Stability Enhancement and Direct Speed Control of DFIG Inertia Emulation Control Strategy

With the increasing penetration of renewable energy generators in power grid, traditional vector control (VC) strategy for double fed induction generator (DFIG) is unable to provide extra active power support to grid because DIFG inertia is made decoupled from grid frequency fluctuations. To solve this problem, Virtual Synchronous Generator (VSG) control strategy as well as Inertial Synchronization Control (ISynC) strategy are proposed for DFIG rotor side converter (RSC) and grid side converter (GSC) respectively, so that DFIG rotor speed will experience an acceleration or a deceleration process to release or absorb the kinetic energy stored in DFIG wind turbines, which can prevent grid frequency from deep drop or increase. However, VSG-ISynC control strategy has its limitations in that rotor speed may lose its stability when large load is added into power system, at the same time, the secondary frequency drop is serious if rotor speed has decreased lower than the admissible minimum value. To address this issue, a modified VSG (M-VSG) control strategy is proposed by dynamically changing the P-f droop coefficient of conventional VSG control strategy, aiming to expand the stability boundary of DFIG operation. Additionally, an extra rotor speed closed loop is added into VSG control strategy, which can significantly reduce serious frequency secondary drop by controlling rotor speed directly. Simulation and hardware-in-loop (HIL) verification are both carried out in RTDS & GH Bladed co-simulation research platform to verify the effectiveness of proposed M-VSG control strategy.