Three-phase induction motor open-circuit fault mitigation control method and system

Abstract

This invention relates to the field of motor control technology, specifically to a method and system for mitigating open-circuit faults in a three-phase induction motor. The method includes: obtaining a speed setpoint and the actual speed to form a speed deviation; inputting the speed deviation into a composite speed controller in a closed-loop V / f control structure to generate a frequency adjustment quantity; determining a target frequency command based on the frequency adjustment quantity and pole number conversion relationship, and generating a stator voltage amplitude command under a constant V / f ratio; obtaining the synchronous electrical angle through integration and generating a modulation signal; performing pulse width modulation based on the modulation signal to drive the three-phase inverter to output three-phase drive voltage; and when a stator phase open circuit causes a double-frequency disturbance in the dq coordinate system, using a resonant adjustment branch for tracking compensation to reduce speed fluctuations and electromagnetic torque pulsation, maintaining continuous motor rotation. This invention solves the problem of high control system complexity in existing induction motors due to reliance on independent fault detection and complex fault-tolerant switching mechanisms.

Description

Technical Field

[0001] This invention relates to the field of motor control technology, and in particular to a method and system for mitigating open-circuit faults in a three-phase induction motor. Background Technology

[0002] Three-phase induction motors are widely used in industrial drives and vehicle electric drives due to their robust structure, low cost, and wide applicability. Voltage-frequency ratio control, as a simple and cost-effective speed regulation method, has high practical value in related applications. However, induction motors may experience abnormal operating conditions such as open-circuit faults during operation. These faults can cause current imbalance, decreased torque output, reduced efficiency, and increased vibration, and in severe cases, can affect equipment lifespan and operational reliability. Existing fault-tolerant control schemes for open-circuit faults typically rely on complex fault detection, parameter switching, or control mode reconfiguration mechanisms, leading to increased system complexity and implementation costs. On the other hand, conventional speed closed-loop control methods struggle to balance continuous operation during open-circuit fault conditions with dynamic performance after fault recovery, thus leaving room for further improvement. Summary of the Invention

[0003] In view of the above technical problems, the present invention provides a method and system for mitigating open circuit faults in three-phase induction motors, aiming to solve the problems that existing three-phase induction motors are prone to speed instability, increased torque pulsation, poor dynamic performance during the recovery process after the fault under open circuit fault conditions, and high complexity of the control system due to reliance on independent fault detection and complex fault-tolerant switching mechanisms.

[0004] Other features and advantages of this disclosure will become apparent from the following detailed description, or may be learned in part from practice of this disclosure.

[0005] According to one aspect of the present invention, a method for mitigating open-circuit faults in a three-phase induction motor is proposed, the method comprising: The setpoint and actual speed of the three-phase induction motor are obtained, and the speed deviation is calculated based on the setpoint and the actual speed. The speed deviation is input into the composite speed controller in the closed-loop V / f control structure to generate a frequency adjustment amount. The composite speed controller includes a proportional adjustment branch and a resonant adjustment branch arranged in parallel. The resonant adjustment branch is used to compensate for the double frequency disturbance component caused by the stator phase open circuit. The double frequency disturbance component is the disturbance component formed in the dq coordinate system current after the three-phase current imbalance. The target frequency command is determined based on the frequency adjustment amount and the pole conversion relationship of the three-phase induction motor, and a stator voltage amplitude command corresponding to the target frequency command is generated while maintaining a preset constant V / f ratio. The target frequency command is integrated to obtain the synchronization electrical angle, and a modulation signal is generated based on the synchronization electrical angle and the stator voltage amplitude command. Pulse width modulation is performed according to the modulation signal to obtain gate drive pulses for driving the three-phase inverter, and the three-phase inverter outputs three-phase drive voltage to the three-phase induction motor. During the operation of the three-phase induction motor, the actual speed is continuously used to form a closed-loop feedback regulation. Even when any phase of the stator is open-circuited, causing the corresponding phase current to drop to zero, the currents of the other phases to become unbalanced, and the current in the dq coordinate system to exhibit a double-frequency disturbance, the closed-loop V / f control structure is still kept working continuously. The resonant regulation branch tracks and compensates for the double-frequency disturbance to reduce speed fluctuations and electromagnetic torque pulsation and maintain the continuous rotation of the motor.

[0006] Furthermore, the proportional adjustment branch is used to generate a basic adjustment amount based on the speed deviation, and the resonant adjustment branch is used to generate a resonant compensation amount based on the double-frequency disturbance. The basic adjustment amount and the resonant compensation amount are superimposed to form the frequency adjustment amount.

[0007] Furthermore, the resonant frequency of the resonant adjustment branch is determined in the following manner: First, the fundamental frequency of the input voltage corresponding to the target frequency command is determined based on the given speed and the number of poles of the three-phase induction motor. Then, the angular frequency corresponding to the fundamental frequency of the input voltage is multiplied according to the double frequency relationship of the current in the dq coordinate system under open circuit fault to obtain the resonant frequency that is synchronized with the double frequency disturbance.

[0008] Furthermore, the composite speed controller includes an integral control branch connected in parallel with the proportional control branch and the resonant control branch to form a proportional-integral-resonant controller. The integral control branch is used to reduce the steady-state deviation under normal operating conditions and fault recovery conditions, and together with the resonant control branch, it suppresses speed fluctuations and electromagnetic torque pulsations during open-circuit faults.

