ISSN 2319-8885
Vol.05,Issue.07,
March-2016,
Pages:1258-1263
www.ijsetr.com
A Fuzzy Based Maximum Boost Controller Z-Source Inverter Fed
Induction Motor
G. YAMUNA1, K. BHADRAJI2
1
2
PG Scholar, Dept of EEE, Anurag Group of Institutions, Ranga Reddy (Dt), TS, India.
Assistant Professor, Dept of EEE, Anurag Group of Institutions, Ranga Reddy (Dt), TS, India.
Abstract: A closed loop speed control of z source converter fed induction motor drive with peak dc link voltage control is
proposed here. Induction motor control is based on closed loop scalar control strategy. It can overcome the limitations of voltage
source inverter and can offer better speed control and drive operation during voltage sags and normal working conditions. The
peak dc link voltage employed in order to achieve excellent transient performance which enhances rejection of disturbance,
including thee input voltage ripple and load current variation, and have good ride through for voltage sags. A maximum boost
control PWM is used in switching algorithm. The proposed concept is implemented using fuzzy logic controller. The simulation
results of proposed scheme presents good dynamic and steady state performance over traditional voltage source inverter fed
induction motor drive.
Keywords: Induction Motor, Z Source Inverter, Peak DC-Link Voltage Control, Maximum Boost Control, Scalar Control.
I. INTRODUCTION
The use of induction motors has increased tremendously
since the day of its invention. They are being used as
actuators in various industrial processes, robotics, house
appliances and other similar applications. The reason for its
day by day increasing popularity can be primarily attributed
to its robust construction, simplicity in design and cost
effectiveness. Speed control is one of the application imposed
constraints for the choice of a motor. Out of all the speed
control mechanisms, the Volts/Hertz control scheme is very
popular because it provides a wide range of speed control
with good running and transient performance. This control
mechanism is referred to as scalar control mode.
The traditional adjustable speed drives system is based on the
voltage source inverter (VSI), which consists of a diode
rectifier front end, dc link capacitor, and an inverter bridge. It
suffers from common limitations and problems, such as: the
obtainable output is limited below the input line voltage, the
voltage sags can interrupt an ASD system and shut down
critical loads and processes and the performance and
reliability are compromised by the VSI structure [1],[2] . In
order to satisfy the pressing needs for a single converter
capable of both voltage boosting and inversion, many new
inverter topologies have been proposed in the recent past.
Among these new topologies, Z-Source Inverter is the most
promising and competitive technology over the others mainly
because it continues to employ a conventional VSI as the
power converter yet with a modified dc link stage [1],[2].
The impedance source inverter employs a unique
impedance network coupled with inverter and rectifier; it
overcomes the conceptual barriers and limitations of the
traditional converters. The Z-source inverter intentionally
utilizes the shoot through zero states to boost dc voltage and
to produce an output voltage greater than the original dc
voltage. At the same time, the Z-source structure enhances the
reliability of the inverter greatly because the shoot-through
states, which might cause by EMI noise, can no longer
destroy the inverter. Control strategies of the ZSI are
important issue and several feedback control strategies have
been investigated in recent publications. There are four
methods for controlling the dc link voltage of the ZSI:
capacitor voltage control [3], indirect dc-link voltage control
[4], direct dc-link control [5], and unified control [6]. Out of
this, peak dc link voltage control is the simple method to
design and easy to implement. The paper presents detailed
analysis of closed loop speed control of z source converter fed
induction motor drive from low speed to rated speed. The
peak dc link voltage control is used to enhance the
performance of the system.
Fig.1. Closed loop scalar controlled induction motor drive.
Copyright @ 2016 IJSETR. All rights reserved.
G. YAMUNA, K. BHADRAJI
The closed loop operation of a scalar controlled induction
motor drive is presented in section II. The configuration,
(1)
operating principle and control method of the proposed
electric drive system is explained in section III. A detailed
analysis of z source converter fed induction motor drive and
(2)
design of impedance network is carried out in this section.
Alternatively, when in a non-shoot-through active or null
The theoretical and modulation concepts presented in the
state during time interval T1, current flows from the Z source
paper have been verified through detailed PSIM simulation in
network through the inverter topology to the connected ac
section IV. Finally the derived conclusions are presented in
load. The inverter side of the Z-source network can now be
section V.
represented by an equivalent current source, as shown in Fig.
3(b).
