The invention concerns a method, voltage source converter and computer program product for supporting an associate AC system and comprising: a number of cells (CA1, CA2, CA3, CA4, CA5, CA6, CB1, CB2, CB3, CB4, CB5, CB6, CC1, CC2, CC3, CC4, CC5, CC6), each cell comprising a string of switching elements in parallel with a cell capacitor, at least some cells further including a battery module group comprising at least one battery module connectable in parallel with the cell capacitor and a control unit (20) configured to selectively connect the battery module groups of a number of cells in parallel with corresponding cell capacitors for exchanging power with the associated AC system.