Full Bridge Resonant Inverter For Induction Heating Applications

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Sreenivas Peram, Vaddi Ramesh, J.Sri Ranganayakulu / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January-February 2013, pp.066-073

Full Bridge Resonant Inverter For Induction Heating Applications Sreenivas peram* vaddi ramesh, J.SRI RANGANAYAKULU ** *(Department of Electrical & Electronics Engineering, JNTU University, Ananthapur) ** (Department of Electrical & Electronics Engineering, JNTU University, Ananthapur)

ABSTRACT Induction heating is a well-known technique to produce very high temperature for applications. A large number of topologies have been developed in this area such as voltage and current source inverter. Recent developments in switching schemes and control methods have made the voltage-source resonant inverters widely used in several applications that require output power control. The series-resonant inverter needs an output transformer for matching the output power to the load but it carry high current as a result additional real power loss is occur and overall efficiency also is reduced. This project proposes a high efficiency LLC resonant inverter for induction heating applications by using asymmetrical voltage cancellation control .The proposed control method is implemented in a full-bridge topology for induction heating application. The output power is controlled using the asymmetrical voltage cancellation technique. The LLC resonant tank is designed without the use of output transformer. This results in an increase of the net efficiency of the induction heating system. The circuit is simulated using MATLAB .The circuit is implemented using PIC controller. Both simulation and hardware results are compared. Index Terms—Asymmetrical control, induction heating, zero-voltage switching (ZVS).

1) INTRODUCTION INDUCTION heating is a well-known technique to produce very high temperature for applications like steel melting, brazing, and surface hardening. In each application, an appropriate frequency must be used depending on the work piece geometry and skin-depth requirements. In general, the induction-heating technique requires high-frequency current supply that is capable of inducing high-frequency eddy current in the work piece that results in the heating effect A large number of topologies have been developed in this area. Current-fed and voltage-fed inverters are among the most commonly used types . Recent developments in switching schemes and control methods have made the voltage-source resonant invert-ers to be widely used in applications that require

output-power control capability. For example, in pulse-frequency modulation (PFM), the output power can be controlled by varying the switching frequency while the inverter operates under zerovoltage switching (ZVS) scheme The pulse-density modulation method regulates the output power by varying the period in which the inverter supplies highfrequency current to the induction coil. The phase-shift (PS) control technique in [8] varies the output power by shifting the phase of the switch conduction sequences. The asymmetrical duty-cycle control technique employs an unequal duty-cycle operation of the switches in the converter . The asymmetrical voltage-cancellation (AVC) is then proposed in where the authors describe voltage-cancellation for conventional fixed-frequency control strategies. In , the AVC is implemented in a full-bridge seriesresonant inverter. The series-resonant inverter needs an output transformer for matching the output power to the load. Most induction-heating applications require accuracy in output-power control capability. For example, cooking appliances require accurate power control over a wide range of power for different cooking purposes where a ZVS condition must be met to ensure high efficiency . By using the mentioned techniques in fixed frequency and the optimum duty cycle for ZVS operation, it is rather difficult to control the output power due to variation of parameters in the resonant load during the heating process. In high temperature applications, a high current must flow in the surface of the metal for heating effect. The seriesresonant inverter may need a transformer for matching the output power and high current in the induction coil. Previous work has shown that an LLC configuration can offer a better performance than the series resonant while providing short-circuit immunity and lower current on the transformer’s secondary Note that the closed-loop PFM method presented in may sacrifice the efficiency due to switching losses at high-frequency operation. However, the LLC resonant load offers better performance with high-quality factor (Q > 30) and only requires a small series inductance in the circuit configuration. This implies that the output transformer can be omitted. The disadvantage of the LLC resonant load is that the output current may no longer be sinusoid in the case of low Q (Q < 10) . The current in the induction coil is unavoidably small and

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