Richard Bonert

Modeling of iron losses of permanent-magnet synchronous motors

Permanent-magnet (PM) motors offer potential energy savings as compared with induction motors because of the virtual elimination of rotor loss and the reduction of stator loss from operation near unity power factor. In PM machines, iron losses form a significant fraction of the total loss partly due to the nonsinusoidal flux density distribution. Design optimization therefore requires good means of predicting these iron losses. Finite-element analysis can be employed but this approach is cumbersome and costly when used in the many iterations needed in optimizing the design. This paper presents a set of improved approximate models for the prediction of iron loss. They can be used in design optimization programs and, since they are directly related to machine dimensions and material properties, they also provide quick insight into the effects of design changes. A time-stepped finite-element method is employed to evaluate the iron losses in a range of typical PM machines and the results are used to evaluate the adequacy of the models. The predictions of overall iron losses are then compared with measurements made on two PM motors.

Stand alone induction generator with terminal impedance controller and no turbine controls

Induction generators with hydraulic turbines are often used for cogeneration. The same turbine generator configuration can be used for stand-alone generation if an impedance controller is connected to the generator terminals; this configuration requires no hydraulic controls on the turbine. The authors propose an electronic impedance controller to control the voltage and the frequency of a stand-alone induction generator. The controller concept and its control range are discussed. Particular attention is given to the harmonic distortion caused by the controller and measures to reduce these distortions. The controller design is discussed, and data from an experimental generator set are provided to verify the proposed concept. >

New synchronization method for thyristor power converters to weak AC-systems

An improved approach to obtaining good zero-voltage-crossing signals is presented. These signals are subsequently used as synchronization signals for a phase-controlled thyristor power converter. Detection of accurate zero crossings is possible even when there are large frequency changes, sudden load changes, or large commutation overlap angles. The improved accuracy in the integrity of the zero crossing is obtained by reconstructing a voltage representing the AC source voltage. This voltage is determined from the distorted thyristor converter input voltage, the converter input current, and an online identification of the source impedance using a microcontroller-based adaptive algorithm. The improvement provided by the new zero crossing detection scheme is verified experimentally. >

A technique for the steady-state analysis of a self-excited induction generator with variable speed

A method to analyze the steady-state open loop behaviour of a self-excited induction generator with an unregulated prime mover is presented. The proposed method needs little mathematical effort and does not require an assumption about the generator speed. The proposed approach based on nodal analysis allows one to use arbitrary functions for the torque-speed characteristic of the prime mover and for the saturation of the magnetizing inductance without complicating the solution process. It always leads to a single equation for the frequency. An example is presented demonstrating the advantages of the proposed method. The analytical results are verified by measurements. >

Minimization of iron losses of permanent magnet synchronous machines

In permanent magnet (PM) synchronous machines, iron losses form a larger portion of the total losses than in induction machines. This is partly due to the elimination of significant rotor loss in PM machines and partly due to the nonsinusoidal flux density waveforms in the stator core of PM machines. Therefore, minimization of iron losses is of particular importance in PM motor design. This paper considers the minimizing of iron losses of PM synchronous machines through the proper design of magnets and slots, and through the choice of the number of poles. Both time-stepped finite element method (FEM) and the iron loss model from a previous study are used in this paper to draw the conclusions.

Design of a high performance digital tachometer with a microcontroller

The design of a very flexible, low-cost speed evaluation system is presented. The system provides fast dynamic response and high accuracy over a wide speed range. The design is suitable for a broad range of applications and can be integrated as part of an existing tachometer assembly. Hardware requirements and appropriate software structures for a microcontroller implementation are discussed. The algorithm used to calculate the speed is based on the method of constant elapsed time. The predicted performance is verified experimentally. >

Design of a real-time digital Simulator for a D-STATCOM system

Real-time digital simulation of power electronic systems requires significant computational resources due to increasingly complex system configurations, control algorithms, and higher switching frequency. Consequently, it is prudent to exploit various computer resources for optimizing the design of simulators/controllers for such systems. This paper presents the design and implementation details of a real-time digital simulator for a Voltage-Source-Converter-based Distribution STATic COMpensator (D-STATCOM) power system. The design process adopts a modular approach utilizing distributed digital signal processor/field-programmable gate array resources of a digital processing platform. The design has been validated by using an experimental setup of a 5-kVA D-STATCOM system.

Load Independent AC/DC Power Supply for Higher Frequencies with Sine-Wave Output

For ac voltage power supplies with a dc voltage input, a series inverter can be used. The advantage of sine-wave output and low switching losses is in contrast to the poor regulation of the output voltage and the load dependence of most series inverter circuits. An improved series inverter with a divided resonance capacitor is described. This inverter can operate from no load to full load and for inductive load as well as for resistive or capacitive load. It provides excellent output voltage regulation for all kinds of loads. A steady- state analysis of the inverter for reactive load is given as well as the optimal design for the divided capacitor. A second circuit formed from two of the above inverters provides a controllable output voltage independent of the input voltage and the load and thus overcomes a disadvantage of many series inverters. Both circuits were tested in experimental setups for an output frequency of 400 Hz, and the results are discussed.

Digital Tachometer with Fast Dynamic Response Implemented by a Microprocessor

A digital tachometer consists of an incremental shaft encoder and an electronic circuit to evaluate the digital or analog speed signal. The method of evaluation and the design of the electronic circuit determine the dynamic performance and the accuracy of the tachometer. The usual method of counting pulses coming from the shaft encoder normally provides a poor dynamic performance, particularly if high accuracy and a wide speed range are required. A method is suggested which provides a good dynamic response combined with good accuracy over a wide speed range. Though the process is very fast, it is possible to use this method in an electronic circuit based on a microprocessor and other highly integrated programmable chips. This implementation is discussed, and it is shown how using a microprocessor-controlled circuit affects the achievable accuracy of the tachometer.

Measurement techniques for the evaluation of double-layer power capacitors

Double-layer capacitors for power applications have become available in the last few years. Their high energy density and power capacity make them attractive for power applications, but the terminal behaviour differs considerably from an ideal capacitor. This paper discusses the terminal behaviour and, based on this, proposes measurement procedures to test these new capacitors and to achieve consistent repeatable measurements.