06 2015 pesgm_wllv_vsc

1
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: [email protected]. 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 4 0.8 0.9 1 Time (s) |V|(p.u.) Vmag-true Vmag-meas. Vmag-est. 1 1.5 2 2.5 3 3.5 4 10 -5 10 0 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) Vrdc(p.u.) Hvdc-true Hvdcm Hvdc-est 1 1.5 2 2.5 3 3.5 4 10 -5 10 0 Time (s) Vrdc(p.u.) Vrdc-residual-error 1 1.5 2 2.5 3 3.5 4 0.6 0.8 1 Time (s) Idc (p.u.) Hvdc-true Hvdcm Hvdc-est 1 1.5 2 2.5 3 3.5 4 10 -4 10 -2 Time (s) Idc (p.u.) Idc-residual-error Figure 3. A point-to-point VSC-HVDC link model

Upload: luigi-vanfretti

Post on 12-Aug-2015

6 views

Category:

Engineering


0 download

TRANSCRIPT

Page 1: 06 2015 pesgm_wllv_vsc

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:

[email protected].

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