The 30th Annual Conference of the lEEE Industrial Electronics Society, November 2 - 6,2004, Busan, Korea

Commercial Utility Frequency AC to High Frequency AC Soft Switching Power Conversion Circuit with Non Smoothing DC Llnk for IH Dual

Packs Heater

Hisayuki Sugimura, 'Tarek Ahmed, 3Mohamed Orabi, *Hyun-Woo Lee, and '2Mutsuo Nakaoka,

'Division of Electrical and Electronics Engineering, The Graduate School of Science and Engineering, Yamaguchi University, Yamagucbi, Japan

e-mail : supimura@me-newsl .eee.vamapchi-u.ac.jip 'The Electric Energy Saving Research Center & Technology Innovation Research Center for Production Automation,

Department of Electrical and Electronics Engineering, Kwgnam University, Masan, Korea 'Elecmcal Power and Machines Department, Faculty of Engineering, South Valley University, Aswan, Egypt

1

Abstrucf- In this paper, a novel topology of soft switching PWM high frequency AC power conversion conditioning and processing circuit without DC smoothing Capacitor filter link from the voltage grid of utility frequency AC power supply source with 60Hz-100V or 6OHz-ZOOV is proposed and intro- duced for innovative consumer induction heating OH) boiler applications as a hot water producer, steamer and super heated steamer. The operating principle of utility frequency AC-high frequency AC power frequency conversion circuit defined as high frequency cycloinverter is described, which can etliciently operate under a principle of zero voltage soft switching and regulate by means of positive and negative alternate asymmet- rical PWM synchronized with the utility frequency single phase AC voltage. The dual mode control scheme based on high fre- quency PWM and commercial frequency AC voltage PDM for high frequency cycloinverter are discussed in order to extend its soft switching commutation operating range in spite of power regulation. This power frequency changer as high fre- quency cycloinverter is developed originally for the high fre- quency induction heating boiler in consumer and industrial fluid pipeline system,

It is verified on the basis of experiment and simulation re- sults in the steady state operation of the high frequency cyc- loinverter using IGBTs which is suitable for the business-use IH boiler using new electromagnetic induction heating dual packs fluid beater. Finally, the power regulation characteristics in addition to utility AC side line current harmonic components and power factor characteristics and power conversion effi- ciency characteristics of this high frequency cycloinverter are evaluated and discussed from an experimental point of view.

fndex fems- High kquency cycloinverter, Soft switching PWM, Utility AC-PDM, Dual mode control strategy, Non DC smoothing capacitor DC link, Induction heating, Spiral type dual packs fluid heater

I. INTRODUCTION

In general, the electromagnetic induction heating (IH) is concemed with non-contact, high efficiency, and clean electric heating method due to the energy conversion heated device by induction eddy current based on Faraday's law of electromagnetic induction principle in addition to Joule's heating principle. Attractive IH technology used for indus-

trial and consumer applications is roughly classified into two; low frequency IH and high kquency IH (over 20kHz). In recent years, significant verifications of effective appli- cations of IH have been recognized as follows: metal heat treatment process in the industry application fields, including thermal treatment process such as forging and casting, elec- tromagnetic induction based plasma generation process, high-speed dissolution process for the new materials and melting process of semiconductor manufacturing, high fie- quency induction heating soldering process with the self temperature function using magnetic alloy heating element, and induction h i o n processing of the polyethylene pipe. On the other hand, the latest technology developments of IH application products emphasized on the environment have attracted special interest in the consumer application fields as follows: IH cooking device, rice cooker and warmer, boiler, hut-water producer, floor and wall fluid heater, ti-yer, dryer, wastes treatment and soil sterilization equipment using cleaning, sterilization and drymg of atmospheric pressure super heated steamer. Under these technological require- ments, research and development of circuits and control schemes of the high ftequency power supply equipment for the electromagnetic induction heating by a variety of high efficiency voltage source type series capacitor compensated and parallel capacitor compensated load resonant high fre-

I I

(a) Transformer type (b) fi-L series equivalent equivalent circuit model circuit model

Fig. 1 Equivalent circuit modeling of electromagnetic induction eddy current based Joule's heating load.

