High and low frequency hybrid modulation medium-voltage direct-hanging active filter composed of silicon carbide and silicon-based module

Abstract

The invention provides a high-low frequency hybrid modulation medium-voltage direct-hanging active filter device composed of silicon carbide and a silicon-based power module, and the high-low frequency hybrid modulation medium-voltage direct-hanging active filter device is used for compensating background harmonics of a medium-voltage power distribution network under hybrid switching frequency modulation and providing damping to suppress resonance. A voltage similar to a power grid is generated through low switching frequency modulation of the silicon-based power module to provide synchronous support, the silicon carbide power module is connected between the silicon-based power module and the medium-voltage power distribution network in series, and rapid tracking of medium-voltage harmonic waves is realized through high-frequency modulation of the silicon carbide power module, so that high-frequency modulation of the silicon carbide power module is realized. Harmonic waves generated by the silicon-based power module and power grid background harmonic waves are suppressed by the silicon carbide power module, and damping is provided by the silicon carbide power module. The method can adapt to a complex harmonic compensation scene under high distortion of a power grid, maintains the rapidity control performance of an original all-silicon carbide device while reducing the switching loss, is low in price, and has obvious advantages in the aspects of power quality control effect and economy.

Description

TECHNICAL FIELD

[0001] The application is suitable for harmonic compensation complex scenes under high distortion of medium voltage distribution network, and the mixed medium voltage active power filter proposed by the application is a device composed of silicon carbide power modules and silicon-based power modules, which can reduce switching loss while retaining the original fast control performance of silicon carbide devices, and has obvious advantages in power quality control effect and economy. BACKGROUND

[0002] With the rapid development of distributed new energy, more and more distributed new energy is put into use, and the distributed new energy and the power electronic degree are significantly improved. The system presents a high proportion of power electronic characteristics, which leads to a wider frequency band of harmonics than before. The previous harmonics were mainly distributed on the low-voltage side, and now they are gradually penetrating into the medium-voltage distribution network, and harmonic compensation is needed on the medium-voltage side.

[0003] The traditional active power filter device can inject reverse harmonic current to treat the harmonic current caused by rectifying load, but when there are background harmonics in the medium-voltage network, the parallel active filter device does not have the treatment ability. The use of medium-voltage compensation equipment will increase the cost, and the transformer has a damping effect on harmonics, resulting in poor harmonic compensation effect.

[0004] With the wide application of power electronic converter devices in traditional distribution networks, the use of cascaded devices and direct-hanging devices such as isolation transformers can compensate for harmonics. Generally, harmonic compensation needs to work at a high switching frequency, resulting in high switching loss and high cost. To solve the above problems, a high-low frequency mixed modulation medium-voltage direct-hanging active filter device composed of silicon carbide and silicon-based modules is invented. The silicon-based power module has the same amplitude and phase as the power grid, providing voltage support. The silicon carbide power module adjusts the harmonic current and provides damping. The low-frequency power module itself generates certain harmonics. The high-frequency power module can compensate for external harmonics and suppress the harmonics of the low-frequency power module, so that the harmonics generated by the low-frequency power module do not flow into the power grid. This silicon carbide and silicon-based module high-low frequency mixed modulation medium-voltage direct-hanging active filter device has low cost and high compensation capacity, and has obvious advantages in economy. Through mixed switching frequency modulation, the high-power cascaded H-bridge has low switching loss and fast dynamic response capability, which has obvious advantages in power quality control effect and economy. SUMMARY

