The increasing use of power electronics apparatus in three phase industrial systems is giving rise to transmission of power with high level of harmonic distortion. As a consequence, the problem of the definition and measurement of powers and current components under unbalanced and distorted conditions is of extreme practical and theoretical importance. It has to be remembered that the non-active components of the load currents do not contribute to the energy transfer, but cause undesired losses, voltage drops and EMC problems. In order to improve the efficiency of the power transmission and to increase the power factor, it is necessary to detect these components for their compensation. Defmitions and standards should give rules how determine these non-active currents, but the problem of defining them is still far from a satisfactory solution. In the last years, a generalized theory (p-q theory) based on the decomposition of the instantaneous complex power into its real and imaginary components has been proposed. This theory seems to be the most suitable for characterizing three-phase distorting and unbalanced loads and can contribute to the solution of the dispute on the definitions of non-active current components. In this paper we recall the main features of this generalized theory to give suggestions for definitions and standards, applicable both to sinusoidal and non-sinusoidal waveforms in balanced or unbalanced systems. In particular, the concept of the instantaneous power factor and the definition of the active and reactive components of the instantaneous current space vector are revised. Then, the expressions of the instantaneous complex power in terms both of active and reactive current components and of voltage and current harmonic symmetrical components are derived. At the end, it is suggested to measure the active power and the d.c. component of the imaginary power by means of a line-by-line product of the spectra of the instantaneous voltage and current space-vectors.

Contribution to the Definition and Measurement of Powers and Current Components

STASI, Silvio
1992

Abstract

The increasing use of power electronics apparatus in three phase industrial systems is giving rise to transmission of power with high level of harmonic distortion. As a consequence, the problem of the definition and measurement of powers and current components under unbalanced and distorted conditions is of extreme practical and theoretical importance. It has to be remembered that the non-active components of the load currents do not contribute to the energy transfer, but cause undesired losses, voltage drops and EMC problems. In order to improve the efficiency of the power transmission and to increase the power factor, it is necessary to detect these components for their compensation. Defmitions and standards should give rules how determine these non-active currents, but the problem of defining them is still far from a satisfactory solution. In the last years, a generalized theory (p-q theory) based on the decomposition of the instantaneous complex power into its real and imaginary components has been proposed. This theory seems to be the most suitable for characterizing three-phase distorting and unbalanced loads and can contribute to the solution of the dispute on the definitions of non-active current components. In this paper we recall the main features of this generalized theory to give suggestions for definitions and standards, applicable both to sinusoidal and non-sinusoidal waveforms in balanced or unbalanced systems. In particular, the concept of the instantaneous power factor and the definition of the active and reactive components of the instantaneous current space vector are revised. Then, the expressions of the instantaneous complex power in terms both of active and reactive current components and of voltage and current harmonic symmetrical components are derived. At the end, it is suggested to measure the active power and the d.c. component of the imaginary power by means of a line-by-line product of the spectra of the instantaneous voltage and current space-vectors.
First European Conference on Reliability, Standardization and Certification of Industrial Electric D
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11589/23691
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