Iec 61400-27-1-2015.Pdf

IEC 61 400 27 1 Edition 1 0 201 5 02 INTERNATIONAL STANDARD NORME INTERNATIONALE Wind turbines – Part 27 1 Electrical simulation models – Wind turbines Eoliennes – Partie 27 1 Modèles de simulation él[.]

Terms and definitions 1 2

For the purposes of this document, the terms and definitions given in IEC 60050-41 5, as well as the following apply:

3.1 1 available aerodynamic power maximum possible power taking into account wind speed, power rating, rotor speed limits and pitch angle constraints

3.1 2 generic model model that can be adapted to simulate different wind turbines or wind power plants by changing the model parameters

3.1 3 integration time step simulation time interval between two consecutive numerical solutions of the model’s differential equations

The negative sequence component of a three-phase system is one of the three symmetrical sequence components that arises solely in unsymmetrical three-phase systems of sinusoidal quantities It is characterized by a specific complex mathematical expression.

X = + + where a is the 1 20 degree operator, and X L1 , X L2 and X L3 are the complex expressions of the phase quantities concerned, and where X denotes the system current or voltage phasors

Note 1 to entry: Negative sequence voltage or current components may be significant only when the voltages or currents, respectively, are unbalanced For example, if phase voltage phasors are symmetrical U L1 = U e jθ , U L2 =

[SOURCE: IEC 60050-448:1 995, 448-1 1 -28, modified (addition of Note 1 to entry)]

The nominal active power of a wind turbine is the value specified by the manufacturer, serving as the per-unit base for all power types, including active, reactive, and apparent power.

3.1 6 nominal current nominal value I n of wind turbine current, which must be calculated from nominal active power

P n and nominal voltage U n according to n n 3Un

3.1 7 nominal frequency nominal value of wind turbine frequency, which must be stated by the manufacturer

3.1 8 nominal voltage nominal value of wind turbine voltage, which must be stated by the manufacturer

3.1 9 phasor complex rms value for a sinusoidal quantity a ( ) t =A ˆ cos (ω +t υ0 ), complex value A=Ae j υ 0 with

A= , where j is the imaginary unit, Aˆ is complex amplitude, ω is angular frequency, and υ 0 is initial phase

3.1 1 0 point of connection reference point on the electric power system where the user’s electrical facility is connected [SOURCE: IEC 60050-61 7:2009, 61 7-04-01 ]

The positive sequence component of a three-phase system is one of the three symmetrical sequence components that can be found in both symmetrical and unsymmetrical three-phase systems of sinusoidal quantities It is defined by a specific complex mathematical expression.

X = + + where a is the 1 20 degree operator, and X L1 , X L2 and X L3 are the complex expressions of the phase quantities concerned, and where X denotes the system current or voltage phasors [SOURCE: IEC 60050-448:1 995, 448-1 1 -27]

Power system stability refers to the ability of a power system to return to a steady state following a disturbance, such as fluctuations in power or changes in impedance This stability is characterized by the synchronous operation of generators within the system.

Power system stability refers to the capacity of an electric power system to return to a state of operating equilibrium after experiencing a physical disturbance, while maintaining most system variables within bounds to ensure the integrity of the entire system.

A quasi steady state of a system refers to a short-term steady state, such as during a voltage dip, where the duration is sufficient for the system's state variables to be regarded as effectively constant.

3.1 1 4 reaction time elapsed time from the issue of a step change command until the observed value reaches

Note 1 to entry: Reaction time is illustrated in Figure 2

Figure 2 – Example of step response

3.1 1 5 response time elapsed time from the issue of a step change command until the observed value first time enters the predefined tolerance band of the target value

Note 1 to entry: Response time is illustrated in Figure 2

3.1 1 6 settling time elapsed time from the issue of a step change command until the observed value continuously stays within the predefined tolerance band of the target value

Note 1 to entry: Settling time is illustrated in Figure 2

3.1 1 7 short-circuit power product of the current in the short-circuit at a point of a system and a nominal voltage, generally the operating voltage

Note 1 to entry: Using physical units for line current (A) and nominal voltage (V), the product should also include the factor 3

3.1 1 8 short-circuit ratio ratio of the short-circuit power at the point of connection to the nominal active power of the wind power plant or wind turbine

3.1 1 9 steady state of a system operating conditions of a network in which the system state variables are considered to be sensibly constant

3.1 20 system state variables variable quantities associated with the electrical state of a system

Examples: Voltages, currents, powers, electric charges, magnetic fluxes

3.1 21 transient time period time periods with measured electromagnetic transients which are not included in fundamental frequency models

The unbalance factor in a three-phase system is defined as the percentage ratio of the root mean square (r.m.s.) values of the negative sequence (or zero sequence) component to the positive sequence component of voltage or current.

UVRT ability of a wind turbine or wind power plant to stay connected during voltage dips

3.1 24 voltage dip sudden reduction of the voltage at a point in the system, followed by voltage recovery after a short period of time, from a few cycles to a few seconds

3.1 25 wind power plant power station comprising one or more wind turbines, auxiliary equipment and plant control

3.1 26 wind turbine rotating machinery in which the kinetic wind energy is transformed into another form of energy [SOURCE: I EC 60050-41 5:1 999,1 987, 41 5-01 -01 ]

3.1 27 wind turbine terminals a point being a part of the wind turbine and identified by the wind turbine supplier at which the wind turbine is connected to the power collection system

Note 1 to entry: Same definition as in IEC 61 400-21 defining the measurement point of the tests

The zero sequence component of a three-phase system is one of the three symmetrical sequence components that only appears in unsymmetrical three-phase systems of sinusoidal quantities It is defined by a specific complex mathematical expression.

IEC 61 400-27-1 :201 5  I EC 201 5 – 1 7 – where X L1 , X L2 and X L3 are the complex expressions of the phase quantities concerned, and where X denotes the system current or voltage phasors

Abbreviations and subscripts 1 7

Abbreviations 1 7

The following abbreviations are used in this standard:

CIGRE the I nternational Council on Large Electric Systems

DFAG doubly fed asynchronous generator 4

IEEE the Institute of Electrical and Electronics Engineers, Inc

LSC line (grid) side converter

MSC mechanically switched capacitor bank, which is not switched dynamically during voltage dips NERC the North American Electric Reliability Corporation

ROCOF rate of change of frequency

SCADA supervisory control and data acquisition

STATCOM static synchronous compensator based on a power electronics voltage-source converter SVC static var compensator

TSC thyristor switched capacitor bank, which is switched dynamically during voltage dips UVRT under voltage ride through

4 Often referred to as a doubly-fed induction generator (DFIG), but it is not operated as an induction generator when the rotor current is controlled

VRRAG asynchronous generator with variable rotor resistance

Subscripts 1 8

ag air gap base per-unit base value cmd current command to generator system drt drive train

DTD active drive train damping

E error between simulation and measurement err controller input error gen generator init initial value filt filtered

MAE mean absolute error between simulation and measurement max maximum

ME mean error between simulation and measurement mea measured min minimum

MXE maximum error between simulation and measurement n nominal ord active or reactive power order from WT controller p active component q reactive component u voltage

WTref WT reference value sim simulated

UVRT under voltage ride through

General 1 9

In this standard, voltage and current values are positive sequence fundamentals unless otherwise stated

This standard utilizes additional symbols alongside the parameters defined in module library 5.6 Physical unit variables are accompanied by their respective units in brackets, while per-unit variables include their per-unit bases also indicated in brackets.

