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A Design Approach for a Microprocessor Based Complex Control System for Application to a Generator Turbine Unit
Cop yri).{ hl © IF ,\ C ~1 "1 Triennial World C() l1 grCS~ Buda jleSl , HUIl).{
A DESIGN APPROACH FOR A MICROPROCESSOR BASED COMPLEX CONTROL SYSTEM FOR APPLICATION TO A GENERATOR TURBINE UNIT O. P. Malik*, G. S. Hope*, VU. M. Gorski**, V. A. Ushakov** and A. L. Rackevich** *Drpartlllfnt of £Ia trical EIl{(inrfTing. Unlt'Prsi!y of Calgar)' . Calglln . Albn ta. Cmwda **Siberian P ower [",tilute. USS R AcadelllY of ScirncfS. h kutsk. USS R
Abstract. A design approach for a microprocessor-based complex controller for appllcation to a synchronous generator is described in this paper . It is shown that the proposed complex regulator can be used to enhance the capabilities of the regulators and improve the generator performance as it allows the application of adaptive controls. An algorithm for an adaptive stabilizer is described. Test results on a microprocessor-based excitation regulator using this adaptive algorithm show that the performance of the generator is improved. Keywords.
Computer Control; Power System Control ; Generators, electric. - restorat i ve - special.
INTRODUCTION The initial versions of microcomputer based excitation and speed regulators have been previously reported by Malik et. al, 1980; CiJrski, et. al , 1981; Lubarski et. al, 1979; Bashnin et. al , 19 82.
A state di agram representation of these regimes with transition between regimes is shown in Fig. 1. Double lines symbolize a transition forced by random causes. Ordi na ry 1i nes symbol i ze transitions forced by control actions. In each regime the system operation requi rements can be characterized as a hierarchy of state goals. There is a corresponding set of action goals which correspond to a transition into a new state.
The ne xt step in the impl ementat i on of microcomputer techniques for the control of a generating unit lies in the transition to a complex control system. In this transition one may face difficulties which are not caused by the hardware and software but by the necessity to coordinate various tasks to meet the changing system operation regimes and by the need to select a rational structure for the complex regulator itself.
This is given in more detail by the so called Lorgraph of Fi~. 2. It shows stat,e goals hierarchies (G n ( t)) and action goals (G n (a)). In the normal regime, ~, all loads are at rated voltage and frequency. There i s e~ugh angl e and voltage stability, i.e. the system in this regime meets all th~ r)equi rements for the state goal s hierarchy, ~\st •
Thi s paper is devoted to the definition of the main regimes of operation in a power system as applied to i) ii)
T he prevent i ve state, Pr. , occu rs when all loads are met but the appara'tus is overloaded. The rotor or stator currents may be above rated or the rotor angl e steady state stabi 1 i ty is be low de?ired. The action objectives in this regime, G la), are organized to return to the normal state b~ restorative action. This is done by shedding load or putting on back up units and so on.
the control of a generating unit and the formation of regulation goals.
The development of complex regulator offers the possibility of the application of adaptive control. The advantages of adaptive control and the type of problems that can be tackled with the adaptive control are outlined. The algorithm for an adaptive stabilizer using frequency as the input si gna 1 is descri bed and test results on a microprocessor-based excitation regulator using this adaptive algorithm are given.
When there is a danger of losing synchronism or when synchronism has been lost after a disturbance this sy stem is in the emergenc'y'( :;tate,~. The action goal in this regime, Gac a), is to return t he system to norma 1 or to tlie prevent i ve regi me to avoid stability violation and to damp out distu rbances. I n the ca se of asynch ronous ope rat i on it is returned by synchronization to the r estorat i ve state and subsequent ly to the norma 1 state.
REGIMES Regimes or system states can be described different operating conditions and may classified as:
as be
The restorative regime, Ar, takes place after an emergency has been stabilized. When load has been shed and there is not enough stability margin or a
- normal - prevent i ve - emergency 27 59
O. P. Malik et aL.
2760
unit is functioning asynchronously restorative action must be taken. The action goals in this case are associated with resynchronization, a change in voltage level or a change in power 1 evel.
system, its functions are passed to the back up or complementary structure. Sufficient computational resources must be available so that reconfiguration or removal of program modules for general repair and maintenance can be accommodated.
Load shedding in such functions is considered to be in the special regime.
ADAPTIVE CONTROL
TASKS Each of the above states has been di vi ded i nt 0 operating conditions. For example the normal state is di vi ded into generat i ng power or zero power. The states are further subdivided depending upon the reactive power. Tasks are then a ss i gned accordi ng to the des i red ope rat i on, e. g. , maintain voltage, maintain security, maintain damping, etc. The tasks which the complex system must perform are subdivided into basic and auxiliary categories. The basic tasks are voltage regulation of a generator and speed governing of a turbine, and the auxiliary tasks are those of measurement, state recognitiion and data communication. Using this classification there are about 20 states and substates and approximately 30 tasks. Four tables - two for excitation control and two for speed control - have been constructed. To keep the paper length within limits, Tables I and Il for the excitation control are only given in the paper. The classification shown in these tables is done using matrix elements with the following meanings:
+ -
o6 e -
the appropriate task must be executed in the corresponding regime this task must be blocked the task performed has no meaning for the regime involved verifying conditions for the task performance must be executed task performed in this regime must be executed under certain limiting conditions.
