paper presents a Field Oriented Control scheme using space vector pulse width
modulation technique for torque ripple minimization of a permanent magnet
synchronous motor drive. This control scheme consists of two control loops,
namely an inner current loop and an outer speed loop. The reference voltage
signal generated by the vector control is fed to SVPWM technique to generate
gating pulses for three phase inverter. The proposed system is implemented in
MATLAB simulink and the response of PMSM drive has been analysed for different
speed operations. The simulation results show that the FOC based PMSM drive
provides improved dynamic response and minimum torque ripples.
Magnet Synchronous Motor (PMSM), Field Oriented Control (FOC), Space Vector
Pulse Width Modulation (SVPWM), Vector control.
magnet synchronous motors are more preferable compared to other AC drives due
to its various advantages such as high efficiency, high power factor, fast
dynamic response, high power density and wide power-speed range 1-3. PMSM is
widely used in electric vehicles, robotics, nuclear power stations,
agricultural and industrial applications 4-5. Owing to the recent development
of permanent magnet materials, induction motors are replaced by PMSM in various
fields. Due to no excitation current loss, PMSMs are more efficient than
induction motors 6. PMSMs have an ability to follow the reference command
values and can operate in specified limits of current, voltage and power
availability of several control methods for controlling speed, torque and current
of PMSM, makes them more suitable for industrial and domestic applications 7.
Due to recent development in digital electronics, digital signal processors and
other ICs, DC motors are slowly replaced by PMSM drive systems 8. Both scalar
and vector control (Field Oriented Control) techniques are used to control
speed, torque and current of a PMSM drive. The use of proportional integral
(PI) control technique in PMSM drive system is still popular due to its simple
implementation 9. The limitations of scalar control are as follows,
Scalar control controls only magnitude
and has no control over angles.
It has low dynamic performance due to
lack of feedback.
It creates instability of the drive
system after exceeding a certain applied frequency.
performance motor drives require an accurate and fast response, rapid recovery
from disturbances, and insensitivity to parameter changes. The performance of a
drive system can be significantly improved using vector control method. This
method decomposes a stator current into flux generating part and torque
generating part. After decomposition both parts can be controlled separately.
Vector control allows smooth rotation over the entire speed range of motor and
fast acceleration and deceleration is achieved. The structure of vector control
resembles as that of separately excited DC motor. Vector control method
eliminates torque ripples, oscillating flux in inverter fed synchronous motor
pulse width modulation is the easiest technique to implement in both software
and hardware. The main disadvantages of SPWM technique are lower modulation
index, less flexibility and less utilization of dc bus voltage. SVPWM is widely
used in power converters, AC machine control, UPS and low power applications.
Space vector PWM technique has lower switching losses, better utilization of dc
voltage, less harmonic and current distortion and better power factor as
compared to sinusoidal pulse width modulation technique 11. Torque ripple of
PMSM affects the machine reliability, accuracy and causes speed fluctuation. The
vector control based SVPWM technique is an efficient method to suppress the
torque ripple of PMSM.
this paper, section II discusses about block diagram of PMSM drive. Section III
develops the mathematical model of PMSM. Section IV discusses the
implementation of PMSM drive system. Results and discussions are presented and
discussed in section V. Finally, the conclusion is given in section VI.