Symbols (units) 1 9

The pitch angle (in degrees) is crucial for optimizing turbine performance, while the initial torque value (Τ base) serves as a reference point for torque measurements in per unit (p.u.) values The relationship between torque (Τ) and power (P) is expressed in Newton-meters (Nm), and the generator's rotational speed is measured against the base rotational speed (Ω base) Additionally, the reference rotational speed (ω ref) and the WTR rotational speed (ω WTR) are also compared to the base speed to ensure efficient operation.

= referringto WTR gen to referring gear n n base n

Ω n nominal generator rotational speed (rad/s) f n nominal grid frequency (50 Hz or 60 Hz)

F OCB open-circuit-breaker flag (0,1 )

F UVRT under voltage ride through flag (0,1 ,2) f sys global power system grid frequency (f n ) f WT WTT grid frequency (f n )

The nominal current at WTT (A) is represented by the generator current phasor in power system coordinates (I_n) The WTT current phasor in power system coordinates (I_n) is measured and processed as the signal (I_WTmea), while the raw WTT current is measured according to IEC 61400-21 (I_WTraw) Additionally, the simulated and processed WTT current is denoted as (I_WTsim) The active current command to the generator system follows the generation sign convention (I_pcmd), with the maximum active current also defined under this convention (I_pmax) For reactive current, the command to the generator system adheres to the capacitive sign convention (I_qcmd), with the maximum (I_qmax) and minimum (I_qmin) reactive currents specified accordingly The mechanical gear ratio between the wind turbine rotor (WTR) and the generator is denoted as (n_gear) The generator's air gap power is represented as (P_ag), while the aerodynamic power is indicated as (P_aero), and the power order from the wind turbine controller is noted as (P_ord).

The nominal active power of a wind turbine (WT) is denoted as \$P_n\$, while the active power generated, following the generation sign convention, is represented as \$p_{WT}\$ The reference active power for the wind turbine is indicated as \$p_{WTref}\$ Reactive power, adhering to the capacitive sign convention, is expressed as \$q_{WT}\$, with the maximum and minimum reactive power values being \$q_{WTmax}\$ and \$q_{WTmin}\$, respectively Additionally, the rotor resistance is represented by \$r_{rot}\$, which is based on the base impedance \$Z_{base}\$.

T com common sample time used to compare measured and simulated values (s)

T mea sample rate of raw measured data (s)

T s integration time step (s) u gen generator voltage phasor in power system coordinates (I n )

The nominal phase-to-phase voltage at the wind turbine transformer (WTT) is denoted as \$U_n\$ This includes the WTT voltage phasor in power system coordinates, the measured and signal processed WTT voltage (\$U_{WTmea}\$), the raw WTT voltage measured according to IEC 61400-21 (\$U_{WTraw}\$), and the simulated and signal processed WTT voltage (\$U_{WTsim}\$).

W fault time window defining the fault period (s)

W faultQS quasi steady state part of W fault (s)

W post time window defining the post-fault period (s)

W postQS quasi steady state part of W post (s)

The pre-fault period is defined by the time window $ W $, during which the simulation error time series $ E(n) $ is analyzed Key metrics include the mean absolute error (MAE), mean error (ME), and maximum error (MXE) calculated within this time window The measured time series $ mea(n) $ and the simulated time series $ sim(n) $ are both provided by signal processing, allowing for a comprehensive evaluation of the simulation accuracy.

IEC 61 400-27-1 :201 5  I EC 201 5 – 21 – x WTref WTT reactive power reference (capacitive sign convention) or delta voltage reference, depending on WT control mode (P n or U n )

Z base impedance base value n base Pn

Overview

The objective of Clause 5 is to specify a set of generic simulation models covering the existing WT types, and a structure to develop models for future WT types

WTs are generally divided into 4 types, which are currently significant in power systems (Hansen 2004, NERC 201 0) Using the NERC nomenclature (type 1 to 4), the 4 types have the following characteristics:

– Type 1 : WT with directly grid connected asynchronous generator with fixed rotor resistance (typically squirrel cage)

– Type 2: WT with directly grid connected asynchronous generator with variable rotor resistance

– Type 3: WT with doubly-fed asynchronous generators (directly connected stator and rotor connected through power converter)

– Type 4: WT connected to the grid through a full size power converter

The model specification is organised in the following subclauses:

– 5.3 specifies the interface between the WT model, WP model and the grid model

– 5.4 specifies categories of WT model parameters and how these categories are affecting the model initialisation

– 5.5 specifies the generic modular structure of WT models modular structure for type 1 to 4 models respectively and for the corresponding control models

– 5.6 specifies the detailed models for the individual modules used in 5.5.

General specifications

This subclause describes the general specifications for the WT models The specifications are not performance requirements of the WTs, but requirements to model structure

These models have been developed with the following specifications in mind:

The current wind turbine (WT) technologies encompass four main categories: conventional asynchronous generators, variable rotor resistance asynchronous generators, doubly-fed asynchronous generators, and full-converter interface wind turbines.

– The models are modular in nature to allow for the potential of augmentation in case of future technologies being developed, or future supplemental controls features

– The models are to be used primarily for power system stability studies and thus should represent all positive sequence dynamics affected and relevant during

• balanced short-circuits on the transmission grid (external to the wind power plant, including voltage recovery),

• electromechanical modes of synchronous generator rotor oscillations (typically in the 0,2 Hz to 4 Hz range), and

– The models are for fundamental frequency positive sequence response 6

– The models should be valid for typical power system frequency deviations (recommended ± 6 % from system nominal frequency)

– The models should be able to handle numerically the simulation of phase jumps

– The models should be valid for steady state voltage deviations within the range from 0,85 p.u to 1 ,1 5 p.u

– The models should be valid for dynamic voltage phenomena (e.g faults) where the voltage can dip temporarily close to zero 7

– The typical dynamic simulation time frame of interest is from 1 0 seconds to 30 seconds Wind speed is assumed to be constant during such a time frame

– The models should work with integration time steps up to ẳ cycle 8 As a consequence, the bandwidth of the models cannot be greater than 1 5 Hz 9

– The models should initialize to a steady state from power flow solutions at full or partial nominal power

– External conditions like wind speed should be taken into account implicitly through the available aerodynamic power

To ensure a realistic representation of wind turbine (WT) disconnection during grid disturbances, it is essential to model over/under frequency and over/under voltage protection within the control system These protections may be implemented as separate modules that interface with the main WT model.

– The turbine-generator inertia and first drive train torsional mode should be taken into account where it can have significant influence on the power swings 1 1

Models must be numerically robust to function effectively in both high and low short-circuit systems Equipment suppliers are responsible for defining the minimum short-circuit ratio and system conditions applicable to their specific equipment It is important to note that the dynamics of phase-locked loops are not incorporated into these models.

Frequency control is absent in the WT models outlined in IEC 61400-27-1 However, primary frequency control is incorporated in the plant-level models detailed in the informative Annex D and will also be included in the plant-level models specified in IEC 61400-27-2.

