A method, system, device and medium for suppressing three-phase four-bridge-arm converter parallel ring current by using a sliding mode

Abstract

The application discloses a three-phase four-bridge-arm converter parallel sliding mode circulating current suppression method, system, device and medium, and belongs to the technical field of power converter control. The method is as follows: a zero sequence current feedback value obtained is subtracted from a preset zero sequence current reference value, a first current difference value obtained is input into a zero sequence current sliding mode controller, and a zero sequence modulation signal is obtained; the initial modulation signal is corrected according to the zero sequence modulation signal, a fourth bridge arm output current is subtracted from a preset fourth bridge arm current reference value, a second current difference value obtained is input into a fourth bridge arm sliding mode controller, and a fourth bridge arm modulation signal is obtained; the pulse width modulation signals of the bridge arms are obtained according to the modulation signals of the bridge arms, and the circulating current during multi-machine parallel operation is suppressed according to the pulse width modulation signals. Therefore, by implementing the application, the circulating current during multi-machine parallel operation of the three-phase four-bridge-arm converter can be effectively suppressed, and the stability and power quality of the system are improved.

Description

Technical Field

[0001] This invention relates to the field of power converter control technology, and in particular to a method, system, device and medium for suppressing parallel sliding mode circulating current in a three-phase four-arm converter. Background Technology

[0002] Flexible interconnection devices are key equipment for achieving power exchange between low-voltage substations and efficient consumption of distributed energy resources. Their control performance directly determines the system's stability and power quality. Flexible interconnection devices, represented by three-phase four-arm inverters, have advantages such as simple topology, small size, and low cost. Furthermore, because they can independently control the neutral line (N line), they can reduce the risk of line and equipment overload and achieve better load balance. Therefore, optimizing the modulation and control strategies of three-phase four-arm inverters has significant theoretical and practical implications. However, when multiple three-phase four-arm inverters are connected in parallel, due to factors such as parameter differences and inconsistent switching actions, serious circulating current problems arise between the inverters during actual operation. This leads to increased losses in the flexible interconnection system, decreased system stability, and even system oscillations.

[0003] Traditional control methods, such as proportional-integral (PI) controllers, while simple in structure, suffer from slow dynamic response under nonlinear and strongly coupled conditions and are sensitive to parameter disturbances. The parameter adjustment process for PI controllers is cumbersome, hindering practical applications. Furthermore, introducing the third harmonic is a classic method for addressing circulating current suppression and improving DC voltage utilization in three-phase four-arm inverters, but its control is relatively complex. In a three-phase four-arm system, the third harmonic is a zero-sequence component and will superimpose on the neutral (N) line. When the load is unbalanced or the control is inadequate, the neutral point potential will shift, worsening waveform distortion. Summary of the Invention

[0004] This invention provides a method, system, device, and medium for suppressing circulating current in a three-phase four-arm parallel sliding mode converter, which can effectively suppress circulating current during the parallel operation of multiple three-phase four-arm converters, thereby improving system stability and power quality.

[0005] This invention provides a method for suppressing sliding mode circulating current in a three-phase four-arm parallel bridge, comprising: Based on the obtained first bridge arm output current, second bridge arm output current and third bridge arm output current, the zero-sequence current feedback value is calculated, the difference between the zero-sequence current feedback value and the preset zero-sequence current reference value is obtained, the first current difference value is input to the preset zero-sequence current sliding mode controller to obtain the zero-sequence modulation signal. The first bridge arm initial modulation signal, the second bridge arm initial modulation signal, and the third bridge arm initial modulation signal are corrected according to the zero-sequence modulation signal to obtain the corrected first bridge arm modulation signal, the second bridge arm modulation signal, and the third bridge arm modulation signal. The difference between the obtained fourth bridge arm output current and the preset fourth bridge arm current reference value is obtained to obtain the second current difference value. The second current difference value is input to the preset fourth bridge arm sliding mode controller to obtain the fourth bridge arm modulation signal. Based on the modulation signals of the first bridge arm, the second bridge arm, the third bridge arm, and the fourth bridge arm, the pulse width modulation signal of each bridge arm is calculated to suppress the circulating current when multiple three-phase four-bridge arm converters are operating in parallel.

