Quasi-Single-Stage Multi-Input Distributed Power Generation System With Series-Time-Overlapping Supply

Distributed power generation system supplied by single kind of new energy,such as photovoltaic panels,wind turbines,usually has the defects of unstable and discontinuous power supply.In order to improve the stability and flexibility of new energy power generation system,and to achieve the prior or full use of new energy,the distributed power generation system that combines multiple new energy is implemented.Therefore,the distributed power generation systems with excellent performance which combined by multiple new energy are the research orientation in the field of power electronics and new energy power generation,and have important theoretical and engineering application values.Based on the elaboration of traditional two-stage single-input or multi-input DC-DC converter type distributed power generation systems,a kind of quasi-single-stage multi-input distributed power generation system with series-time-overlapping supply is proposed.The key techniques,such as the circuit structure and its topological family,energy management control strategy,principle characteristic,duty cycle of multi-inputs,system stability and circuit parameters design criteria are theoretically analyzed in depth and verified by simulation and experiment,with important conclusions obtained.The circuit structure and topological family of quasi-single-stage multi-input distributed power generation system with series-time-overlapping supply are proposed.The circuit structure is composed of a unidirectional or bi-directional DC-DC converter with multi-input selected switches in series and an unfold bridge.The topological family include six Buck type circuits and four Buck-Boost type circuits.The maximum power output energy management control strategy for the proposed grid-connected power generation systems with low voltage ride-through capability is proposed and studied in depth.The control strategy is consisted by n MPPT voltage loops,a grid-connected current loop and current-limiting circuits.The control strategy of Buck type power generation turns the single grid-connected current control,which is affected by n input sources,into n grid-connected current control,which is only effected by each one of the inputs.N independent regulators are used to realize the decoupling of n grid-connected current control.The control strategy of Buck-Boost type power generation is by controlling the instantaneous grid-connected current and the power ratios of multi-inputs to realize the energy management of input sources.The master-slave power distribution energy management control strategy for the proposed stand-alone power generation systems with smooth and seamless transition between different power supply modes is proposed and studied in depth.The control strategy is consisted by n-1 MPPT voltage loops,an output instantaneous voltage loop and power distribution circuits.The control strategy is by controlling the instantaneous output voltage and the power ratios of multi-inputs to realize the master-slave power distribution of multi-inputs.And it only requires n-channel power distribution circuit to achieve power adjustment of the inputs and smooth switching between different power supply modes.The steady-state principle characteristic and external characteristics of the proposed power generation system are discussed in detail.In order to reduce current sensors and control units,an implement method of control strategy by using parallel bus and CPU time-sharing is proposed.The active clamp circuits which are applied to suppress the voltage spike caused by the transformer leakage are also presented.Moreover,the system model and system stability are discussed,a compound control strategy which is made up of feedforward control,PI control and repetitive control is proposed.Major circuit parameters,for example,turns ratio of transformer are also deduced.By using the proposed topologies and energy management control strategy,three prototype,containing 1.5kW Buck type converter and 500W Buck-Boost type converter for grid-connected power generation system,500VA Buck-Boost type converter for stand-alone power generation system,are designed and developed.The experimental results have shown that the proposed power generation system has excellent performances such as quasi-single-stage conversion,galvanic isolation between the output and the inputs,time-overlapping power supply,wide regulating range of duty cycle,high conversion efficiency and smooth transition among different modes,etc.Which validates the feasibility and advancement of the proposed circuit configuration,topological family and energy management control strategy.Therefore,the schemes proposed in this thesis are new and effective methods in the distributed power generation systems which combined by multiple new energy.