6 I n general, positive sequence simulations are sufficient for bulk power system stability studies Correct representation of the negative sequence and zero sequence components is cumbersome

7 The models are not validated for dynamic overvoltage events For very low voltages, the validity is also limited in the case of instability of the converter control (Gửksu 201 4)

The models can operate stably with ẵ cycle integration time steps; however, certain time constants may require adjustment to be at least twice the integration time step This modification of parameters can impact the accuracy of the model.

The minimum time constant that can be incorporated into a dynamic model is typically twice the integration time step, necessitating a cycle integration time step of 0.005 seconds in the worst-case scenario (50 Hz) Consequently, the minimum time constant is established at 0.01 seconds For a first-order lag with this time constant, the 3 dB bandwidth is calculated to be 10 rad/s, which is approximately 15.9 Hz, and is rounded down to 15 Hz.

1 0 The specified fundamental frequency models do not reflect any grid protection faster than 1 cycle

The eigenfrequency of the first drive train torsional mode must fall within the model's bandwidth, which is typically the case for nearly all wind turbines (WTs).

The dynamics of the Phase-Locked Loop (PLL) are typically an order of magnitude faster than those of the turbine power controller, resulting in a minimal impact on bulk power system studies.

The models must be clearly defined using block diagrams, detailed explanations of non-linear components, and relevant equations, along with a discussion of any unique initialization challenges to facilitate implementation by software vendors While the standard will not outline the specific algorithms used in time series simulation tools, it will focus on the linear, non-linear, and differential relationships that are modeled.

The generic models for protection and control systems will differ from specific manufacturer systems, allowing for easy parameterization to represent any manufacturer-specific configurations This approach involves defining distinct blocks for protection and control, enabling the seamless replacement of generic blocks with those tailored to specific manufacturers.

– The model should include the reactive power capability of the WT.

Model interface

This subclause outlines the interface specifications for the WT models, detailing their connection to the grid model within the power system simulation tool and the WP model as defined in IEC 61400-27-2.

The general dynamic simulation interface between WT model, grid model and WP model is illustrated in Figure 3

Figure 3 – General interface between WT model, grid model and WP model

The model can either be excited by an event in the grid model such as a short-circuit, or by a change in a WT reference value from the WP controller

The WT model takes the grid voltages as input from the grid model and gives the grid currents as output These inputs and outputs refer to WTT

Wind turbines (WTs) can obtain online reference values through the wind power plant SCADA system, either from a wind power plant controller or remote control The specific set of reference values varies based on the type of wind turbine, the manufacturer, and the operational mode Generic wind turbine models consider the following reference values.

The WT models are capable of simulating power factor control mode, assuming a constant power factor reference value during the simulation.

WT model model Grid grid variables WT

WP model grid variables WP

W T re fe re nc e va lu es

Parameters and initialisation

General

To utilize a generic model as outlined in section 5.5, the wind turbine (WT) manufacturer must provide the model parameters for each module listed in the corresponding table for the chosen model type While the global WT model parameters are detailed in section 5.4.3, most parameters are specified in the module library tables found in section 5.6 These parameters are organized according to the categorization in section 5.4.2.

Certain modules mentioned in section 5.6 utilize initialization variables that are determined by the model initialization, usually based on the load flow case An overview of this initialization process can be found in section 5.4.4.

Parameter categories

Each parameter of the WT model is classified into three categories: type dependent, project dependent, and case dependent The specific category for each WT model parameter can be found in the parameter tables within module library 5.6.

The three parameter categories are defined as follows:

– Type dependent parameters are characteristic to the specific WT type This is typically the case for mechanical and electrical parameters

Project-dependent parameters can vary for each wind turbine (WT) type based on the specific project, particularly for control parameters that are aligned with unique grid code requirements.

Case-dependent parameters can fluctuate based on the specific steady state before a disturbance, influenced by whether the actual or potential power is nominal or partial It is essential for wind turbine manufacturers to clearly define how these parameters relate to each unique simulation scenario.

The WT manufacturer has the authority to upgrade certain parameters listed in section 5.6 as applicable to specific WT types The goal is to minimize the number of case-dependent parameters while clearly defining the limited application range for each set of parameters.

Global parameters

The global wind turbine (WT) model parameters are detailed in Table 1, which are utilized in module library 5.6 and the block symbol library Annex G, alongside the specific parameters for each individual model in section 5.6.

Table 1 – Global WT model parameters

Symbol Base unit Description f n Hz Nominal frequency

Initialisation

The initialization of the wind turbine (WT) model must align with the initialization of both the grid model and the wind power plant model as outlined in IEC-61400-27-2 Figure 4 illustrates the interface connecting the initialization processes of the grid model, wind power plant model, and WT model.

Figure 4 – General interface for initialisation of WT model,

WP model and grid model

Before initializing the model, it is essential to update the case-dependent parameters, which include the load flow parameters in the grid model as well as the case-specific wind turbine (WT) and wind power (WP) parameters.

The grid model is initialized through a load flow that aligns with the control modes of both the wind power plant and wind turbine (WT) models This load flow is crucial as it establishes the initial voltages and currents, impacting the initialization of both models Additionally, the initial reference values can cause the wind power plant model's initialization to influence that of the WT model.

Table 2 lists the initialisation variables which are explicitly used in the models

Table 2 – Initialisation variable used explicitly in model block diagrams

Symbol Base unit Description p i ni t P n Initial power τ i ni t Τ base Initial steady state drive train torque tan(φ i ni t ) - Power scaling factor used in power factor control

Modular structure of models

Generic modular structure

The standard employs the generic modular structure of the WT model, as illustrated in Figure 5, which aligns with the interface defined in Figure 3 The central horizontal sequence of blocks represents the conversion of aerodynamic power to electrical power at the WTTs, with protection mechanisms displayed above and control systems below.

Case dependent load flow parametersIn iti al W T re fe re nc e va lu es

Figure 5 – Generic modular structure of WT models

Type 1

The type 1 WT uses asynchronous generators directly connected to the grid, i.e without power converter Most Type 1 WTs have a soft-starter, but this is only active during start-up

Figure 6 shows the main electrical and mechanical components which are included in the type

The WT rotor (WTR) is linked to the asynchronous generator (AG) through a gearbox (GB), with a capacitor bank providing reactive power compensation Most Type 1 wind turbines (WTs) utilize mechanically switched capacitor banks (MSC), which are treated as fixed for short-term simulations In contrast, Type 1 WTs equipped with fault-ride-through capabilities employ thyristor switched capacitor banks (TSC) that are dynamically controlled during and after faults The main circuit breaker (CB) disconnects both the generator and capacitors simultaneously, and according to IEC 61400-21, the wind turbine transformer (WTT) can be positioned on either side of the transformer (TR).

