General comments on the report-The report gives a good overview of the power system components involved in Subsea DC Grid Collection Techniques. Although each component were well organized in every chapters and section, some of the description seem to be too technical which at this stage should be more informative and easier to read so the person who not come from the power electronics background can understand the reason behind the variety of the available system options involved in the system studied. - When refer to HVDC breaker that currently available commercially, the author may missed to acknowledged the work from ABB that already claimed on developing such a HVDC breaker that can fulfil the requirement of reliable DC grid. The report should clearly state the reason the need of the development of novel LCL DC-DC converter; such as a very high cost off ABB DC breaker, LCL has multipurpose function including of interrupting HVDC currents and etc. - Although brief analysis of the economics is made in section 6.2, some deeper analysis may require in case study comparing the proposed topology with the conventional HVDC topology which could involve estimated cost such as hardware, labor, maintenance, economic evaluation of losses and other raise issues such as space utilization, installation time, system monitoring and communication between the components that need to be explained in quite detail at this stage.

What was useful

The objective of including the HVDC breaker in the Subsea DC Grid to avoid the voltage level in the main bus from collapsed which are too fast is clearly understand that cannot be cleared by the conventional AC breaker.

The report shows the capability of the LCL-HVDC converter of dispatching/interrupting the power within the subsea DC Grid collection point.What you would like to be included/what is missing that you expected

The report well shows the performance of the LCL-HVDC converter in the simulation study. However the reliability issues need to covered as well during the study; such as what is the worst condition should happens if the fast communication between the converters fail (ex: master-slave), so what the back-up operation need to be done to assure safe operation within the DC hub. What could we expand upon for you to make it more relevant for your company.As a wave energy company that deployed our wave devices submerged below the water, issue like corrosion is among our main priority beside of delivering power to the shore. This could be easily occurred if there is a current flowing through the sea bed due to the unbalanced of the voltage level between two DC terminals. Is there any control mechanism either from AC VSC side or DC-DC side that can prevent this to happen?What parts would you like to see as a technical seminar to help you or your company

As the power coming from the wave device is varying we still need to have a further discussion to see whether the proposed DC hub converter are capable to handle/dispatching such this varying power where the control on the converter need to be efficient so that the power sending to the shore is optimized.