三相级联H桥光伏并网控制研究

Study on Control of Three-Phase Cascaded H-bridge PV Grid

级联H桥多电平逆变器由于开关管承受应力较小,且并网电流谐波含量低等优点,使得其在高压大容量光伏并网发电系统中,具有广阔的应用前景。级联H桥多电平逆变器光伏并网发电存在光照强度和温度不均匀、光伏板老化或被遮光等问题,会造成级联H桥逆变器各相输出功率不平衡,从而导致并网电流不对称。文章以基于DC/DC变换器的三相级联H桥光伏并网系统为研究对象,提出了一种零序注入法,通过特定方波减去正序外包络电压得到所需零序分量,使得在各相输入功率不相等的情况下,并网电流仍能与电网电压同相。在MATLAB/Simulink环境下进行仿真研究,结果表明,并网电流谐波含量满足IEEE Std.929-2000标准,能够实现单位功率因数运行。

The cascaded H-bridge multilevel inverter has wide application prospects in high-voltage and large-capacity photovoltaic grid-connected power generation system owing to the advantages of low loading stress of the switch tube and low harmonic content of grid-connected current. The cascaded H-bridge multilevel inverter grid-connected photovoltaic power generation has some problems, such as uneven light intensity and temperature, aging of photovoltaic panels or being shaded, which may lead to unbalanced output power of each phase of the H-bridge inverter, resulting in unbalanced grid-connected current. In this paper, a zero-sequence injection method based on DC/DC converter for three-phase cascaded H-bridge photovoltaic grid-connected system was proposed. The required zero-sequence component was obtained by subtracting the positive sequence envelope voltage from the specific square wave, so that the grid-connected current can still be in phase with the grid voltage under the condition of unbalanced input power. The simulation results in MATLAB / Simulink environment show that the harmonic content of grid-connected current meets the IEEE Std. 929-2000 standard and can realize the operation of unit power factor.