Improved Modification of the Closed-Loop-Controlled AC-AC Resonant Converter for Induction Heating

Transcription

1 Improved Modification of the losedoopontrolled AA Resonant onverter for Induction Heating Kirubakaran Dhandapani and Rama Reddy athi A singleswitch parallel resonant for induction heating is implemented. The circuit consists of an input filter, a bridge rectifier, and a controlled power switch. The switch operates in soft commutation mode and serves as a high frequency generator. The output power is controlled via the switching frequency. A steady state analysis of the operation is presented. A closedloop circuit model is also presented, and the experimental results are compared with the simulation results. Keywords: Electronics, AA, resonant switching, induction heater, closedloop control. I. Introduction tatic frequency s have been extensively applied in industry as a source of medium frequency power supply for induction heating and melting installations. They are applied in all branches of the military and machinebuilding industries, as well as for jewelry, forge heating, domestic heating, cooking devices, and other purposes. The ordinary circuit of an AA for induction heating typically includes a controlled rectifier and a frequency controlled current source or a voltage source inverter. It is well known that the input rectifier does not ensure a sine wave input current and that it is characterized by low power [][3]. Recently, many studies of high power factor rectifiers with a single switch have been made [4], [5]. These schemes are also characterized by a near sine wave input current. In addition, in [6][], the scheme of the A A for induction heating is described. The input circuit of the is constructed similarly to the input circuit in [4], [5], which also ensures a high power factor. However, the inverting circuit is constructed in the traditional mode with four controlled switches. D r Vin R Manuscript received Nov. 3, 8; revised Apr. 3, 9; accepted Apr., 9. Kirubakaran Dhandapani (phone: , kiruba_d@yahoo.com) is with the Department of Electrical and Electronic Engineering, t. Joseph s ollege of Engineering, Tamil Nadu, India. Rama Reddy athi ( vit_srr@yahoo.com) is with the Department of Electrical and Electronic Engineering, Jerusalem ollege of Engineering, hennai, India. D 4 D 3 V Fig.. ircuit diagram. 98 Kirubakaran Dhandapani et al. 9 ETRI Journal, Volume 3, Number 3, June 9

2 D r I R V D 4 D 3 V (a) Mode I (t o t ) D r I D R I D3 V I D D 4 D 3 I D4 (b) Mode II (t t ) V t D r T T T V R t t t t 3 Fig. 3. Ideal switching waveforms. D 4 D 3 (c) Mode III (t t 3 ) charges up practically linearly at a rate and a polarity corresponding to the instantaneous input voltage. Fig.. Equivalent circuits. In the scheme of the AA shown in Fig., there are two main advantages. It is characterized by a high power factor and a sine wave input current. On the other hand the inverter circuit is constructed with a single controlled switch, which serves as a highfrequency generator for induction heating. The resonant circuit in the output produces the highfrequency output required by the load. II. Principle of Operation The operating principles of the circuit are illustrated in Fig., and the theoretical waveforms are shown in Fig. 3. We suppose the switching frequency is much higher than the input line frequency, and in the analysis, we arbitrarily chose the time interval where >.. Interval T : t <t<t The equivalent circuit is shown in Fig. (a). Four diodes, to D 4, and the switch are off. In this interval, the capacitor. Interval T : t <t<t The equivalent circuit is shown in Fig. (b). Two diodes, and D 3, and the switch are on. In this interval, the capacitor discharges via the circuit r loadd 3. This interval ends when the capacitor voltage reduces to zero. 3. Interval T : t <t<t 3 The equivalent circuit is shown in Fig. (c). All the diodes and the switch are on. In this interval, the switch current flows through switch via two parallel bridge branches. This interval ends when this switch current decreases to zero. At that moment, the switch turns off, and the process starts from the beginning. III. Operation Analysis Analysis of the circuit operation is based on the commonly accepted assumption that all circuit components are ideal. The approximate analytical calculations are based on two additional assumptions: that the switch current can be approximated by a semisinusoidal and that the load power is determined by the first harmonic of the load voltage. In this, the optimal ETRI Journal, Volume 3, Number 3, June 9 Kirubakaran Dhandapani et al. 99

