Dual winding Generator and Thermo-photovoltaic (TPV) based

Hybrid Generation as an Efficient and Reliable Small-scale Power

Supply in Iron and Steel Industry

Arunava Chatterjee, Debashis Chatterjee

Department of Electrical Engineering, Jadavpur University, Kolkata, India-700032

Tel: +91-9433887966

Fax: +91-33 -24132384

Email: debashisju@yahoo.com

Iron and steel industry is energy demanding industry whose demand and usage is directly dependent

on national energy scenario. Renewable energy sources such wind and solar thermo-photovoltaic

(TPV) systems or combination of both can be used as an alternative generation option. These can be

utilized in iron and steel industries as a reliable source of power for small scale power applications

such as emergency lighting, providing black-start to alternators in the captive power plants or for

supplying critical loads. The surplus energy can be stored for further use. A self excited dual stator

winding induction generator (DWIG)-TPV based hybrid microgrid structure is proposed in herewith

for generation of medium to small scale power to meet the emergency needs in an iron and steel

industry. Suitable simulation in MATLAB/Simulink environment sums up the suitability of the

proposed generation scheme.

Key words: Dual winding Induction Generator, Thermo-photovoltaic (TPV), Hybrid generation

INTRODUCTION Development of global economy has led to severe energy scarcity especially with depletion of fossil

fuel reserves. As the conventional sources of energy are becoming scarce and costly day by day,

solar and wind energy sources have evolved into attractive energy sources for electric utilities. Solar

photovoltaic in combination with wind/hydel is a great choice for hybrid generation purposes [1] as

ABSTRACT

solar and wind generally well complement each other. Iron and steel industry is energy demanding

industry whose demand and usage is directly dependent on national energy scenario. Curtailing the

fuel cost is an imperative issue in an iron and steel industry owing to the cost of energy. For this

matter, cogeneration is adopted by most of the integrated steel producers for on-site electricity

generation. Usually throughout production of pig iron and also during steelmaking process, great

amounts of high temperature furnace gas and steam is produced which is wasted. This source of

energy is free in nature and should be instantaneously utilized. The blast furnace gas is used by the

steam boilers to run turbines for electricity in captive plants [2]. This free energy in the form of heat

is cyclical and dynamic and can be utilized in heat recovery systems in cogeneration.

In addition to renewable energy harvesting and utilization, energy recovery schemes such as Organic

Rankine cycle [3], Transcritical Rankine cycle [4], energy storage integration systems [5], and

thermoelectric power generator have also been researched and studied extensively. Renewable

energy sources such wind and solar thermo-photovoltaic (TPV) systems or combination of both can

be used as an alternative generation option. For harnessing steam or wind power, induction

generators are commonly used which are coupled to turbines for generation of electricity in grid

connected as well as standalone systems [6]-[9].Development of a DWIG in wide speed range

applications is of immense importance as it can be used as a portable source of electricity to meet the

ever increasing demands of electricity especially in grid isolated areas. It will also be a renewable

source of electrical power with almost no negative impact on the environment. Technically, the

conventional induction generator shortcomings of low voltage regulation can be eliminated using a

DWIG using a proper control scheme. Also a DWIG, contrasting to a conventional induction

generator can produce constant output voltage under variable conditions of speed and load which can

be especially helpful in connection to a microgrid structure. It can be helpful in hybrid generation

scheme where PV, diesel or battery can be used along with wind power. A DWIG will consist of

standard squirrel cage rotor windings and the stator will carry two sets of windings, one for

controlling and other for harnessing the power generated. The output voltage will be regulated by

means of an inverter to control the reactive power requirement on the control winding side.

Thermo-photovoltaic systems (TPV) are the use of photovoltaic effect for generation of electricity

from a high-temperature source. Numerous combustion-based TPV schemes are in a prototype stages

usable mainly for CHP or portable power applications [10]. The primary objective of the present

research is to investigate the potential of TPV heat recovery along with use in a hybrid system

consisting of IG based generation for use in iron and steel industry.It is expected that this hybrid

generation based study will be beneficial in development of an efficient and reliable power source

for small scale applications.

