Common-mode Current Suppression Of Nested Multilevel Converter

Renewable energy such as photovoltaic power generation is growing rapidly development Three-phase transformerless multilevel converters are getting more and more attention in this field because of the simple structure and high efficienc.However,the numbers of converter power electronic devices grow in multiples with the number of output levels increase,and the increasingly complex application condition cause the failure of power electronic devices.Due to the lack of isolation transformer,the common mode current is generated in the transformerless multilevel converters and degrades the performance of converters and brings security issues.1、A new methodology of constructing nested multilevel converters is proposed,which combines the main switches,the clamp switches,the capacitors and so on.New multilevel converters are formed which has the multiplexing capability of the device.The nested multilevel converters named five level T-type ANPC converter,M-MC converter,ANPC converter are derived from the nested objects of diode neutral point clamped(NPC)converter,the flying capacitor(FC)converter and the T-type converter,and a detailed analysis about the power device quantity,power device voltage stress and capacitive voltage balance ability of traditional multilevel converter is presented.2.Five-level T-type ANPC converter and traditional SVM mehod is introduced.Then,the common-mode equivalent circuit model of the nested five-level converter is initially derived to further explore its common mode current generation mechanism.CMC is verified by simulation and experiment.3、A zero common-mode voltage space vector modulation by choosing the zero common-mode voltage space vectors to synthesize the reference vector is proposed.An advanced coordinate transformation is introduced to realize the sectors flexible selection and fast calculation of the vectors action time.The CMC is successfully suppressed in the high range of modulation ratio.Finally,the effectiveness of the proposed ZCM-SVM strategy is verified by the simulation and experimental results.