Figure 6 – Main electrical and mechanical components of type 1 WTs

Type 1 WTs may have fixed blade pitch angles or pitch systems allowing the blades to be turned away from stall (positive pitch angle) or into stall (negative pitch angle, also denoted active power control or Combi Stall control) The blade angle control is in some type 1 WTs used in active UVRT control

Therefore, two type 1 models are specified in 6.5.5.2 and 6.5.5.3:

Generator system reference WT values grid variables WT

– Type 1 A: WTs with fixed pitch angle

– Type 1 B: WTs with UVRT pitch angle control

Figure 7 shows the modular structure for the type 1 A WT model This model assumes that the pitch angle is fixed

NOTE The aerodynamic block is included in the figure, but it only represents a simplistic constant aerodynamics torque model

Figure 7 – Modular structure for the type 1 A WT model The details for each block are given in the Modules referred to in Table 3

Table 3 – Modules used in type 1 A model

Block Module clause Module name

Aerodynamic 5.6.1 1 “Constant aerodynamic torque model“

Generator system 5.6.3.1 “Asynchronous generator model“

Grid protection 5.6.6 “Grid protection model“

Figure 8 shows the modular structure for the type 1 B WT model This model includes UVRT pitch angle control

Generator system u i gen gen p ag p aero ω gen

F OCB u WT f sys ω WTR u WT i WT f sys

NOTE The aerodynamic block is not included in the figure because the aerodynamic effects are embedded in the control model

Figure 8 – Modular structure for the type 1 B WT model The details for each block are given in the Modules referred to in Table 4

Table 4 – Modules used in type 1 B model

Aerodynamic 5.6.1 1 “Constant aerodynamic torque model“

Control 5.6.5.1 “Pitch control power model“ “

Type 2

Figure 9 illustrates the key electrical and mechanical components of the type 2 wind turbine (WT) model Unlike the type 1 WT, the type 2 turbine features a variable rotor resistance (VRR) and utilizes a variable rotor resistance asynchronous generator (VRRAG) Additionally, type 2 WTs typically include blade angle control for enhanced performance.

Generator system u i gen gen p ag ω gen

F OCB u WT f sys u WT i WT f sys p ag

Figure 9 – Main electrical and mechanical components of type 2 WTs

The type 2 model specified in this standard is based on the generic WT models specified by the I EEE / WECC working groupand used in the 2 nd generation WECC models (Pourbeik

201 3) The modular structure for the type 2 WT model is shown in Figure 1 0

NOTE The aerodynamic block is not included in the figure because the aerodynamic effects are embedded in the control model

Figure 1 0 – Modular structure for the type 2 WT model

The modular structure of the type 2 control model, as illustrated in Figure 1, incorporates a "Pitch control emulator" module for active power management, complemented by the rotor resistance control model Additionally, it directs the reactive power or voltage control reference, denoted as \$x_{WTref}\$, to the shunt capacitor model within the electrical equipment module.

Mechanical Generator system p ag ω gen

Control p aero ω gen u gen i gen r rot

F OCB u WT f sys u WT i WT f sys p WT u WT f sys

Figure 1 1 – Modular structure for the type 2 control model The details for each block are given in the Modules referred to in Table 5

Table 5 – Modules used in type 2 model

Type 3

Type 3 wind turbines (WTs) utilize a doubly fed asynchronous generator (DFAG), where the stator is directly connected to the grid and the rotor connects via a back-to-back power converter The main components of type 3 WT models include the generator side converter (GSC), line side converter (LSC), and a DC link (DCL) with a capacitor (C) These turbines are designed with adequately sized GSC and chopper (CH) to ensure voltage ride-through without the need to bypass or disconnect the converter Additionally, some type 3 WTs are equipped with a crowbar device (CRB) that short-circuits the rotor during electromagnetic transients, effectively transforming the WT generator into an induction machine during this period.

Pitch control power p WT p aero

Rotor resistance control r rot u WT ω gen f sys

Figure 1 2 – Main electrical and mechanical components of type 3 WTs

The generic type 3 model encompasses both mechanical system and aerodynamic modules, although this level of detail may not always be necessary In certain instances, a generic type 4 model may adequately simulate the behavior at the wind turbine (WT) terminals The modular structure of the type 3 WT model is illustrated in Figure 1.

Figure 1 3 – Modular structure for the type 3 WT model Figure 1 4 shows the modular structure for the type 3 control models

Control Θ p WT q WT u WT i pcmd i qcmd i pmax i qmax i qmin ω WTR ω WTR ω gen u WT f sys p ag Generator system u gen p WTref x WTref u WT i WT f sys

Figure 1 4 – Modular structure for the type 3 control models The details for each block are given in the Modules referred to in Table 6

Table 6 – Modules used in type 3 model

Aerodynamic 5 6 1 3 “Two-dimensional aerodynamic model“ or “One-dimensional aerodynamic model”

Generator system 5 6 3 2 or 5 6.3.3 “Type 3A generator set model“ or “Type 3B generator set model“ Electrical equipment 5 6 4 2

“Constant Q limitation model“ or “QP and QU limitation model“

Grid protection 5 6 6 “Grid protection model“

Pitch control p ord Θ ω WTR u WT p WT q WT ω ref

F UVRT limitation Q q WTmax q WTmin i qmin ω gen

Type 4

Type 4 WTs are WTs connected to the grid through a full scale power converter Figure 1 5 shows the main electrical and mechanical components which are considered in the type 4 WT models in this standard Type 4 WTs use either synchronous generators (SG) or asynchronous generators (AG) Some type 4 WTs use direct drive synchronous generators, and therefore have no gearbox

Figure 1 5 – Main electrical and mechanical components of type 4 WTs

Type 4 WTs with choppers can normally be modelled neglecting the aerodynamic and mechanical parts of the WT Type 4 WTs without choppers inject post-fault power oscillations due to damping of torsional oscillations This is also the case for type 4 WTs with partially rated choppers These oscillations are normally not affecting the power system stability, but the effect of torsional oscillation damping may be included using a two-mass mechanical model If partially rated chopper is applied, then the damping coefficient in the two-mass model can be adjusted to match the rating of the chopper The type 3A model may be used to simulate type 4 WTs, but simplified models are usually sufficient because of the converter decoupling of the drive train from the grid

Therefore, two type 4 models are specified in 6.5.5.2 and 6.5.5.3:

– Type 4A: a model neglecting the aerodynamic and mechanical parts and thus not simulating any power oscillations

– Type 4B: a model including a 2-mass mechanical model to replicate the power oscillations but assuming constant aerodynamic torque

The modular structure for the type 4A WT model is shown in Figure 1 6

Figure 1 6 – Modular structure for the type 4A WT model Figure 1 7 shows the modular structure for the type 4A control models

Figure 1 7 – Modular structure for the type 4A control model The details for each block are given in the Modules referred to in Table 7

Q control x WTref i qcmd i qmax u WT q WT p WT

F UVRT limitation Q q WTmax q WTmin i qmin

Control p WT q WT u WT p WTref x WTref u WT f sys

Grid protection i pcmd i qcmd i pmax i qmax i qmin u gen u WT i WT f sys

Table 7 – Modules used in type 4A model

Generator system 5.6.3.4 or 5 6 3 2 “Type 4 generator set model“ or “Type 3A generator set model“ a Electrical equipment 5 6 4 2

The Type 3A generator set model is compatible with type 4 wind turbine models, effectively reducing the reactive power spike that occurs during voltage recovery, which is primarily attributed to numerical effects in simulations.