PROPOSED HYBRID GENERATION SCHEME

The proposed scheme is mainly aimed at using the waste heat of the industrial sector for generation

purpose; also the same generated power form TPV process can be combined with an induction

generator which can be used for small scale power supply. The block diagram for the proposed

generation scheme is shown in Fig.1.

DWIG

Variable Frequency

Inverter

to A

C

loa

ds

Turbine

wr

Bridge

rectifier

+

_

Fixed Frequency

inverterT

PV

mo

du

le

Bo

ost co

nve

rte

r

&

ch

arg

e c

on

tro

ller

DC loads

Fig. 1.0: Block diagram for the proposed generation scheme

Technically, theconventional induction generator shortcomings of low voltage regulation can be

eliminated usinga DWIG using a proper control scheme.Also a DWIG can produce constant output

voltage under variable conditions of speed and load using a variable frequency inverter which can be

especially helpful in connection to a microgrid structure. It can be supportive in hybrid generation

scheme where PV, diesel or battery can be used along with wind power as depicted in Fig.1.The

DWIG structure has two separated stator windings wound for same number of poles. One winding is

used as control winding for controlling the generation while the other winding, which is the power

winding which is used to harness the generated output. The common bus in the power winding is

used to connect the TPV module.The induction generator is modeled using the generalized d-q-axes

machine model in stator reference frame as,

ds ds ds ds

dv R i

dt (1)

qs qs qs qs

dv R i

dt (2)

0 dr dr dr r qr

dR i

dt w

(3)

0 qr qr qr r dr

dR i

dt w

(4)

Where, Rds, Rqs, are respectively the d and q axis stator resistances with ids, iqs,idrand iqrthe stator d-

axis and q-axis and rotor d-axis and q-axis currents respectively. ωr is the speed of the rotor. Flux

linkage relations can be given as,

( )ds lds ds dm ds drL i L i i (5)

( )qs lqs qs qm qs qrL i L i i (6)

( )dr ldr dr dm ds drL i L i i (7)

( )qr lqr qr qm qs qrL i L i i (8)

Where,ψds, ψqs, ψdr and ψqrare the stator d- q-axes and rotor d- q-axes flux linkages respectively, Llds,

Llqs, Lldr and Llqrare the stator d- q-axes and rotor d- q-axes leakage inductances withLdm and Lqm are

the magnetizing inductances of d- q-axes.

TPVcells work the same way as PV cells do, the exception is that instead of the light striking the

cells and producing an electric field, the TPV cell uses a complex semiconductor structure designed

for longer wavelengths for non-visible light (infrared) from a suitable source.The TPV unit consists

of a radiator unit, a special control filter unit for filtering the radiated heat and TPV modules for

generation of DC power. A typical power flow diagram for TPV unit is shown in Fig.2 with the basic

TPV cell shown in Fig.3. The input heat radiation is used to warm a thermal emitter, which is

arranged to radiate onto a PV active module. This creates a combination of usable electricity and

low-grade waste heat.In general, the conversion efficiency of a TPV system can reach much higher

than a simple photovoltaic cell. The efficiency can typically approach to that of a Carnot engine

which is given as,

1 cellc

emit

T

T

(9)

Where, Tcell is the PV cell temperature and Temit is the emitted temperature.

Iro

n a

nd

Ste

el In

du

str

y

Fossil fuelsHigh

temperature

TPV

Ra

dia

tor

Co

ntr

ol

Filte

r

PV

Mo

du

leRadiation

Filtered

Radiation

DC power

output

Fig.2.0: Power flow diagram for typical TPV unit

Fig.3.0: Representation of basic TPV cell [10]

The thermally released photons can be used for generation as long as their energy is at least equal to

that of the photovoltaic material. Suppose GaInAsSb material is chosen for TPV cell having a

bandgap of 0.53 eV, the system can work favorably for emitter temperatures around 1000oC. Larger

bandgap energy is preferred for higher temperatures. Thus, the TPV systems are temperature

specific.

