Digital Voltage Regulator


AVR D550 The D550 digital automatic voltage regulator (AVR) provides excitation current up to 8 A with excellent reliability and precision for SHUNT, permanent magnet (PMG) or AREP (auxiliary winding) excitation types.

D550 includes advanced protections such as over-excitation limitation and voltage sensing loss, and also features voltage droop for genset parallel operation. The D550 is also equipped with a Load Acceptance Module (LAM) to handle load impact events.

The D550 AVR is also optimized for grid paralleling operation, and complies with the latest grid code regulations, including the latest German grid code regulations VDE 4110 and VDE 4105. In this context, the D550 also includes active & reactive reverse power alarms.

Key specifications

Technology Digital
Excitation mode SHUNT, AREP, PMG
Rated excitation current 8 A at 55°C / 7 A at 70°C
Regulation accuracy (+/- %) 0.25 %
Frequency range 10 – 400 Hz
Voltage setting range (+/- %) 30 %
kU/F limitation 0.5 < k< 5
Loss of sensing voltage
Over-excitation limitation
Short circuit current limitation
Voltage droop
Parallel operation between alternators
Load Acceptance Module (LAM)

Compatible products

Configuration & setup

D550 can be configured using the Leroy-Somer EasyReg Advanced software.

Firmware update release notes

D550 Firmware version 1.2.7
D550 Note for Grid Code Application



  • Black Start module

    The Black Start module for D550 provides a 24VDC voltage, generated using the power supply (AREP, PMG) for digital AVRs of the D510C or D550 type.
    Black start can also accept an external voltage 8-35VDC coming from a customer power supply.

  • EasyLog / EasyLog PS

    Your alternator is equipped with a digital AVR type D510C or D550, then our EASYLOG and EASYLOG PS modules are made for you!
    They allow to record in a user friendly way the data and events of your installation.


    • Easylog module
    • SD card for data storage
    • Battery



    • Easy and fast connection on the CANBus port of your regulator
    • Tool for on-site failure root causes analysis:
      -  Selection of parameters to record via a dedicated page on  the user friendly software "Easyreg advanced"
      - Recording of data either continuously or using trigger
      - Monitoring of grid events such as "Low voltage ride through" or "High voltage ride through"
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