Grid Observer - Sample approach

This document contains a report on the project ‘Grid Observer for Grid-tied-Inverter’.

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Grid observer for Grid-tied-Inverter

Project title Grid observer for Grid-tied-inverter

Project type Project 2 Status Report

Prepared by Abraha Biruke Advisor DI (FH) Alfred Karl Steinhuber, MSc

University FH Joanneum University of Applied Science

Department Advanced Electronic Engineering

Major Automotive Electronics Version 0.1

E-Mail [email protected]

Date 02.04.2015

Grid Observer for GTI

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Contents Acknowledgement ……………………………………………………………………………………………………………………………………. i

1 Introduction .................................................................................................................................................... 1

2 Scope ............................................................................................................................................................... 1

3 Background ..................................................................................................................................................... 2

4 Grid observer design ....................................................................................................................................... 4

4.1 Functional and non-functional requirements ........................................................................................ 4

4.2 Design idea and approach ..................................................................................................................... 4

4.3 Models ................................................................................................................................................... 5

4.3.1 Grid voltage deviation detection ....................................................................................................... 5

4.3.2 Voltage dip ........................................................................................................................................ 7

4.3.3 Availability of phase .......................................................................................................................... 8

4.3.4 DC bias deviation detection .............................................................................................................. 9

4.3.5 Frequency deviation detection ....................................................................................................... 10

4.3.6 Overall control model...................................................................................................................... 13

4.4 Simulation and test .............................................................................................................................. 14

4.4.1 Simulation ....................................................................................................................................... 14

4.4.2 Test .................................................................................................................................................. 15

5 Conclusion ..................................................................................................................................................... 24

6 Appendix ....................................................................................................................................................... 25

7 References..................................................................................................................................................... 27

Grid Observer for GTI i

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Acknowledgement

I would like to thank my advisor, DI (FH) Alfred Karl Steinhuber, MSc for his committed

guidance, valuable advices and tips during the research part of the project entitled ‘Modular

concept for grid-tied- converter till 1MVA’ and this design related extension part on grid

observer of GTI.

Grid Observer for GTI 1

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1 Introduction

The aim of this paper is to present the design of a grid observer for grid-tied-inverter (GTI) using

Matlab/Simulink based on the international norms and standards documented on the project ‘Modular

Concept for grid tie converter till 1MVA’.

2 Scope

This paper explains the steps followed to model a grid observer of a GTI. The grid observer algorithm

implemented here observes (detects) grid faults and disconnects the GTI according to specified grid

parameter variations and disconnection times. The designed algorithm covers the most important grid

faults and works in single precision floating point arithmetic. It is possible to generate the code of the

algorithm for hardware testing and implementation but this is not covered in this paper.


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3 Background

Grids can sometimes fail. This can be due to weather conditions such as lightening, wind, rain and

other mechanical or material related reasons. Renewable energy sources such as PV systems tied to

the grid then need to disconnect from the grid in case of abnormal grid conditions in terms of voltage

and frequency. This response is to ensure the safety of utility maintenance personnel and the general

public, as well as to avoid damage to connected equipment, including the PV system. A more detailed

explanation on this can be found on the first part of this project, ‘Modular Concept for grid tie

converter till 1MVA’.

Grid observer is an on-board processor integrated in GTIs and is a control structure which detects grid

faults and disconnects the GTI from the utility line. The figure below shows a generic topology-invariant

control structure for a typical transformerless topology with boost stage:

Figure 1 Generic control structure for a PV inverter with boost stage [1]

The basic abnormal grid conditions which are integrated into the grid observer algorithm of this project

include:

Voltage deviation

Voltage dip

Frequency deviation

DC bias

Reconnection after trip


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The table below outlines grid faults due to voltage deviations and the related disconnection times

according to standards IEEE Std 1547 and IEC 61727.

