Simulation Study On Stand-Alone Photovoltaic Generation System Based On Passive Hybrid Control

For increasingly serious environmental problems and energy crisis, the use of renewable and clean energy is particularly important. Photovoltaic technology for the use of solar power is widely applied because of the universality and limitless of solar power and transport convenience of electrical energy. Stand-alone photovoltaic generation system has important application value for the power supply of remote area household and unattended equipment.In order to maximize the power output of photovoltaic power generation unit, taking into account the energy storage unit constraints in the charging and discharging processes, maintaining the DC bus voltage constant, it is needed to establish an effective overall control strategy. For stand-alone photovoltaic generation system with DC/DC converters, the overall control strategy is ultimately achieved through the bottom DC/DC converter controllers, which regulate the DC/DC converters to complete the conversion of power. Aimming at the fact that DC/DC converters belong to the essential nonlinear systems and overcoming the parameter sensitivity of the DC/DC converters, passive hybrid control, passive control-monlinear control, combined with PI(Proportional-Integral) control, is used for the DC/DC converter.The main work and the achievements of this paper are as follows:(1) On the basis of analysis of the advantages and disadvantages within the common structures of stand-alone photovoltaic generation system, the structure of stand-alone photovoltaic generation system is determined, which contains power conversion interfaces to respective photovoltaic power generation unit and energy storage unit respectively. On the basis of circuit modeling of photovoltaic cell and photovoltaic module, a M-file document for simulation of PV array is written by Newton iterative method. Then the mainteenance-free lead-acid battery is selected as energy storage unit and unidirectional Boost and bidirectional Buck-Boost DC/DC converters are selected as the interfaces to respective photovoltaic power generation unit and energy storage unit. Finally, according to the choice of the type of load, the specific structure of the stand-alone photovoltaic generation system is determined.(2) According to the lead-acid battery charging and discharging current and voltage constraints, the lead-acid battery charging and discharging strategies are determined and six working modes are adopted for the operation of stand-alone photovoltaic generation system and control modes of unidirectional Boost and bidirectional Buck-Boost DC/DC converters are respectively identified, combined with the analysis of energy flow in stand-alone photovoltaic generation system. According to the control mode for unidirectional Boost, in order to make a smooth transition between the control modes of tracking maximum power point and limiting the power output, a PV array power regulator is employed, which includes PI voltage outer loop fed the DC bus voltage into, and then photovoltaic maximum power point tracking method-short circuit current law is improved.finally the overall control strategy is built for stand-alone photovoltaic generation system.(3) On the basis of analysis of relative degree of affine form of nonlinear equations for respective Boost converters and Buck converters,one conclusion is drawn that Boost converters contain inner dynamic and Buck converters don’t.Then directly passive voltage control law is designed for Buck converters. For Boost converters, the inner dynamic stability is verified when state variable-inductor current is regareded as the output variable. the inductor current regareded as the state feedback variable,static passive current control law and dynamic passive current control law are respectively designed for Boost converters and then according to better control performance, shown by static passive current control law, static passive current control law is chosen as passive control law for Boost converters.on the basis of static passive current control law,with which PI voltage outer loop is series,through PI voltage outer loop, the desired variable is automatively configured to solve the problem of changes of parameters.(4) For stand-alone photovoltaic generation system, the main circuit and control circuit models are established in Matlab/Simulink simulation software environment. Then, the conventional PI control is introduced to be compared with passive hybrid control. According to typical working modes for the operation of stand-alone photovoltaic generation, respectively, the overall control strategy proposed is verified for the effectiveness of energy management and stand-alone photovoltaic generation system based on passive hybrid control is verified for better dynamic and static characteristics and stronger robustness.