Current limiting protection method and system for variable speed constant frequency device

Abstract

This application provides a current limiting protection method and system for a variable speed constant frequency device. The method includes: First, the variable speed constant frequency device operates in a constant voltage state during normal operation; Second, it determines whether a hardware overcurrent protection event has occurred. If so, it proceeds to the third step; otherwise, it returns to the first step; Third, it performs a fault reset and automatically restarts the variable speed constant frequency device to operate in a constant current state. Furthermore, after operating in this constant current state, it determines whether the hardware overcurrent protection event is caused by a short circuit, overload, or other temporary sudden anomaly. If it is a short circuit, it maintains a preset current output for a certain duration, allowing the downstream circuit time to switch power and maintain circuit stability. If it is an overload, it performs overload protection and shuts down to prevent circuit damage. If it is neither a short circuit nor an overload, it is generally a temporary sudden anomaly, and it can switch back to operating in a constant voltage state.

Description

Technical Field

[0001] This application relates to the field of power electronic control technology, and in particular to a current limiting protection method and system for a variable speed constant frequency device. Background Technology

[0002] As a type of frequency converter, the variable speed constant frequency device is a typical nonlinear power electronic device. Its core components have high design and control requirements. Furthermore, marine AC power grids require the source end to meet grid selectivity requirements; therefore, its stability during transient faults is crucial to the safety of ship operation. Several patents offer solutions to this problem.

[0003] Patent CN201710102802.7, "Inverter and Wave-by-Wave Current Limiting Protection Circuit", solves the problems of complex structure, low product reliability and poor user experience of inverter wave-by-wave current limiting circuits that cannot be solved in the prior art by adopting a wave-by-wave current limiting protection circuit including a comparison module, a logic module and a judgment module in the inverter. However, wave-by-wave current limiting still has the problem of excessive DSP resource consumption and the problem of sacrificing some protection functions.

[0004] Patent CN201420212360.3, "An IGBT Drive Protection Circuit for Overcurrent Problems in Frequency Converters," utilizes a fault signal and an OR gate. When the frequency converter experiences overcurrent at the output, a detection circuit uses three OR gates to shut down the drive of the lower arm of the IGBT module, cutting off the drive voltage of the lower arm and reducing the output current amplitude, thus protecting the frequency converter and motor from damage due to overcurrent. Testing has shown that this protection circuit design meets the requirements of various frequency converter functions. However, this method is relatively basic and cannot solve the current limiting problem.

[0005] Patent CN201510584009.6, "Inverter Overcurrent Protection Circuit," proposes an inverter overcurrent protection circuit. By setting a preset current threshold and adding a current-limiting resistor, it effectively reduces damage to the inverter and IGBT circuit during overcurrent, achieving a safe and reliable purpose. However, the additional current-limiting resistor makes it unsuitable for high-power equipment. Summary of the Invention

[0006] The purpose of this application is to provide a simple and easy-to-implement current limiting protection method and system for variable speed constant frequency devices.

[0007] To achieve the above objectives, this application provides a current limiting protection method for a variable speed constant frequency device, comprising:

[0008] The first step is that the variable speed constant frequency device operates under constant voltage when working normally;

[0009] The second step is to determine whether a hardware overcurrent protection event has occurred. If so, proceed to the third step; otherwise, return to the first step.

[0010] The third step is to reset the fault and automatically restart the variable speed constant frequency device to operate in constant current mode.

[0011] Furthermore, after the third step, the method further includes:

[0012] The fourth step is to determine whether the output voltage of the variable speed constant frequency device is greater than the first voltage threshold. If it is, proceed to the first step of the fifth step; otherwise, proceed to the second step of the fifth step.

[0013] Step 5, slowly increase the current input;

[0014] Step 5, part 2: Maintain the predetermined current output.

[0015] Furthermore, the method includes the following after one of the fifth steps:

[0016] Step 6.1: Determine if overload protection has occurred. If yes, proceed to Step 7.1; otherwise, proceed to Step 7.2.

