Research On Coordinated Control Of Dcmicro-grid Based On DSPACE Rapid Control Prototyping

The energy sources and environment problem becomes increasingly prominent with the sustained rapid development of economy and massive fossil fuel consumption. The distributed generation of renewable energy is widely applied. The key technology of renewable technology is how to integrate renewable energy into the grid. The micro-grid technology can just solve this difficult problem. The DC micro-grid of PV has been paid more and more attention because there is no complexity control of frequency、phase and reactive power. How to coordinate the relationship between the micro power sources is the key to the micro-grid because of different features of different micro power sources.This paper takes a DC micro-grid which consists of photovoltaic array, storage battery and fuel cell as the study object. Using advanced semi-physical simulation technology, management control strategy of system and every power supply in island mode、control strategy of grid connected converter in grid mode are researched as following based on rapid control prototyping of d SPACE real-time simulation system.First of all,energy management platform for DC micro-grid is established based on rapid control prototyping technology of d SPACE real-time Simulation System. Various operation states of DC micro-grid are simulated under laboratory conditions using semi-physical simulation technology. The general structure of the platform and the selection and design of the key components of the system are introduced in detail which lays a good experiment foundation for the research of control strategy of DC micro-grid.The photovoltaic power unit is the most important energy source of DC micro-grid. In order to further improve the efficiency of photovoltaic arrays, an improved method was proposed due to shortcoming of conventional perturbation and observation in for photovoltaic system. This method makes use of the characteristics of changes in symbols of voltage difference on either side of maximum power to change the step. The oscillation in maximum power of fixed step P&O was eliminated without disturbance in steady state and the quality of electric power was optimized. This scheme is simple and easy to realize.Secondly, an adaptive management strategy of the DC micro-grid in island mode is studied to coordinate the energy balance between each power supply of DC micro-grid. Each power supply unit control the bus voltage by time taking the DC bus voltage as information carrier without centralized control unit in system. On the basis of analyzing the characteristics of battery charge and discharge, combination of double loop PI and anti droop control are used. The method can charge and discharge on time when the fluctuation of PV generation and load demand so as to maintain the bus voltage stability and realize the system energy balance. The full cell can operate accurate when the system energy shortage by setting the threshold voltage. The simulation results proved that the control strategy of the DC micro-grid in island mode is correct and effective.Finally, the control strategy of converter in grid connected mode is studied based on direct power control technology especially in the case of asymmetric failure of grid. The mathematical model of grid connected converter is established with instantaneous active power and reactive power as the state variables under two-phase stationary coordinate. According to this model, the direct power control strategy of grid connected converter based on space vector modulation(SVM) is designed by combining the space vector modulation technique. The influences of the asymmetrical grid faults on output active and reactive power are analyzed in detail on the basis of introducing common failure of grid. The method of adding oscillation compensation to the reactive power is adopted to effectively suppress the grid current harmonic effectively. An improved power optimal compensation control strategy which eliminate the voltage fluctuation of the DC bus by compensating the AC side impedance power oscillation of the grid connected converter is proposed to further improve the fault ride-through capability Simulation and experimental results show that the proposed scheme is effective and feasible.