Design of active power-factor-correction converters for environmentally green energy management systems

Pao Yue-kong Library Electronic Theses Database

Design of active power-factor-correction converters for environmentally green energy management systems

 

Author: Wen, Wei
Title: Design of active power-factor-correction converters for environmentally green energy management systems
Degree: M.Phil.
Year: 2004
Subject: Hong Kong Polytechnic University -- Dissertations
Electric current converters -- Design and construction
Electric current converters -- Environmental aspects
Department: Dept. of Electronic and Information Engineering
Pages: xvi, 155 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1762029
URI: http://theses.lib.polyu.edu.hk/handle/200/1957
Abstract: The input stage of a conventional AC - DC converter is often a rectifier bridge followed by a large bulk capacitor. As a result, the circuit draws pulsed current from the mains, which will lead to poor utilization of the capacity of the AC power source and produce harmonic pollution. In order to reduce the harmonic currents and meet the regulatory requirements such as EN 61000-3-2, both passive and active power-factor-correction (PFC) circuits have been widely used. Compared with passive circuits, active circuits can operate over a wider line voltage range and have smaller size. Therefore, for most applications, active circuits are used. In low power applications, single-stage active PFC converters are attractive for their low cost and simplicity. A typical single-stage PFC converter includes two parts: an input-current waveform shaper and an isolated DC - DC convener. These two parts are integrated with a shared switch and controller. However, the active switch in a single-stage PFC circuit often suffers large voltage spike during switching because of the unavoidable leakage inductance of the transformer. Such voltage spike can increase the switching loss and lower the conversion efficiency. It can even damage the switch if the voltage rating of the switch is not high enough. When the switching frequency is pushed higher, the problem will become even worse. In order to solve the voltage spike problem, a novel single-switch high-power-factor regulator with low output current ripple is proposed in this thesis. The proposed regulator employs a modified-boost converter cell as the input stage and a double-ended forward converter cell as the output stage. In the modified-boost cell, only one clamping capacitor is necessary to suppress the voltage spike and to recycle the energy trapped in the transformer leakage inductance. The modified-boost cell operates in discontinuous conduction mode (DCM) and a high power factor is attained. In the double-ended forward cell, near-zero output current ripple is achieved and an integrated transformer is used to reduce the number and size of the magnetic components. The basic circuit topology and the operation principle of the proposed regulator are explained. Design considerations are given. Simulation and experimental results are reported to verify the operation and performance of the proposed regulator. For high power applications, single-ended boost converters operating in continuous conduction mode (CCM) have been widely adopted as the front-end of PFC regulators. Compared with DCM operation, CCM operation has better utilization of power devices, lower conduction loss, and lower input current ripple. However, the large reverse-recovery current of the output rectifier in a CCM boost converter will cause not only extra switching loss, but also severe electromagnetic interference (EMI) noise. Two-channel interleaved boost converters have been proposed by many articles to eliminate the reverse-recovery problem while keeping the input current smooth. In such a two-channel boost converter, each individual channel can operate in DCM or critical conduction mode (CRM). The combined input current is continuous and smooth because of the interleaving arrangement. The two inductors in a two-channel boost converter can be directly coupled to reduce the number of the magnetic components and to attain good current sharing characteristics between the two channels. However, since both the inductors have considerable number of turns, the large inductor current ripple in each channel will cause a high copper loss. In order to improve the efficiency, a two-channel interleaved boost converter using an integrated magnetic component to reduce the core and copper losses is proposed. The integrated magnetic component functions as three inductors. All inductor windings are wound on a single El or EE core. In the proposed winding arrangement, inductors can be designed to have smaller inductances and lower copper losses. The windings on the two outer legs of the integrated magnetic component are inversely coupled, which helps to reduce the ripple of the magnetic flux. The design of the proposed integrated magnetic component and its electrical circuit model are discussed. Experimental results show that the proposed approach can offer significant improvement in efficiency. In order to further increase the power level, a highly efficient three-channel interleaved CCM boost converter is also proposed for high power applications. This converter consists of effectively three channels and the current in each channel is discontinuous. However, the overall input inductor current is continuous and smooth. In the converter, three inversely-coupled integrated inductors are employed to control the sharing of the three output rectifier currents. As a result, the current in each output rectifier is decreased in steps and finally reduced to zero before the associated active switch is turned on to start the next cycle of operation. All the output rectifiers are softly turned off. A very high efficiency is attained because the reverse-recovery loss is eliminated. The winding arrangement of the inversely-coupled integrated inductors (tree inductors with inverse coupling between any two) is discussed and the equivalent-circuit model is derived. The principle of operation of the converter and the design issues are explained. The converter is verified by simulation and experimental setup and the results show good agreement with the theoretical predictions.

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