Short-circuit current limiting method for three-phase inverter power supply based on activating virtual impedance based on stereo criteria

Abstract

The present invention discloses a short-circuit current limiting method for a three-phase inverter power supply based on activating virtual impedance based on a three-dimensional criterion, and relates to the technical field of power electronics. The method comprises: connecting a current and voltage detection device to the output end of the inverter power supply, sampling the output current and voltage in real time, sending the data to a short-circuit fault monitoring and type discrimination module, monitoring the short-circuit fault through a multi-criteria three-dimensional short-circuit fault recognition algorithm, and discriminating the fault type as a three-phase symmetrical fault or an asymmetrical fault after recognition; according to the fault type, the virtual impedance module activates the corresponding virtual impedance value and switches the inverter power supply to a short-circuit current limiting control mode, the voltage outer loop exits, and the current inner loop reference value is clamped to a constant state, so that the output current is limited, ensuring that the current limiting is successfully completed under different short-circuit situations.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a short-circuit current limiting method for a three-phase inverter power supply based on activating virtual impedance according to a three-dimensional criterion. Background Art

[0002] With the rapid development of power electronics, three-phase inverter power modules are playing a vital role in renewable energy generation, specialty power supplies, microgrids, and other fields. However, load short circuits are one of the most damaging faults in inverter power systems. Existing technologies use inverter power systems to shut down for self-protection. While this provides rapid protection, in the case of multiple loads, loads on non-faulty lines may also experience power outages, reducing power supply reliability.

[0003] Currently, numerous methods are available for rapidly identifying short-circuit faults, including instantaneous current values, fast Fourier transforms (FFTs), current average detection, peak detection, dq transform detection, wavelet transforms, and Kalman filtering algorithms. FFTs, current average detection, and peak detection require at least half a cycle of data, and fault detection takes at least 10ms. Kalman filtering and wavelet transforms are also complex. Commonly used short-circuit fault indicators include the instantaneous short-circuit current value and the current swell rate. However, relying solely on these indicators can lead to misjudgments and slow responses.

[0004] Existing short-circuit current-limiting control methods, such as those based on the maximum output current RMS value, positive and negative sequence control, and current-command-adjusted current-limiting control, also suffer from slow response or complex control structures. Furthermore, the virtual impedance used in conventional control strategies suffers from mechanical rigidity and the inability to precisely control various short-circuit fault types. Summary of the Invention

[0005] The purpose of the present invention is to solve the shortcomings of the short-circuit current limiting strategy of the three-phase inverter power supply in the prior art and to provide a short-circuit current limiting control method based on a multi-criteria three-dimensional short-circuit fault identification algorithm.

[0006] The technical solution of the present invention is to provide a three-phase inverter power supply short-circuit current limiting method based on three-dimensional criterion activation of virtual impedance, the method comprising:

[0007] S1. Connect a current detection device and a voltage detection device to the output end of the inverter power supply to sample the output current and output voltage of the three-phase inverter power supply in real time, and send them to the short-circuit fault monitoring and type discrimination module;

[0008] S2, the short-circuit fault monitoring and type discrimination module reads the real-time output current and output voltage values, and completes the monitoring of short-circuit faults through a multi-criteria three-dimensional short-circuit fault identification algorithm;

[0009] S3. After identifying the presence of a short-circuit fault, the fault type is determined. The fault type is categorized as a three-phase symmetrical fault or an asymmetrical fault. If the characteristic values ​​of the three phases are all identified as short-circuit faults in the multi-criteria three-dimensional short-circuit fault identification algorithm, then it is determined that a three-phase symmetrical short-circuit fault has occurred; otherwise, it is an asymmetrical short-circuit fault. The fault type is sent to the virtual impedance module.

[0010] S4. After the virtual impedance module receives a short-circuit fault, it activates different virtual impedance values ​​according to the fault type. The inverter power supply control switches from the normal mode to the short-circuit current limiting control mode. The voltage outer loop exits the inverter control link, and the current inner loop reference value is clamped to a constant value. Through the inner loop control, the output current is limited. In combination with the different virtual impedance values ​​activated according to the fault type, the inverter power supply module can successfully complete short-circuit current limiting under different short-circuit situations.

