Fast, real-time monitoring of AC-alternators under heavy transient loading conditions

This paper describes work towards controlling the output of fast AC-alternators to drive transient loads through intelligent triggering of SCR (thyristor) switches. The project entails the extension of methods and techniques that have been developed for high performance control of relatively small and slow turning industrial machines, to the more demanding regime of AC-machines used for kinetic energy storage and fast AC-servos for military applications. One of these techniques is a rotational transformation, where the (sinusoidal) AC output voltage of an alternator is converted to a DC level representing the instantaneous amplitude. This transformation, also called ´vector rotation´ can be used for very fast observation of the momentary amplitudes of all electrical machine quantities, since no averaging is necessary. Through the use of vector rotations, advanced sensors and real time signal processing it is possible to demonstrate fast real-time monitoring of the energy extraction from a high frequency AC-altemator with a full-bridge SCR converter. A low-voltage DC machine was selected as the load for the system, which closely resembles the transient impedance of an electric launcher.