WP 5: SYSTEMS MODELS DEVELOPMENT

All the ECS thermal systems (VCS, LCU and ACU) have been developed and tested at both steady and transient conditions as well as for the electrical drive system. The coupling between thermal units and electrical drive system has also been addressed.

Several numerical challenges have been successfully addressed when developing the thermal units tackled within the MALET project. A global approach to manage the refrigerant amount flowing inside the VCS circuit has been implemented. The VCS flow regulation carried out by the thermal expansion valve in the VCS, which is based on a PID controller, has shown to be appropriate. Specific numerical components have been developed to assist the user when initializing both variable values and initial conditions for each particular thermal system. A methodology based on dynamic relaxation has been achieved to calculate steady-state cases with optimized computational time. Thermal systems have been tested at different transient conditions including sharp transients such as compressor/pumps start-ups and shut-downs. The numerical stability of systems has been assessed by  subjecting them to different external conditions. The reservoir models used in closed liquid circuits such as the CLLCU and the HLLCU have shown to appropriately account for the fluid expansion. The resolution of parallel circuitry in various systems has been successfully tested. Reversed flows have been tested on liquid closed loops. An approach based on a minimum mass flow rate has been implemented to simulate the VCS when the compressor is switched off. 

(VCS. Left: main scheme, right: transient simulation example)

(LCU hot unit. Left: main scheme, right: transient simulation example)

The electrical drive system includes ATRU, inverter and machine models in two reference frames. These are namely the ABC and DQ reference frames. The main difference between these two frames of reference is that AC voltages and currents which are sinusoidal, and hence time varying, in the ABC frame become constant values in the DQ frame. Computationally this decreases simulation times significantly. 

(electrical drive system scheme)

All the individual systems developed, namely, the VCS, the CLLCU, the HLLCU, the ACU and the electrical drive system have been combined and linked according to the main ECS architecture layout provided by the Topic Manager. New issues have arisen as multiple systems had to be solved together, in this sense, new initialization procedures and combined resolution strategies have been implemented.  This process has been done step-by-step: initially the VCS has been linked to the cold liquid loop, then to the hot liquid loop, then to the air conditioning unit, and finally to the electrical drive system. The linking between the VCS and the electrical drive system is based on mechanical and thermal connections. An additional component to account for the heat losses has been added to the VCS . The losses of each particular component of the electrical drive system are transferred to the VCS through independent connections.