Open Stator Winding Research Articles

A 5-Level Inverter Scheme Using Single DC Link With Reduced Number of Floating Capacitors and Switches for Open-End IM Drives

This paper presents a 5-level inverter topology for open-end induction motor drives by using a single dc source. The open stator windings of the drive are supplied with a 3-level flying capacitor inverter from one end and capacitor-fed 2-level inverter from another end. The voltage ratio of the dc link to the capacitor in 2-level inverter is maintained at 4:1 ratio to generate five-level voltage output. The capacitor in 2-level inverter is balanced by the switching redundant vector combinations from both the inverters while the floating capacitors in the 3-level inverter are balanced by using redundant switching states. The proposed topology gives 5-level operation with less number of floating capacitors and power semiconductor switches compared to other existing topologies. Also, the balancing of the capacitors is independent of load power factor and modulation index. Further, the generalization of the proposed dual inverter scheme for any n -level inverter is also included in this paper. The experimental results and required analysis are also presented to validate the inverter scheme.

Discontinuous decoupled SVPWM schemes for a four‐level open‐end winding induction motor drive with waveform symmetries

A four-level open-end winding induction motor drive (OEWIMD) is realised by feeding the open stator windings of a three-phase induction motor from either end with two-level voltage source inverters (VSIs). These VSIs are operated with unequal DC-link voltages, which are in the ratio of 2:1. This circuit configuration has the disadvantage of overcharging the DC-link capacitor of the inverter operated with the lower input voltage. Decoupled space vector pulse-width modulation (DSVPWM) schemes, which were suggested in the previous literature to circumvent this problem, result in higher switching power loss in the dual-inverter topology. It is known that the discontinuous pulse-width modulation (PWM) schemes reduce the switching power loss. However, lack of structural symmetry of the power circuit renders it unwieldy to devise these PWM schemes. This study explores the applicability of discontinuous decoupled SVPWM (DDPWM) techniques for the four-level OEWIMD, without compromising on the waveform symmetries. With the aid of an improvised loss model, it is shown that these PWM schemes achieve the reduction of the overall loss of the four-level OEWIMD compared to the DSVPWM schemes. It has also been observed that one of the proposed DDPWM schemes result in reduced dv⁄dt in the motor phase voltages.

Principle of Operation and Performance of a Synchronous Machine Employing a New Harmonic Excitation Scheme

This paper presents a new harmonic current excitation principle for a synchronous machine drive based on control of the spatial third harmonic MMF. Unlike existing harmonic excitation technologies, which utilize the third harmonic components of the rotor magnetic field, this brushless harmonic excitation principle is realized by injecting an ac single-phase current component or dc component into three-phase open stator windings thereby utilizing the resultant third harmonic spatial stator MMF component. This additional component generates either a stationary or time pulsating magnetic field which will induce voltages in a specially designed rotor winding. Through rectification, the induced voltage is used to supply dc current to the rotor excitation winding. To verify the aforementioned principle, theoretical analyses, magnetic field calculations by finite-element analysis and experiments with a 1.0-kW prototype machine have been performed and key influential factors have been investigated. The test results are shown to be consistent with the theoretical analysis, which validates the correctness of the theory.

Comprehensive Analytical and Experimental Analysis of a Self Excited Induction Generator for Renewable Energy Application

Self excited induction generators have attracted a lot of interest from the researchers in recent past. The main focus in this regard has been on modeling techniques and their verification. Such analyses are invariably restricted exclusively either to dynamic or steady state characteristic evaluation. The objective of this paper is to highlight the operational features of self excited induction generators through detailed experimental results. For analytical verification steady state and dynamic models are implemented through symbolic programming and Simulink modeling approaches respectively. Diverse set of static loads of different power factors as well as dynamic loading is employed to carry out power quality analysis of SEIG on a Fluke 435 II power quality and energy analyzer to conclude the paper. The tests are carried out on an open stator winding, squirrel caged induction motor operated as SEIG

Optimal Pulsewidth Modulation of a Dual Three-Level Inverter System Operated From a Single DC Link

Operating a dual three-level inverter system from a single dc link circuit is an economic solution for generating five-level output voltage waveforms and to double the output power compared to a single three-level inverter. Such an inverter system is used for feeding a drive motor with open stator windings. A mechanism is then required to reduce the common-mode voltage components of the motor voltages. This paper describes an offline optimization method that minimizes both the harmonic distortion of the motor currents and the common-mode voltage components. The optimization permits reduction of the switching frequency to a very low value of 200 Hz without compromising the harmonic distortion. High performance operation of the drive system at low switching frequency is experimentally demonstrated.