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assistants:hub1_and_hub2_notes

Hub-1 and Hub-2 Assistant notes

1. Special states

A system running the Hub-1 or Hub-2 Assistant, has the following special states:

1.1 Grid assist

Normal mode was inverting, but now the system is temporarily connected to the grid to power high loads, which in total exceed the maximum inverter power. As soon as those loads are below threshold for 60 seconds, the system will switch back to invert mode again.

1.2 Prevent feedback (hub-2 only)

Normal mode is connected during the grid (at least during the day). When it sees power flowing back into the grid, it will disconnect from the grid and work in island mode. AC output frequency will be increased, to reduce the PV output power from the PV inverter. As soon as there is no excess of PV available any more, (AC output frequency has dropped back to 50 Hz), the system will connect to the grid again.

Note that preventing this switch-over is not instantaneous, it takes 20 seconds. And when feedback occurs while connected to the grid because of a low battery or overload, the prevent-feedback mechanism will be disabled. (The overload will be active for the time the user specifies in the 'Load connect condition' step. The default value is 60 seconds.)

To summarize: 'prevent feedback' is not the solution when connected behind a meter that immediately disconnects upon feedback.

1.3 Maintenance charge

A full charge cycle will be completed every 28 days (programmable). This full charge cycle includes the absorption charge, which is normally not included. And the maintenance charge cycle also includes an equalization charge if appropriate for the chosen battery type.

Power from the grid will be used, if at the end of the day the cycle has not yet been completed. Put differently: power from the grid will be used when there has not been enough PV power available to complete the maintenance charge.

1.4 PV Reduction / Frequency shift (hub-2 only)

In inverter mode with increased AC output frequency to reduce PV power.

1.5 Sustain

The purpose of the Sustain Mode is to prevent leaving batteries in a deeply discharged state during several days. The Sustain Mode is entered when during 30 seconds the following two conditions are met without interruption:

  1. the battery voltage is below the sustain level: 12.5V for Lithium batteries and 12V for other batteries
  2. the current drawn from the battery is smaller than 1/20th of the battery capacity.
    Important: Because of this, one should NOT disable the internal battery monitor (even if the battery monitor is unreliable as it is for instance in a HUB1 system). Disabling the battery monitor will set the battery capcity to zero and this will result in a wrong current limit.

During Sustain, the system will be connected to the grid and the internal charger is enabled. The system will stay connected to mains as long as the battery voltage stays low.

Note that, for non-lithium systems, the sustain level is 12 V for the first 24 hours, and after that it is raised to 12.5 Volts DC.

DC voltages specified are for a 12V system. These voltages should be multiplied by 2 or 4 for a 24V or 48V system.

2. Use and working of State of Charge (SOC) in a Hub2 system

In a HUB2 assistant the SOC is used. From the SOC a flag is derived named SOCLow. This flag can be either true or false. The assistant will allow to enter a SOCLowLevel and a SOCHighLevel. This flag is determined as follows:

if SOCLow=true then SOCLow:=SOC<SOCHighLevel
else SOCLow:=SOC<SOCLowLevel

Now both SOC and SOCLow are used in the HUB2 assistant to determine actions. However the HUB2v2 and HUBv3 behave differently

HUB2v2

When the SOCLow flag is true, next things are performed:

  • Power assist is disabled
  • LowBat LED in the L1 master is lit (only when connected to grid)
  • the system connects to the grid if possible

Under certain conditions the SOC (and with that the SOCLow flag) is changed:

  1. SOC is changed to 100% when a connected Lynx-Ion BMS signals a High cell voltage

  2. SOC is changed to SOCLowLevel when:
    1. a connected BMS signals 'low cell'
    2. In the L1 master the UBatIn voltage drops below the PreAlarm level during 5 seconds

  3. SOC is changed to 'Bulk finished' value from VEConfig when the charge state changes to Absorption.
    (This is normal behaviour for a charger and is normally done in the firmware. The HUB2v2 assistant does this because in the 2xx firmware the charge engine is stopped when the Multi is inverting. However in a HUB2 system we want to charge with PV power when the Multi is invertering. Therefore the HUB2V2 assistant contains a 'charge engine')

HUB2v3

When the SOCLow flag is true, next things are performed:

  • Power assist is disabled
  • LowBat LED is lit
  • the system connects to the grid if possible
  • when load shedding is active it stays active as long as SOCLow is true

THE SOC value is used for:

  • stopping the charge process during 'Low night rate' use when SOC reaches SOCHighLevel
  • When, in a Multi phase system, a Low Bat 'overload' occurred, this condition will stay active until the SOC reaches SOCLowLevel. This is needed to prevent the system from switching to invert if also the option 'do not feed back' is enabled.

