Journal of Applied Sciences 5 (2): 249-252, 2005
© 2005 Asian Network for Scientific Information
Corresponding Author: Dr. Sinan Mahmod, Department of Electrical and Electronic Engineering, Faculty of Engineering,
University Putra Malaysia, 43400 Serdang, Selangor, Malaysia E-mail: email@example.com
Development of Single Phase Induction Motor Adjustable Speed
Control Using M68HC11E-9 Microcontroller
Senan M. Bashi, I. Aris and S.H. Hamad
Department of Electrical and Electronic Engineering, Faculty of Engineering,
University Putra Malaysia, 43400 Serdang, Selangor, Malaysia
Abstract: This study investigates the performance of single-phase induction motor using microcontroller
M68HC11E-9. The microcontroller senses the speed’s feedback signal and consequently provides the pulse
width variation signal that sets the gate voltage of the chopper, which in turn provides the required voltage for
the desired speed. A Buck chopper has been used to control the input voltage of a fully controlled single
phase isolated gate bipolar transistor (IGBT) bridge inverter. PWM technique has been employed in this
inverter to supply the motor with ac voltage. The proposed drive system is simulated using Matlab/Simulink.
Its results were compared with the hardware experimental results. The simulation and laboratory results proved
that the drive system can be used for the speed control of a single-phase induction motor with wide speed
Key words: Single phase induction motor, microcontroller M68HC11E-9
during the entire motor operation. This type of motor can
be chosen as the standard choice for designing
The use of microcontrollers in industrial and
domestic electrical devices has become very common
over the past decade. Motorola MC68HC11E-9
microcontroller has been chosen for this
implementation because it is easy to development,
instantly response, high performance, high speed and
low-power chip with multiplexed capable of running at up
to 2 MHZ. Traditionally, variable speed operation of a
single- phase induction motor is suffer from large
harmonic injection into the supply and low power factor,
in addition to the limited speed.
Correa et al. have demonstrated that the operation
of start capacitor (SC) and split-phase capacitor (SPC)
motors in the two-phase mode provides a significant
improvement of the motor performance. In the
single-phase mode it is required to use a split-phase
capacitor (SPC) motor. It is important to remark that the
capacitor is designed for the nominal speed and
consequently the performance is not optimized for
variable-speed operation. The use of a start capacitor (SC)
motor is not recommended for adjustable-speed motor
drive systems due to the presence of the centrifugal
switch that changes the motor characteristics during the
operation. In two-phase mode, as stated before, the
single-phase motor is treated as a two-phase motor. The
SPC motor has main and auxiliary windings that are used
single-phase adjustable-speed motor drive systems either
in single-phase or in the two-phase modes. It must be
noted that it is also possible to use an SC motor for
implementing single-phase adjustable-speed motor drive
systems. Moreover, it is important to evaluate the use of
SC motors in the two-phase mode because its use is more
widespread and it is cheaper than a SPC motor of the same
power. The advantages with respect to the standard
single-phase mode are related with reduction of the
start-up current and elimination of the torque pulsations.
Besides, that is possible to increase up to the double the
value of the average motor torque, in the case of the SC
Jiangmin Yao has implemented the PIC17C756
microcontroller in a single phase induction motor
adjustable speed drive control with hardware setup and
software program in C code. The main feature used in this
microcontroller was its peripherals to realize pulse width
modulation. in the single phase motor control.
Furthermore, one chip and re-programmable ROM
replaces the conventional complicated circuit solution.
He concluded that this brought low cost, small size and
flexibility to change the control algorithm without changes
The problem for this microcontroller was that it had
no dead band register and only had a three PWM output.
J. Applied Sci., 5 (2): 249-252, 2005
Therefore, additional logic analog circuits were added to
generate their complement signals and to generate dead
time in order to avoid the overlapping of turn on for both
upper and lower switches.