[0017] Step 7: Enter overload protection mode and shut down the machine;

[0018] Step 7.2: Determine whether the output voltage of the variable speed constant frequency device is greater than the second voltage threshold. If it is, proceed to step 8; otherwise, return to step 5.1.

[0019] Step 8: Follow the synchronization signal and switch back to constant voltage mode for operation.

[0020] Furthermore, the method includes the following after step five, second:

[0021] Step 6.2: Determine whether the duration of maintaining the predetermined current output is greater than the time threshold. If yes, proceed to Step 7.3; otherwise, proceed to Step 7.4.

[0022] Step 7.3: Shut down the machine and report a short circuit fault;

[0023] Step 7.4: Determine whether the output voltage of the variable speed constant frequency device is greater than the second voltage threshold. If it is, proceed to step 8; otherwise, return to step 5.2.

[0024] Furthermore, the determination of whether a hardware overcurrent protection event has occurred is based on the instantaneous value of the DC current as the hardware blocking current limiting condition. When the current of the DC bus is detected to exceed the upper limit of the set point, the hardware blocking circuit will forcibly pull down the drive pulse of the switching transistor, blocking the switching transistor that is conducting. This is the occurrence of a hardware overcurrent protection event.

[0025] Furthermore, the predetermined current is twice the rated current, and the time threshold value is 0.6s.

[0026] This application also provides a current limiting protection system for a variable speed constant frequency device. The system includes: a variable speed constant frequency device, a PWM modulation unit, a decoupling control unit, a first PI controller, a second PI controller, a main controller, a first coordinate rotation transformation unit, a second coordinate rotation transformation unit, a first adder, a second adder, a third adder, and a switching switch. The main controller outputs a given voltage and a given current. The main controller and the first coordinate rotation transformation unit are both connected to the first adder. The output terminal of the first adder is connected to the input terminal of the first PI controller, providing the given voltage output by the main controller to the first PI controller. The output terminal of the first PI controller is connected to the second adder through one end of the switching switch, and the main controller is connected to the second adder through the other end of the switching switch. The second coordinate rotation transformation unit is also connected to the second adder. The system is composed of several interconnected adders. The output of the second adder is connected to the second PI controller, providing the given current output by the main controller to the second PI controller. The output of the second PI controller is connected to the third adder, which is also connected to the third adder via the decoupling control unit. The output of the third adder is connected to the PWM modulation unit, which is connected to the variable speed constant frequency device. The PWM modulation unit outputs a switching signal to control the output of the variable speed constant frequency device. The output of the variable speed constant frequency device is simultaneously connected to the first coordinate rotation transformation unit and the second coordinate rotation transformation unit. The voltage and current output by the variable speed constant frequency device are fed back to the first coordinate rotation transformation unit and the second coordinate rotation transformation unit. The controller executes the current limiting protection method of the variable speed constant frequency device as described above.

[0027] Furthermore, the given voltage output by the main controller includes active voltage and reactive voltage, and the given current output by the main controller includes active current and reactive current; the number of the first PI controller, the second PI controller, the first adder, the second adder, the third adder, and the switching switch are all two; the active voltage is connected to one of the first PI controllers through one of the first adders, the output terminal of the first PI controller is connected to one of the second adders through one end of the switching switch, the active current is connected to one of the second adders through the other end of the switching switch, the output terminal of the second adder is connected to one of the second PI controllers, the output terminal of the second PI controller is connected to one of the third adders, the output terminal of the second adder is connected to the third adder through the decoupling control unit, and the output of the third adder is... The output terminal is connected to the PWM modulation unit; the reactive voltage is connected to the first PI controller through the second first adder, the output terminal of the second first PI controller is connected to the second adder through one end of the second switching switch, the reactive current is connected to the second adder through the other end of the second switching switch, the output terminal of the second adder is connected to the second PI controller, the output terminal of the second PI controller is connected to the second third adder, the output terminal of the second second adder is connected to the third adder through the decoupling control unit, and the output terminal of the third adder is connected to the PWM modulation unit; the first coordinate rotation transformation unit is simultaneously connected to the first adder and the second first adder, and the second coordinate rotation transformation unit is simultaneously connected to the first adder and the second adder, respectively.

