase-legs including a plurality of power converter modules connected in parallel, each power converter module including power switching elements. The scalable power converter system further includes a control system including: a central controller and a local model predictive controller for each phase-leg. The central controller generates a reference target for each local controller based on sensed characteristics. Each local model predictive controllers controls, based on the reference target and model predictive control, the plurality of power converter modules of the power converter phase-leg that corresponds to the local model predictive controller.

Description

SYSTEMS AND METHODS FOR SCALABLE POWER CONVERTERS WITH RECONFIGURABLE ARCHITECTURE AND MODEL PREDICTIVE CONTROLCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 63 / 593,919, filed on October 27, 2023, which is hereby incorporated by reference in its entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] Not applicable.BACKGROUND

[0003] Power converters of various types have been produced and used in many industries and contexts. Example power converters include alternating current (AC) to direct current (DC) rectifiers, DC to AC inverters, and DC to DC converters. AC to DC rectifiers, also referred to as AC / DC rectifiers, convert AC power to DC power. DC to AC inverters, also referred to as DC / AC inverters, convert DC power to AC power. Power converters can be used for various purposes, such as rectifying AC power from an AC grid power source to DC power for charging a battery, or inverting DC power from a battery to AC power to drive a motor or supply AC power to an AC grid. Further, power converters can be used in various contexts, such as in or connected to an electric vehicle, an engine generator, solar panels, and the like.SUMMARY

[0004] Power conversion systems, and improvements thereof, are in continuously increasing demand. Power converters may be described in terms of power conversion efficiency, power density, and cost, among other characteristics. Generally, it is desirable to have power converters with higher power efficiency, higher power density, and lower cost. Energy costs, including monetary costs and environmental costs, continue to be an important factor across many industries that incorporate power converters. Accordingly, even slight increases (e.g., of tenths of a percent) in power efficiency for a power converter can be significant and highly desirable. Similarly, reductions in materials and size of power converters can be significant and highly desirable, allowing reductions in costs and physical space to accommodate power converters insystems that incorporate power converters. Additionally, power converters with higher power ratings, increased flexibility and scalability, and improved dynamic performance may be desirable.

[0005] Some embodiments disclosed herein address these or other issues. For example, some embodiments disclosed herein are directed to scalable power converters and methods of power conversion with scalable power converters with higher power ratings (e.g., higher current and voltage capabilities), as well as improved efficiency, flexibility, scalability, and dynamic performance. The scalable power converters may use an architecture composed of scalable power modules and local regulation for each phase. Further, the local regulation may use model predictive control (MPC) techniques.

[0006] In one embodiment, a scalable power converter system is provided. The system comprises one or more power converter phase-legs including a plurality of power converter modules connected in parallel, each power converter module including power switching elements. The system further comprises a control system including: a central controller and one or more local model predictive controllers. The central controller is configured to generate one or more reference targets based on sensed characteristics of the one or more power converter phase-legs, each reference target corresponding to a power converter phase-leg of the one or more power converter phase-legs. Each local model predictive controller corresponds to a reference target of the one or more reference targets and a power converter phase-leg of the one or more power converter phase-legs and is configured to control, based on the reference target corresponding to the local model predictive controller and on model predictive control, the plurality of power converter modules of the power converter phase-leg that correspond to the local model predictive controller.

[0007] In one embodiment, a method of power conversion with a scalable power converter is provided. The method comprises generating, by a central controller of a control system, one or more reference targets based on sensed characteristics of one or more power converter phase-legs, each reference target corresponding to a power converter phase-leg of the one or more power converter phase-legs, each power converter phase-leg including a plurality of power converter modules connected in parallel, each power converter module including power switching elements, wherein the control system includes one or more local model predictive controllers, each local model predictive controller corresponding to a reference target of the oneor more reference targets and a power converter phase-leg of the one or more power converter phase-legs. The method further comprises controlling, by each local model predictive controller, the plurality of power converter modules of the power converter phase-leg that corresponds to the local model predictive controller, the controlling being based on the reference target corresponding to the local model predictive controller and model predictive control.

[0008] The foregoing and other aspects and advantages of the present disclosure will appear from the following description. In the description, reference is made to the accompanying drawings that form a part hereof, and in which there is shown by way of illustration one or more embodiment. These embodiments do not necessarily represent the full scope of the invention, however, and reference is therefore made to the claims and herein for interpreting the scope of the invention. Like reference numerals will be used to refer to like parts from Figure to Figure in the following description.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 illustrates a scalable power converter system according to some embodiments.

[0010] FIGS. 2A-2C illustrate example configurations of the scalable power converter system of FIG. 1.

[0011] FIGS. 3A-3B illustrate control system diagrams implemented by a power converter (e.g., the power converter of FIG. 1, FIG. 2A, or FIG. 2B), according to some embodiments.

[0012] FIG. 4 illustrates an example of a half-bridge converter, according to some embodiments.

[0013] FIG. 5 illustrates a method for power conversion using a scalable power converter system, according to some embodiments.

[0014] FIGS. 6A-6C illustrate diagrams of a scalable power converter system (e.g., the power converter system of FIG. 1 or power converter of FIG. 2A-2C), according to some embodiments.

[0015] FIGS. 7A-7D show waveforms from operation of a scalable grid-connected power converter, according to some embodiments.

[0016] FIG. 8 shows waveforms of an example of a scalable power converter.

[0017] FIG. 9 shows waveforms that demonstrate transient performance of a scalable power converter system with a grid side current reference step and using local model predictive control (MPC).DETAILED DESCRIPTION

[0018] One or more embodiments are described and illustrated in the following description and accompanying drawings. These embodiments are not limited to the specific details provided herein and may be modified in various ways. Furthermore, other embodiments may exist that are not described herein. Also, functions performed by multiple components may be consolidated and performed by a single component. Similarly, the functions described herein as being performed by one component may be performed by multiple components in a distributed manner. Additionally, a component described as performing particular functionality may also perform additional functionality not described herein. For example, a device or structure that is “configured” in a certain way is configured in at least that way, but may also be configured in ways that are not listed.

[0019] As used in the present application, “non-transitory computer-readable medium” comprises all computer-readable media but does not consist of a transitory, propagating signal. Accordingly, non-transitory computer-readable medium may include, for example, a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a ROM (Read Only Memory), a RAM (Random Access Memory), register memory, a processor cache, or any combination thereof.

[0020] In addition, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. For example, the use of “comprising,” “including,” “containing,” “having,” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Additionally, the terms “connected” and “coupled” are used broadly and encompass both direct and indirect connecting and coupling, and may refer to physical or electrical connections or couplings. Furthermore, the phase "and / or" used with two or more items is intended to cover the items individually and both items together. For example, “a and / or b" is intended to cover: a (and not b); b (and not a); and a and b.

