The Simple Temperature Control for Induction Cooker based on Class-E Resonant Inverter

Chainarin Ekkaravarodome

Department of Instrumentation and Electronics Engineering, Faculty of Engineering, King Mongkut’s University of

Technology North Bangkok, Bangkok, Thailand. E-mail: chainarine@kmutnb.ac.th

Patipong Charoenwiangnuea Department of Electronic and Telecommunication

Engineering, Faculty of Engineering, King Mongkut’s University of Technology Thonburi,

Bangkok, Thailand. E-mail: patipong.ch@hotmail.com

Kamon Jirasereeamornkul Department of Electronic and Telecommunication Engineering,

Faculty of Engineering, King Mongkut’s University of Technology Thonburi, Bangkok, Thailand. E-mail: kamon.jir@kmutt.ac.th

Abstract— This paper presents a simple temperature control for high efficiency induction cooker based on class-E DC-AC resonant inverter. The active switch can be operated under the zero-voltage switching conditions. The conduction loss of the anti-parallel diode of the active switch and the harmonic currents injected into the public supply system can be reduced. The high power-factor and low line current harmonic distortion can be obtained, which are very attractive in term of commercial production. In order to achieve upon this objective, the induction cooker’s parameters need to be designed properly and details of analysis and design of this induction cooker’s components are described. A proposed high efficiency induction cooker is designed for an operating at a 32-kHz frequency, a 220-V line rms voltage, a 50-Hz line frequency and a 1.2-kW output power. Keywords—Class-E resonant inverter, Induction cooker, Pulse density modulation, Zero-voltage switching

I. INTRODUCTION Nowadays, the most popular types of electric heating for

cooking vessel can be divided into two types depend on the heat generation within the cooking vessel: First, the resistance heating is one of the most commonly of the heat generation and is found in a wide range of domestic application. Resistance heating is a process where thermal energy is produced by passing an electrical current through a resistor converts electrical energy into heat energy. The advantages of resistance heating are the low cost and easy maintenance compared to the electric heating generation because of the simple circuit design configuration. However, the main problem of the resistance heating is low efficiency due to the contact heating method. Second, the induction heating [1]-[2] is the process of heating an electrically conducting object by electromagnetic induction, where eddy currents are generated within the vessel and resistance leads to Joule heating of the vessel. The induction cooker is one of many applications of the induction heating, which developed using a half-bridge circuit, which has been presented previously [3]-[15] and their

improved inverter modifications have been developed for industrial and consumer induction heated applications. Because of reducing switching power losses of discrete power semiconductor switching device, low cost and compactness due to simple circuit topological configuration, as well as easiness on power regulation based on pulse-width modulation (PWM) control scheme, the simplest voltage source load resonant inverter with a single power switch [16]-[24] has attracted special interest for consumer induction heating appliances.

The objective of this paper is to introduce a simple temperature control for high-frequency induction cooker based on class-E DC-AC resonant inverter. The conduction loss of the anti-parallel diode of the active switch and harmonic currents injected into the public supply system can be reduced. The high efficiency, high power-factor and low line current total harmonic distortion (THDi) can be obtained. The induction cooker’s parameters need to be designed properly and details of analysis and design of this induction cooker’s components are described. Presented simulation and experimental results are to verify the theoretical analysis.

Fig. 1 Proposed induction cooker base on class-E DC-AC resonant inverter.

978-1-4799-0545-4/13/$31.00 ©2013 IEEE

This paper is divided into five sections. In Section II, the circuit description is shown. In Section III, the principle of operation is described. The experimental results to support the theoretical analysis are presented in Section V. Some conclusions are given in Section VI.

II. CIRCUIT DESCRIPTION Figure 1 illustrates the circuit of the proposed zero-voltage

switching class-E resonant inverter for induction heating application is studied in this paper. It consists of a bridge rectifier, D1 – D2 – D3 – D4, an electromagnetic interference filter (EMI), Lf – Cf, and a class-E resonant inverter, Q – Lr – Cr. The pulse density modulation of the gate signal, GEυ , is controlled to regulate the temperature. In order to guaruntee the zero-voltage switching (ZVS) condition.