[0028] The current limiting protection method and system for the variable speed constant frequency device described in this application involve the variable speed constant frequency device operating in a constant voltage state during normal operation. It then continuously checks for hardware overcurrent protection events. If a hardware overcurrent protection event occurs, a fault reset is performed, and the variable speed constant frequency device is automatically restarted and operates in a constant current state. Furthermore, after operating in this constant current state, the cause of the hardware overcurrent protection event is determined: is it a short circuit, overload, or other temporary sudden anomaly? If it is a short circuit, a preset current output is maintained for a certain duration, allowing the downstream circuit time to switch power and maintain circuit stability. If it is an overload, overload protection is implemented and the device is shut down to prevent circuit damage. If it is neither a short circuit nor an overload, it is generally a temporary sudden anomaly, and the device will gradually recover in the constant current state, switching back to constant voltage operation, thereby further ensuring the overall stability of the circuit operation. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a flowchart illustrating a current limiting protection method for a variable speed constant frequency device provided in this application;

[0031] Figure 2 This is a schematic diagram of the current limiting protection system of a variable speed constant frequency device provided in this application. Detailed Implementation

[0032] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. In addition, it should be understood that the specific embodiments described herein are only for illustration and explanation of this application and are not intended to limit this application. In this application, unless otherwise stated, directional terms such as "up," "down," "left," and "right" generally refer to up, down, left, and right in the actual use or working state of the device, specifically the drawing directions in the accompanying drawings.

[0033] This application provides a current limiting protection method and system for a variable speed constant frequency device, which will be described in detail below. It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments of this application. Furthermore, in the following embodiments, the descriptions of each embodiment have their own emphasis; parts not described in detail in a certain embodiment can be referred to in the relevant descriptions of other embodiments.

[0034] Please see Figure 1 The diagram shown is a flowchart illustrating a current limiting protection method for a variable speed constant frequency device provided in this application.

[0035] A current-limiting protection method for a variable speed constant frequency device, the method comprising:

[0036] The first step is that the variable speed constant frequency device operates under constant voltage when working normally;

[0037] The second step is to determine whether a hardware overcurrent protection event has occurred. If so, proceed to the third step; otherwise, return to the first step.

[0038] The third step is to reset the fault and automatically restart the variable speed constant frequency device to operate in constant current mode.

[0039] The variable speed constant frequency device operates under constant voltage during normal operation. It then continuously monitors for hardware overcurrent protection events. This is determined by using the instantaneous value of the DC current as the hardware current limiting condition. When the current on the DC bus exceeds the set upper limit, the hardware blocking circuit forcibly pulls down the drive pulse of the switching transistor, blocking the currently conducting transistor; this constitutes a hardware overcurrent protection event. After the hardware overcurrent protection event ends, a fault reset is performed, automatically restarting the variable speed constant frequency device. This is because marine AC power supplies (generators) require the source end to meet time-delay tripping and grid selectivity requirements; automatic restarting after a fault reset allows the downstream end time to switch power. Furthermore, after restarting the variable speed constant frequency device, it enters constant current mode.

[0040] Furthermore, after the third step of fault reset and automatic restart of the variable speed constant frequency device to operate in constant current state, the method further includes:

[0041] The fourth step is to determine whether the output voltage of the variable speed constant frequency device is greater than the first voltage threshold. If it is, proceed to the first step of the fifth step; otherwise, proceed to the second step of the fifth step.

[0042] Step 5, slowly increase the current input;

[0043] Step 5, part 2: Maintain the predetermined current output.

