Novel PV Solar Farm Control as STATCOM (PV-STATCOM) for SSR Mitigation in Synchronous Generators and Wind Farms
Abstract
Transmission lines across the world are extensively compensated by series capacitors to increase their power transfer capacity. However, series compensation can potentially cause subsynchronous resonance (SSR) which can lead to significant damage in shafts of synchronous generators and wind farms. Dynamic reactive power compensators such as STATCOM and SVCs are typically used for mitigation of SSR, but these are quite expensive.
Large scale PV solar farms are growing at a very rapid rate across the world. It is quite likely that they may get installed near synchronous generators or wind farms which are directly or indirectly interfaced with series compensated lines.
For the first time, novel SSR damping controls for the patented technology of PV solar farm controlled as STATCOM (PV-STATCOM) are presented in this thesis for mitigating SSR both during night and day in synchronous generators connected to series compensated lines. The PV-STATCOM successfully mitigates SSR whether the solar farm is located at generator terminals or remotely from it.
New SSR alleviation controls are also developed for PV-STATCOM for mitigating SSR in wind farms connected to series compensated networks, during night and day, irrespective of PV-STATCOM location. The SSR damping controls are based on wind farm generator speed and line current, both of which are locally available signals.
As soon as a system disturbance is detected, the solar farm discontinues its real power generation and makes available its entire inverter capacity for dynamic reactive power exchange as STATCOM, for SSR mitigation. Once subsynchronous oscillations are damped the solar farm utilizes a novel ramp-up technique according to which SSR damping function is kept activated with remaining inverter capacity during power ramp-up. Such a fast ramp-up technique is not envisaged in Grid Codes. The entire process of SSR damping for all cases studied takes less than half a minute.
A novel coordinated control of PV-STATCOM and DFIG based Type 3 wind farms is developed for faster and effective SSR damping, when both are connected to series compensated lines.
MATLAB based eigenvalue analysis validated by nonlinear simulations through SIMULINK and PSCAD software confirm the effectiveness of proposed SSR damping controls.