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SSRG International Journal of Electrical and Electronics Engineering (SSRG-IJEEE) – volume 1 Issue 9 –November 2014
Simulation of Three Phase UPS Systems Operating Under
Variable Non Linear Loads by Using Solar Energy
Integrated SPWM Controller
T.Srinivas*1, Kondapalli Vamsee Krishna*2
M-Tech Student Department of EEE, VBIT, Aushapur, Ghatkesar, R.R (Dt), Telangana, India.
Assistant Professor, Department of EEE, VBIT, Aushapur, Ghatkesar, R.R (Dt), Telangana, India.
ABSTRACT
This paper presents design of high performance sinusoidal pulse width modulation controller (SPWM) is
integrated for three phase uninterruptible power supply (UPS) system is operating on highly non-linear loads by
using solar energy. Generally the SPWM is not sufficient for compensating the harmonic distortions caused
specifically by the nonlinear currents drawn by the rectifier loads. The proposes study is a new design to overcome
the problems of the RMS control. To rectify these problems the closed loop control system is used for highly
reduction of harmonic distortions at the final results. This model design is done by using MATLAB/SIMULINK
environment. Finally the results are evaluated based on steady state error and THD (Total Harmonic Distortion) of
the output voltage. Better efficiency fast transient response and harmonic distortion reduced even instead of highly
non linear loads.
Keywords: SPWM, UPS, MATLAB/SIMULINK.
I.
INTRODUCTION
II.
In military, medical equipment and in information
technologies the increased usage of rectifiers in the
UPS system distort the UPS output because the high
power single phase rectifier loads draw highly non
linear current which cause generation of low dc
output voltage. This distortion result in high current
flow, malfunction of UPS system, increased power
loss. The voltage drop across the inductive element is
the main reason for the distortion. The switching
frequency harmonics in the current waveform is
generated by PWM operation of the UPS system
which can be reduced by the removal of inductive
element [1-3]. Even under the usage of small
inductive value, the distortion cannot be completely
reduced. So the proper controller has to design which
can carry signals for generating of sine voltages. Fast
dynamics response, low THD can be obtained.
ISSN: 2348 – 8379
RELATED WORK
Fig.1 Block diagram of FIXED PWM system
2.1. EXPLANATION
The existing system consists of ac source, filter unit,
rectifier, and inverter and control units. Filter
removes the harmonics generated by the natural ac
source. Rectifier unit is used to convert the ac into dc.
Disadvantages:
 Total harmonic distortion will be more in
the output.
 Circuits become bulky.
 Generate harmonic distortion in the output
voltages.
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SSRG International Journal of Electrical and Electronics Engineering (SSRG-IJEEE) – volume 1 Issue 9 –November 2014

III.
Switching losses will be more in the output.
PROPOSED MODEL
The block diagram consists of ac source, filter unit,
rectifier, and inverter and control units. Filter
removes the harmonics generated by the natural ac
source. Rectifier unit is used to convert the ac into dc.
Fig. 2 Block diagram of SPWM system
The stationary or synchronous-frame space-vector
PWM (SVPWM)-based controllers are the primary
choice of many researchers and the applications
currently used in industry, however, the classical
sinusoidal PWM (SPWM) method is still preferred
by many manufacturers
because
of
its
implementation simplicity, easy tuning even under
load, flexibility, and most importantly the advantages
of controlling each phase independently. The
independent regulation of each phase provides easy
balancing of three phase voltages which makes
heavily unbalanced loading possible. Also, it avoids
problems such as transformer saturation [4-5].
Although the classical SPWM method is quite
effective in controlling the RMS magnitude of the
UPS output voltages, it is not good enough in
compensating the harmonics and the distortion
caused specifically by the nonlinear loads.
Advantages
 The optimization may include obtaining the
lowest THD or the best tracking of the RMS
value or the fastest Dynamic response.
 The easy tuning of the proposed method
under load is verified during the
experimental studies.
 The scalability that It means that the
controller is easy to design and tunable for
any power level.
 Total harmonic distortion (THD) has been
improved.
ISSN: 2348 – 8379
Fig3 : Simulink model of the proposed multiloop
controller
IV.
SIMULATION RESULTS
The simulations are done in theMATLAB/Simulink
environment using the Simulink and PLECS model
of the inverter and the controller as shown. The
results are evaluated based on steady-state error,
transient response, and the THDof the output voltage.
Fig. 3 shows the RMS value and the percent THD of
the output voltage versus three different loads.
According to Fig. 3, when the linear load at 8.5 kW is
applied, the controller achieves 0.3% THD, and
similarly when the nonlinear load at 10 kVA is
applied, the controller achieves 3.1% THD. In
addition, the RMS voltages are very well regulated at
220 V for each phase with an excellent transient
response for the linear load but a fair response for the
nonlinear load case. The transient response from noload to the rated nonlinear load is oscillatory and it
takes 1.1 s; however, the maximum fluctuation in the
RMS voltage is less than }10% of the nominal
(198–242 V).We consider this as an expected
behavior for the nonlinear load case since the
capacitor of the rectifier is made fairly large to get
the desired crest in current; additionally, it is all
empty before the load is applied. At the instant, the
rectifier loads are switched in, a very large inrush
current flows into these capacitors. So, it is this
current that causes the oscillatory behavior.
Fig. 3. RMS fluctuations (top trace) and the profile of
the percent THD of the output voltages (second trace)
versus the load delivered by the inverter (bottom
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SSRG International Journal of Electrical and Electronics Engineering (SSRG-IJEEE) – volume 1 Issue 9 –November 2014
trace). The simulated load consists of a light load, the
linear full load, and the nonlinear full load.
single-phase rectifier load placed at each phase. The
scale of the vertical axis of upper trace is 100 V/div,
and the lower trace is 25 A/div. The scale of the
horizontal axis is 2 cycle/div.
V.
Fig. 4. Upper trace is the profile of the %THD of the
output voltage of one phase measured for three
different loading conditions. The lower trace is the
total output apparent power delivered by the UPS
into these loads.
Fig.5. Measured transient response of output voltages
(upper trace) and currents (lower trace) when the load
changes from no load to the full linear load. The scale
of the vertical axis of upper trace is 100 V/div, and
the lower trace is 25 A/div. The scale of the
horizontal axis is 2 cycle/div.
CONCLUSION
The design and performance of SPWM controller is
used for three phase UPS system operating under
highly nonlinear loads with zigzag transformer.
Finally the modified controller is designed to carry
signals for the generator of voltages. This proposed
method gives fastest and transient response is
received by using SPWM controller system in the
UPS design model. However the to add inner loops to
the closed loop control system effectively the
reduction of harmonic distortions.
REFERENCES
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Fig.6. Measured transient response of the output
voltages (upper trace) and the currents (lower trace)
when the load changes from no load to the rated
ISSN: 2348 – 8379
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