[0011] In any of the above technical solutions, further, the multi-criteria three-dimensional short-circuit fault identification algorithm in step S2 includes:

[0012] Three criteria are set: instantaneous current value, current swell rate, and load impedance. These criteria are mapped to the horizontal and vertical axes of a three-dimensional coordinate system, so that each state of the actual operating circuit can correspond to a sampling point in the coordinate space. Under normal operating conditions, all sampling points constitute a normal operating criterion body. When the corresponding points calculated by sampling at a certain operating moment exceed the normal operating criterion body and the number of points exceeds the rated number, a short circuit fault is determined to have occurred.

[0013] In any of the above technical solutions, further, the details of the three criteria and the method of mapping them to coordinates are:

[0014] Current instantaneous value: Compare the real-time sampled current value with the set current threshold value to calculate the coordinate of the current instantaneous current value on the x-axis;

[0015] The x-axis coordinate value corresponding to the instantaneous value of current is:

[0016]

[0017] I o (n) represents the current sampling value at a certain moment, I th is the set current instantaneous value threshold;

[0018] Current rise rate: Calculate the current rise rate by taking the difference between the current sampling value and the current value at the previous sampling point to determine the coordinate on the y-axis.

[0019] The calculation process of the current climbing rate K and the corresponding y-axis coordinate value is:

[0020]

[0021] Io (n-1) represents the current value at the previous sampling moment, Δt is the sampling interval, K th Indicates the set current climbing rate threshold;

[0022] Load impedance: Calculate the load impedance through the real-time sampled voltage and current RMS values ​​to determine the coordinate on the z-axis;

[0023] The calculation of load impedance is based on Ohm's law and is calculated by dividing the output voltage RMS value by the output current RMS value. To speed up the detection, the RMS value is calculated using a sliding window algorithm. The calculation result is updated once each sampling, thereby ensuring that the load impedance calculation changes more smoothly and enabling the system to respond more accurately and quickly. The calculation formula for the load impedance value and the corresponding z-axis coordinate value using the sliding window algorithm is:

[0024]

[0025] U o_rms (n), I o_rms (n) are the effective values ​​of output voltage and output current obtained by sliding window algorithm at the nth sampling point, N is the number of sampling points in each fundamental wave period, Z load is the actual value of the load impedance, Z th is the selected load impedance threshold value. The selection of this threshold value is related to the rated voltage, rated capacity and overload capacity of the three-phase inverter power supply system. At the same time, since the selected sampled information is the output line current and output phase voltage, the threshold value Z th The selection of load side connection mode should also be considered. If the load side is Δ connection, the coefficient should be multiplied.

[0026] In any of the above technical solutions, further, when the fault type in step S4 is a three-phase symmetrical short circuit fault, the fixed value virtual impedance Z is activated. vir_sym , enhance system robustness, improve the output characteristics of the three-level inverter, reduce the impact of the inherent resonant spike on the output side of the inverter, eliminate output voltage and current ripples, and ensure the output waveform quality under harsh working conditions of three-phase short circuit.

[0027] In any of the above technical solutions, further, when the fault type in step S4 is an asymmetric short circuit fault, the adaptive virtual impedance ΔZ is activated. vir_asym The virtual impedance value is adjusted in real time according to the adaptive virtual impedance control method to avoid the voltage limiting phenomenon caused by excessive output voltage due to the large load impedance value of the non-fault phase under the short-circuit current limiting instruction, and to ensure that the output current reaches the current limit value under the premise of continuous use of three-phase unified control to ensure the correct operation of the circuit breaker.

