Timothy M. Rowan

Bio: Timothy M. Rowan is an academic researcher from University of Wisconsin-Madison. The author has contributed to research in topics: Direct torque control & Stator. The author has an hindex of 14, co-authored 18 publications receiving 1014 citations.

A New Synchronous Current Regulator and an Analysis of Current-Regulated PWM Inverters

Abstract: Detailed models are presented for the stationary and synchronous sine-triangle current regulators. Analytical and test results are compared for purposes of model verification and regulator evaluation. The results demonstrate the limitations of the two most often used current regulators and the robustness of the synchronous current regulator. The stationary sine-triangle and hysteretic current regulators are shown to have steady-state characteristics that depend on slip, operating frequency, and motor impedance. In contrast the synchronous regulator, because it lacks these dependencies, exhibits ideal steady-state current regulator characteristics without sacrificing bandwidth. Moreover, the complexities traditionally associated with the synchronous regulator are overcome with a simple equivalent implementation.

A Quantitative Analysis of Induction Motor Performance Improvement by SCR Voltage Control

Abstract: Minimum input power and maximum efficiency operation occur at characteristic slip values which can be realized for any induction motor operating at part load by properly adjusting the amplitude of the applied stator terminal voltages. These two criteria are shown to yield perceptibly different results when the motor is driven from a silicon-controlled rectifier (SCR) voltage controller. In addition, it is demonstrated that a constant power factor controller results in an operating regime which is substantially poorer than operation at either minimum input power or maximum efficiency. It is further shown that minimum stator current and minimum power factor angle criteria yield results which are closer to the ideal than the constant power factor controller.

Operation of Naturally Sampled Current Regulators in the Transition Mode

Abstract: A fundamental component model of current-regulated naturally sampled PWM inverters operating in the pulse-dropping mode is proposed. Analytical and test results are compared for purposes of model verification and regulator evaluation. The results demonstrate the problems with the classical (stationary reference frame) current regulator that occur in this region of operation. In contrast, the synchronous reference frame regulator is shown to have ideal steady-state response in this region.

Slip control based on sensing voltage fed to an induction motor

Abstract: An electronic motor drive for vector control of an induction motor controls slip and operating frequency in response to changes in stator voltage. The drive includes a torque control loop, a flux control loop and a frequency control loop which includes slip control in response to a voltage difference. In the constant horsepower range, above base speed, slip is controlled in response to an error between a d-axis reference voltage that is sampled at base speed and a d-axis feedback voltage that is sensed when the motor is operating above base speed. Flux-weakening is provided in response to an error between a q-axis reference voltage that is sensed when the motor is operating at base speed and a q-axis feedback voltage that is sensed when the motor is operating above speed.

A quantitative analysis of induction motor performance improvement by SCR voltage control

Abstract: Minimum input power and maximum efficiency operation occur at characteristic slip values which can be realized for any induction motor operating at part load by properly adjusting the amplitude of the applied stator terminal voltages. It is shown that these two criterion yield perceptibly different results when the motor is driven from an SCR voltage controller. In addition, it is demonstrated that a constant power factor controller results in an operating regime which is substantially poorer than operation at either minimum input power or maximum efficiency. It is further shown that minimum stator current and minimum power factor angle criterion yield results which are closer to the ideal than the constant power factor controller.

Current control techniques for three-phase voltage-source PWM converters: a survey

Abstract: The aim of this paper is to present a review of current control techniques for three-phase voltage-source pulsewidth modulated converters. Various techniques, different in concept, have been described in two main groups: linear and nonlinear. The first includes proportional integral (stationary and synchronous) and state feedback controllers, and predictive techniques with constant switching frequency. The second comprises bang-bang (hysteresis, delta modulation) controllers and predictive controllers with on-line optimization. New trends in current control-neural networks and fuzzy-logic-based controllers-are discussed, as well. Selected oscillograms accompany the presentation in order to illustrate properties of the described controller groups.

Stationary frame current regulation of PWM inverters with zero steady-state error

Abstract: Current regulators for AC inverters are commonly categorized as hysteresis, linear PI, or deadbeat predictive regulators, with a further sub-classification into stationary ABC frame and synchronous d-q frame implementations. Synchronous frame regulators are generally accepted to have a better performance than stationary frame regulators, as they operate on DC quantities and hence can eliminate steady-state errors. This paper establishes a theoretical connection between these two classes of regulators and proposes a new type of stationary frame regulator, the P+Resonant regulator, which achieves the same transient and steady-state performance as a synchronous frame PI regulator. The new regulator is applicable to both single-phase and three phase inverters.

Stationary frame current regulation of PWM inverters with zero steady state error

Abstract: Current regulators for AC inverters are commonly categorised as hysteresis, linear PI or deadbeat predictive, with a further subclassification into stationary ABC frame and synchronous DQ frame implementations. Synchronous frame controllers are generally accepted to have a better performance than stationary frame controllers do, as they operate on DC quantities and hence can eliminate steady state errors. This paper establishes a theoretical connection between these two classes of regulators and proposes a new type of stationary frame controller, which achieves the same steady state performance as a synchronous frame controller. The new controller is applicable to both single phase and three phase inverters.

Relationship between space-vector modulation and three-phase carrier-based PWM: a comprehensive analysis [three-phase inverters]

Abstract: This paper comprehensively analyzes the relationship between space-vector modulation and three-phase carrier-based pulse width modulation (PWM). The relationships involved, such as the relationship between modulation signals (including zero-sequence component and fundamental components) and space vectors, the relationship between the modulation signals and the space-vector sectors, the relationship between the switching pattern of space-vector modulation and the type of carrier, and the relationship between the distribution of zero vectors and different zero-sequence signal are systematically established. All the relationships provide a bidirectional bridge for the transformation between carrier-based PWM modulators and space-vector modulation modulators. It is shown that all the drawn conclusions are independent of the load type. Furthermore, the implementations of both space-vector modulation and carrier-based PWM in a closed-loop feedback converter are discussed.

Stationary-frame generalized integrators for current control of active power filters with zero steady-state error for current harmonics of concern under unbalanced and distorted operating conditions

Abstract: The paper proposes several concepts of integrators for sinusoidal signals. Parallel and series associations of the basic PI units using the stationary frame generalized integrators are used for current control of active power filters. Zero steady state error for the concerned current harmonics are realized, with reduced computation, under unbalanced utility or load conditions. Designing of the PI constants, digital realization of the generalized integrators, as well as compensation of the computation delay etc. are studied. Extensive test results from a 10 kW active power filter prototype are demonstrated.