Method and device for controlling starting of three-phase inverter with motor and medium

Abstract

The invention provides a control method and device for starting a three-phase inverter with a motor and a medium. The method comprises the following steps: sampling a three-phase inverter current signal and a three-phase inverter voltage signal in real time; processing the current through a low-pass filter to obtain a current signal after low-pass filtering; performing differential processing on the filtered current signal by using a differential method to obtain a current change rate, and processing the voltage signal to obtain a voltage angle; judging whether a voltage reduction condition is met or not according to the current differential value and the voltage angle; and if the voltage reduction condition is met, voltage reduction current limiting control is carried out in the motor starting stage until excitation of the motor is established. According to the invention, through real-time sampling and low-pass filtering of a three-phase current signal, high-frequency noise interference is fully reduced; performing differential processing on the filtered current signal by using a high-order difference method so as to accurately capture the current change rate; and voltage reduction control is carried out through dual discrimination of a voltage angle and a current differential value, so that the robustness and accuracy of the system are effectively improved, and misoperation of equipment is avoided.

Description

Technical Field

[0001] This invention belongs to the field of motor control technology, and in particular relates to a control method, device and medium for starting a motor in a three-phase inverter. Background Technology

[0002] The large current surge during motor load startup places higher demands on inverter design. Due to the inductive characteristics and mechanical structure of motors, large instantaneous current pulses may be generated during startup. This can lead to inverter overload and undervoltage protection issues, as well as voltage distortion, affecting the overall system stability. Existing technologies employ TZ protection technology to quickly disconnect the inverter's pulse output to protect the inverter; or use external soft-start devices to avoid large current surges; or use current control methods based on predictive current changes and adaptive control.

[0003] While traditional TZ protection technology can act quickly after detecting overcurrent, the direct blocking of pulse output can cause severe voltage waveform distortion, thus affecting the stability of the entire control loop. Adding an external soft-start device increases system cost and size, making system modification difficult. During current control, rapid changes in load characteristics or other unforeseen factors can still result in a large starting inrush current. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a control method for starting a motor in a three-phase inverter, used to control a motor load without a frequency converter when the three-phase inverter is off-grid running, including the following steps: Step S1: Real-time sampling of three-phase inverter current and voltage signals; Step S2: Process the current of each phase through a low-pass filter to obtain the low-pass filtered current signal; Step S3: Differentiate the filtered current signal using the differential method to obtain the current change rate, and process the voltage signal sampled in S1 to obtain the voltage angle. Step S4: Determine whether the voltage reduction condition is met based on the differential value of the current and the voltage angle. The voltage reduction condition is the judgment condition that requires protective measures to be taken when the motor starts. Step S5: If the voltage reduction condition is met, implement voltage reduction and current limiting control during the motor startup phase until the motor establishes excitation.

[0005] Preferably, the cutoff frequency of the low-pass filter in step S2 is 250Hz, which is used to filter out high-frequency harmonics of the sampled current signal in step S1 and quickly respond to the motor load.

[0006] Preferably, the differential method is a higher-order finite difference method—the five-point difference method, with the following formula: ; where \(x\) is the sampling point, is the current value corresponding to the sampling point \(x\), and the sampling interval is \(h\), is the corresponding first-order derivative; Differentiate the current signal processed in step S2 by using the five-point difference method to obtain the current change rate.

[0007] Based on the above solution, the voltage angles include the phase-A voltage angle \(U_A\), the phase-B voltage angle \(U_B\), and the phase-C voltage angle \(U_C\), the current change rates include the phase-A current change rate \(D_A\), the phase-B current change rate \(D_B\), and the phase-C current change rate \(D_C\). When making the judgment in step S4, it meets the step-down condition when the current change rate of a certain phase is detected to exceed the current differential threshold \(D_{th}\) or be lower than \(-D_{th}\) within the specific voltage angle range of each phase.

[0008] Based on the above solution, when \(-30^{\circ}<U_A<30^{\circ}\) and \(D_A > D_{th}\), or \(150^{\circ}<U_A<210^{\circ}\) and \(D_A < -D_{th}\), it is determined that the step-down condition is met; when \(90^{\circ}<U_B<150^{\circ}\) and \(D_B > D_{th}\), or \(270^{\circ}<U_B<330^{\circ}\) and \(D_B < -D_{th}\), it is determined that the step-down condition is met; when \(210^{\circ}<U_C<270^{\circ}\) and \(D_C > D_{th}\), or \(30^{\circ}<U_C<90^{\circ}\) and \(D_A < -D_{th}\), it is determined that the step-down condition is met.

[0009] Based on the above solution, when the step-down condition is met, perform step-down and current-limiting control to make the motor enter the low-current state before establishing excitation and transition to the normal operating state after entering excitation.

