Calculation And Measu Rement Of Low Inductance Bus Bar In Converter Valve Components Of Modular Multilevel Converter

The stray inductance in current commutation loop causes these problems such as overvoltage, much loss, electromagnetic interference, etc. when IGBTs are turned off. Reduction of stray inductance of bus bar between DC-link capacitors and semiconductor devices is one effective solution to suppression of above-mentioned impacts. There are two difficuties for measuremet of low-sense bus bar inductance. Because inductance of low-sense bus bar is very low, it is much difficult to measure it accurately. There are many input ports for DC-link capacitance in one same low-inductance bus bar that are equivalent excitation input port. Therefore, the actual inductance in low-inductance bus bar is the total one composed by many respective inductances of spatial distribution pattern. As a result, the further difficulty is brought to measurement of the total inductance.In order to obtain the total inductance value of composite of many respective inductances of bus bar, the plane geometry synthesis method is presented in this thesis. Based on the actual structure of bus bar, respective inductance is regarded as having direction, that is vector, and the total inductance is obtained by applying plane geometry synthesis method. Two close and parallel enameled wires have been designed to be measuring lines in order to reduce measurement error caused by measuring lines. Meanwhile external inductance of measuring lines have been reduced. We designed two short copper cylinders at the ends of this linking line connected with planar bus bar, which have made the connection more compliant like actual connection and measurement process is standardized.Based on actually designed low-inductance bus bar with 15 input ports that are connected with DC-link capacitors, respective inductance of single port of bus bar is measured respectively by impedance analyzer. After comparison study on different measurement schemes, the feasibility, which copper enamel wires are connected to both impedance analyzer and bus bar, is verified. The 15 stray inductances of bus bar are researched by 3D electromagnetic simulation method when respective stimulus is applied to the port of respective capacitor. Accuracy and feasibility of measurement are verified through comparison with simulation results. Forthermore, contribution of two planar parallel plates and short linking leads to inductances is researched. This study demonstrates that appropriate reduction of this linking leads area can make the total inductance reduce greatly. Respective inductances from simulation calculation computes the total inductance by using the geometric synthesis method. The effectiveness for synthesis method to affect total inductance measurement of low-inductance bus bar in this thesis is verified theoretically through comparison between total inductances obtained by geometric synthesis and a simulation. To eliminate measuring lines effect, inductance measurement calibration process based on impedance analyzer is improved, which compensate partial inductance due to overcompensation by impedance analyzer. Based on improvement of measurement method, not only accuracy of single port inductance measurement results but also synthesis method of the plane geometry is verified from experimental point of view.