Guenther Dannerer

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.

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.

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

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.

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.

Design of small potable water power plants, with regard to grid connection and efficiency

The utilization of very small hydro power plants has been gaining more and more interest lately. In this context the activation and utilization of the potential energy that is inherent in the drinking water stored in highlevel tanks of waterworks is of growing interest. In the paper at hand, considerations about the modification of a small potable water pipeline for electric power generation are presented. Subsequently the complexity of different generator concepts concerning grid connection is compared. Measurements concerning the efficiency of small three-phase induction machines during generator operation are presented. The system described is installed in a box in the basement of the house. A pelton turbine is used because of its high efficiency. An induction machine is installed as a generator, without inverter. For high efficiency, an intermittent mode of operation is proposed.

Rotor resistance adaptation for vector controlled induction motors considering deviations of the main inductance caused by the quadrature current

The vector control scheme for induction motors using the rotor flux reference frame is well known. To provide proper torque production, knowledge of the rotor time constant is essential. Many adaptation schemes have been presented using different paradigms. In this paper a scheme for rotor time constant adaptation is applied, which uses the difference between the measured and the calculated reactive power to calculate a correcting factor for the rotor time constant. Measurements have shown that the main inductance which is crucial to the calculation of the reactive power depends both on the magnetizing current and on the quadrature current. The adaptation scheme is therefore modified to consider this effect, improving the accuracy of torque production.

Investigating the dependency of an induction machine's main inductance on the torque building current component using FEM

According to several papers, the main flux path of an induction machine is saturated not only due to the magnetizing current. Measurements and related parameter estimations show the influence of the torque building current component on the magnetization curves. The paper at hand presents 2D FEM calculations carried out in order to support and possibly verify the experimental investigations by means of a numerical approach. The outcome of the FEM calculations shows a high level of agreement with the results obtained by measurement.

Investigating the dependency of an induction machine's main inductance on the supply frequency

According to several papers, an induction machines main flux paths saturation state is not only conditioned by the magnetizing current. In the paper at hand the dependency of the magnetization curve on the supply frequency is investigated. Measurements show that the flux linkage decreases with rising supply frequency. This should be considered when incorporating control algorithms based on the main inductance. The magnetization curves calculated from the data retrieved are presented and compared to FEM calculations for validation of the effect under investigation.

Modeling the induction machine's main inductance as a function of the magnetizing and the torque building component of the stator current

According to earlier work and papers by other authors, the main flux path of an induction machine is not only saturated due to the magnetizing current or, in other words, ldquothe magnetizing inductance can be modeled as a function of torquerdquo. In the paper a method is proposed to extend the induction machines standard fundamental wave model taking into consideration the changes of the main inductance in dependence of the magnetizing and the torque building component of the stator current. Furthermore, a method is presented to estimate the required parameters from measurements carried out during normal operation of the induction machine. Validation is achieved via FEM calculations and additional measurements.