TLI Series Application Note-中心点钳位三电平介绍.pdf

  First Release June 1, 2009 Introduction to Three Level Inverter (TLI) Technology  This Application Note reviews three level inverter topology, often referred to as Neutral Point Clamped (NPC) inverter. The three level inverter offers several advantages over the more common two level inverter. As compared to two level inverters, three level inverters have smaller output voltage steps that mitigate motor issues due to long power cables between the inverter and the motor. These issues include surge voltages and rate of voltage rise at the motor terminals and motor shaft bearing currents. In addition, the cleaner output waveform provides an effective switching frequency twice that of the actual switching frequency. Should an output filter be required, the components will be smaller and less costly than for an equivalent rated two level inverter. Most often the NPC inverter is used for higher voltage inverters. Because the IGBTs are only subjected to half of the bus voltage, lower voltage IGBT modules can be used. Powerex’s TLI series of IGBT modules provides a cost effective way to bring the advantages of this topology to 460V applications. For more detailed information please refer to the datasheets located on the Powerex web site. Basic Circuit Configuration and Its Behavior Figure 1 shows the circuit configuration of the NPC inverter. Each leg has four IGBTs connected in series. The applied voltage on the IGBT is one-half that of the conventional two level inverter. The bus voltage is split in two by the connection of equal series connected bus capacitors. Each leg is completed by the addition of two clamp diodes. Bus Voltage W U V