Grid-connected control method, system and equipment for four-quadrant frequency converter

Abstract

The invention discloses a grid-connected control method, a grid-connected control system and grid-connected control equipment for a four-quadrant frequency converter, and particularly relates to the technical field of grid-connected control, and the technical key points are as follows: determining a grid voltage phase sequence and a phase reference angle of a grid voltage signal by using a three-phase phase-locked loop under a DQ coordinate system; determining a voltage input signal and an initialization angle of an SOGI phase-locked loop according to the power grid voltage phase sequence and the phase reference angle, performing phase locking on the power grid voltage of which the total harmonic distortion rate exceeds a preset distortion threshold by using the SOGI phase-locked loop, and outputting a grid-connected feedforward signal when the power grid voltage and the power grid voltage phase sequence meet a grid-connected condition; according to a preset grading rule, each power unit in the four-quadrant frequency converter is divided into different grid-connected grades, and based on a grid-connected feedforward signal, the phase-locked four-quadrant frequency converter controls a switching device to realize grading grid-connected control on the power units of different grid-connected grades according to a preset grid-connected mode.

Description

Technical Field

[0001] The present invention relates to the technical field of grid-connected control, and in particular to a grid-connected control method, system and device for a four-quadrant frequency converter. Background Art

[0002] At present, the domestic demand for large-capacity motor drives is increasing, especially for large-capacity motor test benches, compressed air energy storage, and steam-electric dual-drive, etc. These fields require the configuration of large-capacity four-quadrant inverters for motor speed regulation and energy feedback. In the cascaded three-phase rectifier four-quadrant inverter, the high-voltage variable frequency power supply system is powered by the grid bus, and each power unit is powered by a phase-shifting transformer. Each phase of a single inverter is cascaded by multiple power units, and the rectifier side of the power unit adopts multiple AFE (Active Front End) rectification / feedback.

[0003] AFE rectifier achieves grid connection by switching on and off the rectifier bridge IGBT to output PWM waves. Under large power grids, the inverter will hardly have any impact on the power grid. However, since the PWM wave output by the AFE rectifier grid connection is not a standard sine wave, in actual working conditions, the on-site power grid capacity is far smaller than the capacity of the four-quadrant inverter. The PWM wave will have a greater impact on the power grid, causing the four-quadrant inverter to have excessively high impact current during the grid connection process, worse grid voltage harmonics, and instability in the system grid connection control. Grid connection cannot be achieved normally, affecting the normal operation of the equipment.

[0004] Therefore, the present invention aims to provide a grid-connected control method, system and device for a four-quadrant inverter to solve the above-mentioned related problems. Summary of the invention

[0005] The technical problem to be solved by the present invention is that in the prior art, a four-quadrant frequency converter has excessively high impact current, deteriorated grid voltage harmonics, and unstable system grid control during the grid connection process, which makes it impossible to achieve normal grid connection and affects the normal operation of the equipment. The purpose is to provide a grid connection control method, system and equipment for a four-quadrant frequency converter, by adopting a dual phase-locked loop mode consisting of a three-phase phase-locked loop and a SOGI phase-locked loop in a DQ coordinate system, to achieve stable and accurate phase locking and control under different phase sequences and under large harmonic voltages; at the same time, by dividing each power unit in the four-quadrant frequency converter into different grid connection levels and adopting a graded grid connection strategy, the current impact in the initial stage of grid connection can be effectively reduced, and the grid current can be lower than the on-site protection current value during the grid connection process, and the grid voltage amplitude can be quickly restored; thus, by adopting the technical solution, various abnormal situations such as excessively high impact current, greatly reduced grid voltage, increased grid harmonics, and unstable system grid control during the grid connection process of a large-capacity four-quadrant frequency converter under a weak grid can be effectively solved, and stable grid connection operation of the system can be achieved.

