A method for controlling current in the field weakening region of a permanent magnet synchronous motor

Abstract

A method for controlling the current in the weakening magnetic region of a permanent magnet synchronous motor belongs to the technical field of weakening magnetic control of permanent magnet synchronous motors. The present invention solves the problem that the existing method has poor current following performance under multiple dynamic processes and cannot reduce the generation of saturation voltage. The present invention uses the speed outer loop PI controller to output a torque current reference value and limits it to obtain a torque current reference value after limiting; then uses the weakening magnetic compensation component calculated based on the torque current reference value after limiting to compensate the excitation current reference value output by the voltage loop PI controller to reduce the weakening magnetic control delay and improve the current dynamic response and current following capability; and uses the compensated excitation current reference value to limit the torque current reference value output by the speed outer loop PI controller; calculates the stator voltage feedback based on the torque current reference value after limiting and the excitation current reference value after compensation, which can reduce voltage fluctuations and reduce the generation of saturation voltage. The method of the present invention can be applied to the weakening magnetic control of permanent magnet synchronous motors.

Description

Technical Field

[0001] The present invention belongs to the technical field of permanent magnet synchronous motor field weakening control, and in particular relates to a method for controlling current in a field weakening region of a permanent magnet synchronous motor. Background Art

[0002] Permanent magnet synchronous motor (PMSM) is a type of motor widely used in industry. In some special occasions, a wide speed range is required. When the speed is higher than the rated speed, field weakening control is required. In the field weakening area, the stator voltage can be increased to increase the torque output, so that the motor can run stably in a wide speed range. This control method is called voltage closed-loop control. The control process is as follows: Figure 1 However, traditional voltage closed-loop control cannot achieve coupling control between the d-axis and q-axis currents, resulting in problems such as poor dynamic performance.

[0003] To optimize the current dynamics, some researchers have proposed several solutions, but most of these solutions are unable to achieve optimal control of multiple dynamic processes. For example, the paper "Analytical Design and Autotuning of Adaptive Flux-Weakening Voltage Regulation Loop in IPMSM Drives With Accurate Torque Regulation" analyzes, designs, and autotunes an adaptive flux-weakening voltage regulation loop for a permanent magnet synchronous motor based on precise torque regulation. However, current limiting is required to achieve control under maximum torque conditions. To address this issue, the paper "Analysis and Applicability Comparison of Single Current Regulator Methods of PMSM Under Square-Wave Mode" adjusts the maximum torque trajectory to achieve a smooth transition from the base speed region to the flux-weakening region. However, the optimized control scheme can only be implemented in specific dynamic processes and is not universal. To enhance the versatility of the method, the paper "Virtual Current Constraint Based Segmented Trajectory Control Strategy for Flux-Weakening Operation of SPMSM Drives" designs adaptive controller parameters for fast coupling control in the flux-weakening region. Since the control structure remains unchanged, dynamic performance can be further improved. The paper "Online Adaptive Current Vector Adjustment for Deep Flux-Weakening Control of IPMSM" designs a d-axis current priority structure by limiting the q-axis voltage to achieve faster anti-winding control, but this method cannot reduce the generation of saturation voltage.

[0004] In summary, the current following performance of the existing methods under multiple dynamic processes is still poor, and it is unable to reduce the generation of saturation voltage. Therefore, it is very necessary to propose a control method that can optimize the current dynamic performance and reduce the generation of voltage saturation under multiple dynamic processes. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems that the existing methods have poor current following performance under multiple dynamic processes and cannot reduce the generation of saturation voltage, and to propose a current control method for the weakening field of a permanent magnet synchronous motor.

[0006] The technical solution adopted by the present invention to solve the above technical problems is:

[0007] A method for controlling current in a field-weakening region of a permanent magnet synchronous motor, the method specifically comprising the following steps:

[0008] Step 1: Use the PI controller of the speed outer loop to output the torque current reference value i' sq,ref , and then the torque current reference value i′ sq,ref Perform amplitude limiting to obtain the torque current reference value i″ after amplitude limiting sq,ref ;

[0009] According to the torque current reference value i" after limiting sq,ref Calculate the weak magnetic compensation component i sd,补偿 , using the weak magnetic compensation component i sd,补偿 The excitation current reference value i′ output by the voltage loop PI controller sd,ref Compensation is performed to obtain the excitation current reference value i after compensation sd,ref ;

[0010] Step 2: Use the compensated excitation current reference value i sd,ref The torque current reference value i' output by the speed outer loop PI controller sq,ref Perform amplitude limiting to obtain the torque current reference value i after amplitude limiting sq,ref ;

[0011] Step 3: Use the actual current of the q-axis and d-axis as feedback values, and based on the torque current reference value i after limiting sq,ref and the compensated excitation current reference value i sd,ref , the PI controller of the current loop outputs the q-axis stator voltage value u sq and d-axis stator voltage u sd ;

[0012] Step 4: Set the stator voltage As the input of the voltage loop PI controller, the new excitation current reference value i' is output through the voltage loop PI controller sd,ref ;

[0013] The new excitation current reference value i′ for the output sd,ref Return to step 1.