The initial material to define input data requirements are given in the Tables. These classifications are used to develop and coordinate algorithms in different regimes. For the sake of s impl icity every problem is assumed to have its own algorithm. The structural synthesis of the general algorithms can be developed from the tabl es. The task of the structural synthesis is to define the regimes which must be detected by recognition system and then to establish the performance criteria of the subprograms in these regimes. The structural synthesis also forms the requi rements of the subprograms or program modules. The flexibility of the overall program composition must be emphasized. Even simple changes are made by the exclusion and addition of program modules. A high degree of back up and system operation verification is used to achieve high security. Verification is a combination of internal self-control, external control and cross mutual control from the back up system. The functional scheme for the control system with back up channel s is gi ven in Fi g. 3. The system consists of two parts and there is likely to be a different task distribution between the parts. For example, one part performs the excitation regulation functions and the other part performs the speed governor functions. The functional distribution of this system is dependent upon the condition of the effective control for the operation of both parts of the system. In case of a failure of one part of the control
Analog regulators have constant parameters and offer no adaptive properties. Development of first microprocessor-based excitation regulators (Malik, et. al, 1980; Fadeev, et. al, 1983) is the initial step towards the development of a complex regulator as that proposed in this paper. These regulators offer the possibility of improved control such as the application of adaptive control algorithm. With the use of microprocessors in the construct i on of excitat ion regul ators, adaptat ion can be used to solve the following types of problems: 1) 2) 3) 4) 5) 6)
steady-state stability, zone of maximum damping of forced oscillations, decrease of maximum generator rotor angle in the first swing associated with short circuits, to assure against stability loss in the second and the third swings after large disturbances in the system, reduction of asynchronous step time and facilitating to pull the system into synchronism during resynchronization, reduction of low frequency oscillations induced by power flows along the tie 1 i nes in the system.
Besides when regulating a generating unit in the complex manner described above, one more problem i.e. the adaptation to regime, arises (Table Ill). Taking into account such an adaptation to regime, all the abovementioned adaptive control problems should be considered as "internal" being solved within regimes. A number of adaptation methods, that can di rect ly or i ndi rect ly be related to the second and th e third "internal" adaptation problems, have been proposed in the literature. A modification of the table adaptation approach is described by Bonamoni, et. al (1979) and Limbeer, et. al (1979). An electrical power system state is recognized by the average values of active and reactive power of a synchronous generator and precalculated values of the regulator coefficients that provide the predetermined control are chosen. Another technique (Shierah, et. al, 1979) is to minimize the variance of the output variable of the system. Using a linear low order discrete mOdel, model parameters associ ated with external disturbances are computed using an identification algorithm. A modification of this method is given by Vi shtebeev and Chernev (1977) who obtai ned the desired steady-state and dynamic properties of the system in all normal operating conditions by tuning the system to the centre of the area limited by a curve obtained by D - decomposition. The first adaptive problem is solved by an approach offered by Gorsk i (1964). Anothe r approach (Venikov, et. al 1972) is based on the location control of the reliable (high-frequency) 1 imit. In this case the value of one coefficient ri ses slowly and when the system dampi ng become s equal to a predetermined value, it decreases at a preselected rate. The second coefficient is treated similarly.
2761
Microprocessor Application to a Generator Turbine Unit
ADAPTIVE STABILIZATION SIGNAL USING FREQUENCY In the excitation regulators of large turbo- and hyd rogenerators in USSR, the controls i gna 1 is synthes i zed from the error and the fi rs t der~va~ive of ~he generator voltage, the frequency devlatlon and ltS flrst derivative combined with a forcing relay and excitation voltage feedback, and the first derivative of the current in the field winding as
where
u - the excitation forcing relay, 68 v _ the controlled voltage deviation from the setting, 6f - the frequency deviation from the stabilized value, kOu' k 1u' k Of' kIf' k 1 I - the contro 1 coeffi c i ent s
The microprocessor based excitation regulator DARE-Mc1 has got a similar control law also where the frequency control component, uf' is formed as or
kOf6 f i + k If (6 f i - 6f i-I)
( 1)
k1~f i-I
(2)
( k Of + k If )6 f i
Taking into account the important role in providing stabil ization and efficient damping of rotor .oscillations, the feasibility of building an adaptl~e contour of regulation in frequency accordlng to eqn. (2) is considered. The coefficients kor and kIf i n ~qn. (2) would be selected automa11cally and provlde the dispersion minimum 6 f. This is done by using the approach of Shierah et. a 1 (1979). Let the system be represented by a stochastic discrete model: 8u(t-k-l) + A[e(t) + c e(t-l) + c e(t-2)] 1 2
(3)
where y(t), u(t) - output and input of the model respect i ve 1y, k - pure time delay of the system, e(t) - model uncertainty with the zeroth average value and closed deviation, a, 8, c, - the parameters, y(t-i), u(t-i), e(t-i) - the variables at time (t-iT), where T - the sampl ing period.
As Ee:(t+1) = 0 ande:(t+l) does not depend on8u(t) - 8u(t) - a y(t) - a;>y(t-1), so the last term in 1 eqn. (5) becomes zerO". Thus E/(t+1) = E[£(t+1d + E{8u(t) -a y (t) 1 2 - azY(t-1)}
Parameter B can be predetermi ned and set equal to 1. The rest of the parameters can be estimated using a real-time identification method. Then u(t) = ~1 y(t) + ~2y(t-l)
This algorithm was tested on the digital-analogphysical model complex at The Siberian Power Institue. The effectiveness of a voltage regulator with and without self-tuning, in damping the oscillations caused by a short-circuit on a transmission line, was observed. In e~ch case the input and output Clrcults used were exactly the same.
The results given in Figs. 5 and 6 demonstrate that the introduction of the self-tuning system 1 mproves conslderably the qual ity of damping. CONCLUSIONS It is contended that the next logical step in the application of microprocessors for the development of regu 1ators is to deve lop comp 1ex cont ro 11 e rs. Such controllers offer the possibi 1 ities of considerable improvement in the generator performance. Test results on a microprocessor based excitation regulator using an adaptive stabi 1 i zer illustrate such an improvement.
