Impedance-based local stability criterion for standalone photovoltaic-battery hybrid system

Instability problem is known to be a big issue of the DC distributed power system (DC DPS). The impedance-based stability-assessment methods have turned out to be very effect tools and are proposed for “voltage-source system” and “current-source system”, respectively. However, these methods may not be suitable choices in standalone photovoltaic (PV) system with battery energy storage. Due to variation of the available sunlight intensity, the battery voltage and the load condition, the system´s operating modes are switched from time to time. The dynamic behaviour is thus quite complex, and the system can no longer be defined as simply a “voltage-source system” or “current-source system”. In order to solve this problem, this paper analyses all the possible operation modes of the standalone PV-battery Hybrid system and then proposes a novel impedance-based local stability criterion to assess the system´s stability. Finally, a 480 W PV-battery hybrid system is fabricated to validate the effectiveness of the proposed criterion ¹.