II. CLOSED LOOP SPEED CONTROL OF SCALAR
CONTROLLED INDUCTION MOTOR DRIVE
A simplified diagram of the V/f controlled induction motor
is shown in Fig.1. The closed loop control by slip regulation
of combined inverter & induction machine improves the
dynamic performance. The speed loop error generates the slip
command through a proportional integral (PI) controller and
limiter. The slip is added to the speed feedback or observer
signal to generate the frequency command. Thus frequency
command generates the voltage command through a
volts/hertz generator which incorporate low frequency stator
drop compensation .Since slip generated is proportional to the
developed torque at constant flux ,the scheme considered as
open loop with speed control loop[7].
III. Z SOURCE INVERTER FED INDUCTION MOTOR
DRIVE
A. Z Source Inverter
Fig.3. Z source inverter equivalent circuits when in (a)
shoot through state and (b) non shoot through state.
This current source sinks a finite current when in a nonshoot through active state and sinks zero current when in a
non shoot-through null state. From Fig. 3(b), the following
equations can be written:
Fig. 2. Z source converter.
Fig2 show the topologies of voltage type three phase Z
source inverter, where a dc voltage source and a conventional
VSI with three phase legs are connected at opposite ends of
the Z-source impedance network. A voltage type Z-source
inverter can assume all active and null switching states of
VSI. Unlike conventional VSI, a Z-source inverter has a
unique feature of allowing both power switches of a phase leg
to be turn ON simultaneously (shoot-through state) without
damaging the inverter[1] ,[2]. The impact of the phase leg
shoot-through on the inverter performance can be analyzed by
considering the equivalent circuits shown in Fig.3. When in a
shoot-through state during time interval T0, the inverter side
of the Z-source network is shorted as in Fig. 3(a). Therefore
(assuming L1 = L2 = L and C1 = C2 = C):
(3)
Averaging the voltage vL across a Z-source inductor over
a switching period (0 to T=T0 +T1) then gives:
(4)
Using (7) and (8), the peak dc voltage vi across the
inverter phase-legs and the peak ac output voltage vx can be
written as:
International Journal of Scientific Engineering and Technology Research
Volume.05, IssueNo.07, March-2016, Pages: 1258-1263
(5)
A Fuzzy Based Maximum Boost Controller Z-Source Inverter Fed Induction Motor
C. Peak dc Link Voltage Control
In order to obtain good performance, the feedback control
(6)
for dc link voltage of z source inverter is used [9] .This will
Where, B is the boost factor introduced by the shoot-through
help in achieving good reference tracking and disturbance
state, M is the modulation ratio commonly used for
rejection and can improve dynamic response. The capacitor
conventional VSI modulation and the term within { } gives
voltage Vc is equivalent to the dc link voltage of inverter, and
the ac output of a conventional VSI. Obviously, equation (10)
can be boosted by controlling the shoot-through time duty
shows that the ac output voltage of a Z-source inverter is
ratio. The ZSI utilizes the shoot-through state to step up the
boosted by a factor of B (always ≥1), which cannot be
dc link voltage by conducting both upper and lower switches
achieved with a conventional VSI.
of any phase legs. Thus, the ZSI can boost voltage to desired
ac output voltage, which is greater than the available dc link
B. Maximum Boost Control Method
voltage. The relationship between the capacitor voltage and
Reducing the voltage stress under a desired voltage gain
the dc link voltage bears a non linear relationship, which can
now becomes important to the control of ZSI. MBC turns all
affect the transient response of the system. In order to
traditional zero states into shoot-through zero state. The
overcome the problem, an algorithm is proposed to control
implementation block diagram of the MBC is shown in Fig. 4
the capacitor voltage linearly [10].The block diagram for the
and 5. MBC maintains the six active states unchanged and
control can be represented as shown in Fig.6.
turns all zero states into shoot through zero states. Thus
maximum T0 and B are obtained for any given modulation
index without distorting the output waveform. As can be seen
from Fig. 3, the circuit is in shoot-through state when the
triangular wave is either greater than the maximum curve of
the references (Va , Vb and Vc ) or smaller than the minimum
of the references. The shoot-through duty cycle varies each
Fig. 6. Linearization of capacitor voltage.
cycle [11].
The K factor can be defined as
(7)
Thus, the shoot through time can be calculated by the
equation
(8)
Fig. 4. Implementation of maximum boost control.
Fig. 7. Closed loop scalar controlled Z source inverter fed
IM drive.
Fig. 5. Waveforms of maximum boost control.
