the implementation of upqc technology to mitigate both ... implementation... · the quality of the...

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


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


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



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.


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


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.


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.


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.


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


❖ 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


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 !

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