Tapas Kumar Bhattacharya

Bifurcation Analysis of PWM-1 Voltage-Mode-Controlled Buck Converter Using the Exact Discrete Model

Nonlinear phenomena in power electronic circuits are generally studied through discrete-time maps. However, there exist very few circuit configurations (like, for example, the current-mode-controlled dc-dc converters or current programmed H-bridge inverter) for which the map can be obtained in closed form. In this paper, we show that, in a voltage-mode-controlled dc-dc converter, if the switching is governed by pulse-width modulation of the first kind (PWM-1), an explicit form of the stroboscopic map can be obtained. The resulting discrete-time state space is piecewise smooth, divided into five regions, each with a different functional form. We then analyze the bifurcation behavior using the explicit map and demonstrate the different types of border collision bifurcations that may occur in this system as a fixed point moves from one region to another. This includes the very interesting case of a direct transition from periodicity to quasi-periodicity through the route of border collision bifurcation. Mode-locking periodic windows are also obtained at certain ranges of the parameters. The two-parameter bifurcation diagram is presented, showing the domains of existence of different oscillatory modes in the system parameter plane

Development of Closed Loop Control Schemes for Constant Speed Operation of a Thyristorized Commutatorless Series Motor Drive

This paper presents the development of closed loop control schemes for constant speed mode operation of a thyristorized commutatorless series motor (CLSM) drive. Constant speed mode of operation of electrical drives with closed loop control is commonly required to be realized in most practical industrial drive applications. Two control schemes, one using only a speed loop and the other using an outer speed loop and an inner current loop, as are generally done with standard drives, are separately studied for this unconventional machine. The strategies are tested for different controller settings after simulating the entire speed-controlled drive, utilizing the analytical model. The simulation results are presented. An analytical guideline has been proposed to provide a starting point for designing stable speed and current controllers. The discussed schemes are finally implemented in the laboratory on a small prototype and experimental results are presented.

Constant power operation of a thyristorized commutatorless series motor

Constant power control of drives in general, like constant torque control, is often required in practical industrial applications. This paper describes the constant power operation of a thyristorized commutatorless series motor (CLSM), which is expected to be competitive for high power (MW ranges), normal speed (1500-3000 r/min) applications. The basic thyristorized CLSM drive, developed in recent past S. SenGupta, et al (2000) is described first along with its simplified analytical model K. Mukherjee, et al (2005). Described next is the system for achieving constant power control of this basic CLSM, where it is operated in conjunction with a front-end thyristorized rectifier. A suitable PI controller controls the front-end rectifier for achieving the constant power operation. The overall drive, including the basic CLSM, the front-end thyristorized rectifier and the respective controller, is modeled and simulated for predicting the performances. The simplified analytical model of the basic CLSM (K. Mukherjee, et al 2005) is utilized to model the overall drive and also for tuning of controller parameters. The discussed scheme is finally implemented in the laboratory and experimental results are validated with the simulation results.

Field simulation of linear induction motor showing speed dependence of phase-to-phase unbalance

In this paper, results of Field Analysis of a Circular Track SLIM have been shown for the whole speed range at rated voltage and rated frequency. Particular emphasis has been laid on the Phase-to-Phase Unbalance and the resulting ripple in propulsive force. It has been shown that the unbalance becomes more prominent as the speed of the motor increases. It has been shown that the unbalance becomes more prominent as the speed of the motor increases. The Thrust-Speed Characteristic and Current Speed Characteristic are drawn, and validated using the existing Equivalent Circuit Model.

Field simulation of linear induction machines illustrating the peak-to-peak ripple in propulsive force and its dependence on the length of the primary

In this paper, results of Finite Element Analysis of three Linear Induction Machines have been presented and compared. The three LIMs are identical in all respects except that the length of their primaries are different from one another. Due to magnetic asymmetry, it is noted that in all the LIMs, the induced EMF in the three primary windings have got unequal magnitude when supplied from a balanced three phase voltage source. This unbalance is reflected in the waveform of the Propulsive Force or Thrust. The thrust waveform shows a ripple component in addition to the average value. Since the ripple arises due to the magnetic asymmetry of the LIMs, the dominant frequency of the ripple is twice the supply frequency. It has been shown that in all the LIMs the amount of ripple increases with increase in speed of the machine. Also, for a given speed, the LIM whose primary is the longest has the lowest ripple component in its thrust.

Cogging torque reduction in surface mounted permanent magnet synchronous machine

This work examines minimization of cogging torque in surface mounted permanent magnet synchronous machines (SPMSM). Cogging torque arises due to magnetic interaction between slotted stator and permanent magnets at no load. Fractional slot winding machines have low value of cogging torque as dissimilar positions of the magnets increase the frequency of tooth harmonics. This work verifies two methods— pole shifting and proper selection of permanent magnet (PM) pole width—to reduce cogging torque in an 18-slot, 4-pole (fractional slot winding) SPMSM. These two methods reduce the harmonics and improve THD in back electromotive force (EMF). The proper selection of pole width also compensates the reduction in back EMF caused by pole shifting. Finite element method is used to verify the results.

A position sensor using analogue devices for a SR motor without shaft mounted encoder

In the present work an analogue method to find the unsaturated (air-gap) inductance of the energized phase of a SR motor, on-line, has been developed. The air-gap inductance is an indirect indicator to the rotor position and this fact has been used to decide the turn-on instant of the next phase by comparing it with a reference value of inductance that is equivalent to a reference position. The method eliminates the need for a shaft mounted encoder, has the advantage that it requires no extra inputs other than the voltage and current of the presently energized phase and does not depend on the level of saturation of the magnetic circuit. Further, the self inductance being quite large as compared to mutual inductance between phases, this method is more robust than the methods which depend on the measurement of mutual inductance for position sensing. The effect of saturation on self inductance has been taken care in an interesting and simple way. This is considered to be a significant contribution. Contrary to the methods found largely in literature the present method is implemented with analogue devices thereby eliminating the need for fast digital processors.