Prof. Dr. Joachim Holtz
Editor-in-Chief
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Prof. Dr. Joachim Holtz |
IEEE Transactions on Industrial
Electronics
Volume 45, Number 6, December 1998
Overview Paper
Abstract - Concepts for sensorless position control of induction motor drives rely on anisotropic properties of the machine rotor. Such anisotropies can be incorporated as periodic variations of magnetic saliencies in various ways. The built-in spatial anisotropy is detected by injecting a high-frequency flux wave into the stator. The resulting stator current harmonics contain frequency components that depend on the rotor position. Models of the rotor saliency serve to extract the rotor position signal using phase-locked loop techniques. A different approach makes use of the parasitic effects that originate from the discrete winding structure of a cage rotor. It has the merit of providing high spatial resolution for incremental positioning without sensor. The practical implementation of sensorless position identification, and of a high-accuracy position control system are reported.
Special Section on Micromachining
Abstract - We present two designs for electrostatically actuated polysilicon relays with a stationary mercury micro-drop contact: a large displacement cantilever design and a comb drive design, both fabricated using MCNC's Multi-User MEMS Process (MUMPs). Microscale mercury relays combine the high density and batch fabrication of a microscale device with the quality and reliability of a mercury contact. Contact resistance of the devices were found to be around 1 kOhm in air with no attempt made to reduce the oxidation of the polysilicon and mercury surfaces. The devices can switch currents over 10 mA. Switching results are presented. The cantilever device is based on a curved electrode design, providing both relatively large force and large displacement of the tip, which contacts the mercury for switching. Nonlinear modeling of the beam movement is also provided. The comb drive device has the usual double-folded beam design, but has a mercury drop near its center. Fabrication of 10 micron diameter mercury drops as the last step of the processing sequence is also discussed.
Abstract - The characteristics of a fabricated micro mirror were determined using an optical measurement system. The system consisted of a helium-neon (He-Ne) laser, a PIN lateral-effect photodiode, and other fundamental optical elements. For testing we used a micro mirror array (1 x 4) in which each mirror was composed of a mirror plate, two torsional flexure hinges, two address electrodes, and two support posts. A mirror plate was designed to a size of 100 x 110 x 1.5 µm³ and the hinge size was 20 µm long, 5 µm width and 0.5 µm thick. The micro mirror array was fabricated using micromachining technology and an LIGA (Lithography Galvanoformung Abformung) - like process using nickel electroplating. The variation in the mirror's deflection angle with applied voltage was measured as a static characteristic. The downward threshold voltage of 0.5 µm thick hinge was 48V. The step response time, as a dynamic characteristic, was 21.8 µs when a 64V step voltage higher than the downward threshold voltage was applied to an address electrode. The lifetime of the fabricated micro mirror was tested for both uni- and bi-directional operation.
Abstract - This paper describes micromachined three planar inductors (a spiral type, a solenoid type and a toroidal meander-type) with electroplated nickel-iron permalloy cores which have been realized on a silicon wafer using micromachining techniques. The electrical properties between the fabricated inductors are compared and the related fabrication issues are discussed, emphasizing on the low temperature-CMOS-compatible process, the high current carrying capacity, the high magnetic flux density, the closed magnetic circuits, and the low product cost. The micromachined on-chip inductors can be applied for magnetic microelectromechanical systems (MEMS) devices such as micromotors, microactuators, microsensors, and integrated power converters, which envisages new micropower magnetics on a chip with integrated circuits (IC).