[0005] The purpose of the present application is achieved by the following technical solutions: The voltage sensor according to claim 1 measures the DC side voltage of each phase of the three-phase cascaded H-bridge converter and grid voltage ; the current sensor of claim 1, measuring three-phase cascaded H-bridge inverter output current , grid current , nonlinear load current ; The controller obtains the load harmonic current through the characteristic harmonic extraction link ; The controller obtains the phase reference of the grid voltage through the phase-locked loop , obtains the fundamental current reference of the three-phase cascaded H-bridge inverter according to the DC voltage control and coordinate transformation, superimposes the load harmonic current extracted above as the current reference of the three-phase cascaded H-bridge inverter, and obtains the compensation control modulation voltage of the three-phase cascaded H-bridge inverter through the current controller; The controller obtains the harmonic current of the cascaded H-bridge inverter output flowing through the LCL type filter inductor L1 , obtains the damping modulation voltage of the three-phase cascaded H-bridge inverter through the damping coefficient ; The controller obtains the DC side voltage of the a-phase n H-bridge sub-modules of the three-phase cascaded H-bridge inverter , calculates the sum of the a-phase DC side voltage ; the controller obtains the DC side voltage of the b-phase n H-bridge sub-modules of the three-phase cascaded H-bridge inverter ; calculates the sum of the b-phase DC side voltage ; the controller obtains the DC side voltage of the c-phase n H-bridge sub-modules of the three-phase cascaded H-bridge inverter , calculates the sum of the c-phase DC side voltage , the controller calculates the average value of the three-phase interphase DC voltage according to the above formula ; The controller subtracts the average value of the three-phase interphase DC voltage from the sum of the DC voltages of the abc three-phase respectively, and multiplies the phase angle of the respective current to obtain the zero sequence voltage of the interphase voltage balance control ; superimposed with the above current compensation control voltage and damping modulation voltage, obtains the modulation signal of the three-phase cascaded H-bridge inverter ; The controller divides the obtained sum of the a-phase DC side voltage by (m+n) as the reference voltage of the a-phase intra-phase voltage balance control, and respectively subtracts the DC side voltage of the a-phase (m+n) H-bridge The difference is multiplied by the phase angle of the a-phase current to obtain an a-phase in-phase voltage balance control modulation voltage, and b-phase and c-phase in-phase voltage balance control modulation voltages can be obtained in the same way, so that three-phase in-phase voltage balance control of the cascade H-bridge converter is realized. The controller obtains the control signal of the three-phase cascade H-bridge converter through the unipolar frequency multiplication carrier phase-shifting sine pulse width modulator based on the obtained modulation wave voltage of the three-phase cascade H-bridge converter.

[0006] Compared with the prior art, the technical scheme of the present application has the following beneficial effects: The silicon-based power module is cheap, the silicon carbide power module has fast response speed and fast switching action, the performance of the power electronic converter is improved, the three-phase cascade multilevel converter has obvious advantages in power quality control effect and economy under hybrid switching frequency modulation, the low switching frequency can reduce the loss caused by the switching frequency, and the high switching frequency can have fast dynamic response and anti-interference ability in harmonic control. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 The electrical connection structure of the silicon carbide and silicon-based module high-low frequency hybrid modulation medium voltage direct hanging type active filter system provided by the embodiment of the present application; Figure 2 The control strategy implementation flowchart of the silicon carbide and silicon-based module high-low frequency hybrid modulation medium voltage direct hanging type active filter provided by the embodiment of the present application; Figure 3 The control block diagram of the silicon carbide and silicon-based module high-low frequency hybrid modulation medium voltage direct hanging type active filter provided by the embodiment of the present application; Figure 4 The point of common coupling voltage of the hybrid medium voltage active power filter without harmonic compensation and damping algorithm Simulation running effect diagram; Figure 5 The grid current without harmonic compensation and damping algorithm Simulation running effect diagram; Figure 6 (a) is the output voltage of the silicon carbide module; Figure 6 (b) is the output voltage of the silicon-based module; Figure 7 The point of common coupling voltage of the hybrid medium voltage active power filter with harmonic compensation and active damping control Simulation running effect diagram; Figure 8 The grid current after treatment Simulation running effect diagram; Figure 9 (a) is the output voltage of the silicon carbide power module; Figure 9 (b) is the output voltage of the silicon-based power module; Figure 10 (a) is the modulation voltage of the high-frequency power module; Figure 10 (b) is the modulation voltage of the low-frequency power module. Figure 11A schematic diagram of a medium voltage directly-hung active filter device module of a silicon carbide and silicon-based module high-low frequency hybrid modulation provided by the embodiment of the present application; Figure 12 A schematic diagram of a medium voltage directly-hung active filter device of a silicon carbide and silicon-based module high-low frequency hybrid modulation provided by the embodiment of the present application. DETAILED DESCRIPTION

