Application Considerations for PWM Inverter-fed Low-voltage Induction Motors

| Introduction | Power Basics | PWM Controller Basics | PWM vs. Sine Wave Power | Conclusions | Acknowledgements | References |

Introduction

PWM inverter-fed induction motor drives are being used in greater numbers throughout a wide variety of industrial and commercial applications. PWM inverters provide many benefits to their users including improved control of processes, reduced energy consumption, and expanded diagnostics. Despite these benefits, PWM inverters should be applied with special consideration for low-voltage induction motor operation. The power supplied to the motor by a PWM inverter has some adverse effects which this paper will describe. These effects include increased heating, high peak voltages, and increased audible noise.

Many manufacturers of PWM inverters promote to the marketplace that their PWM inverters can successfully operate any low-voltage induction motor. This is often not true. There are many PWM inverter-motor applications which require long periods of low speed operation, wide constant torque speed range, and high starting torque all of which could cause the motor additional stress resulting in a possible unsuccessful application.

The intent of this paper is to highlight some of the known, possible adverse effects PWM inverters cause low voltage induction motors and the impact these effects have on the given application. This paper is written for those that are applying PWM inverter-fed low voltage induction motors, not those designing them.

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Note: This material is not intended to provide operational instructions.

Appropriate Reliance Industrial Company instruction manuals
and precautions should be studied prior to installation, operation, or
maintenance of equipment.