Harmonic mitigation using modular multilevel converter

1. 1
HARMONIC MITIGATION USING
MODULAR MULTILEVEL
CONVERTER

2. 2
PRESENTATION OVERVIEW
• Harmonics in Non-Linear Load
• Problem caused by Harmonics
• Harmonic Mitigation Measures
• Proposed - Active Harmonic Conditioner
• Harmonic Detection method
• Modular Multilevel Converter
• Active Vs Traditional Solutions

3. 3
HARMONICS
• Quality of Power - Stable Voltage
- Undistorted Waveform
• HARMONICS -Technique to analyze
Distorted Waveform
• Non-Linear System - V not proportional to I
-Distorted wave hard to analyze
=
Fourier Analysis : Distorted Periodic Pulse = Fundamental +
Series of Sine of varying
Amplitude, Multiple of
Fund. Frequency
HARMONICS

4. 4
PROBLEMS CAUSED BY HARMONIC
CURRENT
• Neutral Conductor Over-Heating
• Effects on Transformer
- Eddy Current Loss
-High temperature
• Skin Effect -Significant above H7
• Nuisance Tripping of Circuit
Breakers
• Over Stressing of Power Factor
Capacitor

5. 5
SOLUTONS
• Over Sizing of Neutral Conductor
• Using separate Neutral Conductors
• Special Transformers-K-Rated transformers
• Passive Filters
L/C Circuit Tuned to Trap
Harmonic Current
• Active power filters
• Hybrid Filters – Prominent harmonic – PF others by AF

6. 6
EVALUTION OF MITIGATION MEASURES
Advantage Disadvantage
K-Transformer
 elimination of voltage drops
due to harmonic current
circulation;
 Elimination of third
harmonic.
 derating of transformer
 influence of inrush current on
.
 high price:
Passive Filter
 Ease of implementation.
 Low Cost
 Influenced by modification in
supply frequency
 Influenced by change in circuit
impedance
increase of
neutral
conductor size
 no change of the earthing
system and mastering of
circulating neutral current.
 no reduction of the voltage
distortion;
 slight reduction of the voltage
drop in the neutral conductor;
 a lot of cabling works.
 Only for triple –N harmonics

7. 7
CURRENT INJECTION ACTIVE HARMONIC
CONDITIONER
• Removes Current Harmonics by Injecting Equal but
Opposite Harmonic Current
• Harmonics of Load Current is Cancelled
• Current Drain from Mains become Sinusoidal

8. 8
HARMONIC DETECTION METHODS
DISADVANTAGES OF FREQUENCY DOMAIN
•Antialiasing filter design
•Careful sync. between the sampling and
fundamental frequency
•Proper usage of zero-padding
•Large memory to store samples
•Large computation power needed
ADVANTAGES
Increased speed
Fewer calculations

9. 9
• Extensively used
• Load currents in the abc
coordinates (stationary
reference frame) from the
current sensors
• Transformed into dq (Direct
Quadrature) coordinates
(rotating reference frame with
harmonic frequency) by means
of the Park transformation
• dq frame rotates with the
angular speed of the harmonic
frequency that makes that
particular harmonic currents a
dc component and the
fundamental and other
harmonics ac components
SYNCHRONOUS INDIVIDUAL HARMONIC dq frame

10. 10
CONTROL ELECTRONICS
• DC output of LPF compared to zero- desired harmonic content
• To compensate static error – PI controllers are used
• O/P of PI controller – Harmonic reference for output current controller

11. 11
MODULAR MULTILEVEL CONVERTER
• MMC – In HVDC and FACTS as static synchronous compensator
(STATCOM) that act as either a source or sink of reactive AC
power in an electricity network
• But its application as active harmonic conditioning is used here
• Modularity – structure with identical modules
• Scalabe and no DC link voltage limitation
• Low losses due to low switching frequency in each submodule
but effective switching frequency of the converter is high

12. 12
MMC – DOUBLE STAR SCHEMATICS
• Two IGBT (S1 and S2)
with free wheeling diode
in antiparallel
• Capacitor : Depending on
the current direction the
capacitor can charge or
discharge
Half-bridge submodule

13. 13
WORKING OF HALF-BRIDGE SUBMODULE
• ON or inserted state S1 is on, S2 is
off. Output voltage, Vx = capacitor
voltage
capacitor charges if the multivalve
current is positive and discharges
otherwise
• OFF or bypassed state S2 is on, and
S1 is off. Output voltage= zero and the
capacitor voltage is constant, i.e. the
capacitor will not charge nor
discharge.
• Blocked state, S1 ad S2 - off, and
the current can only conduct through
the freewheeling diodes. The capacitor
will charge if the current is positive,
but ideally it cannot discharge

