3.4 DER Capabilities and DER System Architectures
3.4.1 Overview of Advanced “Smart Inverter” Capabilities
Many of the challenges posed by DER systems may have solutions or mitigations of their impacts through the advanced “smart” inverter capabilities, more comprehensive planning and near-real-time studies, and communications with DER systems. Some of these solutions involve combining intermittent renewable DER systems with energy storage systems which can smooth out or eliminate the changes in power output.
Some of these challenges can also be offset by the capabilities provided by advanced DER technologies. These newer DER technologies generally include electronic controllers that can adjust output properties of “smart inverters” to mitigate impact on power quality and reliability in response to local voltage and frequency issues as well as modify generation and storage actions based on communicated requests.
A smart inverter is not only capable of performing traditional inverter functionalities (i.e. converting DC to AC) but also has the capability of providing advanced features that support grid reliability and stability. These capabilities include reactive power support, volt/VAR response, voltage and frequency ride-through, and the addressing of ramp rate issues, in conjunction with enhanced management controls.
Studies have identified many functions that DER systems could provide to support the grid. The following list identifies the advanced capabilities of “smart” DER systems (more details can be found in Appendix 4.2):
- Anti-Islanding: Support anti-islanding in cases of unintentional islanding
- L/HVRT: Provide ride-through of low/high voltage excursions beyond normal limits within preset voltage-time limits
- L/HFRT: Provide ride-through of low/high frequency excursions beyond normal limits within preset frequency-time limits
- Frequency-Watt: Counteract frequency excursions beyond normal limits by decreasing or increasing real power
- Dynamic Current Support: Counteract abnormal high or low voltage excursions by providing dynamic reactive current support
- Soft-Start Reconnection: Reconnect autonomously after grid power is restored
- Command DER to Connect or Disconnect or Delay Connection: Perform soft or hard connect or disconnect from grid via direct command
- Backup: Provide backup power after disconnecting from grid
- Support Creation and Operation of Islanded Microgrid: Disconnect from the Area EPS while establishing a pre-designed microgrid
- Decrease Export of Real Power at PCC: Response to command/ requests either to increase import or to decrease export of real power
- Limit Maximum Real Power: Limit maximum real power output at the ECP or PCC to a preset value
- Increase Export of Real Power at PCC: Response to command/ requests either to decrease import or to increase export of real power
- Set Real Power: Set actual real power output at the ECP or PCC either as a specific real power setpoint or as a percentage of local load
- Follow Schedule of Real Power: Follow schedule of actual or maximum real power output at specific times
- Follow Schedule for Storage: Set or schedule the storage of energy for later delivery, indicating time to start charging, charging rate and/or “charge-by” time
- Volt-Var Control: Execute volt-var control in response to settings that define reactive power output for different voltages
- Operate by Fixed Power Factor: Provide reactive power by a fixed power factor
- Use Ramp Rates: Use the different ramp-up and ramp-down rates that have been defined for normal, emergency, and reconnection
- Voltage Smoothing: Modify real power output in response to local voltage variations
- Frequency Smoothing: Smooth minor frequency deviations by rapidly modifying real power output to counteract these deviations
- Automatic Generation Control (AGC): Support frequency regulation by direct automatic generation control (AGC) commands
- Operational Reserves: Provide “spinning” or operational reserve by increasing real power from generation or storage as bid into market and upon command
- Black Start Capability: Provide black start capabilities upon command
- Emission-constrained Dispatch : Set output real power on command, based on emissions produced
- Support Situational Awareness: Provide real-time or near-real-time DER information
- DER Registration: Provide operational characteristics at initial interconnection and upon changes