[0044] After restarting the variable speed constant frequency device, it is necessary to determine the cause of the previous hardware overcurrent protection event: whether it was a short circuit, overload, or other temporary problem. If it was a short circuit, even after restarting the variable speed constant frequency device, its output voltage will be very small and cannot rise. Therefore, in the fourth step, the cause of the hardware overcurrent protection event can be determined by judging whether the output voltage of the variable speed constant frequency device is greater than the first voltage threshold. If the output voltage of the variable speed constant frequency device is greater than the first voltage threshold, it means that it is not caused by a short circuit, and the current setpoint can be slowly increased, i.e., step five one; if the output voltage of the variable speed constant frequency device is not greater than the first voltage threshold, it means that it is caused by a short circuit, and in this case, it is necessary to maintain the output at the predetermined current to ensure that the circuit can work, i.e., step five two.

[0045] Furthermore, after the fifth step of slowly increasing the given current, the method further includes:

[0046] Step 6.1: Determine if overload protection has occurred. If yes, proceed to Step 7.1; otherwise, proceed to Step 7.2.

[0047] Step 7: Enter overload protection mode and shut down the machine;

[0048] Step 7.2: Determine whether the output voltage of the variable speed constant frequency device is greater than the second voltage threshold. If it is, proceed to step 8; otherwise, return to step 5.1.

[0049] Step 8: Follow the synchronization signal and switch back to constant voltage mode for operation.

[0050] After determining that the cause of the hardware overcurrent protection event is not a short circuit, and after slowly increasing the current setting, it is necessary to further determine whether the cause of the hardware overcurrent protection event is an overload. Therefore, after slowly increasing the current setting in step five, a sixth step is performed to determine whether overload protection has occurred. If overload protection occurs, the system enters overload protection mode and shuts down to ensure the equipment is not damaged; this is step seven. If no overload protection occurs, it indicates that the problem is not due to overload, but rather a temporary voltage or current surge. In this case, it can be further determined whether the output voltage of the variable speed constant frequency device is greater than the second voltage threshold; this is step seven. If the output voltage of the variable speed constant frequency device is greater than the second voltage threshold, it indicates that the circuit has returned to normal, and step eight can be initiated, following the synchronization signal to switch back to constant voltage mode. If the output voltage of the variable speed constant frequency device is not yet greater than the second voltage threshold, step five can be resumed, i.e., the current setting can be slowly increased. This cycle continues until the output voltage of the variable speed constant frequency device is greater than the second voltage threshold, indicating that the circuit has returned to normal, and step eight can be initiated, following the synchronization signal to switch back to constant voltage mode. Specifically, for parallel equipment, the system can exit constant current mode and enter constant voltage mode at the rising or falling edge of the synchronization signal to quickly restore the rated voltage.

[0051] In addition, after maintaining the predetermined current output in step five-two, the method further includes:

[0052] Step 6.2: Determine whether the duration of maintaining the predetermined current output is greater than the time threshold. If yes, proceed to Step 7.3; otherwise, proceed to Step 7.4.

[0053] Step 7.3: Shut down the machine and report a short circuit fault;

[0054] Step 7.4: Determine whether the output voltage of the variable speed constant frequency device is greater than the second voltage threshold. If it is, proceed to step 8; otherwise, return to step 5.2.

[0055] After restarting the variable speed constant frequency device, and determining the cause of the hardware overcurrent protection event, it is determined that after a short circuit, the output voltage of the variable speed constant frequency device will be very small and cannot rise. Therefore, it needs to maintain an output at a predetermined current to allow the downstream circuit to switch power. Furthermore, it is necessary to determine whether the duration of maintaining the predetermined current output is greater than a time threshold, which is step six, part two. If the duration of maintaining the predetermined current output is greater than the time threshold, it indicates that the circuit has been in a short circuit state, and the duration of maintenance is sufficient for the downstream circuit to switch. Therefore, the device can be stopped, and a short circuit fault can be reported, which is step seven, part three. If the duration of maintaining the predetermined current output has not yet reached the time threshold, it is necessary to determine whether the output voltage of the variable speed constant frequency device is greater than a second voltage threshold, which is step seven, part four. If the output voltage of the variable speed constant frequency device is greater than the second voltage threshold, it indicates that the circuit has returned to normal (for example, the downstream circuit has isolated and protected the short-circuited portion, and this portion does not affect the circuit). (The main function), at this point, can also proceed to step eight, that is, following the synchronization signal, switching back to the constant voltage state for operation; if the output voltage of the variable speed constant frequency device is not greater than the second voltage threshold, and the previously determined duration of maintaining the predetermined current output has not yet reached the time threshold, then the circuit needs to continue maintaining the predetermined current output, that is, return to step five two; this cycle continues until the duration of maintaining the predetermined current output is greater than the time threshold, then the machine stops and a short circuit fault is reported, or the output voltage of the variable speed constant frequency device is greater than the second voltage threshold, then following the synchronization signal, switching back to the constant voltage state for operation. The preset current can be N times the rated current, such as 2 times. In a specific embodiment, the time threshold is 0.6s. Incidentally, the specific values ​​of the preset current, time threshold, and the aforementioned first and second voltage thresholds can all be adjusted according to actual conditions. Furthermore, the first and second voltage thresholds use average voltage, while the current limiting protection uses instantaneous value judgment.

