A Single DC Source Multilevel Inverter With Extended Linear Modulation Range to the Full Base Speed and Predictive Capacitor Control for Induction Machine Drives

Abstract

This article proposes a four-level multilevel converter configuration achieved through the stacking of low voltage basic inverter cells coupled with an cascaded H-bridge (CHB) structure. Three series connected identical capacitors fed from a single common dc source is feeding the CHB converter unit. This results in the formation of two common coupling points (CCPs) along with the dc-link terminals. Ensuring balanced voltages at these CCPs is critical. This is achieved by maintaining zero instantaneous currents drawn or injected from each CCP at any given instant during pulsewidth modulation operation. In addition, this present scheme enables extended linear modulation operation with absence of lower order harmonics, expanding its operational range up to the full base speed of an induction motor drive. This article also presents an capacitor balancing method using a single-step predictive control to achieve balanced capacitor voltages of CHBs effectively. The method entails predicting capacitor voltages for various redundancies, aiming to select the switching vector with minimal deviation from the nominal values using space vector redundancies. This approach enhances the converter's performance by actively regulating the capacitor voltages within each sampling period.