[0006] The present invention is achieved through the following technical solutions:

[0007] A grid-connected control method for a four-quadrant inverter, the method comprising:

[0008] Determine the grid voltage phase sequence and phase reference angle of the grid voltage signal using a three-phase phase-locked loop in a DQ coordinate system;

[0009] Determine the voltage input signal and initialization angle of the SOGI phase-locked loop according to the grid voltage phase sequence and the phase reference angle, use the SOGI phase-locked loop to phase-lock the grid voltage whose total harmonic distortion rate exceeds the preset distortion threshold, and output a grid-connected feedforward signal when the grid voltage and the grid voltage phase sequence meet the grid-connected conditions;

[0010] According to the preset classification rules, each power unit in the four-quadrant inverter is divided into different grid-connected levels, and based on the grid-connected feedforward signal, the phase-locked four-quadrant inverter controls the switching devices according to the preset grid-connected mode to realize graded grid-connected control of power units of different grid-connected levels.

[0011] Furthermore, before determining the grid voltage phase sequence and the phase reference angle of the grid voltage signal by using the three-phase phase-locked loop in the DQ coordinate system, the method further includes:

[0012] An RC filter circuit is arranged between the grid bus output terminal and the inverter input terminal to filter the grid voltage to obtain a filtered grid voltage.

[0013] Furthermore, the preset classification rule is specifically to classify the levels in sequence according to the cascade order with the inverter in the four-quadrant inverter; different grid-connected levels include first-level units, second-level units, third-level units and fourth-level units.

[0014] Furthermore, the preset grid-connection modes include manually confirmed hierarchical grid-connection, timed automatic hierarchical grid-connection, and automatic hierarchical grid-connection after power grid recovery.

[0015] Further, the manual confirmation of hierarchical grid connection specifically includes: controlling the operation of the switch devices of each power unit in the first-level unit based on the grid-connected feedforward signal to realize grid voltage grid connection control of each power unit in the first-level unit;

[0016] After detecting that the grid voltage of each power unit of the first-stage unit is connected to the grid and stable, a grid connection enable signal is input by the host computer, and the grid connection control of the second-stage unit is controlled based on the grid connection enable signal.

[0017] Furthermore, the timing automatic hierarchical grid connection is specifically as follows: based on the grid connection feedforward signal, the switch devices of each power unit in the first-level unit are controlled to work, so as to realize the grid voltage grid connection control of each power unit in the first-level unit;

[0018] After detecting that the grid voltage of each power unit of the first-stage unit is connected to the grid stably, a grid connection enable signal is output at a preset time interval, and the grid connection control of the second-stage unit is controlled based on the grid connection enable signal.

[0019] Furthermore, the automatic hierarchical grid connection of the power grid recovery is specifically as follows: based on the grid connection feedforward signal, the switch devices of each power unit in the first-level unit are controlled to work, so as to realize the grid voltage grid connection control of each power unit in the first-level unit;

[0020] After detecting that the grid voltage of each power unit of the first-stage unit is connected to the grid and stable, a grid connection enable signal is output, and the grid connection control of the second-stage unit is controlled based on the grid connection enable signal.

[0021] The present invention further provides a grid-connected control system for a four-quadrant frequency converter, which is used in any one of the above-mentioned grid-connected control methods for a four-quadrant frequency converter, and the system comprises:

[0022] The first module is used to determine the grid voltage phase sequence and phase reference angle of the grid voltage signal by using a three-phase phase-locked loop in a DQ coordinate system;

[0023] The second module is used to determine the voltage input signal and initialization angle of the SOGI phase-locked loop according to the grid voltage phase sequence and the phase reference angle, use the SOGI phase-locked loop to phase-lock the grid voltage whose total harmonic distortion rate exceeds the preset distortion threshold, and output the grid-connected feedforward signal when the grid voltage and the grid voltage phase sequence meet the grid-connected conditions;

[0024] The third module is used to divide each power unit in the four-quadrant inverter into different grid-connected levels based on the preset grading rules, and in response to the grid-connected feedforward signal, the phase-locked four-quadrant inverter controls the switching devices according to the preset grid-connected mode to realize graded grid-connected control of power units of different grid-connected levels.

