Power inverse time control strategy for permanent magnet synchronous motor

Abstract

The application provides a power inverse time limit control strategy of a permanent magnet synchronous motor, collects operation data of the permanent magnet synchronous motor, constructs a three-dimensional query table function for mapping operation power of the permanent magnet synchronous motor and maximum allowed operation duration, calculates the maximum allowed operation duration under current operation power in real time according to the three-dimensional query table function, enters an inverse time limit mode when the maximum allowed operation duration is less than a set first threshold, exits the inverse time limit mode when the maximum allowed operation duration is greater than a set second threshold, limits the motor torque current component iq in the inverse time limit mode, suspends speed loop operation and locks the motor torque current component iq when entering the power inverse time limit mode, and resumes speed closed loop operation based on the locked motor torque current component iq after exiting the inverse time limit mode. Smooth switching of overload operation is realized, and control impact is avoided.

Description

Technical Field

[0001] This invention relates to the field of motor control technology, and specifically to a power inverse-time control strategy for a permanent magnet synchronous motor. Background Technology

[0002] A permanent magnet synchronous motor (PMSM) is a high-efficiency motor that uses permanent magnets to establish a rotor magnetic field that operates in strict synchronization with the stator magnetic field. With its high efficiency, high power / torque density, and excellent dynamic control performance, PMSMs are widely used in high-performance drive applications such as electric vehicles, industrial servo systems, and new energy equipment, and are a core power component of modern electric drive systems.

[0003] To meet the demands of short-term high-power conditions such as rapid acceleration of electric vehicles and peak loads of industrial equipment, it is necessary to fully exploit the overload potential of motors within safety boundaries while avoiding damage to equipment. Existing research mainly focuses on two aspects: first, predicting the sustainable operating time under short-term high-power conditions based on real-time operating conditions; and second, designing reasonable transition control strategies to achieve smooth switching of overload modes and reduce the impact on system operation.

[0004] However, existing methods often rely on empirical parameters or data under a single operating condition, making it difficult to take into account different voltage, temperature and power conditions, resulting in insufficient prediction accuracy; at the same time, the lack of systematic control logic makes the motor uncertain when entering and exiting short-term overload states, thus affecting the safety and stability of the motor. Summary of the Invention

[0005] This invention proposes a power inverse-time control strategy for permanent magnet synchronous motors to solve the technical problem that existing technologies cannot guarantee the safe and smooth entry and exit of the motor from overload state when a rapid response to load changes is required.

[0006] To solve the above-mentioned technical problems, the present invention provides a power inverse-time control strategy for a permanent magnet synchronous motor, comprising the following steps: Step S1: Collect permanent magnet synchronous motor operating data and construct a three-dimensional lookup table function that maps the permanent magnet synchronous motor's operating power to its maximum allowable operating time; Step S2: Calculate the maximum allowable running time under the current operating power in real time according to the three-dimensional lookup table function. When the maximum allowable running time is less than the set first threshold, enter the inverse time limit mode; when the maximum allowable running time is greater than the set second threshold, exit the inverse time limit mode. In the inverse-time mode, the motor torque current component iq is limited, the speed loop operation is paused, and the motor torque current component iq is latched when entering the power inverse-time mode. After exiting the inverse-time mode, the speed loop operation re-enters the speed closed-loop operation based on the latched motor torque current component iq.

[0007] Preferably, the operating data in step S1 includes: DC bus voltage, motor winding temperature, and current power.

[0008] Preferably, in step S2, a three-dimensional linear interpolation algorithm is used to process the three-dimensional lookup table function to calculate the maximum allowable runtime in real time.

[0009] Preferably, the expression for limiting the motor torque current component iq in step S2 is as follows: iq = iq_old × k; k=1+(time-10)×0.01×(1+rate×0.5) In the formula, iq_old represents the motor torque current component when entering the inverse time mode; k represents the limiting ratio; time represents the maximum allowable running time; and rate is the temperature change rate.

[0010] Preferably, a minimum threshold is set for the limiting ratio.

[0011] Preferably, in the inverse time mode, when the motor feedback speed exceeds a times the reference speed, the inverse time mode is exited, where a > 1.

[0012] Preferably, the permanent magnet synchronous motor operating data collected in step S1 is subjected to a first-order low-pass filter.

