Design of a robust PI controller for photovoltaic energy storage system in constant voltage charging mode

To improve the reliability of photovoltaic (PV) energy storage (PVES) system, the output voltage robust PI controller design criteria and method are proposed in this paper. First, the boost converter with an input capacitor is taken as an example, and its small signal model including the dynamic equivalent circuit of solar cell is built up. Based on this, the stable condition of the PVES system in constant voltage charging (CVC) mode is deduced with Routh stability criterion, which indicates that environmental factors as well as load condition affect the system stability, in deed, by influencing the small signal dynamic resistance r
D
of diode in solar cell. And, the system stability gets worse with the decrease of r
D
. Besides, the junction-capacitance of solar cell also has impact on system stability. Hence, the output voltage controller should be designed with r
D
=0, which means the junction-capacitance is shorted (its effect can be ignored) and the load reaches its minimum value. The controller parameters obtained with this method can ensure the PVES system operate stably throughout the entire variation range of environmental factors as well as charging power. Finally, the correctness of theoretical analysis has been verified by a 150W prototype.