[0025] The present invention also provides a computer device, comprising a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of any one of the above-mentioned methods when executing the computer program.

[0026] The present invention also provides a computer-readable storage medium having a computer program stored thereon, and when the computer program is executed by a processor, the steps of any one of the methods described above are implemented.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] In the present invention, by adopting a dual phase-locked loop mode consisting of a three-phase phase-locked loop and a SOGI phase-locked loop in a DQ coordinate system, stable and accurate phase locking and control are achieved under different phase sequences and large harmonic voltages; at the same time, by dividing each power unit in the four-quadrant inverter into different grid-connected levels and adopting a graded grid-connected strategy, the current impact in the initial stage of grid connection can be effectively reduced, and the grid current is lower than the on-site protection current value during the grid connection process, and the grid voltage amplitude is quickly restored; thus, by adopting this technical solution, various abnormal situations such as excessive impact current, significant reduction in grid voltage, increased grid harmonics, and instability of system grid-connected control that occur during the grid-connected process of a large-capacity four-quadrant inverter under a weak grid can be effectively solved, and stable grid-connected operation of the system can be achieved; at the same time, by adding an RC filtering circuit before grid connection, the grid voltage harmonics will be significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0030] Figure 1 is a method flow chart of a grid-connected control method for a four-quadrant frequency converter in this embodiment;

[0031] Figure 2 Schematic diagram of the inverter topology structure in a grid-connected control method for a four-quadrant inverter in this embodiment;

[0032] Figure 3 Schematic diagram of a power unit topology structure in a grid-connected control method for a four-quadrant inverter in this embodiment;

[0033] Figure 4 is a schematic diagram of an example inverter topology structure given in this embodiment;

[0034] Figure 5 This is a schematic diagram of the grid voltage waveform before adding the RC filter circuit in this embodiment;

[0035] Figure 6 This is a schematic diagram of the voltage waveform of the grid connected to the grid after adding an RC filtering circuit in this embodiment;

[0036] Figure 7 A schematic diagram of a grid voltage waveform when the grid connection control method provided by this embodiment is not adopted;

[0037] Figure 8 A schematic diagram of a grid voltage waveform using the grid connection control method provided by this embodiment;

[0038] Fig. 9 A schematic diagram of a grid-side current waveform when the grid-connected control method provided in this embodiment is not adopted;

[0039] Fig.10 A schematic diagram of a grid-side current waveform using the grid-connected control method provided in this embodiment;

[0040] Fig.11 A schematic diagram of a bus voltage amplitude waveform of each power unit when the grid-connected control method provided by this embodiment is not adopted;

[0041] Fig.12 A schematic diagram of a bus voltage amplitude waveform of each power unit using the grid-connected control method provided by this embodiment;

[0042] Fig.13 This is a schematic diagram of module connection of a grid-connected control system for a four-quadrant frequency converter in this embodiment;

[0043] Fig.14 It is a structural schematic diagram of a computer device in this embodiment. DETAILED DESCRIPTION

[0044] The following is a description of exemplary embodiments of the present disclosure in conjunction with the accompanying drawings, including various details of the embodiments of the present disclosure to facilitate understanding, which should be considered as merely exemplary. Therefore, it should be recognized by those of ordinary skill in the art that various changes and modifications may be made to the embodiments described herein without departing from the scope of the present disclosure. Similarly, for the sake of clarity and conciseness, the description of well-known functions and structures is omitted in the following description.

[0045] In the present disclosure, unless otherwise specified, the use of the terms "first", "second", etc. to describe various elements is not intended to limit the positional relationship, timing relationship, or importance relationship of these elements, and such terms are only used to distinguish one element from another element. In some examples, the first element and the second element may refer to the same instance of the element, and in some cases, based on the description of the context, they may also refer to different instances.

