Steven D. Pekarek

Parametric average-value model of synchronous machine-rectifier systems

A new average-value model of a rectifier circuit in a synchronous-machine-fed rectifier system is set forth. In the proposed approach, a proper state model of the synchronous machine in the qd-rotor reference frame is used, whereas the rectifier/dc-link dynamics are represented using a suitable proper transfer function and a set of nonlinear algebraic functions that are obtained from the detailed model using numerical averaging. The new model is compared to a detailed simulation as well as to measured data and is shown to be very accurate in predicting the large-signal time-domain transients as well as small-signal frequency-domain characteristics.

MPC of Switching in a Boost Converter Using a Hybrid State Model With a Sliding Mode Observer

In this paper, a model of a DC-DC (boost) converter is first expressed as a hybrid/switched/variable-structure system state model for the purpose of applying recently developed hybrid optimal control theory to control switching in a boost converter. Switching control is achieved by forming the embedded form of the hybrid state model, which enables the derivation of a control that solves for the switching function that minimizes a user-defined performance index. This approach eliminates the need to form average-value models and provides flexibility to balance competing objectives through appropriate weighting of individual terms in the performance index. Since, in practical situations, both the source voltage and the load resistance vary with time in unknown and unmeasurable ways, we introduce a sliding mode observer based on an enlarged state model which allows implicit estimation of the unknown variables. The combined optimal switching control and sliding mode observer are applied to a boost converter in which several nonidealities and losses are represented. The results of time-domain simulation and hardware experiments are used to validate and compare the response of the hybrid optimal control-sliding mode observer to that of a traditional current-mode control strategy.

A Comparison of Nodal- and Mesh-Based Magnetic Equivalent Circuit Models

The magnetic equivalent circuit (MEC) technique is a powerful analysis and design tool that combines relative accuracy with moderate computational effort. In this paper, a nodal-based MEC formulation and a mesh-based MEC formulation of a magnetic system are compared. The Newton-Raphson algorithm is used to solve the algebraic system, and to draw conclusions about the computational efficiency of the two formulations under linear and nonlinear operation. Although the two formulations exhibit similar performance under linear operating conditions, the performance of the mesh-based model is significantly better than that of the nodal-based model under nonlinear operation.

Modeling of Salient-Pole Wound-Rotor Synchronous Machines for Population-Based Design

In recent years, population-based methods (evolutionary algorithms, particle swarm methods, etc.) have emerged as an effective tool for component and system design. Although relatively straightforward to apply, to capitalize on their potential, one must be able to explore a large design space. Herein, a magnetic equivalent circuit model is described to enable large-design-space exploration of salient-pole wound-rotor synchronous machine drive systems. Specifically, the model has been derived to evaluate machines with an arbitrary number of poles, stator slots (integer slots/pole/phase), winding layout, magnetic material, and a wide range of stator and rotor geometries. In addition, the model and solution technique have been structured to minimize the computational effort. An important attribute of the model is that saturation is handled with relatively few iterations and without the need for a relaxation factor to obtain convergence.

A Medium Voltage DC Testbed for ship power system research

Medium voltage dc distribution systems are currently of interest for future naval warships. In order to provide hardware validation for research associated with the development of these systems, a low power Medium Voltage DC Testbed (MVDCT) is being constructed. This paper documents the system being constructed and provides some initial test results.

An efficient multirate Simulation technique for power-electronic-based systems

A novel multirate method of simulating power-electronic-based systems containing a wide range of time scales is presented. In this method, any suitable integration algorithm, with fixed or variable time-step, can be applied to the fast and/or slow subsystems. The subsystems exchange coupling variables at a communication interval that can be fixed or varied dynamically depending upon the state of the system variables. The proposed multirate method is applied to two example power systems that include power-electronic subsystems. Increases in simulation speed of 183-281% over established single-rate integration algorithms are demonstrated.

Fast procedure for constructing an accurate dynamic average-value model of synchronous machine-rectifier systems

The analytical derivation of the average-value models (AVMs) for synchronous-machine-fed rectifier systems depends on many factors and is challenging in general. Various models presented in the literature rely on a single operating mode and a dc filter configuration. A recently proposed parametric approach utilizes a detailed simulation as a basis to establish an AVM that uses a proper full-order qd generator model. This paper presents a procedure to extract the appropriate nonlinear algebraic functions to represent the rectifier averaged behavior. In contrast to existing methods, the proposed procedure does not require significant analytical derivations and/or computational resources and results in a highly accurate dynamic AVM. The proposed methodology is validated with the results of detailed simulation and hardware experiment, and is shown to be very accurate in predicting the large-signal time-domain transients as well as the small-signal frequency-domain characteristics.

Versatile hardware and software tools for educating students in power electronics

A new power electronics laboratory has been constructed at the University of Missouri-Rolla. Key components of the laboratory are a set of custom-designed hardware and software tools. The novel hardware tools include five mobile power electronics testbeds that each contain the semiconductor devices, gate-drive boards, voltage and current sensors, and computer interface connections required to study a wide range of circuit topologies and control techniques. Novel software tools include a set of virtual instruments used for control, data capture, and data analysis. A description of these tools, along with their use in power electronics courses, laboratory exercises, and student research projects, is presented.

Performance Indices for the Dynamic Performance of FACTS and FACTS with Energy Storage

The integration of energy storage into flexible AC transmission systems (FACTS) devices leads to increased controller flexibility by providing decentralized active power capabilities. Combined FACTS/energy storage systems (ESS) can improve power flow control, oscillation damping, and voltage control. This article presents performance indices that have been developed for quantifying the active power, reactive power, and voltage performance enhancement of different FACTS combinations. The dynamic responses of a shunt (StatCom), a StatCom/battery energy storage system (BESS), a synchronous series compensator (SSSC), a SSSC/BESS, and a unified power flow controller (UPFC) are presented to support the validity of the developed indices.

Incorporating Motion in Mesh-Based Magnetic Equivalent Circuits

Recent research has compared the numerical efficiency of magnetic equivalent circuit (MEC) models based upon Kirchhoffs voltage law (mesh equations) and Kirchhoffs current law (nodal equations). For stationary magnetic components, it was shown that mesh-based methods converge in significantly fewer iterations. Although the numerical advantages would seemingly apply to electric machines, two issues have limited the application of mesh-based MEC models to electric machines. With movement, the number of meshes (unlike the number of nodes) is position dependent. Additionally, the loss of an airgap element creates an infinite reluctance. In this paper, both issues are addressed. Specifically, it is first shown that a relatively straightforward algorithm can be used to dynamically update meshes with rotor position. In addition, it is shown that the mesh model remains stable for very large values of tube reluctance. Tube reluctance values that are large enough to cause numerical issues can be easily avoided by excluding a very narrow range of rotor positions. Based upon these results, a mesh-based MEC model of a wound-rotor synchronous machine is developed and is shown to provide a significant advantage over its nodal-based model equivalent.