两级式级联H桥光伏并网逆变器功率平衡控制策略

Power Balance Control Strategy for Two-stage Cascaded H-bridge Photovoltaic Grid-connected Inverter

针对两级式级联H桥光伏并网逆变器中因每个光伏单元功率不同而出现的过调制问题,本文介绍了一种基于最优三次谐波注入与限功率最大功率点跟踪混合控制策略的两级式单相并网级联H桥光伏逆变器的控制方法。最优三次谐波的注入能够提高调制范围,限功率最大功率点跟踪算法能够在超过三次谐波补偿范围的条件下,通过限制最大调制比所在单元的光伏模块的功率,使其继续满足并网运行条件。仿真结果表明,在严重失配条件下,本文所提混合控制策略能够始终将调制比维持在给定范围内,具有保证系统并网稳定运行的内在能力。

Aimed at the over-modulation problem caused by the power difference in photovoltaic(PV)units in a twostage cascaded H-bridge(CHB)PV grid-connected inverter,a control method for a two-stage single-phase grid-con⁃nected CHB PV inverter is introduced based on the hybrid control strategy of optimal third harmonic(OTH)injection and power-limited maximum power point tracking(MPPT).In this scheme,the OTH injection can improve the modula⁃tion range.In addition,under the condition of exceeding the third harmonic compensation range,the power-limited MPPT algorithm can ensure that the PV module with the maximum modulation ratio satisfies the grid-connected opera⁃tion condition continuously by limiting its power.Simulation results show that under the condition of severe mismatch,the hybrid control strategy proposed in this paper can maintain the modulation ratio within a given range,and it has the inherent capability of ensuring the grid-connected operation and stabilizing the system.