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The Grid Master Power Controller (GMPC) controls the generation at the Cahora Bassa hydro power station in Mozambique and its dispatch through parallel ac and dc interconnections. The bulk dc power flows directly to South Africa, while ac power is delivered to Zimbabwe, which is also interconnected with the South African ac grid. This paper describes the GMPC functions in its various control modes that are required for the different system configurations. It features adaptive gain and offset compensation for precision open-loop control of the HVDC and the turbines; robust control strategies for non-responsive generation or transmission; fast GPS-based angle measurement for damping control; robust automatic control-mode-selection independent of remote signaling; controls for proposed braking resistors; and smooth and safe control transfers between the GMPC and its emergency standby controller (EC). The success of the GMPC is evident from the fact that the angle-control mode, in which the high power HVDC system operates parallel with the weak ac interconnection, has become the unreserved and preferred choice ever since its commissioning in October 1999.