Comparative Study of Two Adaptive Resonant Controllers in a Modular Multilevel Converter

Abstract

The paper investigates adaptive proportional-resonant controllers in stationary reference frame used for suppression of second harmonic circulating current in the modular multilevel converter especially for lower controller bandwidth. The current controller is implemented as an IIR filter. The resonant frequency of the controller is altered by changing the coefficient in one method and by changing sampling time in the other. Lower THD and reduction in magnitude of second harmonic component of the circulating current is obtained for controller with coefficient modification than the sample-time variation. Both the methods use PLL for detection of change in frequency.