The modular structure for the generic type 4B WT model is shown in Figure 1 8

Figure 1 8 – Modular structure for the type 4B WT model Figure 1 9 shows the modular structure for the type 4B control models

Control p WT q WT u WT p WTref x WTref ω gen u WT f sys p ag Generator system i pcmd i qcmd i pmax i qmax i qmin u gen u WT i WT f sys p aero

Figure 1 9 – Modular structure for the type 4B control model The details for each block are given in the Modules referred to in Table 8

Table 8 – Modules used in type 4B model

Generator system 5.6.3.4 or 5 6 3 2 “Type 4 generator set model” or “Type 3A generator set model” a Electrical equipment 5 6 4 2

The Type 3A generator set model in Grid Protection 5.6.6 can effectively be utilized in Type 4 wind turbine models to eliminate the reactive power spike that occurs during voltage recovery, which is primarily attributed to numerical effects in simulations.

Q control x WTref i qcmd i qmax ω gen u WT q WT

F UVRT p aero p WT limitation Q q WTmax q WTmin i qmin

Module library

Aerodynamic models

The block diagram for the constant aerodynamic model, illustrated in Figure 20, operates without the need for manufacturer-supplied parameters It is essential to establish the initial torque, denoted as \$\tau_{init}\$, through the load-flow process.

Figure 20 – Block diagram for constant aerodynamic torque model

This aerodynamic sub-model is based on the one-dimensional framework established by Price and Sanchez-Gasca (2006) It accounts for the pitch angle dependency while omitting the rotor speed influence Key parameters of the one-dimensional aerodynamic model are detailed in Table 9, and a corresponding block diagram is illustrated in Figure 21 The initial power, denoted as $ p_{\text{ini}} $, must be determined through the load-flow analysis.

Table 9 – Parameter list for one-dimensional aerodynamic model

Symbol Base unit Description Category Θ w0 deg Initial pitch angle Case k a P n / deg 2 Aerodynamic gain Type

Figure 21 – Block diagram for one-dimensional aerodynamic model

The two-dimensional aerodynamic sub model corresponds to the model proposed in Fortmann

(201 4).The two-dimensional aerodynamic model parameters are given in Table 1 0, and the block diagram is given in Figure 22

Table 1 0 – Parameter list for two-dimensional aerodynamic model

Symbol Base unit Description Category p avai l P n Available aerodynamic power a Case Θ 0 deg Pitch angle if the WT is not derated b Case

The rotor speed (\$ω_0\$) represents the base speed of the wind turbine (WT) when not derated The partial derivative of aerodynamic power (\$dp/Θ\$) indicates how power changes with pitch angle adjustments, while \$dp/ω\$ reflects changes in power concerning rotor speed The blade angle (\$Θ\$) is set at twice the rated wind speed, and the partial derivative at rated wind speed is denoted as \$dp/v_1\$ The available aerodynamic power is crucial for modeling derated operations, enabling the integration with wind power plant controllers to boost active power when sufficient aerodynamic power is present It is essential that the initial aerodynamic power does not exceed the available power (\$p_{avail}\$), and the pitch angle should typically be zero when \$p_{avail} < 1\$ and greater than zero when \$p_{avail} = 1\$ or if the initial aerodynamic power is less than \$p_{avail}\$.

Figure 22 – Block diagram for two-dimensional aerodynamic model

Annex E outlines the foundational aspects of the two-dimensional aerodynamic model, offering guidance to wind turbine (WT) manufacturers on how to identify case-dependent model parameters It also provides instructions for software vendors on calculating initialization when the required parameters are supplied by the manufacturer.

Mechanical models

The module parameters are given in Table 1 1 , and the block diagram is given in Figure 23 1 3

Some software tools incorporate generator inertia within their built-in generator models In such instances, the additional mechanical model should connect to the generator shaft rather than the generator air gap, thereby excluding the generator inertia As a result, the overall mechanical model remains a two-mass model as previously outlined.

IEC dp ω + 0.5dp v1 Σ + Σ Σ p aero p avail

Table 1 1 – Parameter list for two-mass model

Symbol Base unit Description Category

H WTR s I nertia constant of WT rotor Type

H gen s Inertia constant of generator Type k d rt T base Drive train stiffness Type c d rt T base / Ω base Drive train damping Type

Figure 23 – Block diagram for two mass model

Generator set models

The standard does not define a specific model for the asynchronous generator; instead, it recommends using the standard asynchronous generator model available in the simulation tool In stability studies, it is common practice to focus on rotor flux transients while neglecting stator flux transients.

If motor models are used, then the user must take into account that the modules in this standard assumes generator sign convention

The module parameters are given in Table 1 2, and the block diagram is given in Figure 24

The generator model's output is a current injected through a current source with parallel impedance $X_s$ In certain power system simulation software, the 'control' and 'grid' components of a model are handled separately To enhance the simulation's convergence behavior, it is advisable to integrate the parallel impedance $X_s$, defined as the "stator voltage divided by the transient reactance," into the grid equations, as recommended by Fortmann et al (2014).

The losses in the generator system are neglected setting the generator air gap power p ag equal to the WT terminal power

Table 1 2 – Parameter list for type 3A generator set model

K Pc - Current PI controller proportional gain Type

The current PI controller integration time constant is crucial for system performance, while the electromagnetic transient reactance should be derived from the electromagnetic transient inductance as outlined by Fortmann et al (2014) Additionally, the maximum active current ramp rate is defined as \$d_i p_{max} I_n/s\$ and the maximum reactive current ramp rate is defined as \$d_i q_{max} I_n/s\$ for the project.

Figure 24 – Block diagram for type 3A generator set model

The parameters for the module are detailed in Table 1 3, while the block diagram is illustrated in Figure 25 The type 3B generator set model represents an advanced simplification of the type 3A generator set model, incorporating a crowbar model (Buendia et al., 2012).

The generator model produces a current that is injected via a current source In certain power system simulation software, it is necessary to include a parallel impedance to enhance the convergence behavior of the simulation Therefore, it is advisable to implement this approach for optimal results.

R ef er en ce F ra m e R ot at io n

Grid Reference Frame Controls Reference Frame

0 i pcmd i qcmd di pmax i pmax i WT

IEC 61 400-27-1 :201 5  I EC 201 5 – 41 – move the term “stator voltage divided by the transient reactance” so that it is incorporated into the grid equations as suggested in Fortmann et al (201 4)

Table 1 3 – Parameter list for type 3B generator set model

T g s Current generation Time constant Type di pmax I n /s Maximum active current ramp rate Project di q max I n /s Maximum reactive current ramp rate Project x S Z base Electromagnetic transient reactance Type

T CW (du) s vs U n Crowbar duration versus voltage variation look-up table Case

T wo s Time constant for crowbar washout filter Case

M WTcwp - Crowbar control mode Case

Figure 25 – Block diagram for type 3B generator set model

The module parameters for the type 4 generator model are given in Table 1 4, and the block diagram is given in Figure 26

R efe re nc e F ra m e R ota tio n

1 : crowbar deactivated wo wo sT

1 du T CW (du) TIMER i qcmd x S

Table 1 4 – Parameter list for type 4 generator set model

T g s Time constant Type di pmax I n /s Maximum active current ramp rate Project di q max I n /s Maximum reactive current ramp rate Project di q mi n I n /s Minimum reactive current ramp rate Project

Figure 26 – Block diagram for type 4 generator set model

The module parameters for the reference frame rotation model are given in Table 1 5, and the block diagram is given in Figure 27

Table 1 5 – Parameter list for reference frame rotation model

The time constant for the first-order filter model in a Phase-Locked Loop (PLL) is denoted as $ u_{PLL1} $, which represents the voltage threshold below which the angle of the voltage is filtered and potentially frozen Additionally, $ u_{PLL2} $ is the voltage level below which the angle is frozen if $ u_{PLL2} \leq u_{PLL1} $ This filtering and freezing of the angle is crucial to prevent instabilities arising from a lack of voltage reference It is important to coordinate the values of $ u_{PLL2} $ and $ u_{PLL1} $, typically ensuring that $ u_{PLL2} \leq u_{PLL1} $ The use of $ u_{PLL2} $ helps to mitigate numerical issues when the voltage approaches zero, ensuring that the angle remains numerically valid.

