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Evaluation of a shunt active power conditioner with a modified control scheme under nonperiodic conditions
Abstract
Nonperiodic waveforms are produced in power systems under various operating conditions; it is convenient to suppress such waveforms via the active filter dedicated to harmonics. An active power conditioner is scrutinised and modified to treat both periodic and nonperiodic waveform distortions. A new consistent and practical index to assess the distortion of nonstationary and nonperiodic signals is established. Its fidelity and potential for real applications are also addressed. The conditioner operation is examined under nonperiodic load currents with different types of nonperiodicity. The proposal is compared with both Fryze's and instantaneous power control techniques. The active conditioner is shown to be competent in compensating periodic and nonperiodic current distortions.
... By definition, any power system quantity (voltage, current) whose frequency content is not integer multiples of the system supply frequency (i.e. 50 Hz, 60 Hz) is considered nonperiodic [1]. The time duration of the non-periodicity could be from a fraction of one period of the power system frequency up to a steady state component of the current or voltage. ...
... One of the main advantages of modulation index criterion, compared to the frequency based criteria is the fact that its calculation merely needs half of one period of the modulation frequency. On the other hand, to calculate the frequency based criteria, such as distortion factor [1], at least one period of the modulation frequency is needed. ...
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 general, any power system quantity (voltage, current) whose frequency content is not integer multiples of the system supply frequency (i.e. 50 Hz, 60 Hz) is con- sidered a non-periodic quantity [40]. The time duration of the non-periodicity could be from a fraction of one period of the power system frequency up to a steady state component of the current or voltage [36]. ...
... One of the main advantages of modulation index criterion, compared to the fre- quency based criteria is the fact that its calculation merely needs half of one period of the modulation frequency. On the other hand, to calculate the frequency based crite- ria, such as distortion factor [40], at least on the period of the modulation frequency is needed. ...
In this dissertation, a new technique is proposed for the compensation of nonperiodic 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). To improve the flexibility of the technique, a fuzzy based adaptive window is proposed for the slow compensator to find the optimum window for different load characteristics. Moreover, three power quality criteria are proposed specifically for the non-periodic current compensation, namely, time-frequency distortion index, modulation index, and high frequency distortion index. The method is verified using both simulation and real-time implementation. First, the proposed method is verified in simulation using real-world data acquired from a local steel mill. Second, it is validated using a real-time controller-in-the-loop implementation. The proposed compensation approach demonstrates high flexibility and effectiveness in increasing power quality under various non-periodic load conditions. Finally, some practical aspects of the implementation of a three-part compensator including cost analysis are presented.
... 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. ...
... 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.
... 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]. ...
... The instantaneous active current i a (t) and the instantaneous non-active current i n (t) are given in Eqs. (5) and (6) respectively. ...
... 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]. ...
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. ...
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.
To overcome the limitations of conventional shunt passive filters, which are invariably used for harmonic filtering, a quasi-passive filter (QPF) has been proposed. It comprises a parallel and series tuned LC tank circuit. Unlike the conventional shunt passive filter, the QPF utilises a large value AC capacitor. Unipolar DC capacitors and power semiconductor devices have been used to realise the large value AC capacitor. The operation of the QPF is simple and it does not require the complex control methods of active power filters. With certain modifications in the QPF, a modified quasi-passive filter (MQPF) has been proposed, which can be used for reactive power compensation in addition to harmonic filtering. The proposed QPF and MQPF have been verified through analysis and simulation. Experiments are carried out to verify the validity of the QPF.
Power quality is an important measure of the performance of an electrical power system. This paper discusses the topology, control strategies using artificial intelligent (AI) based controllers and the performance of a unified power quality conditioner (UPQC) for power quality improvement. UPQC is an integration of shunt and series compensation to limit the harmonic contamination within
5 %, the limit imposed by IEEE-519 standard. The novelty of this paper lies in the application of neural network control (NNC) algorithms such as model reference control (MRC), and nonlinear autoregressive-moving average (NARMA)L2 control to generate switching signals for the series compensator of the UPQC system. The entire system has been modeled using MATLAB 7.0 toolbox. Simulation results demonstrate the applicability of MRC and NARMA-L2 controllers for the control of UPQC.
This paper charts the development of a network-wide harmonic control scheme using an active filter. The individual components required are discussed and developed. By examining the operation of the scheme as a whole, fresh insights are gained into the applicability of previously proposed techniques. The final scheme was shown to systematically reduce harmonic voltage levels across a network to within specified limits, without the need for a priori network impedance information. This work hence demonstrates the feasibility and effectiveness of active filter based network-wide harmonic control.
Many definitions have been formulated to characterize, detect and
measure active and nonactive current and power for nonsinusoidal and
nonperiodic waveforms in electric power systems. This paper presents
definitions and compensation of nonactive current from the compensation
standpoint
Major power quality indices such as total harmonic distortion,
power factor, K-factor and others are presented, analysed and discussed.
The limitations, deficiency and difficulty of practical application of
these FFT-based indices in quantifying the quality of three-phase power
systems are manifested. Modified versions of each index that avoid its
unwanted drawbacks are suggested utilising the potential of wavelet
multiresolution signal decomposition. A load nonlinearity indicator is
proposed as a novel power quality index. Advantages of the new indices
are highlighted
A new universal power quality manager is proposed. The proposal
treats a number of power quality problems simultaneously. The universal
manager comprises a combined series and shunt three-phase PWM controlled
converters sharing a common DC link. A control scheme based on fuzzy
logic is introduced and the general features of the design and operation
processes are outlined. The performance of two configurations of the
proposed power quality manager are compared in terms of a recently
formulated unified power quality index. The validity and integrity of
the proposed system is proved through computer simulated experiments
This paper addresses the subject of transient electric power
quality problems. The quantification of power quality in terms of simple
indices such as total harmonic distortion and other measures is
revisited in terms of the windowed Fourier transform. This transform is
a short term Fourier transform evaluated over a time window. The result
is a set of new power quality indices which collapse to the familiar
forms for the cases of periodic steady state, but which capture
transient amplitudes for nonsteady state applications. Applications are
suggested
- Elmitwally