Control method of a power converter having an inverter block with a silicon carbide MOSFET

Abstract

Systems and methods for operating a power converter are provided, the power converter having a plurality of inverter blocks, the plurality of inverter blocks having silicon carbide MOSFETs. The converter may include a plurality of inverter blocks. Each inverter block may include a plurality of switching devices. The plurality of switching devices may include one or more silicon carbide MOSFETs. The control method may include: providing, by a control system, one or more gate commands to a first inverter block of the plurality of inverter blocks. The control method may further include: implementing, by the control system, a gate command delay to generate a first delayed gate command based at least in part on the one or more gate commands. The control method may further include: providing, by the control system, the first delayed gate command to a second inverter block of the plurality of inverter blocks.

Description

Technical Field

[0001] The present subject matter generally relates to power systems, and more particularly to systems and methods for providing gating commands to a power converter that utilizes inverter blocks with silicon carbide MOSFETs. Background Art

[0002] Power generation systems can use power converters to convert power into a form suitable for an energy grid. In a typical power converter, multiple switching devices, such as insulated gate bipolar transistors (IGBTs) or metal oxide semiconductor field effect transistors (MOSFETs), can be used in an electronic circuit such as a half-bridge or full-bridge circuit to convert power. Recent developments in switching device technology have allowed for the use of silicon carbide (“SiC”) MOSFETs in power converters. Compared to conventional IGBTs, using SiC MOSFETs allows for operating the power converter at a much higher switching frequency. Summary of the Invention

[0003] Aspects and advantages of embodiments of the present disclosure will be set forth in part in the description below, or may be learned from the description, or may be learned by practice of the embodiments.

[0004] One example aspect of the present disclosure is directed to a control method for operating a converter. The converter can include a plurality of inverter blocks. Each inverter block can include a plurality of switching devices. The plurality of switching devices can include one or more silicon carbide MOSFETs. The control method can include: providing, by a control system, one or more gating commands to a first inverter block of the plurality of inverter blocks. The control method can further include: implementing, by the control system, a gating command delay to generate a first delayed gating command based at least in part on the one or more gating commands. The control method can further include: providing, by the control system, the first delayed gating command to a second inverter block of the plurality of inverter blocks.

[0005] Another example aspect of the present disclosure is directed to a power conversion system. The power conversion system may include a converter. The converter may include a plurality of inverter blocks. Each inverter block may include a plurality of switching devices. The plurality of switching devices may include one or more silicon carbide MOSFETs. The power conversion system may further include a control system that includes a plurality of gate driver cards. The control system may be configured to control the operation of the converter by providing one or more gating commands to the plurality of inverter blocks. Each inverter block may have one or more associated gate driver cards among the plurality of gate driver cards, and the plurality of gate driver cards are configured to provide one or more gating commands to the plurality of switching devices in the inverter block. At least one of the one or more associated gate driver cards of each inverter block may be daisy-chained to at least one of the one or more associated gate driver cards of another inverter block.

[0006] Another example aspect of the present disclosure is directed to a wind power generation system. The wind power generation system may include: a wind turbine configured to generate AC power; and an AC-to-DC converter coupled to the wind turbine. The AC-to-DC converter may be configured to convert the AC power from the wind turbine into DC power. The wind power generation system may further include a DC link coupled to the AC-to-DC converter. The DC link may be configured to receive DC power from the AC-to-DC converter. The wind power generation system may further include a DC-to-AC converter coupled to the DC link. The DC-to-AC converter may be configured to receive DC power from the DC link. The DC-to-AC converter may include a plurality of inverter blocks. Each inverter block may include a plurality of switching devices. The plurality of switching devices may include one or more silicon carbide MOSFETs. The wind power generation system may further include a control system that includes a plurality of gate driver cards. The control system may be configured to control the operation of the DC-to-AC converter by providing one or more gating commands to the plurality of inverter blocks. Each inverter block may have one or more associated gate driver cards among the plurality of gate driver cards, and the plurality of gate driver cards are configured to provide one or more gating commands to the plurality of switching devices in the inverter block. At least one of the one or more associated gate driver cards of each inverter block may be daisy-chained to at least one of the one or more associated gate driver cards of another inverter block. The control system may further be configured to implement a gating command delay in the gating commands provided by the gate driver cards.

[0007] Variations and modifications may be made to these example aspects of the present disclosure.

[0008] These and other features, aspects, and advantages of the various embodiments will be better understood with reference to the following description and the appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure and, together with the description, serve to explain the relevant principles. Description of the Drawings

[0009] A detailed discussion of embodiments for those of ordinary skill in the art is set forth in the specification, which refers to the accompanying drawings, wherein:

[0010] Figure 1 An example wind power generation system is depicted;

[0011] Figure 2 Example elements for use in a power converter according to example aspects of the present disclosure are depicted;

[0012] Figure 3 A power converter according to example aspects of the present disclosure is depicted;

[0013] Figure 4 A portion of a power converter according to example aspects of the present disclosure is depicted;

[0014] Figure 5 A control system for a power converter according to example aspects of the present disclosure is depicted;

[0015] Figure 6 A graph of electromagnetic interference in a conventional power converter is depicted;

[0016] Figure 7 A graph of electromagnetic interference in a power converter according to example aspects of the present disclosure is depicted;

[0017] Figure 8 An example switching strategy according to example aspects of the present disclosure is depicted;

[0018] Figure 9 An example method according to example aspects of the present disclosure is depicted; and

[0019] Figure 10 Elements suitable for use in a control device according to example aspects of the present disclosure are depicted. DETAILED DESCRIPTION

[0020] Embodiments of the present invention will now be referred to in detail, one or more examples of which are shown in the accompanying drawings. Each embodiment is provided by way of explanation of the present invention, not limitation of the present invention. Indeed, those skilled in the art will appreciate that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For example, features shown or described as part of one embodiment can be used with another embodiment to yield yet another embodiment. Accordingly, it is intended that the present invention cover such modifications and variations that fall within the scope of the appended claims and their equivalents.

[0021] As used herein, the terms "first," "second," and "third" may be used interchangeably to distinguish one component from another and are not intended to denote the position or importance of individual components or to limit the number of individual components in the device. As used herein, the term "about" means within plus or minus ten percent of the stated value.

