These are several issues that I need to raise while reading this report.On Page 9The stringent requirements on DC grid security will require the fault currents to be interrupted in a few milliseconds, typically 2-5ms, at the rising slope before it reaches steady-state. DC CBs (Circuit Breakers) with such high performances (magnitude and speed) may take 30% of VSC converter cost, and up to date such DC CBs are not commercially available [4].Such a high cost HVDC breakers (interrupt the HVDC fault in less than 5ms) is commercially available which developed by ABB using hybrid HVDC breaker topology, although the author already refer it in his reference paper no 36.

Page 9 under the topic of VSC HVDC vs LCC HVDCAlthough the brief discussion on the advantage of VSC HVDC over LCC HVDC is mentioned, however the main advantages and disadvantages of VSC HVDC are not well said. As example, among the main advantage of the VSC HVDC; it is not required an auxiliary regulating device such as STATCOM to perform reactive control and voltage commutation that normally required by the LCC HVDC. The issue of high losses and reliability in VSC HVDC are its main drawback and has yet to be proved while the technology in the LCC HVDC is already operated over the years with high reliability. Page 21

I didnt see any DC CBs (symbol) in Figure 16.

Page 22 It is not really clear when referring Figure 18 with Figure 17, where latter figure only shown 4 port 5 buses DC/DC hub without any possibility for further extension port, while in Figure 18 shows the DC/DC hub at least has 10 DC port. Is it each port represent conventional high and low DC voltage terminal?