pi current controller for grid connected vsi in dpgs applications dpgs ...

PI CURRENT CONTROLLER FOR GRID CONNECTED VSI IN DPGS APPLICATIONSPI CURRENT CONTROLLER FOR GRID CONNECTED VSI IN DPGS APPLICATIONSPI CURRENT CONTROLLER FOR GRID CONNECTED VSI IN DPGS APPLICATIONSPI CURRENT CONTROLLER FOR GRID CONNECTED VSI IN DPGS APPLICATIONS

Buletinul AGIR nr. 3/2012 iunie-august 1

PI CURRENT CONTROLLER FOR GRID CONNECTED VSI IN PI CURRENT CONTROLLER FOR GRID CONNECTED VSI IN PI CURRENT CONTROLLER FOR GRID CONNECTED VSI IN PI CURRENT CONTROLLER FOR GRID CONNECTED VSI IN DPGS APPLICATIONSDPGS APPLICATIONSDPGS APPLICATIONSDPGS APPLICATIONS

Lecturer Eng. Ana Luminita BAROTE, PhD1, Prof. Eng. Corneliu MARINESCU, PhD

1

1University „Transilvania” from Braşov

REZUMAT. REZUMAT. REZUMAT. REZUMAT. In aceasta lucrare se prezinta In aceasta lucrare se prezinta In aceasta lucrare se prezinta In aceasta lucrare se prezinta un studiu asupra un studiu asupra un studiu asupra un studiu asupra controlulcontrolulcontrolulcontroluluiuiuiui de de de de curent cu regulatore PI implementat in curent cu regulatore PI implementat in curent cu regulatore PI implementat in curent cu regulatore PI implementat in sistemul de referinta rotativ sistemul de referinta rotativ sistemul de referinta rotativ sistemul de referinta rotativ dqdqdqdq pentru convertoare de retea pentru convertoare de retea pentru convertoare de retea pentru convertoare de retea utilizate utilizate utilizate utilizate in aplicatii cu sisteme distribuite de generare. in aplicatii cu sisteme distribuite de generare. in aplicatii cu sisteme distribuite de generare. in aplicatii cu sisteme distribuite de generare. PrincipalePrincipalePrincipalePrincipalele obiective ale lucrariile obiective ale lucrariile obiective ale lucrariile obiective ale lucrarii suntsuntsuntsunt implementarea controlimplementarea controlimplementarea controlimplementarea controlului de curentului de curentului de curentului de curent in convertorul de in convertorul de in convertorul de in convertorul de rererereteateateatea si si si si compensarecompensarecompensarecompensareaaaa armonicelor de ordin armonicelor de ordin armonicelor de ordin armonicelor de ordin inferior.inferior.inferior.inferior. Se realizeaza un studiu comparativ in ceea ce priveste distorsiunea armonica a Se realizeaza un studiu comparativ in ceea ce priveste distorsiunea armonica a Se realizeaza un studiu comparativ in ceea ce priveste distorsiunea armonica a Se realizeaza un studiu comparativ in ceea ce priveste distorsiunea armonica a curentului intre doi factori proportionali diferiti ai regulatorului PI in regim permanent de functionare. Structura curentului intre doi factori proportionali diferiti ai regulatorului PI in regim permanent de functionare. Structura curentului intre doi factori proportionali diferiti ai regulatorului PI in regim permanent de functionare. Structura curentului intre doi factori proportionali diferiti ai regulatorului PI in regim permanent de functionare. Structura analizata analizata analizata analizata aaaa fost simulata in fost simulata in fost simulata in fost simulata in SimulinkSimulinkSimulinkSimulink apoi implementata si testata in laborator cu ajutorul unui sistem de comanda si apoi implementata si testata in laborator cu ajutorul unui sistem de comanda si apoi implementata si testata in laborator cu ajutorul unui sistem de comanda si apoi implementata si testata in laborator cu ajutorul unui sistem de comanda si control in timp real dSPACE. control in timp real dSPACE. control in timp real dSPACE. control in timp real dSPACE. Cuvinte cheie: Cuvinte cheie: Cuvinte cheie: Cuvinte cheie: convertor de retea, regulator de curent, compensator armonic, calitatea energiei.

