具有故障穿越能力的T型桥臂交替多电平换流器及其调制策略

针对常规模块化多电平换流器(MMC)难以兼顾直流故障穿越能力与系统经济性的问题,提出一种T型桥臂交替多电平换流器(T-AAMC)及其调制策略,其直流桥臂采用半桥子模块并配合桥臂移相的新型调制策略,有效降低换流器建造成本与运行损耗,同时由全桥子模块串联组成的交流桥臂实现了直流故障穿越.首先,介绍了T-AAMC的拓扑结构,再基于各桥臂能量平衡条件,明确T-AAMC的桥臂移相调制策略,进而分析了T-AAMC的运行参数与硬件配置;同时,设计闭环控制系统,实现交直流桥臂能量的动态平衡;然后,将T-AAMC与现有的MMC进行了对比,相比于混合型MMC,T-AAMC在子模块数量、功率器件数量、电容取值上均实现了削减;最后,在MATLAB/Simulink中搭建仿真平台,验证了拓扑、调制与控制设计的有效性.所提T-AAMC在正常工况下能够实现宽范围、高效率的能量转换,同时具有直流故障穿越能力,可保障系统持续可靠运行.

T-type Alternate Arm Multilevel Converter with Fault Ride-through Capability and Its Modulation Strategy

The conventional modular multilevel converter (MMC) is difficult to balance the DC fault ride-through capability and the system economy. Aiming at this problem, this paper proposes a T-type alternate arm multilevel converter (AAMC) and its modulation strategy. With the proposed new arm phase-shift modulation strategy, the DC arm of T-AAMC can be constructed by half-bridge sub-modules, which reduces the construction cost and operation losses. Meanwhile, the DC fault ride-through capability is realized by the AC arm constructed with full-bridge submodules in series. First, the topology of T-AAMC are described. The arm phase-shift modulation strategy is determined according to the energy balance condition of each arm, and the operation parameters and hardware configuration of T-AAMC are analyzed. Then, the closed-loop control system is also designed to dynamically balance the energy in AC and DC arms. Furthermore, a comprehensive comparison between T-AAMC and the existing modular multilevel converters is demonstrated. It is shown that, compared with the hybrid MMC, the submodule number, power device number and submodule capacitance of T-AAMC are all reduced. Finally, the proposed topology, the modulation method and the control design are verified by the simulation in the MATLAB/Simulink environment. The proposed T-AAMC can realize the energy conversion with a wide operation range and high efficiency under the normal condition, and it has the DC fault ride-through capability to ensure continuous and reliable operation of the system.