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An Improved Transformer for LLC Resonant Inverter for Induction Heating Applications

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An Improved Transformer for LLC Resonant Inverter for Induction Heating Applications (IJACSA) International Journal of Advanced Computer Science and Applications, Vol. 7, No. 2, 2016 An Improved Transformer for LLC Resonant Inverter for Induction Heating Applications Amira ZOUAOUI- Hamed belloumi Ferid KOURDA KHEMAKHEM Laboratoire Systèmes Electriques Laboratoire Systèmes Electriques Laboratoire Systèmes Electriques (L.S.E.-LR11ES15) (L.S.E.-LR11ES15) (L.S.E.-LR11ES15) Ecole Nationale d’Ingénieurs de Ecole Nationale d’Ingénieurs de Ecole Nationale d’Ingénieurs de Tunis, Université Tunis El Manar Tunis, Université Tunis El Manar Tunis, Université Tunis El Manar BP.37-1002-Tunis le Belvédère, BP.37-1002-Tunis le Belvédère, BP.37-1002-Tunis le Belvédère, Tunisie Tunisie Tunisie Abstract—A new trend in power converters is to design a Copper resistivity planar transformer that aims for low profile. However, at high ξ : Normalized value of the diameter of a strand frequency, the planar transformer AC losses become significant µ: Permeability due to the proximity and skin effects. In this paper the most important factors for planar transformer (PT) design including I. INTRODUCTION winding loss, core loss, leakage inductance, and stray capacitance have individually been investigated. The tradeoffs among these High-frequency power transformers (HFPT) are largely factors have to be analysed to achieve optimal parameters. We used in many electrical and electronic designs. Switching at will show a strategy to reduce losses in the primary coil of the higher frequencies is an interesting option to reduce passive transformer. The loss analysis of th PT was verified by the Finite components and isolation transformers. They allow adapt Element Method (FEM) Simulations (ANSOFT MAXWELL different levels of voltage and provide electrical and galvanic FIELD SIMULATOR 2D) and could be utilized to optimize the isolation between both windings. However, there is not a transformer design procedure. Finally, the proposed PT has been standardized procedure for design transformers, and every integrated into an LLC Resonant Inverter for Induction Heating manufacturer keeps confidential his method. Optimized design Application to test at high signal levels. can save power, volume, weight and money for the manufacturer and for the customer. Most of researchers Keywords—planar transformer; induction heating; Finite studied the theory of HFPT and its usage in power systems. Element Method; skin effect; diffusive representation Due to eddy current effects, winding losses in high- List of Symbols: frequency magnetic components are appreciably greater than b : Width of the plate those Calculated from the dc resistance of the winding. These losses must then be computed from the AC resistance of the : Compensation capacitor winding which includes the DC resistance and a factor of : Resonant frequency excess loss related to skin and proximity effects [1]. h : Height of the plate I : Primary current We have shown in [2] two options to reduce high- frequency copper losses without significantly increasing the : Secondary current K: Coefficient of additional losses space occupied by these connections. Both options rely on the parallelization of copper plates. In the first, plates are : Secondary inductance interchanged to equalize the flux experienced by them. In the : Load inductance second, plates are interleaved to decrease the magnetic energy m : Number of layers around the conductor. : Primary turns of the transformer p : Diameter of the cross section of the conductor PCB implementation of planar windings replicates the : Power structure of conventional litz wires to reduce the AC losses. This structure consists of a set of fine trace electrically : Load resistance connected in parallel which transposed using changes of both : AC resistance of the winding trajectory and layer. An appropriate transposition strategy is : DC resistance of the winding essential to reduce the winding AC losses. However PCBs S : Area of the cross section of the conductor with a high number of vias could result expensive and not : Rectangular section reliable [3]. : Fundamental voltage : Primary voltage A quick and simple method derived for obtaining the AC leakage impedance of a transformer, from the calculated Φ : Phase shift between fundamental voltage and current values of DC winding resistance and DC leakage inductance. Skin depth 476 | P a g e www.ijacsa.thesai.org (IJACSA) International Journal of Advanced Computer Science and Applications, Vol. 7, No. 2, 2016 It is rather unfortunate that calculating the DC leakage- configuration for induction-heating applications. The inverter inductance components accurately is a fairly lengthy process, consists