Gerald Francis

Future home uninterruptible renewable energy system with vehicle-to-grid technology

This paper presents the structure and capabilities of a small, grid-interactive distributed energy resource system comprised of a photovoltaic source, plug-in hybrid electric vehicle, and various local loads. Implemented at the residential level, this system, with a plug-in hybrid electrical vehicle, has the ability to isolate a house from the utility grid (intentionally due to a fault or other abnormal grid conditions), work in the standalone mode, synchronize and reconnect to the utility grid, without load power interruptions. Plug-in hybrid electrical vehicles, with a built-in bidirectional power converter, present the opportunity for demand-response operation in the grid connected mode, whereas in the islanded mode, it can perform frequency and voltage regulation of the power bus. In this paper, system structure and modes of operation are described, and measured results are presented for two main modes of operation and mode transitions.

On the Ac stability of high power factor three-phase rectifiers

This paper presents a comprehensive study of the ac stability of high power factor rectifiers, proposing a new stability criterion to assess this condition under constant power load dynamics. Specifically, based on the multivariable generalized Nyquist stability criterion developed by MacFarlane and Postlethwaite, this paper shows how the fundamental stability problem at such ac interface is indeed reduced to a single-input single-output (SISO) case. It is shown that the ac stability is fully determined by the SISO return-ratio of the d-d channel—or the power transfer channel of the desired d-q frame alignment; that is, the stability is determined by the d-d channel input and output impedances. Correspondingly, it is shown that the q-q channel trajectory on the complex plane is such that it cannot encircle the critical point (−1+j0) and therefore be the cause of instability. The ac stability at the input terminals of the rectifier can then be fully assessed using the standard SISO Nyquist stability theorem, in sheer duality of Middlebrooks criterion for dc-dc converters. Simulation results are used to verify and appraise the implications of the proposed ac system stability criterion.

An algorithm and implementation system for measuring impedance in the D-Q domain

As power electronics infiltrates the electric power distribution and conversion systems, stability issues become increasingly significant. The risk of instability due to the use of constant power loads stems from the implementation of controlled output power conversion systems. In three phase converters, these issues are difficult to measure. Although there have been developments in the determination of system stability at interfaces due to stability, a framework to perform measurements necessary for such a determination has not been fully developed. This paper presents a method to measure three phase impedances in the D-Q rotating reference frame for three phase AC systems and demonstrates the successful implementation and operation of such a system. Results are shown measuring a three phase passive load with a 2 kW source.

Ac stability of high power factor multi-pulse rectifiers

This paper studies the ac stability of high power factor multi-pulse rectifiers, proposing a new stability criterion to assess this condition under constant power load dynamics. Specifically, based on the multivariable generalized Nyquist stability criterion developed by MacFarlane and Postlethwaite, this paper shows how the fundamental stability problem at such ac interface is reduced to a single-input single-output (SISO) case. It is shown that the ac stability is fully determined by the SISO return-ratio of the d-d channel—or the power transfer channel of the desired d-q frame alignment; that is, the stability is solely determined by the d-d channel input and output impedances. Correspondingly, it is shown that the q-q channel trajectory on the complex plane is such that it cannot encircle the critical point (−1+j0) and be the cause of instability. Furthermore, it is shown that the multi-pulse rectifier stability can be indistinctively determined at either ac or dc terminals, which has great significance from a practical point of view. Simulation and experimental results are used to verify the implications of the proposed stability criterion.

Model-Based Digital Generator Control Unit for a Variable Frequency Synchronous Generator With Brushless Exciter

This paper presents the design and implementation of a digital signal processor (DSP)-based generator control unit (GCU) for a variable frequency synchronous generator with brush-less exciter. A novel model-based control algorithm is proposed to better account for the wide operating frequency range and various load conditions. In addition to the model-based inner-loop exciter field current regulator and outer-loop generator voltage regulator, the control algorithm also adopts a generator-model-based d-axis current feed-forward loop to compensate for the load disturbance. Simulation and test results show a considerable performance improvement for the new controller when compared to the existing controllers, including better dynamics, better damping stability margin, and more uniform response over the operating range.

Dynamic interactions in hybrid ac/dc electronic power distribution systems

Hybrid electronic power distribution systems have majority of loads interfaced to energy sources through power electronics converters. Furthermore, all alternative, sustainable, and distributed energy sources can only be connected to electric grid through power electronics equipment. However, one of the main challenges in designing and developing of these hybrid ac/dc systems has been modeling and analysis of dynamic interactions between converters at the synchronous and higher frequencies. In order to address these problems, this paper employs terminal-behavioral modeling of power converters as possible methodology for analysis, system-level design, stability, and subsystem interactions study. Some simulation and experimental results are both shown for model verification and validation purposes.

Design and Evaluation of a 33-kW PEBB Module for Distributed Power Electronics Conversion Systems

The power electronics building blocks (PEBB) concept has evolved into an alternative to conventional power converter design, and many industries have adopted this concept. This paper outlines the design process of a 33 kW PEBB, from power stage design and component selection to the design of the hardware manager board. The hardware manager encompasses the intelligence behind the PEBB, managing control commands and sensing functions, as well as local protection schemes. Finally, the paper shows thorough experimental evaluation of the PEBB module in standalone and system tests

Virtual Prototyping of Universal Control Architecture Systems by means of Processor in the Loop Technology

This paper presents the use of virtual prototyping and processor in the loop (PIL) technology for the design and synthesis of digital control systems for power electronics applications. Specifically, the proposed method simulates the converter power stage using Virtual Test Bed (VTB) and controls it using the actual converter digital controller-a hybrid DSP/FPGA control system-interfaced through the PCI bus of the host computer. The paper presents the VTB PIL model developed as interface, the PIL simulation strategy, and experimental PIL simulations results with a three-phase power converter modeled in VTB. From these results the great flexibility attained by the proposed design methodology is ascertained.

A power electronics communication protocol for distributed digital control architectures

This paper presents a distributed control system architecture for power electronics conversion systems. Control partitioning is described and a two-level control hierarchy is proposed. Specifically, a hardware manager-controlling the actual power conversion process-, and an application manager, hardware independent Universal Controller are introduced and implemented. A detailed description of these controllers is given using a voltage-source inverter as test system. Additionally, a high-speed real-time protocol (PESNet) is introduced for communication purposes of the proposed distributed control architecture. The synchronous nature of the protocol is described in addition to its data types and commands. From the analysis presented the usage of such an architecture and controllers for reconfigurable zonal distribution systems becomes apparent.

A universal controller for distributed control of power electronics systems in electric ships

This paper presents a distributed control system architecture for power electronics conversion systems. Control partitioning is explored under this scheme by analyzing spatial, temporal, and functional aspects of a family of power converters, finally proposing a two level control hierarchy. Specifically, a hardware manager-controlling the actual power conversion process, and an application manager, hardware independent universal controller are introduced and implemented. A detailed description of these controllers is given using a voltage-source inverter as test system. Additionally, a high-speed real-time protocol (PESNet) is introduced for communication purposes of the proposed distributed control architecture. From the analysis presented the usage of such an architecture and controllers for reconfigurable zonal distribution systems becomes apparent.