Parameterization of Reactive Power Characteristics for Distributed

Generators: Field Experience and Recommendations

M. Kraiczy1, G. Lammert2, T. Stetz1, S. Gehler2, G. Arnold1, M. Braun1, 2, S. Schmidt3, H. Homeyer4, U. Zickler5, F. Sommerwerk5,

C. Elbs6

(1) Fraunhofer IWES, Königstor 59, 34119 Kassel, Germany

Phone +49(0)561/7294-268, Fax +49(0)561/7294-400, E-Mail: markus.kraiczy@iwes.fraunhofer.de

(2) University of Kassel, Kassel, Germany

(3) Bayernwerk AG, Regensburg, Germany

(4) Avacon AG, Salzgitter, Germany

(5) TEN Thüringer Energienetze GmbH, Erfurt, Germany

(6) Vorarlberger Energienetze GmbH, Bregenz, Austria

Abstract This paper presents recommendations for an effective commissioning and operation of distributed generators (DGs),

focussing on the aspect of reactive power control for static voltage support. Error-sensitive tasks in the process chain

from commissioning to operation are revealed, based on first-hand field experience of major German and Austrian dis-

tribution grid operators. The evaluation shows that the share of DGs, which currently cannot be operated in compliance

with the requirements of relevant grid codes and guidelines, is noticeable. The issues and challenges related to grid code

compliant DG operation are multilateral. For example the parameterization of reactive power controllers turned out to

be an error-sensitive task, due to the diversity of manufacturer-specific GUIs and the lack of clear parameter definitions.

Different, typical DG parameterization errors are categorized and measurement examples from the field are presented.

Furthermore, the impact of non-grid code compliant parameterizations of DGs on the distribution grid operation is dis-

cussed. As a consequence, the authors recommend founding a European, industry-driven working group for defining

binding parameter definitions and further commissioning standards.

1 Introduction

Reactive power control by distributed generators (DGs)

has been identified as an effective measure for maintain-

ing service voltages of distribution grids within its limita-

tion. Recent studies showed that reactive power control

by DGs can be used by the distribution grid operator

(DSO) for static voltage support and hence for avoiding

or delaying extensive grid reinforcement measures (e.g.

[1], [2]). As of today, reactive power control capabilities

are generally required from DGs in accordance to several

European and national grid codes (see Section 2). This

paper presents field experience on reactive power control

by DGs from the perspective of major German and Aus-

trian distribution grid operators, focussing on non-grid

code compliant DG operation and their origins. The au-

thors neither question the positive effect of decentralized

reactive power provision on the grid voltage nor its ap-

plicability in the field. On the contrary, by revealing typi-

cal error-sensitive tasks, the authors would like to con-

tribute to improve the general acceptance of decentralized

reactive power provision by DGs.

The aim of this paper is to improve the reader’s awareness

for various challenges that might occur during the design,

parameterization and operation process of DGs, which

can pave the way for non-grid code compliant DG reac-

tive power provision. In this context the paper addresses

the following aspects:

Introduction to the present DG commissioning process

according to the present regulatory framework and the

practical parameterization of a DG’s reactive power

controller

Discussion of different error-sensitive tasks within the

DG design, parameterization and operation process

Discussion of consequences of a non-grid code com-

pliant DG operation for the grid operation

Recommendations for an improved utilization of de-

centralized reactive provision

First, an overview on the regulatory framework for DG

reactive power provision with the focus on the German

and Austrian distribution grid is presented in Section 2.

The error types of a non-grid code compliant DG parame-

terization are categorized and measurement samples from

the field are presented in Section 3. The consequences of

a non-grid code compliant DG operation for the grid op-

eration are analysed and discussed in Section 4. In Section

5, the potential of an improved utilization of decentralized

reactive power provision is discussed and recommenda-

tions are derived. Finally, the conclusions are presented.

2 Regulatory framework and prac-

tical implementation of DG reac-

tive power control

This Section gives a brief overview on the regulatory

framework of DG reactive power provision (Section 2.1)

and the DG commissioning process (Section 2.2). In Sec-

© 2015 Power Engineering Society in the VDE (ETG) .

