A Position Stepping Method for Predicting Performances of Switched Reluctance Motor Drives

This paper presents a novel numerical method, which will be referred as the position stepping method (PSM), to predict the performances of switched reluctance motor (SRM) drives. The 2D bicubic spline is employed to generate the finite rectangular elements. The 2D bilinear spline is used to model the nonlinear magnetic characteristics in SRMs. Consequently, the conventional nonlinear first-order differential voltage equation for describing the performances of SRM drives can be simplified into an analytical expression in terms of the current with respect to the rotor position. Furthermore, the position stepping algorithm is developed according to the boundary and continuity conditions, to accurately and rapidly compute the current from the proposed current expression. Simulated and measured current waveforms are reported to validate the developed PSM. The CPU execution time required by the PSM compares very favorably with that of the analytical method. Overall, this paper provides an accurate and speedy approach to predict the currents and torques of SRM drives.     

A hybrid observer for high performance brushless DC motor drives

Brushless DC motor drive systems are used in a wide variety of applications. These drives may be classified as being one of two types: sinusoidal drives in which there are no low-frequency harmonics in the current waveforms and no low-frequency torque ripple; and nonsinusoidal drives in which there is considerable low-frequency harmonic content, both in the current and torque waveforms. Although sinusoidal drives feature superior performance, they are generally more expensive since rotor position must be sensed on a continuous basis, thus requiring an optical encoder or a resolver, whereas relatively inexpensive Hall-effect sensors may be used for nonsinusoidal drives. In this paper, a straightforward hybrid observer is set forth which enables rotor position to be estimated on a continuous basis using information available from the Hall-effect sensors. The proposed observer is experimentally shown to perform just as well as an optical encoder for steady-state conditions and nearly as well as the optical encoder during transient conditions. The proposed scheme provides designers with a new option for rotor position sensing, one which offers an excellent compromise between accuracy and expense     

Combined Flux Observer With Signal Injection Enhancement for Wide Speed Range Sensorless Direct Torque Control of IPMSM Drives

This paper proposes a motion-sensorless control system using direct torque control with space vector modulation for interior permanent magnet synchronous motor (IPMSM) drives, for wide speed range operation, including standstill. A novel stator flux observer with variable structure uses a combined voltage-current model with PI compensator for low-speed operations. As speed increases, the observer switches gradually to a PI compensated closed-loop voltage model, which is solely used at high speeds. High-frequency rotating-voltage injection with a single D-module bandpass vector filter and a phase-locked loop state observer with a new synchronization procedure are used to estimate the rotor position, which is needed only by the current model in stator flux observer at low speeds. A new rotor speed estimator for the whole speed-loop range, based on the stator flux speed estimation with a new dynamic correction depending on estimated torque, is proposed and tested. Extensive simulation results and significant experimental results provided good performance for the proposed IPMSM sensorless system in more than 1:1000 speed range, under full-load operation, from very low speeds (1 r/min experimental) up to rated speed.     

Adaptive self-tuning MTPA vector controller for IPMSM drive system

This paper presents an adaptive self-tuning maximum torque per ampere (MTPA) vector controller for an interior permanent-magnet synchronous motor (IPMSM) drive system. The control scheme consists of a synchronous frame decoupling current controller, MTPA torque controller, and adaptive parameter estimator. The estimator is applied to the q-axis current dynamics as the d-axis inductance can be assumed to be constant without loss of accuracy. Since the q-axis current dynamics is being disturbed by the magnet's back-EMF voltage, the proposed estimator is combined with a robust active-state decoupling scheme to ensure unbiased parameter estimate. The robust decoupling scheme is realized by estimating the magnet's flux linkage by a simple adaptation algorithm based on the steepest descent method. The system's model is greatly simplified when the robust decoupling scheme is combined with the q-axis current dynamics. Relying on the simplified model, a natural adaptive observer is used to estimate the q-axis current. Unknown motor parameters are estimated by minimizing the state estimation error using an iterative gradient algorithm offered by the affine projection. The estimated parameters are used for the self-tuning control. Experimental results are presented to demonstrate the validity and usefulness of the online parameter estimation and control loop tuning technique.     

