A current optimization-based method for suppressing torque ripple of switched reluctance motor
By using Fourier series to represent the current in a switched reluctance motor and optimizing the turn-on and conduction angles, a current optimization model is established. This solves the problem of low root mean square current utilization in torque ripple suppression, achieving efficient torque ripple suppression and improved motor efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-12-16
- Publication Date
- 2026-03-27
AI Technical Summary
Existing methods for suppressing torque ripple in switched reluctance motors have failed to effectively improve the root mean square current utilization rate when reducing torque ripple, resulting in reduced motor efficiency and decreased output capacity.
By representing the phase current with the coefficients of the Fourier series and the turn-on and conduction angles, a new current optimization model is established. These parameters are then adjusted using an optimization algorithm to optimize the current waveform, thereby fixing the root mean square of the current and minimizing torque ripple. Hysteresis control is then used to achieve the actual current waveform tracking the optimal waveform.
Without reducing the torque-to-current ratio, it improves the root mean square current utilization rate, reduces copper losses, enhances motor efficiency, and effectively suppresses torque ripple.
Smart Images
Figure CN115800862B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of motor control, more particularly, to a torque ripple suppression method for switched reluctance motor based on current optimization. BACKGROUND
[0002] The stator and rotor of switched reluctance motor are double salient pole structures, and the rotor has no winding, which has the advantages of simple structure, low cost, high reliability, strong fault tolerance and wide constant power speed range, and has received more and more attention in recent years. However, the electromagnetic characteristics of switched reluctance motor are highly nonlinear, which makes the torque ripple of conventional control method larger, and this shortcoming limits the further development and application of switched reluctance motor.
[0003] Some scholars have reduced the torque ripple of switched reluctance motor by optimizing the turn-on angle and turn-off angle, but this method has limited effect on reducing torque ripple. In order to further reduce the torque ripple of switched reluctance motor, domestic and foreign scholars have proposed control methods such as torque distribution control, vector control, harmonic injection and direct instantaneous torque control. However, these control methods only consider the suppression of torque ripple in implementation, without considering the negative impact on the root mean square of current, which inevitably causes the problem of torque current ratio decline, and the utilization rate of root mean square of current is not high. While the copper loss of motor is proportional to the square of root mean square of current, the decline of torque current ratio means that the root mean square of current increases and the copper loss increases under the same output torque, resulting in reduced efficiency, and the average torque decreases under the same root mean square of current, resulting in reduced output capacity of motor. SUMMARY
[0004] In view of the defects of the prior art, the purpose of the present application is to provide a torque ripple suppression method for switched reluctance motor based on current optimization, which aims to solve the problem of low utilization rate of root mean square of current in torque ripple suppression method.
[0005] To achieve the above-mentioned purpose, the present application discloses a torque ripple suppression method for switched reluctance motor based on current optimization, which proposes a new current expression and establishes a new current optimization model based on the current expression. The phase current is represented by a set of Fourier series coefficients and turn-on angle and conduction angle, and the root mean square of phase current is set to a fixed value. Under the premise of not reducing the torque current ratio of motor, the Fourier series coefficients and the turn-on angle and conduction angle are adjusted through optimization algorithm, and then the phase current of motor at each rotor position is optimized, so as to obtain the theoretical optimal phase current waveform with high utilization rate of root mean square of current and low torque ripple. The actual phase current waveform of motor is made to track the theoretical optimal phase current waveform through hysteresis control, so as to achieve the effect of torque ripple suppression.