0-7803-8730-9/04/$20.00 02004 IEEE 1155

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quency inverter which incorporate soft switching pulse modulation technologies (PFM, PWM, PAM, PDM, PSM) using the latest MOS gate controlled power semiconductor switching devices (IGBTs, CSTBTs) are actively proceeded from a practical point of view.

However, the harmonic distortion inherently causes in the commercial AC input grid side because of rectified DC smoothing voltage link with capacitor input filter. In addition, the significant problems on power conversion efficiency, volumetric physical size, reliability and life of the electro- lytic capacitor DC link power stage have actually appeared by using the electrolytic capacitor bank or assembly for the DC voltage smoothing.

This paper proposes the utility frequency AC - high h- quency AC power conversion circuit defined as high f?e- quency cycloinverter or cycloconverter, which does not in- clude DC smoothing fdter stage. In addition, the circuit op- eration of the soft switching PWM AC- high fiequency (HF) AC power converter as high fkequency cycloinverter is de- scribed for the hot-water producer and steamer using new M Dual Packs Fluid Heater @PH) . Then, the circuit operation verification of high fiequency cycloinverter is carried out in experiment and simulation. Finally, the power regulation characteristics and power conversion efficiency characteris- tics of high fiequency cycloinverter is evaluated and dis- cussed, along with active filtering characteristics on har- monic line current components and total harmonic power factor in utility AC power grid side. The feasible effective- ness and practicability of soR switching PWM controlled high-frequency cycloinverter treated here are substantially proved on the basis of experimental results for consumer M-DPH applications in pipeline systems.

Direct heating

11. EQUIVALE~ CIRCUIT OF hTl"DTI0N HEATDTG LOAD AND MEASUREMEhT OF CIRCUIT PARAMETERS

The equivalent circuit modeling of the electromagnetic

Fluid heating

I

Indirect heatiap.

Fig. 2 Soft switching pulse modulaicd utility frequency AC-high fie- qucncy AC power conversion circuit without electmiytic capacitor.

induction fluid heating load (DPH) discussed below is shown in Fig. 1. Figure 1 is a linear model of the induction heated load circuit represented by equivalent effective inductor Lo in series with equivalent effective resistor Ro in the input side of working coil terminals of the induction heater or IH-DPH. R, and L, are respectively determined by the self-inductance LI and internal resistance RI of the work coil, self-inductance L2 of eddy current heated device in electromagnetic induction transformer secondary side and mutual inductance M be- tween LI and L2. It is considered that these circuit parameters in spite of output power regulation of the IH-DPH load is

[a) Top view of spiral type dual packs heater

Output nuid Spin1 type heater

Bar &e. Eeating vessel

Input maid Utility AC power

@) spiral heater 6truCtu;e

Fig. 3 Internal structure of IH spiral type dud packs heater heater.

Fig. 4 Soft switching pulse modulated utility kquency AC-hi& fre- quency AC power conversion circuit without elech-olytic capacitor.

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kept constant, when the output fkequency of high frequency AC voltage.

Structures of IH load are shown in F i g 2 The metal sw- face hardening trpe utilizes the skin effect by high fkquency current. The indirect heating type heats the heating vessel in the induction beating. The direct heating type can heat di- rectly heating object in which induction currents are gener- ated such as the metal. The fluid heating type is inserted into the non-metal heating vessel in the pipeline. When high frequency current flows through working coil h m high hquency inverter, induction heater is heated quickly. Water flows through into heating vessel from lower side. After that, bot water i s outputted from upper side.

