Input–Output Linearization and PI controllers for AC–AC matrix converter based Dynamic Voltage Restorers with Flywheel Energy Storage: a comparison

Abstract

This paper presents the theoretical development and performance of novel Input–Output Linearization (IOL) AC voltage controllers applied to Dynamic Voltage Restorers (DVR) with Flywheel Energy Storage (FES). IOL performance is compared to decoupled proportional integral (PI) controllers, both relying on a backward Euler predictive current controlled AC–AC matrix converter. The critical load AC decoupled voltage control using IOL or PI is detailed as well as the backward Euler predictive current control. The matrix input and output current tracking control uses a backward Euler predictive current control minimizing a weighted cost functional. The stable backward Euler matrix vector estimation enables the AC–AC matrix to perform as a current tracking converter. Experimental results are obtained using a laboratory level DVR fitted with FES device made from a vertical axis rotating seamless steel hollow cylinder (flywheel) storing kinetic energy. The flywheel is coupled to a Permanent Magnet Synchronous Machine (PMSM) motor/generator, which is driven by the AC–AC matrix converter. The DVR was tested to mitigate voltage sags in isolated neutral critical loads, using IOL and PI controllers. The DVR is able to compensate the critical load voltage without noticeable delays, voltage undershoots or overshoots, overcoming the input/output coupling problem of matrix converters. IOL controller proves to be faster and more aggressive than the PI controller, which is softer introducing less voltage distortion.