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Compensation of nonperiodic currents using the instantaneous power theory
Abstract
This paper presents a discussion about the use of the
instantaneous active and reactive power theory (p-q theory) for the
compensation of nonperiodic currents in three-phase circuits. First, the
concept behind the term nonperiodic is discussed. A summary of the basic
points of the instantaneous power theory is presented and them some
examples of nonperiodic currents and their identification and
compensation by active filters are presented. This paper shows that it
is not possible to have at the same time a perfect compensation, where
the source currents are purely sinusoidal and the power flowing in the
circuit is constant. The user has to decide which condition has higher
priority and adapt the compensation characteristics of the active filter
... Generally, power electronic converters generate harmonic components which frequencies that are integer multiplies of the line frequency. However, in some cases, such as controlled 3-phase rectifiers, arc furnaces and welding machines are typical loads, the line currents may contain both frequency lower than the line frequency and frequency higher than the line frequency but not the integer multiple of line frequency [1]-[4]. These currents interact with the impedance of the power distribution system and disturb voltage waveforms at point of common coupling (PCC) that can affect other loads. ...
... These currents interact with the impedance of the power distribution system and disturb voltage waveforms at point of common coupling (PCC) that can affect other loads. These waveforms are considered as non-periodic for the period of the currents is not equal to the period of the line voltage [1], [2]. ...
... Generally, power electronic converters generate harmonic components which frequencies that are integer multiplies of the line frequency. However, in some cases, such as controlled 3-phase rectifiers, arc furnaces and welding machines are typical loads, the line currents may contain both frequency lower than the line frequency and frequency higher than the line frequency but not the integer multiple of line frequency [1][4]. These currents interact with the impedance of the power distribution system and disturb voltage waveforms at point of common coupling (PCC) that can affect other loads. ...
In this paper, a generalized non-active power theory based control strategy is implemented in a 3-phase 4-wire combined series-parallel active filter (CSPAF) system for periodic and non-periodic waveforms compensation. The CSPAF system consists of a series active filter (SAF) and a parallel active filter (PAF) combination connected a common dc-link. The generalized non-active power theory is valid for single-phase and multi-phase systems, as well as periodic and non-periodic waveforms. The theory was applied in previous studies for current control in the PAF. In this study the theory is used for current and voltage control in the CSPAF system. The CSPAF system is simulated in Matlab/Simulink and an experimental setup is also built, so that different cases can be studied in simulations or experiments. The simulation and experimental results verify that the generalized non-active power theory is suitable for periodic and non-periodic current and voltage waveforms compensation in the CSPAF system.
... Many of the loads encountered in modern power electronics cause a significant level of nonsinusoidal and/or nonperiodic voltage and current disturbances in electrical power systems. Arc furnaces, welders, and motor drives are typical nonlinear loads that can cause not only characteristic harmonics (frequency integer multiple of the line frequency) but also subharmonic (frequency lower than the line frequency) and stochastic nonperiodic (frequency higher than the line frequency but not the integer multiple of the line frequency) components to appear in the spectra of voltages and currents [1][2][3][4][5]. ...
... The harmonic currents will produce voltage distortions that can affect other sensitive loads at points of common coupling (PCC) as they interact with the impedance of an electrical distribution system. These current and voltage waveforms are considered as nonperiodic, although mathematically the currents may still have a periodic waveform; in any event, the period of the currents is not equal to the period of the line voltage [1,2]. The effects of nonperiodic components of voltage and current are similar to those caused by harmonics. ...
This paper presents a 3-phase, 4-wire unified series-parallel active filter (USPAF) system for periodic and nonperiodic disturbance compensation using a generalized nonactive power theory. The USPAF system consists of a series active filter (AF), parallel AF, and split DC-link capacitors with the midpoint of the DC-link connected to the neutral wire. The generalized nonactive power theory is applicable to singlephase or multiphase, sinusoidal or nonsinusoidal, periodic or nonperiodic, and balanced or unbalanced electrical systems. The theory was implemented previously in a parallel AF. In this study, the USPAF system is proposed to compensate for the nonsinusoidal and nonperiodic currents and voltages. Distorted source voltages, source voltage sag, and unbalanced nonlinear load current compensation were simultaneously tested in the experiments. Subharmonic and stochastic nonperiodic current and voltage compensation were simulated in MATLAB/Simulink. Simulation and experimental results verified the validity of the generalized nonactive power theory for the compensation of periodic (nonsinusoidal) and nonperiodic current and voltage disturbances with the USPAF system.
... Many of the loads encountered in modern power electronics cause a significant level of nonsinusoidal and/or nonperiodic voltage and current disturbances in electrical power systems. Arc furnaces, welders, and motor drives are typical nonlinear loads that can cause not only characteristic harmonics (frequency integer multiple of the line frequency) but also subharmonic (frequency lower than the line frequency) and stochastic nonperiodic (frequency higher than the line frequency but not the integer multiple of the line frequency) components to appear in the spectra of voltages and currents12345. The harmonic currents will produce voltage distortions that can affect other sensitive loads at points of common coupling (PCC) as they interact with the impedance of an electrical distribution system. ...
... The harmonic currents will produce voltage distortions that can affect other sensitive loads at points of common coupling (PCC) as they interact with the impedance of an electrical distribution system. These current and voltage waveforms are considered as nonperiodic, although mathematically the currents may still have a periodic waveform; in any event, the period of the currents is not equal to the period of the line voltage [1,2]. The effects of nonperiodic components of voltage and current are similar to those caused by harmonics. ...
