J. K. Chatterjee

A novel non-fragile single-loop voltage and frequency controller for induction generator based isolated renewable energy conversion system

Poor voltage and frequency regulation under source and load perturbations limit the use of self excited induction generator (SEIG) in isolated and dispersed generation, which can exploit wind/microhydro type renewable energy sources. In the present work, a Generalized Impedance Controller (GIC), which is a pulse-width-modulated voltage-source-inverter with a dc-link battery, is used to regulate both, amplitude and frequency of the SEIG terminal voltage using only PI controller in voltage feedback loop. The important aspect of the present work is to show the dependence and sensitivity of the dynamic response of both amplitude and frequency of the SEIG terminal voltage, following source and load perturbations, on the PI controller gain settings of the voltage feedback loop. For non-fragile system operation, optimum gain settings of the voltage-loop controller are selected within a stabilizing range to minimize the frequency disturbances caused by the source/load perturbations.

Synchronized Operation of DSP-Based Generalized Impedance Controller With Variable-Speed Isolated SEIG for Novel Voltage and Frequency Control

In this paper, the performance of a novel two-loop control strategy for a three-phase self-excited induction generator (SEIG), used in wind/microhydro/biogas-based isolated generation schemes, is presented. The implementation of the grid-interactive synchronization of the generalized impedance controller (GIC), an impedance-controlled operation of pulse width modulation (PWM) voltage-source converter, with SEIG is described. The SEIG frequency is tracked using digital phase-locked loop implemented on a dSpace DSP platform. The open-loop SEIG-GIC system is experimentally analyzed for the sensitivity of the SEIG voltage and frequency to GIC modulation index m and phase angle δ. Based on this, a simple and practical control strategy with proportional-integral (PI)-based voltage and frequency feedback loops is evolved for the regulation of the SEIG voltage and frequency. A novel design procedure for both the PI controllers for stable closed-loop operation is presented. The performance of the proposed closed-loop system is experimentally tested under speed and load perturbations.

Single-loop vs two-loop voltage and frequency control of isolated SEIG based RECS

Present investigation deals with the comparison of performance of a Generalized Impedance Controller (GIC) based 3-phase self excited induction generator (SEIG) terminal voltage and frequency regulator, having single and two-loop control, in an isolated wind/microhydro type renewable energy conversion system (RECS). Where, GIC is a PWM voltage source converter with dc-bus battery, having controlled four-quadrant equivalent impedance. Amplitude and frequency regulation of SEIG terminal voltage under source and load perturbations, are accomplished by controlling modulation index m of the GIC and phase angle δ of fundamental component of GIC terminal voltage with respect to SEIG terminal voltage. These m and δ control are achieved by operating the GIC in closed loop with, (i) only voltage feedback, and (ii) voltage and frequency feedbacks. The PI-controllers in both the schemes are designed for non-fragile system operation with optimized transient response of both amplitude and frequency of SEIG terminal voltage. The integrated SEIG-GIC closed loop system with single and two-loop control schemes are modeled and simulated in MATLAB/Simulink to highlight the superior performance of single-loop control scheme in transient and steady states.

Performance improvement in selective harmonic compensation of Shunt Hybrid Active Filter

Present work aims to improve the dynamic response and reliability of Shunt Hybrid Active Filter (SHAF) configuration using improved methods of harmonic detection. A method of introduction of only “positive inductance” through an active filter for mistuned conditions of the passive filter has been presented. “PLL free” scheme of harmonic detection for an uncontrolled rectifier type of non linear load has been studied. Intense simulation studies are carried out using MATLAB/Simulink to validate the functioning of the developed techniques under all conditions of operation. Experimental implementation of the proposed strategy using Digital Signal Processor TMS320F2812 processor is also presented.

Shaft input adaptive source current compensation based novel voltage and frequency control of autonomous induction generator

In this paper a novel scheme for regulation of amplitude and frequency of an autonomous self-excited induction generator (SEIG) terminal voltage under perturbations in shaft speed and connected load has been presented, which does not require voltage and frequency feedback. In this technique, compensation of active and reactive component of SEIG stator phase current using a generalized impedance controller (GIC) provides the regulation of SEIG output. The stator current compensation is different from standard hysteresis current compensation technique. The GIC is a voltage controlled PWM voltage source converter, offering controlled bidirectional flow of active and reactive power, while connected at the PCC via coupling reactance. For wide range of shaft input to the given generator, the relationship between the shaft input and reference amplitude of active and reactive component of SEIG stator phase current, at rated PCC voltage and frequency, is pre-established for proper GIC based compensation. A mathematical model of SEIG-GIC-load integrated system has been developed and simulated in MATLAB/Simulink to demonstrate capability of the generating system to provide voltage and frequency regulated supply, under variety of source and load perturbations.

Reduction of grid current harmonic injection in matrix converter controlled induction generator for wind applications

A technique has been presented for reducing the injection of harmonic current into the grid for matrix converter controlled induction generator, for application in wind energy conversion systems. A composite arrangement has been proposed where, multiple matrix converter controlled induction generators are kept in parallel and connected to the grid with appropriate phase shifting transformers that help in reducing the grid current harmonics. This technique of harmonic reduction with minimal use of the filter component will have an enormous impact in cases like wind farms having multiple generating units.

Improved operation of a three phase matrix converter using simple modulation strategy

Present work relates to improved operation of a 3-phase matrix converter using simple modulation strategy. A simple approach for input displacement power factor control is described, which can make the matrix converter as a source or sink of controlled reactive power. Novel feature of this investigation is the study relating to parallel operation of two matrix converters, from the point of view of reduction of input current harmonic, using a simple and reliable control strategy for matrix converter operation. These aspects enhance the possibility of application of matrix converters in grid connected wind energy conversion systems (wind farms).