This work has been implemented using
MH68HC11E-9 microcontroller. The microcontroller has
been programmed to vary the pulse width variation that
controls the duty cycle of the dc chopper. The inverter
receives the dc signal from the chopper and converted to
ac power to feed the motor.
Miroslav Chomat and Thomas , considered a system
connected to a single-phase supply, the output portion of
the converter consisting of two IGBT switches, generates
a pulse width modulated (PWM) output supplying one or
both stator windings of a single-phase machine. The
variable speed operation is characterized by the fact that
the both stator windings are fed from the inverter. The
phase shift between the currents in the main and auxiliary
windings of the machine is maintained by means of an ac
capacitor connected in series with the auxiliary winding.
The generation of the triggering pulses for the solid-state
switches and the state of the output relay are controlled
by a single-chip microcontroller.
The system could be technically possible and
economical, but the operation of the drive is not optimal
throughout the entire speed range and the significant
torque ripple may arise in some operating points.
SIMULATION OF THE SYSTEM
Matlab/Simulink software has been used as a tool to
simulate, the circuit which consist of a single-phase
rectifier, buck regulator chopper and inverter circuit.
In the steady state the motor can be simulated as R-L
lumped circuit without loss of accuracy. The resistance R
reflects the losses in the stator and rotor cores and the
inductance for the winding.
An experiment is carried out to measure R and L and
the measured values were used in the simulation on
Matlab/Simulink. Figure 2 shows the simulation result for
the complete circuit and waveforms at different points in
In this study, the power supply Vac of this circuit
was fed via a variable transformer. The full bridge rectifier
has been used to convert the ac supply to a dc voltage
Vdc. The output of the rectifier is the input to the dc
chopper which controls the voltage level. The
microcontroller-based adjustable closed loop control
system hardware has been implemented and tested in the
laboratory. The M68HC11E-9 microcontroller has been
programmed to vary the PWM that controls the duty
cycle of the dc chopper. The last component of this set up
is the inverter which receives the dc signal from the
MATERIALS AND METHODS
chopper and converts it to ac power to feed the motor
under control. Figure 2 shows the hardware circuit
The power supply 110 Vac of this circuit was fed from
a variable transformer. The full bridge rectifier has been
used to convert the ac supply to a dc voltage of an rms
value of 155.56 Vdc. The output of the rectifier is the input
to the dc chopper which controls the voltage level. The
M68HC11E-9 microcontroller has been programmed to
vary the PWM that controls the duty cycle of the dc
chopper. The last component of this set up is the inverter,
which receives the dc signal from the chopper and
converts it to ac power to feed the motor under control.
Figure 1 shows the hardware circuit implemented for this
implemented for this work.
Dc Chopper performance: Controlling the voltage level
of the dc chopper can be obtained by changing the PWM
signal through the microcontroller. Figure 3 shows the
block diagram for the dc chopper. Via the user interface
command, the operator can change the variable command
through the keypad. The operator can also select either
manual or auto mode.
Fig. 1: Block diagram of the circuitroutine and speed measurement
Fig. 2: Block diagram representation of the software
J. Applied Sci., 5 (2): 249-252, 2005
The chopper circuit implemented in this work is a
buck regulator (step-down chopper). High frequency of
variable width is generated by the microcontroller and the
XOR gate. Variable width pulse is applied to the gate of
IGBT through an Optocoupler, the Optocoupler used to
isolate between high voltage of the chopper and low
voltage of the microcontroller. A capacitor and an
inductor are connected to form a smoothing filter .
The M68HC11 Family offers a selection of variable
pulse width options to support a variety of applications.
Up to six PWM inputs were selected to create continuous
waveforms with programmable rates and software
selectable duty cycles from 0 to 100%.
The pulse width variation module receives the duty
percentage of duty cycle calculated by speed control
module (SCM) and frequency in kHz. It adjusts the pulse
width accordingly. The pulse width variation module
is realized by software codes programmed in the
microcontroller. The pulse width modulated signal
outputted by this module is fed to the gate of the IGBT
Count is computed from the duty percentage which
is the output of the SCM.