[0009] Furthermore, the step of determining the target frequency command based on the frequency adjustment amount and the pole conversion relationship of the three-phase induction motor, and generating the stator voltage amplitude command while maintaining a preset constant V / f ratio, includes: Convert the frequency adjustment amount into the target frequency command; The target frequency command is subjected to amplitude constraint and frequency shaping processing; The processed target frequency command is integrated to obtain the synchronization electrical angle; The target frequency command is converted into the stator voltage amplitude command according to the preset constant V / f ratio, and the modulation index is determined by the stator voltage amplitude command. The modulation signal for pulse width modulation is generated based on the synchronization electrical angle and the modulation index.

[0010] Furthermore, under normal operating conditions, the three-phase stator currents maintain a balanced sinusoidal relationship with mutual phase shifts; under open-circuit fault conditions, the fault phase current drops to zero, and the currents of the remaining phases are in opposite directions and distorted. After being converted to the dq coordinate system, a dq current signal is formed, which includes a DC component and an AC component that varies twice with the synchronous electrical angle; the resonant adjustment branch performs fixed-frequency tracking compensation on the AC component to weaken the influence of the AC component on the speed response and electromagnetic torque response.

[0011] Furthermore, under normal operating conditions, the actual rotational speed is acquired in real time by an encoder connected to the three-phase induction motor. The encoder simultaneously outputs angular position feedback information and rotational speed feedback information. The rotational speed feedback information is used to form the rotational speed deviation, and the sampling results of the encoder are continuously fed back to the closed-loop V / f control structure so that the gate drive pulse is continuously updated during open-circuit faults and after the faults are cleared.

[0012] According to a second aspect of this disclosure, a three-phase induction motor open-circuit fault mitigation control system is provided, the system comprising: The deviation generation module is used to obtain the speed setpoint and actual speed of the three-phase induction motor, and to generate a speed deviation based on the speed setpoint and the actual speed. The speed regulation module is used to input the speed deviation into the composite speed controller in the closed-loop V / f control structure to generate a frequency regulation amount. The composite speed controller includes a proportional regulation branch and a resonant regulation branch arranged in parallel. The resonant regulation branch is used to compensate for the double frequency disturbance component caused by the stator phase open circuit. The double frequency disturbance component is the disturbance component formed in the dq coordinate system current after the three-phase current imbalance. The instruction generation module is used to determine the target frequency instruction based on the frequency adjustment amount and the pole conversion relationship of the three-phase induction motor, and generate a stator voltage amplitude instruction corresponding to the target frequency instruction while maintaining a preset constant V / f ratio; perform integration processing on the target frequency instruction to obtain the synchronization electrical angle, and generate a modulation signal based on the synchronization electrical angle and the stator voltage amplitude instruction; The inverter drive module is used to perform pulse width modulation according to the modulation signal to obtain the gate drive pulse for driving the three-phase inverter, and the three-phase inverter outputs a three-phase drive voltage to the three-phase induction motor. The fault-tolerant operation module is used to continuously utilize the actual speed to form a closed-loop feedback regulation during the operation of the three-phase induction motor. When any phase of the stator is open-circuited, causing the corresponding phase current to drop to zero, the currents of the other phases to become unbalanced, and the current in the dq coordinate system to exhibit a double-frequency disturbance, the closed-loop V / f control structure is still kept working continuously. The resonant regulation branch tracks and compensates for the double-frequency disturbance to reduce speed fluctuations and electromagnetic torque pulsation and maintain continuous motor rotation.

[0013] The technical solution disclosed herein has the following beneficial effects: Compared with existing technologies, this invention improves the control method for open-circuit fault conditions, enabling the three-phase induction motor to maintain continuous operation even when current imbalance and related disturbances occur due to stator phase open circuits. This reduces speed fluctuations and electromagnetic torque pulsations, and improves the dynamic response during the fault recovery phase, thereby enhancing system stability and reliability. Furthermore, this invention eliminates the need for independent and complex fault detection mechanisms and additional fault-tolerant mode switching procedures, reducing implementation complexity and application costs. It is suitable for drive scenarios requiring high reliability and continuous operation. Attached Figure Description

[0014] Figure 1 This is a flowchart of a three-phase induction motor open-circuit fault mitigation control method in one of the embodiments of this specification; Figure 2 This is a structural block diagram of a three-phase induction motor open-circuit fault mitigation control system as described in the embodiments of this specification. Detailed Implementation

[0015] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make this disclosure more comprehensive and complete, and to fully convey the concept of the example embodiments to those skilled in the art. The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced with one or more of the specific details omitted, or other methods, components, apparatus, steps, etc., can be employed. In other instances, well-known technical solutions are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0016] Furthermore, the accompanying drawings are merely illustrative of this disclosure. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities may be implemented in software, in one or more hardware modules or integrated circuits, or in different network and / or processor devices and / or microcontroller devices.

[0017] This invention provides a method for mitigating open-circuit faults in a three-phase induction motor. (Refer to...) Figure 1 The diagram shown is a flowchart illustrating a method for mitigating open-circuit faults in a three-phase induction motor according to an embodiment of the present invention. This method can be applied to electronic devices such as personal computers, servers, controllers, and host computers. The method can be executed by a device, which can be implemented by software and / or hardware. Specifically, the method may include the following steps S101-S108: In step S101, the setpoint speed and actual speed of the three-phase induction motor are obtained, and a speed deviation is formed based on the setpoint speed and the actual speed.

