International Conference on Electrical, Electronics, and Optimization Techniques (ICEEOT) - 2016
An Embedded-Z (EZ) Source Inverter Feed Based
Industrial Adjustable Speed Drive System
Chakor Atmaram Munjaji
Tamhane A.V.
Electrical Engineering Department
Sinhgad Institute of Technology
Lonavala, India
atm.sairam@gmail.com
Electrical Engineering Department
Sinhgad Institute of Technology
Lonavala, India
Abstract-This paper represents the new topology and
hardware modeling of Embedded-Z (EZ) source feed industrial
drives and comparative analysis of Z source and EZ-source
inverter. In industrial application conventionally there are two
converters used for ASD systems i.e. Voltage Source Inverter
(VSI) and Current Source Inverter (CSI), but they have a limited
output voltage range. Conventional VSI and CSI support only
either buck or boost DC-AC power conversion and need a
relatively complex modulator. The problems in traditional source
converters can be overcome by Z source inverter. In this LC
impedance are employed for fast power conversion. Due to
requirement of additional LC filter the cost of operation also
increases. Therefore, instead of using an external LC filter in Zsource inverters, this paper gives an alternative family of Zsource inverters i.e. EZ-source inverter. In which input DC
source has embedding between LC impedance, which perform
the current and voltage filtering operation in current type and
voltage type EZ source inverter. This paper illustrate the
hardware design of EZ source inverter fed induction motor
which overcome problems of conventional VSI and CSI inverters.
And it gives the smooth speed control of induction motor.
Keywords— EZ-source inverters, Z-Source inverter, Pulse
Width Modulation, Adjustable Speed Drive System (ASD), PIC
Controller.
I
INTRODUCTION
Due to the recent advancements in the fields of power
conversion and energy storage, it is essential to design a new
topology of inverter which can operate efficiently with
variable voltage sources. In particular, the converter may need
to provide voltage enhancing capability in renewable energy
(e.g. fuel cell and solar energy) applications due to unbalanced
output voltage from the electrical sources, which are
unnecessarily affected by their output current and the ambient
condition [1]. Industrial drives are customarily used in
concomitant industry as loads. These being nonlinear in nature
are responsible for the increased THD levels in currents which
ultimately affect the power quality in a power distribution
system. These harmonic currents when flow in the distribution
network result in voltage distortions and increased heating in
consumer and system equipment. These unbalance load
current with large reactive components produces voltage
fluctuations and imbalance due to system impedance. The
industrial drives in a distribution network lead into substantial
harmonic contents resulting in restraining the power quality
978-1-4673-9939-5/16/$31.00 ©2016 IEEE
level. The performance of other loads connected in the
distribution network may also get distressed due to the
subsistence of industrial drives. An alternative solution for
this is Z-source inverter, which has a unique passive elements
structure which provide voltage buck-boost capability but Zsource source inverter has some deficiencies which overcome
by advanced family of Z-source inverter i.e. Embedded Zsource inverter. An EZ-source inverter provides inherent
features for ASD system. As we know, we have two
conventional converters i.e. VSI and CSI where they have
operate only in either voltage buck operation or boost
operation at a time [2].
As shown in Fig. 1, diode (D) and X shaped impedance
network is connected in between the input voltage source and
converter. As figure illustrates there is asymmetrical X shaped
impedance network consisting of two identical inductors L1
and L2 and two identical capacitors C1 and C2 connected in
such manner to achieve the desired output voltage. The X
shaped impedance network changing the configuration of
circuit from that of a voltage source to an impedance source
(i.e. Z-source) [3]. It allows the converter gets operates in a
new state of condition called the condition of shoot through
state in which the two semiconductor switching devices in the
same leg of converter are switched-on simultaneously which
cause dc link get short- circuit [4]. During this state of
condition, the energy is capacitors to inductors get transferred,
due to this there is achieve the voltage boost capability of the
Z-source inverter. There may be chances to capacitors to be
charged at higher voltages than the input supply source
voltage, so it is necessary to prevent discharging of capacitors
through input source of supply, due to this the diode D is
provided [4].
Fig. 1.
Basic Structure of Z-source inverter.