ETG-Fb. 147: International ETG Congress 2015

tion 2.3 typical error sources in the DG design, parameter-

ization and operation process are discussed.

2.1 DG reactive power provision

The regulatory framework for DG reactive power control

comprises general technical guidelines and grid codes,

which specify general reactive power requirements for

DGs. Table 1 gives an overview on such currently appli-

cable grid codes and guidelines. These general require-

ments are usually complemented by specifications on pa-

rameter settings (e.g., for cosϕ(P)- or Q(U)-

characteristics), defined by the technical guidelines of the

respective DSOs (e.g. [8] - [11]). Due to the heterogene-

ous structure of distribution grids and the different grid

operation philosophies of DSOs, the specifications for

DGs reactive power control can vary significantly be-

tween DSOs. Figure 1 exemplary shows different reactive

power control characteristics, as currently required by

chosen German DSOs. The characteristics can differ re-

garding the absolute set values (e.g. Q, U, P, and cosϕ),

the number of set points, the dead-band or a hysteresis

function. Furthermore, the required dynamic behaviour of

DG reactive power control can differ (e.g. response time).

Figure 1 Examples of different Q(U) characteristics for MV

DGs (left) and different cosϕ(P) characteristics for LV DGs

(right); examples according DSO 1 [8], DSO 2 [9], DSO 3 [10],

DSO 4 [11] and VDE-AR-N 4105 [4]

2.2 Commissioning process of DGs

The commissioning procedure varies between voltage

levels, DSO, DG type, the date of commissioning and the

country. This Section gives a brief overview on the DG

commissioning process according to the presently applied

general grid codes and guidelines in Germany. Figure 2

shows an example of the timeline and relevant certificates

and verifications for the DG interconnection with the pub-

lic MV grid in Germany. Different certificates and proofs

have to be delivered to the respective DSO for the DG in-

terconnection with the public grid. The certificates are

verified by independent accredited certification authori-

ties and are based on laboratory tests and verified simula-

tion models of the DG unit/plant. Detailed information’s

about the DG certification procedure in Germany are giv-

en in the FGW technical guidelines [12], [13]. Different

types of DG certificates are required for the DG intercon-

nection with the public grid:

The unit certificate specifies the electrical properties

and proofs the conformity of single DG units (e.g.

photovoltaic (PV) inverter) with the respective guide-

line. The certificate is required for high voltage (HV)

DGs [5] and medium voltage (MV) DGs [3].

The plant certificate also includes the internal DG

plant components (e.g. plant transformer, cables) and

proofs the conformity of the entire DG plant at the

network connection point (NCP) with the respective

guideline. The certificate is required for HV DG [5]

and large MV DG (with a maximum apparent connec-

tion power SA > 1 MVA or line length from the NCP

to the generation unit(s) > 2 km) [3]

Application DG unit

Network compatibility

test

Network connectionacceptance

Network connection

contract

Unit Certificate

Plant certificate

DG owner/ installer

DSO

DG installation

DG Start-upDG parameterization

DG functional test

Conformity declaration

Initial start-up records

May request additional proofs or functional test for reactive

power control of DG

DG grid operation

t

Figure 2 Illustrative timeline with relevant verification and cer-

tificates for the interconnection of a MV DG in Germany

The DG parameterization and functional test in the field is

not part of these certificates. The parameterization of DG

reactive power control in the field is usually performed by

the DG installation company or another specialist compa-

ny. In some cases, the DG reactive power control is pre-

defined by the DG manufacturer using a standard reactive

power characteristic. For the initial start-up of the DG

unit/plant a conformity declaration is required. The con-

formity declaration determines that the DG unit/plant is

designed and configured according to the relevant certifi-

cates and guidelines, which consider the requirements of

the respective DSO. The FGW technical guideline Part 8

(FGW TR8) [13] specifies the certification procedure of

DG units/plants in the extra high voltage, high voltage

and medium voltage level. According [13] the conformity

declaration has to be ratified by an accredited certification

authority, an independent expert or a specialised company

with knowledge of the DG unit/plant. According the new

VDE-AR-N 4120 [5] the conformity declaration in the

HV level has to be ratified by an accredited certification

authority. In the LV level the conformity declaration is

usually provided by the DG manufacturer. However this

conformity declaration in the LV level does not necessari-

ly include the requirements of the respective DSOs. The

necessity of functional test of the DG reactive power con-

trol also depends on the voltage level of the interconnec-

tion. At HV level, the new VDE-AR-N 4120 [5] defines

functional tests of the DG reactive power control in the

field. At MV level, the respective DSO may define func-

tional tests of DG reactive power control in the field (e.g.

