POWER DEMAND MANAGEMENT

A method is disclosed of determining the power demand on a power subsystem (2) of a system (1) by optimising a respective demand-dependent operating characteristic based on one or more operating conditions affecting the power subsystem, the method comprising: using a system-authority (3, 14) to determine system-level power demand limits on the basis of a system-level objective associated with an operating period; inputting the power demand limits to a separate power control processor (4, 16) configured for regulating the power demand on the power subsystem (2); determining each of said operating conditions; and using the power control processor (4, 16) autonomously to determine the overall power demand on the power subsystem (2) within said system-level limits, based on each of said operating conditions, thereby to optimise said operating characteristic. A method of regulating the power demand during the operating period is also disclosed. The method finds particular application in vehicles, turbomachinery and plant equipment, notably multi-engine aircraft and marine vehicles.