基于子模块电容能量波动的MMILC下垂控制策略

交直流混合配电网中，孤岛模式下互联换流器(interlinking converter, ILC)具有实现配网间功率平衡、维持交流频率和直流电压稳定的作用。模块化多电平互联换流器(modular multilevel interlinking converter, MMILC)作为ILC的拓扑之一，具有谐波特性好、波形质量高、开关损耗低等优势。文中提出一种适用于MMILC的两级式下垂控制策略，首先基于子模块电容能量波动特性建立了适用于MMILC的新型交直流侧统一下垂特性；然后推导得出了MMILC直流侧电压与等效子模块电容电压间的数学关系，使MMILC仍可通过直流电压偏差进行功率调节，同时设置了下垂特性曲线的死区和最低允许运行范围；最后，分别对MMILC在不同负载模式和过载情况下的控制性能进行了仿真。仿真结果表明，所提出的MMILC两级式下垂控制策略可以自动平衡不同负载模式下交直流侧配网的功率偏差，过载情况下可以瞬时闭锁，验证了控制策略的正确性和有效性。

Droop control strategy of MMILC based on energy fluctuation in sub-module capacitor

In hybrid AC/DC microgrid,interlinking converter (ILC) can balance power flow between AC and DC microgrid,thus stabilizing AC frequency and DC voltage in islanding mode. As a topology of ILC,modular multilevel interlinking converter (MMILC) has advantages of good harmonic characteristics,high quality waveforms and low switching loss. A two-stage droop control strategy for MMILC is proposed. Firstly,based on the energy fluctuation characteristics of the sub-module capacitance,a new unified droop characteristic of AC and DC side for MMILC is established. Then,a mathematical relation between DC voltage and equivalent sub-module capacitor voltage is given to adjust power reference according to deviation of dc voltage. Also the dead zone and an allowable minimum operation range of the droop characteristic are set. Finally,the control performance of MMILC in different load profiles and overload conditions are simulated. The simulation results show that the proposed two-stage droop control strategy of MMILC can automatically compensate the power to both AC/DC sides in different load profiles. Under overload conditions,MMILC can instantaneous block the active power transmission,which validates the correctness and availability of the control strategy.