Performance optimization in switched reluctance motor drives with online commutation angle control

The problem of performance optimization in current controlled switched reluctance motor (SRM) drives is investigated. Two controllers are proposed that determine the optimal turn-on and turn-off angles, respectively, for improving motor efficiency and torque ripple. The suggested controllers are simple, do not affect the complexity of the drive, and are easily implemented since the knowledge of torque-angle-current characteristics or magnetization curves is not required. The proposed control scheme is demonstrated on a prototype experimental system.     

A new sliding mode position controller with adaptive load torqueestimator for an induction motor

A new sliding mode control algorithm with an adaptive load torque estimator is presented to control the position of the induction motor in this paper. First, the rotor flux is estimated with the simplified rotor flux observer in the rotor reference frame and the feedback linearization theory is used to decouple the rotor position and the rotor flux amplitude. Then, a new sliding mode position controller with an adaptive load torque estimator is designed to control the position of the induction motor such that the chattering effects associated with the classical sliding mode position controller can be eliminated. Stability analysis is carried out using the Lyapunov stability theorem. Experimental results are presented to confirm the characteristics of the proposed approach. The good position tracking and load regulating responses can be obtained by the proposed position controller     

非对称中点钳位型逆变电路的开关磁阻电机模型预测直接转矩控制方法

针对开关磁阻电机(SRM)转矩脉动过大的问题,提出一种非对称中点钳位型逆变电路的模型预测直接转矩控制方法,该控制方法基于开关磁阻电机的电感特性及转矩产生原理对扇区进行重新划分,对非对称中点钳位型逆变电路的基本工作模式进行分析并选取基本电压状态,根据直接转矩控制原理及扇区实际意义制定新型矢量选择方案,减少每个控制周期中的预测状态数;在每个采样时刻求解基于离散时间非线性预测模型的最优控制问题来抑制转矩脉动。在Matlab/Simulink环境下搭建电机仿真模型,与直接转矩控制对比仿真结果表明,该控制方法对开关磁阻电机具有更好的调节效果.能有效抑制转矩脉动。     

Instantaneous Shaft Radial Force Control with Sinusoidal Excitations for Switched Reluctance Motors

Unbalanced radial forces acting on a rotor shaft exist in motor applications where the external load is not balanced or when the rotor is not centered causing a nonuniform air gap. These forces are undesirable as they cause motor vibrations. In view of its special structure, the shaft radial force and the torque of a three-phase 12/8 pole switched reluctance motor (SRM) can be separately controlled by proper pole current selection in the energized phase. Therefore, radial forces can be produced intentionally to cancel the existing radial force produced by rotor eccentricity and the unbalanced load inertia. The motor vibrations are thereby reduced. In this paper, a sinusoidal current excitation scheme is proposed for the torque and radial force control of a 12/8 pole SRM. When controlled with the selected sinusoidal currents, the SRM can simultaneously produce the desired shaft radial force in any rotational plane direction and the required rotational torque. As all pole currents are individually controlled, a more sophisticated phase commutation strategy is also proposed that provides smoother torques and radial force ripples.     

Electromagnetic modeling and control of switched reluctance motor using finite elements

This paper considered the implementation of a current control method for switched reluctance motors (SRMs) and presented a novel approach to the accurate online modeling of a three phase 6/4 SRM drive. A three phase 6/4 SRM is given theoretical calculation of inductance of the SRM model. The SRM was then tested in a Matlab/Simulink environment and numerically analyzed by using nonlinear 2D look-up tables created from its calculated flux linkage and static torque data. The simulation studied the hysteresis and voltage control strategies. The ideal waveform of stator current under the voltage-current condition and improved shape of rotor were proposed.     

