Copy of Impact of Modern Controllers in Power Network.ppt

Impact of Modern Controllers in Power Network

1. Impact of Modern
Controllers in Integrated
AC/DC Power Network
Dr. R. K. Pandey
Dept. of Electrical Engineering
Institute of Technology
Banaras Hindu University, INDIA

2. •Introduction
Structure of Modern Power Systems
Power Network Operation before Restructuring
Impact of Restructuring in the overall Power
Network
Factors affecting Power System Stable
Operation
Earlier Approach for Power System Stabilization
Modern Power System Analysis from Control
View Point
Impact of Multi-Controllers and need for Control
Coordination

3. Modern Power Systems
Components
Power Producing Companies Comprising
both Govt. Sector and Private Sector
Transmission Utilities such as POWERGRID
and State Owned Transmission Lines
Load Dispatch Centers such as RLDC
Distribution Companies both Govt. and
Private Sector
Control Systems Components such as SVS,
HVDC and PAR

4. Power Network Operation before
Restructuring
Classical Mode of Frequency Control such as
generating request to detach loads for
maintaining frequency
Arranging Power by the near by units to
manage the excess load, if possible
The integration of the various regions were not
perfectly realized
The Outage of one major Generating unit was
very dangerous from Stabilization view point

5. Impact of Restructuring in the
overall Power Network
Three Major Sectors were formed such as
Generation, Transmission and Distribution with
the concept of accountability and mutual
cooperation for maintenance of Safe Network
Operation
Power Generating units both owned by the
Govt. Sector and Private Sector were
enthrusted the responsibility of good plant
load factor thus maintaining the need of the
hour

6. Further new dimensions were added
incorporating the formation of regional load
dispatch centers in order to generate the
command for proper maintenance of the area
requirement
The regional load dispatch centers equipped
with latest monitoring devices are capable of
providing the reliable data up to some extent
for real time control
Many new control devices were added in order
to damp the power swing such as HVDC link,
SVS and PAR

7. Recent developments in the integrated network
operation has generated a lot of boundary
conditions for the individual sectors
In general, the power companies are supposed
to do the justice in terms of power generation
as the loading conditions are changing
Normally the central utility sector such as
POWERGRID has to carry the large power for
very long distance with the preconditions of
maintaining the voltage profile and frequency
of the network

8. Well known facts are that north eastern region
is having high frequency and the other belt is
having low frequency problem
The accountability of Grid maintenance lies on
the transmission utility sector
This requires an adequate control of Vars and
also real power control
However, the real and reactive power control
are not very well coordinated with systems
changing conditions at present
Therefore, the new power system configuration
need to be evolved looking the real life
situations with modern control concept

9. Factors affecting Power System
Stable Operation
Each generating unit connected to the grid
must participate stably along with the constant
terminal voltage thus ensuring the perfect local
controls
The connected load dynamics need to be
monitored properly by the suitable sensors
The load dispatch centers are capable to have
proper communication link ensuring the proper
feedback of the control variables

10. Normally the distribution companies do not
have the load predictor and thus the mismatch
in the loading becomes especially dangerous
when the large reactive loads are added
Ultimately, the bus voltage at the load end is
severely penalized, resulting into the
repercussions, which is adverse for the entire
network
In situations the power transmission company
does not balance the load requirement, the
network may land to oscillations, if not
controlled. Finally leading to multimachine
oscillations and followed by tripping of the grid
How to recover?

11. Earlier Approach for Power System
Stabilization
Classical way of disconnecting the loads and
thereby stabilizing the local voltage profile
Also a request has been generated to raise the
generation in order to match the load demand
However, the generation could not be raised
within time, the system may lead to
unacceptable oscillations
The controls of alternators were not as of today
which involve the microprocessor based
control/computer control strategy

12. The communication of the signals important
from control view point have been not possible
as the communication channels were not so
good
The sectors such as generation, transmission
and distribution have been almost
uncoordinated thereby landing to the problem
Virtually, there was only fixed reactors at the
end of the transmission lines and no concept of
variable reactance/ susceptance was realized

