Michael W. Degner

Position estimation in induction machines utilizing rotor bar slot harmonics and carrier-frequency signal injection

This paper presents a simple and robust way of utilizing harmonic saliencies created by rotor and stator slotting, present in some induction machine designs, for the estimation of rotor position. The injection of a carrier-signal voltage, in addition to the fundamental excitation, produces a carrier-signal current that contains the desired spatial information. A closed-loop tracking observer is then used to extract this spatial information for the estimation of the rotor position. Due to its reliance on a spatial saliency and carrier-frequency signal injection, the technique is very robust over a wide speed range, including low and zero speed.

Discrete-Time Current Regulator Design for AC Machine Drives

This paper analyzes the behavior of discrete-time current regulators for ac machines operating at high ratios of fundamental-to-sampling frequencies, a situation common for high-speed automotive drives and large-traction drives. At high ratios of fundamental-to-sampling frequencies, highly oscillatory, or unstable, response can occur if the current regulator design does not properly incorporate the effects of the discrete nature of the controller, including delays between the sampling of signals and the application of the voltage commands through pulse-width modulation (PWM). This paper investigates these issues for different design methods and current regulator topologies. As part of this investigation, a simple discrete-time domain ac machine model is developed that includes the delays associated with PWM. This model is then used to design a discrete-time domain version of the complex vector PI current regulator that demonstrates improved response compared with the other regulators studied. Simulation and experimental results are provided to compare the performance, stability, and robustness of the current regulators analyzed.

Broken Rotor Bar Detection in Line-Fed Induction Machines Using Complex Wavelet Analysis of Startup Transients

Fault detection of line-connected induction machines using complex vector wavelets to analyze the transient stator currents during startup is proposed in this paper. When a machine is connected to the line, the startup transient is characterized by large stator (and rotor) currents, as well as by large slips (i.e., rotor speed significantly smaller than the excitation frequency). The stator current of machines with damaged rotors include large rotor speed dependent components during the startup transient. Such components, however, fade away or coincide with components not containing fault related information (e.g., saturation-induced components) once the machine reaches steady-state. Because of this, the startup transient provides an opportunity for performing diagnostics on the machine. The paper shows that the information contained in the startup transient signal can be effectively separated and detected using a complex vector wavelet transform.

Measuring, modeling and decoupling of saturation-induced saliencies in carrier signal injection-based sensorless AC drives

The focus of this paper is the measuring, modeling, and decoupling of saturation-induced saliencies in carrier signal injection based sensorless control. First techniques for the measurement of saturation-induced saliencies are presented. The goal of these measurements is to provide useful information on the position and magnitude of the various saturation-induced saliencies. Using the results from several different experimental measurements, models are developed explaining the source and behavior of the saturation-induced saliencies. The paper concludes by presenting methods for decoupling the effects caused by the parasitic saturation-induced saliencies, eliminating the errors that they cause in rotor position or flux angle estimation.

Using multiple saliencies for the estimation of flux, position, and velocity in AC machines

This paper presents an improved method of estimating the flux angle, rotor position and velocity by tracking the position of spatial saliencies in an AC machine. Specifically, a machine model is presented which accurately models the behavior of AC machines with multiple spatial harmonic saliencies. The effects of multiple spatial harmonic saliencies on the estimation of flux angle, position and velocity is analyzed, and methods are presented utilizing multiple spatial harmonic saliencies to provide wide bandwidth, high accuracy estimates of machine flux angle, rotor position and velocity.

Online diagnostics in inverter-fed induction machines using high-frequency signal injection

Fault diagnostics for induction machines using an injected high frequency carrier signal is presented and analyzed in this paper. Both stator winding fault and broken: rotor bar detection is covered. Measurement of the resulting high frequency negative sequence current is shown to be capable of detecting both types of faults at their incipient stage. Though sharing similar physical principles to techniques applied to line-connected machines, the use of a high frequency signal is shown to provide important advantages for inverter fed machines, such as providing the same performance and drastically reduced sensitivity to the working condition of the machine, i.e. torque and flux levels, and fundamental excitation frequency.

Accuracy, Bandwidth, and Stability Limits of Carrier-Signal-Injection-Based Sensorless Control Methods

This paper studies the performance limits of carrier-signal-injection-based sensorless control methods. When a high-frequency carrier-signal voltage is injected into a salient ac machine, two types of signals are created that can be used to estimate the rotor position: 1) the negative-sequence carrier-signal current and 2) the zero-sequence carrier-signal components. The limitations of ac machine sensorless control using each of these signals are analyzed in this paper. The analysis focuses on three key performance metrics: 1) the accuracy; 2) the bandwidth; and 3) the stability of the estimated position.

Magnet Temperature Estimation in Surface PM Machines Using High-Frequency Signal Injection

This paper proposes a method to estimate the magnet temperature in surface permanent-magnet machines using high-frequency carrier signal injection. The injection of a high-frequency signal, superimposed on the fundamental excitation, allows the estimation of the stator high-frequency impedance, which is a function of both the stator and rotor impedances. The temperature of the magnets is shown to have a significant weight on the overall stator high-frequency impedance, from which it can be estimated. The high-frequency carrier signal is injected intermittently in order to minimize potential adverse effects on the normal operation of the machine. This paper first explains the physics behind the magnet temperature dependence. Then, the principles of the method, as well as its practical implementation, are discussed. Experimental verification of the method is provided.

Online stator winding fault diagnosis in inverter-fed AC machines using high-frequency signal injection

The diagnosis of stator winding faults in inverter fed AC machines using an injected high frequency carrier signal is presented and analyzed in this paper. Measurement of the resulting high frequency negative sequence current (or alternatively of the negative sequence impedance) is used to detect turn faults at an incipient stage. Though sharing the same physical principles of similar techniques applied to line-connected machines, the use of a high frequency signal will be shown to present important advantages, such as providing the same performance almost independent of the fundamental excitation frequency, and drastically reducing the sensitivity to the working condition of the machine, i.e. torque and flux levels.

Static and dynamic behavior of saturation-induced saliencies and their effect on carrier-signal-based sensorless AC drives

This paper analyzes the origin and the behavior of saturation-induced saliencies in induction machines, and their influence on carrier signal injection based sensorless techniques. The modeling of saturation-induced saliencies is necessary for the estimation of flux position, while the minimization of their influence is desired for the estimation of rotor position. Specifically focusing on rotor position estimation, there are two ways to achieve this minimization, the first being the use of a machine design that reduces the magnitude of the undesired saturation-induced saliencies and the second being the compensation in the estimator of the undesired saturation-induced saliencies. The modeling of saturation-induced saliencies, not only statically, but also dynamically, i.e. when the operating point of the machine changes, is addressed by this paper.