ABSTRACT. ABSTRACT. ABSTRACT. ABSTRACT. This papThis papThis papThis paper deals with the design and implementation of PI current control method in the er deals with the design and implementation of PI current control method in the er deals with the design and implementation of PI current control method in the er deals with the design and implementation of PI current control method in the dqdqdqdq synchronous synchronous synchronous synchronous rotating reference frame for grid side converterrotating reference frame for grid side converterrotating reference frame for grid side converterrotating reference frame for grid side converter usedusedusedused in in in in DPGSDPGSDPGSDPGS applications. The goals of this paper are to implement a applications. The goals of this paper are to implement a applications. The goals of this paper are to implement a applications. The goals of this paper are to implement a current current current current control technique for the grid sidcontrol technique for the grid sidcontrol technique for the grid sidcontrol technique for the grid side e e e VSI andVSI andVSI andVSI and a compensation method a compensation method a compensation method a compensation method for lowfor lowfor lowfor low----order harmonicsorder harmonicsorder harmonicsorder harmonics. . . . A comparative A comparative A comparative A comparative study in terms of current harmonic distortion between study in terms of current harmonic distortion between study in terms of current harmonic distortion between study in terms of current harmonic distortion between two different valuestwo different valuestwo different valuestwo different values of PI of PI of PI of PI proportional gain proportional gain proportional gain proportional gain running in steady running in steady running in steady running in steady state condition is made. state condition is made. state condition is made. state condition is made. The analyzed structureThe analyzed structureThe analyzed structureThe analyzed structure was swas swas swas simulated with Simulated with Simulated with Simulated with Simulink softwareimulink softwareimulink softwareimulink software then then then then implemented and tested in implemented and tested in implemented and tested in implemented and tested in laboratory using a dSPACE setup.laboratory using a dSPACE setup.laboratory using a dSPACE setup.laboratory using a dSPACE setup. Keywords:Keywords:Keywords:Keywords: grid converter, current controller, harmonic compensator, power quality.

1. INTRODUCTION

The energy demand has increased in the last years as

a result of the industrial development, and is predicted

to continue increasing, by at least 50 % in the next 10

years. This has focused more research attention on

Distributed Power Generation Sources (DPGS), a

promising alternative to satisfy the ever-growing need

for electricity, like wind turbines, photovoltaic systems,

etc. and the parameters of their connection to the grid,

[1], [2]. The increase interest in renewable energy

production together with higher and higher demand

from the energy distribution companies (TSO),

regarding grid energy injection and grid support in case

of a failure raises new challenges in terms of control for

renewable energy sources (RES) systems [3]. A general

block diagram of a DPGS is shown in Fig. 1.

Fig. 1. DPGS block diagram.

The main objectives investigated in this paper are

the control part of the power converter connected to the

grid by means of a passive filter and a harmonic

compensation technique. In the literature, different

power converter topologies are used to interface DPGS

with the utility network, [4]-[7].

In this work, the investigation is limited to the

control of three phase pulse width modulated (PWM)

voltage source inverter (VSI), the most used power

electronic interface for RES [8].

In order to apply to a broad range of DPGS, the

input power sources are not considered, the inverter

being powered by a DC power source.

Current control technique for the grid inverter is

modeled, simulated and implemented in laboratory

using dSpace setup, followed by a comparative analysis

between the obtained results.

A synchronous rotating dq frame PI current

controller was chosen to control the VSI. This method

is analyzed and implemented in the paper. A description

of dq-PI current controller advantages and

disadvantages is presented in [9], [10].

As a tradeoff between a good noise rejection and

good dynamics for the analyzed structure, the PI

integrator gain was set to Ki=1000 [11] and for the size

of the proportional gain Kp, which determines the

Buletinul AGIR nr. 3/2012 iunie-august_____________________________________________________________________________________

31

WORLD ENERGY SYSTEM CONFERENCE – WESC 2012


bandwidth and stability phase margin [11]-[13], were

chosen two different values (Kp=10 and Kp=20).

A comparative study between these two values will

be presented in the simulation and experimental results

session.

By adding a Harmonic Compensator (HC) to the

current controller, a good harmonics rejection is

obtained in both analyzed cases.

A PLL is used also in this strategy in order to detect

the grid phase angle θ and grid frequency.

The paper is organized as follows: in Section II the

grid connected system configuration with the control

methods, Section III describes the simulation and

experimental results while conclusions are provided in

Section IV.

