Design of Robust MMC Controls Considering HVDC Grid Protection: Small Signal-Based Tuning

In High Voltage Direct Current (HVDC) grids, system parameter and/or topology changes following HVDC grid protection actions affect system dynamics and in combination with the existence of line inductors in series with HVDC circuit breakers (DCCB), pose a challenge to designing converter controls that satisfy desired performance and stability requirements. To date, several methods have been proposed for evaluating the influence of the line inductors on system stability; however, tuning of the MMC controls considering system parameter and/or topology changes following HVDC grid protection actions haven't been studied in detail. This paper presents a systematic tuning procedure for a robust operation of MMCs in any HVDC grid configuration. The proposed method analyzes the impact of variations in HVDC grid system parameters and control bandwidths (BWs) using small-signal based stability analysis and Singular Value Decomposition (SVD)-based performance analysis methods. In addition, it considers the impact of line outages associated with HVDC grid protection actions in order to select optimal control gains that fulfill performance and stability requirements of the HVDC grid for given HVDC Circuit Breakers (DCCBs) line inductor values. To illustrate the proposed methodology, a detailed step-by-step stability analysis in a 4-terminal HVDC grid test system is presented.