SHEPWM control method and system of open-winding dual-converter grid-connected system

Abstract

The application discloses a SHEPWM control method and system of an open-winding double-converter grid-connected system, and the method comprises the following steps: acquiring grid voltage and voltage angle of a grid-connected point of the open-winding double-converter grid-connected system; calculating a modulation ratio and an output current given value according to the grid voltage of the grid-connected point; finding an optimal switching angle combination adaptive to the modulation ratio, the voltage angle and the switching angle number through searching an optimal switching angle lookup table, and delivering the optimal switching angle combination to a synchronous pulse generation module; generating 24-path SHEPWM voltage synchronous pulse signals through the synchronous pulse generation module, and delivering the 24-path SHEPWM voltage synchronous pulse signals to switching devices of two converters respectively to complete real-time control on the switching devices. The application aims at reducing photovoltaic system grid-connected voltage harmonics, reducing switching times of power devices, reducing overall switching loss of the system, improving overall efficiency of the system and overall harmonic performance of the system.

Description

Technical Field

[0001] This invention belongs to the field of voltage control technology for open-winding dual converters in electrical engineering, specifically relating to a SHEPWM control method and system for an open-winding dual converter grid-connected system. Background Technology

[0002] Photovoltaic (PV) power generation is a technology that directly converts light energy into electrical energy using the photovoltaic effect of semiconductors. A PV power generation system mainly consists of three parts: solar cell modules, a controller, and a converter (inverter). In a PV power generation system, the converter is the main source of harmonics, and its control quality largely determines whether the power quality generated by the PV power generation can meet the grid's demands. Since its inception, the open-winding topology has been widely used in various power conversion scenarios due to its advantages such as dual converters sharing the power load, high control freedom, and low output voltage harmonics. Therefore, the open-winding topology dual-converter system can be applied to PV power generation systems to achieve even lower system output voltage harmonics.

[0003] Control methods for grid-connected systems include SPWM (Sinusoidal Pulse Width Modulation), SVPWM (Space Vector Pulse Width Modulation), and SHEPWM (Specific Harmonic Elimination Pulse Width Modulation). Among these, SHEPWM control calculates and solves an nth-order equation composed of the (n-1)th harmonic of the system output voltage, deriving n combinations of switching angles excluding even-order terms and the (n-1)th harmonic, thereby achieving harmonic suppression of the system output voltage. Compared to traditional control methods such as SPWM and SVPWM, it exhibits superior harmonic characteristics, offering advantages such as better output voltage harmonic characteristics and lower switching frequency under the same output waveform quality conditions. It is an effective method for solving a series of problems related to grid-connected harmonics and device switching losses. Existing technology discloses a reactive power compensation control strategy for an open-winding dual-converter photovoltaic power generation system. By combining a mathematical model of the open-winding dual-converter photovoltaic power generation system, a control scheme suitable for the system is proposed to achieve the maximum power output of each photovoltaic array. A simple and effective reactive power compensation scheme is also proposed to avoid over-modulation. However, this existing technology does not consider the overall output voltage harmonic quality of the system, and its topology is mainly an independent dual-converter topology, which cannot maximize the improvement of grid-connected voltage quality. For SHEPWM grid-connected technology under an open-winding topology, how to leverage the advantages of open-winding topology and SHEPWM technology in grid-connected harmonic suppression, reduce the total harmonic distortion of the grid-connected voltage, and optimize the system's harmonic performance is a key technical problem that urgently needs to be solved. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a SHEPWM control method and system for a grid-connected system with an open-winding dual converter, which addresses the above-mentioned problems in the prior art. The present invention aims to reduce the grid-connected voltage harmonics of the photovoltaic system, effectively reduce the switching frequency of power devices, reduce the overall switching losses of the system, and improve the overall system efficiency and overall harmonic performance.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A SHEPWM control method for an open-winding dual-converter grid-connected system includes the following steps: S101, obtain the grid voltage and voltage angle at the grid connection point of the open-winding dual converter grid-connected system; S102, calculate the modulation ratio and output current setpoint based on the grid voltage at the grid connection point; S103, the calculated modulation ratio, combined with the voltage angle and the preset number of switching angles, is used to find the optimal switching angle combination that matches the three variables of modulation ratio, voltage angle and number of switching angles for the two converters in the open winding dual converter grid-connected system by looking up the optimal switching angle lookup table, and then the combination is sent to the synchronization pulse generation module; the optimal switching angle lookup table stores the switching status of N switching angles of each phase under different modulation ratio conditions within 1 / 4 cycle; S104 generates 24 SHEPWM voltage synchronization pulse signals based on the optimal switching angle combination and the output current setpoint through the synchronization pulse generation module, and sends them to the switching devices of the two converters to complete the real-time control of the switching devices.

