Upload
others
View
0
Download
0
Embed Size (px)
Citation preview
Session: 2B.1 @ 13:45 -14:10
03rd Oct. 2018
Presenter: NGOGA B. JuliusEmail: [email protected]
The implementation of UPQC technology to mitigate both
current & Voltage based power quality problems
in modern distribution grid.
• Smart Grid: Main Goal
Linking electricity system stakeholder objectives
Upgrade the grid in Smart way
Electrical Infrastructure-Conv
“Smart/Intelligent” Infrastructure
• 1.Introduction
3
1.1 Background:
The quality of the electrical power supply has
a direct impact on the corrective function and
operation of equipments connected to the
public electricity supply network.
Because of non linear loads that are
connected to the grid ,Power quality
problems like load current harmonic
distortion, unbalanced voltage,
source voltage swells(over voltage)
and sags(under voltage) are
introduced.
Ever since,Researchers and utility
service providers have always suggested
and implemented many useful
technologies to mitigate the Voltage and
current based PQ problems.
When power utility consumers think of
PQ, they think of reliable power supply
at the load centres and at their
consumer equipments that is free of
interruption, and clean power that is
free from any disturbances at any time
of service
4
1.3 Objectives:
The Main objective of my work is to make a
detailed analysis on how to simulteneously
mitigate both voltage and current based power
quality problems in distribution power grid using
UPQC system.
To Investigate the Shunt APF for compensating
load current harmonics and so that the current
drawn from supply is completely sinusoidal in
nature.
To narrate the behavior of active
and reactive Power flow through-
out the entire UPQC system
To Investigate the Series APF to
purposely mitigate under voltages and
over voltages from the source and
make load voltage perfectly balanced
and sinusoidal in nature.
In pursuit of these objective:
An elaborated simulation is carried out in
MATLAB/SIMULINK2016.b to validate the perfomance of
APFs and the whole UPQC equipment in General.
FFT analysis techniques are used to enhance and prove the
correctness of the compensation techniques based on IEEE-
519 Std
• Introduction-cont....
2.Unified Power Quality Conditioner
Working principle and system topology:
Electric utility System + Transfomer + Feeder Load
Fif. 1: Single line diagram of a real system with out CP devices Fig 2: Single line diagram of a real system with CP devices
UPQC -conti....
6
Fig 3 : Detailed topology of UPQC
Fig 4: The equivalent circuit for UPQC
:Voltage at the power supply
:Series-APF for voltage compensation
The source voltage can be expressed as:
s sr LV V V
❖ To obtain a balance sinusoidal load voltage with fixed
amplitude V,the output voltage of the series-APF should be
given by:
1 1 2( ) sin( ) ( ) ( )sr p p Ln kk
V V V wt Q V t V t
:The positive sequence voltage
:The initial phase of voltage for positive seq.
:Negative sequence component
❖ The terminal source current in the shunt APF is
harmonic free sinusoidal and has the same phase
angle as the phase voltage at the load terminal:
1 1 1 2cos( ) sinL p p p Ln LKk
i I wt Q i i
s L Shi i i
1 1 1sin( )cosp p pI wt
LOAD
Vs+
is
Rs LsVt
Vsr
Vsh
VL
iL
Load bus
+
1pQ
1nV
1pV
sV
SRV
3. Subsystem II: Shunt APF
7
3.1 Shunt APF system topology:
❖ The role of SAPF is to supply the desirable current
components such that the utility source supply only the
active current component required by the load.
Equivalent circuit of SAPF
Shunt APF system topology
abchabcLabc iii ,,,1
The primary input is the load current
abchabcabcL iii ,,1,
❖ The load current at fundamental
frequency is given by:
Shunt APF -conti....
8
3.2 Harmonic current detection algorithm:
❖ The performance of SAPF strictly depends on the features of the current-detection algorithms and controllers. The figure shows the SAPF control system.
❖ Based on TTA and FFT techniques, the
operation principle of the proposed
harmonic current extraction algorithm is
introduced and analyzed:
1 1 2 2
1
2 2 2 2( ) sin sin
3 3x k k k k
k
l li n I nk I nk
N N
1
2
o x a
l x b
x c
❖ The three phase load currents can
be drawn into positive and negative
components as follows:
Shunt APF control system
Shunt APF -conti....