[0021] Power conversion systems, and improvements thereof, are in continuously increasing demand. Power converters may be described in terms of power conversion efficiency, power density, and cost, among other characteristics. Generally, it is desirable to have power converters with higher power efficiency, higher power density, and lower cost. A highly efficient power converter is able to convert power (e.g., AC to DC, DC to AC, and / or DC to DC) without significant losses in energy. A low efficiency power converter experiences higher losses in energy during the power conversion. Such energy losses may manifest as heat generated by the power converter while converting power, for example. Power efficiency for a power converter, inductor, or other electronic component may be expressed as a percentage between 0 and 100% and determined based on the power input to the component and the power output from the component using the equation: Power Efficiency =A power converter with high power densityhas a high ratio of power output by the power converter compared to the physical space occupied by the power converter. The power density can be calculated using the equation:Power OutPower Density =Volume of Power Converter[0022J Energy costs, including monetary costs and environmental costs, continue to be an important factor across many industries that incorporate power converters. Accordingly, even slight increases (e.g., of tenths of a percent) in power efficiency for a power converter can be significant and highly desirable. Similarly, reductions in materials and size of power converters can be significant and highly desirable, allowing reductions in costs and physical space to accommodate power converters in systems that incorporate power converters. Additionally, power converters with higher power ratings, increased flexibility and scalability, and improved dynamic performance may be desirable.

[0023] Some embodiments disclosed herein address these or other issues. For example, some embodiments disclosed herein are directed to scalable power converters and methods of power conversion with scalable power converters with higher power ratings (e.g., higher current and voltage capabilities), as well as improved efficiency, flexibility, scalability, and dynamic performance. The scalable power converters may use an architecture composed of scalable power modules and local regulation for each phase. Further, the local regulation may use model predictive control (MPC) techniques. The power modules may be scalable in that a different number of the power modules can be connected in parallel with the local model predictive control(MPC) for each module to stabilize the output voltage and attenuate the circulating current among different modules. A central level controller may be responsible for regulating lumped output current (e.g., idq), attenuating the circulating current, and generating target references for the MPC control of each local power module.

[0024] FIG. 1 illustrates a scalable power converter system 100 in accordance with some embodiments. The scalable power converter system 100 includes a control system 105, a first direct current (DC) load / source 110, a scalable power converter 115, a second source / load 130, and one or more sensors 140. The control system 105 includes a central controller 150 with an electronic processor 155 and a memory 157 and one or more local controllers 160, each having an electronic processor 165 and a memory 167. The scalable power converter system 100, as well as the other power converter systems provided herein, may be non-isolated power converter systems. That is, the power converter system may be coupled to an AC source (e.g., single- or three-phase power grid) or AC load (e.g., single or 3-phase motor) without a transformer. Use of a transformer is common in electrical circuits to provide isolation between the power converter and an AC source or load. However, such a transformer can add inefficiencies and size or volume to the power converter. Accordingly, some examples of the power converter systems provided herein are non-isolated, also referred to as transformerless, to increase efficiency and / or reduce size of the power converter systems. Because the power converters are provided without isolation by a transformer, the power converters may include additional features to prevent transmission of unwanted signals or current (e g., leakage current) from passing between the power converters and other circuit components (e.g., DC sources, DC loads, AC sources, AC loads, and other structures in contact with or supporting the power converters). These additional features may include LC filters, zero-sequence control of common mode voltage, harmonic injection, model predictive control, variable frequency critical soft switching, and the like. However, in other examples of the power converter systems described herein, the power converter system is isolated and may be coupled to an AC source (e.g., single- or three-phase power grid) or AC load (e.g., single or 3-phase motor) with a transformer.

[0025] In operation, generally, the control system 105 controls power switching elements of the power converter 115 with control signaling (e.g., pulse-width modulated (PWM) signals) to convert power (i) from the DC load / source 110 functioning as a source to the second source / load 130 functioning as a load, or (ii) from the second source / load 130 functioning as asource to the DC load / source 110 functioning as a load. Accordingly, when the DC load / source 110 is functioning as a source for the power converter 115, the second source / load 130 is functioning as a load for the power converter 115. Conversely, when the DC load / source 110 is functioning as a load for the power converter 115, the second source / load 130 is functioning as a source for the power converter 115.

[0026] The DC load / source 110 may be a direct power (DC) load, a DC source, or both a DC load and DC source (i.e., functioning as DC source in some instances and as a DC load in other instances, depending on the mode of the power converter 115). In some examples, the DC load / source 110 is a battery. In other examples, DC load / source 110 may be a capacitor, an ultracapacitor, a DC power supply from rectified AC source (e.g., AC grid power converted to DC power by diode bridge rectifier), or the like. The second source / load 130 may be an AC load, an AC source, both an AC load and AC source (i.e., functioning as an AC source in some instances and as an AC load in other instances, depending on the mode of the power converter 115), a DC load, a DC source, both a DC load and DC source (i.e., functioning as a DC source in some instances and as a DC load in other instances, depending on the mode of the power converter 115). In some examples, the source / load 130 may be an electric (AC) motor, an AC generator, AC power supply grid, a DC battery, a DC capacitor, a DC ultracapacitor, a DC power supply from rectified AC source (e.g., AC grid power converted to DC power by diode bridge rectifier), or the like.

[0027] The DC load / source 110 is coupled to the power converter 115 at a first (DC) side or section of the power converter 115, and the second source / load 130 is coupled to the power converter 115 at a second (AC) side or section of the power converter 115. The first side may also be referred to as an input side or an output side of the power converter 115, depending on the mode of the power converter, or as a DC side of the power converter 115. The second side may also be referred to as an input side or an output side of the power converter, depending on the mode of the power converter, or as an AC side of the power converter 115. In some embodiments, the second side of the power converter 115 may be an AC side having single-phase AC power, three-phase AC power, or AC power with another number of phases.

[0028] In some embodiments, the power converter 115 operates with a high DC voltage level. For example, in operation, the DC side of the power converter 115 has a DC voltage (e.g., across input terminals of the power converter 115) of at least 200 V, at least 600 V, at least 800V, at least 1000 V, at least 1200 V, between 200 V and 1200 V, between 600 V and 1200 V, between 800 V and 1200 V, or another range. Such high DC voltage levels may be desirable in some contexts, such as some electric vehicles. For example, some current electric vehicles (e.g., passenger vehicles and hybrid electric vehicles) operate with a DC bus voltage of between about 200 V and 400 V. This DC bus voltage for passenger electric vehicle may increase in the future. Further, some current electric vehicles (e.g., class 4-8, off-road, or otherwise larger electric vehicles) can operate with a DC bus voltage of more than 1000 V. However, high DC voltage levels may introduce challenges into a typical power converter system, such as an increase in leakage currents, increases in common mode voltage, higher rates of change in common mode voltage, and the like. These challenges can lead to resonance on an LC fdter, shaft voltages, excessive bearing currents (e.g., from discharge events when lubricant dielectric breakdown occurs) that can result in bearing failures, excessive motor shaft currents, excessive motor winding currents (e.g., insulation may be damaged), and excessive gear train currents (e.g., bearing currents can propagate into the geartrain via electromagnetic interference (EMI) or noise, vibration, harshness (NVH) resulting from the damaged bearing race walls). Embodiments described herein, however, can mitigate such challenges through improved LC filters and through control techniques including control techniques that use harmonic injection, cascaded (or hierarchical) central and local controllers, MPC control, and / or variable frequency critical soft switching (VFCSS).

[0029] The sensor(s) 140 include, for example, one or more current sensors and / or one or more a voltage sensors. For example, the sensor(s) 140 may include a respective current sensor and / or voltage sensor to monitor a current and / or voltage of one or more of the DC load source 110, each phase of the second source / load 130, or other nodes or components of the power converter 115. In some embodiments, additional or fewer sensors 140 are included in the system 100. For example, the sensors 140 may also include one or more vibration sensors, temperature sensors, and the like. In some examples, the control system 105 infers a characteristic (e.g., current or voltage) of the power converter 115, rather than directly sensing the characteristic. The sensor(s) 140 may provide sensor data to the control system 105 indicative of the sensed characteristics of the system 100. Such sensor data may, accordingly, indicate electrical operational characteristics of the system 100. In some examples, the control system 105 infers or estimates a characteristic (e.g., current or voltage) at one or more nodes of the power converter1 15 based on the sensor data of a sensor 140 that senses a different type of characteristic or even a different component, rather than directly sensing the characteristic.