This paper gives a new family of EZ-source inverter will
have capability to reduce the total harmonic distortion (THD)
as compared to traditional Z source inverter. This EZ-source
inverter enhances the overall efficiency of adjustable speed
drive system due to presence of X-shaped LC impedance
network [8].
II
•
•
EXISTING SYSTEM
Inverters are used to dc to ac power conversion where the
input is dc supply either voltage or current is converted in to
variable output ac voltage. The output of inverter can be
controlled by controlling input dc supply or by varying gain of
the inverter [2]. Nowadays there are two types of conventional
inverter are using in industries for adjustable speed drive
system. They are:-
•
In this one of the upper switching devices and one of
the lower switching devices have to be gated on and
remained on at any time. Otherwise, there will be
open the DC inductor and it will damage the circuit
component.
For safe current commutation overlap time is needed
in the current source converter, which causes
distortion in waveform [5].
For CSI large DC inductors are needed so cost of
operation increases.
So, to overcome all above problems and get both buck
and boost operation in single stage a new topology is
implemented i.e. Z-source inverter. The network is shown in
fig 2.
1) Voltage source Inverter
2) Current source Inverter.
In conventional voltage source inverter (VSI), the DC
input voltage source connected across a large capacitor. The
voltage produced by this dc link is feed to main network [7].
The input dc supply may be a battery or fuel cell or diode
rectifier, or capacitors. The inverter circuit consists of six
switches; each is consist of ant parallel combination of power
transistors and diode which gives bidirectional flow of current
and blocking capability reverse voltage [5].
In conventional current-source inverter (CSI), the large DC
inductor are connected to form a DC current source and
connected in series with input dc supply such as a battery or
fuel-cell or diode rectifier or converter etc. Like VSI network
CSI also consist of six switches each consist of ant parallel
combination of power transistors and diode which gives
bidirectional flow of current and blocking capability reverse
voltage [3]. The control voltage pulse width modulation
(PWM) technique used for on/off time of the switching
devices in voltage source inverter and current source inverter
[5].
A. Disadvantages of Existing System
The VSI based system has the following disadvantages and
limitations•
•
•
•
•
•
They are only either a buck or a boost converter.
In VSI main network of inverter circuits cannot be
interchangeable. In other words the VSI main
network cannot use as CSI main circuit or vice versa.
The output voltage range is limited below and DC
bus voltage cannot exceed.[11]
In this upper and lower semiconductor switching
devices of each leg of phase cannot switched on
simultaneously.[10]
There is problem of electromagnetic interference
(EMI), which reduces reliability of inverter.
An additional LC filter is provided for filtering the
AC output voltage.
The CSI based system has the following disadvantages and
limitations-
Fig. 2.
Traditional Z-Source inverter
Z-Source inverter consists of a X –Shaped Z-source
impedance structure which consists of L1, L2, C1, and C2 .Due
to this X-shaped LC components we get both buck-boost
operations in single stage power conversion [10]. In this
network the input DC Source is placed at long left in series
with diode. So, due to this, in the source current chopping is
occurred which is caused by diode D commutation, so to avoid
this problem and to smoothen out the source current an extra
LC filter is required which increase the overall cost of the
system and by addition of additional LC filter network become
more complex [11].
So there is an alternative to overcome the above drawbacks,
proposed new technique is embedded Z (EZ) source inverter
shown in fig.3.
III
EMBEDDED Z-SOURCE INVERTER
In the proposed Embedded EZ-Source Inverter input DC
sources embedded in between the X shaped LC impedance
network [4]. Its L1 and L2 inductive elements used in voltage
type EZ-source inverters for filtering the currents and its C1
and C2 capacitive elements are used for voltage filtering in
current EZ-Source inverter, so in EZ-source inverter
smoothens out the source current without adding an additional
LC filter but the Z-Source and EZ-Source has same gain. By
dividing the input DC source between LC impedance it does
not require any additional filter [2] and [4]. So in EZ-source
inverter requires two sources which are cost effective. So the
input Dc voltage is divided as Vdc/2, due to this no extra
stresses occurs at time of loading condition. In this paper,
induction motor is taken as a load[8]. The proposed topology
of Embedded Z source inverter provides voltage ride through
capability and increase the output voltage range also [4].
Fig. 5.
