A control method and device of a permanent magnet motor

Abstract

The application discloses a control method and device of a permanent magnet motor. The control method of the permanent magnet motor comprises the following steps: if it is detected that the speed instruction of the permanent magnet motor is positive and the actual speed of the permanent magnet motor is negative, determining the current feedback acceleration of the permanent magnet motor in each judgment period; if the current feedback acceleration of the permanent magnet motor is less than zero and the permanent magnet motor meets a first preset condition, determining that the permanent magnet motor is faulty; if it is detected that the directions of the speed instruction and the actual speed are the same and the actual speed is greater than the speed instruction, determining the current feedback acceleration of the permanent magnet motor in each judgment period; if the current feedback acceleration of the permanent magnet motor is greater than zero and the permanent magnet motor meets a second preset condition, determining that the permanent magnet motor is faulty; when the permanent magnet motor is faulty, issuing a prompt information, stopping outputting the voltage to the permanent magnet motor, and controlling the three-phase winding of the permanent magnet motor to be in a short-circuit state. The technical scheme of the application improves the accuracy of the control of the permanent magnet motor.

Description

Technical Field

[0001] This invention relates to the field of motor control technology, and in particular to a control method and device for a permanent magnet motor. Background Technology

[0002] Permanent magnet motors can operate without external excitation, achieving energy conversion through the synchronous action of the stator rotating magnetic field and the rotor magnetic field, and are therefore widely used.

[0003] Permanent magnet motors can be used in electric vehicles. An encoder can be installed on the permanent magnet motor to obtain its rotational speed. Permanent magnet motors can be three-phase motors, and the encoder requires corresponding three-phase cables, with each phase cable including both positive and negative wires.

[0004] However, during vehicle assembly or maintenance, there may be instances where the encoder's positive and negative cables are reversed, or the three-phase cables of the permanent magnet motor are incorrectly connected. This can cause the motor controller to obtain inaccurate readings of the motor's actual speed, leading to a loss of control of the permanent magnet motor and making it impossible to accurately control it. Summary of the Invention

[0005] This invention provides a control method and apparatus for a permanent magnet motor to improve the accuracy of permanent magnet motor control.

[0006] According to one aspect of the present invention, a control method for a permanent magnet motor is provided, the control method for the permanent magnet motor comprising: If the speed command of the permanent magnet motor is detected to be positive and the actual speed of the permanent magnet motor is negative, then the current feedback acceleration of the permanent magnet motor is determined in each judgment cycle. If the current feedback acceleration of the permanent magnet motor is less than zero, and the permanent magnet motor meets the first preset condition, then the permanent magnet motor is determined to be faulty. If the direction of the speed command and the actual speed are the same, and the actual speed is greater than the speed command, then in each judgment cycle, the current feedback acceleration of the permanent magnet motor is determined; If the current feedback acceleration of the permanent magnet motor is greater than zero, and the permanent magnet motor meets the second preset condition, then the permanent magnet motor is determined to be faulty. When the permanent magnet motor malfunctions, a warning message is issued, the output voltage to the permanent magnet motor is stopped, and the three-phase windings of the permanent magnet motor are controlled to be in a short-circuit state.

[0007] Optionally, when the speed command of the permanent magnet motor is detected to be positive and the actual speed of the permanent magnet motor is negative, the method further includes: The moment when the speed command of the permanent magnet motor is detected to be positive and the actual speed of the permanent magnet motor is negative is taken as the first starting moment, and the actual speed at the first starting moment is taken as the first starting speed. The permanent magnet motor satisfies a first preset condition, including at least one of the following: The duration during which the current feedback acceleration of the permanent magnet motor is less than zero is greater than a first time threshold. The absolute value of the current feedback acceleration is greater than the acceleration threshold of the permanent magnet motor; The absolute value of the difference between the current rotational speed of the permanent magnet motor and the first starting rotational speed in the current judgment period is greater than the duration of the maximum rotational speed of the permanent magnet motor being greater than the second time threshold.

[0008] Optionally, when it is detected that the direction of the rotational speed command and the actual rotational speed are the same, and the actual rotational speed is greater than the rotational speed command, the method further includes: The moment when the direction of the speed command and the actual speed are the same and the actual speed is greater than the speed command is taken as the second starting moment, and the actual speed at the second starting moment is taken as the second starting speed. The permanent magnet motor satisfies a second preset condition, including at least one of the following: The duration during which the current feedback acceleration of the permanent magnet motor is greater than zero is greater than the second time threshold. The absolute value of the current feedback acceleration is greater than the acceleration threshold of the permanent magnet motor; The absolute value of the difference between the current speed of the permanent magnet motor and the second starting speed in the current judgment period is greater than the duration of the maximum speed of the permanent magnet motor being greater than the second time threshold.

[0009] Optionally, determining the current feedback acceleration of the permanent magnet motor includes: The current feedback acceleration of the permanent magnet motor is obtained by subtracting the current speed of the permanent magnet motor in the current judgment cycle from the previous speed of the permanent magnet motor in the previous judgment cycle, and then dividing the result by the cycle length of the judgment cycle.

[0010] Optionally, before issuing a warning message and stopping the output voltage to the permanent magnet motor when the permanent magnet motor malfunctions, and before controlling the three-phase windings of the permanent magnet motor to be in a short-circuit state, the method further includes: When the duration during which the cross-axis target current and the cross-axis actual current of the permanent magnet motor are in opposite directions exceeds a third time threshold, the permanent magnet motor is determined to be faulty.

[0011] Optionally, before issuing a warning message and stopping the output voltage to the permanent magnet motor when the permanent magnet motor malfunctions, and before controlling the three-phase windings of the permanent magnet motor to be in a short-circuit state, the method further includes: When the absolute value of the actual rotational speed of the permanent magnet motor is greater than the sum of the maximum rotational speed and the maximum overspeed rotational speed of the permanent magnet motor for a duration greater than a fourth time threshold, the permanent magnet motor is determined to be faulty.