[0030] The input-output (I / O) interface 142 includes or is configured to receive input from one or more inputs (e.g., one or more buttons, switches, touch screen, keyboard, and the like), and / or includes or is configured to provide output to one or more outputs (e.g., LEDs, display screen, speakers, tactile generator, and the like). Other electronic devices and / or users may communicate with the system 100 and, in particular, the control system 105, via the I / O interface 142. For example, the control system 105 may receive commands (e.g., from a user or another device) for the scalable power converter system 100 indicating a target torque, target speed, target power level, conversion type, or the like. The control system 105, in response, may drive the power converter 115 to achieve the target and / or conversion type indicated by the command.

[0031] The control system 105 generally monitors the system 100 including the power converter 115 (e.g., based on sensor data from the sensor(s) 140), receives commands (e.g., via the input / output interface 142), and controls the power switching elements of the power converter 115 with control signaling (e.g., pulse-width modulated (PWM) signals) to convert power (e.g., in accordance with the sensor data and / or the commands). In some embodiments, the control system 105 includes a controller (e.g., the central controller 150) that performs this monitoring and control without additional local controllers. In other embodiments, the control system 105 is a cascaded control system including a central controller 150 and one or more local controllers 160. The cascaded control system may communicate in real time (e.g., each control cycle) monitoring information (e.g., sensor data) and control information between the central controller 150 and the one or more local controller 160. In some examples, the local controller(s) 160 each implement model predictive control (MPC) or another regulation control scheme (e.g., PID control, PI control, or the like). In some examples, the central controller implements a non-MPC regulation technique, such as proportional integral derivative (PID) control or proportional integral (PI) control.

[0032] Each controller of the control system 105, including the central controller 150 and the local controller(s) 160, is an electronic controller that may include an electronic processor. Such an electronic controller may further include a memory (e.g., the memory 157 or 167). The memory is, for example, one or more of a read only memory (ROM), random access memory (RAM), or other non-transitory computer-readable media. The electronic processor 155, 165 maybe configured to, among other things, receive instructions and data from the memory 157, 167 and execute the instructions to, for example, carry out the functionality of the associated controller described herein, including the processes described herein. For example, the memory may include control software. In some embodiments, instead of or in addition to executing software from the memory to carry out the functionality of the controller described herein, the electronic processor includes one or more hardware circuit elements configured to perform some or all of this functionality. In some examples, the electronic processor is implemented as one or more of an FPGA (field programmable gate array), an ASIC (application specific integrated circuit), a complex programmable logic device (CPLD), a DSP processor, a graphics processing unit (GPU), application processing unit (APU), or the like. Additionally, although a particular controller, electronic processor, and memory may be referred to as a respective, single unit herein, in some embodiments, one or more of these components is a distributed component. For example, in some embodiments, an electronic processor includes one or more microprocessors and / or hardware circuit elements.

[0033] FIGS. 2A to 2C illustrate example configurations of the scalable power converter system 100, identified as power converters 200, 220, and 250, respectively. In other examples, the scalable power converter system 100 is implemented in another configuration. In FIGS. 2A- C, the DC source 110, sensors 140, and input / output 145 are not illustrated to simplify the diagrams. In FIG. 2A, the power converter 200 is a half-bridge single-phase converter. The power converter 200 includes a central controller 150, one local controller 160, and a scalable power converter 115. The scalable power converter 115 includes one or more scalable power converter modules 205. When two or more of the scalable power converter modules 205 are present, the scalable power converter modules 205 are coupled in parallel with one another, such as shown in FIG. 6A. In this example, each of the scalable power converter modules 205 include a half-bridge single-phase converter circuit (see, e.g., FIG. 4) that is coupled to two terminals of a (singlephase) AC load 130.

[0034] In FIG. 2B, the power converter 220 is a full-bridge single-phase converter. The power converter 220 includes a central controller 150, two local controllers 160, and a scalable power converter 115. In this example, the scalable power converter 115 includes a first set of one or more scalable power converter modules 205 (also referred to as scalable power converter circuits 205) and a second set of one or more scalable power converter modules 205. In some-loexamples, each set of scalable power converter module 205 is coupled to a respective terminal of a (single-phase) AC load 130. The first set of one or more scalable power converter modules 205 may be driven to output an AC signal that is 180 degrees out of phase with respect to the other set of one or more scalable power converter modules 205. As noted, each scalable power converter module 205 may include a half-bridge single-phase converter circuit (see, e g., FIG. 4). Additionally, for each set of scalable power converter modules 205, when two or more of the scalable power converter modules 205 are present in a set, these scalable power converter modules 205 of the set are coupled in parallel with one another, such as shown in FIG. 6B.

[0035] In FIG. 2C, the power converter 250 is a three-phase converter. The power converter 250 includes a central controller 150, three local controllers 160, and a scalable power converter 115. In this example, the scalable power converter 115 includes three sets of one or more scalable power converter modules 205. In some examples, each set of scalable power converter module 205 is coupled to a respective phase-leg 130a, 130b, 130c of a (three-phase) AC load 130. Each set of the scalable power converter modules 205 may be driven to output an AC signal that is 120 degrees out of phase with respect to the other sets of scalable power converter modules 205. As noted, each scalable power converter module 205 may include a halfbridge single-phase converter circuit (see, e.g., FIG. 4). Additionally, for each set of scalable power converter modules 205, when two or more of the scalable power converter modules 205 are present in a set, these scalable power converter modules 205 of the set are coupled in parallel with one another, such as shown in FIG. 6C.

[0036] FIG. 3A-3B illustrate control system diagrams for a converter system 300. The converter system 300 may be an example of, for example, the power converter system 100, the power converter 200, the power converter 220, and / or the power converter 250.

[0037] FIG. 3 A illustrates a converter system 300 including a central controller 150, three local controllers 160a, 160b, 160c (each being an instance of the local controller 160 previously introduced), and scalable power converter modules 205a, 205b, and 205c (each being an instance of the scalable power converter module 205 previously introduced). The local controllers 160a-c may be referred to generically as the local controllers 160 or each local controller 160. The scalable power converter modules 205a-c may be referred to generically as the scalable power converter modules 205 or each scalable power converter module 205. When implemented by the power converter 200 (half bridge, single-phase), the converter system 300 may include the localcontroller 160a and the scalable power converter modules 205a, while the remaining dashed components of the converter system 300 (local controllers 160b, 160c and modules 205b, 205c) may not be present. When implemented by the power converter 220 (full bridge, single-phase), the converter system 300 may include the local controllers 160a and 160b and the scalable power converter modules 205a and 205b, while the remaining dashed components of the converter system 300 (local controller 160c and module 205c) may not be present. When implemented by the power converter 250 (three-phase), the converter system 300 may include the local controllers 160a, 160b, and 160c and the scalable power converter modules 205a, 205b, and 205c.

