Control design for a very low-frequency high-voltage test system

In recent two decades the application of high voltage test systems using the concept of very low frequency is more and more accepted by industries. This contribution deals with the control design for a novel high voltage test system generating a true sinus test voltage of 85 kV (RMS) at 0.1 Hz based on a zero-voltage switched LCC-resonant converter and a 3-stage Cockcroft Walton voltage multiplier rectifier. The cascade control strategy using an output current observer enables substitution of voluminous and costly high-voltage current sensors. The true sinus test generator was implemented and verified by experimental tests, affirming the optimum choice of the topology for the demanding requirements and indicating a better THD-quality of the test voltage as compared to previous solutions.