Bashnin, 0.1., Buevich, et. al, (1982), "Microprocessors based automatic voltage regulator for powerful synchronous machines", paper presented at Second Joint Soviet-Canadian Seminar, Calgary, Canada.
+ 2[e(t+k+l) + c e(t+k) + c e(t+k-1)] 2 1 For k = 0 y(t+1) +a y (t) +a y (t-l) =8u(t) +£(t+1) 1 2 noise
slip
average
Control law is derived using the model the dispersion criterion of deviation, i.e. min Ey2(t+1).
of
( 4) the
minimum output
Ey2(t+1) = Ee: 2(t+1) + E{B u(t)
IWC5-0
zY(t-1)] (t+1)
Bonamoni, P., Guth, G., Blaser, F., Glavitsch, H., (1979), "Concept of a practical adaptive regulator for excitation control", IEEE Power. Eng. Soc. Text "A", Paps Summer Meet., Vancouver, New York, N. Y., 1979, p. 1-5. Fadeev, A.V., Lotkov, M.A., Obratsov, V.S., (1983), "Microprocessor based automatic voltage regulator for powerful synchronous machines", paper presented at Second Joint Soviet-Canadian Seminar, Calgary, Canada. rOpCK~H ~.M.,
(1969),
caMoHcTpO~KH
- a y (t-1)}2 + 2E{ [liu(t) 2 -
regulator
REFERENCES
y (t+k+ 1) + a y(t+k) + a y (t+k+ 1) = 8 u(t) 2 1
the
(7)
Comparing eqns. (2) and (7) one can see that using 6f. as y(t) and a model of the kind (3) the t~o-chanhel excitation control system shown in Flg. 4 can be built wherein the stabilization contour self-tunes on minimum deviation of 6f to ensure effective damping of oscillations. Selftuning is achieved as the model i parameters track the system using a real-time identifier and the cont.r0l derived from the model of eqn. (3) provldes the output, i.e.6f with minimum dispersion.
Write eqn. (3) at time (t+k+1) as
where £(t+1) is noise value.
(6)
It is seen from eqn. (6) that Ei(t+1) ) Ee: 2(t+1) when {8u(t) - a y(t) - a y (t-1)} = 0 1 2 1 Hence u(t) = B [a y(t) + a y(t-1). 1 2
B030ymAeH~H
( 5)
CCCP.
~cnonb30BaH~e np~Hu~na
B aByoMaTH~eCKHX c~nbHoro AeHCTB~H.
3HepreT~Ka ~ TpaHcnopT,
pernRTopax - ~3B AH W I, c. 28-37.
O. P. Malik et al.
2762
YwaKoB B. A., PaKeBH4 A. n., Xoyn r.c., (1981), H Ap· UH~POBO~ perYJlHTOp B036Y~AeHHH H CKOPOCTH CHHXPOHHWX MaWHH. 3JleKTpH4ecTBo, ~ I, c.8-13
rOpCKH~
n.
MaJlHK
M. , O.
n.,
Restoration regime (A r )
Limbeer, D.J.N., Harley, R.G., Nattrass, H.L., (1979), "Agile computer control of a t urboa 1ternator", Proc. Inst. El ec. Eng., 126, ill p. 385- 39 2.
I~
...... Preventive ..- regime (Ap)
Normal regime (An)
-" -~
rF
i 9l
Lubarsky, V.G., Fadeev, A.V., et. al, (1979), "Automatic excitation regulation system of power synchronous micro-computer based generator", Moscow, Electrotechniques, N. 4, p. 6-9.
Special regime (Asp)
Malik, O.P., Hope, G.S., Gorsky, Vu. M., Ushakov, V.A., et. al, 19BO, "Development plans for joint Soviet-Canadian microprocessor based voltage and speed regulators", IEEE PES Winter Meeting, New York, Paper #ABO 105-7.
Fi g. 1.
Emergency regime (Aa)
j
Main regi mes
Shierah, M.A.H., Malik, O.P., Hope, G.S., (1979), "A self-tuning automatic voltage regulator", Elec. Power Syst. Res., 2(3), p. 199-213. BeHHKOB B.A., Cyxa30B O.A., CTHxaHoBcKH~ n.H., (1972), npHMeHeHHe npHH4HnOB aAanTa4HH npH perYJlHpOBaHHH B03~Y~AeHHH CHHXPOHHWX ManHH - TpYAbl M311, Bbln. I33. 3JleKTpH4ecKHe CHCTeMbl 11 ceTH. M., M1M, c. 51-56 BHWTe6eeB B.I1., YepHeB B.T.(1977), CHCTeMa aAanTHBHoro ynpaaJleHHH perJlHpOa a HHeM B035Y~AeHHH CHxpOHHoro reHepaTopa, o6ecne4HBa~~aH nOAAep~aHHe pa604 e ~ HacTpo~KH APB a 3aAaHHo~ 06aCTH YCTO~4"BOCTH. - B KII.: nOHMeHeHH e 4aCTOTHWX MeTOAoa a 3JleKTp03HereTHKe. "TpYAW 3HI1H", awn. 65, c. 66-75 .
Fig . 2.
