the energy storage unit 11 outputs a high voltage typically 300 vdc or more the output of the energy storage unit 11 is connected to the high voltage bus 21 the high voltage bus 21 serves to distribute the high voltage to various high voltage systems in the vehicle 15 some of the systems that may be connected to the high voltage bus 21 include a traction motor drive inverter a power steering motor drive inverter an air conditioning compressor motor drive inverter and an accessory power system the power modules 23 1 23 2 23 n typically comprise high efficiency switching power supplies the switching power supplies tend to generate unwanted electrical noise and are therefore filtered the input filter 22 is provided to isolate the noisy power modules 23 1 23 2 23 n from the energy storage unit 11 the input filter 22 is designed to minimize ripple current drawn from the energy storage unit 11 such that conducted and radiated electromagnetic noise emissions from the system 20 are acceptable the input filter 22 also serves to minimize harmful transients which may be generated at the energy storage unit 11 and propagate to the power modules 23 1 23 2 23 n causing degradation of components and system failure the control methods 40 50 60 used in the high efficiency distributed staged power system 20 process the load demand and provides a smart decision to switch in or out a specific number of the power modules 23 1 23 2 23 n at a given operating load of the accessories of the hybrid electrical vehicle 15 fig2 and 6 illustrate three exemplary control methods 40 50 60 for controlling.