Research On Operation And Control Of Doubly-Fed Induction Generators With Hybrid Energy Storage System

Wind power has great development advantage as clean, renewable forms of energy. Doubly-fed induction generator has been widely applied for its excellent control performance and economy efficiency. However, Due to the volatility of the wind, the active power output to the grid will fluctuate and then threaten the stability of the grid operation directly, so it’s necessary to study effective technology to restrain the fluctuation of wind power.This thesis first analyzes the basic operation principle of doubly-fed induction generator and control strategy of inverter, then puts forward that battery-super capacitor hybrid energy storage system(HESS) be installed on the DC bus of each doubly-fed wind power generator. With the energy storage devices absorbing or releasing the active power, the fan power fluctuations will bring down. Based on this, the topology structure of HESS is established. The battery pack is paralleling with the super-capacitor(SC) pack by the DC/DC converter and the SC pack is connected to DC bus through DC/DC converter. Then this thesis decides the energy management solutions of HESS. According to the solution, the super-capacitor exchanges power with the DFIG and the battery makes the capacitor work in the optimal voltage range by charging or discharging. DC/DC converters use complementary PWM control mode. Simulation is carried out in PSCAD and proves the effectiveness of the HESS.Finally, this paper proposes a novel two-layer constant power control scheme for a wind farm equipped with doubly fed induction generator (DFIG) wind turbines. The high-layer wind farm supervisory controller (WFSC) generates the active power references for the low-layer wind turbine generator(WTG) controllers according to the active power generation plan or demand from the grid. The low-layer WTG controllers then regulate each DFIG to generate the desired amount of active power, and the deviations between the available wind energy and desired active power are compensated by the HESS which is controlled by the lower controllers. Simulation model with 5 DFIG wind turbines on one wind farm are operated in PSCAD to verify the effectiveness of the proposed control scheme.