COUPLING
Name of the coupling group this device belongs to.
Devices sharing the same coupling name are constrained to have proportionally related power flows, via a hard equality constraint.
Use this to model a device that converts one commodity into another, by describing each of its commodity ports as a separate device.
For example, a combined heat and power (CHP) unit is described as a gas input device, a heat output device and an electricity output device, all sharing one coupling name.
Use together with coupling-coefficient to set the flow ratios.