ELECTRICAL POWER SUPPLY SYSTEM

An electrical power supply system is provided. The system has: a DC distribution bus (10); a rechargeable battery module (24) which delivers DC power to the DC distribution bus (10) in a discharge mode of operation, and absorbs DC power from the DC distribution bus in a recharge mode of operation; a DC/DC converter (26) comprising an inductor (L) and plural switches, the DC/DC converter being operatively connected between the DC distribution bus (10) and the rechargeable battery module (24); and heat transfer means configured to transfer heat between the DC/DC converter (26) and the rechargeable battery module (24). The rechargeable battery module (24) also has an idling mode of operation in which it neither delivers DC power to nor absorbs DC power from the DC distribution bus (10). The DC/DC converter (26) is arranged such that, in the idling mode of operation, the DC/DC converter is repeatedly switchable between (i) a ramping-up configuration of the switches in which a current is withdrawn from a source which is one of the DC distribution bus (10) and the rechargeable battery module (24), flows through the inductor (L) and is returned to said source, and (ii) a freewheeling configuration of the switches in which the current from the ramping-up configuration is isolated from said source to flow in a continuous loop within the converter. The electrical power supply system further has a controller which is configured to control the repeated switching between the ramping-up configuration and the freewheeling configuration such that, in the idling mode of operation, heat resulting from the repeated switching and the current flow produced thereby in the DC/DC converter (26) is transferred by the heat transfer means from the DC/DC converter to heat the rechargeable battery module (24).