A Method for Improving Torque Performance of Electrically Excited Doubly Salient Pole Motors Based on Current Coordination Control

Abstract

This invention presents a method for improving the torque performance of an electrically excited doubly salient pole motor based on current-coordinated control. By analyzing the influence mechanism of excitation current and armature current on the magnetomotive force, the concept of equivalent current is proposed, and the excitation current and armature current are equivalently converted. Based on this, a current-torque model is established to derive the current distribution ratio that maximizes the output torque, optimizing the allocation of excitation current and armature current. Furthermore, this invention employs an asymmetric current control method, which effectively utilizes reluctance torque for compensation, further improving the average torque and significantly reducing torque ripple. This invention can calculate the optimal current distribution ratio in real time under low-speed and dynamic operating conditions, achieving dynamic adjustment of excitation current and armature current, and significantly improving the torque output capability of the electrically excited doubly salient pole motor. This invention is suitable for applications with stringent requirements for torque output performance, such as aircraft starting systems.

Description

Technical Field

[0001] This invention belongs to the field of electrical control, specifically relating to a method for improving the torque performance of an electrically excited doubly salient pole motor based on current coordinated control. Background Technology

[0002] The electrically excited doubly salient pole motor is a typical reluctance motor. The stator has both field windings and armature windings, while the rotor has neither windings nor permanent magnets. Electrically excited doubly salient pole motors are simple in structure, highly reliable, and flexible in control, and have attracted considerable attention in recent years in fields such as aerospace electric propulsion and wind power generation. Because both the stator and rotor use salient pole structures, the motor exhibits significant nonlinearity and strong magnetic coupling characteristics during operation. Electrically excited doubly salient pole motors generally suffer from problems such as large torque ripple and low torque-to-current ratio. Especially at low speeds, they experience starting difficulties and insufficient output performance.

[0003] Most existing control methods only optimize the armature current, neglecting the influence of the excitation current on the aeromagnetic field and torque characteristics. In reality, the number of turns in the excitation winding is much higher than that in the armature winding, and its magnetization effect is more significant. If the distribution ratio between the excitation current and the armature current can be properly coordinated, torque output and efficiency can be significantly improved without increasing losses.

[0004] Existing control strategies for electrically excited doubly salient pole motors still suffer from large torque ripple and low output torque under low-speed conditions, failing to maximize the output performance of the motor. Therefore, a method is lacking to achieve coordinated control of the excitation current and armature current, thereby improving the overall torque output performance of the motor.

[0005] The technical differences compared to existing technologies are as follows:

[0006] Technical comparison with patent CN110829939A "A control method for reducing torque ripple in an electrically excited doubly salient pole motor"

[0007] Patent CN110829939A proposes a control method to reduce torque ripple in an electrically excited doubly salient pole motor. Aiming to minimize torque ripple, it uses the torque generation principle of the electrically excited doubly salient pole motor and designs a current setpoint function through a mutual inductance model to control the three-phase current. In contrast, this application aims to improve overall torque performance, balancing the increase in average torque with the reduction of torque ripple. It proposes an equivalent current model and a current coordination control strategy to achieve joint optimization of the excitation current and armature current. The purposes and functions of the two methods are fundamentally different.

[0008] Patent CN110829939A calculates the three-phase current setpoint based on a mutual inductance function model, which belongs to static current distribution; while this application, based on the equivalent current proposed by magnetic field analysis, establishes a current torque model and a current distribution optimization model, which can calculate the optimal current ratio in real time, belonging to dynamic adjustment and control. The control mechanisms and modeling methods of the two are different.

[0009] Patent CN110829939A proposes an improvement to address the problem of the inability to independently control the three-phase current during the commutation stage; while this application is not only applicable to the commutation zone, but also features real-time optimized coordinated control of excitation and armature currents, combined with an asymmetrical current control strategy, and can improve torque output performance under all operating conditions (especially in the low-speed range), thus possessing greater versatility. The two applications differ in their control implementation and scope of application.

[0010] Technical comparison with patent CN114665771B "A method for suppressing torque ripple in an electrically excited doubly salient pole motor"

[0011] Patent CN114665771B proposes a torque ripple suppression method for electrically excited doubly salient pole motors based on direct torque control. It uses a torque error threshold to determine the ripple; if the difference is large, it adjusts the excitation current and armature current, and vice versa. This is a hierarchical control strategy. In contrast, this application establishes a current-torque model and a current distribution optimization model, enabling real-time calculation of the optimal current ratio and achieving continuous optimization control with higher smoothness. The two applications differ in their control strategy hierarchy.