This paper presents a 3-phase, 4-wire unified series-parallel active filter (USPAF) system for periodic and nonperiodic disturbance compensation using a generalized nonactive power theory. The USPAF system consists of a series active filter (AF), parallel AF, and split DC-link capacitors with the midpoint of the DC-link connected to the neutral wire. The generalized nonactive power theory is applicable to single-phase or multiphase, sinusoidal or nonsinusoidal, periodic or nonperiodic, and balanced or unbalanced electrical systems. The theory was implemented previously in a parallel AF. In this study, the USPAF system is proposed to compensate for the nonsinusoidal and nonperiodic currents and voltages. Distorted source voltages, source voltage sag, and unbalanced nonlinear load current compensation were simultaneously tested in the experiments. Subharmonic and stochastic nonperiodic current and voltage compensation were simulated in MATLAB/Simulink. Simulation and experimental results verified the validity of the generalized nonactive power theory for the compensation of periodic (nonsinusoidal) and nonperiodic current and voltage disturbances with the USPAF system.
... However, in some cases, such as cycloconverters and linecommutated three-phase thyristor-based rectifiers, the line currents may contain both sub-harmonics (frequency lower than fundamental frequency) and super-harmonics (frequency higher than fundamental frequency but not an integer multiple of it). These waveforms are considered as nonperiodic , although mathematically the currents may still have a periodic waveform, but in any event, the period of the currents is not equal to the period of the fundamental voltage [1], [2]. ...
... However, in some cases, such as cycloconverters and linecommutated three-phase thyristor-based rectifiers, the line currents may contain both sub-harmonics (frequency lower than fundamental frequency) and super-harmonics (frequency higher than fundamental frequency but not an integer multiple of it). These waveforms are considered as nonperiodic , although mathematically the currents may still have a periodic waveform, but in any event, the period of the currents is not equal to the period of the fundamental voltage [1], [2]. An arc furnace is an example of a non-linear load that may draw rapidly changing non-sinusoidal currents from the source, that is, the current wave shape is constantly changing. ...
This paper presents a new definition of non-active current, which is valid for single-phase and polyphase systems as well as for periodic and non-periodic waveforms. The definition is applied to a shunt compensation system, and different cases of non-periodic current compensation are studied. A variety of compensation characteristics of non-periodic currents and the rating requirements for the compensator are illustrated by simulation.
... These currents are considered as non-periodic, though mathematically they may still have a periodic waveform. The period of the currents is not equal to that of the line voltage [8], [9]. Most previous efforts [1]-[5] focused on the compensation of periodic non-sinusoidal currents. ...
... These currents are considered as non-periodic, though mathematically they may still have a periodic waveform. The period of the currents is not equal to that of the line voltage [8], [9]. Most previous efforts [1][5] focused on the compensation of periodic non-sinusoidal currents. ...
Compensation of irregular currents such as those associated with arc furnaces, transient disturbances, and power electronic converters is presented. The compensation is based on a well-defined nonactive current definition. The basic concepts required in the definition of nonactive current are presented and illustrated by compensation simulations for a variety of different types of nonperiodic currents found in distribution electrical systems, including disturbance, subharmonic, and stochastic currents. Further, based on the compensation objectives for different types of load waveforms, the specifications such as current ratings or capacitance requirements of the active filter are also presented.
... Indeed, if the load corresponds to a six-pulse rectifier operating in steady state, for example, the average component can be determined using a low-pass filter with a time interval equal to 1/6 of the grid frequency period. However, as it is shown in [9] [10], depending on the application, the period for the calculation of the average value may be much higher than the period of the line frequency. In micro-grids applications the problem of load and/or generation variations will certainly require an averaging period greater than the grid frequency period. ...
... As we can see in this figure, the voltage and current distortion have been greatly reduced and the frequency is now constant. This simple simulation shows that a shunt power compensator can be designed to compensate for oscillating power as in [9] and [10] with the difference that in these references the power supply was running at constant frequency. In a micro-grid the inertia in the electrical system may be too small to keep constant frequency, without the help of a power compensator. ...
The main objective of this tutorial is to present the basic concepts on the instantaneous p-q Theory and then show its applicability for controlling switching converters connected in a micro-grid. These converters can be used for connecting renewable energy sources (solar, wind, and others) to the micro-grids or for harmonic, reactive power or unbalance compensation, and even for voltage regulation. The emphasis is given on the compensation characteristics derived from the p-q Theory, and simulation results of test cases are shown. Special attention is put on the oscillating component of the instantaneous real power, as it may produce torque oscillations or frequency variations in weak systems (micro-grids) generators. This oscillating component, as defined in the p-q Theory, gives the amount of oscillating energy between the source and the load, and its compensation through a switching compensator must have an energy storage element to exchange it with the load. With the p-q Theory this energy storage element can be easily calculated as a function of the average component of the instantaneous real power, which depends on the observation period.
... The p-q Theory also allows a comprehensible explanation as to why imaginary power can be compensated without the need of energy storage elements [5][6]. Besides, it also allows determining the amount of energy that must be stored in a compensation device, in order to compensate oscillating powers that are exchanged between source and loads [7][8]. Furthermore, the p-q Theory allows two compensation strategies: constant power at source and sinusoidal currents at source (using the fundamental positive-sequence components of voltage in the control algorithm) [13]. ...
... It is worth to notice that, generally, the average components are calculated by considering the period of the line frequency as the time reference. However, as it was shown in [7][8], depending on the application the period for the calculation of the average value may be much higher than the period of the line frequency. In micro-grids applications this problem may occur. ...