IEC i pcmd i qcmd di pmax i pmax i qmax i WT

R ef er en ce F ra m e R ot at io n i qmin

Figure 27 – Block diagram for the reference frame rotation model

Electrical equipment

The standard does not define models for shunt capacitors For mechanically switched capacitor banks (MSC), the fundamental frequency capacitor model in the simulation tool is recommended In the case of thyristor switched capacitor banks (TSC), a standard SVC model is applicable Typically, turbine compensations exclude the reactor, which is a common feature in SVCs.

The standard circuit breaker model in the simulation tool should be used The circuit breaker model must open the circuit breaker when it receives the F OCB flag

This standard does not specify a model for the transformer The standard transformer model in the simulation tool should be used.

Control models

This module features the type 1 and type 2 wind turbine (WT) pitch controller designed for the second generation WECC models, as proposed by Pourbeik in 2013 Detailed parameters for the module can be found in Table 16, while the corresponding block diagram is illustrated in Figure 28.

Table 1 6 – Parameter list for pitch control power model

T r s Voltage measurement time constant Type dp max P n Rate limit for increasing power Type dp mi n P n Rate limit for decreasing power Type

T 1 s Lag time constant Type p mi n P n Minimum power setting Type p set P n If p i ni t < p set then power will be ramped down to p mi n Type

T d ( u WT ) s( U n ) Lookup table to determine the duration of the power reduction after a voltage dip, depending on the size of the voltage dip a

To ensure compatibility with WECC models, the lookup table for dip detection must be defined in steps between four points Additionally, it is essential that the value of $ u \, UVRT $ matches the highest voltage in $ T_d $ (denoted as $ u \, WT $).

NOTE The initial power p i ni t is set by the load flow

Figure 28 – Block diagram for pitch control power model

Table 1 7 – Parameter list for pitch angle control model

K Pω deg/Ω base Speed PI controller proportional gain Type

K I ω deg/Ω base /s Speed PI controller integration gain Type

K Pc deg/P n Power PI controller proportional gain Type

K I c deg/P n /s Power PI controller integration gain Type

The K PX Ω base/P n represents the pitch cross coupling gain, while Θ max deg indicates the maximum pitch angle and Θ min deg denotes the minimum pitch angle Additionally, dΘ max deg/s refers to the maximum positive ramp rate of pitch, and dΘ min deg/s signifies the maximum negative ramp rate of pitch.

1 dp max dp min sT 1

NOTE The block diagram uses the anti windup integrator described in Annex G.8 and the first order filter with limitation detection described in Annex G.1 0

Figure 29 – Block diagram for pitch angle control model 5.6.5.3 Rotor resistance control model

Table 1 8 – Parameter list for rotor resistance control model

T pfi l trr s Filter time constant for power measurement Type

K pfi l t - Filter gain for power measurement Type

T ωfi l t rr s Filter time constant for generator speed measurement Type

K ωfi l t - Filter gain for generator speed measurement Type p rr (Δω) P n

(Ω base ) Power versus speed change (negative slip) lookup table Type

K Prr Z base /P n Proportional gain in rotor resistance PI controller Type

/P n /s Integral gain in rotor resistance PI controller Type r max Z base Maximum rotor resistance Type r mi n Z base Minimum rotor resistance Type

AntiWindUp dΘ max dΘ min dΘ max dΘ min

The original IEEE/WECC model employs a motor sign convention for power and slip, aligning with textbook models for asynchronous machines In contrast, this standard adopts a generator sign convention, resulting in a reversal of the PI controller input sign compared to the original IEEE/WECC model.

Figure 30 – Block diagram for rotor resistance control model

The module parameters are given in Table 1 9, and the block diagrams are given in Figure 31 and Figure 32

Table 1 9 – Parameter list for p control model type 3

Symbol Base unit Description Category ω offset Ω base Offset to reference value that limits controller action during rotor speed changes Case ω(p) Ω base (P n ) Power vs speed lookup table Type

K Pp Τ base /Ω base PI controller proportional gain Type

K I p Τ base /Ω base /s PI controller integration parameter Type

T pfi l tp3 s Filter time constant for power measurement Type

T ufi l tp3 s Filter time constant for voltage measurement Type

T ωref s Time constant in speed reference filter Type

T ωfi l t p3 s Filter time constant for generator speed measurement Type

The active drive train damping is characterized by the base gain, denoted as \$K_{DTD} P_n / \Omega_{base}\$, and the maximum damping power, represented as \$P_{DTDmax} P_n\$ The damping coefficient is indicated by \$\zeta\$, while the active drive train damping frequency, \$\omega_{DTD} \Omega_{base}\$, can be derived from the parameters listed in Table 1.

The time constant in power order lag, denoted as \$T_{pord}\$, is crucial for understanding the dynamics of wind turbine (WT) performance The maximum wind turbine power ramp rate, represented as \$dp_{max} P_n/s\$, indicates the highest rate at which power can increase Conversely, the minimum ramp rate of the WT reference power, denoted as \$dp_{refmin} P_n/s\$, defines the lowest rate of power decrease Additionally, the voltage dip threshold for P-control, indicated as \$updip U_n\$, is an essential parameter in turbine control, often differing from converter thresholds, typically set at around 0.8.

Project dτ max Τ base /s Ramp limitation of torque, required in some grid codes Project

K + 1 r rot Σ ω gen f WT p rr ( Δ ω ) p WT filtrr filt ω ω sT

Symbol Base unit Description Category τ emi n Τ base Minimum electrical generator torque Type τ uscal e Τ base /U n Voltage scaling factor of reset-torque Project

The M pUVRT feature allows users to enable UVRT power control mode, with options for reactive power control (0) or voltage control (1) It includes a project parameter, dτ maxU VRT Τ base /s, which limits the torque rise rate during UVRT Additionally, the project parameter u DVS U n establishes a voltage limit to maintain UVRT status following significant voltage sags.