Measured methods of circuit parameters Ro and La in the M-DPH load are as follows. High fresuency AC voltage is provided to the IH-DPH load via, working coil by high fie- quency inverter as well as high frequency cycloinverter or high fiequency linear power amplifier. The effective value V,, of hi@ fieequency (HF) AC voltage and effective value I,, of high frequency AC current with electrical angular fiequency ( w = ~ j ) , power factor cost!? (cos@ : difference angle between output voltage and output current) are meas- ured for IH-DPH load with working coil driven by high fie- quency power supply. Equation (1) is obtained on the basis of the sine wave alternating current theory.

-_ vms -zm = j m 1-

cos e = (1) Rn2 + t m 4 1 .............

she=*

The impedance of the induction heating load Z,, for the

Switching frequency Dead time

Filter and resomnt capacitors Lossless snubbing

Inductance of utility AC side fil- quasi-resonant capacitor

ter inductor

Fig. 5. Gate voltage pulse signal sequences of asymmetrical PWM control scheme.

f 2lkwz T d 2 P

C,,C2 5P

0.lpF CO

Ll I&

Fig. 6 Utility AC kquency-based pulse density modulation control strategy (dPD,,, 4 . 7 ) .

Effective resistance component

Effective inductance component

R,

L,

of IH load

of IH load

angular frequency U of output voltage and current of high frequency linear power amplifier (high ftequency inverter or high frequency cycloinverter) is calculated using the equa- tion (1). By using measured power factor, the equivalent parameters R, and L, of IH-DPH load with working coil is estimated. In case of considering internal resistance RI of the work coil, the equivalent effective resistance value becomes R, + R I . The circuit parameters k and r expressed in Fig. 1 (a) are represented as follow s by using R, and L,.

1.65s2

34.2pH

1x1. NOVEL TYPE OF INDUCTION HEATING DUAI, PACKS nun, HEATER

In the high frequency ZH, improvement of high frequency power supply due to AC-smoothing DC-HFAC indirect power conversion processing is required practically. The high fiequency cycloinverter due to utility fkquency AC-HPAC power conversion processing is more effective for unity power factor and sine wave current in utility AC grid high-hquency power conditioning in the IH-DPH load side. Moreover, the development and improvement of IH-DPH device With higher beating conversion efficiency are suitable for IH heat exchanger of the fluid heating device in pipeline systems.

The appearance of business use IH-DPH driven by the high hquency inverter is shown in Fig.3. This spiral IH-DPH device developed newly works as a heat exchanger of the new spiral structure with the end ring with a low re- sistance, which is formed spirally by the thin plate of non- magnetic stainless steel SUS316, which is inserted into the non metal vessel. The material of the IH-DPH device as must consider the followings: temperature distribution is mi- formity, corrosion protection for fluid (water, vapor, gas, powder) is excellent, low pressure moving fluid in pipeline becomes clean. SUS3 16 is the stainless steel which is espe- cially more excellent in corrosion protection than non-magnetic material SUS304 used most widely. The work coil uses enamel copper wire twisting together of the insu- lation to each other. This work coil is called litz wire for power. In this IH heating device (see Fig.3), thermally stable temperature of this wire is about 170 degrees centigrade.

Table 1 Design specifications and circuit parameters

Item

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Actually, the water tube part is not over 120 degrees centi- grade, because tbe heat insulating material is packed in IH-DPH hot-water producer between work coil and IH heating element. Therefore, the security of enough thermally stable temperature is possible for fluid heating container made of ceramics and nitrogen resin. This M heating ele- ment is based on the mechanism, which heats the low pres- sure continuous movement fluid in the pipeline tube by the heat exchange action between IH heating element and fluid. Therefore, thermally stable temperature is also necessary for the pipeline tube. The fluid heating vessel tube uses the polycarbonate, and the thermally stable temperature is below 120 degrees centigrade.