At 12% and 92% of the duty cycle the V
chopper is recorded and is shown in Fig. 4 and 5. The
duty cycle can be changed automatically by the
microcontroller and can be set manually by the user to get
the desired speed.
It is clear from Fig. 5 and 6 that the output of the
chopper contains harmonics or ripples. The ripples can be
reduced by changing the value of the capacitor filter C.
Fig. 3: Block diagram of dc chopper
Fig. 4: Dc chopper output at 12% duty cycle
Fig. 5: Dc chopper output at 92% duty cycle
Fig. 6: Firing signal for the bridge inverter
Inverter: In this study four switches have been used to
convert the dc to ac voltage. The frequency is fixed and
variable output voltage is obtained by varying the pulse
width of the chopper switch.
It can be seen from Fig. 6, when IGBT Q and Q are
positive voltage signal, Q and Q are OFF by the negative
voltage signal and vice versa. These waveforms show
that the four IGBT's of Q ,Q ,Q and Q will not be ON at
the same instant of time.
MOTOR SPEED CONTROL RESULTS
The adjustable speed drive during experiment
performed satisfactory and the results are shown in
Figure 9-12. Speed Sensing is realized using shaft
encoded digital tachometer. It measures the immediate
speed (MSD) and feeds it to the speed control module
(SCM) block within the microcontroller.
The speed measurements were taken by the
microcontroller in hexadecimal units. These data were
stored in the microcontroller memory. In order to get the
actual Fig. of the curve representing the speed response,
these data were plotted on the Excel software, which
changes the hexadecimal values to decimal values.
Under no-load the control of the motor speed was
smooth and the response of the drive system was as
expected. During starting there was overshoot up to 1
Fig. 7: Motor speed response under no-load
Fig. 8: System’s sudden stop command response
J. Applied Sci., 5 (2): 249-252, 2005 Download full-text
Fig. 9: Motor speed under load condition
Fig. 10: Load voltage during experimental
Fig. 11: Load voltage during simulation
Fig. 12: Detail of figure 11 waveform
second then there was less than 7% oscillation, where the
oscillation depends on the system parameters. Then the
system reached its steady state speed after 4 seconds as
shown on Fig. 7.
Under sudden stop command that initiated manually
by the operator using the keypad, the speed of the motor
has gone to zero in a very short time. This proves that the
drive system’s response is quit fast as shown in Fig. 8.
Under load changes and the speed command was
changed according to a pre-defined value 700 to 2230 rpm,
the drive system performed as shown on Fig. 9.
Comparison between simulation and experimental
results: With reference to the results of the drive system
for the single-phase induction motor which are shown in
Fig. 11 and the Matlab simulation results which are shown
in Fig. 12 and considering that the motor at the simulation
circuit represented at steady state operation, a good
agreement between experimental and simulation results is
observed with respect to the voltage value, frequency and
the waveform shape. The value of the voltages at the load
terminal in both cases was 110 V.
It is shown in Fig. 11 that the load signal is a
modulation between the pulse width chopping signal and
50 Hz sinusoidal signal. The signal in Fig. 10, has the same
nature but since it has been taken by oscilloscope, the
chopping is not visible.
The experiments results obtained using the proposed
drive system proved the simplicity of the application of
the M68HC11E-9 microcontroller kit in the speed control
of the single phase induction motor. The simulation
results confirmed that the possibility of obtaining of the
same results with a representative Simulink block
In general, the AC-DC-AC conversion was
successful, on the other side, some overshoot were found
due to suspected causes such as the control algorithm
used in the microcontroller and harmonic content at the
inverter output. However, good results confirming the
initial intention for design.
This concludes that the single-phase induction motor
can be successfully driven from a variable voltage
amplitude control and the motor’s speed can be easily
adjusted using the proposed drive system. Single-phase
AC induction motor controls offer new, low-cost
solutions for light commercial and consumer applications.
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