[0013] The beneficial effects of this invention include at least the following: By collecting operating data of a permanent magnet synchronous motor, constructing a three-dimensional lookup table of power and allowable operating time, and calculating the operating time in real time, this invention achieves accurate prediction of the motor state under short-term high-power conditions. By setting entry and exit thresholds to limit the motor torque current component iq, thermal load can be effectively suppressed in overload mode, preventing motor overheating failure. Simultaneously, when entering the limit, the speed loop calculation is paused and the reference value is latched; when exiting, closed-loop control is smoothly restored, reducing switching shocks and improving system stability. This strategy balances overload capacity and safety protection, significantly improving the reliability and dynamic response performance of permanent magnet synchronous motors in scenarios such as electric vehicles and industrial servos. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the method flow according to an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the maximum allowable runtime for real-time calculation in an embodiment of the present invention. Figure 3 This is a schematic diagram of the set power inverse time-limit mode flag according to an embodiment of the present invention; Figure 4 This is a schematic diagram showing the feedback and reference values ​​of the motor torque current component in an embodiment of the present invention; Figure 5 This is a schematic diagram of the reference and feedback rotation speeds in an embodiment of the present invention. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0016] like Figure 1 As shown, this embodiment of the invention provides a power inverse-time control strategy for a permanent magnet synchronous motor, including the following steps: Step S1: Collect the operating data of the permanent magnet synchronous motor and construct a three-dimensional lookup table function that maps the operating power and maximum allowable operating time of the permanent magnet synchronous motor.

[0017] Specifically, in this embodiment of the invention, the operating data of a permanent magnet synchronous motor, including DC voltage, motor winding temperature and current power, are collected, and a three-dimensional lookup table function is constructed to determine the maximum allowable operating time of the motor under the current power.

[0018] To prevent excessive fluctuations in the calculation results, this embodiment further implements first-order low-pass filtering on key operating parameters such as DC voltage, motor winding temperature, and current power, with the filter bandwidth initially set at 10Hz.

[0019] Step S2: Calculate the maximum allowable running time under the current operating power in real time according to the three-dimensional lookup table function. When the maximum allowable running time is less than the set first threshold, enter the inverse time limit mode; when the maximum allowable running time is greater than the set second threshold, exit the inverse time limit mode. In inverse-time mode, the motor torque current component iq is limited, the speed loop operation is paused, and the motor torque current component iq is latched when entering the power inverse-time mode. After exiting the inverse-time mode, the speed loop operation is based on the latched motor torque current component iq and re-enters the speed closed-loop operation.

[0020] Specifically, in this embodiment, a three-dimensional linear interpolation algorithm is used to calculate the maximum allowable running time corresponding to the current operating condition in real time.

[0021] When the allowed runtime is less than the set entry threshold, the system enters the power inverse time limit mode and sets the warning signal flag=1; when the calculation result is higher than the exit threshold, it exits the power inverse time limit mode and clears the warning signal flag=0. In this embodiment, the entry threshold is set to 8s and the exit threshold is set to 10s, forming a hysteresis band between them.

[0022] In the inverse-time power mode, the motor torque current component iq is limited. The specific limiting value selection rule in this embodiment is as follows: iq = iq_old × k; Where iq_old is the reference value before the speed PI regulator is suspended, and k represents the limiting ratio.

[0023] In this embodiment, the iq limiting ratio k is related to the actual temperature and temperature rise rate of the winding. The higher the temperature and the greater the temperature rise rate, the faster the iq decreases. Meanwhile, to prevent equipment malfunction, a minimum threshold is set for k in this embodiment. When k is less than the minimum threshold, k is no longer reduced to limit the iq.

[0024] In this way, after entering the iq limiting mode, as the maximum allowable operating time calculated in real time gradually exits the threshold, the limiting ratio k gradually increases to 1, and then exits the iq limiting mode and re-enters the speed closed-loop mode. The smooth entry and exit of the power limiting mode prevents large shocks to the inverter control.

[0025] After the inverter enters the IQ limiting state, the motor speed becomes difficult to maintain due to the decrease in output torque, resulting in a speed drop. If the speed loop continues to run at this time, the error between the target speed and the actual speed will continuously increase, and the integrator output will accumulate until it reaches the upper limit, thus forming an excessively high reference value in the power inverse-time mode, causing a large impact during system switching. To avoid this problem, this invention suspends the speed loop operation after entering the limiting state and latches the output value before the limiting as the current limiting reference. In this way, a smooth recovery can be achieved when exiting the power inverse-time mode, reducing the impact on the motor control system.

[0026] In summary, this embodiment sets the following expression for the limiting ratio k: k=1+(time-10)×0.01×(1+rate×0.5); Where time is the maximum allowed running time, ranging from 0 to 8; rate is the temperature change rate, with a maximum of 2℃ / s.