[0018] The setpoint speed characterizes the target speed that the drive system expects to achieve, while the actual speed characterizes the real speed of the three-phase induction motor under its current operating state. Both serve as inputs for the speed closed-loop regulation. The setpoint speed can be output by a host control unit, speed control command unit, or operation control unit, while the actual speed can be acquired in real time by a speed feedback device connected to the three-phase induction motor. In one embodiment, the actual speed is output by an encoder, which simultaneously provides angular position feedback information and speed feedback information to meet the requirements of continuous and real-time speed feedback in closed-loop regulation.

[0019] Speed ​​deviation is obtained by comparing the setpoint speed with the actual speed, and is used to characterize the degree of deviation of the current operating state from the target operating state. Speed ​​deviation can be expressed as: ; in, For speed deviation, The given value is the rotational speed. This refers to the actual rotational speed.

[0020] The speed deviation serves as the input for speed regulation in the subsequent closed-loop V / f control structure. When the actual speed is lower than the speed setpoint, the speed deviation represents the acceleration regulation demand; when the actual speed is higher than the speed setpoint, the speed deviation represents the deceleration regulation demand; when the actual speed approaches the speed setpoint, the speed deviation decreases, indicating that the system is gradually approaching a steady-state operating state.

[0021] This step establishes the basis for comparison in the outer-loop speed closed loop by synchronously acquiring target speed information and feedback speed information, enabling the closed-loop V / f control structure to continuously adjust the input frequency and voltage around the speed deviation. The speed, input voltage frequency, and number of poles of the three-phase induction motor satisfy the following relationship: ; in For rotational speed, The fundamental frequency of the input voltage. It is an extreme number.

[0022] Based on the above correspondence, the acquisition of the speed setpoint and the actual speed is not only used to form the closed-loop error, but also to provide target constraints and feedback basis for the generation of subsequent frequency adjustment, so that the speed adjustment process matches the electromagnetic operating state of the motor.

[0023] During operation, the actual rotational speed is preferably continuously collected and fed back, so that the speed deviation is updated in real time according to the motor's operating status. With this setting, the speed closed loop can remain effective when the motor is in normal operating condition, open circuit fault condition, and fault recovery condition, avoiding the loss of adjustment basis of the control link due to the interruption of speed feedback.

[0024] In step S102, the speed deviation is input to the composite speed controller in the closed-loop V / f control structure to generate a frequency adjustment amount. The composite speed controller includes a proportional adjustment branch and a resonant adjustment branch connected in parallel. The resonant adjustment branch is used to compensate for the double frequency disturbance component caused by the stator phase open circuit. The double frequency disturbance component is the disturbance component formed in the dq coordinate system current after the three-phase current imbalance.

[0025] The proportional adjustment branch is used to generate a basic adjustment amount based on the speed deviation, and the resonance adjustment branch is used to generate a resonance compensation amount based on the double frequency disturbance. The basic adjustment amount and the resonance compensation amount are superimposed to form the frequency adjustment amount.

[0026] The resonant frequency of the resonant regulation branch is determined as follows: First, the fundamental frequency of the input voltage corresponding to the target frequency command is determined based on the given speed and the number of poles of the three-phase induction motor. Then, the angular frequency corresponding to the fundamental frequency of the input voltage is multiplied according to the double frequency relationship of the current in the dq coordinate system under open circuit fault to obtain the resonant frequency that is synchronized with the double frequency disturbance.

[0027] In this system, the speed deviation is input to the composite speed controller, which then performs closed-loop regulation to output a frequency adjustment. The composite speed controller is located in the outer speed loop of the closed-loop V / f control structure. Its function is to correct the input voltage frequency based on the speed deviation, causing the operating speed of the three-phase induction motor to converge towards the speed setpoint. The composite speed controller employs a parallel structure, including a proportional regulation branch and a resonant regulation branch. In one embodiment, an integral regulation branch can be further configured in the parallel structure to form a proportional-integral-resonant control structure. However, in the basic implementation of this step, the composite speed controller includes at least a proportional regulation branch and a resonant regulation branch.

[0028] The proportional control branch generates a basic adjustment amount based on the speed deviation. The output of the proportional control branch maintains a proportional relationship with the speed deviation; when the speed deviation increases, the basic adjustment amount output by the proportional control branch increases accordingly to improve the adjustment response speed; when the speed deviation decreases, the basic adjustment amount decreases accordingly, allowing the speed regulation process to gradually stabilize. The proportional control branch undertakes the basic speed regulation function under normal operating conditions and also provides basic regulation capability for speed maintenance under open-circuit fault conditions.

[0029] The resonant adjustment branch is used to generate resonant compensation based on the double-frequency disturbance. After an open-circuit fault occurs in the stator phase, the current of the corresponding faulty phase drops to zero, and the currents of the remaining phases become unbalanced and distorted. After transformation to the dq coordinate system, the dq current no longer maintains the constant component characteristics under normal operating conditions, but instead forms a state where DC components and double-frequency AC components coexist. This double-frequency AC component is transmitted to the speed response and electromagnetic torque response, causing speed fluctuations and electromagnetic torque pulsations. The resonant adjustment branch establishes a fixed-frequency compensation channel around this double-frequency disturbance, enabling the composite speed controller to specifically suppress this disturbance in the outer speed loop, thereby mitigating the impact of the open-circuit fault on the closed-loop V / f control structure.

