We describe a fault-tolerant power semiconductor switching device control system (100), the control system comprising: a coordinating control system (110); and a plurality of switching device controllers (120) each coupled to said coordinating control system and each configured to control a respective power semiconductor switching device (130); wherein said coordinating control system is configured to send real time switching control data to said switching device controllers to control switching of said power semiconductor switching devices, and to receive real time acknowledgement data from said switching device controllers; wherein a said switching device controller is configured to receive said real time switching control data from said coordinating control system, to control a said power semiconductor switching device responsive to said real time switching control data, and to provide said real time acknowledgement data confirming said switching device control to said coordinating control system; and wherein said coordinating control system is further configured to control further switching of said power semiconductor switching devices responsive to said real time acknowledgement data.