Micro Grid -
This post is going to be about how I deployed a micro grid base on Victron inverters. This will include what I did as well as all the problems I discovered.
Let's talk about how the system is laid out.
The house has its own full Victron setup.
- Victron Multiplus-II 48/5000/70-50
- Victron SmartSolar Charger MPPT 150/60
- Victron SmartSolar Charger MPPT 150/35
- Victron Cerbo GX
- Victron CT for Multiplus
- Freedomwon 10/8 Lite Battery
This system is the Master and is the grid forming inverter, it also handles connecting and disconnecting from grid in the case of an outage or if we want to isolate for any reason.
The Garage has 2 systems on it.
The first is a victron system that consists of:
The Garage has 2 systems on it.
The first is a victron system that consists of:
- Victron Multiplus-II 48/5000/70-50
- Victron SmartSolar MPPT RS 450/100
- Victron Cerbo GX
- Freedomwon 10/8 Lite Battery
The second is an Enphase system:
- Enphase Envoy-S Metered
- 5x Enphase IQ7 Micro Inverters
The control system for this microgrid is split across the two GX's which are both running the large firmware which includes NodeRed. All the control of the Microgrid is done in NodeRed.
The point of this system to equally split the load between the 2 Victron systems. Keep the SOC and cycles of the batteries as close as possible but also allow for independent operation.
The Victron Multiplus-II 48/5000/70-50 is a 5000VA, 4000W inverter. It can provide 9000W of peak power for a few seconds to minutes depending on temperature. Being able to use this peak power is really important as it takes time to ramp up and down the slave systems. This graph shows what happens when a 2kw load is turn on and off. The master inverter immediately ramps up and provides the full 2kw for the load, soon after the slave inverter ramps up and provides 50% of the load which leaves the Master only carrying 1kw. This does allow us to run loads that are larger than 4kw as long as the Master can run it long enough for the slaves to ramp up. You will also see when a load is turned off the master as to absorb that power while the slaves ramp down. This is valuable information when sizing the master as it has to be able to handle any change in load for a few seconds.
The point of this system to equally split the load between the 2 Victron systems. Keep the SOC and cycles of the batteries as close as possible but also allow for independent operation.
The Victron Multiplus-II 48/5000/70-50 is a 5000VA, 4000W inverter. It can provide 9000W of peak power for a few seconds to minutes depending on temperature. Being able to use this peak power is really important as it takes time to ramp up and down the slave systems. This graph shows what happens when a 2kw load is turn on and off. The master inverter immediately ramps up and provides the full 2kw for the load, soon after the slave inverter ramps up and provides 50% of the load which leaves the Master only carrying 1kw. This does allow us to run loads that are larger than 4kw as long as the Master can run it long enough for the slaves to ramp up. You will also see when a load is turned off the master as to absorb that power while the slaves ramp down. This is valuable information when sizing the master as it has to be able to handle any change in load for a few seconds.
Red Master, Green Slave
The control system is 3 layers of control.
Layer 1 is PID for load leveling on inverters.
Layer 2 sets layer 1's set point. Layer 2 is trying to level battery charge and discharge rates, also PID
Layer 1 is PID for load leveling on inverters.
Layer 2 sets layer 1's set point. Layer 2 is trying to level battery charge and discharge rates, also PID
Layer 3 sets layer 2's set point based on SOC imbalance, this keeps the battery SOC at the same value. This may mean shipping power from 1 system to another, this control gets complicated as you want to do this in the most efficient way. Which leads into why I have some AC coupled PV as that can be access by both systems.
Victron Specific Problems:
Loss of Mains (LOMs) can not be used on Slave inverters as then they frequency shift they fight the Master and the Slave will stop producing power for a few seconds but does not disconnect. This maybe less of a problem if the Master is 2 or 3 times the size of any one slave. This still works on the Master, which is great as it is the only unit connected to grid.
UPS option on Slaves needs to be turned off, else when grid fails or grid disconnect event happens the Slaves will disconnect from the Microgrid for 30secs or more. If you disable the UPS function they are more forgiving and will stay connected during the period. Both connecting and disconnecting from grid. This doesn't mean the loads will see an interruption, It my testing it worked fine even if being disconnected from Microgrid.
Other Grid code, may need to be set on the inverter to allow frequency shifting of the master to work correctly. I have slave GX monitoring input frequency so that if the Master shifts the frequency the slave will reduce it's export to the Microgrid and eventually disconnect. This is to prevent the master inverter and battery from getting overcharged or overloaded, This is only used if comms failure or to control Enphase system. You also need to disable Overvoltage feed-in via Modbus on the slaves if the grid is lost. This allows more control over export when batteries are full or close to full.
Other than that everything has been working without any problems for almost a year now.
If you have an questions or comments please leave them below so I can update or maybe write some more as I am not sure what else people would like to know.
Thanks,
Shane
Loss of Mains (LOMs) can not be used on Slave inverters as then they frequency shift they fight the Master and the Slave will stop producing power for a few seconds but does not disconnect. This maybe less of a problem if the Master is 2 or 3 times the size of any one slave. This still works on the Master, which is great as it is the only unit connected to grid.
UPS option on Slaves needs to be turned off, else when grid fails or grid disconnect event happens the Slaves will disconnect from the Microgrid for 30secs or more. If you disable the UPS function they are more forgiving and will stay connected during the period. Both connecting and disconnecting from grid. This doesn't mean the loads will see an interruption, It my testing it worked fine even if being disconnected from Microgrid.
Other Grid code, may need to be set on the inverter to allow frequency shifting of the master to work correctly. I have slave GX monitoring input frequency so that if the Master shifts the frequency the slave will reduce it's export to the Microgrid and eventually disconnect. This is to prevent the master inverter and battery from getting overcharged or overloaded, This is only used if comms failure or to control Enphase system. You also need to disable Overvoltage feed-in via Modbus on the slaves if the grid is lost. This allows more control over export when batteries are full or close to full.
Other than that everything has been working without any problems for almost a year now.
If you have an questions or comments please leave them below so I can update or maybe write some more as I am not sure what else people would like to know.
Thanks,
Shane
Hi Shane,
ReplyDeleteThanks for the nice write up.
I saw a video from Andy from the Off Grid Garage where he connected a phoenix inverter into AC IN on the Multiplus and used the Multiplus to turn the Phoenix on and off, based on the load requirements, effectively having the multiplus power assist the phoenix during heavy loads. (https://youtu.be/SsTkgoN6ENM)
My question is, would this work in grid parallel installation? Would I be correct in assuming the secondary inverter has to be grid tie(able).
What I have: Solis Mini 3kW inverter & 8x365W Longi panels totaling 2.92kWp What I want to do: Build ESS using EasySolar-II and LiFePO4 batteries, and add more panels in my garden(1.5kWp).
The Easysolar is 3KVA so it can only supply 2.4kW continuously, so I would like to add a cheap inverter (up to 2kW) on the Input to help with heavy loads.
Do you know if that is possible?
This is the inverter i'm considering for the slave: https://www.amazon.co.uk/gp/product/B0978WWXW4/ref=ox_sc_saved_image_1?smid=A2J7W1M0JR7O3Z&psc=1
Hi, I've been keen on doing something like this and saw your post on victron. The UPS and LOM issues are interesting to see as I want to set up an island system where a third multiplus is acting as the grid.
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