with and with out snubber
TRANSCRIPT
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Int. J. Elec&Electr.Eng&Telecoms. 2013 S Prakash and R Dhanasekaran, 2013
COMPARISON OF CLOSED LOOP CONTROLLEDBUCK CONVERTER FED PMBLDC DRIVE SYSTEMS
WITH AND WITHOUT SNUBBER
S Prakash1* and R Dhanasekaran2
*Corresponding Author: S Prakash,[email protected]
Permanent Magnet Brushless DC Motor (PMBLDC) is one of the best electrical drives that has
increasing popularity, due to their high efficiency, reliability, good dynamic response and very
low maintenance. This makes the interest of modeling an ideal PMBLDC motor and its associated
Drive System in simple and lucid manner. In this paper the drive system is proposed with a buck
converter topology. It has the advantages of reduced switching losses, low inductor power loss,
reduced ripple by using a pi-filter, which in turn makes the DC link voltage to be stable. A Snubber
consists of a resistor and capacitor, where the resistor is connected in parallel with a diode. The
voltage across the capacitance cannot change instantaneously, but it increases exponentially.
So the critical rate of rise of voltage is slowed down. The capacitor stores the energy, Hence
same output can be obtained for reduced input. This improves motor efficiency. Snubber Circuit
has the advantages of reduced switching losses, great impact on control of dv/dt and di/dt,
reduced device heating, ripples and voltage transients. The modeling and simulation of the
Buck Converter controlled PMBLDC motor drive with and without snubber is done using the
software package MATLAB/SIMULINK. The operation principle of the buck converter is analyzed
with and without snubber, and the simulation results are presented in this paper to verify the
theoretical analysis.
Keywords: Permanent Magnet Brushless DC (PMBLDC) motor, Drive, Converter, Filters,
Snubbers
INTRODUCTION
Permanent magnet Brushless DC (BLDC)
motor is increasingly used in automotive,
industrial, and household products because of
its high efficiency, high torque, ease of control,
ISSN 2319 2518 www.ijeetc.com
Vol. 2, No. 1, January 2013
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Int. J. Elec&Electr.Eng&Telecoms. 2013
1 St. Peters University, EEE Department, Chennai, Tamil Nadu, India.
2 Syed Ammal Engineering College, Ramanathapuram, Tamil Nadu, India.
and lower maintenance (Krishnan, 2003),
(Krishnan and Shiyoung, 1997). A BLDC motor
is designed to utilize the trapezoidal back EMF
with square wave currents to generate the
constant torque. A conventional BLDC motor
Research Paper
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Int. J. Elec&Electr.Eng&Telecoms. 2013 S Prakash and R Dhanasekaran, 2013
drive is generally implemented via a six-switch,
three phase inverter (Rahul et al., 2003) and
Position sensors that provide six commutation
points for each electrical cycle. Cost
minimization is the key factor in an especially
fractional horse-power BLDC motor drive for
Home applications. It is usually achieved by
elimination of the drive components such as
power switches and sensors. Therefore
effective methodology should be discussed for
the desired performance and the relevant drive
system which in turn controls the motor for all
its defined applications with high efficiency, as
well as good in maintaining the speed for
variable torque. The mathematical modeling
of DC to DC converter is given by Muo (2004)
and Luo and Ye (2005). Voltage provided to
the motor is fed by high side switch, so that its
average value may be altered by changing the
switch on period. Here keeping the average
voltage across the motor constant whatever
may be the load condition by correcting theduty cycle. The motor output is taken as
feedback through PI Controller and the
corresponding signal is going to control the
High Side Switch duty cycle. The purpose of
the inductor is to oppose a change in current.
The larger you make the inductor, the less its
current changes. This changing current flows
in to the low reactance of the capacitor,
charging it.
The first capacitor offers low reactance to
the AC component and it offers infinite
resistance to the DC component. As a result
the capacitor shunts an appreciable amount
of the AC component while the DC component
continues its journey to the inductor L. The
inductor L offers high reactance to the AC
component but it offers almost zero resistance
to the DC component. As a result the DC
component flows through the inductor while the
AC component is blocked. The Second
capacitor bypasses the AC component which
the inductor had failed to block. As a result only
the DC component appears across the load
.The objective of the present work is to model
and simulate buck converter fed PMBLDC
drive systems with and without snubber.
PMBLDC MOTOR
The brushless DC motor is actually a
permanent magnet AC motor whose torque-
current characteristics mimic the DC motor.