[0022] Example aspects of the present disclosure are directed to systems and methods for controlling a power converter having multiple inverter blocks utilizing SiC MOSFETs. For example, a power generation system such as a system using a doubly-fed induction generator ("DFIG") as a power generation unit may use one or more power converters to convert power from low-voltage polyphase AC power to medium-voltage polyphase AC power. As used herein, "LV" voltage may be power less than about 1.5 kilovolts. As used herein, "MV" voltage may be power greater than about 1.5 kilovolts and less than about 100 kilovolts. As used herein, the term "about" may mean within 20% of the stated value.

[0023] In an embodiment, the power converter may be a polyphase (e.g., three-phase) power converter configured to convert polyphase power output from a generator. The power converter may include, for example, a first power converter configured to convert AC power output from a generator such as a DFIG to DC power and provide the DC power to a DC link. A second power converter may be configured to convert the DC power from the DC link to AC power suitable for use on a power grid. For example, the second power converter may be a DC-to-DC-to-AC power converter and may utilize SiC MOSFETs as power semiconductors, allowing for a very high switching frequency.

[0024] The second power converter may include, for example, multiple inverter blocks. Each inverter block may include multiple bridge circuits configured to convert power, and each bridge circuit may include one or more SiC MOSFETs as switching devices. For example, each inverter block may be a DC-to-DC-to-AC inverter block, and the multiple inverter blocks may be coupled in parallel on the LV side and in series on the MV side. Each DC-to-DC-to-AC inverter block may include: a first DC-to-AC conversion entity configured to convert LV DC power from the DC link to a high-frequency LV AC voltage, an isolation transformer configured to provide isolation, a second AC-to-DC conversion entity configured to convert the LV AC power to LV DC power, and a third DC-to-AC conversion entity configured to convert the LV DC power to LV AC power suitable for use on an energy grid. The multiple inverter blocks may be connected in series to build an MV AC voltage suitable for use on an MV AC power grid.

[0025] In an example topology, a three-level topology from line to neutral can be employed to configure multiple inverter blocks, allowing for output voltages of positive, zero, or negative voltage for each phase. For example, a power converter may include six inverter blocks, where each inverter block includes a plurality of switching devices, such as one or more SiC MOSFETs. A control device can provide one or more gating commands to each inverter block to turn the switching devices on and off to generate an output voltage waveform. For example, the control device can provide one or more gating commands to a plurality of gate driver cards, and then the plurality of gate driver cards can turn the individual switching devices in the inverter block on and off.

[0026] In such a system, each gate driver card can be configured to drive only a subset of the switching devices in the inverter block, such as, for example, four switching devices in a switching entity forming a bridge circuit. Thus, for a power converter utilizing a DC-to-DC-to-AC inverter block with three switching entities, each inverter block may require at least three gate driver cards. Additionally, in a three-phase power converter having six inverter blocks per phase, at least 54 gate driver cards may be required to drive all of the switching devices in the power converter. However, a typical control device configured to provide gating commands to the gate driver cards may only have sufficient communication channels to provide gating commands to one or two gate driver cards. Thus, in a typical configuration where control signals are provided directly from the control device to each gate driver card, a large number of control devices may be required. In such a control system, the complexity of the control system and the cost associated with the control devices can be quite significant.

[0027] Furthermore, if all of the switching devices in the power converter are turned on simultaneously, the electromagnetic interference ("EMI") generated in the voltage at frequencies above certain levels can be very high. Generally, as the EMI generated by the switching devices increases, larger and more expensive filters may be required in order to condition the power into a form suitable for use on the power grid. Thus, due to the cost associated with the filters, high EMI can increase the cost of the power conversion system.

[0028] Example aspects of the present disclosure are directed to systems and methods for providing gating commands to inverter blocks in a power converter to reduce the cost and complexity of a control system and reduce EMI generated by the power converter. For example, a power converter may include a plurality of inverter blocks. Each inverter block may include a plurality of switching devices, such as one or more SiC MOSFETs. A control system may be configured to provide one or more gating commands to a first inverter block of the plurality of inverter blocks. For example, a control device may be configured to provide one or more gating commands to one or more gate driver cards, which may be configured to drive one or more of the switching devices in the inverter block to convert power. Additionally, the control system may be configured to implement a gating command delay to generate a first delayed gating command based at least in part on the one or more gating commands. For example, a first gate driver card associated with the first inverter block may be configured to receive the one or more gating commands and then implement a gating command delay, such as a delay of 1-2 microseconds, to generate a first delayed gating command. The control system may then be configured to provide the first delayed gating command to a second inverter block of the plurality of inverter blocks. For example, the first gate driver card may be configured to send the first delayed gate command to a second gate driver card associated with the second inverter block, which is configured to drive one or more of the switching devices in the second inverter block. In an embodiment, a daisy chain configuration may be employed to arrange the plurality of gate driver cards, such as the first gate driver card and the second gate driver card.

[0029] Additionally, the control system may implement additional gating command delays to generate additional delayed gating commands and provide these additional delayed gating commands to other inverter blocks of the plurality of inverter blocks. For example, a gate driver card associated with the second inverter block may be configured to implement a second gating command delay to generate a second delayed gating command based at least in part on the first delayed gating command and may also provide the second delayed gating command to a third inverter block of the plurality of inverter blocks. Similarly, a gate driver card associated with each inverter block may be configured to implement a gating command delay to generate a delayed gating command and may provide the delayed gating command to another inverter block, such as by providing the delayed gating command to a downstream gate driver card in the daisy chain. In this way, gating command delays may be implemented in the one or more gating commands provided to each inverter block in the power converter.