[0028] In any of the above technical solutions, further, the adaptive virtual impedance control method includes:

[0029] Using the load impedance value calculated in the short-circuit fault monitoring and type discrimination module, a fault depth parameter F is set. The parameter F is defined as:

[0030]

[0031] where Z full is the full load value of the three-phase inverter power system, and the adaptive virtual impedance ΔZ is set by the fault depth parameter vir_asym for:

[0032]

[0033] where Z vir_asym is the constant value parameter of the virtual impedance during asymmetric faults. To ensure the current limiting effect of asymmetric short-circuit, the adaptive virtual impedance value has upper and lower limits. The upper limit can be obtained by analyzing the system stability through the impedance analysis method, and the lower limit is obtained by avoiding the critical value of voltage saturation limiting.

[0034] In any of the above technical solutions, further, in step S1, since the voltage on the load-side inductor is small, the voltage detection device measures the capacitor voltage that is similar to the output voltage to replace the output voltage.

[0035] The beneficial effects of the present invention are:

[0036] The technical solution of the present invention utilizes a multi-criteria three-dimensional short-circuit fault identification algorithm, which can quickly detect and identify the fault type when a short-circuit fault occurs, significantly shortening the fault response time and avoiding system damage caused by delayed response; it uses three criteria: current instantaneous value, current rise rate and load impedance for three-dimensional comprehensive judgment, effectively improving the accuracy of short-circuit fault identification and reducing the possibility of misjudgment and missed judgment.

[0037] By introducing virtual impedance technology, the stability and robustness of the system are effectively enhanced in short-circuit current limiting control, the output current characteristics are improved, the current ripple is reduced, and the operation reliability of the system is improved. Depending on the type of short-circuit fault (three-phase symmetrical fault and asymmetrical fault), the corresponding virtual impedance value is activated, so that the optimal current limiting effect can be achieved under different fault conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The advantages of the above and additional aspects of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0039] Figure 11 is a schematic diagram of the overall framework of a three-phase inverter power supply short-circuit current limiting method based on activating virtual impedance based on a three-dimensional criterion according to an embodiment of the present invention;

[0040] Figure 2 1 is a schematic diagram of a multi-criteria three-dimensional short-circuit fault identification algorithm for a three-phase inverter power supply short-circuit current limiting method based on three-dimensional criteria to activate virtual impedance according to an embodiment of the present invention;

[0041] Figure 3 This is a schematic diagram of the control logic of the adaptive virtual impedance value activated under an asymmetric short circuit fault of a three-phase inverter power supply short circuit current limiting method based on a three-dimensional criterion to activate virtual impedance according to an embodiment of the present invention;

[0042] Figure 4 1 is a schematic diagram of an output current waveform in which a false short circuit is detected under overload conditions when using a traditional short circuit criterion in an embodiment of a three-phase inverter power supply short circuit current limiting method based on a three-dimensional criterion to activate a virtual impedance according to an embodiment of the present invention;

[0043] Figure 5 1. A schematic diagram of an output current waveform when the overload control is normally entered under overload conditions when a multi-criteria stereo short-circuit fault identification algorithm is used in an embodiment of a three-phase inverter power supply short-circuit current limiting method based on stereo criteria activated virtual impedance according to an embodiment of the present invention;

[0044] Figure 6 1 is a schematic diagram of a three-phase short-circuit fault output current waveform in an embodiment of a three-phase inverter power supply short-circuit current limiting method based on three-dimensional criterion activation of virtual impedance according to an embodiment of the present invention;

[0045] Figure 7 The figure is a schematic diagram of an asymmetric short-circuit fault output current waveform in an embodiment of a three-phase inverter power supply short-circuit current limiting method based on three-dimensional criterion activation of virtual impedance according to an embodiment of the present invention. DETAILED DESCRIPTION

[0046] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present invention and the features therein can be combined with each other without conflict.

[0047] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0048] like Figure 1As shown, this embodiment provides a three-phase inverter power supply short-circuit current limiting method based on activating virtual impedance based on a three-dimensional criterion, the method comprising:

[0049] S1. Connect a current detection device and a voltage detection device to the output end of the inverter power supply to sample the output current and output voltage of the three-phase inverter power supply in real time, and send them to the short-circuit fault monitoring and type discrimination module.

[0050] Specifically, since the voltage on the load-side inductor is small, the voltage detection device measures the capacitor voltage which is similar to the output voltage instead of the output voltage.