[0006] This invention constructs a dual sliding mode control architecture with closed-loop zero-sequence current in the three-phase bridge arm and closed-loop current in the fourth bridge arm through a preset zero-sequence current sliding mode controller and a fourth bridge arm sliding mode controller. This achieves dual suppression of zero-sequence current through voltage source regulation and current path blocking. Combined with the sliding mode controller's insensitivity to parameter perturbations and external disturbances, it ensures that the zero-sequence current and the fourth bridge arm current can converge to the desired value quickly and accurately, enhancing the robustness of the multi-machine parallel system. At the same time, each converter is controlled independently without the need for mutual communication, simplifying the system structure. Compared with the complex control methods in the prior art, such as the slow dynamic response of proportional-integral controllers, sensitivity to parameter disturbances, and third harmonic injection or zero-sequence circulating current feedforward, this application, through the independent adjustment and dual suppression mechanism of the dual sliding mode controllers, ultimately drives the action of each bridge arm according to the pulse width modulation signal. This effectively suppresses the circulating current in the parallel operation of three-phase four-bridge arm converters, improving system stability and power quality.

[0007] Further, the first current difference is input to a preset zero-sequence current sliding mode controller to obtain a zero-sequence modulation signal, specifically as follows: By using a preset zero-sequence current sliding mode controller and combining it with the first current difference, a first integral sliding mode surface for the zero-sequence current is constructed. The zero-sequence modulation signal is calculated based on the first integral sliding surface and the preset current state equation.

[0008] Furthermore, the first integral sliding surface of the zero-sequence current is constructed, as shown in the following formula: in, This is the first integral sliding surface; This is the first current difference value; is the first integral gain constant of the zero-sequence current sliding mode surface.

[0009] Furthermore, the zero-sequence modulation signal is calculated using the following formula: in, It is a zero-sequence modulated signal, containing equivalent control terms and switching control terms; The first integral gain constant of the zero-sequence current sliding surface; For the output current of the first bridge arm; For the output current of the second bridge arm; Output current for the third bridge arm; The approach law parameters are obtained based on the preset current state equation; This is the first integral sliding surface; It is a symbolic function.

[0010] By constructing a first integral sliding surface for the zero-sequence current and calculating the zero-sequence modulation signal based on this sliding surface and the current state equation, sliding mode control of the zero-sequence current in the three-phase bridge arm is achieved. The introduction of the integral sliding surface eliminates steady-state error and improves the tracking accuracy of the zero-sequence current. The equivalent control term ensures the ideal dynamics of the system on the sliding surface, while the switching control term effectively overcomes parameter perturbations and external disturbances, so that the system state can approach and stabilize at the sliding surface within a finite time. This significantly improves the robustness and dynamic performance of zero-sequence current suppression, effectively suppresses the zero-sequence circulating current in the parallel operation of multiple three-phase four-bridge arm converters, and enhances the stability and power quality of the system.

[0011] Further, the second current difference is input to a preset fourth bridge arm sliding mode controller to obtain a fourth bridge arm modulation signal, specifically: By using a preset fourth bridge arm sliding mode controller and combining it with the second current difference, the second integral sliding mode surface of the fourth bridge arm is constructed; The modulation signal of the fourth bridge arm is calculated based on the second integral sliding surface and the preset dynamic equation of the fourth bridge arm.

[0012] Furthermore, the second integral sliding surface of the fourth bridge arm is constructed as follows: in, This is the second integral sliding surface; This is the second current difference; It is the second integral gain constant of the sliding surface of the fourth bridge arm.

[0013] Furthermore, the modulation signal of the fourth bridge arm is calculated using the following formula: in, This is the modulation signal for the fourth bridge arm; The second integral gain constant of the sliding surface of the fourth bridge arm; Output current for the fourth bridge arm; The sliding mode reaching law parameters for the fourth bridge arm are obtained based on the preset dynamic equations of the fourth bridge arm. This is the second integral sliding surface; It is a symbolic function.

[0014] By using a pre-defined fourth-arm sliding mode controller and constructing a second integral sliding surface based on the second current difference, and calculating the fourth-arm modulation signal, closed-loop sliding mode control of the fourth-arm current is achieved. Introducing the integral sliding surface eliminates the steady-state tracking error of the fourth-arm current, improving current control accuracy. Combined with the invariance and finite-time convergence characteristics of sliding mode control, the robustness and dynamic performance of the fourth-arm current control are significantly enhanced. Furthermore, this controller operates independently without communicating with other converters, simplifying the control structure of multi-unit parallel systems. Driving the fourth arm based on the generated fourth-arm modulation signal effectively suppresses current fluctuations and circulating current in the fourth arm, further improving the overall stability and power quality of the three-phase four-arm converter operating in parallel.

