International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 4, Issue 4, April 2015
ISSN 2319 - 4847
Fault Analysis and HVDC Power Transmission
Using VSC Technique Integrated With Wind
Turbine Grid System
1.
Ashish Immanuel, Dr. A.K. Bhardwaj2
1
M.Tech. Student Electrical Engineering Dept. SHIATS-DU, Naini, Allahabad, U.P., India
2
Associate Professor Electrical Engineering Dept. SHIATS-DU, Naini, Allahabad, U.P., India
ABSTRACT
Development of Electrical Power System with increase the Demand of an Energy create many Problem in Electrical Power
System, like Sag and Swell in the Voltage level, also Swing in the Frequency value of Power System, and Instability in the
Power System .In this paper study has been made to ensure uninterrupted power supply with increased reliability and
performance of HVDC power supply by using VSC technique. Two converter stations are used in this technique, converter
station 1 used for rectification of power which is generated by wind turbine and conventional generating stations and station 2
is used to rectify DC power into three phase HVAC power at the load end. The converter station of HVDC system use
arrangement of power switches which work on the principle of VSC technique. Performance of transmission line has been
analyzed on occurrence of three phase fault and after clearance of three phase fault.
Keywords: VSC (voltage source converter), LCC (Line commutated converter), HVDC (High Voltage Direct Current),
HVAC( High Voltage Alternating Current).
1.INTRODUCTION
The efficient and uninterrupted power supply via transmission line is most important for a developing and developed
country in this modern era. It is seen from many researches high voltage DC transmission (HVDC) is more efficient
and reliable in long transmission system. HVDC transmission also make makes overall system more economical. As
per researches of these days’ shows High Voltage Direct Current transmissions have more advantage than classical 3
phase power transmission methods. This HVDC power transmission technology is superior than 3 phase AC power
transmission technology at the points as power transmission cost means power transmission cost increase more in 3
phase AC system than HVDC system for the same amount of increment in power transfer. The per unit power transfer
price will also raise more in case of AC power transmission than HVDC when distance of power transfer is increases.
The power carrying capabilities also show limitations when distance increase for power transfer in 3 phase AC system
but these limitations are not present in HVDC transmission system.
Figure 1
From above figure it is seen that HVDC power transmission becomes necessary and advantageous after certain
distance, the point beyond which HVAC power transmission becomes uneconomical and inefficient is called break-even
distance. The HVDC transmission has the capability to control the flow of power by means of fast acting solid state
devices like IGBT MOSFET etc. The problem of line compensation and asynchronous connection of grid has overcome
with HVDC transmission. The 3 phase AC grid system need to be synchronized with each other from generation to
transmission and connected load but HVDC system have no need to be synchronized with each other due to use of
rectifier and inverter circuit. HVDC power transmission network provide freedom to connect load of different
frequencies with same power transmission network.
Volume 4, Issue 4, April 2015
Page 115
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 4, Issue 4, April 2015
ISSN 2319 - 4847
HVDC power transmission can be done with two techniques i.e. Line commutated Converter (LCC) technique and
Voltage Source Converter (VSC) technique.
2. COMPARISON BETWEEN VSC-HVDC AND LCC-HVDC POWER TRANSMISSION
Line commutated converter (LCC) HVDC can be type of a Current Sourced Converter or Thyristor based Technology,
while Self Commutated Converter and Transistor (IGBT,GTO etc.) based Technology are the type of Voltage Source
converter.
Line commutated converter also known as LCC technique which have dependency upon polarity appearance across the
power switches of converter but Voltage source converter (commonly known as VSC) technique do not such
dependency. VSC-HVDC system needs auxiliary circuitry to control the power flow, thus this system have better power
flow controlling capability.
The LCC-HVDC is line commutated means switching action takes place at supply frequency i.e.at 50 or 60 Hz, while
VSC-HVDC systems have switching frequencies of 1-2 kHz. Therefore, the necessary filter size is reduced; and
therefore cost is reduced.
LCC-HVDC converters can control reactive power only and controlling depends on the firing angle of thyristors and
various FACTS devices like STATCOMs.VSC-HVDC systems can control the active and reactive power at both ends
and it can help to control the grid’s voltage and enhance power quality.