[0027] To prevent overspeeding caused by increased speed due to load reduction and constant torque current, speed feedback is monitored. When the feedback speed exceeds the reference speed by 2%, the forced control mode switches to speed mode to stabilize the speed. At this time, the iq current required to track the speed is less than the current after the limit is applied, which is more conducive to reducing the motor's thermal load.

[0028] The following describes the application of the methods of the present invention to specific examples.

[0029] A bench test was conducted on the power inverse-time strategy. The test DC bus voltage was 400V and the permanent magnet synchronous motor speed was 1920 RPM. For ease of testing, the actual measured temperature of the motor windings was increased by 100 to obtain the motor feedback temperature, and the actual value of the winding current iq was increased by 85 to obtain the feedback iq. These values ​​were used to calculate the maximum allowable operating time under the current conditions. The calculation results are as follows: Figure 2 As shown.

[0030] from Figure 2 It can be seen that as the motor winding temperature rises, when the operating time under the current condition is less than 8 seconds, the motor enters the power inverse time mode at t=1.937s. The corresponding setting of the power inverse time mode flag is as follows: Figure 3 As shown; at this time, the current speed loop output iq is latched and the current limit is activated as follows. Figure 4 As shown, specifically, the test bench uses a six-phase permanent magnet synchronous motor. For ease of control, this six-phase motor is equivalent to two independent three-phase systems, each with its own current controlled. Therefore, in Figure 4 The test waveforms simultaneously display iq feedback 1 and iq feedback 2. iq feedback 1 represents the torque and current components of the first group of three-phase equivalent systems, and iq feedback 2 represents the torque and current components of the second group of three-phase equivalent systems.

[0031] As the motor torque current decreases, and the load torque current remains constant and is greater than the motor torque current, the speed decreases as follows: Figure 5 As shown, at t=3.378s, the load side reduces the load, and the torque current on the electric side is greater than the load torque current, causing the speed to increase; at t=4.616s, the feedback speed is detected to be greater than 1.02 times the reference speed threshold, indicating that the current limited electric torque current is greater than the torque current required to maintain the reference speed, and thus switches to speed mode to achieve speed tracking control.

[0032] The entire power inverse time control logic and timing are consistent with the design process, and the switching between power inverse time control mode and speed mode is seamless.

[0033] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described; only preferred embodiments of the present invention are illustrated. The descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. As long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification.

[0034] It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept, and these all fall within the scope of protection of this invention. Therefore, the scope of protection of this invention should be determined by the appended claims.

Claims

1. A power inverse-time control method for a permanent magnet synchronous motor, characterized in that: Includes the following steps: Step S1: Collect permanent magnet synchronous motor operating data and construct a three-dimensional lookup table function that maps the permanent magnet synchronous motor's operating power to its maximum allowable operating time; Step S2: Calculate the maximum allowable running time under the current operating power in real time according to the three-dimensional lookup table function. When the maximum allowable running time is less than the set first threshold, enter the inverse time limit mode; when the maximum allowable running time is greater than the set second threshold, exit the inverse time limit mode. In the inverse-time mode, the motor torque current component iq is limited, the speed loop operation is paused, and the motor torque current component iq when entering the power inverse-time mode is latched; after exiting the inverse-time mode, the speed loop operation is based on the latched motor torque current component iq and re-enters the speed closed-loop operation. In the inverse time mode, when the motor feedback speed exceeds a times the reference speed, the inverse time mode is exited, where a > 1.

2. The power inverse-time control method for a permanent magnet synchronous motor according to claim 1, characterized in that: The operating data in step S1 includes: DC bus voltage, motor winding temperature, and current power.

3. The power inverse-time control method for a permanent magnet synchronous motor according to claim 1, characterized in that: In step S2, a three-dimensional linear interpolation algorithm is used to process the three-dimensional lookup table function and calculate the maximum allowable runtime in real time.

4. The power inverse-time control method for a permanent magnet synchronous motor according to claim 1, characterized in that: The expression for limiting the motor torque current component iq in step S2 is as follows: iq = iq_old × k; k=1+(time-10)×0.01×(1+rate×0.5) In the formula, iq_old represents the motor torque current component when entering the inverse time mode; k represents the limiting ratio; time represents the maximum allowable running time; and rate is the temperature change rate.

5. The power inverse-time control method for a permanent magnet synchronous motor according to claim 4, characterized in that: Set a minimum threshold for the amplitude limiting ratio.

6. The power inverse-time control method for a permanent magnet synchronous motor according to claim 1, characterized in that: The permanent magnet synchronous motor operating data collected in step S1 is subjected to a first-order low-pass filter.

Images