International Journal of Advanced Engineering Technology
E-ISSN 0976-3945
Review Article
A NOVEL MATLAB/ SIMULINK MODEL OF A SOFTSWITCHING CONVERTER FOR BRUSHLESS DC MOTOR
DRIVES
Souvik Ganguli
Address for Correspondence
Assistant Professor, EIED, Thapar University, Patiala
Email: souvik.ganguli@gmail.com
ABSTRACT
Brushless DC motors have widely been used in industrial applications because of its low inertia, fast response, high power
density, high reliability and maintenance-free operation. It is usually supplied by a hard-switching PWM inverter, which
normally has low efficiency since the power losses across the switching devices are high. In order to reduce these losses, many
soft switching inverters have so far been designed. Unfortunately, there are many drawbacks, such as high device voltage stress,
large DC link voltage ripple and complex control scheme. This paper proposes a new IGBT based soft-switching converter for a
brushless dc motor drive using Matlab Simulink. The simulation results truly justify the design. Moreover, the results like stator
current, rotor speed, output torque and voltages are compared with the model without soft-switching techniques.
KEYWORDS Brushless DC motor drive, Pulse Density Modulation (PDM), Pulse Width Modulated (PWM) Inverter, SoftSwitching, Zero-Voltage-Transition (ZVT).
INTRODUCTION
The earliest work reported in the literature involved
the speed control of a brushless DC motor using
pulse density modulation (PDM) in a soft-switched
inverter. The implementation of zero voltage
switching and pulse density modulation enabled
increased switching frequency, which allowed more
precise inverter control. Moreover, MOS-controlled
thyristors (MCTs) were used as the power
semiconductor devices in the inverter [1]. Few years
later, a DC-AC converter for variable AC drives
using soft commutation technique was developed.
The converter designed combined the advantages of a
soft commutated converter and those of PWM control
[2]. A double stage DC-AC-AC converter including
a high frequency transformer link was reported in [3].
It integrates the soft switching techniques and was
intended to be used for driving two high voltage (400
V) high power (18 KW) synchronous brushless DC
motors. Power switches were realized with IGBT
transistors for the second stage. However, for the first
stage, MOSFETs were used. [4-5] introduced a softswitching inverter based on transformer which can
generate DC link voltage notches during chopping
switches commutation to guarantee all switches
working in zero voltage switching condition. [6]
outlines the use of Hall sensors and PWM control in
the design of a driver IC for three-phase full wave
control of a brushless DC motor. A resonant pole
inverter was developed in [7] which prove unique to
a BLDC drive system and also easy to implement.
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This inverter possesses the advantages of low
switching power loss, low inductor power loss, low
device voltage stress, and simple control scheme. A
power converter with inrush current protection was
designed in [8]. A zero voltage transition (ZVT)
parallel resonant DC link voltage source inverter
(VSI) was proposed in [9-10] for brushless DC
machine used in electric vehicle propulsion. A zerovoltage-transition (ZVT) soft-switching converter for
brushless DC motor drives was presented in [11]. The
proposed ZVT converter possesses the definite
advantages that both main transistors and diodes can
operate with zero-voltage switching (ZVS), unity
device voltage and current stresses. It is a very
desirable feature for high frequency switching power
conversion where power MOSFETs are used. This
converter is especially advantageous for brushless
DC motor drives, such as electric scooter
applications. Another zero voltage transition (ZVT)
three-phase soft-switching voltage source inverter
(VSI) was proposed for BLDC motor drive systems
in [12]. The proposed ZVT-VSI consists of three
switches, six diodes, three capacitors and an inductor.
Soft switching operation of all switching devices in
inverter was realized by adding auxiliary resonant
unit to DC link of conventional one. Auxiliary
switches were also operated under zero current
switching (ZCS) or zero voltage switching (ZVS).
The proposed inverter is suitable for PWM operation.
The soft-switching operation of the ZVT-VSI is
explained in terms of modes. [13] presents a new low
International Journal of Advanced Engineering Technology
cost, highly efficient, reliable and compact motor
drive topology for residential and commercial
applications, such as building air-conditioning,
appliances etc. The drives consist of a three-phase
permanent magnet brushless DC (BLDC) motor, a
soft switching dc-dc converter and a three-phase
inverter containing six silicon-controlled rectifiers
(SCRs). A micro controller or a digital signal
processor (DSP) is used to control the overall system.