Development of a Switched-Reluctance Motor Drive With PFC Front End

In this paper, the development and control for a switched-reluctance motor (SRM) drive with front-end switch-mode rectifier (SMR) are presented, and good motor driving performance and line drawn power quality are obtained. In the SMR, the dc-link voltage spikes caused by periodic pulse-type motor currents are eliminated using high-frequency small capacitor. And the bulky capacitor is designed according to the specified double-frequency voltage ripple. Then, the robust voltage and current schemes are developed to yield excellent and robust SMR control performance. Having well-regulated and adjustable dc-link voltage source, the performance enhancements of the SRM in vibration as well as current and speed dynamic responses are performed and evaluated. The robust current and speed control schemes are designed to yield improved driving performance. In addition to voltage boosting, the commutation advanced shift is proposed to further the improve current and speed dynamic responses, the torque-generating capability, and the vibration of SRM.      

Iterative learning-based high-performance current controller for switched reluctance motors

Switched reluctance motors (SRMs) are being considered for variable speed drive applications due to their simple construction and fault-tolerant power-electronic converter configuration. However, inherent torque ripple and the consequent vibration and acoustic noise act against their cause. Most researchers have proposed a cascaded torque control structure for its well-known advantages. In a cascaded control structure, accurate torque control requires accurate current tracking by the inner current controller. As SRM operates in magnetic saturation, the system is highly nonlinear from the control point of view. Developing an accurate current tracking controller for such a nonlinear system is a big challenge. Additionally, the controller should be robust to model inaccuracy, as SRM modeling is very tedious and prone to error. In this paper, we have reviewed various current controllers reported in the literature and discussed their merits and demerits. Subsequently, we have proposed and implemented a novel high-performance current controller based on iterative learning, which shows improved current tracking without the need for an accurate model. Experimental results provided for a 1-hp, 8/6-pole SRM, demonstrate the effectiveness of our proposed scheme.     

Simulation and experimental study of interharmonic performance of a Cycloconverter-FedSynchronous motor drive

High-power synchronous motor drives are usually fed from naturally commutated cycloconverters. The output voltage of the cycloconverter contains interharmonics/subharmonics which affect the power quality and restrict the allowable frequency range. Further, a practical circulating current-free cycloconverter usually gives rise to stator current discontinuities. The present paper deals with a simulation method to study the performance of a cycloconverter-fed synchronous motor drive in the presence of interharmonics/subharmonics taking into account the discontinuities in the output current as well as the effect of ripple in the output current on the input current of the cycloconverter. Interharmonics in output phase voltage, output phase current, input supply current, and the field current are estimated and verified with experimental results on a laboratory prototype. The significant oscillating torque components due to these interharmonics are identified in a typical case. The simulation results are useful in power quality studies for such drives and in devising methods for suppression of these interharmonics/subharmonics.     

A wavelet transform‐adaptive unscented Kalman filter approach for state of charge estimation of LiFePo4 battery

LiFePo₄ battery is widely used in electric vehicles; however, its flatness and hysteresis of the open‐circuit voltage curve pose a big challenge to precise state of charge (SOC) estimation. The issue is discussed and addressed in this paper. First, a cell model with hysteresis is built to describe real‐time dynamic characteristics of the LiFePo₄ battery. Second, the model parameters and SOC are estimated independently to avoid the possibility of cross interference between them. For model identification, an adaptive unscented Kalman filter (AUKF) algorithm is used to identify the cell parameters as they change slowly. While SOC could change rapidly, wavelet transform AUKF algorithm is put forward to estimate SOC. In the novel algorithm, the measurement noise can be estimated and updated online. Finally, the performance of the proposed method is verified under dynamic current condition. The experimental results show that estimated value based on the proposed method is more accurate than unscented Kalman filter‐based method and AUKF‐based algorithm. Meanwhile, the proposed estimator also has the merits of fast convergence and good robustness against the initialization uncertainty.     

Simulation of switched reluctance motor drives using two-dimensional bicubic spline

In this paper, a novel simulation algorithm of switched reluctance motor drives is presented. With the proposed algorithm the two-dimensional (2-D) bicubic spline interpolation is used to describe the nonlinear magnetic characteristics in switched reluctance motors. The corresponding computational method of 2-D bicubic spline function is described in detail. The simulation results are also compared with and validated by experimental data. Compared with conventional techniques, the presented simulation algorithm is more accurate even though it requires relatively little information on the magnetic characteristics of the motor.     