[0014] Furthermore, the torque current reference value output by the PI controller of the speed outer loop is:

[0015]

[0016] Among them, k p is the proportional gain of the PI controller of the speed outer loop, k i is the integral gain of the PI controller of the speed outer loop, s is the complex vector in the Laplace transform, ω eis the motor angular velocity, ω e,ref is the motor reference angular velocity, i′ sq,ref It is the torque current reference value output by the PI controller of the speed outer loop.

[0017] Furthermore, the torque current reference value i′ sq,ref Perform amplitude limiting to obtain the torque current reference value i″ after amplitude limiting sq,ref Specifically:

[0018] Step 1: The maximum current constraint equation of the permanent magnet synchronous motor is:

[0019]

[0020] Among them, i smax is the maximum current, i sq is the actual current value of the q axis, i sd is the actual current value of the d-axis;

[0021] Substitute formula (2) into have to

[0022]

[0023] Among them, ω e is the motor angular velocity, L q is the q-axis inductance, L d is the d-axis inductance, ψ f is the permanent magnet flux, u smax is the maximum voltage;

[0024] Then the limit value i sqmax1 for:

[0025]

[0026] Step 2: Compare the limit value i sqmax1 with i′ sq,ref size;

[0027] If i′ sq,ref Less than or equal to i sqmax1 , then i″ sq,ref Equal to i′ sq,ref ;

[0028] If i′ sq,ref Greater than i sqmax1 , then i″ sq,ref Equal to i sqmax1 .

[0029] Furthermore, the weak magnetic compensation component i sd,补偿 The calculation process is:

[0030] In the two-phase rotating coordinate system, the maximum voltage constraint equation of the permanent magnet synchronous motor is:

[0031]

[0032] Among them, u smax is the maximum voltage;

[0033] The voltage balance equation of the motor is:

[0034]

[0035] Among them, R s is the motor resistance;

[0036] Ignoring the voltage drop caused by the resistor, equation (6) is simplified to:

[0037]

[0038] Substituting formula (7) into formula (5) yields:

[0039]

[0040] Then the weakening magnetic compensation component is:

[0041]

[0042] Furthermore, the use of the weak magnetic compensation component i sd,补偿 The excitation current reference value i′ output by the voltage loop PI controller sd,ref Compensation is performed to obtain the excitation current reference value i after compensation sd,ref Specifically:

[0043] i sd,ref =i′ sq,ref +i sd,补偿 (10)

[0044] Among them, i sd,ref It is the reference value of the excitation current after compensation.

[0045] Furthermore, the compensation-compensated excitation current reference value i sd,ref The torque current reference value i' output by the speed outer loop PI controller sq,ref Perform amplitude limiting to obtain the torque current reference value i after amplitude limiting sq,ref Specifically:

[0046] Calculate the limit value i sq,max2 :

[0047]

[0048] Among them, i smax is the maximum current, isd,ref is the reference value of the excitation current after compensation;

[0049] If the torque current reference value output by the PI controller of the speed outer loop is less than or equal to the limit value i sq,max2 , the torque current reference value output by the PI controller of the speed outer loop is used as the torque current reference value after limiting i sq,ref ;

[0050] If the torque current reference value output by the PI controller of the speed outer loop is greater than the limit value i sq,max2 , then the limit value i sq,max2 As the torque current reference value after limiting i sq,ref .

[0051] Furthermore, the actual current of the q-axis and d-axis is used as the feedback value, and the torque current reference value i after the limit is obtained. sq,ref and the compensated excitation current reference value i sd,ref , the PI controller of the current loop outputs the q-axis stator voltage value u sq and d-axis stator voltage u sd Specifically:

[0052]

[0053] Among them, k′ p is the proportional gain of the PI controller of the d-axis current loop, k′ i is the integral gain of the PI controller of the d-axis current loop, k″ p k″ is the proportional gain of the PI controller of the q-axis current loop i is the integral gain of the PI controller of the q-axis current loop.