[0038] FIG. 3A further illustrates communications between the components of the converter system 300 during operation (e.g., when a power converter utilizing the converter system 300 is operating to convert power). As illustrated, each scalable power converter module 205 provides sensor data to a respective local controller 160. The scalable power converter module 205 may have incorporated therein one or more sensors of the previously described sensors 140 (see FIG. 1). In some examples, the sensor data includes one or more of inductor current for an LC filter of the module 205, capacitor voltage for a capacitor of the LC filter of the module 205, output current output by the LC filter of the module 205, and / or temperature indicating temperature of or surrounding one or more components of the scalable power module 205 (e.g., a power switching element, capacitor, inductor, etc.). Each local controller 160 further provides the sensor data to the central controller 150. Accordingly, the central controller 150 receives sensor data for each scalable power converter module 205 present in the converter system 300. The central controller 150, in turn, generates a reference target for each local controller 160. The reference target is specific to each local controller 160.

[0039] The central controller 150 may be, for example, a PID controller that generates the reference target(s) based on the sensor data received and an overall power demand or command (e.g., received via I / O interface 142 or a memory). In some examples, the central controller 150 includes a current controller block 302 (also referred to as a grid current controller block) that translates the sensor data from a stationary reference frame (e.g., abc reference frame) to a rotational reference frame (e.g., a direct-quadrature (DQ or DQ0) reference frame). For example, the current controller block 302 may translate, via translator 304, output or grid current (ig) provided as sensor data (e.g., Sensor Dataa,b.c) from ig,abc to ig,dq. To translate, the translator 304 may use Park and Clarke transformations. The central controller 150 may then generate referencetargets for each leg of the rotational reference frame (e.g., a voltage target for the D component, a voltage target for the Q component, a voltage target for the 0 (zero) component)). The reference targets may be set based on the sensed values (i.e., values indicated by sensor data) relative to desired values for these characteristics to cause the sensed values to approach the desired values (e.g., using PID techniques). For example, a regulator 306 may receive the grid current (ig,dq) and a command (e.g., a current command in the DQ reference frame received from a memory or the VO interface 142), and may output a voltage target (vc,dq) to cause the grid current to approach the current command. The voltage target (vc,dq) may be referred to as a global reference target. The current controller block 302 may output the voltage target in the stationary reference frame by translating, via translator 308, the voltage target from the rotational reference frame to the stationary reference frame (e.g., vc.dqto Vc.abc). The translator 308 may translate from the DQO reference frame to the stationary (abc) reference frame using Park and Clark inverse transformations. The voltage targets in the stationary reference frame may be referred to as local reference targets.

[0040] In some examples, the central controller 150 includes zero-sequence control. For example. The central controller 150 may include a zero-sequence control block 310 where the zero sequence (0-axis of the DQO reference frame) is set to half a DC link voltage to control leakage current in the system. In some embodiments, the central controller further injects a harmonic eO* (e.g., a sinusoidal or triangular wave voltage signal as a harmonic injection) into the 0 component (e.g., summed with the half DC link voltage). The harmonic may be a 3rdorder harmonic of the fundamental frequency of an output AC signal or AC grid to which the converter is coupled. The central controller 150 may then, via a reference generation block 312, add the zero-sequence component (vc.o*) to the voltage targets (vcabc). In other examples, the zerosequence component may be provided to the translator 308 as the zero-sequence component (vc.o*) of the voltage target in the rotational DQO reference frame that is translated to the voltage target in the stationary (abc) reference frame (vcabc).

[0041] The central controller 150 may then output a reference target (Ref) for each local controller 160 present in the converter system 300 (e.g., Refa, Refb, Refc to the local controllers 160a, 160b, 160c). For example, Refa may be set to ve,a*, Refb may be set to vc,b*, and Refc may be set to Vc.c* as output by the reference generation block 312 or as output by the current control block 302. In examples in which three phases are not present (e.g., half bridge, single-phaseconverter or full bridge, single-phase converter), the “b” and / or “c” components of the grid current (ig,b and / or ig,c) and target voltage (ig,b and / or vg,c) may be omitted from the central controller reference generation process described with respect to FIG. 3A.

[0042] As described with respect to FIG. 3A, the reference target is a voltage value for the voltage across a capacitor of an LC fdter of the scalable power converter modules 205 (see, e.g., LC filter 445 of FIG. 4). In other examples, the reference target is another electrical characteristic of the scalable power converter module 205 (e.g., another voltage or a current target).

[0043] Each local controller 160 receives the corresponding reference target from the central controller 150. Each local controller 160, in turn, generates control signals, based on the received reference target, for controlling the corresponding scalable power converter modules 205. By generating appropriate control signals, each local controller 160 may thereby regulate the electrical characteristic of the reference target (e.g., capacitor voltage) to approach the value indicated by the reference target.

[0044] Turning to FIG. 3B, a more detailed diagram 320 of the local controller 160a and the scalable power converter module 205a of FIG. 3A is provided. The diagram similarly applies to the other local controllers 160b and 160c and scalable power converter modules 205b and 205c.

[0045] As illustrated, the local controller 160a includes the electronic processor 165 and a gate driver 330; and the scalable power converter modules 205a each include a switching circuit 335 and are associated with sensors 340. The scalable power converter modules 205a include N modules, where N is an integer that is greater than or equal to two. With reference to FIG. 3B, the scalable power converter modules 205a are individually identified as scalable power converter modules 205a-l, 205a-2, 205a-3, ... 205a-N. Generally, the more modules (i.e., the greater the value of N), the higher the output current and / or power may be provided by the power converter system (i.e., the higher the output current and / or power rating).

[0046] In operation, the electronic processor 165 receives the reference target (Refa) from the central controller 150 and sensor data 345 (Sensor Dataa) from the sensors 340. The sensor data 345 may be as previously described with respect to FIG. 3A. From the reference target and sensor data, the electronic processor 165 determines a duty cycle reference (da*) and a switching frequency (fsw).

[0047] The gate driver 330 receives the duty cycle reference (da*) and the switching frequency (fsw) and generates variable frequency soft switching (VFSS) control signals 350. The VFSS control signals 350 may include, for each scalable power converter module 205a, a first pulse width modulated (PWM) signal having a frequency set to the switching frequency (fsw) and a duty cycle set to the duty cycle reference (da*) and a second PWM signal that is an inversion of first PWM signal (an inverted PWM signal). In some examples, the PWM signals for a set of scalable converter modules 205 (e.g., module 205a) are synchronized (e.g., using a sensor to ensure synchronization). For example, the PWM signals may be synchronized for a vehicle traction motor. This approach can lead to a cleaner AC signal being output. In some examples, the PWM signals are not synchronized and can be different, for example, in a grid application in which an AC signal may be less clean. Although inverter gates that provide the inverted PWM signals of the control signals 350 are shown external to the gate driver 330 in FIG. 3B, the inverter gates may be internal to the gate driver 330 and / or may represent virtual inverter gates where the gate driver 330 produces an inverted signal through control techniques without a separate hardware inverter gate.

[0048] Each noninverted and inverted signal pair of the VFSS control signal 350 controls the switching of a pair of power switching elements of a respective switching circuit 335. In some examples, the switching frequency (fsw) is varied during operation such that each pair of power switching elements is controlled to soft switch (zero voltage switching). By soft switching, the converter may reduce switching losses and increase conversion efficiency. In some examples, current ripple through an inductor of an LC filter of the switching circuit 335 should or must be above a certain minimum threshold to enable soft switching. The amplitude of current ripple may vary according to switching frequency, where the higher the switching frequency, the smaller the current ripple. Accordingly, in some examples, the local controller may determine the largest switching frequency (fsw) that will still enable soft switching, potentially limited by a maximum switching frequency associated with high switching loss. Generally, the duty cycle of the PWM control signals controls the output voltage of the converter, while frequency does not. Accordingly, the duty cycle may be determined based on the desired voltage conversion ratio to achieve the desired output voltage, while the frequency may be used to adjust current ripple (and thereby achieve soft switching).

