Caracterización del CDC realizada por Pinto

Regardless of the structure of the microgrid management system utilized, the development of a comprehensible model for DGs with FCL is inevitable. The operation principle of different FCLs outlined in the previous chapters is almost identical. Regardless of its type, an FCL follows the fault current limitation characteristics given in Figure 6.2. Below the threshold value, there is no control on output current and it is free-flowing. Once the threshold is passed, a predetermined ifault is observed at the output after the reaction time (td – tƒ).

Therefore, the control parameters that are required in the communication system are the same. These are; the threshold current (ith), the limited fault current (if), the time required for

the FCL to react (td – tƒ). These parameters are required to anticipate the behavior of the FCL

Figure 6.2. Fault current limitation for inverter topology [160].

The extension of IEC 61820-7-420 to accommodate FCL can be achieved in three different ways:

1. Updating DRAT (direct-coupled DGs) ZINV (inverter interfaced DGs) with FCL control parameters

2. Updating DRCT (both for direct-coupled and inverter interfaced DGs) with FCL control parameters

3. Proposing a new block, FACL, for FCLs at DG output (placed before DER Circuit Breaker in Figure 6.1)

The first method requires repetition of the same adjustment for each DG type while the second method already encompasses both types of the DGs through updating DRCT block. Since DRCT is a universal block for all types of DGs, updating its structure shall be sufficient. Therefore, following sub-sections focus only on the latter two methods above.

6.4.1.1. Updating the DER controller LN (DRCT)

Table 6.1 shows the updated version of DRCT class which includes the data given in IEC 61850-7-420 [197] as well as the appended FCL parameters. Following the definition of IEC 61850 - Part 7.3 [198], Common Data Classes, the two current values `ThrshldCrnt` and `FCLCrnt` are defined as Analogue Setting (ASG) class while `FCLDelay` is defined as Integer Status Setting (ING). These parameters are indicated to be Optional „O‟ since DRCT is a universal class for all DG controllers including DGs without a fault current limiter.

TABLE 6.1.UPDATED DRCTCLASS DRCT class

Data Name CDC Explanation T M/O/C LNName Shall be inherited from logical-node class (see IEC 61850-7-2)

Data

System logical node data

LN shall inherit all mandatory data from common logical node class M Data from LLN0 may optionally be used O

Settings

DERNum ING Number of DER units connected to controller M

DERtyp ING

Type of DER unit:

Value Explanation

0 Not applicable / Unknown 1 Virtual or mixed DER 2 Reciprocating engine 3 Fuel cell

4 Photovoltaic system 5 Combined heat and power 99 Other

M

MaxWLim ASG Nominal max output power

MaxVarLim ASG Nominal max output reactive power M StrDlTms ING Nominal time delay before starting or restarting M StopDlTms ING Nominal time delay before stopping M LodRampRte ING Nominal ramp load or unload rate, power versus time M ThrshldCrnt ASG Threshold current for the Fault Detection O FCLCrnt ASG The Fault Current of FCL O FCLDelay ING Time required for the fault detection O

If a FCL is implemented in DG, these data can be updated and the microgrid management and/or protection system can retrieve the related current and timing values through communication system. Transient behavior estimation or fault condition planning of the microgrid, or the DG in particular, can be done accordingly.

6.4.1.2. Information Modeling for the FCL Logical Device

The IEC 61850 standard identifies all known functions in a system and splits them into sub- functions or so called Logical Nodes (LNs). In other words, a LN is a sub-function located in

a physical node, which exchanges data with other separate logical entities. LNs are virtual representations of real devices [161]. Conforming with the same approach, a new LN, FACL, which will be used in the representing FCLs in the virtual data communications world, has been designed. Figure 6.3 depicts the association between FCL devices in the real world and the LNs used in their virtualization. In this figure, FCL LD has a single LN, FACL, which includes the necessary control and communication parameters.

Figure 6.3. Virtualization of Fault Current Limiters with proposed LNs

Table 6.2 shows the new model designed for the modeling of FCLs in an independent manner. In addition to the parameters added in sub-section A, (`ThrshldCrnt`, `FCLCrnt`, and `FCLDelay`) the proposed class FACL, includes several other entries on ratings which are proposed in parallel with the existing FCL devices and datasheets [199]. There are four rating entries which are all defined as ASG class. Of these, `VRtg` holds the rated voltage, `IRtg` holds the rated current, PfVRtg holds the rated power-frequency withstand voltage and `LiRtg` holds rated lightning impulse withstand voltage values. Since they are not vital to the operation of FCL these rating entries are defined as optional (O) parameters.

TABLE 6.2.FACLCLASS FACL class

Data Name CDC Explanation T M/O/C LNName Shall be inherited from logical-node class (see IEC 61850-7-2)

Data

System logical node data

LN shall inherit all mandatory data from common logical node

class M

Data from LLN0 may optionally be used O

Settings

ThrshldCrnt ASG Threshold current for the Fault Detection M FCLCrnt ASG The Fault Current Value of FCL M FCLDelay ING Time required for the fault detection M

VRtg ASG Rated Voltage O

Irtg ASG Rated Current O

PfVRtg ASG Rated power-frequency withstand voltage O LiRtg ASG Rated lightning impulse withstand voltage O

Status Information

FaultCount INS Count of Fault Occurrences M FCLStatus SPS True: Fault Current Limitation is ON

False: Fault Current Limitation is OFF M FaultDetect SPS True: Fault is Detected

False: No Fault is Detected M FCLOpticSignal SPS True: Fault Current Limitation Indicator is ON

False: Fault Current Limitation Indicator is OFF O FCLAudibleSignal SPS True: Fault Current Limitation Audible Signal is ON

False: Fault Current Limitation Audible Signal is OFF O

Controls

FCLControl DPC Switch on/off, Fault current limitation, On=True, Off=False M

Measured Values

OutACV MV FCL voltage in AC volts O OutACA MV FCL current in AC amps O

Furthermore, FACL class provides more information on the status of the FCL. `FaultCount`, for example, holds the count of the fault occurrences for protection system planning. `FCLStatus` belongs to Single Point Status (SPS) data class and indicates whether FCL is switched on or off. This operation is performed with `FCLControl` variable which belongs to Controllable Double Point (DPC) class. `FaultDetect` indicates whether the existing current value is higher than ` ThrshldCrnt` and a fault is detected. `FCLOpticSignal` and `FCLAudibleSignal` are optional (O) entries which indicate whether these signals are activated.

Two different entries are proposed as measurement parameters. OutACV holds FCL voltage in AC volts while OutACA holds FCL current in AC amps. Both of these parameters are defined as Measured Value (MV) class. Not every FCL topology requires or has a measurement device equipped on them. Therefore these measurements are defined as optional (O). The connection of the proposed block, FACL, will be as shown in Figure 6.4.

Figure 6.4. FACL Class in Generic DER system (IEC 61850-7-420)