2. SYSTEM CONFIGURATION AND CONTROL

The analyzed system configuration of the grid

connected inverter is presented in Fig. 1. The input

power sources are considered a DC power supply, a

VSI with PI current controller + HC and a

synchronization technique, a LCL filter, a transformer

and a utility grid.

The structure of the grid side converter based on PI

current controllers in dq frame control involving cross

coupling and feed forward of the grid voltages as

depicted in Fig. 2. By using the Park transformations,

the three phase currents and voltages from abc frame

are transformed in dq frame currents and voltages.

The iq current component determines reactive power

while id decide the active power flow. Thus the active

and reactive power can be controlled independently.

Employment of PI controllers for current regulation

as Fig. 2 illustrates, cross-coupling terms and grid

voltage feed-forward may be necessary in order to

obtain best results [14].

dI

*

dI

abcI

θ

0*=qI

qI

Lω

Lω

*

dV

dV

qV qHCV

dHCV

*

qV

dqPdqI

*

abcV

×÷

dcV

*P *Q

Fig. 2. The dq current control based on PI controller with HC.

The input of the current controller is the error

between the measured and reference grid current. The

current controller output is the reference grid voltage,

which divided by the DC source voltage gives the duty

cycle for the inverter.

A HC is applied in synchronous reference frames,

where the currents being regulated are dc quantities,

which eliminates the steady-state error, in order to

obtain an improved power quality in the analyzed

configuration.

As can be seen in Fig. 3, two controllers should be

implemented in two frames rotating at -5ω and +7ω.

Two transformation modules are necessary to transfer

the αβ stationary quadrature system into dq

synchronous rotating frame and vice versa. Noticeable

is in this case the complexity of the control algorithm,

compared with the structure implemented in stationary

reference frame, [11], [15].

As the most important harmonics in the current

spectrum are the 5th and 7th, in this paper HC is

designed to compensate these two selected harmonics.

0*

5=dI

0*

5=qI

αI

βI

θ θ

θ5je

θ5je

−

ω5−

0*

7=dI

0*

7=qI

θ θ

θ7je

− θ7je

ω7+

αV

βV

αV

βV

αI

βI

s

Ki5

s

K i7

s

Ki5

s

Ki7

Fig. 3. The HC diagram for PI controller.

In order to synchronize the injected grid current with

the grid voltage, a PLL block is used. A Dual Second

Order Generalized Integrator – DSOGI are employed in

the Quadrature-Signals Generator (QSG) to obtain two

couples of orthogonal and cleaned signals. Practically

the grid disturbances are filtered before entering in the

PLL scheme [11], [16]. Block diagram of a DSOGI-

PLL is presented in Fig. 4.

abcV

αV

βV

'

αV

'

αqV+

βV

'

βqV

+

αV+

qV

+

dV

ffω

'ω

'ω

'+θ

'+θ∫

Fig. 4. Block diagram of the three-phase DSOGI-PLL.

32_____________________________________________________________________________________

Buletinul AGIR nr. 3/2012 iunie-august

_____________________________________________________________________________________WORLD ENERGY SYSTEM CONFERENCE - WESC



The output of the PI controller in addition with the

feed forward frequency ωff is modulated and gives the

phase angle (θ). The grid phase angle obtained during

experiments with the voltages (+

αV ,+

βV ) are represented

in Fig. 5.

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1-400

-200

0

200

400

Time [s]

SO

GI-

PLL

Valpha+ Theta PLL Vbeta+

Fig. 5. Grid phase angle.

The active and reactive powers flowing from an

inverter to a grid can be described and expressed as in

Fig. 6. The used P/Q droop control method [17], [18]

has the ability to change the active and reactive power

reference according with the system requirements.

Therefore, in the studied configuration, the reference

active power values are set at P*=500; 1000; 1500;

2000 W and Q*=0 var. It is mentioned that, the nominal

power of the grid side inverter is 2.2 kVA.

Fig. 6. P/Q droop functions in studied configuration.

3. SIMULATION AND EXPERIMENTAL RESULTS

The proposed system has been modeled and

simulated using the Matlab/Simulink environment.

Fig. 7 shows the block diagram. The simulation

results will be used and verified during the practical

implementation.

