Download performance analysis of z-source inverter fed induction

International Journal On Engineering Technology and Sciences – IJETS™
ISSN (P): 2349-3968, ISSN (O): 2349-3976
Volume 2 Issue 2, February 2015
PERFORMANCE ANALYSIS OF Z-SOURCE INVERTER FED
INDUCTION MOTOR DRIVE USING FUZZY LOGIC CONTROLLER
C.Pitchai (Assistant Professor)
Department of Electrical & Electronics Engineering
A.S.L.Pauls College of Engineering and Technology
Coimbatore, India
[email protected]
P.A.Prassath (Assistant Professor)
Department of Electrical & Electronics Engineering
A.S.L.Pauls College of Engineering and Technology
Coimbatore, India
[email protected]
ABSTRACT
This paper presents z-source inverter fed induction motor drive using fuzzy logic controller. The Z-source
inverter is a recently invented a new power conversion concept mainly developed for fuel cell vehicular applications.
The Z source inverter system can boost the given input voltage by controlling the boost factor, to obtain the maximum
voltage. PWM technique which is used as to given the gating pulse to the inverter switches. The four-switch inverter,
having a lower number of insulated gate bipolar transistors (IGBTs), has been studied for the possibility of reducing the
inverter cost. These inverters use a unique impedance network coupled between the power source and inverter circuit, to
provide both voltage buck and boost properties, which cannot be achieved with conventional voltage source and current
source inverters. It has single stage power conversion, high performance, minimal component count, increased
efficiency, improved power factor and reduced cost. The obtained AC voltage must be pure sinusoidal but it can’t
obtained because the harmonic content are highly present. Higher order harmonics are eliminated by with the help of
filters. Here impedance network act as a filter to reduce the lower order harmonics. This paper describes the design of
Fuzzy logic controller for Z-source inverter.
1.INTRODUCTION
Inverters are the dc to ac converters. The input dc
supply is either in the form of voltage or current is
converted in to variable output ac voltage. The output ac
voltage can be controlled by varying input dc supply or
by varying the gain of the inverter. In the late nineties,
Fang Zheng Peng popularized the concept of the ZSource Converters, which employ a unique impedance
network (or circuit) to couple the Converter with the
main circuit and then fed to the power source. They
provide unique features that cannot be obtained in the
traditional voltage-source and current-source converters
which use capacitor and inductor, respectively. The
conceptual and theoretical barriers and limitations of the
traditional voltage-source converter and current-source
converter are overcome by the Z-source converter
providing a novel power conversion concept that can be
applied to all dc-to-ac, ac to-dc, ac-to-ac, and dc-to-dc
power conversion.
Fig. 1 Proposed Block Diagram
The four-switch inverter topology is attractive
cost wise when it is compared with conventional sixswitch voltage source inverters. In the four-switch
inverter, one motor terminal is connected to the center
tap of the dc-link capacitors so that is utilizes two less
insulated gate bipolar transistor (IGBT) switches.
However, four-switch inverters are known to have
several disadvantages compared to normal six-switch
inverters: the voltage utilization factor is halved
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International Journal On Engineering Technology and Sciences – IJETS™
ISSN (P): 2349-3968, ISSN (O): 2349-3976
Volume 2 Issue 2, February 2015
compared to the six-switch inverter.Fig.1 shows the
proposed block diagram. Specifically, the peak phase
voltage of the four-switch inverter is , while that of sixswitch inverters is . On the other hand, capacitor center
tap voltage is fluctuating, and it destroys the balance
among the motor phase currents. The reason for this is
that current flow through a capacitor either increases or
decreases the voltage steadily for each half cycle.
Therefore, the voltage fluctuation increases as the load
torque becomes higher or the frequency becomes lower.
The unbalanced motor current leads to an inverter failure
and torque pulsation.
When input current is maintained constant, then it is
called Current Source Inverter (CSI) or Current Fed
Inverter (CFI). Sometimes, the DC input voltage to
the inverter is controlled to adjust the output. Such
inverters are called variable DC link inverters.
B) Z Source Inverters
Z source inverter operated with the combination
of VSI(Voltage Source Inverter) and the CSI(Current
Source Inverter). Normally the traditional inverters
convert the DC voltage in to AC voltage.
