P. Mehta

Switched-capacitor filters

A novel technique for building active filters using switched-capacitor (SC) circuits is proposed. The principle of operation, methods of control, and analysis and design of a typical SC filter are presented. To assess its effectiveness, the technique is used to control input current harmonics in a phase-controlled converter. It is shown that by using a single filter a wide range of harmonics can be controlled. >

Improvement in DC Motor Performance by Asymmetrical Triggering, Part I: One-Quadrant Drive

The static Ward-Leonard drive suffers from two major disadvantages: 1) poor power factor when the phase-controlled converter supplying the motor is operated at a delayed triggering angle, and 2) the problems associated with discontinuous armature current when the machine is lightly loaded. If asymmetrical triggering technique is judiciously applied to a converter-controlled dc drive, it improves not only the power factor but also the overall performance of the drive. It reduces the ripple content of the armature current and the value of the extra inductance necessary to achieve current continuity for low-current operation.

Switched-capacitor technique for power electronic applications

A new family of switched-capacitor (SC) circuits that can be used for a variety of applications is proposed. A typical circuit consists of several branches connected in parallel, each branch incorporating a capacitor in series with a semiconductor switch. The SC circuits are classified into three categories: (1) single-switch single-capacitor; (2) double-switched double-capacitor; and (3) triple-switch double-capacitor. Applications of these circuits, including reactive power control and active filters are presented.<<ETX>>

Control strategies for active filters using pattern recognition techniques

In recent years there has been considerable interest in the use of active filters for eliminating harmonic currents in power supply systems. Most filter configurations require detection of the harmonic content and generating switching waveforms for the filter. The feasibility of using pattern recognition techniques for detection of harmonics and generation of information suitable for controlling active filters is investigated. The relative merits of time and frequency domain representation are studied. The experimental investigation uses fast Fourier transforms to detect the harmonic spectra which are used to train the system and store the corresponding pre-determined switching patterns for control of a filter. On receiving an unknown signal the system compares it with the stored image and identifies the appropriate switching pattern for the filter. The feasibility of this approach is assessed in an application incorporating a switched-capacitor filter to eliminate current harmonics in the input current to a rectifier system such as that used for uninterruptible power supply (UPS) systems.<<ETX>>

Analytical load model for power system components

This paper deals with the derivation of software models for low and medium voltage power systems, including distribution transformers and different loads with regard to the harmonics and power factor corrections. For this purpose, each element of the system is discussed and load models have been developed. The distribution substations can be supplied by medium or low voltage systems which require different solutions. The results presented in this paper are based on the calculation and measurements according to the IEC regulations.

A new contribution into the improvement of power factor correction

This paper presents an improved new method for power factor correction and harmonic current reduction using IGBTs and a passive filter which is suitable to compensate rapidly changing loads and reactive power. Furthermore, a single-phase control concept is discussed for simplicity. The results can be implemented in three-phase systems without any problems. It also presents a brief discussion of the main problems in the distribution power systems. The increased use of nonlinear devices cause voltage distortion in the network. This leads to malfunctions of the electric facilities and to costly interruptions of production. The filter circuit parameters are analysed and described. This filter configuration provides an alternative approach to the existing one. According to the test results, the proposed approach can achieve a complete elimination of harmonics.

Analysis and Design of a New Switching Power Amplifier

Summary This paper presents a new switching power amplifier suitable for testing equipment such as computers, lighting and rotating machines with non-sinusoidal voltage waveforms and with specific harmonic content. The proposed system overcomes the disadvantages inherent in existing techniques, which are briefly reviewed. The detailed analysis and design together with the results of simulation studies and experimental work are also included

Variable capacitor filter for smoothing rectifier output

A novel technique for smoothing rectifier output using variable characteristics filters is proposed. A major advantage of this technique is that it can eliminate a range of harmonics using a single switched-capacitor circuit. Principles of operation, methods of control, the analysis, and the design, supported by computer simulation and experimental work, are presented for a three-phase rectifier circuit.<<ETX>>