[0006] Optionally, the functional expression for calculating the modulation ratio m in step S102 is: ; in, The modulation ratio, and Let dq-axis components be the grid voltage at the grid connection point. This refers to the bus voltage of the two converters in a grid-connected system with open winding dual converters.

[0007] Optionally, the calculation function expression for the output current setpoint in step S102 is: ; ; in, and These represent the given output active power and reactive power, respectively. and Let dq-axis components be the grid voltage at the grid connection point. and The dq-axis component is the given value of the output current.

[0008] Optionally, before step S103, an optimal switching angle lookup table is generated, which includes the optimal switching angle combination that matches the three variables: modulation ratio, voltage angle, and number of switching angles. S201, for the first converter in a grid-connected system with two open-winding dual converters, the following switching angle equation is established: ; in, The bus voltage of the two converters in the open-winding dual-converter grid-connected system. The modulation ratio, For the number of switching angles, ~ They are respectively number 1 to One switching angle; S202, with modulation ratio A value of 1 represents the maximum modulation ratio. A value of 0 represents the minimum modulation ratio, which is then subdivided into a specified number of parts. For each part of the modulation ratio... The Newton-Raphson method was used to optimize the switching angle equation of the first converter, and the modulation ratio was obtained. The switching status of N switches under the current condition is determined within 1 / 4 cycle and stored in the optimal switching angle lookup table of the first converter. S203, for the optimal switching angle lookup table of the first converter, subtract the given phase difference from all the switching angles to generate a new optimal switching angle lookup table, which is then used as the optimal switching angle lookup table for the second converter.

[0009] Optionally, the phase difference given in step S203 is 120° to eliminate the common-mode third pulsation of the output voltage, and the given voltage amplitude of the two converters is 1.15 times the actual output given voltage amplitude U* of the system.

[0010] Optionally, the calculation function expression for the voltage at the grid connection point of the open-winding dual-converter grid-connected system is as follows: ; in, , and These are the A, B, and C phase voltages at the grid connection point, respectively. , and These are the A, B, and C phase voltages output from the first converter, respectively. , and These are the A, B, and C phase voltages output from the second converter, respectively.

[0011] A SHEPWM control system for an open-winding dual-converter grid-connected system includes: The voltage angle calculation program module is used to obtain the grid voltage and voltage angle at the grid connection point of the open-winding dual converter grid-connected system; The modulation ratio and current calculation module is used to calculate the modulation ratio and output current setpoint based on the grid voltage at the grid connection point. The lookup table module is used to take the calculated modulation ratio, combine it with the voltage angle and the preset number of switching angles, and find the optimal switching angle combination that matches the three variables of modulation ratio, voltage angle and number of switching angles for the two converters in the open winding dual converter grid-connected system by looking up the optimal switching angle lookup table, and then send it to the synchronization pulse generation module; the optimal switching angle lookup table stores the switching status of N switching angles of each phase under different modulation ratio conditions within 1 / 4 cycle; The synchronous pulse generation program module is used to generate 24 SHEPWM voltage synchronous pulse signals based on the optimal switching angle combination and the output current setpoint, and send them to the switching devices of the two converters to complete the real-time control of the switching devices.