[0012] Optionally, before issuing a warning message and stopping the output voltage to the permanent magnet motor when the permanent magnet motor malfunctions, and before controlling the three-phase windings of the permanent magnet motor to be in a short-circuit state, the method further includes: When the absolute value of the speed command of the permanent magnet motor is greater than the minimum speed of the permanent magnet motor, and the absolute value of the actual speed of the permanent magnet motor is less than the minimum speed, and the duration of the speed loop output saturation of the permanent magnet motor is greater than the fifth time threshold, the permanent magnet motor is determined to be faulty.

[0013] Optionally, the speed loop output of the permanent magnet motor is saturated, including: The output value of the speed loop of the permanent magnet motor is equal to the maximum or minimum quadrature axis target current of the permanent magnet motor.

[0014] Optionally, stopping the output voltage to the permanent magnet motor and controlling the three-phase windings of the permanent magnet motor to be in a short-circuit state includes: The voltage conversion circuit of the permanent magnet motor controls the lower bridge arm of each phase to be turned on and the upper bridge arm of each phase to be turned off, so that the three-phase windings of the permanent magnet motor are in a short-circuit state.

[0015] According to another aspect of the present invention, a control device for a permanent magnet motor is provided, which is used to execute the control method for a permanent magnet motor according to any embodiment of the present invention; The control device for the permanent magnet motor includes: The first acceleration determination module is used to determine the current feedback acceleration of the permanent magnet motor in each judgment cycle if the speed command of the permanent magnet motor is detected to be positive and the actual speed of the permanent magnet motor is negative. The first judgment module is used to determine that the permanent magnet motor is faulty if the current feedback acceleration of the permanent magnet motor is less than zero and the permanent magnet motor meets the first preset condition. The second acceleration determination module is used to determine the current feedback acceleration of the permanent magnet motor in each judgment cycle if it is detected that the direction of the speed command and the actual speed are the same, and the actual speed is greater than the speed command. The second judgment module is used to determine that the permanent magnet motor is faulty if the current feedback acceleration of the permanent magnet motor is greater than zero and the permanent magnet motor meets the second preset condition. The motor control module is used to issue a prompt message and control the three-phase windings of the permanent magnet motor to be in a short-circuit state when the permanent magnet motor fails.

[0016] In the technical solution of this invention, if the speed command of the permanent magnet motor is detected to be positive, but the actual speed of the permanent magnet motor is negative, then in each judgment cycle, the current feedback acceleration of the permanent magnet motor is determined. If the current feedback acceleration of the permanent magnet motor is less than zero, the permanent magnet motor may be faulty. At this time, it is determined whether the permanent magnet motor meets a first preset condition. For example, when the speed command of the permanent magnet motor is positive and the actual speed of the permanent magnet motor is negative, it is determined whether the current feedback acceleration of the permanent magnet motor remains less than zero for a relatively long time. If the permanent magnet motor meets the first preset condition, then a fault is determined in the permanent magnet motor, thus avoiding misjudgment. If the speed command and the actual speed are detected to be in the same direction, and the actual speed is greater than the speed command, then in each judgment cycle, the current feedback acceleration of the permanent magnet motor is determined. If the current feedback acceleration of the permanent magnet motor is greater than zero, it indicates that the permanent magnet motor may be faulty. At this point, it is determined whether the permanent magnet motor meets the second preset condition. For example, when the direction of the speed command and the actual speed of the permanent magnet motor are the same, and the actual speed is greater than the speed command, it is determined whether the current feedback acceleration is maintained at a greater than zero for a relatively long time. If the permanent magnet motor meets the second preset condition, then a fault is determined to be in the permanent magnet motor, thus avoiding misjudgment. When a fault is determined to be in the permanent magnet motor, a fault warning message can be issued so that the user can be informed in a timely manner. By stopping the output voltage to the permanent magnet motor and controlling the three-phase windings of the permanent magnet motor to be in a short-circuit state, the motor current becomes the braking current, which creates a deceleration effect on the entire vehicle. That is, the braking current reduces the motor speed, and the absolute value of the braking current decreases, which in turn causes the motor speed to continue to decrease. In this way, the vehicle can be stopped. If the encoder of the permanent magnet motor is connected in reverse or the permanent magnet motor cable is connected incorrectly, it can be detected in time and the permanent magnet motor can be stopped, avoiding the control of the permanent magnet motor based on the incorrect detected speed, thus achieving the effect of accurate control of the permanent magnet motor.

[0017] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, 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 the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart of a control method for a permanent magnet motor provided in an embodiment of the present invention; Figure 2 This is a flowchart of another control method for a permanent magnet motor provided in an embodiment of the present invention; Figure 3 This is a flowchart of another control method for a permanent magnet motor provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of a control device for a permanent magnet motor provided in an embodiment of the present invention. Detailed Implementation

[0020] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. 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 should fall within the scope of protection of the present invention.

[0021] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0022] As mentioned in the background section, existing permanent magnet motors suffer from issues such as reversed positive and negative encoder cables or incorrect three-phase cables. This leads to inaccurate readings of the actual motor speed from the motor controller, resulting in motor malfunction and inability to accurately control the permanent magnet motor. The inventors have discovered that this problem arises because permanent magnet motors employ speed and current loops for control. The current loop can include a quadrature-axis current loop and a direct-axis current loop. All three loops can utilize a proportional-integral (PI) control strategy. The speed and current loops execute periodically. In each speed control cycle, a control signal is output to the control terminal of the power device in the voltage conversion circuit connected to the permanent magnet motor, controlling the power device's on / off state. This, in turn, controls the voltage output from the voltage conversion circuit to the permanent magnet motor, thereby controlling the motor's speed.

