Torque Sharing Function Research Articles

Torque Ripple Minimization of a Switched Reluctance Motor using a Torque Sharing Function based on the Overlap Control Technique

Torque Ripple Minimization of a Switched Reluctance Motor using a Torque Sharing Function based on the Overlap Control Technique

Model Predictive Control of Switched Reluctance Starter/Generator With Torque Sharing and Compensation

To enhance the mechanical safety, guarantee sufficient temperature margin and reduce the high-frequency electromagnetic interference of the starter/generator embedded in the aero engine, a multiobjective optimization control method is proposed for the switched reluctance machine based on the model prediction and the torque sharing function (TSF). For the model predictive control, the instantaneous phase torque is estimated through the Hermite interpolation with the flux-linkage characteristics at the aligned and unaligned rotor position, and the reference phase torque is obtained by the TSF. The error between the estimated and real instantaneous torque, especially around the unaligned rotor position, will result in the performance degradation, which is effectively compensated by the new TSF. The performances of the proposed control method are evaluated in detail by the simulation and experiment, and comparison with other representative methods is carried out as well.

Synchronized Switching Modulation to Reduce the DC-Link Current in SRM Drives

Switched Reluctance Machines (SRM) are emerging as a possible alternative in terms of cost and supply stability to rare earth based electric vehicle traction systems. However, because of the huge amounts of energy stored and transferred back and forth between the DC source and the SRM, large DC-link capacitors must be used as buffers, which increases overall costs and size. This paper proposes a novel modulation technique which forces the exchange of energy between phases while decreasing the energy transfer between the DC bus and the SRM. This means lower DC bus currents (capacitor size and cost reduction) and lower Joule-effect conduction losses (better efficiency). The proposed modulation has been validated experimentally in a test bench and compared with the conventional torque-sharing function.

An Improved Torque Sharing Function for Torque Ripple Reduction in Switched Reluctance Machines

An offline torque sharing function (TSF) is introduced in this paper for torque ripple reduction in switched reluctance machines (SRM). This TSF uses static flux linkage characteristics of the machine obtained from finite element analysis or experiments that describe the machine dynamics to determine optimal current profiles such that the torque ripple reduction is achieved with minimal copper losses. Due to this feature, the proposed TSF performs well across a wide speed range. Additionally, the objective function of the proposed TSF uses only one weight parameter, which facilitates the use of this TSF. In this paper, an intuitive justification for the selection of this weight parameter is given, and the performance of this TSF is validated in simulation and experimentally on a 5.2 kW, four phase SRM. To baseline its performance, the proposed TSF has been compared to the offline TSF in the literature, which shows that it has better current tracking performance at higher speeds due to the inclusion of flux linkage characteristics. Finally, it has been compared to conduction angle control at speeds above the base speed to show that it can be a viable alternative for the control of SRM even in an operation region normally not considered for TSF.

Sensorless Direct Torque Control Using the Inductance Inflection Point for a Switched Reluctance Motor

This paper proposes a new position sensorless method for a direct torque control system using the inductance inflection point of a switched reluctance motor (SRM). The SRM essentially requires knowledge of the rotor position in the torque control system; this is because it generates torque by exciting the stator windings according to the rotor position. This rotor position information is an important factor used to obtain phase commutation point and to calculate instantaneous torque. Various rotor position detection methods have been used, but most of the methods increase the construction cost by requiring additional hardware and use many parameters for high-order analysis modeling, causing problems such as increasing the number of calculations. Therefore, in this paper, we propose a method using the inductance inflection point to solve these problems. It is possible to estimate the position of the rotor by detecting where the inductance inflection point occurs due to the rotor and stator overlapping with each other, and the phase commutation point and instantaneous torque can be calculated. The calculated instantaneous torque is used for direct torque control and torque ripple reduction through the torque-sharing function. The proposed method is verified through simulation and experiments.

Torque Ripple Reduction for Switched Reluctance Motor with Optimized PWM Control Strategy

The high current ripple and torque ripple are the main drawbacks of the switched reluctance motor (SRM) since the nonlinearity and double saliency, which limits its applications. In order to eliminate the current variation and torque ripple, an optimized pulse width modulation (PWM) control is presented in this paper. The voltage ratio duty is able to be predicted precisely according to the information of the motor running parameter. Based on torque sharing functions (TSFs), the current profile is pre-computed and four regions are defined according to the reference current profiles. The three modes, excitation, demagnetization and freewheeling, are flexibly chosen according to the characteristic of the current profile. It is indicated that it is better than that of conventional PWM modulation in terms of current ripple and the current tracing performance is improved without increasing the switching frequency or changing the hysteresis band. The current ripple is defined as the peak-to-peak value dividing the average value and it is reduced by 40%. A comparison in terms of the torque ripple and copper loss is also carried out: the torque ripple is significantly reduced via the proposed scheme under both magnetic linear and saturation conditions. The torque ripple and copper loss are reduced by about 70% and 12%, respectively. The validity and effectiveness of the proposed control strategy is verified by simulation and experimental results.