The experimental results are obtained on a

laboratory test bench in the Green Laboratory at

Aalborg University of Denmark. The current control

method of the grid side inverter have been implemented

in dSPACE platform and tested for evaluating their

performance. The setup block diagram is presented in

Fig. 8 and consists in a three-phase inverter with the

rated power of 2.2 kVA , 2 series connected DC power

supplies (3 kW, 330 V), LCL filter (see Table I), LEM

boxes for measurement of Vdc, Iabc and Vabc, three-phase

transformer (5 kVA) and a dSPACE system. The

parameters of the system are presented in Table I.

The LCL filter implemented is composed by three

reactors with resistance RI and inductance LI on the

converter side and three capacitors CF; a further branch

of the filter, represented as three reactors with

resistance RG and inductance LG, comes from taking in

account the impedance of the transformer adopted for

connection to the grid and the grid impedance. Effect of

the filter is the reduction of high frequency current

ripple injected by the inverter [19].

The control system was developed in

Matlab/Simulink and then automatically processed and

run by the DS1103 PPC card. A Graphical User

Interface (GUI) (see Fig. 9) has been build using the

Control Desk software in order to allow a real time

control and evaluation of the system.

The GUI can be used to control inputs like: start/stop

of the system; active and reactive power reference and

current control methods. Also, it can be used to view

different outputs like: measured three phase grid

currents and voltages; measured DC voltage; measured

active and reactive power; phase angle provided by the

PLL, etc.

As well, different experimental cases can be tested,

like a step or stairs in the active power reference to

confirm the good implementation of the analyzed

current control method.

Table 1

Details of the hardware setup

Parameter Value

Grid voltage (line-line rms) 380 V

Grid frequency 50 Hz

Inverter-side inductance mHLI 9.6=

Inverter-side resistance Ω= 1.0IR

Grid side inductance (Transformer

inductance)

mHLG 2=

Grid side resistance Ω= 4.1GR

Filter capacitance FCF µ7.4=

Switching frequency kHzf s 10=


33



Vdc=650 V

g

A

B

C

+

-

A

B

C

A

B

C

Ri, Li

Vabc

Iinv

Iout

Vdc

w_sync

Duty Cycles

Pl Current Control

Vabc

Iabc

A

B

C

a

b

c

IabcA

B

C

a

b

c

Vabc

Iabc

A

B

C

a

b

c

Grid Currents

N

A

B

C

650

Vg

Vmg

w_sync

A

B

C

A

B

C

Rg, Lg

A B C

A B C

Fig. 7. Simulink block diagram.

Fig. 8. Experimental setup.

Fig. 9. Control Desk GUI.

34_____________________________________________________________________________________





In order to validate proper system operation, the

following simulations and experiments were carried

out:

Case 1: PI controller parameters (Kp=10,

Ki=1000, Ki5,7=150) without and with HC;

Case 2: PI controller parameters (Kp=20,

Ki=1000, Ki5,7=150) without and with HC.

A. Case 1: PI controller parameters (Kp=10, Ki=1000, Ki5,7=150) without and with HC

Measurements were performed at four different

reference values of active power (starting with 500 W

to 2000 W), without and with HC and the reactive

power reference sets to 0. Is analyzed how the control

parameters are varying in function of the input power

variation and can be seen that the id and iq (Fig. 10) / P

and Q (Fig. 11) measured signals are tracking very well

their references.

0 0.005 0.01 0.015 0.02 0.025 0.03-2

-1

0

1

2

3

4

5

6

Time [s]

Id,

Iq m

ea

su

red

an

d r

efe

ren

ce

[A

]

iq-meas iq-ref id-ref id-meas

Fig. 10. Id and Iq reference and measured currents.

0 0.005 0.01 0.015 0.02 0.025 0.03-1000

-500

0

500

1000

1500

2000

2500

3000

Time [s]

P&

Q

Pref Qref Qmeas Pmeas

Fig. 11. P and Q reference and measured powers.

In Fig. 12 is shown the injected current to the grid

for phase A (IA) in the case of control with PI controller

without HC in both, simulation (Fig. 12a) and

experimental (Fig. 12b) cases.

Total harmonic distortion (THD) is an important

index widely used to describe power quality issues in

transmission and distribution systems.