IV. UT"Y FREQUENCY AC - HIGH FREQUENCY AC POWER CONVERSION CIRCUIT

A. Circuit description

The circuit structure of the AC-HFAC power converter or high frequency cycloinverter in which converts utility fre- quency AC into high frequency AC without the electrolytx capacitor DC link or complete DC smoothing busline is shown in Fig.4. The proposed power frequency conversion circuit as a high frequency cycloinverter is a power fie- quency changing circuit topoIogy which converts the utility fiequency AC into high frequency AC voltage over 20 kHz. This circuit structure is defined as high frequency cycloin- verter which is different from the conventional high fre- quency inverter. The main power conversion circuit structure is composed of: two power switching blocks QI ( SWl/DI ) and Q2 ( SW2/D2 ), filter inductor LI in utility AC input-side, two capacitors Cl and C2 as active clamp resonance in ac- cordance with M-DPH load and low pass filter, lossless quasi-resonant snubber capacitor CO and, induction heated DPH load. This cycloinversion circuit operation is equal to that of active clamp quasi-resonant invertr due to the ca- pacitor C, in parallel with the induction heated DPH load. h w e of using each CJ2 in parallel with Ql and Q2, the active clamp inverter becomes the same equivalent U in Fig.4.

d ~ ~ ~ 0 . 3 dm+O.l Fig.7 Input voltage and current waveforms

B. Dual mode control of asymmetrical PWMand utilip Jrequency AC PDM

The gate pulse signal timing sequences for asymmetrical PWM control of the cycloinverter are shown in Fig.5. The asymmetrical PWM as control variable is defined as the equation (2). That is the duration proportion of on time Ton] of the main power switch for a high frequency cycloinverter period Tis defined as Duty Factor or Duty Cycle d p w in the alternate asymmetrical PWM control scheme exchanged synchronkingly by the polarity of the utility AC voltage. The duration time of Toni contains a dead time T,. In addition, the gate pulse trains of the main and auxiliary power switch must be reversed to supply the desired AC power for M-DPH load, because each role of SW) and SW, is reversed in accordance with either positive or negative voltage of utility AC power source. By introducing this control strategy, the high fre- quency cycloinverter enables to supply of the desired output AC power for the M-DPH load.

- To,, .............................. (2) dPWM -- T

In addition to this asymmetrical P W M control strategy, the commercial utility frequency AC-PDM (Pulse Density Modulation) Z V S control scheme or commercial utility AC voltage cycle control scheme is also introduced herein. 3y the commercial utiIity fiequency AC-ZVS-PDM control, the output HFAC effective power by changing the discrete cycle numbers of commercial utility fiequency AC voltage pulse sains in some intervals Tp~Au to the IH-DPH load. New concepts of the commercial utility hquency AC-ZVS-PDM

r I

vQ2

iQ2

i t : : : : ; : :

. . . . . . . . . c I

----.........-..-.- i i i i i i i i ;

~~,,r~~~:2OO[V/div] vM:250[v/div] iQ,,io?: I OO[A/div] Time: IOb/div] Fig 8 Soft switching voltage and current waveforms in c u e of ~ P R U

4 . 5 in asymmetrical ZVS-PWM sch-. (LeR traccs:SimuIaiion, Right traces:Expeliment)

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control strategy are conceptually shown in Fig.6. The ZVS-based commercial utility frequency AC-PDM time ra- tio as a control variable dpDM i s defined as the equation (3). In the high fiequency cycloinverter, the quantity in a period of utility AC power source under in 1/10 periods of utility AC voltage can be regulated discretely.

