A short-circuit current limiting method and system for non-fault phase continuous power supply three-phase inverter

Abstract

The application discloses a kind of non-fault phase continuous power supply three-phase inverter short-circuit current limiting method and system, belong to independent power supply system protection control field.The system described in the application includes normal control system and fault control system, normal control system includes capacitor voltage outer ring, fault control system includes non-fault phase capacitor voltage outer ring and adaptive phase angle adjusting link based on SOGI filter, both are connected with inductance current inner ring by switching module.The application has the advantages of fast current limiting response speed, simple control structure compared with existing strategy.When asymmetric fault occurs, the output current of fault phase can be maximized and the reliable power supply of non-fault load of the system can be ensured.The application can adaptively change the phase angle between fault and non-fault inductance current, which can make the inverter always meet the system power supply and current limiting requirements with good robustness.

Description

Technical Field

[0001] This invention belongs to the field of independent power supply system protection and control, and more specifically, relates to a short-circuit current limiting method and system for a three-phase inverter with continuous power supply to non-faulty phases. Background Technology

[0002] With the development of modern industry, three-phase inverters are widely used in aerospace, marine power, microgrids, uninterruptible power supplies (UPS), and other fields. In many cases, three-phase inverters serve as the main power source, supplying power to multiple loads. The increase in load power and quantity has placed higher demands on the power quality and reliability of three-phase inverters. Among the faults of three-phase inverters, load short-circuit faults are one of the most serious. When a load short-circuit fault occurs, the fault current flowing through the power semiconductor devices is much greater than the rated current. If current limiting measures are not taken, the power semiconductor devices will be damaged by overcurrent, ultimately leading to the paralysis of the power supply system. Blocking the power semiconductor devices is a simple and effective short-circuit protection method, but it will interrupt the operation of the entire power supply system.

[0003] From the perspective of system power supply reliability and continuity, three-phase inverters must possess short-circuit fault ride-through capability. For grid-connected three-phase inverters, low-voltage ride-through under AC faults has been extensively studied, but these methods are not applicable to stand-alone three-phase inverters. A typical fault ride-through scheme for stand-alone three-phase inverters is as follows: Under normal conditions, the inverter operates in voltage-controlled mode (VCM). When a metallic short-circuit fault occurs in the load, the inverter switches to current-controlled mode (CCM) and outputs 2-3 times the rated current to quickly trip the faulty branch circuit breaker. After the short-circuit fault is cleared, the inverter returns from CCM to VCM.

[0004] Traditional current-based current limiting control strategies lead to voltage limiting under asymmetrical faults. Most existing short-circuit current limiting control strategies focus more on the inverter's output current during short-circuit current limiting, rarely considering the voltage of non-faulty phases. However, with the increasing load on three-phase inverter power supply systems, industry requirements for system power supply reliability are also rising. During short-circuit current limiting, in addition to outputting the fault current, the inverter is also needed to ensure reliable power supply to non-faulty phases. This objective will significantly improve the power supply reliability of independent power systems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a short-circuit current limiting method and system for three-phase inverters that ensures continuous power supply to non-faulty phases. This method and system are designed to solve the problems of maximizing short-circuit current limiting for faulty phases and ensuring continuous power supply to non-faulty phases under asymmetrical short-circuit faults in three-phase inverters, thereby improving the fault ride-through reliability and power supply reliability of independent power systems.

[0006] To achieve the above objectives, the present invention provides a short-circuit current limiting method for a three-phase inverter with continuous power supply to non-faulty phases, comprising the following steps:

[0007] When no short-circuit fault occurs in the independent power system, the three-phase inverter operates in voltage control mode;

[0008] When a short-circuit fault occurs in the independent power system, the three-phase inverter switches from voltage control mode to current control mode. The short-circuit fault is divided into symmetrical short-circuit fault and phase-to-phase short-circuit fault. After the short-circuit fault is cleared, the three-phase inverter switches back from current control mode to voltage control mode.

