Conservative DC Voltage Prediction of Floating Capacitor H-bridge Converters for Soft Start of Grid Connected Induction Motors

A methodology is described to conservatively predict the behavior of DC capacitor voltage for floating capacitor H-bridge converters, which are located in each phase between the utility grid and a squirrel cage induction motor. Under the proposed methodology, an algorithm is developed to predict the DC voltage level before motor starting. In this way, DC capacitor voltage overshoot problem can be avoided, which greatly improves the safety and reliability of the proposed power electronics. The paper presents the theory necessary to understand how to model AC bridge voltage trend under various motor loading conditions and how to conservatively predict the behavior of DC capacitor voltage before motor starting. Hardware experimental results show that the voltage level of DC capacitor for the proposed system can be accurately predicted.