Krishna Vasudevan

Sensorless Brushless DC Motor Drive Based on the Zero-Crossing Detection of Back Electromotive Force (EMF) From the Line Voltage Difference

This paper describes a position sensorless operation of permanent magnet brushless direct current (BLDC) motor. The position sensorless BLDC drive proposed, in this paper, is based on detection of back electromotive force (back EMF) zero crossing from the terminal voltages. The proposed method relies on a difference of line voltages measured at the terminals of the motor. It is shown, in the paper, that this difference of line voltages provides an amplified version of an appropriate back EMF at its zero crossings. The commutation signals are obtained without the motor neutral voltage. The effectiveness of the proposed method is demonstrated through simulation and experimental results.

Online cage rotor fault detection using air-gap torque spectra

This paper discusses use of air-gap torque spectra as a means of identifying faults in cage rotors. Being dependent on both stator and rotor currents, the torque is very sensitive to faults in the rotor. Through a comparative study using a detailed machine model and the standard dq model, the paper shows that the characteristic frequencies generated by a particular fault are preserved even if the standard dq model is used for estimation of air-gap torque. This is validated through a practical hardware implementation for online spectrum estimation of air-gap torque using TMS320C31, where several faulted cage rotors were used for study.

An improved scheme for extended power loss ride-through in a voltage source inverter fed vector controlled induction motor drive using a loss minimisation technique

Critical production processes in industry require the drives to smoothly ride-through during momentary power interruptions. This paper presents a method to extend the duration of the ride-through for VSI-fed vector controlled induction motor drives with a front end diode bridge rectifier. The proposed method minimises the losses in the system during the ride-through thereby enabling a longer ride-through duration. It requires only modification of the control software and hence is easy to implement. Hardware implementation of the method on a 30 kW induction machine indicates an extension of upto 34 % in the ride-through time by minimising the losses.

Comparative Evaluation of Harmonic Extraction Techniques for Three-Phase Three-Wire Active Power Filter

In this paper the performance of four harmonic extraction algorithms for active power filters are evaluated based on their steady state and dynamic performance. The techniques which are considered for comparative study are (i) filtering approach using the conventional low pass filter, (ii) instantaneous real and imaginary power (pq) theory, (iii) instantaneous active and reactive currents method (dq), and (iv) nonlinear least squares (NLS) estimation method. Comparison is based on simulation studies carried out in SABER. It is shown through simulation results that the dynamic behaviour of the harmonic extraction approach has an effect on the active power filter ratings. The simulation study reveals the superiority of the nonlinear least squares approach. This method provides good dynamic response and also extracts the load current harmonics explicitly.

Nonlinear Least Squares Current Estimator for Three Phase Loads

In the control strategies for an active power filter, determination of harmonic components of the load current is the most important stage. We propose a model-based method to extract the harmonic components of the load current in a three-phase three-wire load, where we solve the Fourier synthesis equations using the nonlinear least squares estimation method. The system is considered to contain only harmonic distortions. The proposed algorithm also takes care of fluctuations in the supply frequency. The advantage of this technique over other methods is that it can generate all the harmonic currents explicitly. It is shown through simulation results that the algorithm generates the references quickly with minimum delay under dynamic load conditions. This reduces the burden on the active power filter. Further, the results obtained with non-sinusoidal supply voltage are also satisfactory.

Parallel Operation of Power Factor Corrected AC-DC Converter Modules With Two Power Stages

This paper presents a new control method for paralleling single-phase power factor corrected AC-DC converter modules with two power conversion stages. The control algorithm varies the number of converter modules in operation and their power sharing in accordance with the load power demand. This control method offers advantages such as tight output DC voltage regulation, very low output voltage ripple, inherent input power factor correction, flexibility to expand power capability, and high overall efficiency. The paper presents the topological composition of the AC-DC converter module. The principle of operation of the new control method is explained. Simulation results are presented. The results demonstrate that the proposed topology and control method are able to produce tight regulation and good transient response.

Experimental studies and performance evaluation of solar PV powered BLDC motor drive with an integrated MPPT in fan applications

Power converters operating from solar PV array are typically operated in maximum power extraction mode, by the use of MPPT algorithms. Besides MPPT, buffering needs between PV and loads may require battery storage as well. Storage is expensive and also requires periodic maintenance and replacement. In this work, solar PV powered BLDC fans are developed without the use of storage and studied for their suitability in day time use like offices, schools, colleges. Two modes of operation are devised for operation of the fan- MPPT mode and Speed Regulation (SR) mode. In order to keep cost of the fan low, the optimal MPPT strategy to be used is determined from simulations. Hardware implementation is carried out to determine the actual operation of the system with respect to daily solar irradiation changes. From the experimental results it is seen energy efficient operation of BLDC motor drive, compared to single phase AC motor driven fan are achieved while keeping the scheme simple and cost low.

A novel hysteresis switching strategy for harmonic compensation

A simple and novel control technique for harmonic current compensation is presented. For each 60° duration of line cycle, the three-phase controlled bridge can be considered as dual buck, buck and boost, or dual boost configuration depending on the grid voltage and injected current polarities, and that only two switches are controlled at high frequency at any instant of time. A three-phase diode bridge with R, R-L, or R-C loads has been considered as nonlinear loads. Harmonics currents have been extracted and used as reference current signal. A switching algorithm for injection of any type of harmonic current has been developed and constant frequency hysteresis current control is proposed. The magnitude of the injected current can be controlled to bring the harmonics at source side to a minimum. The simplicity of the control circuit and the reduction in switching losses with excellent dynamic performance are the salient features of this control technique.

Analysis of subsystems behaviour and performance evaluation of solar photovoltaic powered water pumping system

Photovoltaic powered pumps are becoming popular. Their operation differs from that of the AC Mains powered pump, as they work under varying input power conditions. The efficiency figures of different subsystems will keep changing due to varying solar radiation conditions, causing the variations in overall efficiency under partial load operating conditions of the pump. The aim of this work is to study the performance of the various subsystems under these operating conditions. The system developed here consists of a Photovoltaic (PV) array of 900 Wp with 72 V nominal DC bus, a DC to DC Converter, a Variable Frequency Drive (VFD) and a three phase induction motor driven submersible pump. Maximum Power Point Tracking (MPPT) algorithm has been developed and implemented to maximize the use of PV power generated at any given instant. The system was installed and tested at Indian Institute of Technology Madras in Chennai, where daily average Peak Sun Hours is 5.6. Ambient temperature, total pressure head, water flow and power levels at different points starting from the output of the PV array upto the electrical power equivalent of water delivery were determined under varying solar radiation levels from sunrise to sunset. Continuously varying power efficiency figures of the subsystems were determined and power budget prepared. Wire to Water Energy Efficiency figures as well as System Performance Indices were determined.

Use of air-gap torque spectra for squirrel cage rotor fault identification

Identification of rotor faults in squirrel cage induction motors by estimation of the air-gap torque spectra has gained considerable attention recently. This has the advantage that the signature spectrum generated by faults is in the low frequency region. But the torque computation needs a machine model. The standard healthy machine model has been proposed in the literature to estimate the signatures but the correlation between the actual torque and the estimated torque is not clear. This paper presents a simulation study of an induction motor with faulted rotor bars and presents a comparison with torque spectra predicted by healthy machine dq model excited with faulted machine currents. It is shown that the spectral information produced by the latter is able to reproduce not only the frequency but also the amplitude of the torque spectrum to a fair degree of accuracy.