Fig.4.0:Irradiance vs. wavelength for a blackbody source at 1000oC

The illustration for the irradiance versus wavelength for a blackbody source at 1000oC is shown in

Fig.4. The PV module in general can be modeled using the voltage-current relationship [11] as,

[exp( / ) 1]pv P PH P S pv S cellI N I N I qV N KT A

(10)

In (10) the IPH is the photo diode current, IS the diode saturation current, charge of an electron is

denoted as qandK is the Boltzmann constant and the PV cell temperature is denoted as Tcell, A as the

ideal factor for cell. A TPV module similar to PV module is made of series parallel connection of PV

cells andthe number of such parallel and series connected cells are denoted as NP and NS

respectively. Shown in Fig.5 is the TPV module approximated electrical equivalent circuit.

+

-

VpvNPIPH

NP

NS

Solar

InsolationIpv

}

Fig.5.0:TPV module approximate electrical equivalent circuit

Applications

The general applications of a typical TPV based generation system can be a portable source of

power, in spacecrafts, in industrial processes. CHP or combined heat and power process can be one

potential application where the CHP would employ a SiC emitter operating at 1425°C withTPV

modules. The TPV CHP can potentially output 85,000 BTU/hr and can generate 1.5 kW[12].

However, with a hybrid TPV system with wind or steam based generation, the generated power will

exceed this limit. The lifetime of the CHP furnace is approximately 20 years with limited cost for

operation and maintenance. Gaseous fuels in common use in Steel plants are blast furnace gas, coke

oven gas and mixed gas. Blast furnace gas is generated in blast furnace in the process of iron making

and can be regarded as a by-product similar to coke oven gas. Blast furnace gas unlike coke oven gas

has low calorific value and high quantity is produced which can be utilized in TPV systems for

heating via heat exchanging systems.

SIMULATION RESULTS & DISCUSSION

A MATLAB/SimulinkR2014bbased simulation is carried out for the proposed generation scheme. In

the proposed generation scheme, a 1.5 kW generator system is considered with 1 kW TPV module.

The generation system considered can be modeled using the equations already represented in this

paper. The initial voltage build-up can be shown in Fig.6.

Fig.6.0:Waveform for DWIGinitial voltage build-up

Fig7.0:Waveform for DWIGsteady state voltage

Fig.8.0: Rectified DC voltage

Steady state voltage for the DWIG is shown in Fig.7. This generated power can be converted to DC

for DC loads or can be used for three-phase AC loads, lighting loads or critical loads as shown in

rectified voltage of Fig.8. During total failure of the grid, the same can be used for initial excitation

of the synchronous generators and can be regarded as reliable as batteries.

Fig.9.0:Plot for PV module power vs. voltage

The typical PV module power versus voltage plot is shown in Fig.9. The majorities of the industrial

high-temperature processes are considered to have flue gas temperatures higher than 1050 oC and

normally use heat recovery process for air combustion or preheating of products, but still reject flue

gases at relatively high temperatures. The high temperature flue gases can be recovered for TPV

generation purpose. However, use of heat exchangers for heat recovery has proved to be complicated

due to contamination from flue gas. Similar problem could also occur for flue gas recovery and

heating for TPV system operation.

Advantages:

The major advantages of the proposed generation scheme are listed as,

(i) The proposed scheme is a clean source of energy where the raw material used is mostly a

renewable source and a by-product source of industrial process.

(ii) The proposed IG-TPV configuration can be used in small scale applications such as lighting and

generator black start as a standalone micro generation scheme.

(iii) The voltage buildup process of the generation scheme starts fromlower speeds compared to

conventional IG and thus it is suitable for generation duringlow turbine speeds.

(iv) TPV module is used to along with the generator making the scheme more suitable to operate in

isolation from the main grid.

(v) Coordinated control of the two generation sources are possible and can be used simultaneously

for power generation also.