Evaluation of synchronized operation of isolated induction generator with DSP based Generalized Impedance Controller

Performance evaluation of an isolated wind/hydro electric generation scheme having variable speed 3-phase Self Excited Induction Generator (SEIG) operating in synchronism with a Generalized Impedance Controller (GIC) has been presented in this paper. The GIC is an impedance controlled operation of Pulse-width-modulated voltage source inverter (PWM-VSI). The performance of the SEIG-GIC integrated synchronized operation under open loop condition, with fixed excitation and balanced isolated load, has been analyzed in detail for variations in modulation index ‘m’ of the GIC and relative phase angle ‘δ’ between the fundamental components of the GIC and the SEIG terminal voltages. The GIC operation is controlled by implementing Space Vector Pulse Width Modulation (SVPWM) technique. Detailed experimental studies have been undertaken on a laboratory prototype of the SEIG-GIC system for steady state operation. The effects of variations in ‘m’ and ‘δ’ on the amplitude and frequency of the SEIG terminal voltage and active and reactive power flow between the SEIG and the GIC are presented here.

A Multirate Multilevel Carrier Space Vector Modulation DTC Based IM Drive: A Novel Approach for Torque Ripple Minimization

This paper describes the implementation of multirate sampling technique for 3-level carrier space vector pulse width modulation based direct torque control (CSVPWM DTC) of induction motor (IM) drive with an objective to reduce the electromagnetic torque ripple for medium to high power applications. The benefit of the proposed multirate technique for 3-level CSVPWM DTC based IM drive; it gives lower torque ripple as compared to single rate sampling technique. In multirate sampling technique, for the same digital signal processor, two sampling periods are used. The fundamental sampling period which is smaller than the sampling period used in single rate sampling technique, is used for data capturing and estimation of speed, torque and flux parameters. The other sampling period which is an integer multiple of the fundamental sampling period, is used for speed, flux and torque error processing and also for the implementation of CSVPWM algorithm for synthesizing gate pulses. The 3-level inverter gives the smaller voltage steps lead to the production of higher power quality waveforms. This give superior performance compared to two-level inverters from the view point of lower common-mode voltage, lower harmonics in output voltage and current, and reduced voltage on the power switches Using simulation results relative merits of the multirate 3-level and single rate 2-level control strategy have been evaluated from the viewpoint of torque ripple minimization. The simulation results are experimentally validated. Index Terms-- Induction motor (IM) drive, Multirate sampling, direct torque control (DTC), torque ripple, space vector pulse width modulation (SVPWM), voltage source inverter (VSI). I. INTRODUCTION Present work demonstrates the improvement in performance of a CSVPWM DTC based IM drive using multirate sampling technique. The basic problems associated with the conventional DTC (1, 2) based IM drive are variable switching frequency and high torque ripple. In the past various modifications have been suggested by the researchers to overcome the above problems associated with conventional DTC drive. In case of conventional DTC, depending on the sampling period and the width of the hysteresis band, selected active voltage may create overshoot and undershoot which are responsible for the torque ripple. The above problems of conventional DTC are addressed by various researchers in (3, 4) using space vector pulse width modulation (SVPWM) principle for wave fabrication in DTC based IM drive. SVPWM technique using symmetrical regular sampling provides constant switching frequency operation of the inverter which takes care of the problem of variable switching frequency present in conventional DTC. For DSP based implementation of SVPWM technique, device switching frequency depends on the sampling period used in the program. It can be observed from the above that sampling period is an important parameter which limits the performance of conventional and SVPWM DTC based IM drive in terms of reduction of high torque ripple. In the present work the implementation of discrete CSVPWM DTC based IM drive system has been discussed for 3-level inverter. An attempt has been made to reduce the electromagnetic torque ripple in an IM drive by using multirate sampling technique for data capturing, processing and control. In (5-7), multirate sampling technique is discussed for the controlling the digital system. Multirate feed forward control and its application in position control of servo motor is discussed in (6). Multirate sampling technique has also been applied for modeling and control of wind energy generation scheme (7) in order to improve the reactive power injection for superior generator terminal voltage profile. In the present work the multirate sampling technique is not only used for control purpose but its major contribution is in the use for fast input data capturing and accurate estimation of stator flux, electromagnetic torque and speed which helps in accurate estimation of the stator flux linkage, corresponding speed and electromagnetic torque, which helps to reduce the electromagnetic torque ripple. In (8) a multirate sampling technique has been applied for SVPWM DTC based IM drive to further reduce its electromagnetic torque ripple.

Torque ripple reduction in direct torque control based induction motor drive using novel optimal controller design technique

In the present work a novel strategy for optimum design of flux and torque controller for carrier space vector pulse width modulation based direct torque control (CSVPWM DTC) of induction motor (IM) drive has been implemented. Two positive and one negative torque slope levels per half the switching period has been predicted for CSVPWM DTC IM drive based on which a new optimal control strategy is proposed for the design of flux and torque controllers where, a P controller is used in the flux loop and a PI controller is used in the torque loop. Performance investigation shows that optimally tuned controllers used in CSVPWM DTC technique are helpful in reducing torque ripple. In proposed control strategy flux and torque slopes are derived using d-q axis induction motor model in stationary reference frame. These slope parameters are respectively utilized to find the transfer function (TF) of flux and torque loops. Using these TF, flux P and torque PI controller settings are obtained such that they give the best results in terms of reduced torque ripple for any flux and torque slopes. In order to show the superiority of the proposed control strategy for CSVPWM DTC IM drive over conventional DTC technique, comparison of simulation and hardware results are presented.