Table 1 Disconnection time for grid nominal voltage deviations [1]

IEEE Std 1547 IEC 61727 Voltage range (%) Disconnection time (sec) Voltage range (%) Disconnection time (sec)

V < 50 0.16 V < 50 0.10

50 ≤ 𝑉 < 88 2.00 50 ≤ 𝑉 < 85 2.00

110 < 𝑉 < 120 1.00 110 < 𝑉 < 135 2.00

𝑉 ≥ 120 0.16 𝑉 ≥ 135 0.16

The disconnection times for grid frequency deviations is also presented in the table below. The

standard IEEE Std 1547, a US standard, works for grid frequency of 60𝐻𝑧 and IEC 61727, a European

standard, is for grid operating frequency of 50𝐻𝑧.

Table 2 Disconnection time for grid frequency deviations [1]

Once the GTI is disconnected from the grid due to grid faults, the tolerable voltage and frequency

ranges where the GTI can be reconnected (also called reconnection after trip) are outlined in the next

table.

Table 3 Conditions for reconnection after trip [1]

IEEE Std 1547 IEC 61727

88<V<110(%) 85<V<110(%)

𝐴𝑁𝐷 𝐴𝑁𝐷

59: 3 < 𝐹 < 60.5 𝑓𝑛 − 1 < 𝑓 < 𝑓𝑛 + 1(𝐻𝑧)

The next section presents procedures followed to develop the algorithm for grid observer in

Matlab/Simulink.

IEEE Std 1547 IEC 61727 DR peak capacity(KW)

Frequency range (Hz) Disconnection time (sec)

Frequency range (Hz)

Disconnection time (sec)

≤ 30 < 59.3 𝑜𝑟 > 60.5 0.16 𝑓𝑛 − 1 < 𝑓𝑛 < 𝑓𝑛 + 1 0.20

> 30 < 57 𝑜𝑟 > 60.5 0.16

57-59.8 (Adjustable set point)

Adjustable 0.16 to 300


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4 Grid observer design

As outlined in the background section of this paper, the grid observer was designed so that it would

detect the specified fault types and disconnect the inverter according to the disconnection time of the

specific standards implemented.

4.1 Functional and non-functional requirements

The algorithm for the grid observer had the following functional requirements:

Detect grid faults

Disconnect GTI during faults

Reconnect after trip

Single point precision

Sampling period of 10𝜇𝑠

The main non-functional requirement was that the algorithm should have general user interface (GUI)

so that the user can easily modify parameters and/or make a model test on specific fault types.

4.2 Design idea and approach

The basic concept of the model for the control algorithm was that the grid is connected to the inverter

using a main switch which can be controlled by the grid observer in accordance to the existence of grid

faults. The figure below shows this:

Figure 2 Block diagram for the control algorithm


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Designing the algorithm involved the following considerations:

Implement the basic fault detection algorithms using ‘State Flow Chart’ of Simulink library.

Design each faults to be detected in a separate State flow chart for simplicity and easy

modification.

The control algorithm should be able to work with at least two of the main standards

presented in the previous section of this paper and newly inserted user standards/norms.

The solver type should be fixed step with fixed step size of 10𝜇𝑠.

Use Simulink blocks that simplify the extra effort in design such as ‘RMS’ and ‘Mean’ blocks.

The Simulink design should be fully controllable from a Matlab script.

4.3 Models

This section presents each major blocks of the grid observer separately.

4.3.1 Grid voltage deviation detection

The algorithm which detects voltage deviation faults and disconnect the grid from the GTI is shown in

the figure below:

Figure 3 Voltage deviation fault detector block

The above block detects grid rms voltage deviations. Assuming that the grid faces voltage deviation

faults, say one or all of its three phases’ rms voltage exceeds by 10 − 20% of the maximum rms value,


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then the algorithm makes sure an error flag with a disconnection time of 1 sec is set. This is outlined

in Table 1 of this paper.