CONCLUSION

A DWIG-TPV based generation scheme is proposed which can be used for generation purpose for

small scale industrial processes effectively. The same can supply emergency lighting loads, can

supply excitation to alternators during black-start and can also be used for supplying critical loads.

The TPV system can be costly but can be used for long periods with minimal maintenance and

higher efficiency. Especially TPV based hybrid systems can be suitable for iron and steel industry

CHP systems owing to heat recovery systems used therein.

LIST OF SYMBOLS

Rds, Rqs d and q axis stator resistances (Ohms)

ids, iqs,idr,iqr stator d-axis and q-axis and rotor d-axis and q-axis currents (A)

ψds, ψqs, ψdr,ψqr stator d- q-axes and rotor d- q-axes flux linkages (Wb)

Llds, Llqs, Lldr,Llqr stator d- q-axes and rotor d- q-axes leakage inductances (H)

Ldm,Lqm magnetizing inductances of d- q-axes (H)

IPH photo diode current (A)

IS diode saturation current (A)

q charge of an electron (Coulombs)

K Boltzmann constant

c Carnot engine efficiency

Tc PV cell temperature (oC)

Temit emitter temperature (oC)

A ideal factor for PV cell

DWIG Dual stator Winding Induction Generator

TPV Thermophotovoltaic

CHP Combined Heat and Power

REFERENCE

1. M.R. Patel, “Wind and Solar Power Systems”, 2006, 2nd edn., CRC Press.

2. D. Qiu, L. Wang, J. Wang, L. Zhu, “Study on Energy Supply Chain in Integrated Steel Manufacturing”; Proceedings

of the 2008 IEEE International Conference on Information and Automation, June 20 -23, 2008, Zhangjiajie, China.

3. D. Chinese, A. Meneghetti, G. Nardin, “Diffused introduction of Organic RankineCycle for biomass-based power

generation in an industrial district: a systemsanalysis”;Int J Energy Res,Vol-28(2004), No 11, p. 1003.

4. Y.M. Kim, C.G. Kim,D.Favrat,“Transcritical or Supercritical CO2Cycles using both Low- and High-temperature

Heat Sources”; Energy, Vol-43 (2012), p. 402.

5. G. Li, Y. Hwang, R. Radermacher, H-H. Chun,“Review of Cold Storage Materials for Subzero Applications”;

Energy, Vol-51 (2013), p. 1.

6. J.M Elder, J.T. Boys, J.L. Woodward, “Self-excited Induction Machine as a Small Low-cost Generator”; IEE Proc.

C, Vol- 131 (1984), No. 2, pp. 33-41.

7. L. Wang, C.H. Lee, “A Novel Analysis on the Performance of an Isolated Self-excited Induction Generator”; IEEE

Trans Energy Conv., Vol-12 (1997), No. 2, pp. 109-117.

8. T. Ahmed, K. Nishida, M. Nakaoka, “A Novel Stand-alone Induction Generator System for ac and dc power

Applications”; IEEE Trans. Ind. Appl., Vol- 43 (2007), No-6, pp. 1465-1474.

9. G. Marra and J.A. Pomilio, “Self-excited induction generator controlled by a VS-PWM bidirectional converter for

rural applications”; IEEE Trans. Ind. Appl., Vol-35 (1999), No-4, pp. 877–883.

10. Z. Utlu, U. Parali, “Investigation of the Potential of Thermophotovoltaic Heat Recovery for the Turkish Industrial

Sector”; Energy Conv. Manage, Vol-74 (2013), p. 308.

11. Q. Kou, S.A. Klein, W.A. Beckman, “A Method for Estimating the Long-term Performance of Direct Coupled PV

Pumping Systems”; Sol. Energy, Vol- 64 (1998), No-1, pp. 33–40.

12. G. Palfinger, B.Bitnar, W. Durisch, J.C. Mayor, D. Grützmacher, J. Gobrecht, “Cost Estimate of Electricity

Produced by TPV”; Semiconductor Science and Technology, Vol-18 (2003), No-5, S254.

AUTHORS

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Prof. Debashis Chatterjee Arunava Chatterjee