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Universal power quality manager with a new control scheme
Abstract
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
... Fig. 1 shows the general power circuit configuration of the USPAF system. The USPAF structures are used in the literature such as two three-phase three-leg (3P3L) voltage source inverter (VSI) with split capacitor [7,[10][11][12][13][14], a 3P3L VSI for the series AF and a three-phase four-leg (3P4L) VSI for the parallel AF [15,16] and two 3P4L VSI topology [17] for solving power quality disturbances at the point of common coupling (PCC). ...
... In the previous studies, the control algorithms for current and voltage compensators were often based on the assumption that the load currents and the source voltages were periodic. The USPAF systems have been applied to the compensation of voltage fluctuations related non-periodic waveform in recent years [6,10,[20][21][22]. Different non-active power theories in the time domain have been discussed in [23]. ...
... Generally, it adopts three-phase three-wire system in the independent and small power system, and the main circuit structure of parallel active power filter is shown as Figure 4. (Thomas et al., 1998;Elmitwally et al., 2000;Komurcugil and Kukrer, 2006;Han et al., 2005). From Figure 4, it can get the VSR voltage vector equation if neglect the VSR ac side resistance, as follow: ...
Aiming at the serious influence on the power frequency stabilisation for independent power system when its loads are largely changed, a control strategy of active power filter is presented. Firstly, the principle of second-order direct type IIR (infinite impulse response) digital notch filter is described, and the frequency real-time detection model is established based on least mean power (LMP, p = 3) adaptive algorithm to track the notch filter parameters. Then, combining the instantaneous reactive power theory and hysteresis current method, the simulation model of active filter control strategy with power frequency's change is established. Finally, the simulation results proved that the active power filter model can track the changing frequency quickly and compensate harmonic current accurately. Therefore, the power quality and reliability of the small power grid are enhanced.
... The unified power quality conditioner (UPQC) has been widely studied to compensate for the disturbances of source voltages and load currents simultaneously. The UPQC has been applied to the compensation of voltage fluctuations related to nonperiodic waveforms in recent years [7][8][9][10][11]. In addition, some recent UPQC topologies have been proposed, such as UPQC with distributed generation [12], MC-UPQC [13], and modular UPQC [14], for solving power quality problems at the PCC. ...
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.
... The unified power quality conditioner (UPQC) has been widely studied to compensate for the disturbances of source voltages and load currents simultaneously. The UPQC has been applied to the compensation of voltage fluctuations related to nonperiodic waveforms in recent years7891011. In addition, some recent UPQC topologies have been proposed, such as UPQC with distributed generation [12], MC-UPQC [13], and modular UPQC [14], for solving power quality problems at the PCC. ...
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.
... In general, these methods make use of feature extraction techniques followed by traditional pattern recognition techniques. The wavelet transforms are been widely employed for feature extraction [6, 7, 8, 9, 10] and for pattern recognition the artificial neural networks [11, 12], fuzzy logic [13, 14], genetic algorithms [15] and support vector machines [16] are been used. In this paper, the proposed method for PQ event classification is presented and a comparison with two other methods [6, 7] and [12] is performed. ...
This paper presents a novel method for classification of power quality events in voltage signals which makes use of higher order statistics based technique for extracting a re-duced and representative event signature vector. The signa-ture vectors composed of samples from the diagonal slices of the second and forth order cummulants, which are selected with Fisher's discriminant ratio (FDR), provide enough sep-arability among classification regions resulting in classifica-tion rate as high as 100% if the voltage signals are corrupted by the presence of isolated events. A comparison perfor-mance among the proposed method and two other ones found on the literature is provided and reveals that the proposed method not only achieve a good performance, but it also sur-pass the performance of previous techniques.
... For the type of transient event, it has been shown that the method has advantages of being faster and more precise in discrimination than conventional approaches. A two-stage system that employs the wavelet transform and the adaptive neuro fuzzy networks for power quality identification is proposed in [13]. In this method, the wavelet multiresolution signal analysis is exploited to reduce noise and then decompose the monitored signals of the power quality events to extract its detailed information. ...
