A method, User Equipment (UE), and radio base station or NodeB for controlling the downlink transmit power of a Fractional Downlink Physical Control Channel (F-DPCH) in a multi-carrier High-Speed Packet Access (HSPA) system. Single-carrier Transmit Power Control (TPC) commands are modified to support different kinds of multi-carrier scenarios. The UE defines at least one TPC command for adjustment of the transmit power of the F-DPCH of N downlink carriers, the number of TPC commands being equal to or less than N, and transmits the TPC command(s) on at least one of M uplink carriers. The NodeB receives the TPC command(s) and adjusts the transmit power of the F-DPCH of the N downlink carriers based on the received TPC command(s).