[0008] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings. The specific operation methods in the method embodiment can also be applied to the device embodiment or the system embodiment. It should be noted that in the description of the present application, "at least one" means one or more, and the plurality means two or more. In the embodiment of the present application, "plurality" can also be understood as "at least two". "And / or", which describes the association relationship of the associated objects, means that there can be three kinds of relationships, for example, A and / or B can mean that A exists alone, A and B exist together, and B exists alone. In addition, the character " / ", if not specially stated, generally represents that the front and rear associated objects are in an "or" relationship. In addition, it should be understood that in the description of the present application, "first", "second", etc. are used only for the purpose of distinguishing the description, and cannot be understood as indicating or implying relative importance. The following will be further described in detail with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0009] The silicon carbide and silicon-based module high-low frequency hybrid modulation medium voltage directly-hung active filter provided by the present application comprises the following steps: Please refer to Figure 1 The silicon carbide and silicon-based module high-low frequency hybrid modulation medium voltage directly-hung active filter device, characterized in that, comprising: a three-phase cascaded H-bridge converter, a medium voltage distribution network, a weak current network impedance, a controller, a three-phase uncontrollable rectifier bridge, an LCL type filter, a current sensor, and a voltage sensor; Each phase of the three-phase cascaded H-bridge converter is cascaded by (m+n) H-bridges, wherein m modules are modulated at a high switching frequency, and n modules are modulated at a low switching frequency. Each H-bridge is composed of four fully controlled devices. The first end of the three-phase cascaded H-bridge converter is connected to the medium voltage distribution network through the LCL type filter. The medium voltage distribution network is connected in parallel with the three-phase uncontrollable rectifier bridge. The output of the controller is connected to the fully controlled devices of the three-phase cascaded H-bridge converter. The voltage sensor collects the grid voltage. The first current sensor is connected to the distribution network through the weak current network impedance. The second current sensor is connected to the first end of the three-phase uncontrollable rectifier bridge through the inductor L. The third current sensor is connected to the first end of the cascaded H-bridge converter through the LCL type filter. Please refer toFigure 2 , the silicon carbide and silicon-based module high-low frequency hybrid modulation medium voltage direct hanging type active filter control strategy comprises: Step S201: measuring the DC side voltage of each phase of the three-phase cascaded H-bridge converter according to the voltage sensor of claim 1 ; grid voltage ; the current sensor of claim 1 measures the output current of the three-phase cascaded H-bridge converter , grid current , nonlinear load current ; Please refer to Figure 3 , the silicon carbide and silicon-based module high-low frequency hybrid modulation medium voltage direct hanging type active filter control strategy provided by the embodiment of the present application comprises: Step S202: the controller calculates the sum of the DC side voltage of the a-phase (m+n) H-bridge sub-modules of the three-phase cascaded H-bridge converter by extracting the DC side voltage of the a-phase (m+n) H-bridge sub-modules of the three-phase cascaded H-bridge converter , as shown in the following formula: (1) The controller calculates the sum of the DC side voltage of the b-phase n H-bridge sub-modules of the three-phase cascaded H-bridge converter by obtaining the DC side voltage of the b-phase n H-bridge sub-modules of the three-phase cascaded H-bridge converter , as shown in the following formula: (2) The controller calculates the sum of the DC side voltage of the c-phase n H-bridge sub-modules of the three-phase cascaded H-bridge converter by obtaining the DC side voltage of the c-phase n H-bridge sub-modules of the three-phase cascaded H-bridge converter , as shown in the following formula: (3) The controller calculates the average value of the three-phase interphase DC voltage according to the above formula , as shown in the following formula: (4) The controller subtracts the average value of the three-phase interphase DC voltage from the sum of the DC side voltage of the abc three-phase respectively, and multiplies the phase angle of the current to obtain the zero sequence voltage , and the obtained zero sequence voltage realizes the interphase voltage balance.

[0010] The controller calculates the average value of the three-phase DC side voltage by extracting the voltage of the DC side of the three-phase cascaded H-bridge converter, as the reference voltage of the intra-phase voltage balance control, subtracts the DC side voltage of each H-bridge, and multiplies the cosine value of the corresponding current phase angle to obtain the modulation signal of the intra-phase voltage balance control of the cascaded H-bridge converter.​​​​ (5) ; wherein, k p and k i are proportional and integral coefficients of the in-phase voltage balance control; j =a, b, c represent three phases of abc; k =1, 2, 3… (m+n) represent the number of H-bridge power modules.

[0011] Step S203: the controller obtains the phase reference of the three-phase cascaded H-bridge converter through the phase-locked loop, and obtains the fundamental current reference of the three-phase cascaded H-bridge converter according to the DC voltage control and the coordinate transformation , as shown in the following formula: (6) wherein, θ is the voltage phase reference obtained by the phase-locked loop of the controller, and are proportional and integral coefficients of the DC voltage controller, is the average value of the DC bus voltage of the three-phase H-bridge sub-module, is the reference voltage.

[0012] Step S204: the controller superimposes the obtained load harmonic current on the obtained fundamental current reference as the current reference of the three-phase cascaded H-bridge converter, and obtains the compensation control modulation voltage of the three-phase cascaded H-bridge converter through the current controller , as shown in the following formula: (7) wherein, and are proportional and resonant coefficients of the current controller, represents the bandwidth of the controller at the center frequency, represents the fundamental frequency, h represents the characteristic harmonic order, which is 5, 7, 11, and 13; Step S205: the controller obtains the current flowing through the inductor L1 of the LCL filter , obtains the damping modulation voltage of the cascaded H-bridge converter according to the damping coefficient , superimposes the above compensation control modulation voltage and the zero sequence voltage of the cascaded H-bridge converter for inter-phase voltage balance control, and obtains the modulation signal of the cascaded H-bridge converter , as shown in the following formula: ​​(8) wherein, is the damping coefficient of the cascaded H-bridge converter, is the zero sequence voltage of the cascaded H-bridge converter for phase-to-phase voltage balancing, is the damping modulation voltage.