[0006] The technical scheme of the present application is as follows:
[0007] A current optimization-based method for suppressing torque ripple of switched reluctance motor, comprising the following steps:
[0008] Step 1: Express the phase current with a set of Fourier series coefficients and turn-on angle and turn-off angle:
[0009]
[0010] In the formula, i1, i2, …, i n are Fourier series coefficients of the nth order, N is the highest order of the Fourier series, θ on , θ exc are turn-on angle and turn-off angle, respectively, and only when the rotor electrical angle θ e is in the interval [θ on , θ on + θ exc ], there is current in the phase winding, and the phase winding current is 0 for other rotor positions;
[0011] Step 2: Let the root mean square of the phase current be a fixed value i rms , and give the initial values of the Fourier series coefficients, turn-on angle, and turn-off angle i 10 , i 20 , …, i n0 , θ on0 , θ exc0 , to obtain the initial phase current waveform I0 with current root mean square i rms ;
[0012] Step 3: Under the premise of meeting the constraints of current root mean square, torque current ratio, etc., taking the minimum torque ripple as the optimization target, taking the Fourier series coefficients and turn-on angle and turn-off angle as optimization variables, using optimization algorithm, continuously changing the optimization variables to optimize the phase current waveform, calculating the related parameters of the constraints and optimization target based on the torque-current-position data table of the switched reluctance motor, obtaining the Fourier series coefficients i 1opt , i 2opt , …, i nopt and turn-on angle θ onopt and turn-off angle θ excopt corresponding to the current waveform that meets the constraints and has the minimum target function, thereby obtaining the optimal phase current waveform I opt with high current root mean square utilization rate and small torque ripple:
[0013]
[0014] Step 4: Standardize the optimal phase current waveform obtained in step 3 to obtain the optimal phase current waveform I norm under unit phase current root mean square:
[0015]
[0016] Step 5: match the current waveform to the actual operation condition of the motor. The motor controller calculates the required phase current root mean square i fms_load according to the difference between the given speed and the actual speed, and through proportional integral operation, and multiplies it with the best phase current waveform obtained in step 4, to obtain the best phase current waveform under the corresponding load condition I ref Expression:
[0017] I ref (θ e )=I norm (θ e )i rms_load
[0018] Step 6: through hysteresis control, the actual phase current of the motor tracks the best phase current waveform under the corresponding load condition I ref obtained in step 5, achieving the effect of torque ripple suppression.
[0019] In the above steps, the constraint conditions include fixing the phase current root mean square to i rms , and the torque current ratio ratio set is not less than the set value ratio .
[0020] In the above steps, the root mean square of the phase current waveform can be conveniently calculated according to the following formula:
[0021]
[0022] In the above steps, the torque current ratio is the ratio of the average torque to the current root mean square:
[0023]
[0024] where T mean is the average torque corresponding to the phase current waveform I(θ e ).
[0025] In the above steps, the torque ripple is the ratio of the maximum torque to the minimum torque in an electrical period to the average torque:
[0026]
[0027] where T max is the maximum torque in an electrical period, and T max is the minimum torque in an electrical period.
[0028] In the above steps, the optimization algorithm can use the active set method, or other optimization algorithms such as the interior point method, the sequential quadratic programming method, etc.
[0029] In the above steps, all the calculations and optimizations are performed within one electrical cycle.
[0030] In the above steps, the torque-current-position data table can be obtained by finite element analysis, analytically calculated according to motor design parameters, or measured by experiment.
[0031] The switching reluctance motor torque ripple suppression method based on current optimization provided by the application has excellent universality and is applicable not only to switching reluctance motors but also to other structures of reluctance motors such as segmented rotor switching reluctance motors and segmented stator switching reluctance motors.
[0032] Compared with the prior art, the application has the following characteristics:
[0033] The method proposes a current optimization and establishes a new current optimization model based on the current optimization, expresses the phase current by a set of Fourier series coefficients and turn-on angle and conduction angle, considers the current root mean square in the suppression of torque ripple, fully utilizes the current root mean square, has small copper loss and low torque ripple at the same output torque, and has high efficiency; expresses the current in one cycle by a set of Fourier series coefficients and turn-on angle and conduction angle instead of a large number of discrete current data points, has few optimization variables, reduces the memory requirement of the controller, and does not need additional interpolation; not only optimizes the turn-on angle and turn-off angle, but also adjusts the current at each rotor position by adjusting the Fourier series coefficients, and theoretically the current expression proposed by the method can express the current of any waveform, the optimization model based on the current expression has strong search capability, and the current waveform obtained by optimization has good torque ripple suppression effect; compared with the harmonic injection method, the frequency and phase of each harmonic of the Fourier series can be adjusted by changing the turn-on angle and conduction angle, the harmonic number can be freely adjusted by changing the highest order of the Fourier series, and the optimization degree of freedom is large; for the switching reluctance motor, the torque output capacity is low when the current is input in the interval with low inductance rise rate, and even negative torque is generated when the current is input in the interval with low inductance drop, the current expression proposed by the method has the ability to directly set the current utilization rate in the interval with low current utilization rate to zero, there is no negative phase torque, and the current utilization rate is high; the current expression is ingeniously designed, not only can the current root mean square be conveniently calculated, but also the current is continuous in the whole electrical cycle, which is convenient for the controller to realize; and the application has excellent universality and is applicable not only to switching reluctance motors but also to other structures of reluctance motors such as segmented rotor switching reluctance motors and segmented stator switching reluctance motors. BRIEF DESCRIPTION OF DRAWINGS
[0034] Figure 1 The phase current optimization flowchart of the switching reluctance motor torque ripple suppression method based on current optimization of the application;
[0035] Figure 2 A whole control block diagram of a current-optimized switch reluctance motor torque ripple suppression method of the present application;
[0036] Figure 3 A phase current schematic diagram of a current-optimized switch reluctance motor torque ripple suppression method of the present application;
[0037] Figure 4 An inductance, current and torque waveform diagram of a three-phase 12 / 8-pole switch reluctance motor using traditional current chopping control according to one embodiment of the present application;
[0038] Figure 5 An inductance, current and torque waveform diagram of a three-phase 12 / 8-pole switch reluctance motor using the control method of the present application according to one embodiment of the present application. DETAILED DESCRIPTION
[0039] In order to make the objectives, technical solutions and advantages of the present application clearer and more comprehensible, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.
