Scott D. Sudhoff

Admittance space stability analysis of power electronic systems

Power electronics based power distribution systems (PEDSs) are becoming increasingly common, particularly in marine and aerospace applications. Stability analysis of this class of systems is crucial due to the potential for negative impedance instability. Existing techniques of stability analysis introduce artificial conservativeness, are sensitive to component grouping, and at the same time do not explicitly address uncertainties and variations in operating point. A new stability criterion, which reduces artificial conservativeness and is also insensitive to component grouping is described. In addition, a means of readily establishing design specifications from an arbitrary stability criterion which specifically includes a provision to incorporate uncertainty, parameter variation, and nonlinearities is set forth. The method is presented in the context of a hardware test system and is experimentally validated.

A Power Electronic-Based Distribution Transformer

The distribution transformer has been in use by utilities throughout the twentieth century. Until now, it has consisted of a configuration of iron or steel cores and copper/aluminum coils, with mineral oil serving as both coolant and dielectric medium. Inherent in this type of construction are regulation, significant weight, losses, environmental concerns, and power quality issues. A new kind of distribution transformer is proposed for the twenty-first century, one that can be made self-regulating, oil-free, and able to correct power quality problems. A power electronic transformer has been analyzed, simulated, prototyped, and tested. Results of this effort, as well as the novel features of this new type of transformer, are discussed herein.

Performance characteristics of a cascaded two-level converter

A cascaded two-level power converter is proposed which utilizes two six-transistor inverters and is capable of producing voltages which are identical to those of three-level and four-level converters. Since the machine voltages are the same, the converter performance is the same as is verified through laboratory tests. The advantages and disadvantages of the proposed cascaded converter are explored. The proposed converter is simpler to construct and offers more nonredundant switching states per number of active semiconductors than standard multi-level converters.

Analysis and average-value modeling of line-commutated converter-synchronous machine systems

Analytical relationships are established which can be used to predict the steady-state characteristics of line-commutated AC-DC-converter-synchronous machine systems. In particular, basic relationships are established in which the average DC voltage and the average electromagnetic torque are related to the converter firing delay angle. It is shown that these average-value relationships predict the steady-state performance with significantly higher accuracy than the classical converter average-value equations in which the d-axis subtransient reactance is used as the commutating reactance. >

Transient and dynamic average-value modeling of synchronous machine fed load-commutated converters

A new average-value model of a synchronous machine fed load-commutated converter is set forth in which the stator dynamics are combined with the DC link dynamics. This model is shown to he extremely accurate in predicting system transients and in predicting frequency-domain characteristics such as the impedance looking into the synchronous machine fed load-commutated converter. The model is verified against a detailed computer simulation and against a hardware test system, thus providing a three-way comparison. The proposed model is shown to be much more accurate than models in which the stator dynamics are neglected.

Analytical Design Model for Surface-Mounted Permanent-Magnet Synchronous Machines

Design of electric machinery using population-based optimization requires a highly computationally efficient means of predicting the field distribution as well as the lumped-circuit model parameters. This paper proposes and validates a relatively straightforward analysis appropriate to this end.

A brushless exciter model incorporating multiple rectifier modes and Preisach's hysteresis theory

A brushless excitation system model is set forth that includes an average-value rectifier representation that is valid for all three rectification modes. Furthermore, magnetic hysteresis is incorporated into the d-axis of the excitation using Preisachs theory. The resulting model is very accurate and is ideal for situations where the exciters response is of particular interest. The models predictions are compared to experimental results.

Three-dimensional stability analysis of DC power electronics based systems

Power electronics based power distribution systems are becoming increasingly common, particularly in marine and aerospace applications. Stability analysis of this class of systems is crucial due to the potential for negative impedance instability. Existing techniques of stability analysis introduce artificial conservativeness, are sensitive to component grouping, and at the same time do not explicitly address uncertainties and variations in operating point. Recently, a new stability criterion which reduces artificial conservativeness and is also insensitive to component grouping has been set forth along with a means of readily establishing design specifications from an arbitrary stability criterion which specifically includes a provision to incorporate uncertainty, parameter variation, and nonlinearities. Therein, the method is used to develop a load admittance constraint based on a generalized source impedance. In this paper, that work is further explained and the converse problem, that of generating a constraint on the source impedance from the load admittance, is also illustrated.

Population-Based Design of Surface-Mounted Permanent-Magnet Synchronous Machines

Permanent-magnet synchronous machines can be designed to obtain high efficiency and high torque density. Population-based optimization methods such as genetic algorithms and particle swarm optimization are gaining acceptance as a means of optimizing the design of this class of machines. This paper builds on the literature by utilizing a computationally efficient machine analysis appropriate for use with population-based optimization methods that enables the consideration of a significantly larger search space than previously reported in the literature. It is also unique in that the relative performance of different parameter encoding and objective function formulations are considered.

An induction machine model for predicting inverter-machine interaction

The conventional qd induction motor model typically used in drive simulations is very inaccurate in predicting machine performance, except perhaps for the fundamental component of the current and the average torque near rated operating conditions. Predictions of current and torque ripple are often in error by a factor of two to five. This work sets forth an induction machine model specifically designed for use with inverter models to study machine-inverter interaction. Key features include stator and rotor leakage saturation as a function of current and magnetizing flux, distributed effects in the rotor circuits, and a highly computationally efficient implementation. The model is considerably more accurate than the traditional qd model, particularly in its ability to predict switching frequency phenomena. The predictions of the proposed model are compared to those of the standard qd model and to experimental measurements on a 37 kW induction motor drive.