Real-time estimation of AC-grid short circuit capacity for HVDC control application

Being able to estimate the AC grid strength using short circuit capacity (SCC) from the perspective of a connected high-voltage direct current (HVDC) station allows adjustment of converter control parameters or to select the converter's operational control mode. The SCC can be calculated by estimation of the grid's impedance and its equivalent voltage. This study presents the operational and practical challenges in real-time implementation of the grid estimation algorithms especially for HVDC applications. This study shows that the recursive least-square algorithm can be very efficiently used for the real-time estimation of SCC. This technique forms a regression problem using algebraic complex equations with an objective to minimise the error between estimated and measured parameters. The algorithm has been reformulated and simplified to make it non-complex without the use of matrices, in order to facilitate further implementation on an industrial real-time controller. The performance of the real-time implementation has been evaluated using a hardware-in-the-loop platform. A sensitivity analysis has been also carried out to study the impact of different parameters and operational conditions on the performance of the estimation algorithm. Finally, the actual application of real-time SCC estimation for the HVDC systems has been demonstrated.