The main objective of this paper is to compare the applicability and performance of a switching compensator when it is controlled by algorithms derived from the pq-Theory and from the Current's Physical Components Power Theory (CPC-theory) considering a micro-grid application. Compensation characteristics derived from each one of these set of power definitions are highlighted, and simulation results of test cases are shown. Special attention is put on the oscillating instantaneous real power, as it may produce torque oscillations or frequency variations in weak systems (micro-grids) generators. The oscillating instantaneous real power, as defined in the pq-Theory, gives the amount of energy oscillating between the source and the load, and its compensation using a switching compensator must have an energy storage element to exchange it with the load. The energy storage element can be easily calculated with the pq-Theory.
... Generally, power electronic converters generate harmonic components with frequencies that are integer multiplies of the line frequency. However, in some cases, such as line commutated three-phase thyristor based rectifiers, arc furnaces and welding machines are typical loads, the line currents may contain both frequency lower than the line frequency (subharmonic) and frequency higher than the line frequency (stochastic non-periodic, the wave-shape and amplitude are constantly changing) components but not integer multiple of the line frequency [1][2][3][4][5]. These waveforms are considered as non-periodic, although mathematically the currents may still have a periodic waveform, but in any event, the period of the currents is not equal to the period of the line voltage [1,2]. ...
... However, in some cases, such as line commutated three-phase thyristor based rectifiers, arc furnaces and welding machines are typical loads, the line currents may contain both frequency lower than the line frequency (subharmonic) and frequency higher than the line frequency (stochastic non-periodic, the wave-shape and amplitude are constantly changing) components but not integer multiple of the line frequency [1][2][3][4][5]. These waveforms are considered as non-periodic, although mathematically the currents may still have a periodic waveform, but in any event, the period of the currents is not equal to the period of the line voltage [1,2]. The non-periodic components can occur as well in the source voltage. ...
... Power properties of three-phase systems are described by the IRP p-q Theory in two orthogonal α and β coordinates in terms of two, p and q instantaneous powers. They are referred to [3] as the instantaneous real and the imaginary powers or more commonly [4][5][6], as the instantaneous active and reactive powers. According to Authors' of Ref. [3] claim: "…the instantaneous imaginary (reactive) power q was introduced on the same basis as the conventional real power p in threephase circuits and then the instantaneous reactive power in each phase was defined with the focus on the physical meaning and the reason for naming…" Because of it, the IRP p-q Theory has become a very attractive theoretical tool not only for the active power filter control [3][4][5][6], but also for analysis and identification [7][8][9][10][11][12]18] As long as the IRP p-q Theory is considered only as a control algorithm then, the interpretation of power phenomena as suggested by this theory is irrelevant. ...
... They are referred to [3] as the instantaneous real and the imaginary powers or more commonly [4][5][6], as the instantaneous active and reactive powers. According to Authors' of Ref. [3] claim: "…the instantaneous imaginary (reactive) power q was introduced on the same basis as the conventional real power p in threephase circuits and then the instantaneous reactive power in each phase was defined with the focus on the physical meaning and the reason for naming…" Because of it, the IRP p-q Theory has become a very attractive theoretical tool not only for the active power filter control [3][4][5][6], but also for analysis and identification [7][8][9][10][11][12]18] As long as the IRP p-q Theory is considered only as a control algorithm then, the interpretation of power phenomena as suggested by this theory is irrelevant. It is sufficient for an algorithm to be acceptable that it enables us to reach the control objectives. ...
This paper investigates how power phenomena and properties of three-phase systems are described and interpreted by the Instantaneous Reactive Power (IRP) p-q Theory. This paper demonstrates that this theory misinterprets power properties of electrical systems or provides some results that at least defy a common sense or meaning of some notions in electrical engineering. For example, it suggests the presence of an instantaneous reactive current in supply lines of purely resistive loads and the presence of an instantaneous active current in supply lines of purely reactive loads. Moreover, it suggests that line currents of linear loads with sinusoidal supply voltage contain a nonsinusoidal component. This paper shows, moreover, that the IRP p-q Theory is not capable to identify power properties of three-phase loads instantaneously. A pair of instantaneous values of p and q powers does not allow us to conclude whether the load is resistive, reactive, balanced, or unbalanced. It is known that a load imbalance reduces power factor. However, the IRP p-q Theory does not identify the load imbalance as the cause of power factor degradation.
... The apparent power can also be represented by an expression taking into account its components [23]: ...
In the electrical installations of buildings, there is an increasing number of non-linear energy receivers, which introduce strong distortions of the load current of electronic energy meters. Since the readings of these meters are the basis for financial settlements of electricity consumers, it is very important to determine how much the distortion of the receiver current affects the correct operation of commonly used electronic energy meters. The article will present exemplary results and analyses of research work on the impact of individual current harmonics on the readings and errors of selected energy meters.
... For commonly known power theory [21,22], the non-linearity of a load is represented by harmonic components due to the distortion of the current flowing through the load. When the mains voltage is sinusoidal and the load is non-linear, then the current is distorted. ...
Various metrological aspects for the correct measurements of electrical energy that is consumed by energy-saving (mainly LED) single phase loads are discussed in this paper. One of the most important problems presented here concerns the question of how strong distortions of the current waveform, introduced by typical LED lighting, affects the operation of electronic energy meters. Measurement results for the energy consumption of different LED lamps used in households in various conditions, alongside comparative results that were obtained by electronic and electromechanical energy meters, were also offered and the appropriate conclusions were then drawn.