[0030] Under normal operating conditions, the three-phase stator currents maintain a balanced sinusoidal relationship with each phase out of phase, which can be expressed as: ; in, The phase current frequency, These are the current amplitudes of each phase under normal operating conditions. This is the initial phase angle.

[0031] The rotor flux linkage position satisfies: ; Under normal operating conditions, the dq current remains constant, which can be expressed as: ; When an open-circuit fault occurs in phase A, the three-phase current relationship becomes: ; in, This represents the amplitude of the remaining phase current under open-circuit fault conditions. This is the phase angle under open-circuit fault conditions.

[0032] Under open-circuit fault conditions, the dq current can be expressed as: ; As can be seen from the above formula, under the open circuit fault condition and Both components contain an AC component that varies twice with the synchronous electrical angle and a corresponding DC component. The AC component that varies twice is the double-frequency disturbance component. The resonant regulation branch in the composite speed controller compensates for this double-frequency disturbance component, enabling the outer speed loop to maintain effective regulation even under current imbalance.

[0033] The basic adjustment value generated by the proportional control branch and the resonant compensation value generated by the resonant control branch are superimposed at the output of the composite speed controller to form the frequency adjustment value. This frequency adjustment value includes both the basic correction component for speed deviation and the fixed-frequency compensation component for double-frequency disturbance, thus achieving both speed tracking performance under normal operating conditions and disturbance suppression capability under open-circuit fault conditions.

[0034] When the composite speed controller adopts a proportional-resonant control structure, its transfer function can be expressed as: ; in, For proportional gain, For resonant gain, The resonant frequency is used to provide basic speed regulation capability, the resonant gain is used to enhance the suppression capability of double-harmonic disturbances, and the resonant frequency is used to synchronize the resonant compensation channel with the double-harmonic disturbance under open-circuit fault conditions.

[0035] The resonant frequency is determined based on the fundamental frequency of the input voltage. The fundamental frequency of the input voltage is related to the given rotational speed and the number of poles. The resonant frequency corresponds to twice the angular frequency of this fundamental frequency, and its expression is: ; The fundamental frequency of the input voltage can be expressed as: ; Where P is the extremum, The target rotational speed corresponding to the given rotational speed. This is the fundamental frequency of the input voltage corresponding to the target rotational speed. After determining the resonant frequency in the above manner, the resonant adjustment branch can maintain synchronization with the double-frequency disturbance in the dq coordinate system current under open-circuit fault conditions, thereby achieving targeted tracking compensation.

[0036] Regarding parameter tuning, the proportional gain can be set to a range that satisfies closed-loop stability and reduces overshoot, while the resonant gain can be set to a range that balances disturbance suppression capability and system stability. With this setting, the composite speed controller can maintain its closed-loop speed regulation performance under normal operating conditions, and under open-circuit fault conditions, it can utilize the resonant regulation branch to weaken the impact of double-frequency disturbances on speed response and electromagnetic torque response, enabling continuous output of the frequency regulation and providing a stable input for subsequent target frequency command generation.

[0037] In step S103, a target frequency command is determined based on the frequency adjustment amount and the pole conversion relationship of the three-phase induction motor, and a stator voltage amplitude command corresponding to the target frequency command is generated while maintaining a preset constant V / f ratio; the target frequency command is integrated to obtain the synchronization electrical angle, and a modulation signal is generated based on the synchronization electrical angle and the stator voltage amplitude command.

[0038] Specifically, this includes: converting the frequency adjustment amount into the target frequency command; performing amplitude constraint and frequency shaping processing on the target frequency command; integrating the processed target frequency command to obtain the synchronization electrical angle; converting the target frequency command into the stator voltage amplitude command according to the preset constant V / f ratio, and determining the modulation index by the stator voltage amplitude command; and generating the modulation signal for the pulse width modulation based on the synchronization electrical angle and the modulation index.

[0039] The frequency adjustment quantity, as the output of the speed outer loop, enters the closed-loop V / f control link to generate the target frequency command. The target frequency command corresponds to the fundamental frequency of the input voltage of the three-phase induction motor. Motor speed regulation is achieved by changing the input voltage frequency, while maintaining a relatively constant voltage-frequency ratio to ensure stability and efficiency during operation. To avoid abrupt changes in the frequency command during dynamic adjustment, the target frequency command undergoes amplitude constraint and frequency shaping before entering subsequent calculations, ensuring continuous frequency changes and keeping the output frequency within the controllable range of the drive system. Under conditions exceeding the base speed, the stator voltage remains within the allowable range to prevent excessive voltage stress on the insulation.

[0040] After the target frequency command is determined, it is integrated to obtain the synchronization electrical angle. The synchronization electrical angle is used to establish the phase reference of the modulation wave, ensuring continuous phase variation of the subsequent output voltage. This synchronization electrical angle is consistent with the phase current frequency, and its expression has been given in the previous steps; in this step, it continues to serve as the angle input for generating the modulation signal. Based on the synchronization electrical angle and the stator voltage amplitude command, a modulation signal for pulse width modulation (PWM) can be formed. Combined with the V / f control link, the target frequency command, after proportional conversion, amplitude limiting and shaping, angular frequency transformation, and integration, outputs the synchronization electrical angle. The stator voltage amplitude command, after amplitude conversion, determines the modulation index. The synchronization electrical angle and the modulation index together form the modulation wave input to the PWM unit, thus providing the front-end signal for the inverter switching drive.