To calculate the rms voltage, a ‘Running RMS’ block which calculates the real time rms of each grid

phase voltage was used. The ‘Standard Reference’ subsystem shown above stores grid fault standards

set from the Matlab workspace. Both the rms calculations and reference of standards were fed as

inputs to the ‘Voltage Deviation Detector’ state flow chart which checks for faults and acts accordingly.

This state flow chart is shown in the figure below:

Figure 4 Voltage deviation detector

In the above figure, the Matlab function 𝒓𝒎𝒔(𝑤, 𝑥, 𝑦, 𝑧) takes in a previously calculated (using Running

RMS block) rms values of each grid phase voltages, and the standard references. It then returns the

error status and disconnection time (if non-tolerable deviation occurs) in accordance to the rms

voltage deviation of each phase. The Matlab function 𝒎𝒚𝑾𝒂𝒊𝒕(𝑎, 𝑏, 𝑐) compares the disconnection

time delay of each phase and returns the least. During the existence of fault, the error status flag is set

with a specific time delay and this was implemented using the temporal logic ‘𝒂𝒇𝒕𝒆𝒓(𝑡, 𝑠𝑒𝑐)’. This

function creates the time delay required but it should be noted here that this is a simulation time (not

a real time) delay. The code snippet of the aforementioned functions can be found in the appendix of

this paper.


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4.3.2 Voltage dip

Similarly here, ‘Running RMs’ block was required for rms calculation of each grid phase voltage.

Additionally, an rms reference value was required. The outputs of these two subsystems were fed as

inputs to the voltage dip detector state flow chart which outputs error status, fault type and GTI

disconnection time delay. This is shown in the block diagram below:

Figure 5 Voltage dip fault detector block

The above state flow chart uses a truth table to check if deviation of the rms voltages of the three

phases occurs.

Figure 6 Voltage dip detector

The truth table in the above figure was implemented through the use of Condition and Action table.

Each ‘condition’ inside the condition table, when fulfilled, called a related ‘Action’ from the action

table. The return values of the truth table which included error, fault type and disconnection time

delay were inserted into the ‘Action’ part of the action table to be modified in accordance to the


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conditions satisfied. These return parameters are then used to control the connection status of the GTI

with the grid. The detail of the conditions used for the truth table 𝒎𝒚𝑽𝑫𝒊𝒑(𝑥, 𝑦, 𝑧, 𝑞) can be found

in the appendix of this paper.

4.3.3 Availability of phase

An algorithm with a state flow chart was built which helps to identify phases with voltage deviation

fault. This block takes the error status outputs of the block ‘Voltage deviation detector’ and displays

phases with fault.

Figure 7 Phase fault detector

The figure below shows the way the ‘Availability of phase’ block works:


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Figure 8 States identifying phases with fault

4.3.4 DC bias deviation detection

This block works through calculating the mean value of the grid voltages on a real time basis and

comparing these calculated values with the tolerable DC offsets set according to a specified standard.

For this ‘Running Mean’ block, which runs and calculates the mean of each phase voltage, was used.

This block simplifies the effort required for computation which otherwise would require one to write

a potentially complex algorithm just to calculate the mean of a continuous signal on a real time basis.

The overall block is shown in the figure below:

Figure 9 DC bias fault detector


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The ‘DC bias fault detector’ state flow chart is presented in the figure below:

Figure 10 DC bias offset algorithm

As can be seen above, the DC bias offset fault detector was built with a simple algorithm using truth

table. ‘Condition’ and ‘Action’ table were used to control the three parameters(error, fault type and

disconnection time delay) where in case a non-tolerable DC offset occurs, the GTI is disconnected from

the grid after a time delay 𝒕 set according to the specific standard used. The detail of the truth table

𝒎𝒚𝑴𝒆𝒂𝒏(𝑥, 𝑦, 𝑧, 𝑞) can be found in the appendix of this paper.

