Research On Three-port Power Converter And Multi-peak MPPT For Photovoltatic And Storage

In recent years,the world’s environmental problems have become increasingly serious,which has promoted the continuous development of renewable energy generation and photovoltaic energy storage.The traditional photovoltaic energy storage system uses multi-stage converter,which mainly has the problems of low power density and low efficiency.The boost and bidirectional buck converter(3BC)researched in this dissertation integrates the photovoltaic port,energy storage port and load port,realizes the maximum power point tracking of photovoltaic cells,the control of battery charging and discharging,the stability of load voltage.3BC improves the power density of photovoltaic energy storage converter,and it has a modular structure,with the ability of power expansion.In this dissertation,the topology of 3BC is studied,its working principle is analyzed,the two-loop control structure and two-domain control strategy applied to 3BC topology are determined,and the loop compensator of the converter is designed.On the basis of two-loop and two-domain control,the improvement of multi-module parallel stability of converter is studied.The phase characteristic of the current inner loop in the MPPT control domain of 3BC has the problem of sharp phase decrease,which brings difficulties to the design of the voltage regulator,and the increase of the number of the converters in parallel will lead to the rise of the amplitude frequency curve,making the crossover frequency shift to the right,resulting in the poor control stability.In this dissertation,a adaptive three-loop control method is adopted,which keeps the original two-domain control strategy and changes the two-loop control structure.An auxiliary loop is added between the voltage outer loop and the current inner loop.When the condition changes and the transfer function of the inner loop changes,the auxiliary loop can adaptively reshape the inner loop so that the voltage regulator can adapt to various conditions.The simulation results in time domain and frequency domain verify the feasibility of the three-loop two-domain control method.When the number of converters in parallel is larger,the stability of the adaptive three-loop method is stronger.When the number of converters in parallel is larger than three,the device cost is lower than the loop shaping method.To solve the problem of multi-peak PV curve caused by partial shading on photovoltaic array,a dynamic light intensity model of photovoltaic cell isestablished according to the simplification of cloud shading solar radiation model.The output characteristics of photovoltaic array under dynamic shadow are studied.The Z-shaped moving trajectory of the maximum power point under dynamic shadow provides a theoretical basis for the multi-peak MPPT control strategy.In this dissertation,a novel MPPT algorithm combining particle swarm optimization and perturbation and observation method is proposed,and corresponding control strategies are proposed for various lighting conditions.Partial shading simulation experiments show that the algorithm has fast convergence speed and can track the maximum power point under the condition of dynamic shadow,and at the same time,it can suppress the power fluctuation problem of traditional particle swarm optimization algorithm.Compared with the MPPT control using only perturbation and observation method,the new algorithm can improve the energy extraction by at least 17.5% in theory under the condition of four photovoltaic cells in series with cloud shading.