I. M. Alsofyani

Simple Flux Regulation for Improving State Estimation at Very Low and Zero Speed of a Speed Sensorless Direct Torque Control of an Induction Motor

This paper presents a simple flux regulation for a direct torque control (DTC) of an induction motor (IM) to improve speed and torque estimations at low- and zero-speed regions. To accomplish this, a constant switching frequency controller (CSFC) is used to replace the three-level hysteresis torque comparator of a DTC IM. The DTC of IM utilizing CSFC (DTC-CSFC) retains the simple structure of a lookup table-based DTC drive. With DTC-CSFC, constant switching frequency is maintained, and at the same, the flux droop problem that normally occurs in DTC with the hysteresis controller (DTC-HC) at low speed is solved; subsequently, the stator flux and torque estimations at low speed are also improved. In the proposed system, the speed feedback for the closed-loop speed control is estimated using an extended Kalman filter, which requires heavy real-time computation. However, due to the simple structure of DTC-CSFC, small sampling time, hence large control bandwidth is possible. The performances of the speed sensorless DTC-HC and DTC-CSFC are compared experimentally under different operating conditions. With the improved stator flux regulation, experimental results of the DTC-CSFC showed a significant improvement in speed and torque estimations at very low and zero-frequency operations.

Using NSGA II multiobjective genetic algorithm for EKF-based estimation of speed and electrical torque in AC induction machines

High-performance AC drives require accurate speed and torque estimations to provide a proper system operation. The selection and quality of extended Kaiman fitter (EKF) covariance elements have a considerable bearing on the effectiveness of motor drive. Many EKF-based optimization techniques involve only a single objective for the optimal estimation of speed without giving concern to the torque. This paper presents a new methodology for the selection of EKF filters that uses non-dominated sorting genetic algorithm-II (NSGA-II) developed for filter element selection in order to investigate the concurrent optimization of speed and torque. The proposed optimizing technique for EKF-based estimation scheme is used in the combination with the sensorless direct torque control of induction motor. The multi-optimal based-EKF is tested with three regions of Pareto front curve.

Lookup-Table-Based DTC of Induction Machines With Improved Flux Regulation and Extended Kalman Filter State Estimator at Low-Speed Operation

Direct torque control (DTC) based on lookup table is known to have poor flux regulation at low speed that can cause a significant deterioration in the speed estimation of a sensorless drive. In this paper, stator flux regulation at low speed is improved under no load by replacing the hysteresis torque comparator with constant switching frequency controller, without any changes to the conventional lookup table; hence, the simple structure of DTC is maintained. In order to reduce the sampling time and hence improve the estimation process at very low speed, a simple fifth-order extended Kalman filter (EKF) is used in this paper. The fast execution time helps the linearization process of the EKF; hence, results in an improvement in its performance. Simulations and experimental results of the proposed sensorless drive system with the EKF estimator proves excellent flux regulation, and good speed robustness and stability at very low speed.

Modeling and RFOC of faulty three-phase IM using Extended Kalman Filter for rotor speed estimation

This research discusses d-q model and Rotor Flux-Oriented Control (RFOC) technique for faulty three-phase Induction Motor (three-phase IM when one of the stator phases is opened). In the controlling technique, two transformation matrixes are applied to the equations of faulty three-phase IM. As a result, the equations of faulty three-phase IM become similar to the balanced IM. Therefore, by employing some modifications in the conventional block diagram of the balanced IM, faulty motor control is possible. Additionally, for high performance vector control of the faulty IM, an Extended Kalman Filter (EKF) is used for motor speed estimation. Simulation results demonstrate the validity and applicability of this technique to improve performance of the faulty IM.

