A Very High Resolution Stacked Multilevel Inverter Topology for Adjustable Speed Drives

This paper proposes a novel 49-level stacked inverter topology for drives. The 49 levels are achieved by stacking three 17-level inverters. Each of the 17-level inverter is developed by cascading a flying capacitor (FC) inverter with three capacitor-fed H-bridges. The device count can be reduced by making the FC and the three cascaded H-bridges common to the dc link in each phase using selector switches in between them. The selector switches need to operate at fundamental frequency only. Also, the devices need to block very low voltages. Hence, MOSFETs can be used. This topology requires three dc sources, each of Vdc/6 only, which can be replaced with stacked batteries for electric vehicle applications. The reduction in the dc voltage requirement is achieved by using a normal symmetric six-phase induction motor with parallel connection of the opposite phase windings. All the floating capacitors in the topology can be balanced irrespective of any modulation index or load power factor. Due to the high number of voltage levels, nearest level control can be used instead of pulse width modulation, which reduces the switching losses. The dv/dt during the inverter operation is also less. Detailed experimental results at different speeds of operation and during transients ensure that the novel topology can be a viable option for high-power adjustable speed drives

Generation of Higher Number of Voltage Levels by Stacking Inverters of Lower Multilevel Structures With Low Voltage Devices for Drives

This paper proposes a new method of generating higher number of levels in the voltage waveform by stacking multilevel converters with lower voltage space vector structures. An important feature of this stacked structure is the use of low voltage devices while attaining higher number of levels. This will find extensive applications in electric vehicles since direct battery drive is possible. The voltages of all the capacitors in the structure can be controlled within a switching cycle using the switching state redundancies (pole voltage redundancies). This helps in reducing the capacitor size. Also, the capacitor voltages can be balanced irrespective of modulation index and load power factor. To verify the concept experimentally, a nine-level inverter is developed by stacking two five-level inverters and an induction motor is run using V/f control scheme. Both steady state and transient results are presented

A Novel Forty Nine Level Stacked Inverter Topology Using Low Voltage Devices for Drives

This paper proposes a new forty nine level stacked inverter topology using low voltage devices for drives applications. The forty nine level inverter is developed by stacking three seventeen level inverters. The seventeen level inverter is developed by cascading a flying capacitor inverter and three H-Bridges. The inverter can operate with lower number of voltage levels if any of the H-Bridges fail. The capacitor voltage balancing in the inverter can be done irrespective of modulation index and load power factor. The topology is further modified to reduce the capacitor and switch count. Also, the inverter does not use any pulse width modulation between the different voltage levels. Therefore switching losses are reduced. In addition, since the switches need to block only lower voltages, MOSFETs can be used which will further improve the efficiency. An induction motor driven by this inverter using V/f control is simulated in MATLAB simulink and both steady state and transient results are presented

Stacked Multilevel Inverter fed Six Phase Induction Motor with Reduced DC Link and Lower Voltage Devices

This paper proposes a novel configuration of six phase IM to drive from a three phase stacked multilevel inverter. Apart from greater fault tolerance compared to three phase, a six phase machine enables the use of low voltage devices for the inverter. Also the inverter used here is a three phase nine level stacked inverter which itself uses low voltage devices. Thus MOSFETs can be used for the inverter. The nine level inverter is formed by stacking 2 five level inverters each of which is developed by cascading an FC and a capacitor fed H-bridge. The inverter can be stacked further to obtain still higher number of voltage levels. This enables the use of batteries at the front end and still lower voltage devices which will significanly improve the efficiency. Hence this will find applications in electric vehicles because of the direct battery drive. Experiment is conducted on a 15 KW six phase IM by reconfiguring it as a three phase machine and driven by the three phase nine level stacked inverter using V/f control scheme. Detailed experimental results are provided to validate the concept

Novel Symmetric Six-Phase Induction Motor Drive Using Stacked Multilevel Inverters With a Single DC Link and Neutral Point Voltage Balancing

This paper proposes a novel six-phase stacked multilevel inverter drive with only one dc source for a sixphase IM with symmetrically placed windings (60 degrees apart). Using one dc source allows direct ac-ac conversion and the inverter can feed the power back to the grid at any power factor. This paper presents a systematic approach to use one dc source for the six-phase stacked multilevel inverter fed symmetric IM drive. Here the individual dc supply is realized by series connected (split) capacitors with inherent balancing of the neutral point (dc link capacitor mid point) current within a switching cycle. This also helps in reducing the dc-link capacitor size. To verify the concept experimentally, a six-phase stacked nine-level inverter is developed in the laboratory for a symmetric six-phase IM and it is run with V/f control. Detailed experimental results are presented to validate the concept