THESIS ON POWER ENGINEERING, ELECTRICAL ENGINEERING, MINING ENGINEERING LC Circuit with Parallel and Series Resonance Alternation in Switch-Mode Converters JEVGENI SHKLOVSKI TALLINN 2007 Faculty of Power Engineering Department of Electrical Machines and Fundamentals of Electrical Engineering TALLINN UNIVERSITY OF TECHNOLOGY Dissertation was accepted for the defence of the degree of Doctor of Philosophy in Power Engineering and Geotechnology on February 1, 2007 Supervisor: Professor Jaan Järvik Department of Electrical Machines and Fundamentals of Electrical Engineering, Faculty of Power Engineering, Tallinn University of Technology Co-supervisor: Associate Professor Kuno Janson Head of the Department of Electrical Machines and Fundamentals of Electrical Engineering, Faculty of Power Engineering, Tallinn University of Technology Opponents: Professor, Dr. Manfred Sakulin, Graz Technical University, Austria Senior Design Engineer, Doctor of Technology Juhani Tellinen, Adaptamat LTD, Finland Professor, Vello Kukk, Tallinn University of Technology, Estonia Oral defence: March 16, 2007. Tallinn University of Technology, room VII-422 Declaration: “Hereby I declare that this doctoral thesis, my original investigation and achievement, submitted for the doctoral degree at Tallinn University of Technology has not been submitted for any degree or examination”. Jevgeni Shklovski, ………………………. Copyright Jevgeni Shklovski, 2007 ISSN 1406-474X ISBN 978-9985-59-687-6 2 Acknowledgments Herewith, I would like to thank all of those people and organizations who have helped and supported me in my work. First of all, I am very grateful to my parents for their invaluable support and care throughout the whole of my life and study. Their extensive knowledge, continuous encouragement and interest in my educational and personal development have motivated and will motivate me to continue my life-long learning. I would like to express my sincere gratitude to my advisors, Professor Jaan Järvik and Dr. Kuno Janson, for their scientific guidance, helpful advice and encouraging attitude that made the research described in this dissertation possible. I gratefully thank Madis Reivik for technical discussions, suggestions and help with practical implementation. I express my gratitude to Magnetics Inc and Wima GmbH for the samples and technical guidance they rendered to me. My thanks are due to component suppliers Harry Pale from Teamtron OY and Regina Kolts from EBV Elektronik OÜ who provided me with samples and information. I also thank Michael Schmelzer from MS Balti Trafo for the efforts to design and produce high-frequency inverter transformers needed in my research. The financial support of my doctoral study and research activities from the TUT Development Foundation (Eesti Energia Scholarship), Estonian National Culture Foundation and the Archimedes Foundation (Kristjan Jaak Scholarship) are greatly appreciated. I also wish to thank my present and former colleagues and friends for their contribution to my research and enjoyable discussions: Viktor Bolgov Ph.D., Mohamed Sidon M.Sc., Ants Kallaste M.Sc., Andrei Shkvorov lecturer, and many others. Finally, I would like to thank my beautiful and loving wife Jelena, for her love, patience and support. I hope this accomplishment will be a good sign for our soon expected child. JEVGENI SHKLOVSKI Tallinn, Estonia December 2006 3 Table of Contents List of Abbreviations..........................................................................................6 List of Symbols...................................................................................................7 1. Introduction....................................................................................................8 1.1 Current trends in power electronics.............................................................8 1.2 Resonant switch-mode converters...............................................................10 1.2.1 Resonant networks................................................................................10 1.2.2 Control techniques for load-resonant converters..................................14 1.3 Power factor correction in single-phase AC/DC converters........................15 1.4 PSA converter basics...................................................................................16 1.5 Modeling and analysis.................................................................................17 1.6 Purpose of the study.....................................................................................18 2. Mains frequency resonant converter with parametric parallel and series resonance alternation..............................................................................19 2.1 Development of a single-phase PSA converter............................................19 2.2 Role of additional resonant inductor............................................................22 2.3 PSA converter with resonant components on the primary side...................23 2.4 Basics of PSA converter parameter calculation...........................................24 2.4.1 Distribution factors...............................................................................24 2.4.2 Defining of reactive component values................................................25 2.5 Characteristics and peculiarities of single-phase PSA converter.................26 2.6 Commutations in output diode bridge rectifier............................................27 2.7 Self-adjusting to load...................................................................................29 2.8 