T ABLE I
Ii
Main tasks of excitation
Support of a terminal -- ~
II ~
0
( 1
i E'"'-
II z: 0
P= 0
le iQ,l > Overload iti ~ ·rII >. Syn ch ron i sm Q)
+0
u
e
Q)
E'Loss of ~ synchronism w
L
Maximum damping of little and big osci 11 at ions mE 3
N 1
+
+
+
Q< 0 IQ> 0
tl 2 N 3
+ +
+ +
+ +
o<0
rI 4 P 1
Vr<>f
1>
t.
vref
1>
>1 >1 ~ - > °max I I
I'
P 3
+
E1
(±)
tightly cs overload loosely cs
E2 E3 E4
G) (+)
-,
tightly cs emergency stop loosely cs
E5
+ + + + + + - + - - - - - - f - - - ---..,.'--
+ +
+
loose Iy cs
In static > (after 1arg e disturbance) tightly cs +0 '"'-0 SynchronIsm exact +0 restorat ion VI selfsynchr Q) 0:: Normal ! start-up Norma 1 ';;; shut-down u Isolated Q) 0operation V> .~
' '---'
Q> 0
-
-
-
-
-
-
+
E6 R1
Vref t
R2
V{'f'f.. t
Q)
.~
Secu ri ty of a steady state stabil itiy mE 2
voltage in accordance ith the reference mE 1
REGIMES
L - orgraph of system life activity (on the level of government-turbine-block).
-
+ +
--,----_.- - +
+
t--,!
+
+
S 1
0 - - -- -,-
-
S 2
+
t.
6
R4 R5
-
-
-
,
-
-- -+- -- - --- I-----=-
. ._..
- - - -------
, .- . 4 - - _ _ _
-
-
-
r ----+
+ +
---L , __ I i -
+
+
.,
+
-
RJ
Maximum reduce of fi rst cycle swing of a roto r mE4
+
I
-
r----=----' ! -
i I
i
-- -- --- ~---=:]i !
-
!
+!
, I
I
-
6
!
----,i iI I
Mi c r op r ocesso r Sys t e m f o r Contr ol of Ro b o t s
TABLE 11
Lo..~~
I g Synchronism
I
Help under resynchronisation a) field is removed b) field is not removed
Help under start-up and synchronisation
Joint contro 1
+
<0
+
+
-+-_-=_________.__~_. ___ .____~~
8
I > 1 0 \
I"
Control from st at i on 1evel Supervi sory control system +
Q
Overload
Limitation of minimum exc itat ion in accordance with conditions
Q>0
o ~g;
Additional tasKs of excitation
Limitation of overload stator and for rotor current
REGIME S
27 63
~
0
2 max loose 1y cs E.1
. -- -~ . - ---4l--i
I
t--: -.. -----
' + - -- - - - -----.----+------.- -- ... -..-
+ ---
1-.
~ - -___ fv~o~ ~L ~-----+.-~~ ....- .-~--. ~.-+~=~=-:-~~-- ~-~.: ::- -~~~.~~=t=--Er~~
~ ;;~~h::"i'm ¥,~:!U: ::: In static loosely cs ~ (after large l--- - -:.::; ~turbance) tightly cs ~ Synchronism e xact.
£;::~~~ation ~~~~ IL.f start-u~
: -~-t-~~ == ~ :~::-F:- - = : ==~:t~
R.1 -- -R.2 R. 3
I
(;-- - -·I- - -:;- -- ---T--_- - - - -..
(; (;
,
(; 0
+ +
:
0
+
!
(;
I~o '0
z:
P
=
0
CCIJ CIJ>
-
. - --
-
. .
--:------t---~
-
Adaptation bangbang cont ro 1 system
A.l
+
+
+ +
+ +
+ +
N.4 P.1
+ +
+ +
+ +
oD > ° ma x
P.2 P.3
+ +
+ +
+ +
loosely c. s. tightly c .s. overload loosely c.s. tightly c.s. emergency stop loosely c.s
t.l
E.2 E.3 E.4 E.5 E.6 R.1
-
-
N.1
+
Q> 0
o<0
N.2 N.3
<0 I > 1 I > 1
,
Overload
>~
CIJ+..'
'-
0..
~Synchroni sm
C CIJ
'- Loss of ~ synchronism In static
~ (after large
---
Adaptat ion 0 n domain of a steady stability
A.3
Q > 0
~
,
-
Adaptat i on
Adaptation on zone max. damping of osci 11 at ions A.2
.; 1
- -
+
S.2
REGIME S
11
S.1_ __-=(;_ _ _ t------"O- - - i - -+- -- - + -- - - -+-- - - - - 4- ---I
TABLE III
I!
--- ---+-- --~
--.;..... -- --- -.----- -----
--t;------ ----O ---I---..2...- - --uT-~ ·-:~:~ ._h._~= ~~=~:==-
R.5
'".;; Norma 1 shut-down ~ Isolated ~ operation
(;
.-------+----.-
:.::; d i sturbance\ tightly c.s. ~ Synch ron ism exact ~ res torat i on selfsynchr. ~ Norma 1 a:: s tart-u2. Normal '".;; shutdown -::; Iso 1ated -~ operat i on Vl
R.2 R.3 R.4
+ +
+ +
S.l
-
-
S.2
-
(;
R.5
-
-
+
+
-
2764
O. P. Malik et al.
Additional conditions Cij
al gorithm sequence execution
, .~" . ' . . ':.. .': ,'
'u ,.
Verification system Measurement system al gorithm sequence execution
'at Fig . 5.
The oscillogramme of the transient process induced by three-phased short circuit of 0,22 s.-duration with the excitation regulator without a self-tuning.
Additional conditions C ij Fig. 3.
Functional scheme of control system with back up channels
rvJ--.....,...--u
r
---- --I'
I'
f
I'
Non-adaptive control contour
f
I
<,> u
U'
<'>
f
8
------/~------~-------,
Identificator
o~
Model
Fig. 6.
Control
I I
,
l.. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ .......
Fig. 4.
Block-scheme of the excitation regulator forming excitation actions in frequency .