[0015] Another embodiment of the present invention provides a three-phase four-arm parallel sliding mode circulating current suppression system, comprising: a zero-sequence modulation signal acquisition module, a modulation signal correction module, a fourth arm modulation signal acquisition module, and a parallel circulating current suppression module; The zero-sequence modulation signal acquisition module is used to calculate the zero-sequence current feedback value based on the acquired first bridge arm output current, second bridge arm output current and third bridge arm output current, subtract the zero-sequence current feedback value from the preset zero-sequence current reference value to obtain the first current difference value, and input the first current difference value to the preset zero-sequence current sliding mode controller to obtain the zero-sequence modulation signal. The modulation signal correction module is used to correct the acquired first bridge arm initial modulation signal, second bridge arm initial modulation signal and third bridge arm initial modulation signal according to the zero-sequence modulation signal, respectively, to obtain the corrected first bridge arm modulation signal, second bridge arm modulation signal and third bridge arm modulation signal. The fourth bridge arm modulation signal acquisition module is used to subtract the acquired fourth bridge arm output current from the preset fourth bridge arm current reference value to obtain a second current difference value, and input the second current difference value to the preset fourth bridge arm sliding mode controller to obtain the fourth bridge arm modulation signal. The parallel circulating current suppression module is used to calculate the pulse width modulation signal of each bridge arm based on the first bridge arm modulation signal, the second bridge arm modulation signal, the third bridge arm modulation signal, and the fourth bridge arm modulation signal, so as to suppress the circulating current when multiple three-phase four-bridge arm converters are running in parallel according to the pulse width modulation signal.

[0016] This invention constructs a dual sliding mode control architecture with closed-loop zero-sequence current in the three-phase bridge arm and closed-loop current in the fourth bridge arm through a preset zero-sequence current sliding mode controller and a fourth bridge arm sliding mode controller. This achieves dual suppression of zero-sequence current through voltage source regulation and current path blocking. Combined with the sliding mode controller's insensitivity to parameter perturbations and external disturbances, it ensures that the zero-sequence current and the fourth bridge arm current can converge to the desired value quickly and accurately, enhancing the robustness of the multi-machine parallel system. At the same time, each converter is controlled independently without the need for mutual communication, simplifying the system structure. Compared with the complex control methods in the prior art, such as the slow dynamic response of proportional-integral controllers, sensitivity to parameter disturbances, and third harmonic injection or zero-sequence circulating current feedforward, this application, through the independent adjustment and dual suppression mechanism of the dual sliding mode controllers, ultimately drives the action of each bridge arm according to the pulse width modulation signal. This effectively suppresses the circulating current in the parallel operation of three-phase four-bridge arm converters, improving system stability and power quality.

[0017] Another embodiment of the present invention provides a terminal device, including: a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor. When the processor executes the computer program, it implements the steps of the three-phase four-bridge arm parallel sliding mode circulation suppression method of the present invention.

[0018] Another embodiment of the present invention provides a computer-readable storage medium item, including: a stored computer program, which, when the computer program is running, controls the device where the computer-readable storage medium is located to perform the steps of the three-phase four-bridge arm parallel sliding mode circulating current suppression method of the present invention. Attached Figure Description

[0019] To more clearly illustrate the technical solution of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 This is a schematic flowchart of an embodiment of the three-phase four-bridge arm parallel sliding mode circulation suppression method provided by the present invention; Figure 2 This is a flowchart illustrating the parallel circulating current suppression method for a three-phase four-arm converter, which is another embodiment of the parallel sliding mode circulating current suppression method provided by the present invention. Figure 3 This is a diagram of a three-phase four-bridge arm converter multi-machine parallel structure, which is another embodiment of the three-phase four-bridge arm parallel sliding mode circulating current suppression method provided by the present invention. Figure 4 This is a control block diagram of a three-phase four-arm converter, which is another embodiment of the three-phase four-arm parallel sliding mode circulating current suppression method provided by the present invention. Figure 5 The circulating current peak diagram is shown when both three-phase four-arm converters are operating at a constant power of 3100W without using the three-phase four-arm parallel sliding mode circulating current suppression method provided by this invention. Figure 6 The circulating current peak diagram is shown when two three-phase four-bridge-arm converters are operating at a constant power of 3100W, using the three-phase four-bridge-arm parallel sliding mode circulating current suppression method provided by this invention. Figure 7 The diagram shows the circulating current peak value when one three-phase four-arm converter operates at a constant power of 3100W and another operates at a constant power of 2100W, without using the three-phase four-arm parallel sliding mode circulating current suppression method provided in this invention. Figure 8 The diagram shows the circulating current peak value when one three-phase four-bridge-arm converter operates at a constant power of 3100W and another operates at a constant power of 2100W, using the three-phase four-bridge-arm parallel sliding mode circulating current suppression method provided by this invention. Figure 9 This is a schematic diagram of another embodiment of the three-phase four-bridge-arm parallel sliding mode circulation suppression system provided by the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0023] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0024] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0025] In the description of this invention, the term "for example" is used to mean "used as an example, illustration, or description." Any embodiment described as "for example" in this invention is not necessarily to be construed as being more preferred or advantageous than other embodiments. The following description is provided to enable any person skilled in the art to make and use the invention. Details are set forth in the following description for purposes of explanation. It should be understood that those skilled in the art will recognize that the invention can be made without using these specific details. In other instances, well-known structures and processes will not be described in detail to avoid obscuring the description of the invention with unnecessary detail. Therefore, the invention is not intended to be limited to the embodiments shown, but is consistent with the broadest scope of the principles and features disclosed herein.