[0013] Step S206: The controller extracts the fundamental component of the modulation signal of the cascaded H-bridge converter through the sliding Fourier transform module , and divides it equally to each power module of the cascaded H-bridge converter, and superimposes the modulation signal of the above obtained in-phase voltage balancing control on the low-frequency module , to obtain the modulation signal of the low-frequency module of the cascaded H-bridge, as shown in the following formula: (9) (10) wherein is the transfer function of the sliding Fourier transform, m is the number of high-frequency modules, and n is the number of low-frequency modules.

[0014] Step S207: The controller subtracts the fundamental component of the extracted modulation signal , to obtain the harmonic component of the modulation signal , and divides the harmonic part and the fundamental part to each high-frequency power module, and adds the opposite number of the harmonic of the low-frequency power module obtained according to the sliding Fourier transform to the high-frequency power module for feedforward compensation , and superimposes the modulation voltage of the in-phase voltage balancing control , to obtain the modulation voltage of the high-frequency power module, as shown in the following formula: (11) (12) (13) m represents the number of high-frequency power modules of the H-bridge, and n represents the number of low-frequency power modules of the H-bridge.

[0015] Step S208: The controller obtains the control signal of the three-phase cascaded H-bridge converter through the sinusoidal pulse width modulator based on the obtained modulation wave voltage of the high-frequency power module and the low-frequency power module of the cascaded H-bridge converter.

[0016] Figure 4 is the simulation running effect diagram of the point of common coupling voltage under the harmonic compensation and damping algorithm without adding the mixed medium-voltage active power filter, and the point of common coupling voltage has a total harmonic distortion (THD) of 4.50%, Figure 5 ​​Grid current without harmonic compensation and damping algorithm i The simulation running effect diagram, the grid current harmonic distortion rate (THD) is 21.85%, and the grid current harmonic distortion rate (THD) is 21.85%, Figure 6 (a) is the output voltage of the silicon carbide module, Figure 6 (b) is the output voltage of the silicon-based module.

[0017] Figure 7 The simulation running effect diagram of the grid voltage after the mixed medium-voltage active power filter provided by the embodiment of the present application is added with harmonic compensation and active damping control, and the grid voltage after treatment The harmonic distortion rate (THD) is only 2.18%; Figure 8 The grid current after treatment The simulation running effect diagram, the grid current harmonic distortion rate (THD) is only 2.46%; Obviously, the harmonic compensation effect is very good. After the medium-voltage direct hanging type active filter harmonic compensation strategy of the high-low frequency mixed modulation of the silicon carbide and silicon-based module is adopted, the high-frequency silicon carbide power module provides harmonic compensation and active damping, Figure 9 (a) is the output voltage of the silicon carbide power module, and the low-frequency silicon-based power module plays a voltage support role, Figure 9 (b) is the output voltage of the silicon-based power module. Figure 10 (a) is the modulation voltage of the high-frequency power module, Figure 10 (b) is the modulation voltage of the low-frequency power module.

[0018] The present application is not limited to the above-described embodiments. The above description of the specific embodiments is intended to describe and explain the technical solutions of the present application, and the specific embodiments described above are only illustrative and not restrictive. Without departing from the purpose of the present application and the scope protected by the claims, those skilled in the art can make many forms of specific changes under the inspiration of the present application, which are all within the protection scope of the present application.