[0030] In an embodiment, the strobe command delay can be at least partially based on the number of blocks in the converter. For example, one or more strobe commands can include on / off pulses that are configured to turn on the converter for a period of time before turning off the converter. For example, one or more strobe commands can be commands to turn on the power converter for a period of 20 microseconds. One or more strobe commands can be provided to the first inverter block, and the control system can implement a strobe command delay (such as a 1-microsecond delay) to generate a delayed strobe command and provide the delayed strobe command to the second inverter block. Similarly, the control system can be configured to implement a strobe command delay for each successive inverter block. For example, in a power converter having six inverter blocks, the control system can implement a strobe command delay before providing delayed strobe commands to the second through sixth inverter blocks. Thus, if, for example, a 1-microsecond delay is implemented for each of the second through sixth inverter blocks, the total delay, which includes the strobe command delays for each of the second through sixth inverter blocks added together, will be 5 microseconds. In an embodiment, the total delay (such as 5 microseconds) can be shorter than the on period of the on / off pulse (such as 20 microseconds).

[0031] In an embodiment, one or more strobe commands can be one or more strobe commands that are configured to generate a fixed pulse output. Additionally, in an embodiment, the strobe command delay can be a delay that generates a phase shift in the fixed pulse output of each inverter block. Further, the phase shift can be at least partially based on the number of inverter blocks in the converter. For example, the converter can include six inverter blocks. One or more strobe commands can be one or more strobe commands for generating a fixed pulse output (such as a full voltage output) for a specified period of time. For example, the fixed pulse output can be a duty cycle of two-thirds such that the inverter block provides full voltage for two-thirds of a half cycle and zero voltage for one-third of a half cycle. One or more strobe commands that are configured to generate a fixed pulse output can be provided to each inverter block in the converter. A strobe command delay can be implemented to generate a phase shift in the fixed pulse output of each inverter block. Additionally, the fixed pulse output of each inverter block can be phase shifted relative to the fixed pulse outputs of all other inverter blocks. For example, the fixed pulse output of each inverter block can be phase shifted to generate a sinusoidal voltage waveform. Further, the average power processed by each inverter block can be normalized, which can simplify the cooling system of the power converter because all inverter blocks can process approximately equal power.

[0032] Thus, the systems and methods according to example aspects of the present disclosure can have the following technical effects: By reducing the number of control devices required by the control system, the control system required to control a power converter having a plurality of inverter blocks can be simplified. This can reduce the cost associated with the control system. Additionally, by introducing a delay, the amount of EMI generated by the plurality of inverter blocks can be reduced, thereby reducing the size and cost of the filter for the power converter. Further, the systems and methods according to example aspects of the present disclosure can account for a desired output voltage waveform to be generated.

[0033] Reference will now be made to the drawings to discuss example aspects of the present disclosure in more detail. Figure 1 Depicted is a wind power system 100 according to example aspects of the present disclosure, which includes a DFIG 120. For purposes of illustration and discussion, the present disclosure will be discussed with reference to Figure 1 the example wind power system 100. Those of ordinary skill in the art using the present disclosure provided herein should understand that aspects of the present disclosure can also be applied to other systems, such as full power conversion wind turbine systems, solar systems, energy storage systems, and other power systems.

[0034] In the example wind power system 100, the rotor 106 includes a plurality of rotor blades 108 coupled to a rotating hub 110 and together define a propeller. The propeller is coupled to an optional gearbox 118, which in turn is coupled to a generator 120. According to aspects of the present disclosure, the generator 120 is a doubly-fed induction generator (DFIG) 120.

[0035] The DFIG 120 is generally coupled to a stator bus 154 and a power converter 162 via a rotor bus 156. The stator bus provides output polyphase power (e.g., three-phase power) from the stator of the DFIG 120, and the rotor bus 156 provides output polyphase power (e.g., three-phase power) of the DFIG 120. The power converter 162 can be a bidirectional power converter configured to provide output power to the power grid 184 and / or receive power from the power grid 184. As shown, the DFIG 120 is coupled to a rotor-side converter 166 via the rotor bus 156. The rotor-side converter 166 is coupled to a line-side converter 168, which in turn is coupled to a line-side bus 188. An auxiliary power feed (not depicted) can be coupled to the line-side bus 188 to provide power to components (e.g., fans, pumps, motors, and other components) used in the wind power system 100.

[0036] In an example configuration, the rotor side converter 166 and / or the line side converter 168 are configured for normal operation modes in a three-phase pulse width modulation (PWM) arrangement using SiC MOSFETs and / or IGBTs as switching devices. Compared to conventional IGBTs, SiC MOSFETs can switch at very high frequencies. For example, SiC MOSFETs can switch at frequencies from approximately 0.01 Hz to 10 MHz, where typical switching frequencies are 1 kHz to 400 kHz, while IGBTs can switch at frequencies from approximately 0.01 Hz to 200 kHz, where typical switching frequencies are 1 kHz to 20 kHz. Additionally, when operating within some voltage ranges, SiC MOSFETs can offer advantages over ordinary MOSFETs. For example, in a power converter operating at 1200 V - 1700 V on the LV side, the SiC MOSFET has lower switching losses than an ordinary MOSFET.

[0037] In some implementations, the rotor side converter 166 and / or the line side converter 168 may include a plurality of conversion modules, each associated with a phase of the polyphase power output of the generator, as will be discussed in more detail with respect to Figure 2 and Figure 3 to be discussed in more detail. The rotor side converter 166 and the line side converter 168 may be coupled via a DC link 126, across which may be a DC link capacitor 138.

[0038] The power converter 162 may be coupled to a control device 174 to control the operation of the rotor side converter 166 and the line side converter 168. It should be noted that in a typical embodiment, the control device 174 is configured as an interface between the power converter 162 and the control system 176.

[0039] In operation, power generated by the rotating rotor 106 at the DFIG 120 is provided to the power grid 184 via a dual path. The dual path is defined by the stator bus 154 and the rotor bus 156. On the stator bus 154 side, a sinusoidal polyphase (e.g., three-phase) is provided to the power delivery point (e.g., the power grid 184). In particular, the AC power provided via the stator bus 154 can be medium voltage (“MV”) AC power. On the rotor bus side 156, a sinusoidal polyphase (e.g., three-phase) AC power is provided to the power converter 162. In particular, the AC power provided to the power converter 162 via the rotor bus 156 can be low voltage (“LV”) AC power. The rotor-side power converter 166 converts the LV AC power provided from the rotor bus 156 into DC power and provides the DC power to the DC link 126. The switching devices (e.g., SiCMOSFET and / or IGBT) used in the parallel bridge circuit of the rotor-side power converter 166 can be modulated to convert the AC power provided from the rotor bus 156 into DC power suitable for the DC link 126. Such DC power can be LV DC power.