4.3.5 Frequency deviation detection

This part of the grid observer algorithm works using a phase locked loop (PLL) block which synchronizes

to the frequency of the grid. The PLL´s oscillator has to first be adjusted to synchronize with a 50Hz or

60Hz grid frequency, according to the standard the GTI is intended to be used with. If the grid voltage

and frequency face no faults, the PLL would synchronize to that frequency. But during an imbalance of

grid voltage or frequency or the existence of a deviation of a phase grid frequency, the PLL´s frequency

fluctuates.

Figure 11 Phase Locked Loop (PLL)


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The PLL block was built first by performing the so called ‘Park transformation’ of the three phase (𝑎𝑏𝑐)

voltages to two phase 𝑑𝑞0 reference frame which made the task of synchronizing the oscillator

simpler. Park transformation is a space vector transformation of three-phase time-domain signals from

a stationary phase coordinate system (𝑎𝑏𝑐) to a rotating coordinate system (𝑑𝑞0) [3]. This

transformation was done first by transforming the natural three-phase coordinate system (𝑎𝑏𝑐) into

a stationary two-phase reference frame (𝛼𝛽) and then 𝛼𝛽 to 𝑑𝑞0.

To convert 𝑎𝑏𝑐 to 𝛼𝛽 coordinate system, the following Matrix equation was used:

[

𝑈𝛼

𝑈𝛽

𝑈0

] =2

3

[ 1 −

1

2−

1

2

0√3

2−

√3

21

2

1

2

1

2 ]

[

𝑈𝑎

𝑈𝑏

𝑈𝑐

] 1.1

Then the 𝑑𝑞0 rotating coordinate system was then calculated as in the Matrix equation below:

[

𝑈𝑑

𝑈𝑞

𝑈0

] = [cos𝜃 sin 𝜃 0−sin𝜃 cos𝜃 0

0 0 1] [

𝑈𝛼

𝑈𝛽

𝑈0

] 1.2

The figure below shows the Simulink model used for the above transformation:

Figure 12 𝒂𝒃𝒄 to 𝒅𝒒𝒐 transformation

The overall model for the frequency deviation detector is shown below:


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Figure 13 Frequency deviation detector

The PLL´s frequency and the standard for frequency deviation were fed as inputs to the ‘Frequency

deviation detector’ block as shown in the figure above.

Figure 14 State flow chart for identifying frequency faults

The code snippet for the function 𝒇𝒓𝒆𝒒(𝑤, 𝑥, 𝑦, 𝑧) can be found at the appendix section of this paper.


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4.3.6 Overall control model

All the above blocks were now integrated into one system. The next figure shows this:

Figure 15 Overall grid observer model

The block diagram for the whole system is shown below where the grid observer which is an on-board

processor on the GTI is shown separately for easier understanding of how the grid observer works. The

signal sent from the grid observer to the main switch is a grid fault status generated by the above fault

detection blocks.

Figure 16 Block diagram of the built system


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4.4 Simulation and test

This section outlines how the model works and the tests implemented for validation.

4.4.1 Simulation

The developed model is controlled from a Matlab script where input dialog box was used to take in

user data for the three phase grid voltage. These included peak voltage, frequency, phase shift and DC

offset of each phase. The sampling period and other reference parameters of rms voltage, DC offset

and operating frequency were also easily modifiable using the GUI. The figure below shows this:

(a) (b)

Figure 17 showing input dialogs for phase 'a' and other reference parameters

‘Choice quest’ dialog box was also used which prompts the user to select a standard. Here, standards

IEC 61727 and IEEE Std 1547 were configured into the algorithm. If required, the user can also insert a

different standard.

Figure 18 Prompt for choosing a Standard

The figure below shows the way the errors and fault types would be displayed. This helps in identifying

fault types and phases with fault.


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Figure 19 Display with no faults or errors showing all phases are available

The ‘SystemError’ is set if the error for any of the fault types is set.