The high fiequency cycloinverter circuit topology de- picted in Fig.4 can adjust high-frequency AC output power on the basis of dual-mode control of asymmetrical PWM and comrnetcial frequency AC-PDM under a condition of zero voftage soft switching commutation. The zero voltage soft switching commutation operation can be realized over all the output power regulation area on the basis of dual mode con- trol implementation in case of low power setting area using the utility frequency AC-ZVS-PDM control and the ssym- metrical PWM control in case of high power setting area. The changing point of asymmeh-ical PWM and commercial frequency AC PDM changed by in this high frequency cyc- loinverter is set to dpwM 4 . 3 . The changing point of pulse modulation scheme is determined by time ratio which de- pends on IH-DPH load power and switching hquency. In all the high fiequency AC power regulation ranges, this high frequency cycloinverter operate in soft switching commuta- tion by changing the control scheme changing point ofpulse modulation, even if the IH-DPH load might be replaced by

i Q l iQI

VQ2 VQ2

i Q 3 iQ2

SRL VRL

, " " " : " ,

v~,,Vy::200[v/diVJI vu:250[v/di~J, i@,:5O[AldivJ, i pM l [A id i~ ] im: IW[Aidivj, T i m e M ~ d i v J

Fig.9 Soft swilcbing voltage and current waveforms in case of utility AC frequency-based utility AC-ZVS-PDM control scheme in asym-

metrical ZVS-PWM scheme. (dPII1( 4 . 3 , dpDu=0.S). (Left trsces:Simularion, Right traces:Experiment)

the different IH-DPH load.

v. SIMULATION AND EXPERIMENTAL RESULTS

The results in simulation and experiment of the high fk- quency cycloinverter using IGBT module are described as follows. The design specifications and circuit parameters for experimental setup of high fiequency cydoinverter are in- dicated in Table 1.

Figure 7 shows input voltage and current survey wave- forms of the cycloinverter. When duty factor d p m =0.4,0.3, 0.2, the input current form is sine wave. Although, input current wave form is not sine wave when dpwM 4 . 1 .

The relevant simulation and measured operating wave- forms near the peak value of utility sine wave AC as the high fiequency cycloinverter set up in case of d p m -0 .5 are shown in Fig.8. Tbe typical voltage and current operation wavefonns of simulation and measured ones have a good agreement within the slight error. Therefore, it is noted that the proposed pulse modulation control scheme i s more ef- fective for the high frequency cycloinverter.

4 . 0

si

B

t9 .I

l o e, 2.

2 1. a 0

[

1 2 3 4 Duty factor ~ P W

5 6

Fig.10 Inputbutput power vs. duty factor cbaractaistics in case of asymmdrical ZVS-PWM control scheme.

Pulse density mnml variable dmw

Fig. 1 I InpuVoutput power vs. ZVS-PDM characteristics in case of utility AC voltage and duty factor dpw =0.3.

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70 I I I I I t l o 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Inputpower Pin [kwl

Fig. 12 Actual power conversion efficiency vs. input powex charac- teristics in dual mode control and nou dual mode control schemes.

The simulation and measured operating waveforms in case of the utility frequency AC-ZVS-PDM control strategy and the asymmetrical ZVS-PWM control strategy are shown in Fig.9. This figure shows the operating waveforms in case of dpm 4 . 3 and dpDM =OS. The operation waveforms of simulation and measured ones are comparatively illustrated herein. The utility fkquency AC and high-frequency AC are synchronized each other. As a result, the utility frequency AC-ZVS-PDM control can operate accurately.

The input or output power vs. the duty factor charackr- istics of this high frequency cycloinverter is depicted in Fig.10. The input or output power vs. the pulse density modulation characteristics of this high fiequency cycloin- verterincaseofdp~=O.3 isshowninFig.11. InFig.lO,the high frequency cycloinverter by the asymmetrical ZVS-PWM controlor Duty Cycle control is hard switching commutation operation mode in low power setting area. However, the high hquency cycloinverter operated by the asymmetrical PWM control and the utility fiequency AC-PDM control becomes soft switching operation mode even in low power setting area. Therefore, the input power or output power of high fiequency cycloinverter can be regu- lated up to about 150W in the zero voltage sot? switching operation, when the utility hquency AC-ZVS-PDM control is implemented in addition to the asymmetrical ZVS-PWM.