[0040] In the wind power system 100, the power converter 162 can be configured to convert LV AC power into MV AC power. For example, the line-side converter 168 can convert the LV DC power on the DC link 126 into MV AC power suitable for the power grid 184. In particular, the SiC MOSFETs used in the bridge circuit of the line-side power converter 168 can be modulated to convert the DC power on the DC link 126 into AC power on the line-side bus 188. In addition, one or more isolation transformers coupled to one or more of the bridge circuits can be configured to step up or step down the voltage from the DC link as needed. Additionally, multiple inverter blocks can be connected in series on the MV side to jointly step up the voltage of the power on the DC link 126 to MV AC power. The MV AC power from the power converter 162 can be combined with the MV power from the stator of the DFIG 120 to provide polyphase power (e.g., three-phase power) having a frequency that is substantially maintained at the frequency of the power grid 184 (e.g., 50 Hz / 60 Hz). In this way, the MV line-side bus 188 can be coupled to the MV stator bus 154 to provide such polyphase power.

[0041] The wind power generation system 100 may include various circuit breakers and switches, such as circuit breaker 182, stator synchronous switch 158, etc., for isolating various components necessary for the normal operation of the DFIG 120 during connection to and disconnection from the power grid 184. In this way, for example, when the current is too large and may damage the components of the wind power generation system 100 or for other operational considerations, such components can be configured to connect or disconnect the corresponding bus. Additional protection components may also be included in the wind power generation system 100. For example, as Figure 1 depicted, a multiphase crowbar circuit 190 may be included to prevent overvoltage conditions from damaging the circuits of the wind power generation system 100.

[0042] The power converter 162 may receive control signals from, for example, the control system 176 via the control device 174. The control signals may be based on, among other things, the sensed conditions or operating characteristics of the wind power generation system 100. Generally, the control signals provide control over the operation of the power converter 162. For example, feedback in the form of the sensed speed of the DFIG 120 can be used to control the conversion of the output power from the rotor bus 156 to maintain an appropriate and balanced multiphase (e.g., three-phase) power supply. Other feedback from other sensors can also be used by the control device 174 to control the power converter 162, including, for example, stator and rotor bus voltage and current feedback. Using various forms of feedback information, switch control signals (e.g., gating timing commands for switching devices), stator synchronous control signals, and circuit breaker signals can be generated.

[0043] Now referring to Figure 2 , the topology of the components in the DC - to - DC - to - AC converter is depicted. Figure 2 An example DC - to - DC - to - AC inverter block 206 is depicted, which may be included in the conversion module 200 of the line - side converter 168, as Figure 3as depicted. Each inverter block 206 may include a plurality of conversion entities. For example, inverter block 206 may include a first conversion entity 212, a second conversion entity 214, and a third conversion entity 216. Each conversion entity 212 - 216 may include a plurality of bridge circuits coupled in parallel. For example, conversion entity 216 includes bridge circuit 218 and bridge circuit 220. As shown, each bridge circuit may include a plurality of switching devices coupled in series. For example, bridge circuit 220 includes an upper switching device 222 and a lower switching device 224. The switching devices may be SiC MOSFETs, which may operate at a higher switching frequency than conventional IGBTs. As shown, inverter block 206 also includes an isolation converter 226. Isolation converter 226 may be coupled to conversion entity 212 and conversion entity 214. As shown, inverter block 206 may also include capacitors 228 and 230. For example, capacitor 230 may be connected across the DC link between the second conversion entity 214 and the third conversion entity 216.

[0044] The first conversion entity 212, the isolation converter 226, and the second conversion entity 214 may together define an internal converter 240. The internal converter 240 may be operated to convert LV DC power from the DC link 126 into MV DC power. In an embodiment, the internal converter 240 may be a high - frequency resonant converter. In a resonant converter configuration, a resonant capacitor 232 may be included in the internal converter 240. In various embodiments, the resonant capacitor 232 may be included on the DC - link side of the isolation converter 226 as Figure 2 depicted, on the grid side of the isolation transformer 226 (not depicted), or on both the DC - link and grid sides of the isolation transformer 226 (not depicted). In another embodiment, by removing the resonant capacitor 232, the internal converter 240 may be a hard - switching converter. The third conversion entity 216 may also be referred to as an external converter 216. The external converter 216 may convert the LV DC power from the internal converter into LV AC power suitable for use on the energy grid 184. In a typical application, the external converter 216 may be a hard - switching converter and thus does not include a resonant capacitor.

[0045] Figure 3Depicts an example line - side converter 168 in accordance with an example embodiment of the present disclosure. As shown, the line - side converter 168 includes conversion module 200, conversion module 202, and conversion module 204. The conversion modules 200 - 204 may be configured to receive LV DC power from the rotor - side converter 166 and convert the LV DC power into MV AC power for feeding to the power grid 184. Each of the conversion modules 200 - 204 is associated with a single phase of the three - phase output AC power. In particular, conversion module 200 is associated with the A - phase output of the three - phase output power, conversion module 202 is associated with the B - phase output of the three - phase output power, and conversion module 204 is associated with the C - phase output of the three - phase output power.

[0046] Each of the conversion modules 200 - 204 includes a plurality of inverter blocks 206 - 210. For example, as shown, conversion module 200 includes inverter block 206, inverter block 208, and inverter block 210. In an embodiment, each of the conversion modules 200 - 204 may include any number of inverter blocks 206 - 210. The line - side converter 168 may be a bidirectional power converter. The line - side converter 168 may be configured to convert LV DC power into MV AC power and vice versa. For example, when supplying power to the power grid 184, the line - side converter 168 may be configured to receive LV DC power from the DC link 126 on the LV side of the line - side converter 168 and output MV AC power on the MV side of the line - side converter 168. The inverter blocks 206 - 210 may be coupled together in parallel on the LV side and may be coupled together in series on the MV side.