[0019] It should be understood that the size of the serial number of each step in the above embodiments does not mean the order of execution, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0020] As shown in the embodiment module, Figure 11 A medium-voltage direct hanging type active filter of high-low frequency mixed modulation of silicon carbide and silicon-based module, comprising: A first obtaining module 1101 obtains the grid voltage according to the voltage sensor, and obtains the three-phase cascaded H-bridge converter output current, the grid current and the load current according to the current sensor; The second acquisition module 1102, the controller obtains the DC side voltage of the cascaded H-bridge through the voltage sensor, and calculates the zero-sequence voltage for phase-to-phase voltage equalization and the modulation voltage for phase-to-phase voltage equalization. The third module 1103 obtains the cascaded H-bridge fundamental current reference through DC voltage control and coordinate transformation. The third determining module 1104, the controller extracts the load harmonic current, superimposes the obtained fundamental current reference as the cascaded H-bridge current reference, and determines the compensation control modulation voltage of the cascaded H-bridge converter through the current controller. The fourth module 1105 determines the damping modulation voltage of the cascaded H-bridge converter based on the output harmonic current of the cascaded H-bridge converter and the damping coefficient. This voltage is then superimposed with the current compensation control voltage and the zero-sequence voltage to obtain the modulation signal of the cascaded H-bridge converter. The fifth determining module 1106 extracts the fundamental component of the modulation signal of the cascaded H-bridge based on the sliding Fourier transform module. The voltage is evenly distributed to each module of the cascaded H-bridge. The low-frequency module is superimposed with the above-mentioned intra-phase voltage equalization control modulation signal to determine the modulation voltage of the low-frequency module. The sixth determining module 1107, the controller obtains the harmonic components of the modulation signal and the harmonic components of the low-frequency power module according to the sliding Fourier transform, and feeds them to the high-frequency power module and superimposes the phase equalization control signal to determine the modulation voltage of the high-frequency power module; The seventh module 1108 obtains the control signals of the cascaded H-bridge high-frequency power module and low-frequency power module through the sinusoidal pulse width modulator based on the obtained modulation wave voltages of the high-frequency power module and low-frequency power module of the cascaded H-bridge converter.

[0021] Figure 12 This is a schematic diagram of a medium-voltage direct-connected active filter device composed of silicon carbide and silicon-based modules, provided in an embodiment of the present invention.

[0022] The schematic diagram of the cascaded multilevel converter power quality control device and control system is shown below. Figure 12 As shown, it includes: a converter 1201, a controller 1202, a memory 1203, and a computer program 1204 stored in the memory 1203 and executable on the controller 1202. When the controller 1202 executes the computer program 1204, it implements the steps described in the power quality control embodiment above, for example... Figure 2 The steps S201 to S208 are shown. Alternatively, when the controller 1202 executes the computer program 1204, it implements the power of each module / unit in the above embodiments, for example... Figure 11 The functions of modules 1101 to 1108 are shown.

[0023] By way of example, the computer program 1204 can be segmented into one or more modules / units that are stored in the memory 1203 and executed by the controller 1202 to accomplish the embodiments of the present application. The one or more modules / units can be a series of computer program instruction segments capable of accomplishing a specific function. For example, the computer program 1204 can be segmented into a first obtaining module, a second obtaining module, a third obtaining module, a third determining module, a fourth obtaining module, a fifth determining module, a sixth determining module, and a seventh obtaining module, and the functions of the modules are as follows: The first obtaining module 1101 obtains, according to the voltage sensor, a grid voltage; and obtains, according to the current sensor, a three-phase cascaded H-bridge inverter output current, a grid current, and a load current. The second obtaining module 1102 controls the controller to obtain, through the voltage sensor, a cascaded H-bridge DC side voltage, to calculate a zero sequence voltage for inter-phase voltage balancing and a modulation voltage for intra-phase voltage balancing. The third obtaining module 1103 controls the controller to obtain, through DC voltage control, a fundamental wave current reference of the cascaded H-bridge through coordinate transformation. The third determining module 1104 controls the controller to extract a load harmonic current, to superimpose the obtained fundamental wave current reference as a cascaded H-bridge current reference, to determine, through the current controller, a compensation control modulation voltage of the cascaded H-bridge inverter. The fourth obtaining module 1105 determines, according to the output harmonic current of the cascaded H-bridge inverter, a damping modulation voltage of the cascaded H-bridge inverter through a damping coefficient, to superimpose the current compensation control voltage and the zero sequence voltage, to obtain a modulation signal of the cascaded H-bridge inverter. The fifth determining module 1106 extracts, according to the sliding Fourier transform module, a fundamental wave component of the modulation signal of the cascaded H-bridge , to divide the fundamental wave component into each module of the cascaded H-bridge, to superimpose the intra-phase voltage balancing control modulation signal on the low-frequency module, to determine a modulation voltage of the low-frequency module. The sixth determining module 1107 controls the controller to obtain, according to the sliding Fourier transform, a harmonic component of the modulation signal and a harmonic component of the low-frequency power module, to give the harmonic component to the high-frequency power module to superimpose the intra-phase voltage balancing control signal, to determine a modulation voltage of the high-frequency power module. The seventh obtaining module 1108 obtains, according to the obtained modulation wave voltage of the high-frequency power module and the low-frequency power module of the cascaded H-bridge inverter, a control signal of the high-frequency power module and the low-frequency power module of the cascaded H-bridge through the sine pulse width modulator.