[0023] For example, in the j-th speed control cycle (where j is a positive integer), the difference Vref between the speed command Vref(j) of the permanent magnet motor and the actual speed Vfab of the permanent magnet motor is used. （j） -Vfab, and the speed proportionality coefficient K P1 Multiplying them together gives the velocity proportional term U of the velocity loop. P（j） For U P（j） = (Vref （j） -Vfab)×K P1 Then, the proportional term of the speed loop and the speed integral coefficient K are... i1 Multiply by the integral term U of the speed control cycle from the previous speed control cycle. i（j-1） The speed integral term U of the current speed control cycle is obtained. i（j） For U i（j） =U P（j） ×K i1 +U i（j-1） For example, when j is 1, U i（j-1） The value is 0. The sum of the speed integral term and the speed proportional term U in the current speed control cycle is... P（j） +U i（j） This is the output value Vout of the speed loop in the current speed control cycle, i.e., Vout = U. P（j） +U i（j） When the encoder is reversed, for example, when the speed command is positive, the detected actual speed is negative, while the true actual speed is positive and increasing. The difference between the speed command and the detected actual speed becomes larger and larger, causing the speed loop output value to increase, resulting in speed loss of control. Consequently, the operation of the permanent magnet motor cannot be accurately controlled.

[0024] This invention provides a control method for a permanent magnet motor, which can be executed by a control device for the permanent magnet motor. The permanent magnet motor can be used in vehicles, specifically electric vehicles. The vehicle also includes a motor controller, which incorporates the control device for the permanent magnet motor.

[0025] Figure 1 This is a flowchart of a control method for a permanent magnet motor provided in an embodiment of the present invention, see reference. Figure 1 The control methods for permanent magnet motors include: S110. If the speed command of the permanent magnet motor is detected to be positive, but the actual speed of the permanent magnet motor is negative, then in each judgment cycle, the current feedback acceleration of the permanent magnet motor is determined.

[0026] In controlling a permanent magnet motor, a speed loop and a current loop can be used. The current loop can include a quadrature-axis current loop and a direct-axis current loop. All three loops can employ a proportional-integral (PI) control strategy. When the vehicle is running, if the driver depresses the accelerator pedal, the target speed of the permanent magnet motor can be determined based on the pedal's travel. For example, when the accelerator pedal travel is zero, the target speed of the permanent magnet motor is zero. When the accelerator pedal travel is 100%, the target speed of the permanent magnet motor is its maximum speed. The maximum speed of the permanent magnet motor can be the maximum speed specified in the motor's user manual.

[0027] The speed loop and current loop execute periodically. In each speed control cycle, based on the speed command from the previous speed control cycle and the preset acceleration driving the speed command for the current speed control cycle, the speed command for the current speed control cycle and the current speed of the permanent magnet motor are input into the speed loop. The speed loop outputs the speed command as the target value. The output value of the speed loop is the quadrature-axis target current of the quadrature-axis current loop. The quadrature-axis target current and the actual quadrature-axis current are input into the quadrature-axis current loop. After coordinate transformation of the output values ​​of the quadrature-axis current loop and the direct-axis current loop, Space Vector Pulse Width Modulation (SVPWM) or Pulse Width Modulation (PWM) is performed to obtain a control signal. The control signal is output to the control terminal of the power device in the voltage conversion circuit connected to the permanent magnet motor, controlling the on and off of the power device, thereby controlling the voltage output from the voltage conversion circuit to the permanent magnet motor, and thus controlling the speed of the permanent magnet motor, so that the speed of the permanent magnet motor is close to or equal to the speed command of the current speed control cycle. By periodically executing the speed control cycle, the speed command gradually changes to the target speed, causing the permanent magnet motor to gradually reach the target speed. The voltage conversion circuit connected to the permanent magnet motor can be an inverter circuit, connected between the battery and the permanent magnet motor, converting the battery voltage into a three-phase voltage to power the permanent magnet motor. The direct-axis target current and the actual direct-axis current can be input to the direct-axis current loop, which outputs the target value. The direct-axis target current can be equal to the quadrature-axis target current.

[0028] Specifically, while executing the speed control cycle, the direction of the speed command and the direction of the actual speed of the permanent magnet motor can be judged in real time or periodically. If the speed command of the permanent magnet motor is detected to be positive and the actual speed of the permanent magnet motor is detected to be negative, then the judgment cycle is entered, that is, the judgment cycle is executed cyclically.

[0029] In each judgment cycle, the current feedback acceleration of the permanent magnet motor in the current judgment cycle is determined, which is the actual acceleration of the permanent magnet motor in the current judgment cycle.

[0030] S120. If the current feedback acceleration of the permanent magnet motor is less than zero and the permanent magnet motor meets the first preset condition, then the permanent magnet motor is determined to be faulty.

[0031] Specifically, when the speed command of the permanent magnet motor is positive and the actual speed of the permanent magnet motor is negative, the speed of the permanent magnet motor should gradually increase, and the current feedback acceleration should be greater than zero. If the current feedback acceleration of the permanent magnet motor is less than zero, the permanent magnet motor may be faulty. In this case, it is determined whether the permanent magnet motor meets a first preset condition. For example, when the speed command of the permanent magnet motor is positive and the actual speed of the permanent magnet motor is negative, it is determined whether the current feedback acceleration is less than zero for a relatively long time, and / or whether the absolute value of the current feedback acceleration is large, and / or whether the speed change is too large. If the permanent magnet motor meets the first preset condition, then a fault is determined in the permanent magnet motor, thus avoiding misjudgment.

[0032] Among them, when the speed command of the permanent magnet motor is positive and the actual speed of the permanent magnet motor is negative, the current feedback acceleration of the permanent magnet motor is less than zero. This may be due to the encoder being reversed, that is, the detected actual speed of the permanent magnet motor is reversed, or the three-phase windings of the permanent magnet motor being connected incorrectly. In this case, the permanent magnet motor is determined to have a positive feedback fault.

