Indian lournal of Engineering & Materials Sciences Vol. 9, lune 2002, pp. 172-176

High efficient contamination free clean heat production

Pradip Kuma.r Sadhua, Sanat Kumar Mukherjee", Rupendranath Chakrabartib

, Shamapada Chowdhur/, Bhuwan Mohan Karan", Rajesh Kumar Guptaa & C V S C Reddy"

"Department of Electrical & Electronics Engineering, B.I.T.(Mesra), Ranchi, India bDepartment of Electrical Engineering, Jadavpur University, Calcutta 700 032, India

Received 21 March 2001; accepted 5 FebruQl'y 2002

The present li nvestigations relate to the process of electromagnetic induction heat flow through metallic package (stainless steel) in glass pipeline or vessel. The inverter fed fluid heating appliance is more acceptable than gas combustion, steam heating and electrical resistive heating methods for better heat transfer and delivery processing under precise temperature management. This technology has been found to improve heat energy storage and heat exchange processing of lank flu id healing in the container or vessel or pipeline directly. The other advantages are: contamination··free heat production, good compactness, high reliability, quick response, absence of combustion waste and shock hazards in the boiling vessel. Besides, enrouting water through specially designed metallic assemblies will permit eddy-cUlTent based healing through electromagnetic induction. In the case of steel vessel plant, heat can be generated directly on the vessel without heat conduction loss. The series-resonant constant-frequency PWM IGBT inverter system has been introduced as a new conceptual induction-heated pipeline fluid or vessel fluid heating for medicinal plant, sterilization plant and drier for surgical instruments.

In general, an induction heating is known as a contactless method of generating heat energy in a magnetically-conductive work piece assembly by producing both eddy current losses and hysteresis losses in the work piece from an external high frequency alternating magnetic field produced by a high frequency PWM inverter using IGBT'-4. High­frequency magnetic field is usually established by a magnetic coil wrapped around the work piece or held parallel to the work piece surface. Resonant inverters are widely used for induction-heating over wide frequency ranges (4-500 kHz.i. The inverter operating frequency selected for a particular application is based on heat effectiveness and power conversion efficiencl. The constant high-frequency resonant inverter circuits using IGBT appear more efficient, compact in size and of faster response as compared to the conventional electrical heating method3

.5

. Keeping in view the tremendous advances in power semiconductor switching devices, an electromagnetic induction based fluid heating appliance using a voltage-fed high-frequency PWM resonant inverter using IGBT is reported here.

The electromagnetic induction based fluid heating appliance using the high-frequency resonant inverter and its related system control technologies proposed by the authors can attract interest in the fields of medical, chemical, mechanical and consumer heat energy processing utilization in the pipeline system.

Direct fluid heating based on electromagnetic induction principle can be done in two ways, viz. pipeline surface and wall skin effect heating and package-in-pipeline internal eddy current heating. The latter method seems a new and attractive concept. The eddy currents are induced in flow-through metallic package with a large number of heating surface incorporated into the non-metallic pipeline by means of an external working-coil connected to the high­frequency resonant inverter operated by phase·-shifted PWM scheme. This paper presents a comparison between constant frequency phase-shifted PWM series load resonant inverter using IGBT modules and conventional electric heating to find out the most efficient fluid heating appliance.

Experimental Electromagnetic-induction fluid heating appliance

System description-Fig. I shows the schematic system configuration of electromagnetic induction fluid heating appliance using a series resonant PWM inverter with an active power filter. The fluid heating appliance used in the pipeline system is composed of a diode rectifier without smoothing fi lter so as to operate at a unity power factor. For harmonic current compensation, a voltage-fed full bridge type series load resonant IGBT inverter with a phase-shifted PWM control is provided. A specially-designed electromagnetic induction fluid heating assembly with

-

SADHU et al. : CONTAMINATION FREE CLEAN HEAT PRODUCTION 173

High temperature fluid Temperature sensor

Driver Circuit of I.G.B.T. Inverter

PI.D. Controller Non-metal pipe

(vessell tank)

200 V

Tabulance Mixed fluid

Working cell

50/60Hz on-Smooth Filte Inverter \ Flew-through Heating Pack

N\ Low temperature fluid

Fig. I-New schematic induction-heated electrical energy conversion in non-metallic pipeline for industrial set-up

Low temperature fluid

Fig. 2-A voltage-fed full-bridge type series loaded resonant inverter

a metallic package to achieve eddy current heating in the pipe line system is incorporated into the non­metallic vessel in addition to the working coil wrapped around for generating high-frequency flux . This appliance is highly acceptable for fluid heat­transfer and delivery processing plants as well as heat energy storage and heat exchange processing because of clean, compact, efficient and smart response. From practical view point, the above appliance seems cost­effective for induction heated boiler, evaporator, hot water supplier and super heating unit in the pipeline system.