... Time-domain based approaches are mostly originated from the Fryze power theory [10]- [11], instantaneous p-q theory [12]- [13,14], and synchronous d-q frame theory [15]. In [16] and [17] an extension of Fryze power theory, and instantaneous power theory is utilized for the compensation of non-periodic current. ...
This paper presents a new technique for the compensation of non-periodic load current. The method provides control references for three co-located devices, each corresponding to one moving calculation window and one decomposed part of the compensated current. They are slow compensator with high power rating, large calculation window, and low switching frequency; fast compensator with lower power rating, shorter calculation window, and higher switching frequency; and the reactive compensator which is an ordinary static VAR compensator (SVC). A fuzzy based adaptive window is proposed for the slow compensator to find the optimum window for different load characteristics. The technique is evaluated using real-world data and controller hardware-in-the-loop (HIL) implementation.
... In [52,53] a summary of the basic formulation of the p -q theory is presented and some examples of non-periodic currents and their compensation by active filters are discussed. The authors claim that it is not possible to have perfect compensation at the same time when the source currents are purely sinusoidal and the power flowing in the circuit is constant. ...
The increasing aggregation of renewable-based distributed generating units besides the impressive growing usage of non-linear loads raises unwanted challenges for traditional power terms definition in power engineering. This fact consequently affected the performance of the conventional control frameworks and industrial compensation techniques. In this study, the authors aim to provide an insightful summary over the most recognised time domain-based instantaneous power theories and discuss their advantages and disadvantages within a comprehensive mathematical-conceptual and applicational framework for professionals who are using instantaneous power theories within the smart grid applications. They conclude that there is still a need for a modified power theory which can be validated under non-sinusoidal-unbalanced load/source conditions respecting the physical meaning of different power and current components.
... D'après [4], [5], [6] et [7], la théorie de la puissance réactive instantanée (en anglais "Instantaneous Reactive Power Theory") avec un filtre actif est appliqué pour résoudre le problème du déséquilibre dans un réseau quatre fils (trois phases + neutre) avec des charges non-linéaires. Cependant, dans notre étude, les harmoniques sont ignorés dans notre réseau électrique, les charges donc supposées linéaires. ...
... However, in some cases, such as cycloconverters and linecommutated three-phase thyristor-based rectifiers, the line currents may contain both sub-harmonics (frequency lower than the line frequency) and super-harmonics (frequency higher than the line frequency but not the integer multiple of line frequency). These waveforms are considered as non-periodic, although mathematically the currents may still have a periodic waveform, but in any event, the period of the currents is not equal to the period of the line voltage [1],[2]. Arc furnaces are another example of a non-linear load that may draw non-periodic currents because they draw rapidly changing power from the source and the waveshape and amplitude are constantly changing. ...
This paper presents a discussion of the compensation of non-periodic currents such as those associated with arc furnaces. Based on the compensation objectives for different types of load waveforms, the energy storage requirements of the compensator are also presented. Further, basic concepts required in the definition of nonactive current are presented and illustrated by simulations for a variety of different compensation characteristics of non-periodic currents. Key Words non-active power, reactive power, compensator, nonperiodic current, arc furnace 1.
... In the presence of non-periodic currents, [Watanabe et al., 2000] showed that -theory cannot give constant power and sinusoidal current at the same time. However, with proper formulation and signal decomposition technique, modified -theory can give sinusoidal source current and unity power factor, even with the presence of non-linear non-stationary currents. ...
This paper describes an active power filter (APF) control strategy, which
eliminates harmonics and compensates reactive power in a three-phase four-wire
power system supplying non-linear unbalanced loads in the presence of
non-linear non-stationary currents. Empirical Mode Decomposition (EMD)
technique developed as part of the Hilbert-Huang Transform (HHT) is used to
singulate the harmonics and non-linear non stationary disturbances from the
load currents. The control strategy for the APF is formulated by hybridizing
the so called modified p-q theory with the EMD algorithm. A four-leg
split-capacitor converter controlled by hysteresis band current controller is
used as an APF. The results obtained are compared with those obtained with the
conventional modified p-q theory, which does not possess current harmonics or
distortions separation strategy, to validate its performance.
... However, it introduces new harmonics to the active current which is not desired in nonactive power compensation. Non-integer multiple harmonics are defined as non-periodic currents in [7] , and the compensation is discussed. Nonperiodic currents are also discussed in [8]. ...
This paper presents a generalized nonactive power theory, in which the instantaneous currents (active and nonactive) and instantaneous powers (active and nonactive) are defined. This theory is implemented in a parallel nonactive power compensation system. The theory is valid if the system is three-phase or single-phase, sinusoidal or non-sinusoidal, periodic or non-periodic, balanced or unbalanced. Four cases, three-phase balanced RL load, three-phase unbalanced RL load, diode rectifier load, and single-phase RL load are tested in the experiments. Subharmonic load compensation and non-periodic load compensation are simulated in Matlab. The simulation and experimental results not only verify the validity of the theory, but also show that this theory can perform instantaneous nonactive power compensation with fast dynamic response
... Given that the pq-Theory is very well-known and accepted by the power electronics community, some authors tend to consider it a theoretical tool not only for active filter control [16,[19][20][21], but also for power properties' definitions and understanding [22,23], regardless of all the misunderstanding about physical phenomena under non sinusoidal and unbalanced conditions [18,[31][32][33][34]. ...