[0009] Under a symmetrical short-circuit fault, all three phases are faulty phases, and the current control mode is inductor current inner loop control: the inductor current reference value i is controlled separately. Ld * with i Lq * Assign fault phase current amplitude I LF Achieving current limiting control of the three-phase inductor current with a value of 0;

[0010] Under a phase-to-phase short-circuit fault, there are two faulty phases and one non-faulty phase in the three-phase system. The current control mode consists of an outer loop control of the non-faulty phase capacitor voltage in the three-phase stationary coordinate system and an inner loop control of the inductor current in the dq rotating coordinate system. The inductor current reference value is i. Ld * with i Lq * It is calculated by an adaptive phase angle adjustment circuit based on an SOGI filter.

[0011] Furthermore, the outer loop control of the capacitor voltage of the non-faulty phase under phase-to-phase short-circuit fault specifically includes:

[0012] The error between the outer loop reference value and the feedback value of the capacitor voltage of the non-faulty phase is used by the fundamental frequency quasi-proportional resonant controller to obtain the reference value of the inductor current i of the non-faulty phase. LNF * The reference value i of the non-faulty phase inductor current LNF * The in-phase reference value i of the non-faulty phase inductor current is obtained after passing through the SOGI filter. LNFd * Orthogonal reference value i LNFq * And calculate the reference amplitude I of the non-faulty phase inductor current in real time based on both. LNF * ; by current limiting setting value I LF Reference amplitude I of non-faulty phase inductor current LNF *The trigonometric functions cos(β) and sin(β) of the angle β between the inductor current of the non-faulty phase and the inductor current of the faulty phase are calculated; according to i LNFd * i LNFq * I LNF * I LF The reference values ​​i of the inductor currents of the two fault phases are obtained by calculating cos(β) and sin(β). LF1 * with i LF2 * , where i LF1 * i is the fault phase current that lags behind the non-fault phase β. LF2 * The fault phase current is ahead of the non-fault phase β; i LNF * i LF1 * and i LF2 * The reference value of the inductor current i in the dq coordinate system is obtained after the abc / dq transformation. Ld * with i Lq * .

[0013] The transfer function of the fundamental frequency quasi-proportional resonant controller is expressed as:

[0014]

[0015] Where, k p and k r These are the proportional coefficient and the resonance coefficient, ω. r It is the resonant frequency, ω c It is a parameter related to the bandwidth of the fundamental frequency quasi-proportional resonant controller, and s is the Laplace operator.

[0016] Furthermore, the inner loop control of the inductor current in the dq rotating coordinate system under phase-to-phase short-circuit fault specifically includes:

[0017] The inductor current reference value i Ld * and i Lq * The error is compared with the feedback of each, and the composite controller composed of the PI controller and the second harmonic quasi-proportional resonant controller generates a modulation wave, which finally completes the fault control of the three-phase inverter.

[0018] The transfer function of the composite controller is expressed as:

[0019]

[0020] Where, k p 'k' represents the sum of the proportional coefficients of the PI controller and the second harmonic quasi-proportional resonant controller. i 'and k r 'These are the integral coefficient and the resonance coefficient, respectively, ω r ' is the resonant frequency, ω c ' is a parameter related to the bandwidth of the second harmonic quasi-proportional resonant controller, and s is the Laplace operator.

[0021] Furthermore, the voltage control mode is a dual-loop control, including an outer loop control of capacitor voltage and an inner loop control of inductor current, with the output of the outer loop of capacitor voltage serving as a reference for the inner loop of inductor current.

[0022] The outer loop control of the capacitor voltage is a decoupled control of the capacitor voltage on the dq axis, and the dq axis controller is a proportional-integral controller.

[0023] The inner loop control of the inductor current is a decoupled control of the dq axis inductor current, and the dq axis controller is a proportional-integral controller and a second harmonic quasi-proportional resonant controller.

[0024] This invention proposes a short-circuit current control strategy combining an outer loop for non-faulty phase voltage and an inner loop for inductor current. The outer loop for non-faulty phase voltage employs a quasi-proportional resonant controller (resonant frequency 50Hz) for closed-loop control of the non-faulty phase voltage. The output of the quasi-proportional resonant controller in the outer loop serves as a reference for the non-faulty phase inductor current in the inner loop. This non-faulty phase inductor current reference, along with the amplitude of the faulty phase inductor current, is then processed by an adaptive phase angle adjustment stage based on an SOGI filter to generate two-phase faulty phase inductor current references. These two references, after PARK transformation, serve together as the dq-axis inductor current reference signals in the inner loop. In the inner loop, the controller employs a parallel configuration of a proportional-integral controller and a quasi-proportional resonant controller (resonant frequency 100Hz), with a control structure that decouples the dq-axis inductor current.

