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19МАЛЫЕ И МИКРОГИДРОЭЛЕКТРОСТАНЦИИ SMALL AND MICRO HYDRO-POWER PLANTS
STUDY OF THE REGULATION OF A MICRO HYDROELECTRIC
POWER PLANT PROTOTYPE
M. Chennani*, I. Salhi**, S. Doubabi***
Laboratory of Electric Systems and Telecommunications (LEST), Faculty of Science and Technology of Marrakesh BP 549 Marrakesh, Morocco medchennani@yahoo.fr, issamvotremi@gmail.com, doubabi@fstg-marrakech.ac.ma
Received: 23 Sept. 2007; accepted: 29 Oct. 2007
In this article we present the study of the regulation of a micro hydroelectric power plant (MHPP) prototype. The Prototype is installed in our laboratory in the Faculty of Science and Technology. A model of the MHPP was developed with simulink based on some of our preceding works. The downstream regulation ensures good frequency regulation results. The used controllers are the "P" and "PI". The practical results obtained are not far from those in simulation. Measurement and the command are done by an acquisition card controlled by computer.
Keywords: micro hydroelectric power plant, modelling, regulation, simulation.
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Оф
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Pr. Mohammed Chennani
Obtained his diploma in Electrical Engineering from the ENSEM (Ecole Nationale Superieure d'Electricité et de Mécanique) of Casablanca in 1995. Since he is a professor of electrotechnics at the Faculty of Science and Technology of Marrakech. He has participated in several research and scientific projects and he is the author of more than 10 communications and publications.
Obtained his master degree in December 2006 from Cadi Ayyad University -Morocco. He is a researcher member of the Electric Systems and Telecommunications Laboratory and preparing his doctorate thesis.
Issam Salhi
Obtained his doctorate thesis in 1998 form Cadi Ayyad University - Morocco ( CAUM ). Since 1998, he is a professor at the Faculty of Science and Technology of Marrakesh, Ex-responsible of the Automatic and Industrial Informatic Laboratory, subdirectory to Electrical Systems and Telecommunication Laboratory of CAUM. He has participated in and led several research and cooperation projects and he is the author of more than 20 international communications and publications.
Dr. Said Doubabi
Introduction
A Micro Hydroelectric Power Plant (MHPP) is equipped generally with an upstream hydraulic system which forwards water to the turbine equipped with a motorized injector which controls the turbine's flow. The MHPP is coupled with a generator that supplies a mini electrical network. The regulation system must guarantee a good level of voltage with an industrial frequency (50 Hz). In the event of low consumption, it act on the opening of the injector to adapt the production to the needed power. The surplus of energy is switched on a resistance. Some departures are disconnected in the moment of overload. In this article, we present a model of the MHPP developed with simulink [1, 2]. The simulation results of
the downstream regulation are compared with the practical ones used on a prototype of the MHPP. The downstream regulation used on the prototype uses a resistance of dissipation controlled by an electronic variator. Measurement is made by a acquisition card and the regulations used are P (proportional) and PI (proportional and integral) implemented in computer and control permanently the system.
Description of the MHPP Real MHPP
The upstream hydraulic part of the MHPP consists of [3]: water supply on a river, a feeder canal, a regulation basin, a pressure pipeline whose section is accorded to the flow and the available power.
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Nozzles direct water jet against a series of spoon-shaped buckets mounted around the edge of a turbine. The system ensures the hydraulic energy transformation into mechanical energy. The wheel of the turbine is coupled to a generator. The general diagram of this system is represented in Fig. 1. The servo-motor related to the nozzle must be relatively slow to minimize the water hammers effect.
Fig. 1. Synoptic diagram of a micro hydroelectric power plant
Description of the MHPP prototype The nominal values of the system parameters are: Electric power: 185 W
Frequency: 50 Hz
Voltage: 220 V
Flow: 10 l/s
Speed of racing: 1400 tr/min
The installation allows to impose a variable flow between 0 and 20 l/s. The functional plan of the installation is represented in Fig. 2. The used turbine is of type "Pelton". The generator is a synchronous machine which feeds directly a load formed by lamps. The frequency is measured by a frequency sensor "ARDETEM DIP 605". The numeric regulation is done using an acquisition card. The actuator is an analogue power controller "Type ACI 30-1". In the Fig. 3, we give the real system prototype photo.
