Philip Jose

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 Outdated topics that waste time and mislead students are deleted.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.

An approach to connect ultracapacitor to fuel cell powered electric vehicle and emulating fuel cell electrical characteristics using switched mode converter

Future generation automobiles are being developed on fuel cell as the principal source of power generation in automobiles. Automobiles have fast changing load requirements like acceleration or sudden uphill, thus drastically increasing load torque. Fuel cell cannot respond to these fast changing load due to its slow dynamic response. A solution is to provide the additional energy required by increased load with secondary source of energy like ultracapacitor till fuel cell responds to the increased load current. This paper proposes a new approach to interface ultracapacitor with fuel cell as secondary source of energy using bi-directional synchronous buck converter. A novel scheme to control fuel cell terminal voltage is presented. This control scheme prevents any substantial droop in fuel cell terminal voltage during sudden load change or disturbance. The whole system with fuel cell model was simulated in SIMULINK for step change in load current. Simulation results show gradual transformation of fuel cell terminal voltage from initial steady state to final steady state with ultracapacitor providing energy during transients, hence avoiding the characteristic fuel cell voltage droop. This paper also proposes a novel method to emulate steady and dynamic electrical characteristics of fuel cell using DSP controlled buck converter.

A Novel Carrier-Based PWM Scheme for Matrix Converters that is Easy to Implement

Since the inception of matrix converter concept, various modulation schemes have been proposed for its control. But the explanation of matrix converter operation is complex, and so is the control methodology of it. In this paper a 3-phase to 3-phase matrix converter is explained from the point of view of multi-level inverter topology, and a novel modulation scheme is proposed where the need for sector information and corresponding look-up tables is avoided

A novel bidirectional DC-DC converter with ZVS and interleaving for dual voltage systems in automobiles

This paper presents a novel bidirectional DC-DC converter for 42V/14V dual voltage systems in automobiles. The converter uses clamped zero voltage switching to minimize losses, and interleaving for reduced current ripple. SABER simulations are presented to verify the design. The simulation results are confirmed by hardware implementation.

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.

A novel ZVS bidirectional Cuk converter for dual voltage systems in automobiles

The automotive industry is heading towards a higher electrical voltage system of 42 V for next generation vehicles. In the interim, there will be dual voltage systems which would require a bi-directional dc-dc converter to regulate power flow between the 42 V and 14 V buses. Cuk converter with integrated magnetics has the advantage of zero ripple in both input and output currents, and also can handle power in both directions. This paper proposes a simple zero voltage switching scheme for the Cuk converter using only passive components. ZVS is effective at all loads, including reverse power flow, and thus improves the overall converter efficiency. The paper discusses the design methodology for the zero-ripple converter and the synthesis of the ZVS scheme. Computer simulations are used to verify the design.

An instructional laboratory for the revival of electric machines and drives courses

This paper describes the developments at the University of Minnesota of new approach in teaching of electric drives, focusing on the associate state-of-the-art laboratory. The mission of these developments is to nationally revitalize courses in industrially and strategically vital fields of electric drives (and power electronics). This is accomplished by making these courses appealing to students (undergraduate enrollments have significantly increased subsequent to adopting these approaches) where they receive a first-rate education in just one undergraduate course in a way that ensures a seamless continuity to advanced courses. The laboratory is based on a dSPACE development board and several custom designed power converter boards and electric motors, working on a 42 V DC-bus voltage system.

A building-block-based power electronics instructional laboratory

This paper describes a new power electronics instructional laboratory based on the building block (switching pole) methodology. This methodology provides a common basis for describing all practical converter topologies and gives the student a unified top-down presentation of power electronic converters. The novel features of this laboratory include: a unifying building-block methodology (the Power Pole), tight coupling with lectures, use of low voltages (<50 V) for enhanced safety, and ease of use and low cost. A key component of the laboratory is the use of a reconfigurable circuit board (the Power Pole board) which contains the Power Pole circuit as well as on-board isolated drive circuits, PWM generation, fault protection, output filter, and switched load. The detailed circuit board layout is described and several examples of its use are presented.

A novel H/sub /spl infin// based controller for wind turbine applications operating under unbalanced voltage conditions

Doubly-fed induction generator (DFIG) based wind turbines are highly susceptible to grid voltage imbalances. Normally the turbines are disconnected from the grid in the event of even moderate imbalances which contribute to poor utilization of the turbine. In this paper, a control strategy to use the grid-side converter in the rotor circuit of the DFIG to compensate for the grid voltage imbalance is presented. A robust Hinfin controller is synthesized to minimize the adverse effects of the imbalances even while providing reactive power support to the grid. The control scheme is tested on a small-scale DFIG prototype and the results are presented

Explaining synthesis of three-phase sinusoidal voltages using SV-PWM in the first power electronics course

In undergraduate power electronics courses, students are taught the sinusoidal pulse-width-modulation (Sine- PWM) principle to synthesize three-phase sinusoidal voltages. It is well known that the space vector PWM approach (SV-PWM) utilizes the available dc-bus voltage of the inverter to its maximum, resulting in an improved voltage capability of nearly 15% compared to Sine-PWM. However, SV-PWM is not discussed in the first course due to its perceived complexity in explanation and implementation. This paper describes how SV- PWM can be discussed in a basic course on power electronics. This paper can be categorized in thee parts. The first part reviews a new approach that uses a switching power-pole as the building block of switch-mode converters (1). It describes the choice of the carrier signal for PWM that is better suited for this building-block approach in synthesizing dc and ac outputs. It also shows the limitation of Sine-PWM for three- phase synthesis. The second part describes the reasons and the approach for using space vector PWM (SV-PWM) in synthesizing three-phase outputs, and how it utilizes the dc- bus voltage of the inverter to its maximum. The third part explains how the carrier-based modulation, like in Sine-PWM, can be used for implementing SV-PWM. This digest provides the framework and further details would be provided in the