| Motors,as the industrial equipment with the largest consumption of electricity,are widely applied in military industry,aerospace,chemical industry,metallurgy,and other branches of industry.Power converters,as the key equipment of energy conversion systems,are crucial for the reliable operation of motor drives.However,long-time operating in severe industrial environments,e.g.,high voltage,large current,strong electromagnetic interference,limited heat dissipation,etc.,will cause device(e.g.,semiconductor switches)failures and considerably deteriorate the reliability of power converters,resulting in substantial economic losses.Therefore,it is necessary to carry out the research on fault diagnosis and tolerant control for power converters,in order to enhance the reliability of motor drives.Semiconductor device failures are the biggest threat to the reliability of power converters,and open-circuit fault occurring in these devices still remains unresolved.In this paper,two open-circuit fault,diagnosis methods based on Tellegen’s theorem and state residuals are proposed respectively for two-level and three-level converters,and three fault tolerant control strategies for back-to-back converters,including healthy leg shared,DC-link shared,and switching state shared strategies,are comparatively analyzed,aiming to set up an open-circuit fault ride-through scheme for converters.In the former open-circuit fault diagnosis method,Tellegen’s theorem is utilized in the topological analysis of power converters for the first time.A dedicated“quasipower”concept is developed to describe the quantitative relation between voltage and current magnitudes.Based on this concept,the variation of quasi-power in all open-circuit fault cases is analyzed in detail,and a novel open-circuit fault diagnosis method for two-level converters is proposed.The proposed method is able to identify any faulty device among IGBTs and freewheeling diodes at a time scale of only one sampling period,that is the upper limits of any digital controller-based techniques.Besides,the proposed method applies to various operation scenarios and is robust again large parameter variations.The effectiveness and robustness of the proposed method is verified by both experimental and hardware-in-the-loop results.In the latter open-circuit fault diagnosis method,the current paths of three-level neutral-point-clamped power converters are analyzed.The concepts of voltage and current residuals are defined and their variation in all open-circuit fault cases is described in detail.Then an open-circuit fault characteristic table of current residuals is summarized,based on which a fast and accurate fault diagnosis method is proposed.The proposed method can identify any open-circuit fault device among the IGBTs,clamping diodes,and freewheeling diodes in three-level converters within several sampling periods.Both experimental and hardware-in-the-loop results confirm the effectiveness and robustness of the proposed method.The healthy leg shared,DC-link shared,and switching state shared fault tolerant control strategies all apply to back-to-back converters.The working principles and application scenarios of these strategies are presented in detail,and their control performance in transient and steady-state condition is comparatively tested on a hardware-in-the-loop bench.Experimental results show that all three fault tolerant control strategies are able to ensure the safe and controllable operation of converters in open-circuit fault condition,with four-quadrant operation capability.However,the operating range of converters with fault tolerant configuration is limited by the magnitude of their modulated output voltage and the number of their available switching states,and it is incapable for such converters to operate in rated operating conditions. |