[0025] The present invention also provides a short-circuit current limiting system for a three-phase inverter with continuous power supply to non-faulty phases, comprising: a computer-readable storage medium and a processor;

[0026] The computer-readable storage medium is used to store executable instructions;

[0027] The processor is used to read executable instructions stored in the computer-readable storage medium and execute the above-described three-phase inverter short-circuit current limiting method for continuous power supply to non-faulty phases.

[0028] Compared with existing technologies, the technical solutions conceived in this invention address various industry requirements for short-circuit fault ride-through in independent power supply systems. Specifically, it maximizes short-circuit current limiting in the faulty phase to achieve selective protection against short-circuit faults and ensures continuous and reliable power supply during non-fault ride-through. The specific details are as follows: 1) A closed-loop control of the faultless phase voltage is proposed, utilizing a quasi-proportional resonant controller to achieve closed-loop control of the faultless phase. This method ensures continuous power supply to the non-faulty phase under asymmetrical fault conditions, thereby stabilizing the non-faulty phase voltage in Y and Δ connection types at the rated voltage and 0.88 times the rated voltage, respectively. 2) A closed-loop control of the faulty phase current is proposed to maximize short-circuit fault current limiting. During metallic short-circuit faults, it can stably achieve 2-3 times the rated current output, which is beneficial for achieving short-circuit selective protection on the load side. 3) An inner-loop control of the inductor current based on adaptive phase angle adjustment is proposed. This method adaptively adjusts the angle between the inductor currents of the non-faulty and faulty phases to ensure that the three-phase inverter can maximize the fault output current in real time and guarantee power supply to the non-faulty phase load under short-circuit conditions. In addition, the proposed current limiting method has the advantages of fast response speed and simple control structure. Attached Figure Description

[0029] Figure 1 This is a typical structure of a three-phase independent power system;

[0030] Figure 2 The main circuit topology of the three-phase three-wire inverter power supply;

[0031] Figure 3 A general block diagram of a short-circuit current limiting method for a three-phase inverter that enables continuous voltage supply to non-faulty phases;

[0032] Figures 4(a)-(d) show the control block diagrams for the outer loop of capacitor voltage, the inner loop of inductor current, the outer loop of capacitor voltage for non-faulty phases, and the adaptive phase angle adjustment loop based on SOGI filter, respectively.

[0033] Figure 5(a) shows the structure of the SOGI filter; Figure 5(b) shows the frequency response of the SOGI filter.

[0034] Figure 6 Phasor diagram of three-phase inductor current under current limiting control target;

[0035] Figure 7 The phase-to-phase short-circuit test waveforms (output voltage and output current) of a three-phase inverter that can achieve continuous voltage power supply to non-faulty phases are shown.

[0036] Figure 8 The phase-to-phase short-circuit test waveforms (inductor current and output current) of a three-phase inverter that can achieve continuous voltage power supply to non-faulty phases are shown.

[0037] Figure 9 Experimental waveforms of phase-to-phase short-circuit load sudden change for a three-phase inverter that enables continuous voltage supply to non-faulty phases. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0039] A typical structure of a three-phase independent power system is as follows: Figure 1 As shown. A three-phase independent power system typically consists of a DC bus, circuit breakers (CBs), and multiple loads. Throughout the power system, power flows single-phase from the DC side to the loads to ensure reliable power supply. Figure 2 This is the main circuit topology of a three-phase, three-wire inverter power supply, where L and C are the AC filter inductor and capacitor, respectively, G1-G6 are IGBT modules, and DSP is a digital signal processor. In the three-phase inverter power supply system, U dc This refers to the DC bus voltage; i Lk i ck with i ok (k = a, b, c) represent the inductor current, capacitor current, and output current, respectively; u oab u obc and u oca These are the output line voltages; u sab u sbc and u sca These are the line voltages of the three-phase bridge arms, respectively.