[0056] Please see Figure 2As shown, this application also provides a current limiting protection system for a variable speed constant frequency device. The system includes: a variable speed constant frequency device, a PWM modulation unit, a decoupling control unit, a first PI controller, a second PI controller, a main controller (not shown), a first coordinate rotation transformation unit, a second coordinate rotation transformation unit, a first adder, a second adder, a third adder, and a switching switch; the main controller outputs a given voltage and a given current; the main controller and the first coordinate rotation transformation unit are both connected to the first adder, and the output terminal of the first adder is connected to the input terminal of the first PI controller, providing the given voltage output by the main controller to the first PI controller; the output terminal of the first PI controller is connected to the second adder through one end of the switching switch, the main controller is connected to the second adder through the other end of the switching switch, and the second coordinate rotation transformation unit is also connected to the second adder. The output of the second adder is connected to the second PI controller, providing the given current output by the main controller to the second PI controller; the output of the second PI controller is connected to the third adder, and the output of the second adder is also connected to the third adder through the decoupling control unit; the output of the third adder is connected to the PWM modulation unit, and the output of the PWM modulation unit is connected to the variable speed constant frequency device, the PWM modulation unit outputs a switching signal to control the output of the variable speed constant frequency device; the output of the variable speed constant frequency device is simultaneously connected to the first coordinate rotation transformation unit and the second coordinate rotation transformation unit, and the voltage and current output by the variable speed constant frequency device are fed back to the first coordinate rotation transformation unit and the second coordinate rotation transformation unit, and the controller executes the aforementioned current limiting protection method of the variable speed constant frequency device. This is an inverter employing dual closed-loop control, consisting of an inner current loop and an outer voltage loop. The variable speed constant frequency device, PWM modulation unit, decoupling control unit, second PI controller, second coordinate rotation transformation unit, second adder, and third adder constitute the inner current loop. The main controller, first PI controller, first coordinate rotation transformation unit, first adder, and switching switch together with the inner current loop constitute the outer voltage loop.

[0057] Furthermore, the given voltage output by the main controller includes active voltage Udref and reactive voltage Uqref, and the given current output by the main controller includes active current Idref and reactive current Iqref; the number of the first PI controller, the second PI controller, the first adder, the second adder, the third adder, and the switching switch are all two; the active voltage Udref is connected to one of the first PI controllers through one of the first adders, the output terminal of the first PI controller is connected to one of the second adders through one end of the switching switch Td, the active current Idref is connected to one of the second adders through the other end of the switching switch Td, the output terminal of the second adder is connected to one of the second PI controllers, the output terminal of the second PI controller is connected to one of the third adders, and the output terminal of the second adder is connected to the third adder through the decoupling control unit. The output terminal of one of the third adders is connected to the PWM modulation unit; the reactive voltage Uqref is connected to the second of the first PI controllers through the second of the first adders, the output terminal of the second of the first PI controllers is connected to the second adder through one end of the second switch Tq, the reactive current Iqref is connected to the second adder through the other end of the second switch Tq, the output terminal of the second adder is connected to the second PI controller, the output terminal of the second PI controller is connected to the second of the third adder, the output terminal of the second adder is connected to the third adder through the decoupling control unit, and the output terminal of the third adder is connected to the PWM modulation unit; the first coordinate rotation transformation unit is simultaneously connected to both the first adder and the second adder, and the second coordinate rotation transformation unit is simultaneously connected to both the first adder and the second adder.

