Research On Novel Topology Of DC/DC Converter And Its MPPT Control For Photovoltaic Generation

At present,distributed photovoltaic power plants are developing rapidly due to its higher operation reliability and installation flexibility.In the distributed photovoltaic power generation system,the output of two or more various boost-type DC/DC converters are connected in parallel with DC bus capacitors,and the DC power is converted into AC power by DC/AC inverters.Each boost-type DC/DC converter with maximum power point tracking(MPPT)function can track the individual maximum power point for independent photovoltaic module.Thus,the design of high performance and high efficiency boost-type DC/DC converter is of great significance on distributed photovoltaic power generation system.This thesis presents a non-isolated dual-input series-connected boost-type(DI-SCB)converter.The working principle of DI-SCB converter under continuous conduction mode(CCM)and discontinuous conduction mode(DCM)is studied respectively.In addition,the steady-state voltage gain,voltage/current stresses of switchs and diodes are derived,and the design criteria of main circuit parameters are deeply investigated.Compared with the topologies of various traditional converter,the proposed DI-SCB converter has higher voltage gain,and significantly reduces the voltage/current stresses of switches and diodes.In order to further investigate the dynamic performance of the proposed DI-SCB converter,the DI-SCB converter is modeled and analyzed by using the state space averaging(SSA)method to obtain its AC small-signal model and transfer function.Furthermore,the stability of DI-SCB converter is analyzed,and the digital compensator is designed according to the required frequency,phase margin and gain margin to achieve closed-loop control.In order to promote its performance under the condition of unbalanced inductance currents and photovoltaic power,the automatic inductance current sharing control method and central capacitor voltage control method are proposed respectively in this paper.The proposed control method could reduce the unbalanced degree of inductance currents,improve its ability to handle the differential power,and reduce the risks of over-voltage operation.In order to ensure photovoltaic power generation system based on DI-SCB converter operating at the maximum power point,this thesis proposes a kind of variable step perturbation and observation method based on hysteresis comparison technique which could be utilized in the DI-SCB converter.Moreover,a decision-making method with variable step size is given,which effectively restrains the misjudgment and disturbance problems existing in the traditional fixed step size perturbation and observation method,and improves the stability of the system operating at the maximum power point.The experimental prototype of DI-SCB converter verifies the correctness and feasibility of its operating principle,design criteria of circuit parameters and control methods.The photovoltaic power generation system with MPPT function based on DI-SCB converter is simulated,which verifies the correctness of theoretical analysis and the feasibility of control methods.