Circuits for dc energy stores

A method of operating a dc energy store circuit comprising:

• a dc energy store having auxiliary systems;
• an AC/DC power converter including a plurality of semiconductor power switching devices, the AC/DC power converter having ac terminals that are electrically connected to an ac supply network and dc terminals;
• a DC/DC power converter including a plurality of semiconductor power switching devices, the DC/DC power converter having first dc terminals electrically connected to the dc terminals of the AC/DC power converter by means of a dc link and second dc terminals electrically connected to dc terminals of the dc energy store;
• a first controller for the AC/DC power converter;
• and a second controller for the DC/DC power converter;
• wherein the method comprises the step of operating the dc energy store in a self-supporting mode in which power is supplied from the dc energy store to the auxiliary systems of the dc energy store such that:
• the first controller uses a voltage demand signal indicative of desired ac voltage at the ac terminals of the AC/DC power converter to control the semiconductor power switching devices of the AC/DC power converter to achieve the desired level of ac voltage that corresponds to the voltage demand signal, the voltage demand signal being derived from a comparison of a voltage feedback signal and a second voltage demand signal that is preset to provide the desired ac voltage for the auxiliary systems of the dc energy store;
• and
• the second controller uses a current demand signal indicative of desired dc link current to control the semiconductor power switching devices of the DC/DC power converter to achieve the desired level of dc link current that corresponds to the current demand signal, the current demand signal being derived from a comparison of a dc link voltage demand signal indicative of desired dc link voltage and a dc link voltage feedback signal.