[0049] To generate the duty cycle reference (da*) from the reference target and sensor data, the local controller 160a (e.g., via the electronic processor 165) may implement model predictive control (MPC). As used herein, MPC can refer to a control algorithm that relies on or is aware of a system dynamic (e.g., implements or uses a dynamic model representing the converter under control) and predicts, through computation based on electrical characteristics of the converter and the dynamic model, input commands or reference values to control the system's behavior. Accordingly, MPC, as used herein, may refer to a model predictive control algorithm in a stricter use of the term (such as described in further detail below) as well as other dynamic prediction algorithms (e.g., a linear-quadratic regulator (LQR) control algorithm).

[0050] In one example, to implement the MPC algorithm, the electronic processor 165 may, in each control period, solve a cost function using the electrical characteristics and the control reference target for that phase. By solving the cost function, the electronic processor 165 can predict future steps of control signaling to actuate the power switching elements to control power on that phase of an AC voltage section of the power converter to trend towards the control reference target. The electronic processor 165 may then generate the control signaling for that particular phase based on a first step of the future steps of control signals. Accordingly, in contrast to a PI control algorithm, the MPC algorithm derives an optimal duty cycle by processing a state variable and tracking error in a linear way with specific coefficients. Because no integration procedure is needed in MPC, the dynamic performance of MPC may be improved relative to a PI technique with less overshoot and higher tracking speed. Additionally, because MPC has higher control bandwidth, the electronic processor 165 can provide an active damping term to mitigate (reduce or eliminate) LC or LCL resonance that may otherwise be present in a filter circuit in the AC section of the power converter 115.

[0051] In some examples, to implement MPC, the electronic processor 165 receives sensor data (e.g., the inductor current, lL a, lower capacitor voltage, vcf a, grid current, ig a) and the reference target (Refa). The electronic processor 165 may execute the MPC algorithm explicitly with a pre-configured piecewise affine function to generate the desired duty cycle for the per phase switching modulation. For the digital execution of the MPC algorithm, the state space equations can be configured as

[0052] The standardized matrix format can be expressed as k+i =Ak + Buk+ Eek(3) where A = [1, -Ts / Lfs; Ts / Cf, 1], B = [Ts / Lfs; 0], E = [0; -Ts / Cf], Xk= [iL(ky, vcf(k \, uk= [vDcd(k)] and ek= [igk].

[0053] The cost function can be composed of two itemsrepresent the weighting matrices for the tracking error and input variable terms in the cost function. In some examlpes, the weighting of Vcf (k)Xkmay be configured to be 100-500 times larger than other terms to track the lower output capacitor voltage references more accurately.

[0054] In other examples, the local controller 160 implements a non-MPC control technique, such as, for example, a PID control technique.

[0055] Generally, and as illustrated in FIG. 4, each pair of power switching elements includes a first transistor receiving a first (non-inverted) control signal (e.g., PWM) and a second transistor receiving an inversion of the first control signal (e.g., inverted PWM). Accordingly, during operation, when the first transistor of the pair is enabled (ON), the second transistor of the pair is disabled (OFF), and vice versa. The terms power switching element and transistor are used interchangeably herein. In some examples, the transistors may be a type of field effect transistor (FET), such as, for example, a metal oxide semiconductor (MOS) FET, silicon carbide (SiC) FET, or Gallium Nitride Transistors (GaN) FET.

[0056] FIG. 4 illustrates an example of a switching circuit that may serve as the switching circuit 335 in one or more of the scalable power converter modules 205 that may be present in a power converter (e.g., the scalable power converter system 100, power converter 200, 250). More particularly, FIG. 4 illustrates an example of a converter circuit 400 that may serve as the switching circuit 335. As illustrated, the converter circuit 400 is a half bridge converter circuit that includes DC terminals 420 (also referred to as DC nodes, DC links, DC rails, etc.) having a positive DC terminal 422 and a negative DC terminal 424. The converter circuit 400 further includes interface terminals 425 (also referred to as interface nodes or grid nodes) having a positive interface terminal 427 and negative interface terminal 429. The converter circuit 400 maybe operated as a bidirectional converter or as a unidirectional converter (in either direction), depending on the configuration and control of the system in which it is implemented. Accordingly, the DC terminals 420 may be input terminals and the interface terminals 425 may be output terminals in some examples (e.g., DC / DC conversion and DC / AC inversion), and the DC terminals 420 may be output terminals and the interface terminals 425 may be input terminals in some examples (e.g., AC / DC rectification). Additionally, the interface terminals 425 may be AC input terminals (e.g., for AC / DC rectification), may be AC output terminals (e.g., for a DC / AC inverter), or may be DC output terminals (e.g., for DC / DC conversion).

[0057] The converter circuit 400 further includes a DC link capacitor (CDC) 430, a, a high side (upper) power switching element (Ml) 435 (also referred to as upper switch or upper FET 435), a low side (lower) power switching element (M2) 440 (also referred to as lower switch or lower FET 440), a midpoint node 442 connecting a drain terminal of upper switch 435 and a source terminal of lower switch 440, and an LC filter 445. The voltage across the DC link capacitor 430 (and, thus, across the DC terminals 420) may be referred to as the DC link voltage.

[0058] The power switching elements 435 and 440 may be field effect transistors (FETs), each having a respective gate, source, and drain terminal. The FETs may be, for example, a MOSFET, a silicon carbide (SiC) FET, a gallium nitride (GaN) FET, among other types of FETs.

[0059] The LC filter 445 includes a switch-side inductor Lsw 450, a lower capacitor CD 455, and an upper capacitor CA 415. The switch-side inductor Lsw 450 is coupled between the midpoint node 442 and a filter node 260. For example, a first end of the switch-side inductor Lsw 450 is coupled to the midpoint node 442, and a second end is coupled to the filter node 460. The lower capacitor CB 455 is coupled between the filter node 406 and the negative DC terminal 424. For example, a first end of the lower capacitor CB 455 is coupled to the filter node 460, and a second end is coupled to the negative DC terminal 424. The upper capacitor CA 415 is coupled between the filter node 460 and the positive DC terminal 422. For example, a first end of the lower capacitor CA 415 is coupled to the filter node 460, and a second end is coupled to the positive DC terminal 422.

[0060] In some examples, the LC filter 445 is an LCL filter (an LC filter with an additional inductor (L)), in which an additional (interface) inductor is coupled between the filter node 460 and the positive interface terminal 427.

[0061] The upper capacitor 415 allows for the ripple currents at both input nodes and output nodes (nodes 422, 427) of the power converter 200 to be shared. Because the ripple currents on the input nodes and the ripple currents on the output nodes have some correlation, differential mode currents of these input and output nodes can be canceled through this capacitance. This reduction in differential mode current can result in improved EMI performance and decreased total capacitor ripple current when compared with a typical half-bridge converter (e.g., when the total capacitance between the two converters is held constant). Furthermore, the reduction in total capacitor ripple current can allow for a decrease in capacitor size, for example, when capacitor ripple current drives capacitor sizing.