[0012] Patent CN114665771B relies on a torque observer and torque feedback calculation to achieve observation of the outer loop adjustment, but does not analyze the coupling mechanism of the current; while this application, based on the analysis of the magnetic field, proposes an equivalent current model to directly optimize current distribution from the electromagnetic mechanism level. The modeling mechanisms of the two are different.

[0013] Patent CN114665771B primarily addresses the torque drop and fluctuation issues during commutation; while this application focuses on improving torque performance across all operating conditions, balancing the increase in average torque with the suppression of torque ripple, and is applicable to various operating conditions. The two applications differ in their control objectives and scope of application. Summary of the Invention

[0014] This invention addresses the problems of insufficient torque output, large torque ripple, and complex coupling control of excitation current and armature current in existing electrically excited doubly salient pole motors (ESPs) at low speeds. It provides a method for improving the torque performance of ESPs based on current-coordinated control. This invention introduces the concept of equivalent current, establishes a current-torque relationship model, and calculates the torque variation under different combinations of excitation current and armature current in real time, thereby obtaining the optimal current allocation parameters that maximize output torque. Using this method, the controller can quickly and in real-time determine the optimal excitation current and armature current control commands during operation, achieving effective torque control of the ESP and improving its torque performance.

[0015] To achieve the above objectives, the present invention adopts the following technical solution:

[0016] A method for improving the torque performance of an electrically excited doubly salient pole motor based on current coordinated control includes the following steps:

[0017] S1. Based on the topology and magnetic field analysis of the electrically excited doubly salient pole motor, establish an equivalent current model between the excitation current and the armature current.

[0018] S2. Under the same equivalent current, establish a current-torque model based on the inductance change rate and current distribution characteristics of the motor at different rotor positions.

[0019] S3, Define the current distribution ratio parameter R c and torque ripple rate R t , will R c Set as an adjustable variable within the controller to coordinate the distribution between the excitation current and the armature current;

[0020] S4. Keep the motor speed constant, keep the operating conditions constant, keep the speed constant, control parameters, and the current commutation angle in the asymmetrical current control of the electrically excited doubly salient pole motor constant.

[0021] S5. Calculate the optimal excitation current i based on the current-torque model. f *With armature current i p *. Based on the equivalent current, the target current i f * and i p * This is achieved through current closed-loop control;

[0022] S6. Based on the motor's operating status, automatically correct the proportional parameters in the current-torque model to achieve online distribution of excitation current and armature current, as well as optimal torque output.

[0023] As a further improvement to the present invention, in step S1, the equivalent current model between the excitation current and the armature current is established as follows:

[0024] The formula for calculating the equivalent current model is as follows:

[0025] ;

[0026] In the formula, F is the magnetomotive force, and N is the magnetomotive force. f N p These are the number of turns in the excitation winding coil, the number of turns in the armature winding coil, and i. f i p These are the magnetizing current and the armature current, i eq It is the equivalent current.

[0027] As a further improvement of the present invention, in step S2, the calculation formula of the current-torque model is as follows:

[0028] ;

[0029] In the formula, k1 and k2 are the self-inductance rate of the excitation winding, the mutual inductance rate between the armature winding and the excitation winding, and the self-inductance rate of the armature winding, respectively, and k is the turns ratio of the excitation winding coil to the armature winding coil.

[0030] As a further improvement of the present invention, in step S3, the current distribution ratio R c The calculation formula is as follows:

[0031] ;

[0032] The torque ripple rate R t The calculation formula is as follows:

[0033] ;

[0034] In the formula, T max T min T avg These are the maximum torque, minimum torque, and average torque within one electrical cycle. Torque ripple rate is an important indicator used to measure the degree of fluctuation in the motor's output torque. R t The larger the value, the greater the output torque fluctuation.

[0035] As a further improvement of the present invention, in step S5, the optimal excitation current i f *With armature current i p *The excitation current and armature current that maximize the output torque are derived through the current-torque model under the same equivalent current. Their calculation formulas are as follows:

[0036] , ;

[0037] As a further improvement of the present invention, the closed-loop control implemented by the current closed-loop control in step S5 is implemented by a TMS320F28335 controller, including sampling, pulse width modulation and proportional-integral adjustment.

