HIGH FREQUENCY INVERTER FOR MULTI- COIL INDUCTION HEATING

Transcription

1 Volume 114 No , ISSN: (printed version); ISSN: (on-line version) url: ijpam.eu HIGH FREQUENCY INVERTER FOR MULTI- COIL INDUCTION HEATING S. Ravi Teja 1 and G.V.S.Sai Manikanta 2 1 Assistant Professor, K L university, Guntur, Andhra pradesh, India srungaramraviteja@kluniversity.in 2 UG student, K L University, Guntur, Andhra pradesh, India gvssaimanikanta@gmail.com Abstract This paper proposes the control of high frequency resonating inverter for multicoil induction heating. The Full bridge voltage source inverter is operated at high frequency to induce high amount of eddy currents as eddy current heat generation vary as square of the eddy current frequency. To obtain high power-output two coils are used together which adds one more leg to the full bridge inverter. Output power is varied by asymmetrical duty cycle modulation which varies width of positive half-cycle of bridge output voltage to vary rms value of output voltage. Secondly, the inverter is resonated with series LLC load to reduce switching losses at high frequencies around khz khz. The principle proposed is verified through PSIM software. The results for control of power and ZVS across the switches in inverter legs are presented.. Key Words: PWM technique, Induction heating, Eddy current control technique, resonant inverter 1 INTRODUCTION Induction heating is well known technique to produce very high temperature. The heat is generated by eddy currents in the work piece which in turn vary as square of frequency which necessitates the high frequency operation of inverter [1]. Voltage fed and current fed inverters are most commonly used topologies for induction heating applications. Owing to the simple switching and control, voltage-fed topologies are more popular especially in the applications where output power is to be controlled as like an induction cooker [2]. In this paper a full-bridge voltage source inverter is considered. 555 Further a third leg is added to provide control of second

2 heating coil. Secondly the inverter is load resonated to achieve zero voltage switching (ZVS) for all the inverter switches [3]. A series LLC resonant load provides the better performance [4]. It requires a matching transformer for impedance matching for the load to receive maximum power. The output power can be controlled by a variety of control methods. Constant on time or off time with variable time period control in [5] which require a variable frequency tracking for resonance. The pulse density modulation in [3] varies period of switch conduction. The phase shift control [6] varies the phase of switch conduction sequences. The asymmetrical voltage modulation varies pulse width of positive half cycle conducting switches leaving the duty cycle of negative half cycle conducting switches at constant 50 percent thus varying the effective value of the output voltage [7]. In this paper asymmetrical voltage modulation is applied between legs 1 and 2 to control voltage applied to one coil and between legs 1 and 3 to control voltage applied to the other coil. The paper is organized as follows. Section II presents the proposed topology of voltage source resonant inverter for two-coil induction heating. Section III presents the working principle of proposed converter and asymmetrical voltage modulation technique.section IV presents the simulation Results. Section V the Conclusion. 2 CIRCUIT DESCRIPTION The high frequency full bridge voltage source inverter fed induction heating coil topology is shown in fig.1. The switches S1,S2 - S3,S4 form a full bridge which feed coil1 and S1,S2 - S5,S6 form another full bridge which feed coil2. Here the leg containing switches S1,S2 is common to both the coils. The combination of Ls, Cp along with load coil form the series LLC resonant load. The transformation ratio of 5:1 is obtained for matching transformer to transfer maximum power to the load. The blocking capacitor Cb prevents the saturation of transformer core by blocking dc component in full bridge output voltage. The switching frequency chosen is given in table1. The corresponding values of resonant elements Ls and Cp are calculated according to [8]. The load parameters are selected so as to represent a typical induction cooker application 556