T DVS s Time delay after deep voltage sags Project

NOTE The TORQUE PI block is detailed in Figure 32

Figure 31 – Block diagram for type 3 P control model

+ sT ω offset p WTref x / Π i pcmd ω ref ω gen p ord

+ sT 1 1 dp max Π x i pmax u WT Π

TORQUE PI τ emax dp refmax dp refmin τ out ω err u WT

NOTE The Freeze function is detailed in G 4, i e using Figure G 6 without limitations

Figure 32 – Block diagram for type 3 torque PI

The module parameters are given in Table 20, and the block diagram is given in Figure 33

Table 20 – Parameter list for p control model type 4A

T ufi l tp4A s Voltage measurement filter time constant Type

T pordp4A s Time constant in power order lag Type dp maxp4A P n /s Maximum WT power ramp rate Project

Figure 33 – Block diagram for type 4A P control model

+ sT 1 u WT 1 p WTref i pcmd Π 0,01 x x i pmax

Pp Ip s 1 τ emin τ emin Σ dτ m ax

+ + ω err τ emax dτ maxUVRT u WT τ uscale

The module parameters are given in Table 21 , and the block diagram is given in Figure 34

Table 21 – Parameter list for p control model type 4B

T ufi l tp4B s Voltage measurement filter time constant Type

T pordp4B s Time constant in power order lag Type

T paero s Time constant in aerodynamic power response Type dp maxp4B P n /s Maximum WT power ramp rate Project

NOTE The type 4B P control model assumes that τ i ni t = p i ni t , i.e the initial value of ω gen is 1

Figure 34 – Block diagram for type 4B P control model

The Q-control model supports the 5 different general Q control modes M qG listed in Table 22

Table 22 – General WT Q control modes M qG

2 Open loop reactive power control (only used with closed loop at plant level)

4 Open loop power factor control

The Q-control model facilitates three distinct UVRT Q control modes, M qUVRT, as outlined in Table 23 These control modes dictate the injection of reactive current during voltage dips and may also apply during an optional post-fault period.

+ sT 1 u WT 1 p WTref i pcmd ω gen Π Π 0,01 x x i pmax dp maxp4B x x paero

Table 23 – UVRT Q control modes M qUVRT

0 Voltage dependent reactive current injection

1 Reactive current injection controlled as the pre-fault value plus an additional voltage dependent reactive current injection

Reactive current injection is managed by maintaining the pre-fault value, supplemented by a voltage-dependent reactive current injection during a fault, and by adding a constant reactive current injection after the fault.

The module parameters for the Q-control module are given in Table 24, and the block diagram is given in Figure 35

Table 24 – Parameter list for q control model

M q G - General Q control mode (see Table 22) Project

M q UVRT - UVRT Q control modes (see Table 23) Project

T ufi l tq s Voltage measurement filter time constant Type

T pfi l tq s Power measurement filter time constant Type

K Pq U n /P n Reactive power PI controller proportional gain Type

K I q U n /P n /s Reactive power PI controller integration gain Type

K Pu I n /U n Voltage PI controller proportional gain Type

K I u I n /U n /s Voltage PI controller integration gain Type u db1 U n Voltage dead band lower limit Type u db2 U n Voltage dead band upper limit Type

The voltage scaling factor for UVRT current is denoted as \$K_{qv} = \frac{I_n}{U_n}\$ The maximum voltage in the voltage PI controller integral term is represented as \$u_{max} = U_n\$, while the minimum voltage is \$u_{min} = U_n\$ A user-defined bias in the voltage reference is given by \$u_{ref0} = U_n\$, and the adjusted reference is \$u_{WTref} = u_{ref0} + \Delta u_{WTref}\$, applicable when \$M_{qG} = M_{qGu}\$ Additionally, the voltage threshold for UVRT detection in q control is indicated as \$u_{qdip} = U_n\$.

T qord s Time constant in reactive power order lag Type

The T post s represents the duration for which post-fault reactive power is injected The maximum reactive current injection is denoted as i q max I n, while the minimum reactive current injection is indicated by i q mi n I n Additionally, i q h1 I n refers to the maximum reactive current injection during a dip, and i q post I n signifies the post-fault reactive current injection The resistive component of voltage drop impedance is represented by r d roop Z base, and the inductive component is indicated by x droop Z base.

Extreme care should be taken in coordinating the parameters u d b1 , u db2 and u qd i p so as not to have an unintentional response from the reactive power injection control loop

NOTE 1 The implementation of the “Freeze” function is described in Annex G 4

NOTE 2 tan(φ i ni t ) is initialised by the load flow

Figure 35 – Block diagram for Q control model

Voltage droop (r droop +jx droop ) tan(φ init ) pfiltq

K qv i qh1 i qmin i qpost i qv i qbase

The external reference $ x_{WTref} $ can represent either a reactive power or delta voltage command from the park controller, depending on the Q control mode In the absence of a park controller model, this signal is set as a constant input.

The “Delay Flag” block outputs the F UVRT flag in 1 of 3 stages described in Table 25

Table 25 – Description of F UVRT flag values

2 Post fault stays in stage 2 with ( u WT > u d i p ) for t = T post

The “Voltage droop” block shall calculate the voltage in a point which is located with the serial impedance distance r+jx from WTT (typically a transformer), i.e

WT droop WT WT droop WT

The current limitation model combines the physical limits and the control limits

Table 26 – Parameter list for current limiter model

Symbol Base unit Description Category i max I n Maximum continuous current at the WT terminals Type i maxdi p I n Maximum current during voltage dip at the WT terminals Project

M DFSLi m a - Limitation of type 3 stator current (0: total current limitation, 1 : stator current limitation) Type

M q pri - Prioritisation of q control during UVRT (0: active power priority –

1 : reactive power priority) Project i pmax (u WT ) Ι n (U n ) Lookup table for voltage dependency of active current limits Project i q max (u WT ) Ι n (U n ) Lookup table for voltage dependency of reactive current limits Project

T ufi l tcl s Voltage measurement filter time constant Type u pqu max U n WT voltage in the operation point where zero reactive current can be delivered Type

K pq u I n / U n Partial derivative of reactive current limit vs voltage Type a M DFSLi m = 1 for type 4 WTs.

NOTE ω gen input is not used for type 4 which is ensured by setting M DFSLi m = 1

Figure 36 – Block diagram for current limiter

Table 27 – Parameter list for constant Q limitation model

Symbol Base unit Description Category q max P n Maximum reactive power Type q mi n P n Minimum reactive power Type

NOTE The constant Q limitation model is not using the Q limitation model inputs F UVRT , u WT and p WT

Figure 37 – Block diagram for constant Q limitation model

IEC q max q WTmax q WTmin q min

M DFSLim i pm ax (u WT ) i pcmd i q max (u WT )

F UVRT sqr u WT i pmax Σ – + i qmin

1 sqr sqr min min sqrt sqrt min min abs

5.6.5.1 0 QP and QU limitation model

Table 28 – Parameter list for QP and QU limitation model

T ufi l tql s Voltage measurement filter time constant for Q capacity Type

The power measurement filter time constant for Q capacity is defined by the maximum limit of active power dependency on reactive power, represented as Type \$q_{maxp}(p)\$ and Type \$q_{minp}(p)\$ Additionally, the voltage dependency of reactive power is characterized by the maximum limit Type \$q_{maxu}(u)\$ and the minimum limit Type \$q_{minu}(u)\$ These parameters are essential for understanding the relationship between active and reactive power in electrical systems.

Figure 38 – Block diagram for QP and QU limitation model

Grid protection model

The grid protection model safeguards against over and under voltage and frequency fluctuations It features definite time protection, which is defined by specific protection levels and disconnection times as outlined in IEC 61400-21 Users can customize tripping profiles by inputting user-definable curves that establish voltage/time or frequency/time coordinates, with interpolation between points ensuring a smooth trip characteristic.

The module parameters are given in Table 29, and the block diagrams are given in Figure 39 and Figure 40

Industry typically adopts a conservative approach to protection modeling, ensuring that tripping occurs whenever voltage or frequency levels surpass established protection thresholds However, actual equipment can often exceed these minimum ride-through protection levels without triggering a trip in the wind turbine (WT).