[0033] Because when using speed loop and current loop control, it normally operates on a negative feedback basis, with the actual speed of the permanent magnet motor getting closer and closer to the speed command. However, when the speed command for the permanent magnet motor is positive and the actual speed is negative, the actual speed becomes a large absolute negative value. The deviation between the speed command and the actual speed is significant, resulting in a larger output value from the speed loop. This increases the actual speed controlled by the permanent magnet motor, while the detected actual speed shows an even larger absolute amplitude, indicating a positive feedback fault in the permanent magnet motor.

[0034] S130. If the direction of the speed command and the actual speed are the same and the actual speed is greater than the speed command, then determine the current feedback acceleration of the permanent magnet motor in each judgment cycle.

[0035] Specifically, while executing the speed control cycle, the direction of the speed command and the direction of the actual speed of the permanent magnet motor can be judged in real time or periodically. If it is detected that the direction of the speed command and the actual speed of the permanent magnet motor are the same, and the actual speed is greater than the speed command, then the judgment cycle is entered, that is, the judgment cycle is executed cyclically. In each judgment cycle, the current feedback acceleration of the permanent magnet motor in the current judgment cycle is determined, which is the actual acceleration of the permanent magnet motor in the current judgment cycle.

[0036] S140. If the current feedback acceleration of the permanent magnet motor is greater than zero and the permanent magnet motor meets the second preset condition, then the permanent magnet motor is determined to be faulty.

[0037] Specifically, when the speed command and actual speed of the permanent magnet motor are in the same direction, if the actual speed is greater than the speed command, the actual speed should gradually decrease to approach the speed command, meaning the current feedback acceleration should be less than zero. If the current feedback acceleration of the permanent magnet motor is greater than zero, it indicates a possible fault in the permanent magnet motor. At this point, it is determined whether the permanent magnet motor meets a second preset condition. For example, when the speed command and actual speed of the permanent magnet motor are in the same direction, and the actual speed is greater than the speed command, it is determined whether the current feedback acceleration remains greater than zero for a relatively long time, and / or whether the absolute value of the current feedback acceleration is large, and / or whether the speed change is excessive. If the permanent magnet motor meets the second preset condition, a fault is confirmed, thus avoiding misdiagnosis.

[0038] S150: When the permanent magnet motor malfunctions, issue a warning message, stop outputting voltage to the permanent magnet motor, and control the three-phase windings of the permanent magnet motor to be in a short-circuit state.

[0039] Specifically, stopping the output voltage to the permanent magnet motor means controlling the voltage conversion circuit connected to the permanent magnet motor to stop outputting voltage to the permanent magnet motor.

[0040] Specifically, when a permanent magnet motor malfunction is detected, a fault warning message can be issued so that the user can be notified promptly. When a permanent magnet motor malfunctions, if the encoder cable is reversed or the permanent magnet motor cable is incorrectly connected, the vehicle cannot be stopped normally. Therefore, the output voltage to the permanent magnet motor is stopped. However, if only the output voltage to the permanent magnet motor is stopped, based on the characteristics of the permanent magnet motor, the motor speed is proportional to the back electromotive force (EMF). If the permanent magnet motor speed is high, the back EMF will be large. Since no voltage is output to the permanent magnet motor, that is, no control is made over the quadrature-axis current and direct-axis current, and no reverse excitation current is applied, the motor's back EMF will further increase. The back EMF of the permanent magnet motor may become too large, damaging the motor. By stopping the output voltage to the permanent magnet motor and controlling the three-phase windings of the permanent magnet motor to be in a short-circuit state, when the permanent magnet motor is equivalent to a DC motor, the voltage Uout output to the motor can be expressed as Uout = E + I × R, where E is the back electromotive force of the motor, E = N × Vspd, N is a constant, Vspd is the motor speed, I is the motor current, and R is the equivalent resistance of the motor. Therefore, when the voltage Uout output to the motor is 0, the motor current is negative. At this time, the motor current is the braking current, which creates a deceleration effect on the vehicle. That is, the braking current reduces the motor speed, and the absolute value of the braking current decreases, which in turn causes the motor speed to continue to decrease. This ensures that the vehicle stops.

[0041] In this way, if the encoder of the permanent magnet motor is connected in reverse or the cable of the permanent magnet motor is connected incorrectly, the permanent magnet motor can be detected in time and stopped. This avoids controlling the operation of the permanent magnet motor based on the incorrect detected speed, thus achieving the effect of accurately controlling the permanent magnet motor.

[0042] In this embodiment, if the speed command of the permanent magnet motor is detected to be positive, but the actual speed of the permanent magnet motor is negative, the current feedback acceleration of the permanent magnet motor is determined in each judgment cycle. If the current feedback acceleration of the permanent magnet motor is less than zero, the permanent magnet motor may be faulty. At this time, it is determined whether the permanent magnet motor meets a first preset condition. For example, when the speed command of the permanent magnet motor is positive and the actual speed of the permanent magnet motor is negative, it is determined whether the current feedback acceleration of the permanent magnet motor remains less than zero for a relatively long time. If the permanent magnet motor meets the first preset condition, it is determined that the permanent magnet motor is faulty, thus avoiding misjudgment. If the speed command and the actual speed are detected to be in the same direction, and the actual speed is greater than the speed command, the current feedback acceleration of the permanent magnet motor is determined in each judgment cycle. If the current feedback acceleration of the permanent magnet motor is greater than zero, it indicates that the permanent magnet motor may be faulty. At this point, it is determined whether the permanent magnet motor meets the second preset condition. For example, when the direction of the speed command and the actual speed of the permanent magnet motor are the same, and the actual speed is greater than the speed command, it is determined whether the current feedback acceleration is maintained at a greater than zero for a relatively long time. If the permanent magnet motor meets the second preset condition, then a fault is determined to be in the permanent magnet motor, thus avoiding misjudgment. When a fault is determined to be in the permanent magnet motor, a fault warning message can be issued so that the user can be informed in a timely manner. By stopping the output voltage to the permanent magnet motor and controlling the three-phase windings of the permanent magnet motor to be in a short-circuit state, the motor current becomes the braking current, which creates a deceleration effect on the entire vehicle. That is, the braking current reduces the motor speed, and the absolute value of the braking current decreases, which in turn causes the motor speed to continue to decrease. In this way, the vehicle can be stopped. If the encoder of the permanent magnet motor is connected in reverse or the permanent magnet motor cable is connected incorrectly, it can be detected in time and the permanent magnet motor can be stopped, avoiding the control of the permanent magnet motor based on the incorrect detected speed, thus achieving the effect of accurate control of the permanent magnet motor.

