This abstract presents the development of an electrode-based electric boiler (Eboiler) user defined model for dynamic simulations in both electromagnetic transient (EMT) and electromechanical (RMS) domains. The models were specifically developed to support grid compliance studies of a large-scale multi-technology power plant to be connected to the Danish power system. In this power plant, several Eboiler units will be connected, ranging from 30 to 50MW. As such, robust and accurate unit models are essential for detailed grid compliance studies that ensure the TSOs of the secure and stable operation of their system under normal and disturbed conditions with this type of plant connected to their system.

The Eboiler converts electrical power into heat through a controlled process occurring within an inner vessel, where electrodes are submerged in water, acting as a pure resistive load. The system consists of two vessels (inner and outer) and a piping system feeding water into a heat exchanger. Active power consumption is controlled by changing the water level inside the inner vessel: more water increases the electrode area which in turn increases resistance and therefore the load, while less water reduces both.

The modelling approach was divided into three systems: control, protection and physical systems. In the control system, the load setpoint management system was modelled via a ramp rate limiter and a PI controller. For the protection system, all protection mechanisms present in the real product were modelled, including Faul-Ride-Through mechanism, undervoltage, earth faults, overcurrent, underfrequency, and overpower protections. The physical system, which represents the Eboiler behaviour, was modelled by a transfer function inferred using System Identification techniques applied to the manufacturer’s real product operation time-series data, ensuring an accurate dynamic representation.

All three systems were connected and modelled as a single MATLAB/Simulink model, which was used to generate the source code to build a common dynamic-link library (DLL). This DLL was then linked via specific wrapper DLLs for PSCAD (EMTDC simulations) and DigSilent PowerFactory (RMS simulations) models. Such modelling framework ensures consistent performance and behaviour across both EMT and RMS simulation models.

After the model development, a validation test phase was conducted that included testing the model’s outputs against the manufacturer’s real product operation time-series data and a comprehensive grid compliance set of tests utilizing the open-source Model Test Bench (MTB) tool from the Danish TSO, which ensured the models’ performance was correct, robust and grid code compliant during faults and other specific events. In addition, the results from EMT and RMS simulation models were benchmarked.