[0054] The beneficial effects of the present invention are:

[0055] The present invention incorporates a field-weakening compensation component. Therefore, when the torque current reference value changes, the excitation current reference value changes immediately. This reduces field-weakening control delay and improves the current dynamic response and current tracking capabilities during acceleration, deceleration, and loading and unloading. Furthermore, compared with traditional control methods, the present invention reduces voltage fluctuations during dynamic processes, minimizes voltage overshoot during sudden acceleration and loading, and reduces the generation of saturation voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is the block diagram of the traditional voltage closed-loop control of permanent magnet synchronous motor;

[0057] During the system's dynamic changes in the field weakening region, the torque current changes first. Only after passing through the q-axis current controller, voltage controller, and d-axis current controller can the excitation current change. The series structure of these three controllers causes control delays, which deteriorates the system's dynamic performance.

[0058] Figure 2 This is a structural block diagram of the current dynamic performance optimization control of the permanent magnet synchronous motor in the field weakening region of the present invention;

[0059] Since the field weakening compensation component is added, the excitation current reference value will change immediately when the torque current reference value changes;

[0060] Figure 3 This is a curve showing the changes in voltage and current when the motor is accelerated from 1080r / min to 1680r / min using the traditional voltage closed-loop control method under no-load conditions.

[0061] Figure 4 This is a curve diagram showing the changes in voltage and current when the motor is accelerated from 1080r / min to 1680r / min using the control method of the present invention under no-load conditions;

[0062] Figure 5 This is a graph showing the voltage and current changes of the traditional voltage closed-loop control method when 30% of the rated load is suddenly applied during steady-state operation at 1440 r / min.

[0063] Figure 6 The graph is a curve showing the changes in voltage and current of the control method of the present invention when 30% of the rated load is suddenly applied under the condition of 1440 r / min steady-state operation. DETAILED DESCRIPTION

[0064] Specific implementation method 1: Combination Figure 2 This embodiment describes a method for controlling the current in the field weakening region of a permanent magnet synchronous motor. The field weakening region refers to a motor speed greater than the rated speed. The method specifically includes the following steps:

[0065] Step 1: Use the PI controller of the speed outer loop to output the torque current reference value i' sq,ref , and then the torque current reference value i′ sq,ref Perform amplitude limiting to obtain the torque current reference value i″ after amplitude limiting sq,ref ;

[0066] According to the torque current reference value i" after limiting sq,ref Calculate the weak magnetic compensation component i sd,补偿 , using the weak magnetic compensation component i sd,补偿 The excitation current reference value i′ output by the voltage loop PI controller sd,refCompensation is performed to obtain the excitation current reference value i after compensation sd,ref ;

[0067] Step 2: Use the compensated excitation current reference value i sd,ref The torque current reference value i' output by the speed outer loop PI controller sq,ref Perform amplitude limiting to obtain the torque current reference value i after amplitude limiting sq,ref ;

[0068] Step 3: Use the actual current of the q-axis and d-axis as feedback values, and based on the torque current reference value i after limiting sq,ref and the compensated excitation current reference value i sd,ref , the PI controller of the current loop outputs the q-axis stator voltage value u sq and d-axis stator voltage u sd ;

[0069] Step 4: Set the stator voltage As the input of the voltage loop PI controller (i.e. voltage feedback), the new excitation current reference value i' is output through the voltage loop PI controller sd,ref ;

[0070] The new excitation current reference value i′ for the output sd,ref Return to step 1 (i.e. calculate the compensation value based on the torque current reference value output by the PI controller of the speed outer loop at the next moment, and directly use the compensation value to adjust the new excitation current reference value i' sd,ref Compensation is performed to improve the following performance of the excitation current reference value).

[0071] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the torque current reference value output by the PI controller of the speed outer loop is:

[0072]

[0073] Among them, k p is the proportional gain of the PI controller of the speed outer loop, k i is the integral gain of the PI controller of the speed outer loop, s is the complex vector in the Laplace transform, ω e is the motor angular velocity, ω e,ref is the motor reference angular velocity, i′ sq,ref It is the torque current reference value output by the PI controller of the speed outer loop.

[0074] Other steps and parameters are the same as those in the first embodiment.

