Alberto Abbondanti

Static Exciters for Induction Generators

The utilization of the squirrel cage induction motor as an autonomous induction generator is briefly reviewed. In view of potential new applications, the discussion focuses on a simple exciter scheme based on using a static reactive power generator implemented with fixed capacitors and thyristor controlled inductors. The feasibility of the proposed scheme with naturally commutated thyristors is verified by measurements on a test setup employing a standard 15-hp induction motor.

Variable Speed induction Motor Drives Use Electronic Slip Calculator Based on Motor Voltages and Currents

In certain types of adjustable frequency induction motor drives, optimal control of the motor can be best implemented by using information on the motor slip frequency. Unfortunately, this generally requires the use of an electromechanical speed transducer coupled to the shaft. The presence of this transducer spoils the general characteristics of ruggedness and mechanical simplicity typical of an ac drive. This paper discusses an improved method of obtaining the slip information without the use of rotary transducers of any kind. By sensing the electrical quantities applied to the motor (voltages, currents, and phases) and by performing simple signal processing operations on the sensed quantities, an analog signal proportional to the slip level is derived and used in motor control functions.

Pulsewidth Modulated Inverter Motor Drives with Improved Modulation

The performance of inverter drives, which use the pulsewidth modulated (PWM) technique to control motor applied voltage and frequency, are critically influenced by the choice of the modulation policy used in the control circuits. This paper deals with practical inverter drives for squirrel cage induction motors and presents some basic considerations on modulation requirements. The advantages and limitations of popular modulation methods are discussed, and an improved modulation scheme, which allows us to extend the practical speed range of PWM ac drives, is presented.

A Criterion for Performance Comparison Between High Power Inverter Circuits

The efficiency and economics of inverter circuits with high power ratings tend to be determined largely by the size of the passive elements required in the commutation circuit and, to a lesser extent, by the combined current-voltage requirements of the semiconductors. In order to facilitate comparative evaluation of inverter circuits of different configurations which are all candidates for the same application, an analytical expression representative of the total kVA rating of the passive components can be derived for each circuit from the data defining the application. Combining this with a similar expression reflecting the volt-ampere requirements of the active devices, an overall circuit figure of merit can be generated. In certain paper studies, a comparison between such figures of merit can provide a useful, if not infallible, tool for appraising several candidate circuits.