Equivalent network of EZ-source inverter during
non-shoot through state
The equations derived for this state as follows.
Fig. 3.
Proposed Embedded Z-source Inver
(sy= s’y = ON, y=A, B or C;D=OFF)
An EZ-source inverter has good filtering capability, this
advantages illustrated in following section which consist of
two states i.e. shoot through state and non-shoot state. In this
semiconductor switches of same phase leg of network can be
switched on simultaneously as shown in fig. 4 and In that
diode D performing the bidirectional current flow and
blocking of unidirectional voltage operation.
Vo= Vdc /2 - Vc, Vi =2 Vc, Vd = VD = 0
(3)
idc = IL + Ic; Ii = IL – Ic, Idc ≠ 0
(3)
An EZ-source and Z-source inverter has equal gain
but due embedding the LC impedance there is overloading
input source is reduced, providing the filtering capability and
reduced the sizing of capacitor. [10]
By executing the state space averaging on equation
(1) and (3), the expression derived below as result for the
capacitive voltage (Vc), dc link peak voltage (VI) and ac
output peak voltage (Vx).
Vc = (1- T0 / T) / (1- 2T0 / T) Vdc
(5)
VI = Vdc / (1- 2T0 / T) = B Vdc
(6)
V x = M VI / 2
= B (M Vdc / 2)
Fig. 4.
Equivalent network of EZ-source inverter during
shoot through state.
Where T0 / T is shoot through ratio and it is always less
than 0.5 per period of switching , M is the modulation index
and B is the boost factor . Then the diode blocking voltage is
VD = - Vdc / (1- 2T0 / T)
When inverter circuit is in shoot through state, the diode
D gets reverse biased with its blocking voltage state and the
equations derived for this state as follow
(7)
(8)
Then the inductor voltage is
VL = Vdc (1- T0 / T) / (1- 2T0 / T)
(9)
(During shoot through state)
VL = - Vdc (T0) / (1- 2T0 / T)
(sy= s’y = ON, y=A, B or C;D=OFF)
Vo=Vc+ Vdc /2, Vi = 0, Vd = VD = -2Vc
(1)
IL = -Ic; Ii = IL – Ic, Idc = 0
(2)
When the inverter circuit is in non shoot through state, as
shown in fig. 5 then the diode D gets conducts and output load
is replaced by current source, where it has value non zero for
active state and zero null state.
IV
(10)
HARDWARE MODELLING FOR PROPOSED EZSOURCE SYSTEM
The block diagram of single phase E-Z-source inverter
using PIC controller for speed control of induction motor is
shown in fig.6. It contains following main section EZ-source
inverter, pic controller, driver section, triggering circuit, speed
control circuit.
RECTIFIER
CIRCUIT
PIC
MICROCONTROLER
+
+
RECTIFIER
CIRCUIT
AC SUPPLY
-
Fig. 6.
The ac input from the main supply is stepped down using a
230 /5V step down transformer. The stepped down AC voltage
is converted into dc voltage using a diode bridge rectifier. The
diode bridge rectifier consists of four diodes arranged in two
legs. The diodes are connected to the stepped down AC
voltage. For positive half cycle of the ac voltage, forward
biased the diodes D1 and D4. For negative half cycles diodes
D2 and D3 are forward biased. Thus dc voltage is produced to
provide input supply to the Converter.
+
EZ-SOURCE
INVERTER
IMPEDENCE
NETWORK
-
ASD
-
Block diagram of Hardware implementation
A prototype has been built to verify the hardware results.
It should be noted that the inductors and capacitors were
oversized in the prototype for possible regenerative operation
during inverter trips. The requirement of z source network is
similar to the traditional drives. The inductor used to minimize
the line harmonics current and voltage distortion. The required
dc capacitance is relatively small for a tolerable voltage ripple
mainly resulted from rectification. The dc capacitance should
be sized for possible regenerative operation [8]. The fig. 4
Shows block diagram for z source inverter, the prototype
system rectifier bridge produces the dc output. The parameter
used for hardware selected on their output performance. PIC
microcontroller is used for prototype system because PWM
technique is inbuilt and switching period depends on input
frequency of the system. In simulation model the simple boost
control is used to generate the gate pulse for inverter [9].