2. INVERTER
An inverter is an electric device that converts DC
to AC, the converted AC can be at any required voltage
and frequency with the use of switching device and
control circuits. Solid state inverters have no moving
parts and are used in a wide range and application, from
small switching power supplies in computers, to large
electric utility high voltage dc applications that transport
bulk power. Inverters are commonly used to supply AC
power from DC sources such as solar panel or batteries.
Inverters are used in various applications such as
induction motor drives, UPS, standby power supplies,
induction heating etc. Normally they are used for high
power applications.
Fig 2.Basic circuit of Z source inverter
Z source inverter not like the traditional inverter
it is buck or boost the voltage at the maximum level. The
impedance network is connected which is used to boost
the voltage to maximum level and it act as a filter. The
structure is as shown in Figure 2. Z-source inverters are
single-stage electronic power converters which have both
voltage-buck and boost capabilities. A Z-source inverter
is proposed, which can operate at wide range load (even
no-load) with small inductor, eliminating the possibility
of the dc-link voltage drops, and simplifying the inductor
and controller design. The Z-source inverter is a buck–
boost inverter that has a wide range of obtainable
voltage. The traditional V- and I-source inverters cannot
provide such feature. This shoot-through zero state is
forbidden in the traditional V-source inverter, because it
would cause a shootthrough. The shoot-through zero
state, which can be generated by seven different ways:
shoot-through via any one phase leg, combinations of
any two phase legs, and all three phase legs. The Zsource network makes the shoot-through zero state and
A) Principle
 The output voltage waveform of the inverter can be
square wave, quasi-square wave or low distorted sine
wave. The output voltage can be controlled (i.e.
adjustable) with the help of drives of the switches.
 The pulse width modulation (PWM) techniques are
most commonly used to control the output voltage of
inverters. Such inverters are called PWM inverters.
The output voltage of the inverter contains harmonics
whenever it is non-sinusoidal. These harmonics can
be reduced by using proper control schemes.
 The inverters can be classified as voltage source
inverters or current source inverters. When input DC
voltage remains constant, then it is called Voltage
Source Inverter (VSI) or Voltage Fed Inverter (VFI).
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International Journal On Engineering Technology and Sciences – IJETS™
ISSN (P): 2349-3968, ISSN (O): 2349-3976
Volume 2 Issue 2, February 2015
non shoot through switching state is possible. This shootthrough zero state provides the unique buck-boost feature
to the inverter.
C) Inductor selection
During traditional operation mode, when there is
no shoot-through, the capacitor voltage is always equal to
the input voltage; therefore, there is no voltage across the
inductor and only a pure dc current going through the
inductors. The purpose of the inductor is to limit the
current ripple through the devices during boost mode
with shoot-through. The average current through the
inductor is
Fig. 3 Z-Source inverter structure
The Z-source inverter consists of a unique impedance
network which couple the converter main circuit to the
power source, load, or other converter, for providing
unique features that cannot be observed in the traditional
VSI and CSI inverters. The impedance network consists
of two inductors and two capacitors connected to each
other as shown in the figure forms the second order filter
network. The values of both inductor and both capacitor
are equal. The two inductors can be two separate
inductors or two inductors inductively coupled to each
other on a single core. For size and cost reduction film
capacitors of desired value and voltage rating can be
selected.
IL=P/Vin
During shoot-though, the inductor current increases
linearly, and the voltage across the inductor is equal to
the voltage across the capacitor; during non-shootthrough modes (six active modes and the two traditional
zero modes), the inductor current decreases linearly and
the voltage across the inductor is the difference between
the input voltage and the capacitor voltage.