Fig. 3. The real prototype
Modelling of the MHPP
Model of the Pelton turbine
The Pelton turbine is used for the high falls and small flows. It Consists of a set of specially shaped buckets mounted on the periphery of a circular disc. It is turned by jets of water discharged from one or many nozzles which strike the buckets (see Fig. 4). The flow is adjustable using a mobile needle inside the nozzle, which is moved by an electric servo-motor.
wheele
Bucket
\
! —J
Fig. 4. The geometrical shape of a Pelton turbine
The water fall power is given by:
P =PgQHe
(1)
with: Pt - turbine power [W], Qt - water flow of the turbine [m3/s], g - gravity acceleration [m/s2], p = = 1000 kg/m3 - water's density, He - effective high [m]. The parameter He in (1) is calculated by the following expression [2, 4, 5] :
He = U (V - U)(1 + m cos ß) g
(2)
Fig. 2. The functional plan of the installation
with: U - drive speed of the turbine, V - water speed in the contact of the jet with buckets, m - report of V and V2 the water speed at the exit of the bouckets, p - angle
between V1 and V2 .
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The torque provided by the turbine is:
Pt
Ct =
q,
with: Qt - angular speed of the turbine (rd/s). The linear speed of the turbine expression is:
u = ntd t 2
with: Dt - Diameter of the turbine (m). With the relations (1) - (4) we obtain:
(3)
(4)
Ct=pQt q-
V - f Q t
(i + m cos ß). (б)
Dt
ct = pqßm -C
2Ctr
We note:
Y Vin - D Qtnnt
k = Dt Qtn
(i + m cos ß). (6)
2 Vin
(7)
For nominal values: qt = 1; ft = 1; nt = 1; ct = 1. From the relations (6), (7) we can write:
Qn =
2C„
pDtVin (i - kt )(i + m cosß)
(S)
Replacing Qtn in (6) by its expression in (S) we end at:
c = q (Yt - ktnt) t 1 - kt •
The turbine power is given by:
Pm = Ctnt •
By considering some approximations, we have:
Vi =^2gHt , where Ht the effective fall is given by:
Ht = htHtn
with: Htn - nominal fall, ht - effective fall in "pu". The relation (11) is written by using "pu" units as:
(9)
(iO)
(i2)
=Y^n (13)
from where the expression of the turbine speed in (pu) is: Jt=4h. (14)
The turbine can be represented by the following model
(Fig. 5):
In this paper we use the "IS" unities for the physical values and the reduced sizes "per unit system: pu" for the model.
qt - Turbine flow (pu), yt - Jet speed (pu), nt - Turbine speed (pu), ct - Turbine torque (pu), Qtn - nominal flow of the turbine (m3/s), Ctn - nominal torque of the turbine (N.m), V1n - nominal speed of the jet (m/s), Q.tn -nominal speed of the turbine (rd/s). The relation (5) becomes:
Fig. S. Simulink mo,el of a Pelton turbine
Model of the injector The injector is formed by a needle which moves in a conical form, its model is obtained by calculation of the area trough which the water jet passes [4, 5]. By taking an injector with the following form (Fig. 6):
Fig. б. Diagram of an injector The surface by which water passes is:
D, - , Sd =K2— X, sinа
(iS)
with: Dd - external diameter of the injector, d -tangential diameter of the needle with the opening of the injector, a - aperture angle of the punch, Xd - opening in meter of the punch (advance). However:
d = Dd - 2Xd - sin а - cos а .
(ii) By replacing d in (i6) we obtain Sd:
Sd =n sin а
D,X, -X^l.
2
)
The flow in the turbine is:
Qt = SVi.
(i6)
(i7)
(iS)
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S1
In pu, surface Sd and the needle advance Xd are expressed by:
Sd = SdDdn , (19)
Xd = XdXdn
(20)
By combining the relations (19), (20) and (17) we end:
( - kdX2d ) (21)
s w =
nDdXdn sin «
Jdn
with:
kd =
sin 2a'
2 Dd
X
dn
For nominal values: sd = 1 ; xd = 1 we have:
1 =nDdXdn sin a (1 - d )
S
dn
Thus:
Sdn =n sin aDdXdn (1 - kd ).
After replacing Sdn by his value we will have:
S = xd(1 - kdxd) Sd = ■ ; 1 - kd
and:
q = Sd Yt
(22)
(23)
(24)
(25)
(26)
Fig. 7. Simulink model of the injector
Regulation of the MHPP and simulation results
Speed regulation of the MHPP
The regulation of a MHPP consists in maintaining fixed the frequency of the electrical network by action on the injector position [2, 5, 6]. This usual regulation is represented in Fig. 8.
The regulation based on a simple PID becomes insufficient in case of an important discharges [5, 7] (see Fig. 9). At the moment of important overload, the needle's speed saturates and generates oscillations of frequency. The stability of the system can be completely lost as show in Fig. 10, 11.
