Edge2Edge Master-Slave Issue

HamzaElyaakoubi · September 19, 2025, 1:10pm

Hello OpenEMS community,

I’m currently working on controlling a slave Edge from a master Edge using Edge2Edge, and I’m facing some issues. The setup includes an ESS on the slave.

On the master Edge, I activated the ESS Fix Active Power controller and set it to 5000 W (charge/discharge). On the slave Edge, I also activated the ESS Fix Active Power controller and set it to 2000 W (charge/discharge). I placed the Modbus TCP/IP read-write controller at the top of the scheduler, followed by the second ESS Fix Active Power controller.

With this setup, the master successfully controls the slave and sends 5000 W to the ESS on the slave. However, the problem occurs when the ESS Fix Active Power controller on the master is turned off instead of the slave using its own local ESS Fix Active Power setting (2000 W), the master sends 0 W, and the ESS takes that value.

My goal is that when the controller on the master is turned off or not actively controlling the battery , the slave should automatically fall back to managing the ESS using its own local controller.

Could you please explain why this happens and guide me on how to solve this issue?

Looking forward to your advice.

Best regards,
Hamza

tsicking · September 23, 2025, 11:27am

Hi Hamza,

First of all you can configure the log verbosity in the modbus bridge on the master to WRITES_VERBOSE. Then you’ll see in the log files what commands are written to the slave, and you’ll find out if the error is happening on the master or the slave.

I’m not 100% sure, but I suspect you will see that 0 is written to the slave because the following is happening: After switching the controller off, no strict setpoint is given for the ESS. Therefore, the solver in the ESS Power component runs into this line:

github.com/OpenEMS/openems

io.openems.edge.ess.core/src/io/openems/edge/ess/core/power/optimizers/AddConstraintsForNotStrictlyDefinedCoefficients.java

fa081fe29


      
          				min = Double.MIN_VALUE;
          			}
          
          			if (min == max) {
          				// Already strictly defined.
          				continue;
          			}
          
          			// find the best value to set for EQUALS constraint
          			double target;
          			if (0 < max && 0 > min) {
          				// set to zero
          				target = 0;
          			} else if (Math.abs(max) < Math.abs(min)) {
          				// set to smallest distance from zero -> max
          				target = max;
          			} else {
          				// set to smallest distance from zero -> min
          				target = min;
          			}

and the active power is set to 0.

If that is the case, unfortunately I don’t see an easy solution for your problem. Maybe one can use the StartStoppable functionality of the modbus bridge on the master? It’s quite new and I haven’t worked with it yet, but maybe you can use it.

Best regards,
Thomas