Research On DC Grid Connected Control Of Isolated Triple-active-bridge DC-DC Converters With Integrated PV-Storage

Photovoltaic(PV)power generation technology is an important means to develop sustainable clear energy and alleviate environmental pollution.However,the output power of PV generation is intermittent caused by ambient temperature and solar irradiation.In order to reduce the fluctuation of PV output power and improve the quality of power generation,it is necessary to add energy storage devices into the PV power generation system.To integrate PV and storage devices into the DC micro-grid and realize the electrical isolation between the connected DC sources,an isolated tripleactive-bridge(TAB)DC-DC converter is studied in this paper.Firstly,the dual-active-bridge DC-DC converter and the single-phase-shift control is introduced in this paper.According to the operating principle of TAB converters,the equivalent circuit,power equations and small signal model of the converter are deduced.To eliminate the coupling between input/output variables of the TAB converter and improve the system dynamic performance,diagonal matrix decoupling control method is applied,and then inner voltage/current loop control systems of the converter is designed.Secondly,this paper analyses the stability of inner voltage/current control loop for the TAB converter respectively.It is found that the port current flow to the DC microgrid will oscillate due to the filter resonance.Then,the methods to suppress the current resonance are studied by increasing the resonant frequency of the filter and using the damping effect of the Equivalent Series Resistance(ESR)of the filter capacitor.Through the analysis,the port current can avoid resonance by increasing the resonant frequency of the filter.However,the port current ripple will be increased because the filtering effect is weaken.Moreover,the current resonance suppression effect of the filter capacitor ESR is limited,which leads to the problem of relevant controller parameter selection.Thirdly,to deal with the problem of DC-grid-port current oscillation,the controller in the inner current control loop is optimized in this paper and the stability control of the TAB converter system is realized.On this basis,outer power control loops of the TAB converter are designed.The maximum power tracking of PV power is realized by using the perturbation observation method.Moreover,the power control of DC microgrid is realized.Therefore,the converter can switch freely among the working modes of grid connection,energy storing and grid connected energy storing.Finally,this paper designs the TAB converter hardware circuit and the software program to realize the control function.The modular converter experimental platform is set up.The experimental results verify the effectiveness of the stability control strategy.