基于模块级联拓扑的光伏智能并网系统

Smart Photovoltaic Integration System Based on Module Cascaded Converter Topology

针对复杂光照条件下大量光伏阵列的并网问题,提出了一种基于模块级联换流器拓扑的光伏并网系统,各个光伏模块接入级联半H桥换流器后再通过逆变器并网。并网逆变器用于向光伏电站提供稳定的总直流电压,实现交直流侧功率的平衡。光伏电站侧级联半H桥换流器将固定数量的半H桥模块置于投入状态,实现升高直流电压输送光伏电能。级联半H桥换流器根据各光伏模块的直流电压高低来改变光伏模块的投切状态,主动调节光伏阵列的输出功率,使各光伏模块的直流电容电压保持稳定。各个光伏模块中的DC/DC斩波器基于稳定的直流电容电压向所连光伏阵列输出合适的端电压,实现独立的最大功率点跟踪。通过详细电磁暂态仿真验证了该光伏并网系统的效果,表明该光伏并网系统能够在不平衡的光照条件下,使每个光伏模块的直流电压保持稳定,使每个光伏阵列独立地工作在最大功率点,提升光伏并网系统的工作效率。

We put forward a system of the grid integration of photovoltaic （PV） power based on the module cascaded converter topology. Each PV module is connected to a half-bridge of the cascaded converter, which is integrated to the AC grid by an inverter. A constant DC voltage control is utilized to ensure the power balance between the AC and DC sides. In the presence of the cascaded half-bridge converter, the high-voltage level for the DC transmission purpose is built by series connections of low-voltage PV modules. The switching of half-bridges is determined according to the DC capacitor voltages of the PV modules. Thus, the output power of each PV module can be regulated accordingly, and the corres- ponding DC capacitor voltage is controlled at the desired value. Thus, the DC chopper in each PV module is able to convert the constant DC voltage from the related DC capacitor to a desired value for the maximum power point track （MPPT） of the PV array. The effectiveness of the proposed PV integration scheme is validated by detailed time-domain simulation results. Each PV array is operated at its maximum power point independently, and the DC voltages of the PV modules are kept to be balanced during unbalanced irradiance, which increases the efficiency of the PV integration.