[0047] In one particular example implementation, when supplying power to the power grid 184, the conversion entity 212 may be configured to convert the LV DC on the DC link 126 into LV AC power. The isolation transformer 226 may be configured to provide isolation. The conversion entity 214 may be configured to convert the LV AC power into LV DC power. The conversion entity 216 may be configured to convert the LV DC power into LV AC power suitable for supplying to the power grid 184. Multiple inverter blocks may be connected in series to build an MV AC voltage suitable for use on an MV AC power network.

[0048] The inverter blocks 206-210 can be configured to contribute to the total MV AC power provided by the conversion module 200. In this way, any suitable number of inverter blocks can be included within the conversion modules 200-204. As indicated, each conversion module 200-204 is associated with a single phase of the output power. In this way, suitable gate timing commands (e.g., provided by one or more suitable drive circuits) can be used to control the switching devices of the conversion modules 200-204 to generate a suitable phase of the output power to be provided to the power grid. For example, the control device 174 can provide suitable gate timing commands to the gates of the switching devices of the bridge circuit. The gating timing commands can control the pulse width modulation of the SiC MOSFETs and / or IGBTs to provide the desired output.

[0049] It will be understood that although Figure 3 only the line-side converter 168 is depicted, Figure 2 the rotor-side converter 166 depicted in

[0050] may include the same or similar topologies. In particular, the rotor-side converter 166 can include a plurality of conversion modules having one or more conversion entities, as described with reference to the line-side converter 168. Additionally, it will be understood that the line-side converter 168 and the rotor-side converter 166 can include SiC MOSFETs, IGBT switching devices, and / or other suitable switching devices. In an implementation where the SiC MOSFETs are used to implement the rotor-side converter 166, the rotor-side converter 166 can be coupled to a bus bar circuit (e.g., the multi-phase bus bar circuit 190) to protect the SiC MOSFETs from high rotor currents during certain fault conditions. Figure 4 Now referring to Figures 1-3 , a portion of an example power converter is depicted. Elements that are the same or similar to those in

[0051] are denoted with the same reference numerals. As shown, the inverter block 206 is depicted together with the control device 174. The control device 174 can be configured to control the operation of the inverter block 206 by, for example, providing one or more gating commands to operate the switching devices of the inverter block 206.

[0052] In addition, as shown, the first gate card driver 402A can be connected to the second gate drive card 404A. Similar to the first gate drive card 402A, the second gate drive card 404A can be configured to control the operation of the switching devices in the second conversion entity 214. Similarly, the third gate drive card 406A can be connected to the second gate drive card 404A, and the third gate drive card 406A can be configured to control the operation of the switching devices in the first conversion entity 212. For example, the control device 174 can be connected to the first gate drive card 402A through one or more fiber optic cables, and one or more fiber optic cables can be connected between the first gate drive card 402A and the second gate drive card 404A and between the second gate drive card 404A and the third gate drive card 406A.

[0053] The first gate drive card 402A can be further daisy-chained to other inverter blocks. For example, the first gate drive card 402A associated with the first inverter block 206A can be connected to the first gate drive card 402B associated with the second inverter block 206B, as Figure 4 depicted. In addition, the first gate drive card 402A can be configured to implement a gate delay, such as a 1 to 2 microsecond delay, to generate a delayed gate command. The first gate drive card 402A can also be configured to provide the delayed gate command to a second gate card driver, such as the first gate drive card 402B associated with the second inverter block 206B.

[0054] Now referring to Figure 5 , an example control system 500 in accordance with example aspects of the present disclosure is depicted. Elements that are the same or similar to those in Figures 1-4 are denoted with the same reference numerals. As shown, the control device 174 can be configured to provide one or more gate commands to the first gate drive card 402A associated with the first inverter block 206A. As depicted, the first gate drive card 402A can be connected to the second gate drive card 404A, which can be connected to the third gate drive card 406A, both of which are also associated with the first inverter block 206A. In addition, as depicted, the first gate drive card 402A can be arranged in a daisy-chain configuration with the second gate drive card 402B, which is associated with the second inverter block 206B, and the second gate drive card 402B can similarly be arranged in a daisy-chain configuration with the third gate drive card 402C, which is associated with the third inverter block 206C. Any number of inverter blocks and associated gate drive cards 402 can be arranged in a daisy-chain configuration similarly. For example, as Figure 5As shown, six gate driver cards 402A - F are arranged in a daisy chain configuration, where each gate driver card 402 associated with an inverter block is daisy chained to at least one of one or more associated gate driver cards of another inverter block. Additionally, as Figure 5 depicted, each gate driver card 402 associated with an inverter block can be connected to gate driver cards 404 and 406.

[0055] As Figure 5 depicted, one or more strobe commands can be provided by control device 174 to the first gate driver card 402A. For example, as shown, a strobe command 502A can be provided by control device 174. The strobe command 502A can be, for example, an on / off pulse that is configured to turn on a converter for a period of time before turning off the converter. For example, as depicted, the strobe command 502A from time 0 to time I is an off command, it is an on command from time I to time III, and it is an off command from time III onwards.

[0056] The control system 500 can be configured to implement a delayed strobe command to generate a first delayed strobe command 502B based at least in part on one or more strobe commands. For example, the first gate driver card 402A can be configured to implement a strobe command delay, such as a 1 - 2 microsecond strobe command delay, to generate the first delayed strobe command 502B. Additionally, the first delayed strobe command 502B can be provided by the control system to a second inverter block. For example, the first gate driver card 402A associated with the first inverter block 206A can provide the first delayed strobe command 502B to the first gate driver card 402B associated with the second inverter block 206B. Similarly, the first gate driver card 402B associated with the second inverter block 206B can be configured to implement a second strobe command delay to generate a second delayed strobe command 502C based at least in part on the first delayed strobe command 502B. Additionally, the control system can provide the second delayed strobe command 502C to the third inverter block 206C, such as, for example, by providing the second delayed strobe command 502C from the first gate driver card 402B associated with the second inverter block 206B to the first gate driver card 402C associated with the third inverter block 206C. Similarly, a third delayed strobe command 502D can be generated and provided to the fourth inverter block 206D, a fourth delayed strobe command 502E can be provided to the fifth inverter block 206E, and a fifth delayed strobe command 502F can be provided to the sixth inverter block 206F. In this way, the control system 500 can implement a strobe command delay to generate delayed strobe commands based at least in part on one or more strobe commands. Additionally, in this way the control system 500 can employ a daisy chain configuration to provide one or more delayed strobe commands to downstream inverter blocks 206.

