This paper presents an optimal control model for photovoltaic-diesel-battery stand-alone system. To minimize the long-term operating cost

the control strategy for the battery and diesel generators is optimized. That is

for the stochastic characteristics of the photovoltaic output and load demand

the energy control of the system is modeled as a semi-Markov decision process(SMDP). The system state is composed of the states of photovoltaic power and load demand

the quantity of operating diesel generators and the levels of battery state of charge. A stochastic dynamic programming method is adopted to find the optimal control strategy consisting of optimal actions for each state. The simulation result shows the rationality of the stochastic model and the effectiveness of the optimization method. This work is supported by National Natural Science Foundation of China(No. 61573126)

Program for New Century Excellent Talents in University(No. NCET-11-0626)and Specialized Research Fund for the Doctoral Program of Higher Education(SRFDP)of China(No. 20130111110007).