Study On The Topology Improvement And One-cycle Control Strategy Of Z-source Grid-connected Inverter

Compared with the traditional bridge inverter, Z-source inverter can achieve theadvantages of the DC-side boost transformation and allow the inverter bridge armworking in the shoot through state with its unique impedance network. So there is noneed to insert the dead time, and the power quality and stability of the system can beimproved. Z-source inverter provides a low-cost, high efficiency, high reliability,single-stage boost inverter program, and it is especially suitable for the renewableenergy applications, such as solar power systems and wind power system, which has alarge range of input voltage, with a very broad application prospects. However, thetraditional Z-source inverter also has the defects, such as low boost capability, largecircuit size and large start impact, and its performance is to be further enhanced.To solve the above problem, the paper optimizes the impedance network of thetraditional Z-source inverter, and two kinds of modified Z-source grid-connectedinverter topology are proposed to enhance the performance of Z-source inverter; on theother hand, the performance of one cycle strategy in the control system of Z-sourcegrid-connected inverter is researched, and then based on the state equations of systemthe indirect one cycle current control strategy is proposed to expand the scope ofapplication of one cycle control.Firstly, the research statued of Z-source inverter topology transformation, modelingand control strategy, shoot through state injection method and its application in therenewable energy power generation systems were analyzed. Then based on the in-depthanalysis of the working principle of the Z-source inverter, the state averagemathematical model and the control system were built, and made a simulation researchto verify the performance of the output of the Z-source inverter.Secondly, the defects and defect generating mechanism of the traditional Z-sourceinverter was analyzed, to overcome its shortcomings and optimize the original topology,two modified Z-source inverter topology were proposed. Then analyzing the workprinciple of the two topologies, derivation the input-output relationship, and designingthe control system of three-phase Z source grid-connected inverter, the control loop ofwhich was designed based on the dq axis decoupling and impedance network capacitorvoltage constant. Finally build the simulation model to simulate and analyze thesteady-state output and mutation of input power or input voltage disturbance simulation to verify the feasibility and the superiority of the topology.Again, on the basis of simulation analysis, the improved Z-source grid-connectedinverter topology of the Boost circuit-based was taken for experimental verification.This paper design the overall structure of the experimental prototype, and thepre-inductor parameters, the Z-source network capacitors, inductors parameters as wellas the AC side filter inductor parameters. Then design to achieve program of thesampling unit, the current control unit, shoot through unit, driving unit in the controlsystem. Finally, experimental results were analyzed to further verify the feasibility andperformance of the proposed topology.Finally, this paper analyzed the basic principles of one cycle control and itsswitching circuit, then use one cycle control method in the control system of Z-sourcegrid-connected inverter. The direct one cycle current control equations of three-phaseZ-source grid-connected inverter are derivate and the simulation model is built. Then anindirect one cycle current control strategy based on the state average model of thesystem is proposed, derivation the equations, and build a simulation model, simulationof steady output, the mutation of the input power or input voltage disturbances wereresearched, and the comparative results show that the proposed indirect one cyclecontrol strategy was practicable, and effectively improve the dynamic characteristics ofthe traditional indirect current control and the control system has the advantages ofsimple, low cost, so it has a certain practical value.