Steven C. Peak

Transistorized PWM Inverter-Induction Motor Drive System

The development of a transistorized pulsewidth modulated (PWM) inverter-induction motor traction drive system is described. A vehicle performance analysis was performed to establish the vehicle tractive effort-speed requirements. These requirements were then converted into a set of inverter and motor specifications. The inverter was a transistorized three-phase bridge using General Electric power Darlington transistors. The description of the design and development of this inverter is the principal object. The high-speed induction motor is a design which is optimized for use with an inverter power source. The primary feedback control is a torque angle control with voltage and torque outer loop controls. A current-controlled PWM technique is used to control the motor voltage. The drive has a constant torque output with PWM operation to base motor speed and a constant horsepower output with square wave operation to maximum speed. The drive system was dynamometer tested, and the results are presented.

Selection and Design of an Inverter-Driven Induction Motor for a Traction Drive System

The considerations and trade-offs involved in the selection and design of an inverter-driven induction motor for a traction drive system are described. The inverter is transistorized and operates in a pulsewidth modulation (PWM) mode in the constant torque region and in a six-step square wave mode in the constant power region. Drive system requirements establish the 50-hp peak motor rating and the motor voltage. The aspects of an induction motor designed to be driven from an inverter are presented. These include the number of poles and rotor bar shape of the motor. Expressions relating the motor performance to motor design parameters are derived. The aspects of the inverter power source are presented. These include the constant volt-ampere characteristics of the inverter and the relationship of motor inductance to the inverter design. A final motor design is reached, Contrary to previous expectations, the best design is a two-pole motor.

A Study of System Losses in a Transistorized Inverter-Induction Motor Drive System

A study is described of the system losses in a transistorized pulsewidth modulated (PWM) inverter and induction motor in a traction drive system and the development of a strategy for minimizing them. The losses include inverter losses, conventional fundamental frequency motor losses, and motor harmonic losses. The losses in both PWM and six-step square wave (SSSW) inverter operation are studied. The loss models are introduced into a motor performance analysis program allowing the computation of the drive system performance over the entire speedtorque range. The study shows that a strategy for minimizing drive system losses is a function of torque. The air gap flux density should be held at its maximum level until the torque requirement is reduced to a low value, and then the air gap flux level is reduced.