Figure.2Typical layout of VSC-HVDC transmission
The reactive power is responsible to control the voltage of the system and by controlling the active power frequency of
the system can be controlled in VSC-HVDC system, but in case of LCC-HVDC system frequency control does not
possible.
3.MATHEMATICAL MODELLING
To generate proper signal for controlling the switching action perform by power switches is main concern of sending
end converter station. These station are use to convert 3 phase current convert into Direct current and feed to HVDC
buss bar system. Generation of switching signals for power switches is based on values of direct current and quadeture
current which obtain by planks 3 to 2 conversion transformation technique. These direct value of line current and
quadeture value of line current are compare with preset values of Id and Iq in comparator circuit to generate error
signal these error signals are fed to the PI controller. Selection of PI controller is done on the basis of need to reduce the
value of steady state error as well as reduction of peak over shoot values of the output of HVDC sending end station due
to HVDC transmission system have certain magnitude based limitation over DC power transmission capabilities.
With the help inner current controller and outer current controller the DC link voltage, active and reactive power can
be controlled by VSC-HVDC system. The inner current controller (ICC) transforms the converter current and the AC
three phase voltages into the rotating direct-quadrature (d-q) co-ordinate system. The outer controllers are used to
generate and to provide reference currents (iq & id) to ICC.
Volume 4, Issue 4, April 2015
Page 116
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 4, Issue 4, April 2015
ISSN 2319 - 4847
Figure 3 inner current controllers
Figure 4 Active and Reactive power outer current controller
The schematic diagram and the vector-based equivalent circuit of a VSC station in the synchronous dq reference frame
is shown in Fig.4.
Figure. 5 Schematic diagram and equivalent circuit of a VSC station
Vc=Vs-RcIc-jωLcIc-Lcdi/dt
Ic=Is-jωsωfVs-CfdVs/dt
CdcVdc/dt=Idc-IL
Ps+jQs=3/2VsIs
Pdc=Ps - IcRc =VdcIdc
CfdVs/dts=Is-Ic-jωCfVs
Rc=total loss of vsc, Lc=filter inductor,Cf=filter capacitor
4.RESULT AND DISCUSSION
The figure 6 represents sending end voltage waveform when fault is not occurred. From this figure we see that the
voltage waveform is mostly pure sine-wave. The power, which is to be transmitted over the transmission line, is
generated by conventional generating station. The conventional generating station is also integrated with wind turbine
system. The integration of wind generation and conventional power generation makes the system reliable and ensures
the uninterrupted power supply to the consumer end.
Since the wind flow does not constant during the whole day, hence to synchronize the two types of generating plant
converter stations are used. These converter stations, consists of rectifier station i.e. converter station 1 and inverter
station i.e. converter station 2, used to transmit the high voltage direct current (HVDC) power along with voltage
source converters .
Volume 4, Issue 4, April 2015
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 4, Issue 4, April 2015
ISSN 2319 - 4847
Figure 6 Sending end voltage waveform
Figure 7 represents the load end voltage waveform during the three phase condition. During three phase fault condition
the waveform is disturbed. Because of disturbed waveform voltage sag or swell occurs at load end which affects
performance of numerous equipments and finally get damaged if fault sustains for more time.
Figure 7 Load end voltage waveform during fault.
The figure 8 shows the load end waveform after the clearance of fault, the harmonics content in the waveform is almost
removed and total harmonic distortion (THD) minimised. The THD is 88.7% without wind turbine and it gets reduced
21.3% with wind generation. Hence wind generation not only provides uninterrupted power supply but it improves
power quality also.
Figure 8 Load end voltage waveform after fault clearance.
Figure 9 shows the successful DC power transmission between two converter stations. To control the flow of DC power
after station 1 and ac power after station 2 voltage source converters are used. The VSC-HVDC system enable to use of
multi-terminal system.
Figure 9 DC voltage transmitted between station-1 and station-2
5. CONCLUSION
Simulation results show that HVDC power successfully transmitted and can be controlled with help of voltage source
converter (VSC). After the clearance of three phase fault, the voltage profile as well as power quality is improved. The
integration of wind turbine enhances the system reliability and it also serves as peak load plant.
Volume 4, Issue 4, April 2015
Page 118
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 4, Issue 4, April 2015
ISSN 2319 - 4847
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