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2015 International Conference on Control, Communication & Computing India (ICCC) | 19-21 November 2015 | Trivandrum
Supply Voltage Boosting Using a Floating
Capacitor Bridge in a 3 Level Space Vector
Modulated Inverter System for an Open-End
Winding Induction Motor Drive
Drisya V
Samina T
PG Scholar
Department of Electrical and Electronics Engineering
CET-Kerala, India-695016
Email id: [email protected]
Asst Professor
Department of Electrical and Electronics Engineering
CET-Kerala, India-695016
Email id: [email protected]
Abstract—Dual inverter fed open winding induction motor
drives can be used to minimize the problem of flux weakening
during higher speed applications. If a floating dc-link capacitor
is used in the second inverter, it can provide voltage boosting to
increase the motor voltage during higher speeds. This leads to
the minimization of supply current during high speed operation
along with the supply voltage regulation. Previous works have
been done on dual 2-level inverters. In this paper, a controller is
designed so as to adjust the capacitor voltage to maintain constant
motor voltage along with a 3-level output from a space vector
modulated dual inverter system during high speed operation.
During low speed operation motor current charges the capacitor
and the capacitor discharge is controlled so as to obtain the
required motor voltage. Entire system is modeled and simulated
in MATLAB and the results are verified.
Index Terms—open end winding induction motor drive; dual
inverter system; floating capacitor bridge
Fig. 1. OEIM drive with floating capacitor
I. I NTRODUCTION
High speed induction motor drives are having applications
in wide areas. Hence new technologies are being introduced in
the existing drive systems to improve their efficiency. A major
issue of using conventional IM drives in systems with constant
battery source like electric vehicles is that, during high speeds
motor voltage drops down thus affecting the performance of
the vehicle. Power electronic boost converters can be used to
solve this problem. But, the use of inductor in them tends to
make the system noisy and bulky [1].
Open end winding induction motor (OEIM) drives are finding their increased applications in electric vehicle systems,
replacing the conventional induction motors. Opening the
stator windings of the conventional induction motor drives
and feeding it from both sides using separate inverter systems
have their own advantages like low ripple in the motor output
torque, ability to combine different power sources, fault tolerant and less noise[2]. Thus the system can find its application
in hybrid electric vehicles.
However, in a dual inverter fed OEIM, if both inverters are fed
from separate battery sources, problem of circulating currents
978-1-4673-7349-4/15/$31.00 ©2015 IEEE
and common mode voltage arises [3].Different PWM controls
for eliminating these problems have been developed [4] - [6]. If
the second inverter is not having a battery source and is being
fed by a floating capacitor, these problems can be solved. Also,
by controlling the capacitor voltage, motor supply voltage can
be boosted at high speeds [7]-[9].
This paper describes a method for the supply voltage boosting
in an induction motor with open winding configuration. The
previous works on floating capacitor bridge configuration has
been done on two level inverter systems. Here a dual two
level inverter scheme is employed to achieve resultant three
level inversion. Three phase inverter can reduce the number
and size of capacitors required. A controller is employed for
regulating the charging and discharging of the capacitor and
thus the supply voltage regulation. The proposed method leads
to minimization of supply current through the elimination of
common mode currents.
II. CIRCUIT TOPOLOGY AND OPERATION
When the stator windings of a conventional Y connected
induction motor is opened and fed using two separate
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Fig. 3. Capacitor voltage controller
Fig. 2. Equivalent circuit of OEIM
inverters, its magnetizing branch is exposed to the difference
of the two inverter voltages. Main bridge inverter (MB)
supplies constant voltage throughout the drive operation. The
floating bridge inverter (FB), that uses the capacitor voltage
as dc supply delivers output depending on the speed of
the motor. A PI controller is used to regulate the capacitor
voltage and there by the output of the backup inverter. Thus,
motor terminal voltage is given by
Vs = Vmb + Vf b
(1)
and is maintained at a constant value.
III. MODELLING
A. Induction motor
Conventional induction motor is modeled based on the
following dynamic equations [10]
vqs
dλqs
= iqs rs + ωλds +
dt
0
vqr
= i0qr rr0 + (ω − ωr )λ0dr +
vds = ids rs + ωλqs +
dλ0qr
dt
dλds
dt
(4)
dλ0dr
(5)
dt
Where vqs : q axis component of stator voltage
vqr : q axis component of rotor voltage referred to stator
vds : d axis component of stator voltage
vdr : d axis component of rotor voltage referred to stator
0
vdr
= i0dr rr0 + (ω − ωr )λ0qr +
In the proposed model, squirrel cage induction motor is
being considered and hence rotor voltages are taken to be zero.
B. Voltage source inverter
Two voltage source inverters were mathematically modeled
based on the following equations. Pole voltages of the inverter
are given by,
vao =
vdc
vdc
s1 −
s4
2
2
vdc
vdc
s3 −
s6
2
2
(7)
vco =
vdc
vdc
s5 −
s2
2
2
(8)
Where vdc is the input dc voltage of the inverter ands1 to s6
are the gate signals to the corresponding switches.Space vector
PWM was applied to both the inverters. When the reference
voltage of MB and FB inverters are at a phase difference
of 180, three level inversion is obtained using dual two-level
inverters [11].
C. Controller
A PI controller is designed so as to control the floating
bridge inverter output voltage. Capacitor is charged from the
main inverter through the motor current and during higher
speeds it provides suitable voltage so as to maintain the
supply voltage as a constant. Capacitor voltage,
vc =
(2)
(3)
vbo =
1
c
Z
is dt
(9)
c is the value of the capacitor and is is the motor current. This
voltage is compared with a reference voltage to and given to a
PI controller so as to calculate the input of the floating bridge
inverter. Thus the output voltage of the floating bridge inverter
is varied as per requirement of the motor. Reference voltage
is selected according to the speed of operation of the motor.