[0040] A current-optimized switch reluctance motor torque ripple suppression method, as shown in Figure 1 , comprises the following steps:
[0041] Step 1: Express the phase current I with a set of Fourier series coefficients and turn-on angle and turn-off angle:
[0042]
[0043] In the formula, i1, i2, …, i n are the Fourier series coefficients of the nth order, N is the highest order of the Fourier series, θ on , θ exc are the turn-on angle and turn-off angle respectively. Only when the rotor electrical angle is in the interval [θ on , θ on + θ exc ], the phase winding has current, and the phase winding current is 0 at other rotor positions.
[0044] Step 2: Let the root mean square of the phase current be a fixed value i rms , give the initial values of the Fourier series coefficients, turn-on angle and turn-off angle i 10 , i 20 , …, i n0 , θ on0 , θ exc0 , and obtain the initial phase current waveform I0 with the current root mean square i rms .
[0045] Step 3: Under the premise of satisfying constraints such as root mean square current and torque-to-current ratio, with minimum torque ripple as the optimization objective, and using the coefficients of the Fourier series, turn-on angle, and conduction angle as optimization variables, an optimization algorithm is adopted to optimize the phase current waveform by continuously changing the optimization variables. Based on the torque-current-position data table of the switched reluctance motor, the relevant parameters of the constraints and optimization objective are calculated to obtain the coefficients i of the Fourier series corresponding to the current waveform that satisfies the constraints and minimizes the objective function. 1opt i 2opt ,…,i nopt and the opening angle θ onopt and conduction angle θ excopt This yields the optimal phase current waveform I with high root mean square current utilization and low torque ripple. opt :
[0046]
[0047] Step 4: Standardize the optimal phase current waveform obtained in Step 3 to obtain the optimal phase current waveform I under the root mean square of unit phase current. norm expression:
[0048]
[0049] Step 5: Match the current waveform to the actual operating conditions of the motor. The motor controller, based on the difference between the given speed and the actual speed, performs proportional-integral calculations to obtain the root mean square (RMS) phase current i required for the corresponding load condition. rms_load Multiply it by the optimal phase current waveform after standardization in step 4 to obtain the optimal phase current waveform I under the corresponding load condition. ref expression:
[0050] I ref (θ e ) = I norm (θ e )i rms_load
[0051] Step 6: Through hysteresis control, make the actual phase current of the motor track the optimal phase current waveform I obtained in Step 5 under the corresponding load condition. ref This achieves the effect of suppressing torque pulsation.
[0052] In the above steps, the calculations and optimizations are all performed within one electrical cycle; the constraints include a fixed root mean square current of i. rms The torque-to-current ratio is not lower than the set value ratio. setThe torque-current-position data table can be obtained by finite element analysis, analytically calculated according to motor design parameters, or measured by experiment; the optimization algorithm can be an effective set method, or other optimization algorithms such as an interior point method and a sequential quadratic programming method.
[0053] In the above step, the root mean square of the current waveform can be conveniently calculated according to the following formula:
[0054]
[0055] In the above step, the torque-current ratio is the ratio of the average torque to the root mean square of the current:
[0056]
[0057] In the above step, the torque ripple is the ratio of the difference between the maximum torque and the minimum torque in an electrical period to the average torque:
[0058]
[0059] In the present embodiment, the initial current waveform I0 only contains the coefficient of the first-order Fourier series, and the coefficients of the remaining order Fourier series are 0; the initial opening angle is set as the electrical angle corresponding to the minimum inductance, and the initial conduction angle is set as m is the number of motor phases, so the initial current I0 can be expressed as:
[0060]
[0061] Figure 2 FIG. 1 is a whole control block diagram of a torque ripple suppression method for a switched reluctance motor based on current optimization according to the present application, Figure 3 FIG. 2 is a phase current schematic diagram of a torque ripple suppression method for a switched reluctance motor based on current optimization according to the present application. Figure 4 FIG. 3 is an inductance, current and torque waveform diagram of a three-phase 12 / 8-pole switched reluctance motor using traditional current chopping control according to one of the embodiments of the present application, Figure 5 FIG. 4 is an inductance, current and torque waveform diagram of a three-phase 12 / 8-pole switched reluctance motor using the method according to the present application. Compared with the traditional current chopping control, after using the method, the torque output capability and the root mean square of the current remain unchanged, and the torque ripple is reduced from 103.78% to 3.12%. It can be seen that the torque ripple suppression method for a switched reluctance motor based on current optimization according to the present application has obvious effect on torque ripple suppression, and does not increase copper loss and does not reduce torque output capability.