This paper investigates the main similarities and discrepancies among three important current decompositions proposed for the consideration of unbalanced and/or non linear three-phase three-wire power circuits. The considered approaches were the so called FBD Theory, the pq-Theory and the Conservative Power Theory (CPT), recently presented by Tenti et al. Such decompositions and related definitions may influence the power measurement techniques, revenue metering, instrumentation technology and also power conditioning strategies. The three methods have been summarized, discussed and compared by means of computational simulation. Although the three methods are based on different concepts, the results obtained under ideal conditions are very similar. The main differences appear in the presence of unbalanced and non linear load conditions. Under linear unbalanced conditions, both FBD and pq-Theory suggest that the some current components contain a third-order harmonic. Besides, neither pq-Theory nor FBD method are able to provide accurate information for reactive current under unbalanced and distorted conditions, what can be done by means of the CPT-Theory. The paper tries to explain the causes of these differences in terms of the decomposition's foundations and the resulting waveforms and spectra.
... However, it introduces new harmonics to the active current which is not desired in nonactive power compensation. Non-integer multiple harmonics are defined as non-periodic currents in [7] and the compensation is discussed. Nonperiodic currents are also discussed in [8]. ...
This paper presents a theory of instantaneous nonactive power/current. This generalized theory is independent of the number of phases, whether the load is periodic or non-periodic, and whether the system voltages are balanced or unbalanced. By choosing appropriate parameters such as the averaging interval T<sub>c</sub> and the reference voltage V<sub>p</sub>, the theory has different forms for each specific system application. This theory is consistent with other more traditional concepts. The theory is implemented in a parallel nonactive power compensation system, and several different cases, such as harmonics load, rectifier load, single-phase pulse load, and non-periodic load, are simulated in MATLAB. Unity power factor or pure sinusoidal source current from the utility can be achieved according to different compensation requirements. Furthermore, the dynamic response and its impact on the compensator's energy storage requirement are also presented.
... Three-phase abc currents and voltages must be transformed into the ~$ 0 space. The abc -aP0 transformation is shown in (2). ...
This research presents the detailed implementation of a current controller with three-dimension (3D) space vector pulse width modulation (SVPWM) for active filters used in four-wire unbalanced power systems. Many techniques of current control are widely known for three-wire balanced systems. However some modifications must be done in the original techniques when the system is unbalanced and has a neutral conductor. Few works are explicit and detailed on this subject. This paper shows the complete process of implementation of a four-wire current controller with a three-leg inverter and makes a comparison of its performance with the performance of the conventional hysteresis-based current controller.
... However, in some cases, such as cycloconverters and line-commutated three-phase thyristor-based rectifiers, the line currents may contain both sub-harmonics (frequency lower than fundamental frequency) and super-harmonics (frequency higher than fundamental frequency but not an integer multiple of it). These waveforms are considered as non-periodic, although mathematically the currents may still have a periodic waveform, but in any event, the period of the currents is not equal to the period of the fundamental voltage [1], [2]. An arc furnace is another example of a non-linear load that generates non-periodic currents because it draws rapidly changing power from the source and the waveshape and amplitude are constantly changing. ...
Based on a new definition of nonactive current/power, this paper presents the application of a parallel active filter for the compensation of nonperiodic currents. Analysis of the compensation characteristics required for a variety of nonperiodic currents such as those associated with arc furnaces is presented. In addition, the corresponding current rating and energy storage requirements of the compensator are also presented.
... T HE WIDESPREAD use of nonlinear loads and power electronics converters, such as cycloconverters and linecommutated three-phase thyristor-based rectifiers, has increased the generation of nonsinusoidal and nonperiodic currents and voltages in power systems [1], [2]. An arc furnace is an example of a nonlinear load that may draw rapidly changing nonsinusoidal currents. ...
... The values of the instantaneous power p and q, which are the real respective imaginary powers, contain dc-and accomponents [25], [28] depending on the existing active, reactive and distorted powers in the system. The dccomponents of p and q represent the active and reactive powers and must be removed with high-pass filters (HPF in Fig. 7 with a cutting frequency between 5 Hz -35 Hz) to retain only the ac-signals. ...
This article gives a survey of the commonly used methods for harmonic detection in active power filters (APFs). The work proposes a simulation setup that decouples the harmonic detection method from the active filter model and its controllers. In this way, the selected methods can be equally analyzed and compared with respect to their performance, which helps in anticipating possible implementation issues. A comparison is given that may be used to decide the future hardware setup implementation. The comparison shows that the choice of numerical filtering is a key factor for obtaining a good accuracy and dynamic performance of an active power filter.
Symmetry is not only used to simplify the analysis of three-phase electrical systems, but it is also used to define its voltages, currents and loads. When the loads are symmetrical, the currents of a three-phase AC system are expected to be symmetrical as well. Given the proper conditions, in converters such as the matrix converter (MC), the output voltages and currents are expected to be sinusoidal with periodic symmetry. However, in some cases this symmetry is broken so that, there appears nonlinear behaviors such as quasiperiodicity and so on. Based on simulations and experiments, this paper focuses on an analysis of a quasiperiodic behavior and the presence of a DC component in the output currents of a Venturini modulated MC. The presence of such behaviors in the output currents indicates that the symmetry in a period is broken. The broken symmetries appear when the input and output frequencies are mismatched. In addition, this paper shows the possibility to recover the symmetry of the output currents of the MC. The method for symmetry recovery is based on a time-delayed feedback control. The simulation and experimental results indicate the possibility of attenuating the quasiperiodic behavior and DC component.