The proposed system is fault tolerant due to its
current regulated nature; where it can even withstand
a solid short-circuit at its output terminals. The drive
is low cost with respect to the commercially used
IGBT-based systems. Since all the switches used in
the output three phase inverter are current
commutated, and the dc-dc converter uses softswitching techniques, this drive has much lower
switching losses than the conventional PWM drive. A
simple soft switch inverter is proposed in [14] which
are applicable to battery-fed BLDC drive systems.
This inverter has low switching-power loss, less
voltage stress on the main switches, simple control
scheme and easy to implement. Thus from the
literature survey we found that several soft-switching
techniques are applied to brushless dc motor drives.
Our aim was to develop a novel soft-switching
converter using Matlab Simulink. Simultaneously we
have made a simulink model without soft-switching
converters and made a comparison between the two
with respect to stator current, rotor speed, torque and
voltage.
SOFT-SWITCHING REQUIREMENTS
Soft Switching converters improve torque by
following requirements:
All switches work under soft-switching
condition, so their power losses are small.
For the purpose of the phase current control, it is
necessary to modulate the phase voltage. This is
especially important at low speed, when the
motor back-emf is low.
The voltage gain of the converter should be
maximum possible in order to extend the
constant power operation mode and increase the
maximum speed.
Large fall time of phase current results in
negative torque and this time can be reduced if
demagnetizing voltage is as high as possible.
It is necessary, at the same time, to control
current in one phase and force demagnetizing of
IJAET/Vol.II/ Issue II/April-June, 2011/164-171
E-ISSN 0976-3945
some other phase of the motor. This is crucial for
reduction of the torque ripple.
Converter has to be single rail in order to reduce
the voltage stress across the semiconductor
switches.
The power converter must not require bipolar
windings or rely upon the motor construction.
A low number of semiconductor switches is
desirable.
SWITCHING STATES
Phase current in IGBT based power converter is
controlled by selecting from three possible
states:
Both switches in a phase leg are on and phase is
energized from power supply (220 V) here
(magnetizing stage).
Both switches in a phase leg are off. Phase
current commutates to the diodes and decays
rapidly (demagnetizing stage).
Only one of the switches is off. The voltage
across the winding is near zero and phase current
decays slowly (freewheeling).
CIRCUIT OPERATION WITHOUT SOFTSWITCHING
Current is passed through one of the stator windings.
Torque is generated by the tendency of the rotor to
align with the excited stator pole. If the poles a1 and
a2 are energized then the rotor will align itself with
these poles. Once this has occurred it is possible for
the stator poles to be de-energized before the stator
poles of b1 and b2 are energized. The rotor is now
positioned at the stator poles b1 and b2. This sequence
continues through c before arriving back at the start.
This sequence can also be reversed to achieve motion
in the opposite direction. This sequence can be found
to be unstable while in use. The direction of the
torque generated is a function of the rotor position
with respect to the energized phase, and is
independent of the direction of current flowing
through the phase winding. Continuous torque can be
produced by intelligently synchronizing each phase’s
excitation with the rotor position. The amount of
current flowing through the BDLC winding is
controlled by switching on and off power electronic
devices, IGBTs here, which can connect each BLDC
phase to the DC bus. The model without softswitching is simulated using MATLAB Simulink
which is shown in Fig.1.
International Journal of Advanced Engineering Technology
E-ISSN 0976-3945
Fig.1 BLDC without soft switching
PROPOSED SOFT-SWITCHING MODEL
RESULTS & DISCUSSIONS
The soft-switching circuit uses 3 IGBTs .The IGBTs
The stator currents, rotor speed, torque and voltage
act as switches to provide a series of DC pulses to the
outputs of both the BLDC models-without and with
brushless dc motor. Since brushless dc motor
soft-switching are compared using the simulation
frequency controls are for 3-phase motors, there are 3
results obtained. We compared the outputs of stator
IGBTs, one for each phase. IGBT connects each
current of both the without soft switching model and
motor terminal to the positive side of the DC supply
IGBT soft switching model which are shown in Fig.
