This project aims at a new low capacitance cascade H-Bridge multilevel inverter based StatCom. This system is able to operate with extremely low dc capacitance values.

1. LOW CAPACITANCE CASCADED H
BRIDGE MULTILEVEL BASED
STATCOM
PRESENTED BY
ANU THOMAS VDA16EE007
ASWATHY S ANAND VDA16EE015
RESHMA M D VDA16EE034
GUIDED BY
Mrs. NAVYA N
Asst. Professor

2. AIM
Our project aims at a new low capacitance cascade H-Bridge
multilevel inverter based StatCom.
This system is able to operate with extremely low dc
capacitance values.

3. INTRODUCTION
The increased electric power consumption causes transmission
lines to be driven close to or even beyond their transfer
capacities resulting in overloaded lines and congestions.
FACTS devices provide an opportunity to resolve congestions
by controlling active and reactive power flows as well as
voltages.
FACTS devices can be connected to a transmission line in
various ways, such as in series, shunt, or a combination of
series and shunt.

4. STATCOM BASIC WORKING PRINCIPLE
The Static Synchronous Compensator (STATCOM) is a shunt
connected reactive compensation equipment.
It is capable of generating or absorbing reactive power.
Its output can be varied so as to maintain control of specific
parameters of the electric power system.
The VSC generates a controllable AC voltage source.
This voltage is compared with the AC bus voltage system.

6. when the AC bus voltage magnitude is above that of the VSC
voltage magnitude, the AC system sees the STATCOM as an
inductance connected to its terminals.
Otherwise, if the VSC voltage magnitude is above that of the
AC bus voltage magnitude, the AC system sees the STATCOM
as a capacitance connected to its terminals.
If the voltage magnitudes are equal, the reactive power
exchange is zero
If the STATCOM has a DC source or energy storage device on
its DC side, it can supply real power to the power system.
This can be achieved adjusting the phase angle of the
STATCOM terminals and the phase angle of the AC power
system.

7. WHY STATCOM
Faster response
Better characteristics
Smaller in size
It has no moving parts and hence the maintenance is easier
WHY MULTILEVEL INVERTER
Improving power quality
Nearly sine wave output voltage as increase in level output
No need of passive filter at output
THD is reduced
Filter size is reduced and reduction in losses

8. WHY CASCADED H BRIDGE
It does not need any capacitors or diodes for clamping.
The wave is quite sinusoidal in nature even if you don’t filter it.
Easy and quick Manufacturing
We can control it Easily with a transformer
Inexpensive
WHY IGBT
High voltage capability
Low ON resistance
Ease of drive
Relatively fast switching speed

9. WHY REACTIVE POWER COMPENSATION
Improvement in voltage profile
Improves system power factor
Reduction of KVA demand
Higher load capability
Reduction in system losses
Increases system capacity and saves cost on new installations
Better efficiency of power generation, transmission and
distribution

10. DRAWBACKS OF LARGE CAPACITANCE VALUES
High direct cost of large dc capacitors.
The indirect cost on reliability of the system due to the
tendency of electrolytic capacitors to fail.
The indirect cost on cell protection due to the very large energy
that is dissipated in the dc-link.
The weight and volume of the converter, make it difficult to
containerize high-power Starcom’s.

11. LITERATURE SURVEY

12. A NOVEL CONTROL METHOD FOR
TRANSFORMERLESS H BRIDGE CASCADED
STATCOM WITH STAR CONFIGURATION
•Flexible ac transmission systems (FACTS) are being
increasingly used in power system to enhance the system
utilization, power transfer capacity as well as the power quality
of ac system interconnections.
•As a typical shunt FACTS device, static synchronous
compensator (STATCOM) is utilized at the point of common
connection (PCC) to absorb or inject the required reactive
power, through which the voltage quality of PCC is improved.

13. •In recent years, many topologies have been applied to the
STATCOM. Among these different types of topology, H-bridge
cascaded STATCOM has been widely accepted in high-power
applications for the following advantages.
•Quick response speed
•small volume
•high efficiency
•minimal interaction with the supply grid
•Its individual phase control ability
•Compared with a diode-clamped converter or flying capacitor
converter, H-bridge cascaded STATCOM can obtain a high
number of levels more easily and can be connected to the grid
directly without the bulky transformer.

