Effect of power measurement filter properties on CERTS microgrid control performance

In order to ensure resilient and high power quality microgrid operation, P-f and Q-V microgrid droop control algorithms rely on the calculation of active and reactive power outputs based on locally-measured voltage and current. A low-pass filter (LPF) on the calculated power signal is often incorporated by design into the droop controller, but the complete effect of the LPF on microgrid dynamics has not been adequately studied in the literature. This paper analytically and experimentally investigates the impact of the power measurement LPF bandwidth on several important aspects of microgrid performance. These include the dynamics of the interaction between network swing modes, voltage regulator dynamics, and filter dynamics as the filter bandwidth is swept across a large range. Three different voltage regulators are studied. Additionally, the role of the controller's LPF characteristics on the reduced-order large-signal nonlinear dynamics of inverter-based microgrids is investigated using an equivalent electromechanical system. Using a Lyapunov energy function, a family of linear power measurement filters is identified that ensures stability for a grid-tied frequency-droop-controlled inverter.