双馈异步风力发电机开关频率恒定的直接功率控制

与矢量控制相比,直接功率控制（DPC）结构简单,应用于风电系统的双馈异步发电机（DFIG）能简化变频器控制结构,提高系统动态性能。在分析DFIG暂态数学模型的基础上推导了内部状态量与控制量之间的关系,提出了分别基于转子磁链、转子电流和电磁转矩的3种DPC策略,并通过引入空间矢量调制（SVM）技术使DPC策略的开关频率保持恒定。这些策略在电网正常情况下能获得优良的静态性能,而在非正常运行状态各自表现出不同的动态特性,能适用于不同的控制目标。理论分析与仿真实验证明,电网正常情况下各定频DPC可有效实现有功、无功功率的解耦控制;电网电压波动时基于转子磁链DPC（RF-DPC）可使DFIG快速进入稳定状态,缩短振荡时间;基于转子电流DPC（RC-DPC）可抑制转子电流振荡,防止变频器过流;基于电磁转矩DPC（EMT-DPC）可消除电磁转矩脉动,减少对机组转轴剪切应力冲击。

Direct Power Control for Doubly fed Induction Generator Wind Turbines with a Constant Switching Frequency

Compared with vector controls, a direct power control (DPC) is simpler in structure and better in dynamic performances when applied to the doubly fed induction generator (DFIG). Three DPC strategies with constant switching frequencies are presented by using the space vector modulation (SVM) technique. These strategies aim to control the rotor flux (RF-DPC), rotor current (RC-DPC) and electromagnetic torque (EMT-DPC) of a DFIG respectively, based on the relationships between DFIG state-variables and control variables. Their satisfactory steady-state and dynamic performances suits for different control objectives. Simulation results demonstrate that the DPC strategies can control the active and reactive power separately in the steady-states. RF-DPC effectively reduces oscillation time during voltage fluctuation periods; RC-DPC is capable of depressing the magnitudes of oscillating rotor currents; and EMT-DPC has the capability of eliminating electromagnetic torque vibration and consequently diminishing stresses on the turbine shaft.