3 The relationship between input and output voltages M g = V o / 3 M g I π A = = I in D ( D D ), D π D sw.max cos( ).max D A = = cos( π D), 4.max π ( 4 D ) () (3) R o * 4. ω s *.9 I R.max 3 = = I * * * sw.max R ( ω / ω) A, (4) D D r *=. r *= ω s * (a) ω r *=3 ω r *=5 π D R ( ω ) ( cos( )) * * o * Vo.r.m.s ω D M g = = = V in.r.m.s A A A 3. π ( D D ). This relationship is shown in Fig. 4(a). The values of duty cycles and D may be calculated from the plot in Fig. 4(b). The values of duty cycles and D may also be found from the following approximate polynomial expressions: * * * D ( ωr 33.4ωs 5.4R * * * * 3.ω R 7.4 R ω ), r o s D ( ω 75.ω 9.3R 75.3 R ). IV. imulation Results * * * r s s * * * * * 3 rωs ωs The circuit model of the AA is shown in Fig. 5. copes are connected to measure the output voltage, driving pulses, and capacitor voltage. The AA fed induction heater system was simulated using Matlab imulink. witching pulses are shown (5) (6) ω s * (b) Pulse cope Fig. 4. (a) Factor M g = V o / against parameters R o * & ω s *and (b) duty cycle against parameters r * & ω s *. cope4 D 3 Mosfet T cope3 range of normalized parameters is chosen. The maximum normalized value of switch voltage is V * swmax = V swmax / V B = 4 5. To provide these values, it is necessary to choose the following ranges of the normalized circuit parameters: * * / r r * = =..; ωr = = 3 5; ωs=..9. () ω B A Vol Vol D D 4 cope Fig. 5. Diagram of the openloop circuit. Vol cope5 3 Kirubakaran Dhandapani et al. ETRI Journal, Volume 3, Number 3, June 9

4 urrent (ma) Voltage (V) urrent (ma) Voltage (V) (a) Driving pulses (b) Voltage across (V ds ) (c) urrent through (d) A output voltage Fig. 6. AA fed induction heater system simulation results. in Fig 6(a). The switching frequency was 33 khz. Voltage and current waveforms of the switch are shown in Figs. 6(b) and (c), respectively. Output of the is shown in Fig. 6(d). Input voltage (V) Table. Performance comparison. Output voltage (V) Efficiency (%) onventional ingle switch onventional ingle switch Disturbance D D Pulse Pulse Pl controller et point 3 Fig. 7. Diagram of the closedloop controlled AA. Voltage (V) Voltage (V) M M Pulse Vol cope6 Mosfet T Pl Vol cope5 5 G Rectifier Vol (a) Openloop system cope (b) losedloop system Fig. 8. Output voltages of the openloop and closedloop systems. A comparison of the performance of a conventional AA and the single switch AA is presented in Table. The results confirm that the single switch achieves better performance efficiency than any other. The closedloop circuit model of the AA is shown in Fig. 7. copes and displays are connected to measure output voltage. A disturbance is introduced at the input by using two switches. The output voltage is sensed and it is ETRI Journal, Volume 3, Number 3, June 9 Kirubakaran Dhandapani et al. 3

