Research Of Photovoltaic Pumping System Based On Three-phase AC Motor

A photovoltaic pumping system is a mechanical and electrical system in which the solar energy from photovoltaic panels is converted into electric power, thus driving all kinds of pump motor to pump water from deep wells, rivers, lakes, ponds. It plays an important role in solving the problems such as human and animal drinking water in the remote power shortage and water-deficient region, agricultural irrigation, desertification control, etc. So far, ones have conducted extensive research on the photovoltaic pumping system, but there have still been many problems to remain to solve. Therefore, the research on the photovoltaic pumping system has very important practical significance.In this thesis, a thorough research of a three-phase AC motor pumping system driven by PV has been made with the emphasis on the four aspects of the problem such as system startup, matching of water pump and panels output power, pumping system efficiency, and system protection, etc. The main research work is as follows:1.The models of each component of the system are established by mechanism modeling method, their characteristic curve is obtained through the simulation of these models, and a system control scheme is determined by analyzing the curves.2.A in-depth study the matching problem of water pump motor and the panels output power and the method for raising efficiency of pumping system is performed. A MPPT algorithm based on variable step length disturbance observation method plus CVT and a control strategy combined with the U/f frequency control of motor speed are proposed. The structure of double loop PI controller with feedforward+feedback is determined, and the detail design process of its parameters is given.3. The startup and protection of the system are studied, and a new method of startup aided by the super capacitor and a over-voltage and over-current protection scheme are put forward.4.The system hardware and software design are completed. The hardware design mainly includes the parameter calculation and equipment selection of some important components such as photovoltaic panels, super capacitor, pump parameters and the design and making of the main controller circuit, power circuit, push-pull booster main circuit and control circuit, three-phase inverter circuit, voltage and current sampling circuit. The software design mainly includes the control algorithm and programming of the system main program, the initializaion program, the interrupt subroutine, ADC sampling control subroutine, the pump speed control subroutine, sine wave modulation control subroutine, the PSC module control subroutine, super capacitor charge and discharge control subroutine.5. A2.2kW experiment platform is constructed. The charging and discharging experiments on the super capacitor and the whole machine system experiment are conducted, and the actual test of the controller and the inverter output waveform is carried out. The results show that the developed system based on this scheme can supply short-time big current power for pump start-up; can effectively solve the problem of voltage overshoot and sudden drop; can effectively balance the DC bus voltage by severe variation due to the photovoltaic panels output power caused by the external environment changes; raise the ability of tracking system, enhance the system adaptability to the external environment; effectively improve system efficiency, and solve the problem of system power match.