0.87 0.875 0.88 0.885 0.89 0.895 0.9 0.905-5

-4

-3

-2

-1

0

1

2

3

4

5

Time [s]

Grid C

urr

ent P

hase

with P

I contr

olle

r w

ithout

HC

[A

]

500 W

1000 W

1500 W

2000 W

THD

Simulation Results

PI without HCKi=1000;Kp=10.

(a)

0.06 0.065 0.07 0.075 0.08 0.085 0.09 0.095 0.1-5

-4

-3

-2

-1

0

1

2

3

4

5

Time [s]

Grid C

urr

ent P

hase

with P

I contr

olle

r w

ithout H

C [A

]

500 W

1000 W

1500 W

2000 W

THD

Experimental Results

(b)


Fig. 12. Grid current phase (IA) in the case of PI controller without

HC: a) Simulation results; b) Experimental results.

The THD of grid current with the 5th and 7

th

harmonics were presented numerically using the control

desk graphical interface (see Fig. 9). But for the graphic

representation of the harmonic spectrum for both cases,

measured grid currents have been implemented in

Matlab and with the discrete powergui, the FFT

analysis was made for each active power value.

The THD spectrum of the grid currents in the

simulation and experimental cases was analyzed

starting at 0.888 s and 0.08 s for 1 cycle in all analyzed

cases. By using a Kp=10 gain for PI controller without

HC, the results can be seen in Fig. 13.

(a)

PI controller without HC, Ki=1000, Kp=10.

0

5

10

15

20

25

30

TH

D C

urr

en

ts [

%]

Simulation 28,37 21,95 16,63 12,34

Experiment 28,59 22,14 16,75 12,35

500 W 1000 W 1500 W 2000 W


35



(b)

0 2 4 6 8 10 12 14 16 18 200

2

4

6

8

10

Harmonic order

Mag (

% o

f F

undam

enta

l)

SimulationExperiment

P=2000 WQ=0 var

Fig. 13. THD representation of the grid current in the Case 1 in

both simulation and experimental cases for: (a) different values of

active power; (b) P=2000 W (harmonics spectrum).

It can be seen that the used current control method

provides a THD that is higher than the limit imposed by

the standard IEEE 1547.1 [20], therefore, the power

quality delivered to the network must be improved by

using the HC technique in order to keep the THD below

the requested 5 %.

After HC implementation, the THD level decreases

and a good power quality is obtained. The results

obtained for grid currents with harmonics level at

different reference values of active power are presented

in Fig. 14 and Fig. 15.

0.87 0.875 0.88 0.885 0.89 0.895 0.9 0.905-5

-4

-3

-2

-1

0

1

2

3

4

5

Time [s]

Grid C

urr

ent P

hase

with P

I C

ontr

olle

r +H

C [A

]

500 W

1000 W

1500 W

2000 W

(a)

Simulation Results

PI with HCKi=1000;Kp=10.

THD

0.06 0.065 0.07 0.075 0.08 0.085 0.09 0.095 0.1-5

-4

-3

-2

-1

0

1

2

3

4

5

Time [s]

Grid C

urr

ent P

hase

with P

I contr

olle

r + H

C [A

]

500 W

1000 W

1500 W

2000 W

(b)


THDPI with HC Ki=1000;Kp=10.

Fig. 14. Grid phase current (IA) in the case of PI controller with


As it can be seen in Fig. 13a, at P*=2000 W, the PI

control technique without compensation provides a

THD of 12.35 % (experiment results) and after HC

implementation, the THD level decreases to 3.9 %

(Fig. 15a) and a good power quality is obtained.

(a)

PI controller with HC, Ki=1000, Kp=10.

0

2

4

6

8

10

12

14

TH

D C

urr

en

ts [

%]

Simulation 12,73 6,95 4,77 3,81

Experiment 12,93 7,07 4,97 3,9

500 W 1000 W 1500 W 2000 W

(b)

0 2 4 6 8 10 12 14 16 18 200

1

2

3

Harmonic order

Mag (

% o

f F

undam

enta

l)

Simulation

ExperimentP=2000 WQ=0 var

Fig. 15. THD representation of the grid current in the Case 1 in

both simulation and experimental cases for: (a) different values of

active power; (b) P=2000 W (harmonics spectrum).

In order to check if the unity power factor is

achieved in Fig. 16, the A phase of the grid voltage

(VA/50) is plotted together with the A phase of the grid

current for the same case presented before. It can be

noticed that the grid current and voltage are in phase,

for the reactive power value fixed to 0.