[0026] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0027] See Figure 1 To address the problem of suppressing sliding mode circulating current in three-phase four-arm parallel bridges in the prior art, an embodiment of the present invention provides a method for suppressing sliding mode circulating current in three-phase four-arm parallel bridges, comprising steps S1 to S5, the specific steps of which are as follows: S1. Based on the obtained first bridge arm output current, second bridge arm output current and third bridge arm output current, calculate the zero-sequence current feedback value, subtract the zero-sequence current feedback value from the preset zero-sequence current reference value to obtain the first current difference value, and input the first current difference value to the preset zero-sequence current sliding mode controller to obtain the zero-sequence modulation signal. S2. Based on the zero-sequence modulation signal, the acquired first bridge arm initial modulation signal, second bridge arm initial modulation signal, and third bridge arm initial modulation signal are corrected respectively to obtain the corrected first bridge arm modulation signal, second bridge arm modulation signal, and third bridge arm modulation signal. S3. Subtract the obtained fourth bridge arm output current from the preset fourth bridge arm current reference value to obtain a second current difference value. Input the second current difference value to the preset fourth bridge arm sliding mode controller to obtain the fourth bridge arm modulation signal. S4. Calculate the pulse width modulation signal of each bridge arm based on the first bridge arm modulation signal, the second bridge arm modulation signal, the third bridge arm modulation signal, and the fourth bridge arm modulation signal, so as to suppress the circulating current when multiple three-phase four-bridge arm converters are running in parallel according to the pulse width modulation signal. Among them, the parallel structure of two three-phase four-bridge converters is as follows: Figure 3 As shown, the fourth arm of the converter is connected to the three-phase neutral point n (grounded). The three-phase outputs of the converters are connected to the power grid (including line impedance Lg) in parallel. The converter operates in grid-connected mode, outputting three-phase sinusoidal currents, namely the output currents of the first, second, and third arms. Each converter is independently controlled. d - q The control block diagram in the -0 coordinate system is as follows: Figure 4 As shown; in, P ref This is a reference value for active power. Q ref This is a reference value for reactive power. P The active power output of the converter; Q The reactive power output value of the converter; v P This represents the capacitor voltage value on the DC side bus of the converter. v N This refers to the capacitor voltage value on the DC side bus of the converter; i * d and i * q For grid-side current d - q -0 axis reference value; v * d and v * q Output voltage of grid-side converter d - q -0 axis reference value; i d and i q For grid-side current d - q The value of the -0 axis; v d and v q Grid-side voltage d - q The value of the -0 axis; u a , ub and u c This is the grid-side voltage value; i a , i b and i c This is the grid-side current value; i Nx ( x =1, 2) is the first x The output current of the fourth bridge arm of the converter; m abc The modulation signal is for the three-phase output; m a+b+c The modulation signal is the zero-sequence voltage. m N This is the modulation signal for the voltage of the fourth bridge arm of the converter; S a , S b , S c and S N These are the PWM signals for the four bridge arms of the converter; For constant power mode, the three-phase four-arm converter in d - q The reference current in the -0 axis coordinate system is as follows: in, G P and G Q These are active and reactive power controllers, respectively; Three-phase four-bridge converter in d - q The reference voltage in the -0 axis coordinate system is as follows: in, G d and G q They are respectively d - p Current controller in the -0 axis coordinate system; Obtained from voltage decoupling control d - p The converter output voltage in the -0 axis coordinate system is determined by the voltages of the upper and lower capacitors on the DC side of the converter. v P and v N The size of the signal is used to optimize the modulation signal of the three-phase output voltage of the converter.

