Group 8 hvdc

Simulation of VSC HVDC
Transmission System and Fault
Analysis
DEPARTMENT OF EEE,
NATIONAL INSTITUTE OF TECHNOLOGY
TIRUCHIRAPPALLI-620015

Project Members
Aaron Saldanha 107111002
Akam Singh Patel 107111011
Mahesh Bolavakar 107111026
John D. Cheerotha 107111038
GROUP 8 ,B.TECH. FINAL YR. , NIT TRICHY 2

Project Aim
Simulation of VSC based HVDC line in MATLAB / SIMULINK
Simulation and Analysis of various DC Fault Condition

 This project aims at the implementation of VSC based HVDC systems, which will help
bidirectional power flow along with stable operation of the system during disturbances like
Faults.
 A PWM control system has been designed for the sending-end of the HVDC link.
 The control strategy is studied and corresponding performance is observed in MATLAB/
SIMULINK.
 The simulation results verify that the PWM controller has good transient and steady state
performance.

What is HVDC …?
1. A high-voltage, direct current (HVDC) electric power transmission system uses
direct current for the bulk transmission of electrical power, in contrast with the
more common alternating current (AC) systems.
2. For long-distance transmission, HVDC systems may be less expensive and suffer
lower electrical losses.
3. For underwater power cables, HVDC avoids the heavy currents required to
charge and discharge the cable capacitance each cycle.
4. For shorter distances, the higher cost of DC conversion equipment compared to
an AC system may still be warranted, due to other benefits of direct current
links.

Types of HVDC Converters
Line Commutated Converter (LCC)
− Current Sourced Converter
− Thyristor based Technology
Voltage Sourced Converter (VSC)
− Self Commutated Converter
− Transistor (IGBT, GTO etc.) based Technology

LCC v/s VSC

Why VSC over LCC….?
LCC VSC
 Use semiconductors which can
turn on by control action
 Use semiconductors which can
turn on or off by control action
 Requires stronger AC systems  Operates into weaker AC
systems
 Requires additional equipment
for “Black” start capability
 “Black” start capability
 Generates harmonic distortion,
AC & DC harmonic filters
required
 Insignificant level of harmonic
generation, hence no filters
required
 Coarser reactive power control  Finer reactive power control
 Large site area, dominated by
harmonic filters
 Compact site area, 50 – 60% of
LCC site area
 Power is reversed by changing
polarity of the converters
 Power is reversed by changing
direction of current flow

What is VSC HVDC System…?
VSC-HVDC is a new dc transmission system technology. It is based on the voltage source
converter, where the valves are built by IGBTs and PWM is used to create the desired voltage
waveform. With PWM, it is possible to create any waveform (up to a certain limit set by the
switching frequency), any phase angle and magnitude of the fundamental component. Changes
in waveform, phase angle and magnitude can be made by changing the PWM pattern, which can
be done almost instantaneously. Thus, the voltage source converter can be considered as a
controllable voltage source.

Components of VSC - HVDC
a. Physical Structure
b. Converters
c. Transformer
d. Phase Reactors
e. AC Filters
f. DC Capacitors
g. DC Cables
h. IGBT Valves
i. AC Grid

Layout of Project

HVDC allows power transmission between unsynchronized AC transmission systems.
Since the power flow through an HVDC link can be controlled independently of the phase angle
between source and load, it can stabilize a network against disturbances due to rapid changes in
power.
HVDC also allows transfer of power between grid systems running at different frequencies, such
as 50 Hz and 60 Hz. This improves the stability and economy of each grid, by allowing exchange
of power between incompatible networks.

HVDC can transfer power between separate AC networks. HVDC power flow between separate
AC systems can be automatically controlled to support either network during transient
conditions, but without the risk that a major power system collapse in one network will lead to a
collapse in the second.
HVDC improves on system controllability, with at least one HVDC link embedded in an AC grid in
the deregulated environment, the controllability feature is particularly useful where control of
energy trading is needed.

Part 1 : Three Phase Sinusoidal PWM
Rectifier

Supply Voltage data
Output of Three Phase Source (Vp-ground) =325kV (AC)
Output of Three Phase Source (Vp line to line) = 3X (Vp-ground)
=563kV (AC)

Supply Voltage (Phase Voltage)

Three Phase Rectifier Unit

Calculations for Rectifier
Input voltage to the Rectifier (Vp - AC) = 325kV (AC)
Vout = (3 3 × Vp)/π
= 1.654*Vin
= 537.5kV (DC)
This is the Theoretical value.
Output voltage of the Rectifier (Vdc) = 503kV (DC)
This is the Experimental Value.

Output of Rectifier (SIMULINK)

VDC (approx. 500kV)

IDC (approx. 4.325kA)

PDC (approx. 2175MW)

Pulse Sequence Generation

Part 2: Three Phase Inverter

Calculations for Inverter
Input voltage to the Inverter (Vdc) = 537.5kV
Peak value of output line voltage = 1.10266*Vdc
= (4 × Vp × cos(π/6))/π
= 592.6kV (AC Line-Line)
= 592.6kV/√3
= 342.13kV (AC Line-Ground)
This is the Theoretical value.
Output voltage of the Inverter = 580kV (AC Line-Line)
= 334.8kV (AC Line-Ground)
This is the Experimental Value .

Output of Inverter

Three Phase AC output

Line-Line AC (approx. 580kV)

Line-Ground AC (approx. 320kV)

AC Filter cum Load

DC Faults
The DC Link in subjected to fault at t=0.2 at the mid point of the link.
1) Short Duration Faults . Time Period ≤0.2s
2) Medium Duration Faults. Time Period 0.2 ≤ 0.6s
3) Long Duration Faults . Time Period ≈ 1s

a) Short Duration Fault

b) Medium Duration Fault

c) Long Duration Fault

Advantages
A long distance point to point HVDC transmission scheme generally has lower overall investment
cost and lower losses than an equivalent AC transmission scheme.
HVDC conversion equipment at the terminal stations is costly, but the total DC transmission line
costs over long distances are lower than AC line of the same distance.
HVDC requires less conductor per unit distance than an AC line, as there is no need to support
three phases and there is no skin effect.
HVDC transmission losses are quoted as about 3.5% per 1,000 km, which is less than typical AC
transmission losses.

Applications
a) Endpoint-to-endpoint long-haul bulk power transmission, usually to connect a remote generating
plant to the main grid.
b) Increasing the capacity of an existing power grid in situations where additional wires are difficult
or expensive to install.
c) Power transmission and stabilization between unsynchronized AC networks, with the extreme
example being an ability to transfer power between countries that use AC at different
frequencies. Since such transfer can occur in either direction, it increases the stability of both
networks by allowing them to draw on each other in emergencies and failures.
d) Stabilizing a predominantly AC power-grid, without increasing fault levels.
e) Integration of renewable resources such as wind into the main transmission grid. HVDC overhead
lines for onshore wind integration projects and HVDC cables for offshore projects have been
proposed in North America and Europe for both technical and economic reasons. DC grids with
multiple voltage-source converters (VSCs) are one of the technical solutions for pooling offshore
wind energy and transmitting it to load centers located far away onshore.

Conclusion
This project work dealt with the theoretical concepts of the PWM controller scheme
implemented in the simulation of VSC based HVDC system with fault analysis.
The controller has been developed and then implemented in MATLAB in order to trigger the
VSC. The model used in MATLAB/SIMULINK consists of 6-pulse IGBT VSC based HVDC system.
The performance of the system under normal condition and under different types of faults is
comprehensively analyzed.

Thank You…!!

Group 8 hvdc

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