In this article the conclusion of methods useful for determining instantaneous power in the three-phase circuits with periodic nonsinusoidal waveforms, published in Przegla̧d Elektrotechniczny, R. 82 Nr. 6/2006, have been presented. This paper also answers the criticism to the paper [7] published in Nr.7-8/2006. The theoretical considerations have been illustrated by a simulation examples. P-Q instantaneous power theory - a correct theory or useful algorithm for switched compensator control - the conclusion.
The paper investigates how the Instantaneous Reactive Power (IRP) p-q Theory describes power properties of electrical loads operating under sinusoidal conditions. This study demonstrates that the IRP p-q Theory suggests the presence of a reactive current in supply lines of purely resistive loads and the presence of an active current in supply lines of purely reactive loads. Moreover, it suggests the presence of nonsinusoidal current components in linear circuits with sinusoidal supply voltage. This study shows moreover that the IRP p-q Theory does not identify power properties of three-phase loads instantaneously. A pair of instantaneous values of p and q powers does not allow us to conclude whether the load is resistive, reactive, balanced or unbalanced. Moreover, this study shows that the p-q Theory does not identify the load imbalance as the cause of the power factor degradation. Consequently, investigations reported in this paper indicate that the Instantaneous Reactive Power p-q Theory seems to misinterpret power phenomena in unbalanced systems with sinusoidal voltages and currents.
Traditional sinusoidal power theory is not feasible for non-sinusoidal condition. The existing non-sinusoidal instantaneous power theories have no clear physical meanings. To solve this problem, this paper presents a definition of instantaneous active and reactive power based on the parameter identification. The simplified equivalent model in time domain is built. Using the least squares approximation method, the approach of definition and measurement of instantaneous power is given. This definition has a distinct physical meaning. It is feasible for arbitrary non-sinusoidal voltage and current, especially for non-periodical waveforms. The theory is evaluated for linear, varying and non-linear loads in the presence of harmonics, showing the rationality and feasibility.
One of the methods for high harmonic reduction, reactive power compensation or symmetrization in three phase system is using Active Power Filter (APF). APF connected to power system, depending on control strategy and configuration, can realize all of these functions or only selected ones. For example parallel APF systems allow to:compensate fundamental frequency of reactive component of load current, symmetrize of load connected to network output terminals, filter higher harmonics of currents regardless of network impedance and with efficiency which is not accessible in the case of passive LC filters. This chapter concerns control algorithms for active power filters (APF). Theoretical considerations have been supplemented by simulation and experimental results.
The main objectives of this paper are to improve power factor and reduce harmonic distortion in the supply voltage and current, thereby improving power and/or voltage quality of the system. The harmonic distortion due to the development of power electronicbased equipment is discussed in this paper. To resolve the energy flow issue due to non-linear loads, we present a new closed loop control system with a simple linear integrated circuit which is proposed for the shunt triggering compensator (STC). The STC is investigated through Matlab simulation for under unbalanced supply and load conditions and simulated results are compared with hardware results.
Traditional sinusoidal power theory is not feasible for non-sinusoidal condition. The existing non-sinusoidal power theories have no clear physical meanings. To solve this problem, this paper presents a time-varying power theory based on the instantaneous sinusoidal expression of DFT (Discrete Fourier Transform). For arbitrary voltage and current signals, use the DFT to get their sinusoidal expression, and calculate the time-varying active power and the time-varying reactive power. This definition is feasible for any periodical and non-periodical signals. It has a distinct physical meanings, especially the time-varying reactive power can show the scale and direction of load's electromagnetic energy oscillation. It can embrace the sinusoidal power, Budeanu power and Fryze'active power. Finally, the rationality and feasibility of this time-varying power is demonstrated by theoretical analysis and work examples.
A shunt active power filter is used to draw reactive and harmonic components of the load power and allow only real component of the load power to be drawn from the source. Whereas a front end converter is used to control the active power flow exchange between the grid and the load. This paper presents a new approach for the shunt active power filter where it also acts as a front end converter. Firstly, it feed active power to the DC loads through the DC link and secondly, it serve as a reactive and harmonic power source for the AC load which is supplied real power from the main grid. A generalized p-q theory is applied for controlling the unified shunt active power filter and front end converter without any addition of extra components. The DC link voltage of the converter is controlled by comparing it with a reference value. Operating principle and working performance for different load perturbations are presented in detail for the converter. Control performance of the proposed shunt active power filter as front end converter is verified through the simulation studies on PSCAD/EMTDC programming platform.
Presents issues related to methods of improving power quality
Focuses on the use of active compensators
Illustrates theoretical considerations with results from laboratory research
Power quality describes a set of parameters of electric power and the load’s ability to function properly under specific conditions. It is estimated that problems relating to power quality costs the European industry hundreds of billions of Euros annually. In contrast, financing for the prevention of these problems amount to fragments of these costs. Power Theories for Improved Power Quality addresses this imbalance by presenting and assessing a range of methods and problems related to improving the quality of electric power supply.
Focusing particularly on active compensators and the DSP based control algorithms, Power Theories for Improved Power Quality introduces the fundamental problems of electrical power. This introduction is followed by chapters which discuss:
•‘Power theories’ including their historical development and application to practical problems,
•operational principles of active compensator’s DSP control based algorithms using examples and results from laboratory research, and
•the key areas of application for these methods and suggested practical solutions.