[0040] Short-circuit current limiting methods for three-phase inverters that can achieve continuous voltage supply to non-faulty phases, such as... Figure 3 As shown, the overall control architecture consists of two layers: a normal three-phase voltage closed-loop control architecture and a three-phase short-circuit current limiting control architecture, both based on the same inductor current control inner loop. When no short-circuit fault occurs in the independent power system, the three-phase inverter operates in voltage control mode, i.e., the normal three-phase voltage closed-loop control architecture; when a short-circuit fault occurs in the independent power system, the three-phase inverter needs to switch from voltage control mode to current control mode, i.e., the three-phase short-circuit current limiting control architecture; after the short-circuit fault is cleared, the three-phase inverter switches back from current control mode to voltage control mode.

[0041] In voltage control mode, a dual-loop control structure is used, with both loops operating in the dq rotating coordinate system: an outer loop for capacitor voltage and an inner loop for inductor current. The control block diagram for the outer capacitor voltage loop is shown in Figure 4(a). The outer loop control is a dq-axis capacitor voltage decoupling control, and the dq-axis controller is a proportional-integral (PI) controller. The output of the outer capacitor voltage loop serves as the reference for the inner inductor current loop. The control block diagram for the inner inductor current loop is shown in Figure 4(b). The inner loop control is a dq-axis inductor current decoupling control, and the dq-axis controller is a combination of a proportional-integral (PI) controller and a second-harmonic quasi-proportional resonant controller (resonant angular frequency 200π rad / s).

[0042] The current control mode is divided into single-loop and dual-loop control structures. The two architectures are respectively for two types of short-circuit faults in a three-phase three-wire independent power supply system, namely symmetrical short-circuit faults and phase-to-phase short-circuit faults.

[0043] Under a symmetrical short-circuit fault, all three phases are faulty phases, and the current control mode only adopts a single-loop control architecture, namely the inductor current inner loop. This is achieved by separately controlling i... Ld * with i Lq * Assignment I LF (Fault phase current amplitude) and 0 achieve current limiting control of the three-phase inductor current, I LF The fault phase short-circuit current limiting value is determined during the three-phase inverter design phase.

[0044] Under phase-to-phase short-circuit faults, there are two faulty phases and one non-faulty phase in the three-phase system. Therefore, a dual-loop control architecture is adopted, with the two loops operating in the three-phase stationary coordinate system and the dq rotating coordinate system, respectively. These are the outer loop for the non-faulty phase capacitor voltage (as shown in Figure 4(c)) and the inner loop for the inductor current (as shown in Figure 4(b)). The outer loop for the non-faulty phase capacitor voltage is constructed from a single fundamental frequency quasi-proportional resonant controller as follows:

[0045]

[0046] Where, k p and k r These are the proportional coefficient and the resonance coefficient, respectively. ω r It is the resonant frequency (100π rad / s), ω c This is related to the control bandwidth of the fundamental frequency quasi-proportional resonant controller. The output of the outer loop of the non-faulty phase capacitor voltage becomes the reference i for the non-faulty inductor current. LNF * The non-faulty phase inductor current reference needs to pass through an adaptive phase angle adjustment stage based on an SOGI filter (as shown in Figure 4(d)) to generate the two-phase faulty phase inductor current reference. The structure and frequency response of the SOGI filter are shown in Figures 5(a) and 5(b), respectively. It can extract the angular frequency ω from the input signal R(s).SOGI The SOGI filter can extract the in-phase and delayed phase shifts of 90° ω. SOGI The components, the two outputs are represented as C respectively. d (s) and C q (s). The continuous-domain transfer function of the SOGI filter is as follows:

[0047]

[0048] Where, k s These are the SOGI filter coefficients. Assume i LNF * =I LNF * ×cos(ωt), which is generated by the SOGI filter i LNFd * and i LNFq * They can be described as

[0049]

