| With the approaching of conventional fossil fuels crisis and intensifying of environment pollution,photovoltaic(PV)power generation has received extensive attention from all over the world because of its unlimited,pollution-free and environmental-protective advantages,which is considered to be one of the most prospective renewable energies.However,photovoltaic power generation is instable,stochastic and susceptible to natural conditions,such as temperature,light and weather.Moreover,the output voltage of a single PV panel is low,and it cannot meet the demands,so a power converter must be adde to increase the PV voltage into a higher voltage level.Inverter is a critical component in the PV power generation system,and its topology,reliability,efficiency and cost are significant for the whole system.The energy storage quasi Z source cascade multilevel inverter(ES-qZS-CMI),proposed recently,combines the advantages of energy storage system,qZS network,and cascaded multilevel inverter.When the ES-qZS-CMI is applied to PV power generation system,the promising features are presented:1)distributed MPPT that to maximize PV power;2)store the extra PV power;3)compensate the power differenc between the PV power and the load demand;4)the power switches in the same bridge leg can conduct together without damage;5)the PV voltage can be increased into a higher level through single-stage power conversion;6)lower harmonics,efficient and higher reliability.The topology has aroused world-wide attention once proposed.The main contribution of this dissertation is to investigate the model,design and control method of the ES-qZS-CMI.The details are as follows:Firstly,a comprehensive model of the ES-qZSI is built.The built model includes the PV terminal capacitor,battery and breaking the limits of L1=L2 and C1=C2.Moreover,the day time model and night model are derived respectively.The influence of qZS network parameters to double-line-frequency(2ω)is investigated,and an ES-qZS impedance design method is proposed to mitigate the 2ω ripple based on the built model.Secondly,for the different operations of the ES-qZS-CMI PV power generation system in daytime and night,a comprehensive control scheme is proposed.When the sunlight is sufficient,shoot-though duty ratio D is adjusted by a PI controller to track the PV panel’s maximum power point,and the battery is used to buffer the fluctuation of PV power;when night comes,PV panel is disconnected from the ES-qZSI system,a closed loop controller is used to control the DC-link voltage to be desired value,and energy storage system provide the power to the grid/load;AC output voltage is controlled by a PI controller to adjust the modulation index.Thirdly,an improved multi-dimensional pulse-width modulation(IMD-PWM)technique is proposed for the ES-qZS-CMI PV power generation system to minimize the computation cost and reduce the hardware resource of the modulation algorithm.To quicken the adjusting speed and improve the stability of the qZS-CMI PV power generation system,a DC-link voltage balancing control strategy is investigated,using multi--dimensional pulse-width modulation(MD-PWM)technique.Moreover,a control method to balance the battery state of charge(SOC)of all modules is proposed,no matter what intermittent states of the module’s PV power according to the current battery SOCs of all modules and the total power injected into the grid.Finally,considering the problem of high power quality permeability appeared in distributed generation(DG)system,this dissertation proposes a PV power generation and static synchronous compensator(PG-STATCOM)based the ES-qZS-CHB system,to implement PV generation and reactive power compensation at the same timeThis dissertation aims at investigating the model,designing and control scheme of the ES-qZS-CMI PV power generation system,which will promote the application of the topology in PV power generation and the development of the PV industry. |
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