Sujit K. Biswas

Gate drive methods for IGBTs in bridge configurations

The insulated gate bipolar transistor (IGBT) combines the advantages of both MOS and bipolar transistor technologies into a near-ideal power semiconductor switch. Of the various application areas, the use of IGBTs in the half or full-bridge power convertor configuration is very common. Such applications have typical requirements like isolated drivers, high dv/dt stress withstand, protection against shoot-through fault, etc. This paper presents various types of gate drive circuits suitable for such situations and their relative performance under actual circuit conditions. This includes pulse-transformer circuits (where a secondary power supply is not required) for PWM control, as well as opto-isolator circuits where the secondary power supply may be derived from the inverter DC bus. Protection schemes for the IGBT that can be incorporated into the drive circuit are also discussed.<<ETX>>

Microgrid: A review

A paradigm shift is evolving for the way electrical power is being generated from the traditional concept of centralized large generators to small generators connected to the distribution system powered by non conventional and renewable sources. These small generators were primarily for back up and were not synchronized to the grid. A trend is being observed to change the role of these distributed generations from back up to primary source of electricity in the form of Microgrid. The paper discusses the effectiveness of the Microgrid in a distribution system and presents a comprehensive review of the Microgrid. Various architecture and control schemes of the Microgrid are reviewed. The use of combined heat and power (CHP) system to enhance the overall efficiency of the power system is discussed. The paper aims at providing a broad perspective on the state of art of the Microgrid to the researchers and application engineers dealing with power quality aspects and Microgrid. The classified manner in which the references are presented in this paper will serve them as quick and useful reference.

A Simple and Generalized Space Vector PWM Control of Cascaded H-Bridge Multilevel Inverters

This paper presents an automatic switching pattern generation for multilevel cascaded H-bridge inverters with equal dc voltage sources, based on the space-vector pulse width modulation (SVPWM) techniques. The proposed switching strategy generates a voltage vector with very low harmonic distortion and reduced switching frequency. This new control method is an attractive alternative to the classic multilevel pulse width modulation techniques considering the following aspects, mainly, minimization of voltage and current total harmonic distortion (THD), extension of range of linear operation; and least number of commutations. To solve the problem of computational complexity in multilevel inverters due to the large number of space vectors and redundant switching states, a simple and general space vector PWM algorithm is proposed. Based on this algorithm, the location of the reference voltage vector can be easily determined and the calculation of dwell times becomes very simple. It is also mentioned that this method requires lower memory spaces as there is no need of any look-up table. To verify the algorithms, a seven-level cascaded H-bridge inverter drive system was constructed and simulation results are present here.

New Fully Soft-Switched Boost-Converter with Reduced Conduction Losses

A new fully soft-switched boost-converter is proposed here, using only one auxiliary switch. All switches used in this converter turn on and turn off under fully soft-switched condition. The diodes also commutate softly. The converter uses minimum number of components in the auxiliary circuit without additional current stress of the main switch. The circuit conduction losses are also minimised, since the resonant capacitor charging current flows only through an inductor and a diode. The main and auxiliary IGBT share a common emitter connection, facilitating direct drive to them. The circuit is suitable for application to active power factor correction. Various operating modes of the converter are presented and analysed. The principle of operation has been verified with computer simulation and experimental results

A three-phase half-controlled rectifier with pulse width modulation

A three-phase pulse-width-modulated (PWM) half-controlled rectifier using a novel PWM control strategy whereby the low-order harmonic content in both the input current and the output voltage is reduced is presented. The circuit operates with a unity displacement factor at its input and uses minimum power components. The PWM strategy developed can be implemented on a three-phase half-controlled rectifier bridge with only three controlled switches to obtain PWM controlled rectification. Although the circuit operation is explained with force-commutated SCR switches, the basic controlled PWM operation is valid for any type of switch control. The circuit has wide applications ranging from rectifiers to battery chargers to motor drives. Even if an input current filter is desired, its size will be small due to the PWM pattern used. >

Optimized design of a fully soft-switched boost-converter suitable for power factor correction

A fully soft-switched boost-converter using a one auxiliary switch is presented here. It uses the minimum number of components in the auxiliary circuit with minimum current stress of the main switch. Since the resonant capacitor charges only through an inductor and a diode, the circuit conduction losses are minimized. The main and auxiliary insulated gate bipolar transistor (IGBT) switches share a common emitter connection, facilitating direct drive to them. Various operating modes of the converter are presented in detail and analysed. The choice of the resonating capacitor and inductor has been done through an optimization process based on the guiding equations working under different modes. In this optimization process, emphasis has been given on minimum voltage stress on the auxiliary switch for a wide duty cycle range of operation. Based on the design, the principle of operation has been verified with computer simulation. Experimental results from a laboratory prototype with active power factor correction confirms the operation of this converter.

A New Control Circuit Extends the Effective Duty Cycle Range of Flyback Converters

Voltage source flyback converters in the discontinuous conduction mode with a new control strategy is presented in this paper, that is capable of operating over a wide range of input and output voltage variation. Over the normal range, pulse width modulation at fixed frequency is used as in conventional system. At low duty cycle demands, constant pulse width with variable frequency is used to extend the effective duty cycle range

Performance Studies of Fuzzy Logic Based PI-like Controller Designed for Speed Control of Switched Reluctance Motor

Switched reluctance motor (SRM) has gained significant interest in the field of industrial drive. The controller used to drive the machine is conventional PI controller. But the machine characteristics are very much nonlinear. This poses a problem for conventional controller design as regards to maintaining steady performance. There is also a need to adapt to the variable operating conditions. Fuzzy logic based heuristics is prospective since the exact analytical modelling of the system is difficult. PC implementation of the controller offers great flexibility in both design and maintenance phase. This work implements a PI like fuzzy logic controller (FLC) for SRM, which is found to work successfully in real time conditions. The work compares the performance of the FLC with respect to the conventional PI controller

Enhancing Quality of Power to Sensitive Loads With Microgrid

The paper discusses the effectiveness of the MicroGrid (MG) in a distribution system. Combined heat and power (CHP) system has been used to enhance the overall efficiency of the power system. Microturbines have been used for CHP operation in this paper. The various methods of controls of the MG are also discussed. A simple and low cost model for MG based on frequency droop control for active power generation, has been proposed. The proposed model can be used in plug and play mode of operation of the MG. The model has been simulated on the MATLAB platform. Performance of the model has been studied under grid connected and under islanded condition.

Performance analysis of an asymmetrical phase-converter-fed induction motor

Of the various types of single-phase-to-three-phase static power converters used to interface a three-phase motor to single-phase supply, one simple type uses an open delta connection of a sinusoidal supply and a pulsewidth modulated (PWM) waveform to feed the motor. This paper presents an analysis of the performance of the three-phase motor when fed from such an asymmetrical supply. The analysis is based on the steady-state approximate-equivalent circuit of the motor, using the method of symmetrical components. The analysis is directed toward prediction of motor phase and line currents, along with the nature of generated torque. The computer-simulated waveforms are presented and compared with results from tests on a laboratory setup.