[0028] As an example of an embodiment of the present invention, such as Figure 2 As shown, each three-phase four-arm converter adopts a power-current dual-loop control architecture to achieve constant power grid-connected control. The sum of the three-phase (A-phase, B-phase, C-phase) current signals is used as the zero-sequence current feedback signal and compared with the reference value (the desired zero-sequence current is 0A). A sliding mode controller tracks the reference value and outputs a zero-sequence voltage modulation signal based on the input zero-sequence current comparison value. The zero-sequence voltage modulation signal is then superimposed on the modulation signal of the three-phase voltage. The current of the fourth arm after passing through the filter circuit is used as the current feedback signal. The sliding mode controller tracks the reference value (with the filter current as the reference signal of 0A) and outputs the voltage modulation signal of the fourth arm. Finally, the PWN modulation signal (pulse width modulation signal) of the three-phase four-arm converter is output. Through two sliding mode controllers, the zero-sequence current suppression of the three-phase arms and the fourth arm is realized respectively, that is, the zero-sequence current suppression of a single inverter is realized, and the zero-sequence current of each inverter is controlled to 0, realizing the parallel circulating current control of the three-phase four-arm converter.

[0029] In one embodiment, the first current difference is input to a preset zero-sequence current sliding mode controller to obtain a zero-sequence modulation signal, including steps S201 to S202, each step of which is as follows: S201. Using a preset zero-sequence current sliding mode controller and combining the first current difference, a first integral sliding mode surface for the zero-sequence current is constructed, as shown in the following formula: in, This is the first integral sliding surface; This is the first current difference value; The first integral gain constant of the zero-sequence current sliding surface; S202. Based on the first integral sliding surface and the preset current state equation, the zero-sequence modulation signal is calculated as follows: in, It is a zero-sequence modulated signal, containing equivalent control terms and switching control terms; The first integral gain constant of the zero-sequence current sliding surface; For the output current of the first bridge arm; For the output current of the second bridge arm; Output current for the third bridge arm; The approach law parameters are obtained based on the preset current state equation; This is the first integral sliding surface; It is a symbolic function; In the zero-sequence current closed-loop control, the zero-sequence current feedback calculation formula is as follows: i 0= i a + i b + i c in, This is the zero-sequence current feedback value; For the output current of the first bridge arm; For the output current of the second bridge arm; Output current for the third bridge arm; The formula for calculating the zero-sequence current tracking error is as follows: e u =0 － ( i a + i b + i c )= －i 0 in, e u For zero-sequence current tracking error, used to ensure that the zero-sequence current tracks the target reference value (0A) without steady-state error. For the output current of the first bridge arm; For the output current of the second bridge arm; Output current for the third bridge arm; This is the first current difference value; The first integral sliding surface of the preset zero-sequence current sliding mode controller is used to eliminate the steady-state error of the system and ensure good dynamic response; the first integral gain constant is used to determine the convergence speed of the system on the sliding surface; based on the sliding mode arrival condition and the current state equation of the system, the sliding mode control law of the zero-sequence voltage modulation signal is derived, and the reaching law parameters are obtained. This is used to output a zero-sequence voltage modulation signal and correct the initial modulation signal of the three-phase bridge arm.

[0030] This invention constructs a first integral sliding surface for zero-sequence current and calculates the zero-sequence modulation signal based on this sliding surface and the current state equation, thereby achieving sliding mode control of the zero-sequence current of the three-phase bridge arm. By introducing the integral sliding surface, steady-state error is eliminated, improving the tracking accuracy of the zero-sequence current. The equivalent control term ensures the ideal dynamics of the system on the sliding surface, while switching the control term effectively overcomes parameter perturbations and external disturbances, enabling the system state to approach and stabilize at the sliding surface within a finite time. This significantly improves the robustness and dynamic performance of zero-sequence current suppression, effectively suppresses the zero-sequence circulating current in the parallel operation of multiple three-phase four-bridge arm converters, and enhances the stability and power quality of the system.