Reduction of Torque and Voltage Ripple in a Doubly Salient Permanent Magnet Generator

Large torque and voltage ripple are inherent drawbacks of doubly salient generators. This paper first introduces torque sharing function (TSF) into the application of a dual-channel three-phase 12/8 poles doubly salient permanent magnet generator (DSPMG) to reduce torque and voltage ripple. Based on the principle of copper losses minimization, a new TSF is proposed through theoretical analysis and numerical computation. The proposed TSF is compared to conventional TSFs according to three evaluation criteria. In order to achieve satisfying and consistent steady state and dynamic performances over the whole operation range, gain scheduling PI controller is adopted to overcome the highly nonlinear characteristic of the DSPMG. Besides, with compensators of back-EMF, cogging torque and losses adopted as feed-forward, a dual closed-loop generation control system is detailed designed. Both simulation and experimental results verify the effectiveness of the proposed control system and the copper losses minimization TSF in reducing torque and voltage ripple.

Improvement of the Torque-Speed Performance and Drive Efficiency in an SRM Using an Optimal Torque Sharing Function

In this paper, by evaluating the extreme value of the qth-power current, a torque sharing function (TSF) family for reducing the torque ripples in the switched reluctance motor (SRM) is proposed. The optimization criteria of the TSF has two secondary objectives, including the maximization of the torque-speed range and the minimization of copper loss. The evaluation indices in terms of the peak phase current, the rms (root mean square) phase current, and the torque ripple factor are compared between the proposed TSF family and four conventional TSFs including linear, sinusoidal, exponential, and cubic TSFs. An optimization objective function that combines the maximum absolute value of the rate-of-change of the flux linkage (MAV-RCFL) and the qth-power of current is proposed and a weighting factor is used to balance the influence of the two optimization objectives. An optimal TSF can be easily obtained by solving the optimization problem from the TSF family. The proposed TSF is validated by using simulations and experiments with a three-phase 6/4 SRM with 7.5 kW, 3000 rpm, and 270 V DC-link voltage. The dynamic simulation model is implemented in Matlab/Simulink. The results demonstrate the validity and superiority of the proposed control method; the optimal TSF provides better torque-speed performance, and a better reduction in copper loss and torque ripples at high speed, as compared to conventional TSFs.

A Novel Modified Turn-on Angle Control Scheme for Torque-ripple Reduction in Switched Reluctance Motor

In recent years, Switched Reluctance Motors (SRM) have been dramatically considered with both researchers and industries. SRMs not only have a simple and reliable structure, but also have low cost production process. However, discrete torque production of SRM along with intensive magnetic saturation in stator and rotor cores are the major drawbacks of utilizing in variety of industrial applications and also causes the inappropriate torque ripples. In this paper, a modified logical-rule-based Torque Sharing Function (TSF) method is proposed considering turn-on angle control. The optimized turn-on angle for conducting each phase is achieved by estimating the inductance curve in the vicinity of unaligned position and based on an analytical solution for each phase voltage equation. Simulation results on a four-phase switched reluctance motor and comparison with the conventional methods validates the effectiveness of the proposed method.

A Non-Unity Torque Sharing Function for Torque Ripple Minimization of Switched Reluctance Generators in Wind Power Systems

This paper deals with a new torque ripple minimization method for a Switched Reluctance Generator (SRG). Although, the SRG has many advantages including simple and robust construction, and high power density as a generator, it has not been widely employed in the industry. One of the major drawbacks of the SRG is its high torque ripple that results in high noise operation of the generator. In this paper, a non-unity Torque Sharing Function (TSF) is proposed to minimize the torque ripple over a wide speed range of operation. Simulations as well as experimental results are presented to verify the effectiveness of the proposed torque ripple minimization technique.

