Development On Automatic Solar Pumping System

Substitutable energy, especially the clean and durative solar energy, has receivedconsiderable attention due to the consumption of conventional energy. Solar energypower system, of which the maximum power point tracking (MPPT) control strategyis the key, is one of the main research fields in the applications of solar energy. Sodevelopment on automatic solar pumping system is selected as the research theme.According to operation characteristic of the water pump with a asynchronousmotor, VVVF control and saddle wave PWM technique are used to control theasynchronous motor.The whole MPPT control process consists of two steps: 1) MPPT algorithm: thejudgment of speed up or down;2) the selection algorithm of step size based on theterminal voltage of the PV array: the selection of step size of speed command.Multi-criterion method and hybrid MPPT algorithm are proposed for the automaticsolar pumping system. Although Multi-criterion method is a kind of first derivativecriterion, it has a good sensitivity. As the system disturbance process is analyzed,Hybrid MPPT algorithm is proposed. Basically, the system with this algorithm iscontrolled in constant voltage method, while the reference voltage is periodicallyupdated by the multi-criterion algorithm.According to the functions and characteristics of automatic solar pumpingsystems, two identical solar pumping systems are implemented. The hardware designincludes main circuits and control circuits of special inverters. Function modules aredivided and Structured design is adopted in software development. Two experimentalsystems are used to validate the proposed algorithm such as the selection algorithm ofstep size, Multi-criterion method and hybrid MPPT algorithm. Experimental resultsshow that both proposed MPPT algorithms can track the maximum power point welland truly and ensure the stability of solar systems. In addition, the system with thehybrid MPPT algorithm has smaller disturbance.