14. 14
EXPERIMENTAL RESULT
15 % REDUCTION IN
HARMONIC CURRENT
WITHOUT COMPENSATION
WITH HARMONIC COMPENSATION

15. 15
• Harmonic Voltage = Source Impedance X
Harmonic Current
• Harmonic current mitigated means major V harmonic
corrected
• Same process
• Vpcc – ref.
grid value used
• line impe
-ance Znh to
be considered
VOLTAGE HARMONIC CONTROL

16. 16
DISADVATAGES
SM CAPACITOR BALANCING ALGORITHM
• Extra controller for balancing of capacitor voltage
• Need for monitoring capacitor voltage
• Circulating current between arms

17. 17
ADVANTAGES
• Passive component reduction
• Continuity of operation even under the failure of any
submodule
• Ease of maintenance
• Lower conduction losses
• There is no risk of resonance with any harmonic
frequency
• Flexible in terms of load expansion and shift in load
profile

18. 18
ACTIVE VS PASSIVE
passive filter
active harmonic
conditioner
harmonic-current control
requires a filter for each
frequency (bulky)
simultaneously monitors
several frequencies
influence of a frequency
variation
reduced effectiveness no effect
influence of a modification in
the impedance
risk of resonance no effect
influence of an increase in
current
risk of overload and damage
no risk of overload, but less
effective
added equipment (load)
in certain cases, requires
modifications to the filter
no problem if I_conditioner >
I_load_harmonics
harmonic control by order very difficult Possible
modification in the
fundamental
frequency
cannot be modified
possible via reconfiguration

19. CONCLUSION
19
• Non-linear loads makes harmonic distortion on power
networks a phenomenon of increasing amplitude.
• Most popular solution was passive filtering.
• Attractive alternative to this complex and non risk-free
solution is now commercially available in the form of
active harmonic conditioners.
• Possible to mitigate harmonics upto 13th order
• Results show 15 % reduction in THD

20. REFERENCE
20
• IEEE ACCESS- HIGH ORDER VOLATGE AND CURRENT HARMONIC
MITIGATION USING MODULAR MULTILEVEL CONVERTER - SEPT
2017
• IEEE - HARMONIC DETECTION METHOD FOR ACTIVE POWER FILTER
APPLICATION – 2007
• SINGLE-PHASE SHUNT AND SERIES ACTIVE HARMONIC FILTERING
FOR IMPROVING POWER QUALITY By Suresh Kuamr K.S. Associate
Professor, Dept. of Elect. Engg. N.I.T ,Calicut
• IEEE - A STUDY ON SAPF BASED ON MODULAR MUTILEVEL CONVERTER
• POWER ELECTRONICS BY B.K. GUPTA

21. THANK YOU
21

22. 22
HARMONIC SEQUENCE
A
BC
A
B
C
BA
C

23. 23
GENERALLY KNOWN AS
• Even Harmonics-Even Multiple of Fundamental
• Odd Harmonics- Odd Multiple of Fundamental
• Inter Harmonics-Non-Integral Multiple of Fundamental
• Sub Harmonics-Inter Harmonics with Frequency Less
than Fundamental
EVENS CANCEL
Signals Symmetrical about Centerline

24. 24
EQUIVALENT CIRCUIT OF NON-LINEAR LOAD
• Non-Linear Load = Linear Load + Current Source
(one for each Harmonic)
• Harmonic Generator – Current Source
• Harmonic Voltage = Source Impedance X Harmonic
Current

25. 25
HARMONIC CURRENT CALCULATOR
• DISTORTION = Iactual — (Iactive + Ireactive)

26. 26
DETAILED BLOCK DIAGRAM
• FU1 : Ultra fast protection fuse
• R1 and K1: Precharge system for chemical capacitors C2 C3
• Lf and Cf : Filter to attenuate the effects of chopping
• L1 : DC/AC Converter
• CT1 : External Sensor for current drawn by Load
• CT2 : Sensors for Inverter Current

27. 27
DESIGN CONCERNS
• DC bus nominal voltage, greater than or equal to line
voltage peak in order to actively control.
• Selection of Interface Inductance is based on the
compromise of keeping the output current ripple of the
inverter low and able to track the desired source current.
• Capacitor value is dictated by the maximum acceptable
voltage ripple.

28. 28
IF
Then
For pure current source
type of harmonic source
Then
Result: Compensation
Characteristics of AF not
Influenced by Zs
hS
h
L Z
G1
Z


LhC II 
SL ZZ 
 G1
I
I
LH
S 
1G1 h


29. 29
EQUIVALENT CIRCUIT
Zs =Source Impedance
ZL =Equivalent Load Impedance
ILH = Equivalent Harmonic Current Source
G =Equivalent Transfer Function of Active
Filter

30. 30
ACTIVE FILTER EQUATIONS
G1
Z
Z
V
I
G1
Z
Z
Z
I
L
S
S
LH
L
S
L
S






G1
Z
Z
V
G1
1
I
G1
Z
Z
G1
Z
I
L
S
S
LH
L
S
L
L








1h
G0G1

LC GII 