[0041] While maintaining a constant V / f ratio, the target frequency command and the stator voltage amplitude command maintain a proportional correspondence. This setting ensures that as the frequency increases, the output voltage increases accordingly to maintain the flux linkage within a reasonable range; conversely, as the frequency decreases, the output voltage decreases synchronously to prevent excessive flux linkage deviation. The stator voltage amplitude command is further used to determine the modulation index, which characterizes the degree of normalization of the inverter's output voltage amplitude relative to the DC bus voltage. The modulation index, together with the synchronization angle, determines the amplitude and phase of the modulation signal, ensuring that the three-phase output voltage meets both frequency and amplitude regulation requirements.

[0042] This step works in conjunction with the previous speed regulation step. The frequency regulation quantity, after being progressively converted from the target frequency command, synchronous electrical angle, and stator voltage amplitude command, forms a modulation signal that can directly enter the pulse width modulation link. Therefore, the speed closed-loop output does not directly act on the inverter, but rather achieves scalar control through a continuous conversion relationship between frequency, voltage, and phase. Using this method, the same V / f control link can be used under normal operating conditions, open-circuit fault conditions, and fault recovery conditions, without requiring a reconfiguration of the main control structure.

[0043] In another embodiment, the composite speed controller includes an integral control branch connected in parallel with the proportional control branch and the resonant control branch to form a proportional-integral-resonant controller. The integral control branch is used to reduce steady-state deviation under normal operating conditions and fault recovery conditions, and together with the resonant control branch, it suppresses speed fluctuations and electromagnetic torque pulsations during open-circuit faults.

[0044] Specifically, the composite speed controller includes an integral control branch connected in parallel with the proportional control branch and the resonant control branch, forming a proportional-integral-resonant controller. The proportional-integral-resonant controller introduces an integral element into the proportional-resonant control structure to improve steady-state deviation under normal operating conditions and fault recovery conditions, and to enhance dynamic response capabilities before and after a fault. Its transfer function is: ; in, For proportional gain, For integral gain, For resonant gain, The resonant frequency is defined as follows: the proportional gain ensures the basic response speed of the outer speed loop, the integral gain reduces steady-state error, and the resonant gain enhances the suppression of double-frequency disturbances under open-circuit faults. With this configuration, the integral control branch improves steady-state speed tracking accuracy under normal operating conditions and reduces speed deviation during fault recovery, while the resonant control branch continues to compensate for double-frequency disturbances. Both components work together on the frequency regulation, ensuring good performance of the closed-loop V / f control structure during both fault periods and recovery phases.

[0045] The resonant frequency continues to synchronize with the double-harmonic disturbance in the dq coordinate system current under open-circuit fault conditions, and its expression is: ; Where P is the extremum, The target speed is set at this resonant frequency. This resonant frequency is coordinated with the aforementioned target frequency command, ensuring that the resonant compensation channel always corresponds to the disturbance frequency under open-circuit fault conditions. After the integral control branch and the resonant control branch are connected in parallel, the basic form of the V / f main control link remains unchanged, and no independent fault detection stage is introduced. Instead, steady-state error correction and disturbance suppression are completed within the existing speed outer loop. Therefore, after the frequency regulation quantity enters the frequency, voltage, and phase conversion link of this step, it can still continuously generate modulation signals, thereby maintaining continuous control of the motor during fault periods and fault recovery periods.

[0046] In step S104, pulse width modulation is performed according to the modulation signal to obtain gate drive pulses for driving the three-phase inverter, and the three-phase inverter outputs three-phase drive voltage to the three-phase induction motor.

[0047] In step S104, after the modulation signal is input to the pulse width modulation unit, the pulse width modulation unit generates corresponding gate drive pulses based on the amplitude and phase changes of the modulation signal. These gate drive pulses are used to control the on and off times of each power switching device in the three-phase inverter, enabling the three-phase inverter to output three-phase drive voltages according to the target frequency and target voltage amplitude requirements. With this configuration, the frequency, amplitude, and phase information generated by the front-end speed closed loop and V / f control link can all be converted into switching drive signals suitable for power conversion execution through the pulse width modulation process.

[0048] After receiving the gate drive pulse, the three-phase inverter converts the DC-side electrical energy into an AC drive voltage for the three-phase induction motor. The frequency of this three-phase drive voltage is determined by the synchronous electrical angle variation corresponding to the modulation signal, and the amplitude is determined by the modulation index corresponding to the modulation signal. Therefore, the output of the three-phase inverter is not a fixed voltage output, but a controlled three-phase voltage output that continuously changes with the results of the preceding control stage. In this way, the power supply frequency and voltage of the three-phase induction motor are unified into the same control link, enabling motor speed regulation to be achieved through voltage-frequency ratio control.