[14]). At LV level, functional tests of DG reactive power

control are usually not applied.

This Section gives a brief overview of the DG commis-

sioning process in the presently applied grid codes and

guidelines in Germany. For DG units/plants, which were

installed in the past years in Germany, the commission

process may differ significantly.

Grid Code Scope Control Modes Reactive Power Capability* Dynamics*

VDE-AR-N 4120

(01/2015) [5]

High voltage

(HV) (Germany)

Qfix, Q(U), Q(P),

cosϕfix, remote con-

trol

Different operating ranges

specified by the DSO

Q(U): response time between

5 s to 60 s

Qremote and Q(P): settling time

max. 4 min

BDEW Technical

Guideline MV DG

(06/2008) [3]

Medium voltage

(MV) (Germany) Qfix, Q(U), cosϕfix,

cosϕ(P), remote

control

cosϕ = 0.95underexcited to

0.95overexcited

cosϕ(P): target value with-

in 10 s

Q(U): target value within 10 s

to 60 s

TOR D4 (09/2013)

[6]

Medium voltage

and low voltage

(LV) (Austria)

Qfix, Q(U), cosϕfix,

cosϕ(P), remote

control (MV DG)

MV DG: see BDEW Tech-

nical Guideline MV

LV DG: see VDE AR-N-4105

-

VDE AR-N-4105

(08/2011) [4]

Low voltage (LV)

(Germany) cosϕfix,

cosϕ(P), Q(U)**

cosϕ = 0.95/0.9underexcited to

0.95/0.9overexcited

cosϕ(P): target value with-

in 10 s

DIN EN 50438

(06/2014) [7]

Low voltage DG

with IN ≤ 16A per

Phase (Europe)

Q(U), cosϕfix,

cosϕ(P)

cosϕ = 0.9underexcited to

0.9overexcited

Q(U): First order filter, time

constant: 3 s to 60 s.

Table 1: Overview of selected general grid codes and guidelines for DG interconnection with the public grid (* requirements partly

simplified; **in VDE AR-N-4105: Q(U) noted as a possible future characteristic)

2.3 Typical error sources of DG reactive

power provision during commission-

ing and operation

The implementation of DG reactive power control ac-

cording to the relevant grid codes and guidelines faces

various challenges in the field. These challenges are:

Large number of different DG types and manufac-

turers: high diversity of user interfaces for the pa-

rameterization of DG reactive power control

Large number of DSOs (e.g. in Germany approxi-

mately 850): the settings of the DG reactive power

control can vary significantly between the DSOs

(see for example Figure 1)

Large number of DG planning, installation and op-

eration companies with a different technical back-

ground

Full verification of the DG reactive power control

in the field is time consuming and sometimes dif-

ficult (e.g. test of Q(U)-functionality).

The typical error sources are separated between errors in

the DG parameterization process and errors in the DG

design process or during grid operation.

2.3.1 DG parameterization process

The diversity of manufacturer dependent user interfaces

is one major source for reactive power parameterization

errors. The following list gives an example for the di-

versity of parameter values, needed to configure the

Q(U) characteristic of LV PV inverters from different

manufacturers (see also [15]):

Voltage:

o Input value in [V]

o Input value in [%] or [p.u.]

Reactive power:

o Sign of reactive power not standardized

o Input value in [%] of Smax

o Input value in [%] of Qmax

o Input value in [%] of Pmax

o Input value in [kvar]

Reactive power per phase

Total reactive power

o Input value maximum cosϕ

Dynamic behaviour:

o Sometimes no setting options available

o Often no precise instruction

This list illustrates that the manual configuration of the

DG reactive power control can be very challenging in

the field. Therefore, DG installation companies have to

be trained for the relevant guidelines and for different

DG types to avoid parameterization errors in the field.