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1-10

-5

0

5

10

Time [s]

Va&

Ia

Va

Ia

(a)

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1-10

-5

0

5

10

Time [s]

Va&

Ia

Va

Ia

(b)

Fig. 16. Experimental results for voltage and current phase at

Kp=10, Ki=1000 in the case of: a) PI without HC; b) PI with HC.

36_____________________________________________________________________________________





B. Case 2: PI controller parameters (Kp=20,

Ki=1000, Ki5,7=150) without and with HC

In the second case, simulation and experimental

conditions remain the same as in the first case, except

the proportional gain of the PI controller, which was set

to Kp=20. For comparative analysis, the simulations and

measurements were performed for the same values of

active power, without and with HC. The grid phase

current in the case of PI controller without HC is

presented in Fig. 17.

0.87 0.875 0.88 0.885 0.89 0.895 0.9 0.905-5

-4

-3

-2

-1

0

1

2

3

4

5

Time [s]

Grid C

urr

ent

Phase

with P

I contr

olle

r w

ithout

HC

[A

]

500 W

1000 W

1500 W

2000 W

(a)


Simulation Results

THD

0.06 0.065 0.07 0.075 0.08 0.085 0.09 0.095 0.1-5

-4

-3

-2

-1

0

1

2

3

4

5

Time [s]

Grid C

urr

ent

Phase

with P

I contr

olle

r w

ithout

HC

[A

]

500 W

1000 W

1500 W

2000 W

(b)



THD

Fig. 17. Grid phase current (IA) in the case of PI controller without


It can be seen that the value of grid current is

changed with the increasing the active power, starting

from approx. 1 A at 500 W until circa 4 A at 2000 W.

As can be seen in Fig. 18a, grid currents THD

decreases with proximity of the rated power of the VSI.

A detailed harmonic order representation for 2000 W is

presented in Fig. 18b.

(a)

PI controller without HC, Ki=1000, Kp=20.

0

5

10

15

20

25

TH

D C

urr

en

ts [

%]

Simulation 22,26 15,48 9,23 8,09

Experiment 22,34 15,49 9,33 8,16

500 W 1000 W 1500 W 2000 W

(b)

0 2 4 6 8 10 12 14 16 18 200

2

4

6

8

Harmonic order

Ma

g (

% o

f F

un

da

me

nta

l)

Simulation


Fig. 18. THD representation of the grid current in the Case 2

(without HC) in both simulation and experimental cases for: (a)

different values of active power; (b) P=2000 W (harmonics level).

0.87 0.875 0.88 0.885 0.89 0.895 0.9 0.905-5

-4

-3

-2

-1

0

1

2

3

4

5

Time [s]

Grid C

urr

ent

Phase

with P

I contr

olle

r+H

C [

A]

500 W

1000 W

1500 W

2000 W

(a)

THDPI with HCKi=1000;Kp=20.

Simulation Results

0.06 0.065 0.07 0.075 0.08 0.085 0.09 0.095 0.1-5

-4

-3

-2

-1

0

1

2

3

4

5

Time [s]

Grid C

urr

ent

Phase

with P

I contr

olle

r +

HC

[A

]

500 W

1000 W

1500 W

2000 W

(b)

THD


PI with HCKi=1000;Kp=20.

Fig. 19. Grid phase current (IA) in the case of PI controller with HC

(Ki=1000, Kp=20): a) Simulation results; b) Experimental results.

As can be seen in Fig. 18, the THD level is lower

than the values of Fig. 13, without HC implementation,

which means that in this case, increasing the PI

proportionl gain leads to decrease THD.


37



After HC implementation, in Fig. 20 is observed that

the THD is within the limits imposed by the standard

[20] at P*= 2000 W for Kp = 20.

(a)

PI controller with HC, Ki=1000, Kp=20.

0

2

4

6

8

10

12

14

16

TH

D C

urr

en

ts [%

]

Simulation 14,31 8,72 5,8 4,61

Experiment 14,49 8,88 5,81 4,81

500 W 1000 W 1500 W 2000 W

(b)

0 2 4 6 8 10 12 14 16 18 200

1

2

3

Harmonic order

Mag (

% o

f F

undam

enta

l)

Simulation


Fig. 20. THD representation of the grid current in the Case 2 (with HC) in both simulation and experimental cases for: (a) different

values of active power; (b) P=2000 W (harmonics spectrum).