[0049] The pulse width modulation (PWM) process plays a transforming role in the control link, converting the modulated signal generated in the previous stage into a switching control quantity that can be directly applied to the power devices, establishing a correspondence between the control algorithm output and the inverter drive execution. The gate drive pulse is preferably updated continuously so that the three-phase drive voltage output by the three-phase inverter can be adjusted in real time according to changes in frequency regulation and stator voltage amplitude commands. With this setting, the motor can use the same PWM drive process under normal operating conditions, open-circuit fault conditions, and fault recovery conditions without changing the inverter drive structure; dynamic adjustment of the output voltage is achieved solely through continuous changes in the previous stage modulation signal.

[0050] The three-phase drive voltage output from the three-phase inverter is applied to the stator windings of the three-phase induction motor, forming a balanced drive under normal operating conditions. Under open-circuit fault conditions, although the faulty phase branch is open-circuited, the three-phase inverter maintains a controlled output state, and the gate drive pulses are uninterrupted, thus ensuring the continuity of the execution link of the entire closed-loop V / f control structure. The purpose of this step is not to identify the fault, but to stably implement the results of the preceding control stage into inverter drive actions, providing a continuous power output basis for subsequent speed regulation and fault mitigation during motor operation.

[0051] In step S105, during the operation of the three-phase induction motor, the actual rotational speed is continuously used to form a closed-loop feedback regulation. When any phase of the stator is open-circuited, causing the corresponding phase current to drop to zero, the currents of the other phases to become unbalanced, and the current in the dq coordinate system to exhibit a double-frequency disturbance, the closed-loop V / f control structure is still kept working continuously. The resonant regulation branch tracks and compensates for the double-frequency disturbance to reduce speed fluctuations and electromagnetic torque pulsation and maintain the continuous rotation of the motor.

[0052] Under normal operating conditions, the three-phase stator currents maintain a balanced sinusoidal relationship with each phase out of phase. Under open-circuit fault conditions, the fault phase current drops to zero, and the currents of the other phases are in opposite directions and distorted. After being converted to the dq coordinate system, a dq current signal is formed, which includes a DC component and an AC component that varies twice with the synchronous electrical angle. The resonant adjustment branch performs fixed-frequency tracking compensation on the AC component to reduce the influence of the AC component on the speed response and electromagnetic torque response.

[0053] Furthermore, under normal operating conditions, the actual rotational speed is acquired in real time by an encoder connected to the three-phase induction motor. The encoder simultaneously outputs angular position feedback information and rotational speed feedback information. The rotational speed feedback information is used to generate the rotational speed deviation, and the sampling results of the encoder are continuously fed back to the closed-loop V / f control structure so that the gate drive pulse is continuously updated during open-circuit faults and after the faults are cleared.

[0054] Specifically, in step S105, the three-phase induction motor enters a continuous closed-loop operation state. The actual speed is continuously fed back to the closed-loop V / f control structure as a speed feedback quantity, used to continuously update the speed deviation and drive the composite speed controller to continuously output frequency adjustment quantities. With this setting, the speed outer loop will not be interrupted due to changes in operating state, and the gate drive pulse of the three-phase inverter can be continuously updated with the feedback results, thereby ensuring continuous output of the three-phase drive voltage and maintaining consistency of the control link under normal operating conditions, open-circuit fault conditions, and fault recovery conditions. The encoder plays a real-time feedback role in this process. Its output speed feedback information is used to form the speed closed-loop input, and its output angular position feedback information is used to reflect the motor operating state. The two types of feedback quantities together ensure the real-time performance and continuity of the closed-loop regulation.

[0055] Under normal operating conditions, the three-phase stator currents remain in balance, with a fixed phase difference between each phase. After transformation to the dq coordinate system, the current components exhibit stable characteristics, and the speed outer loop mainly adjusts routinely around the speed deviation. When any stator phase becomes open-circuited, the faulty phase current drops to zero, and the currents of the other two phases become unbalanced and distorted. This current imbalance, after coordinate transformation, is reflected as a disturbance component in the dq coordinate system current. This disturbance component includes a DC component and an AC component that varies twice with the synchronous electrical angle. This double-frequency AC component further affects the electromagnetic torque output and mechanical speed response, causing speed fluctuations, torque pulsations, vibration, and increased noise during the fault period. In severe cases, it can affect continuous operation capability.

[0056] This step does not introduce independent fault detection and mode switching mechanisms. Instead, it maintains continuous operation of the closed-loop V / f control structure, ensuring that the resonant regulation branch in the composite speed controller is always operational. When an open-circuit fault causes a double-frequency disturbance, the resonant regulation branch performs fixed-frequency tracking compensation around the disturbance frequency, directly adding the compensation effect to the frequency regulation. This allows the outer speed loop to maintain effective regulation even under current imbalance conditions. With this setup, the control action is not accomplished by switching to another faulty controller, but rather disturbance suppression and speed maintenance are achieved within the original closed-loop V / f control framework. Therefore, the control link structure remains consistent, and the control process before, during, and after the fault occurs is continuous.

[0057] After the resonant regulation branch performs tracking compensation on the double-frequency AC component, it can weaken the transmission of this disturbance component to the speed response and electromagnetic torque response, thereby reducing the speed drop during open-circuit faults, narrowing the speed fluctuation range, and alleviating electromagnetic torque pulsation. The motor can still maintain rotation within the fault range. After the fault is cleared, because the closed-loop feedback link remains uninterrupted, the controller continues to adjust based on real-time speed feedback, the gate drive pulses are continuously updated, the three-phase inverter output returns to normal drive mode, and the motor can quickly return to a stable operating state. When using a proportional-integral-resonant control structure that includes an integral regulation branch, the integral regulation branch can further reduce the steady-state deviation under normal operating conditions and fault recovery conditions, and together with the resonant regulation branch, suppress speed fluctuations and electromagnetic torque pulsation during faults.