[0050] Among them, I LNF * This is the reference amplitude of the inductor current in the non-faulty phase. Since the non-faulty phase uses voltage closed-loop control, therefore I... LNF * During a short circuit, the impedance of the non-faulty phase load is determined. In a three-phase three-wire independent power supply system, the sum of the three-phase inductive currents is always equal to 0. Therefore, if we want the amplitude of the inductive current of the non-faulty phase to be equal to I... LNF * and I LF Therefore, it is necessary to adjust the phase angle difference β between the non-faulty phase and the faulty phase. In other words, the inductor current of the faulty phase needs to vary according to the magnitude of the inductor current of the non-faulty phase. The phase angle difference β between the inductor current of the faulty phase and the inductor current of the non-faulty phase can be calculated as follows:

[0051]

[0052] Then, the fault phase inductor current reference (i LF1 * and i LF2 * ) can be calculated separately as

[0053]

[0054]

[0055] Among them, i LF1 * It is the fault phase inductor current that lags behind the non-fault phase current, iLF2 * This refers to the fault phase inductor current that leads the non-fault phase. The phasor diagram of the three-phase inductor currents is as follows: Figure 6 As shown, the inductor current of the non-faulty phase is used as the reference phasor. After obtaining i... LNF * i LF1 * and i LF2 * Then, i can be obtained according to the following Park transformation. Ld * and i Lq * .

[0056]

[0057]

[0058] i La * i Lb * and i Lc * This serves as a reference for the three-phase inductor current. Under a phase-to-phase short-circuit fault, there are three possible distributions of faulty and non-faulty phases in the three phases; therefore, any one of the three phases could potentially become a non-faulty phase. Ld * and i Lq * It is fed into the inner loop of the inductor current as a reference for control.

[0059] The inner loop of the inductor current uses a composite controller consisting of a PI controller and a second-harmonic quasi-proportional resonant controller connected in parallel, employing a control mode with dq-axis inductor current decoupling. The transfer function of the composite controller is as follows:

[0060]

[0061] Where, k p 'k' represents the sum of the proportional coefficients of the PI controller and the second harmonic quasi-proportional resonant controller. i 'and k r 'These are the integral coefficient and the resonance coefficient, respectively. ω r ' is the resonant frequency (200π rad / s), ω c It is related to the control bandwidth of the second harmonic quasi-proportional resonant controller.

[0062] Figure 7 and Figure 8These are experimental waveforms of a three-phase inverter under full load when a phase-to-phase short circuit occurs, demonstrating a short-circuit current limiting method that enables continuous voltage supply to non-faulty phases. Phase A is the non-faulty phase, while phases B and C are the faulty phases. When a phase-to-phase short circuit fault occurs in phases B and C, phase A can still maintain normal power supply. During the short-circuit current limiting period, the voltage of phase A remains near its rated voltage. Figure 7 As shown. Figure 8 The experimental waveforms of inductor current and output current during a phase-to-phase short-circuit fault are shown. The inductor current is strictly controlled within the current-limiting target (e.g., ...). Figure 6 That is, the non-faulty phase and the faulty phase are respectively I LNF * and I LF .

[0063] When a short-circuit fault occurs in the power system, the circuit breaker may disconnect some sensitive and critical loads in the system if the fault is not cleared. In this case, the inverter needs to respond to sudden load changes. The current limiting method proposed in this paper uses voltage closed-loop control for non-faulty phases and has good robustness to load surges. Figure 9 In the test, 240ms after a phase-to-phase short-circuit fault occurred, one-third of the load was disconnected. The voltage of the non-faulty phases was almost unaffected by load changes, and the current of the faulty phase also tended to stabilize after several fundamental cycles. It can be seen that the three-phase inverter can ensure a constant voltage of the non-faulty phases under any load without affecting the short-circuit current limiting control.