The output of the PI controller equals K, from which it is
possible to find out the shoot through duty ratio. As the K is
proportional to the capacitor voltage, the good transient
performance of capacitor voltage can be obtained. The shoot
through signals can be obtained can be OR ed with the PWM
signal to obtain the desired response.
International Journal of Scientific Engineering and Technology Research
Volume.05, IssueNo.07, March-2016, Pages: 1258-1263
G. YAMUNA, K. BHADRAJI
D. Proposed Closed Loop Z Source Inverter Fed Scalar
Controlled Induction Motor Drive
The closed loop speed control and peak dc link voltage
strategies of the proposed Z source inverter ASD system is
shown in fig.7.
IV. INTRODUCTION TO FUZZY LOGIC
CONTROLLER
L. A. Zadeh presented the first paper on fuzzy set theory in
1965. Since then, a new language was developed to describe
the fuzzy properties of reality, which are very difficult and
sometime even impossible to be described using conventional
methods. Fuzzy set theory has been widely used in the control
area with some application to dc-to-dc converter system. A
simple fuzzy logic control is built up by a group of rules
based on the human knowledge of system behavior.
Matlab/Simulink simulation model is built to study the
dynamic behavior of dc-to-dc converter and performance of
proposed controllers. Furthermore, design of fuzzy logic
controller can provide desirable both small signal and large
signal dynamic performance at same time, which is not
possible with linear control technique. Thus, fuzzy logic
controller has been potential ability to improve the robustness
of dc-to-dc converters. The basic scheme of a fuzzy logic
controller is shown in Fig.8 and consists of four principal
components such as: a fuzzyfication interface, which converts
input data into suitable linguistic values; a knowledge base,
which consists of a data base with the necessary linguistic
definitions and the control rule set; a decision-making logic
which, simulating a human decision process, infer the fuzzy
control action from the knowledge of the control rules and
linguistic variable definitions; a de-fuzzyfication interface
which yields non fuzzy control action from an inferred fuzzy
control action [10].
Fig.9. Block diagram of the Fuzzy Logic Controller (FLC)
for dc-dc converters.
A. Fuzzy Logic Membership Functions
The dc-dc converter is a nonlinear function of the duty
cycle because of the small signal model and its control
method was applied to the control of boost converters. Fuzzy
controllers do not require an exact mathematical model.
Instead, they are designed based on general knowledge of the
plant. Fuzzy controllers are designed to adapt to varying
operating points. Fuzzy Logic Controller is designed to
control the output of boost dc-dc converter using Mamdani
style fuzzy inference system. Two input variables, error (e)
and change of error (de) are used in this fuzzy logic system.
The single output variable (u) is duty cycle of PWM output as
shown in Figs.10 to 12.
Fig. 10.The Membership Function plots of error.
Fig.8. General Structure of the fuzzy logic controller on
closed-loop system.
The fuzzy control systems are based on expert knowledge
that converts the human linguistic concepts into an automatic
control strategy without any complicated mathematical model
[10]. Simulation is performed in buck converter to verify the
proposed fuzzy logic controllers as shown in Fig.9.
Fig.11. The Membership Function plots of change error.
International Journal of Scientific Engineering and Technology Research
Volume.05, IssueNo.07, March-2016, Pages: 1258-1263
A Fuzzy Based Maximum Boost Controller Z-Source Inverter Fed Induction Motor
Fig.12. the Membership Function plots of duty ratio.
B. Fuzzy Logic Rules
The objective of this dissertation is to control the output
voltage of the boost converter. The error and change of error
of the output voltage will be the inputs of fuzzy logic
controller. These 2 inputs are divided into five groups; NB:
Negative Big, NS: Negative Small, ZO: Zero Area, PS:
Positive small and PB: Positive Big and its parameter [10].
These fuzzy control rules for error and change of error can be
referred in the table that is shown in Table II as per below:
Fig.14. Performance characteristics of mbc z-source
converter im without fuzzy logic.
TABLE II: Table Rules For Error And Change Of Error
IV. SIMULATION ASPECTS
Simulation results of this paper is as shown in bellow
Figs.13 to 17.
Fig. 13. Simulation system response of ZSI fed induction
motor with fuzzy controller.
Fig.15. performance characteristics of MBC z-source
converter in with fuzzy controller at rated torque (=10NM) and rated speed (=1500rpm).
Fig.16. Performance Characteristics Of Mbc Z-Source
Converter Im with Fuzzy Controller At 3/4th Load
Torque (=7.5n-M).