[0012] Furthermore, the present invention also provides a SHEPWM control system for an open-winding dual-converter grid-connected system, including a microprocessor and a memory interconnected thereto, wherein the microprocessor is programmed or configured to execute the SHEPWM control method for the open-winding dual-converter grid-connected system.

[0013] Furthermore, the present invention also provides a computer-readable storage medium storing a computer program or instructions that are programmed or configured to execute the SHEPWM control method of the open-winding dual converter grid-connected system by a processor.

[0014] Furthermore, the present invention also provides a computer program product, including a computer program or instructions, which are programmed or configured to execute the SHEPWM control method of the open-winding dual converter grid-connected system via a processor.

[0015] Compared with existing technologies, the present invention mainly achieves the following beneficial effects: The method of the present invention includes obtaining the grid voltage and voltage angle at the grid connection point of the open-winding dual-converter grid-connected system; calculating the modulation ratio and output current setpoint based on the grid voltage at the grid connection point; finding the optimal switching angle combination that matches the three variables of modulation ratio, voltage angle, and number of switching angles for the two converters of the open-winding dual-converter grid-connected system by searching an optimal switching angle lookup table and sending it to the synchronization pulse generation module; generating 24 SHEPWM voltage synchronization pulse signals through the synchronization pulse generation module and sending them to the switching devices of the two converters respectively to complete the real-time control of the switching devices. Through the above-mentioned SHEPWM control strategy, the present invention can effectively reduce the grid-connected voltage harmonics of the photovoltaic system. Unlike the complex control methods of traditional open-winding topologies, this control method is simple and easy to implement. On the other hand, under the same harmonic requirements, this method can effectively reduce the switching frequency of power devices, reduce the overall switching loss of the system, improve the overall system efficiency, and improve the overall harmonic performance of the system. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the topology of the grid-connected system with open winding dual converters in an embodiment of the present invention.

[0017] Figure 2 This is a schematic diagram of the basic process of the method in an embodiment of the present invention.

[0018] Figure 3 This is a simulated phase voltage waveform output by the method of this embodiment of the invention, wherein... Figure 3 (a) is the waveform of the combined total phase voltage. Figure 3 (b) is a waveform diagram of the output phase voltage of converter #1 and converter #2.

[0019] Figure 4 This is a diagram of the switching angle sequence calculated based on the constraint equations of converter #1 in an embodiment of the present invention.

[0020] Figure 5 The diagram shows the phase voltage harmonic waveforms of the traditional space vector modulation method under an experiment with 5 switching cycles (N=5).

[0021] Figure 6 The diagram shows the phase voltage harmonic waveform of the method of this invention under the experiment of switching times (N=5). Detailed Implementation

[0022] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings in the embodiments of the present invention.

[0023] like Figure 1As shown, the open-winding dual-converter grid-connected system in this embodiment includes a photovoltaic panel, converters #1-#2, filter inductors #1-#2, and a grid-connected transformer. The photovoltaic panel is the power source for the entire system, and its output DC voltage is directly used as the bus voltages Udc1 and Udc2 of converters #1 and #2. Converters #1 and #2 are midpoint clamped three-level converters. To reduce interference caused by non-algorithm factors, the midpoint fluctuation problem will not be considered in this scheme. The capacitors C1, C2, C3, and C4 in converters #1 and #2 are regarded as DC sources, and T1, T2, T3, T4, T5, T6, T7, and T8 are the power switching devices of phase A in converters #1 and #2, respectively. The switching angles generated by the SHEPWM control algorithm are achieved by controlling the on / off state of the three-phase power devices. D1, D2, D3, D4 are the freewheeling diodes of converters #1 and #2, respectively, providing current loops. To achieve SHEPWM control in the open-winding dual-converter grid-connected system, the SHEPWM control strategy needs to be applied to converters #1 and #2 respectively. After the bus voltages Udc1 and Udc2 are input, the DC voltage is distributed by converters #1 and #2 according to a set of switching angles issued by the control system to generate output voltage signals. The voltage signals are then controlled by the power device drive module to generate optimized grid-connected voltage outputs. The grid-connected voltage outputs of converters #1 and #2 are filtered by filter inductors #1 and #2 respectively and connected to the primary side of the grid-connected transformer from both ends, and then connected to the grid through the secondary winding of the grid-connected transformer. The SHEPWM control method of the open-winding dual-converter grid-connected system in this embodiment will be further explained below.