[0062] The converter further includes drain-source capacitors CDS 465a and 465b, each respectively coupled across one of the switches 435, 440. In particular, a first drain-source capacitor 465a is provided across a source terminal 470a and drain terminal 475a of the upper switch (Ml) 435, and a second drain-source capacitor 465b is provided across a source terminal 470b and drain terminal 475b of the lower switch (M2) 440. The drain-source capacitors (CDS) 465a-b may be generically and collectively referred to herein as drain-source capacitor(s) (CDS) 465.

[0063] The drain-source capacitors (CDS) 465 can slow a voltage rise during an ON-to- OFF transition of the switches 435 and 440. This slowed voltage rise can, in turn, reduce the switching losses of the switches 435 and 440.

[0064] In some examples of the converter circuit 400, one or both of the upper capacitor CA 415 and the drain-source capacitors CDS are not included in the converter 400.

[0065] In some examples, N instances of the converter circuit 400 are paralleled to serve as the scalable power converter modules 205a. Additionally, if a second phase-leg is present, N instances of the converter circuit 400 are paralleled to serve as the scalable power converter modules 205b. Further, if a third phase-leg is present, N instances of the converter circuit 400 are paralleled to serve as the scalable power converter modules 205c (see FIG. 3A). Accordingly, because the modules are paralleled, the DC link voltage across DC terminals (or nodes) 420 and DC link capacitor 430 may be shared by each of the N power converter modules of a phase-leg or all phase-legs. Additionally, because the modules are paralleled, each of the N power converter modules of a phase-leg may connect to an interface terminal (or grid node) 425 via a respective LC filter 445 of that power converter module. Thus, the current output by each power convertermodule of a phase-leg may be summed at the interface terminal (or grid node 425. The converter circuit 400 is one example of a circuit that may serve as the switching circuit 335. In other examples of the converter system 300, other converter circuits are used.

[0066] FIG. 5 illustrates a method 500 for power conversion with scalable power converters. The method 500 is described as being carried out by the scalable power converter system 100, implemented as illustrated in FIGS. 2A-2C and / or 3A-3B (e.g., using a converter circuit 400 as scalable converter modules 205), and with respect to control diagrams of FIGS. 3A- 3B. However, in some examples, the method 500 may be implemented by another power converter system. Additionally, although the blocks of the method 500 are illustrated in a particular order, in some embodiments, one or more of the blocks may be executed partially or entirely in parallel, may be executed in a different order than illustrated in FIG. 5, or may be bypassed.

[0067] In FIG. 5, at block 505 of the method 500, a central controller of a control system generates one or more reference targets based on sensed characteristics of one or more power converter phase-legs. For example, with reference to FIG. 3 A, the central controller 150 of the control system 105 may generate reference targets Refa, Refb, and / or Refc, depending on the number of phase-legs in the scalable power converter system 100. With continued reference to FIG. 3A, each reference target (Refa, Refb, and / or Refc) corresponds to a power converter phaseleg of the one or more power converter phase-legs (QA, B, and / or QC), and each power converter phase-leg includes a plurality of power converter modules (e.g., modules 205a, 205b, and / or 205c) connected in parallel. For example, with reference to FIG. 3B, the phase-leg QA includes N power converter modules 205a connected in parallel. Similarly, the phase-leg QB (if present) and QC (if present) may also respectively have N power converter modules 205b connected in parallel and N power converter modules 205c connected in parallel. Further, each power converter module 205a, 205b, and / or 205c includes power switching elements, such as, for example, when implemented as the converter circuit 400 of FIG. 4. Additionally, as shown in FIG. 3A, the control system 105 further includes one or more local controllers 160a, 160b, and / or 160c implementing model predictive control (also referred to as local model predictive controllers 160a, 160b, 160c), each local model predictive controller corresponding to a reference target of the one or more reference targets and to a power converter phase-leg of the one or more power converter phase-legs (QA, QB, and / or QC).

[0068] In some examples, the central controller 150 generates the one or more reference targets (Refa, Refb, and / or Refc) for the local controllers 160a, 160b, and / or 160c using the techniques previously described with respect to FIGS. 3 A and 3B (e.g., based on sensor data from the phase-legs, and using one or more of the current controller block 302, zero-sequence control block 310, and reference generation block 312).

[0069] Returning to FIG.5, at block 510, each local model predictive controller controls the plurality of power converter modules of the power converter phase-leg that corresponds to the local model predictive controller. The controlling by the local model predictive controller is based on the reference target received by the local model predictive controller and is based on model predictive control. For example, each local controller 160a, 160b, and / or 160c may control the plurality of power converter modules 205a, 205b, and / or 205c of the phase-leg associated with the local controller 160a, 160b, and / or 160c based on the respectively received reference targets Refa, Refb, and / or Refc. For example, with reference to FIG. 3B, the local controller 160a may generate control signals 350 to drive each power converter module 205a, and, with reference to FIG. 3 A, the other local controller(s) 160b and 160c (if present) may similarly generate control signals for their corresponding power converter modules 205b and 205c (if present). As described with respect to FIG. 3B, the local controllers 160 may generate the control signals 350 based on the received reference target and sensor data (e.g., from sensors 340), and using model predictive control techniques. Accordingly, the local controllers 160 may also be referred to as local model predictive controllers.

[0070] As an example, to use model predictive control techniques to generate the control signals 350, the electronic processor 165 of each local controller 160 may execute an MPC algorithm explicitly with a pre-configured piecewise affine function to generate the desired duty cycle for the per phase switching modulation. The MPC algorithm and, thus, the piecewise affine function, may be based on the above-provided state space equations (1) and (2) and cost function (4).

[0071] Additionally, to control, based on the reference target and model predictive control, the plurality of power converter modules of the power converter phase-leg that corresponds to the local model predictive controller, each local model predictive controller may generate control signals 350 that, as shown in FIG. 3 A, include a PWM signal and an inverted PWM signal for the power converter modules of the power converter phase-leg that correspondsto the local model predictive controller. As previously described with respect to FIG. 3A, the PWM signal and the inverted PWM signal may have a variable frequency (fsw) and a duty cycle (d*). The local controller 160 may determine the duty cycle (d*) based on (as an output of) the MPC algorithm. The local controller 160 may determine the variable frequency (fsw) based on a variable frequency soft switching technique to maintain soft switching. For example, the local controller 160 may solve a function to determine the variable frequency (fsw) to be the highest frequency, up to a predetermined maximum frequency, that provides sufficient amplitude of current ripple to enable soft switching.

[0072] As noted above, the method 500 may be carried out by the scalable power converter system 100 being implemented as illustrated in FIGS. 2A, 2B, or 2C. Accordingly, the scalable power converter system 100 carrying out the method 500 may be a half bridge, singlephase converter (FIG. 2A), a full bridge, single-phase converter (FIG. 2B), or a three-phase converter (FIG. 2C). In other examples, the scalable power converter system 100 is configured as another type of converter.

[0073] FIGS. 6A-6C provide respective diagrams 600, 620, and 640 applicable to some examples of the scalable power converter system 100. The diagram 600, like FIG. 2A, illustrates a half bridge, single-phase architecture including one phase-leg, phase-leg A, having parallel converter modules 205. The diagram 620, like FIG. 2B, illustrates a full bridge, single-phase architecture including two phase-legs: phase-leg A and phase-leg QB, each having parallel converter modules 205. The diagram 640, like FIG. 2C, illustrates a three-phase architecture including three phase-legs: phase-leg QA, phase-leg QB, and phase-leg QC, each having parallel converter modules 205.