Improved EKF-based direct torque control at the start-up using constant switching frequency

A sensorless extended Kalman filter (EKF) based direct torque control (DTC) with the use of a constant switching frequency control (CSFC) of induction machine is proposed in this research work. This paper is meant to investigate the dynamic performance for DTC-CSFC and DTC with a hysteresis torque controller by applying different speed step changes from three different low speed operations. The dynamic performance results show that the sensorless EKF-based DTC-CSFC is superior to the conventional EKF-based DTC when reference speed change is applied from 0 to 59 rad/s. Additionally, improvement in the reduction of torque ripples is achieved for all step changes of speed. The effectiveness of the proposed EKF-based DTC-CSFC is confirmed by experimental validation.

Rule-based supervisory control of split-parallel hybrid electric vehicle

Hybrid electric vehicles (HEVs) have been a hot topic of research over recent years due to their features whereby make them a feasible solution to tackle concerns regarding to global warming. HEVs powertrain control plays an important role to accomplish control objectives such as low emission and good vehicle performance. This paper presents a system-level simulation and rule-based supervisory control strategy of a Split-Parallel Hybrid electric vehicle (SPHEV) which can be regarded as Parallel-HEV powertrain family. Advance vehicle Simulator (ADVISOR) is used to determine the sizing and ratings of key components of SPHEV driveline to satisfy specific performance constraints. Then physical model of the vehicle of interest is developed and simulated in Matlab/Simscape environment. Subsequently, simulation results are presented and discussed in terms of their effectiveness and accuracy.

Improving start-up operation of sensorless DTC of induction machines using simple flux regulation

This paper presents a direct torque control drive system utilizing constant switching frequency controller (CSFC) with EKF based speed estimation. By employing CSFC instead of the conventional hysteresis controller, the torque ripple is reduced and constant switching frequency is achieved, and more importantly, the simple structure of DTC without any modification to the look-up table is maintained. The main contribution to the use of CSFC is on the improvement of speed estimation at start-up and low speed operations. This is accomplished due to the improvement in the stator flux regulation. The experimental results of the proposed system showed a significant improvement in speed and torque estimations at very low and zero speed and are comparable to a more complex implementation of DTC.

A simple approach for designing a PID controller for an experimental air blower system

This paper focuses on the identification and control of an air blower system PT-326. Modelling of the PT-326 system is required before designing the controller. Hence, it is estimated by using system identification toolbox available in MATLAB. The process of identification began with the collection of input and output data from an experiment. The collected data is used for model estimation based on the selection of auto-regressive with exogenous ARX model structure of the PT-326 system. Based on the input and output data of the system, best fit criterion and correlation analysis of the residual are analysed to determine the adequate parameters of ARX model representing the PT-326 system. To achieve a good performance for the air blower system, right selection of the PID controller parameters is essential. This paper also presents a simple approach for designing a PID controller using minimum square error tuning scheme and compares it with a conventional Ziegler-tuning method for the identified model via simulation and experiment. The results obtained from both tuning methods show that the outputs of the system with the PID controller in simulation and experiment are almost similar.

Sliding mode observer-based MRAS for direct torque control of induction motor

This paper proposes a sensorless sliding mode observer based model reference adaptive system applied to a direct torque control of the induction motor drive. The reference model is a sensorless sliding mode observer and the adaptive model is a typical current model. The proposed scheme provides speed and rotor flux estimations with the derivative of rotor flux set as the state of the adaptive mechanism. The simulation results show the effectiveness of the proposed observer compared with the conventional model reference adaptive system.

An improved flux regulation using a controlled hysteresis toque band for DTC of induction machines

This paper presents a dynamic hysteresis toque band strategy for improving flux regulation at low and zero speeds in a direct torque control (DTC)-look-up-table-based induction machine. The hysteresis torque band is controlled based on speed variation to solve the stator flux magnitude droops which normally occur at low frequency. The main benefit of the proposed approach is its simplicity, since it only requires a minor modification to the hysteresis band value and does not require an alteration on the lookup table. The simulation results of the proposed system showed a significant enhancement in speed and torque estimations at very low and zero speed and at the same time removes the problem of flux droop in the conventional hysteresis based DTC.