[0058] During normal operation, the active and reactive components of the output voltage, provided by the main controller, are processed by the first PI controller, and their outputs serve as the current inputs for the d-axis and q-axis current inner loops, respectively. The current inner loop, after passing through the second PI controller and undergoing decoupling compensation control, outputs a signal that serves as the input for the PWM modulation unit. After PWM modulation, the signal is directly output as a switching signal to control the output of the variable speed constant frequency device. The voltage and current outputs of the variable speed constant frequency device, after rotational coordinate transformation, are fed back to the inputs of the voltage outer loop and the current inner loop, respectively. In the event of a hardware overcurrent fault, the fault is reset, and the input to the current loop switches from the original voltage loop output to directly providing the active and reactive currents. The control loop then uses only the current inner loop control. The directly provided active and reactive currents change according to the amplitude of the feedback current, for example, up to twice the rated current.

[0059] The current limiting protection method and system for the variable speed constant frequency device described in this application involve the variable speed constant frequency device operating in a constant voltage state during normal operation. It then continuously checks for hardware overcurrent protection events. If a hardware overcurrent protection event occurs, a fault reset is performed, and the variable speed constant frequency device is automatically restarted and operates in a constant current state. Furthermore, after operating in this constant current state, the cause of the hardware overcurrent protection event is determined: is it a short circuit, overload, or other temporary sudden anomaly? If it is a short circuit, a preset current output is maintained for a certain duration, allowing the downstream circuit time to switch power and maintain circuit stability. If it is an overload, overload protection is implemented and the device is shut down to prevent circuit damage. If it is neither a short circuit nor an overload, it is generally a temporary sudden anomaly, and the device will gradually recover in the constant current state, switching back to constant voltage operation, thereby further ensuring the overall stability of the circuit operation.

[0060] In summary, the technical effects of this application are as follows:

[0061] 1) Meet the short-delay trip requirements of ship AC power supply (generator), such as maintaining the rated current of 200% to 250% for a maximum AC trip of 0.6 seconds;

[0062] 2) The original protection mechanism of the equipment is utilized, and no additional modifications are required to drive the protection circuit;

[0063] 3) Through the improvements in this application, the requirements for short-circuit short-delay tripping can be met, and overload faults can be distinguished to avoid false alarms and malfunctions;

[0064] 4) Synchronous exit signal during parallel operation to prevent current circulation in light load mode.

[0065] The above provides a detailed description of the current limiting protection method and system for a variable speed constant frequency device provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A current limiting protection method for a variable speed constant frequency device, characterized in that, The method includes: The first step is that the variable speed constant frequency device operates under constant voltage when working normally; The second step is to determine whether a hardware overcurrent protection event has occurred. If so, proceed to the third step; otherwise, return to the first step. The third step is to reset the fault and automatically restart the variable speed constant frequency device to operate in constant current mode. The fourth step is to determine whether the output voltage of the variable speed constant frequency device is greater than the first voltage threshold. If it is, proceed to the first step of the fifth step; otherwise, proceed to the second step of the fifth step. Step 5, slowly increase the current input; Following step one of the fifth steps: Step 6.1: Determine if overload protection has occurred. If yes, proceed to Step 7.1; otherwise, proceed to Step 7.

2. Step 7: Enter overload protection mode and shut down the machine; Step 7.2: Determine whether the output voltage of the variable speed constant frequency device is greater than the second voltage threshold. If it is, proceed to step 8; otherwise, return to step 5.

1. Step 8: Following the synchronization signal, switch back to constant voltage mode for operation; Step 5, part 2: Maintain the predetermined current output.