An Energy Difference of Multiresolution Analysis (EDMRA) method for power quality (PQ) disturbances analysis has been proposed in this paper. At each wavelet decomposition level, the squared value of the detail information is calculated as their energy to construct the feature vector for analysis. Following the criteria proposed in this paper, different kinds of power quality disturbances can be detected, localized, and classified effectively. The choice of the decomposition levels of appropriate wavelets are of the critical importance for the EDMRA method, since they will influence quality of the reconstructed signal as well as the computational cost. It is presented in this paper that the Minimum Decomposition Level (MDL) is related to the sampling frequency by the proposed function. The comparison study among different kinds of wavelets for the EDMRA method is presented in details. The EDMRA method is scalable and has robustness characteristics in common design paradigm. It can be realized economically using wavelets with shortest length, such as Harr, Db2, Sym2 or Coif 1. Two types of noise, namely, Gaussian white noise and band limited spectrum noise are considered in this paper to show the effectiveness of the proposed method in noisy environment.
... The compensation signals for series filter are thus obtained by comparing these reference load voltages with actual source voltage, compensation signals are compared with actual signals at the terminals of series filter and the error is taken to hysteresis controller to generate the required gating signal for series filter. The shunt APF compensates current harmonics in addition to maintaining the dc link current at a constant level [17]. To achieve this, dc link current of the UPQC is compared with a constant reference current of magnitude equal to peak of harmonic current. ...
In this paper unified power quality conditioner (UPQC) is being used as a universal active power conditioning device to mitigate both current as well as voltage harmonics at a distribution end of power system network. The performance of UPQC mainly depends upon how quickly and accurately compensation signals are derived. The steady state and dynamic operation of control circuit in different load current and/or utility voltages conditions is studied through simulation results. The presented method has acceptable dynamic response with a very simple configuration of control circuit. This paper presents performance validation of Current Source Inverter (CSI)-based UPQC using Fuzzy Logic Controller (FLC) and Results are compared with conventional PID Controller and improvements are observed by FLC. The FLC-based compensation scheme eliminates voltage and current magnitude of harmonics with good dynamic response. Extensive simulation results using Matlab/Simulink for RL load connected through an uncontrolled bridge rectifier validates the performance of FLC compensator.
... It can regulate the terminal voltage, eliminate the harmonic current and compensate the reactive power at the same time. In the control strategy for this type of circuit structure, the series active filter (AF) is controlled as a voltage source to compensate source voltage flicker and harmonics, whereas the shunt AF is controlled as a current source to absorb the current harmonics generated by the nonlinear load and regulate the DC link voltage [8][9][10][11][12]. After such compensation the voltage at the load terminal will be sinusoidal in the normal magnitude, the power source output current will be sinusoidal and the input power factor will be unity. ...
A universal power quality manager (UPQM) is presented. The active power balance of this UPQM is analysed. Based on the analysis a control scheme is established in a two-phase synchronous rotating dq-frame. In this control scheme the series active filter (AF) is controlled as a current source and makes the input current sinusoidal, while the shunt AF is controlled as a voltage source and it keeps the load voltage at the normal value. The performance of a UPQM with the proposed control scheme under different nonlinear load and source disturbance conditions is experimentally investigated.
... Ibrahim et al. provided an excellent survey of the advanced AI techniques for PQ application [2]. The most interesting AI tools for PQ Manuscript problems include Expert Systems (ES) [3], Fuzzy Logic (FL) [4]- [7], Artificial Neural Networks (ANNs) [5], [8]- [10] and Genetic Algorithms (GA') [11]. Recent advances in wavelet transforms provide another powerful tool for PQ classification. ...
This paper proposed a novel approach for the Power Quality (PQ) disturbances classification based on the wavelet transform and self organizing learning array (SOLAR) system. Wavelet transform is utilized to extract feature vectors for various PQ disturbances based on the multiresolution analysis (MRA). These feature vectors then are applied to a SOLAR system for training and testing. SOLAR has three advantageous over a typical neural network: data driven learning, local interconnections and entropy based self-organization. Several typical PQ disturbances are taken into consideration in this paper. Comparison research between the proposed method, the support vector machine (SVM) method and existing literature reports show that the proposed method can provide accurate classification results. By the hypothesis test of the averages, it is shown that there is no statistically significant difference in performance of the proposed method for PQ classification when different wavelets are chosen. This means one can choose the wavelet with short wavelet filter length to achieve good classification results as well as small computational cost. Gaussian white noise is considered and the Monte Carlo method is used to simulate the performance of the proposed method in different noise conditions.