[0058] Through the above closed-loop feedback and disturbance compensation process, the control system maintains the same main control link to continue operating even when the stator phase is open-circuited. It does not require a separate switching process after open-circuit fault identification, nor does it require interruption of inverter drive output. This enables the three-phase induction motor to have continuous operation capability during open-circuit faults and maintain good recovery performance after the fault is cleared.

[0059] Based on the same line of thought, such as Figure 2The diagram shown is a structural block diagram of a three-phase induction motor open-circuit fault mitigation control system provided in an embodiment of the present invention. The system includes: The deviation generation module 201 is used to obtain the speed setpoint and actual speed of the three-phase induction motor, and to generate a speed deviation based on the speed setpoint and the actual speed. The speed regulation module 202 is used to input the speed deviation into the composite speed controller in the closed-loop V / f control structure to generate a frequency regulation amount. The composite speed controller includes a proportional regulation branch and a resonant regulation branch arranged in parallel. The resonant regulation branch is used to compensate for the double frequency disturbance component caused by the stator phase open circuit. The double frequency disturbance component is the disturbance component formed in the dq coordinate system current after the three-phase current imbalance. The instruction generation module 203 is used to determine the target frequency instruction based on the frequency adjustment amount and the pole conversion relationship of the three-phase induction motor, and generate a stator voltage amplitude instruction corresponding to the target frequency instruction while maintaining a preset constant V / f ratio relationship; perform integration processing on the target frequency instruction to obtain the synchronization electrical angle, and generate a modulation signal based on the synchronization electrical angle and the stator voltage amplitude instruction; The inverter drive module 204 is used to perform pulse width modulation according to the modulation signal to obtain the gate drive pulse for driving the three-phase inverter, and the three-phase inverter outputs a three-phase drive voltage to the three-phase induction motor. The fault-tolerant operation module 205 is used to continuously utilize the actual speed to form a closed-loop feedback regulation during the operation of the three-phase induction motor. When any phase of the stator is open-circuited, causing the corresponding phase current to drop to zero, the current of the other phases to become unbalanced, and the current in the dq coordinate system to exhibit a double-frequency disturbance, the closed-loop V / f control structure is still continuously operated. The resonant regulation branch tracks and compensates for the double-frequency disturbance to reduce speed fluctuations and electromagnetic torque pulsation and maintain continuous motor rotation.

[0060] The specific details of the above system have been described in detail in the method section of the implementation plan. For any undisclosed details, please refer to the implementation plan of the method section, and therefore will not be repeated here.

[0061] Compared with existing technologies, this system improves the control method for open-circuit fault conditions, enabling the three-phase induction motor to maintain continuous operation even when current imbalance and related disturbances occur due to stator phase open circuits. This reduces speed fluctuations and electromagnetic torque pulsations, and improves the dynamic response during the fault recovery phase, thereby enhancing the system's operational stability and reliability. Furthermore, this invention eliminates the need for independent and complex fault detection mechanisms and additional fault-tolerant mode switching procedures, reducing implementation complexity and application costs. It is suitable for drive scenarios requiring high reliability and continuous operation.

[0062] The accompanying drawings are merely illustrative of the processes included in the methods according to exemplary embodiments of this disclosure and are not intended to be limiting. It is readily understood that the processes shown in the drawings do not indicate or limit the temporal order of these processes. Furthermore, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0063] It should be noted that although several modules or units of the system have been mentioned in the detailed description above, this division is not mandatory. In fact, according to exemplary embodiments of this disclosure, the features and functions of two or more modules or units described above can be embodied in one module or unit. Conversely, the features and functions of one module or unit described above can be further divided and embodied by multiple modules or units.

[0064] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the claims.

[0065] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. A method for mitigating open-circuit faults in a three-phase induction motor, characterized in that, The method includes: The setpoint and actual speed of the three-phase induction motor are obtained, and the speed deviation is calculated based on the setpoint and the actual speed. The speed deviation is input into the composite speed controller in the closed-loop V / f control structure to generate a frequency adjustment amount. The composite speed controller includes a proportional adjustment branch and a resonant adjustment branch arranged in parallel. The resonant adjustment branch is used to compensate for the double frequency disturbance component caused by the stator phase open circuit. The double frequency disturbance component is the disturbance component formed in the dq coordinate system current after the three-phase current imbalance. The target frequency command is determined based on the frequency adjustment amount and the pole conversion relationship of the three-phase induction motor, and a stator voltage amplitude command corresponding to the target frequency command is generated while maintaining a preset constant V / f ratio. The target frequency command is integrated to obtain the synchronization electrical angle, and a modulation signal is generated based on the synchronization electrical angle and the stator voltage amplitude command. Pulse width modulation is performed according to the modulation signal to obtain gate drive pulses for driving the three-phase inverter, and the three-phase inverter outputs three-phase drive voltage to the three-phase induction motor. During the operation of the three-phase induction motor, the actual speed is continuously used to form a closed-loop feedback regulation. Even when any phase of the stator is open-circuited, causing the corresponding phase current to drop to zero, the currents of the other phases to become unbalanced, and the current in the dq coordinate system to exhibit a double-frequency disturbance, the closed-loop V / f control structure is still kept working continuously. The resonant regulation branch tracks and compensates for the double-frequency disturbance to reduce speed fluctuations and electromagnetic torque pulsation and maintain the continuous rotation of the motor.