[0062] Those skilled in the art can easily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.
Claims
1. A method for suppressing torque ripple in a switched reluctance motor based on current optimization, characterized in that, Includes the following steps: Step 1: Express the phase current using a set of Fourier series coefficients, as well as the turn-on and conduction angles: In the formula, i1,i2,…,i n These are the coefficients of the nth order Fourier series, where N is the highest order of the Fourier series, and θ is the coefficient of the series. on θ exc These are the opening angle and the conduction angle, θ. e The rotor electrical angle; Step 2: Set the root mean square of the phase current to a fixed value i. rms Given the coefficients, opening angle, and initial value i of the Fourier series. 10 i 20 ,…,i n0 θ on0 θ exc0 The initial phase current waveform I0 is obtained; Step 3: Under the constraints of the root mean square current and torque-to-current ratio, with the minimum torque ripple as the optimization objective, and the coefficients of the Fourier series, as well as the turn-on and conduction angles, as optimization variables, the phase current waveform is optimized by continuously changing the optimization variables. The relevant parameters of the constraints and optimization objective are calculated, and the coefficients i of the Fourier series corresponding to the phase current waveform that satisfies the constraints and minimizes the objective function are obtained. 1opt i 2opt ,…,i nopt and the opening angle θ onopt and conduction angle θ excopt This yields the optimal phase current waveform I with high root mean square current utilization and low torque ripple. opt : Step 4: Standardize the optimal phase current waveform obtained in Step 3 to obtain the optimal phase current waveform I under the root mean square of unit phase current. norm : Step 5: Based on the difference between the given speed and the actual speed, obtain the root mean square (RMS) phase current i required for the corresponding load condition through proportional-integral (PI) calculation. rms_load Multiply it by the optimal phase current waveform after standardization in step 4 to obtain the optimal phase current waveform I under the corresponding load condition. ref expression: I ref (θ e )=I norm (θ e )i rms_load Step 6: Through hysteresis control, make the actual phase current of the motor track the optimal phase current waveform I obtained in Step 5 under the corresponding load condition. ref This achieves the effect of suppressing torque pulsation.
2. The method for suppressing torque ripple in a switched reluctance motor based on current optimization as described in claim 1, characterized in that, The constraints include fixing the root mean square value of the phase current to i. rms The torque-to-current ratio is not lower than the set value ratio. set .
3. The method for suppressing torque ripple in a switched reluctance motor based on current optimization as described in claim 1, characterized in that, The root mean square definition of the phase current waveform is:
4. The method for suppressing torque ripple in a switched reluctance motor based on current optimization as described in claim 1, characterized in that, The torque-to-current ratio is the ratio of the average torque to the root mean square of the phase current. Among them, T mean The phase current waveform I(θ) e The average torque corresponding to ).
5. The method for suppressing torque ripple in a switched reluctance motor based on current optimization as described in claim 4, characterized in that, The torque pulsation is the ratio of the difference between the maximum and minimum torques within one electrical cycle to the average torque. Among them, T max T is the maximum torque within one electrical cycle. max This is the minimum torque within one electrical cycle.
6. The method for suppressing torque ripple in a switched reluctance motor based on current optimization as described in claim 1, characterized in that, The algorithm for optimizing the phase current waveform in step 3 is the effective set method, the interior point method, or the sequential quadratic programming method.
7. A method for suppressing torque ripple in a switched reluctance motor based on current optimization as described in any one of claims 1 to 6, characterized in that, The calculations or optimizations are all performed within one electrical cycle.
8. The method for suppressing torque ripple in a switched reluctance motor based on current optimization as described in claim 1, characterized in that, The relevant parameters for calculating the constraints and optimization objectives described in step 3 are based on the torque-current-position data table and are obtained through finite element analysis, analytical calculation based on motor design parameters, or experimental measurement.