Input current distortion.................................................................................30 2.9 Conclusions..................................................................................................31 3. Switch-mode PSA converter..........................................................................33 3.1. Basics of a generalized switch-mode PSA converter..................................33 3.1.1 Power circuit of SM-PSA and control..................................................33 3.1.2 Inverter circuit topology.......................................................................34 3.1.3 Switching frequency of the inverter......................................................34 3.1.3.1 Discrete reactive components........................................................35 3.1.3.2 Planar transformer and combined planar LCT components..........36 3.1.4 Conclusion............................................................................................37 3.2 Basic calculation procedure for resonant network of a SM-PSA converter.38 3.3 Some features in the design of the inverter transformer..............................45 3.3.1 Selection of transformer no-load voltage..............................................45 3.3.2 Distribution factor K ...........................................................................46 E 3.3.3 Leakage inductance..............................................................................46 3.3.4 Inductance of wires or busbars in the resonant network.......................48 3.4 Comparison of different resonant topologies of a SM-PSA converter........49 3.4.1 L L C resonant network........................................................................49 1 3 3.4.1.1 Output and regulation properties...................................................49 3.4.1.2 Operation in the switching cycle...................................................53 3.4.1.3 Conclusion.....................................................................................54 4 3.4.2 L L C resonant circuit...........................................................................55 1 2 3.4.2.1 Output and regulation properties...................................................55 3.4.2.2 Operation in the switching cycle...................................................58 3.4.2.3 Conclusion.....................................................................................59 3.4.3 L L L C resonant circuit.....................................................................60 1 2 3 3.4.3.1 Output and regulation properties...................................................60 3.4.3.2 Operation in the switching cycle...................................................63 3.4.4 Summary of different SM-PSA converter LC topologies.....................65 3.5 Transients during the welding process.........................................................67 3.5.1 Inverter circuit......................................................................................67 3.5.2 Resonant network.................................................................................67 3.6 Alternative way of output regulation – frequency control...........................69 3.7 Output filter design......................................................................................70 3.8 Experimental results.....................................................................................71 3.8.1 Resistive load........................................................................................72 3.8.2 Welding................................................................................................74 3.8.3 Battery charging...................................................................................75 3.9 Conclusions..................................................................................................76 4. PFC in the SM-PSA converter......................................................................78 4.1 Background - reasons of poor power factor and state of art........................78 4.2 Properties of PSA appropriate for PFC........................................................80 4.3 Principles of operation.................................................................................81 4.4 Simulation of PFC SM-PSA........................................................................83 4.4.1 Input current and THD vs output voltage............................................83 i 4.4.2 Converter operation in a mains cycle...................................................85 4.4.3 Converter operation in a switching cycle.............................................87 4.4.4 Conclusions..........................................................................................89 4.5 Experimental results.....................................................................................91 4.5.1 Resistive load........................................................................................91 4.5.2 Battery charging...................................................................................93 4.5.3 Welding................................................................................................94 4.6 Conclusions..................................................................................................97 5. Conclusions.....................................................................................................99 5.1 Load-resonant switch-mode SM-PSA converter.........................................99 5.2 Power factor correction in the SM-PSA