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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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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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(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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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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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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Figure 2b: Phase Voltages of Inverter with Snubber

Figure 2c: Output Currents of Inverter with Snubber


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Figure 2d: Inverter Phase Voltage Without Snubber and with Snubber

Figure 2e: Inverter Output Current Without Snubber and with Snubber


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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.

REFERENCES

1. Atef Saleh Othman and Al-Mashakbeh

(2009), Proportional Integral and

Derivative Control of Brushless DC

Motor, European Journal of Scientific

Research, Vol. 35, No. 2, pp. 198-203,ISSN 1450-216X.

2. Byoung-KukLee, Tae-Hyung Kim and

Mehrdad Ehsani (January 2001), On the

Feasibility of Four-Switch Three Phase

BLDC Motor Drives for Low Cost

Commercial Applications Topology and

Control, IEEE Transactions on Power

Electronics , APEC, Vol. 18, No. 1,

pp. 428-433.

3. Krishnan R (July 2003), A Text Book on

Electric Motor Drives, Modelling, Analysis

and Control, Prentice Hall of India Pvt.

Ltd., New Delhi.

4. Krishnan R and Shiyoung Lee (July/

August 1997), PM Brushless DC Motor

Drive with a New Power-Converter

Topology, IEEE Transactions on

Industry Applications, Vol. 33, No. 4,pp. 973-982.

5. Luk P C K and Lee C K (March 1994),

Efficient Modeling for a Brushless DC

Motor Drive, 20 th International

Conference on Industrial Electronics,

Control and Instrumentation, Vol. 1,

pp. 188-191, IECON94.

6. Luo F L and Ye H (March 2005), Energy

Factor and Mathematical Modeling for

Power dc-dc Converters, Proc. Inst.

Elect. Eng., Vol. 152, No. 2, pp. 191-198.

7. Muo E L (November 2004), Mathematical

Modelling for Power dc-dc Converters, IEEE

International Conference, pp. 323-328,

Powercon04, Singapore.

8. Rahul Khopkar, Madani S M, Masoud

Hajiaghajani and Hamid A Toliyat (June2003), A Low Cost BLDC Motor Drive

Using Buck-Boost Converter for

Residential and Commercial

Applications, IEEE International

Conference on Electric Machines and

Drives, Vol. 2, pp. 1251-1257, IEMDC03.


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