[0024] like Figure 2 As shown, the SHEPWM control method for the open-winding dual-converter grid-connected system in this embodiment includes the following steps: S101, obtain the grid voltage and voltage angle at the grid connection point of the open-winding dual converter grid-connected system; S102, calculate the modulation ratio and output current setpoint based on the grid voltage at the grid connection point; S103, the calculated modulation ratio, combined with the voltage angle and the preset number of switching angles, is used to find the optimal switching angle combination that matches the three variables of modulation ratio, voltage angle and number of switching angles for the two converters in the open winding dual converter grid-connected system by looking up the optimal switching angle lookup table, and then the combination is sent to the synchronization pulse generation module; the optimal switching angle lookup table stores the switching status of N switching angles of each phase under different modulation ratio conditions within 1 / 4 cycle; S104 generates 24 SHEPWM voltage synchronization pulse signals based on the optimal switching angle combination and the output current setpoint through the synchronization pulse generation module, and sends them to the switching devices of the two converters to complete the real-time control of the switching devices.

[0025] The functional expression for calculating the modulation ratio m in step S102 of this embodiment is: ; in, The modulation ratio, and Let dq-axis components be the grid voltage at the grid connection point. This refers to the bus voltage of the two converters in a grid-connected system with open winding dual converters.

[0026] The function expression for calculating the output current setpoint in step S102 of this embodiment is: ; ; in, and These represent the given output active power and reactive power, respectively. and Let dq-axis components be the grid voltage at the grid connection point. and The dq-axis component is the given value of the output current.

[0027] Given system output voltage U S Based on the open winding characteristics of the system, the system output voltage U S Equal to the output voltage of converter #1 U 1. Output voltage of converter #2 U 2 output combinations:

[0028] in, U a ~ U c These are the output voltages of phases A, B, and C, respectively. U a1 ~ U c1 These are the output voltages of the three phases A, B, and C of converter #1, respectively. U a2 ~ U c2 These are the output voltages of the three phases A, B, and C of converter #2, respectively.

[0029] In this scheme, the converter output voltage U 1 and UThe amplitudes of phases 2 and 3 are equal, but their phases differ by 120° to eliminate the common-mode voltage of the converter. For converter #1, taking phase A as an example, its SHEPWM synchronous output phase voltage, after Fourier transform and elimination of even-order harmonics using 1 / 4-cycle even symmetry and 1 / 2-cycle odd symmetry, can be expressed as: ; ; in, The output voltage of phase A after eliminating even-order harmonics, where n is the harmonic order. Let n be the amplitude of the nth harmonic voltage. Let t be the phase voltage angular velocity, and t be time. For a grid-connected system with two open-winding dual converters, the bus voltages of the two converters are given, N is the total harmonic order to be considered, and k is the number of switching angles. Let be the k-th switching angle, and satisfy: .

