30-06-2012, 01:55 PM
A Fast Space-Vector Pulse with Modulation Method for Diode-Clamped Multi-level Inverter fed Induction Motor
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Abstract
This paper presents a fast space-vector pulse width
modulation (SVPWM) method for five-level inverter. In this
method, the space vector diagram of the five-level inverter is
decomposed into six space vector diagrams of three-level
inverters. In turn, each of these six space vector diagrams of
three-level inverter is decomposed into six space vector
diagrams of two-level inverters. After decomposition, all the
remaining necessary procedures for the three-level SVPWM
are done like conventional two-level inverter.
INTRODUCTION
Recent developments in power electronics and
semiconductor technology have led improvements in power
electronic systems. Hence, different circuit configurations
namely multilevel inverters have become popular and
considerable interest by researcher are given on them.
Three-level voltage fed PWM inverters are recently
showing popularity for multi-megawatt industrial drive
applications. The main reason for this popularity is that the
output voltage waveforms in multilevel inverters can be
generated at low switching frequencies with high efficiency
and low distortion and large voltage between the series
devices is easily shared [1].
FIVE-LEVEL SVPWM INVERTER
Fig.1 shows diagram of a five-level diode clamping
inverter. Each leg is composed of four upper and lower
switches with anti-parallel diodes. Four series dc-link
capacitors split the dc-bus voltage in half, and eighteen
clamping diodes confine the voltages across the switches
within the voltages of the capacitors. The necessary
conditions for the switching states for the five-level
inverter are that the dc-link capacitors should not be
shorted, and the output current should be continuous. As
indicated in Table I, each leg of the inverter can have five
possible switching states, P1, P2, O, N1 or N2. When the top
four witches Sx1, Sx2, Sx3 and Sx4 (x = a, b, c) are turned on,
switching state is P2. When the switches Sx2, Sx3, Sx4 and
Sx5 are turned on switching state is P1. When the switches
Sx3, Sx4, Sx5 and Sx6 are turned on, the switching state is O.
when the switches Sx4, Sx5, Sx6 and Sx7 are turned on.
EXPERIMENTAL TEST SETUP
The experimental setup employed a powerful
TMS320LF2407, 16-bit DSP processor working at 40
MIPS as its controller and PEC16DSMO10A, an intelligent
power module (IPM) of three phase three-level diode
clamped inverter. It consists of 12No’s, 1200V, 50A IGBT
with proper heat sink and snubber circuit. Three number of
Hall Effect sensors are provided for current measurement
and protection. The inverter is connected to a load of 3Ø,
0.5HP, 415V, 50 Hz, 4-pole, 1.05A, 1380 rpm induction
motor and the results are obtained. The experimental setup
has done only for three-level inverter as shown in Fig. 9.
RESULTS AND DISCUSSIONS
In order to prove the validity of the proposed fast space
vector pulse width modulation (SVPWM) method, a three
phase three-level and five-level inverter fed induction
motor is simulated with the simulation parameters shown in
Table V. The simulation results of five-level inverter are
shown in Fig. 10- 13. The gate pulses of phase A are shown
in Fig. 10. The inverter output line to line voltage (Vab) and
its harmonic spectrum is shown in Fig. 11. The total
harmonic distortion (THD) is only 0.64% and it proves the
effectiveness of the proposed SVPWM method. Fig. 12
shows the load current and its harmonic spectrum. The
THD of load current is decreased with increasing the level
of inverter.
CONCLUSION
In this paper, a fast space vector pulse width modulation
method has been proposed and described for a five-level
inverter. In this method, the space vector diagram of the
five-level inverter is decomposed into six space vector
diagrams of three-level inverters. In turn, each of these six
space vector diagrams of three-level inverter is decomposed
into six space vector diagrams of two-level inverters.