9
❖ Therefore, the fundamental current component is
expressed as follows:
❖ Figure below shows the block diagram of the proposed current-detection algorithm:
1 11 11 21 21
11 11 11 11
21 21
21 21
2 2 2 2(1) sin sin
3 3
2 2 2 2sin cos sin sin
3 3
2 2 2sin cos
3 3
2 2 2cos sin
3 3
x
l li I n I n
N N
l lI n I n
N N
l lI n
N
l lI n
N
Current detection block diagram
Shunt APF -conti....
10
3.3 Shunt APF simulation results:
❖ The figure shows the simulation model of shunt
APF where the load current waveform is non
sinusoidal due to nonlinear load and the source
current waveform may be sinusoidal but due to
nonlinear load there is small variation in source
current
❖ For example,the nonlinear load
is formed by using three-phase
uncontrolled rectifier module.
The output current of this load
has big percentage of harmonic
content. Compansation current
is generated by the Shunt APF
and is injected in anti-phase
with the load current at the
point of common coupling-
PCC.
Load current ,grid current and grid voltage
11
❖ The results represent the robustness of the
proposed algorithm for estimating
compensating current even when the supply is
distorted and unbalanced and the proposed
algorithm is fast enough to give the response in
less than one cycle.
Load current, fundamental component and harmonic
component.
Single phase component of load,fundamental and
harmonic currents
Proposed harmonic current extraction approach
Shunt APF -conti....
Shunt APF -conti....
12
❖ After compensating the current harmonic using
SAPF/ TTA approach, it is observed that the total
harmonic distortion is now 0.13% within IEEE-
519 limits and the correctness of the approach
used can be proved here below by studying the
FFT analysis of the fundamental component.
FFT analysis of the current before compansation
FFT analysis of fundamental componentFFT analysis of the current before compansation
13
❖ A sample case of distorted current supply
with fifth and seventh harmonic is
considered for the simulation study and the
waveforms corresponding to above case are
shown
❖ Calculating the corresponding
frequency for fifth order harmonic:
Load current, fifth order component and harmonic
component.
❖ Calculating the corresponding
frequency for seventh order
harmonic:
Load current, Seventh order component and harmonic component.
Shunt APF -conti....
7
7 7
7 *50 350
2* *
700
th
th th
F Hz
Phase pi F
pi
5
5 5
5*50 250
2* *
500
th
th th
F Hz
Phase pi F
pi
4. Subsystem II: Series APF
14
4.1 Series APF system topology:
❖ A series active power filter is a power
distribution equipment that is used to remove
all the voltage problems from supply voltage
and make load voltage perfectly balanced and
regulated
Electrical power Grid Non linear Load
Vca
Vcb
Vcc
.
.
.
...
controller Converter
.
a
b
c
n
Vsa
Vsb
Vsc
ia
ib
ic
va
vb
vc
ia
ibic
Vsa
Vsb
Vsc
c av
c bv
c cv
Series APF
An equivalent series APF power circuit
Series APF topology
❖ The series APF is connected between the supply
and load terminals using three single phase
transformers. In addition to injecting the voltage,
these transformers are used to filter the
switching ripple of the series active filter and
also help to compansate the distorted supply
voltage.
15
4.2 Voltage Sag/Swell Detection
E-PLL Method
1
Hysteresis comparator
Sag/swell Detection signal
-
+
c t
Phase voltage Sprop
Reference
Series APF -conti....
❖ The voltage sag/swell detection method based is based
on E-PLL approach and is shown in the figure below:
❖ By subtracting the error C(t) signal from the ideal
voltage magnitude , the voltage sag/swell depth (Sprop)
can be detected.
Reference computation
E-PLL
Comparator
Sag/swell Detection
Supply Voltage
Vs VPLL-S
Vamp-s
Verr-S
EnableGate signals of
VSI-1
-
+
Structure of series APF control
Proposed sag detection methods
g f hV V V
Where:• Vg is the grid voltage• Vf is the fundamental voltage• Vh is the harmonic voltage and• Vc is the compansation voltage
Series APF -conti....
16
4.3 Series APF simulation results:
❖ The figure shows the simulation model of series APF where the supply
voltage waveform is non sinusoidal due to nonlinear load
Matlab model of series APF
17
Voltages across series APF
during sags and swells.
Series APF -conti....
Grid voltage(sag),load voltage and compensation voltage
❖ Voltage sags and voltage swells for source voltages are
considered for simulation study at the same time and
the waveforms corresponding to all the cases are
shown in Figures below.
❖ Also shown is the FFT analysis of grid voltage before
compansation.
