Research On Neutral Point Potential Control And Fault Detection In ANPC Three-level Converters

The integrated development of energy and transport stems from the close connection and interdependence of the energy and transport sectors and is an inevitable choice to solve the common problems faced in the development of energy and transport.In view of the current energy requirements of the road system,the selection of a suitable grid-connected inverter as the interface between the new road transport self-consistent energy system and the grid is of great significance for improving the overall performance of the system.Traditional two-level inverters are no longer sufficient to meet the requirements of the new power system.The use of multi-level inverters effectively reduces the harmonic content and protects against electromagnetic interference,advantages that make multi-level inverters better suited for medium and high voltage high power applications.However,as the number of levels increases,the control algorithms of multilevel inverters become more complex and require more rigorous design and testing to maintain system stability and reliability.In this paper,the active neutral point clamped(ANPC)three-level converter is used as the research object to evaluate the power loss of the mid-point clamped topology,and the research is carried out around the mid-point potential control and the fast location of broken power devices in fault mode,the main contents of the work are as follows:In order to address the problem of uneven power losses in the existing diode point clamped three-level(NPC),this paper completes the evaluation of the power losses in each module of the active neutral point clamped three-level(ANPC).Firstly.the dynamic commutation paths corresponding to the various switching states of the topology are clarified,and the overall paths are divided into short and long commutation loops in terms of the size of the parasitic inductance caused by the current loop.On this basis,the thermal loss simulation models of ANPC and NPC are built respectively,and as a comparison experiment it is verified that the power loss of each module of ANPC structure is relatively uniform and there is no problem of overheating of individual modules.In order to improve the reliability of the system,the traditional software modulation algorithm considering the midpoint potential balance has a high complexity.By studying the basic principle of three-level space vector pulse width modulation,we propose a three-level vector decomposition SVPWM algorithm and add mid-point voltage PI control to simplify the control algorithm process and improve the response speed.Finally,a simulation model is built to verify the rationality of the proposed algorithm under both rectifier and inverter operating conditions.To address the problem that the traditional fault current detection method cannot pinpoint the specific fault device,this paper proposes a fault location method based on a three-phase average current Park vector mode length based on the characteristics that the average current of the corresponding fault phase changes within one cycle depending on the location of the switching tube fault.At the same time,a new fault criterion is introduced for clamped switching tube faults to improve the accuracy and speed of the fault location method.