[0038] As a further improvement of the present invention, the proportional parameters in the current-torque model in step S6 are obtained through experimental self-calibration and are applicable to DSEM topologies with different pole pair numbers.

[0039] Compared with the prior art, the advantages of the present invention are as follows:

[0040] This invention establishes equivalent expressions for the excitation current and armature current by introducing an equivalent current model, achieving dynamic coordinated control between the two. This invention maintains torque output performance under different operating conditions. Employing an asymmetric current control strategy, it effectively utilizes reluctance torque to compensate for torque drop during commutation, reducing torque ripple. Based on the current-torque model, it can automatically calculate the optimal current distribution ratio according to the real-time operating state of the motor, achieving adaptive adjustment of the excitation current and armature current, avoiding the complex calculations required in traditional control. This invention can achieve coordinated control of the excitation current and armature current without changing the motor structure, significantly improving the average torque of the motor and reducing torque ripple. The method is computationally simple, can be run in real-time in the controller, and has good versatility. Attached Figure Description

[0041] Figure 1 This is a block diagram of the overall structure of a method for improving the torque performance of an electrically excited doubly salient pole motor based on current coordination control.

[0042] Where n represents the real-time rotational speed, n* represents the reference rotational speed, PI represents the proportional-integral controller, PWM represents pulse width modulation, and i f Indicates the real-time excitation current, i f * indicates the optimal excitation current, i p Indicates the real-time armature current, i p * indicates the optimal armature current, i a i b i c These represent the armature currents of phase A, phase B, and phase C, respectively.

[0043] Figure 2 A structural diagram of a 12 / 8 structure electrically excited doubly salient pole generator;

[0044] The attached diagram is labeled as follows: 1. Stator; 2. Excitation winding; 3. Rotor; 4. Armature winding;

[0045] Figure 3 This is the internal magnetic circuit diagram of an electrically excited doubly salient pole generator;

[0046] Figure 4 These are characteristic curves of the current-torque relationship model under different equivalent currents;

[0047] Figure 5 This is a comparison chart of experimental results under different current distribution ratios;

[0048] Figure 5 (a) is R c The experimental waveform diagram with a value of 0.87;

[0049] Figure 5 (b) is R c =1.64 experimental waveform diagram;

[0050] Figure 5 (c) is R c =14 experimental waveform diagram;

[0051] Where T represents torque, t represents time, 30 N.m / div means that each cell on the vertical axis of the graph represents 30 N.m, 40 A / div means that each cell on the vertical axis of the graph represents 40 A, and 2.5 ms / div means that each cell on the horizontal axis of the graph represents 2.5 ms.

[0052] Figure 6 This is a comparison chart of torque output performance under different flow distribution ratios. Detailed Implementation

[0053] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. It should be understood that the described embodiments are only some examples of the present invention and not all of the present invention. Other embodiments obtained by those skilled in the art without creative effort should also be considered within the scope of protection covered by the present invention.

[0054] Example 1:

[0055] This invention provides a method for improving the torque performance of an electrically excited doubly salient pole motor based on current coordination control. For example... Figure 1 As shown, this invention provides an overall structural block diagram of a method for improving the torque performance of an electrically excited doubly salient pole motor based on current coordination control. The system mainly includes an electrically excited doubly salient pole motor, a controller, a current sensing module, a PWM modulation module, and a control unit based on optimal current coordination. The controller calculates the equivalent current i by acquiring real-time signals of the armature current and the excitation current. eq And the optimal current distribution ratio R is obtained based on the optimization model. c To obtain the optimal excitation current i f *With armature current i p * Closed-loop control using a PI controller enables optimized torque performance control of the motor.

[0056] The structure of a 12 / 8-pole electrically excited doubly salient pole generator is as follows: Figure 2 The diagram shows a stator 1, an excitation winding 2, a rotor 3, and an armature winding 4. The stator 1 has the excitation winding 2 and the armature winding 4. The rotor 3 consists of eight salient poles and has no windings or permanent magnets. The magnetic circuit between the stator and rotor changes at different rotor positions, resulting in varying inductance characteristics, which provides the basis for establishing the equivalent current model of this invention. Figure 3 This is the internal magnetic circuit diagram of an electrically excited doubly salient pole generator. The combined magnetomotive force generated by the field winding and armature winding determines the generator's torque output. This invention determines the coupling coefficient between the field current and armature current through magnetic field analysis, thereby defining the equivalent current. Figure 4 The figure shows the characteristic curves of the current-torque relationship model under different equivalent currents. By considering different i... eq Changing the excitation current i under certain conditions f That is, change R c Simulation results analysis reveals the mapping relationship between current and torque. The results show that, under the same operating conditions, by changing the current distribution ratio, the electrically excited doubly salient pole motor can achieve its maximum output torque.

