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A NOVEL ON SUPPRESSION OF NEGATIVE SEQUENCE CURRENTS IN HIGH SPEED
ELECTRIC RAILWAY BY USING POWER QUALITY COMPENSATOR.
1
.Sravani.p, 2. Kiran kumar.p
1
M.Tech Student of JNTUA,EEE Dept,Kuppam Engineering college,Chittor,A.P, India
2
Asst.prof, EEE Dept, JNTU,Anantapur,Kuppam Engineering College,Chittor, AP-India,
Abstract- In order to suppress negative sequence currents harmonics for full bridge circuit of
four quadrant converter in high speed electric railway, a method is proposed i.e., pulse width
modulation. The four-quadrant converter of EMUs is single-phase full bridge circuit, which
enables two-direction flow of electrical energy, and to ensure that the power factor of the net
side to approximate. Each unit of the EMUs adopts parallel two level by the two groups of fourquadrant converters through the transformer winding, through which can further reduce the
harmonic currents of the grid side. By switching devices appropriately through turn-on and
turn-off control, the frequency of the converter input voltage us can be the same with that of the
grid voltage. Four-quadrant converter can achieve unity power factor in traction and braking
conditions. In regenerative braking condition, as to achieve the purpose of a stable DC voltage
and unity power factor ,the phase between U and I should be 180 degrees. when the fourquadrant converter is running at the form of parallel two-level, the harmonic characteristics is
similar with the double-time switch frequency. As a result, interlaced PWM converters can
reduce the harmonic grid current with the same switching losses in the same frequency.
Keywords-single phase full bridge circuit, crh5 emu’s ,railway static power conditioner, negative
sequence currents, electric railway.
I. INTRODUCTION
In railways negative sequence currents become a signifificant
problem , to solve this
problem a power quality compensator is proposed. Which is constituted by RPC, two thyristor
controlled reactors, two thyristor controlled filters. Normal filters are not reduces the negative
sequence currents it only suppress the harmonics. CRH5 EMUs are produced by the Changchun
Railway Vehicles Factory. The maximum operating speed of crh5 emu’s is up to 250km/h
and they are running from Harbin to Beijing. CRH5 EMUs adopt 8 grouping, and may even
be linked to run the two groups. EMUs have two proportionately independent main traction
systems, one is constructed of three EMUs units and a trailer, the remaining is constructed of
two units EMUs and two trailers.EMUs can withstand upto very low temperature. The bogies
of crh5 emu’s made of Alstom Pendilino i.e., it has lite weight bogies.
Harmonic Filters may be used to less intense, and in some cases eliminate power
system harmonics. Non-linear loads like rectifiers, converters, home electronic appliances,
and electric arc furnaces giving rise to extra losses i.e., harmonics in power equipment like tr
motors, capacitors and transformers. They can also cause other serious problems, when
obstructing with control systems and electronic devices. Placing filters near the harmonic
sources and it can effectively decrease harmonics. Conventional filters are used for large,
easily identifiable sources of harmonics, and designed to meet the demands of the actual
applications. They are the most cost efficient in the view of eliminating harmonics. These
filters contains capacitor banks with suitable tuning reactors and damping resistors. Active
filters based on power electronic converters for small and medium size loads with high
switching frequency, it may be a more aesthetically pleasing solution.
Regulation of the power factor to increase the transmission capability and reduce
transmission losses. Shunt capacitors are primarily used to improve the power factor in
transmission and distribution networks, resulting in reduced network losses, improved
voltage regulation and capable capacity use effectively. Figure shows a plot of terminal
voltage versus line loading for a system that has a shunt capacitor installed at the load bus.
Improved transmission voltage regulation can be obtained during heave power transfer
conditions when the system consumes a large amount of reactive power that must be replaced
by compensation. At the line surge impedance loading level, the shunt capacitor will reduce
the line losses by more than 35%. In distribution and in industrial systems, it is common to
use shunt capacitors to compensate for the highly inductive loads, thus acquiring decreased
launch system losses and network voltage drop.
II. STRUCTURE OF SYSTEM
MMM
Fig.2 shows the four-quadrant converter equivalent circuit. By switching devices
appropriately through turn-on and turn-off control, the frequency of the converter input
voltage us can be the same with that of the grid voltage
Here, s1 u is the fundamental component of AC voltage, 11 i is the current fundamental
component of 1 i,ω is the frequency of the grid voltage. The following formula is relative to
the fundamental phase
⃗ N=𝑈
⃗ S1 +RS⃗𝐼11 +jѠLS𝐼11
𝑈
……………………………(1)
Four-quadrant converter can achieve unity power factor in traction and braking conditions.
As a result, U and I is in the same phase in traction condition. From formula (1) we can see
the phase diagram in Figure 3 (a) U lags behind U. In regenerative braking condition, as to
achieve the purpose of a stable DC voltage and unity power factor ,the phase between U and
I should be 180 degrees, which is shown in Figure 3 (b) U lags behind U We can see that as
long as properly control the amplitude and phase of 1 S U , it will be able to control the
amplitude and phase of I
Here, s1 u is the fundamental component of AC voltage, 11 i is the current fundamental
component of 1 i,ω is the frequency of the grid voltage. The following formula is relative to
the fundamental phase
⃗ N=𝑈
⃗ S1 +RS⃗𝐼11 +jѠLS𝐼11
𝑈
……………………………(1)
Four-quadrant converter can achieve unity power factor in traction and braking conditions.
As a result, U and I is in the same phase in traction condition. From formula (1) we can see
the phase diagram in Figure 3 (a) U lags behind U. In regenerative braking condition, as to
achieve the purpose of a stable DC voltage and unity power factor ,the phase between U and
I should be 180 degrees, which is shown in Figure 3 (b) U lags behind U We can see that as
long as properly control the amplitude and phase of 1 S U , it will be able to control the
amplitude and phase of I
III. SIMULATION RESULTS
Before using the second loop filter see the negative sequence currents in the below waveform
Fig(1): voltage and current waveforms at inverter side
After using the second loop filter see the waveforms without negative sequence currents are
shown below
Fig.voltage and current waveforms at load side
IV CONCLUSION
This article studies the mathematical model and simulation of four-quadrant converter
of CRH5 EMUs, specially studies the current distribution under the steady condition.
Compared with the original “Shaoshan” series locomotives, EMUs use PWM rectifier, thus
the power factor is close to 1 and the low harmonic content is obviously decreased, but the
high-order harmonic content is slightly increased. In this paper, the preparation of the electric
locomotives and EMUs simulation software, data interface can be called for other software to
further analyze the spread law of the harmonic grid current in traction and the probability
distribution of harmonic currents and so on.
The effectiveness of the converter operation is verified for the harmonic supervision
and cancellation when transient or time varying harmonics exhibit in power systems. The
unique features of converter analysis, such as frequency identification without prior
knowledge of frequency and the ability to identify damping factors, are useful to power
system quality study.
Further studies can be carried out for power quality study. Just as converter analysis
was used with harmonic selective active filters, converter analysis may be applied to other
measures to improve power quality.
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