Instead of commutating the armature current
using brushes, electronic commutation is
used. Having the armature on the stator makes
it easy to conduct heat away from the windings,
and if desired, having cooling arrangement for
the armature windings is much easier as
compared to a DC motor. A BLDC is a
modified PMSM with the modification beingthat the back-emf is trapezoidal instead of
being sinusoidal as in the case of PMSM (Luk
and Lee, 1994). The position of the rotor can
be sensed by hall effect position sensors,
namely Hall_A, Hall_B, and Hall_C, each
having a lag of 120 w.r.t the earlier one. Three
Hall position sensors are used to determine
the position of the rotor field. Model of a BLDC
motor Since a BLDC motor is easy to control,it is the motor of choice in many applications
requiring precise control of speed (Byoung-
Kuk et al., 2003; and Atef and Al-Mashakbeh,
2009).
PMBLDC motor with new power converter
topology is given by Krishnan (1997). Four
switch three phase brushless motor for low cost
commercial applications is given by Lee
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Int. J. Elec&Electr.Eng&Telecoms. 2013 S Prakash and R Dhanasekaran, 2013
(2003). The above literature does not deal with
Simulation of Buck Converter fed PMBLDC
drive system with and without snubber. This
work proposes buck converter with and without
snubber for PMBLDC Drive Systems.
SIMULATION RESULTS
Closed loop system is simulated using Matlab
Simulink. The Simulink model of closed loop
controlled buck converter fed PMBLDC drive
system without and with snubber, which is
shown in Figure 1a and Figure 2a. Here 48 V
DC is stepped down to 24 V DC using a buck
converter. The output of buck converter is
filtered using pi-filter. The output of the pi-filter
is applied to the three phase inverter, the
inverter produces three phase voltage required
by the PMBLDC motor. The technical
specifications of the drive systems are as
follows:
Input voltage : 48 V DC
Buck output voltage : 24 V DC
Pulse width to Buck MOSFET: 0.5 duty cycle
(50%)
Toff : 50%
Pulse width (33%) to Inverter MOSFET:
120 mode of operation.
Parameters of BLDC Motor
The inverter is a MOSFET bridge.
Stator resistance Rs : 2.8750 ohmsStator Inductance Ls : 8.5e-3 Henrys
Flux induced by magnets : 0.175 Webers
Back EMF Flat area : 120 degrees
Inertia : 0.8 103
Friction factor : 1 103
Pole pairs : 4
Figure 1a: Simulink Diagram of Closed Loop System Without Snubber
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Int. J. Elec&Electr.Eng&Telecoms. 2013 S Prakash and R Dhanasekaran, 2013
Stator windings are connected in star to an
internal neutral point.
The actual speed is measured and it iscompared with the reference speed, the error
is given to the PI Controller, the output of the PI
controller is one of the inputs to the comparator.
The other input is high frequency triangular
wave. The output of the comparator controls
the pulse width applied to the buck MOSFET.The pulses given to the MOSFETS 1, 3 and 5
are shown in Figure 1b.
Figure 1b: Triggering Pulses
Figure 1c: DC Input Voltage
DC input voltage is shown in Figure 1c
and its value is 48 volts. Phase voltages
of the three phase inverter are shown in
Figure 1d. The voltages are displaced by
120. Three phase currents drawn by the
motor are shown in Figure 1e. The speed
settles at 130 rpm, which is equal to the
set value.
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Int. J. Elec&Electr.Eng&Telecoms. 2013 S Prakash and R Dhanasekaran, 2013
Figure 1d: Phase Voltages of Inverter
Figure 1e: Output Currents of Inverter
Figure 2a: Simulink Diagram of Closed Loop System with Snubber
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Int. J. Elec&Electr.Eng&Telecoms. 2013 S Prakash and R Dhanasekaran, 2013
Figure 2b: Phase Voltages of Inverter with Snubber
Figure 2c: Output Currents of Inverter with Snubber
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Int. J. Elec&Electr.Eng&Telecoms. 2013 S Prakash and R Dhanasekaran, 2013
Figure 2d: Inverter Phase Voltage Without Snubber and with Snubber
Figure 2e: Inverter Output Current Without Snubber and with Snubber
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Int. J. Elec&Electr.Eng&Telecoms. 2013 S Prakash and R Dhanasekaran, 2013
CONCLUSION
Closed loop Buck controlled PMBLDC drive
systems with and without snubber is modeledand simulated using MATLAB/SIMULINK and
the results are presented. Buck converter is
proposed to reduce the input voltage to the
required value. Pi-filter is proposed at the
output of the buck converter to reduce the
ripple. This drive system has advantages like
reduced number of switches and improved
response. The scope of this paper is modeling
and simulation of closed loop Buck controlled
PMBLDC drive system with and without
snubber. The hardware implementation is yet
to be done. The contribution of authors is the
development of new simulink model for buck
converter fed PMBLDC motor drive.
ACKNOWLEDGMENT
The experiment was conducted in power
electronics laboratory, St. Peters University.
The authors would like to thank Head of theDepartment, Electrical Engineering, St.
Peters University for providing the facilities.
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