Gautam Sinha

A four level rectifier inverter system for drive applications

In a motor drive, the converters must be able to handle bidirectional real power flow. So far, DC voltage balancing has not been satisfactorily discussed for the case when real power is drawn from the inverter. This article addresses the control issues involved in a four-level inverter based AC drive application. The DC capacitor voltages are balanced for both motoring and regenerating modes of the inverter-motor system. In addition, DC voltages can be balanced even during motor startup with the associated large overcurrents.

A four level inverter based drive with a passive front end

Multilevel inverters are suited for high power drive applications due to their increased voltage capability. A four level inverter is able to synthesize better waveforms and attain higher voltages while reducing the device ratings. While converter device count and kVA are high, a conventional diode bridge rectifier is a low cost multilevel drive solution for the input rectifier if suitable inverter side DC voltage balancing schemes can be devised. This paper investigates the operation of four level rectifier/inverter based drives under commonly used modulation schemes. Link voltage balancing and output voltage capability are analyzed for a four level inverter. Simulation results are presented to verify the link voltage balancing strategy in the absence of any balancing action from the rectifier.

A new modulation strategy for improved DC bus utilization in hard and soft switched multilevel inverters

Multilevel inverters provide an attractive solution for high power, high voltage applications. While the multilevel topology permits higher voltages using devices of lower ratings, the DC link voltage balancing problem is a serious drawback which limits the applicability of multilevel topologies for motor drives. So far, redundant state selection has been the only method for regulating the capacitor voltages which results in a limited voltage capability. A new control strategy to improve the DC bus utilization, while generating low THD voltages is introduced. The proposed scheme is independent of the type of multilevel inverter topology and can be used for both hard and soft switching inverters. Simulation results are presented to demonstrate the validity of control scheme.

A four level rectifier-inverter system for drive applications

Multilevel converter technology has been receiving increased attention, especially for high power applications. In particular, three level drive systems have been extensively reported. In this paper, a four level rectifier-inverter system is investigated for drive applications. A dynamic control algorithm is described which balances the voltages on a 4 level rectifier-inverter drive system primarily from the rectifier. The proposed control method can also generate unity power factor currents at the utility interface. The inverter modulation is relatively unconstrained and modified to implement a zero sequence compensation for added voltage balancing. Simulation results are used to verify the efficacy of the control algorithm.

Rectifier current regulation in four level drives

A four level inverter based induction motor drive system utilizing an active four level rectifier has been proposed. This paper outlines the strategy for the rectifier control of such a system. A new switching scheme for concurrently balancing the link voltages and drawing unity power factor input currents is introduced. The proposed control scheme is dynamic and does not use lookup tables. Simulation results are used to verify the performance for a variety of load conditions.