| In the electrical power market, it is the inexorable trend for traditional fossil fuels to be replacedby intermittent energy. Since the integration of the intermittent energy generation system will lead to some side-effects, many experts and scholars pay more attention on distributed power generation and the micro-grid to solve the problem of security for the power grid.When it comes to distributed power generation and the micro-grid, it means the volume of the inverter system should be as small as possible. As a result, the switching frequency should be fast as possible. If the switching frequency is very high, there will be some problems like high switching-loss and EMI. The soft switching technology is proposed to solve the problems. After the resonant DC link inverter was discovered in the 1980s, the research on soft switching technology is becoming hotter and hotter.Based on relevant theoretical knowledge and key technologies, a high-efficiency low-cost PV inverter system with soft switching technology is produced in this paper. Through the analysis of the principle of the circuit, mathematical modeling, software test platform and hardware test platform, a single-phase single-loop system and a control three-phase triple-loop control system are constructed respectively. The research findings of this paper is shown below1、Without extra power and magnetic element, the soft switching condition created just by the resonance between electrical capacitor of the switch transistor and inductance at the inverter side. The switching loss is decreased while the cost is saved as well.2、the relevant theory of the micro-inverters and the newest research of the soft switching technology are summarized in this paper. Based on the engineering model and characteristics of photovoltaic array, the micro-inverter topology is designed. Also, the working principle of the proposed micro-inverter system is analyzed.3、To achieve the soft switching, a corresponding control method for switching is required. Therefore, several control methods are produced. Through comparison, a practical method is chosen to be used in the proposed inverter system. Next, the performance of the proposed inverter system with and without damping is compared in this section.4、by mathematical modeling, software platform and hardware platform, the proposed inverter system is operated successfully in condition of single-phase control and in condition of three-phase control respectively.The above experimental results show that the proposed frequency conversion soft switching PV inverter not only has easy topology and low cost, but can operate stably. To sum up, the proposed inverter system has important application value. |
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