Research On Transformerless-Parallel Hybrid Active Power Filter

This thesis deals with a TLS-PHAPF (Transformerless-Parallel Hybrid Active Power Filter), which is mainly used for harmonic compensation in adjustable-speed drive systems based on diode rectifier. With the advantage of low active capacity, low cost and feasibility for medium-voltage usage, this topology is attractive for industry application.In this paper, Firstly, the main operational principle of TLS-PHAPF is discussed, as well as basic filtering characteristic.The harmonic current characteristic produced by diode rectifier with a dc capacitor is also analyzed. In addition, some key points on TLS-PHAPF design are discussed in detail, including parameters such as AC side inductor, DC voltage of inverter, etc. AC side inductor is widely used in industry application for harmonic repression as a most simple way, but the big fundamental voltage across the inductor is a side effect. A compromise is made to balance the filtering performance and fundamental voltage fall. We use vector-graph aided method to design the DC voltage of inverter. The comparison of different types of passive filters is also performed.To make a compromise in cost and filtering performance, we choose a LC passive filter tuned at seventh harmonic frequency, which makes a not so good filtering performance in the most dominant fifth frequency. A fifth harmonic frequency feed forward control scheme is proposed, as well as a fifth harmonic frequency feedback control scheme. Results from both theory analysis and simulation shows that fifth harmonic feedback has better filtering performance than its feed forward counterpart.A 10kVA experimental system is built. In design of LC filter, for the nonlinear magnetization of iron core, it is difficult to measure inductor precisely. A novel inductor measurement method based on half-bridge circuit is proposed.