Research On Control Technology Of Photovoltaic Grid-connected With AC And DC Motor

Technology of grid-connected photovoltaic system is currently a hot research issue on photovoltaic power generation field. At present, most of the photovoltaic grid-connected power generation system is realized by the inverter, which has problems of high cost, high failure rate, high harmonic content and complex control. In this paper, a method of photovoltaic grid-connected with AC and DC motor was proposed based on the advantages of motor, including long service life, power quality of grid-connected power not influenced by the background harmonic of the grid and low operation and maintenance cost under high voltage and large capacity condition. Photovoltaic power use DC-squirrel cage asynchronous motor and DC-synchronous motor to realize the connection with grid were studied respectively. The research and analysis were carried on the photovoltaic power maximum power point tracking(MPPT) control, DC motor speed control, synchronous motor excitation control, and power transmission balance control after photovoltaic grid-connection.This paper first introduced the importance of photovoltaic power generation and its application in domestic and overseas. The problems of photovoltaic grid-connected inverter were discussed, and the method of photovoltaic grid connected with AC and DC motor was proposed.Secondly, the structure of photovoltaic grid-connected system use DC-squirrel cage asynchronous motor was introduced. The mathematical model of each component in this system were established. The control strategy was made, including maximum power point tracking control and dc bus voltage stability control. The disturbance observer method and PI controller was used to realize the maximum power point tracking control. The principle of power transmission balance control after photovoltaic grid-connection was illustrated, and the dc bus voltage stability control was realized through adjusting the terminal voltage of DC motor.Then, the structure of photovoltaic grid-connected system use DC-synchronous motor was introduced. The mathematical model of each component in this system were established. The control strategy was made, including synchronous motor excitation control, motor speed control and power transmission balance control after photovoltaic grid-connection. Synchronous motor frequency control and motor speed control was realized through adjusting the terminal voltage of DC motor. Synchronous motor voltage amplitudes control and the output active power control after grid-connected were realized through adjusting the terminal voltage of excitation system.Finally the model of photovoltaic grid-connected system use DC-squirrel cage asynchronous motor and DC-synchronous motor were built. The simulation results verifythe feasibility of the method, the grid connected voltage and current waveforms are good,and photovoltaic can provide both active and reactive power to the grid using DC-synchronous system which can improve the power factor of the grid.