13. Modern Power System Analysis
from Control View Point
At present the power network has HVDC link,
SVS unit along with local controls at the end of
the alternators
Ideally, the system studies are carried out for
the given configuration. However, the
configuration might change because of either
addition of generation or addition of load or
removal of lines because of fault outage
The concept of power system analysis has now
changed so as to include the dynamics of the
system components

14. The network analysis once performed for the
configuration may provide some information
regarding system variables
System variables such as voltage magnitude,
phase angle between the bus, real and reactive
power requirements are almost changing in
dynamical power network
The need of developing good system model for
the study of the existing network and
proposing the location of the controller and the
control strategy as well is essential
Guideline to incorporate the controller
depending upon the system dynamics?

15. If the bus voltage is fluctuating, it is indicative
of mismatch of the Vars, therefore, the need to
design suitable controller strategy that can
balance the Var
Static Var systems (SVS) had been the only
controller to regulate the Var under the
changing system dynamics
The location of SVS as established by the
researchers and also realized by the utilities is
at the midpoint of the transmission line, the
same performance of the SVS unit may not
sustain for long as overall system dynamics is
changing in due course of time

16. Static Var Compensator (SVC)

17. The SVS control design based upon the
operating point concept may not be valid for
the large change in the operating point and
therefore, redesign/ retuning of the controller
based upon the existing system dynamics is
recommended
In general, It has been the practice to develop
the small signal model of the power network
and through this model the design of control
strategy is proposed
However, the validation of the controller
designed also must pass through the nonlinear
simulation in order to confirm the design
carried out by the small signal stability model
(perturbation model)

18. There must be a modular approach in modeling
systems and also establishing the component
interfaces suitably so as to establish the
connectivity of the various modules and
thereby getting overall system model
This modeling approach and then associated
controller design had been found to be
satisfactory i.e., the predictions based on the
model and also the validation through the
nonlinear simulation is matched

19. Impact of Multi-Controllers and need
for Control Coordination
Role of HVDC Link in modulating the real power
and damping the power oscillations in the
network
HVDC link once embedded in the existing HVAC
network may interact and therefore the proper
analysis should be carried out from the
interaction view point
The impact of short-circuit ratio at the
converter bus must also be thoroughly
investigated so as to establish the good control
design of the converter controls in situations of
weak AC system conditions

20. The harmonic interactions between AC/DC
systems should thoroughly be investigated as it
may distort the fundamental AC bus voltage if
proper filtering etc., is not done.
There is a big need to design the novel control
technology of the converter controls based on
the theory n-step ahead predictor which utilizes
the local variables at the rectified terminal and
estimates the inverter end dynamics and hence
modifies the control law and thus regulates the
power over the DC link
Exploiting the feature of fast controllability of
the HVDC link and also asynchronous
operation, many back to back HVDC links have
come up in our country and served the purpose
of area control in the sense of frequency

21. However, the only care needed at the HVDC
converter terminal is proper management of
reactive power so as to have the reliable converter
bus voltage and thus regulating the required DC
power control
The configuration of master control which is
driving the pole control of HVDC converters must
be advanced in the sense of acquiring the
feedback signals such as deviation in frequency in
either area and also real power mismatch suitably
In situations, AC/ DC network is having also SVS
unit somewhere in the link, the interaction of the
two controls, one at the converter control side and
the other at the SVS side need proper coordination
as the signals on which the entire network is
functioning may override the zone of each control
and then the tuning of the control might get
affected

22. Concept of new control philosophy
with incorporation of FACTS devices
HVDC, SVS, Controllable Series Compensation
(CSC), Phase Angle Regulator (PAR) and
Unified Power Flow Controllers (UPFC) form the
components of the FACTS devices
HVDC controls the real power excellently by the
fast control that too in between two areas.
However, reactive power delivery is not possible
by the HVDC-Link in the nearby AC network
SVS only can support / absorb Vars

