23-05-2012, 11:58 AM
PERFORMANCE EVALUATION OF THREEPHASE INDUCTION
MOTOR DRIVE FED FROM Z-SOURCE INVERTER
Z-SOURCE INVERTER.pdf (Size: 749.87 KB / Downloads: 80)
INTRODUCTION
-SOURCE inverter based induction motor drives provides a low cost and highly efficient two stage
structure for reliable operation. It consists of voltage source for the supply of rectifier section and
impedance network such as their equivalent behaviour as two equal inductors and two equal capacitors, threephase
inverter, and a three-phase induction motor. The rectification of AC voltage is done by rectifier section to
obtain DC voltage for further supply. The rectifier output DC voltage is now fed to the impedance network. The
network inductors are connected in series arms and capacitors are connected in diagonal arms as shown in Fig.1.
Depending upon the boosting factor capability of impedance network the rectified DC voltage is buck or boost
upto the voltage level of the inverter section (not exceed to the DC bus voltage) [1]. This network also acts as a
second order filter and it should be required less number of inductor and capacitor.
This paper presents an efficient PWM based Z-source inverter approach for the control of adjustable speed
drive employing poly-phase induction motor. The Z-source inverter advantageously utilizes the shoot through
states to boost the DC bus voltage by gating on both the upper and lower switches of the same phase leg.
Shoot through mode allows simultaneous conduction of devices in same phase leg. Therefore, on behalf of
boost factor of DC-link, a Z-source inverter can boost or buck to the voltage to a desired output voltage that is
greater / lesser than the DC bus voltage [2].
Z-SOURCE CONVERTER
Many significant problems that occur in the conventional inverter (fig. 2 (a) & (b)) result from their operating
principle. These problems are connected to the following disadvantage:
In case of voltage source inverter (Fig. 2(a)): output voltage V ≤ Vdc/ 1.73; voltage regulation-only
decreasing; problems with short circuits in problems.
In case of current source inverter (Fig. 2(b)): output voltage Um ≥ Udc/ 1.73; voltage regulation-only
increasing; difficult to apply conventional modular IGBT and open circuits problem.
The issues with short circuits in branches and open circuits are connected with vulnerability of inverter to
damages from EMI distortion if the inverter applications require amplitude to be adjusted outside the limited
region, output transformer or additional DC/DC converter Fig. 2(a) & (b), can be used.
PWM CONTROL TECHNIQUE
PWM inverters can be classified such as single phase and three-phase. These inverters are capable of
producing AC voltages of variable magnitude as well as variable frequency. The PWM inverters are very
commonly used in adjustable speed AC motor drive where one needs to feed the motor with variable voltage,
variable frequency supply. For wide variation in drive speed, the frequency of the applied AC voltage needs to
be varied over a wide range. The applied voltage also needs to be varied almost linearly with the frequency.
Carrier-based PWM methods are preferred in implementing modulators for inverters as they are simple and easy
to realize as shown in Fig. 6 and generation of switching signals with interleaved carrier-based PWM is shown
in Fig. 7.
CONCLUSION
In this paper, three-phase induction motor with Z-source inverter was discussed and simulated in
SIMULINK/MATLAB toolbox. The performance parameters of 3-phase induction motor such as rotor current,
stator current, rotor speed, and electromagnetic torque was investigated for the different load conditions. Finally
it is concluded that the proposed scheme of three-phase induction motor drive with Z-source and PWM
technique is fast enough and leads to a satisfactory operation in open loop systems.