电网故障条件下双馈机组运行特性分析及其协调控制

摘要

电网发生暂态故障情况下，风力发电机定、转子均会出现过压、过电流等一系列问题，若不采取及时有效的应对措施，会导致风电机组大规模解列，将使电网故障进一步恶化。为防止上述情况出现，提高风电机组应对电网暂态故障的能力，详细分析了电网故障时双馈感应风力发电机的运行特性，提出了一种电网故障条件下转子侧变流器与Crowbar电路的协调控制策略。重点研究了转子侧变流器与Crowbar电路在暂态故障期间状态切换逻辑；在低电压稳态运行期间，提出采用不同故障类型下的相应控制方法，即对称跌落时采用常规PI控制，不对称跌落时采用PIR控制；并给出了整个跌落期间双馈发电机完整的协调控制流程图。最后基于理论分析，研制了40 kW双馈型风电模拟系统，将该系统应用于电力系统动模试验系统进行实验验证。实验结果表明，采用该协调控制策略，在电网暂态故障下，能有效改善双馈发电机定、转子过流、过压的情况，实现了双馈感应发电机在电网故障时的低电压穿越功能。电力系统动模试验系统与真实电网仿真度较高，研究成果对大功率机组增强应对电网故障能力具有重要的参考意义。%Failure to take timely and effective response measures, grid transient faults will cause series of problems for doubly fed induction generator (DFIG) such as over current in both stator and rotor, which can lead to wind turbine out of grid and further deterioration for the power grid faults. In order to solve these problems and improve the ability to respond to grid transient faults, the DFIG characteristics are analyzed detailedly during the grid transient faults. The coordinated control strategy for DFIG rotor side converter and Crowbar circuit during the grid transient faults is proposed. State switching logic for rotor side converter and Crowbar circuit is mainly researched. The PI controller is adopted under symmetrical drop fault and PIR controller under asymmetric drop fault according to different types of grid transient faults during low voltage steady operation. The complete coordinated control flowchart of doubly-fed generator during the entire grid transient fault is showed. Based on theoretic analysis, the 40 kW double-fed wind power emulation system is developed and then it is applied in power system dynamic simulation experimental system. The experimental results prove that the coordinated control strategy proposed in this paper can effectively improve the doubly-fed generator stator and rotor over-current under the grid transient fault and achieve low voltage ride through of DFIG. A satisfactory simulation result is achieved between the power system dynamic simulation experimental system and the real power grid. Research results have important reference value for large power wind turbines to enhance the ability to respond to grid faults.