The oscillograme of the transient process caused hy three-phased short circuit of 0.2 2 s.-duration with the excitation regulator with a self-tuning.
A DESIGN APPROACH FOR A MICROPROCESSOR BASED COMPLEX CONTROL SYSTEM FOR APPLICATION TO A GENERATOR TURBINE UNIT O. P. Malik*, G. S. Hope*, VU. M. Gorski**, V. A. Ushakov** and A. L. Rackevich** *Drpartlllfnt of £Ia trical EIl{(inrfTing. Unlt'Prsi!y of Calgar)' . Calglln . Albn ta. Cmwda **Siberian P ower [",tilute. USS R AcadelllY of ScirncfS. h kutsk. USS R
Abstract. A design approach for a microprocessor-based complex controller for appllcation to a synchronous generator is described in this paper . It is shown that the proposed complex regulator can be used to enhance the capabilities of the regulators and improve the generator performance as it allows the application of adaptive controls. An algorithm for an adaptive stabilizer is described. Test results on a microprocessor-based excitation regulator using this adaptive algorithm show that the performance of the generator is improved. Keywords.
Computer Control; Power System Control ; Generators, electric. - restorat i ve - special.
INTRODUCTION The initial versions of microcomputer based excitation and speed regulators have been previously reported by Malik et. al, 1980; CiJrski, et. al , 1981; Lubarski et. al, 1979; Bashnin et. al , 19 82.
A state di agram representation of these regimes with transition between regimes is shown in Fig. 1. Double lines symbolize a transition forced by random causes. Ordi na ry 1i nes symbol i ze transitions forced by control actions. In each regime the system operation requi rements can be characterized as a hierarchy of state goals. There is a corresponding set of action goals which correspond to a transition into a new state.
The ne xt step in the impl ementat i on of microcomputer techniques for the control of a generating unit lies in the transition to a complex control system. In this transition one may face difficulties which are not caused by the hardware and software but by the necessity to coordinate various tasks to meet the changing system operation regimes and by the need to select a rational structure for the complex regulator itself.
This is given in more detail by the so called Lorgraph of Fi~. 2. It shows stat,e goals hierarchies (G n ( t)) and action goals (G n (a)). In the normal regime, ~, all loads are at rated voltage and frequency. There i s e~ugh angl e and voltage stability, i.e. the system in this regime meets all th~ r)equi rements for the state goal s hierarchy, ~\st •
Thi s paper is devoted to the definition of the main regimes of operation in a power system as applied to i) ii)
T he prevent i ve state, Pr. , occu rs when all loads are met but the appara'tus is overloaded. The rotor or stator currents may be above rated or the rotor angl e steady state stabi 1 i ty is be low de?ired. The action objectives in this regime, G la), are organized to return to the normal state b~ restorative action. This is done by shedding load or putting on back up units and so on.
the control of a generating unit and the formation of regulation goals.
The development of complex regulator offers the possibility of the application of adaptive control. The advantages of adaptive control and the type of problems that can be tackled with the adaptive control are outlined. The algorithm for an adaptive stabilizer using frequency as the input si gna 1 is descri bed and test results on a microprocessor-based excitation regulator using this adaptive algorithm are given.
When there is a danger of losing synchronism or when synchronism has been lost after a disturbance this sy stem is in the emergenc'y'( :;tate,~. The action goal in this regime, Gac a), is to return t he system to norma 1 or to tlie prevent i ve regi me to avoid stability violation and to damp out distu rbances. I n the ca se of asynch ronous ope rat i on it is returned by synchronization to the r estorat i ve state and subsequent ly to the norma 1 state.
REGIMES Regimes or system states can be described different operating conditions and may classified as:
as be
The restorative regime, Ar, takes place after an emergency has been stabilized. When load has been shed and there is not enough stability margin or a
- normal - prevent i ve - emergency 27 59
O. P. Malik et aL.
2760
unit is functioning asynchronously restorative action must be taken. The action goals in this case are associated with resynchronization, a change in voltage level or a change in power 1 evel.
system, its functions are passed to the back up or complementary structure. Sufficient computational resources must be available so that reconfiguration or removal of program modules for general repair and maintenance can be accommodated.
Load shedding in such functions is considered to be in the special regime.
ADAPTIVE CONTROL
TASKS Each of the above states has been di vi ded i nt 0 operating conditions. For example the normal state is di vi ded into generat i ng power or zero power. The states are further subdivided depending upon the reactive power. Tasks are then a ss i gned accordi ng to the des i red ope rat i on, e. g. , maintain voltage, maintain security, maintain damping, etc. The tasks which the complex system must perform are subdivided into basic and auxiliary categories. The basic tasks are voltage regulation of a generator and speed governing of a turbine, and the auxiliary tasks are those of measurement, state recognitiion and data communication. Using this classification there are about 20 states and substates and approximately 30 tasks. Four tables - two for excitation control and two for speed control - have been constructed. To keep the paper length within limits, Tables I and Il for the excitation control are only given in the paper. The classification shown in these tables is done using matrix elements with the following meanings:
+ -
o6 e -
the appropriate task must be executed in the corresponding regime this task must be blocked the task performed has no meaning for the regime involved verifying conditions for the task performance must be executed task performed in this regime must be executed under certain limiting conditions.