28. PAR can marginally control the stability by
modulating the respective angle of the bus
wherever it is located. Of course, its
contribution is not very significant in the need
of large real power mismatch
CSC can modulate the real power by modifying
the reactance of the line based on thyristor
switching
The role of transmission line compensation with
CSC is encouraging and also, it adds in
damping the power oscillations
The control design for CSC should be properly
taken care of as the operating point concept is
changing

29. TCPAR

30. Controlled Series Capacitor(CSC)

31. UPFC control is the new dimension of real and
reactive power control in which the real and
reactive power is modulated based on the line
requirements
The two converters, one as excitation
transformer connected and the other booster
transformer connected need suitable control
strategy
The converter control in case of real and
reactive power modulation/ requirement need
suitable identification of the associated
converter control with thorough strategy for
matching the demand

32. Unified Power Flow Controller(UPFC)

34. Ideally, reactive power control is obtained
through the ET end converter control activation
and real power control is done through BT end
converter control activation
The role of DC-link capacitor is very important
to realize the control strategy
Normal presumption is, the DC-link capacitor
must maintain 1 p. u. value of voltage.
However, practically, it may not be feasible to
maintain.

35. Additional circuitry is required to maintain the
1 p. u. value of voltage of the DC-link capacitor
and also according to the control need to be
generated
While controlling the real and reactive power
with UPFC, the major block that is of
importance is VSC components firing suitably
realized by the hardware to the tune of online
conditions
This is only possible if the digital control
concept is suitably exploited and interfaced
with the firing circuits of the GTO or IGBT
which is the VSC components

36. If the signal detected by the sensors is having some
noise, the associated control generation might lead to
the improper firing and consequently unmatched
control to the tune of system requirements
Therefore, there is a need of big research in the area
of sensory technology along with the A / D converters
and followed by the digital control and then firing
circuits and finally converter output which ultimately
regulates the line requirements
This is equally applicable at the BT end VSC so as to
ensure adequate real power control. However, the
coordination of real and reactive power control is very
complicated and the control strategy must be so
selected so as to generate or absorb the reactive
power and modulate the real power accordingly

37. In an integrated power system network, the
location of UPFC if more than 1, should be
properly studied in the sense of their contribution
for overall maintenance of the variables of interest
As in the present power system network, the
multi-controllers are embedded such as HVDC,
CSC, PAR, UPFC and SVS. There is a need to
understand the positive and negative contribution
of each controllers in the overall power system
network
As it is well known, HVDC is very good in
arranging the real power over the long distances in
shortest possible time. However, its control might
generate harmonics in the AC network at the
interface of AC/DC bus. This particular point must
be properly handled while designing the harmonic
filters

38. SVS unit once operated online might generate
the harmonics too and therefore, the suitable
filtering/ harmonic elimination device be
properly installed after the thorough study of
the power system network
CSC controllers also are thyristor based and
therefore, they may also create the problem of
harmonics indirectly while being controlled
frequently for matching the online real power
requirements
PAR, as now is based on thyristor control
technology, might exhibit a similar behaviour
and therefore, a complete study of network is
to be done

39. As, all the controllers are doing the job allocated
and moreover, basic objective had been to
maintain the voltage profile and the frequency of
the power network. In process of controlling the
variables of interest, they may interact and
adversely effect the outcoming variables which in
turn may lead to the power network instability
rather than stabilization
This area is very challenging and requires
adequate technological effort to view this
particular problem of interaction of the various
controllers and afterwards effect.
This requires a coordinated approach from the
industry such as power grid, R&D and the power
sector organizations to form a group to look into
the problem in detail and propose the new
philosophy of control coordination in changing
system condition

41. The task allocated for each controller must be
well defined in the process of dedicating the
controller for the particular correction of the
variables and also, its overall impact on the
system
If the boundary is well-defined and the
controller is restrained to over-function, the
malfunctioning of the system might be avoided
There is a need to build the proper system
theory in power network for the control
coordination and multi-controller incorporation
in the power network
Blindly inducting the controllers randomly in the
network may lead afterwards installation
problem which may be detrimental from the
system operation view point

42. Thanks for Patient
Hearing