L1=L2=fsw Vc/∆Il
D) Capacitor Selection
The purpose of the capacitor is to absorb the
current ripple and maintain a fairly constant voltage so as
to keep the output voltage sinusoidal. During shootthrough, the capacitor charges the inductors, and the
current through the capacitor equals the current through
the inductor. Therefore, the voltage ripple across the
capacitor can be roughly calculated by
4. PWM TECHNIQUE
The introduction and wide acceptance of ZSI as
an alternative for traditional voltage source and current
source inverters (VSI/CSI), the modified switching
schemes from the traditional schemes has reached the
point where the further improvements in firing the
switches and inserting the shoot through states bring
crucial benefits. In addition to the four active switching
states for the VSI, ZSI has seven shoot-through zero
states, when the positive and negative switches of a same
phase leg are simultaneously switched on. This shootthrough state is harmful in VSI/CSI and can result short
circuiting and damaging of entire application.ZSI is
suitable for the applications with unstable power supply
such as fuel cell, wind power, photovoltaic etc. Same
pulse width modulation (PWM) logics and methods of
VSIs can be adapted to a switch a ZSI with slight
modifications. The distribution of the shoot-through in
the switching waveforms of the traditional PWM concept
is the key factor to control the ZSI. The DC link voltage
C1=C2=Iav Fsw/∆Vl
3. Z-SOURCE INVERTER
The new impedance-source power inverter has been
recently invented, eliminates all problems of the
traditional V-source and I-source inverters. It is being
used in ac/dc power conversion applications. Fig.3
shows the general Z-source converter structure. The
power source can be either voltage source or current
source.
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International Journal On Engineering Technology and Sciences – IJETS™
ISSN (P): 2349-3968, ISSN (O): 2349-3976
Volume 2 Issue 2, February 2015
high performance (diagonal capacitor voltage),
controllable range of ac output voltage, voltage stress
across the switching devices and harmonic profile of the
ac output parameters are purely based [9].
design [12]. In essence, fuzzy controller is a linguisticbased controller that tries to emulate the way a human
thinks in solving a particular problem. The basic fuzzy
logic control system is composed of a set of input
membership functions, a rule-based controller, and a
defuzzification process.
The fuzzy logic input uses member functions to
determine the fuzzy value of the input. There can be any
number of inputs to a fuzzy system and each one of these
inputs can have several membership functions. The set of
membership functions for each input can be manipulated
to add weight to different inputs. The output also has a
set of membership functions. These membership
functions define the possible responses and outputs of
the system [15]. The fuzzy inference engine is the heart
of the fuzzy logic control system. It is a rule based
controller that uses If-Then statements to relate the input
to the desired output [13].
The fuzzy inputs are combined based on these
rules and the degree of membership in each function set.
The output membership functions are then manipulated
based on the controller for each rule. All of the output
member functions are then combined into one aggregate
topology. The defuzzification process then chooses the
desired finite output from this aggregate fuzzy set. There
are several ways to do this such as weighted averages,
centroids, or bisectors. This produces the desired result
for the output. FLC is the combination of various
different processes which are shown above in the Fig.4.It
means a fuzzy logic controller comprises of numbers of
methods [14] which are described below in stepwise
form. Here the processes are explained in general format
as explained above are described in detail below:
4.1Types Of PWM Techniques
There are number of control methods have been
presented in recent years that include sinusoidal pulse
that include
1. Sinusoidal Pulse Width Modulation Techniques
2. Modified Space Vector Modulation Techniques.
The various PWM control algorithms are
1. Simple Boost Control (SBC)
2. Maximum Boost Control (MBC)
3. Maximum Constant Boost Control (MCBC)
4.
Traditional
Space
Vector
Modulation
(TSVPWM)
5.
Modified
Space
Vector
Modulation
(MSVPWM)[16]
A Z-source inverter is proposed, which can operate at
wide range load (even no-load) with small inductor,
eliminating the possibility of the dc-link voltage drops,
and simplifying the inductor and controller design. The
Z-source inverter is a buck–boost inverter that has a wide
range of obtainable voltage. The traditional V- and Isource inverters cannot provide such feature. This shootthrough zero state is forbidden in the traditional V-source
inverter, because it would cause a shoot through. The
shoot-through zero state, which can be generated by
seven different ways: shoot-through via any one phase
leg, combinations of any two phase legs, and all three
phase legs. The Z-source network makes the shootthrough zero state and non shoot through switching state
is possible. This shoot-through zero state provides the
unique buck-boost feature to the inverter.
5. FUZZY LOGIC CONTROLLER
The Fuzzy Logic Controller (FLC) requires that
each control variables which define the control surface be
expressed in fuzzy set notations using linguistic labels.