(a) (b)

Fig. 2 Equivalent circuit of the induction cooker base on class-E inverter.

(Mode 1) (Mode 2)

Fig. 3 The operation mode of the proposed circuit.

III. PRINCIPLE OF OPERATION

A. Inverter of operation The principle of the operation of the high-frequency

induction cooker based on zero-voltage switching class-E DC-AC resonant inverter [41] is explained by an equivalent circuit shown in Fig. 2. The diodes, D1and D4, of the bridge rectifier operate during the positive half-cycle of the line voltage, which is represented as sinin in LV tυ ω= , where Lω is the line

angular frequency and the diodes D2 and D3 operate during the negative half-cycle. The model of the line-voltage rectifier output is a full-wave rectified sinusoidal voltage source sinin in LV tυ ω= . The equivalent circuit of ZVS class-E resonant inverter with cooking vessel can be replaced the simplest form of a transformer, when the coil of the secondary is turned only once with the resistance R which has connected in parallel with the secondary size of the high frequency transformer, the planar multi turn winding or resonant inductor Lr [25]-[40] means the inductor on the primary side of the transformer is shown as Fig.2 (a). The induction coil and the vessel are insulated by glass-ceramic material.Whenever, the high frequency alternating electric current flow through the induction coil, which produces a high frequency magnetic field. This field induces an eddy current within the cooking vessel and converts electrical energy into heat across the bottom of the cooking vessel. And this can be simplified as in the Fig. 2(b), where Rt indicates the equivalent parallel resistance is converted from the secondary side of the transformer.

The equivalent circuit operation modes of the induction cooker base on class-E inverter as shown in Fig.3. Mode 1 when active switch Q is ON and Mode 2 when active switch Q is OFF. It can be seen that, the conduction loss of the anti -

Fig. 4 Key waveforms of the class-E resonant inverter.

Fig. 5 Principle of PDM control.

Fig. 6 Simplified algorithm for the temperature control.

parallel diode of the active switch can be neglected. Therefore, the high efficiency can be obtained. Figure 4 shows the operation waveforms of the proposed ZVS class-E DC-AC resonant inverter for high efficiency induction cooker.

B. Temperature Control method The principle of the pulse-density modulation (PDM) [8],

[42] based temperature control is shown in Fig. 5. The PDM modulation is implemented keeping the switching frequency constant and adjusting output temperature through controlling the duty cycle, which is a term for a pattern that repeats “ON and OFF” in accordance with a control sequence to adjust its rms output voltage. Where _D Conυ is a low frequency

square wave signal, which can be adjusted the duty cycle, HFυ is a constant switching frequency signal and GEυ is

gate signal from PDM of _D Conυ and HFυ , respectively. Thus,

this technique is suitable for induction cooker application base on class-E DC-AC resonant inverter, due to guaruntee the ZVS operation.

The simplified algorithm for the temperature control is shown in Fig. 6, where T is the vessel temperature and “*”

mean the commanded value. The transfer of output power to the load is depend on the active switch is duty cycle _ ConDυ . Then the temperature control for induction cooking will depend on the duty cycle _ ConDυ of the active switch as well. In this paper presents a simple temperature control by the principle as follows: start measuring the temperature to compare with the commanded value. If less than the command value will be increase the duty cycle _ ConDυ . If not, will be decrease the duty cycle _ ConDυ .

IV. DESIGN PROCEDURE Referring to the equivalent circuit of the equivalent circuit

of the induction cooker base on class-E inverter [41] is shown in Fig. 3. For the steady-state operation, the operating at a 32 kHz switching frequency, the line rms voltage, inυ , of 220 V and a line frequency fL of 50 Hz, a 1.2 kW output power, PO, and the switching frequency, fS, is approximately equal to resonant frequency, fr, where Sω is the switching angular frequency and then the equivalent resistance Rt is:

2

215.326 in

tO

RP

υπ

= (1)

The resonant inductor is given by:

0.205 tr

r

RL

fπ= (2)

The resonant capacitor is obtained by:

