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NOVEL DESIGN FOR SPEED AND ACTIVE POWER CONTROL OF A SMALL HYDRAULIC TURBINE PHUONG PHAP MCil THIET KE H$ T H 6 N G DIEU KHIEN TOC DQ VA CONG SUAT CHO NHA M A Y THUY DIEN NHO Nguyen Ho

NOVEL DESIGN FOR SPEED AND ACTIVE POWER CONTROL OF A SMALL

HYDRAULIC TURBINE (

PHUONG PHAP MCil THIET KE H$ T H 6 N G DIEU KHIEN TOC DQ VA CONG SUAT

CHO NHA M A Y THUY DIEN NHO

Nguyen Hong Quang Hanoi University of Science and Technology

Received Mach 31", 2011

\

ABSTRACT

In recent years, the development of small hydro power stations has been widely applied accros Vietnam This paper shows the complete design process for a hydro turbine controller The algorithm

is given based on the typical mathematical models of the target system The controller parameters are obtained from the novel analytical formulars which take into account the wide range of operating points of hydraulic turbine In addition, the paper also presents the details design of microcontroller based implementation, the use of hardware in loop (MIL) to verify the model in the laboratory condition The expenence result from hydro controller of Rhyninh hydro turbine unit in Central Vietnam is given

as an illustration

TOM TAT

Trong nhung nSm gin d§y, vl^c phat trien nha may thuy dien nho dang day manh tren toan nuoc Vi0t Nam Trong xu hifong lam chu cdng ngh$ dieu khien thuy di$n nay, tdc gia trinh bay h$ thong diiu khien tdc do co ban Thu$t toan dieu khien xay dung tren md hinh toan hoc cua /i# thong

va tinh den dai ho$t dgng cua turbine thuy luc B^i b^o cung trinh bdy ve phan cung he thong sif dung

vi diiu khien va mo hinh biin vat ly trong thi nghiem kiem dinh thuat todn Cuoi cOng, ket qua chay cua

he diiu tdc tai nha mdy thuy di0n Rhyninh, miin Trung Viet Nam tfupc (?tra ra nhw minh hga cho tinh dung din cua phuxyng phap thiet ki

] INTRODUCTION

The motivation of the work presented

here is in the development of digital turbine

governor for the old Rhyninh hydro station The

main problem was to deal with the difficulties

of finding the controller's gain given the poor

information of the hydro turbine, manufactured

by Czechoslovakia neariy 30 years ago The

findings of mathematical model of hydro

turbine unit was somehow presented in [1]

However, the method of parameter

identification, which relies on neural network

algorithms, is very time consuming

Futhermore, the stability is not ensured for

different loads Reference [3] considers the

nonlinear and lime-varying property oi

hydraulic turbine regulating system, and i

robust pole assignment controller was

proposed

The study was accounted for the

uncertainty of wate time constant Tw, which is

serious for the stability of governor system The

applicablities of this design in the real-world turbine controller is still agumented, given the background of field engineers

The model-based controller design procedure for determining governor parameters described in this paper is natural and straitforward The problem was solved in orderly maner First, the appropriate mathematical model of the main system is created in form of different equations The controllers are chosen using the well-known proportionalintegral derivative / proportional -integral (PID/PI) controllers Then, the designer has to choose closed-loop poles from the required characteristics o' the controlled system (overshoot, rise time, s^ulmg time, etc.) The target was to obtain equations for the controller parameters that are flinctions of the system's operating point and the required closed-loop dynamics, thus, there is no need for heuristic tuning The procedure can be uied foi a new turbine governor design and ;or refiirbishing