[0046] The terms used in the description of various examples in this disclosure are only for the purpose of describing specific examples and are not intended to be limiting. Unless the context clearly indicates otherwise, if the number of elements is not specifically limited, the element can be one or more. In addition, the term "and / or" used in this disclosure covers any one of the listed items and all possible combinations.

[0047] Example 1

[0048] See also Figure 1As shown, this embodiment also provides a grid-connected control method for a four-quadrant inverter, the method comprising:

[0049] S1: Determine the grid voltage phase sequence and phase reference angle of the grid voltage signal using a three-phase phase-locked loop in a DQ coordinate system;

[0050] It should be noted that, in this embodiment, the phase reference angle refers to the angle between the d-axis and a reference direction (for example, the initial phase direction of the A-phase voltage) in the three-phase phase-locked loop based on the DQ coordinate system; the positive or negative phase difference Δθ obtained by the three-phase phase-locked loop confirms the grid voltage phase sequence.

[0051] S2: Determine the voltage input signal and initialization angle of the SOGI phase-locked loop according to the grid voltage phase sequence and the phase reference angle, use the SOGI phase-locked loop to phase-lock the grid voltage whose total harmonic distortion rate exceeds the preset distortion threshold, and output a grid-connected feedforward signal when the grid voltage and the grid voltage phase sequence meet the grid-connected conditions;

[0052] It should be noted that, in this embodiment, the preset distortion threshold is set to 15% of the harmonic content in the grid voltage, and in other embodiments, it can also be set to other distortion thresholds, and no excessive restrictions are made here; the three-phase phase-locked loop in the traditional DQ coordinate system can automatically complete phase locking in the positive and negative sequence states, but when the grid harmonics are too high, the phase-locked angle is prone to inaccurate; and the SOGI phase-locked loop can better complete accurate phase locking in larger grid harmonics, but it cannot automatically determine the positive and negative sequence of the grid; therefore, firstly, the three-phase phase-locked loop in the DQ coordinate system is used to determine the grid voltage phase sequence and the phase reference angle, and then The SOGI phase-locked loop is used to accurately phase-lock the voltage with larger harmonics, and thus the combination of the three-phase phase-locked loop and the SOGI phase-locked loop in the DQ coordinate system can achieve accurate phase-locking of the voltage with larger harmonics under different phase sequence states, thereby improving the control stability of the system; at the same time, it should be noted that the use of the three-phase phase-locked loop in the DQ coordinate system to determine the grid voltage phase sequence and the phase reference angle of the grid voltage signal, and the use of the SOGI phase-locked loop to phase-lock the grid voltage whose total harmonic distortion rate exceeds a preset distortion threshold, are both conventional technical means in the field and will not be elaborated here.

[0053] For details, see Figure 2 As shown, this embodiment provides a topological structure diagram of a cascaded four-quadrant high-voltage inverter. The cascaded four-quadrant high-voltage inverter is powered by a 10kV bus, and a phase-shifting transformer is used on the grid side to supply power to each power unit. Each phase of a single inverter is cascaded by 6 power units, three-phase star connection, and output to three ports of the synchronous / asynchronous motor stator; see Figure 3As shown, this embodiment also provides a power unit topology diagram of a cascaded four-quadrant high-voltage inverter, where each power unit is powered by an independent set of secondary windings of a phase-shifting transformer, converts AC input into DC through a three-phase full-bridge rectifier, and stores energy in a capacitor bank; the rectifier side of the power unit receives a PWM signal sent by the main control system and controls the working state of the IGBT to output a PWM voltage waveform to achieve active grid-connected rectification.

[0054] S3: According to the preset classification rules, each power unit in the four-quadrant inverter is divided into different grid-connected levels, and based on the grid-connected feedforward signal, the phase-locked four-quadrant inverter controls the switching devices according to the preset grid-connected mode to realize graded grid-connected control of power units of different grid-connected levels.