[0043] Based on the above technical solution, optionally, when the speed command of the permanent magnet motor is detected to be positive and the actual speed of the permanent magnet motor is negative, the control method of the permanent magnet motor further includes: The moment when the detected speed command of the permanent magnet motor is positive and the actual speed of the permanent magnet motor is negative is taken as the first starting moment, and the actual speed at the first starting moment is taken as the first starting speed. The permanent magnet motor meets a first preset condition, including at least one of the following: The duration during which the current feedback acceleration of the permanent magnet motor is less than zero exceeds the first time threshold; The absolute value of the current feedback acceleration is greater than the acceleration threshold of the permanent magnet motor; The duration during which the absolute value of the difference between the current speed of the permanent magnet motor and the first starting speed in the current judgment period is greater than the maximum speed of the permanent magnet motor is greater than the second time threshold.

[0044] Specifically, when the speed command of the permanent magnet motor is positive and the actual speed of the permanent magnet motor is negative, if the duration for which the current feedback acceleration of the permanent magnet motor is less than zero is greater than the first time threshold, it indicates that no matter how the speed of the permanent magnet motor is controlled to increase, the speed of the permanent magnet motor is still decreasing. This indicates that the encoder is reversed or the permanent magnet motor cable is connected incorrectly, thus indicating a fault in the permanent magnet motor. When the absolute value of the current feedback acceleration is greater than the acceleration threshold of the permanent magnet motor, it indicates that the speed change of the permanent magnet motor is too rapid in two adjacent judgment cycles, thus indicating a fault in the permanent magnet motor. When the absolute value of the difference between the current speed and the first starting speed of the permanent magnet motor in the current judgment cycle is greater than the maximum speed of the permanent magnet motor, it indicates that the difference between the current speed and the first starting speed is too large, that is, the speed change is too large, and the absolute value of the current speed or the absolute value of the first starting speed is too large, thus indicating a fault in the permanent magnet motor.

[0045] Optionally, when the direction of the speed command and the actual speed are the same, and the actual speed is greater than the speed command, the control method for the permanent magnet motor further includes: The moment when the direction of the speed command and the actual speed are the same and the actual speed is greater than the speed command is taken as the second starting moment, and the actual speed at the second starting moment is taken as the second starting speed. The permanent magnet motor meets a second preset condition, including at least one of the following: The duration during which the current feedback acceleration of the permanent magnet motor is greater than zero is greater than the second time threshold; The absolute value of the current feedback acceleration is greater than the acceleration threshold of the permanent magnet motor; The duration during which the absolute value of the difference between the current speed of the permanent magnet motor and the second starting speed in the current judgment cycle is greater than the maximum speed of the permanent magnet motor is greater than the second time threshold.

[0046] Specifically, when the direction of the speed command and the actual speed of the permanent magnet motor are the same, and the actual speed is greater than the speed command, if the duration for which the current feedback acceleration of the permanent magnet motor is greater than zero is greater than the second time threshold, it indicates that the speed of the permanent magnet motor is still increasing regardless of how the speed is adjusted. This indicates that the encoder is reversed or the permanent magnet motor cable is connected incorrectly, thus confirming a fault in the permanent magnet motor. When the absolute value of the current feedback acceleration is greater than the acceleration threshold of the permanent magnet motor, it indicates that the speed change of the permanent magnet motor is too rapid in two adjacent judgment cycles, thus indicating a fault in the permanent magnet motor. When the absolute value of the difference between the current speed and the second starting speed of the permanent magnet motor in the current judgment cycle is greater than the maximum speed of the permanent magnet motor, it indicates that the difference between the current speed and the second starting speed is too large, i.e., the speed change is too large, and the absolute value of the current speed or the absolute value of the second starting speed is too large, thus confirming a fault in the permanent magnet motor.

[0047] Based on the above technical solutions, optionally, the current feedback acceleration of the permanent magnet motor is determined, including: The current feedback acceleration of the permanent magnet motor is obtained by subtracting the current speed of the permanent magnet motor in the current judgment cycle from the previous speed in the previous judgment cycle, and then dividing by the cycle length of the judgment cycle.

[0048] The current speed of the permanent magnet motor in the current judgment period is the current actual speed of the permanent magnet motor in the current judgment period.

[0049] For example, if the current judgment period is the (k+1)th judgment period, and the current speed of the permanent magnet motor in the current judgment period is Vfab （k+1） The speed of the permanent magnet motor in the previous judgment cycle was Vfab. （k） Where k is a positive integer, and the duration of one cycle of the judgment period is T, then the current feedback acceleration Acc_cur of the permanent magnet motor is Acc_cur = (Vfab) / (Vfab) （k+1） -Vfab （k） For example, when the current judgment cycle is the first judgment cycle, the current feedback acceleration of the permanent magnet motor is 0.