4.4.2 Test

Another Matlab script was prepared to test the response of the system where faults can be introduced

to an already running model. This gives the advantage of testing the developed model on a virtual real

time basis. The script first asks the user which one of the parameters is intended to be modified for

test and then displays the specified parameter of the three phases. The next figure shows this for

testing grid voltage faults.

(a) (b)

Figure 20 Grid voltage fault test

Testing the algorithm (grid observer) was made first by running the model with the right parameters

for the grid voltage. i.e., a three phase grid voltage of peak amplitude 325𝑉(230 𝑉𝑟𝑚𝑠), 50𝐻𝑧

frequency, 𝑧𝑒𝑟𝑜 DC offset and 120 0 phase shifted signals. Then after 1 second of simulation time

(where the GTI is expected to stay connected to the grid), a fault was introduced and the response of

the grid observer was analysed. Since reconnection after trip (meaning that the GTI needs to reconnect


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back to the grid once the introduced fault is removed) had to be tested too, the fault was again

manually removed after 2 seconds of simulation time.

Note: All the three testes below were made based on IEC 61727 standard.

Test case #1: Grid voltage

A voltage fault was introduced to phase ‘a’ of the grid voltage after 1 second of simulation time as

shown in figure 20(b) above. The resulting faults and errors is shown below:

Figure 21 showing grid faults for 'voltage dip' and 'voltage deviation'

As the rms of phase ‘a’ is 260V which is 80% of the nominal value of 325V, the algorithm which detects

voltage dip faults should set its error flag. This is because the maximum tolerable voltage dip is 90%. It

can be seen in the above figure that this error flag has been set with a disconnection time of 1 second

and its own fault type code of 4.1. The number ‘4’ here stands for voltage dip faults and ‘1’ for phase

‘a’ which means that phase ‘a’ has faced voltage dip fault. This code is just part of a number of fault

identifying codes used in the overall design to increase the readability and controllability of the

algorithm. Considering that the rms voltage of phase ‘a’, according to standard IEC 61727 shown in

Table 1, falls in a voltage deviation range of 50-85% of the nominal value, the voltage deviation

detection algorithm has to (and did) set its error flag. It can be seen above that the disconnection time

for this is 2 seconds. The display for the voltage deviation additionally shows which of the phases has

introduced this fault and the available single phase the GTI has to get synchronized with (phase ‘b’ in

this case). As a result of the above faults, the overall system error, which is a logical combination of all

error statuses, was set high. A scope block was used to look whether the GTI was disconnected from

the three phase grid within the specified time and reconnected back after the fault is removed.


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Figure 22 Three phase signal over the GTI for an introduced voltage fault

The figure below shows a closer look at the response:

Figure 23 Three phase signal over the GTI for an introduced voltage fault (closer look)

The above figures show that the grid observer has disconnected the GTI from the grid 1 sec after the

fault was detected (close to 2 sec simulation time). This is a result of the error flag set by ‘Voltage dip’

block. The exactness of the disconnection time also depends on how exact the time of fault

introduction was. Even though the fault was removed at time 2 sec, the GTI was able to reconnect

after another 2 seconds. This is because the grid observer was bounded by the time limit the ‘Voltage

deviation’ block has laid, which is 2 seconds.

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

-300

-200

-100

0

100

200

300

Time [sec]

3 P

ha

se

gri

d p

ea

k v

olta

ge

ove

r th

e G

TI [V

]

Grid Voltage deviation (fault) and reconnection after trip

2 2.5 3 3.5 4

-300

-200

-100

0

100

200

300

Time [sec]

3 P

ha

se

gri

d p

ea

k v

olta

ge

ove

r th

e G

TI [V

]

Grid Voltage deviation (fault) and reconnection after trip


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Test case #2: Frequency

With a similar procedure to the previous test case, a frequency deviation fault was introduced at

simulation time of 1 second to phase ‘b’ of the grid voltage as shown in the figure below:

Figure 24 Fault was introduced by deviating the frequency of phase 'b'

