| As the earliest household appliances that use solar energy,solar water heaters have experienced the development stage from ordinary solar water heaters,separated solar water heaters to solar electric water heaters.Ordinary solar water heaters and separated solar water heaters generally have several problems,such as short service life,easy aging and leakage of outdoor connecting pipes,easy bursting of vacuum collecting pipes,compliex installation and maintenance processes,etc.With the development of solar energy and its photovoltaic industry as well as the reduction of the price of photovoltaic cells,solar water heaters have attracted more and more attention due to their advantages of high efficiency,long service life,flexible expansion and easy assembly.In this paper,the application of DC/DC converter in solar electric water heater is studied.The common DC/DC topologies and their advantages and disadvantages are analyzed.A single-tube resonant isolation circuit is proposed for solar electric water heater.Firstly,the working process of the single-tube resonant isolation circuit is analyzed.The equivalent model is established according to its working principle.The equation of state is written,so the relationship between each parameter and voltage gain and output efficiency is obtained.Secondly,the parameters of transformer,switching tube,resonant capacitor and voltage doubling rectifier circuit are designed through the derived formula.The temperature field simulation of the transformer is carried out by JMAG software.Then,the driving circuit and the voltage and current detection circuit of photovoltaic board are designed.Finally,by analyzing the output characteristics of the established photovoltaic cell model and the working characteristics of the single-tube resonant isolation circuit,a control method for changing the switching frequency to achieve maximum power point tracking is proposed.Based on the dsPIC30F2020 microcontroller,the design of the main program is completed.In this paper,the main circuit and the maximum power point tracking control are simulated by Saber,PSIM softwares,a 300 W experimental prototype is built.The detailed experimental verification is carried out.Simulation and experiments show that compared with the traditional DC/DC converter,the converter not only realizes the ZVS of the switch tube and the bidirectional excitation of the transformer,but also has the advantages of simple control,small size,low cost,high efficiency and high reliability,therefore it has a great promotion and application value in solar electric water heater. |
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