Control Strategy Of PV-ESS Multi-Microgrid With Series Structure

In recent years, government supports renewable energy generation, which is promoting the rapid development of distributed photovoltaic power generation. As effective tool for distributed generations effectively connect to the electric distribution network, microgrid can give full play to the effectiveness of distributed generation, which has great economic and social significance. Characteristics of microgrid development are large-scale, diversity and geographical. The microgrids in adjacent areas can interconnect each other to be multi-microgrid system. Due to the complexity of microgrid operation, differences of energy storage capacities, load changes and differences of distributed generation output powers, optimization control of multi-microgrid is becoming more complex. Efficient economic operation of multi-microgrid is the key technologie of the development of the smart grids Therefore, this paper researches to control strategy of photovoltaic and energy storage system(PV-ESS) multi-microgrid with series structure, the main research contents are as follows:1. Based on analysis of structure and operation control method of PV-ESS microgrid, this paper researches topology of PV-ESS multi-microgrid with series structure. It analyses principles, mathematical models and control strategies of power generation units, energy storage units, load units and other electrical units to build model of series structure PV-ESS multi-microgrid.2. Researching grid-connected economical optimization operation of series structure PV-ESS multi-microgrid, this paper presents an algorithm of distributed model predictive considering time-sharing price. Based on the forecast of sources and loads, we formulate the objective function in every layer of subordinate microgrid, and via the distributed model predictive in each subordinate microgrid central controller, we take the method of rolling optimization to solve the function presented. The effectiveness and feasibility of the proposed method is verified by actual example.3. Researching islanded optimization operation of series structure PV-ESS multi-microgrid, based on distributed model predictive control, this paper presents a multi-objective optimization operation strategy which is considering the supply rate and last supply time of load. Based on the forecast of sources and loads, we formulate the multi-objective function in every layer of subordinate microgrid, and via the distributed model predictive in each subordinate microgrid central controller, we take the method of rolling optimization to solve the function presented. The advantages and feasibility of the proposed method is veri-fied by actual example.4. It is the key to guarantee safe and stable operation of microgrid that microgrid central controllers achieve seamless transition between grid-connected operation modes and islanded operation modes of microgrid. Based on the researches of phase-locked loop control and phase adjustment, this paper proposes an islanded-to-grid-connected seamless transition control strategy of multi-microgrid. In dq0 coordinates, microgrid central controllers adjust the voltage amplitude, frequency and phase, and also calculate switching time with different initial phase angle and frequency. The effectiveness and feasibility of the proposed method is verified by actual example. This paper also proposed multi-microgrid initiative and passive grid-connected-to-islanded control strategy, realizes grid-connected-to-islanded seamless transition of multi-microgrid.