2. The current limiting protection method for the variable speed constant frequency device according to claim 1, characterized in that, The method, following step two of the fifth step, includes: Step 6.2: Determine whether the duration of maintaining the predetermined current output is greater than the time threshold. If yes, proceed to Step 7.3; otherwise, proceed to Step 7.

4. Step 7.3: Shut down the machine and report a short circuit fault; Step 7.4: Determine whether the output voltage of the variable speed constant frequency device is greater than the second voltage threshold. If it is, proceed to step 8; otherwise, return to step 5.

2.

3. The current limiting protection method for the variable speed constant frequency device according to claim 1, characterized in that, To determine whether a hardware overcurrent protection event has occurred, the instantaneous value of the DC current is used as the hardware current limiting condition. When the current of the DC bus exceeds the upper limit of the set point, the hardware blocking circuit will forcibly pull down the drive pulse of the switching transistor, blocking the switching transistor that is conducting. This is the occurrence of a hardware overcurrent protection event.

4. The current limiting protection method for the variable speed constant frequency device according to claim 2, characterized in that, The predetermined current is twice the rated current, and the time threshold value is 0.6s.

5. A current-limiting protection system for a variable speed constant frequency device, characterized in that, The system includes: a variable speed constant frequency device, a PWM modulation unit, a decoupling control unit, a first PI controller, a second PI controller, a main controller, a first coordinate rotation transformation unit, a second coordinate rotation transformation unit, a first adder, a second adder, a third adder, and a switching switch; the main controller outputs a given voltage and a given current; the main controller and the first coordinate rotation transformation unit are both connected to the first adder, and the output terminal of the first adder is connected to the input terminal of the first PI controller, providing the given voltage output by the main controller to the first PI controller; the output terminal of the first PI controller is connected to the second adder through one end of the switching switch, the main controller is connected to the second adder through the other end of the switching switch, the second coordinate rotation transformation unit is also connected to the second adder, and the output terminal of the second adder is connected to... The second PI controller is connected to the main controller, which provides the given current output by the main controller to the second PI controller. The output of the second PI controller is connected to the third adder, and the output of the second adder is also connected to the third adder through the decoupling control unit. The output of the third adder is connected to the PWM modulation unit, and the output of the PWM modulation unit is connected to the variable speed constant frequency device. The PWM modulation unit outputs a switching signal to control the output of the variable speed constant frequency device. The output of the variable speed constant frequency device is simultaneously connected to the first coordinate rotation transformation unit and the second coordinate rotation transformation unit. The voltage and current output by the variable speed constant frequency device are fed back to the first coordinate rotation transformation unit and the second coordinate rotation transformation unit. The main controller executes the current limiting protection method of the variable speed constant frequency device according to any one of claims 1-4.

6. The current limiting protection system of the variable speed constant frequency device according to claim 5, characterized in that, The given voltage output by the main controller includes active voltage and reactive voltage, and the given current output by the main controller includes active current and reactive current. There are two of each of the following: a first PI controller, a second PI controller, a first adder, a second adder, a third adder, and a switching switch. The active voltage is connected to one of the first PI controllers via one of the first adders. The output of one of the first PI controllers is connected to one of the second adders via one end of the switching switch. The active current is connected to one of the second adders via the other end of the switching switch. The output of one of the second adders is connected to one of the second PI controllers. The output of one of the second PI controllers is connected to one of the third adders. The output of one of the second adders is connected to one of the third adders via the decoupling control unit. The reactive voltage is connected to the first PI controller through the second first adder. The output of the second first PI controller is connected to the second adder through one end of the second switching switch. The reactive current is connected to the second adder through the other end of the second switching switch. The output of the second adder is connected to the second PI controller. The output of the second PI controller is connected to the second third adder. The output of the second adder is connected to the third adder through the decoupling control unit. The output of the third adder is connected to the PWM modulation unit. The first coordinate rotation transformation unit is simultaneously connected to the first adder and the second first adder. The second coordinate rotation transformation unit is simultaneously connected to the first adder and the second adder.

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