Slow response from ESS system to inverter limits with large loads.

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sean asked Jan 19, '19

Slow response from ESS system to inverter limits with large loads.

I've recently self installed (due to location) a grid parallel ESS with Multi II - and it's working as expected while grid demand is fairly stable.

Let's say the Multi is happy supplying 500w (inverter limited) - total demand is 800w, so demand from grid is 300w

All is fine, until a reasonable additional load is added to grid demand - let's say 750w - which seeing as the Multi is already running at its limited output I would expect that to be grid supplied.

By observation, the Multi is attempting to meet that demand, ramping up its output way beyond that which it is limited to - and slowly (within perhaps 15 seconds) ramping its output back down in line with its limited output setting.

Grid demand sensing is via the external CT - I have a smart meter en route.

Is the slow response to additional grid demand, combined with ramping up the inverter output way passed its limited setting an expected behaviour ?

Or have I missed a setting ?

TIA

ESS

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Guy Stewart (Victron Community Manager) answered · Jan 19, 2019 at 12:05 PM

It sounds like it is operating as intended.

The distribution of power supply in an ESS system is quite fluid and often fluctuating around trying to find the optimal situation. However there are also often 4 or 5 different dynamic variables all moving at once to balance.

Solar production is increasing or decreasing,

Directly connected Load is increasing or decreasing
Grid voltages are rising or falling
Additional measured loads through an energy meter are rising or falling.
Batteries are rising or falling.

And maybe more.

There are priorities within the system, such as to ALWAYS try to run the load first and foremost. Then use the available solar power, then stay within the specified soft 'limits', and so on.

The loads come first and the inverter is the quickest to respond, with the instructions from the CCGX catching up shortly after.

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Answer 1 · 2019-01-19T12:24:01Z

sean answered · Jan 19, 2019 at 12:24 PM

Thank you for your ultra fast response.

I had convinced myself that this was expected behaviour, thank you for the confirmation.

As this is a new installation I have temporarily used DC breakers on the battery feed rated to suit the inverters limited output, they'll be replaced - currently they are acting faster than the CCGXs ability to ramp down.

A little more about the install.

Batrium BMS

24kWh of Nissan cells (another 114kWh to be added)

AC coupled 8kW Fronius Primo + Smart Meter

DC 2kW MPPT

DC 2kW Wind

AC coupled 2.5kW Proven Wind

Given the above, am I correct to assume that DVCC is definitely required (I'm yet to fully comprehend it's full functionality)

TIA

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