The Fuzzy logic controller is appropriate for nonlinear
control because it does not use complex mathematical
equation. Fuzzy controller is a non-linear controller that
does not require a precise mathematical model for its
Fig.4 Structure of fuzzy logic system
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International Journal On Engineering Technology and Sciences – IJETS™
ISSN (P): 2349-3968, ISSN (O): 2349-3976
Volume 2 Issue 2, February 2015
= 1000uF. The purpose of the system is to produce
230Vrms line to line voltage. For PWM generation the
carrier frequency is set to 10 KHz and modulating
reference signal frequency is set to 50Hz. The
modulation index is 0.8 and the input DC voltage is
188V. Maximum constant boost PWM with third
harmonic injection is generated using PWM generator
and logic circuit. The PWM generator block generates
normal three phase PWM waveforms for a given carrier
frequency.
Using triangular function, comparator and adder
repeated shoot-through pulses are generated. These
shoot-through pulses are evenly spread in all the three
phase PWM waveform using OR logic function. The
detailed analysis is given below.
A. Fuzzification
Fuzzy logic uses linguistic variables instead of
numerical variables. In a control system, error between
reference signal and output signal can be assigned as (for
example) Negative Big (NB), Negative Medium (NM),
Negative Small (NS), Zero (ZE), Positive small (PS),
Positive Medium (PM), Positive Big (PB). The triangular
membership function is used for fuzzifications. The
process of fuzzification converts numerical variable (real
number) to a linguistic variable (fuzzy number).
B. Rule Elevator
Conventional controllers like PI and PID have
control gains which are numerical values. Fuzzy logic
controller uses linguistic variables instead of the
numerical values. The linguistic variables of error signal
taken as input (en) and output is represented as in the
form of degree of membership functions.
C. Defuzzification
The rules of fuzzy logic generate demanded
output in a linguistic variable, according to real world
requirements. Linguistic variables have to be transformed
to crisp output. The choices available for defuzzification
are numerous. So far the choice of strategy is a
compromise between accuracy and computational
intensity.
6. SIMULATION RESULTS
Simulation
is
performed
using
MATLAB/SIMULINK software. Simulink library files
include inbuilt models of many electrical and electronics
components and devices such as diodes, MOSFETS,
capacitors, inductors, motors, power supplies and so on.
The circuit components are connected as per design
without error, parameters of all components are
configured as per requirement and simulation is
performed. Maximum constant boost control with third
harmonic injection method is used for PWM generation
and simulation. The complete simulation diagram is
shown in the figure 5. The component values of Z-source
inverter depends on switching frequency only. These
component values are chosen as per design guidelines in
[1] and [3]. For this circuit L1 = L2 = 4mH and C1 = C2
Fig. 5 Simulation configuration
The shoot-through duty ratio can be is calculated as T0/T
= 0.308.
The boost factor = B = 2.593
Average dc link voltage = Vdcl = 337V
Peak dc link voltage = Vdcl = 2.593 * 188 = 487V
Peak ac output voltage = Vacp = 0.8*2.593*188/2 =
194.5V
RMS ac output voltage Vac = 137.5V
Output line to line rms voltage = *137.5 = 238V
The buck-boost factor = BB = 0.8*2.593 = 2.075
The capacitor voltage = Vc = 337V
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International Journal On Engineering Technology and Sciences – IJETS™
ISSN (P): 2349-3968, ISSN (O): 2349-3976
Volume 2 Issue 2, February 2015
Gain of inverter = G = 2.075
The voltage gain of inverter obtained in above
analysis is 2.075. As we increase the shoot-through time
interval (T0), the boost factor will increase and this will
increase the inverter voltage gain. Thus inverter boost
factor and voltage gain are depends on the shoot-through
time. The simulation results with the same input voltage
and carrier frequency are shown in following Figures,
which agrees well with the analysis and theoretical
results. For a traditional inverter, to obtain the output
voltage of 230Vrms with modulation index of 0.8, 486V
dc voltage is required this is undesirable since it will
require additional voltage booster circuit. Figure 10
shows input dc voltage applied to Z-source inverter is
188V.
The capacitor voltage is the average dc link voltage
remains almost constant about 337V as shown in figure
8. Thus the input voltage (188V) is boosted (337V) and
applied as dc link voltage. The peak value of this dc link
voltage appears as input voltage across the main inverter
circuit. The output dc link voltage across Inverter Bridge
appears as shown in the figure 9. The peak dc link
voltage remains almost constant about 480V. It is
observed that during shoot-through state dc link voltage
becomes zero since all devices in main inverter are
switched on simultaneously, short circuiting the dc link.
