If VSC-HVDC links and networks are to be best used, i.e. the most cost-effective investment solution is to be correctly specified, the complete operational capabilities of the AC/DC converter stations need to be understood. Good progress is being made in understanding the implications of different forms of converter hardware. Very good progress is being made on understanding the station control & power control. However the intermediate stages of station operation and control have received scant attention and are less well understood. Given that these are vital to defining the operational limits and capabilities of the station, this is a glaring omission, and a serious weakness and risk in present VSC-HVDC power system models. As a result overly (or even insufficiently) conservative investment choices in future VSC-HVDC investment choices may result without further research into system operational capabilities. Likewise AC plant may not be correctly specified for optimum usage with such systems. The research will also derisk on-going investment in new VSC-HVDC links and allow better informed specification and operational requirements to be formulated.

Key elements include how the central station control communicates with sub-modules, selects which modules to use, sets ramp rates, manages auxiliary functions and avoids DC injection into the AC system. This project will address this knowledge gap, the constraints these stages impose on the station control, operation and protection, and will investigate necessary algorithms for improving system performance to make station control more robust and reliable as seen from the AC network, and consequently appropriate selection and specification of equipment (AC and DC) to be more readily made. Initial simulation will be validated on a highly reduced-scale prototype converter.

Key stages include the following:

1. Formulation of sub-module performance limits and telecommunications

2. Adding presently unmodelled internal converter systems to station hardware model

3. Converter perfomance benchmarking

4. Comparison of simulation models and hardware for a variety of contingencies.

Benefits

The project team anticipate one of the two potential outcomes:

• An updated model for both Detailed Equivalent Model (DEM) and Average Value Model (AVM) models (see Cigre brochure 604, ‘Guide for the Development of Models for HVDC Converters in a HVDC Grid B4-57 working group).

OR

• An assessment that present DEM and AVM models are sufficient and telecommunications/ measurement / internal loops have negligible impact on the model.