Circuits for dc energy stores

A dc energy store (2) that includes auxiliary systems (68) can be operated in one or more different modes, including a self-supporting mode, an island mode and a normal mode. In the self-supporting mode a first controller (24) uses a voltage demand signal (VACr) indicative of desired ac voltage at the ac terminals of an AC/DC power converter (4) to control semiconductor power switching devices of the AC/DC power converter (4) to achieve the desired level of ac voltage that corresponds to the voltage demand signal (VACr). The voltage demand signal (VACr) is derived from a comparison of a voltage feedback signal (VACfb) and a second voltage demand signal (VACsr) that is preset to provide the desired ac voltage for the auxiliary systems (68) of the dc energy store. A second controller (46) uses a current demand signal (Ior) indicative of the desired dc link current to control the semiconductor power switching devices of a DC/DC power converter (14) to achieve the desired level of dc link current that corresponds to the current demand signal (Ior). The current demand signal (Ior) is derived from a comparison of a dc link voltage demand signal (VDCr) indicative of a desired dc link voltage and a dc link voltage feedback signal (VDCbus).