独立光伏系统恒压工作模式下最优工作区的选择

Optimal Work Area Selection of Stand-alone Photovoltaic Generation System Under Constant-Voltage Operation Mode

独立光伏系统中,当光伏电池输出的电能超出蓄电池和负载所需时,系统会过渡到一种非常重要的工作模式,即恒压工作模式。恒压模式下,对应同一负载,光伏电池存在2个工作点,分别位于最大功率点的左侧和右侧,即光伏电池i-u特性曲线的电流源区和电压源区。对这2个不同工作区域内光伏系统的稳定性进行了分析,提出了相应的控制方式。首先对光伏电池进行线性化处理,推导出光伏电池的线性化等效模型,并建立了整个系统的数学建模,在频率域内对不同工作点处系统的稳定性进行了分析。结果表明,恒压工作模式下,独立光伏系统工作于光伏电池的电压源区时,具有更好的稳定性。搭建的仿真模型在时域内验证了上述分析结果的正确性。

In stand-alone photovoltaic （PV） generation system, when the electric energy output from PV cells exceeds the power demand of batteries and loads, the usual operation mode of PV generation system will be turned into a very important operation mode, i.e., the constant voltage mode. Under constant voltage operation mode of PV array, there are two working points for the same load, which locate at the left side and right side of the maximum power point of the PV array, i.e., the current source region and voltage source region of current-voltage characteristics of PV array. The stability of PV system in the two different working regions is analyzed and corresponding control strategies are proposed. Firstly, the linearization of PV array is performed to derive the linearized equivalent model and to build the mathematical model of the whole system, then the stability of PV system at different working points is analyzed in the frequency domain. Analysis results show that under constant voltage operation mode, when stand-alone PV generation system works in the voltage source region of PV array the system is more stable. The correctness of above-mentioned conclusion is verified by the results of the simulation based on the proposed model in time domain.