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Step motors are receiving wide attention in industrial applications which require high performance. They are used in open loop control of position and translation motion but have poor performance. This paper discusses open loop control using field orientation of step motors to improve its dynamic performance. A simplified mathematical model of two phase variable reluctance (VR) stepper motor is introduced. Advance turn-on and advance turn-off is presented to obtain the optimal control angle in order to decrease phase current rise time, produce maximum torque per ampere, elimination of negative torque region, reducing motor losses, and increasing motor efficiency. A drive circuit for two phase VR step motor is implemented. The simulation results of stator current are compared to the experimental results.

Numerous studies had been made to improve the switched reluctance motor operation depend on the modification of the machine design, proposing the converter designs and/or applying a suitable control method. This paper introduces the field orientation control method for that motor using a simple and very efficient DC-DC converter topology. This control method is presented by two techniques; first technique is the advance of the turn-on switching angle and the other technique is the retard/delay of the turn-off switching angle. Instantaneous and average motor characteristics are obtained using Matlab/Simulink software package. Comparison between the simulation results presented using two converter types. A precise speed and torque control are obtained. The average total torque per current is maximized. Keyword:Advance turn-on Angle control FOC Retard/Delay turn-off SRM Copyright © 2017 Institute of Advanced Engineering and Science.All rights reserved. Corresponding Author:Emad S. Abdel-Aliem, Department of Electrical Engineering, Shoubra Faculty of Engineering, Benha University, 108 Shoubra Street, Cairo, Postal code: 11241, Egypt. Email: emad.sami@feng.bu.edu.eg INTRODUCTIONThe switched reluctance motor (SRM) is being used in various number of applications because of it has many merits over the other motor types. The SRM has a simple and robust construction. However, it basically generates large torque ripples compared with the other types of brushless DC motors. For that reason, to improve its operation and reducing the torque ripples, a development in its converter construction and/or a best control strategy is usedOne of the main approaches of the research in SRM drives is the converter design. The operation and the cost of SRM drive system is mainly affected by the performance of the motor converter [7,8]. Many converter topologies have emerged through continued researches by reducing the number of switches in the converter and also getting faster switch commutation time [3,[9][10]. This leads to a simple drive system and enables significant energy savings [11]-[14]. A high performance SRM drive is mainly characterized by minimization of the torque ripples and maximization of the motor efficiency and the torque per current [6], [15]. This criterion can be realized by optimizing the control parameters of the motor such as supply voltage, current level, turn-on, turn-off and the dwell angle [16]-[20].A closed loop control with a simple DC-DC converter construction [21] for a 3-phase 6/4 SRM with Field Orientation Control (FOC) (known as some times; the switching angle control) method is introduced in this research to get the most efficient operation over the entire range operation of the SRM.The complete block control diagram for a 3-ph 6/4 SRM drive system using FOC is shown in Figure 1. A standard DC source of 220V is used with the 3-ph DC-DC converter. The speed sensor is an integral part of the SRM drive system, may be optical encoders, resolver or hall-effect sensor [22]-[24] is mounted on the motor shaft...