14. •First, the control method for the current loop is an important
factor influencing the compensation performance.
•Second, H-bridge cascaded STATCOM is a complicated system
with many H-bridge cells in each phase, so the dc capacitor
voltage imbalance issue which caused by different active power
losses among the cells, different switching patterns for different
cells, parameter variations of active and passive components
inside cells will influence the reliability of the system and even
lead to the collapse of the system. Hence, lots of researches
have focused on seeking the solutions to these problems.

15. RESULT
•This paper has analyzed the fundamentals of STATCOM based
on multilevel H-bridge converter with star configuration. And
then, the actual H-bridge cascaded STATCOM rated at 10 kV 2
MVA is constructed and the novel control methods are also
proposed in detail with fuzzy logic. The proposed methods has
the following characteristics.

16. STATCOM OPERATION STRATEGY UNDER
POWER SYSTEM FAULT
•The STATCOM (Synchronous Static Compensator) operation
can be adversely affected due to Voltage Source Converter
(VSC) over-currents and trips, during power system faults.
•In this paper an “emergency PWM” strategy to prevent over-
currents (and trips) in the VSC during and after system faults is
developed.
•The STATCOM (Synchronous Static Compensator) based on
voltage source converter (VSC) is used for voltage regulation in
transmission and distribution systems.

17. •The STATCOM can rapidly supply dynamic VARs required
during system faults for voltage support.
•STATCOM losses and total system loss penalty preclude the use
of PWM (Pulse-Width Modulation) for VSC based STATCOM
applications.
•The “ emergency PWM” strategy is used to prevent over-
currents (and trips) in the 48-pulse VSC with magnetic
saturation and with slightly different B-H characteristics (due to
manufacturing tolerances) in series connected transformers,
during and after power system faults.
•The impact of B-H curve differences of series connected
transformers on STATCOM operation during system faults is
checked.

18. RESULTS
•The simulation results validate the “emergency PWM” strategy
to prevent VSC over currents and enable the STATCOM to
supply reactive power under system faults, and even with
different B-H characteristics for series connected transformers
in a VSC
•This control method provides a practical solution for high
efficiency non-PWM VSC based STATCOM under normal
system operation, and an “emergency PWM” mode to enable
online operation of the STATCOM during power system faults
and disturbances.

19. MULTILEVEL CONVERTERS A NEW BREED
OF POWER CONVERTERS
•Multilevel voltage source converters are emerging as a new
breed of power converter options for high-power applications.
•They typically synthesis a stare case voltage wave from several
levels of DC capacitor voltages.
•One of the major limitation is voltage unbalance between
different levels.
•To overcome this voltage clamping or capacitor charge control
is used.

20. •Multilevel starts from three levels consist of two capacitor
voltages in series and uses the central tap as the neutral .
•It has a quasi square wave output.
•As number of levels increases the output adds more steps ,
producing a staircase wave which approaches the sine wave
with minimum harmonic distortion.
•Zero harmonic distortion of the output wave can be obtained by
an infinite number of levels.
•But achievable voltage level is limited not only due to voltage
unbalance but also due to voltage clamping requirement , circuit
lay out and packaging constrains

21. RESULT
•This paper presents three transformer less multilevel voltage
source converters that synthesize the converter voltage by
equally divided capacitor voltages.

22. GENERAL BLOCK DIAGRAM

24. MEASUREMENT UNIT BLOCK DIAGRAM

26. PWM PULSE GENERATOR AND PARAMETER
DISPLAY UNIT BLOCK DIAGRAM

28. CASCADED H BRIDGE 7 LEVEL INVERTER
CIRCUIT DIAGRAM

30. Here shows the 7 level cascaded H bridge multilevel inverter.
The 7 levels are: +V, +2V, +3V, 0, -V, -2V, -3V
As the number of levels increased THD decreases(i.e. benefits
of multilevel inverter)
For every h bridge we connect an independent dc source
across it.