Abstract - Two applications of media exposure testing of pressure sensors with barrier coatings are presented. The examples are experiments used to simulate an automotive and a white goods application. Experimentation was performed on an apparatus that was developed specifically for the exposure of these devices with in situ output voltage measurement in organic or aqueous environments. The first example illustrates the swelling of fluorosilicone gels in fuels and establishes a solubility parameter for one fluorosilicone gel between 6 and 8 (cal/cm³)^1/2. While exposure to organic solutions has not been observed to cause catastophic failure of fluorosilicone gel filled devices, corrosion is accelerated in subsequent aqueous solution exposure. An additional experiment was used to simulate automotive exhaust gases and water by exposing devices to a fuel mixture followed by an acidic solution. The second experiment was performed to study corrosion under parylene coatings during exposure to an alkaline test solution for white goods applications. This process has been modeled as a cathodic delamination phenomenon. Acceleration factor expressions have been estimated considering parylene coating thickness, solution pH and applied device supply voltage as acceleration means. These expressions have been used to evaluate parylene coated pressure sensors against a benchmark lifetime requirement: 2000 hours of exposure in a NaOH/NaHCO3 buffer solution at 55 °C with a pH of 11 and a supply voltage of 5 Vdc applied continuously. For a 1 % failure rate, parylene coated pressure sensors survived approximately 500 hours, whereas an alternative, fluorosilicone gel over parylene C coating survived over 2000 hours. The lower limit for parylene C thickness was established through these media compatibility experiments to be 2 µm. Furthermore, these media exposure experiments and experiments that utilized such standard electrochemical techniques as polarization and chronoamperometry provided insight into the failure mechanisms and defined acceleration factors.
Abstract - This paper presents an innovative proximity sensor using microelectro- mechanical system(MEMS)technology. The proximity sensor works on the principle of fringe capacitance. The target object dose not need to be part of the measuring system and could be either a conductor or nonconductor. Modeling of the proximity sensor is performed and closed-form analytical solution is obtained for a ring-shaped sensing pattern. The proximity sensors could be batch fabricated using MEMS technology and the fabrication process is relatively simple. Measurement of the prototype sensors revealed promising results. The size of the proximity sensor could vary from a few hundred micrometers to the size of the substrate. The flexibility on sensor size, sensing patterns and sensing pattern geometrical parameters makes the sensor very versatile and capable of precision measurement of proximity in the range from micrometers to centimeters.The small size of the sensor makes it possible to surface mount the sensor in many space constrained places. This advantage is vital in many areas such as microelectriomechanical systems, microrobotics, precision engineering, machine automation, inspection tools and many other applications. The ability of the proximity sensor in measuring relative permittivity of materials also finds the sensor useful applications in biomedical and tissue engineering. In addition, this micro proximity sensor is an ideal building block for many types of sensors such as force, tactile, and flow sensors.
Power Electronics
Abstract - Current source inverter-based uninterruptible power supplies (UPS) and V/f controlled induction motor drives require sensing of two or more load voltages in addition to the dc voltage sensors used for protection purposes. This paper proposes a DSP-based load voltage control scheme that requires only information provided by the dc bus voltage sensor. Load voltage estimation is based on ac line voltage reconstruction by means of a recursive least square error algorithm that uses the information available on the dc bus and knowledge of the PWM gating pattern. Thus, the system minimizes the transducer count and therefore enhances reliability and ruggedness. Experimental results show that the load voltage can be reconstructed and its rms value controlled for a wide range of operating conditions with errors of at most 4%. Moreover, the use of the space vector modulation technique ensures a reduced load voltage harmonic distortion, which remains within the 5% range at nominal voltage and for all load conditions. The paper presents the DSP algorithms required for the operation of the system and key experimental results obtained on a three-phase 208 V, 60 Hz, 2 kVA prototype unit.
Abstract - Step-up/down ac voltage regulator is proposed, in which the transformer with tap changer and the PWM ac chopper are combined. The proposed regulator can step up or down input ac voltage, and reduces more harmonics of output voltage compared the conventional PWM regulator. The input current flows continuously in the proposed regulator, while it flows discontinuously in the conventional ones. Through digital calculation, several characteristics are investigated theoretically and compared with those of the conventional one.
Drive Control
Abstract - Permanent magnet ac motors generate parasitic torque pulsations, owing to several electromagnetic phenomena, such as imperfections in the motor and in the associated power inverter. Excitation of the mechanical resonances on the load side is generally the worst consequence of such disturbances: speed oscillations arise which may dramatically limit the performances in high precision applications. A compact model of the pulsating torque in sinusoidal permanent magnet motors is presented in this paper, based on a combination of theoretical analysis and experimental identification. Online identification algorithms and a compensation scheme are outlined as well. The control scheme autonomously identifies the parameters of the disturbance model, through simple closed loop motion experiments. The compensation is then applied as a modification of the output of the position controller. Experiments carried out on an industrial robot demonstrate the effectiveness of the control scheme in suppressing oscillations, both on the motor and on the load side.
