Electrical power systems having variable-voltage DC busses and methods of controlling voltage settings of such busses. One electrical power system comprises: a variable-voltage DC bus; a number N≥2 of electrical machines, each electrical machine connected to the variable-voltage DC bus via one of a corresponding number N of converters, each electrical machine and corresponding converter having an index n=(1, . . . , N); and a controller configured to select a voltage setting Vdc_bus for the variable-voltage DC bus and to provide control signals to the converters to control the voltage setting of the variable-voltage DC bus according to the selected voltage setting Vdc_bus. The controller configured to select a voltage setting Vdc_bus greater than or equal to a minimum voltage requirement Vdc_min for the bus. The controller is configured to determine the minimum voltage requirement Vdc_min using present operating speeds of each of the N electrical machines.