ABSTRACT:
Novel
power factor corrected ac-dc rectifier topologies suitable for induction motor
drive based elevator application are proposed. These converters make use of
coupled inductor for power conversion and are capable of providing high voltage
gain at low duty cycle and high efficiency. The current flowing through the
coupled inductor is controlled through a feedback control loop to achieve unity
power factor. The THD value of the current is observed to be approximately 4.8%
which is within the limits prescribed by various standards. With the use of coupled
inductor, the voltage stress of the switches operating at high frequency is
reduced, which reduces switching losses. The loss comparison with the
conventional converters shows a reduction of at least 22% of losses. The
proposed scheme also results in reduction of the variable frequency drive’s dc
link capacitance value as an ultra-capacitor bank is interfaced with the dc
link through a bidirectional converter for improving efficiency and providing
transient power requirements. This also helps in increasing the reliability and
dynamic response of the system. The settling time for a step change in voltage
reference is observed to be reduced by nearly 50%. Proposed topologies and
schemes are validated through MATLAB/Simulink simulations and experiments.
KEYWORDS:
1. Power
Factor Correction
2. Ac-dc
conversion
3. Single
phase controlled rectifier
4. Three
phase controlled rectifier
5. Reliability
and ultra-capacitor
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Fig. 1 Block diagram of an elevator system
EXPECTED SIMULATION RESULTS:
Fig. 2(a) Input current and voltage of the
proposed1-ph rectifier system with PFC; (b)3-ph current for PFC operation of
proposed rectifier configuration; (c) The dc link voltage step changes for 10μF
and 500μF dc link capacitor; and (d) Ultra-capacitor current.
CONCLUSION:
Novel AC-DC PWM
rectifier topologies for 1-ph and 3-ph systems, based on high voltage gain
dc-dc converter principle, were proposed, analyzed and validated through experiments
and simulation studies. A major advantage of these topologies is that it is
possible to achieve higher voltage gain at lower duty ratio. The operation
symmetry is maintained. Input power factor correction is achieved. The use of
coupled inductors enhances gain, but it also increases the ripple in the input
current as the turns ratio is increased. Thus, there is a trade-off between the
achievable gain and the ripple.
The losses of the
proposed converter are compared with the conventional ac-dc converter, and it
was observed that there is a reduction of about 22% losses. The losses
estimated through experimental studies also reduced from 29W to 24W when the proposed
topology was used. This shows a reduction of 17% losses in experiments.
Therefore, the proposed converter gives higher efficiency than the conventional
ac-dc converters. It was also observed that the use of an auxiliary storage reduced
the dc link capacitance value from 500 μF to 10 μF for a 1-ph system. For the
3-ph system, the auxiliary unit can be used as a support during the grid
voltage sag condition thereby reducing the dc link capacitance requirement. A
low value of dc link capacitance not only helps in reducing the size and improving
the reliability of system, but also in improving the dynamic response of the
system.
The complete
system was tested in hardware and the results were presented. A detailed
description of the thought process behind the development of the proposed
converter was also presented. The same thought process can be extended to the development
of such converter topologies. The voltage stress on switch S2 and S3 reduces to
1/8th of its value as compared to the conventional topology. But, the value of
peak current increases ‘n’ times. The increase in peak current increases the
high frequency current ripple in the input side. However, the duty cycle is
decreased with increase in the value of ‘n’. Therefore, the overall efficiency
of the converter is increased.
The ac-dc
topologies proposed in this paper are unidirectional. But, they can be made
bidirectional by connecting a controllable switch across the diodes. This
scheme is useful for the scenarios where the loads are regenerating. These
bidirectional topologies can also be used as dc-ac converters to feed power into
the grid. Thus, the scope of the proposed schemes is very wide and relevant.
REFERENCES:
[1] Ashok B.Kulkarni, Hein Nguyen,
E.W.Gaudet, “A Comparative Evaluation of Line Regenerative and Non-
regenerative Vector Controlled Drives for AC Gearless Elevators” 35th IAS
Annual Meeting and World Conference on Industrial Applications of Electrical
Energy, Rome, Italy: Institute of Electrical and Electronics Engineers Inc.,
Piscataway, NJ, Oct 2000, vol. 3.pp 1431 – 1437.
[2] "IEEE Std. 519", IEEE Recommended
Practices and Requirements for Harmonic Control in Electric Power Systems,
1992.
[3] "IEC 1000-3-2 Int. Std.",
Limits for Harmonics Current Emissions (Equipment Input Current16 A per Phase),
1995.
[4] "IEC 61000-3-4", Limitations
of Emission of Harmonic Current in Low- Voltage Power Supply Systems for
Equipment with Rated Current Greater than 16 A, 1998.
[5] J. Hahn, P. N. Enjeti and I. J. Pitel,
"A new three-phase power-factor correction (PFC) scheme using two
single-phase PFC modules," in IEEE Transactions on Industry Applications,
vol. 38, no. 1, pp. 123-130, Jan/Feb 2002.