[0055] Specifically, in this embodiment, by adopting a dual phase-locked loop mode consisting of a three-phase phase-locked loop and a SOGI phase-locked loop in a DQ coordinate system, stable and accurate phase locking and control are achieved under different phase sequences and large harmonic voltages; at the same time, by dividing each power unit in the four-quadrant inverter into different grid-connected levels and adopting a graded grid-connected strategy, the current impact in the initial stage of grid connection can be effectively reduced, and the grid current can be lower than the on-site protection current value during the grid-connected process, and the grid voltage amplitude can be quickly restored; thus, by adopting this technical solution, various abnormal situations such as excessive impact current, significantly reduced grid voltage, increased grid harmonics, and instability of system grid-connected control that occur during the grid-connected process of a large-capacity four-quadrant inverter under a weak grid can be effectively solved, thereby achieving stable grid-connected operation of the system.

[0056] Furthermore, before determining the grid voltage phase sequence and the phase reference angle of the grid voltage signal by using the three-phase phase-locked loop in the DQ coordinate system, the method further includes:

[0057] An RC filter circuit is arranged between the grid bus output terminal and the inverter input terminal to filter the grid voltage to obtain a filtered grid voltage.

[0058] Specifically, in this embodiment, by adding an RC filter circuit before connecting to the grid, the grid voltage harmonics can be significantly improved.

[0059] Furthermore, the preset classification rule is specifically to classify the levels in sequence according to the cascade order with the inverter in the four-quadrant inverter; different grid-connected levels include first-level units, second-level units, third-level units and fourth-level units.

[0060] It should be noted that in this embodiment, the grid-connected level of the power unit is divided into four levels. In other embodiments, it can also be divided into two levels, three levels, five levels or six levels according to specific actual needs, and no excessive restrictions are made here.

[0061] Furthermore, the preset grid-connection modes include manually confirmed hierarchical grid-connection, timed automatic hierarchical grid-connection, and automatic hierarchical grid-connection after power grid recovery.

[0062] It should be noted that, in this embodiment, manual confirmation of hierarchical grid-connection is usually used in the on-site experimental debugging stage, which can better observe the data and adjust the parameters of various states; the timed automatic hierarchical grid-connection is usually used under the condition of low grid drop and fast recovery, and can quickly complete the full-level unit connection in a fixed time; the grid recovery automatic hierarchical grid-connection is usually used under the condition of large grid drop and inconsistent grid recovery time, which can ensure that the grid voltage is always in a stable state every time each unit is connected to the grid.

[0063] Further, the manual confirmation of hierarchical grid connection specifically includes: controlling the operation of the switch devices of each power unit in the first-level unit based on the grid-connected feedforward signal to realize grid voltage grid connection control of each power unit in the first-level unit;

[0064] After detecting that the grid voltage of each power unit of the first-stage unit is connected to the grid and stable, a grid connection enable signal is input by the host computer, and the grid connection control of the second-stage unit is controlled based on the grid connection enable signal.

[0065] It should be noted that in this embodiment, the host computer adopts a computer device or a mobile terminal device with an operating system. The staff can receive the grid voltage grid-connected stability signal of each power unit detected in the first-level unit through the host computer, and then input the corresponding grid-connected enable signal to control the grid-connected enable of the next level.

[0066] Furthermore, the timing automatic hierarchical grid connection is specifically as follows: based on the grid connection feedforward signal, the switch devices of each power unit in the first-level unit are controlled to work, so as to realize the grid voltage grid connection control of each power unit in the first-level unit;

[0067] After detecting that the grid voltage of each power unit of the first-stage unit is connected to the grid stably, a grid connection enable signal is output at a preset time interval, and the grid connection control of the second-stage unit is controlled based on the grid connection enable signal.

[0068] It should be noted that, in the present embodiment, the interval time is set by the timer, and the timer will be started after it is detected that the grid voltage of each power unit of the first-level unit is connected to the grid and stable. When the timer reaches the set time interval, the grid-connected enable signal will be automatically output, and the grid-connected control of the second-level unit will be controlled based on the grid-connected enable signal. It should also be noted that, in the present embodiment, the preset time interval is 0.2s, and in other embodiments it can also be set to 0.1s, 0.3s, 0.4s or 0.5s, without making too many restrictions here.