The verification of the controllers can be

seen in the real-time digital simulator, which

implemented in Matlab Real-Time Workshop

The desgin allows to represent a wide and

significant class of operating conditions

(turbine startup, normal and emergency

shutdown, no-load generation parallel

operation with shortcircuits) and the

intergration of excitafion system with additional

control loops (PSS, under and over-excitation)

allow deep performances checking and fine

parameters tuning Implementation examples

are given in Rhyninh hydro power to show the

effectiveness of the proposed control algorithm

IL HYDROELECTRIC POWER TURBINE

2.1 Hydroelectric power turbine

Configuration of hydroelectric power

plant system is shown in Fig I SP (Automatic

Power and Frequency Control) generates the

power and IVequency setpoints based on load

demand Governor controller regulates

turbine-generator rotational fi-equency and controls

power generation output Governor actuator is a

mechanical system which actuates guide vane,

adjusting flow rate of hydraulic turbine

discharge- In general, there exist nonlinearities

in the governor actuator dynamics, the

hydraulic turbine characteristics and head losses

of tunnels

2.2 Hydraulic turbine model

The hydro turbine is described by the

water flow ftinction and power fiinction In this

paper, the model according to [4] is used

U = K„G4H C )

P = KpHU (2)

dU

dt L

Q = AU

U : water flow speed [m/s]

G : ideal gate opening [%]

-f{H-H,)

H : working water height [m]

Ho: initial water height [m]

Q : water flow [mVs]

A : area of penstock [m']

L : length of penstock [m]

flg: gravitational constant [mVs]

t : time [s]^

The models described so far are nonlinear; thus, they are not suitable for the controller synthesis using linear method The linear model would be obtained from the vicinity of the operating point Where A is the distance from the operating point, and b|, are the coefficients as functions of the operating point for variables:

W = b AH + b Ao) + b AG (5)

11 12 13

AY = b^AH ^b^^Aw + b^^AG (6)

The b|| coefficients are partial derivatives

of the water flow function

G

b =-^-b^=0; b,,=lH; 24H

= 0,5G; 6,3 = 4 / / " - ' - 0 , 5 ( & ) - I ) ;

Given the Ato is relatively small in grid connecting state, the linear turbine model would

be as follows:

^''m , l + ( ' ' i r * 1 3 ' ' 2 2 l ' * 2 2 3

AG 23 l + *n^w^

'^'m 23 ytl w

AC 1 + » , , V

"'*• V ° * l 3*2 r ' ' ! 1*23

and AU = b„AH + b„AG

KF„=b,AH + b,,AG

)T s

(7)

(8)

(9) (10)

Fig I A typical control structure of a smal hydroelectric power turbine

Figure 2 describes the relation between

turbine mechanical power, water How speed,

water height with gate step openning

• I ,

Figure 2 Gate step openning

2.3 Power-Unit Rotor Dynamics Model

Dynamics of a power unit in the turbine

governing systems, in most of the cases, can be

described by using only inertia moment of the

power unit Using Newton's second law where

torques are expressed as powers divided by the

rotation speed, one can derive the following

Afi),, 1

iS)-AP-AP, Ts + D, (11)

PL: mechanical power on the turbine shaft (per

unit);

D|, : inertia moment of the unit including a rotating parts I T,n : mechanical time constant of the unit (s)

III SYNTHESIS OF A GOVERNOR CONTROLLER

The speed governing and the powe governing are analyzed separately in order ti illustrate the procedure for calculating thi controller parameters in different modes o operation The practical considerations cm should take into account are the different modei

of operation of the turbine governing systen and combined speed and power governing,

3.1 Speed Governing

The control structure of speed governing

is show on Figure 3

Fig 3 Speed governing system

In [5], the linearized model of th(

P: base power (w);

0)^ : angular velocity of the unit (in rad/s);

With the closed loop function:

:y+(7;+6„7;,)5-+rxAi^'

hydraulic turbine is

b^^-b^J^^s Gra{s) =

-\+b,,rs

GAs) ^23^, + ^ton^' + AoP2^' + AonS^-*-bnTJJ,y

With

2 = h^Kj + D„/„ -I- r„ - b^jx^ + b,,D;r^^ - b,j„ K,,

3 = TJ„, - 6.,r., K, - b,„TX + 6,, ?:, (Z)/„ + r„,)

= D-b„

(12)

(13)

(14)

(15) (16) (17)

2A,Hf„ (18)

