A holistic method for optimal design of HVDC grid protection

Protection system design for high-voltage direct-current (HVDC) grids using DC circuit breakers (DCCBs) is not straightforward. Both hardware parameters, such as line inductors and DCCBs, as well as software parameters, such as protection threshold settings and protection margins, have to be taken into account and interact. Previous studies focused on the impact of specific parameters (e.g., line inductors) while other parameters (e.g., maximum DCCB currents) were checked manually for compliance with constraints. This paper presents a new holistic method for HVDC grid protection design. The approach is no longer exclusively based on parameter sweeps but solves HVDC grid protection as a classic optimization problem with an optimization goal and constraints. Electromagnetic transient (EMT) simulations are embedded into the optimization tool such that the system dynamic response is taken into account. Results for two example test cases and two example optimization goals are provided. For instance, the method can achieve a reduced sum of line inductors compared to an initial guess. The proposed method is useful to find a more optimally designed HVDC protection system, and practical because it makes sure that the constraints (e.g., maximum DCCB current, no converter blocking and large protection margins) are fulfilled.