Improved Multilevel Inverter System

Background: Variable frequency inverter drive systems are being used more often for driving electrical machines; these are of particular importance for driving large industrial motors and traction motors for vehicles. However traditional variable frequency drives are limited by high device voltage ratings and poor output waveform quality. Thus multilevel inverters have been considered for such applications because of their improved long-term reliability reduced size improved performance and lower cost. Although multilevel inverters have many advantages unbalances in the capacitor voltages can produce unequal device stresses in the inverter which can lead to device failure as well as degradation of waveform quality. A new inverter configuration with improved waveform quality and output voltages with lower distortion is needed. Technology Description: UW–Madison researchers have developed a multilevel inverter system for use in high voltage high power applications. The system comprises at least three DC bus capacitors an inverter a control means and a rectifier; it also may include one or more transformers. The controller is connected to the switching devices of the inverter. After receiving signals indicating the load currents and the voltages across the DC bus capacitors the controller provides a selected output waveform at the output lines. The system enables an inverter of four levels or higher to achieve desired output voltage generation while obtaining link voltage balancing at higher modulation depths. This reduces costs and improves the performance of the drive. Applications: 1) Electrical power conversion systems particularly multilevel inverters 2) High power industrial and traction drives Patent Status: US6031738 Opportunity for collaboration: The Wisconsin Alumni Research Foundation (WARF) is seeking commercial partners interested in developing a multilevel inverter system for high voltage high power applications.