Abstract-This paper presents the novel synchronous frame hysteresis controller for three phase Uninterruptible Power Supply (UPS)based on Z-Source Inverter (ZSI). The proposedsynchronous frame approach minimizes the hysteresis control time delay to onesixthof the fundamental period such that the dynamic response is significantly improved. The hysteresis band currentcontroller determines the switching signals, and the algorithm based onanextension of Synchronous Reference Frame(SRF) Theory (d-q-0) is used to determine thesuitable current reference signals. A filter is applied to further enhance the accuracy of steadystate tracking.Low total harmonic distortion has been achieved under heavilydistorted nonlinear load and unbalanced load.The ZSI provides agreat alternative with lower cost, higher reliability and higher efficiency.

1. Synchronous Frame Hysteresis Controller for Three
Phase UPS Based on Z-Source Inverter
M.Lakshmana Kumar1
PG Scholar,
1
Bannari Amman Institute of Technology
lakshmanakumar2010@gmail.com
K.Chitra2
Assistant Professor
2
Bannari Amman Institute of Technology
E-mail:chitrak@bitsathy.ac.in
Abstract-This paper presents the novel synchronous frame hysteresis controller for three phase Uninterruptible Power Supply
(UPS)based on Z-Source Inverter (ZSI). The proposedsynchronous frame approach minimizes the hysteresis control time delay to
onesixthof the fundamental period such that the dynamic response is significantly improved. The hysteresis band currentcontroller
determines the switching signals, and the algorithm based onanextension of Synchronous Reference Frame(SRF) Theory (d-q-0) is
used to determine thesuitable current reference signals. A filter is applied to further enhance the accuracy of steadystate tracking.Low
total harmonic distortion has been achieved under heavilydistorted nonlinear load and unbalanced load.The ZSI provides agreat
alternative with lower cost, higher reliability and higher efficiency.
Index Terms- CSI, DQ algorithm,Hysteresis Controller,Uninterruptible power supply, VSI, ZSI,

1. INTRODUCTION
Uninterruptable power supply (UPS) is used to supply
very high-quality,continuous, and disturbance-free ac power to
critical loads such as medical equipment,home appliances,
computers, and communication systems[15]. A good UPS system
requires not onlyexcellent steady-state performance in terms of
voltage regulation, switching losses and Total
HarmonicDistortions (THD) but also a fast transientresponse
during load step change.UPS that differ from an emergency
power system or standby generator in that it will provide
instantaneous protection from input power interruptions by
supplying the energy stored in the batteries. UPS is an electrical
apparatus that providesemergency power to a load when the main
power fails.
Some highperformancefeedback control techniques such
asmultiloopstate feedback control,dead-beat control and
predictive control have been proposed and investigated“[7,8]”.
Highqualityoutput voltage and fast dynamic responsehave been
demonstrated with thesemethods. The controllerbandwidth is
limited due todigital implementation.Selective harmonic
compensation employs the idea that eachorder of
harmonicdistortions can be compensated individually.This
technique is targeted at excellentsteady-state outputand it is
implementable either in the stationary frame or insynchronous
rotating frames[14].
____________________________________
 M.Lakshmanakumar is currently pursuing Master of Engineering in
Bannari Amman Institute of Technology, India,Ph:9578228161,
E-mail:lakshmanakumar2010@gmail.com
 K.Chitra is currently working as Assistant Professor in Bannari Amman
Institute of technology,India,Ph:9976719928,
E-mail: chitrak@bitsathy.ac.in
 Dr.A.Jeevanandham is currently working as Professor in Bannari Amman
Institute of technology,India,Ph:9843688895
E-mail: jeeva932@gmail.com
IJTET©2015
Fig.1 Block Diagram of the Controller.
2. HYSTERESIS CONTROLLER
Hysteresis controllers utilize some type of hysteresis in
the comparison of the line currents to the current
references[2].The hysteresis control schemeprovides excellent
dynamic performance, because it acts quickly.Due to the
advances of power electronics and inverter topology, the
currentcontrolledvoltage-sourcepulsewidth
modulated(PWM)inverterisusuallypreferredfor quick response
and accurate control[3].
These power devices may be applicable in ac motors,
active filters, and Uninterruptible Power Supply (UPS). Current
controlled PWM inverter offers substantial advantages
ineliminating stator dynamics in high performance AC
drives[5].One version of hysteresis control, uses three
independent controllers, one foreach phase.The control for one
inverter leg is shown in Fig.2[6].When the line currentbecomes
greater (less) than the current reference by the hysteresis
band,theinverter leg is switched in the negative (positive)
direction, which providesaninstantaneous current limit if the
neutral is connected to the dc bus midpoint.
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2. Therefore, the hysteresis band specifies the maximum current
ripple as summing neither controller nor inverter delays[1].The
inverter switching frequency will vary over a fundamental
inverter periodsince the current ripple is specified by the
hysteresis band. In a system without a neutral connection, the
actual current error can reachdouble the hysteresis band assuming
the three-phase current reference sums tozero[10].
