| Photovoltaic pump system is an application of off-grid solar power. Because of itspower output characteristic is in cooperate with the sunlight intensity which means incooperate with the agriculture needs, the system can operate safely without humancontrol, and is especially suitable for vast dry area of western China and urban parks.Operation of photovoltaic pump system mainly depends on two aspects of the systemcontroller functions, one is the photovoltaic maximum power point tracking function,and the other is the driving function of the pump motor. At present the electricalstructure of most of the pump controllers have two parts, the DC/DC conversion andthe inverter, respectively, to achieve the above two aspects of power process.In this paper, based on a practical photovoltaic pump system design, combinedwith solar energy photovoltaic systems pump operation and scale characteristics, asingle stage power electronic converter is designed to achieve both the maximumpower point tracking control system and drive power electronics conversion, whichtake place of the original two stage converters to reduce costs and improve efficiency.The main function of the hardware and software structure is given in this part, and thewater pump selection and capacitor calculation are also given for further research andexperiment. Taking into account the load of the system is water pump, its operationdepends on the velocity of the driven motor very much, which means that thefrequency of the motor can control the power of the pump, so we use frequency as theunified control variable of the system. Consequently, the melting of the maximumpower point tracking algorithm and motor drive system design strategy withfrequency is the key part of this research. The scheme can effectively reduce the costand improve the efficiency of the system.Maximum power point tracking (MPPT) control of photovoltaic water pumpingsystem determines the stability and efficiency of the entire system. So the modelingand simulation of PV system and pump system is given initially，and MPPT algorithmdesign is given afterward. It is given as2levels:(1) the frequency perturbation andobservation method, because the system is considered pump load, speed andfrequency control volume inside easily and reduce the amount of conversion as aunified control, and the method is based on the perturbation frequency powerconversion measurements and to determine the direction of the disturbance until thesystem is stable at the maximum power point.(2) Neural network for a given method, using BP neural network to train the nonlinear relationship between the environmentalconditions of the PV model with a given operation frequency, and giving therelationship between the neural network model operating value of the systemoperating frequency characteristics of time and under ambient conditions. Thensimulations of the above two methods and a combination method are given,performance show that the one stage frequency control can be available for MPPTcontrol.Pump motor control method design during low energy level. The pump motormainly use induction motors, to control the current we choose vector control strategy,the excitation and active component decoupling control the use of current trackingcontrol implementation. And for low-light operation condition, the system motor inoperating under light load condition. Relative research is given include proposing amethod of weakening control of the state in order to improve light-load efficiency ofthe pump motor running. To prove the theory， use of SIMULINK simulation systemhas been built, giving the functional verification and analysis of the energy-savingmethods.At last, the frequency control strategy is applied in the photovoltaic single stagephotovoltaic pump system. Both the functions of maximum power point tracking andpump are tested. Through the experiment, the relationship of control frequency andvoltage is also given. |
PDF Full Text Request