of two switches with antiparallel diodes, a although it mainly consists of substituting numbers in the compensation capacitor (C), a series inductor (Ls), and an given formulas [4]. induction coil that comprises a series combination of a resistor (Req) and an induction coil inductor (Lcoil). [5] Explained a new method for core selection, based on the estimation of current density. The final algorithm You need to use half bridge capacitor inverter that presented allows to choice the magnetic core quicker, and eliminates the DC component and ensures a zero average designs a more efficient device. Furthermore, the method current, and voltage in the primary of the transformer. allows design a transformer with a broad range of frequency. If you want to work at full power, you only have to operate An improved high-frequency magnetic-integrated planar the two half bridge, otherwise the half-bridge is sufficient for transformer was demonstrated in [6]. Compared with a power of 5kW. conventional planar integrated magnetic, the improved structure has better leakage inductance adjustment. The transformer was fabricated with two common EE shape magnetic cores along with magnetic insertions placed between the primary and secondary windings outside it. A three- dimensional finite-element model is used to investigate the eddy current losses and the adjustment of the leakage inductance. A compact planar transformer with an improved winding configuration has been designed and fabricated in [11]. The meander-type design was engraved over the surface of a planar ferrite core, so that the primary and secondary windings can fit into the engraved design. This structure, was covered with another ferrite core, thus forming a compact planar transformer. Apical type AV polyimide film of 0.025 mm thickness is used between the windings to prevent short Rectifier and DC bus Two half bridge inverter Resonant tank circuit. A coupling coefficient of >0.93 achieved, while the primary and secondary inductance was ~1600 nH. A coupling Fig. 1. Electrical diagram of the induction heating system coefficient for air core transformer with the windings of To ensure the compensation of the reactive, the commands identical geometry was >0.35 and the inductance of the must coincide with the zero crossing of the current Ic in the windings near 160 nH. Fabricated transformer prototype has compensation capacity C. significantly a higher coupling coefficient and inductance of the windings in comparison with the previously developed Fig. 2 displays the current conduction through the inverter planar transformer of the similar design. during different modes of the power transfer cycle. In this paper, an HFPT for induction heating device is During Mode 1, a positive voltage is applied to the gate of presented, thus its losses analysis. To achieve our HFPT, The the high active power MOSFET. As a consequence, high choice and sizing of the primary and secondary of the MOSFET is turned-on. mosfet is conducting and transfer transformer are necessary. Hence a transformer has been power to the resonant tank through the coupling transformer in designed in order to adapt the voltage and current levels our circuit. In Mode 2, the mosfets are transitioning, and the between the converter and the resonant tank. upper mosfet turns off slightly before the bottom one turns on. Here, current is conducted through the free-wheeling diode of An analytical method for the calculation of losses in HFPT the lower mosfet. In Mode 3, the lower mosfet turns on, and followed by a simulation is perfomed. The simulation results the resonant tank throws the power back through mosfet. In show the good performance of proposed system and verify the Mode 3, both mosfets are off during the transition, and the mathematical analysis. Additionally, this new topology upper mosfet's free-wheeling diode conducts the current. provides higher power rating on utility voltage at the load side. III. LOSSES ANALYSIS OF HIGH FREQUENCY PLANAR TRANSFORMER II. OPERATION OF THE PROPOSED INVERTER When power converters operate at high frequency, the Fig. 1 illustrates the power circuit of proposed induction design difficulty for the transformer becomes much higher. heating diagram that employs an LLC resonant inverter The current density redistribution inside the winding wires (skin and proximity effects) strongly increases the copper losses. 477 | P a g e www.ijacsa.thesai.org (IJACSA) International Journal of Advanced Computer Science and Applications, Vol. 7, No. 2, 2016 1.4mm 1.5mm m m 4 . 0 I I Epoxy plate A coil consisting of four tracks The thickness of the planar turn has to be two times the skin depth. For 100 kHz : δ = 209 µm ; ; ; I I For a length of 100mm: Coppers losses in a single turn in DC are given by: Copper primary losses roundtrip in DC mode: Fig. 2. Analysis of the inverter Now to calculate the AC
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