For a better visualization of data in the analyzed

cases, in Fig. 21 was made a comparative analysis

between them. Based on these results, it can be

concluded that PI controller with HC implemented in

dq synchronous rotating frame has the best performance

for Kp=10.

(a)

0

10

20

30

TH

D C

urr

en

ts [

%]

Kp=10 with HC 12,73 6,95 4,77 3,81

Kp=20 with HC 14,31 8,72 5,8 4,61

Kp=10 without HC 28,37 21,95 16,63 12,34

Kp=20 without HC 22,26 15,48 9,23 8,09

500 W 1000 W 1500 W 2000 W

(b)

0

10

20

30

TH

D C

urr

en

ts [

%]

Kp=10 with HC 12,93 7,07 4,97 3,9

Kp=20 with HC 14,49 8,88 5,81 4,81

Kp=10 without Hc 28,59 22,14 16,75 12,35

Kp=20 without HC 22,34 15,49 9,33 8,16

500 W 1000 W 1500 W 2000 W

Fig. 21. Comparative analysis between the two values of the

proportional gain of the PI controller, with and without HC:

(a) Simulation results; (b) Experimental results.

Small differences in the THD currents values

between simulation and experimental results (for both

studied cases) can be observed in Fig. 21. The

explanation for these is that in a real system the losses

are present that were not considered in simulations.

4. CONCLUSIONS

This paper presents a PI current control method

considering harmonics compensation for grid connected

converters in steady state conditions.

The configuration was modeled and simulated in

Simulink, implemented in a dSPACE platform and

tested with an experimental test setup.

The simulation results validated by the

experimental results show that the proposed control

method (PI current controller without/with HC and a

three-phase DSOGI-PLL) is effective for DPGS

applications.

A better energy quality delivered to the grid with

PI proportional gain set at Kp=10, comparing with

Kp=20 is obtained. However, if HC is not implemented,

the Kp = 20 case has a smaller THD.

ACKNOWLEDGMENT

This paper is supported by the Sectoral Operational

Programme Human Resources Development (SOP

HRD), financed from the European Social Fund and by

the Romanian Government under the project number

POSDRU/89/1.5/S/59323.

BIBLIOGRAPHY

[1] Wang, S., Li, Z., et al., Reliability Analysis of Distributed

System with DGs. DRPT, 6-9 July 2011 pp. 14-17.

[2] Algrain, M., A Multifaceted View of Distributed Generation

Systems and Their Impacts. PES, 26-30 July 2009.

[3] Altın, M., Göksu, Ö., et al., Overview of Recent Grid Codes

for Wind Power Integration. OPTIM 2010, pp. 1152-1160.

[4] Blaabjerg, F., Chen, Z., et al., Power electronics as efficient

interface in dispersed power generation systems. IEEE Trans.

on Power Electronics, 2004, vol. 19, no. 5, pp. 1184-1194.

[5] Carrasco, J., Franquelo, L., et al., Power-electronic systems

for the grid integration of renewable energy sources: A survey.

IEEE Trans. on Ind. Elect., vol. 53, no.4, pp. 1002-1016, 2006.

[6] Guo, X. Q., Wu, W.Y., Improved current regulation of three-

phase grid-connected voltage-source inverters for distributed

generation systems. IET Renewable Power Generation, 2010,

pp. 101-115.

38_____________________________________________________________________________________





[7] Giglia, G., Pucci, M., et al., Comparison of Control

Techniques for Three-Phase Distributed Generation Based on

VOC and DPC, ICREPQ, 15-17 April, 2009.

[8] Kazmierkowski, M. P., Current Control Techniques for

Three-Phase Voltage-Source PWM Converters: A Survey,

IEEE Trans. on Ind. Elect., vol. 45, no. 5, 1998, pp. 691-703.

[9] Zeng, Q., Chang, L., Study of Advanced Current Control

Strategies for Three-PhaseGrid-Connected PWM Inverters for

Distributed Generation, Proc. of Control Application, 2005,

pp.1311-1316.