3 Ls1 Ll1 Cb1 Cp1 Lcoil1 Req1 150v s1 s3 s5 ls2 Ll2 S2 S4 S6 Cb2 Cp2 Lcoil2 Req2 Fig.1 Proposed full-bridge resonant inverter for two-coil induction heating 3 WORKING a)switching sequence for one cycle along with zvs: The switching frequency is maintained close to resonant frequency using a phase-locked loop. The sequence for fullbridge formed by S1,S2 S3,S4 feeding coil1 is explained below which equally applies for the full-bridge feeding coil2.when positive gate pulse applied across S1 and S3 and anti-parallel diodes across them are conducting the voltage across them is clamped to diode forward voltage drop. So when current polarity is reversed voltage across the switches is ideally zero achieving zvs for switches S1 and S3. During negative half cycle when positive gate pulse applied across S2 and S4 and anti-parallel diodes across them are conducting the voltage across them is clamped to diode forward voltage drop. So when current polarity is reversed voltage across the switches is ideally zero achieving zvs for switches S2 and S4. b) Control of output power: The operation of asymmetrical duty-cycle modulation for full-bridge formed by S1,S2 S3,S4 feeding coil1 is explained below which equally applies for the full-bridge feeding coil2. Asymmetrical duty-cycle modulation refers to control of pulse width of either positive half cycle or negative half cycle. A ramp signal of switching frequency is considered. A constant signal such that duty cycle ranging between 0 and 0.5 is compared with the ramp to 557 produce gating pulses for

4 S1 and S2. Duty cycle corresponding to 0.5 gives the maximum pulse and thus maximum possible output power. Three duty cycles can be considered corresponding to three different temperature values of the induction cooker. 4 SIMULATION RESULTS Simulation is carried out in PSIM software. The simulation parameters are given in table1. The output voltage and current waveforms for duty-cycles 0.8, 0.5 are shown below. Fig.2. Load current for coil1 at 0.8 duty cycle Fig.3. Load voltage for coil2 at 0.8 duty cycle Fig.4. Load current for coil1 at 0.8 duty cycle 558

5 Fig.5. Load voltage for coil2 at 0.5 duty cycle The variation in rms values of output voltage for varying duty cycle can be observed from figures 3 and 4 which in turn provides the variation in output power. 5 CONCLUSION Simulation results show the variation of output power at three different duty cycle values corresponding to three operating temperatures of induction cooker. Also zero voltage switching for inverter switches is observed. Thus the proposed resonant inverter provides double the power output and control of temperature with good efficiency at high frequency owing to ZVS operation of switches. References [1] M. Kamli, S. Yamamoto, and M. Abe, A khz half-bridge inverter for induction heating application, IEEE Trans. Ind. Electron., vol. 43, no. 1, pp , Feb [2] P. Viriya, S. Sittichok, and K. Matsuse, Analysis of high-frequency induction cooker with variable frequency power control, in Proc. PCC Osaka, Apr. 2002, vol. 3, pp [3] N. Ahmed, High frequency soft switching AC conversion circuit with dual mode PWM/PDM control strategy for high power IH applications, IEEE Trans. Ind. Electron., vol. 58, no. 4, pp , Apr [4] J. M. Espí Huerta, E. J. Dede García Santamaría, R. García Gil, and J. Castelló Moreno, Design of the L-LC resonant inverter for induction heating based on its equivalent SRI, IEEE Trans. Ind. Electron., vol. 54, no. 6, pp , Dec [5] S. Chudjuarjeen, C. Koompai, and V. Monyakul, Fullbridge currentfed inverter with automatic frequency control for forging application, in Proc. IEEE TENCON, 2004, vol. 4, pp [6] L. Grajales and F. C. Lee, Control system design and small-signalanalysis of a phase-shift controlled seriesresonant inverter for inductionheating, in Proc. IEEE Power Electron. Spec. Conf., 1995, pp [7] S. Chudjuarjeen and C. Koompai, Asymmetrical control with phase lock loop for induction 559 cooking appliances, in

6 Proc. ECTI-CON, 2008, pp [8] P. Imbertson and N. Mohan, New directions in dc-dc power conversion based on idealized concepts leading ultimately to the asymmetrical dutycycle power converter, IEEE Trans. Circuits Syst. I,Fundam. Theory Appl., vol. 44, no. 8, pp , Aug

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