This paper presents the operation of unified power quality conditioner(UPQC) as a universal active powerconditioning device to mitigate both current as well as voltage distortions at a distribution end ofpower system network. The UPQC is designed by combining a series active power filter(DVR) and shunt active power filter (DSTATCOM) which shares a common DC link capacitor. Series compensator which is meant for voltage restoring is controlled by a fuzzy logic controller. Shunt compensator's operation is controlled by extracting d axis and q axis current from load current and DC link voltage is maintained through a fuzzy logic controller. The performance of UPQC mainly depends upon how quickly and accurately compensation signals are derived. The steady state and dynamic operation of control circuit in different load current and/or utility voltages conditions is studied through simulation results. The presented method has acceptable dynamic response with a very simple configuration of control circuit. The designed UPQC is tested with an induction motor load. It is able to mitigate voltage sag/ swell, reactive power compensation, voltage fluctuations, harmonic elimination etc. under these load conditions. The proposed system and controller is validated using MATLAB/simulink. The simulation results expresses a low THD and a perfect compensation.
With electric power industry deregulation and conflicts caused by power quality (PQ) disturbances becoming serious, the solution to PQ problems has not only involved engineering technology, but also social economy and resource optimization. As an important content of ancillary service market, PQ service needs to be realized in market circumstance. This paper introduces the concept of PQ market and its research objects, establishes the framework of PQ market theory, proposes the research approaches and explains the three pieces of preliminary knowledge. As an elementary study of PQ market theory, some problems worthy of research are described.
The conflicts caused by PQ(Power Quality) disturbances turn more serious and solution to PQ problems becomes more important It depends on both engineering technology and management policy of government. The PQ mitigation technology and equipment are reviewed. The disparities in the consciousness and management policies of power quality between domestic and foreign electric utilities are summarized and contrasted, as well as the power quality mitigation levels. Aiming at the problems in China, the author gives some suggestions about system reformation, standards improvement and technology elevation.
Recent times due to the increased usage of loads, maintaining
the power factor and harmonic standards are the major
challenging task for control engineer. This paper presents the
power quality enhancement in power distribution system both
linear and nonlinear with the help of shunt active power filter
(D-STATCOM) and series active power filter (DVR) using PI
controller. The proposed method mitigates current and voltage
related power quality problems with dc link voltage. The total
harmonic distortion value is reduced from 8.05 percent to 0.44
percent using MATLAB software
This paper presents a new compensating system, consisting of series and shunt active filters, for mitigating voltage and current disturbances. The shunt filter is used to compensate for unbalanced and distorted load currents. The series filter comprises two inverters, used to suppress voltage disturbances and handle source currents independently. This configuration is devised to reduce the overall cost of active compensators by using low-frequency high-current switches for the latter inverter. The filters are controlled separately using a novel control strategy. Since voltages at the point of common coupling contain interharmonics, conventional methods cannot be used for extracting voltage references. Therefore, voltage references are obtained from generated sinusoidal waveforms by a phase-locked loop. Current references are detected based on rotating frame vector mapping. Simulation results are presented to verify the system.
This paper proposes a novel reference signal gener- ation method for the unified power quality conditioner (UPQC) adopted to compensate current and voltage-quality problems of sensitive loads. The UPQC consists of a shunt and series converter having a common dc link. The shunt converter eliminates current harmonics originating from the nonlinear load side and the series converter mitigates voltage sag/swell originating from the supply side. The developed controllers for shunt and series converters are based on an enhanced phase-locked loop and nonlinear adaptive filter. The dc link control strategy is based on the fuzzy-logic con- troller. A fast sag/swell detection method is also presented. The ef- ficacy of the proposed system is tested through simulation studies using the Power System Computer Aided Design/Electromagnetic Transients dc analysis program. The proposed UPQC achieves su- perior capability of mitigating the effects of voltage sag/swell and suppressing the load current harmonics under distorted supply conditions.
In this paper, the reason for the deterioration of electric power quality in ship networks these years is discussed. And the necessity of improvement of marine power quality is described considering the effects of this phenomena on economical operation of ship and reliability of marine systems. Afterwards, the criteria of power quality that have been issued in China are introduced, as well as the specific demands on marine power quality. Then, relevant solutions which are applied nowadays to improve power quality of electric network according to the five aspects of power quality - harmonics, fluctuation and flick of voltage, voltage deviation, unbalance of three-phase voltage and current, frequency deviation - are discussed. Finally, the applicability of the employment of the relevant solutions to marine electric power system is discussed, and a new solution that is more suitable for marine use is proposed after its theoretical analysis
This paper introduces a novel strategy of total quality management (TQM) in the electricity supply industry (ESI) in order to achieve quality improvement. Statistical process control tools, such as control charts, cumulative sum charts, correlation coefficients, and scatter diagrams are introduced to analyze the stability and capability of attributes and variables data affecting the quality of real power and reactive power supply. Also Taguchi's technique is applied for quality improvement of the ESI process. The designed TQM technique demonstrates the quality state of power process in the Hellenic ESI. More specifically, the quality condition, relationship, and capability of frequency and voltage are examined, before and after the installation of flexible AC transmission systems devices in the northeastern Hellenic system.
