Research on Synchronous Condensers to Suppress Subsynchronous Oscillation Caused by New Energy Power Generation

Studies and practices indicate that new energy power generation (NEPG) such as wind and photovoltaic power may cause subsynchronous oscillation (SSO). A typical event caused by wind farms occurred in Qomul, Xinjiang, China, in July 2015, which led up to three steam turbines tripped off the grid in succession, and the ±800kV Qomul-Zhengzhou HVDC had to suffer a large power plummet. Different from similar phenomena relevant to steam turbines with series compensation or HVDC, the oscillation frequency due to NEPG is not a constant, but a variable value in a broadband. This characteristic makes it difficult to be effectively and economically suppressed. Nowadays in China, bursting synchronous condensers (SC) are more common to be installed in HVDC rectifier stations to provide reactive power and voltage support, and distributed synchronous condensers are employed more widely in new energy plants to improve voltage safety and stability of the grid. This paper proposes a new suppression method for SSO caused by NEPG, that is to append a subsynchronous oscillation damping control loop to the excitation system of the synchronous condensers, which are already employed in NEPG bases and HVDC rectifier stations. Simulation work has been carried out to verify the suppression effect preliminarily.