The invention relates to a fail-safe power control apparatus (3) for supplying power between an energy source (4) and the motor (5) of a transport system. The power control apparatus comprises a power supply circuit (6), which comprises at least one converter (7, 8) containing controllable change-over switches (32), and the power control apparatus comprises means (24) for controlling the converter change-over switches, a data transfer bus (10), at least two controllers (1, 2) adapted to communicate with each other, and a control arrangement (11) for controlling a first braking device, and possibly a control arrangement (43) for controlling a second braking device.