Study On Single-phase Photovoltaic Energy Storage Inverter System And Its Control Method

Since entering the new century,the global energy shortage,China's energy shortage has become increasingly prominent.In order to solve the global energy crisis and realize the sustainable development of China's economy,the development of new energy industry is imperative.Photovoltaic energy storage technology is a necessary technology for the development of distributed energy,smart grid and energy internet.It is also an important technical support to solve the problem of peak-shaving and valley-filling of conventional power,improve the efficiency of conventional energy generation,transmission,security and economy.The photovoltaic energy storage inversion system can improve the utilization rate of energy and alleviate the problem of energy shortage in China to a certain extent.In this paper,the structure of single-phase photovoltaic energy storage system is studied,which consists of battery charging and discharging circuit,MPPT control circuit and bidirectional inverter circuit.Aiming at the disadvantages of complex design,high cost and low cost performance of traditional two-stage bi-directional charging and discharging circuit,this paper presents a new scheme of double active bridge battery charging and discharging circuit based on parallel-series combination.Compared with traditional two-stage charging and discharging circuit,it can improve energy conversion efficiency,and help to improve product power density and cost performance.In this paper,a new ZVT-Boost PWM circuit for MPPT controller is studied,its working principle and maximum power point tracking control method are analyzed,and the software configuration method of pulse control signal is given for the main switch and auxiliary switch in the circuit,so as to realize the soft switching of the two switches,which is helpful to improve the energy conversion efficiency of the system.Aiming at the bi-directional inverters in single-phase photovoltaic energy storage system,this paper studies the working principle,modulation method and control method of single-phase full-bridge bidirectional inverters.Through single-phase full-bridge bidirectional inverters,grid-connected generation,off-grid inverters and high power factor rectifiers are realized.Grid-connected power generation can feed the energy of photovoltaic modules into the grid,or the energy of energy storage cells into the grid if necessary;off-grid inversion can feed the energy of cells or photovoltaic modules to the load for power supply;high power factor rectification can realize the charging of the grid for batteries,while meeting the requirements of unit power on the grid side.Aiming at the application of photovoltaic energy storage inverters in micro-grid and distributed power generation,the energy management strategy of photovoltaic energy storage system including general mode,off-grid mode,standby mode and economic mode is proposed.The three parts of the circuit of the energy storage system are coordinated,and the working method and control realization of backup load power supply are emphatically studied.Based on the realization of charging and discharging function of shunt-series combined double active bridge circuit,a wide adaptability charging and discharging circuit is proposed in this paper.In the case of high battery voltage,the full bridge circuit on the battery side can be connected in series by switching the normal closed contacts of two relays.In the case of low battery voltage,the full bridge circuit on the battery side can be connected in parallel by the normal open contacts of two relays.Both applications have high efficiency.The paper also studies and analyses the insulation impedance protection circuit and leakage detection protection circuit in photovoltaic energy storage system,in order to achieve the safe and reliable operation of the system.Finally,an experimental prototype of 4.6kW single-phase photovoltaic energy storage inverters is built,and the design method of main circuit parameters is given.The tuning method of control parameters and the design method of safety protection circuit are given for the invertible converter circuit.The feasibility of the theory and the correctness of the design are verified by experiments.