The resulting error and fault flags are shown below:

Figure 25 Fault and error flags set for frequency deviation

The display for frequency deviation shows that the error flag is set with a fault code identity of ‘2.1’

and grid disconnection time delay of 0.2 seconds meaning that the grid observer should be able to

disconnect the grid within 0.2 seconds of fault detection. All phases are available as shown in the

display for voltage deviation. The identity code ‘7’ stands for this. The response of the grid observer

is shown below:


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Figure 26 Three phase signal over the GTI for an introduced frequency fault

A closer look for the above plot can be seen in the figures below:


0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

-300

-200

-100

0

100

200

300

Time [sec]

3 P

ha

se

gri

d v

olta

ge

ove

r th

e G

TI [V

]Grid frequency deviation fault

phase a

phase b

phase c

1 1.5 2 2.5

-300

-200

-100

0

100

200

300

Time [sec]

3 P

ha

se

gri

d v

olta

ge

ove

r th

e G

TI [V

]

Grid frequency deviation fault

phase a

phase b

phase c


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As can be seen in figures 26 and 27, the GTI was disconnected from the grid as per the original

expectation showing that the algorithm works fine. But, it can be seen in the above figures that the

GTI was reconnected back to the grid for a very short period. The reason has not be clear and can be

due to the way the designed algorithm for the frequency detection works. Reconnection of the GTI to

the grid could not be achieved here because the frequency of the PLL´s oscillator wasn´t able to re-

synchronize to the operating frequency of the grid and this is a result of the disturbance the unbalance

of the phase frequencies has already introduced.

Figure 29 PLL synchronization to Grid voltage before and after frequency fault introduction

The above figure shows how the PLL responds to the frequency fault introduced after 1 second of simulation time. It can be seen that the PLL was able to synchronize to the 50Hz three-phase grid prior to fault introduction.

1.98 2 2.02 2.04 2.06 2.08 2.1

-300

-200

-100

0

100

200

300

Time [sec]

3 P

ha

se

gri

d v

olta

ge

ove

r th

e G

TI [V

]

Grid frequency deviation fault

phase a

phase b

phase c

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 544

46

48

50

52

54

56

Time [sec]

Fre

qu

en

cy [H

ert

z]

PLL frequency synchronization to grid


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Test case #3: DC Bias

Similarly here, a DC bias offset was introduced to phase ‘c’ of the grid voltage.

Figure 30 DC bias fault introduced to phase 'c' of the grid voltage

The following displays the resulting fault and error flags:

Figure 31 showing DC bias error flag was set

It can be observed in the DC bias display that the error flag is set with fault type identity of ‘3.1’, a code

used to identify DC bias faults. The GTI was disconnected and reconnected back in accordance to the

disconnection time limits fixed by the grid observer.


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Figure 32 Three phase signal over the GTI for an introduced DC bias fault

Figure 33 Three phase signal over the GTI for an introduced DC bias fault (closer look)

Since the fault was manually removed at time 2 sec, the GTI was reconnected back at time 3 sec. This

shows that the grid observer is working as expected.

0 0.5 1 1.5 2 2.5 3 3.5 4

-300

-200

-100

0

100

200

300

Time [sec]

3 P

ha

se

gri

d p

ea

k v

olta

ge

ove

r th

e G

TI [V

]

Grid DC bias fault and reconnection after trip

1.8 2 2.2 2.4 2.6 2.8 3 3.2

-300

-200

-100

0

100

200

300

Time [sec]

3 P

ha

se

gri

d p

ea

k v

olta

ge

ove

r th

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TI [V

]

Grid DC bias fault and reconnection after trip


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Figure 34 3V DC Offset for phase 'c'

Figure 35 3V DC Offset for phase 'c'

The above two figures show a closer look at the 3V DC offset introduced to phase ‘c’ of the grid voltage.