Power Theories for Improved Power Quality is a key study resource for students in engineering and technical degrees as well as a reference for professional and practitioners in the electrical energy sector working with power quality.
This paper investigates the major similarities and discrepancies of three important current decompositions proposed for the interpretation of unbalanced and/or non linear three-phase four-wire circuits. The considered approaches were the so-called FBD theory, the pq-theory and the CPT. Although the methods are based on different concepts, the results obtained under ideal conditions (sinusoidal and balanced signals) are very similar. The main differences appear in the presence of unbalanced and non linear load conditions. It will be demonstrated and discussed how the choice of the voltage referential and the return conductor impedance can influence in the resulting current components, as well as, the way of interpreting a power circuit with return conductor. Under linear unbalanced conditions, both FBD and pq-theory suggest that the some current components contain a third-order harmonic. Besides, neither pq-theory nor FBD method are able to provide accurate information for reactive current under unbalanced and distorted conditions, what seems to be done by means of the CPT.
Presently available voltage sag compensators are unable to handle neutral current caused by unbalanced and/or nonlinear loads or unbalanced source. In this paper, a 3-phase, 4-wire voltage sag compensator base on 3 dimensional voltage space vector is proposed which can handle the neutral current under voltage sag and nonlinear load conditions. A computer simulation model using PSIM has been developed to analyses the performance of the systems and its effectiveness to mitigate voltage sags
In the attempt to minimize the harmonic disturbances created by the non-linear loads the choice of the active power filters comes out to improve the filtering efficiency and to solve many issues existing with classical passive filters. One of the key points for a proper implementation of an active filter is to use a good method for current/voltage reference generation. There exist many implementations supported by different theories (either in time- or frequency-domain), which continuously debate their performances proposing ever better solutions. This paper gives a survey of the common used theories. Then, the work here proposes a simulation setup that decouples the harmonic reference generator from the active filter model and its controller. In this way the selected methods can be equally analyzed and compared with respect to their performance, which helps anticipating possible implementation issues. The conclusions are collected and a comparison is given at the end, which is useful in deciding the future hardware setup implementation. The comparison shows that the choice of numerical filtering is a key factor for obtaining good accuracies and dynamics for an active filter.
This paper presents a general definition of nonactive current/power and the implementation for a shunt compensation system. This definition is universal for different loads, such as nonperiodic, unbalanced or single phase, and also flexible in terms of the compensation results. Unity power factor, pure sinusoidal source current, or zero nonactive power supply from the utility can be achieved according to different compensation requirements. In addition, the corresponding current rating and energy storage requirements of the compensation system are also presented.
The paper discusses the operation and control characteristics of a Distribution Static Compensator (DSTATCOM). The main aim of the DSTATCOM is to protect the utility system from the ill effects of customer loads. The DSTATCOM, when operated in current control mode, cancels the distortion caused by the load, such that current drawn by the compensated load is a pure balanced sinusoid. In this paper it is assumed that the load draws noninteger harmonic current such that its waveform is aperiodic in nature. An algorithm is proposed for extracting phasor symmetrical components from the samples of these waveforms. The proposed algorithm is verified through extensive digital computer simulation studies using MATLAB.
Active filters have been drawing a lot of attention and have been put into practice to compensate the harmonies generated by nonlinear loads, mainly rectifiers, in electric power systems. By now, the shunt active filter is the most popular type of active filter. It has been noticed that the shunt active filter may have very different compensation characteristics for different types of rectifier loads but no detailed quantitative analysis and results have been reported so far. The purpose of this paper is to investigate and have a good understanding of the compensation characteristics of the shunt active filter under different type and parameters of rectifier converter load. Two approaches are employed. Firstly, circuit analysis based on simplified models for the active filter and the rectifier with different load is carried out, which generates qualitative results that are very helpful to the understanding of different compensation effects. Then computer simulations on a shunt active filter compensating a rectifier load is the major approach to this investigation. The simulation results verify the theoretical analysis and provide a thorough insight of the compensation characteristics of the shunt active filter under different type and parameter of rectifier loads, and therefore hopefully reveal answers to some of the previous questions regarding the compensation characteristics.
This paper presents a general control method that fully utilizes the inherent capability of AC-fed PWM converters to compensate for reactive and harmonic currents absorbed by other loads. For this purpose, suitable definitions of instantaneous active and reactive current and power terms are introduced. Simulated results demonstrate the capabilities of the proposed compensation method, which can also be implemented in existing systems, as only modifications of the control section are needed.
Different power theories are examined, with regard to their applicability in controlling dynamic filters for non-active power. Frequency-domain approaches and a range of time-domain approaches are considered, the latter being inherently more suitable for real-time control of dynamic filters. Finally, some detailed attention is devoted to a combination of the approaches by Fryze, Buchholz and Depenbrock. This FBD-approach leads to a general time-domain resolution of power components in a generalized m-wire system that can be used effectively in deriving control algorithms for dynamic filters of non-active power.
