单相半桥三电平并网逆变器中点电压不平衡机理及其均压控制策略

Research on Mechanism of Single-phase Three-level Half-bridge Grid-tied Inverter Voltage Unbalance of Input Capacitors and Voltage Balance Control Strategy

针对半桥逆变器的中点电位不平衡问题,以电流控制型三电平半桥并网逆变器的闭环模型为研究对象,给出半桥逆变器中点电位不平衡机理,根据已有文献分析的电感电流初始角度不可控和PI控制器对于交流量存在调节静差相结合,理论推导得到调制波存在直流分量,最终导致输入电容中点电位不平衡。分别从控制电感电流初始角度和选择合适电流调节器的角度出发,提出两种半桥逆变器输入电容中点电位平衡的控制方法:①采用PI调节器,近似控制电感电流初始角度θL0=90°并反馈电感电流直流分量进行补偿均压控制;②采用准PR控制器替代PI控制器作为闭环控制器,消除调制波的直流偏置。仿真和实验结果表明,提出的两种均压控制方法可实现中点电位的平衡,且无需增加硬件成本。

To deal with the neutral point voltage unbalance problem in the single-phase three-level half-bridge grid-tied inverter, the paper takes a current closed-loop control model as a research plant, and analyzes the half-bridge inverter neutral potential unbalance mechanisms：According to the published papers, two factors, the random initial angle of inductor current and DC component in the modulation waveform resulting from the steady error of PI controller in an AC system, contribute to the neutral point voltage imbalance. Starting from the points of view on controlling the initial inductor current angle and selecting appropriate current regulators, the paper proposed two approached to keep the neutral point voltage balanced：① Feedback DC component of the inductor current; ② Employing Quasi-PR controller instead of PI controller to eliminate DC bias in the modulation wave. The simulation and experimental results show that two proposed control methods both can achieve neutral-point potential balance without additional hardware cost.