Research On Control Strategy Of Single/Three Phase Islanded Multi-microgrid Based On PV And Energy Storage System

As the extension and deepening of the development of microgrids,multi-microgrids not only have advantages of independence,security,reliability and economy,but also have a more flexible mode of operation,which can coordinate the power exchange between microgrids in off-grid mode,so as to achieve the power complementary between microgrids and maximally meet the load power requirements in each microgrid.The single/three phase multi-microgrid based on PV and energy storage system is a form of multi-microgrids.When all sub-microgrids run in the island mode,the master power supply of the three-phase sub-microgrid will provide voltage support for the single-phase and three-phase sub-microgrids at the same time.Because the voltage control of the master power affects the normal operation of multiple sub-microgrids,the voltage control of the master power supply in the single/three phase multi-microgrid is put forward higher requirements.In addition,the unbalance of power exchange between the three single-phase sub-microgrids and the three phase sub-microgrids could lead to the unbalance of the transmission power of the multi-microgrid bus,thus causing the unbalance of the bus voltage.Aiming at the problems existing in the operation of the single/three phase multi-microgrid,in this paper,the voltage control of the master power supply,the power control of the slave power supply and the coordination and optimization control between the single-phase sub-microgrids and the three phase sub-microgrids are studied in depth,the main research contents are as follows:Firstly,the voltage control strategy of the energy storage master power supply is studied,and a novel compound V/f control strategy based on robust control is proposed.The novel compound V/f control consists of feedforward control and robust feedback control.The control strategy can make the output voltage have better power quality in response to unbalanced loads and nonlinear loads,and have strong robustness in coping with the load mutation and power output fluctuation of the micro-power supply.In this paper,the performances of the proposed control strategy,the traditional V/f control strategy and the compound control based on the traditional V/f control and feedforward control are compared and analyzed to verify the superiority of the proposed control strategy.Secondly,the power control strategy of the photovoltaic power is studied,and a novel current control strategy based on quasi proportional resonant control and improved robust repetitive control is proposed.The control strategy not only has the good dynamic regulation performance of the quasi proportional resonant control,but also has the good steady-state control performance and harmonic suppression capability of the repetitive control.In addition,in order to solve the problem that the conventional design method of weighting function in robust control needs to be adjusted repeatedly and the design process is complicated,a design method of weighting function is proposed.In this paper,the performances of the proposed control strategy,the quasi-proportional resonance control and the robust repetitive control are compared and analyzed to verify the superiority of the proposed control strategy.Thirdly,the power coordinated and optimal control strategy of the multi-microgrid based on PV and energy storage system in the islanded operation mode is studied,and a power coordinated and optimal control strategy is proposed for the common coupling point between the single-phase microgrid and the three-phase microgrid.Under the condition of making full use of renewable energy generation and meeting the requirements of security,economic and stable operation of the multi-microgrid,the control strategy could improve unbalance factor at the point of common coupling,the master power inverter terminal and the load side by coordinating the exchange power between the three single-phase microgrid and three-phase microgrid.In this paper,the performances of the proposed power coordinated and optimal control strategy,PI control and unbalanced compensation control are compared and analyzed to verify the superiority of the proposed power coordinated and optimal control strategy.Fourthly,the method to solve the coordination and optimization objective function is studied,and an optimization algorithm is proposed to solve the coordinated optimization objective function.The algorithm has faster algorithm convergence rate and higher solving precision of optimal value.In this paper,the iterative processes of the proposed optimization algorithm and the particle swarm optimization algorithm are compared and analyzed to verify the superiority of the proposed optimization algorithm.