This paper is proposed to reconsider the development of **active** **power** **filter** (APF) technologies that are routinely utilized to mitigate **harmonics** in utility **power** lines. This reconsider can furthermore be considered as a “tutorial-type paper” as it provides a holistic coverage of the APF technologies by omitting the tedious details, but without losing the major essence of the subject matter. It is wanted that by this approach, it would be likely to lure more **power** engineering readers to be involved in this important and growing area. The discussion starts with a short overview of harmonic distortion difficulties and their impacts on electric **power** and powered value. The operation of common APF topologies, namely the shunt, sequence and hybrid APFs are recounted in minutia. This is followed by a reconsider on different types of reference pointer estimation extraction methods. In specific, the application of the p-q and elongation p-q theorems to extract the quotation pointers are elaborated, as they are the most commonly discovered in practical APF systems eventually, an overview of the APF command schemes is provided. A short consideration on the APF-solar photovoltaic scheme is furthermore granted. At the end of the paper, important references are cited to aid readers who are interested to discover the subject in larger detail.

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Single phase SMPS/UPS are widely used in commercial, residential and many other applications due to advantages in efficiency and smaller size. Typical SMPS is commonly built with un-controlled bridge rectifier with a **filter** capacitor providing a narrow pulse current that contains significant amount of **harmonics** polluting utility [1] and making input **power** factor low which is against international agency regulation and also it is in-efficient. For that matter typical single phase UPS is built with Thyristor controlled bridge as front end which permits to control DC voltage. However this measure increases the control complexity and its use leads to additional generation of reactive **power**.

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1. Introduction: Methods for limitation and elimination of disturbances and harmonic pollution in the **power** system have been widely investigated. This problem rapidly intensifies with the increasing amount of electronic equipment (Computers, radio set, printers, TV sets etc.). This equipment, a nonlinear load, is a source of current **harmonics**, which produce increase of reactive **power** and **power** losses in transmission lines. The **harmonics** also cause electromagnetic interference and, sometimes, dangerous resonances. They have negative influence on the control and automatic equipment, protection systems, and other electrical loads, resulting in reduced reliability and availability. Moreover, nonlinear loads and non-sinusoidal currents produce non-sinusoidal voltage drops across the network impedance’s, so that non-sinusoidal voltages appear at several points of the mains. It brings out overheating of line, transformers and generators due to the iron losses.

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Series **active** **filter** and parallel passive **filter** topology shown in fig. 3,An **active** **power** **filter** is implemented with a three-phase pulse width modulation (PWM) voltage-source inverter operating at fixed switching frequency. When this equipment is connected in series to the ac sourceimpedance it is possible to improve the compensation characteristicsof the passive filters in parallel connection.In order to allow current harmonic compensation, a parallel LC **filter** must be connected between the nonlinear loads and the series transformers. It is well known that series **active** **power** filters compensate current system distortion caused by non-linear loads by imposing a high impedance path to the current **harmonics** which forces the high frequency currents to flow through the LC passive **filter** connected in parallel to the load. The high impedance imposed by the series **active** **power** **filter** is created by generating a voltage of the same frequency that the current harmonic component that needs to be eliminated. Current harmonic and voltage unbalance compensation are achieved by generating the appropriate voltage waveforms with the three phase PWM voltage-source inverter (Fig.3). **Active** **power** **filter** is used with passive filters to improve the compensation characteristic of passive **filter**, also it avoid the possibility of generation of series or parallel resonance [4].

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Abstract—Use of nonlinear loads has been increased in large extent in industries now-a-days which injects harmonic currents in supply system. These **harmonics** creates **power** quality issue. Shunt **Active** **Power** **Filter** (SAPF) is the popular and efficient solution to reduce these **harmonics**. SAPF can overcome voltage sag, eliminate **harmonics** and improves **power** factor. SAPF reduces total harmonic distortion (THD) to acceptable level. Reference current generation is the heart of APF. Reference current generation **using** instantaneous reactive **power** (IRP) theory is presented in this paper. IRP theory is widely used to control **active** **power** filters (APFs). Modeling of this technique is implemented in MATLAB/simulink. The system is experimentally implemented **using** DS1104 card of dSPACE system.