The initial material to define input data requirements are given in the Tables. These classifications are used to develop and coordinate algorithms in different regimes. For the sake of s impl icity every problem is assumed to have its own algorithm. The structural synthesis of the general algorithms can be developed from the tabl es. The task of the structural synthesis is to define the regimes which must be detected by recognition system and then to establish the performance criteria of the subprograms in these regimes. The structural synthesis also forms the requi rements of the subprograms or program modules. The flexibility of the overall program composition must be emphasized. Even simple changes are made by the exclusion and addition of program modules. A high degree of back up and system operation verification is used to achieve high security. Verification is a combination of internal self-control, external control and cross mutual control from the back up system. The functional scheme for the control system with back up channel s is gi ven in Fi g. 3. The system consists of two parts and there is likely to be a different task distribution between the parts. For example, one part performs the excitation regulation functions and the other part performs the speed governor functions. The functional distribution of this system is dependent upon the condition of the effective control for the operation of both parts of the system. In case of a failure of one part of the control
Analog regulators have constant parameters and offer no adaptive properties. Development of first microprocessor-based excitation regulators (Malik, et. al, 1980; Fadeev, et. al, 1983) is the initial step towards the development of a complex regulator as that proposed in this paper. These regulators offer the possibility of improved control such as the application of adaptive control algorithm. With the use of microprocessors in the construct i on of excitat ion regul ators, adaptat ion can be used to solve the following types of problems: 1) 2) 3) 4) 5) 6)
steady-state stability, zone of maximum damping of forced oscillations, decrease of maximum generator rotor angle in the first swing associated with short circuits, to assure against stability loss in the second and the third swings after large disturbances in the system, reduction of asynchronous step time and facilitating to pull the system into synchronism during resynchronization, reduction of low frequency oscillations induced by power flows along the tie 1 i nes in the system.
Besides when regulating a generating unit in the complex manner described above, one more problem i.e. the adaptation to regime, arises (Table Ill). Taking into account such an adaptation to regime, all the abovementioned adaptive control problems should be considered as "internal" being solved within regimes. A number of adaptation methods, that can di rect ly or i ndi rect ly be related to the second and th e third "internal" adaptation problems, have been proposed in the literature. A modification of the table adaptation approach is described by Bonamoni, et. al (1979) and Limbeer, et. al (1979). An electrical power system state is recognized by the average values of active and reactive power of a synchronous generator and precalculated values of the regulator coefficients that provide the predetermined control are chosen. Another technique (Shierah, et. al, 1979) is to minimize the variance of the output variable of the system. Using a linear low order discrete mOdel, model parameters associ ated with external disturbances are computed using an identification algorithm. A modification of this method is given by Vi shtebeev and Chernev (1977) who obtai ned the desired steady-state and dynamic properties of the system in all normal operating conditions by tuning the system to the centre of the area limited by a curve obtained by D - decomposition. The first adaptive problem is solved by an approach offered by Gorsk i (1964). Anothe r approach (Venikov, et. al 1972) is based on the location control of the reliable (high-frequency) 1 imit. In this case the value of one coefficient ri ses slowly and when the system dampi ng become s equal to a predetermined value, it decreases at a preselected rate. The second coefficient is treated similarly.
2761
Microprocessor Application to a Generator Turbine Unit
ADAPTIVE STABILIZATION SIGNAL USING FREQUENCY In the excitation regulators of large turbo- and hyd rogenerators in USSR, the controls i gna 1 is synthes i zed from the error and the fi rs t der~va~ive of ~he generator voltage, the frequency devlatlon and ltS flrst derivative combined with a forcing relay and excitation voltage feedback, and the first derivative of the current in the field winding as
where
u - the excitation forcing relay, 68 v _ the controlled voltage deviation from the setting, 6f - the frequency deviation from the stabilized value, kOu' k 1u' k Of' kIf' k 1 I - the contro 1 coeffi c i ent s
The microprocessor based excitation regulator DARE-Mc1 has got a similar control law also where the frequency control component, uf' is formed as or
kOf6 f i + k If (6 f i - 6f i-I)
( 1)
k1~f i-I
(2)
( k Of + k If )6 f i
Taking into account the important role in providing stabil ization and efficient damping of rotor .oscillations, the feasibility of building an adaptl~e contour of regulation in frequency accordlng to eqn. (2) is considered. The coefficients kor and kIf i n ~qn. (2) would be selected automa11cally and provlde the dispersion minimum 6 f. This is done by using the approach of Shierah et. a 1 (1979). Let the system be represented by a stochastic discrete model: 8u(t-k-l) + A[e(t) + c e(t-l) + c e(t-2)] 1 2
(3)
where y(t), u(t) - output and input of the model respect i ve 1y, k - pure time delay of the system, e(t) - model uncertainty with the zeroth average value and closed deviation, a, 8, c, - the parameters, y(t-i), u(t-i), e(t-i) - the variables at time (t-iT), where T - the sampl ing period.
As Ee:(t+1) = 0 ande:(t+l) does not depend on8u(t) - 8u(t) - a y(t) - a;>y(t-1), so the last term in 1 eqn. (5) becomes zerO". Thus E/(t+1) = E[£(t+1d + E{8u(t) -a y (t) 1 2 - azY(t-1)}
Parameter B can be predetermi ned and set equal to 1. The rest of the parameters can be estimated using a real-time identification method. Then u(t) = ~1 y(t) + ~2y(t-l)
This algorithm was tested on the digital-analogphysical model complex at The Siberian Power Institue. The effectiveness of a voltage regulator with and without self-tuning, in damping the oscillations caused by a short-circuit on a transmission line, was observed. In e~ch case the input and output Clrcults used were exactly the same.
The results given in Figs. 5 and 6 demonstrate that the introduction of the self-tuning system 1 mproves conslderably the qual ity of damping. CONCLUSIONS It is contended that the next logical step in the application of microprocessors for the development of regu 1ators is to deve lop comp 1ex cont ro 11 e rs. Such controllers offer the possibi 1 ities of considerable improvement in the generator performance. Test results on a microprocessor based excitation regulator using an adaptive stabi 1 i zer illustrate such an improvement.
