Monday, August 7, 2017

IEC 61850-90-9 Models for Electrical Energy Storage Systems

IEC 61850 Part 90-9: Use of IEC 61850 for Electrical Energy Storage Systems is progressing these days. The latest draft describes the basic functions of Electric Energy Storage System (EESS) and the information model of the interface to integrate EESS in intelligent grids and establish the necessary communication with standardised data objects. The next official draft is expected to be published soon.
This draft  is  connected  with  IEC 61850-7-420,  as  well  as  IEC 61850-7-4:2010, explaining how the control system and other functions in a battery based electric energy storage unit utilizes logical nodes and information  exchange services  within the IEC 61850 framework to specify the information exchanged between functions as well as information that individual functions need and generate. The first Edition of IEC 61850-7-420 provides an information model for batteries which was derived from the proposed data objects of part 7-4. Those data objects follow the requirements of batteries that are supposed to be used in substations as an auxiliary power system and as backup power supplies. For this purpose it was sufficient to only model the discharge function. Therefore it is necessary to prepare new logical nodes to be applicable for grid connected electrical energy storage systems.
This draft provides necessary information within 61850 based object model in order to model functions of a battery based electrical energy storage system as a DER unit. For intelligently operated and/or automated grids, storing energy for optimising the grid operation is a core function. Therefore shorter periods of storing energy with charging and discharging capability is also an indispensable function. Charging and discharging operations need to be modelled thoroughly and are in the focus of this technical report.

The draft lists several use-cases found in the real world:

UC1 Retrieve current status and capabilities of EESS
UC2 Set charging power to EESS
UC3 Set discharging power to EESS
UC4 Set Operating mode/ schedule  to EESS
UC5 EESS Alarm / Asset Monitoring

UC1 current capability /status information as an example:

1-2-1 EESS Generic Status Reporting
•  ES-DER on or off
•  Storage available or not available
•  Inverter/converter active power output
•  Inverter/converter reactive output
•  Storage remaining capacity (% and/or kW)
•  Storage Free capacity (% and/or kW)

1-2-2 EESS inverter /converter status
•  Current connect mode:  connected or disconnected at its ECP
•  Inverter on, off, and/or in stand-by status: inverter is switched on (operating), off
(not able to operate), or in stand-by
•  mode, e.g. capable of operating but currently not operating
•  DC current level available for operation: there is sufficient current to operate
•  Value of the output power setpoint
•  Value of the output reactive power setpoint
•  Value of the power factor setpoint as angle (optional)
•  Value of the frequency setpoint (optional)

1-2-3 EESS (battery) internal status
 •  Amp-hour capacity rating
•  Nominal voltage of battery
•  Maximum battery discharge current
•  Maximum battery charge voltage
•  High and Low battery voltage alarm level
•  Rate of output battery voltage change
•  Internal battery voltage
•  Internal battery current
•  State of charge (energy % of maximum charge level)
•  Reserve (Minimum energy charge level allowed, % of maximum charge level)
•  Available Energy (State of charge – Reserve)
•  Type of battery

1-2-4 Power measurements
•  Total Active Power (Total P): Value, High and Low Limits
•  Total Reactive Power (Total Q): Value, High and Low Limits
•  Average Power factor (Total PF): Value, High and Low Limits, and averaging time
•  Phase to ground voltages (VL1ER, …): Value, High and Low Limits

More to come ...

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