Roland R. Seebacher

Low cost speed control for single phase induction motors - comparing different approaches with regard to efficiency

Operating single phase fed motors across a wide range of speed and load single phase fed motors across a wide range of speed and load with high efficiency is of growing interest. The paper at hand presents an investigation into the efficiency of different low cost variable speed drive concepts (namely phase control, integral (half) cycle control and integral switched cycle control) based on capacitor run single phase induction motors. Simulations and measurements concerning for example the efficiency achieved and the speed-torque characteristics of the different concepts are presented. Subsequently, ideas for improvements (selecting a different run capacitor, lowering the inrush current and the amplitude of the fundamental component by combining phase control with integral switched cycle control) are put forward.

Condition monitoring and failure prognosis of IGBT inverters based on on-line characterization

An inverter characterization technique is used to improve inverter fault diagnosis and prognosis techniques with the demonstrative bond wire lift-off fault. Knowledge of the nonlinear voltage-current characteristic of each inverter device is used to achieve these improvements. Three contributions are made in this paper to the field of inverter condition monitoring by using the characterization technique: use of the inverter device characteristics to improve a classifier-based diagnostic technique, direct use of the device characteristics for diagnosis, and improving the calculation of remaining useful life with the device characteristics. The diagnostic method improvements are verified experimentally by adding resistances to create an artificial fault. Thermal and electrical simulations are used to demonstrate the improvements made to the prognostic method.

Steady state modeling of doubly fed induction generators for mega watt class wind turbines

Doubly fed induction generators in conjunction with frequency converters allow the economic construction of large wind power plants with variable speed drives and a rated power output of up to several MW. Compared to fixed speed generators, the advantages of this configuration are high energy yields despite changing wind speeds, reduced negative effects on the grid and the possibility of reactive-power control. Furthermore, only a fraction of the rated power has to be carried by the frequency converter, which reduces its size and cost. It is vital to the manufacturer of these generators, to reliably predict the operating behaviour by using a suitable mathematical model. This paper elaborately describes such a model for the simulation of the steady state behaviour with a special focus on saturation and losses. Methods for modeling the nonlinearities and for solving the resulting nonlinear equations are described. Simulation results are verified by comparing them to measurement values. Results show that strong saturation of the main field increases the necessary rotor current when the wind power plant has to deliver reactive power to the grid while operating under overvoltage conditions.

Inverter Device Nonlinearity Characterization Technique for Use in a Motor Drive System

This paper introduces a detailed nonlinearity characterization technique for insulated-gate bipolar transistor inverters in a drive system which is able to measure device nonlinearities. Methods are derived from measurements of the voltage on the inverter phases. These measurements are obtained while applying a set of direct currents to an electrical machine. These methods are then applied to tests using alternating current. The study of inverter nonlinearities is useful in order to conduct condition monitoring. These methods fulfill the need to characterize each device in an inverter. In addition to characterizing every device using either ac or dc current, the method is resistant to noise; for these reasons, the method is applicable in the field. Simulations and experimental work demonstrate the benefits and applicability of the methods.

Analysis and modelling of the oscillations of the induced voltage in a dc-motor caused by slotting effects

An extended permanent magnet dc-motor model is set forth including the oscillations of the induced voltage that are caused by slotting effects. The model is used in a hardware in the loop system that easily allows to improve the control strategy of the power split unit in an all-wheel driven automobile. In order to find out which effect causes the ac part of the induced voltage and thus of the current, and how this can be modelled best measurements; an analytical approximation; and FEM calculations were used and the results are compared. The resulting extended model is very accurate and is ideal for situations where the current is of particular interest. Nevertheless, the computational time is just risen moderately. The models predictions are compared to experimental results which clearly show the improvement

Enhanced and fast detection of open circuit faults in inverters for electric drives

Open circuit faults in inverter driven electric drives have recently gained increasing attention in the scientific community. Since these faults may lead to undesired effects, their fast and unambiguous detection is desirable. This paper proposes a detection algorithm for open circuit faults which is based on the observation of the current control deviation and a subsequent test procedure. This algorithm detects the fault immediately after its occurrence within a few switching periods even during transient operation. The proposed method is tested via simulations and experiments at different operating points of a surface permanent magnet drive.