Furthermore, it is required, that the DG manufacturer

comprehensively describes the procedure for the DG

reactive power configuration. Other sources of error in

the DG parameterization process are:

Application of an outdated guideline

Misinterpretation of the relevant guidelines

Takeover of a pre-defined DG standard configura-

tion (e.g. standard cosϕ(P) characteristic according

VDE-AR-N 4105), which is not required by the re-

spective DSO

Inattention in the DG parameterization process

2.3.2 DG design process or grid operation

Error sources in the DG reactive power provision can

also occur in the DG design process or during the DG

grid operation. Examples of errors sources are:

The DG unit is technically not capable of provid-

ing the required reactive power characteristic (es-

pecially for existing DGs without unit certificate)

The impedances of the DG plant components are

not sufficiently considered during the planning or

operation of the DG plant (especially for existing

DG without plant certificate)

The requested reactive power is provided at con-

nection terminals of the DG units and not at NCP

of the entire DG plant

Interactions with other DG plant components (e.g.

intrinsic protection devices of DG unit)

Failure of DG unit/plant components (e.g. com-

munication devices)

The described error sources are described more in detail

and with specific examples in the next Section.

3 Field experience – DG reactive

power control

Section 3.1 shows different examples of a non-requested

DG reactive provision in the field. The results are based

on measurement samples from different DSOs. The rel-

evance and the validity of the findings are discussed in

Section 3.2.

3.1 Examples of a non-requested DG reac-

tive power provision in the field

In this Section the examples are separated between the

errors in the DG parameterization process and the errors

in the DG design process or during grid operation. Fur-

thermore, an example of the dynamic behaviour of a DG

Q(U) characteristic is analysed in detail.

3.1.1 Error in the DG parameterization process

Different examples of a wrong reactive power configu-

ration have been observed in the field:

No reactive power control applied (cosϕ of 1 in-

stead of required reactive power control)

Wrong control characteristic applied (e.g. cosϕ(P)

instead of a required Q(U)-characteristic)

Wrong set values of the reactive power control ap-

plied (e.g. cosϕ of 0.9 instead of cosϕ of 0.95)

Sign error of the reactive power control (e.g. over-

excited instead of an under-excited operation)

Figure 3 shows a sample measurement, recorded at the

NCP of a MV wind turbine. The wind turbine applies a

fixed power factor of 0.9 (under-excited). However, the

DSO required a fixed power factor of 0.95 (under-

excited), in accordance to the German MV grid code

[3].

Partially, the DG user interfaces do not specify the sign

of reactive power (see also Section 2.3) and sometimes

this is not even indicated in the documentation. This as-

pect can lead to a sign error of the DG reactive power

control (e.g. over-excited instead of under-excited be-

haviour). Figure 4 shows an example of a sign error,

recorded from a MV biogas plant. During operation, a

fixed power factor of 0.95 (under-excited) is requested

by the DSO (red line). However, the DG is operating

with a fixed power factor of 0.95 (over-excited).

Figure 3 Example for wrong set values of the reactive power

control (MV wind turbine, Pmax=800 kW, initial start-up

06/2009)

Figure 4 Example of a direction error of DG reactive power

control ( MV biogas plant, Pmax = 1,2 MW)

3.1.2 Error in the DG design process or during

grid operation

In this category, the DG unit/plant is technically not ca-

pable of providing the required reactive power charac-

teristic at the NCP. The sources of error are multilateral

(see Section 2.3.2). Figure 5 shows an example of an

inaccurate performance of a cosϕ(P)-characteristic of a

MV PV plant at the NCP. The reason for this inaccurate

performance remains vague, it might be caused by tech-

nical constrains of the PV inverters.

Figure 6 illustrates the challenge of a grid code compli-

ant reactive power provision of large DG plants. The

requirements of the DG reactive power provision are

specified for the NCP in the HV [5] and MV grid [3]. In

the LV grid the requirements are specified for the con-

nection terminals of the DG unit [4]. The plant equip-

ment (cables, transformers etc.) can lead to a mismatch

between the operation points of the single DG units and

the operation points of the entire DG plant at the NCP

(Figure 6, bottom). A simple adoption of the required

control characteristic by the DG units, without consider-

ation of the DG plant equipment, will lead to insuffi-

cient results in many cases [16]. Different solutions for

this behaviour are analysed in [16].