[0050] Based on the above technical solutions, Figure 2 This is a flowchart of another control method for a permanent magnet motor provided in an embodiment of the present invention. Optionally, refer to... Figure 2 The control methods for permanent magnet motors include: S210. If the speed command of the permanent magnet motor is detected to be positive, but the actual speed of the permanent magnet motor is negative, then in each judgment cycle, the current feedback acceleration of the permanent magnet motor is determined.

[0051] S220. If the current feedback acceleration of the permanent magnet motor is less than zero and the permanent magnet motor meets the first preset condition, then the permanent magnet motor is determined to be faulty.

[0052] S230. If the direction of the speed command and the actual speed are the same and the actual speed is greater than the speed command, then determine the current feedback acceleration of the permanent magnet motor in each judgment cycle.

[0053] S240. If the current feedback acceleration of the permanent magnet motor is greater than zero and the permanent magnet motor meets the second preset condition, then the permanent magnet motor is determined to be faulty.

[0054] S250. When the duration during which the cross-axis target current and the cross-axis actual current of the permanent magnet motor are in opposite directions exceeds the third time threshold, a fault is determined in the permanent magnet motor.

[0055] For example, in the j-th speed control cycle, the quadrature-axis target current is I. ref（j） The actual current across the quadrature axis is I. fab The cross-axis scaling factor is K. P2 The integral coefficient of the cross axis is K.i2 Then the proportional term I of the intersection axis Pq（j） For I Pq（j） =(I ref（j） -I fab )×K P2 Cross-axis integral term I iq（j） For I iq（j） =I iq（j-1） +I Pq（j） ×K i2 The output value Iout of the quadrature axis current loop （j） For Iout （j） =I iq（j） +I Pq（j） If the permanent magnet motor's cable is incorrectly connected, the actual cross-axis current collected will be negative. This will cause the cross-axis proportional term to become increasingly larger, the cross-axis integral term to become increasingly larger, and the output value of the cross-axis current loop to become increasingly larger. This will result in excessive voltage output to the permanent magnet motor, which may damage the motor.

[0056] When the target current of the quadrature axis of the permanent magnet motor is maintained in the opposite direction to the actual current of the quadrature axis for a duration longer than the third time threshold, a fault is identified in the permanent magnet motor, namely a positive feedback fault. This allows for timely issuance of warning information and control of the permanent magnet motor to stop, thus achieving accurate control of the permanent magnet motor.

[0057] S260. When the permanent magnet motor malfunctions, issue a warning message, stop outputting voltage to the permanent magnet motor, and control the three-phase windings of the permanent magnet motor to be in a short-circuit state.

[0058] Based on the above technical solutions, optionally, when a permanent magnet motor malfunctions, a warning message is issued, and the output voltage to the permanent magnet motor is stopped. Before the three-phase windings of the permanent magnet motor are controlled to be in a short-circuit state, the control method for the permanent magnet motor also includes: A permanent magnet motor fault is determined when the absolute value of the actual speed of the permanent magnet motor is greater than the sum of the maximum speed and the maximum overspeed speed of the permanent magnet motor for a duration that exceeds the fourth time threshold.

[0059] Among them, the maximum overspeed is the maximum permissible overspeed of the permanent magnet motor. The maximum permissible overspeed can be the product of the maximum speed and a preset ratio. The preset ratio can be a value less than 10%, 1%, 2%, etc., and is not limited here.

[0060] Specifically, when the absolute value of the actual speed of the permanent magnet motor is greater than the sum of its maximum speed and maximum overspeed, it indicates that the motor speed is too high. This may be due to a reversed encoder cable connection, leading to inaccurate speed readings and causing the speed control cycle to repeat excessively, resulting in a potential motor malfunction. If the duration of this overspeed exceeding the sum of the maximum speed and maximum overspeed exceeds a fourth time threshold, a permanent magnet motor malfunction can be confirmed, thus avoiding misdiagnosis.

[0061] Based on the above technical solutions, Figure 3 This is a flowchart of another control method for a permanent magnet motor provided in an embodiment of the present invention. Optionally, refer to... Figure 3 The control methods for permanent magnet motors include: S310. If the speed command of the permanent magnet motor is detected to be positive, but the actual speed of the permanent magnet motor is negative, then in each judgment cycle, the current feedback acceleration of the permanent magnet motor is determined.

[0062] S320. If the current feedback acceleration of the permanent magnet motor is less than zero and the permanent magnet motor meets the first preset condition, then the permanent magnet motor is determined to be faulty.

[0063] S330. If the direction of the speed command and the actual speed are the same and the actual speed is greater than the speed command, then determine the current feedback acceleration of the permanent magnet motor in each judgment cycle.

[0064] S340. If the current feedback acceleration of the permanent magnet motor is greater than zero and the permanent magnet motor meets the second preset condition, then the permanent magnet motor is determined to be faulty.

[0065] S350. When the duration during which the cross-axis target current and the cross-axis actual current of the permanent magnet motor are in opposite directions exceeds the third time threshold, a fault is determined in the permanent magnet motor.

[0066] S360. When the absolute value of the speed command of the permanent magnet motor is greater than the minimum speed of the permanent magnet motor, and the absolute value of the actual speed of the permanent magnet motor is less than the minimum speed, and the duration of the speed loop output saturation of the permanent magnet motor is greater than the fifth time threshold, a permanent magnet motor fault is determined.

[0067] The minimum speed of a permanent magnet motor can be obtained from its user manual. The minimum speed of a permanent magnet motor is a positive value.