[0057] In an embodiment, the gate command delay can be at least partially based on the number of inverter blocks in the converter. For example, the total delay T can be defined as the gate command delays of each of the inverter blocks 206A-F added together, as Figure 2 depicted. The total delay T can be a delay shorter than the on-time of the on / off pulse in one or more of the gate commands 502A. For example, the on / off pulse can be one or more gate commands to turn on all of the inverter blocks 206 in the converter such that all of the inverter blocks 206 contribute to the total output voltage of the converter. To generate a desired voltage output, the total delay T can be shorter than the on-time of the on / off pulse such that all of the inverter blocks 206 contribute to the output voltage for at least a portion of the on-time, as Figure 5 depicted therein.

[0058] Now referring to Figure 6 and Figure 7 , a diagram of EMI generated by the converter is depicted. Figure 6 Depicted is an EMI spectrum for various frequencies in the converter where no delay is implemented in the gate commands provided to the inverter blocks 206 of the converter. Due to the rapid change in voltage over time (dv / dt), EMI can be generated by electromagnetic induction of components in the converter. For example, an inverter block utilizing a SiC MOSFET can be configured to turn on from 0 V to 1000 V in 25 nanoseconds; thus, the change in voltage over time (dv / dt) can be 40 kV / microsecond. Additionally, in a converter utilizing six inverter blocks, when all of the inverter blocks are turned on simultaneously, the change in voltage over time can be 240 kV / microsecond. However, by implementing a 1 microsecond delay between inverter blocks for a total delay of up to 5 microseconds, the dv / dt of a 6000 volt transition can be reduced to 1.2 kV / microsecond. By implementing the delay, the EMI generated by the inverter blocks 206 can be significantly reduced.

[0059] For example, Figure 7 depicted is an EMI spectrum for various frequencies in the converter where a 2 microsecond delay has been implemented in the gate commands provided to the inverter blocks 206 of the converter. As Figure 7 shown, the EMI generated by the inverter blocks across the same spectrum is significantly reduced compared to the EMI spectrum where no delay as depicted in Figure 6 has been implemented. By implementing the delay, the amount of EMI generated can be reduced, which can allow for the use of a smaller filter in the power converter to condition the power output into a form suitable for use on the power grid. Since larger filters are generally more expensive than smaller filters, this can reduce the cost of the power conversion system.

[0060] Now referring to Figure 8, depicts a switching strategy in accordance with an example aspect of the present disclosure. Figure 8 Depicts a plurality of gating commands, each configured to generate a fixed pulse output. For example, a first gating command 802A may be provided to a first inverter block 206A to switch an internal converter 240 and an external converter 216 simultaneously for a period of time. For example, as depicted, the first gating command 802A is a two-thirds duty cycle gating command such that full voltage is provided through the first inverter block 206A for two-thirds of a half cycle and zero voltage is provided for one-third of a half cycle.

[0061] Similarly, a second gating command 802B may be provided to a second inverter block 206B, a third gating command 802C may be provided to a third inverter block 206C, a fourth gating command 802B may be provided to a fourth inverter block 206D, a fifth gating command 802E may be provided to a fifth inverter block 206E, and a sixth gating command 802F may be provided to a sixth inverter block 206F.

[0062] However, as Figure 8 depicted, each of the gating commands 802B-F may be shifted by one or more phase shifts. For example, the second gating command 802B has been shifted by a phase shift "P", which may be achieved by implementing a gating command delay to generate the phase shift. For example, a control system may be configured to generate a delayed gating command, such as the second gating command 802B, by implementing a gating command delay to generate a phase shift P in a fixed pulse output generated by one or more gating commands, such as the first gating command 802A. Similarly, the control system may implement additional gating command delays to generate additional phase shifts in the fixed pulse outputs generated by the gating commands 802C-F.

[0063] In addition, the phase shift for the gating commands may be at least partially based on the number of inverter blocks in the converter. For example, a phase shift may be generated by delaying one or more gating commands to generate a fixed pulse output based on the number of inverter blocks in the converter. In an embodiment, a phase shift may be used to generate a sinusoidal output waveform by shifting the fixed pulse output of each inverter block by a phase shift P, which may be calculated by dividing 360 degrees by the number of modules. For example, in a converter having six inverter blocks, the phase shift P may correspond to a 60-degree phase shift, while in a converter having five inverter blocks, the phase shift P may correspond to a 72-degree phase shift. In addition, the fixed pulse duty cycle may be modulated to generate a specific peak voltage output.

[0064] Thus, the strobe command delay can be used to generate a phase shift and can be implemented in one or more strobe commands that are configured to generate a fixed pulse output to generate a desired voltage waveform, such as a sinusoidal waveform suitable for use on an alternating current power grid. Additionally, the average power processed by each inverter block through this configuration can be normalized across the inverter blocks, thereby equalizing the thermal stress on the inverter blocks. Further, since all inverter blocks will have approximately equal cooling requirements, this can simplify the cooling system for the converter.

[0065] Now referring to Figure 9 , an example control method (900) for operating a converter in accordance with example aspects of the present disclosure is depicted. The converter may include a plurality of inverter blocks. Each inverter block may include one or more SiC MOSFETs. For example, each inverter block may be a DC-to-DC-to-AC inverter block that may include a first conversion entity, a second conversion entity, a third conversion entity, and an isolation transformer. Each inverter block may include a plurality of switching devices, which may be one or more SiC MOSFETs. The converter may be, for example, the line side converter 168 in the wind power system 100.

[0066] At (902), the control method (900) may include providing, by a control system, one or more strobe commands to a first inverter block of the plurality of inverter blocks. For example, a first strobe command 502A / 802A may be provided by a control device 174 to a first gate drive card 402A associated with the first inverter block 206A. The first gate drive card 402A may be configured to drive one or more switching devices in the first inverter block 206A, such as one or more SiC MOSFETs.