Figure 5 Example of an inaccurate performance of a cosϕ(P)-

characteristic (MV PV plant, Pmax = 354 kW, initial start-up

03/2010)

LV plantimpedance

MV plantimpedance

Plant transformer

Public MV grid

NCP

DG unitDG plant

=

~

PV inverters

=

~

Inverter connection pointNetwork connection point

Reacitve power [p.u.]

Aci

tve

po

wer

[p

.u.]

0.2

0.4

0.6

0.8

1.0

0 0.2 0.4-0.4 -0.2

Figure 6 Example of MV PV plant (top) and the typical PQ

operating range (bottom) at the Inverter and the NCP (genera-

tor reference-arrow system) (own diagram based on [16])

In some cases a tripping of the overvoltage protection of

DG units has been observed in the field, whereat the

voltage at the NCP was within the specified limits. The

protection devices even trip before the DG reactive

power provision (e.g. Q(U)-characteristic) is fully acti-

vated. The intrinsic protection of the DG unit can trip

because of relevant internal DG plant impedance and

high voltages at DG unit connection terminals. Howev-

er, the intrinsic protection should not undermine the re-

quirements of the relevant guidelines (at MV-level

[21]).

In the HV and MV grid the reactive power provision of

the DG units/plants can be adjusted by the DSO via re-

mote control (see Section 2.1). However, in a noticeable

number of cases a failure in the communication system

of the DG unit/plant avoids a remote control by the

DSO.

In other examples the DG units/plants shows a non-

compliant DG reactive power control after a firmware

update by the DG manufacturer, whereat the update

overwrite the tested and verified DG configurations.

Furthermore, problems have been observed after the ex-

change of DG plant components (e.g. PV inverters),

whereat the DG parameterization and tests were not ad-

equately repeated by the DG installation company.

3.1.3 Detailed example - dynamic behaviour of

a Q(U) characteristic

The configuration of the dynamic behavior of the Q(U)

characteristic is an error-sensitive task, which concerns

the DG design, parameterization and operation process.

The dynamic behavior is limited by technical constrains

of the DG unit/plant (e.g. measurement dead-time, con-

trol cycles). Section 2.3 shows that in the DG user inter-

face sometimes no dynamic setting options are available

or that the configuration is not precisely instructed.

In several studies (e.g. [17] - [19]) the stability of a

closed loop voltage control (Q(U)-characteristic) by DG

systems is analyzed. The stability of the Q(U)-control

depends on the NCP characteristics (short-circuit power,

R/X-ratio) and the settings of the Q(U)-controller (gain,

measurement dead-time, filter settings). For a secure

and stable operation of a Q(U)-characteristic a first or-

der filter (PT1-behaviour) with a sufficient time con-

stant is suggested in [18] and [19]. However, most gen-

eral grid codes and guidelines do not define the step re-

sponse sufficiently. For example, the German MV

guideline describes the required dynamic behaviour of

reactive power settings as “adjustable between 10 sec-

onds and 1 minute for the Q(U)-characteristic“ [3]. The

EN 50438 is already more precise as it describes the re-

quired dynamic behaviour of the Q(U)-characteristic

with a first order filter and a time constant between

τ = 3 s to τ = 60 s (see Table 1). However, important

parameters, such as the actual voltage measurement val-

ue (3 phase, 1 phase, average values or actual values

etc.) and the maximum dead-time T between voltage

measurement and the change of the operation point need

to be defined, too.

For a stable operation of the Q(U)-characteristic the

time constant τ of the reactive power control should be

sufficiently larger than the dead-time T of the reactive

power control [18]. A detailed description of the stabil-

ity analysis of the Q(U)-characteristics is given in [18].

Figure 7 shows the Q(U)- step responses resulting from

an a) unfavourable plant design and controller-

parameterization (left, extreme dead-time between

measurement and change of operation point, very high

gain, no filtering) and b) a more reasonable implementa-

tion. According to recent studies (e.g. [18], [19]), the

dynamic behavior of the first PV system (Figure 7, left)

can be inappropriate for the voltage stability within the

distribution grid. The second PV system (Figure 7,

right) instead clearly shows the recommended dynamic

behavior using a first order filter with a relevant time

constant τ whilst having a relatively small dead-time T.