V
HARDWARE DESIGN DESCRIPTION
A. Control Strategy
a. DC regulated power supply
The regulated power supply is needed for driver circuit and
controller. In this regulated power supply is obtained from
bridge rectifier and regulator which are feed to step down
transformer. The 5V is for controller and 12V for controller
circuit .This circuits generates a PWM pulses which are
utilized for on and off operation of switching devices.
b. Step Down Transformer
The step down transformer is used to step down the input
230V to 12V for operation of control circuit. Then the 12V
supply is feed to bridge rectifier and it converts in 12V DC
which is required for the operation for control circuit. The
maximum current rating of this transformer is 1A. For control
circuit DC is needed so conversion takes place by rectifier and
rectifier component also rated at 1A.
c. Diode Bridge Rectifier
d. Filtering Unit
The output Dc voltage obtained from bridge rectifier will
not be pure DC, so in order to get a pure DC without
containing harmonics and ripple content a filtering circuit is
provided. It provides DC voltage of 0 Hz; we have to use a
low pass filter. So that a capacitive filter circuit is used where
a capacitor is connected at the rectifier output & a dc is
obtained across it. The filtered waveform is essentially a dc
voltage with negligible ripples & it is ultimately fed to the
load. A R1 is connected as a load resistor so the ground is
maintained. In this network for bypassing ripples the passive
elements C1R1 is used and for low pass filter C2R2 is used, i.e.
this filter passes only low frequency signals and high
frequency signals get blocks.
e. Voltage Regulator
The voltage regulators are an important device in any
electric power supply circuits. The primary function of a
voltage regulator is to provide a constant DC voltage to the
electric device. In this hardware design we use regulator
IC7805 which provides 12 V constant DC voltages. This
regulator IC has chosen because it has inherent features asFeatures
•
It is 3-Terminal Regulators
•
Output Current up to 1.5 A & regulated O/P Voltage
is 5V
•
Voltage rating 35V
•
For 5v power supply we need LM7805
•
IC ratting- Input voltage -7v to35 volt, Ic -1A, output
voltage range=Vmax- 5.2v,Vmin- 4.8v
B. Peripheral Interfacing Controller
Peripheral Interface Controllers (PIC) is an advanced
microcontrollers developed by microchip technologies. In
modern electronics applications these microcontrollers are
widely used. This PIC controller is an integration of all type
of memory modules and interfacing ports. This PIC controller
is much more advanced controller than 8051 microcontroller.
PIC controller is an also combination of central processing
unit (CPU) and different memory modules and I/O and O/P
ports. In this hardware PIC16F877A IC is used for PWM
pulse generation purpose because it has inbuilt PWM
generation port [12].
PIC16F877A IC of microcontroller has chosen to obtain
the gate pulses for the switching operation of MOSFETS to
drive the three phase Induction Motor. This IC PIC
Microcontroller has inherent features as•
•
•
•
•
•
Operating speed is 20 MHz, 200ns instruction cycle
time.
Maximum operating voltage 4V to 5V.
Maximum temperature withstand range -400 to +850
Interrupt sources-15
Flash memory-14.3 Kbytes, data EPROM-256 bytes.
It has inbuilt PWM technique.
C. Driver Circuit
The primary function of driver circuit is to amplify PWM
pulses coming from PIC microcontroller and pass to
individual gate terminals of respective switching devices .For
the operation of driver circuit 12 V supply is required and
which is provided from 230V/12V step down transformer. The
driver circuit consists of optocoupler, buffer and transistors.
a. Optocoupler
In project the optocoupler is used as protection device in
the driver circuit. When if there is problem of overvoltage
occur in driver circuit it will damage to complete circuit, so to
avoid this optocoupler are used to isolate the voltage between
the main circuit and microcontroller circuit. The pulse is
provided to the MOSFET switch using a microcontroller
circuit; this circuit produces a waveform of 5V DC. This pulse
is supplied to MOSFET switch which is supplied by 12V AC
as the source and destination voltage is different they have to
be isolated, which is done using optocoupler [10].
b. Buffer IC
•
Storage Temperature Range (TS) -65°C to +150°C
Dual-In-Line 700 mW
Small Outline 500 mW
Lead Temperature (TL5)
c. Transistor
In this hardware transistor is used to amplify the signal
pulse coming from the microcontroller circuit. In this there
two transistors are used in Darlington pair of connection in
driver circuit. The transistors IC 2N2222 and CK100 are
selected for signal amplification purpose. The transistors
circuit is an additional in driver circuit but it is necessary to
get desired amplitude of PWM signals from PIC controller.