[0068] Specifically, when the absolute value of the speed command of the permanent magnet motor is greater than the minimum speed of the permanent magnet motor, the speed loop and current loop will control the speed of the permanent magnet motor to increase. Since the absolute value of the actual speed of the permanent magnet motor is small (less than the minimum speed), in order to make the speed of the permanent magnet motor reach the speed command, the speed loop output of the permanent magnet motor is saturated. However, if the duration of the speed loop output saturation is longer than the fifth time threshold, there is still a situation where the absolute value of the speed command of the permanent magnet motor is greater than the minimum speed of the permanent magnet motor, and the absolute value of the actual speed of the permanent magnet motor is less than the minimum speed, and the speed loop output of the permanent magnet motor is saturated. That is, if the permanent magnet motor maintains a state where the absolute value of the speed command of the permanent magnet motor is greater than the minimum speed of the permanent magnet motor, and the absolute value of the actual speed of the permanent magnet motor is less than the minimum speed, and the speed loop output of the permanent magnet motor is saturated for a long time, it indicates that the permanent magnet motor has a fault.

[0069] When the encoder cable is reversed, the actual output speed is negative, while the actual speed is positive. This means that the speed of the permanent magnet motor has increased but the increase is not detected, which will cause the speed loop to be continuously saturated. This indicates that the permanent magnet motor has a positive feedback fault.

[0070] S370: When the permanent magnet motor malfunctions, a warning message is issued, the output voltage to the permanent magnet motor is stopped, and the three-phase windings of the permanent magnet motor are controlled to be in a short-circuit state.

[0071] Based on the above technical solution, optionally, the speed loop output of the permanent magnet motor is saturated, including: The output value of the speed loop of the permanent magnet motor is equal to the maximum or minimum quadrature axis target current of the permanent magnet motor.

[0072] The maximum cross-axis target current is the maximum output value of the speed loop, and the minimum cross-axis target current is the minimum output value of the speed loop. The maximum output value of the speed loop is positive, and the minimum output value of the speed loop is negative. The absolute value of the maximum output value of the speed loop is equal to the absolute value of the minimum output value of the speed loop.

[0073] Specifically, the control device of the permanent magnet motor controls the speed loop to output based on the maximum and minimum quadrature axis target currents. That is, when the speed loop's output value is greater than or equal to the maximum quadrature axis target current, the speed loop's output value is the maximum quadrature axis target current; when the speed loop's output value is less than or equal to the minimum quadrature axis target current, the speed loop's output is the minimum quadrature axis target current. Therefore, if the speed loop outputs between the minimum and maximum quadrature axis target currents, and the speed loop's output value equals either the maximum or minimum quadrature axis target current of the permanent magnet motor, it indicates that the permanent magnet motor's speed loop output is saturated.

[0074] Based on the above technical solutions, optionally, the output voltage to the permanent magnet motor is stopped, and the three-phase windings of the permanent magnet motor are controlled to be in a short-circuit state, including: The voltage conversion circuit of the permanent magnet motor controls the lower bridge arm of each phase to be turned on and the upper bridge arm of each phase to be turned off, so that the three-phase windings of the permanent magnet motor are in a short-circuit state.

[0075] The permanent magnet motor is a three-phase motor. The voltage conversion circuit can be an inverter circuit, comprising a three-phase line. Each phase includes an upper bridge arm and a lower bridge arm, which are connected in series between the positive and negative busbars. The positive busbar is connected to the positive terminal of the battery, and the negative busbar is connected to the negative terminal of the battery. The connection node between the upper and lower bridge arms is connected to the windings of the permanent magnet motor. The control terminals of both the upper and lower bridge arms are connected to the control device of the permanent magnet motor. The upper bridge arm may include power devices, and both the upper and lower bridge arms may include power devices.

[0076] Specifically, by controlling the lower bridge arm of each phase of the voltage conversion circuit of the permanent magnet motor to be turned on and the upper bridge arm of each phase to be turned off, the three-phase windings of the permanent magnet motor are connected to the negative bus through the corresponding lower bridge arm, so that the three-phase windings of the permanent magnet motor are in a short-circuit state. The permanent magnet motor can convert the braking current into heat, and the absolute value of the braking current gradually decreases, so that the speed of the permanent magnet motor gradually decreases, thereby stabilizing the shutdown.

[0077] This invention also provides a control device for a permanent magnet motor, which is used to execute the control method for a permanent magnet motor provided in any embodiment of this invention. Figure 4 This is a schematic diagram of the structure of a control device for a permanent magnet motor provided in an embodiment of the present invention. (Refer to...) Figure 4 The control device for the permanent magnet motor includes a first acceleration determination module 101, a first judgment module 102, a second acceleration determination module 103, a second judgment module 104, and a motor control module 105; The first acceleration determination module 101 is used to determine the current feedback acceleration of the permanent magnet motor in each judgment cycle if the detected speed command of the permanent magnet motor is positive and the actual speed of the permanent magnet motor is negative. The first judgment module 102 is used to determine that the permanent magnet motor is faulty if the current feedback acceleration of the permanent magnet motor is less than zero and the permanent magnet motor meets the first preset condition. The second acceleration determination module 103 is used to determine the current feedback acceleration of the permanent magnet motor in each judgment cycle if it is detected that the direction of the rotation speed command and the actual rotation speed are the same, and the actual rotation speed is greater than the rotation speed command. The second judgment module 104 is used to determine that the permanent magnet motor is faulty if the current feedback acceleration of the permanent magnet motor is greater than zero and the permanent magnet motor meets the second preset condition. The motor control module 105 is used to issue a prompt message and control the three-phase windings of the permanent magnet motor to be in a short-circuit state when the permanent magnet motor fails.

[0078] The control device for the permanent magnet motor provided in the embodiments of the present invention can execute the control method for the permanent magnet motor provided in any embodiment of the present invention, and has the corresponding functional modules and beneficial effects of the method.

[0079] It should be understood that the various forms of processes shown above can be used, with steps reordered, added, or deleted. For example, the steps described in this invention can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution of this invention can be achieved, and this is not limited herein.