converter......................................101 5.3 Plans for future studies.................................................................................101 References...........................................................................................................102 Kokkuvõte...........................................................................................................110 List of Publications.............................................................................................111 Intellectual property..........................................................................................112 Appendix 1..........................................................................................................113 ELULOOKIRJELDUS......................................................................................113 CURRICULUM VITAE....................................................................................115 Appendix 2..........................................................................................................117 Schematic diagram of the SM-PSA prototype converter...................................117 5 List of Abbreviations AC – Alternating Current DC – Direct Current DPF – Displacement Power Factor EMC – Electro Magnetic Compatibility EMI – Electromagnetic Interference FEM – Finite Element Method IEC – International Electrotechnical Committee IEEE – Institute of Electrical and Electronics Engineers IGBT – Insulated Gate Bipolar Transistor LC – Resonant circuit composed of an inductor L and a capacitor C MMA – Metal Manual Arc MOSFET – Metal-Oxide-Semiconductor Field-Effect Transistor PF – Power Factor PFC – Power Factor Correction PRC – Parallel Resonant Converter PSA – Parallel and Series Resonance Alternation RMS – Root Mean Square SMPS – Switch Mode Power Supply SM-PSA – Switch Mode converter with Parallel and Series resonance Alternation SRC – Series Resonant Converter THD – Total Harmonic Distortion ZCS – Zero Current Switching ZVS – Zero Voltage Switching 6 List of Symbols Inverter and resonant circuit a – relative gating pulse width f – switching frequency sw t – delay time between gating pulses (“dead time”) d W – primary winding of transformer 1 W – one secondary winding of transformer (inductive branch) 2 W – other secondary winding of transformer (capacitive branch) 3 I – current in primary winding of transformer tr1 U –voltage on transformer primary winding tri1 L – inductor/inductance of main resonant inductor in inductive branch 1 L – inductor/inductance of additional inductor in middle branch 2 L - inductor/inductance of resonant inductor in capacitive branch 3 C – capacitor/capacitance of resonant capacitor in capacitive circuit I – current through the inductive branch of resonant circuit L1 I , I – current through the middle branch L2 mb I or I – current through the capacitive branch C L3 U – voltage of resonant capacitor C K – transformer turns ratio T K – transformer secondary windings voltage distribution factor E K – inductance distribution factor in resonant network of PSA L K – reactive power distribution factor for the short-circuit mode Q Load circuit C – output filter capacitor f L – output filter inductor f U or U – load voltage d load I or I – load current d load P – power delivered to load d I – converter output current before output filter conv Mains and input rectifier u – input voltage of AC/DC converter S i – input current of AC/DC converter S U – DC-link voltage after the mains rectifier dc 7 Chapter 1 1. Introduction 1.1 Current trends in power electronics Electrical energy, the final product of different energy kind transformations, is most widely used in modern living environment compared to other energy kinds. Rational consumption of electrical energy is not only the problem of cost reduction, but it also could prevent unreasonable energy waste and help us to solve some issues of electromagnetic ecology. In recent decades power electronics has extended to almost any area, from low- power consumer electronics and to high-power industrial devices. Here, most of the electronic devices and equipment must be supplied with some DC voltage. However, presently AC voltage generation, transmission and distribution are commonly used in the world. To obtain a required DC voltage from the AC network to switch-mode power semiconductor-based converters. The following common trends in the design of modern switch-mode AC/DC power converters could be distinguished: 1) lower cost and simpler design, 2) better construction density, or in other words, smaller volume and weight, 3) high efficiency (lower losses), 4) reduced distortion of input current. As it is known, a smaller and more compact power supply unit can be designed by the reduction of power loss in the converter and an increase in the operation frequency. Thus, the size and cost of magnetic components can be reduced. Moreover, minimization of switching losses contributes significantly to increased efficiency and reasonable thermal design of the whole power supply. In addition to higher-frequency operation and lower losses, the issue of input current distortion becomes more significant. A wide use of switch-mode converters has created a new situation where the use of converters with incorporated power factor correction is beneficial. Power switching devices Development of new, faster generations of switching devices stimulates the increase of switching frequencies in converters leading to a smaller volume of power supplies. There are two main kinds of energy loss in a switch device: switching losses and conduction