IV. SIMULATION AND ANALYSIS
A 2 HP, 415 V, 1500 rpm open end winding induction motor
is modeled and fed from both ends using separate inverters.
Space vector PWM is applied to both inverters. Motor is
started on no load and it accelerates so as to reach the rated
speed of 314 rad/sec. At t = 1sec, speed of the machine
is increased to 439.82 rad/sec in order to verify the supply
voltage during high speed region. At t = 1.5 sec a load torque
of 8 Nm is applied.
Separate analysis is conducted for single inverter operation
which is same as the conventional induction machine operation
and for dual inverter fed open winding configuration.
(6)
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Fig. 4. MATLAB-simulink model of the proposed system
Fig. 7. Motor characteristics with MB only(a) Torque (b) Current (c) Speed
A. With only MB inverter
When only main bridge inverter is connected, simulation
results are shown in Fig 7 to Fig 9. From the simulation
results, it is clear that when only main inverter is used to
supply the motor, stator voltage is reduced during high speed
operation. Thus motor cannot reach the higher speeds.
B. Using MB and FB inverters
Fig. 5. Three phase output voltage of main inverter
Using main bridge and floating bridge inverters, and including the proposed controller, the simulation results are as shown
in Fig 10 to Fig 14.
From the simulation results, it is clear that, when the
proposed controller is used, motor voltage remains constant
even during higher speeds by controlled discharge of the
capacitor. When the floating bridge inverter is connected,
during the higher speed region, the output of the dual inverter
system is similar to a 3 level inverter. Also common mode
voltages are eliminated from the dual inverter system and
hence there is no common mode circulating currents also.
Advantages of the proposed system are
•
•
•
Regulation of motor voltage without the use of power
electronic boost converters.
Elimination of common mode voltage between the two
inverters.
Realization of 3-level inverter using two 2-level inverters.
V. CONCLUSION
Fig. 6. Stator voltage of the motor with MB inverter only
A dual inverter fed open end winding induction motor drive
system was developed with a floating capacitor feeding one of
the inverters. A PI controller was used to regulate the capacitor
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Fig. 11. Common mode voltage in the proposed system
Fig. 8. Inverter phase voltage (a) MB Voltage (b) FB Voltage
Fig. 12. Motor characteristics (a) Torque (b) Current (c) Speed
Fig. 9. Dual inverter phase voltage
voltage so as to maintain the motor voltage as a constant
even during high speed operation. The proposed dual inverter
system can produce a 3-level output and also eliminate the
common mode voltage thus eliminating the common mode
circulating currents.
R EFERENCES
Fig. 10. Stator voltage of the dual inverter fed motor
[1] Du, B. Ozpineci, L.M. Tolbert and J.N. Chiasson. DC-AC Cascaded
H-bridge multi-level boost inverter with no inductors for electric/hybrid
electric vehicle applications. IEEE Trans. Ind. Appl., vol. 45, no. 3,
May/June 2009, pp. 963-970 .
[2] H. Stemmler and P. Guggenbach. Configurations of high-power voltage
source inverter drives. Proc. EPE 93., vol. 1, 1993, pp. 7-14 .
[3] ApurvaSomani, Ranjan K. Gupta, Krushna K. Mohapatra, Ned Mohan.
On the Causes of Circulating Currents in PWM Drives With Open-End
Winding AC Machines. IEEE Transactions on industrial electronics,
VOL. 60, NO. 9, SEPTEMBER 2013 .
[4] S. KazemHoseini, JafarAdabi, A. Sheikholeslami and Alireza Nami4.
Current Controlled-Based Modulation Strategies for Common-Mode Voltage Mitigation in PWM Inverters-Fed AC Motor Drive Systems. 15th
International Power Electronics and Motion Control Conference., EPEPEMC 2012 ECCE Europe, Novi Sad, Serbia.
168
[5] M. R. Baiju, K. K. Mohapatra, R. S. Kanchan, and K. Gopakumar. A
dual two-level inverter scheme with common mode voltage elimination
for an induction motor drive. IEEE Trans. Power Electron., vol. 19, no.
3, pp. 794?805, May 2004.
[6] V.T. Somasekhar, K. Gopakumar, A. Pittet and V.T. Ranganathan . PWM
inverter switching strategy for a dual two-level inverter fed open-end
winding induction motor drive with a switched neutral. IEE Proc Electronic Power Appl., Vol 149,No 2, Mairli 2002 pp. 152-160.
[7] J. Ewanchuk, J. Salmon . A Square-wave Controller for a high speed
induction motor drive using a three phase floating bridge inverter 2010
IEEE Energy Conversion Congress and Exposition (ECCE)., pp.25842591, 12-16 Sept. 2010.
[8] R.U.Haque, A.Kowal, J.Ewanchuk, A.Knight, J.Salmon . PWM control
of a dual inverter drive using an open-ended winding induction motor
IEEE conference on applied power electronics Conference and exposition(APEC)., March 2013.
[9] J Ewanchuk, John Salmon, Chris Chapelsky. A method for supply voltage
boosting in an open ended induction machine using a dual inverter system
with a floating capacitor bridge IEEE transactions on power electronics.,
vol. 28, no.3, pp1348-1357, March 2013.
[10] Burak Ozpineci, Leon M.Tolbert. Simulink Implementation of Induction
Machine Model-A Modular Approach IEEE International Electric
Machines and Drives Conference.,2003,pp 728-734.
[11] Shivakumar, E.G., Gopakumar, K., and Ranganathan, V.T. Space vector
PWM control of dual inverter fed open-end winding induction motor drive
IEEE-APEC-2000., pp. 394-404 .
169