K.,=-2A,H, —(PU 1 + Pu,., + A.„ + Pu,^ + Pu.,1 + Pu « + A„„9) (19)

With

A,™i - 'JHrc«P,PiP;Pj Go - PiPlP-.P^'l.u L - H,„(p,p,p, + p,p,/7j + P I P J P J + P2/),p,)

Pl„l,M=-^ylHrc„PP2P,P,qMT,'GiTJ,„

PM,3=PIP2P,P,'!IIT'TJ.,G„

Pu,.s = -3//rro?:, G„'£>„ + //^„7;, TJ.,G„(p,p, + p,p, + p,p, + /),p, + p,p, + P J P J

Pu.-,=D,.H'.^,(-2H^J, +2q,JJ-ZD„Hi„TA

Pu., =-'iD„q^^H'jiJ„ G„ + Hi.l,T;G-TJ,„(p,p,p, + p,p,p, + A A A + A P I A ) PuM= HTcJ'«GJX,(p,p,p,q^,+ p,p,p.,q^^+ p,p,p,q„^+ p,p,p,q„^+ p,p,p,T„.Gi) (20)

3.2 Synthesis of power governing In which :

The block diagram of the power Bs : numerator of the controlled system transfer controlled system is shown in Fig 4 function

As : denominator of the controlled system transfer function

Ys : numerator of the controller transfer fiinction R

Xs : denominator of the controller transfer function R

Kpp: feedforward gain

The controller will be designed using the pole placement method, with the PI controller

K

Fig 4 Power governing system

The transfer ftinction describing the

change of the unit power in respect to the

reference power is given in

in form: R = K„

AX^+BX

We would come to the transfer funtion

P^f " b,,TJ,y -)-(6,,7; + T„- TJ^,,,Kp)s- + ib,,^K^, +1 -TJ,.,,K,)s + b, K, (22)

parameters as ftinctions can be calculated as follows

It can be seen that by designing

K =—K- it is possible to compensate for

one of the zeros With the assumptions of i^ _ ^ (_Aipi2

turbine operating point hrc =H[co, nominal "•/> ~ AjUi ^ T^ PIJ'P, '^P'PI" '^P'TPI '

PPlP,TJ G„

2A,H' (23)

Trong do :

/v„ =2w„,(ftp,+/),/), + /),f.,)7;,7;,q, (24)

p^r,:=i"^'PihPjJ:.G;, (25)

A,H =-p,P:P,T,V:(^,i '2q,, + 2 q „ / 7 ^ ) (2(,)

TV SIMULATION

4.1 Speed governing simulation

Simulation parameters are obtained from

the Ryninh hydro power unit with: nominal

power P|,= 1.2 (MW), H= 76 (m), penstock:

DTC= 1.3 (ml, f= 50 (Hz), Tw= 0.87 (s), y , , "

0.97 (u) qNi= 0.09 (mVs), T,„= 5 (s), K,= 5,

T,= 0.02

The desired poles are chosen as:

p, = -0,1 ; p: = -0,l; pj=-0,14

It then calculates Kp= 1,82;K,=0,08; Kj= 7,51

according to (17)-(19)

Fig 5 Step response in position control

The results of the model simulation usin| nonlinear model and responses of the rea system for the unit with the implementet controller are shown in Fig 5 In these figures compensation by the speed controller for th( load step change is given

The simulation was conducted with step changes of 10% and al the time t = 660s, the load was suddenly rejected to test for Uirbine over speed The simulated results are shown ir figure 6 It can be seen that the oveshool is less

than \% and in he suddenly rejected load case,

the turbine over speed is about 30%, which is much less than the 50% allowable standanj 4.2 Power governing simulation Similar simulation was also conducted for power govering With the desired poles are chosen as pi=-1,2 vi p:= - 1,2 and the controller parameters K.p=0,08; Ki= 0,1; Kpp= -0,08 The simulated results are shown in Figure 7

oirixt'-••.••«

L

Fig 6 Pisewise step response in speed

Fig 7 Step response in power governing

\ IMPLEMENTATION EXAMPLES The experiments given in this section were conducted throughout the whole operating range of the turbines The hardware, which integrates the main controller and the Human Machine Interface (HMI), is applied to develop the dynamic real-time system The hardware consists of a 16-bit CPU of Microchip DsPIC 33F, a 5.7 inch QVCA (320*240 pixels), 256