[0010] Based on the same inventive concept, the present application provides a control device for starting a motor with a three-phase inverter, including: A sampling module for real-time sampling of three-phase inverter current signals and voltage signals; A first processing module for processing each phase of current through a low-pass filter to obtain a low-pass filtered current signal; A second processing module, where the second processing module includes a current processing module and a voltage processing module. The current processing module is used to differentiate the filtered current signal by using the differentiation method to obtain the current change rate, and the voltage processing module is used to process the voltage signal to obtain the voltage angle; A judgment module for judging whether the step-down condition is reached according to the current differential value and the voltage angle; A step-down control module for performing step-down and current-limiting control on the motor starting stage when the step-down condition is met until the motor establishes excitation.

[0011] Based on the above scheme, the current processing module uses a higher-order difference method to differentiate the current signal in order to accurately capture the rate of change of current.

[0012] This application also provides an electronic device, including a memory and a processor. The memory stores a computer program that runs on the processor, and when the processor executes the computer program, it implements the steps of the control method for starting a motor with a three-phase inverter as described above.

[0013] This application also provides a computer-readable storage medium having a computer program that, when executed by a processor, implements the steps of the control method for starting a motor with a three-phase inverter as described above.

[0014] Compared with the prior art, the present invention has the following beneficial effects: 1. By sampling and low-pass filtering the three-phase current signal in real time, high-frequency noise interference is reduced to balance high-frequency noise suppression and system instantaneous responsiveness; 2. The filtered current signal is differentiated using a higher-order difference formula to accurately capture the rate of change of current and improve the accuracy of discrimination. 3. By using both voltage angle and current differential value for step-down control, the robustness and accuracy of the system's judgment are effectively improved, equipment malfunctions are avoided, and the smooth start-up process effectively reduces the impact stress on the motor and inverter during startup. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the electrical connections in this application; Figure 2 This is a flowchart of the control method of the present application; Figure 3 This is the control logic diagram of the method in this application; Figure 4 This is a diagram of the three-phase voltage waveforms in this application. Detailed Implementation

[0016] The invention will be further described below with reference to specific embodiments.

[0017] This invention primarily addresses the scenario of a three-phase inverter operating off-grid with a motor load, including both three-phase three-wire and three-phase four-wire inverter operation. The electrical connections are as follows: Figure 1As shown, when a three-phase inverter is operating off-grid and a motor load without a frequency converter is suddenly connected, the inverter will generate a large reactive current surge. This current surge can not only cause inverter overload and undervoltage protection problems, but also potentially cause voltage distortion, affecting the overall stability of the system. To solve this problem, this invention designs a control strategy with motor starting. By monitoring and processing the three-phase current signal in real time, filtering and high-order differential analysis are used to analyze the current change rate, and the voltage reduction is determined accordingly. This allows for effective current limiting before the motor is excited, smoothly transitioning to normal operating conditions.

[0018] like Figure 2 and Figure 3 As shown, the system first starts up and the three-phase inverter is in off-grid operation. At this time, a motor load is connected, and the impulsive load detection method is executed, which includes the following steps: The three-phase inverter current signal is sampled at high frequency in real time, and a low-pass filter is used to filter the current of each phase to remove high-frequency noise interference while maintaining the system's fast dynamic response capability. Preferably, the cutoff frequency of the low-pass filter is 250Hz. If the cutoff frequency is too high, it will cause high-frequency signals to interfere with the detection, and if it is too low, it will cause the dynamic response to be too slow. Experimental verification shows that a cutoff frequency of 250Hz can filter out most of the high-frequency harmonics of the three-phase inverter, while ensuring a fast response when the motor load is initially applied.

[0019] The current signal obtained after filtering the sampled three-phase inverter current is differentiated to capture the rate of change of current. In order to capture the current change more accurately, further reduce the calculation error and improve the discrimination accuracy, a higher-order difference method is used to differentiate the current rate of change.

[0020] Preferably, this application uses the five-point difference method to differentiate the current signal, as shown in the following formula: ; Where x is the sampling point, Here is the current value corresponding to sampling point x, and the sampling interval is h. for The corresponding first derivative is the rate of change of current. This method improves accuracy while being relatively simple to operate, thus increasing system efficiency. This application can also use higher-order difference methods such as the three-point central difference method, the seven-point central difference method, the five-point forward difference method, and the five-point backward difference method. Compared to these, the five-point difference method achieves a better balance between accuracy and computational complexity, providing higher accuracy while reducing computational complexity, enabling the system to respond quickly to current changes and take timely measures.