Fig. 9. Charge and discharges implemented to the turbine: discharge from 70 % (dotted line) and 30 % (solid line)
from where the following model of the injector (Fig. 7): |
52 51.5 51 50.5 50 49.5 49 48.5 48
il
0
60 time (s)
Fig. 10. Upstream regulation with PID: stability for the small discharges
65
60
55
50
45
ITT
20
40
60 time (s)
80
100
120
Fig. 8. Synoptic of an upstream regulation with PID
Fig. 11. Upstream regulation with PID: instability for the important discharges
Downstream regulation
The downstream regulation is used in order to simplify the MHPP regulation systems and to limit damages caused by the motorized injector [8]. It consists in putting a resistance of dissipation in parallel with the
International Scientific Journal for Alternative Energy and Ecology № 5 (61) 2008
© Scientific Technical Centre «TATA», 2008
mini electrical supply network (see Fig. 2). The regulator ordres an electronic variator whose time reponse is very short, that makes it possible to absorb immediately the disturbances of the netwark and guarantee a better stability.
The injector is opened to the maximum then the stability is obtained by the dispatching of the electrical power between the load and the resistance of dissipation. The P controller gives good simulation results with a tiny static error. PI controller cancels the static error and gives good simulation results [9-10] (Fig. 12).
Simulation with measured or calculated parameters of the MHPP, gives good result of regulation.
!................................................. -
1C1 : (v ft.
f r -
i i
time (s)
20
Fig. 13. Evolution of real system's output after a variation of disturbance (P = - 85W) in open loop
The functional plan of our system regulation which we proposed, is given by the Fig. 14. The Fig. 15 shows the components of the real chain of regulation.
Fig. 14. Functional diagram of the regulation chain
Fig. 12. Downstream regulation with PI controller: stability after an important discharge at 20 s
Practical results and discussion
The practical study is made on MHPP prototype described previously. The electrical load will be considered as a disturbance. It causes the variation of prototype's output (Frequency), as shows in the following Fig. 13.
Fig. 15. The real chain of regulation
regulator gives an excellent frequency response after an important discharge (see Fig. 12). This is practically confirmed with the MHPP prototype (see Fig. 16). The system finds stability in approximately 2 s after the important discharge at 0.3 s and the important overload at 5 s.
Fig. 16. Downstream regulation with PI (MHPPprototype): stability after the important discharge at 5 s
Conclusion
Hydroelectric energy is renewable, clean and free. Its exploitation requires good regulation systems to produce alternative current with an industrial frequency (50 Hertz). The simulation allows us to test various techniques of regulation: upstream regulation, mixed and downstream regulation.
The technique tested practically and in the simulation is the downstream regulation. It gives good results with few equipments.
The prototype allows the realization of the simulation; the obtained results are satisfying with a PI controller. The regulation is implemented on a PC connected to an acquisition card. Our system can be installed on the existing MHPP and ensure an alternative replacement solution of the complicated and irreparable systems after failure.
References
1. The math works, Inc (1997), simulink user's guide.
2. Chennani M., Doubabi S. Study in simulation of the regulation and the improvement of the output of a micro hydroelectric power station // ICM 05: MARRAKECH, Novembre 2005.
3. CDER. Manuel d'entretien de l'équipement électromécanique de la micro centrale hydraulique de Ouinskra, 1997.
4. Hugo N. Project dynasim // EPF Lausanne Laboratoire d'électronique industrielle, 1999.
5. Chennani M., Doubabi S. Simulation numérique de la régulation d'une micro-centrale hydroélectrique // CIFA 2004: conférence internationale francophone d'automatique, Douz Tunisie, 22-23-24 Novembre 2004.
6. Oscar Daniel Quiroga. Modelling and nonlinear control of voltage frequency of hydroelectric power plants // Doctoral thesis, Universidad Politécnica de Cataluna, Instituto de Organizacion y Control de Sistemas Industriales, July 2000.
7. Goran Andersson. Dynamic and control of electric power system // Lectures 35-528; ITET ETH, March 2003.
8. PACER. Petites centrales hydrauliques, régulation et sécurité d'exploitation // Programme d'action PACER-énergies renouvelables, 1992.
9. Àstrom K.J, Rundquist L. Integrator windup and How to avoid it // Proceeding of the America control conference, Pittsbourgh, 1989. P. 1693-1698.
10. Hanus R. A new technique for preventing control windup // Journal A. 1980. Vol. 21, No. 1. P. 15-20.
International Scientific Journal for Alternative Energy and Ecology № 5 (61) 2008
© Scientific Technical Centre «TATA», 2008