High-frequency inverter

Constant High-frequency phase shifted PWM inverter-Fig. 2 shows the voltage-fed full-bridge series load-resonant inverter using IGBT

,,3. The

output voltage of this inverter can be continuously regulated by phase-shifted PWM scheme at constant frequency. The operating voltage and current

. .. .......... .. ..................... . .......... ~ ...........• .........•.• ....... ::: ... Gate . . , lPulse

Fig. 3-Voltage and current waveform

' 51 52

waveforms of this phase shifted PWM inverter are illustrated in Fig. 33

, It is seen from Fig. 3 that the turn-on switching currents of S 1/S2 in the bridge left leg are positive in PWM regulation mode. As a result, S 1/S2 operate at hard-switching. But, S 1/S2 can realize turn-off under a condition of zero current and zero voltage soft-switching in spite of phase shifted PWM conditions. On the other hand, S3/S4 in the bridge right leg can ideally turn-on under a condition of zero current and zero voltage soft switching in spite

174 lNDIAN J. ENG. MATER. SCI. , JUNE 2002

Bridge leg 1

Fig. 4-A phase-sh ifted PWM high-frequency inverter using lossless inductor and loss less capacitor

I I I I I I

'Y'

High-temperaJture side

ii I I

J

Flow-through

Metal package

Working coil

Magnetic flux

-' Liquids or Gases

Low-temperature side

Fig. 5--Heating package in the vessel and tank in the pipeline sys tem

of a phase-shifted PWM conditions but turn off at a hard switching condi,tion. The operating waveforms as obtained from computer simulation are shown in Fig. 3. Fig.4 indicates a newly-proposed topology of a soft-switched PWM type series load-resonant inverter using loss less inductor snubber bridge leg and lossless capacitor snubber bridge leg independently of a phase-shifted PWM regulation mode. The lumped R l-Ll series circuit is an equivalent circuit of the induction-heated load transformer modeling. The resistance compon~nt of the lumped temperature­dependent series load circuit is relatively large. The series compensated capacitor shown Fig. 4 is introduced for optimizing from the view point of power conversion . In this case, the resistance component of the lumped series load circuit is relatively small, matching transformer is not required

Flow through spot

Fig. 6--Internal structure fluid through specially designed meta l layer packing to generate tabulance fluid

and the parallel capacitor compensated load structure in series with a small auxiliary compensated inductor is more suitable as compared to series load-resonant operation.

Induction heated flow-through metallic package assembly-Fig. 5 indicates a specially-designed eddy current heated metallic package developed by the authors which is tightly incorporated into the nonmetallic vessel or tank in the pipeline. The mechanically processed thin stainless-steel layer package with many spots and fluid channels for cylindrical induction-heated assembly is demonstrated in the figure. Internal structure of this metallic package to be heated by eddy current losses is depicted in Fig. 6. When the fluid flows through the inherent package in the vessel or tank having a working coil connected to pipeline, the tabulant fluid is heated abruptly by eddy current losses generated inside the stainless-steel package.

Salient features of appliance High power-Since the heating coil does not get

hot directly for the purpose of heating the load, high power density, large heating surface and high temperature heating are achieved by introducing high-frequency induction heating principle.

Flexibility of heating distribution-The distribution of power density to the pipeline or vessel can be easily changed with the coil configuration including local heating.

Controllability-The response of load temperature is quite high because of the high frequency inverter regulation strategy. Implementation of microprocessor-based control can be easily introduced. Phase-shifted PWM regulation under a precise temperature setting condition by an auto-

SADHU et at. : CONTAMINATION FREE CLEAN HEAT PRODUCTION

ruwu· ·:-···- ·· : ·--··--·- - · -~=--- "·=~:'····"···:l:Ou~!

