A power distribution system adapted to operate with a variable system frequency, the power distribution system comprising: an ac busbar adapted to carry a variable-frequency ac distribution voltage; two or more ac generators (G1...G4), each ac generator (G1...G4) being connected to the ac busbar and having an associated prime mover (D1...D4) and an associated generator-specific controller, each ac generator (G1...G4) being further adapted to provide a variable frequency output voltage during normal operation of the power distribution system; and a power management controller that includes a speed control function adapted to select and maintain the rotational speed of the prime movers (D1...D4), and hence the frequency of the output voltage of the ac generators (G1...G4), with reference to the electrical load on the ac busbar, the power management controller being further adapted to select a new system frequency in response to detected changes in load demand on the ac busbar and to automatically vary the rotational speed of the prime movers (D1...D4) such that the frequency of the output voltage of the ac generators (G1...G4) matches the new system frequency; the speed control function being further adapted to select the rotational speed of the prime movers (D1...D4) using a load profile for the prime movers (D1...D4) which relates output power to frequency and is adapted to receive an averaged power feedback signal (kWf av) from the generator-specific controller of each ac generator (G1...G4), or a single ac generator if the generator ratings and characteristics are identical, and output a minimum system frequency setpoint or reference (SFSP); and wherein the power management controller further includes a load sharing control function, the power management controller being further adapted to automatically vary the load sharing between the two or more ac generators (G1...G4) with reference to the rotational speed of the prime movers (D1...D4); the load sharing control function being further adapted to use information data about the individual generator ratings through a load profile for each ac generator (G1...G4) that relates load capability to frequency, each load profile being adapted to receive an average frequency feedback signal (Ff av) from the respective generator-specific controller. an ac busbar adapted to carry a variable-frequency ac distribution voltage; two or more ac generators (G1...G4), each ac generator (G1...G4) being connected to the ac busbar and having an associated prime mover (D1...D4) and an associated generator-specific controller, each ac generator (G1...G4) being further adapted to provide a variable frequency output voltage during normal operation of the power distribution system; and a power management controller that includes a speed control function adapted to select and maintain the rotational speed of the prime movers (D1...D4), and hence the frequency of the output voltage of the ac generators (G1...G4), with reference to the electrical load on the ac busbar, the power management controller being further adapted to select a new system frequency in response to detected changes in load demand on the ac busbar and to automatically vary the rotational speed of the prime movers (D1...D4) such that the frequency of the output voltage of the ac generators (G1...G4) matches the new system frequency; the speed control function being further adapted to select the rotational speed of the prime movers (D1...D4) using a load profile for the prime movers (D1...D4) which relates output power to frequency and is adapted to receive an averaged power feedback signal (kWf av) from the generator-specific controller of each ac generator (G1...G4), or a single ac generator if the generator ratings and characteristics are identical, and output a minimum system frequency setpoint or reference (SFSP); and wherein the power management controller further includes a load sharing control function, the power management controller being further adapted to automatically vary the load sharing between the two or more ac generators (G1...G4) with reference to the rotational speed of the prime movers (D1...D4); the load sharing control function being further adapted to use information data about the individual generator ratings through a load profile for each ac generator (G1...G4) that relates load capability to frequency, each load profile being adapted to receive an average frequency feedback signal (Ff av) from the respective generator-specific controller.