Fig. 7 Capacitor voltage = 337V
Fig.8. Peak dc Link voltage across inverter Bridge = 480V
Three phase stator current waveforms and stator
voltage for a given load condition is shown in the figure
9 and 10 respectively. Stator current waveforms are
observed to be very smooth sinusoidal waveform as
compared to the traditional PWM inverter.
Fig. 6 Input DC voltage = 188V
Fig. 9 Three phase stator current
Fig.12 shows the simulation and experimental results of
diode voltage and inductor current. The diode is reverse
biased by capacitor voltage during shoot-through when
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International Journal On Engineering Technology and Sciences – IJETS™
ISSN (P): 2349-3968, ISSN (O): 2349-3976
Volume 2 Issue 2, February 2015
all the six switches are turned on, blocking the reverse
flow of current. Also, we can see that during the shootthrough period, the capacitor voltage becomes equal to
the inductor voltage. The capacitor charges the inductor
so that the inductor current increases during this time
and releases its energy during active state
voltage-source converter and current-source converter
and provides an advanced power conversion concept.
The Z-source inverter system can produce an output
voltage greater than the dc input voltage by controlling
the shoot-through duty ratio, which is impossible for the
traditional ASD systems. In this work, described the
operating principle, analyzed the circuit characteristics,
and demonstrated its concept and superiority. Different
PWM techniques and their comparison are presented.
Maximum constant boost control method is more
advantageous PWM control method among the other
PWM control methods. Maximum constant boost with
third harmonic injection PWM control method increases
output voltage boost while minimizing voltage stresses
across switching devices. It allows over-modulation
where modulation index can be varied from 0.57 to
1.154. Z-Source inverter fed IM drive system is
simulated using Simulink software using above described
PWM method.
In future Performance Analysis of Z-Source fed
induction motor using Nero Fuzzy, genetic algorithm,
Renewable energy etc..,
Fig. 10 line to line stator voltage
Fig. 11 Diode voltage and inductor current
8. REFERENCES
[1] Fang Zheng Peng, “Z- Source Inverter”, IEEE
Transaction on Industry Applications. 39: 2003,2.
Wuhan,China.
[2] Miaosen Shen, Jin Wang, Alan Joseph, Fang Zheng Peng,
Leon M. Tolbert, and Donald J. adams, “Constant Boost
Control of the Z-Source Inverter to Minimize Current
Ripple and Voltage Stress”, IEEE Transactions on
industry application vol. 42, no. 3, May/June 2006
[3] S. Rajakaruna, Member, IEEE and Y. R. L. Jayawickrama,
“Designing Impedance Network of Z-Source Inverters”
IEEE Transactions on industry application.
[4] G. Pandian and S. Rama Reddy, “Embedded Controlled Z
Source Inverter Fed Induction Motor Drive” IEEE
transaction on industrial application, vol.32, no.2,
May/June 2010.
[5] K. Srinivasan and Dr. S. S. Das, “Performance Analysis of
a Reduced Switch Z-Source Inverter fed IM Drives”,
Journal of Power Electronics, Vol. 12, No. 2, May/June
2010
[6] Omar Ellabban, Joeri Van Mierlo and Philippe Lataire,
“Comparison between Different PWM Control Methods
Fig. 12 Speed Variation
This is the basic property of the Z-source inverter. Due to
this operational behavior, z-source inverter can boost the
output voltage to any value greater than input voltage.
The simulation result for speed variation of the induction
motor is shown in the following figure 12. Initially speed
of induction motor increase linearly where at that time
the motor fetches more current so as to maintain the
torque. Under steady state condition the maximum speed
of induction motor is observed to be about 157rad/s. In
terms of rpm the maximum speed is 1500rpm
7. CONCLUSION
The Z-source converter overcomes the conceptual
and theoretical barriers and limitations of the traditional
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International Journal On Engineering Technology and Sciences – IJETS™
ISSN (P): 2349-3968, ISSN (O): 2349-3976
Volume 2 Issue 2, February 2015
for Different ZSource Inverter Topologies” IEEE
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