[0021] While collecting the current signal, the present application also needs to collect three-phase voltage signals, and the voltage angle can be obtained through phase-locked control for the three-phase voltage signals. The voltage angle of the present application is obtained through conventional phase-locked loop technology. For example, the phase-locked control processes the three-phase voltage signals in real time through a phase-locked loop (PLL), uses a phase detector to compare the phase difference between the voltage signal and the reference signal, and dynamically adjusts the frequency and phase of the output signal through a loop filter and a voltage-controlled oscillator, ultimately achieving precise tracking of the phase of the voltage signal. In the locked state of the phase-locked loop, the phase of the output signal corresponds to the phase angle of the input voltage signal (i.e., the voltage angle).

[0022] The step-down condition is a discriminant condition for taking protection measures during motor startup. The present application further determines whether the step-down condition is met by combining the current differential value and the voltage angle. If the step-down condition is met, step-down current-limiting control is implemented during the motor startup stage. Specifically, as Figure 4 shown, the voltage angle includes the phase A voltage angle UA, the phase B voltage angle UB, and the phase C voltage angle UC, and the current change rate includes the phase A current change rate DA, the phase B current change rate DB, and the phase C current change rate DC.

[0023] When making the judgment, it is considered that the step-down condition is met when the current change rate of a certain phase is detected to exceed the current differential threshold Dth or be lower than -Dth within a specific voltage angle range of each phase. Specifically, the step-down condition is reached when any of the following conditions is met: within the positive effective range of phase A, -30° < UA < 30° and DA > Dth; within the negative effective range of phase A, 150° < UA < 210° and DA < -Dth; when within the positive effective range of phase B, 90° < UB < 150° and DB > Dth; within the negative effective range of phase B, 270° < UB < 330° and DB < -Dth; within the positive effective range of phase C, 210° < UC < 270° and DC > Dth; within the negative effective range of phase C, 30° < UC < 90° and DA < -Dth. Through the dual-condition judgment of the present application, the step-down process is made more sensitive, enabling accurate distinction between normal operation and startup overload situations, adapting to the complexity of different loads and motor conditions, improving the adaptability and robustness of the overall system, and avoiding misoperation.

[0024] Once it is detected that the motor startup process meets the above step-down condition, step-down current-limiting control is immediately implemented during the motor startup stage. For example, step-down current-limiting control is achieved by actively controlling the voltage output setting of the inverter, enabling the motor to enter a low-current state before fully establishing excitation, thereby smoothly transitioning to the normal operation state. After the motor establishes excitation, the system解除 the step-down current-limiting control and transitions to the normal operation state.

[0025] Based on the same inventive concept, the present application provides a control device for a three-phase inverter with motor startup, including: The sampling module is used to sample the three-phase inverter current and voltage signals in real time. The first processing module is used to process the current of each phase through a low-pass filter to obtain the low-pass filtered current signal. The second processing module includes a current processing module and a voltage processing module. The current processing module is used to perform differential processing on the filtered current signal using the differential method to obtain the current change rate. The voltage processing module is used to process the voltage signal to obtain the voltage angle. The judgment module is used to determine whether the voltage reduction condition has been met based on the differential value of the current and the voltage angle. The step-down control module is used to implement step-down current limiting control during the motor startup phase when the step-down conditions are met, until the motor establishes excitation.

[0026] Preferably, the current processing module uses a higher-order difference method to differentiate the current signal in order to accurately capture the rate of change of current.

[0027] The specific implementation of this device is basically the same as the specific embodiments of the above detection method, and will not be repeated here.

[0028] This application also provides an electronic device, including a memory and a processor. The memory stores a computer program that runs on the processor. The processor executes the computer program to implement the steps of the control method for starting a motor with a three-phase inverter as described above.

[0029] A processor can perform various actions and processes according to a program stored in memory. Specifically, a processor can be an integrated circuit chip with signal processing capabilities. The aforementioned processor can be a general-purpose processor, a digital signal processor, an application-specific integrated circuit (ASIC), an off-the-shelf programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic device, or discrete hardware component. It can implement or execute the methods, steps, and logic block diagrams disclosed in the embodiments of this invention. The general-purpose processor can be a microprocessor or any conventional processor, and can be based on an x86 architecture or an ARM architecture.

[0030] The memory stores computer-executable instructions that, when executed by a processor, implement the aforementioned control method for starting a motor in a three-phase inverter. The memory can be volatile or non-volatile, or a combination of both. Non-volatile memory can be read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), or flash memory. Volatile memory can be random access memory (RAM) used as an external cache. By way of example, but not limitation, many forms of RAM are available, such as static random access memory (SRAM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), double data rate synchronous dynamic random access memory (DDRSDRAM), enhanced synchronous dynamic random access memory (ESDRAM), synchronous linked dynamic random access memory (SLDRAM), and direct memory bus random access memory (DRRAM). It should be noted that the memory used in the methods described herein is intended to include, but is not limited to, these and any other suitable types of memory.

