An Active Damping Technique for PI and Predictive Controllers of an Interlinking Converter in an Islanded Hybrid Microgrid

Abstract

This article highlights a voltage instability when the bidirectional interlinking converter (BIC) of a hybrid ac-dc microgrid operates as a constant power load (CPL). The instability is attributed to the impedance interactions seen at the dc port of the BIC. The BIC is operated with two different controllers, viz., a PI controller and a model predictive controller (MPC). In order to avert the instability, prohibiting impedance interactions is proposed as a design objective while determining the bandwidth of the PI controller. However, since a flexible control over bandwidth is not available with MPC, an active damping technique is proposed to address the instability. The proposed technique works equally well for the PI controllers with fixed or predetermined bandwidths. An important feature of the proposed technique is that it does not interfere with the original objectives of the controllers, once the instability is addressed. The technique comprises only one tuning factor, which does not depend on the BIC's internal parameters. As a result, it can easily be implemented as a general stabilizing scheme in any BIC. The efficacy of the proposed technique is verified through simulations, frequency-domain impedance analyses as well as experiments on a laboratory prototype of the BIC.