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 <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</inf> to 0.637V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</inf> in the extended linear modulation region. In the proposed method, a five-level inverter topology with a single DC source (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</inf> ) 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.