A self-commissioning method for permanent magnet dc-motor drives

The conventional model describing the electrical and mechanical properties of a permanent magnet dc-motor drive is extended in order to take into account the oscillations of the induced voltage that are caused by slotting effects, and - as the electrical machine investigated is fed from a PWM-inverter - in order to include the inverters voltage drop. Furthermore, a method is proposed to estimate the extended models parameters from one single experiment that is easy to be carried out. The method is based on recording the inverters dc-link voltage, the dc-motors armature current and the rotors angular position as a function of time while the dc-motor is fed from the inverter. As the inverter is controlled by a digital signal processor system, this can be done without using additional measuring devices, but just with the dsp-systems measurement facility which is required anyway for the controlled operation of the drive. No additional mechanical components have to be coupled if the motor is equipped with an incremental encoder. Besides the methods aptitude for self commissioning purposes, it is also perfectly suited for quality control as in addition to the relevant electrical parameters one can also estimate mechanical parameters (e.g. to describe the load torque). This makes it easy to control the assembly quality of the motor. Last but not least the models predictions are compared to experimental results and this comparison clearly shows the benefits of the method proposed.

Post-fault operation strategy for single switch open circuit faults in electric drives

Single switch open circuit faults in three-phase AC-drives lead to undesired effects and potentially to a total failure of the drive. This paper proposes a post-fault operation strategy for such faults with the focus on the limitation of losses after the reconfiguration and thereby an extension of the possible range of operation. The performance of the strategy is shown both via simulations and experiments.

Doubly fed induction generators for wind turbines – modeling the steady state

ZusammenfassungDoppelt gespeiste Asynchrongeneratoren erlauben in Verbindung mit Frequenzumrichtern den wirtschaftlichen Betrieb von drehzahlvariablen Windkraftanlagen der MW-Leistungsklasse. Im Vergleich zu drehzahlstarren Systemen bieten diese den Vorteil größerer Leistungsausbeute bei gleichzeitigem Beitrag zur Netzstützung. Da der Umrichter nur einen Teil der Anlagenleistung führt, können dessen Baugröße und Kosten reduziert werden. Die Vorhersage des Betriebsverhaltens anhand geeigneter mathematischer Modelle ist für den Generatorhersteller von entscheidender Bedeutung. Diese Arbeit skizziert anhand eines einfachen Maschinenmodells den grundlegenden Berechnungshergang. Auf ein detailliertes Simulationsmodell für stationäre Betriebszustände mit besonderem Augenmerk auf Sättigungs- und Verlust-Erscheinungen wird ebenso hingewiesen. Die Simulationsergebnisse werden mit Hilfe von Messungen verifiziert. Ferner werden auch Untersuchungen zur Spannungsqualität angestellt. Die von der gesamten Windkraftanlage erzeugten Oberschwingungsemissionen finden dabei besondere Berücksichtigung.SummaryDoubly fed induction generators with frequency converters on the rotor side are well established for large wind power plants up to several MW. This technology concept represents some advantages compared to fixed speed generators such as variable reactive power control, higher energy yield and better power quality behaviour. Furthermore, only a fraction of the rated power has to be carried by the frequency converter, which reduces its size and cost and improves the efficiency. For the manufacturer of these generators it is important to predict with high accuracy the rotor current and voltage despite its saturation and non linear effects. Moreover, the power quality of such a grid connected plant is getting more and more important as the number of the installed plants is rapidly increasing and the grid codes are becoming stricter. That is why the prediction of the emitted harmonic current levels is of importance.

Comparing low cost speed control for single phase induction motors concerning line reaction and electromagnetic compatibility

Low cost speed control of capacitor run single phase induction motors across a wide range of speed and load continues to be of interest. In the paper at hand the line reaction as well as the electromagnetic compatibility of three different methods for speed control - Phase Control, Integral (Half) Cycle Control or Integral Switched Cycle Control - is investigated. Measurements are carried out at different rotor speed and load torque, comparing the methods at approximately the same operating points. FFT is computed for the line currents and measurements on electromagnetic compatibility are presented as well. Subsequently, a method for lowering the induction machine currents amplitude and the magnitude of the fundamental component of the line current by combining Integral Cycle Control with Phase Control is investigated, again concerning line reaction and electromagnetic compatibility.