1.9 1.92 1.94 1.96 1.98 2 2.02320

321

322

323

324

325

326

327

328

329

330

Time [sec]

3 P

ha

se

gri

d v

olta

ge

ove

r th

e G

TI [V

]

DC Offset of 3V for phase 'c'

phase a

phase b

phase c

1.9 1.92 1.94 1.96 1.98 2 2.02-327

-326

-325

-324

-323

-322

-321

-320

Time [sec]

3 P

ha

se

gri

d v

olta

ge

ove

r th

e G

TI [V

]

DC Offset of 3V for phase 'c'

phase a

phase b

phase c


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5 Conclusion

This paper has demonstrated the procedures followed to design a control algorithm for grid observer

and it was possible to see that the algorithm works fine in accordance to interconnection standards

and fault detections it is expected to abide to. It has to be noted here that the on-board processor (grid

observer) is a more complex system than is already modelled for this project. The intention of this part

of the overall project was to design and show how a basic grid observer works in order to detect basic

grid abnormalities. The reader, if interested, is advised to look into the first part of this paper ‘Modular

Concept for grid tie converter till 1MVA’ or other sources for additional international standards related

to interconnection of distributed resources with the utility line.

This project can further be extended with additional fault detection algorithms. It is also possible to

generate the code of the overall control algorithm (grid observer model) for a specific platform and

processor and implement a hardware test procedure.


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6 Appendix

% Voltage deviation function %

function [er,tdelay]= rms(w,x,y,z) %#codegen

% w - real time grid rms voltage % x - Standard voltage limit data structure % y - Standard disconnection time data structure % z - Error status data structure % tdelay - disconnection time delay % er - error status

% Initialize variables for storage t_temp=0; e_temp=0;

% Start 'for' loop for i=length(x):-1:1 % Check fault deviation range if w<x(i) t_temp=y(i); e_temp=z(i); elseif i==length(x) && w >= x(i) t_temp=y(i+1); e_temp= z(i+1); end % End of 'If' statement

end % End of 'for' loop tdelay=t_temp; er= e_temp;

% Time Delay function %

function td= myWait(a,b,c) %#codegen

% This code compares time delays for set faults and % % chooses the least as the disconnection time % td=a; if (b~=0 && (b<td || td==0)) td=b; if c~=0 && c<td td=c; end % End of 2nd 'If' statement elseif b>=td if (td==0 || c<td) td=c; end % End of 3rd 'If' statement end % End of 1st 'If' statement


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% Voltage dip function %

% DC Bias function %


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% Frequency deviation detector function %

function [tdelay,err,st]=freq(w,x,y,z) %#codegen

% w - PLL synchronized frequency % x - freq. variation limit (standard) % y - disconnection time limit (standard) % z - error status

% td - disconnection time delay % error - error status % st - fault status

% initialize storage variables t_temp=0; e_temp=0; st_temp=0;

for i=length(x):-1:1 if w<x(i) t_temp=y(i); e_temp=z(i); elseif i==length(x) && w >= x(i) t_temp=y(i+1); e_temp= z(i+1); end % End of 1st 'if' statement if t_temp ~= 0 st_temp = 2.1; else st_temp=0; end % End of 2nd 'if' statement

end % End of 'for' loop tdelay=t_temp; err= e_temp; st=st_temp;

7 References

[1] Remus Teodorescu, Marco Liserre and Pedro Rodríguez, ‘’Grid Converters for Photovoltaic and Wind Power Systems’’ © 2011

[2] DI (FH) Alfred Karl Steinhuber, MSc, Modular Concept for grid tie converter till 1MVA, FH Joanneum University of Applied Sciences

[3] R. H. Park, "Two-Reaction Theory of Synchronous Machines: Generalized Method of Analysis - Part I". Transactions of the AIEE 48: 716–730, 1929

http://ece.uwaterloo.ca/~ccanizar/papers/classical/park.pdf

Date post:	18-Nov-2023
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Grid Observer - Sample approach

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