SOLID STATE TRANSFORMER - USING FLYBACK CONVERTER

ABSTRACT
 In recent years, the complexity of the electrical grid has grown due to the
increased use of renewable energy and other distributed generation
sources. To cope with this complexity, new technologies are required for
better control and a more reliable operation of the grid. One of such
technologies is the Solid-State Transformer (SST).
 regarded as one of the 10 most emerging technologies by Massachusetts
Institute of Technology (MIT) Technology Review in 2010.

INTRODUCTION
• The solid state transformer(SST) is one of the key elements in power
electronic-based micro-grid systems.
• The main purpose of SST is to convert ac to ac for step-up or step-down
with a function same as that of a conventional transformer with an
additional advantage of obtaining an intermediate DC voltage for useful
purpose.
• The traditional 50 Hz transformer is replaced by a high frequency
transformer plus solid state devices. Therefore, it potentially reduce the
weight and volume of it compared with the traditional power transformer.

WHY DO WE NEED SST?
Weakness of conventional transformer
The weakness of conventional transformer is the strength of SST

SST
FUNCTIONALITIES :-
• Protects Load from Power System Disturbance
– Load Voltage Regulation
– Voltage Harmonics Compensation
• Protects Power System from Load Disturbance
– Unity Input Power Factor
– Sinusoidal Input Current for Distorted / Non-Linear
Load
– Protection against Overload & Output Short Circuit
• Integrates Energy Storage (Energy Buffer)
• Medium Frequency Isolation →Low Weight / Volume
• Encourages the use of non-conventional distributed
energy sources by allowing easier integration with the
grid.

BASIC BLOCK DIAGRAM
A
C
S
u
p
p
l
y
AC SUPPLY
AC to DC
CONVERSION
(RECTIFIER)
DC to DC
CONVERSION
(FLYBACK
CONVERTER)
DC to AC
CONVERSION
(INVERTER)

STAGE ONE : RECIFICATION
• converts ac to dc current.
• The kind of rectifier used in the circuit is Bridge
rectifier.
– provides full wave rectification
– low cost and weight compared to a rectifier with
a 3 wire output from a transformer with a
center- tapped secondary winding.

STAGE TWO : FLYBACK CONVERTER
• Simplest isolated DC-DC converter topology because
of absence of inductor at the output filter, only one
semiconductor switch and only one magnetic
component transformer or coupled inductor.
• Transient response is fast because of output inductor
absence.

V O
C
Gate pulses
Edc
Switch S
DN 1 N: 2
Fig. 3.1 Fly Back Converter
LoadPrimary Side
CIRCUIT OF FLYBACK CONVERTER :-

FLYBACK CONVERTER
PRINCIPLE OF OPERATION
+
Edc
V pri V sec
N1 : N2
V O
Fig. 6.3.3(a): Current path during Mode-1 of circuit operation
+
Edc V O
Fig. 6.3.3(b): Equivalent circuit in Mode-1
MODE-1
(MOSFET ON-STATE)

FLYBACK CONVERTER
MODE-2
(MOSFET OFF-STATE)
+
E dc
V O
Vpri = V O*N1/N2 , Vsec= V O
V pri V sec
N1: N2
+
E dc
V O
Fig. 6.3.4(a): Current path during Mode-2 of
circuit operation

FLYBACK CONVERTER
MODE-3
(MOSFET OFF-STATE, DIODE REVERSE BIASED)
+
E dc V O
During discontinuous mode, after complete transfer of the magnetic field
energy to the output, the secondary winding emf as well as current fall to
zero and the diode in series with the winding stops conducting. The output
capacitor however continues to supply uninterrupted voltage to the load.

STAGE THREE : INVERTER
Output of Flyback converter is fed to an
inverter.
 Inverter is an arrangement used to convert
DC to AC. Here we use 4 MOSFET arrangement
for this purpose.

POWER CIRCUIT
• Consist of MOSFET Driver TLP250
which drives MOSFET IR540 with pulses
obtained from PWM signals from PIC
Microcontroller.
• Flyback Converter Arrangement.
• Rectification of Input Voltage is done
using Bridge Rectifier.
CIRCUIT DIAGRAM

CONTROL CIRCUIT
• Consist of PIC 16F8774
Microcontroller which is
clocked by crystal oscillator
at 20Mhz frequency.
• LM7805 Voltage Regulator
is used to generate 5v from
12v for the operation of
PIC Microcontroller.

INVERSION CIRCUIT
• Consist of a combination of 4 MOSFETS
(Q1,Q2,Q3,Q4) in which (Q1 and Q4) is turned
ON during one cycle and (Q2 and Q3) during the
other cycle, thus acting as inverter. Gate pulses is
obtained from Port B of PIC through optocoupler
4N35 (for isolation). Two MOSFET Drivers IR2110
is used for driving these MOSFETs.

Optoisolater 4N35 is used to isolate the 5v voltage of the inversion
circuit from the voltages in rest of the circuit and ensure smooth
working.

ADVANTAGES
• Makes transmission and distribution using DC possible.
• DC grid can be used at places where there is a chance of
distributed renewable energy generation. It can be easily
integrated to grid without inverter.
AC grid can be used to power domestic loads.
• AC voltage as well as DC voltage can be obtained from
terminals on this transformer, which is useful for chemical
industries and energy storage systems.
• In small scale, size of various electronic devices and electrical
systems can be reduced, as most of the devices utilise DC in its
internal circuitry. Eg : Cars

OVERVIEW OF TYPICAL APPLICATIONS
OF SST

SMART GRID
• In future power systems, the usage of renewable generation is expected to
increase, and will require an energy management scheme that is
fundamentally different from the classic methods. For fast and efficient
management of the changes in different loads and sources, the SST can be
used to dynamically adjust the energy distribution in the grid. SST is
sometimes also called an energy router

Locomotives and other traction systems
The transformer used in current
locomotive vehicles is 16.7Hz and
is ±15% of the total weight of the
locomotive. The SST can
provide a significant weight
reduction.
 Additionally, the SST is also
able to improve the efficiency

Desired Renewable Energy Generation
Offshore generation, whether
from wind, tidal or any other
source, can benefit from the
reduction in weight and size.
leads to smaller and thus cheaper
offshore platforms.
SST can achieve unity power
factor, thus increasing the
efficiency in power transmission.

SST IN THE FUTURE SMART ELECTRIC SYSTEM
• Voltage transformation with decreased volume and space.
• Thus FASTER CHARGING..

HARDWARE MODEL
INPUT : 12v AC/ DC
OBSERVED OUPUT :
DC : 20v-120v,
AC : 0-55v
OUPUT can be varied by
VARYING DUTY RATIO OF PIC
USING POT.
INPUT and OUPUT VALUES CAN
BE INCREASED BY INCREASING
RATING OF EACH COMPONENT
AT OCCUPYING SAME SPACE
and VOLUME.

CONCLUSION
• Finally it is concluded that the conventional transformer which was used
widely in industrial applications so far having disadvantages like poor
voltage regulation, bulkiness etc. Majority of these problems can be
reduced or completely eliminated by solid state power electronic based
intelligent transformer. Also it has the capability to work as energy router
for smart grid energy internet.
The field of application of power electronic based solid state
transformer should not be limited up to only distribution level but
research work suggested that this intelligent solid state transformers are
having capacity to replace the conventional power transformer too in near
future.

SOLID STATE TRANSFORMER - USING FLYBACK CONVERTER

SOLID STATE TRANSFORMER - USING FLYBACK CONVERTER

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