The features of transistors ICs are
Features of 2N2222:• High current (max. 800 mA)
• PD-500 mW/1.8 W
• FT-300 MHz
Features of CK100
•
•
•
•
•
•
Maximum collector power dissipation (Pc), W: 0.8
Maximum collector-base voltage |Vcb|, V: 60
Maximum collector-emitter voltage |Vce|, V: 50
Maximum emitter-base voltage |Veb|, V:
Maximum collector current |I c max|, A: 1
Maximum temperature (Tj), °C: 175.
D. Adjustable speed drive System
In this work Induction motors is taken as ASD which has
many advantages compared to DC motors and synchronous
motors in many aspects, such as size, efficiency, cost, life span
and maintainability. Low cost and ease of manufacturing have
made the induction motors a good choice for electric and
hybrid vehicles. In this project prototype motor is used. It is
3phae induction of 0.25 HP rating.
VI
The buffer provide the excepted magnitude of PWM signal
.In this hardware buffer IC CD4050BC is used. The output
from the buffer IC is passed to the two optocoupler where
buffer IC acts as a NOT gate. This IC operates on logic level
configuration which provides only VDD. When these devices
are used for logic level conversions then input signal high
level (VIH) can exceed the VDD supply voltage [10]. This IC
has inherent features which make a system supply voltage
reliable and that features are
•
•
•
•
•
•
Wide range of supply voltage: 3.0V to 15V
Direct drive loads operates at 5.0V over full
operating temperature range
Sink current capability and high source
When input voltages greater than VDD Special input
protection is available.
Supply Voltage (VDD) -0.5V to +18V
Input Voltage (VIN) -0.5V to +18V Voltage at Any
Output Pin (VOUT) -0.5V to VDD + 0.5V
PROTOTYPE MODEL FOR EMBEDDED ZSOURCE INVERTER
The performance of proposed control approach is validated
with the help of scaled laboratory prototype system comments
as given in table 1 below
TABLE I.
Sr.No.
HARDWARE COMPONENT DESCRIPTION
Name Of Component
Specification
1
Micro controller
PIC 16F877A
2
Bridge Rectifier
IR BR 6840
3
Opto Coupler
4
Filter Capacitor
1000µF/100V
5
Voltage Regulator
IC LM7805C
6
Supply Transformer
7
MOSFET
MCT2E
230/12V
IRF 840-250V-20A
The new advanced topology for adjustable speed drive
system has been implemented based on hardware component
as elaborated in above section. All components are mounted
on the printed circuit board due to this the model has required
very less space and implementation cost also reduced. The
hardware component is purchase in nearer electronics market.
This design can be best suitable for industrial adjustable speed
drive system for higher application and which will provide
desired speed controlling characteristics as per requirement in
area of application. The proto type hardware design image for
proposed topology is shown in fig. 7 below.
Electrical Engineering Department, SIT College for their
technical support.
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[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
Fig. 7.
Practical prototype model for Embedded Z-source
Inverter.
[12]
CONCLUSION
This paper has presented a new ASD system based on the
EZ-source inverter. The operating principle and analysis have
been given. This paper presents, the theoretical analysis and
prototype design of EZ-source inverter is studied. Due to
presence of unique LC impedance in network EZ-source
inverter it overcomes all theoretical and practical barriers and
limitation conventional VSI and CSI inverter. The EZ-source
inverter for adjustable speed drive (ASD) in industrial
application system is implementing then it provides
1. Desired output ac voltage.
2. Extend output voltage range during voltage sags without
using any additional energy storage system and due to this
minimizes the motor ratings to deliver a required power.
3. Reduce the harmonics and improve the power factor.
This new proposed topology can be suitable for large
industrial application and it can be improve overall efficiency
of induction motor.
Acknowledgment
This work is undergoing at SIT Lonavala, Pune University.
The author would like to thank principal and Head of
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