Bashnin, 0.1., Buevich, et. al, (1982), "Microprocessors based automatic voltage regulator for powerful synchronous machines", paper presented at Second Joint Soviet-Canadian Seminar, Calgary, Canada.
+ 2[e(t+k+l) + c e(t+k) + c e(t+k-1)] 2 1 For k = 0 y(t+1) +a y (t) +a y (t-l) =8u(t) +£(t+1) 1 2 noise
slip
average
Control law is derived using the model the dispersion criterion of deviation, i.e. min Ey2(t+1).
of
( 4) the
minimum output
Ey2(t+1) = Ee: 2(t+1) + E{B u(t)
IWC5-0
zY(t-1)] (t+1)
Bonamoni, P., Guth, G., Blaser, F., Glavitsch, H., (1979), "Concept of a practical adaptive regulator for excitation control", IEEE Power. Eng. Soc. Text "A", Paps Summer Meet., Vancouver, New York, N. Y., 1979, p. 1-5. Fadeev, A.V., Lotkov, M.A., Obratsov, V.S., (1983), "Microprocessor based automatic voltage regulator for powerful synchronous machines", paper presented at Second Joint Soviet-Canadian Seminar, Calgary, Canada. rOpCK~H ~.M.,
(1969),
caMoHcTpO~KH
- a y (t-1)}2 + 2E{ [liu(t) 2 -
regulator
REFERENCES
y (t+k+ 1) + a y(t+k) + a y (t+k+ 1) = 8 u(t) 2 1
the
(7)
Comparing eqns. (2) and (7) one can see that using 6f. as y(t) and a model of the kind (3) the t~o-chanhel excitation control system shown in Flg. 4 can be built wherein the stabilization contour self-tunes on minimum deviation of 6f to ensure effective damping of oscillations. Selftuning is achieved as the model i parameters track the system using a real-time identifier and the cont.r0l derived from the model of eqn. (3) provldes the output, i.e.6f with minimum dispersion.
Write eqn. (3) at time (t+k+1) as
where £(t+1) is noise value.
(6)
It is seen from eqn. (6) that Ei(t+1) ) Ee: 2(t+1) when {8u(t) - a y(t) - a y (t-1)} = 0 1 2 1 Hence u(t) = B [a y(t) + a y(t-1). 1 2
B030ymAeH~H
( 5)
CCCP.
~cnonb30BaH~e np~Hu~na
B aByoMaTH~eCKHX c~nbHoro AeHCTB~H.
3HepreT~Ka ~ TpaHcnopT,
pernRTopax - ~3B AH W I, c. 28-37.
O. P. Malik et al.
2762
YwaKoB B. A., PaKeBH4 A. n., Xoyn r.c., (1981), H Ap· UH~POBO~ perYJlHTOp B036Y~AeHHH H CKOPOCTH CHHXPOHHWX MaWHH. 3JleKTpH4ecTBo, ~ I, c.8-13
rOpCKH~
n.
MaJlHK
M. , O.
n.,
Restoration regime (A r )
Limbeer, D.J.N., Harley, R.G., Nattrass, H.L., (1979), "Agile computer control of a t urboa 1ternator", Proc. Inst. El ec. Eng., 126, ill p. 385- 39 2.
I~
...... Preventive ..- regime (Ap)
Normal regime (An)
-" -~
rF
i 9l
Lubarsky, V.G., Fadeev, A.V., et. al, (1979), "Automatic excitation regulation system of power synchronous micro-computer based generator", Moscow, Electrotechniques, N. 4, p. 6-9.
Special regime (Asp)
Malik, O.P., Hope, G.S., Gorsky, Vu. M., Ushakov, V.A., et. al, 19BO, "Development plans for joint Soviet-Canadian microprocessor based voltage and speed regulators", IEEE PES Winter Meeting, New York, Paper #ABO 105-7.
Fi g. 1.
Emergency regime (Aa)
j
Main regi mes
Shierah, M.A.H., Malik, O.P., Hope, G.S., (1979), "A self-tuning automatic voltage regulator", Elec. Power Syst. Res., 2(3), p. 199-213. BeHHKOB B.A., Cyxa30B O.A., CTHxaHoBcKH~ n.H., (1972), npHMeHeHHe npHH4HnOB aAanTa4HH npH perYJlHpOBaHHH B03~Y~AeHHH CHHXPOHHWX ManHH - TpYAbl M311, Bbln. I33. 3JleKTpH4ecKHe CHCTeMbl 11 ceTH. M., M1M, c. 51-56 BHWTe6eeB B.I1., YepHeB B.T.(1977), CHCTeMa aAanTHBHoro ynpaaJleHHH perJlHpOa a HHeM B035Y~AeHHH CHxpOHHoro reHepaTopa, o6ecne4HBa~~aH nOAAep~aHHe pa604 e ~ HacTpo~KH APB a 3aAaHHo~ 06aCTH YCTO~4"BOCTH. - B KII.: nOHMeHeHH e 4aCTOTHWX MeTOAoa a 3JleKTp03HereTHKe. "TpYAW 3HI1H", awn. 65, c. 66-75 .
Fig . 2.