[0069] Furthermore, the automatic hierarchical grid connection of the power grid recovery is specifically as follows: based on the grid connection feedforward signal, the switch devices of each power unit in the first-level unit are controlled to work, so as to realize the grid voltage grid connection control of each power unit in the first-level unit;

[0070] After detecting that the grid voltage of each power unit of the first-stage unit is connected to the grid and stable, a grid connection enable signal is output, and the grid connection control of the second-stage unit is controlled based on the grid connection enable signal.

[0071] For details, see Figure 4 As shown, in this embodiment, a 20MVA / 10kV high-voltage cascade four-quadrant inverter is taken as an example. The four-quadrant inverter is used for a motor test bench in a motor factory. The system grid capacity in the factory is only 3150kVA. Originally, the grid and the inverter were directly connected. In the actual grid-connected process, the grid harmonics were large and stable grid-connected control could not be achieved. Then refer to Figure 4 As shown, firstly, an RC filter circuit is added externally, where the filter resistor value is selected as R = 3.3Ω, and the filter capacitor value is selected as C = 15.8uf. The simulation diagram of the grid-connected voltage waveform before and after adding the RC filter circuit is shown in Figure 5 and Figure 6 As shown;

[0072] In the actual grid connection process, see Figure 7 As shown, if the grid-connected control method of this embodiment is not adopted, at the actual grid-connected moment, the grid voltage amplitude is significantly lowered, the instantaneous voltage peak is reduced by up to about 5000V, and the recovery time is long, which will seriously affect the normal operation of other equipment in the factory; at the same time, see Fig. 9 As shown, the instantaneous impact current of grid connection is extremely high, and the high-voltage switch cabinet protection tripping occurred many times on site due to excessive impact;

[0073] Then, by adopting the grid-connected control method of this embodiment and using the timed grid-connected mode, it is set that after the previous unit is connected to the grid, the next unit is connected to the grid 0.2s later, until all power units complete the grid-connected function. At the same time, in the grid-connected control, the input current of each grid-connected unit is quickly followed by closed-loop regulation; the grid voltage at the time of grid connection is referred to Figure 8 As shown, it can be seen that after adopting the grid-connected control method provided by this embodiment, the voltage drop amplitude becomes smaller, and the voltage recovery and stabilization time is fast, and there is no obvious impact on the power consumption of other equipment on site; at the same time, see Fig.10 After changing to hierarchical grid connection, the actual grid connection capacity is reduced each time, and the impact current is also significantly reduced;

[0074] Finally, see Fig.11 and Fig.12As shown, by comparing the unit bus voltages in the two modes of adopting and not adopting the grid-connected control method provided in this embodiment, it is not difficult to see that the use of the hierarchical grid-connected mode has no effect on the unit bus voltage control in actual applications, and the hierarchical grid-connected mode can be completed within only 1.5 seconds, without any impact on the actual on-site operation.

[0075] Example 2

[0076] See also Fig.13 As shown, the present invention also provides a grid-connected control system for a four-quadrant frequency converter, which is used in any one of the above-mentioned grid-connected control methods for a four-quadrant frequency converter, and the system includes:

[0077] The first module 100 is used to determine the grid voltage phase sequence and the phase reference angle of the grid voltage signal by using a three-phase phase-locked loop in a DQ coordinate system;

[0078] The second module 200 is used to determine the voltage input signal and the initialization angle of the SOGI phase-locked loop according to the grid voltage phase sequence and the phase reference angle, use the SOGI phase-locked loop to phase-lock the grid voltage whose total harmonic distortion rate exceeds the preset distortion threshold, and output a grid-connected feedforward signal when the grid voltage and the grid voltage phase sequence meet the grid-connected conditions;

[0079] The third module 300 is used to divide each power unit in the four-quadrant inverter into different grid-connected levels based on a preset grading rule, and in response to a grid-connected feedforward signal, the phase-locked four-quadrant inverter controls the switching devices according to a preset grid-connected mode to implement graded grid-connected control of power units of different grid-connected levels.

