Research On Electric Power Control Technique Of Dc Micro-grid With PV Generation And Mixed Energy Storage

In the typ ica l PVGS (Photovolta ic Generatio n System) a nd direct-drivewind turbine generation syste m, and ultracapacitor/battery storage devices, theoutput power is always DC mode. DC micro-grid could be introduced to realizethe concordant operation of multi power generatio ns, to avoid the dc-acconvertion, and to control output power expedie ntly. This paper researches eachsubsystem’s electric power control technique by studying each subsystem’stopology, stability and control strategy, researches total syste m’s electric powercontrol a nd coordination technique to optimize effic ienc y and realize concordantcontrol.The mathematical modeling of PVGS is made. A new fast-response and higheffic ient variab le structure control of MPPT method is proposed. Cons idering theproblems occur in full output P-U curve, a self-regulating CVC (constant volta gecontrol) method based on PVGS’s half output P-U curve is proposed. Then avolta ge-current dual-loop control strategy is designed based on sma ll signa lmodel to ensure the stability of the closed loop system. A mixed storage topolo gysystem to optimize battery’s working performance is stud ied. Both ultracapacitorstorage system and battery storage system’s vo ltage-current dual-loop controlstrategy are constituted when operating in CVC mode, and battery storagesystem’s current closed loop control strategy is constituted when operating inconstant power discharge (CPD) mode. A binary form charge method is designedfit for the storage system’s charge characteristic.A simplified source and load model is established to describe DC micro-grid,which is utilized to analyze and derive power matching, control and s mall s igna lstability conditions. An impedance criterion is carried out to ensure DCmicro-grid’s small s igna l stability based on impedance analysis method.An effective and re liable design method of DC micro-grid’s energymana geme nt system is proposed, and the design process is discussed. First,utilizes figure codes to enumerate all DC micro-grid’s operating modes, thenselects availab le modes based on steady-state operation princip les, afterwards adds switching rules between ava ilable modes cons idering the differentoperational cond itions to form a who le dyna mic operation mode, and cha lks upthe control flow chart of energy ma nage ment syste m.Each subsystem a nd DC micro-grid’s s imulation model are establis hed inMATLAB s imulation environment. The control strategy, stability andmicro-grid’s energy ma nage ment strategy are tested and verified by simulatio n.A low volta ge and power prototype is designed, and correspond ingexperiments is conducted. The corresponding experiment results validate thevalid ity and feasib ility of conducted research of e lectric power control techniq ueof DC micro-grid with PV generation and mixed energy storage.