220 V. In that way, each terminal to terminal or line
3 and Fig. 4. Maximum current in both the model’s
to line voltage can be either positive or negative. By
output is 10A. As clear from the output, the stator
controlling the switching sequence of the IGBTs, the
current decreases in the interval (0-0.02 sec), start
control provides a simulated 3-phase sine voltage
fluctuating thereafter and then becomes constant after
with frequency and voltage control. The waveform is
0.2 sec and remain constant until 0.5 sec. and then
composed of DC pulses and does not look too much
gives sine wave after 0.5 onwards in without soft
like a sine wave, but the effective value is a
switching model. The stator current with soft
reasonably good simulation of a sine wave. Torque
switching model is more sinusoidal than without soft
switching model. It remains constant in the interval
ripple of motor is reduced significantly. For a given
(0.3 to 0.5 sec).Moreover, the stator current with soft
voltage of supply, torque and speed of the motor are
switching technique is more stable and it gives better
doubled. For a given speed of the motor, the voltage
torque. We compared the outputs of rotor speed of
stress of switching device is reduced to half when
without soft switching model and IGBT soft
compared with the model without soft-switching. The
switching model as shown in Fig. 5 and Fig. 6.
insulation class requirement can be also reduced. The
Maximum speed obtained without soft switching is
BLDC motor used requires 220 V to operate. Two
225 radians/sec and maximum speed obtained in the
phases of BLDC are excited at a time (it can be A, B
or B, C or A, C) depending upon the input signal.
soft switching converter model is 300 radians/sec. As
The speed precisely follows the acceleration ramp.
clear from the simulation results, rotor speed improve
The simulation model of the proposed model is
with soft switching using IGBTs. Rotor speed starts
shown in Fig. 2.
increasing from zero and after some time it becomes
constant.
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International Journal of Advanced Engineering Technology
Fig.2 BLDC with soft switching
Fig.3 Stator Current without Soft Switching
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International Journal of Advanced Engineering Technology
Fig.4 Stator Current with Soft Switching
Fig.5 Rotor Speed without Soft Switching
Fig.6 Rotor Speed with soft switching
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International Journal of Advanced Engineering Technology
We then compared the torque outputs of without soft
switching model and IGBT soft switching model as
shown in Fig. 7 and Fig. 8 respectively. Maximum
torque in both models is 14 N-m. As clear from the
output, torque start decreasing in interval (0-0.01 sec)
and after that it becomes constant up to 0.22 sec and
further decreases and becomes negative. After that it
again starts increasing and becomes constant in
interval from 0.23 sec to 0.5 sec. From 0.5 sec it
again starts increasing to maximum value and after
that it again decreases and become constant for the
model without soft switching. Torque in soft
switching model decreasing in interval (0-0.01 sec)
and after that it become constant up to 0.3 sec and
further decreases and become negative. After that it
again starts increasing and becomes constant in
interval from 0.3 sec to 0.5 sec. From 0.5 sec it again
starts increasing to maximum value and after that it
again decreases and become constant. From the
outputs we observed that torque improves with soft
switching technique.
Finally, we compared the voltage outputs of without
soft switching model and IGBT soft switching model
whose outputs are shown in Fig. 9 and Fig. 10.
Voltage in without soft switching model decreases
first and after that it becomes constant. In soft
switching model, voltage remains constant over the
whole period. So we can infer that there is no effect
on the bus voltage when motor starts with soft
switching.
Fig.7 Torque without Soft Switching
Fig.8 Torque with Soft Switching
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E-ISSN 0976-3945
International Journal of Advanced Engineering Technology
E-ISSN 0976-3945
Fig.9 Votage without Soft Switching
Fig.10 Votage with Soft Switching
CONCLUSIONS
A sincere effort is made to develop a novel softswitching converter for a BLDC motor drive using
MATLAB Simulink. The waveforms for stator
current, rotor speed, torque and voltage were studied
in comparison with the existing hard-switching
converters for the BLDC motor drive. Simulation
results obtained justify these facts. A hardware
circuitry now needs to be developed to verify the
simulation results which can be taken up as a future
scope of work.
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