Victron PV Assistant: Frequency Droop Setup

Key Takeaways

• Off-grid AC-coupling foundation: Use this Assistant in Off-grid systems that have AC-Coupled solar power: a grid-tie PV inverter connected to the AC out of an inverter inverter/charger.
• Broad VE.Bus hardware support: Compatible with Multis, Quattros as well as Inverters that have a VE.Bus connection.
• ESS assistant isolation rule: Usually all mains-connected systems do need the ESS Assistant, and in that case do not also install the PV Inverter Assistant as well.
• Frequency shift regulation: When the system is in inverter mode, this Assistant controls the output power of the grid-tie inverter by changing the AC output frequency of the system. A mechanism commonly refered to as Frequency Shifting.
• Grid-connected standby state: This Assistant will be idle when the Multi or Quattro is connected to mains.
• Dynamic voltage/current protection: The Assistant will use the AC-output frequency to keep both the charge current and the charge voltage within limits.
• Proactive charge current throttling: To prevent DC and AC voltage overshoots because of varying solar irradiance and/or load fluctuations, it will limit the charge current already before battery voltage has rised up to the absorption voltage.
• Stepwise current derating curve: It will derate the maximum charge current from 100% at 13.5 / 27 / 54V to 10% at 14.4 / 28.8 / 57.6V.
• Battery overvoltage trip response: Its locked to the upper limit because of a battery over voltage.
• Lithium lockout reset condition: For lithium batteries this threshold is defined as the float voltage minus 0.8V.
• AC input utility recovery: the system is connected to mains or generator power. As soon as it sees a voltage on AC-in, it will sync the AC frequency to 50Hz and then connect.
• Default disconnect frequency ceiling: the mentioned 53 Hz is the PV Inverter disconnect frequency as configured in the Assistant, default 53 Hz.

Frequency Shifting Architecture & Operating Roles

The PV Inverter Support Assistant allows Victron MultiPlus and Quattro inverter/chargers to safely govern AC-coupled grid-tie PV inverters in islanded off-grid microgrids by modulating output frequency.

The Victron PV Inverter Support Assistant operates a VE.Bus frequency shifting droop curve (50.2 Hz to 53.0 Hz) and charge regulation from 54V (100%) to 57.6V (10%) with lockout reset at Float - 0.8V:

• Frequency Control: Modulates AC-Out Hz, Idle on Mains Supply, 53 Hz Disconnect, Factor 1.0 Compl.
• Proactive Derating: Pre-Absorption, 100% @ 54.0V, 10% @ 57.6V, Voltage Overshoot.
• Lockout Reset: 53 Hz Lockout, Float - 0.8V, AC-In Sync 50, Auto Recovery.

Installation Rules & Programming Guidelines

1. Assistant Application: Verify that you Use this Assistant in Off-grid systems that have AC-Coupled solar power: a grid-tie PV inverter connected to the AC out of an inverter inverter/charger. on hardware that is Compatible with Multis, Quattros as well as Inverters that have a VE.Bus connection.
2. Assistant Exclusivity: Adhere strictly to the rule where Usually all mains-connected systems do need the ESS Assistant, and in that case do not also install the PV Inverter Assistant as well.
3. Mains Operating Behavior: Note that This Assistant will be idle when the Multi or Quattro is connected to mains.

Frequency-Watt Droop Curves & Charge Current Derating

During islanded operation:

• Active Power Curtailment: When the system is in inverter mode, this Assistant controls the output power of the grid-tie inverter by changing the AC output frequency of the system. A mechanism commonly refered to as Frequency Shifting. ensuring The Assistant will use the AC-output frequency to keep both the charge current and the charge voltage within limits.
• Proactive Surge Suppression: To prevent DC and AC voltage overshoots because of varying solar irradiance and/or load fluctuations, it will limit the charge current already before battery voltage has rised up to the absorption voltage.
• Defined Derating Slope: Specifically, It will derate the maximum charge current from 100% at 13.5 / 27 / 54V to 10% at 14.4 / 28.8 / 57.6V.

High-Frequency Lockout & Automatic System Reset

• 53 Hz Lockout: If solar power exceeds load and absorption limits, Its locked to the upper limit because of a battery over voltage. where the mentioned 53 Hz is the PV Inverter disconnect frequency as configured in the Assistant, default 53 Hz.
• Lithium Recovery Voltage: The system automatically resets when For lithium batteries this threshold is defined as the float voltage minus 0.8V.
• AC Mains Reconnection: When grid power returns, the system is connected to mains or generator power. As soon as it sees a voltage on AC-in, it will sync the AC frequency to 50Hz and then connect.

Technical Specifications & Parameter Summary