Figure 7 Example of an unrecommended Q(U) step response

(left, MV PV, Pmax=665 kW, initial start-up 08/2011) and a

recommed Q(U) step response (right, MV PV, Pmax=621 kW,

initial start-up 07/2010).

3.2 Discussion of the given examples

Section 3 discusses different examples of a non-grid

code compliant DG reactive power control in the field.

The results are based on measurement samples from dif-

ferent DSOs. The frequency and relevance of the errors

differs per voltage level, DG type, DSO, region and date

of the initial start-up of the plant. Although the follow-

ing statistics cannot be considered as representative,

they clearly show that a non- grid code compliant DG

unit/plant operation might occur if the plants functional-

ity is not thoroughly checked during commissioning

and/or after reconfigurations. The base population co-

vers 186 DG systems (HV DG and MV DG) from with-

in the service of one particular DSO. The test is per-

formed via remote control by the DSO. The DSO re-

quests an active power curtailment and a reactive power

target value by the DG unit/plant. The measurements

reveal that:

84 DGs show requested behaviour

62 DGs show deficits

40 DGs with failure in the communication

(no tests possible)

For approximately 30 % of the 62 DG systems with def-

icits, an error with the reactive power control was ob-

served. Other frequently observed deficits concern the

active power curtailment or incorrect measurements by

the DG units/plants.

4 Impact of DG parameterization

errors on grid operation

This Section gives an overview of the consequences of

DG parameterization errors for the operation of distribu-

tion grids. The consequences cover different topics,

such as:

Voltage quality

Loading of grid assets and losses

Protection system

4.1 Voltage quality

The aim of reactive power provision by DGs is to sup-

port the voltage in the distribution grid and to keep the

grid voltage within specified limits, which are defined

in DIN EN 50160 [20] for Germany. However, DG pa-

rameterization errors could lead to unpredictable grid

voltages, which worsen the voltage quality of the distri-

bution grid. The worst case scenario for the voltage

quality would be a direction error of the DG reactive

power provision (see Section 3.1.1).

Furthermore, a parameterization error of a closed loop

voltage control (e.g. Q(U) characteristic) could lead to

reactive power and voltage oscillations in the grid.

Therefore recent studies [18], [19] suggest a first order

filter with a sufficient time constant for the Q(U) char-

acteristics (see also Section 3.1.3). In addition, it is con-

ceivable that a sign error of the Q(U) or cosϕ(U) char-

acteristic (see Section 3.1.1) could lead to reactive pow-

er and voltage oscillations in parallel operation with

other voltage regulators or reactive power compensa-

tors.

4.2 Loading of grid assets and losses

In cases, where the reactive power output of DGs is

larger than originally planned by the DSO or the DG

plant designer/operator, the DG parameterization error

can lead to an overloading of grid or DG plant assets.

Due to the increased reactive power flow, the losses of

these components can also increase.

4.3 Protection system

DG parameterization errors may also have an impact on

the protection coordination of the power system. A

wrong parameterization can lead to interferences with

the voltage protection, especially the under and over

voltage function. Due to a wrong parameterization of

DG, e.g., sign error of reactive power provision (see

Section 3.1.1), the voltage protection might trip. This

can lead to disconnection of DGs, consumers or other

grid components. A DG parameterization error can also

lead to interferences with the distance protection. In

case, the DG reactive power provision is larger than ex-

pected, the measured current and voltage values of the

distance protection can lead to an impedance value,

which lies within the protection zone and leads to a trip-

ping signal of the protection system as seen in Figure 8.

Thus, a wrong parameterization might lead to a discon-

nection of lines, busbars or other grid components.

