Wideband Series Harmonic Voltage Compensator Using Look-Ahead State Trajectory Prediction for Network Stability Enhancement and Condition Monitoring

A wideband series harmonic voltage compensator (WSHVC) with an operating bandwidth of 10 kHz for microgrids with a plurality of grid-connected inverters (GCIs) is proposed. It generates a voltage to compensate for high-frequency harmonic voltage at the point of common coupling (PCC), resulting in a virtually zero high-frequency impedance at the aggregate output of the GCIs and, thus improving system stability. The generation of the harmonic voltage is based on predicting the state trajectory of the WSHVC after a switching period per half-switching cycle to determine the moment at which the switches in the WSHVC change their states. The PCC impedance and the equivalent impedance of the GCI network are extracted by analyzing the system response after injecting the entire system with particle-swarm-optimization (PSO) optimized multisine power disturbances. Therefore, system stability is predicted. The condition of passive components in the WSHVC is also monitored by estimating their values with the sampled state variables. A 500 VA, 1 MHz, FPGA-controlled, GaN-based prototype is evaluated on a 6.5 kVA testbed that consists of three commercial GCIs, nonlinear load, and adjustable grid impedance. A comparative study of the system performance with and without the WSHVC is conducted. Experimental results are favorably compared with theoretical predictions.

Automated summary

A wideband series harmonic voltage compensator (WSHVC) is proposed for microgrids with multiple grid-connected inverters (GCIs), with an operating bandwidth of 10 kHz. The WSHVC generates a compensating voltage to counter high-frequency harmonic voltage at the point of common coupling (PCC), resulting in a nearly zero high-frequency impedance at the aggregate output of the GCIs and improving system stability. The WSHVC predicts its state trajectory to determine the moment of switch state changes, extracts the PCC impedance and GCI network impedance through system response analysis, and monitors the condition of passive components using sampled state variables. Experimental results on a 6.5 kVA testbed demonstrate favorable comparison with theoretical predictions.