单相多电平并网级联逆变器调制技术的研究

Research on Modulation Technology of Single-phase Multilevel Grid-connected Cascaded Inverter

摘要:

为简化单相多电平并网级联逆变器控制复杂度，设计了一种 H 桥模块独立控制的 LCL 型单相多电平并网逆变器。首先，在单相 LCL 型并网逆变器基础上设计了单相多电平并网级联逆变器的主电路和控制电路；其次，基于单极倍频正弦脉冲宽度调制控制方法提出了两种多电平调制策略，并且分析了它们在开环控制和闭环控制中的特性；然后，根据所提逆变器特点推导了 LCL 滤波器参数计算公式；最后，在仿真平台上验证所提理论的有效性。仿真实验结果表明：两种调制策略均会受到并网逆变器闭环控制策略和调制比的影响，导致正弦调制信号跟随载波信号而发生变化；两种策略均能保障所提单相级联逆变器实现多电平输出；从并网电流总谐波畸变率指标来看，基于三角载波同相移动的策略 1 的调制效果更好。

Abstract:

In order to simplify control complexity of single-phase multilevel grid-connected cascaded inverters, a single-phase multilevel grid-connected inverter with LCL filter is designed with independent control. Firstly, the main circuit and control circuit of single-phase multilevel grid-connected cascaded inverter based on single-phase grid-connected inverter with LCL filter are designed. Secondly, two multilevel modulation strategies are proposed based on unipolar frequency doubling SPWM control method, and their characteristics in open-loop control and closed-loop control are analyzed. Then, based on the characteristics of the proposed inverter, a formula for calculating the parameters of LCL filter is derived. Finally, the effectiveness of the proposed theory is verified on a simulation platform. The simulation experiment results show that both modulation strategies are affected by the closed-loop control strategy and the modulation ratio of grid-connected inverter, resulting in the sinusoidal modulation signal changing with the carrier signal. And both strategies can ensure the proposed cascaded inverters to achieve multilevel output. From the perspective of the total harmonic distortion index of grid-connected current, the modulation effect of the first strategy based on triangular carrier phase shift is better.