[0031] In one embodiment, the second current difference is input to a preset fourth bridge arm sliding mode controller to obtain a fourth bridge arm modulation signal, including steps S301 to S302, each step of which is as follows: S301. Using a preset fourth bridge arm sliding mode controller and combining the second current difference, construct the second integral sliding surface of the fourth bridge arm, as shown in the following formula: in, This is the second integral sliding surface; This is the second current difference; The second integral gain constant of the sliding surface of the fourth bridge arm; S302. Based on the second integral sliding surface and the preset dynamic equation of the fourth bridge arm, the modulation signal of the fourth bridge arm is calculated as follows: in, This is the modulation signal for the fourth bridge arm; The second integral gain constant of the sliding surface of the fourth bridge arm; Output current for the fourth bridge arm; The sliding mode reaching law parameters for the fourth bridge arm are obtained based on the preset dynamic equations of the fourth bridge arm. This is the second integral sliding surface; It is a symbolic function; Under ideal conditions and with three-phase symmetry in the power grid, the desired current of the fourth bridge arm is 0A. The formula for calculating the tracking error of the fourth bridge arm current is as follows: e i =0 －i Nx in, e i This refers to the current tracking error of the fourth bridge arm; i Nx This is the filter inductor current of the fourth bridge arm.

[0032] In practical applications, such as Figure 5 , Figure 6 , Figure 7 and Figure 8As shown, a system simulation model was built in Matlab / Simulink for simulation research. The main circuit parameters were set as follows: three-phase grid voltage amplitude of 380V, filter inductor L=3mH, filter capacitor Cf=4.7μF, three-phase frequency of 50Hz, DC side upper and lower capacitors of 3300μF, switching frequency of 20kHz, and DC voltage reference value set to 750V. Under constant power conditions of 3100W for both three-phase four-arm converters, without employing the three-phase four-arm parallel sliding mode circulating current suppression method described in this invention, the circulating current peak... The value exceeds 10A, while the circulating current peak value is suppressed to within 2A. In two three-phase four-arm converters, one operates under a constant power condition of 3100W and the other operates under a constant power condition of 2100W. Without the three-phase four-arm parallel sliding mode circulating current suppression method described in this invention, the circulating current peak value exceeds 13A, while with the method described in this invention, the circulating current peak value is suppressed to within 2A. The simulation waveforms show that this invention can effectively suppress parallel circulating current under different operating conditions, and also performs well in terms of steady-state performance, effectively ensuring the quality of output current.

[0033] This invention utilizes a pre-defined fourth-arm sliding mode controller to construct a second integral sliding mode surface based on the second current difference, and calculates the fourth-arm modulation signal to achieve closed-loop sliding mode control of the fourth-arm current. By introducing the integral sliding mode surface, the steady-state tracking error of the fourth-arm current is eliminated, improving current control accuracy. Combined with the invariance and finite-time convergence characteristics of sliding mode control, the robustness and dynamic performance of the fourth-arm current control are significantly enhanced. Furthermore, this controller operates independently without communicating with other converters, simplifying the control structure of multi-unit parallel systems. Driving the fourth arm based on the generated fourth-arm modulation signal effectively suppresses current fluctuations and circulating current in the fourth arm, further improving the overall stability and power quality of the three-phase four-arm converter operating in parallel.

[0034] like Figure 9 As shown in the three-phase four-bridge arm parallel sliding mode circulating current suppression, a corresponding system embodiment is provided based on the above method embodiment. This invention provides a three-phase four-arm parallel sliding mode circulating current suppression system, including: a zero-sequence modulation signal acquisition module 401, a modulation signal correction module 402, a fourth arm modulation signal acquisition module 403, and a parallel circulating current suppression module 404; The zero-sequence modulation signal acquisition module 401 is used to calculate the zero-sequence current feedback value based on the acquired first bridge arm output current, second bridge arm output current and third bridge arm output current, subtract the zero-sequence current feedback value from the preset zero-sequence current reference value to obtain a first current difference value, and input the first current difference value to the preset zero-sequence current sliding mode controller to obtain a zero-sequence modulation signal. The modulation signal correction module 402 is used to correct the acquired first bridge arm initial modulation signal, second bridge arm initial modulation signal and third bridge arm initial modulation signal according to the zero-sequence modulation signal, respectively, to obtain the corrected first bridge arm modulation signal, second bridge arm modulation signal and third bridge arm modulation signal. The fourth bridge arm modulation signal acquisition module 403 is used to subtract the acquired fourth bridge arm output current from the preset fourth bridge arm current reference value to obtain a second current difference value, and input the second current difference value to the preset fourth bridge arm sliding mode controller to obtain the fourth bridge arm modulation signal. The parallel circulating current suppression module 404 is used to calculate the pulse width modulation signal of each bridge arm based on the first bridge arm modulation signal, the second bridge arm modulation signal, the third bridge arm modulation signal and the fourth bridge arm modulation signal, so as to suppress the circulating current when multiple three-phase four-bridge arm converters are running in parallel according to the pulse width modulation signal.

