Increasing the Linear Modulation Range of a Five-Level Inverter to the Full base Speed with the Elimination of Lower-Order Harmonics for Variable-Speed Drive Applications.

In many variable speed drive applications, the drive operates at full base speed in flux weakening region. In such cases, conventional inverters produce lower-order harmonics while working in the extended modulation region, but in the proposed work inverter can run at full base speed in the absence of lower-order harmonics in the extended modulation region, and hence, this forms a better alternative for variable speed drive applications. This method applies to the loads with a maximum power factor of 0.9, making it suitable for most Industrial drive applications. Using this method, the peak phase fundamental voltage can be increased from 0.577V dc to 0.637V dc in the extended linear modulation region. In the proposed method, a five-level inverter topology with a single DC source (V dc ) is used. The inverter topology consists of a 3-level Flying capacitor stage with Flying capacitor voltage held at Vdc/2, cascaded with a 3-level H-bridge stage with the capacitor voltage held at Vdc/4, feeding a three-phase Induction motor load. Simulation results for the steady state V/f operation, along with the experimental verification are presented. Hence, the proposed method can be used for better utilization of the DC bus.