[0074] FIGS. 7A and 7B show waveforms of a scalable operation by a grid-connected power converter system 100 using MPC control and having, for each phase-leg, two parallel converter modules 205. FIG. 7A shows a plot 700 with output (grid) current and converter module-side current waveforms. FIG. 7B further shows a plot 710 with output (grid) current, converter module-side current, and grid voltage waveforms.

[0075] FIGS. 7C and 7D show waveforms of a scalable operation by a grid-connected power converter system 100 using MPC control and having, for each phase-leg, three parallel converter modules 205. FIG. 7C shows a plot 720 with output (grid) current and convertermodule-side current waveforms. FIG. 7B further shows a plot 730 with output (grid) current, converter module-side current, and grid voltage waveforms.

[0076] FIG. 8 shows waveforms 800 of an example of a scalable power converter system 100, as described herein, including: grid side output current, module side output current, DC (link) bus voltage, and output capacitor voltage with two scalable modules.

[0077] FIG. 9 shows waveforms 900 that demonstrate transient performance of the scalable power converter system 100, showing the transient of DC (link) bus voltage and output capacitor voltage with a 40V DC (link) bus voltage reference step. As illustrated, the reference can be tracked quickly (short response time) and steadily with less (small) oscillation.

[0078] As noted above, the scalable power converter system 100 (and power converter 115), may function as a DC-AC inverter, as an AC-DC rectifier, and / or as a DC-DC converter. In some examples, the scalable power converter system 100 operates only as an inverter, only as a rectifier, or only as a DC-DC converter. In other examples, the scalable power converter system 100 operates as two or more of an inverter, a rectifier, or a DC-DC converter. In some examples, at various moments in time, the power converter system may operate in an inverter mode to converter DC to AC, in a rectifier mode to converter AC to DC, or in a DC converter mode to convert DC at one voltage level to another voltage level. Accordingly, in some examples, (e.g., when used in an electric vehicle), the scalable power converter system 100 may be used in one or more of the following modes: in an inverter mode to drive a motor with an AC signal generated from a received DC signal from a battery; in a rectifier mode to implement regenerative breaking and converter AC power from the (braking) motor to charge a battery; in a rectifier mode to charge converter AC power from an external source (e.g., grid) to charge a battery; in an inverter mode to inverter DC power from a battery to an AC signal for output to other AC loads (e.g., on a local microgrid or utility grid). The scalable power converter functionality described with respect to FIG. 5 applies to the scalable power converter system 100 (and the power converter 115) in each of these modes of operation, including as an inverter, rectifier, and / or DC-DC converter.

[0079] The present specification describes one or more electronic controllers (e.g., the central controller 150, the local controller(s) 160). An electronic controller includes one or more processors configured to facilitate power conversion (e.g., by controlling the switching devices of, for example, a scalable power converter system as described herein) and one or more memories or storage devices. The storage device(s) may thus include a computer program productthat when executed on the electronic controller (which, as noted, may be a processor-based device) causes the processor-based device to perform operations to facilitate the implementation of procedures and operations described herein. The electronic controller may further include peripheral devices to enable input / output functionality. Such peripheral devices may include, for example, flash drive (e.g., a removable flash drive), or a network connection (e.g., implemented using a USB port and / or a wireless transceiver), for downloading related content to the connected system. Such peripheral devices may also be used for downloading software containing computer instructions to enable general operation of the respective system / device. Alternatively and / or additionally, in some embodiments, special purpose logic circuitry, e.g., an FPGA (field programmable gate array), an ASIC (application specific integrated circuit), a complex programmable logic device (CPLD), a DSP processor, a graphics processing unit (GPU), application processing unit (APU), etc., may be used in the implementations of the electronic controller or electronic processor. Other modules that may be included with the electronic controller may include a user interface to provide or receive input and output data. The electronic controller may include an operating system.

[0080] Computer programs (also known as programs, software, software applications or code) include machine instructions for a programmable processor, and may be implemented in a high-level procedural and / or object-oriented programming language, and / or in assembly / machine language. As used herein, the term “machine-readable medium” refers to any non-transitory computer program product, apparatus and / or device (e.g., magnetic discs, optical disks, memory, Programmable Logic Devices (PLDs)) used to provide machine instructions and / or data to a programmable processor, including a non-transitory machine-readable medium that receives machine instructions as a machine-readable signal.

[0081] In some embodiments, any suitable computer readable media can be used for storing instructions for performing the processes / operations / procedures described herein. For example, in some embodiments computer readable media can be transitory or non-transitory. For example, non-transitory computer readable media can include media such as magnetic media (such as hard disks, floppy disks, etc.), optical media (such as compact discs, digital video discs, Blu-ray discs, etc.), semiconductor media (such as flash memory, electrically programmable read only memory (EPROM), electrically erasable programmable read only Memory (EEPROM), etc ), any suitable media that is not fleeting or not devoid of any semblance of permanence duringtransmission, and / or any suitable tangible media. As another example, transitory computer readable media can include signals on networks, in wires, conductors, optical fibers, circuits, any suitable media that is fleeting and devoid of any semblance of permanence during transmission, and / or any suitable intangible media.

[0082] Although particular embodiments have been disclosed herein in detail, this has been done by way of example for purposes of illustration only, and is not intended to be limiting with respect to the scope of the appended claims, which follow. Features of the disclosed embodiments can be combined, rearranged, etc., within the scope of the invention to produce more embodiments. Some other aspects, advantages, and modifications are considered to be within the scope of the claims provided below. The claims presented are representative of at least some of the embodiments and features disclosed herein. Other unclaimed embodiments and features are also contemplated.FURTHER EXAMPLES

[0083] Example 1: A method, apparatus, and / or non-transitory computer-readable medium storing processor-executable instructions for a scalable power converter system comprising: one or more power converter phase-legs including a plurality of power converter modules connected in parallel, each power converter module including power switching elements; and a control system including: a central controller configured to generate one or more reference targets based on sensed characteristics of the one or more power converter phase-legs, each reference target corresponding to a power converter phase-leg of the one or more power converter phase-legs; and one or more local model predictive controllers, each local model predictive controller corresponding to a reference target of the one or more reference targets and a power converter phase-leg of the one or more power converter phase-legs and configured to control, based on the reference target corresponding to the local model predictive controller and on model predictive control, the plurality of power converter modules of the power converter phase-leg that correspond to the local model predictive controller.

[0084] Example 2: The method, apparatus, and / or non-transitory computer readable medium of Example 1, wherein to control, based on the reference target and model predictive control, the plurality of power converter modules of the power converter phase-leg that corresponds to the local model predictive controller, each local model predictive controller is configured to execute an MPC algorithm explicitly with a pre-configured piecewise affinefunction to generate a duty cycle for a pulse width modulated (PWM) signal to control the plurality of power converter modules of the power converter phase-leg that corresponds to the local model predictive controller.

[0085] Example 3: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 1 to 2, wherein to control, based on the reference target corresponding to the local model predictive controller and model predictive control, the plurality of power converter modules of the power converter phase-leg that corresponds to the local model predictive controller, each local model predictive controller is configured to: generate control signals that include a PWM signal and an inverted PWM signal for the power converter modules of the power converter phase-leg that corresponds to the local model predictive controller, the PWM signal and the inverted PWM signal having a variable frequency and a duty cycle.

