This paper account for 3-level NPC and T-type inverter system. A major advantage of 3-level inverter system is the lower current THD than 2-level inverter. Because 3-level inverter has lower voltage rating of power switches than 2-level inverter. So low voltage rated switches which are used in 3-level inverters are faster, smaller, and cheaper than high voltage rated switches used in 2-level inverters. Above all, 3-level inverter is the possibility to use IGBTs with breakdown-voltage that are lower than the DC-link voltage. So the lower blocking voltage devices have a lower losses and the efficiency can be increased. By using same blocking voltage as in a 2-level inverter higher DC-link voltage can be realized.
Conventionally, there have been some studies about the calculation of power losses in the inverter system and it has been recommended that the well known topologies are the NPC(Neutral Point Clamped) and T-type inverter. A power loss analysis based on discrete type module. Discrete type module has a only two IGBTs. So, this module formed in inverter which has a line impedance more than inverter module. On the other hand, among the IGBTs in inverter type module are optimizing the manufacturing process, so inner loss is lower than discrete IGBT module. Thus, this paper choose inverter type modules then, analysis power losses for 3-level NPC and T-type inverters. T-type inverter (called by 3-level T-type inverter) compared with NPC inverter, the count of switch is reduced. So T-type inverter is better than the 3-level NPC inverter (called by 3-level NPC inverter) based on the power loss analyses. In a material way the T-type inverter with the NPC inverter, it has the advantage of the short conducting path and the small number of switches due to no clamping diodes. But the comparative study about the power losses is not simple and it may lead some different results depending on the parameter characteristics of the switching devices, the switching frequency. Estimates of switching losses have been obtained using approximations of IGBT and diode I-V switching characteristics. However, a more convenient approach based on calculating switching loss using the switching energy-current characteristics curve, reveals that the switching losses of an IGBT-diode pair are approximately proportional to the switching voltage and current. This observation can be verified based on IGBT-Diode module data sheets. The conduction loss depends on the modulation index(MI) and power factor(PF), whereas the switching loss depends on the switching frequency. Power losses for the T-type and NPC inverters are analyzed and calculated at the different operating points of MI, PF and the switching frequency.
In this paper, the power loss analysis for the 3-level inverter has been analyzed. Also, the conducting loss and the switching loss in the switching devices as the different switching state are analyzed with the change of the switching frequency based on the previous works. Through these analyses, it can be confirmed that the total losses in NPC and T-type inverter may be different as the choice of switching devices with the different parameter characteristics. To prove the above, the power losses are calculated using the technical report and compared with the simulation results from the PSIM thermal module analysis. Then, power losses of the three different devices for 3-level NPC and T-type inverter modules are adopted. Finally, the total power losses of these devices in the inverters are mainly compared with conduction and switching loss. And then select to the most loss less device.