5 Fig. 9. Hardware layout. Fig.. Oscillogram output voltage. compared with the reference voltage. The error signal is sent to the controller. The output of the PI controller controls the dependent source. The response of the openloop system is shown in Fig. 8(a). The output voltage of closedloop system is shown in Fig. 8(b). The disturbance is applied at.3 secs. The settling time is.3 secs. The control circuit takes proper action to reduce the amplitude to the set value. Thus, the closedloop system reduces the steady state error. Output power (kw) 4 3 V. Experimental Verification The singleswitch AA (Fig. 9) was built and tested at 3 V. The circuit parameters are R =6 Ω, =5 µh, =.35 µf, r = µh, i =8. mh, in =.94 µf, and the switching frequency ω = (6 3) 3 s. The experimental waveform of the output voltage is shown in Fig.. The output power control was also checked, and its dependence versus the switching frequency is shown in Fig.. VI. onclusion An AA circuit for induction heating was tested. Its input current is practically sinusoidal, and its power factor is close to unity. The circuit topology is very simple because it includes only one power switch. This switch operates in a soft commutation mode. The provides a widerange power control. This has advantages including reduced hardware, reduced stresses, and high power density. A closedloop circuit model was developed, and it was successfully used for simulation studies. The simulation and experimental results demonstrate the actual capability. The experimental and simulation results show good agreement. References Frequency (khz) Fig.. Output power versus switching frequency. [] N.. Bayindir, O. Kukrer, and M. Yakup, DPBased P ontrolled 5 khz kw HighFrequency Induction Heating ystem for urface Hardening and Welding Applications, IEE Proc.Electr. Power Appl., vol. 5, no. 3, May 3, pp [] A. Okuno et al., Feasible Development of oftwitched IT Inverter with oadadaptive FrequencyTracking ontrol cheme for Induction Heating, IEEE Trans. Ind. Applicat., vol. 34, no. 4, July/Aug. 998, pp [3] H. Kifune, Y. Hatanaka, and M. Nakaoka, ost Effective Phase hifted Pulse Modulation oft witching High Frequency Inverter for Induction Heating Applications, IEE Proc.Electr. Power Appl., vol. 5, no., Jan. 4, pp. 95. [4] H. Ogiwara and M. Nakaoka, Z High Frequency Inverter Using IT for Induction Heating Applications, IEE Proc. Electr. Power Appl., vol. 5, no., Mar. 3, pp [5].V. Mollov, M. Theodoridis, and A.J. Forsyth, High Frequency VoltageFed Inverter with Phasehift ontrol for Induction 3 Kirubakaran Dhandapani et al. ETRI Journal, Volume 3, Number 3, June 9

6 Heating, IEE Proc.Electr. Power Appl., vol. 5, no., Jan. 4, pp. 8. [6] H. Ogiwara,. Gamage, and M. Nakaoka, Quasiresonant oft witching PWM VoltageFed High Frequency Inverter Using IT for Induction Heating Applications, IEE Proc.Electr. Power Appl., vol. 48, no. 5, ept., pp [7] B. ingh et al., A Review of inglephase Improved Power Quality AD onverters, IEEE Trans. Ind. Electron., vol. 5, no. 5, Oct. 3, pp [8] B. ingh et al., A Review of ThreePhase Improved Power Quality AD onverters, IEEE Trans. Ind. Electron., vol. 5, no. 3, June 4, pp [9] J. Acero, R. Alonsjo, and J.M. Burdio Modeling of Planar piral Inductors between Two Multilayer Media for Induction Heating Applications, IEEE Trans. Magn., vol. 4, no., Nov. 6, pp [] B. aha et al., elective Dual Duty ycle ontrolled High Frequency Inverter Using a Resonant apacitor in Parallel with an Auxiliary Reverse Blocking witch, J. Power Electron., vol. 7, no., Apr. 7, pp. 83. Kirubakaran Dhandapani obtained the ME degree from Bharathidasan University, Tamil Nadu, India, in. He is presently doing his research in the area of AA s for induction heating. He has years of teaching experience. He is a life member of ITE. Rama Reddy athi obtained the ME degree from Anna University, Tamil Nadu, India, in 989. He has pursued research in the area of resonant s in 995. He has years of industrial experience and 8 years of teaching experience. He is a life member of IE, IETE, ITE, IR, and PE. He has authored text books on power electronics and electronic circuits. He has published papers in the area of power electronics and FATs. ETRI Journal, Volume 3, Number 3, June 9 Kirubakaran Dhandapani et al. 33