Parallel hybrid linear-switched power amplifier and control strategy for machine emulation

Abstract

Machine Emulation (ME) is one of the main applications of Power-Hardware-In-the-Loop (PHIL) simulations. The performance and cost of an ME system depends heavily on the type of Power Amplifier (PA) it employs. Linear Power Amplifiers (LPAs) produce ripple free outputs and offer high bandwidths but are costly. Switch-Mode Power Amplifiers (SMPAs) are more affordable, with higher power density, but produce switching harmonics that yield distorted waveforms and reduce the closed loop bandwidths. In order to get a compromise between these technologies for ME, this paper proposes an ME based on a Hybrid Power Amplifier (HPA), with parallel LPA and SMPA. A new current control scheme for the HPA, suitable for voltage-in current-out machine models, is proposed to reduce the required current rating, and thus the cost, of the LPA. A design procedure for the control scheme of the HPA is presented and illustrated for the emulation of a direct-online start-up of an Induction Machine (IM). Simulation results evaluate and compare systems built exclusively with SMPA or LPA for ME. Experimental results are shown to validate the proposed control scheme for the parallel HPA in ME systems. Besides, the impact of the bandwidths of the control loops of the LPA and SMPA and the switching frequency of the SMPA, on the accuracy of the ME system and on the current requirement of the LPA are highlighted.