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This paper describes the construction and operation of an Electrical Machines Laboratory. The reasons for choosing mobile machines and modular instrumentation for a laboratory are enumerated. The functional and safety features of the electrical distribution system for the laboratory are explained and a description of the laboratory activities is given.

Power MOSFETs are fast-switching devices suitable for high-frequency operations. However, high-speed switching and circuit inductance may cause voltage spikes to appear across the device and damage it. Three types of voltage clamp circuits that can be used with power MOSFETs are considered, and their essential features and characteristics are studied. The different modes of operation with these clamp circuits are discussed, and the design equations to determine these parameters in each clamp circuit are presented. The losses in the three clamp circuits are evaluated and compared. One clamp circuit is shown to offer outstanding advantages and is found to be suitable for high-frequency applications such as PWM inverters.

The application of sliding mode control for improving the dynamic response of a self-controlled synchronous motor (SCSM) based position servo system is presented. Sliding mode control gives fast dynamic response with no overshoot and zero steady-state error. It has the important feature of being highly robust, i.e., insensitive to plant parameter variations and external disturbances. A design procedure is outlined for the sliding mode controller for a servo driving using the self-controlled synchronous motor. A novel scheme for fast torque reversal is proposed and implemented. Digital computer simulation of the overall position control system is carried out using a time domain model in the d-q reference frame. The rigorous simulation of the servo system with sliding mode control shows the existence of limit cycles in the position response with certain type of speed encoder. Experimental results are provided for a 3-hp synchronous motor based servo drive. The sliding mode controller is implemented using a single-board microcomputer which controls a GTO thyristor current source inverter to drive the motor.

Two different pulsewidth modulation (PWM) schemes for current source inverters (CSI) are described. The first one is based on off-line optimization of individual switching angles and requires a microprocessor for implementation and the second one uses a special subharmonic modulation and could be implemented with analog and medium-scale integration (MSI) digital circuits. When CSI's are used in ac motor drives, the optimal PWM pattern depends on the performance criteria being used, which in turn depend on the drive application. In this paper four different performance criteria are considered: 1) current or torque harmonic elimination, 2) current harmonic minimization, 3) speed ripple minimization, and 4) position error minimization. As an example a self-controlled synchronous motor (SCSM) supplied by the PWM CSI is considered. The performance of the CSI-SCSM with the optimal PWM schemes proposed herein are compared with that using a conventional 120° quasi-square wave current.

The study of the speed control of induction motor drive using digital phase-locked loop is discussed. The block diagram and the control circuitry have been outlined. A mathematical model has been developed to predict the system performance. Different types of filters have been considered as part of the feedback control system, and their effects on the overall system behavior have been qualitatively studied. The system is tested using a 5-hp induction motor and an integrating type filter. Excellent speed regulation in the order of 0.002 percent has been obtained.