Fig.2 Circuit for Hysteresis Current Controller
3. SYNCHRONOUS FRAME CONTROL ALGORITHM
In the SRF control, the load current signals are
transformed into the conventional rotating frame d-q. If theta is
the transformation angle, the transformation is defined by:
xd
xq
x0
=
cos⁡(⍬) cos⁡(⍬ −
2π
3
) cos⁡(⍬ −
4π
3
)
−sin⁡(⍬) −sin⁡(⍬ −
2π
3
) −sin⁡(⍬ −
4π
3
)
1
2
1
2
1
2
xa
xb
x0
(1)
Fig.3 shows the basic configuration of synchronous
reference frame [13]. In the SRF is atime varying anglethat
represents the angular position of the referenceframe which
isrotating at constant speed insynchronism with the three phase ac
voltages. In the SRF is a time varying angle that represents the
angular position of the reference framewhich is rotating at
constant speed in synchronism with the three phase ac voltages
[16]. In this case thespeedof the reference frame is practically
constant, that is, the method behaves as if the reference frame
moment of inertia is infinite.
Fig.3 Principle of Synchronous Frame Theory
This is accomplished using high pass filters (HPF).
Inspite of a high pass filter, allow low pass filter is used to obtain
the reference source current in d-q coordinates[4].
IJTET©2015
Fig.4 Block Diagram of Synchronous Frame DQ Extraction
Unbalanced and sinusoidal mains voltage conditions
withangle θ is a uniformlyincreasing function of time.This
transformation angle is sensitive to voltageharmonicsand
unbalance; therefore dθ/dt may not beconstant over a mains
period[9]. With thistransformation the direct current component is
iα
iβ
= C
Ia
Ib
Ic
(2)
id
iq
=
cos ⍬ sin ⍬
− sin ⍬ cos ⍬
iα
iβ
(3)
where ⍬ = tan−1 vβ
vα
id
iq
=
1
vα
2+vβ
2
vα vβ
−vβ vα
iα
iβ
(4)
Icomp ,a
Icomp ,b
Icomp ,c
= [c]T
iα
iβ
(5)
The fundamentalcurrents of the d-q components are now dc
values. Theharmonics appear like ripple. Harmonic isolationof the
d-q transformed signal isachieved byremoving the dc offset [11].
4. SIMULATION AND RESULTS
The Fig.5 shows the simulation of Synchronous frame
hysteresis controlled Z-Source inverter for UPS applications. The
input DC voltage of 100V is given to the three phase inverter
through the impedance network. The current from the inverter is
given to the DQ extraction frame in order to increase the dynamic
response of the system and to reduce the switching frequency of
the hysteresis current controller.
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3. Fig.5 Simulation Diagram of Proposed Method
Thepulses generated from the hysteresis current
controller are given to the three phaseinverter.
Fig.6 Simulation Diagram of DQ Extraction
The simulation diagram of DQ extraction frame is shown
in the Fig 6. Theload voltage is compared with the reference
voltage and the error signal is amplifiedwith the PI controller. The
output of the PI controller is given to the Low pass filter inthe DQ
transformation block. The output current waveform shows the
dynamicresponse of the system.
IJTET©2015
Fig.7 Simulation of Hysteresis Controller
The simulation diagram of the Hysteresis Current
Controller is shown in Fig 7.The output current of DQ
extraction and the actual current is given as input to
thecontroller. The error signal is passed through the hysteresis
band and pulses aregenerated.
4.1 OUTPUT WAVEFORMS
Fig.8 Current waveform after DQ Extraction
Fig.9 Reference Current Given To the Hysteresis Controller
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4. Fig.10 Actual Current Waveform for Hysteresis
Controller
Fig.11 Pulse Generated From the Hysteresis
Controller
Fig.12 Output Voltage Waveform
IJTET©2015
Fig.13 Output Current Waveform
4.2 THD ANALYSIS OF THE SYSTEM
Fig.13 THD analysis of the system
The output waveforms of the Synchronous frame
hysteresis controlled Z-sourceinverter at various stages are
shown. The output current from the DQ extraction showsthe
dynamic response of the system. The pulses generated from the
hysteresiscontroller are shown in Fig 11. THD analysis of the
system is carried out whichresults in 17.11%.
5. CONCLUSION
A new synchronous frame hysteresis control Strategy
has been developed forthree phase UPS inverters. By designing
the Hysteresis control to compensate theharmonics in three
different synchronous rotating frames, all the stationary
frameharmonic distortions are reduced considerably. Therefore,
the voltage regulationrequirement can be satisfied under general
load conditions (linear and non-linear loads). But this
controlstructure also hassome drawbacks, such as the
destructionof the inverter if its highest switchingfrequency is not
limitedand the interdependence of the load phases. In order to
limitthis frequency in a single-phase case and extend this result to
the three-phase case througha transformation (were dq
transformation is employed)avoiding thecomplexity.Hysteresis
current controller results high dynamic response,easy
toimplementand eliminates the complex calculations of the
existing methods. The Totalharmonic distortion of the proposed
method achieved is 17.11%.
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