[0080] It should be noted that the modules in the system of Example 2 correspond to the steps in the method of Example 1. The steps in the method of Example 1 have been described in detail in Example 1. In this Example 2, the contents of the modules in the system will not be described in detail.

[0081] Example 3

[0082] See also Fig.14 As shown, this embodiment further provides a computer device, including a memory 1005 and a processor 1001, wherein the memory 1005 stores a computer program, and the processor 1001 implements the steps of any one of the above methods when executing the computer program.

[0083] It should be noted that the processor 1001 is used to execute the steps in the above method embodiments according to the instructions in the program code. Alternatively, the processor 1001 implements the functions of each module / unit in the above system / device embodiments when executing the computer program.

[0084] Specifically, in this embodiment, the computer program may be divided into one or more modules / units, one or more modules / units are stored in the memory 1005, and are executed by the processor 1001 to complete the present application. One or more modules / units may be a series of computer program instruction segments that can complete specific functions, and the instruction segments are used to describe the execution process of the computer program in the terminal device.

[0085] The terminal device may be a computing device such as a desktop computer, a notebook, a PDA, a cloud server, etc. The terminal device may include, but is not limited to, a processor 1001 and a memory 1005. Those skilled in the art will appreciate that this does not constitute a limitation on the terminal device, and may include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, the terminal device may also include an input / output device 1003, a network access device 1002, a bus 1006, etc.

[0086] The processor 1001 may be a central processing unit (CPU), or other general-purpose processors 1001, digital signal processors 1001 (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor 1001 may be a microprocessor or any conventional processor, etc.

[0087] The memory 1005 may be an internal storage unit of the terminal device, such as a hard disk or memory of the terminal device. The memory 1005 may also be an external storage device 1004 of the terminal device, such as a plug-in hard disk, a smart memory card (SmartMedia Card, SMC), a secure digital (Secure Digital, SD) card, a flash card (Flash Card), etc. equipped on the terminal device. Further, the memory 1005 may also include both the internal storage unit of the terminal device and the external storage device 1004. The memory 1005 is used to store computer programs and other programs and data required by the terminal device. The memory 1005 may also be used to temporarily store data that has been output or is to be output.

[0088] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the above-described systems, systems and units can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0089] Example 4

[0090] This embodiment provides a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps of any one of the above methods are implemented.

[0091] Among them, the computer-readable storage medium can be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared or semiconductor system, system or device, or any combination of the above. More specific examples of computer-readable storage media (a non-exhaustive list) include: an electrical connection with one or more wires, a portable computer disk, a hard disk. Random Access Memory (RAM), Read-Only Memory (ROM), Erasable Programmable Read Only Memory (EPROM), registers, hard disks, optical fibers, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the above, or any other form of computer-readable storage medium known in the art.

[0092] An exemplary storage medium is coupled to a processor so that the processor can read information from the storage medium and write information to the storage medium. Of course, the storage medium can also be a component of the processor. The processor and the storage medium can be located in an application-specific integrated circuit (ASIC). In an embodiment of the present invention, a computer-readable storage medium can be any tangible medium containing or storing a program that can be used by or in combination with an instruction execution system, system, or device.

[0093] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A grid-connected control method for a four-quadrant inverter, characterized in that the method include: Determine the grid voltage phase sequence and phase reference angle of the grid voltage signal using a three-phase phase-locked loop in a DQ coordinate system; Determine the voltage input signal and initialization angle of the SOGI phase-locked loop according to the grid voltage phase sequence and the phase reference angle, use the SOGI phase-locked loop to phase-lock the grid voltage whose total harmonic distortion rate exceeds the preset distortion threshold, and output a grid-connected feedforward signal when the grid voltage and the grid voltage phase sequence meet the grid-connected conditions; According to the preset classification rules, each power unit in the four-quadrant inverter is divided into different grid-connected levels, and based on the grid-connected feedforward signal, the phase-locked four-quadrant inverter controls the switching devices according to the preset grid-connected mode to realize graded grid-connected control of power units of different grid-connected levels.

