Coordinated HVDC Damping Control basedon WAMS

1
Coordinated HVDC Damping Control based on WAMS

• Wu Xiao-chen
• China Southern Power Grid Co., Ltd
• Oct., 2008

2
Background
2002.4.4
2003.2.23
2003.3.7
2005.5.13
2005.9.1
Osci. Events in CSG
2006.8.29
2008.4.21
2008.8.25
18000MW

8
3
HVAC
HVDC
3
Background
GZ
YN
GD
4
Rapid development
South China in one of the most booming area in
the world
CSG
5
WAMS in CSG
6
Challenges and Chances
Challenges to Security of Grid
Chances to new damping tech.

• Oscillatory instability, especially inter-area
  oscillation, limits the transfer capability of
  CSGs backbone
• CSG plants larger than 200 MW (Coal) or 50 MW
  (hydro) are all equipped with PSSs
• Oscillatory instability problems will be more
  severe in next 5 years

• Three HVDC links with total transmission capacity
  of 7800 MW in backbone
• HVDC modulation can change the dynamic of AC
  systems effectively
• A large scale WAMS had been established in CSG

CSG launching a project to develop HVDC Damping
Control System based on WAMS (ab. HDCS)
7
Process of the Project
6
2008.7
5
2008.4

• Closed-loop testing in the field

4

• Open-Loop trial operation and close-loop test
  operation

2007.12
3

• Installation at seven stations

2007.6
2

• Manufacture of central station, control unit

2007.3
1

• Prototype and RTDS test

2006.5
From 2005 to 2008, theory to implementation

• Theoretical study and designing

8
Overview of Key technologies

• Tuning of multiple damping controllers

• Countermeasures to time delay

• Adaptive of controller para.

• Interface to HVDC Pole Control

• Safe Failure technology

• Selection of input signals

9
Basic designing ideas

• There are two dominant oscillation modes in CSG.
  One is generators in GZ YN swing against GD
  around 0.4 Hz, while the other is generator in GZ
  swing against YN around 0.57 Hz
• The GGI HVDC, with the rectifier station locating
  in the GZ, shows good performance in damping
  oscillation mode of YN .vs. GZ. The GGII HVDC,
  with the rectifier station near the middle of
  intertie of YN GZ, has much more impact on GD
  .vs. GZYN mode than GZ .vs. YN mode
• GGI damping YN .vs. GZ oscillation GGII
  damping GD .vs. GZYN oscillation

10
Architecture of HDCS

• CSGs HDCS is a six inputstwo-outputs control
  scheme. Inputs are colleted from three 500 kV AC
  stations and three 500 kV converter stations.
  Two stations are at GZ (AnShun, GaoPo), one near
  the GZYN border (XingRen), one is at YN
  (LuoPing), and two are at GD (LuoDong, BaoAn).
  There inputs are not only for control order
  calculation, but for some criteria to start/stop
  control actions

11
Architecture of HDCS

• Centralized control scheme. The central control
  station is located at control center of CSG in
  Canton
• Control unit placed at the rectifier station of
  HVDC systems

12
Deal with Time-delay in Wide-Area Control Loops

• Time delay in control loops may deteriorate the
  performance of damping controller, even leading
  to adverse control actions
• During the design and RTDS test of CSGs HDCS, it
  is first time observe that high frequency
  constant amplitude oscillations can be caused by
  a certain value of time delay exist in control
  loops
• Lead-lag blocks plus band-pass filter are used to
  mitigate the effect of time-delay

13
Control Blocks and Tuning

• One contribution of our project is to develop a
  practical tuning method for MIMO control systems
  in bulk power system. With a hybrid stochastic
  programming method combined with GA SA, an
  optimization-based tuning algorithm is
  successfully used in tuning of CSGs HDCS.

14
Adaptive Control algorithm base on Online Prony

• An online Prony algorithm was developed in HDCS
  to monitor change of oscillation mode in real
  time environments
• In case of the current oscillation modes bias the
  center frequency of filter too much, adaptive
  algorithm will adjust parameters of filter and
  lead-lag blocks

15
Hardware and software

• Central control station has three functional
  components control computer, data storage
  computer and HMI computer
• Control unit connected to Pole Control cubicles
  of HVDC through cables has a small text display
  status monitor and a sequence of events recorder

16
Hardware and software

• The control execution rate at present is 100
  control executions per second (10-ms intervals),
  which is the same rate as the phasor measurement
  packets
• All the data are stored and managed in a
  real-time database of central control station,
  tagged with precise time

17
Delay Time in the Control Loop

• The total delay time in control loop of WADC is
  around 110 ms.
• Delay time for fiber-optic communications is less
  than 15 ms
• Data processing in central control station around
  15 ms,
• execution of command from control unit in Pole
  Control of HVDC is around 40 ms
• 40 ms is contributed by data processing in PMU

18
Safe Failure Technology

• PMU will add alarm status word to the data
  transmitted to central station in case of
  disconnect of CT of GPS failure
• Interruption of communication will trig the
  central control system to send Control-off
  command to control unit which will ramp down the
  current modulation command.
• The current HVDC active power is also inputted
  into central station to evaluate the ability of
  HVDC to execute modulation orders

19
Interface to HVDC

• The interface receives binary and analog signals
  from control units, and interprets them to Pole
  Control of HVDC
• The interface can block the input from control
  unit as soon as external signals are implausible

20
Test of HDCS

• Three tests Scheme Checks, Logic Tests and
  Remote Modulation Tests
• The Scheme Checks is used to verify the physical
  connections between components of HDCS.
• The Logic Test tests logic inside central control
  station, involving control blocks and
  block/deblock functions.
• The Remote Modulation Test verifies that the
  continuous modulation orders from central control
  station can be executed by Pole Control of HVDC
  exactly.
• At the end of tests, the HDCS was operating in
  closed-loop manner for three hours to observe its
  steady-state performance.

21
Trial operation in open-loop mode

• During trial operation, the cable connection
  between control units and cubicles of HVDC Pole
  Control were disconnected. All functions of WADC
  were normally operating except that the command
  from HDCS will not be executed by HVDC.

22
Two osci. Events during trial operation of HDCS
23
Outputs of HDCS in two osci. events
Inputs during 1st event
1V output of control unit corresponding to 200 MW
modulation of HVDC
Inputs during 2nd event
24
Torque analysis of HDCSs output
0.01
-0.01
25
Closed-loop field testing

• In the early morning of July 20, 2008, CSG
  triggered the same kind of large disturbances
  twice within one hour. Before the first
  disturbance, the connection between HDCS and Pole
  Control of HVDC was restored and the control
  system can really work. Before the second
  disturbance, the control system was shut down.
  Power system dynamics during the two events were
  recorded and compared
• The test results showed that the control system
  can increase damping ratio of critical inter-area
  oscillation mode by 0.1 (without the control
  system damping ratio 9 with the control
  system damping ratio 19)

26
Output of HDSC during the test
27
Comparison of osci. in AC lines
28
Prony analysis of the results
29
Wavelet transform of the results
Open-loop
Closed-loop
30
Conclusions

• Moving from wide-area measurements to wide-area
  stability control is a challenge in the new
  century.
• CSG HDCS exploits advances in digital/optical
  communications and computation.
• For inter-area oscillation, HDCS improved
  observability and controllability compared to
  local control
• High reliability of HDCS has been proved in
  open-loop trial operation
• Closed-loop field testing shows that HDCS can
  improve the damping of inter-area oscillations in
  CSG effectively.

31
Thank you for your attention!