Sreal

Expected Operation Zone of DG

R

XProtectionZone Operation

Zone

R

XProtectionZone

OperationZone

Operation Zone of DG larger then expected

Figure 8: Example: Impact of a DG parameterization error on

the distance protection

5 Improved utilization of decen-

tralized reactive power provision

In an energy system, with increasingly adopted system

responsibility by distributed resources, it is mandatory,

that the DGs operate predictable and according the rele-

vant guidelines and grid codes. The aim of this paper is

to raise the awareness of error-sensitive tasks in the DG

design, parameterization and operation process for DG

plant designers, DG manufacturers, DG installation

companies, DSOs and other relevant parties. The previ-

ous chapters show, that the issues and challenges related

to grid code compliant DG operation are multilateral.

Table 2 shows several ideas for an improved utilization

of decentralized reactive power provision. The ideas in

Table 2 should be discussed by experts of the relevant

parties (e.g. DG plant designer, DSOs, DG manufactur-

er, DG installers). Therefore, an implementation of an

industry-driven working group with the focus on a non-

grid code compliant DG operation is recommended. The

working group can analyse the frequency and relevance

of non-grid code compliant DG operations on a repre-

sentative database and can define binding parameter

definitions and further commissioning standards.

6 Conclusion and outlook

This paper contributes field experience of DG reactive

power control in the German and Austrian distribution

grid and addresses error-sensitive tasks in the DG de-

sign, parameterization and operation process. The au-

thors neither question the positive effect of decentral-

ized reactive power provision on the grid voltage nor its

applicability in the field. However, the paper reveals

that the share of DGs, which currently cannot be operat-

ed in full compliance with the requirements of relevant

grid codes and guidelines, is noticeable. The paper dis-

cussed typical errors sources and shows measurement

samples of non-grid code compliant DG operations in

the field. Furthermore, the impact of a non-grid code

compliant DG operation on the grid operation is dis-

cussed. The examples reveal that a non-grid code com-

pliant DG operation can affect a secure DG plant or grid

operation, which can increase the outage time of DGs,

consumers or grid segments. Finally, an improved utili-

zation of decentralized reactive power provision is dis-

cussed. The paper recommends the implementation of

an industry-driven working group for defining binding

parameter definitions and further commissioning stand-

ards.

Guidelines, grid codes, standards

Further standardization of DG parameterization (e.g. communication interfaces1, input values of DG configuration)

Detailed definition of the required measurement values (e.g. 3 phase, 1 phase, average values or actual values) and

the dynamic behavior of the DG control (esp. Q(U), cosϕ(U)-characteristic)

Clarification of responsibilities, rights and obligations of the relevant parties in case of a non-grid code compliant

DG operation

Certification of DG

DG certification should remain an essential part of the DG commissioning process

Comprehensive analysis of a non-grid code compliant DG operation in the field and a reflection with the DG certi-

fication may identify further improvement potential in the DG certification process

Parameterization of DG

Comprehensive documentation and demonstrative examples2 of the DG configuration by the DG manufacturer

Training programs for DG installation companies about DG configuration for different DG types and guidelines

Long term goal: Automated and/ or semi-automated DG parameterization according variable requirements in the

smart grid

DG start-up and conformity declaration

Further standardization of DG start-up and functional test (e.g. definition of DG standard test procedures)

Discussion and clarification of the qualifications of the responsible person for the conformity declaration

Long term goal: Automated and/ or semi-automated test procedures

Repetitive inspections in DG operation

Firmware updates, exchange of DG components, failure in DG components can cause parameterization errors dur-

ing DG operation and may require repetitive inspections

Discussion and clarification of the regulatory framework for repetitive inspections

Long term goal: Automated and/or semi-automated repetitive inspections Table 2: Ideas for an improved utilization of decentralized reactive power provision

1 Standardized DG unit/plant communication interfaces can simplify the DG configuration and the DG test procedure and can enable an automatic

adoption of the DG unit/ plant configuration due to variable requirements in the smart grid, e.g. standards for DG plug & play (http://sunspec.org) 2 Examples of demonstrative videos of the DG configuration are given by Vorarlberg Netz (http://www.vorarlbergnetz.at/inhalt/at/1163.htm)

Acknowledgement

The authors thank the German Federal Ministry for Economic Affairs and Energy

and the “Forschungszentrum Jülich GmbH

(PTJ)” for the support within the frame-work of the project “HiPePV2” (FKZ:

0325785) and “SmartGridModels” (FKZ:

0325616). The authors are solely responsi-ble for the content of this publication.

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