2. The method for mitigating open-circuit faults in a three-phase induction motor according to claim 1, characterized in that, The proportional adjustment branch is used to generate a basic adjustment amount based on the speed deviation, and the resonance adjustment branch is used to generate a resonance compensation amount based on the double frequency disturbance. The basic adjustment amount and the resonance compensation amount are superimposed to form the frequency adjustment amount.

3. The method for mitigating open-circuit faults in a three-phase induction motor according to claim 1, characterized in that, The resonant frequency of the resonant adjustment branch is determined in the following manner: First, the fundamental frequency of the input voltage corresponding to the target frequency command is determined based on the given speed and the number of poles of the three-phase induction motor. Then, the angular frequency corresponding to the fundamental frequency of the input voltage is multiplied according to the double frequency relationship of the current in the dq coordinate system under open circuit fault to obtain the resonant frequency that is synchronized with the double frequency disturbance.

4. The method for mitigating open-circuit faults in a three-phase induction motor according to claim 1, characterized in that, The composite speed controller includes an integral control branch connected in parallel with the proportional control branch and the resonant control branch to form a proportional-integral-resonant controller. The integral control branch is used to reduce the steady-state deviation under normal operating conditions and fault recovery conditions, and together with the resonant control branch, it suppresses speed fluctuations and electromagnetic torque pulsations during open-circuit faults.

5. The method for mitigating open-circuit faults in a three-phase induction motor according to claim 1, characterized in that, The step of determining the target frequency command based on the frequency adjustment amount and the pole conversion relationship of the three-phase induction motor, and generating the stator voltage amplitude command while maintaining a preset constant V / f ratio, includes: Convert the frequency adjustment amount into the target frequency command; The target frequency command is subjected to amplitude constraint and frequency shaping processing; The processed target frequency command is integrated to obtain the synchronization electrical angle; The target frequency command is converted into the stator voltage amplitude command according to the preset constant V / f ratio, and the modulation index is determined by the stator voltage amplitude command. The modulation signal for pulse width modulation is generated based on the synchronization electrical angle and the modulation index.

6. The method for mitigating open-circuit faults in a three-phase induction motor according to claim 1, characterized in that, Under normal operating conditions, the three-phase stator currents maintain a balanced sinusoidal relationship with each other in opposite phases; under open-circuit fault conditions, the fault phase current drops to zero, and the currents of the other phases are in opposite directions and are distorted. After being converted to the dq coordinate system, a dq current signal is formed that includes a DC component and an AC component that changes twice with the synchronous electrical angle. The resonant adjustment branch performs fixed-frequency tracking compensation on the AC component to reduce the influence of the AC component on the speed response and electromagnetic torque response.

7. The method for mitigating open-circuit faults in a three-phase induction motor according to claim 1, characterized in that, Under normal operating conditions, the actual rotational speed is acquired in real time by an encoder connected to the three-phase induction motor. The encoder simultaneously outputs angular position feedback information and rotational speed feedback information. The rotational speed feedback information is used to form the rotational speed deviation, and the sampling results of the encoder are continuously fed back to the closed-loop V / f control structure so that the gate drive pulse is continuously updated during open-circuit faults and after the faults are cleared.

8. A three-phase induction motor open-circuit fault mitigation control system, the system comprising: The deviation generation module is used to obtain the speed setpoint and actual speed of the three-phase induction motor, and to generate a speed deviation based on the speed setpoint and the actual speed. The speed regulation module is used to input the speed deviation into the composite speed controller in the closed-loop V / f control structure to generate a frequency regulation amount. The composite speed controller includes a proportional regulation branch and a resonant regulation branch arranged in parallel. The resonant regulation branch is used to compensate for the double frequency disturbance component caused by the stator phase open circuit. The double frequency disturbance component is the disturbance component formed in the dq coordinate system current after the three-phase current imbalance. The instruction generation module is used to determine the target frequency instruction based on the frequency adjustment amount and the pole conversion relationship of the three-phase induction motor, and generate a stator voltage amplitude instruction corresponding to the target frequency instruction while maintaining a preset constant V / f ratio; perform integration processing on the target frequency instruction to obtain the synchronization electrical angle, and generate a modulation signal based on the synchronization electrical angle and the stator voltage amplitude instruction; The inverter drive module is used to perform pulse width modulation according to the modulation signal to obtain the gate drive pulse for driving the three-phase inverter, and the three-phase inverter outputs a three-phase drive voltage to the three-phase induction motor. The fault-tolerant operation module is used to continuously utilize the actual speed to form a closed-loop feedback regulation during the operation of the three-phase induction motor. When any phase of the stator is open-circuited, causing the corresponding phase current to drop to zero, the currents of the other phases to become unbalanced, and the current in the dq coordinate system to exhibit a double-frequency disturbance, the closed-loop V / f control structure is still kept working continuously. The resonant regulation branch tracks and compensates for the double-frequency disturbance to reduce speed fluctuations and electromagnetic torque pulsation and maintain continuous motor rotation.

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