The Design And Implementation Of Solar Charge And Discharge Controller Based On Improved MPPT Algorithm

The major functions of solar charge and discharge controller are control and protection the storage battery in its process of charging and discharging. MPPT technique is an important way to increase utilization of photovoltaic cell. This study devises a solar charge and discharge controller applied to stand-alone photovoltaic system, make solar panels to maximize the use of power and extend battery life by an in-depth analyses of MPPT combined with the property of phosphoric acid iron battery. This thesis has mainly studied the following contents:Firstly, according to the equivalent circuit model and mathematical property of photovoltaic cell, its simulated model is constructed. On this base, this thesis analyze output characteristic of photovoltaic cell and influence on it arising from change of outside environment. For the output characteristic of photovoltaic cells, through an in-depth analysis the realization principle of MPPT and its existed algorithm, this thesis puts forward an improved control algorithm which combines PID control algorithm with incremental conductance algorithm. In this way, performance of the maximum power point tracking can be improved. By contrast of incremental conductance algorithm, PID control algorithm and improved control algorithm in a simulated experiment, the last one has shown superiority, with further simulation of the algorithm on the condition of changing lights, the algorithm still can perform a good tracking even if it is placed under the complex environmental changes.Secondly, according to the functional requirements of solar charge and discharge controller, conducted a hardware and software design. At the aspect of hardware, the study selects the single-chip of Stm32 as a micro controller, and adopts buck converter. By adjusting the duty cycle of PWM, the load of photovoltaic cell equivalent output is changed, so that photovoltaic cell can work on the maximum power point; Design system signal sampling and processing circuit, various protection circuits and TFT display circuit and other circuit modules. For the high voltage suspended driver problem of MOS tube, the thesis designs an efficient and stable driving scheme based on driving chip IRS21171. At the aspect of software, the study compiles fundamental driving module and control algorithm. Combined with the property of phosphoric acid iron battery, three-step charging and control of load switch are realized. And software is devised for protecting the battery in its process of charging and discharging. The experimental result shows: every module of the solar charge and discharge controller can work smoothly, and the system has ability to track the maximum power point and charge by the tree-step mode.