Investigation On The Operation And Control Of Wireless Parallel-Connected Inverters

In recent years, aiming to solve problems of the energy shortage and the pollution caused by traditional fossil fuels, the development and utilization of sustainable and renewable energy such as solar, wind has been attracted widespread attention increasingly. With the rapid development of power electronics, the utilization of renewable energy based on distributed generation has opened up a new path. Meanwhile, the parallel-connected inverters technology which is one of the key technologies in distributed generation system has been rapid development. At present, the wireless parallel-connected inverters control has become a focus in the field of power electronics technology. However, the research on this control strategy is still existing problems and there has been many published literature worldwide. This dissertation aims to study wireless parallel-connected inverters some existing problems. Concrete research work is as follows:① The working principle of a single-phase inverter including SPWM modulation and main circuit topology are introduced. On the mathematic model basis, this paper deduces the closed-loop transfer function of single-phase inverter system. Then, through analysis of amplitude-frequency characteristic of open- and closed-loop transfer function, the closed-loop controller with highly improved output voltage performance has been designed.② Based on the illustration of power droop control without communication wire, the paper presents the parallel model of two single-phase inverters, and its mathematic model is established. Meanwhile, the causing mechanism of circulation within parallel-connected inverters system is described in detail. Finally, the control strategy of power sharing is studied.③ An improved adaptive droop method is investigated for parallel-connected inverters control. In the proposed method, a linear function of the power and droop coefficient is introduced to realize the adaptive regulation for the droop coefficients with the power variation, while a power derivative term is introduced to instantaneously reflect the trend of power, which effectively improving the stable operation performance and dynamic response capability.④ An experimental platform of parallel-connected inverters system is developed based on the 32-bit advanced digital signal processor(DSP). The experimental results of single inverter operation show that the dual closed-loop has good output voltage performance. In addition, the improved droop control scheme and conventional control scheme are compared by the experiment. The feasibility and validity of improved droop control scheme to enhance stable operation performance and dynamic response capability has been further demonstrated.