[0051] S2, the short-circuit fault monitoring and type discrimination module reads the real-time output current value and output voltage value, and completes the monitoring of the short-circuit fault through the multi-criteria three-dimensional short-circuit fault recognition algorithm.

[0052] The multi-criteria three-dimensional short-circuit fault identification algorithm includes:

[0053] like Figure 2 As shown in the figure, based on the characteristics of a series of characteristic quantity changes when a short circuit occurs on the load side of the inverter power module, namely, a sudden increase in output current, a sharp drop in output voltage, and a rapid decrease in load impedance, three criteria are set, namely, the instantaneous value of current, the current climbing rate, and the load impedance. These criteria are mapped to the horizontal, vertical, and vertical axes of the three-dimensional coordinate system, so that each state of the actual operating circuit can correspond to a sampling point in the coordinate space. Under normal operating conditions, all sampling points constitute a normal operating criterion body. When the corresponding points calculated by sampling at a certain operating moment exceed the normal operating criterion body and the number of points exceeds the rated number, it is determined that a short circuit fault has occurred.

[0054] The sampled voltage and current values ​​enter the analog-to-digital converter, and then enter the three signal coordinate processing processes respectively. They are matched and calculated with the three judgment threshold values ​​through the divider to obtain the corresponding coordinates of different coordinate axes, and finally enter the cube judgment unit for diagnosis of the operating status.

[0055] Current instantaneous value: By comparing the real-time sampled current value with the set current threshold value, the coordinate of the current instantaneous current value on the x-axis is calculated.

[0056] The x-axis coordinate value corresponding to the instantaneous value of current is:

[0057]

[0058] I o (n) represents the current sampling value at a certain moment, I th It is the set current instantaneous value threshold.

[0059] Current rise rate: The current rise rate is calculated by the difference between the current sampling value and the current value at the previous sampling point to determine the coordinate on the y-axis.

[0060] The calculation process of the current climbing rate K and the corresponding y-axis coordinate value is:

[0061]

[0062] I o (n-1) represents the current value at the previous sampling moment, Δt is the sampling interval, K th Indicates the set current rise rate threshold.

[0063] Load impedance: The load impedance is calculated using the real-time sampled voltage and current RMS values ​​to determine the coordinate on the z-axis.

[0064] The load impedance is calculated based on Ohm's law and is obtained by dividing the output voltage RMS value by the output current RMS value. To speed up the detection, the RMS value is calculated using a sliding window algorithm. The calculation result is updated once each sampling, ensuring smoother changes in the load impedance calculation and enabling the system to respond more accurately and quickly. The calculation formula for the load impedance value and the corresponding z-axis coordinate value using the sliding window algorithm is:

[0065]

[0066] U o_rms (n), I o_rms (n) are the effective values ​​of output voltage and output current obtained by sliding window algorithm at the nth sampling point, N is the number of sampling points in each fundamental wave period, Z load is the actual value of the load impedance, Z th is the selected load impedance threshold value. The selection of this threshold value is related to the rated voltage, rated capacity and overload capacity of the three-phase inverter power supply system. At the same time, since the selected sampled information is the output line current and output phase voltage, the threshold value Z th The selection of load side connection mode should also be considered. If the load side is Δ connection (three-phase power system has two layout modes, namely Y connection and Δ connection), the coefficient should be multiplied.

[0067] The three criteria of current instantaneous value, current climbing rate and load impedance are used together to ensure that the three-phase inverter power supply system can quickly and accurately identify short-circuit faults. The requirement for load impedance value enables a better distinction between short-circuit current limiting control and overload control, avoiding the phenomenon of mistakenly entering the current limiting loop within the overload capacity range.

[0068] S3. After identifying the presence of a short-circuit fault, the fault type is determined. The fault type is divided into three-phase symmetrical fault and asymmetrical fault. If the characteristic values ​​of the three phases are all identified as short-circuit faults in the multi-criteria three-dimensional short-circuit fault identification algorithm, it is determined that a three-phase symmetrical short-circuit fault has occurred; otherwise, it is an asymmetrical short-circuit fault. The fault type is sent to the virtual impedance module.

