Design And Control Of A Central Capacitor Photovoltaic Converter

Currently,string or multi-string distributed photovoltaic(PV)inverters have been widely used owing to their flexible configuration,high maximum power point tracking(MPPT)efficiency and high reliability.However,high reliability and low cost cannot be achieved simultaneously,since the power semiconductor devices integrated in conventional topologies suffer high voltage/current stress and high power dissipation.This thesis proposes dual-input central capacitor(DICC)converter,which could be utilized in string or multi-string distributed PV inverters as the front DC/DC stage.The voltage/current stresses and power dissipations of power semiconductors have been reduced.In order to further reduce the power dissipation of power semiconductor devices,this thesis also proposes a zero-voltage-transition(ZVT)circuitry,along with its operation principle and design methodology.An experimental prototype was constructed to testify this ZVT circuitry.In order to promote its performance under unbalanced PV power and grid voltage condition,this thesis proposes an adaptive control method and an active double line-frequency oscillation elimination menthod respectively.These proposed methods could improve the MPPT precision,reduce the risks of over-voltage operation and promote the grid current quality.The main contents of this thesis are as follows:(1)The application background of grid-tied PV inverter is presented;also the state-of-art for string or multi-string distributed PV inverter is analyzed.(2)The operation principle and the design procedure of the proposed ZVT auxiliary circuitry are presented;also the proposed ZVT circuitry is verified through an experimental prototype.(3)The central capacitor voltage adaptive control method is proposed,also the powe flow diagram of central capacitor converter is presented.The proposed adaptive control method is verified through an experimental prototype.(4)The operational strategy for central capacitor converter to operate under unbalanced grid voltage condition is studied.The double line-frequency voltage/current waveform oscillation is analyzed,and the circuitry parameters are designed accordingly.