06 2015 pesgm_wllv_vsc
TRANSCRIPT
CONTACT INFORMATION
A PMU-Based State Estimator For Networks Containing VSC-HVDC links
Wei Li¹ and Luigi Vanfretti¹,²
KEYWORDS:
State estimation
VSC-HVDC link
PMU
Hybrid AC and DC state estimation
• A PMU-only state estimator (SE) algorithm that reduces the nonlinearities of network and measurement models.
• It safeguards the network model from missing meas.
• VSC-HVDC link model in the presence of different control modes.
• Allows to solve hybrid AC/DC SE simultaneously.
• Demonstrated using a six-bus test system.
Abstract:
Network Models:
The AC network model is composed of a line with series admittance and shunt admittance, and transformers.
Figure 1: AC line with transformer
VSC station model:
Figure 4: Voltage magnitudes at Bus 4 for multiple snapshots
Conclusion:
• A PMU-only state estimator for networks containing VSC-HVDC links has been introduced and validated by a six-bus test system.
• Although estimation accuracy during system dynamic changes decreases compared to that for steady state, it is expected to be greatly improved as long as the network model is updated in each measurement snapshot.
• Therefore, future work will focus on including network model update or topology processing into the state estimator.
Figure 2. Basic diagram of a VSC station
Case Studies:
A six-bus hybrid AC/DC test system is applied to validate the proposed VSC model and SE algorithm. A line breaker was opened at t = 2 s and after three cycles it was re-closed at t = 2.06 s.
Figure 5: DC voltage at rectifier side for multiple snapshots
Figure 6: DC current for multiple snapshots
CONTACTS:
1.School of Electrical
Engineering
Electric Power
Systems Department
KTH Royal Institute of
Technology
Teknikringen 33
100 44 Stockholm -SE
Email: [email protected]
Email: [email protected]
2.Statnett SF, R & D,
Oslo, Norway
E-mail:
The AC line connecting bus i and VSC station i can be represented by the AC branch model with Y = 0 to build up the relation between bus voltage and current phasors with converter voltage and current phasors.
The converter is represented by an average value model (AVM).
Vector-current control is commonly used for VSC’s high-level control scheme. Either active power or DC voltage can be selected for d-axis control; either reactive power or AC voltage can be selected for q-axis control.
Point-to-point VSC-HVDC link model:
Meas. model and SE Algorithm:
When PMUs are used for data acquisition, the state variables can be measured directly.
If the conventional meas. model is used, the choice of state variables in z can not be uniquely determined, this affects the estimation accuracy of different states. Therefore, the new measurement model is formulated as:
Performance index J(x):
Iteration procedure:
1 1.5 2 2.5 3 3.5 40.8
0.9
1
Time (s)
|V|(
p.u
.)
Vmag-true
Vmag-meas.
Vmag-est.
1 1.5 2 2.5 3 3.5 410
-5
100
Time (s)
|V|(
p.u
.)
Vmag-estimation-residual
1 1.5 2 2.5 3 3.5 4
0.95
1
1.05
Time (s)
Vrd
c(p
.u.)
Hvdc-true
Hvdcm
Hvdc-est
1 1.5 2 2.5 3 3.5 4
10-5
100
Time (s)
Vrd
c(p
.u.)
Vrdc-residual-error
1 1.5 2 2.5 3 3.5 40.6
0.8
1
Time (s)
Idc
(p
.u.)
Hvdc-true
Hvdcm
Hvdc-est
1 1.5 2 2.5 3 3.5 410
-4
10-2
Time (s)
Idc
(p
.u.)
Idc-residual-error
Figure 3. A point-to-point VSC-HVDC link model