The use of a designed quality plan for application in the electrical power industry is presented. Some contributions of Taguchi’s technique in power process parameter design are reviewed. Recommendations are made for developing a quality-training plan that will incorporate the design of experiments and description of training sources. A case study of the experiment design in the Hellenic power production process is discussed. Difficulties with design of experiments applications to the power process are outlined and suggestions are offered for resolving these difficulties.
In this paper, a control scheme is proposed for a three-phase isolated photovoltaic (PV)-diesel system without an energy storage element. The scheme aims to: Track maximum power from the PV array, regulate the load voltage, compensate the load unbalance viewed by the diesel generator, and to control the diesel engine speed. The first three tasks are achieved by controlling the PWM inverter interfacing the PV array to the system. The fourth is realized by a modified fuzzy logic controller of the diesel engine. The obstacles encountered on operating the system under certain probable loading conditions are addressed. Two strategies are proposed to adapt the control scheme to accommodate all loading scenarios maintaining excellent technical and economic performance. The system operation is investigated under a variety of conditions to prove the aptness of the proposed techniques.
A new optimal control strategy for unified power quality conditioners (UPQC) is presented. This strategy is based on feedback linearisation. The UPQC consists of series and shunt converters, where the series converter usually works as a voltage source, and the shunt converter works as a current source. However, it is possible to use the series converter as a current source, and the shunt converter as a voltage source, as utilised in this study. As for this scheme, an optimal voltage angle at load terminals, in order to minimise the converter losses, is proposed. A comparison with the traditional UPQC, where series and shunt converters are considered to be voltage and current sources, respectively, is also presented.
In this paper, a control scheme is proposed for a three-phase isolated photovoltaic (PV)-diesel microgrid without energy-storage element. The scheme aims to: track maximum power from the PVA, regulate the load voltage, compensate the load unbalance viewed by the diesel generator, and to control the diesel-engine speed. The first three tasks are achieved by controlling the pulse width modulation inverter interfacing the PV array to the system. The fourth is realized by a modified fuzzy logic controller of the diesel engine. The obstacles encountered on operating the system under certain probable loading conditions are addressed. Two different operation strategies are proposed to provide high-quality power under all loading scenarios, and to achieve the targets of the control scheme. The system operation is investigated under a variety of conditions to prove the aptness of the proposed techniques.
Dynamic voltage restorer can provide the most cost effective solution to mitigate voltage sags by establishing the proper voltage quality level that is required by customer. This device is connected in series with the distribution feeder at medium voltage. A fuzzy logic control is proposed. As is known, the PWM converter is actually non-linear, but the PI is a linear controller, so it can only guarantee the stability of this converter in a local area. Simulation results are shown to validate these control methods.
This paper discusses the application of unified power quality conditioner (UPQC) for improving power quality of a system supplying an electric arc furnace (EAF). The UPQC comprises combined series and shunt active filters sharing a common DC link. It is used to mitigate voltage disturbances and compensate for reactive power, harmonics and interharmonics. A novel control strategy of the UPQC is presented. Since voltages at the point of common coupling (PCC) contain low frequency interharmonics, conventional methods cannot be used for extracting voltage reference signals. In the proposed method, voltage references are extracted using active power processing to generate sinusoidal waveforms. Current compensating signals are detected based on current vector mapping on a rotating reference frame constituted by instantaneous phase voltages. A real system is simulated using a three-phase EAF model. Simulation results are presented to verify the control strategy and to assess the performance of UPQC in improving quality of power.
In this paper, a proposed system comprising of a series active
filter and passive branches tuned at some characteristic harmonics is
introduced. The system is capable of compensating current and voltage
harmonics, three-phase voltage unbalance, reactive power and voltage
sags and swells in distribution networks supplying nonlinear loads. It
combines the features of both the universal power quality conditioner
and the dynamic voltage restorer. The series active filter is
current-controlled to force the drawn current to be sinusoidal in phase
with the mains voltage. A fuzzy logic-based controller is adopted to
adjust the reference signal for the system. Thus, the source current and
voltage waveforms are almost sinusoidal and in phase. Meanwhile, load
voltage magnitude is fixed under a wide range of faulty and healthy
operating conditions. Moreover, the compensation capacity of the
proposed system is compared to the conventionally-controlled series
active filter. The integrity and efficacy of the system are verified
through simulation results
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.
