Amit Kumar Jain

Restructuring of first courses in power electronics and electric drives that integrates digital control

Since 1994, the University of Minnesota has been undertaking a long overdue restructuring of power electronics and electric machines/drives courses. This restructuring allows digital control to be integrated into first courses, thereby teaching students what they need to learn, making these courses appealing, and providing a seamless continuity to advanced courses. By a concise presentation in just two undergraduate courses, this restructuring motivates students to take related courses in programmable logic controllers, microcontrollers and digital signal processor applications. This ensures a first-rate education that is meaningful in the workplace as well as in graduate education leading to a research and development oriented career. This restructuring has several components to it. Outdated topics that waste time and mislead students are deleted. To integrate control in the first courses, unique approaches are developed to convey information more effectively. In the first course in power electronics, a building block is identified in commonly used power converter topologies in order to unify their analysis. In the field of electric drives, the use of space vectors is introduced on a physical basis to describe operation of ac machines in steady state in the first course, and to discuss their optimum control under dynamic conditions in the advanced course. Appropriate simulation software and software-reconfigurable hardware laboratories using a DSP-based rapid prototyping tool are used to support the analytical discussion.

Nonlinear controllers for fast Voltage regulation using STATCOMs

This paper presents system modeling and nonlinear control design of static compensators (STATCOMs) for fast voltage regulation in the presence of load uncertainty and voltage flicker. A simplified power distribution system is modeled using ideas similar to field oriented control of three phase ac machines. Zero dynamics of the system show that the system is nonminimum phase for certain operating conditions, thus, imposing restrictions on the achievable dynamic response. The control design involves estimation of the load conductance via a gradient-based estimator, and state feedback control to reach an equilibrium point established by the estimated load conductance and knowledge of system parameters. A Lyapunov function is used to establish asymptotic stability in the large for the closed-loop system. To account for practical implementation issues, a new controller relying on feedback of a readily measurable state is also proposed. Simulations results are presented to show efficacy of both controllers with regard to bus voltage regulation and suppression of voltage flicker.

Teaching utility applications of power electronics in a first course on power systems

Power electronics applications in utility systems are growing very rapidly and promise to change the landscape of future power systems in terms of generation, operation, and control. This paper attempts to justify the importance of introducing undergraduates to these applications in the first course in power systems, so they become familiar with current and future practices and technologies. It presents a roadmap of doing so, taking a top-down approach where first various utility applications of power electronics are briefly described along with the role of power electronics as an interface, and then the power electronics systems are discussed in appropriate detail to fulfill these roles.

Study of new stator pole geometry for improvement of SRM torque profile

In this paper, new stator pole tip geometry has been investigated. The new stator pole tip and conventional stator pole tip SRM are analyzed using finite element analysis (FEA). It is observed that a small change in stator pole tip geometry results in a significant change in the characteristics of motor. The new stator pole tip results in more flux linkages and hence more saturation of motor at same current. The new pole tip is further analyzed by constructing 5 designs of the SRM with different pole tip parameters and doing a single phase and two-phase FEA analysis. It is observed that with certain pole tip parameters, the single phase torque has a smooth profile. Using the FEA data, torque profile for two phase operation of motor, is generated for the above 5 designs. Minimum torque ripple obtained for all the designs are compared. It is observed that by choosing the stator pole tip parameter properly, the torque ripple can be optimized for a particular motor operation

Novel converter topology and algorithm for simultaneous charging and individual cell balancing of multiple Li-ion batteries

This work presents a novel lithium-ion battery charger based on pulse charging technique. A central power supply acting as a controlled current source is sequentially connected in parallel with different batteries through an array of switches. A forward converter realizes the controlled current source. Magnetics are restricted to the inductor and transformer of the forward converter. Each battery contains plurality of Li-ion cells, the number being determined by the voltage level of the application. The switch array at the output provides charging and discharging pulses to individual cells. Charging algorithm expected to increase the lifetime and performance of Li-ion cells along with charge balancing for applications involving series string of Li-ion cells is presented. Simulation results to demonstrate the proposed methodology are presented.

Nonlinear controller for a single phase one quadrant unity power factor rectifier

In this paper, a nonlinear control strategy is designed for a single quadrant unity power factor rectifier. Asymptotic (exponential) stability is demonstrated via a Lyapunov stability argument.

System modeling and control design for fast voltage regulation using STATCOMs

Fast voltage regulation using static compensators requires a dynamic system model that is valid on an instantaneous basis. This paper presents a general modeling strategy that allows design of fast voltage regulation controller while accounting for system parameters. The co-ordinate transform used to model the system facilitates extraction of linearized system dynamics with the help of circuit simulators. It is shown that the problem of voltage regulation using instantaneous reactive current is non-minimum phase for certain operating conditions, thereby limiting achievable dynamic response irrespective of the control design method. Simulation results with a controller designed using input output bode plots are presented to illustrate efficacy of the proposed method.

Local Discontinuous Galerkin Formulations for Heat Conduction Problems Involving High Gradients and Imperfect Contact Surfaces

A Local Discontinuous Galerkin (LDG) method is described here which provides a unied mathematical setting and framework for solving various kinds of heat conduction problems to include thermal contact conductance/resistance, sharp/high gradient problems and the like. For these applications, the LDG method does not require much modications to the basic formulation or the need to employ ad hoc approaches as with the Continuous Galerkin (CG) nite element methods. In this paper, we describe the LDG formulation for elliptic heat conduction problems which is then extended to parabolic problems. The advantages of the LDG method over the CG method are shown using two classes of problems|problems involving sharp/high gradients, and imperfect contact between surfaces. So far, interface/gap elements have been primarily used to model the imperfect contact between two surfaces to solve thermal contact resistance problems. The LDG method eliminates the use of interface/gap elements and provides a high degree of accuracy. It is further shown in the problems involving sharp/high gradients, that the LDG method is less expensive (requires less number of degrees of freedom) as compared to the CG method to capture the peak value of the gradient. Several illustrative 1-D/2-D applications highlight the eectiv eness of the present the LDG formulation.

A novel power distribution system using a central buck-based current source for multiple individually regulated outputs

This paper presents a novel power distribution system for supplying multiple individually regulated outputs from a central power supply acting as a controlled current source that contains all the magnetic components. The individual output voltages are filtered by means of capacitors. The current source is realized with a buck converter. The outputs are connected to the current source on a time-shared basis and regulated individually by constant frequency PWM. The buck converter is controlled using average current control. Simulation results and experimental results from a laboratory prototype are presented.

Parabolic Heat Conduction Specialized Applications Involving Imperfect Contact Surfaces: Local Discontinuous Galerkin Finite Element Method—Part 2

Parabolic heat conduction specialized applications involving imperfect thermal contact surfaces are analyzed via the Local Discontinuous Galerkin (LDG) finite element method. In this paper, we describe the advantages of the LDG finite element formulation over the traditional continuous Galerkin (CG) finite element method for modeling imperfect thermal contact between surfaces. To-date, mostly interface/gap elements have been primarily used to model the imperfect contact between two surfaces to solve thermal contact resistance problems. The LDG method eliminates the use of such interface/gap elements and provides a higher degree of accuracy. Several illustrative 2-D applications highlight the effectiveness of the present LDG finite element formulations for this class of problems.