[10] Bahrani, B., Kenzelmann, S., et al., Multivariable-PI-Based

dq Current Control of Voltage Source Converters With

Superior Axis Decoupling Capability, IEEE Trans. on

Industrial Electronics, 2011, vol. 58, no. 7, pp. 3016-3026.

[11] Teodorescu, R., Lisserre, M., Rodigruez, P., Industrial/Ph.D.

Course in Power Electronics for Renewable Energy Systems

(PERES) - in theory and practice, Aalborg University, 2010.

[12] Teodorescu, R., Blaabjerg, F., et al., A New Control Structure

for Grid-Connected LCL PV Inverters with Zero Steady-State

Error and Selective Harmonic Compensation, APEC 2004,

pp. 580-586.

[13] Yuan, X., Merk, W., et al., Stationary-Frame Generalized

Integrators for Current Control of Active Power Filters with

Zero Steady-State Error for Current Harmonics of Concern

Under Unbalanced and Distorted Operating Conditions, IEEE

Trans. on Ind. App., 2002, vol. 38, no. 2, pp. 523 – 532.

[14] HamrouniHamrouniHamrouniHamrouni,,,, N., et.al.,N., et.al.,N., et.al.,N., et.al., New method of current control for

LCL-interfaced grid-connected three phase voltage source

inverter, Revue des Energies Renouvelables, vol. 13, no.1,

2010.

[15] Blaabjerg, F., Teodorescu, R., et al., Overview of Control and

Grid Synchronization for Distributed Power Generation

Systems, IEEE Trans. Ind. Elect., vol. 53, no. 5, pp. 1398-1409,

Oct. 2006.

[16] Rodriguez, P., Teodorescu, R., et al., New Positive-sequence

Voltage Detector for Grid Synchronization of Power

Converters under Faulty Grid Conditions, PESC 2006,

pp. 129-135.

[17] Vasquez, J. C., Guerrero, J. M., et al., Adaptive Droop

Control Applied to Voltage-Source Inverters Operating in

Grid-Connected and Islanded Modes, IEEE Trans. on Ind.

Elect., 2009, vol. 56, pp.4088 - 4095.

[18] Guerrero, J. M., Vasquez, J. C., et al., Hierarchical Control

of Droop-Controlled AC and DC Microgrids – A General

Approach Towards Standardization, IEEE Trans. on Ind.

Electr., 2011, vol. 58, pp.158 - 172.

[19] Liserre, M., Dell’Aquila, A., et al., Genetic Algorithm-Based

Design of the Active Damping for an LCL-Filter Three-Phase

Active Rectifier, IEEE Trans. on Power Electronics, vol. 19,

no.1, 2004, pp. 76 – 86.

[20] *** IEEE 1547.2 ** IEEE standard for interconnecting

distributed resources with electric power systems, 2008.

About the authors

Lecturer Eng. Luminita BAROTE, PhD

University “Transilvania” from Braşov

email: [email protected]

She received the Dipl. Ing. degree in Electrical Engineering and Computers Science from “Transilvania” University,

Brasov in 2005, Dipl. Master degree in 2007 and the Ph.D in 2009 in Electrical Engineering from the same university.

Currently, she is a researcher at the Department of Electrical Engineering, Faculty of Electrical Engineering and

Computers Science, Transilvania University of Brasov. Her current research interests are in the area of renewable energy

systems: small power wind turbine working in stand-alone system with storage devices (lead acid battery, vanadium redox

flow battery) and also current control techniques for the grid side converter in DPGS applications.

Prof. Eng. Corneliu MARINESCU, PhD.

University “Transilvania” from Braşov

email: [email protected]

He received the Dipl. Ing. degree in Electromechanics from Politehnic Institute, Brasov, in 1971, and the Ph. D. from the

Politehnica University Bucharest in 1991. Currently, he is full professor at the Department of Electrotechnics, Faculty of

Electrical Engineering and Computers Science, Transilvania University of Brasov. Also, he is head of POWERELMA

(Power Electronics and Electrical Machines) research laboratory in the same faculty mentioned above. His areas of

interests include power electronics applied to renewable energy sources. He is author or co-author of more than 100

journal/conference papers in his research fields.


39



40_____________________________________________________________________________________



pi current controller for grid connected vsi in dpgs applications dpgs ...

Documents

Transcript of pi current controller for grid connected vsi in dpgs applications dpgs ...