5-Level 3-Phase Back To Back E-Type Power Converter Topology: design, modulation and control
The use of variable speed drive plays an important role in commercial, industrial and military applications, where small size and lightweight, low maintenance, reliability in a wide range of environments and good efficiency are required. For these applications, the complete drive system can be basically composed of three main parts: high-speed generators, double conversion AC/DC-DC/AC ((Back To Back)) and load. Starting from a variable three-phase input AC voltage provided by grid or the permanent-magnet synchronous generator (PMSG) at high fundamental frequency, the power electronic systems must be able to convert electric power to a regulated DC voltage, and then into AC voltage to feed the load. Since the high fundamental frequency of the machine, the synchronous inductance is reducing to limit the reactive voltage drop. Consequently, to limit the current ripple, the switching frequency of the converter must be increased. Since the switching frequency is ultimately limited by losses and device speed limits, multilevel converters are considered an alternative due to their ability to reduce the ripple current without an increase in the switching frequency. The research activity is mainly focused on the design, modulation and control of multilevel power electronic converters topologies operating as a double conventions AC/DC-DC/AC in high speed generating and UPS (Uninterruptible Power Supply) applications. The new power converter topology, called 5-Level 3-phase Back To Back E-Type Converter (5L 3-P BTB E-Type Converter), is composed by three main parts: 5-level unidirectional T-type rectifier topology (5L E-Type Rectifier), 5-level Inverter (5L E-Type Inverter) and two balancing circuits that are used to transfer power in order to obtain four equal voltage. It is of outmost importance and practical interest to evaluate the converter conduction and switching power losses for the appropriate design of the 5L 3-P BTB E-Type Converter. To obtain the conduction and switching losses into 5L 3-P BTB E-Type Converter as a function of converter output power, PF, switching frequency and modulation index, the analytical equations for computing RMS and average currents of the power semiconductors have been presented. Numerical results of the obtained analytical equations for calculation of RMS and average currents of power devices have been compared with simulation results using Plexim/PLECS tool in the Matlab/Simulink environment. Afterward, the thermal model of the IGBTs, MOSFETs and diodes have been created considering the parameters provided by the manufactures.