0.512r

r tC

f Rπ= (3)

The maximum voltage across the switch is calculated as

5.443SM inV υ= (4)

The maximum switch current is

2.828 OSM

in

PI

ηυ= (5)

V. EXPERIMENTALS RESULTS The prototype induction cooker was constructed using the

component values obtained from the design procedure given above. The circuit parameters are presented in Table I. The switching frequency was fixed at about 32 kHz. The PDM modulation is implemented keeping the switching frequency constant and adjusting output temperature through controlling the duty cycle. The low frequency square wave signal was 5 Hz. The line voltage was 220 Vrms, and the line frequency was 50 Hz.

TABLE I. CIRCUIT PARAMETERS OF THE PROTOTYPE

Symbol Value and part number 1 4D D− GBP25-08 Q IRG4PH40UD2

fC 4.7μF

rC 82 nF

fL 500μH

rL 127μH

Fig. 7. Input line voltage and the current waveforms.

Fig. 8. Measured THD of iin from the power analyzer.

The input line voltage and current were measured with a power analyzer (Fluke model 43B) and 100% duty cycle _ ConDυ . The measured input line power, Pin, was about 1.25 kW. The input power-factor near unity and is shown in Fig. 7. The total harmonic distortion of the input current iin (THDi) was about 4.8% and is shown in Fig. 8. The digital oscilloscope and current probe used in this experiment were Yokogawa models DL1620 and 701930, respectively. The switch voltage waveforms and the switch current of the ZVS class-E DC-AC resonant inverter near the peak and the zero crossing of the line voltage, respectively, are shown in Fig. 9. It can be seen that the conduction loss of the anti-parallel diode of the active switch can be reduced when compared with the conventional technique, and the active switch turns on at a low dυ/dt, which reduces turn-on switching loss and noise. The ringing in the switch current can be attributed to the loop inductance required for the current probe and a parasitic capacitance.

(a)

(b)

Fig. 9. Measured waveforms of CEυ and iQ: (a) near the line voltage peak of the line voltage, with the lower two waveforms as zoomed-in views of the top two waveforms; (b) near the zero crossing, with the bottom two waveforms as zoomed-in views of the top two waveforms.

Fig. 10. Measured output voltage and resonant inductor current waveforms.

Fig. 11. Measured output voltage and resonant capacitor current waveforms.

Fig. 12. Output voltage, induction coil current and power LrP waveforms, with

the lower three waveforms as zoomed-in views of the top three waveforms.

Fig. 13. Output power versus duty cycle characteristic with PWM control.

The experimental waveforms of the output voltage Oυ and resonant inductor current iLr are shown in Fig. 10. Figure 11 shows the output voltage Oυ and resonant capacitor current iCr waveforms. Figure 12 shows the measured waveforms of the output voltage and induction coil current. Thus, the output power was about 1.2 kW, which is approximately equal to power LrP . The relationship between output power and duty cycle characteristic with PWM control is shown in Fig. 13.

VI. CONCLUSION The simple temperature control for high-frequency

induction cooker based on class-E DC-AC resonant inverter is proposed in this paper. The active switch can be operated under the zero-voltage switching conditions. The conduction loss of the anti-parallel diode of the active switch and harmonic currents injected into the public supply system can be reduced. The high efficiency, high power-factor and low line current harmonic distortion can be obtained, which are very attractive in term of commercial production. In order to achieve upon this objective, the induction cooker’s parameters need to be designed properly and details of analysis and design of this induction cooker’s components are described. A proposed high efficiency induction cooker is designed for an operating at a 32-kHz frequency, a 220-V line rms voltage, a 50-Hz line frequency and a 1.2-kW output

power. Experimental results verified theoretical analysis. The designed induction cooker had a near unity power-factor, a 4.8% THDi, the PDM technique is suitable for induction cooker application base on ZVS class-E resonant inverter, due to guaruntee the ZVS operation.

ACKNOWLEDGMENT

The author would like to thank King Mongkut's University of Technology North Bangkok, Thailand, for financially supporting this research under Contract No. KMUTNB-NEW-55-02.

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