یک اینورتر تک پایه سه فازی برای برنامه های فتوولتائیک متصل به شبکه
Abstract
I- Introduction
II- Proposed topology and its switching states
III- Switching algorith
IV- Control strategy
V- Reliability improvement
VI- Simulation results
VII- Experimental results
VIII- Conclusion
IX- References
Abstract
This paper presents a new three-phase Single-Stage Multi-Port Inverter (SSMPI). The proposed topology contains no electrolytic capacitors. Therefore, its reliability and lifetime are improved in comparison with well-known two-stage multi-port Voltage Source Inverters (VSIs). In addition, the SSMPI has a modular structure and the number of input ports can be easily increased. The input ports of the SSMPI can be fed by different Photovoltaic (PV) strings. Therefore, the SSMPI can be used in photovoltaic power plants with multiple PV strings to enhance the reliability and the lifetime of the power plant. The SSMPI can extract the maximum power from multiple PV strings with different irradiations, orientations and characteristics. In this paper, the SSMPI structure and its challenges in switching command generation and control are explained. Afterward, a new switching algorithm based on Space Vector Modulation (SVM) and a novel control strategy are developed to fulfill the requirements of the SSMPI. The simulation and experimental test results of a 2.4 kW prototype show that the proposed converter can inject three-phase currents to the grid with a unity power factor and without using any ac current sensors. Moreover, the maximum power is extracted from the input ports in different test conditions.
Introduction
In recent years, the share of renewable energy sources, especially solar and wind, for electricity generation has been increased and it is expected to see further growth of photovoltaic power plants in the next decades [1]. The reliability and the maximum power extraction are two important parameters of the photovoltaic power plants. Solar inverters have an important role in determining these two parameters [2]. Different types of solar inverters are used for integration of PV systems into the electricity network. Among them, multi-string inverters are appropriate and economical solutions for grid-connected PV systems due to their beneficial features such as flexibility, controllability and reliability [2]–[9]. In the multi-string structure, the number of strings can be increased easily. Furthermore, each string can be controlled independently and the net energy yield can be maximized. A lot of research has been conducted to evaluate and improve the performance of the two-stage multi-string VSIs [3]–[6], [10]–[12]. Although, multi-string voltage source inverters are very popular, they need bulky electrolytic capacitors, which restrict their lifetime and they are known as a cause of reliability reduction and inverter failure [13]–[20]. Therefore, converters without electrolytic capacitors are preferred from the reliability viewpoint.