[0030] The basic idea of ​​the SHEPWM control strategy for converters is based on the Fourier expression of phase voltage, solving for the desired objectives. Typically, these objectives are: 1. Achieving the desired fundamental amplitude; 2. Eliminating specific harmonic amplitudes to zero. The variable in the solution equations is the switching angle. A nonlinear equation set is recommended. Unlike other systems applied to three-phase non-open winding topologies, the SHEPWM in this scheme, when applied to an open winding topology, needs to consider the zero-sequence loop introduced by the topology. Therefore, it is necessary to eliminate the 3kth voltage harmonic. Its nonlinear equations can be expressed as follows: ; Among the k switching angle variables, solving the system of equations can eliminate voltage harmonics of the k-1th order, thus obtaining the switching angles. Subsequently, the switching angles of converter #1 and converter #2 can be calculated using the same nonlinear equation. The control system generates 12 power device control pulses from the obtained switching angle signals. These pulses are then used by the drive modules in the converters to control the power devices and generate harmonic-optimized voltages. To reduce common-mode voltage, the switching angle signal of converter #1 leads the switching angle signal of converter #2 by 120°. After the modulation ratio calculation is completed, the switching angle lookup module is used to input the grid feedback angle θ and the number of switching angles N. The lookup table stores the switching status of each phase under different modulation ratio conditions for N switching angles within a 1 / 4 cycle (for example, when m=0.5, the switching status for its 5 switching angles is 5°, 15°, 35°, 60°, and 80°). The lookup table module matches the optimal switching angle combination based on three variables: modulation ratio m, voltage angle θ, and number of switching angles N. The switching angle calculation uses the SHEPWM method, a specific harmonic elimination technique. Its principle is to reduce the harmonic content of the system output voltage by using 1 / 2 odd-symmetric and 1 / 4 even-symmetric synchronous modulation and constructing constrained nonlinear equations to eliminate even-order harmonics and N-1 (N is the number of variables, i.e., the number of switching angles) harmonics. Prior to step S103 in this embodiment, an optimal switching angle lookup table is generated, which includes the optimal switching angle combination matched with the three variables: modulation ratio, voltage angle, and number of switching angles. S201, for the first converter in a grid-connected system with two open-winding dual converters, the following switching angle equation is established: ; in, The bus voltage of the two converters in the open-winding dual-converter grid-connected system. The modulation ratio, For the number of switching angles, ~ They are respectively number 1 to One switching angle; S202, with modulation ratio A value of 1 represents the maximum modulation ratio. A value of 0 represents the minimum modulation ratio, which is then subdivided into a specified number of parts. For each part of the modulation ratio... The Newton-Raphson method was used to optimize the switching angle equation of the first converter, and the modulation ratio was obtained. The switching status of N switches under the current condition is determined within 1 / 4 cycle and stored in the optimal switching angle lookup table of the first converter. S203, for the optimal switching angle lookup table of the first converter, subtract the given phase difference from all the switching angles to generate a new optimal switching angle lookup table, which is then used as the optimal switching angle lookup table for the second converter.

[0031] Assuming the number of switching angles is N, in order to eliminate the N-1 term low-order harmonics and for the open-winding system topology of the dual NPC three-level converter, since the total output voltage of the system is the result of the combination of converter #1 and converter #2, the calculation function expression for the voltage at the grid connection point of the open-winding dual converter grid-connected system described in this embodiment is as follows: ; in, , and These are the A, B, and C phase voltages at the grid connection point, respectively. , and These are the A, B, and C phase voltages output from the first converter, respectively. , and These are the A, B, and C phase voltages output from the second converter, respectively.