losses [H6]. Switching losses occur as the switching device, further mentioned as a switch, turns on and off, and the conduction losses occur, when the switch is in on-state and conducting current. Switching losses are dependent on the switching speed and conditions in the switch during the commutation interval and conduction losses are dependent on the switch resistance, or voltage drop. There are two main types of power switching 8 devices employed in modern switch-mode converters: metal-oxide semiconductor field effect transistor (MOSFET) and insulated-gate bipolar transistor (IGBT). It is accepted that losses in the power converter depend on the parameters of a switch and on the topology in which it is used. Some of the losses can also create stresses to the power semiconductors which in the long term may affect the reliability of the power supply. Thus, it is important to know where they arise and how to control them [H6]. Each switching device has different switching and on-state characteristics. The merits and selection criteria of these devices can be classified according to: 1) on-state conduction capability, 2) permissible reverse voltage, 3) switching characteristics, 4) cost. IGBTs have smaller die areas than power MOSFETs of the same ratings, which typically means a lower cost, while power MOSFETs are used in the majority of applications due to their ease of use and their higher frequency capabilities [H6]. The development of MOSFET and IGBT devices is an unceased process, resulting in increased current, voltage and switching capabilities. Power quality and EMC Operation at an increased frequency leads to certain EMC problems and some topological issues like parasitic inductances and capacitances that often need special solutions. A good practice for EMI reduction is a ZVS implementation in switch-mode converters [H3]. In addition, increasingly more consumer electronics devices should comply to the IEC 61000-3-2 standard (limits for harmonic current emissions, equipment input current ≤16 A per phase). Thus, an input current correction must frequently be provided in modern power supplies. Combined solutions In view of these facts, many new solutions and topologies have been proposed, which appear to improve one or more parameters of AC/DC power supplies. To minimize switching losses some of them use soft-switching techniques, like in [RC1-RC13 or W9, PT3]. Others concentrate on power factor improvement [PF1-PF13]. Another approach is to minimize and hybridize discrete components in one planar structure [L1-L2]. However, an increasing number of present papers describe solutions where one or more approaches are combined [PF4, PF5, PF8, PF10, PF11, RC6, PT6 and PT7]. In this study, in addition to a new resonant topology described, a novel method for the power factor correction by a simple implementation of the mentioned topology is proposed. Thus, the topology belongs to the class of combined solutions. In particular, it would be applicable to low-impedance and sharply varying loads. 9 Conventional hard-switched power converters The most conventional switch-mode power converters are known as “hard- switched”. The output voltage of such converters is controlled by varying the gating pulse width or, in other words, by PWM. At the end of each switching cycle the switch turns off at a current peak value, thereby causing high switching loss in the device. Moreover, additional snubber or other protection circuits are also needed that increase overall complexity of the circuit. At present, the maximum frequency of the “hard-switched” operation is limited to around 40 kHz, depending on the converter power level. 1.2 Resonant switch-mode converters The size and weight of magnetic components, like a power transformer or an inductor, could be significantly reduced by an increase in frequency to hundreds of kHz or above. Such a frequency of operation without over-dimensioned thermal design can be achieved by help of a conversion topology such as in a resonant switch-mode power converter. 1.2.1 Resonant networks As different from “hard-switched” PWM converters, resonant switch-mode converters include additional resonant circuit(s). Thus, they combine properties of both switching and resonant circuits. Natural properties of a resonant circuit allow one to minimize switching losses. Therefore, resonant topologies are applied in high-density power supplies. These converters comprise inductive and capacitive components to achieve a resonant condition. This leads to zero switching current at turn off instants, known as a ZCS. As a result, the switching losses in a switch are significantly decreased, thereby allowing a considerable increase in the switching frequency. The maximum switching frequency in this case is defined by the switching speed of the semiconductor and the parameters of control and gating circuits. The most common types of resonant converters classified by conversion according to [H3] are: 1) DC to high frequency AC inverters, 2) resonant DC - DC converters, 3) resonant inverters or rectifiers producing the line frequency AC. Also, resonant converters could be classified into: quasi-resonant, link-resonant and load-resonant [RC12]. The simplest resonant converter topology is the load- resonant converter in which the load forms a part of the resonant circuit [RC13]. The resonant converter proposed and discussed further in the thesis belongs to the class of load-resonant DC-DC converters. The typical load-resonant converter contains a resonant LC circuit. The most common types of resonant circuits are shown in Figure 1.1. 10