[0024] The silicon carbide and silicon-based module high-low frequency hybrid modulation medium voltage directly hanging type active filter can include, but is not limited to, a converter 1201, a controller 1202, and a memory 1203. Those skilled in the art can understand that Figure 12 The above merely illustrates the cascade multilevel converter power quality control device, and does not constitute a limitation on the cascade multilevel converter power quality control device, which can include more or fewer components than those shown, or combine certain components, or different components, for example, the life evaluation terminal of the cascade multilevel converter power quality control device can also include input and output devices, network access devices, buses, etc.

[0025] The controller 1202 can be a central processing unit (CPU), and can also be other general-purpose processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor.

[0026] The memory 1203 can be an internal storage unit of the silicon carbide and silicon-based module high-low frequency hybrid modulation medium voltage directly hanging type active filter device 12, for example, an external memory circuit of the cascade multilevel converter power quality control device 12. For example, a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, etc. equipped on the cascade multilevel converter power quality control device 12. Further, the memory 1203 can include both the internal storage unit of the system device 12 and the external storage device. The memory 1203 is used to store the computer program and other programs and data. The memory 1203 can be used to temporarily store data that has been output or will be output.

[0027] Those skilled in the art can clearly understand that, for the convenience and brevity of description, only the above-mentioned division of each functional unit and module is exemplified, and in actual application, the above-mentioned functions can be completed by different functional units and modules according to needs, that is, the internal structure of the device is divided into different functional units or modules to complete all or part of the functions described above. Each functional unit and module in the embodiment can be integrated in one processing unit, or each unit can be physically present separately, or two or more units can be integrated in one unit. The above-mentioned integrated unit can be realized in the form of hardware or software. In addition, the specific names of each functional unit and module are only for the convenience of mutual distinction, and do not limit the protection scope of the present application. The specific working process of the units and modules in the above system can refer to the corresponding process in the foregoing method embodiments, which will not be described here.

[0028] In the above embodiments, the description of each embodiment has its own emphasis, and the parts not described or recorded in detail in a certain embodiment can be referred to the related description of other embodiments.

[0029] Those of ordinary skill in the art can realize that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be realized in electronic hardware or a combination of computer software and electronic hardware. Whether the functions are executed in hardware or software depends on the specific application and design constraints of the technical solution. Professional technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0030] In the embodiments provided by the present application, it should be understood that the disclosed apparatus / terminal device and method can be implemented in other ways. For example, the above-mentioned apparatus / terminal device embodiments are only schematic, and the division of the modules or units is only a logical function division, and there can be another division manner in actual implementation. For example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the displayed or discussed mutual coupling or direct coupling or communication connection can be indirect coupling or communication connection through some interface, device or unit, and can be electrical, mechanical or other forms.

[0031] The units described as separate components can or can not be physically separated, and the components shown as units can or can not be physical units, that is, they can be located in one place, or can be distributed on multiple network units. Some units can be selected according to actual needs to achieve the purpose of the embodiment.

[0032] In addition, each function unit in each embodiment of the present application can be integrated in one processing unit, or each unit can be physically present separately, or two or more units can be integrated in one unit. The integrated unit can be realized in the form of hardware or in the form of a software function unit.

[0033] The integrated module / unit, if realized in the form of a software function unit and sold or used as an independent product, can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the above-mentioned embodiment methods can also be completed by a computer program instructing related hardware, and the computer program can be stored in a computer-readable storage medium. When the processor executes the computer program, the steps of each method embodiment described above can be implemented. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or some intermediate forms, etc. The computer-readable medium can include any entity or device capable of carrying the computer program code, recording medium, U disk, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signal, telecommunication signal, and software distribution medium, etc. It should be noted that the content included in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction, for example, in some jurisdictions, according to legislation and patent practice, the computer-readable medium does not include electrical carrier signals and telecommunication signals.

[0034] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements for some technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A medium voltage direct hanging type active filter device of silicon carbide and silicon-based module high-low frequency hybrid modulation, characterized in that, Comprise: Three-phase cascaded H-bridge converter, controller, LCL type filter, current sensor, voltage sensor; Each phase of the three-phase cascaded H-bridge converter is cascaded by (m+n) H-bridges, wherein there are m silicon carbide power modules based on high switching frequency modulation and n silicon-based power modules based on low switching frequency modulation, and each H-bridge is composed of four unipolar devices S1-S4; the first end of the three-phase cascaded H-bridge converter is connected to the 10kV medium voltage distribution network through the LCL type filter; the medium voltage distribution network is connected in parallel with the three-phase uncontrolled rectifier bridge; the output of the controller is connected to the unipolar devices of the three-phase cascaded H-bridge converter; the first current sensor is connected to the power distribution network through the grid impedance, the second current sensor is connected to the first end of the three-phase uncontrolled rectifier bridge through the inductance L, and the third current sensor is connected to the first end of the cascaded H-bridge converter through the LCL type filter; the first voltage sensor is arranged at the connection point of the power distribution network and the three-phase uncontrolled rectifier bridge, and the second voltage sensor is arranged at the two ends of the DC side capacitor of each H-bridge power module.