[0064] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A short-circuit current limiting method for a three-phase inverter with continuous power supply to non-faulty phases, characterized in that, Includes the following steps: When no short-circuit fault occurs in the independent power system, the three-phase inverter operates in voltage control mode; When a short-circuit fault occurs in the independent power system, the three-phase inverter switches from voltage control mode to current control mode. The short-circuit fault is divided into symmetrical short-circuit fault and phase-to-phase short-circuit fault. After the short-circuit fault is cleared, the three-phase inverter switches back from current control mode to voltage control mode. Under a symmetrical short-circuit fault, all three phases are faulty phases, and the current control mode is inductor current inner loop control: the inductor current reference value is controlled separately. i Ld * and i Lq * Assign fault phase current amplitude I LF Achieving current limiting control of the three-phase inductor current with a value of 0; Under a phase-to-phase short-circuit fault, there are two faulty phases and one non-faulty phase in the three-phase system. The current control mode consists of an outer loop control of the non-faulty phase capacitor voltage in the three-phase stationary coordinate system and an inner loop control of the inductor current in the dq rotating coordinate system. The inductor current reference value is as follows: i Ld * and i Lq * It is calculated by an adaptive phase angle adjustment circuit based on an SOGI filter; The outer loop control of the capacitor voltage of the non-faulty phase under a phase-to-phase short-circuit fault specifically includes: The error between the outer loop reference value and the feedback value of the capacitor voltage of the non-faulty phase is used to obtain the reference value of the inductor current of the non-faulty phase through the fundamental frequency quasi-proportional resonant controller. i LNF * The reference value of the inductor current of the non-faulty phase i LNF * The in-phase reference value of the non-faulty phase inductor current is obtained after passing through the SOGI filter. i LNFd * Orthogonal reference value i LNFq * And calculate the reference amplitude of the inductor current of the non-faulty phase in real time based on both. I LNF * ; by current limiting setting value I LF Reference amplitude of inductor current in non-faulty phase I LNF * The angle between the inductor current of the non-faulty phase and the inductor current of the faulty phase was calculated. β The trigonometric function cos( β ) and sin( β );according to i LNFd * 、i LNFq * 、I LNF * 、I LF 、 cos( β ) and sin( β The reference values ​​of the inductor currents of the two faulty phases were calculated. i LF1 * and i LF2 * ,in i LF1 * Lagging non-faulty phase β The fault phase current, i LF2 * For advanced non-faulty phase β The fault phase current; i LNF * , i LF1 * and i LF2 * The reference value of the inductor current in the dq coordinate system is obtained after the abc / dq transformation. i Ld * and i Lq * ; The inner loop control of inductor current in the dq rotating coordinate system under phase-to-phase short-circuit fault specifically includes: The inductor current reference value i Ld * and i Lq * The error is compared with the feedback of each, and the composite controller composed of the PI controller and the second harmonic quasi-proportional resonant controller generates a modulation wave, which finally completes the fault control of the three-phase inverter.

2. The method according to claim 1, characterized in that, The transfer function of the fundamental frequency quasi-proportional resonant controller for the outer loop of the non-faulty phase capacitor voltage is expressed as: in, k p and k r These are the proportional coefficient and the resonance coefficient, respectively. ω r It is the resonant frequency. ω c It is a parameter related to the bandwidth of the fundamental frequency quasi-proportional resonant controller. s For the Laplace operator.

3. The method according to claim 1, characterized in that, The transfer function of the composite controller is expressed as: in, k p ’ It is the sum of the proportional coefficients of the PI controller and the second harmonic quasi-proportional resonant controller. k i ’ and k r ’ These are the integral coefficient and the resonance coefficient, respectively. ω r ’ It is the resonant frequency. ω c ’ These are parameters related to the bandwidth of the second harmonic quasi-proportional resonant controller. s For the Laplace operator.

4. The method according to claim 1, characterized in that, The voltage control mode is a dual-loop control, including an outer loop control of capacitor voltage and an inner loop control of inductor current. The output of the outer loop of capacitor voltage serves as a reference for the inner loop of inductor current. The outer loop control of the capacitor voltage is a decoupled control of the capacitor voltage on the dq axis, and the dq axis controller is a proportional-integral controller. The inner loop control of the inductor current is a decoupled control of the dq axis inductor current, and the dq axis controller is a proportional-integral controller and a second harmonic quasi-proportional resonant controller.

5. A short-circuit current limiting system for a three-phase inverter with continuous power supply to non-faulty phases, characterized in that, include: Computer-readable storage media and processors; The computer-readable storage medium is used to store executable instructions; The processor is used to read executable instructions stored in the computer-readable storage medium and execute the short-circuit current limiting method for a three-phase inverter with continuous power supply to non-faulty phases as described in any one of claims 1 to 4.

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