Freeze q maxu (u) q minu (u) q WTmax q WTmin pfiltql

Table 29 – Parameter list for grid protection model

Symbol Base unit Description Category u over U n WT over voltage protection activation threshold Project

T uover (u WT ) s ( U n ) Disconnection time versus over voltage lookup table Project u und er U n WT under voltage protection activation threshold Project

T uu nder (u WT ) s ( U n ) Disconnection time versus under voltage lookup table Project f over f n WT over frequency protection activation threshold Project

T fover (f WT ) s ( f n ) Disconnection time versus over frequency lookup table Project f u nd er f n WT under frequency protection activation threshold Project

T fund er (f WT ) s ( f n ) Disconnection time versus under frequency lookup table Project

Mzc - Zero crossing measurement mode (true = 1 if the WT protection system uses zero crossings to detect frequency – otherwise false = 0)

Type dΦ max f n /s Maximum rate of change of frequency a Type

TfMA s Time interval of moving average window b Type a dΦ max should be greater than any ROCOF protection activation threshold in the power system Presently,

0,5Hz/s is reported in some grid codes, and 2, 5 Hz/s proposed, so it is recommended to use dΦ max = 5 Hz/s. b Typical values for protection equipment are 3 to 5 line periods.

NOTE The u-f measurement block is detailed in Figure 40

Figure 39 – Block diagram for grid protection system

< u WT f sys u- f m ea su re m en t u WT f WT

The model is designed to trip the wind turbine (WT) when a specific protection level is exceeded continuously for a designated disconnection time It is important to note that the model does not account for the reconnection of a tripped WT.

To utilize a definite-time relay model, a single pair of coordinates can be defined in lookup tables For specific tripping profiles, users have the flexibility to input multiple pairs of coordinates as needed in these tables.

NOTE The model parameter f n is included in the global parameter list Table 1

Figure 40 – Block diagram for u-f measurement

Overview

The objective of Clause 6 is to specify the standard procedure to validate a WT simulation model against tests on the WT in concern

The validation procedure is applicable to fundamental frequency simulation models, including those specified in Clause 5 Additionally, it can be utilized for other fundamental frequency wind turbine models, such as manufacturer-specific or project-specific models.

The accuracy of the model, as outlined in Clause 6, is constrained by unavoidable simulation and measurement errors Additionally, the generic nature of the models specified in Clause 5 limits their ability to capture detailed representations compared to manufacturer-specific models, as further elaborated in Annex B.

The validation procedure does not limit itself to model-to-model validation However, for similar wind turbines (WTs), the validation of one model can be applied to others, given that the WT manufacturer provides adequate justification.

Maintenance, equipment upgrades, and changes in site conditions may lead to modifications in the mechanical components of wind turbines (WT), such as installing new gearboxes, altering blade lengths, or adjusting tower heights However, these changes typically do not significantly affect the electrical transient behavior of the WT generator Wind turbines are considered similar if they share the same type and control schemes, along with identical hardware that influences transient behavior, including converters, crowbars, brake choppers, and voltage dip protection Additionally, variations in transformer primary side voltage ratings, rotor diameters, component manufacturers, and nominal values can also be seen in similar wind turbines during model validation.

The manufacturer’s justification can be obtained using a comprehensive 3-phase equipment-specific model When detailed simulations demonstrate that material changes have not significantly impacted the unit's electrical behavior, new field tests and measurements are unnecessary.

The description of the model validation procedure is organised in the following clauses:

– 6.2 gives the general specifications for the validation procedure

– 6.3 describes the validation procedure in detail

General specifications

The validation procedure has been developed with the following specifications in mind:

– The results of the validation procedure shall be appropriate for quantifying the simulation model accuracy with the purpose of being applied in various grid stability evaluations and planning studies

The validation procedure adheres to WT tests as outlined in IEC 61400-21, without introducing any supplementary tests or procedures It exclusively depends on the established methods provided in IEC 61400-21 for conducting these tests.

Existing test results obtained before the release of this standard may be accepted for validation, provided they cover the same operational range of the wind turbine (WT) as specified in IEC 61400-21 These results must be performed and documented in accordance with the requirements outlined in IEC 61400-21.

– The validation procedure shall include at least the following WT functional characteristics:

• Validation of the simulation model response to tested voltage dips

• Validation of the simulation model response to tested step changes 1 5 in reference values

• Validation of the simulation model grid protection functionality

To ensure accurate measurements and simulations, both the model and test must reference the same wind turbine (WT) terminals, as defined by the manufacturer in IEC 61400-21.

1 ) the low voltage side of the WT transformer, or

2) the high voltage side of the WT transformer

To ensure compliance with the validation procedure, it is essential to validate simulated positive sequence values against the measured positive sequence values Additionally, for models that incorporate negative sequence components, the validation process must also include a comparison of the simulated negative sequence components with the measured negative sequence components, alongside the validation of the positive sequence components.

– A testing plan shall be compiled for every measurement used for the validation

– The results of the validation procedure shall be:

• Time series of measured and simulated fundamental frequency quantities

• Time series of errors between simulated and measured fundamental frequency currents and voltages

• Mean error, mean absolute error and maximum error in pre-fault, during-fault and post- fault windows of voltage dips

• Measured and simulated response time, rise time and settling time of reference point changes

• Measured and simulated protection levels and disconnection times of grid protection

• Specification of the application range 1 6 of the validated simulation model

1 5 The specified procedure for validation of step changes assumes that the controller has an integral term ensuring that the reference value will be reached

1 6 "Application range" means the situations where the electrical simulation model is applicable

Information and data sampling for visualization must occur at a sampling time of 10 ms or less The visualization of both measured and simulated data should comply with IEC 61400-21 standards, which require the representation of fundamental positive and negative phase sequence systems, as well as zero phase sequence systems.

To calculate the deviation between simulated and measured values, it is essential to establish a mutual time base for both data sets This joint time base can be achieved through methods such as time synchronization, decimation, or interpolation of the sampled values.

High-frequency electromagnetic phenomena lasting less than one cycle are excluded from the specified simulation models This includes damped oscillations, like transformer inrush currents, which contain second harmonics and higher, falling outside the frequency range relevant for stability studies.

– If a measured value does not have a corresponding simulated value, an interpolated value shall be used, in order to create a date set of errors

The measured, processed, and simulated values will be expressed in per unit values, using the nominal active power and nominal voltage at the measurement point as the base for calculating the per unit parameters, in accordance with the definitions outlined in Clause 4.2.

Validation can be conducted using two primary methods The first method involves modeling both the wind turbine (WT) systems and their corresponding grid representation, including the interface between them The second method, often called the 'play-back' approach, focuses solely on the WT system, where a measured signal, usually voltage, is input into the model The responses of other measured quantities, such as active and reactive current, as well as active and reactive power, are then compared to the simulated responses of the model.

Validation procedure

Template for validation test results

Use cases

Description of the Software interface

Tiêu đề	Wind Turbines – Part 27-1: Electrical Simulation Models – Eolianness
Trường học	International Electrotechnical Commission (IEC)
Chuyên ngành	Electrical Engineering
Thể loại	Standards Document
Năm xuất bản	2015
Thành phố	Geneva

Định dạng
Số trang	204
Dung lượng	4,21 MB