基于半桥子模块的直流卸荷装置

Energy dissipation device based on half-bridge sub-modules

海上风电柔性直流(柔直)送出系统所接入的陆上交流电网发生故障后,风电场持续输出的盈余功率会造成直流过电压。解决盈余功率最有效的手段是采用卸荷装置对盈余功率进行泄放。文中针对功率器件直接串联的集中式直流卸荷装置投退功率冲击大、器件同时开断难以及分布式直流卸荷装置成本高的问题,提出基于半桥子模块的集中式直流卸荷装置方案,并研究所提拓扑的参数设计方法与控制策略。该方案可以克服大规模功率器件直接串联的技术困难和风险,还可以通过子模块逐步投切降低电阻电压变化率,从而降低功率泄放对直流系统的冲击以及卸荷电阻的制造难度。与分布式直流卸荷装置相比,文中方案仅采用集中式电阻而省去了子模块中的泄放支路,大幅降低设备成本。在PSCAD平台进行海上风电柔直送出系统故障穿越仿真,结果表明所提集中式直流卸荷装置拓扑及控制方案具有良好的性能。

When the onshore accurate current(AC)grid connected to the offshore wind power voltage source converter-based high voltage direct current(VSC-HVDC)transmission system fails,the surplus power continuously output by the wind farm causes DC overvoltage.The most effective way to solve the surplus power is to use the energy dissipation device to discharge the surplus power.A centralized DC energy dissipation device scheme based on half-bridge sub-modules is proposed to solve the problems of large switching power shock when power devices directly connected in series,difficulty in switching devices at the same time and high cost of distributed DC energy dissipation device.The parameter design method and control strategy of the proposed topology are studied.The solution can overcome the technical difficulties and risks of direct series connection of large-scale power devices,and can gradually reduce the resistance voltage change rate by switching sub-modules,thereby reducing the impact of power discharge on the DC system and the difficulty of manufacturing unloading resistors.Compared with the distributed DC energy dissipation device,the proposed scheme only uses the centralized resistance and omits the bleeder branch in the sub-modules,which greatly reduces the equipment cost.The fault ride-through simulation of the offshore wind power VSC-HVDC transmission system is carried out on the PSCAD platform.And the results show that the proposed centralized DC energy dissipation device topology and control scheme have good performance.