[0067] At (904), the control method (900) may include: implementing a strobe command delay to generate a first delayed strobe command based at least in part on the one or more strobe commands. For example, the first gate drive card 402A may be configured to implement a strobe command delay, such as a delay of 1 - 2 microseconds, to generate a first delayed strobe command 502B. Additionally, the strobe command delay may be a delay configured to generate a phase shift in a fixed pulse output for the inverter block. For example, a strobe command delay may be implemented to generate a second strobe command 802B with a shifted phase shift P.

[0068] At (906), the control method (900) may include: providing a first delayed strobe command to a second inverter block among a plurality of inverter blocks. For example, a first gate driver card 402A associated with the first inverter block 206A may provide a first delayed strobe command 502B / 802B to a first gate driver card 402B associated with the second inverter block 206B. Then, the first gate driver card 402B may provide the first delayed strobe command 502B / 802B to the second inverter block 206B. In an embodiment, the first gate driver card 402A associated with the first inverter block 206A and the first gate driver card 402B associated with the second inverter block 206B may be arranged in a daisy-chain configuration.

[0069] At (908), the control method (900) may include: implementing a strobe command delay to generate a second delayed strobe command based at least in part on the first delayed strobe command. For example, the first gate driver card 402B may be configured to implement a second strobe command delay, such as a delay of 1 - 2 microseconds, to generate a second delayed strobe command 502C. Additionally, the strobe command delay may be a delay configured to generate a second phase shift in a fixed pulse output for the inverter block. For example, the strobe command delay may be implemented to generate a third strobe command 802C with a shifted phase shift P.

[0070] At (910), the control method (900) may include: providing the second delayed strobe command to a third inverter block among the plurality of inverter blocks. For example, the first gate driver card 402B associated with the second inverter block 206B may provide the second delayed strobe command 502C / 802C to a first gate driver card 402C associated with the third inverter block 206C. Then, the first gate driver card 402C may provide the first delayed strobe command 502C / 802C to the third inverter block 206C. In an embodiment, the first gate driver card 402B associated with the second inverter block 206B and the first gate driver card 402C associated with the third inverter block 206C may be arranged in a daisy-chain configuration.

[0071] Figure 10Illustrates an example control device 1000 in accordance with example aspects of the present disclosure. The control device 1000 can be used, for example, as the control device 174 or the control system 176 in the wind power generation system 100. The control device 1000 can include one or more computing devices 1100. The one or more computing devices 1100 can include one or more processors 1100A and one or more memory devices 1100B. The one or more processors 1100A can include any suitable processing device, such as a microprocessor, a microcontroller, an integrated circuit, a logic device, and / or other suitable processing devices. The one or more memory devices 1100B can include one or more computer-readable media, including but not limited to non-transitory computer-readable media, RAM, ROM, hard disk drives, flash drives, and / or other memory devices.

[0072] The one or more memory devices 1100B can store information accessible by the one or more processors 1100A, including computer-readable instructions 1100C that can be executed by the one or more processors 1100A. The instructions 1100C can be any set of instructions that cause the one or more processors 1100A to perform operations when executed by the one or more processors 1100A. In some embodiments, the instructions 1100C can be executed by the one or more processors 1100A to cause the one or more processors 1100A to perform operations, such as any of the operations and functions that the computing system 1000 and / or the (one or more) computing devices 1100 are configured to perform, for controlling the operation of a converter as described herein (e.g., control method 900) and / or any other operation or function of the (one or more) computing devices 1100. The instructions 1100C can be software written in any suitable programming language or can be implemented in hardware. Additionally and / or alternatively, the instructions 1100C can be executed logically and / or in a virtualized separate thread on the (one or more) processors 1100A. The (one or more) memory devices 1100B can also store data 1100D that can be accessed by the (one or more) processors 1100A. For example, the data 1100D can include data indicating power flow, current, temperature, actual voltage, nominal voltage, strobe commands, switching patterns, and / or any other data and / or information described herein.

[0073] The (one or more) computing devices 1100 may also include a network interface 1100E that is configured to communicate, for example, with other components of the system 1000 (e.g., via a network). The network interface 1100E may include any suitable components for interfacing with one or more networks, including, for example, transmitters, receivers, ports, control devices, antennas, and / or other suitable components. For example, the network interface 1100E may be configured to communicate with one or more sensors in the wind power generation system 100, such as one or more voltage sensors or temperature sensors. Additionally, the network interface 1100 may be configured to communicate with a control system (e.g., control system 176) or a control device (e.g., control device 174).

[0074] The techniques discussed herein refer to computer-based systems and actions taken by computer-based systems, as well as information sent to and from computer-based systems. Those of ordinary skill in the art will recognize that the inherent flexibility of computer-based systems allows for a wide variety of possible configurations, combinations, and divisions of tasks and functionality among and between components. For example, the processes discussed herein may be implemented using a single computing device or multiple computing devices working in combination. Databases, memories, instructions, and applications may be implemented on a single system or distributed across multiple systems. Distributed components may operate sequentially or in parallel.

[0075] For purposes of illustration and discussion, the present disclosure is discussed with reference to a DFIG power generation system that includes a power converter utilizing SiC MOSFETs. Those of ordinary skill in the art using the present disclosure provided herein will understand that other power generation systems and / or topologies may benefit from example aspects of the present disclosure. For example, the grounding and protection schemes disclosed herein may be used in wind, solar, gas turbine, or other suitable power generation systems. Although specific features of various embodiments may be shown in some figures but not in others, this is merely for convenience. Any feature of any figure may be referenced and / or claimed in combination with any feature of any other figure in accordance with the principles of the present disclosure.

[0076] This written description uses examples to disclose the invention, including the best mode, and also enables any person skilled in the art to practice the invention, including making and using any device or system and performing any incorporated method. The patent scope of the invention is defined by the claims and may include other examples that occur to those skilled in the art. If such other examples include structural elements that are not different from the literal language of the claims, or if such other examples include equivalent structural elements that are not substantially different from the literal language of the claims, then such other examples are intended to fall within the scope of the claims.