2. The medium voltage directly hung active filter device modulated by high and low frequency mixing of silicon carbide and silicon-based module according to claim 1, characterized in that, The upper bridge arm of the three-phase uncontrolled rectifier bridge is composed of the cathodes of three diodes connected in common as a common cathode node, which is the output positive electrode; the lower bridge arm is composed of the anodes of three diodes connected in common as a common anode node, which is the output negative electrode.

3. A high-low frequency hybrid modulated medium voltage directly hung active filter device consisting of silicon carbide and silicon based modules, characterized in that, Comprise: The voltage sensor according to claim 1, measures the DC side voltage of each phase of a three-phase cascaded H-bridge inverter and the grid voltage ; The current sensor according to claim 1, measuring three-phase cascaded H-bridge inverter output current , grid current , non-linear load current ; The controller obtains the load harmonic current through the characteristic sub-harmonic extraction link ; The controller obtains a phase reference of the grid voltage through a phase-locked loop , obtains a fundamental current reference of the three-phase cascaded H-bridge converter according to the DC voltage control and the coordinate transformation , superimposes the extracted load harmonic current , as a current reference of the three-phase cascaded H-bridge converter The controller obtains the harmonic current from the output of the cascaded H-bridge converter, which flows through the LCL filter inductor L1. Through the damping coefficient The damping modulation voltage of the three-phase cascaded H-bridge converter is obtained. ; The controller obtains the sum of the DC side voltages of the (m+n) H-bridge sub-modules of the a-phase of the three-phase cascaded H-bridge converter , calculates the sum of the DC side voltages of the a-phase ; the controller obtains the sum of the DC side voltages of the (m+n) H-bridge sub-modules of the b-phase of the three-phase cascaded H-bridge converter ; Calculate the sum of the DC side voltages of phase b. The controller obtains the DC-side voltage of the c-phase (m+n) H-bridge submodules of the three-phase cascaded H-bridge converter. Calculate the sum of the DC side voltages of phase c. The controller calculates based on the above formula. Calculate the average value of the three-phase interphase DC voltage. ; The controller calculates the difference between the average value of the three-phase interphase DC voltage and the sum of the DC voltages of phases a, b, and c, then multiplies this difference by the phase angle of the respective current, and sums the results to obtain the zero-sequence voltage for interphase voltage balance control. The controller will obtain the sum of the DC side voltages of phase a. Divide by (m+n) as the reference voltage for phase-a voltage equalization control, and then divide by the DC side voltages of the (m+n) H-bridges in phase-a. The difference is multiplied by the phase angle of the phase a current to obtain the phase a voltage equalization control modulation voltage. Similarly, the phase b and phase c voltage equalization control modulation voltage can be obtained, thereby realizing the three-phase phase equalization control of the cascaded H-bridge converter. zero-sequence voltage The modulation signal of the three-phase cascaded H-bridge converter is obtained by superimposing the current compensation control voltage and the damping modulation voltage mentioned above. The controller uses a sliding Fourier transform to divide the modulation signals of each phase into the fundamental frequency component. Harmonic components Harmonic components and fundamental frequency part The harmonics of the low-frequency power modules are distributed to each high-frequency power module. The harmonics of the low-frequency power modules are obtained using a sliding Fourier transform, and their inverses are added to the high-frequency power modules for feedforward compensation. Finally, a modulation voltage for in-phase voltage equalization control is superimposed. The modulation voltage of the high-frequency power module is obtained. The fundamental frequency component of the modulated signal The voltage is distributed to each low-frequency power module and superimposed with the phase-equalizing control modulation voltage. The modulation voltage of the low-frequency power module is obtained. ; The controller derives a high frequency power module modulation voltage for the three-phase cascaded H-bridge inverter based on the derived low frequency power module modulation voltage and a low frequency power module modulation voltage for the three-phase cascaded H-bridge inverter via the unipolar frequency multiplied carrier phase-shifted sinusoidal pulse width modulator.

