Presenter: NGOGA B. Julius Email: Ngogajls@gmail.com Session: - - PowerPoint PPT Presentation

Session: 2B.1 @ 13:45 -14:10 03rd Oct. 2018

Presenter: NGOGA B. Julius

Email: Ngogajls@gmail.com

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

• peration 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

• f 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-

• ut the entire UPQC system

To Investigate the Series APF to purposely mitigate under voltages and

• ver 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 L

V 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 k k

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 2

cos( )sin

L p p p Ln LK k

i I wt Q i i 

 

   

s L Sh

i i i  

1 1 1

sin( )cos

p p p

I wt    

L O A D

Vs

＋

is Rs

Ls

Vt

Vsr Vsh

VL iL

Load bus

＋

1p

Q

1n

V

1p

V

s

V

SR

V

• 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

abc h abc L abc

i i i

, , , 1

 

The primary input is the load current

abc h abc abc L

i i i

, , 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

• peration principle of the proposed

harmonic current extraction algorithm is introduced and analyzed:

1 1 2 2 1

2 2 2 2 ( ) sin sin 3 3

x k k k k k

l l i n I nk I nk N N      

 

                       



1 2

• 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

• f 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 2 sin cos sin sin 3 3 2 2 2 sin cos 3 3 2 2 2 cos sin 3 3

x

l l i I n I n N N l l I n I n N N l l I n N l l I 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 component FFT 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

ib ic

Vsa Vsb Vsc

v

v

v

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

• n 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

Enable

Gate signals of VSI-1

• ＋

Structure of series APF control Proposed sag detection methods

g f h

V 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 voltage FFT 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:

L O A D

Vs

＋

is Rs

Ls

Vt

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

• f 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

• f 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

• ptimize 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

• ther world class Journals, if we truly want to meet

Energy demands of our time.

• 7. Recommandations:

Thank you for your attention @Ngoga Julius !