Real-time Implementation of Optimal Power Flow Calculator for HVDC Grids

The aim of the paper is to present the centralized architecture for power balancing management in an HVDC, High Voltage Direct Current, grid connecting different AC areas with high penetration of variable energy resources. Such a centralized high level DC Supervisory Control (DCSC) that functions in slower time scale compared to outer level controller has been evaluated in a real time co-simulation test-bed. The test platform includes OPAL-RT’s eMEGAsim real time simulator to model the power system, the ABB’s industrial HVDC controller (MACH), real time communication simulator OPNET to model the communication network and finally the DCSC application which is implemented on a Linux machine. The DCSC consists of a network topology manager to identify the grid configuration and employs an Optimal Power Flow (OPF) calculator based on interior point optimization method to determine the set-point values for all HVDC stations in a grid. The OPF calculator takes into account the DC voltage, converter and DC line constraints. The performance of the DC supervisory control has been tested for various test cases for a 7-terminal HVDC grid. Test cases include I) Variable power generation from wind farms, II) Station disconnection and III) DC grid islanding. Besides, the proper sampling rate has been chosen and justified to show the benefit of frequent updating of set-point compared to letting the DC droop control scheme take over the mismatch in the system. The results of different test cases show that a DCSC can improve the power extraction from wind farms by updating the set-points following any change in the system. Using a 3.2 GHz machine, it approximately takes 15 ms for the DCSC to converge to a proper solution and send the updated set-points.