Grid voltage(swell),load voltage and compensation voltageFFT analysis of grid voltage
18
❖ The two figures below show the
single phase levels of voltage
sags and voltage swell that need
to be compensated
Single phase level of voltage sag to be compensated.
Series APF -conti....
Single phase level of voltage swell to be compensated.
19
❖ After compensating the voltage distortions, it is observed
that the total harmonic distortion is now 0.04% which is
within IEEE-519 limits and the correctness of the approach
used can be proved by the FFT analysis results of the
fundamental component
Source voltage, fundamental voltage and harmonic component.
Series APF -conti....
FFT analysis of the fundamental component
20
5. UPQC power flow analysis
5.1 Steady state Power flow analysis in UPQC:
LOAD
Vs+
is
Rs LsVt
Vsr
Vsh
VL
iL
Load bus
+❖ In the following analysis the load voltage is assumed to be
in phase with terminal voltage even during voltage sag
and swell condition.This suggests the real power flow
through the series APF and the voltage injected by series
APF could be positive or negative, depending on the
source voltage magnitude, absorbing or supplying the real
power
❖ Active Power Flow during Voltage Sag Condition:
❖ Ps'= Power Supplied the load during voltage sag
condition
❖ Psr'= Power Injected by Series APF in such way
that sum Psr'+Ps' will be the required load power
during normal working condition.
❖ Psh'= Power absorbed by shunt APF during
voltage sag condition
21
❖ Active Power Flow during Voltage Swell
Condition:
❖ Active Power Flow during Normal Working Condition
Power flow analysis -conti....
❖ Ps"= Power Supplied to the load during voltage
swell condition
❖ Psr"= Power Injected by Series APF in such way
that sum Ps"-Psr" will be
❖ the required load power during normal working
condition
❖ Psh"= Power delivered by shunt APF during
voltage sag condition
❖ There will not be any real power exchange
though UPQC. This is the normal operating
condition.
5.2 Power flow simulation results:
The Matlab Model for the integrated UPQC
equipment:
• Power flow analysis -conti....
23
Power flow analysis -conti....
❖ The power flow results specify the complete
simulation time where the green line
represents the active power (P) and red dash
line for reactive and harmonic power (QH)
through the grid and the load.
Normal sag sag/interrupt swell/interrupt sag/interrupt
Power flow during the simulation time
24
❖ The figure validates the operation
and performance of the series APF
and shunt APF parts of the
proposed UPQC system during
times of voltage sags and voltage
swells.
Normal sag sag/interrupt swell sag swell/interrupt
UPQC performance during sag and swells
Power flow analysis -conti....
25
6. Conclusions:
6.1 General Conclusions:
❖ A detailed study on Unified power quality
conditioner and it's subsystems has been
carried out to obtain proper mitigation results
to the targeted power quality problems.
Harmonic current and sag/swell extraction has
been done based on TTA , FFT and E-PLL
approaches.
❖ The computer simulations based on the FFT
anlysis results prove the correctness of the
UPQC tech. and threfore can be implemented
to agive a more reliable and Quality powerr
supply to the public equipments:
❖ Both current and voltage based power quality
problems in distribution grid have been
mitigated at the same time by customizing and
implementing UPQC.
❖ During simulation of Shunt APF and series
APF ,the effect of current harmonics and
voltage distortions has been minimized to the
tolerant limits based on IEEE-519 as have
shown in the FFT analysis results.
Shunt APF: 0.13% Vs 11.45%
Series APF: 0.04% Vs 20%
❖ Detailed waveforms to determine the behavior
of active and reactive power flow through the
source, load, and UPQC has been achieved (Ref part 5.2 )
6.2 Specific Conclusions:
There are several important points which need to be
investigated/suggested but could'nt be included in the scope
of my work to day:
❖ Investigating the operation of UPQC for the
power quality enhancement in the micro-grid
system
❖ Intelligent and new robust adaptive control
techniques have to be designed for UPQC to
optimize control objectives during different
power system perturbations and to meet the
next PQ demands that Industry 4.0 may bring.
❖ We can connect wind turbines, solar energy system
that is renewable source of energy to UPQC to get
improved power in consumer ends during serious
conditions.
❖ A detailed study to map the cost impact of power
quality problems should be given a clear research
based direction.
❖ Our academic and research Institutions should lead
this work by subscribing to IEEE publications and
other world class Journals, if we truly want to meet
Energy demands of our time.
7. Recommandations:
Thank you for your attention
@Ngoga Julius !