A MULTILEVEL MEDIUM VOLTAGE INVERTER FOR STEP UP TRANSFORMER LESS GRID CONNECTION OF PHOTOVOLTAIC POWER PLANT

1. "A MULTILEVEL MEDIUM-VOLTAGE INVERTER FOR STEP UP
TRANSFORMER-LESS GRID CONNECTION OF PHOTOVOLTAIC
POWER PLANTS"
Under The Guidance Of
Internal Guide: External Guide:
Mrs. ANITA I PATIL DR.H.NAGANAGOUDA
Assistant Professor, Director Of National Training
Department of EEE,DBIT Centre For Solar Technology, KPCL
Mr.VIGHNESH G VERNEKAR 1DB11EE053
Mr.SAIF ULLA BAIG 1DB11EE038
Mr.PRAHALADA.K 1DB12EE406

2. INTRODUCTION
 The stability and control of grid connected PV power plants have attracted interest in recent
years
A power frequency transformer operated at 50 or 60 Hz is generally used to step up the
traditional inverter’s low output voltage to the medium-voltage level.
Because of the heavy weight and large size of the power frequency transformer, the PV inverter
system can be expensive and complex for installation and maintenance.
As an alternative approach to achieve a compact and lightweight direct grid connection, we
make use of a single- phase medium-voltage PV inverter system.
The medium-voltage inverter may be a possible solution to connect the PV power plant to the
medium-voltage grid directly.
Medium-frequency link operated at a few KHz to MHz is proposed to generate multiple isolated
and balanced dc sources for modular multilevel cascaded (MMC) inverters from a single source

3. Block diagram
Boost
Converter
Driver Circuit
Microcontroller
Power Supply
PV
array
Driver Circuit
LoadInverter
(MF)
Driver Circuit
Transformer
(MF)
Auxiliary
inverter
Rectifier

4. Disadvantages
Step-up-transformer-less and line-filter-less medium-voltage grid connection,
An inherent minimization of the grid isolation problem through the magnetic link,
An inherent dc-link voltage balance due to the common magnetic link,
A wide range of MPPT operation, and
An overall compact and lightweight system.
Advantages
 No of switches are more.

5. Photovoltaic array
PV arrays generates power which is input to the proposed system.
PV arrays use an inverter to convert the DC power into alternating current that can power the
motors, loads , lights etc.
PV cell are connected in series (for high voltage) and in parallel (for high current) to form a PV
module for desired output.
The modules in the PV array are usually first connected in series to obtain the desired voltage;
the individual modules are then connected in parallel to allow the system to produce more
current.

6. Maximum Power Point Tracking
Maximum power point tracking technique is used to improve the efficiency of the solar panel.
According to Maximum Power Transfer theorem, the power output of a circuit is maximum
when the source impedance matches with the load impedance.
 In the source side we are using a boost convertor connected to a solar panel in order to
enhance the output voltage.
By changing the duty cycle of the boost converter appropriately we can match the source
impedance with that of the load impedance.

7. Boost converter
A boost converter (step-up converter) is a power converter with an output DC voltage greater than
its input DC voltage.
Switches like IGBT,MOSFET are used in boost converter circuit.
Function of boost converter is to regulate, stabilize and boost the supply voltage.

8. Operation
 In the On state, the switch S is closed, resulting in an increase in the inductor current;
In the Off state, the switch is open and the only path offered to inductor current is through
the fly back diode D, the capacitor C and the load R. These results in transferring the energy
accumulated during the On-state into the capacitor.
a )Switch On b )Switch Off

9. Microcontroller

10. 8051 features
8051 have 128 bytes of RAM
ROM on 8051 is 4 Kbytes in size
8051 have 128 user defined flags
It consist of 16 bit address bus
It also consist of 3 internal and 2 external interrupts
Less power usage in 8051 with respect to other micro-controller
It consist of 16-bit program counter and data pointer
8051 can process 1 million one-cycle instructions per second
It also consist of 32 general purpose registers each of 8 bits
It also consist of Two 16 bit Timer/ Counter

11. Driver circuit
The main purpose of driver circuit is to enhance the switching voltage for the MOSFET or any
switching device and also to isolate the power circuit from the microcontroller circuit.
Since the power circuit current must not enter into the microcontroller circuit, MCT2E which is
the opto coupler will be connected to the buffer CD4050 which send pulse signals of 5V from
microcontroller to the driver circuit.
MCT2E is the device which isolates the power circuit with the microcontroller circuit. After it
gets the signal from the microcontroller it will get enhanced using the 2N2222 transistor to
higher level of voltage.
After this voltage gets regulated by the use of darlington pair. The darlington is made of
2N2222 (NPN) and SK100 (PNP) transistor.
330 OHM
MCT2E
1 K
22 K
100 OHM
100 OHM
100 OHM
1 K
1000mF/25A
G
GROUND
330 OHM
MCT2E
1 K
22 K
100 OHM
100 OHM
100 OHM
1 K
1000mF/25A
G
GROUND
330 OHM
1 K
100 OHM
100 OHM
G
100 OHM22 K

