Voltage Stability Analysis of Wind Farm Integration into Transmission Network

In some regional grids in China, wind power penetration will increase rapidly because of the abundant wind resources in those areas and the government policy impetus. However, the power system security and stability may be affected due to the higher wind power penetration. Because majority of the wind farms with higher installed capacity intends to be connected into the transmission network of 220 kV voltage level, their impacts are becoming more widespread. In the grid impact studies of wind power integration, voltage stability is the mostly concerned problem that will affect the operation and security of wind farms and power grid. In this paper, the detailed wind turbines steady-state model and dynamic model are used to explore the wind power integration impact on voltage stability of the power system; the load flow calculation (P-V curve and V-Q curve) and dynamic contingency study are conducted; the different impacts on voltage stability of integrating wind farms based on different wind turbines technologies are illustrated and the following conclusions are presented: a. Wind turbines equipped with simple induction generator are not provided with reactive power regulation capability. Voltage stability deterioration is mainly due to the large amount of reactive power absorbed by the wind turbine generators during the continuous operation and system contingencies. b. Wind turbines equipped with doubly fed induction generator (DFIG) controlled by the PWM converters are provided with reactive power regulation capability; can absorb or supply reactive power during normal operation. The adverse affect on local network voltage stability is mitigated so that more wind power installed capacity can be incorporated into the grid. c. The transient voltage stability characteristics of wind turbines with DFIG are better than wind turbines with induction generator because of the voltage control capability of the DFIG based wind turbines; The DFIG based wind turbines have a better voltage recovery performance than the IG based wind turbines with same rating.