[0035] This invention constructs a dual sliding mode control architecture with closed-loop zero-sequence current in the three-phase bridge arm and closed-loop current in the fourth bridge arm through a preset zero-sequence current sliding mode controller and a fourth bridge arm sliding mode controller. This achieves dual suppression of zero-sequence current through voltage source regulation and current path blocking. Combined with the sliding mode controller's insensitivity to parameter perturbations and external disturbances, it ensures that the zero-sequence current and the fourth bridge arm current can converge to the desired value quickly and accurately, enhancing the robustness of the multi-machine parallel system. At the same time, each converter is controlled independently without the need for mutual communication, simplifying the system structure. Compared with the complex control methods in the prior art, such as the slow dynamic response of proportional-integral controllers, sensitivity to parameter disturbances, and third harmonic injection or zero-sequence circulating current feedforward, this application, through the independent adjustment and dual suppression mechanism of the dual sliding mode controllers, ultimately drives the action of each bridge arm according to the pulse width modulation signal. This effectively suppresses the circulating current in the parallel operation of three-phase four-bridge arm converters, improving system stability and power quality.

[0036] It is understood that the above system embodiments correspond to the method embodiments of the present invention, and can implement the three-phase four-bridge parallel sliding mode circulation suppression method provided by any of the above method embodiments of the present invention.

[0037] It should be noted that the system embodiments described above are merely illustrative, and some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Furthermore, in the accompanying drawings of the system embodiments provided by this invention, the connection relationships between modules indicate that they have communication connections, which can be specifically implemented as one or more communication buses or signal lines. Those skilled in the art can understand and implement this without any creative effort.

[0038] For ease of description and brevity, the system embodiments of the present invention include all the implementation methods described in the above embodiments of the three-phase four-arm parallel sliding mode circulation suppression method, and will not be repeated here.

[0039] Based on the above embodiments of the three-phase four-arm parallel sliding mode current suppression method, another embodiment of the present invention provides a terminal device, which includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor. When the processor executes the computer program, it implements the three-phase four-arm parallel sliding mode current suppression method of any embodiment of the present invention.

[0040] For example, in this embodiment, the computer program can be divided into one or more modules, which are stored in the memory and executed by the processor to complete the present invention. The one or more modules may be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of the computer program in the terminal device.

[0041] The terminal device may be a desktop computer, laptop, handheld computer, or cloud server, etc. The terminal device may include, but is not limited to, a processor and a memory.

[0042] The processor can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor can be a microprocessor or any conventional processor. The processor is the control center of the terminal device, connecting all parts of the terminal device via various interfaces and lines.

[0043] Based on the above-described method embodiments, another embodiment of the present invention provides a computer-readable storage medium including a stored computer program, wherein, when the computer program is executed, it controls the device where the computer-readable storage medium is located to execute the three-phase four-bridge parallel sliding mode circulating current suppression method described in any of the above-described method embodiments of the present invention.

[0044] The modules / units integrated in the device / terminal equipment, if implemented as software functional units and sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0045] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for suppressing parallel sliding mode circulating current in a three-phase four-arm converter, characterized in that, include: Based on the obtained first bridge arm output current, second bridge arm output current and third bridge arm output current, the zero-sequence current feedback value is calculated, the difference between the zero-sequence current feedback value and the preset zero-sequence current reference value is obtained, the first current difference value is input to the preset zero-sequence current sliding mode controller to obtain the zero-sequence modulation signal. The first bridge arm initial modulation signal, the second bridge arm initial modulation signal, and the third bridge arm initial modulation signal are corrected according to the zero-sequence modulation signal to obtain the corrected first bridge arm modulation signal, the second bridge arm modulation signal, and the third bridge arm modulation signal. The difference between the obtained fourth bridge arm output current and the preset fourth bridge arm current reference value is obtained to obtain the second current difference value. The second current difference value is input to the preset fourth bridge arm sliding mode controller to obtain the fourth bridge arm modulation signal. Based on the modulation signals of the first bridge arm, the second bridge arm, the third bridge arm, and the fourth bridge arm, the pulse width modulation signal of each bridge arm is calculated to suppress the circulating current when multiple three-phase four-bridge arm converters are operating in parallel.