Attention has been paid to active filters for power conditioning which provide the following multifunctions: reactive power compensation; harmonic compensation; flicker/imbalance compensation; and voltage regulation. Active filters in a range of 50 kVA-60 MVA have been practically installed in Japan. In the near future, the term "active filters" will have a much wider meaning than it did in the 1970s. For instance, active filters intended for harmonic solutions are expanding their functions from harmonic compensation of nonlinear loads into harmonic isolation between utilities and consumers, and harmonic damping throughout power distribution systems. This paper presents the present status of active filters based on state-of-the-art power electronics technology, and their future prospects and directions toward the 21st Century, including the personal views and expectations of the author
A simple and cost-effective solution to reduce the passive filter
terminal voltage total harmonic distortion (THD) is outlined. A modified
synchronous reference frame (SRF) based controller for the series active
filter allows injection of a controlled percentage of the higher
harmonic load currents into the supply, in compliance with the IEEE 519
harmonic current standards, thereby reducing the passive filter terminal
voltage THD. This implementation retains all the desirable features of
the original SRF controlled hybrid series active filter system. It
reduces the rating and size of the passive filter system and allows the
use of simpler passive filter system structures such as only a simple
high pass passive filter or a simple power factor correction capacitor
as the passive filter system. Simulation and experimental results are
used to establish the functionality and performance of the SRF
controller and the modified SRF controller for the hybrid series active
filter system
This paper describes a three-phase four-wire shunt active power
filter using a conventional three-leg converter, without the need of
power supply at DC bus. Two approaches have been developed to control
the active filter. Both control strategies consider harmonics and zero
sequence components in the voltage and current simultaneously. The first
one provides constant power and the second one sinusoidal current to the
source, even under unbalanced voltage conditions. Simulation results
from a complete model of shunt active filter are presented to validate
and compare the control strategies
It might be expected that the meaning of the apparent power S, a
quantity of innumerable everyday applications for almost a century, is
well understood. It occurs, however, that this meaning is still a matter
of discussion and some interpretations hard to accept are published.
Also it is suggested in some papers published recently that only
oscillations of the instantaneous power may cause an increase of the
apparent power S, which is not true. Misinterpretations that refer to
fundamental notions such as powers could be particularly harmful for
electrical engineering and should be eliminated as much as possible.
Therefore, this paper shows that the apparent power does not have the
physical meaning suggested recently. Also it shows that load unbalance
in three-phase power systems does not cause any oscillation of the
instantaneous power. The conclusion that load unbalance causes
oscillations of the instantaneous power is a consequence of a
substantial misinterpretation of this quantity in three-phase power
systems
Conventional active and reactive power theory, valid for the
steady-state analysis is reviewed. The instantaneous power theory,
introduced by H. Akagi et al. (1983, 1984) is also presented. This
instantaneous theory is valid for steady and transient states and for
generic voltage and current waveforms. Some examples explaining the
physical meaning of the new concepts are presented. By using the
concepts of symmetrical components together with the new theory, the
powers in an unbalanced system are analyzed, including the zero-sequence
instantaneous power. An example showing how this theory can be used to
design and control an active power filter is presented. Some simulation
results are presented and discussed
A new definition of instantaneous reactive power is presented.
This definition has a clear physical meaning that includes both the
conventional instantaneous reactive power and the instantaneous power of
a zero-phase component. A simple control algorithm for the active filter
derived from the new definition is described. Simulations verified the
control algorithm
The conventional reactive power in single-phase or three- phase circuits has been defined on the basis of the average value concept for sinusoidal voltage and current waveforms in steady states. The instantaneous reactive power in three-phase circuits is defined on the basis of the instantaneous value concept for arbitrary voltage and current waveforms, including transient states. A new instantaneous reactive power compensator comprising switching devices is proposed which requires practically no energy storage components.
Recent surveys of 208/120 V three-phase four-wire electric systems, buildings, and industrial plants with computers and nonlinear loads show excessive currents in the neutral. These neutral currents are fundamentally third harmonic, and their presence is tied to wiring failures, elevating of neutral potentials, transformer overheating, etc. In response to these concerns, this paper proposes a new active power filter scheme to cancel neutral current harmonics. The proposed approach employs a star/delta transformer along with a two-switch PWM-controlled active filter. The closed loop control of the active power filter guarantees cancellation of neutral current harmonics under varying load conditions. The proposed system drastically improves the overall system performance and virtually eliminates transformer overheating due to harmonics. Experimental results from a prototype active power filter confirm the suitability of the proposed approach.
A novel control strategy for an active power filter that consists
of a current-source PWM (pulse width modulation) converter and LC
filters to eliminate the PWM carrier frequency components is
proposed in order to obtain good harmonic compensation characteristics.
The PWM converter is controlled with feedback loops of filter input
currents and their derivatives to suppress the transient oscillations
caused by the LC filters without inserting damping resistors.
Optimum values of feedback gains are investigated. The cut-off frequency
of the optimum design is about one seventh of the PWM carrier frequency,
and the compensation delay time is two times as large as the carrier
period. The performance of the active power filter with the proposed
control strategy was confirmed by experiments in which the harmonic
currents generated by a phase-controlled bridge converter were
compensated. Input current after compensation was essentially
sinusoidal, and the harmonic content was reduced to less than 4%
A novel approach to compensating for harmonics in power systems is
presented. It is a combined system of a shunt passive filter and a small
rated series active filter. The compensation principle is described, and
some filtering characteristics are discussed in detail. Excellent
practicability and validity to compensate for harmonics in power systems
are demonstrated experimentally. Although the source harmonic voltage
was only 1%, the source harmonic current reached about 10% before the
series active filter was started. After it was started, no harmonic
current flowed into the shunt passive filter. In addition, no harmonic
voltage appeared at the terminals of the shunt passive filter, because
the source harmonic voltage was applied to the series active filter. The
total loss of the series active filter was less than 40 W. It is
concluded that the combined system is far superior in efficiency to
conventional shunt active filters
Harmonic Current Compensation Using Three-Phase current source converter
- S.-Y Choe
- K Heumann