Middle-East Journal of Scientific Research 20 (12): 1935-1939, 2014 ISSN 1990-9233 © IDOSI Publications, 2014 DOI: 10.5829/idosi.mejsr.2014.20.12.981 Reduced Component Induction Heater for Domestic Applications B. Vamsikrishna and R. Renuka Department of Electrical and Electronics Engineering, Bharath University, Chennai, Tamilnadu, India Abstract: A new proposed topology is used to improve the efficiency while reducing the power device count for induction heating applications. In the proposed system, the rectifier is constructed using two independent diodes and sharing the other two diodes with snubber diodes of MOSFET switches. So it has minimized components. Also, for the high frequency inversion process, the series inverter topology is selected which will further reduce the number of MOSFET switches required for the inverter. The inverter is provided with resonant circuit to resonate the current and voltage at the switching frequency to achieve ZVS (Zero Voltage Switching) and ZCS (Zero Current Switching) which will greatly reduce the switching losses. In Simulation, pulse generators are used to generate pulses for the inverter switches and the PID is used in the closed loop to achieve the desired output. Key words: Home appliances Induction heating Inverters INTRODUCTION Induction heating appliance market is increasing due to its fastest heating time and efficiency. Domestic induction hobs are now becoming a standard option, especially in Asia and Europe. The development of high frequency AC/AC converters for kitchen equipments is the need of the hour [1]. The development of the new high frequency induction heating cooker, boiler and super heated steamer, that is high-performance, high power density and high efficiency compared with the conventional gas cooking equipment are much more attractive for home and business uses. By such technological background, high-frequency soft switching power supply for the electromagnetic induction heating with the control schemes has been developed. Nowadays, most designs use the half-bridge series resonant topology because of its control simplicity and high efficiency. In the past, several ac-ac topologies have been proposed to simplify the converter and improve the efficiency. The efficiency and cost are compromised due to the use of a higher number of switching devices [2-7]. Other approaches, commonly used in electronic ballasts, simplify the rectifier stage in order to improve the converter performance. This topology, known as halfbridge boost rectifier, reduces the switch count while Resonant power conversion keeping the same performance as more complex solutions. Induction heating is the process of heating an electrically conducting object (usually a metal) by electromagnetic induction, where eddy currents (also called Foucault currents) are generated within the metal and resistance leads to Joule heating of the metal. An induction heater (for any process) consists of an electromagnet, through which a high-frequency alternating current (AC) is passed. Heat may also be generated by magnetic hysteresis losses in materials that have significant relative permeability. The frequency of AC used depends on the object size, material type, coupling (between the work coil and the object to be heated) and the penetration depth.Induction heating is a non-contact heating process. It uses high frequency electricity to heat materials that are electrically conductive [1]. Since it is non-contact, the heating process does not contaminate the material being heated. It is also very efficient since the heat is actually generated inside the work piece. This can be contrasted with other heating methods where heat is generated in a flame or heating element, which is then applied to the work. Conventional converters for radio frequency induction heating usually follow an AC-DC-AC structure, which can exhibit non-unity power factor and introduce large harmonic currents into the utility supply. Then the matrix converter have an additional switches, Corresponding Author: R. Renuka, Department of Electrical and Electronics Engineering, Bharath University, Chennai, Tamilnadu, India. 