4. The silicon carbide and silicon-based modular high-low frequency mixed- mode medium voltage active filter of claim 2, wherein, The controller extracts the DC side voltage of the (m+n) H-bridge sub-modules of the a phase of the three-phase cascaded H-bridge converter , calculates the sum of the DC side voltage of the a phase , as shown in the following formula: (1) The controller calculates the sum of the b-phase DC side voltages of the (m+n) H-bridge sub-modules of the three-phase cascaded H-bridge converter by obtaining the b-phase DC side voltages of the (m+n) H-bridge sub-modules of the three-phase cascaded H-bridge converter , as shown in the following formula: ​ (2) The controller calculates the sum of the c-phase DC side voltages of the (m+n) H-bridge sub-modules in the b-phase of the three-phase cascaded H-bridge converter by obtaining the DC side voltages of the (m+n) H-bridge sub-modules in the b-phase of the three-phase cascaded H-bridge converter , as shown in the following formula: ​ (3) The controller calculates the average value of the three-phase inter-phase DC voltage , calculates the average value of the three-phase inter-phase DC voltage , as shown in the following equation: (4) The controller subtracts the average value of the three-phase interphase DC voltage from the sum of the DC side voltages of the three phases abc, respectively, multiplies the phase angle of each current, and adds to obtain the zero sequence voltage , and the obtained zero sequence voltage is injected to realize the interphase voltage balance.

5. The controller calculates the average value of the three-phase DC side voltage as the reference voltage for the in-phase voltage balancing control by extracting the voltage of the DC side of the three-phase cascaded H-bridge converter, and obtains the modulation signal for the in-phase voltage balancing control of the cascaded H-bridge converter by subtracting the DC side voltage of each H-bridge from the reference voltage and multiplying the cosine value of the corresponding current phase angle ; (5) ； wherein k p and k i are proportional and integral coefficients of the in-phase voltage equalization control; j =a, b, c represent the three phases of abc; k =1, 2, 3… (m+n) represent the number of H-bridge power modules.

6. The silicon carbide and silicon-based modular high-low frequency mixed- mode medium voltage active filter of claim 2, wherein, The controller obtains the phase reference of the three-phase cascaded H-bridge converter through a phase-locked loop, and obtains the fundamental current reference of the three-phase cascaded H-bridge converter according to DC voltage control and coordinate transformation As shown in the following formula: (6) wherein, θ is the voltage phase reference obtained by the controller phase-locked loop, and are the proportional and integral coefficients of the DC voltage controller, is the average value of the DC bus voltage of the three-phase H-bridge sub-module, is the reference voltage.

7. The silicon carbide and silicon-based modular high-low frequency mixed- mode medium voltage active filter of claim 2, wherein, The controller obtains the nonlinear load harmonic current through the superposition extraction link , superimposes the fundamental current reference As a current reference of the three-phase cascaded H-bridge converter, through the current controller, a compensation control modulation voltage of the three-phase cascaded H-bridge converter is obtained As shown in the following formula: (7) wherein, and are the proportional and resonant coefficients of the current controller, respectively, denotes the bandwidth at the center frequency of the controller, denotes the fundamental frequency, h denotes the characteristic sub-harmonic order, taken as 5, 7, 11, 13 orders; The controller extracts the current flowing through the LCL filter inductor L1. According to the damping coefficient Obtain the damped modulation voltage of the three-phase cascaded H-bridge converter In addition to the aforementioned compensation control modulation voltage, there is also zero-sequence voltage. By superposition, the modulation signal of the three-phase cascaded H-bridge converter is obtained. As shown in the following formula: (8) wherein, is a damping coefficient, is a zero sequence voltage, is a damping modulation voltage.

8. The silicon carbide and silicon-based modular high-low frequency mixed- mode medium voltage active filter of claim 2, wherein, Each phase of the three-phase cascaded H-bridge converter has m a high-frequency power module, n a low-frequency power module cascaded, wherein the controller divides each phase modulation signal into fundamental wave part and harmonic wave part by sliding Fourier transform, divides the fundamental wave part of the modulation signal to each low-frequency power module, superimposes the modulation voltage of the equalizing control in the phase to obtain the modulation voltage of the low-frequency power module . ​ (9) (10) is the transfer function of the sliding Fourier transform, m is the number of high frequency modules, and n is the number of low frequency modules. harmonic part and fundamental part The harmonic part of the low frequency power module is obtained according to the sliding Fourier transform, and its opposite number is added to the high frequency power module to make feedforward compensation , and the modulation voltage of the in-phase voltage sharing control is superimposed , to obtain the modulation voltage of the high frequency power module ; (11) (12) (13) Wherein m is the number of high-frequency power modules, and n is the number of low-frequency power modules.

9. The silicon carbide and silicon-based modular high-low frequency mixed- mode medium voltage active filter of claim 2, wherein, The controller obtains the control signal of the three-phase cascaded H-bridge converter based on the obtained modulation wave voltage of the high-frequency power modules and the low-frequency power modules of the cascaded H-bridge converter through the sine pulse width modulator.

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