Krishna Vasudevan

It is well known that the optimum detector based on linear prediction, for frequency-nonselective (flat) fading channels, requires MP states for M-ary signalling, where P is the order of the prediction filter required to decorrelate the received signal. In this paper, we first derive a suboptimal linear predictive-based (SLP) detector for M-ary PSK by making a high SNR assumption. We then demonstrate using the concept of isometry that for M-ary PSK signalling, only MP-1 states are required for this SLP detector. The complexity reduction is achieved with no loss in symbol-error-rate performance compared to the case where MP states are used. As a corollary, we also show that for a first-order prediction filter and M-ary PSK signalling, the SLP detector is identical to the conventional differential detector. © 2001 Elsevier Science B.V.

Permanent magnet synchronous machines (PMSM) are attractive in many applications. Some of the applications require these machines to be operated beyond base/rated speed. This is achieved by weakening of flux through injection of negative direct axis current. However, the injection of this additional current contributes an additional copper loss and reduces the quadrature axis current component thereby reducing the torque. There is also the risk of permanent demagnetization in rotor poles. An alternative method for flux weakening (FW), a variable flux permanent magnet arrangement (VFPM) is analyzed in this paper. Further, a comparative study between a conventional interior permanent magnet machine (IPM) (which has a high constant power speed range (CPSR)) and a VFPM is done.

This paper presents the analysis of real time power quality data collected for 50 days at a domestic site in India. The data is collected using a dedicated PQ analyzer. The measurement and analysis are performed to identify the level of different grid disturbances and compared with relevant standards. Voltage unbalance and individual voltage harmonics are observed to be the major disturbances. In addition, the analysis of different kinds of loads, including new technology loads, present at the house is performed by recording the current waveforms drawn by these loads. The incoming supply voltage and current of the neighbouring houses are also recorded. An aggregate load model is presented based on the measurements performed at different houses connected to the same feeder.

Power quality (PQ) assessment has become a major area of interest in recent years because of increased use of sensitive equipments. It is necessary to know the level of disturbances in order to have necessary remedial or preventive measures to avoid equipment malfunction. Power quality surveys play a major role in achieving that. For the study carried out in this paper, power quality monitoring equipments were installed at three industrial sites to record the data. The observed PQ parameters are analyzed, compared and presented in detail. Observed PQ parameters are also compared with relevant standards to understand their severity levels.

In the control strategies for an Active Power Filter, determination of harmonic components of the load current is the most important stage. In this paper the behaviour of the shunt active power filter using the Nonlinear Least Squares' estimation technique for extracting the harmonic components of the load current is studied. The performance of active power filter under steady state and dynamic load conditions are analyzed. Simulation results depict a satisfactory performance even under step load changes. © 2006 IEEE.

The Uninterrupted Direct Current (UDC) solution has been developed by IIT Madras with a view to provide 24 X 7 power to all homes of India and alleviate power deficit situation prevalent in the country. This concept is being piloted and tested for practical viability in Sasaram, India. This paper discusses the necessary interventions needed at the sub-station end and the consumer end. The design details of the Brown-Out Feeder Energization Automation System (BOFEAS) commissioned in various feeders at Sasaram are also presented in this paper. The new efficient resonant switching power converter design has proven to be critical in developing Uninterrupted DC Power Module (UDPM), which is required to make in-home DC power line and DC power distribution possible. Various implementation challenges while executing UDC solution in Sasaram are also elaborated in this paper. Furthermore, the key role the local DISCOMs have to play in order to ensure UDC solution is implemented effectively is stressed upon. The learnings from Sasaram presented in this paper could be leveraged to ensure 24X7 good quality power supply across India.

This article proposes a model for a three-phase variable frequency drive in frequency domain for balanced harmonic condition. The model is represented by a frequency coupling matrix and is obtained through simulations in MATLAB and experimentation on a commercial drive. Two different model approaches, i.e., average model and lookup table-based model are attempted and difference in their performance is investigated. The model is validated for 70 voltage waveforms recorded at different industrial locations. The results obtained from the model match with the time domain simulation results. The proposed model is very fast with respect to the time of execution. A method to obtain the model in presence of grid impedance is proposed and the impact of variation of the grid impedance on the model parameters is also investigated. Further the application of the model is discussed using case studies.

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.

This article presents the development of a dynamic model and a design approach for the recently proposed buck-boost energy recovery circuit (BBERC) based power converter for a switched reluctance motor (SRM). The advantage of an increased demagnetization voltage in reducing the commutation torque ripple is analyzed using analytical and simulation-based studies. Though there have been several studies on the steady state behavior of the energy recovery stage in the literature, the dynamics of the same have never been investigated. An equation-based small signal model to describe the dynamic behavior of the energy recovery stage is proposed, which can be used to estimate the overshoots and oscillations in the inductor current and capacitor voltage during the dynamics. This article also evaluates the effects of discontinuous conduction mode (DCM) of operation of the BBERC on the drive performance, which has also not been addressed in the prior art. Furthermore, a method for the design of the energy recovery stage considering the continuous conduction of the energy recovery inductor is proposed. Additionally, the advantages of BBERC are reemphasized by comparing it with other energy recovery-based topologies such as energy efficient C-dump converter (EECDC). The analyses presented in this article are validated with experiments and simulations.

Commercial Spaces, domestic sector and agriculture sector constitute major part of electricity usage in India today and has been growing rapidly. Rolling 'power-cuts' have become all too common in rural and urban India, forcing many commercial consumers and households to invest in expensive back-up power sources (diesel generators and/or battery-UPS systems). Utilization of solar-PV in a decentralized manner has the potential of addressing these sectors to a significant extent and help in overcoming India's electricity shortage. The decentralized energy generation and usage however poses new challenges and huge. The paper addresses these issues and presents the design and development approach that would make a difference. © 2013 IEEE.