[0080] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A control method for a permanent magnet motor, characterized in that, include: If the speed command of the permanent magnet motor is detected to be positive and the actual speed of the permanent magnet motor is negative, then the current feedback acceleration of the permanent magnet motor is determined in each judgment cycle. If the current feedback acceleration of the permanent magnet motor is less than zero, and the permanent magnet motor meets the first preset condition, then the permanent magnet motor is determined to be faulty. If the direction of the speed command and the actual speed are the same, and the actual speed is greater than the speed command, then in each judgment cycle, the current feedback acceleration of the permanent magnet motor is determined; If the current feedback acceleration of the permanent magnet motor is greater than zero, and the permanent magnet motor meets the second preset condition, then the permanent magnet motor is determined to be faulty. When the permanent magnet motor malfunctions, a warning message is issued, the output voltage to the permanent magnet motor is stopped, and the three-phase windings of the permanent magnet motor are controlled to be in a short-circuit state.

2. The method according to claim 1, characterized in that, When the speed command of the permanent magnet motor is detected to be positive, and the actual speed of the permanent magnet motor is negative, the method further includes: The moment when the speed command of the permanent magnet motor is detected to be positive and the actual speed of the permanent magnet motor is negative is taken as the first starting moment, and the actual speed at the first starting moment is taken as the first starting speed. The permanent magnet motor satisfies a first preset condition, including at least one of the following: The duration during which the current feedback acceleration of the permanent magnet motor is less than zero is greater than a first time threshold. The absolute value of the current feedback acceleration is greater than the acceleration threshold of the permanent magnet motor; The absolute value of the difference between the current rotational speed of the permanent magnet motor and the first starting rotational speed in the current judgment period is greater than the duration of the maximum rotational speed of the permanent magnet motor being greater than the second time threshold.

3. The method according to claim 1, characterized in that, When it is detected that the direction of the speed command and the actual speed are the same, and the actual speed is greater than the speed command, the method further includes: The moment when the direction of the speed command and the actual speed are the same and the actual speed is greater than the speed command is taken as the second starting moment, and the actual speed at the second starting moment is taken as the second starting speed. The permanent magnet motor satisfies a second preset condition, including at least one of the following: The duration during which the current feedback acceleration of the permanent magnet motor is greater than zero is greater than the second time threshold. The absolute value of the current feedback acceleration is greater than the acceleration threshold of the permanent magnet motor; The absolute value of the difference between the current speed of the permanent magnet motor and the second starting speed in the current judgment period is greater than the duration of the maximum speed of the permanent magnet motor being greater than the second time threshold.

4. The method according to claim 1, characterized in that, Determining the current feedback acceleration of the permanent magnet motor includes: The current feedback acceleration of the permanent magnet motor is obtained by subtracting the current speed of the permanent magnet motor in the current judgment cycle from the previous speed of the permanent magnet motor in the previous judgment cycle, and then dividing the result by the cycle length of the judgment cycle.

5. The method according to claim 1, characterized in that, Before issuing a warning message and stopping the output voltage to the permanent magnet motor when a fault occurs, and before controlling the three-phase windings of the permanent magnet motor to be in a short-circuit state, the method further includes: When the duration during which the cross-axis target current and the cross-axis actual current of the permanent magnet motor are in opposite directions exceeds a third time threshold, the permanent magnet motor is determined to be faulty.

6. The method according to claim 1, characterized in that, Before issuing a warning message and stopping the output voltage to the permanent magnet motor when a fault occurs, and before controlling the three-phase windings of the permanent magnet motor to be in a short-circuit state, the method further includes: When the absolute value of the actual rotational speed of the permanent magnet motor is greater than the sum of the maximum rotational speed and the maximum overspeed rotational speed of the permanent magnet motor for a duration greater than a fourth time threshold, the permanent magnet motor is determined to be faulty.

7. The method according to claim 1, characterized in that, Before issuing a warning message and stopping the output voltage to the permanent magnet motor when a fault occurs, and before controlling the three-phase windings of the permanent magnet motor to be in a short-circuit state, the method further includes: When the absolute value of the speed command of the permanent magnet motor is greater than the minimum speed of the permanent magnet motor, and the absolute value of the actual speed of the permanent magnet motor is less than the minimum speed, and the duration of the speed loop output saturation of the permanent magnet motor is greater than the fifth time threshold, the permanent magnet motor is determined to be faulty.

8. The method according to claim 7, characterized in that, The speed loop output saturation of the permanent magnet motor includes: The output value of the speed loop of the permanent magnet motor is equal to the maximum or minimum quadrature axis target current of the permanent magnet motor.

9. The method according to claim 1, characterized in that, Stopping the output voltage to the permanent magnet motor and controlling the three-phase windings of the permanent magnet motor to be in a short-circuit state includes: The voltage conversion circuit of the permanent magnet motor controls the lower bridge arm of each phase to be turned on and the upper bridge arm of each phase to be turned off, so that the three-phase windings of the permanent magnet motor are in a short-circuit state.

10. A control device for a permanent magnet motor, characterized in that, The control device for the permanent magnet motor is used to execute the control method for the permanent magnet motor according to any one of claims 1-9; The control device for the permanent magnet motor includes: The first acceleration determination module is used to determine the current feedback acceleration of the permanent magnet motor in each judgment cycle if the speed command of the permanent magnet motor is detected to be positive and the actual speed of the permanent magnet motor is negative. The first judgment module is used to determine that the permanent magnet motor is faulty if the current feedback acceleration of the permanent magnet motor is less than zero and the permanent magnet motor meets the first preset condition. The second acceleration determination module is used to determine the current feedback acceleration of the permanent magnet motor in each judgment cycle if it is detected that the direction of the speed command and the actual speed are the same, and the actual speed is greater than the speed command. The second judgment module is used to determine that the permanent magnet motor is faulty if the current feedback acceleration of the permanent magnet motor is greater than zero and the permanent magnet motor meets the second preset condition. The motor control module is used to issue a prompt message and control the three-phase windings of the permanent magnet motor to be in a short-circuit state when the permanent magnet motor fails.

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