Research On The DC/AC Inverter Supplies Powering Nonlinear Loads

Inverters have been widely used to provide high quality AC sources to sensitive equipments. However, inverter always faces the problem caused by nonlinear loads. The traditional method concerning nonlinear loads uses approximating way which can't provide the analytical insight needed for the design and optimization of the inverter system powering them. As the rectifier loads play the most important role in the nonlinear loads, it's reasonable in this dissertation to make the rectifier loads as a representative in the analyses of the characteristics of inverter powering nonlinear loads. This dissertation mainly focuses on the interactions between the nonlinear loads and inverters powering them, as well as in the wireless paralleling inverter applications.In Chapter 2, the characteristics of rectifier loads have been deeply analyzed firstly. Systematic analytical methods have been proposed. It is simple while with high accuracy. The information obtained from these analyses can be used in the controller design for the inverter systems powering rectifier loads. Furthermore, choice of power compensation strategies, as well as design of compensation systems can be optimized with these accurate estimated harmonic currents.Chapter 3 proposed a nonlinear model for rectifier loads. With this model, the dynamic response of the system is derived by the nonlinear control theory, which reveals that the system can be simplified as if it shifts between two different steady states periodically. The distortion mechanism of the inverter output waveform under rectifier load is then studied through the analyses of these two steady state responses. The system stability is analyzed using the phase plane plot of the nonlinear control theory. Based on these analyses, design principle is proposed. And some key issues of inverter system concerning nonlinear loads have also been studied and discussed.Detailed investigation and comparison of major inverter control strategies have been performed in chapter 4, especially concerning nonlinear load's requirements. Based on these works, the double-loop configuration, PI controller + Internal mode controller is believed to be the preferred control strategies of inverter powering nonlinear loads. For single phase inverter, the internal mode controller should be repetitive or resonant controller as the best choice. While in three phase applications, the stationary frame controller or resonant controller are preferred. System optimizing rule has been proposed, as to adopt the output current feedback to provide the load information especially with nonlinear loads. And a nonlinear control strategy for typical nonlinear loads has also been proposed and studied.In chapter 5, an analytical method for wireless-paralleling inverter system has been proposed. The stability, dynamic and steady-state performance of parallel system have been investigated. And a nonlinear control strategy for wireless-paralleling inverter powering nonlinear loads has been proposed.