Study on AC Motor Drive System with Small Passive Components and Auxiliary Energy Storage Circuit in DC-Link

Abstract

In power conversion system, passive components such as grid filter inductor and DC-link capacitor have been widely used. However, they have several problems that they occupy too many spaces in the entire and an electrolytic capacitor which is commonly used in DC-link has a low reliability due to its high failure rate. To reduce or replace them, novel control methods or topologies using extra active devices with low-power-rating have been proposed, and these methods match to a trend of cost reduction of high-performance switching devices. Hence this dissertation proposes control method for diode rectifier-fed system equipping small passive components and an auxiliary circuit called as DC-link shunt compensator (DSC). Owing to the absence of the electrolytic capacitor, the proposed structure is robust in terms of component failure. Moreover the diode rectifier-fed system using the proposed method can satisfy grid regulations such as IEC 61000-3-12 or -3-2 without power factor correction (PFC) or heavy grid filter inductor. The proposed method includes the grid current shaping and system operating methods which improve grid current harmonics and system performances, respectively. This dissertation also presents implementation methods by using either motor drive inverter or DSC. The former is the most cost-effective way to realize proposed method but it necessarily degrades output performances such as torque quality and system efficiency. The latter requires auxiliary switching devices and small passive components, but it has advantages in not only output performances but also system efficiency by cooperation of DSC. The proposed DSC operating strategy is presented in detail and corresponding design guideline is also provided. In this dissertation, the DSC operating method is considered for both single- and three-phase diode rectifier-fed systems. In the case of the diode rectifier system using small passive components, the waveform of DC-link voltage is totally different in accordance with the gird phase, thus the corresponding control algorithms for both single- and three-phase inputs are also established respectively. This dissertation proposes each dedicated control method and discusses the feasibility. As a practical implementation example, boost converter is selected for the structure of DSC, and the validity of proposed methods are verified by simulation and experimental results.