2. A grid-connected control method for a four-quadrant frequency converter according to claim 1, characterized in that: Before determining the grid voltage phase sequence and the phase reference angle of the grid voltage signal by using the three-phase phase-locked loop in the DQ coordinate system, the method further includes: An RC filter circuit is arranged between the grid bus output terminal and the inverter input terminal to filter the grid voltage to obtain a filtered grid voltage.

3. A grid-connected control method for a four-quadrant frequency converter according to claim 1, characterized in that: The preset classification rule is specifically to classify the units according to the cascade order with the inverter in the four-quadrant inverter; different grid-connected levels include first-level units, second-level units, third-level units and fourth-level units.

4. A grid-connected control method for a four-quadrant frequency converter according to claim 3, characterized in that: The preset grid-connection modes include manually confirmed hierarchical grid-connection, scheduled automatic hierarchical grid-connection, and automatic hierarchical grid-connection after power grid recovery.

5. A grid-connected control method for a four-quadrant frequency converter according to claim 4, characterized in that: Manual confirmation of hierarchical grid connection specifically includes: controlling the operation of the switch devices of each power unit in the first-level unit based on the grid-connected feedforward signal to realize grid voltage grid connection control of each power unit in the first-level unit; After detecting that the grid voltage of each power unit of the first-stage unit is connected to the grid and stable, a grid connection enable signal is input by the host computer, and the grid connection control of the second-stage unit is controlled based on the grid connection enable signal.

6. A grid-connected control method for a four-quadrant frequency converter according to claim 4, characterized in that: The timing automatic hierarchical grid connection is specifically as follows: based on the grid-connected feedforward signal, the switch devices of each power unit in the first-level unit are controlled to work, so as to realize the grid voltage grid connection control of each power unit in the first-level unit; After detecting that the grid voltage of each power unit of the first-stage unit is connected to the grid stably, a grid connection enable signal is output at a preset time interval, and the grid connection control of the second-stage unit is controlled based on the grid connection enable signal.

7. A grid-connected control method for a four-quadrant frequency converter according to claim 4, characterized in that: The automatic hierarchical grid connection of power grid recovery is specifically as follows: based on the grid connection feedforward signal, the switch devices of each power unit in the first-level unit are controlled to work, so as to realize the grid voltage grid connection control of each power unit in the first-level unit; After detecting that the grid voltage of each power unit of the first-stage unit is connected to the grid and stable, a grid connection enable signal is output, and the grid connection control of the second-stage unit is controlled based on the grid connection enable signal.

8. A grid-connected control system for a four-quadrant frequency converter, characterized in that: The system is used in a grid-connected control method for a four-quadrant inverter according to any one of claims 1 to 7, and the system comprises: The first module is used to determine the grid voltage phase sequence and phase reference angle of the grid voltage signal by using a three-phase phase-locked loop in a DQ coordinate system; The second module is used to determine the voltage input signal and initialization angle of the SOGI phase-locked loop according to the grid voltage phase sequence and the phase reference angle, use the SOGI phase-locked loop to phase-lock the grid voltage whose total harmonic distortion rate exceeds the preset distortion threshold, and output the grid-connected feedforward signal when the grid voltage and the grid voltage phase sequence meet the grid-connected conditions; The third module is used to divide each power unit in the four-quadrant inverter into different grid-connected levels based on the preset grading rules, and in response to the grid-connected feedforward signal, the phase-locked four-quadrant inverter controls the switching devices according to the preset grid-connected mode to realize graded grid-connected control of power units of different grid-connected levels.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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