An Offline Torque Sharing Function for Torque Ripple Reduction in Switched Reluctance Motor Drives

In this paper, an offline torque sharing function (TSF) for torque ripple reduction in switched reluctance motor (SRM) drives over a wide speed range is proposed. The objective function of an offline TSF is composed of two secondary objectives with a Tikhonov factor to minimize the square of the phase current (copper loss) and derivatives of current references (rate of change of flux linkage). The proposed TSFs with different Tikhonov factors are compared with the conventional TSFs including linear, cubic, and exponential TSFs in terms of efficiency and torque-speed performance while operating in both magnetic linear and saturation regions. Then, the Tikhonov factor is selected based on a tradeoff between the copper loss and torque-speed performance. The maximum torque-ripple-free speed of the selected offline TSF is validated to be seven times as high as the best case in these conventional TSFs. The performance of the offline TSF is verified by simulations and experiments with a 2.3-kW, three-phase 12/8 SRM. Results show that the proposed offline TSF can significantly reduce the torque ripple of SRM without increasing copper loss over a wide speed range.

An Extended-Speed Low-Ripple Torque Control of Switched Reluctance Motor Drives

In this paper, an extended-speed low-ripple torque control of switched reluctance motor (SRM) drives using torque sharing function (TSF) is proposed. Two operational modes are defined for the online TSF during commutation: In Mode I, absolute value of rate of change of flux linkage (ARCFL) of incoming phase is higher than outgoing phase; in Mode II, ARCFL of outgoing phase is higher than incoming phase. In order to compensate the torque error produced by imperfect tracking of phase current, a proportional and integral compensator with torque error is added to the torque reference of outgoing phase in Mode I and incoming phase in Mode II. Therefore, the total torque is determined by the phase with lower ARCFL rather than the phase with higher ARCFL as in conventional TSFs. The maximum torque-ripple-free speed of the proposed TSF is increased to more than ten times as the best case in conventional TSFs. Finally, the proposed TSF is verified by both simulations and experiments with a 2.3 kW, 6000 rpm, three-phase 12/8 SRM operating in both linear magnetic and saturated magnetic regions. Results show that the proposed TSF has higher average torque, and much lower torque ripples compared to conventional TSFs.

Research of Electro-mechanical Actuator in Electric Braking System Based on Instantaneous Torque Control with SRM

In order to improve the reliability and braking torque of aircraft electric braking system, this paper selected switched reluctance motor (SRM) as drive motor of electromechanical actuator, static torque data of SRM calculated by finite element analysis were used as training samples, then characteristics of torque-angle were obtained off-line by Generalized Regression Neural Network with particle swarm optimization (PSO-GRNN), and the nonlinear mapping from the torque to current was completed, torque inverse model is obtained which has large effects on the control performance of Instantaneous torque control, finally combining the torque sharing function (TSF) to constitute the torque control system of SRM. Simulation and experiment are proved: the system has good dynamic performance, and it can quickly and accurately track the expected braking torque.

Torque Ripple Minimization Scheme Using Torque Sharing Function Based Fuzzy Logic Control for a Switched Reluctance Motor

This paper presents an advanced torque ripple minimization method of a switched reluctance motor (SRM) using torque sharing function (TSF). Generally, TSF is applied into the torque control. However, the conventional TSF cannot follow the expected torque well because of the nonlinear characteristics of the SRM. Moreover, the tail current that is generated at a high speed motor drive makes unexpected torque ripples. The proposed method combined TSF with fuzzy logic control (FLC). The advantage of this method is that the torque can be controlled unity at any conditions. In addition, the controller can track the torque under the condition of the wrong TSF. The effectiveness of the proposed algorithm is verified by the simulations and experiments.

Smooth Torque Speed Characteristic of Switched Reluctance Motors

The torque ripple of switched reluctance motors (SRMs) is the main disadvantage that limits the industrial application of these motors. Although several methods for smooth-toque operation (STO) have been proposed, STO works well only within a certain torque and speed range because of the constraints of the supply voltage and peak current. Based on previous work that sought to expand the STO range, a scheme is developed in this study to determine the maximum smooth torque range at each speed. The relationship between the maximum smooth torque and speed is defined as the smooth torque speed characteristics (STSC), a concept similar to torque speed characteristics (TSC). STSC can be utilized to evaluate torque utilization by comparing it with TSC. Thus, the concept benefits the special design of SRMs, especially for the generation of smooth torque. Furthermore, the torque sharing function (TSF) derived from the proposed method can be applied to STO, which produces a higher smooth torque over a wider speed range in contrast to four typical TSFs. TSimulation and experimental results verify the proposed method.

