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Small-signal stability analysis and PHIL experiment validation of power system with WECS voltage/frequency ancillary control

Large scale wind energy conversion systems (WECSs) are gradually required to participate in power system voltage/frequency regulation. As a result, output characteristic of the WECS is changing from traditional current source to voltage source and thus affects small-signal stability (SSS) of power system. This paper investigates SSS of power system with WECS voltage/frequency ancillary control. Through eigenvalue analyses and time-domain simulations, it is found that voltage and frequency responses of the system are improved by the WECS ancillary control. However, original low-frequency power system oscillations can be deteriorated and a new unstable oscillation can be induced, which threatens SSS of the power system and restricts the WECS to fulfill grid code requirement. Subsequently, a power-hardware-in-the-loop (PHIL) platform based on a 3kW WECS, a 50kVA back-to-back converter and RT-LAB real-time simulation software is constructed. The above simulation results are further validated by the PHIL experiments. WECS damping control which aims to improve SSS is also performed and verified in the PHIL environment.