Research on dynamic current sharing method of parallel connected IGBT modules for NPC three level converters

The parallel connection of IGBTs has been being applied in high power neutral point clamped (NPC) three level converters. This paper investigates the impact of gate parameters (gate resistor and capacitance) on dynamic current imbalance of parallel connected IGBT for NPC three level converter. A gate parameters calculation method is proposed in the paper, and the delay time and collector current difference can be analysed quantitatively. Experimental results have shown the effectiveness of the method.

Stray current measurement at the tramway infrastructure in Ostrava, Czech Republic

In most transit systems, rails are used as return conductors for the current from the vehicle to the electrical substations. If the rails are not fully insulated from the ground, some of this current would leak and become stray current, causing stray current corrosion on the rails and metal objects (such as pipelines) in the immediate area. It is very difficult to measure stray current directly, but stray currents can be calculated by measuring other parameters. Stray currents were measured on a 1.3 km section of tramway infrastructure in Ostrava. The potential between rail and earth was measured on the basis of the standard EN 50122-2, where two reference electrodes were placed at an appropriate distance from the tram track at three measuring points in the ground - the first point was located at the beginning of the section, the second in the half of the section and the last at the end of the section. Rail currents were measured at two measurement points - the first point at the beginning of the section and the second point at the end of the section. Using the rail-to-earth potential and the equation from the standard EN 50122-2:2011, the rail-to-earth conductance per length was calculated. The conductance per length was also calculated using Ohm's law, where the current difference is a difference between two measurement points. Since the results obtained using the standard and Ohm's law did not agree, a detailed analysis of the tram section was performed and electrical drainage was found. The drainage represents an electrical connection of the protected metal structure in the area of the tram track by a cable with stray current source. Through the drainage, the stray currents are directly returned to the rail. In this measurement section, the drainage has influenced the current difference between the measurement points - without drainage, this difference would be much smaller.

Majorana Field Effect Transistor. Majorana Fermion Detection and Transport Properties

In this work we obtain analytically the transport properties as current and conductance in a toy model system formed by a quantum dot with a single level connected to a Kitaev chain deposited on a s-wave superconductor to identify the signature of Majorana zero modes (MZMs) called Majorana Fermions in solid state. For this, we use the Non-Equilibrium Green’s Functions (NEGF) also named as Keldysh formalism in the matrix form to obtain the current–voltage (I–V) and conductance– voltage (G–V) curves to which goes to characterize the investigated system. Thus, it’s possible to verify the presence of the Majorana Fermions in three points: (i) Conductance peak in zero polarization; (ii) The current difference depends on the asymmetry of μL and μR. We find that only for μL = μR, the source and drain currents are equal. (iii) The current difference depends on the asymmetry of ΓL and ΓR.