12. Multilevel inverter
An inverter is a device that converts DC power into AC power at desired output voltage and
frequency.
The term multilevel begins with the three levels.
The main merits of the multilevel inverter are high efficiency and good power quality.
As the number of voltage levels increases the harmonics content of the output voltage
waveform decreases significantly.
Power electronic converters are operated in the “switched mode”(turn on or turn off).

13. Circuit
Output waveform of full-bridge configuration.
Conducting switches Load voltages
S1, S4 +Vs
S2, S4 -Vs
S1,S2 or S3&S4 0
 In full bridge configuration, turning on S1 and S4 and turning off S2 and S3 give a voltage of VS
between point A and B ( AB V ) while turning off S1 and S4 and turning on S2 and S3 give a voltage
of Vs.To generate zero level in a full-bridge inverter, the combination can be S1 and S2 on while S3 and S4
off or vice versa..
Table : Load voltage with corresponding conducting switches

14. In transformer design, because the winding emf is proportional to the number of turns,
frequency, and magnetic flux linking the winding, for a given power capacity; as the operating
frequency increases, the required cross sectional area of magnetic core and the number of turns
of the primary and secondary windings can be dramatically reduced.
The silicon sheet steels, which are commonly used as the core material for power frequency
transformers, are not suitable for medium frequency applications because of the heavy eddy
current loss.
The soft ferrites have been widely used in medium and high frequency inductors and
transformers due to the low price and general availability.
This is also called inductive coil, medium frequency link, medium frequency transformer.
MAGNETIC LINK

15. FULL WAVE BRIDGE RECTIFIER
 The Bridge rectifier is a circuit, which converts an ac voltage to dc voltage using both half
cycles of the input ac voltage.

16. Components Driver circuit
1.IRFP460
2.Diode
1N4007
3.Capacitors
1000uF/50V
1000uF/25V
4.Optocoupler MCT2E
5.Transistors
2N2222
CK100
6.Resistors
1k
100ohm
7.Transformers
230V/12V
Boost converter
1. MUR1520
2. IRFP250N
3. CAPACITOR 470uF
Inverter
1. IRFP250N
Bridge rectifier
1. BR1010

17. SIMULATION
SimPowerSystems-SimPowerSystems and SimMechanics of the Physical Modeling product
family work together with Simulink to model electrical, mechanical and control systems.
Building the Electrical Circuit with powerlib Library
Interfacing the Electrical Circuit with Simulink
Measuring Voltages and Currents
Basic Principles of Connecting Capacitors and Inductors
Using the Powerlib Block to Simulate SimPowerSystems Models

18. BOOST CONVERTER CIRCUIT

19. BOOST OUTPUT

20. INVERTER CIRCUIT

21. INVERTER OUTPUT

22. PROPOSED SYSTEM 3 LEVELCIRCUIT

23. PROPOSED SYSTEM 3 LEVEL OUTPUT

24. COMPARING WITH 5 LEVEL CIRCUIT

25. 5 LEVEL OUTPUT

26. FFT ANALYSIS FOR 3 LEVEL CIRCUIT

27. COMPARING FFT ANALYSIS
FOR 5 LEVEL CIRCUIT

28. CONCLUSION
A new medium-voltage PV inverter system is proposed for medium or large-scale PV power
plants.
 A Medium frequency transformer is employed to interconnect PV arrays to form a single
source.
Multiple isolated and balanced dc supplies for the multi level inverter have been generated
through the common magnetic link, which automatically minimizes the voltage imbalance
problem .
The grid isolation and safety problems have also been solved inherently due to electrical
isolation provided by the medium-frequency link.
The elimination of the line filter and step-up transformer from the traditional system will
enable large cost savings in terms of the installation, running and maintenance of the PV power
plants.

29. Future scope
Prototype voltage is limited & current is also limited that can be improved by connecting more
battery banks & PV arrays.
The same concept can be used to develop the inverter for 6–36-kV system by changing the
number of secondary windings and the number of levels.
Research should be carried out to fulfill the future energy demand since it is economic and
renewable.
Voltage can be matched with the grid and power can be transferred from battery to grid
In the future if we are successful in generating higher power with less solar panels then this
method for transmission of power from solar plant will be cost effective and maintenance free.

30. THANK YOU