[0032] For the SHEPWM synchronous modulation strategy, due to the parity of its waveform, it can be known that its voltage waveform contains only odd-order sinusoidal components. Taking the synthesized phase A voltage as an example... For example, its Fourier series can be expanded as follows: ; ; in, and These are the Fourier cosine expansion coefficients, where n is the harmonic order, ω is the phase voltage angular velocity, and E is U. dc / 2. Then the amplitude of the nth harmonic of the phase voltage. U n for: ; Therefore, the Fourier series of the three-phase output voltage of the two-terminal synthesized converter can be obtained: ; in, U A ~ U C These are the combined output voltages of phases A, B, and C, respectively. U A1 ~ U C1 These are the combined output voltages of phases A, B, and C of converter #1, respectively. U A2 ~ U C2 These are the combined output voltages of phases A, B, and C of converter #2, respectively. This refers to the electrical angle phase difference between the output phase voltages of converter #1 and converter #2. In this embodiment, the electrical angle phase difference is selected to eliminate common-mode third-order pulsations. The phase difference is 120°. Since the electrical phase difference is 120°, to maintain the synthesized amplitude as a given value, the phase difference given in step S203 of this embodiment is 120° to eliminate the common-mode third-order pulsation of the output voltage. Furthermore, the given voltage amplitude output by the two converters is 1.15 times the actual given voltage amplitude U* of the system output, i.e., 1.15 / 2U*, where U* is the given amplitude of the two converters. To eliminate the N-1th harmonic, the following set of equations can be constructed: ; Where α1 is the first switching angle of converter #1, up to α k For converter #1, the k-th switching angle follows the following rules: Arrangement. For the calculation of the switching angle of converter #2, since its constraint conditions are the same as those of converter #1, it is only necessary to consider the phase difference between the two. That is, the switching angle of converter #2 is obtained by subtracting 120° from the switching angle calculated for converter #1.

[0033] After obtaining the two sets of equations for calculating the switching angles of the converters, the Newton-Raphson method is used to optimize and solve the equations for the switching angles of converter #1 and converter #2. This yields the combination of switching angle arrangements for converter #1 and converter #2. The modulation ratio m=1 is the maximum modulation ratio of the system, and the modulation ratio 0 is the minimum modulation ratio. For ease of calculation, the modulation ratio can be subdivided into 100 parts (which can be adjusted according to different accuracy requirements), i.e., m=[0, 0.01, … 0.99, 1]. This means that for each different modulation ratio, the optimal value of the switching angles of converter #1 and converter #2 needs to be calculated once. After calculating the switching angles for all modulation ratios, the optimal combination of the switching angles of converter #1 and converter #2 from modulation ratio 0 to 1 can be obtained, which is called the switching angle lookup table. After calculating the optimal switching angle lookup table for converter #1 and converter #2, the switching angle combination of converter #1 and converter #2 is selected in real time based on information such as system modulation ratio m, number of switching angles N, and grid angle θ. The real-time output phase is determined and sent to the synchronization pulse generation module. Based on this switching angle information, the synchronization pulse generation module generates 24 pulse signals, which are sent to converter #1 and converter #2 respectively to complete the real-time control of the switching devices, and finally generate the SHEPWM voltage synchronization pulse under this topology.

[0034] Figure 3 This is a simulated phase voltage waveform output by the method in this embodiment, wherein... Figure 3 (a) is the waveform of the total phase voltage after synthesis. The number of switching cycles in one fundamental cycle is 20, that is, the number of switching angles N=10. Figure 3(b) shows the output phase voltage waveforms of converter #1 and converter #2. The output phase voltages of converter #1 and converter #2 are 120° out of phase. After synthesis, the total phase voltage is five levels. The number of switching cycles of a single converter in one fundamental cycle is 10, which means that the number of switching angles N=5. This also means that the number of switching angles of the two converters can be effectively increased after the open winding topology is superimposed and synthesized, which can effectively reduce voltage harmonics and has a great advantage in high-power application scenarios.

[0035] Figure 4 This is a diagram showing the switching angle sequence calculated based on the constraint equations of converter #1 in this embodiment. The diagram reveals the distribution of each switching angle in the first 1 / 4 of the cycle (N=5). The vertical axis represents the angle of each switching angle, and the horizontal axis represents the modulation ratio m. As the modulation ratio changes, the optimal result calculated by the switching angle constraint equations also changes.