Claims

1. A control method for operating a converter, the converter including a plurality of inverter blocks, each inverter block including a plurality of switching devices coupled in parallel and an isolation transformer, the plurality of switching devices including one or more silicon carbide MOSFETs, the method comprising: Providing, by a control system, one or more gating commands to a first inverter block among the plurality of inverter blocks; Implementing, by the control system, a gating command delay to generate a first delayed gating command based at least in part on the one or more gating commands; And Providing, by the control system, the first delayed gating command to a second inverter block among the plurality of inverter blocks, wherein the one or more gating commands include one or more gating commands configured to generate a fixed pulse output, wherein the gating command delay includes a delay for generating a phase shift in the fixed pulse output for each inverter block, wherein the phase shift is based at least in part on the number of inverter blocks in the converter.

2. The control method according to claim 1, wherein, The control method further comprises: Implementing, by the control system, a second gating command delay to generate a second delayed gating command based at least in part on the first delayed gating command; and Providing, by the control system, the second delayed gating command to a third inverter block among the plurality of inverter blocks.

3. The control method according to claim 1, wherein, The control system includes a plurality of gate driver cards; wherein each gate driver card is configured to provide one or more gating commands to the plurality of switching devices in one of the plurality of inverter blocks; and wherein the plurality of gate driver cards are arranged in a daisy chain configuration.

4. The control method according to claim 1, wherein, The gating command delay is based at least in part on the number of inverter blocks in the converter.

5. The control method according to claim 1, wherein The one or more gating commands include: on / off pulses configured to turn on the converter for a period of time before turning off the converter; wherein the total delay includes the gating command delays of each inverter block added together; and wherein the total delay is shorter than the on-time of the on / off pulses.

6. The control method according to claim 1, wherein, The gating command delay includes a delay of 1 - 2 microseconds.

7. The control method according to claim 1, wherein, Providing to each inverter block in the converter the one or more gating commands configured to generate a fixed pulse output; And wherein the fixed pulse output of each inverter block is phase-shifted from the fixed pulse outputs of all other inverter blocks.

8. A power conversion system, comprising: A converter including a plurality of inverter blocks, each inverter block including a plurality of switching devices coupled in parallel and an isolation transformer, the plurality of switching devices including one or more silicon carbide MOSFETs, and A control system including a plurality of gate driver cards, the control system being configured to control the operation of the converter by providing one or more gating commands to the plurality of inverter blocks; wherein each inverter block has one or more associated gate driver cards from the plurality of gate driver cards, the plurality of gate driver cards being configured to provide the one or more gating commands to the plurality of switching devices in the inverter block; and Wherein, at least one of the one or more associated gate driver cards of each inverter block is daisy-chained to at least one of the one or more associated gate driver cards of another inverter block. Wherein, the control system is further configured to implement a gate command delay in the gate commands provided by the gate driver cards, wherein the one or more gate commands include one or more gate commands configured to generate a fixed pulse output. Wherein, the one or more gate commands configured to generate a fixed pulse output are provided to each inverter block in the converter; and Wherein, the fixed pulse output of each inverter block is phase-shifted from the fixed pulse outputs of all other inverter blocks.

9. The power conversion system according to claim 8, wherein, The gate command delay is at least partially based on the number of inverter blocks.

10. The power conversion system according to claim 8, wherein, The one or more gate commands include: on / off pulses configured to turn on the converter for a period of time before turning off the converter. Wherein, the total delay includes the gate command delays of each inverter block added together; and Wherein, the total delay is shorter than the on-time of the on / off pulses.

11. The power conversion system according to claim 8, wherein, The gate command delay includes a delay of 1 - 2 microseconds.

12. The power conversion system according to claim 8, wherein, The plurality of inverter blocks include a plurality of DC-to-DC-to-AC inverter blocks.

13. The power conversion system according to claim 12, wherein, Each of the plurality of DC-to-DC-to-AC inverter blocks includes a first conversion entity, a second conversion entity, a third conversion entity, and an isolation transformer; Wherein, the first conversion entity is a DC-to-AC conversion entity; Wherein, the second conversion entity is an AC-to-DC conversion entity; Wherein, the isolation transformer is coupled between the first conversion entity and the second conversion entity; and Wherein, the third conversion entity is a DC-to-AC conversion entity.

14. The power conversion system according to claim 13, wherein, The plurality of gate driver cards include: A first gate driver card configured to provide the one or more gate commands to the first conversion entity; A second gate driver card configured to provide the one or more gate commands to the second conversion entity; and A third gate driver card configured to provide the one or more gate commands to the third conversion entity.

15. A wind power generation system, comprising: A wind turbine configured to generate AC power; An AC-to-DC converter coupled to the wind turbine, the AC-to-DC converter being configured to convert the AC power from the wind turbine into DC power; A DC link coupled to the AC-to-DC converter, the DC link being configured to receive DC power from the AC-to-DC converter; A DC-to-AC converter coupled to the DC link, the DC-to-AC converter being configured to receive DC power from the DC link; the DC-to-AC converter includes a plurality of inverter blocks, each inverter block including a plurality of switching devices coupled in parallel and an isolation transformer, the plurality of switching devices including one or more silicon carbide MOSFETs; And A control system including a plurality of gate driver cards, the control system being configured to control the operation of the DC-to-AC converter by providing one or more gate commands to the plurality of inverter blocks. Wherein, each inverter block has one or more associated gate driver cards from the plurality of gate driver cards, and the plurality of gate driver cards are configured to provide the one or more gating commands to the plurality of switching devices in the inverter block; Wherein, at least one of the one or more associated gate driver cards of each inverter block is daisy-chained to at least one of the one or more associated gate driver cards of another inverter block; and Wherein, the control system is further configured to implement a gating command delay in the gating commands provided by the gate driver cards, wherein the one or more gating commands include one or more gating commands configured to generate a fixed pulse output; Wherein, the one or more gating commands configured to generate a fixed pulse output are provided to each inverter block in the converter; and Wherein, the fixed pulse output of each inverter block is phase-shifted from the fixed pulse outputs of all other inverter blocks.

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