Impact of VSC Control Strategies and Incorporation of Synchronous Condensers on Distance Protection under Unbalanced Faults

The short circuit response of a voltage source converter (VSC) under grid unbalanced faults mainly depends on the design of its control system. Due to the limited semiconductor overload capability, the short circuit current contributed by a VSC should be restricted within the limit for each phase. This might bring up challenges to the protection system of a converter-dominated power system.

This paper derives a generic converter peak current limitation method for three different VSC control strategies. The impact of the control strategies and the combined impact of a VSC with a synchronous condenser on distance protection are evaluated using a commercial relay through hardware-in-the-loop (HIL) tests.

Based on the test results, we propose to avoid using constant reactive power control strategy. It poses an adverse impact on the reliability and speed of distance protection regardless of the presence of SC at the point of common coupling (PCC), while constant active power and balanced current control strategies favor the performances of distance protection.