1935 Middle-East J. Sci. Res., 20 (12): 1935-1939, 2014 so it have an increased the control complexity and cost of the system.Next the single phase boost chopper converter produces the harmonic distortion and high input peak current. So the switching losses are high. In the existing system the DC - AC inverter is operated in open loop with fixed PWM ON time for a fixed power output and hence the power output cannot be varied and moreover, for any error or deviation, the output is not corrected automatically. Generally the induction heaters running on 50 Hz ac mains will have a full wave rectifier using 4 diodes followed by high frequency inverter using 4 MOSFET switches. Proposed Power Converter: A new topology is proposed to improve the efficiency and to reduce the power device count for induction heating applications. The proposed system is based on the series resonant half-bridge topology and requires only two rectifier diodes. Because of the reduction of number of diodes, the system components are minimized. It also reduces the switch count while keeping the same performance as more complex solutions. This topology implements resonant capacitors and may use a bus capacitor, due to the symmetry between positive and negative mains voltage, both resonant capacitors have the same value. An input inductoris used to reduce the harmoniccontent to fulfill the electromagnetic compatibility regulations. The inverter is provided with resonant circuit to resonate the current and voltage at the switching frequency to achieve ZVS (Zero Voltage Switching) and ZCS (Zero Current Switching) which will greatly reduce the switching losses. The proposed system employs closed loop system with two microcontrollers: One to generate PWM pulses for MOSFET switches and to read the input voltage, current and output voltage. The other controller is used to compute input and output power and display on the LCD. Serial communication interface is provided between two controllers for data transfer between them.For closed loop operation the desired output power can be entered through keys. The closed loop control is implemented using software based PID control algorithm, which compare the set power with actual power to generate an error signal which in turn is used to modify the ON time of PWM pulses in order to maintain the output at desired value. Analysis: The proposed topology is a series-parallel resonant converter. The inductor-pot system is modeled as an equivalent series resistance Reqand inductance Leq, as shown in Fig. 3.1 [15]. This topology implements resonant capacitors Cr and may use a bus capacitor Cb. Fig. 3.1: Proposed ac-ac converter. Fig. 3.2: States and transition conditions Due to the symmetry between positive and negative mains voltage, both resonant capacitors have the same value. An input inductor Lsis used to reduce the harmonic content to fulfill the electromagnetic compatibility regulations [2]. A 230v,50Hz Ac supply is given to the circuit. The harmonics in the supply is reduced by input inductance Ls. The input Ac supply is converted in to Dc by Half bridge rectifier. Bus capacitor Cb is act as a filter which is used to remove ripples from the Dc voltage. MOSFET is used as switching device in our project. MOSFET performs switching operation at Zero voltage switching condition (ZVS). The diode DH and DL act as inverter in different modes of operation which it convert DC to AC. The AC voltage is given to RL load. The switching operation performed in three different operating modes.The topology presents symmetry between positive and negativeac voltage supply. Its symmetry simplifies analysis and makes possible to redraw the circuit. Although this topology uses different resonant configurations, parallel and series and different resonant tanks for each of them, it is possible to use a normalized nomenclature based on series resonance. Fig. 3.2 shows the simple transition conditions for each state [3]. STATE I: SHActivated : SL Deactivated: State I operates with the high-side switching device SH triggered-on and activated and the low-side switching device (SL) triggered-off. The parallel resonant circuit is set by an 1936 Middle-East J. Sci. Res., 20 (12): 1935-1939, 2014 equivalent capacitor Ceq, obtained from Cr and Cband expressed and the inductor electrical parameters, Req and Leq. The current flowing through SH is the same as the one flowing through the load.State I begins when SL is triggered OFF. In this moment, the anti parallel diode DH conducts and SH can be triggered ON ensuring ZVS switching-on conditions. Transitions from this state can lead either to state II or state III. If voltage across SL reaches zero and DL starts conducting, the transition condition to state II is fulfilled. On the other hand, if SH is switched OFF whenTH conducts, the next state is state III [4]. STATE II: SH Activated: SL Activated: State II is characterized by the conduction of both switching devices, although only SH is triggered ON. That is, TH and DL conduct at the same time. Current through load is supplied by both devices (TH and DL ) and consequently, low conduction stress for the devices is achieved. The equivalent parallel resonant circuit is set by the inductor electrical parameters in parallel with both resonant capacitors. Cbis short-circuited by both switching devices. This state starts when the voltage across SL reaches zero. At