Minimization of Torque-Ripple in Switched Reluctance Motors Over Wide Speed Range

Torque pulsation mechanism and highly nonlinear magnetic characterization of switched reluctance motors(SRM) lead to unfavorable torque ripple and limit the variety of applications in industry. In this paper, a modification method proposed for torque ripple minimization of SRM based on conventional torque sharing functions(TSF) to improve maximum speed of torque ripple-free operation considering converter limitations. Due to increasing phase inductance in outgoing phase during the commutation region, reference current tracking can be deteriorated especially when the speed increased. Moreover, phase torque production in incoming phase may not be reached to the reference value near the turn-on angle in which the incremental inductance would be dramatically decreased. Torque error for outgoing phase can cause increasing the resultant motor torque while it would be negative for incoming phase and yields reducing the motor torque. In this paper, a modification method is proposed in which phase torque tracking error for each phase under the commutation added to the other phase so that the resultant torque remained in constant level. This yields to extend constant torque region and reduce peak phase current when the speed increased. Simulation and experimental results for four phase 4 KW, 8/6 SRM validate the effectiveness of the proposed scheme.

Self-Tuning Fuzzy Controller Design for a Switched Reluctance Motor Drive System

This study adopts the fuzzy control theory to design a self-tuning fuzzy controller (STFC), which allows adjustment to overcome the controller design difficulty caused by switched reluctance motor (SRM) nonlinearity. Based on the torque sharing function (TSF), the proposed STFC was implanted into an SRM direct torque control (DTC) drive system to develop a system with superior speed and electromagnetic torque dynamic responses. In addition, the control strategy possessed excellent electromagnetic torque response, and effectively improved the dynamic response of the system. Keywords: fuzzy control theory, switched reluctance motor (SRM), torque sharing strategy.

A Simple Negative Torque Compensation Scheme for a High Speed Switched Reluctance Motor

SRMs(Switched Reluctance Motors) are much interested in high speed applications due to the mechanical robustness, simple structure and high efficiency. In spite of many advantages of SRMs, a higher torque ripple discourages the adoption of SRMs in a high speed application. This paper presents a simple negative torque of tail current compensation scheme using a modified TSF(Torque Sharing Function) for the high speed SRMs. Because of the short commutation in the high speed region, the negative torque from the tail current makes the high torque ripple. In order to reduce and compensate the negative torque from tail current, the proposed control scheme produces an additional compensating torque with a reference torque in the active phase winding. And the compensating value is dependent on the tail current of the inactive phase winding. Furthermore, the switching signals of the outgoing phase are fully turned off to restrict the extended tail current, and the torque error of the outgoing phase is compensated by the incoming phase. The proposed modified TSF control scheme is verified by the computer simulations with 30,000[rpm] high speed 4/2 SRM. The simulation and experimental results show the effectiveness of the proposed control scheme.

Minimization of Torque Ripple and Copper Losses in Switched Reluctance Drive

This paper presents a control technique for torque-ripple minimization in the switched reluctance motor (SRM) drive, based on a torque-sharing function (TSF) concept. In the proposed method, the reference torque is directly translated into the reference current waveform using the analytical expression. Optimization criteria of a TSF that are concerned with secondary objectives, such as minimization of copper losses or maximization of drive performance, are described. In addition, a novel family of TSFs is introduced. An optimal TSF can be easily extracted from the proposed family to satisfy one of the secondary objectives or to create balance between more of them. Control performances of the two extracted TSFs and the two optimized conventional (linear and sinusoidal) TSFs are compared. These four TSFs keep the copper losses to nearly the theoretical minimum. Each of them provides approximately the same operation efficiency of the considered three-phase 6/4 SRM drive. However, due to extension of the commutation angle between adjacent phases, TSFs from the proposed family provide better torque-speed characteristics. Moreover, one of them expands the possible speed range of torque-ripple-free drive operation, and another one, which provides the best torque-speed characteristics, reduces the peak phase current.

A Study on the Control Method for Torque Ripple Reduction during Phase Commutation

In this paper, an advanced torque control scheme of Switched Reluctance Motor(SRM) using modified non-linear logical TSF (Torque Sharing Function) with PWM is presented. In the proposed control scheme, a simple calculation of PWM duty ratio and switching rules from DITC(Direct Instantaneous Torque Control) can reduce the torque ripple with fixed switching frequency. The proposed control scheme is verified by the computer simulations and experimental results.