T ABLE I
Ii
Main tasks of excitation
Support of a terminal -- ~
II ~
0
( 1
i E'"'-
II z: 0
P= 0
le iQ,l > Overload iti ~ ·rII >. Syn ch ron i sm Q)
+0
u
e
Q)
E'Loss of ~ synchronism w
L
Maximum damping of little and big osci 11 at ions mE 3
N 1
+
+
+
Q< 0 IQ> 0
tl 2 N 3
+ +
+ +
+ +
o<0
rI 4 P 1
Vr<>f
1>
t.
vref
1>
>1 >1 ~ - > °max I I
I'
P 3
+
E1
(±)
tightly cs overload loosely cs
E2 E3 E4
G) (+)
-,
tightly cs emergency stop loosely cs
E5
+ + + + + + - + - - - - - - f - - - ---..,.'--
+ +
+
loose Iy cs
In static > (after 1arg e disturbance) tightly cs +0 '"'-0 SynchronIsm exact +0 restorat ion VI selfsynchr Q) 0:: Normal ! start-up Norma 1 ';;; shut-down u Isolated Q) 0operation V> .~
' '---'
Q> 0
-
-
-
-
-
-
+
E6 R1
Vref t
R2
V{'f'f.. t
Q)
.~
Secu ri ty of a steady state stabil itiy mE 2
voltage in accordance ith the reference mE 1
REGIMES
L - orgraph of system life activity (on the level of government-turbine-block).
-
+ +
--,----_.- - +
+
t--,!
+
+
S 1
0 - - -- -,-
-
S 2
+
t.
6
R4 R5
-
-
-
,
-
-- -+- -- - --- I-----=-
. ._..
- - - -------
, .- . 4 - - _ _ _
-
-
-
r ----+
+ +
---L , __ I i -
+
+
.,
+
-
RJ
Maximum reduce of fi rst cycle swing of a roto r mE4
+
I
-
r----=----' ! -
i I
i
-- -- --- ~---=:]i !
-
!
+!
, I
I
-
6
!
----,i iI I
Mi c r op r ocesso r Sys t e m f o r Contr ol of Ro b o t s
TABLE 11
Lo..~~
I g Synchronism
I
Help under resynchronisation a) field is removed b) field is not removed
Help under start-up and synchronisation
Joint contro 1
+
<0
+
+
-+-_-=_________.__~_. ___ .____~~
8
I > 1 0 \
I"
Control from st at i on 1evel Supervi sory control system +
Q
Overload
Limitation of minimum exc itat ion in accordance with conditions
Q>0
o ~g;
Additional tasKs of excitation
Limitation of overload stator and for rotor current
REGIME S
27 63
~
0
2 max loose 1y cs E.1
. -- -~ . - ---4l--i
I
t--: -.. -----
' + - -- - - - -----.----+------.- -- ... -..-
+ ---
1-.
~ - -___ fv~o~ ~L ~-----+.-~~ ....- .-~--. ~.-+~=~=-:-~~-- ~-~.: ::- -~~~.~~=t=--Er~~
~ ;;~~h::"i'm ¥,~:!U: ::: In static loosely cs ~ (after large l--- - -:.::; ~turbance) tightly cs ~ Synchronism e xact.
£;::~~~ation ~~~~ IL.f start-u~
: -~-t-~~ == ~ :~::-F:- - = : ==~:t~
R.1 -- -R.2 R. 3
I
(;-- - -·I- - -:;- -- ---T--_- - - - -..
(; (;
,
(; 0
+ +
:
0
+
!
(;
I~o '0
z:
P
=
0
CCIJ CIJ>
-
. - --
-
. .
--:------t---~
-
Adaptation bangbang cont ro 1 system
A.l
+
+
+ +
+ +
+ +
N.4 P.1
+ +
+ +
+ +
oD > ° ma x
P.2 P.3
+ +
+ +
+ +
loosely c. s. tightly c .s. overload loosely c.s. tightly c.s. emergency stop loosely c.s
t.l
E.2 E.3 E.4 E.5 E.6 R.1
-
-
N.1
+
Q> 0
o<0
N.2 N.3
<0 I > 1 I > 1
,
Overload
>~
CIJ+..'
'-
0..
~Synchroni sm
C CIJ
'- Loss of ~ synchronism In static
~ (after large
---
Adaptat ion 0 n domain of a steady stability
A.3
Q > 0
~
,
-
Adaptat i on
Adaptation on zone max. damping of osci 11 at ions A.2
.; 1
- -
+
S.2
REGIME S
11
S.1_ __-=(;_ _ _ t------"O- - - i - -+- -- - + -- - - -+-- - - - - 4- ---I
TABLE III
I!
--- ---+-- --~
--.;..... -- --- -.----- -----
--t;------ ----O ---I---..2...- - --uT-~ ·-:~:~ ._h._~= ~~=~:==-
R.5
'".;; Norma 1 shut-down ~ Isolated ~ operation
(;
.-------+----.-
:.::; d i sturbance\ tightly c.s. ~ Synch ron ism exact ~ res torat i on selfsynchr. ~ Norma 1 a:: s tart-u2. Normal '".;; shutdown -::; Iso 1ated -~ operat i on Vl
R.2 R.3 R.4
+ +
+ +
S.l
-
-
S.2
-
(;
R.5
-
-
+
+
-
2764
O. P. Malik et al.
Additional conditions Cij
al gorithm sequence execution
, .~" . ' . . ':.. .': ,'
'u ,.
Verification system Measurement system al gorithm sequence execution
'at Fig . 5.
The oscillogramme of the transient process induced by three-phased short circuit of 0,22 s.-duration with the excitation regulator without a self-tuning.
Additional conditions C ij Fig. 3.
Functional scheme of control system with back up channels
rvJ--.....,...--u
r
---- --I'
I'
f
I'
Non-adaptive control contour
f
I
<,> u
U'
<'>
f
8
------/~------~-------,
Identificator
o~
Model
Fig. 6.
Control
I I
,
l.. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ .......
Fig. 4.
Block-scheme of the excitation regulator forming excitation actions in frequency .
The oscillograme of the transient process caused hy three-phased short circuit of 0.2 2 s.-duration with the excitation regulator with a self-tuning.