Smart Inverter Control

An autonomous function that dynamically absorbs or injects reactive power (VARs) in response to local voltage deviations.\n\n- Mechanism: Uses a configurable volt-VAR curve defined by four setpoints.\n- Action: Injects capacitive reactive power when voltage sags to boost the line; absorbs inductive reactive power when voltage swells to suppress it.\n- Standard: Mandated by IEEE 1547-2018, Category B.\n- Benefit: Eliminates the need for dedicated capacitor banks by leveraging idle inverter capacity.

An autonomous active power response that adjusts real power output proportionally to deviations from the nominal grid frequency (50 or 60 Hz).\n\n- Over-Frequency: Reduces active power output on a defined droop slope (e.g., 5% per Hz) to arrest frequency rise.\n- Under-Frequency: Increases output if the resource has available headroom.\n- Critical Role: Provides a distributed, fast-acting primary frequency response to prevent cascading outages during generation-load imbalances.\n- Deadband: Configurable deadband around nominal frequency prevents unnecessary actuation.

The mandatory capability to remain connected and inject reactive current during transient low or high-voltage disturbances, preventing a sudden loss of generation that would further destabilize the grid.\n\n- Low-Voltage Ride-Through (LVRT): Must tolerate zero voltage for up to 1 second (per IEEE 1547-2018).\n- High-Voltage Ride-Through (HVRT): Must withstand 120% of nominal voltage for up to 1 second.\n- Priority: Reactive current injection takes precedence over active power during the fault.\n- Mandatory Trip: Inverters must cease energizing if voltage remains outside the defined envelope after the ride-through duration.

A function that limits the maximum rate of change of active power output to mitigate the grid impact of sudden solar irradiance fluctuations caused by cloud transients.\n\n- Normal Ramp: Default maximum rate of power increase (e.g., 100% per minute).\n- Soft-Start Ramp: A slower, configurable ramp applied when the inverter first starts up or recovers from a trip.\n- Mechanism: Achieved by curtailing available PV power or buffering energy in a co-located battery.\n- Grid Benefit: Prevents voltage flicker and reduces the need for fast-ramping reserve generation.

A critical safety function that forces the inverter to cease energizing the local circuit within 2 seconds of a utility grid outage.\n\n- Passive Detection: Monitors for sudden changes in voltage, frequency, or phase jump that indicate grid loss.\n- Active Detection: Injects a small, momentary disturbance signal and monitors the grid impedance response.\n- Sandia Frequency Shift: A common active method that creates a positive feedback loop in frequency to force a detectable drift.\n- Requirement: Mandated by UL 1741 and IEEE 1547 to ensure lineworker safety and prevent equipment damage.

A constant reactive power control mode where the inverter maintains a fixed power factor (e.g., 0.95 leading or lagging) regardless of active power output.\n\n- Setting: Defined as a constant displacement power factor (cos φ).\n- Use Case: Simple voltage support on weak feeders where a constant reactive power injection is beneficial.\n- Limitation: Less dynamic than Volt-VAR control; does not respond to real-time voltage fluctuations.\n- Communication: Can be updated remotely via IEEE 2030.5 or DNP3 protocols to adapt to seasonal grid conditions.

An autonomous smart inverter function that dynamically absorbs or injects reactive power in response to local voltage deviations. Key characteristics:

• Voltage rise: Inverter absorbs reactive power (inductive mode) to lower voltage
• Voltage drop: Inverter injects reactive power (capacitive mode) to raise voltage
• Operates on a configurable volt-var curve defined by the utility
• Maintains voltage profiles within ANSI C84.1 regulatory limits without centralized communication

An autonomous active power curtailment function that proportionally reduces inverter output when grid frequency rises above a defined threshold. This provides a critical primary frequency response to generation-load imbalances:

• As frequency exceeds the deadband (e.g., 60.036 Hz), output is reduced on a defined droop slope
• Helps arrest frequency excursions before they trigger under-frequency load shedding
• Essential for grids with high renewable penetration and low synchronous inertia

An advanced control strategy where the inverter establishes a stable voltage and frequency reference independently, rather than following the grid. Unlike grid-following inverters that require an external voltage source to synchronize, grid-forming inverters:

• Enable islanded microgrid operation without synchronous generators
• Provide synthetic inertia by instantaneously injecting power during frequency deviations
• Use virtual synchronous machine algorithms to emulate the damping characteristics of physical rotating mass

A critical safety mechanism that forces a DER to cease energizing the circuit within 2 seconds of a utility outage. This prevents:

• Back-feeding into a de-energized line, endangering lineworker safety
• Unintentional islanding that could damage customer equipment due to unregulated voltage and frequency
• Modern smart inverters use a combination of passive detection (monitoring voltage/frequency anomalies) and active detection (injecting small perturbations to detect grid impedance changes)