A hybrid active filter implementation of an overvoltage suppression scheme

In several practical applications actuators are interconnected to a controlled plant through long cables. If the actuator operates at a fast sampling rate (with respect to the propagation delay of the cable) and its impedance cannot be neglected, wave reflections occur and the transmitted pulse are deformed-degrading the control quality. To overcome this problem (passive linear) filters are often introduced to slow the rise time of the pulse or match the load impedance to the impedance of the line. While the first technique clearly induces a below par performance, in the second approach the choice of the filter parameters is far from obvious if the plant is nonlinear or uncertain. In this paper we present multivariable description of the system - exploiting the scattering variables representation of the transmission line, a physical realization of a generical compensator, via hybrid active filter technology and a discrete implementation of three control laws to remove the wave reflection problem - considering the plant purely resistive. The proposed design method is also illustrated with a benchmark AC drives example consisting of a PWM inverter and an induction motor. The compensator is placed on the actuator side, and the only required prior knowledge is the transmission line characteristic impedance and the propagation delay, i.e.. reduction and. for resistive loads, elimination of the pulse distortion is achieved independently of the actuator or the plant characteristics.