[0069] S4. After the virtual impedance module receives a short-circuit fault, it activates different virtual impedance values ​​according to the fault type. The inverter power supply control switches from the normal mode to the short-circuit current limiting control mode. The voltage outer loop exits the inverter control link, and the current inner loop reference value is clamped to a constant value. Through the inner loop control, the output current is limited. In combination with the different virtual impedance values ​​activated according to the fault type, the inverter power supply module can successfully complete short-circuit current limiting under different short-circuit situations.

[0070] When the fault type is a three-phase symmetrical short circuit fault, the fixed virtual impedance Z is activated. vir_sym , enhance system robustness, improve the output characteristics of the three-level inverter, reduce the impact of the inherent resonant spike on the output side of the inverter, eliminate output voltage and current ripples, and ensure the output waveform quality under harsh working conditions of three-phase short circuit.

[0071] When the fault type is an asymmetric short circuit fault, the adaptive virtual impedance ΔZ is activated. vir_asym The virtual impedance value is adjusted in real time according to the adaptive virtual impedance control method to avoid the voltage limiting phenomenon caused by excessive output voltage due to the large load impedance value of the non-fault phase under the short-circuit current limiting instruction, and to ensure that the output current reaches the current limit value under the premise of continuous use of three-phase unified control to ensure the correct operation of the circuit breaker.

[0072] like Figure 3 As shown in Figure 2, the adaptive virtual impedance control method includes:

[0073] Using the load impedance value calculated in the short-circuit fault monitoring and type discrimination module, a fault depth parameter F is set. The parameter F is defined as:

[0074]

[0075] where Z full is the full load value of the three-phase inverter power system, and the adaptive virtual impedance ΔZ is set by the fault depth parameter vir_asym for:

[0076]

[0077] where Z vir_asymThis is the constant value parameter for the virtual impedance during asymmetric faults. To ensure the current limiting effect of asymmetric short-circuit currents, the adaptive virtual impedance has upper and lower limits. The upper limit can be determined by analyzing system stability using impedance analysis, while the lower limit is determined by avoiding the critical value of voltage saturation limiting.

[0078] In another embodiment of the present invention, a three-phase inverter power supply simulation model was built in Simulink, a professional power system simulation software. A 100kW mid-point-clamped three-level inverter was selected as an example to test the short-circuit current limiting method proposed in this patent through simulation tests. The method requires that the AC load state be correctly identified without misjudgment, and that after a short-circuit fault is identified, the short-circuit current be limited to a protection set value by smoothly switching the control loop and control parameters. The current limiting amplitude is set to 770A.

[0079] Figure 4 、 Figure 5 The output current waveforms for a load-side overload condition at 0.3s using a conventional short-circuit fault identification method and the multi-criteria, three-dimensional short-circuit fault identification algorithm proposed in this invention. The conventional method, which relies solely on output current amplitude and slew rate, misjudged a short circuit, leading to the inadvertent entry into short-circuit control mode and significant current fluctuations. The proposed method eliminated this misjudgment and smoothly entered overload control.

[0080] Figure 6 、 Figure 7 The output current waveforms for a symmetrical three-phase short-circuit fault and an asymmetrical interphase short-circuit fault occurring on the load side at time 0.3s, respectively, are shown. The interphase short-circuit fault is an A-phase short-circuit. As can be seen from the figure, using the short-circuit current limiting method proposed in this invention enables the control system to respond promptly and quickly to various short-circuit fault scenarios. By incorporating the corresponding virtual impedance modules, the output current is controlled to the required limit. Although there is a certain inrush current due to delay, it is within the maximum inrush current tolerance of the inverter power module, verifying the effectiveness of this short-circuit current limiting method.

[0081] In summary, the present invention proposes a short-circuit current limiting method for a three-phase inverter power supply based on a three-dimensional criterion to activate a virtual impedance, comprising:

[0082] S1. Connect a current detection device and a voltage detection device to the output end of the inverter power supply to sample the output current and output voltage of the three-phase inverter power supply in real time, and send them to the short-circuit fault monitoring and type discrimination module.