2. The method for suppressing sliding mode circulating current in a three-phase four-arm parallel connection as described in claim 1, characterized in that, The step of inputting the first current difference to a preset zero-sequence current sliding mode controller to obtain a zero-sequence modulation signal specifically involves: By using a preset zero-sequence current sliding mode controller and combining it with the first current difference, a first integral sliding mode surface for the zero-sequence current is constructed. The zero-sequence modulation signal is calculated based on the first integral sliding surface and the preset current state equation.

3. The method for suppressing sliding mode circulating current in a three-phase four-arm parallel connection as described in claim 1 or 2, characterized in that, The formula for constructing the first integral sliding surface of the zero-sequence current is as follows: in, This is the first integral sliding surface; This is the first current difference value; is the first integral gain constant of the zero-sequence current sliding mode surface.

4. The method for suppressing sliding mode circulating current in a three-phase four-arm parallel connection as described in claim 1 or 2, characterized in that, The zero-sequence modulated signal is obtained through calculation, as shown in the following formula: in, It is a zero-sequence modulated signal, containing equivalent control terms and switching control terms; The first integral gain constant of the zero-sequence current sliding surface; For the output current of the first bridge arm; For the output current of the second bridge arm; Output current for the third bridge arm; The approach law parameters are obtained based on the preset current state equation; This is the first integral sliding surface; It is a symbolic function.

5. The method for suppressing sliding mode circulating current in a three-phase four-arm parallel connection as described in claim 1, characterized in that, The step of inputting the second current difference value to a preset fourth bridge arm sliding mode controller to obtain the fourth bridge arm modulation signal specifically involves: By using a preset fourth bridge arm sliding mode controller and combining it with the second current difference, the second integral sliding mode surface of the fourth bridge arm is constructed; The modulation signal of the fourth bridge arm is calculated based on the second integral sliding surface and the preset dynamic equation of the fourth bridge arm.

6. The method for suppressing sliding mode circulating current in a three-phase four-arm parallel connection as described in claim 1 or 5, characterized in that, The formula for constructing the second integral sliding surface of the fourth bridge arm is as follows: in, This is the second integral sliding surface; This is the second current difference; It is the second integral gain constant of the sliding surface of the fourth bridge arm.

7. The method for suppressing sliding mode circulating current in a three-phase four-arm parallel connection as described in claim 1 or 5, characterized in that, The calculation yields the modulation signal of the fourth bridge arm, as shown in the following formula: in, This is the modulation signal for the fourth bridge arm; The second integral gain constant of the sliding surface of the fourth bridge arm; Output current for the fourth bridge arm; The sliding mode reaching law parameters for the fourth bridge arm are obtained based on the preset dynamic equations of the fourth bridge arm. This is the second integral sliding surface; It is a symbolic function.

8. A three-phase four-bridge-arm parallel sliding mode circulating current suppression system, characterized in that, include: Zero-sequence modulation signal acquisition module, modulation signal correction module, fourth bridge arm modulation signal acquisition module, and parallel circulating current suppression module; The zero-sequence modulation signal acquisition module is used to calculate the zero-sequence current feedback value based on the acquired first bridge arm output current, second bridge arm output current and third bridge arm output current, subtract the zero-sequence current feedback value from the preset zero-sequence current reference value to obtain the first current difference value, and input the first current difference value to the preset zero-sequence current sliding mode controller to obtain the zero-sequence modulation signal. The modulation signal correction module is used to correct the acquired first bridge arm initial modulation signal, second bridge arm initial modulation signal and third bridge arm initial modulation signal according to the zero-sequence modulation signal, respectively, to obtain the corrected first bridge arm modulation signal, second bridge arm modulation signal and third bridge arm modulation signal. The fourth bridge arm modulation signal acquisition module is used to subtract the acquired fourth bridge arm output current from the preset fourth bridge arm current reference value to obtain a second current difference value, and input the second current difference value to the preset fourth bridge arm sliding mode controller to obtain the fourth bridge arm modulation signal. The parallel circulating current suppression module is used to calculate the pulse width modulation signal of each bridge arm based on the first bridge arm modulation signal, the second bridge arm modulation signal, the third bridge arm modulation signal, and the fourth bridge arm modulation signal, so as to suppress the circulating current when multiple three-phase four-bridge arm converters are running in parallel according to the pulse width modulation signal.

9. A terminal device, characterized in that, The method includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, wherein when the processor executes the computer program, it implements the three-phase four-arm parallel sliding mode circulating current suppression method as described in any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, include: A stored computer program, wherein, when the computer program is executed, it controls the device containing the computer-readable storage medium to perform the three-phase four-bridge parallel sliding mode circulation suppression method as described in any one of claims 1-7.

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