A Novel Control Strategy for Subsynchronous Resonance Mitigation Using 11 kV VFD-Based Auxiliary Power Plant Loads

This paper proposes a novel damping controller for subsynchronous resonance (SSR) mitigation using existing 11-kV variable frequency drive interfaced auxiliary power plant loads. The input of the proposed auxiliary damping controller is the turbine output power (P-{t}). This is a standard signal that is monitored in power plant control rooms and is available locally without the need for additional measurement and/or communication infrastructure. The auxiliary damping controller (ADC) adds an auxiliary speed signal to the existing speed reference in the closed-loop motor drive control in response to any torsional range oscillations seen in P-{t}, via a feedback compensator. The ADC extracts damping by exploiting SSR load interactions and is tuned using a residue-based pole placement technique. The ADC performance is evaluated for both torsional interaction and torque amplification types of SSR in the IEEE First Benchmark and IEEE 68-bus networks. The results show that the ADC is effective in providing positive damping to mitigate unstable SSR oscillations under a range of operating conditions. The proposed solution is a simple yet effective means of providing local control of SSR with minimal additional cost.