Harmonic Analysis of Inverter-Based Resources Subject to Unbalance

Operation of wind turbine generators is affected by unbalance in the grid voltage. This paper presents harmonic analysis when type-4 wind turbine is subjected to grid voltage unbalance. For simplicity, in the current research, the type-4 wind turbine's grid-side converter is assumed to have constant dq-frame modulation indices. First, an EMT model for Type-4 wind turbine with unbalanced grid voltage is modeled in PSCAD. The current is found to have positive-, negative-sequence fundamental components as well as positive-sequence 180 Hz harmonic component. Steady-state circuit analysis is then carried out to compute the current harmonic components. The analysis results match the EMT simulation results.