31. By switching the above 12 IGBT’s we get the appropriate
waveforms.
When we have n cascaded h bridge, then we will get a (2n+1)
level output.
Here n=3, 2n+1=2*3+1=7 levels.
To turn ON igbt, it needs a high voltage at its gate terminal.
Sig1, sig2, sig3,…are the gate pulses for different igbt’s.
These signals are the output from ic’s in igbt driver circuit.
To get +V as output voltage, Q1, Q4, Q7, Q8, Q11, Q12 should
be ON.
To get –V as output voltage, Q2, Q3, Q8, Q7, Q11, Q12 be ON.

32. •Across every h bridge, there is a capacitor called dc link
capacitor.
•It is used to smooth the voltage ripple in output voltage.
•In order to make the capacitance value low, we should select a
very high switching frequency for h bridge.
•Capacitor is designed based on: switching frequency and double
fundamental frequency.

33. IGBT DRIVER CIRCUIT

35. •The IC used in igbt driver circuit is V03120
•Inside V03120, there is an optocoupler
•In 2nd and 3rd pin there is a LED connected, i.e. when 2nd pin is
high and 3rd pin is low, LED will turn ON.
•8th pin is Vcc and 5th pin is ground. 7th and 6th pin is output.

36. •We are using an igbt drive circuit to get fast switching.
•Inside V03120, there is LED and photodiode, which acts as a
optocoupler.
•It provides an optical isolation from high voltage, if there is any
short circuit it will not effect the microcontroller.
•It also provides sufficient current for igbt switching.
•2nd and 3rd pin connected to emitter and collector of transistor
BC547.
•When 2nd becomes high and 3rd low, the 7th and 6th pin becomes
high.
•This Vo is given as sig1 through 1k resistor.

37. •The base of BC547 is connected to the microcontroller.
•According to which igbt we need to turn ON, give a high pulse
to the base of the corresponding transistor.

38. PWM PULSE GENERATOR AND
PARAMETER DISPLAY

40. The 12 ports from igbt driver circuit are connected to port D
and port B of microcontroller.
Here we use PIC16F77A.(of crystal frequency=20MHz)
13th and 14th pin are connected 20MHz crystal oscillator.
22pf capacitor is used for impedance matching between
microcontroller ports and crystal and also for noise cancellation.
25th and 26th pins are connected to a connector with 4 ports, the
remaining ports are Vcc and ground.
This connector is from measurement side, from where we get
the details about voltage, current, power factor etc.
The LCD is of 16*7 display(16 characters in two lines) and is
interfaced by 4 bit method.

41. MEASUREMENT UNIT

43. We measure voltage and current across load using CT and PT.
Using a zero crossing detector power factor is measured.
To measure current, we can see a inductor L1(CT coil)
So whenever there is any increase in current, the flux changes
which induce a voltage variation in windings(voltage change
directly proportional to current variation)
The output from CT is connected to a comparator(whenever the
voltage in non inverting terminal is more than inverting
terminal, then output will be high)
So whenever there is a change in zero crossing point we will
get a high pulse at its output

44. •The output of comparator will be a square like wave.
•In potential transformer side, a transformer is connected to step
down high voltage to low voltage.
•The output from both op amp is given to 19th and 20th pin of
microcontroller and monitor it.
•By comparing these zero crossing points, we can say whether it
is lagging or leading.
•The output from both CT and PT is given to a bridge rectifier to
get a dc output.
•A capacitor is connected across it which acts a filter(pulsating
dc to pure dc)

45. •This capacitor is connected to 2 resistors, which acts as a
potential divider network.(because output from load can vary,
our microcontroller can measure only 5V)
•So the output voltage is divided into 2 and protected by a Zener
diode.
•So to the 2nd and 3rd pin we connect the output from CT and PT.
•Here, the 19th and 20th pin is for power factor monitoring and
2nd and 3rd pin for voltage and current measurement.
•1st pin of microcontroller, a resistor is connected, which is
power on reset.