基于模组解耦控制的高调制比混合型MMC电容优化方法

高调制比混合型模块化多电平换流器(modular multi-level converter,MMC)子模块电容的均压控制方法借鉴半桥型MMC,全桥及半桥子模块电容的充放电行为存在强耦合,导致半桥子模块电容电压波动率较小,给电容值的优化带来挑战。为此,文中首先计算高调制比下两类子模块的电容电压波动率,以明确半桥子模块电容值的优化空间。进一步,提出全桥及半桥模组平均开关函数的设计原则,考虑子模块电容电压瞬时最大值的约束,实现半桥子模块电容值的优化。然后,在现有MMC基本控制框架下,提出基于模组解耦的控制策略,实现电容电压动态的准确控制。最后,在MATLAB/Simulink中搭建混合型MMC的仿真模型,对所提电容优化方法进行验证。仿真结果表明:所提电容优化方法不仅可以实现对全桥及半桥子模块电容电压直流分量和纹波分量的控制,还可降低半桥子模块电容值。

Module decoupling control based capacitance optimization for hybrid modular multi-level converter with high modulation index

Hybrid modular multi-level converter (MMC) consisting can operate with a high modulation index,and it borrows the capacitor voltage balance method from half-bridge MMC. Thus,a strong coupling effect occurs in the charging behaviours of full bridge sub-modules (FBSMs) and half bridge sub-modules (HBSMs),which causes a low volatility of the ripple voltage of HBSMs'' capacitors and challenges for its capacitance optimization. To address this issue,the ripple coefficients of HBSMs'' and FBSMs'' capacitor voltages are calculated for MMC operating with a high modulation index quantitatively. The optimize of HBSMs'' capacitance can be clarified. Then,design principles of the optimal HBSMs'' and FBSMs'' average switching functions are explored. Hence,the optimization of HBSMs'' capacitance is achieved with the constraint of the maximal value of sub-modules'' instantaneous capacitor voltages. Further,under the conventional basic control framework of MMC,a control strategy based on module decoupling control which can regulate the dynamics of capacitor voltage accurately is proposed. Finally,hybrid MMC operating is modeled with MATLAB/Simulink. The proposed capacitor optimization method is verified. The simulation results show that the DC component and ripple component of capacitors'' voltages can be regulated accurately,and the capacitance of HBSMs can be reduced effectively.