Coordinated control for wind turbine and VSC-HVDC transmission to enhance FRT capability

PhD Antonio Luque Dr Olimpo Anaya-Lara Dr Grain. P. Adam

University of Strathclyde Institute of Energy and Environment

Outlines

Variable-speed Wind Turbines DFIG FRC

HVDC Systems Voltage Source Converter “VSC”

Case Studies - Control Strategies Case Study VSC Control Strategies

Simulation Results Wind Farms Output (V-I) Cluster Platform (V-I) HVDC Link

Variable Speed Wind Turbines DFIG and FRC Wind Turbine

Higher control flexibility and improve system efficiency and power quality : Independent control of the Pref and Qref

Partially control of the WT: DFIG Full control of the wind turbine: FRC Fast control of the WT: Power electronic system Voltage-reactive support for large transients: without altering the wind turbine dynamics

DFIG

Torque

control

Voltage or

PF control

Crowbar

Pitch

controllerWound rotor

induction generator

IGBT PWM

converters

Generator

controller

Pitch

controller

Grid side

controller

Synchronous or induction

generator

IGBT PWM

converters

AC DC AC

Source: Nick Jenkins

Fig. 2: DFIG Wind Turbine Fig. 1: FRC Wind Turbine

HVDC Systems

Technical advantage of HVDC

1. HVDC link can work between two ac system with different frequency 2. Capability to recover from power failures utilizing adjacent grids: “black start” 3. DC High transmission capacity: “No inductance or capacitance effects “ ,“no skin effect” 4. Accurate and fast control of the active and reactive power

Economic Considerations

1. For distance higher than ≈ 50 km HVAC higher investment 2. Long distance: less power losses

Source: Siemens

Fig. 3: Break curve HVAC-HVDC

HVCD System Voltage Source converter “VSC”

Technical advantage of VSC

1. Fast powers control: Pref and Qref 2. Almost instantly communication between

converters 3. DC link is totally decoupled: Different

frequencies 4. Flexibility to reverse power: Better dynamic

performance 5. Reliable performance in weak or passive

grids 6. Absorb or provide reactive power during

large transients

Technical disadvantage of VSC

1. Mature Technology 2. Switching power losses 3. No specific power protection

Economic Considerations

1. Less harmonics distortion: less filter “offshore”

2. Offshore structure smaller

Intermediate

Converter Platform

Transmission

Platform

33kV AC

132kV AC

300kV DC

132kV AC

33kV AC

Source: Max Parker Fig. 8: AC Star Connection

Case Study – Control Strategies Case Study Electrical Array for large Offshore Wind Farm

Source: Siemens

Control Strategies – Case Study

Basic VSC Control Active and reactive power control

𝑄 = 𝐸𝑔

2 − 𝐸𝑔𝑉𝑡 cos 𝑋𝑔

𝑋𝑔

P = 𝐸𝑔𝑉𝑡

𝑋𝑔sin 𝑋𝑔

Fig. 4: Back to Back Converters

P/f power controller:

Pt= P1+P2+P3

1. The dynamic responds of the P/f power controller has improved the implemented system

2. Faster response to load changes or transients, adaptive to damping support

Reactive Power Controller:

1. Control of reactive power Qt = Q1+Q2+Q3

Fig. 5: Simple VSC scheme with P/f Controller

Control Strategies – Case Study Control Strategies

Coordinated VSC Control: P/f – Vdc/f and Q Control

VSC Control Pd

T1

PWM

Inner Current Controller

Outer Current Controller

PCCBus

Ps

Qs

Isabc

Vsabc

Vdc

fref

fmeas

Ps

Qs Qsref

Id*Pmeas

Qmeas

Pref

Qref Iq*

Idq*

∑

Q1

Q2

Q3

∑ P2

P3

P1

Control strategies:

DC voltage Controller: 1. Combined with Frequency controller improve network

dynamic performance 2. Control of the medium voltage of the inverter capacitors

Third Harmonic Injection: 1. Prevent over-modulation and improving 15 % voltage

output

Control Strategies – Case Study

Fig. 7: Referential signals for the Inner and Outer current controller Fig. 6: Inner and Outer current controller

V-I First Transient

Simulation Results

Fig. 9: Wind Farm Performances Fig. 10: Cluster Collection Platform

V-I Second Transient

Simulation Results

Fig. 11: Wind Farm Performances Fig. 12: Cluster Collection Platform

Simulation Results

Transmission Platform and Grid

Fig. 13: First Transient Fig. 14: Second Transient

Simulation Results

HVDC Link 1

Fig. 15: DC voltage Performance

The results further demonstrate flexibility of the proposed control system to integrate different offshore wind farms during large transients.

It has been shown also high improvements in the fault ride-through capability of both systems. Thus, mentioned controllers have improved the recovery time from large transients in the ac and dc scheme.

By using mentioned controllers, the results has shown great controllability and flexibility of the power transferred from both schemes.

It is possible to conclude that an integration of both layouts into one scheme where DFIG and FRC wind farms are connected together; the mentioned control system should coordinate and transfer the active and reactive without causing major hazards to the control system

Conclusions