Development of Photovoltaic System using PWM Power Inverter

我们研究的最终目的是开发一种结构简单、效率高、成本低的光伏发电系统。在本研究中，我们计划解决以下几个问题：1.高效率降压升压型PWM功率逆变器的研制。建立了以高效降压升压型PWM功率逆变器作为商业线路与太阳能电池接口的光伏系统设计方法。第一，为了获得高效率的PWM功率逆变器，我们研制了一种只用一个开关元件构成的推挽式PWM功率逆变器，并通过开关缓冲器实现了软开关。与采用传统RCD缓冲器的推挽式PWM功率逆变器相比，效率提高了5%~15%。其次，将推挽式PWM功率逆变器连接到电力线上，并进行了功率流和软开关特性的实验。结果表明，该系统具有良好的电能从太阳能电池向负荷和输电线路的传输特性。但是，由于受到逆变器的调制系数和太阳能电池输入电压的影响，软开关的实现比较困难。最后(1996)：我们对软开关进行了重新的研究，并发展了只用一个电容器构成的软开关。在此基础上，以铁氧体、非晶态铁氧体和空芯为材料，研究了电抗器效率与材料和绕组方式的关系。结果表明，材料的不同对逆变器的效率影响不大，采用空芯无隔离电抗器的逆变器效率最高，达到95%。

The final purpose of our research is a development of a photovoltaic system which has a simple construction, high efficiency and low cost. In this research, we have been planning to clear up the following problems :1. Development of a buck-boost PWM power inverter with high efficiency.2. Establishment of the design method of the photovoltaic system using the high efficiency buck-boost PWM power inverter as an interface of the commercial line and solar cells.First term (1995) : First, to obtain a high efficiency PWM power inverter, we developed a pushpull type PWM power inverter which was constructing with only one switching element and realized soft switching by a switch snubber. As a result the efficiency was improved 5 to 15% compared with the push-pull PWM power inverter with a conventional RCD snubber.Next, we have linked the push-pull PWM power inverter to the utility line and performed experiments on power flow and soft switching characteristics. As a results, this system has a good quality about the transfer characteristics of the power to the load and utility line from the solar cells. However, the realization of the soft switching was difficult in order to be affected by the modulation factor of the inverter and the input voltage of the solar cells.Final term (1996) : We have studied again about the soft switching and developed it which was constructed by only one capacitor. We are developing the PWM power inverter with this soft switching method, now.Furthermore, we examined the relations between the efficiency and materials and winding method of a reactor of the PWM power inverter.Ferrite, amorphous and air core were used as the materials. As a result, the efficiency of the inverter was not much affect by the difference of materials.The PWM power inverter with a no isolation reactor using air core was the best efficiency of 95% than that using other materials.