[0036] Figure 5 The diagram shows the phase voltage harmonic waveforms of the conventional space vector modulation (SVPWM) method under an experiment with 5 switching cycles (N=5), with a total harmonic distortion (THD) of 50.03%. Figure 6 The diagram shows the phase voltage harmonic waveform of the method in this embodiment under an experiment with 5 switching cycles (N=5), for comparison. Figure 5 and Figure 6 As can be seen, under the same number of switching operations (N=5), the total voltage harmonic content of the method in this embodiment is much lower than that of the traditional space vector modulation (SVPWM) method. Furthermore, it can be seen that even-order harmonics are eliminated, and the 3rd, 5th, 7th, and 9th harmonics are almost completely eliminated, with a voltage THD of 37.82%. Therefore, compared to the traditional space vector modulation (SVPWM) method, the method in this embodiment has a significant advantage in eliminating voltage harmonics.

[0037] Those skilled in the art will understand that the technical solutions provided by this invention can be in the form of methods, systems, or computer program products. For example, this invention can provide a SHEPWM control system for an open-winding dual-converter grid-connected system, comprising: The voltage angle calculation program module is used to obtain the grid voltage and voltage angle at the grid connection point of the open-winding dual converter grid-connected system; The modulation ratio and current calculation module is used to calculate the modulation ratio and output current setpoint based on the grid voltage at the grid connection point. The lookup table module is used to take the calculated modulation ratio, combine it with the voltage angle and the preset number of switching angles, and find the optimal switching angle combination that matches the three variables of modulation ratio, voltage angle and number of switching angles for the two converters in the open winding dual converter grid-connected system by looking up the optimal switching angle lookup table, and then send it to the synchronization pulse generation module; the optimal switching angle lookup table stores the switching status of N switching angles of each phase under different modulation ratio conditions within 1 / 4 cycle; The synchronous pulse generation program module is used to generate 24 SHEPWM voltage synchronous pulse signals based on the optimal switching angle combination and the output current setpoint, and send them to the switching devices of the two converters to complete the real-time control of the switching devices.

[0038] This invention provides a SHEPWM control system for an open-winding dual-converter grid-connected system, comprising a microprocessor and a memory interconnected, wherein the microprocessor is programmed or configured to execute the SHEPWM control method for the open-winding dual-converter grid-connected system. This invention also provides a computer-readable storage medium storing a computer program or instructions programmed or configured to execute the SHEPWM control method for the open-winding dual-converter grid-connected system via a processor. Finally, this invention provides a computer program product comprising a computer program or instructions programmed or configured to execute the SHEPWM control method for the open-winding dual-converter grid-connected system via a processor.

[0039] Furthermore, the present invention may also take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention may take the form of a computer program product embodied on one or more computer-readable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The present invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, produce implementations of the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1The computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to operate in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The functions specified in one or more boxes. These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable apparatus for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0040] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A SHEPWM control method for an open-winding dual-converter grid-connected system, characterized in that, Includes the following steps: S101, obtain the grid voltage and voltage angle at the grid connection point of the open-winding dual converter grid-connected system; S102, calculate the modulation ratio and output current setpoint based on the grid voltage at the grid connection point; S103, the calculated modulation ratio, combined with the voltage angle and the preset number of switching angles, is used to find the optimal switching angle combination that matches the three variables of modulation ratio, voltage angle and number of switching angles for the two converters in the open winding dual converter grid-connected system by looking up the optimal switching angle lookup table, and then the combination is sent to the synchronization pulse generation module; the optimal switching angle lookup table stores the switching status of N switching angles of each phase under different modulation ratio conditions within 1 / 4 cycle; S104 generates 24 SHEPWM voltage synchronization pulse signals based on the optimal switching angle combination and the output current setpoint through the synchronization pulse generation module, and sends them to the switching devices of the two converters to complete the real-time control of the switching devices.

2. The SHEPWM control method for an open-winding dual-converter grid-connected system according to claim 1, characterized in that, The functional expression for calculating the modulation ratio m in step S102 is: ； in, The modulation ratio, and Let dq-axis components be the grid voltage at the grid connection point. This refers to the bus voltage of the two converters in a grid-connected system with open winding dual converters.