this moment, DL starts conducting at the same time as TH is triggered ON. This state finishes when SH is triggered OFF and the next state is state III. The main benefit results of the lower switch-off current achieved when SH is triggered OFF, due to the fact that the load current is supplied by both devices. In addition, SH achieves ZVS conditions during both switch-on and switch-off transitions, reducing consequently the switching losses [5]. STATE III: SH Deactivated: SL Activated: State III is defined by the conduction of SL while SH is deactivated. The equivalent resonant circuit is set by one resonant capacitor in parallel with the series connection of the Cbcapacitor and the parallel connection of the inductor and the other one resonant capacitance. Note that when Cbis zero (á = 0), theequivalent resonant circuit is a series RLC circuit composed of the inductor-pot system and one resonant capacitor. This state starts when SH is triggered OFF. At this moment, DL starts conducting and SL can be triggered ON achieving ZVS switch-on conditions. This state finishes when SL is deactivated and the next state is state I [6]. The operating principles of the circuit are illustrated by Fig. 3.1 Fig, 3.2 Fig, 3.3 and the theoretical waveforms are shown in Fig. 3.4 The first operation mode uses the three states described earlier: I, II and III. It makes possible to achieve ZVS conditions for the high-side switch in state II [7]. Fig. 3.3: Theoretical Analysis Wave form Simulation Results: The Resonant converter fed induction heater is simulated using Matlabsimulink and their results are presented here. The circuit model of resonant converter is shown in Fig.4 Scopes are connected to measure output voltage, driving pulses and capacitor voltage.The principle of operation is based on the generation of a variable magnetic field by means of a planar inductor below a metallic vessel. The mains voltage is rectified and after that an inverter provides a medium-frequency current to feed the inductor. The usual operating frequency is higher than 20 kHz to avoid the audible range and lower than 100 kHz to reduce switching losses. The diode rectifier is used to convert AC to DC source. The filter capacitor is used to reduce the ripples and given it to the inverter. The MOSFET switches are used because of its fast switching capability. The snubbers in the mosfet is used to protection. The inverter converts dc to ac output. The switching pulses required for the inverter operation are generated by the V-ZCD and a PWM pulse at particular frequency. Each switching pulse is logically ORed with PWM pulse and applied to the gate of MOSFET switches for triggering. PIC16F877A controller is used here for generating PWM pulses. The resonant condition is satisfied using resonant circuit. It can operate with zero-voltage switching conditions during turn-on for both switching devices and also during turn-off transitions for one of them. As a consequence, the efficiency is improved while the device count is reduced. 1937 Middle-East J. Sci. Res., 20 (12): 1935-1939, 2014 Fig. 4.1: Open loop circuit Fig. 4.5: AC output waveform Fig. 4.2: AC input Fig. 4.6: Closed loop circuit Fig. 4.3: Switching pulse waveform Fig. 4.7: AC input Fig. 4.4: Current to load The output waveform is obtained by using CRO. The ac input voltage, current and ac output voltage are then measured and fed to the controller via internal ADC to obtain the desired output voltage in the closed loop. Fig. 4.8: Current to load 1938 Middle-East J. Sci. Res., 20 (12): 1935-1939, 2014 ACKNOWLEDGEMENT I articulated my gratitude to Mr.B. Vamsi Krishna, M. Tech., Assistant Professor of Electrical and electronics Engineering who had thought as the way to do a successful project and without whose constant encouragement and whole idea, the project would not have been possible. I wish to express my sincere thanks to our project co-coordinator Prof.T.Ramamoorthy and External Guide Prof.Dr.S.Arumugam who had helped me lot and has given valuable suggestion, which made me to accomplish this project in very successful and next way. Fig. 4.9: AC output waveform REFERENCES 1. 2. 3. Fig. 4.10: Hardware layout PIC16F628A controller is used to compute the efficiency and power factor of the system. It achieves unity power factor when the voltage and current are in phase with each other. 4. 5. CONCLUSION Thus an embedded based induction heater with reduced components suitable for domestic applications is developed successfully. The efficiency and cost are compromised due to the use of a less number of switching devices. Other approaches, commonly used in electronic ballasts, simplify the rectifier stage in order to improve the converter performance. 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