Performance Analisys of a Three Phase Current
Controlled PWM-inverter with Siliding Mode
Approach
M´onica E. Romero
Depto. de Electr´onica, Universidad Nacional de Rosario
Riobamba 245 bis, (2000) Rosario, Argentina,
During her academic visit period in :
LSIS, Laboratoire des Sciences de l’ Informatiion et des Syst`eme
Ecole Politechnique de Marseille, France
Email: mromero@fceia.unr.edu.a
Abstract—A three phase Current Controlled PWM inverter
under Sliding Mode Approach is analyzed in this article. Main
characteristics and performance indexes are listed and compared
to those describing the clasic PWM modulation methods. The
basic Sliding Mode strategy is applied as well as the Reducing
Chattering Technique.
I. INTRODUCTION
In the field of Power Electronic, the PWM modulation
techniques constitute an important subject as long as most of
the control devices get use of power converter or switching
sources. Moreover, the control of electrical machines are
carried out by means of DC/DC and DC/AC converter, [1], [2],
[3]. Among the different modulation techniques it is possible
to classified them in open loop and closed loop techniques
as well as carrier based and carrierless, [4], [5]. In this
article, a Current Sliding Mode Control, (CSMC), of a three
phase inveter is presented in order to clasified its performance
by means of the indexes defined for classics modulation
techniques.
At first sight, the CSMC can be seen as a current controlled
PWM with hysteresis loop (clossed loop, carrierless method),
but its operation mode doesn’t suits because in this case the
inverter frequency is constant, fixed by the hysteresis width
and, for CSMC, the PWM signal remains k instants in one
position and one in the other (and vice-versa) to synthesize
a sinusiodal voltage signal, that means the inverter doesn’t
work at constant frequency [6]. The most suitable comparison
results with suboscilation method, (SM),(open loop, carrier
based method), even if the SMC surfaces involve current
magnitudes instead of voltages. More over, the way the control
is synthesized allows to make some modification in order to
improve de DC-bus utilization as it happens in the modified
suboscilation method.
The article is organized as follow: suboscilation method is
described in §II, a brief description of Sliding Mode control si
presentes in § III, the CSMC is developed in §IV as well as the
modified CSMC , an analysis of the method performance is
carried out in §V and a comparison with suboscilation method,
finally, simulation results are presented in §VI in order to
confirm the obtained results.
II. SUBOSCILATION METHOD
This section describes the sinusoidal modulation process
consisting in comparing a reference signal u*, and a triangular
carrier signal, uc. The intersection of both signal determines
the on-time switching instant of the power devices. See Figures
(1), (2) and (3), [1], [4].
The carrier frequency is constant, fc = 1
Tc
. The linear slope
of uc guarantees that the on-time of the switches, d = Ton/Tc,
be proportional to the reference signal u*. Then, the resulting
PWM output signal ul has constant frecuency and variable
duty cycled.
In order to quantify the performance of this modulation
technique, there are some index definition, as the amplitud
modulation factor:
ma =
ˆu*
ˆuc
and the frequency modulation factor
mf = fc
f1
.
The maximun modulation factor occurs when ma = 1.
When ma > 1, there are overmodulation. In this case we
obtain a grater value of the amplitude of the fundamental
component but, on the other side, the ul signal has a higher
harmonic content and has no longer constant frequency.
The maximum modulation index for suboscilation method
results (for ma = 1):
m = U1
2Ud/p
= 0.785 (1)
U1: fundamental component amplitude
2Ud/p: fundamental amplitude for six-step-method [4]
Ud: DC- voltage value.
.....