[0086] Example 4: The method, apparatus, and / or non-transitory computer readable medium of Example 3, wherein each model predictive controller controls the variable frequency to provide soft switching and determines the duty cycle using the model predictive control.

[0087] Example 5: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 1 to 4, wherein the central controller is configured to: generate global reference targets in a rotational reference frame; translate the global reference targets to local reference targets in a stationary reference frame; and generate the reference targets for the local model predictive controllers based on the local reference targets.

[0088] Example 6: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 1 to 5, wherein the central controller is configured to generate the reference targets for the local model predictive controllers based on the local reference targets and a zero-sequence control target that is based on half a DC link voltage of the plurality of converter modules and an injected harmonic signal.

[0089] Example 7: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 1 to 6, wherein the one or more power converter phase-legs include a single phase-leg, and the scalable power converter system is configured as a half bridge, singlephase converter.

[0090] Example 8: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 1 to 6, wherein the one or more power converter phase-legs includetwo phase-legs, and the scalable power converter system is configured as a full bridge, singlephase converter.

[0091] Example 9: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 1 to 6, wherein the one or more power converter phase-legs include three phase-legs, and the scalable power converter system is configured as a three-phase converter.

[0092] Example 10: The method, apparatus, and / or non-transitory computer readable medium of any of Examples 1 to 9, wherein each power converter module includes an LC filter and is configured to connect to a grid node via the LC filter.

[0093] Example 11 : The method, apparatus, and / or non-transitory computer readable medium of any of Examples 1 to 10, further comprising: outputting, by each power converter module in response to the controlling by each local model predictive controller, power via an LC filter that is configured to connect to a grid node.

Claims

WHAT IS CLAIMED IS:

1. A scalable power converter system comprising: one or more power converter phase-legs each including a plurality of power converter modules connected in parallel, each power converter module including power switching elements; and a control system including: a central controller configured to generate one or more reference targets based on sensed characteristics of the one or more power converter phase-legs, each reference target corresponding to a power converter phase-leg of the one or more power converter phase-legs; and one or more local model predictive controllers, each local model predictive controller corresponding to a reference target of the one or more reference targets and a power converter phase-leg of the one or more power converter phase-legs and configured to control, based on the reference target corresponding to the local model predictive controller and on model predictive control, the plurality of power converter modules of the power converter phase-leg that correspond to the local model predictive controller.

2. The scalable power converter system of claim 1, wherein to control, based on the reference target and model predictive control, the plurality of power converter modules of the power converter phase-leg that corresponds to the local model predictive controller, each local model predictive controller is configured to execute an MPC algorithm explicitly with a preconfigured piecewise affine function to generate a duty cycle for a pulse width modulated (PWM) signal to control the plurality of power converter modules of the power converter phaseleg that corresponds to the local model predictive controller.

3. The scalable power converter system of claim 1, wherein to control, based on the reference target corresponding to the local model predictive controller and model predictive control, the plurality of power converter modules of the power converter phase-leg that corresponds to the local model predictive controller, each local model predictive controller is configured to:generate control signals that include a PWM signal and an inverted PWM signal for the power converter modules of the power converter phase-leg that corresponds to the local model predictive controller, the PWM signal and the inverted PWM signal having a variable frequency and a duty cycle.

4. The scalable power converter system of claim 3, wherein each model predictive controller controls the variable frequency to provide soft switching and determines the duty cycle using the model predictive control.

5. The scalable power converter system of claim 1, wherein the central controller is configured to: generate global reference targets in a rotational reference frame; translate the global reference targets to local reference targets in a stationary reference frame; and generate the reference targets for the local model predictive controllers based on the local reference targets.

6. The scalable power converter system of claim 5, wherein the central controller is configured to generate the reference targets for the local model predictive controllers based on the local reference targets and a zero-sequence control target that is based on half a DC link voltage of the plurality of converter modules and an injected harmonic signal.

7. The scalable power converter system of claim 1, wherein the one or more power converter phase-legs include a single phase-leg, and the scalable power converter system is configured as a half bridge, single-phase converter.

8. The scalable power converter system of claim 1, wherein the one or more power converter phase-legs include two phase-legs, and the scalable power converter system is configured as a full bridge, single-phase converter.

9. The scalable power converter system of claim 1 , wherein the one or more power converter phase-legs include three phase-legs, and the scalable power converter system is configured as a three-phase converter.

10. The scalable power converter system of claim 1, wherein each power converter module includes an LC filter and is configured to connect to a grid node via the LC filter.

11. A method of power conversion with a scalable power converter, the method comprising: generating, by a central controller of a control system, one or more reference targets based on sensed characteristics of one or more power converter phase-legs, each reference target corresponding to a power converter phase-leg of the one or more power converter phaselegs, each power converter phase-leg including a plurality of power converter modules connected in parallel, each power converter module including power switching elements, wherein the control system includes one or more local model predictive controllers, each local model predictive controller corresponding to a reference target of the one or more reference targets and a power converter phase-leg of the one or more power converter phase-legs; and controlling, by each local model predictive controller, the plurality of power converter modules of the power converter phase-leg that corresponds to the local model predictive controller, the controlling being based on the reference target corresponding to the local model predictive controller and model predictive control.

12. The method of claim 11, wherein the controlling by each local model predictive controller includes: executing, by each local model predictive controller, an MPC algorithm explicitly with a pre-configured piecewise affine function to generate a duty cycle for a pulse width modulated (PWM) signal to control the plurality of power converter modules of the power converter phaseleg that corresponds to the local model predictive controller.

13. The method of claim 1 1 , wherein the controlling by each local model predictive controller includes: generating, by each local model predictive controller, control signals that include a PWM signal and an inverted PWM signal for the power converter modules of the power converter phase-leg that corresponds to the local model predictive controller, the PWM signal and the inverted PWM signal having a variable frequency and a duty cycle.

14. The method of claim 13, further comprising: controlling, by each model predictive controller, the variable frequency of the PWM signal and the inverter PWM signal generated by the model predictive controller to provide soft switching, and determining, by each model predictive controller, the duty cycle of the PWM signal and the inverter PWM signal generated by the model predictive controller using the model predictive control.

15. The method of claim 11, further comprising: generating, by the central controller, global reference targets in a rotational reference frame; translating, by the central controller, the global reference targets to local reference targets in a stationary reference frame; and generating, by the central controller, the reference targets for the local model predictive controllers based on the local reference targets.

16. The method of claim 15, further comprising: generating, by the central controller, the reference targets for the local model predictive controllers based on the local reference targets and a zero-sequence control target that is based on half a DC link voltage of the plurality of converter modules and an injected harmonic signal.

17. The method of claim 11, wherein the one or more power converter phase-legs are of the scalable power converter and include a single phase-leg, and the scalable power converter is configured as a half bridge, single-phase converter.

18. The method of claim 11, wherein the one or more power converter phase-legs are of the scalable power converter and include two phase-legs, and the scalable power converter is configured as a full bridge, single-phase converter.

19. The method of claim 11, wherein the one or more power converter phase-legs are of the scalable power converter and include three phase-legs, and the scalable power converter is configured as a three-phase converter.

20. The method of claim 11, further comprising: outputting, by each power converter module in response to the controlling by each local model predictive controller, power via an LC filter that is configured to connect to a grid node.

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