采用改进下垂控制和双层无功优化的风电场无功均衡分配研究

计及风电场详细模型,按照双馈风电机组(DFIG)无功容量比例分配无功,难以实现风电场无功裕度均衡控制。根据DFIG无功裕度和并网点(PCC)允许电压偏差,提出可变下垂系数以改进无功-电压控制。结合每台DFIG无功裕度及其与PCC间电气距离,定义新的无功不均衡度。针对大规模风电场控制问题,建立双层无功优化模型,其中电网层以减小网损、电压偏差和风电场铜耗为目标,整定电网无功需求量;风电场层以场内线损、DFIG铜耗及无功不均衡度最小为目标,确定各台DFIG无功出力。采用有限记忆拟牛顿信赖域(LBFGS-TR)算法求解无功均衡分配方案。算例结果表明,所提算法可充分利用DFIG无功调控能力,实现风电场无功裕度均衡控制。

Study on reactive power sharing of wind farms with improved droop control and bi-level reactive power optimization

With the detailed model of the wind farm taken into account, it is difficult to achieve reactive power margin sharing by allocating reactive power according to the reactive capacity proportions of the Doubly-Fed Induction Generators (DFIG). According to the reactive power margin of the DFIG and the tolerable voltage deviation at the Point of Common Coupling (PCC), an improved reactive power-voltage droop control incorporating the variable droop coefficient is proposed. Combining the reactive power margin of the DFIG and electrical distance between DFIG and PCC, a novel indicator of the reactive power imbalance is proposed. To deal the control problems of large-scale wind farms, a bi-level reactive power optimization model is established. For the grid level, the reactive power demands of the wind farms that minimize the grid loss, voltage deviation, and copper loss of the wind farms are determined. For the wind farm level, the reactive power sharing among the DFIGs is determined with the control object to minimize the circuit loss of the wind farm, the copper loss of each DFIG, and the reactive power imbalance. The LBFGS-TR optimization algorithm is adopted to solve the reactive power sharing scheme. Simulation results show that the proposed algorithm helps to realize the reactive power margin sharing of the wind farms with the fully utilized reactive power regulation capability of the DFIG. This work is supported by National Natural Science Foundation of China (No. 51877061).