Active filtering of electric power has now become a mature technology for harmonic and reactive power compensation in two-wire (single phase), three-wire (three phase without neutral), and four-wire (three phase with neutral) AC power networks with nonlinear loads. This paper presents a comprehensive review of active filter (AF) configurations, control strategies, selection of components, other related economic and technical considerations, and their selection for specific applications. It is aimed at providing a broad perspective on the status of AF technology to researchers and application engineers dealing with power quality issues. A list of more than 200 research publications on the subject is also appended for a quick reference.

A review of active filters for power quality improvement

Strategies for extracting the three-phase reference currents for shunt active power filters are compared, evaluating their performance under different source and load conditions with the new IEEE Standard 1459 power definitions. The study was applied to a three-phase four-wire system in order to include imbalance. Under balanced and sinusoidal voltages, harmonic cancellation and reactive power compensation can be attained in all the methods. However, when the voltages are distorted and/or unbalanced, the compensation capabilities are not equivalent, with some strategies unable to yield an adequate solution when the mains voltages are not ideal. Simulation and experimental results are included

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Comparison of Control Strategies for Shunt Active Power Filters in Three-Phase Four-Wire Systems

Solid-state controllers are widely used to convert AC power for feeding number of electrical loads such as adjustable speed drives, furnaces, power supplies etc. Some of these controllers behave as nonlinear loads because they draw nonsinusoidal current from the AC mains. Filter technology for improving power quality of such loads has matured to a reasonable level. Moreover, hybrid filters are considered one of best options for improving power quality for a number of considerations. A comprehensive review of hybrid filters configurations is given: their control approaches, state of art, design considerations, selection criteria, potential applications, latest trends, future developments and their comparative features. A broad review of the status of hybrid filters to researchers, design and practice engineers dealing with power quality improvements is presented. A classified list of more than 150 research publications on the hybrid filters is also given for quick reference.

Hybrid filters for power quality improvement

The existence of two different definitions for total harmonic distortion (one in comparison to the fundamental and one in comparison to the signal's root mean square) might cause ambiguity and misinterpretation of measured data. The difference between those definitions is stressed out in this letter. It is suggested that total harmonic distortion measurements in the context of power systems should always adopt the first definition and never the second.

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On the definition of total harmonic distortion and its effect on measurement interpretation

This paper provides the theoretical basis for and demonstrates the practical application of power and rms measurements directly from the wavelet transform data associated with each voltage current element pair. The voltage and current wavelet transforms are derived from concurrent measurements using a common orthonormal wavelet basis. The advantage of using the wavelet transform data directly is that it provides the distribution of the power and energy with respect to the individual frequency bands associated with each level of the wavelet analysis. Frequency separation into the various wavelet levels is achieved using IIR filters because their magnitude characteristics are much better than typical FIR filters of equivalent complexity. The IIR polyphase network strategy yields a simpler wavelet filter bank design.

Power measurement using the wavelet transform

Existing definitions for power terms in alternating current systems work well for single-phase and three-phase systems where both voltages and currents are sinusoidal with respect to time. This paper clarifies and proposes definitions for power terms that are practical and effective when voltage and/or currents are distorted and/or unbalanced. It also suggests definitions for measurable values that may be used to indicate the level of distortion and unbalance.

Practical definitions for powers in systems with nonsinusoidal waveforms and unbalanced loads: a discussion

50 utilities in the United States and Canada responded to a questionnaire survey regarding concerns about nonsinusoidal waveforms in the electric distribution network. Responses regarding instrumentation, apparent and reactive power definitions, meter errors, rates, and trends are presented and discussed.

D. Piehl

Papers

Practical definitions for powers in systems with nonsinusoidal waveforms and unbalanced loads: a discussion

A survey of North American electric utility concerns regarding nonsinusoidal waveforms