[0083] S2, the short-circuit fault monitoring and type discrimination module reads the real-time output current value and output voltage value, and completes the monitoring of the short-circuit fault through the multi-criteria three-dimensional short-circuit fault recognition algorithm.

[0084] S3. After identifying the presence of a short-circuit fault, the fault type is determined. The fault type is divided into three-phase symmetrical fault and asymmetrical fault. If the characteristic values ​​of the three phases are all identified as short-circuit faults in the multi-criteria three-dimensional short-circuit fault identification algorithm, it is determined that a three-phase symmetrical short-circuit fault has occurred; otherwise, it is an asymmetrical short-circuit fault. The fault type is sent to the virtual impedance module.

[0085] S4. After the virtual impedance module receives a short-circuit fault, it activates different virtual impedance values ​​according to the fault type. The inverter power supply control switches from the normal mode to the short-circuit current limiting control mode. The voltage outer loop exits the inverter control link, and the current inner loop reference value is clamped to a constant value. Through the inner loop control, the output current is limited. In combination with the different virtual impedance values ​​activated according to the fault type, the inverter power supply module can successfully complete short-circuit current limiting under different short-circuit situations.

[0086] The steps in the present invention can be adjusted in sequence, combined, or deleted according to actual needs.

[0087] The units in the device of the present invention can be combined, divided and deleted according to actual needs.

[0088] Although the present invention has been disclosed in detail with reference to the accompanying drawings, it should be understood that these descriptions are merely illustrative and are not intended to limit the application of the present invention. The scope of the present invention is defined by the appended claims and includes various modifications, variations, and equivalents made to the invention without departing from the scope and spirit of the present invention.

Claims

1. A three-phase inverter power supply short-circuit current limiting method based on activating virtual impedance based on a three-dimensional criterion, characterized in that: The method comprises: S1. Connect a current detection device and a voltage detection device to the output end of the inverter power supply to sample the output current and output voltage of the three-phase inverter power supply in real time, and send them to the short-circuit fault monitoring and type discrimination module; S2, the short-circuit fault monitoring and type discrimination module reads the real-time output current and output voltage values, and completes the monitoring of short-circuit faults through a multi-criteria three-dimensional short-circuit fault identification algorithm; The multi-criteria three-dimensional short circuit fault identification algorithm in step S2 includes: Three criteria are set: instantaneous current value, current swell rate, and load impedance. These are mapped onto the horizontal, vertical, and vertical axes of a three-dimensional coordinate system, so that each state of the actual operating circuit corresponds to a sampling point in the coordinate space. Under normal operating conditions, all sampling points constitute a normal operating criterion body. When the corresponding points calculated by sampling at a certain operating moment exceed the normal operating criterion body, and the number of points exceeds the rated number, a short circuit fault is determined. S3. After identifying the presence of a short-circuit fault, the fault type is determined. The fault type is categorized as a three-phase symmetrical fault or an asymmetrical fault. If the characteristic values ​​of the three phases are all identified as short-circuit faults in the multi-criteria three-dimensional short-circuit fault identification algorithm, then it is determined that a three-phase symmetrical short-circuit fault has occurred; otherwise, it is an asymmetrical short-circuit fault. The fault type is sent to the virtual impedance module. S4. After the virtual impedance module receives a short-circuit fault, it activates different virtual impedance values ​​according to the fault type. The inverter power supply control switches from the normal mode to the short-circuit current limiting control mode. The voltage outer loop exits the inverter control link, and the current inner loop reference value is clamped to a constant value. Through the inner loop control, the output current is limited. In combination with the different virtual impedance values ​​activated according to the fault type, the inverter power supply module can successfully complete short-circuit current limiting under different short-circuit situations.