A step-down chopper-controlled slip energy recovery induction motordrive

The design of a chopper-controlled slip energy recovery drive, also known as a static Kramer drive, demands an exact knowledge of the steady state and dynamic performance of the system over the complete operating range. To accomplish this, a coupled circuit approach is necessary whereby the self and mutual coupling effects, voltage and current harmonics in the machine and voltage and current ripple at different points in the drive system are duly taken into account. Such a model should enable the accurate prediction of all instantaneous current values which leads to accurate prediction of electric torque and harmonics injected into the supply. This paper presents a model to accomplish the above. Mathematical predictions are verified with experimental results     

Intelligent tuning of commutation for maximum torque capability of a switched reluctance motor

Since the winding current and inductance profiles of a switched reluctance motor (SRM) are far from ideal, its torque generating characteristics are quite ambiguous and difficult to optimize quantitatively. In this paper, the intelligent commutation tuning control to improve the torque generating performance of an SRM is presented. First, the effect of the commutation instant on the torque characteristics of a singly excited SRM is observed. Then accordingly, an intelligent method of commutation tuning is developed to improve the torque generating capability. In making the tuning, the minimization of the motor drawn line current is employed as a performance index to equivalently yield maximum torque per ampere (TPA). Finally, the circuit implementation of the developed tuning scheme is carried out. The appropriate commutation makes the motor draw minimum current under any load condition. It follows that the motor conversion efficiency is also improved. In addition, owing to the increased torque generating capability, the tracking and regulation speed control performances are also improved. Some experimental results are provided to demonstrate the effectiveness of the proposed control scheme.     

Predicting the torque of a switched reluctance machine from itsfinite element field solution

The discretization errors that affect the accuracy of the calculated torque of a switched reluctance machine (SRM) from its finite-element solution are examined. A significant improvement in the accuracy of the computed flux density and torque fan be obtained with a reasonably fine mesh in the air gap by selecting properly shaped and uniform triangular elements. The computed torque/angle characteristic will be smooth and accurate when the proper mesh model is preserved as the rotor is rotated. A reasonably accurate value of the torque can be obtained from three different methods: the global virtual work method, the Maxwell stress-tensor method, and the Coulomb virtual work method. The computed torque/angle characteristics of a 4 kW SRM are generated from the three methods. The computed characteristics are checked against the measured torque/angle characteristics     

Calculation of the overlap angle in slip energy recovery drivesusing a d,q/abc model

A closed-form expression for estimating the overlap angle in a slip energy recovery system is presented. The prediction of the overlap angle is important in the case of doubly-fed induction motor drives, because of its influence on speed and torque. A closed-form expression is derived using a hybrid model of the induction motor and a dynamic model of the rotor rectifier. The ripple content of the DC link current and the inverter input voltage are neglected. The results predicted by the closed-form expression are verified experimentally     

A high-performance induction motor drive with on-line rotortime-constant estimation

A high-performance induction motor (IM) speed drive with online adaptive rotor time-constant estimation and a proposed recursive least square (RLS) estimator is introduced in this paper. The estimation of the rotor time-constant is on the basis of the model reference adaptive system (MRAS) theory; and the rotor inertia constant, the damping constant and the disturbed load torque of the IM are estimated by the proposed RLS estimator, which is composed of an RLS estimator and a torque observer. Moreover, an integral proportional (IP) speed controller is designed online according to the estimated rotor parameters; and the observed disturbance torque is fed forward to increase the robustness of the induction motor speed drive     

A simple model for switched reluctance motors

This letter presents a simple model of nonlinear magnetization characteristics of a switched reluctance motor (SRM). The flux linkage is given as a continuous function of phase current and rotor position. This allows a mathematical formula to be found for the instantaneous torque. The model is valuable for computer-aided designs, especially for sizing and initial estimates where accuracy can be traded with time saving. The model was implemented to verify its degree of accuracy. The simulation program has the ability to calculate numerous parameters that can be very useful for quick estimates of the efficiency of a particular SRM drive or for motor selection