Abstract: The AC power station of the KANTAN IV semi-submersible drilling platform is transformed into a digital control system, and the SCR DC drive still retains the original analog control. In order to realize the power limitation between digital system and analog system, three methods are described in this paper: adding point potential, PLC communication and power transducer. After actual testing, the transducers collect the active power and current signals, then send the signals to SCR analog system. The real-time response and power limitation to static load or sudden load have met the original design requirements.