[0075] Specific embodiment 3: This embodiment is different from specific embodiment 1 or 2 in that the torque current reference value i′ sq,refPerform amplitude limiting to obtain the torque current reference value i″ after amplitude limiting sq,ref Specifically:

[0076] Step 1: The maximum current constraint equation of the permanent magnet synchronous motor is:

[0077]

[0078] Among them, i smax is the maximum current, i sq is the actual current value of the q axis, i sd is the actual current value of the d-axis;

[0079] Substitute formula (2) into have to

[0080]

[0081] Among them, ω e is the motor angular velocity, L q is the q-axis inductance, L d is the d-axis inductance, ψ f is the permanent magnet flux, u smax is the maximum voltage;

[0082] Then the limit value i sqmax1 for:

[0083]

[0084] Step 2: Compare the limit value i sqmax1 with i′ sq,ref size;

[0085] If i′ sq,ref Less than or equal to i sqmax1 , then i″ sq,ref Equal to i′ sq,ref ;

[0086] If i′ sq,ref Greater than i sqmax1 , then i″ sq,ref Equal to i sqmax1 .

[0087] Other steps and parameters are the same as those in the first or second embodiment.

[0088] Specific embodiment 4: This embodiment is different from any one of the specific embodiments 1 to 3 in that the weak magnetic compensation component i sd,补偿 The calculation process is:

[0089] In the two-phase rotating coordinate system, the maximum voltage constraint equation of the permanent magnet synchronous motor is:

[0090]

[0091] Among them, u smax is the maximum voltage;

[0092] When the motor is in steady-state operation, the voltage balance equation of the motor is:

[0093]

[0094] Among them, R s is the motor resistance;

[0095] In the high-speed operation stage, the voltage drop caused by the resistor is ignored and equation (6) is simplified to:

[0096]

[0097] Substituting formula (7) into formula (5) yields:

[0098]

[0099] Then the weakening magnetic compensation component is:

[0100]

[0101] The other steps and parameters are the same as those in the first to third embodiments.

[0102] Specific embodiment 5: This embodiment differs from the specific embodiments 1 to 4 in that the weak magnetic compensation component i is used. sd,补偿 The excitation current reference value i′ output by the voltage loop PI controller sd,ref Compensation is performed to obtain the excitation current reference value i after compensation sd,ref Specifically:

[0103] i sd,ref =i′ sq,ref +i sd,补偿 (10)

[0104] Among them, i sd,ref It is the reference value of the excitation current after compensation.

[0105] The other steps and parameters are the same as those in the first to fourth embodiments.

[0106] The present invention adds a weak magnetic compensation component, so when the torque current reference value changes, the excitation current reference value will change immediately, reducing the delay of weak magnetic control and improving the current following capability.

[0107] Specific embodiment 6: This embodiment is different from any one of the specific embodiments 1 to 5 in that the compensation of the excitation current reference value i is used. sd,refThe torque current reference value i' output by the speed outer loop PI controller sq,ref Perform amplitude limiting to obtain the torque current reference value i after amplitude limiting sq,ref Specifically:

[0108] Calculate the limit value i sq,max2 :

[0109]

[0110] Among them, i smax is the maximum current, i sd,ref is the reference value of the excitation current after compensation;

[0111] If the torque current reference value output by the PI controller of the speed outer loop is less than or equal to the limit value i sq,max2 , the torque current reference value output by the PI controller of the speed outer loop is used as the torque current reference value after limiting i sq,ref ;

[0112] If the torque current reference value output by the PI controller of the speed outer loop is greater than the limit value i sq,max2 , then the limit value i sq,max2 As the torque current reference value after limiting i sq,ref .

[0113] The other steps and parameters are the same as those in the first to fifth embodiments.

[0114] Specific embodiment seven: This embodiment differs from any one of specific embodiments one to six in that the actual currents of the q-axis and d-axis are used as feedback values, and based on the torque current reference value i after limiting sq,ref and the compensated excitation current reference value i sd,ref , the PI controller of the current loop outputs the q-axis stator voltage value u sq and d-axis stator voltage u sd Specifically:

[0115]

[0116] Among them, k′ p is the proportional gain of the PI controller of the d-axis current loop, k′ i is the integral gain of the PI controller of the d-axis current loop, k″ p k″ is the proportional gain of the PI controller of the q-axis current loop i is the integral gain of the PI controller of the q-axis current loop.

[0117] The other steps and parameters are the same as those in the first to sixth embodiments.

[0118] The effectiveness of the control method of the present invention can be seen by comparing Figure 3 、 Figure 4 as well as Figure 5 、 Figure 6 The experimental results shown are obtained. Figure 3 and Figure 4 In the figure, the waveforms from top to bottom are the torque current reference value and feedback value, the excitation current reference value and feedback value, and the feedback voltage. Figure 3 and Figure 4 It can be found that when the system speed changes in the weak magnetic area, the control method of the present invention weakens the magnetic field more timely, the current dynamics and current followability are significantly improved, the feedback voltage overshoot is small, and the voltage desaturation time is shortened. Figure 5 and Figure 6 It can be seen that when a load is suddenly applied, the control method of the present invention reduces current fluctuations and greatly improves current tracking performance. The feedback voltage fluctuation is reduced, and the voltage recovery is faster.