I : I ! ' . . . .. . . .. . . 1 Gale Pulse

i~51 i--Lj--L .. J~~rl 53 ! .... ... _ ..... :. .............. ,: .. _. ___ .... : ............. ~ .... _ .... _ ... 1

(a ) at full power load

~·.~v·· · ····· · ·· · .. ···V\At···· · ·· ~-·-·-·~~·· · .. -··· .. ·· .. ··· ............. i VOU!

. : ' . : . ! lout

- : . :. i . : i . .: . ", . ~ . .... ! Gate Pulse

~:.~~::

(b) at half power load

lout

Vout 50Aldiv 10QV/div 50us/d iv

Fig. 7- 0bserved output vo ltage and current waveforms and simulati ng waveforms

lin

Vin

50Aldiv 100 V/d iv 2 ms/div

Fig. 8-Inpul voltage and current waveforms

ChculatlDv PUlP

(a) Conventional Electronic Heater System

Fig. 9-0utput current waveforms

T18' Co Diiii"it r­fluid I 1'1

DI,tllltory L...J

NlwlY-fmlo,t. ,rototrp, IYltt.

~ ______ J

(b) Newly-proposed prototype heater

lout

50A/d iv

Fig. I O--Application of (a) conventional eleclronic heater system and (b) proposed prototype heater system

175

176 INDIAN 1. ENG. MATER. SCI., JUNE 2002

100

90 · "t> 80 l!

.~ 70

0 60

~ 50 ~ 40 Z :! 30 · ~~-----":::::::: ~~ SET·'

~~---::::::::: ~-____ _ .. _ __ _ -------- SET-N

0. 20 E _T,mp.,.tur. · 10 >- SET·V

0

0 200 600 aoo 1000

Time in _cond

Fig. II-Temperature response for industrial set-up

tuning PID-based feed back implementation scheme would permit stable operation and easy control.

High efficiency-In the proposed scheme, heat is being directly generated in the pan or vessel as load and there is practically no consumption of energy due to conduction. This permits sufficient reduction of the running cost and the energy saving.

High safety and high reliability-Eddy currents in the flow-through magnetically-conductive metallic package incorporated into the vessel or tank is induced through a contactless high-frequency power transmission in the heating package. So, unlike electric heater, there is no scope for any shock hazard.

Results Constant frequency PWM inverter strategy­

Design specification of inverter-fed fluid heating appliance are: (Input voltage-single-phase 200 V root mean square (rms); Regulated output power 0-1 kW; Power regulation strategy-Constant frequency phase­shifted PWM; Operating frequency 30 KHz; Temperature control system autotuning PID control ; Plan t efficiency 98.17%). The practical design specifications of electromagnetic induction fluid­heating appliance w;ing a series load-resonant inverter with self-tuning PID based feedback control scheme are used here. The output power can be continuously regul ated according to the phase-shifted angle (0-180°). Fig. 7 shows the observed operating voltage and current waveforms in the series load-resonant in verter with a . hase-shifted PWM scheme as compared to computer-aided simulating waveforms. The observed input voltage and current waveforms of thi s appliance are displayed in Fig. 8. The output high frequency current waveform is displ ayed in Fig . 9. Fig.IO shows the feasible application of inverter-fed

120

~ 100 l! co ~ 80 . o ~ 60 ~

i 40

~ E 20 . ....

___ _ . Temperatur. SET· I

__ T,mperatur. SET·II

__ Temper'tur. SET·n!

__ Temp,ratur. Sot·V

O+--'~--r-~-~r--r--~-~ o 511 100 1511 200 250 300 350

Tim. In aecond

Fig. 12-Temperature response for home-appliance

electromagnetic induction heated boiler with a precise, intelligent and stable feedback control. Temperature response of industrial set-up and home appliances with respect to time for different temperature modes setting are given in Figs 11-12.

Conclusions An electromagnetic induction based fluid heating

appliance has been proposed here which is fed from a series load-resonant PWM high-frequency inverter using IGBT modules. The working principle of the proposed PWM control inverter topology has been described for modern induction heating. The proposed appliance is expected to be cost··effective for induction-heated boiler heat exchanger and evaporator because of compactness in size, high-efficiency conversion, quick response and precise temperature control than the other method containing more harmonics in high frequency a.c. generation and more noise and also more loss in conventional electric heating. The proposed scheme is likely to be quite useful for microwave oven and medical processes In

the near future.

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