A system for the identification of power quality violations is
proposed. It is a two-stage system that employs the potentials of the
wavelet transform and the adaptive neurofuzzy networks. For the first
stage, the wavelet multiresolution signal analysis is exploited to
denoise and then decompose the monitored signals of the power quality
events to extract its detailed information. A new optimal feature-vector
is suggested and adopted in learning the neurofuzzy classifier. Thus,
the amount of needed training data is extensively reduced. A modified
organisation map of the neurofuzzy classifier has significantly improved
the diagnosis efficiency. Simulation results confirm the aptness and the
capability of the proposed system in power quality violations detection
and automatic diagnosis
Fuzzy logic and active power line conditioners (APLC) are two tools that are being increasingly applied to power quality problems. In this paper, a switch-mode APLC that uses fuzzy logic to control the semiconductor switches is described. Frequency-domain analysis is used to determine the desired compensation current, and a rule-based piecewise-linear fuzzy proportional-integral controller (FPIC) provides the appropriate switching pattern of the APLC to generate the actual compensation current. MATLAB simulations and experimental measurements on a low-power (700 VA), digital signal processor-based, hardware prototype show that the APLC produces excellent results despite the use of a relatively low switching frequency, which is necessary to minimize semiconductor switching losses. The simulations and measurements are in good agreement and show that the APLC/FPIC system can significantly improve line current total harmonic distortion and power factor during both steady-state and transient operating conditions.
Increasing interest in power quality has evolved over the past
decade. This paper surveys the literature for current applications of
advanced artificial intelligence techniques in power quality (PQ).
Applications of some advanced mathematical tools in general, and wavelet
transform in particular, in power quality are also reviewed. An
extensive collection of literature covering applications of fuzzy logic,
expert systems, neural networks, and genetic algorithms in power quality
is included. Literature exposing the use of wavelets in power quality
analysis as well as data compression is also cited
A new control algorithm for a converter based device that is
capable of alleviating the problems of harmonic interference and voltage
regulation on radial distribution lines is introduced. It comprises a
relocatable converter in series with a passive filter and is called the
Power Quality Manager. Simulation results based on an existing 88 kV
line are presented. Experimental results are presented, based on a three
phase 200 VA scaled model of the existing 88 kV system
An active power filter connected in series to the power
distribution system is presented and analyzed in this paper. The series
active power filter is implemented with a PWM voltage-source inverter
and operates in conjunction with a resonant LC filter connected in
parallel to the power lines and is able to compensate current harmonics
and the fundamental negative and zero sequence voltage components
generated by nonlinear unbalanced loads. The proposed series active
power filter also compensates zero sequence current harmonic components
that flow through the neutral conductor. In particular, the active power
filter is discussed in terms of the principles of operations under
steady-state and transient operating conditions. The design of the power
and control circuits are reported
The power circuit of a general active power line conditioner
(APLC) is based on series and shunt power converters that share a single
DC link. In the present paper, a generic control concept for these
series and shunt converters is proposed. It is based on the
instantaneous real and imaginary power theory. In fact, the resulting
equipment deals with the custom power and FACTS concepts. This equipment
incorporates not only the compensation functions at the fundamental
frequency like a unified power flow controller (UPFC), but also provides
active harmonic mitigation capabilities. For these reasons, the
compensator proposed here is called the universal active power line
conditioner (UPLC). Simulation and experimental results are presented to
confirm that the new approach has better performance than those obtained
by controllers based on traditional concepts of active and reactive
power
This paper deals with unified power quality conditioners (UPQCs), which aim at the integration of series-active and shunt-active power filters. The main purpose of a UPQC is to compensate for voltage flicker/imbalance, reactive power, negative-sequence current and harmonics. In other words, the UPQC has the capability of improving power quality at the point of installation on power distribution systems or industrial power systems. This paper discusses the control strategy of the UPQC, with a focus on the how of instantaneous active and reactive powers inside the UPQC. Experimental results obtained from a laboratory model of 20 kVA, along with a theoretical analysis, are shown to verify the viability and effectiveness of the UPQC
A technique is presented for the isolation of harmonic-sensitive loads from harmonic-producing loads, such as rectifiers and power converters. The solution, referred to as a line voltage regulator/conditioner (LVRC), utilizes a combination of a series and a parallel active power filter. The series filter isolates the sensitive loads on the output side of the LVRC from the nonlinear, distortion-producing loads on the input side by correcting for the harmonic voltage distortion present at the input. In addition, the series filter is utilized to regulate the output voltage. The parallel filter acts to generate the harmonic current required by the loads connected on the output side, therefore reflecting a linear load to the source.< >
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