2. The three-phase inverter power supply short-circuit current limiting method based on three-dimensional criterion activation of virtual impedance according to claim 1, characterized in that: The details of the three criteria and the method of mapping them to coordinates are: Current instantaneous value: Compare the real-time sampled current value with the set current threshold value to calculate the coordinate of the current instantaneous current value on the x-axis; The x-axis coordinate value corresponding to the instantaneous value of current is: I o (n) represents the current sampling value at a certain moment, I th is the set current instantaneous value threshold; Current rise rate: Calculate the current rise rate by taking the difference between the current sampling value and the current value at the previous sampling point to determine the coordinate on the y-axis. The calculation process of the current climbing rate K and the corresponding y-axis coordinate value is: I o (n-1) represents the current value at the previous sampling moment, Δt is the sampling interval, K th Indicates the set current climbing rate threshold; Load impedance: Calculate the load impedance through the real-time sampled voltage and current RMS values ​​to determine the coordinate on the z-axis; The calculation of load impedance is based on Ohm's law and is calculated by dividing the output voltage RMS value by the output current RMS value. To speed up the detection, the RMS value is calculated using a sliding window algorithm. The calculation result is updated once each sampling, thereby ensuring that the load impedance calculation changes more smoothly and enabling the system to respond more accurately and quickly. The calculation formula for the load impedance value and the corresponding z-axis coordinate value using the sliding window algorithm is: U o_rms (n), I o_rms (n) are the effective values ​​of output voltage and output current obtained by sliding window algorithm at the nth sampling point, N is the number of sampling points in each fundamental wave period, Z load is the actual value of the load impedance, Z th is the selected load impedance threshold value. The selection of this threshold value is related to the rated voltage, rated capacity and overload capacity of the three-phase inverter power supply system. At the same time, since the selected sampled information is the output line current and output phase voltage, the threshold value Z th The selection of load side connection mode should also be considered. If the load side is Δ connection, the coefficient should be multiplied.

3. The three-phase inverter power supply short-circuit current limiting method based on three-dimensional criterion activation of virtual impedance according to claim 1, characterized in that: When the fault type in step S4 is a three-phase symmetrical short circuit fault, the fixed value virtual impedance Z is activated. vir_sym , enhance system robustness, improve the output characteristics of the three-level inverter, reduce the impact of the inherent resonant spike on the output side of the inverter, eliminate output voltage and current ripples, and ensure the output waveform quality under harsh working conditions of three-phase short circuit.

4. The three-phase inverter power supply short-circuit current limiting method based on three-dimensional criterion activation of virtual impedance according to claim 1, characterized in that: When the fault type in step S4 is an asymmetric short circuit fault, the adaptive virtual impedance ΔZ is activated. vir_asym The virtual impedance value is adjusted in real time according to the adaptive virtual impedance control method to avoid the voltage limiting phenomenon caused by excessive output voltage due to the large load impedance value of the non-fault phase under the short-circuit current limiting instruction, and to ensure that the output current reaches the current limit value under the premise of continuous use of three-phase unified control to ensure the correct operation of the circuit breaker.

5. The three-phase inverter power supply short-circuit current limiting method based on three-dimensional criterion activation of virtual impedance according to claim 4, characterized in that: The adaptive virtual impedance control method comprises: Using the load impedance value calculated in the short-circuit fault monitoring and type discrimination module, a fault depth parameter F is set. The parameter F is defined as: where Z full is the full load value of the three-phase inverter power system, and the adaptive virtual impedance ΔZ is set by the fault depth parameter vir_asym for: where Z vir_asym is the constant value parameter of the virtual impedance during asymmetric faults. To ensure the current limiting effect of asymmetric short-circuit, the adaptive virtual impedance value has upper and lower limits. The upper limit can be obtained by analyzing the system stability through the impedance analysis method, and the lower limit is obtained by avoiding the critical value of voltage saturation limiting.

6. The three-phase inverter power supply short-circuit current limiting method based on three-dimensional criterion activation of virtual impedance according to claim 1, characterized in that: In step S1 , since the voltage on the load-side inductor is relatively small, the voltage detection device measures the capacitor voltage which is similar to the output voltage to replace the output voltage.

Images