Under certain conditions the SOC (and with that the SOCLow flag) is changed:

  1. Changed to 'low level' -10%
    1. when a connected BMS signals a 'Low cell'
    2. when (on any connected Multi) UBat< ('DC input low shut-down'+1V) for 5 seconds (note: 1V is for 12V systems)
      The user can freely choose 'DC input low shut-down'. The assistant will only change this value while stepping through the assistant and if needed to guarantee that “DC input low restart” is below 11 V for Lead-acid or 12V for Li-Ion batteries. (These are the default levels the assistant uses for 'DC input low Pre-Alarm')
    3. while sustain active
      (sustain is actived when IBat is llow and Ubat< 12 or 12.5 for at least 30 seconds)

  2. Changed to 'high level' -10%
    1. when loadshedding enabled and triggered due to overload
      (overload is then also IMains>IMainsLimit)

  3. Changed to 100%
    1. when a Lynx BMS signals 'High voltage/cell'

4. FAQ

Why does my Hub-2 system start charging the first day after setting it up?

This is the maintenance charge. The moment you switch on a HUB2v3 system the daycounter will be on day [0], the day after [day 1] is the first day the first maintaince will be done. If there is no surplus energy for 24h the system will automaticly go to day [1], so start the charge period from grid. If you later on you reconnect VEConfigure and make changed to the Assistant, the same thing will happen, The day counter will be set to [0] again: a maintenance charge, using power from the grid (if necessary) to fully charge the batteries.

How long does it take for the Hub-2 clock to sync with the grid?

This depends on the surplus of PV power. After switching in the hub system assumes its day. When surplus power is seen flowing into the grid this is confirmed and when the SOC reset is met the system will go into day/night mode (when selected in the policy tab) after the pv surplus has stopped. This will not always be at the correct point of the day in the first few days but will get corrected automaticly

How does Hub-2 know when it is day or night?

It looks at the direction of the current at the AC output of the Multi or Quattro. If there is excess PV. The day/night will be adjusted constantly and has a maximal drift of 7 min a day (season changes).

Note that because it looks a the power being fed back to the grid, day/night syncing in a hub-2 system only works well if there really is an excess amount of PV available. If not, for example on most days, or during most part of the day … Also, when having a grid connected wind turbine or such the day/night switch cannot be used!

Can I add a small solar charger to a hub-2 installation?

In order to have the SOC calculation work as accurate as possible this should be avoided.

Input current limiting options

  • It is possible to set (and change) the input current limit with a remote control panel, For example the Digital Multi Control or the Color Control GX.
  • This limit will be used when charging the battery during the periodic battery maintenance cycle. During normal operation it will normally not be used. As long as there is enough sun, the Multi will use a lower current than set with the remote control panel.

The level that is used is depending on the model which is used. (the threshold for powerassist is depending on the size of the inverter and the AC input current range of an inverter) (example for threshold ; 3k/50Amp relay –> 6Amp minimal)

Why does my shown SOC jump (VE.Bus SOC, not BMV SOC)

The SOC is auto-corrected. For example in a low voltage warning, if the SOC is too high, it will be auto-corrected downwards. Mostly when having a charge current higher then 10-15% the rate of charging, the calculated SOC does not match reality. Then the Absorbtion voltage is reached too soon, setting the SOC directly on a certain level (set in the battery monitor page in ve configure) Same at discharging, If the DC voltage become lower then expected at a certain SOC (DC low pre alarm) the SOC at that moment is corrected to be the minimal value - 10%

Why does AES not work when using Hub-1 policy 3?

Hub1 policy3 is 'Disconnect from the mains when possible'. This suggest that the ACin is disconnected and that the AES function should behave the similar to when the ACin is really disconnected. This is not so.

With this policy the unit will be in Inverter mode when possible but will stay synchronized to the mains. So it will be able to switch quickly when the Load connect condition becomes active. Therefor AES does not work.

DISQUS

assistants/hub1_and_hub2_notes.txt · Last modified: 2019-01-22 10:16 (external edit)