[0119] The above examples are merely illustrative of the calculation model and process of the present invention and are not intended to limit the embodiments of the present invention. Persons skilled in the art will readily appreciate that other variations or modifications based on the above description are possible. This list of embodiments is not exhaustive; however, any obvious variations or modifications derived from the technical solution of the present invention remain within the scope of protection of the present invention.

Claims

1. A method for controlling current in a field-weakening region of a permanent magnet synchronous motor, characterized in that: The method specifically comprises the following steps: Step 1: Use the PI controller of the speed outer loop to output the torque current reference value , and then the torque current reference value Perform amplitude limiting to obtain the torque current reference value after amplitude limiting ; The torque current reference value Perform amplitude limiting to obtain the torque current reference value after amplitude limiting ; Specifically: Step 1: The maximum current constraint equation of the permanent magnet synchronous motor is: (2) in, is the maximum current, is the actual current value of the q axis, is the actual current value of the d-axis; Substitute formula (2) into ,have to (3) in, is the motor angular velocity, is the q-axis inductance, is the d-axis inductance, is the permanent magnet flux, is the maximum voltage; The limit value for: (4) Step 2: Compare the limit values and size; like Less than or equal to ,but equal ; like Greater than ,but equal ; According to the torque current reference value after limiting Calculate the field weakening compensation component , using the weak magnetic compensation component The excitation current reference value output by the voltage loop PI controller Perform compensation to obtain the excitation current reference value after compensation ; The weakening magnetic compensation component The calculation process is: In the two-phase rotating coordinate system, the maximum voltage constraint equation of the permanent magnet synchronous motor is: (5) in, is the maximum voltage; The voltage balance equation of the motor is: (6) in, is the motor resistance; Ignoring the voltage drop caused by the resistor, equation (6) is simplified to: (7) Substituting formula (7) into formula (5) yields: (8) Then the weakening magnetic compensation component is: (9) The use of the weak magnetic compensation component The excitation current reference value output by the voltage loop PI controller Perform compensation to obtain the excitation current reference value after compensation ; Specifically: (10) in, is the reference value of the excitation current after compensation; Step 2: Use the compensated excitation current reference value Torque current reference value output by the speed outer loop PI controller Perform amplitude limiting to obtain the torque current reference value after amplitude limiting ; Step 3: Use the actual current of the q-axis and d-axis as feedback values, and the torque current reference value after limiting and the excitation current reference value after compensation , the PI controller of the current loop outputs the q-axis stator voltage value and d-axis stator voltage ; Step 4: Set the stator voltage As the input of the voltage loop PI controller, the new excitation current reference value is output through the voltage loop PI controller ; New excitation current reference value for output Return to step 1.

2. A method for controlling current in a field-weakening region of a permanent magnet synchronous motor according to claim 1, characterized in that: The torque current reference value output by the PI controller of the speed outer loop is: (1) in, is the proportional gain in the PI controller of the speed outer loop, is the integral gain in the PI controller of the speed outer loop, is the complex vector in Laplace transform, is the motor angular velocity, is the motor reference angular velocity, It is the torque current reference value output by the PI controller of the speed outer loop.

3. A method for controlling current in a field-weakening region of a permanent magnet synchronous motor according to claim 2, characterized in that: The compensation-based excitation current reference value Torque current reference value output by the speed outer loop PI controller Perform amplitude limiting to obtain the torque current reference value after amplitude limiting ; Specifically: Calculate the limit value : (11) in, is the maximum current, is the reference value of the excitation current after compensation; If the torque current reference value output by the PI controller of the speed outer loop is less than or equal to the limit value , the torque current reference value output by the PI controller of the speed outer loop is used as the torque current reference value after limiting ; If the torque current reference value output by the PI controller of the speed outer loop is greater than the limit value , then the limit value As the torque current reference value after limiting .

4. A method for controlling current in a field-weakening region of a permanent magnet synchronous motor according to claim 3, characterized in that: The actual current of the q-axis and d-axis is used as the feedback value, and the torque current reference value after limiting is used. and the excitation current reference value after compensation , the PI controller of the current loop outputs the q-axis stator voltage value and d-axis stator voltage ; Specifically: (12) in, is the proportional gain of the PI controller of the d-axis current loop, is the integral gain of the PI controller of the d-axis current loop, is the proportional gain of the PI controller of the q-axis current loop, is the integral gain of the PI controller of the q-axis current loop.

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