A \theta-Converter That Reduces Common Mode Currents, Output Voltage Ripples, and Total Capacitance Required

• Published in: IEEE transactions on power electronics 2016-12, Vol.31 (12), p.8435-8447
• Main Authors: Zhong, Qing-Chang, Ming, Wen-Long
• Format: Article
• Language: English
• Subjects: Capacitance; Capacitors; Common mode (CM) current; Controllers; Density measurement; Electric currents; Electrical equipment; electrolytic capacitor; film capacitor; isolation transformer; Legged locomotion; Reactive power; reliability; Switches; Switching; Topology; Transformers; voltage ripples
• ISSN: 0885-8993; 1941-0107
• DOI: 10.1109/TPEL.2016.2519345

In this paper, a single-phase converter consisting of two legs with four switches, called the θ-converter, is proposed. It has a common ac and dc ground, which reduces common mode currents and removes the need for an isolation transformer, and two capacitors: one across the whole dc bus and the other across the output. The dc bus capacitor provides a direct path for the double-frequency ripple current inherently existing in single-phase converters to return continuously so the output capacitor can be sized very small, only to filter out switching ripples. Moreover, the dc bus capacitor is intentionally designed to store the system ripple energy with large voltage ripples, which reduces its capacitance. Hence, the total capacitance needed and the output voltage ripples are reduced at the same time. This makes it cost-effective to use highly reliable film capacitors instead of bulky and vulnerable electrolytic capacitors. Because of the removed isolation transformers and bulky electrolytic capacitors, the power density and system reliability are improved. In order to properly operate the converter, two independent controllers are designed for the two legs, respectively, to achieve the desired functions and other normal objectives, such as the unity power factor. Experimental results are presented to demonstrate the high performance of the proposed converter.