International Journal of Scientific Engineering and Technology Research
Volume.05, IssueNo.07, March-2016, Pages: 1258-1263
G. YAMUNA, K. BHADRAJI
inverter,” in Proc. IEEE 22nd Annu. Appl. Power Electron.
Conf., 2007, pp. 1145–1148.
[4] X. Ding, Z. Qian, S. Yang, B. Cui, and F. Peng, “A direct
DClink boost voltage PID-like fuzzy control strategy in Zsource inverter,” in Proc. IEEE Power Electron. Spec. Conf.,
2008, pp. 405– 411.
[5] X. Ding, Z. Qian, S. Yang, B. Cui, and F. Peng, “A direct
peak DC-link boost voltage control strategy in Z-source
inverter,” in Proc. IEEE 22nd Annu. Appl. Power Electron.
Conf., 2007, pp. 648–653.
[6] S. Yang, X. Ding, F. Zhang, F. Z. Peng, and Z. Qian,
“Unified control technique for Z-source inverter,” in Proc.
IEEE Power Electron. Spec. Conf., 2008, pp. 3236–3242.
[7] Tsuji, M. ; Shuo Chen ; Hamasaki; Xiaodan Zhao
;Yamada, E. “A novel V/f control of induction motor for wide
and precise speed operation”, International Symposium on
Power Electronics, Electrical Drives, Automation and Motion,
June 2008.
[8] Xinping Ding; Zhaoming Qian; Shuitao Yang; Bin Cui;
Fangzheng Peng, "A New Adjustable-Speed Drives (ASD)
System Based on High- Performance Z-Source Inverter"
.42nd IAS Annual Meeting. Conference, Sept. 2007.
Fig.17. Performance Characteristics Of Mbc Z-Source
[9] X. Ding, Z. Qian, S. Yang, B. Cui, and F. Z. Peng, “A
Converter Im With Fuzzy Controller At Half Load
Direct Peak DC-link Boost Voltage Control Strategy in ZTorque (=5n-M).
Source Inverter” in Proc. IEEE Applied Power Electron.
Conf., Feb. 2007, pp. 648- 653.
V. CONCLUSION
[10] Q. Tran, T. Chun, J. Ahn, and H. Lee, “Algorithms for
This paper presents a new closed loop speed control of an
controlling both the dc boost and ac output voltage of Zinduction motor fed by Z-source inverter based on V/Fcontrol
source inverter,” IEEE Trans. Ind. Electron., vol. 54, no.5, pp.
and fuzzy controller. The peak dc link voltage is controlled by
2745-2750, Oct. 2007.
a single loop controller. The simulation results verified the
[11] Omar Ellabban, Joeri Van Mierlo and Philippe Lataire,”
validity of the proposed closed loop speed control methods
Comparison between Different PWM Control Methods for
during start up and input voltage change. The ZSI can be
Different Z-Source Inverter Topologies”, The 13th European
improved by controlling linearly the capacitor voltage. The
Conference on Power Electronics and Applications, EPE '09.
proposed method of fuzzy controller can achieve the good
8-10 Sept. 2009.
transient responses of variations of both the reference
[12] M. Baba, C. Lascu, I. Boldea,” Z converter control of a
capacitor voltage and reference output voltage, and also
V/f induction motor drive” IEEE conf. On Industry
during dc input voltage sag. Following observations are made.
Applications Conference, 2012.
 Output voltage can be boosted to any desired value by
varying shoot-through period T0, in zero states without
changing active state for a fixed modulation index.
 Stress in the switches is reduced.
 Component size (L & C) and hence cost required is less
as compared to traditional PWM inverter.
 Stator current is smooth as compared with traditional
PWM inverter. The drive system can increase the
effectiveness of overall performance.
VI. REFERENCES
[1] Fang Z. Peng, Miaosen Shen and Alan Joseph, “Z-Source
Inverters, Control and Motor Drive Applications,” KIEE
International Transaction on Electrical Machinery and Energy
Conversion System, 2005.
[2] F.Z.Peng, X.Yuan, X.Fang, and Z.Qian,”Z-Source
Inverter for Adjustable Speed Drives”, IEEE Power
Electronics Letters, June, 2003.
[3] X. Ding, Z. Qian, S. Yang, B. Cui, and F. Peng, “A PID
control strategy for dc-link boost voltage in Z-source
International Journal of Scientific Engineering and Technology Research
Volume.05, IssueNo.07, March-2016, Pages: 1258-1263