[0031] This application also provides a computer-readable storage medium having a computer program that, when executed by a processor, implements the steps of the detection method described above.

[0032] It should be noted that the flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in a flowchart or block diagram may represent a module, program segment, or portion of code containing at least one executable instruction for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0033] In general, various exemplary embodiments of the present invention can be implemented in hardware or dedicated circuitry, software, firmware, logic, or any combination thereof. Some aspects can be implemented in hardware, while others can be implemented in firmware or software that can be executed by a controller, microprocessor, or other computing device. When aspects of embodiments of the present invention are illustrated or described as block diagrams, flowcharts, or represented using certain other images, it will be understood that the blocks, apparatuses, systems, techniques, or methods described herein can be implemented as non-limiting examples in hardware, software, firmware, dedicated circuitry or logic, general-purpose hardware or controllers or other computing devices, or certain combinations thereof.

[0034] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

[0035] While the specific embodiments of the present invention have been described above, they are not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A control method for starting a motor in a three-phase inverter, characterized in that, When the three-phase inverter operates off-grid, it is used to control the motor load without a frequency converter connected, including the following steps: Step S1, sample the three-phase inverter current signal and voltage signal in real time; Step S2, process each phase of the current through a low-pass filter to obtain the low-pass filtered current signal; Step S3, use the differential method to perform differential processing on the filtered current signal to obtain the current change rate, and process the voltage signal sampled in S1 to obtain the voltage angle; Step S4, determine whether the step-down condition is reached according to the current differential value and voltage angle, and the step-down condition is the discrimination condition for taking protection measures when the motor starts; Step S5, if the step-down condition is reached, implement step-down and current-limiting control during the motor startup stage until the motor establishes excitation.

2. The control method for starting a motor in a three-phase inverter according to claim 1, characterized in that, The cut-off frequency of the low-pass filter in step S2 is 250HZ, which is used to filter out the high-frequency harmonics of the sampled current signal in step S1 and quickly respond to the motor load.

3. The control method for starting a motor in a three-phase inverter according to claim 1, characterized in that, The differential method is the high-order difference method - five-point difference method, and the formula is as follows: ； Where x is the sampling point, The sampling point x represents the current value, and the sampling interval is h. for The corresponding first derivative; Use the five-point difference method to perform differential calculation on the current signal processed in step S2 to obtain the current change rate.

4. The control method for starting a motor in a three-phase inverter according to claim 3, characterized in that, The voltage angles include the phase A voltage angle UA, the phase B voltage angle UB, and the phase C voltage angle UC. The current change rates include the phase A current change rate DA, the phase B current change rate DB, and the phase C current change rate DC. When making a judgment in step S4, when the current change rate of a certain phase exceeds the current differential threshold Dth or is lower than -Dth within a specific voltage angle range of each phase, the step-down condition is satisfied.

5. The control method for starting a motor in a three-phase inverter according to claim 4, characterized in that, When -30° < UA < 30° and DA > Dth or 150° < UA < 210° and DA < -Dth, it is determined that the step-down condition is satisfied; when 90° < UB < 150° and DB > Dth or 270° < UB < 330° and DB < -Dth, it is determined that the step-down condition is satisfied; when 210° < UC < 270° and DC > Dth or 30° < UC < 90° and DA < -Dth, it is determined that the step-down condition is satisfied.

6. The control method for starting a motor in a three-phase inverter according to claim 5, characterized in that, When the step-down condition is satisfied, perform step-down and current-limiting control to make the motor enter the low-current state before establishing excitation and transition to the normal operation state after entering excitation.

7. A control device for starting a motor in a three-phase inverter, characterized in that, It includes: A sampling module for sampling the three-phase inverter current signal and voltage signal in real time; A first processing module for processing each phase of the current through a low-pass filter to obtain the low-pass filtered current signal; A second processing module, the second processing module includes a current processing module and a voltage processing module. The current processing module is used to perform differential processing on the filtered current signal using the differential method to obtain the current change rate, and the voltage processing module is used to process the voltage signal to obtain the voltage angle; A judgment module for determining whether the step-down condition is reached according to the current differential value and voltage angle; A step-down control module for implementing step-down and current-limiting control during the motor startup stage until the motor establishes excitation when the step-down condition is satisfied.

8. A control device for starting a motor in a three-phase inverter according to claim 7, characterized in that, The current processing module uses the high-order difference method to perform differential processing on the current signal to accurately capture the current change rate.

9. An electronic device comprising a memory and a processor, wherein the memory stores a computer program that runs on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the control method for starting a motor in a three-phase inverter as described in any one of claims 1-6.

10. A computer-readable storage medium having a computer program, characterized in that, When the computer program is executed by the processor, it implements the steps of the control method for starting a motor in a three-phase inverter as described in any one of claims 1-6.

Images