[0057] like Figure 5 The figure shows a comparison of experimental results under different current distribution ratios. Where (a) represents R... c The experimental waveform diagram with R = 0.87, (b) is the R value. c The experimental waveform diagram is shown with a value of 1.64. (c) shows the R value. c The experimental waveform diagram is shown for R=14. It can be seen that as R... c The changes in R result in a non-monotonic trend in both average torque and torque ripple. c Within this range, the average torque increases and torque fluctuation decreases, verifying the effectiveness of the optimal current distribution ratio proposed in this invention. Figure 6 The figure shows a comparison of torque output performance under different current distribution ratios. Experimental results show that when R... c When the torque is 1.64, the output torque reaches its optimal value, the torque ripple rate is minimized, and the average torque is effectively increased by 57.9%.

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any modifications or equivalent changes made based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. A method for improving torque performance of an electrically excited doubly salient motor based on current coordinated control, characterized in that, The method comprises the following steps: S1, according to the topology structure of the electrically excited doubly salient motor and the magnetic field analysis, an equivalent current model between the field current and the armature current is established; In step S1, the equivalent current model between the field current and the armature current is established as follows: The equivalent current model calculation formula is as follows: ； where F is the magnetomotive force, N f , N p are the number of turns of the field and armature windings, respectively, i f , i p are the field and armature currents, respectively, and i eq is the equivalent current; S2, under the same equivalent current, based on the inductance variation rate and the current distribution characteristics of the motor under different rotor positions, a current-torque model is established; S3, defining a current distribution ratio parameter R c and a torque ripple rate R t setting R c as an adjustable variable within the controller to coordinate distribution between the field current and the armature current; S4, keeping the motor speed unchanged, keeping the working condition unchanged, keeping the speed unchanged, the control parameters and the current commutation angle in the asymmetric current control of the electrically excited doubly salient motor unchanged; S5, according to the current-torque model, the best excitation current i is calculated f *With the armature current i p *, according to the equivalent current, the target current i f *And i p *, through current closed-loop control S6, according to the motor operating state, the proportional parameters in the current-torque model are automatically corrected, the online distribution of the field current and the armature current and the optimal torque output are realized.

2. The method for improving torque performance of current coordinated control based electrically excited doubly salient motor according to claim 1, characterized in that: In step S2, the calculation formula of the current-torque model is as follows: ； In the formula, k1 and k2 are the self-inductance variation rate of the field winding, the mutual inductance variation rate between the armature winding and the field winding, and the self-inductance variation rate of the armature winding respectively, and k is the turn ratio of the field winding coil to the armature winding coil.

3. The method for improving torque performance of current coordinated control based electrically excited doubly salient motor according to claim 2, characterized in that: In step S3, the current distribution ratio R c The calculation formula is as follows: ； The torque ripple rate R t The calculation formula is as follows: ； In the formula, T max , T min , T avg are the maximum torque, the minimum torque, and the average torque in one electric cycle, respectively. The torque ripple is an important index for measuring the degree of output torque fluctuation of the motor, and the greater R t indicates the greater output torque fluctuation.

4. The method for improving torque performance of current coordinated control based electrically excited doubly salient machine according to claim 1, characterized in that: In step S5, the optimal excitation current i f *With armature current i p *The excitation current and armature current that maximize the output torque are derived through the current-torque model under the same equivalent current. Their calculation formulas are as follows: ， 。 5. The method for improving torque performance of current coordinated control based electrically excited doubly salient machine according to claim 4, characterized in that: The closed-loop control realized in step S5 is realized by a TMS320F28335 controller, including sampling, pulse width modulation and proportional integral adjustment links.

6. The method for improving torque performance of current coordinated control based electrically excited doubly salient machine according to claim 1, characterized in that, The proportional parameters in the current-torque model in step S6 are obtained through experimental self-calibration, and are suitable for different pole pair number DSEM topology structures.

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