KB SRAM, a RS232 interface, a CAN interface (electrically isolated, network capable), a 24V

DC power supply, 10 digital input channels (the

former 4 channels can be used for frequency measurement, 8 digital output channels

Additionally, 4 channels analog input (12

bits resolution, 0-lOV) is used to measure the

digital control signal o f the hydraulic governor,

the main servomotor stroke and the wicket gate

opening The hardware configuration is shown

in the figure 8 T, '^'wM'^^'&^!fV^''^^^

=f

/•Vl,' III I'hr rcil KcihT.iKir's frcijii.'iin

\ I ( ()N( l.l SION

llw :iu(li i- pr no^cl g u c n u r c m li_\drockxhK piv.xcr ]

Tl

ted III liiis p;ipcr ihc sirale"V lor ;i small

Fig S The /-Lv/ nine digiia! conlniller

Turbine g o \ c r i i o r was iinplcmcnicd in

the R>nmh hydropower on I 2 M W Fram-i.s

turbines The responses of the real s \ s l e m with

the implemented controller are shown in l-igs

9-10 The experiments are gi\ en tor power

demand change For simplicit\ of controller

implementation, fixed parameters were used,

Howexer the slahiht\- and the d_\namical

belia\ ior in the whole operaling range were

checked experimentali\ and for the particular

planl case, satisfaciory results were achieved

Due to space limit, not all measured results are

given here

^^JBHM*^*iiMt**' W' in imi4*'4 ft^iiit>.rt(i|J

Fig 9 Field tests of the turbine controller

Fig i: The IIMI nilertaec (>t liirhinc i:,'nvn!or

I he author has verified control perRimianee of the luwel governor eiiuipmenl

b \ the sinuikition tool, and also conllnned the effecli\eiiess of the planl simulaiioii model thought experiments

In this brief, it has been shown that PID control can achieve a substantial improvement

PID controller is that it is relatively easy to Acknowlegement

implement and commission This makes testing ^^ ^^^^^^ gratefully ac edge the easy and relatively safe, wh.ch ,s miportant ^^.^ ^^ ^ |.^^^ ^ j C / ^ , , , ID-DTDU

when there are severe mancia consequences if xi • i r* • u- u „«^kUfi •• i i rarrv nut , , , , , , ^ National Project which enabled u; ' ' carry out the planl should hiil durmg operation

REFERENCES

i

1 Jiang Chang Zhihuai Xiao, Shu qingwnag "Neural network predict control for the hydro turbine generator set," The second international conference on machine learning and cybernetics (1CMLC2003) 2003, pp.2-5

2 GUI Xiao-yang, MEI Sheng-wei, LIU Feng and LU Qiang, "Adaptive Nonlinear Control for Hydraulic Turbine Governor," IEEE Trans Proceeding of the CSEE Vol.26, No.8, pp.66-7I, Apr

2006

3 Har\'ey, A., Brown, A., Helliarachi, P and Inversin, A., Micro Hydel Design Manual, A Guide to Small Scale Water Power Schemes, Iniermediate Technology Publications, 1993

4 Kundur, P Power system stability and Control Tala-McGraw Hill Co 1221, Avenue of the Americas, New York, NY 1994

5 Working Group on Prime Movers, Hydraulic turbine and turbine control models for system dynamic studies, IEEE Transaction on Power System, 7, 1992, pp 167-179

6 W Grega, "Hardware-in-the-loop simulation and its application in control education", 29th ASEE/IEEE Frontiers in Education Conference Session 12b6, pp 7 12 November, 1999

Author's address: Nguyen Hong Quang -Tel: 0912.068.608, Email; quangnh(5^mail.hut.edu.vn

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