Abstract - Magnetic Servo Levitation (MSL) is currently being investigated as an alternative to drive fast-tool servo systems that could overcome the range limitations inherent to piezoelectric driven devices while operating over a wide bandwidth. To control such systems, a feedback-linearized controller coupled with a Kalman filter has been previously described. Performance limitations that degrade tracking accuracy suggest the use of a more robust controller design approach, such as sliding mode control. Current literature on sliding mode deals almost exclusively with systems that are affine on the input, while the magnetic fast-tool servo is nonlinear on it when the control action is current command. This paper discusses a sliding mode-based controller that overcomes the aforementioned problem by defining a modified sliding condition to calculate control action. Experimental results demonstrate the feasibility of achieving long-range fast tracking with magnetically levitated devices by using sliding mode control.
Abstract - A newly designed driving circuit for the traveling-wave type ultrasonic motor (USM), which consists of a push-pull DC-DC power converter and a current-source two-phase parallel-resonant inverter, is presented in this study. Moreover, since the dynamic characteristics of the USM are difficult to obtain and the motor parameters are time-varying, a fuzzy neural network controller is proposed to control the USM drive system. In the proposed controller, a fuzzy model-following controller is implemented to control the rotor position of the USM, and an on-line trained neural network (NN) with variable learning rates is implemented to tune the output scaling factor of the fuzzy controller. To guarantee the convergence of tracking error, analytical methods based on a discrete-type Lyapunov function are proposed to determine the desired variable learning rates. From the experimental results, accurate tracking response can be obtained by the proposed controller, and the influences of parameter variations and external disturbances on the USM drive also can be reduced effectively.
Abstract - This paper reports about the successful electrostatic suspension of dielectric materials. In order to implement a stable suspension, the electrostatic forces exerted on a dielectric are actively controlled on the basis of the measured suspension gap lengths. The principle of electrostatic force generation for dielectrics is different from that for conductors. By utilizing a stator electrode pattern containing many boundaries over which potential differences exist, the suspension characteristics such as dynamic stability, suspension initiation time, and stiffness of lateral motion are greatly improved. The dynamic model of the suspension system and the influence of the resistivity of a dielectric on the closed-loop stability will be described, followed by the experimental apparatus and stabilizing controller. As dielectric objects, glass plates have been suspended electrostatically at a gap length of about 0.3 mm. Apart from the structure of the stator electrode, the suspension initiation time is also influenced by air humidity, glass type, supplied voltage and gap length, which has been experimentally explored. Experimental results on the lateral dynamic characteristics will be presented as well.
Letters to the Editor
Abstract - The shortcomings of the model presented by Wu are pointed out and an improved SPICE compatible equivalent circuit that dodges the limitations is presented. It is shown that the proposed model is useful in emulating the fluorescent lamp response to a change in excitation frequency.
Abstract - A novel method of on-line detection and frequency selective feedback to suppress the subharmonic frequency components in a naturally commutated cycloconverter is described. Simulation results show significant reduction of these components over a wide range of frequency and load power factor angle. The scheme also includes a loop for compensating the voltage distortion due to discontinuous current in a practical non-circulating type cycloconverter.
Abstract - This letter proposes the fuzzy logic-based fast gain scheduling (FFGS) controller for regulation problem in nonlinear systems. The proposed controller utilizes the fuzzy scheduling variable which reflects the derivative information on the original scheduling variable from the fuzzy preprocessor. It is applied to various nonlinear systems whereas the previously developed fast gain scheduling controller (Sureshbabu and Rugh, 1995) needs some requirements for available systems. By illustrating example, we conclude that the proposed control scheme provides smaller output error for the fast scheduling variable and shows robust property for the Gaussian noise (or exponentially distributed noise, uniformly distributed noise) added gain scheduling variable.
Abstract - Transient effects in electrical railways networks exhibit frequency variations due to nonlinearities in an otherwise approximately linear system. These effects cannot be analyzed by either pure time- or frequency domain analysis, but a mixed time-frequency analysis using wavelets is found particularly suitable in two practical application examples.
Call for Papers
25th Annual conference of the IEEE Industrial Electronics Society (IECON'99)