3. The SHEPWM control method for an open-winding dual-converter grid-connected system according to claim 1, characterized in that, The function expression for calculating the output current setpoint in step S102 is: ； ； in, and These represent the given output active power and reactive power, respectively. and Let dq-axis components be the grid voltage at the grid connection point. and The dq-axis component is the given value of the output current.

4. The SHEPWM control method for an open-winding dual-converter grid-connected system according to claim 1, characterized in that, Before step S103, an optimal switching angle lookup table is generated, which includes the optimal switching angle combination that matches the three variables: modulation ratio, voltage angle, and number of switching angles. S201, for the first converter in a grid-connected system with two open-winding dual converters, the following switching angle equation is established: ； in, The bus voltage of the two converters in the open-winding dual-converter grid-connected system. The modulation ratio, For the number of switching angles, ~ They are respectively number 1 to One switching angle; S202, with modulation ratio A value of 1 represents the maximum modulation ratio. A value of 0 represents the minimum modulation ratio, which is then subdivided into a specified number of parts. For each part of the modulation ratio... The Newton-Raphson method was used to optimize the switching angle equation of the first converter, and the modulation ratio was obtained. The switching status of N switches under the current condition is determined within 1 / 4 cycle and stored in the optimal switching angle lookup table of the first converter. S203, for the optimal switching angle lookup table of the first converter, subtract the given phase difference from all the switching angles to generate a new optimal switching angle lookup table, which is then used as the optimal switching angle lookup table for the second converter.

5. The SHEPWM control method for an open-winding dual-converter grid-connected system according to claim 4, characterized in that, In step S203, the phase difference is given as 120° to eliminate the common-mode third pulsation of the output voltage, and the given voltage amplitude of the two converters is 1.15 times the actual given voltage amplitude U* of the system output.

6. The SHEPWM control method for an open-winding dual-converter grid-connected system according to claim 1, characterized in that, The calculation function expression for the voltage at the grid connection point of the open-winding dual-converter grid-connected system is as follows: ； in, , and These are the A, B, and C phase voltages at the grid connection point, respectively. , and These are the A, B, and C phase voltages output from the first converter, respectively. , and These are the A, B, and C phase voltages output from the second converter, respectively.

7. A SHEPWM control system for an open-winding dual-converter grid-connected system, characterized in that, include: The voltage angle calculation program module is used to obtain the grid voltage and voltage angle at the grid connection point of the open-winding dual converter grid-connected system; The modulation ratio and current calculation module is used to calculate the modulation ratio and output current setpoint based on the grid voltage at the grid connection point. The lookup table module is used to take the calculated modulation ratio, combine it with the voltage angle and the preset number of switching angles, and find the optimal switching angle combination that matches the three variables of modulation ratio, voltage angle and number of switching angles for the two converters in the open winding dual converter grid-connected system by looking up the optimal switching angle lookup table, and then send it to the synchronization pulse generation module; the optimal switching angle lookup table stores the switching status of N switching angles of each phase under different modulation ratio conditions within 1 / 4 cycle; The synchronous pulse generation program module is used to generate 24 SHEPWM voltage synchronous pulse signals based on the optimal switching angle combination and the output current setpoint, and send them to the switching devices of the two converters to complete the real-time control of the switching devices.

8. A SHEPWM control system for an open-winding dual-converter grid-connected system, comprising a microprocessor and a memory interconnected, characterized in that, The microprocessor is programmed or configured to execute the SHEPWM control method for the open-winding dual converter grid-connected system according to any one of claims 1 to 6.

9. A computer-readable storage medium storing a computer program or instructions, characterized in that, The computer program or instructions are programmed or configured to execute the SHEPWM control method of the open-winding dual converter grid-connected system according to any one of claims 1 to 6 via a processor.

10. A computer program product, comprising a computer program or instructions, characterized in that, The computer program or instructions are programmed or configured to execute the SHEPWM control method of the open-winding dual converter grid-connected system according to any one of claims 1 to 6 via a processor.

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