A modified static Kraemer system operated as a variable speed induction generator

A static Kraemer system with a converter extended by a controllable freewheeling circuit is described. Due to the freewheeling circuit, the converter can be operated with cos φ₁=1 or in an overexcited range. Two different control schemes for the freewheeling circuit are presented, a simple control scheme, permitting minimisation of fundamental reactive power and a control scheme, employing pulse pattern techniques to minimise fundamental reactive power and harmonic distortion. To produce near sinusoidal inverter output currents, a filter was designed to enhance the performance of the freewheeling circuit with the pulse pattern control scheme. Experimental results obtained from a small test drive (11 kW) are presented