Figure 12 illustrates the power conversion efficiency characteristics of the high frequency cycloinverter (see Fig.3). In Fig. 1 1, the actual efficiency of the high frequency cycloinverter using asymmetrical ZVS-PWM control might be reduced in the low power setting area, because the high frequency cycloinverter is hard switching operation mode in low power setting area. The high conversion efficiency over 90% can be almost maintained, when the utility frequency AC-ZVS-PDM is used for low power setting area, since high fiequency cycloinverter can operate under a conhtion of the soft switching commutation in all the high fkquency power regulation areas. Therefore, the dual mode pulse modulation contra1 scheme using asymmetrical ZVS-PWM and utility fiequency AC-ZVS-PDM is more effective, which is put into practical use for the high-efficient power control imple- mentation,

VI. CONCLUSIONS

In this paper, high frequency zero voltage soft switching pulse modulated cycloinverter based on LFAC to HFAC power converter with non electrolytic capacitor DC voltage smoothing filter link was newly proposed, which can achieve compactness in a volumetric physical size and weight, low cost, high reliability, high efficiency, low noise and long life. And then, the sot? switching circuit operation principle and features of the soft switching high frequency cycloinverter were actually clarified for unique consumer induction heat- ing applications based on new type DPH using spiral plate with copper end ring as M heat exchanger. Its high eri- ciency power conversion could be achieved kom an ex- perimental point of view by using LFAC to HFAC power converter using the dual mode pulse modulation time-sharing control implementation due to asymmetrical ZVS-PWM and commercial utility frequency AC-ZVS-PDM over the wide power regulation setting areas ranging from a low power to a high power setting.

In the future, the optimum circuit design method of the input filter part of the high fkquency soft switching cyc- lainverter treated here should be investigated, and the power loss analysis of high frequency soft switching cycloinverter using measured v-i characteristics of soft switching pulse modulated power semiconductor switching devices (IGBTs; CSTBTs) represented by piece wise h e a r characteristics should be analyzed as well as improved. The actual effi- ciency and conventional efficiency characteristics have to be compared and studied in experiment. Finally, the LFAC to HFAC power conversion circuit using bidirectional power switches due to reverse blocking IGBT defined as high fie- quency cycloinverter.

VII. REFERENCES

Hideaki Tan- Milsuru Kmeda, Srawouth chandhaket, M a " Aubdallha At, Mutsuo N h k a "Eddy Current Dual Packs Heater based Continuous Pipeline Fluid Heating using Soft Switching PWM High Frequency Inverter", Proceedings of International Symposium on Industtial Electronics VUE), Mexico. pp306-311, December, 2000 Hanro Taai, Hideki Sadalrata, Hideki Omti, Hidekazu Ymashita, Mutsuo Nakaoka :"High Frequency Soft Switching Inverter for Fluid-Hearing Applianm Using Induction Eddy Cumnt-based Invo- luted Type Heat", Pmecdings of iEEE Power Eleehonics Specialists Conference (PESC), Vo1.4, pp. 1874-1878 Caims, Australia, June,2002 Lahrath Gamage, Tarck Ahmed, Hisayuki SugimUrq Srawouth Chandhket and Mutsuo Nakoka," Series Load Resonant Phase Shifted Z V S - P W High-Frequmcy Inverter with a Single Auxiliary Edge Resonant AC Load Side Snub& for Induction Heating Super Heated Steamer", Proceedings of 2003 International Conference on Power Electronics and Drive System PEDS), no.PS-04,pp.30-37, Singapore, " % m b e r ~ ~ 3 . H i s a m Sugimura, Hide- Muraoka, Kouji Sousbjn, Mikiya Ma- tsuda, and Mutsuo Nalcaoka'?)ual Mode ZVS-PWM High Frequency Load Resonant lnvertet with Auxiliary Edge resonant Snubber for Super Heated Steamer", Proceedings of The 29*Annual Conference of the IEEE Musirial Electronics Society (IECON), pp.1679-16W4. Virginia, USA, November, 2003.

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