Volume 25, Number 2 - April 2009 through June 2009
Closed Loop Controlled AC-AC Converter for Induction Heating By Mr. D. Kirubakaran & Dr. S. Rama Reddy
Peer-Refereed Article Applied Papers
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The Official Electronic Publication of the The Association of Technology, Management, and Applied Engineering • www.nait.org © 2009 Journal of Industrial Technology • Volume 25, Number 2 • April 2009 through June 2009 • www.nait.org Closed Loop Controlled AC-AC Converter for Induction Heating By Mr. D. Kirubakaran & Dr. S. Rama Reddy
Abstract the inverting circuit is constructed by A single-switch parallel resonant con- traditional mode with four controlled verter for induction heating is simu- switches. The above literature does not Mr. D.Kirubakaran has obtained M.E. degree lated and implemented. The circuit con- deal with closed loop modeling and from Bharathidasan University in 2000. He is sists of input LC-filter, bridge rectifier embedded implementation of AC to presently doing his research in the area of AC- AC converter fed induction heater. In AC converters for induction heating. He has 10 and one controlled power switch. The years of teaching experience. He is a life member switch operates in soft commutation the present work AC to AC converter is of ISTE. mode and serves as a high frequency modeled and it is implemented using generator. Output power is controlled an atmel microcontroller. The present via switching frequency. Steady state problem aims to minimize the cost of analysis of the converter operation induction heater system by using an is presented.. A closed loop circuit embedded controller. model for AC to AC converted induc- tion heating system is also proposed. Experimental results are compared with simulation results. Introduction Static frequency converters have been extensively applied in industry as a medium –frequency power supply for induction heating and melting installa- Dr. S. Rama Reddy received his M.E degree tions. They are applied in all branches Fig.1 Circuit Diagram from College of Engineering, Anna University, of the military, machine-building Chennai, India in 1987. He received Ph.D degree industries, jewellery, smithy heating, In the scheme (Fig.1) of the AC-AC in the area of Resonant Converters from College converter there are two main advantag- of Engineering, Anna University, Chennai India domestic heating cooking devices and in 1995. Presently he is working as Dean in other purposes. es: It is characterized by a high power Electrical & Electronics Dept., Jerusalem Colle- factor and a sine wave input current. ge of Engineering, Chennai. He has worked in On the other hand the inverter circuit Tata Consulting Engineers and Anna University, The ordinary circuit of an AC-AC Chennai, India. He is fellow member of Institution converter for induction heating typi- is constructed with a single controlled of Electronics and Telecommunication Engineers cally includes a controlled rectifier and switch, which serves as a high-frequen- (India), Life Member of Institution of Engineers a frequency controlled current source cy generator for induction heating. (India), Member of ISTE, Member of CSI and Member of SPE, India. He has authored text or a voltage source inverter. It is a books on Power Electronics, Electronic Circuits well known fact that the input recti- Principle Of Operation and Electromagnetic Fields. He has published 30 fier does not ensure a sine wave input The operating principles of the circuit research papers in reputed journals. His research are illustrated by Fig.2 and the theoreti- areas are Power Electronic Converters, Drives current, and is characterized by a low and FACTS. power [1-3]. Recently many studies cal waveforms of high power factor rectifiers with a single switch have been made [4-5]. These schemes are also characterized by a close to sine wave input current. In addition, in [6] the scheme of the AC-AC converter for induction heat- ing is described. The input circuit of the converter is constructed similarly to the input circuit in [4, 5], which also Fig.2a. Mode 1 (to-t1) ensures a high power factor. However
2 Journal of Industrial Technology • Volume 25, Number 2 • April 2009 through June 2009 • www.nait.org
(3)
(4)
Fig.2b. Mode 1I (t1-t2)
(5)
This relationship is represented in Fig. 3.a The values of duty cycles D1 and D may be calculated from the plot Fig.3.b. Fig. 3.a Factor M = V /V against pa- Fig.2c. Mode 1II (t -t ) g o in 2 3 rameters R * & ω * o s Fig.2 Equivalent Circuits are shown in Fig.3.We suppose the Fig.3 Ideal Switching Waveforms switching frequency is much higher than the input line frequency and in the analysis we arbitrarily chose the time interval where v >0 Operation Analysis in Analysis of the circuit operation is based on the commonly accepted assumption Interval 1: t0 3 Journal of Industrial Technology • Volume 25, Number 2 • April 2009 through June 2009 • www.nait.org Switching pulses are shown in Fig 4b.Voltage and current waveforms of the switch are shown in Fig.4c & Fig 4d respectively. High frequency AC output of converter is shown in Fig. 4e. The closed loop circuit model of AC- AC converter is shown in Fig.4f. Scopes and displays are connected to measure the output voltage. Fig.4a. open loop Circuit Fig.4f. Closed loop controlled AC-AC Fig.4b. Driving pulses Converter A disturbance is given at the input by using two switches. Output voltage The values of duty cycles D and D may 1 is sensed and it is compared with the also be found from the approximate poly- reference voltage. The error signal is nomial expressions given to the controller. The output of PI controller controls the dependent source. Response of open loop system is shown in fig 4g. (6) Fig.4c. Voltage across S1 (Vds) Simulation Results The AC to AC converter fed induction heater is simulated using matlab simu- link and their results are presented here. The circuit model of AC-AC converter is shown in Fig.4a.. Scopes are con- nected to measure output voltage, driv- ing pulses and capacitor voltage. Fig.4d. Current through S1 Fig 4g. Output voltage of open loop system Fig.4e. AC Output Voltage 4 Journal of Industrial Technology • Volume 25, Number 2 • April 2009 through June 2009 • www.nait.org References Bayindir, N.S.; Kukrer, O.; Yakup, M (May 2003).: DSP-based PLL con- trolled 50–100 kHz 20 kW high- frequency induction heating system for surface hardening and welding applications. IEE Proc.-Electr. Power Appl., Vol. 150, No.3, pp. 365-371. Okuno, A.; Kawano, H.; Sun, J.; Kuroka- wa, M.; Kojina,A.; Nakaoka, M. (July/August 1998) Feasible develop- Fig.6 Oscillogram of output voltage ment of soft-switched SIT inverter with load-adaptive frequency-tracking Fig 4h. Output voltage of closed control scheme for induction heating. loop system The output power control was also IEEE Trans. Ind. Applicat., Vol. 34, checked and its dependency by switch- No. 4, , pp. 713-718. ing frequency is shown in Fig.7. The Kifune, H.; Hatanaka, Y.; Nakaoka, The output voltage of closed loop M. (January 2004 ) Cost effective system is shown in Fig 4h. The distur- output power increases with the in- crease in switching frequency. phase shifted pulse modulation soft bance is applied at 3.0 secs. The control switching high frequency inverter for circuit takes proper action to reduce the induction heating applications. IEE amplitude to the set value and settles Proc.-Electr. Power Appl., Vol. 151, after 0.5 secs. Thus the closed loop No. 1, , pp. 19-25. system reduces the steady state error. Ogiwara, H.; Nakaoka, M. ( March 2003) ZCS high frequency inverter Experimental Verification using SIT for induction heating The single-switch AC-AC converter applications. IEE Proc.- Electr. Power was built and tested at 230V. Experi- Appl., Vol. 150, No. 2, pp. 185-192. mental setup of AC to AC converter is Mollov, S.V.; Theodoridis, M.; Forsyth, shown in Fig. 5. A.J. (January 2004): High frequency voltage-fed inverter with phase-shift control for induction heating, IEE Fig.7 Output power v/s switching Proc.-Electr. Power Appl., Vol. 151, frequency No. 1, pp. 12-18. Ogiwara, H.; Gamage, L.; Nakaoka, M.( September 2001) Quasiresonant soft switching PWM voltage-fed Conclusion high frequency inverter using SIT for An AC-AC converter circuit for induc- induction heating applications. IEE tion heating has been simulated and Proc.- Electr. Power Appl., Vol. 148, tested. The converter input current is No. 5, pp. 385-392. practically sinusoidal and its power fac- Singh, B.; Singh, B.N.; Chandra, A.; Al- tor is close to unity. The circuit topol- Haddad, K.; Pandey, A.; Kothari, D.P ogy is very simple since includes only (October 2003) A review of single- one power switch. This switch oper- phase improved power quality AC-DC ates in a soft commutation mode. The converters. IEEE Trans. Ind. Electron., Fig. 5. Hardware layout converter provides a wide-range power Vol. 50, No. 5, pp. 962-981. control. This converter has advantages Singh, B.; Singh, B.N.; handra, A.; Al- like reduced hardware, reduced stresses Haddad, K.; Pandey, A.; Kothari, D.P. and high power density. Closed loop (June 2004) A review of three-phase The circuit parameters are R0=60Ω; L =150µH; C =2.35µF; L =22µH; circuit model is developed and it is suc- improved power quality AC-DC con- 0 0 r verters. IEEE Trans. Ind. Electron., L =8.0mH; C =0.94µF and the switch- cessfully used for simulation studies. i in Vol. 51, No. 3, pp. 641-660. ing frequency ω = (62-113) x103 s-1. The limitation of this converter is pres- S ence of DC component in the output B.Saha, K.Y. Suh, S.K. Kwon, and The experimental waveform of output M.Nakaoka, (Apr. 2007) “Selec- voltage is shown in Fig.6. current and operating frequency is lim- ited to 11MHz. Simulation and experi- tive dual duty cycle controlled high mental results demonstrate the actual frequency inverter using resonant capacitor in parallel with an auxiliary converter capability to control the heat. reverse blocking switch,” J.Power The experimental results closely agree Elecctron., vol.7, no.2, pp118-123. with the simulation results. 5