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The DSTATCOM is shunt connected, solid state switching **power** converter that exchanges reactive current with the distribution system. It uses three-phase inverters to transfer leading and lagging reactive current with the distribution system via coupling transformer. The DSTATCOM supplies reactive **power** by synthesizing its output for insertion into the AC **power** system through high frequency **power** electronic switching. The most common scheme used to switch on and off the semiconductors is a pulse-width-modulated (PWM) scheme to generate higher than fundamental frequency currents for injection into the distribution system. This injection of high frequency current allows the DSTATCOM to provide harmonic load current compensation. By regulating the output voltage of the inverter, the reactive **power** injected into or absorbed from the system can be controlled and as in the SVC, in such a way that the reactive current variations of the system load compensator are kept as small as possible, mitigating voltage fluctuations. Connecting the compensator to an energy storage device gives it an additional ability to regulate **active** **power** flow in the system.

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The **active** **filter** is based on a PWM voltage source inverter is connected to the PCC through interface **filter**; the **active** **filter** is connected in parallel with the AC/DC converter. This inverter uses dc capacitor as supply and can switch at high frequency to generate the current that will cancel the **harmonics** from AC/DC converter. The current waveform for canceling **harmonics** is achieved by **using** VSI in the current controlled mode and the interface **filter**. This interface **filter** provides smoothing and isolation for high frequency components. The desired currents are obtained by accurately controlling the switching of the MOSFET inverter. We can Control the wave shape of current by limiting the switching frequency of the inverter and by the available driving voltage across the interfacing inductance.

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system is simulated **using** MATLAB and the results are presented in Fig. 1. The waveforms for supply voltage, supply, load, and **filter** currents and dc-link voltage are shown in Fig. 1(a)–(e). It can be seen from Fig. 1(b) and (c) that the supply current becomes sinusoidal while the load continues to draw current in nonsinusoidal pulses. The harmonic spectrum of the supply current before and after compensation is shown in Fig. 2(a) and (b), respectively. The total harmonic current distortion is reduced from 149.7% of the uncompensated load to 4.49% after compensation. The **power** factor is improved to 0.98 from 0.585 of the uncompensated load. The compensated rms supply current is 2.668 A and it is seen that the rise in supply current due to the presence of **harmonics** is effectively brought down. The dynamic response for addition and removal of the load can be observed from Fig. 1(b). The supply current settles smoothly to a new steady- state value within a half cycle of a 50% decrease in load at0.1 ms and a 200% increase in load at 0.3 ms. There is a small change in the dc-bus voltage [Fig. 1(e)] at the instant of disturbance in the load to balance extra energy due to an increased or decreased level of compensation. The dc-bus voltage settles to its steady-state value within a few cycles.

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Abstract – The components of **harmonics** are integral multiple of the fundamental component and the components of inter-**harmonics** are are non integral multiple of the fundamental component. AC-DC-AC conversion systems used in variable speed drive are sources of inter-**harmonics**. There are several reasons for inter-harmonic generation in variable speed drives. In this paper, the generation of inter-**harmonics** in the supply side due to indirect frequency converter is considered. A passive **filter** is designed to mitigate **harmonics** and inter-**harmonics**. The accuracy of the proposed method is verified **using** the simulation tool of PSIM. Simulated results of VSI-fed induction motor with the proposed **filter** prove the effectiveness of **mitigation**.

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An increasing demand for reliable and high quality of electrical **power** and also the increasing number of distorting loads may lead to an increased awareness of **power** quality by the customers and utilities. The electric **power** quality becomes poor due to **power** line disturbances such as sag, swell, interruption, **harmonics**, sag with **harmonics**, swell with **harmonics**, flicker and notches. To improve the **power** quality, it is essential to detect and classify the disturbances initially. Various types of **power** quality disturbances were detected and localized based on wavelet transform analysis as illustrated in [1]. Multi resolution wavelets were also applied to analyze and classify the electromagnetic **power** system transients [2].

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Within the DPFC, the transmission line is used as a connection between shunt converter output and AC port of series converters, instead of **using** DC- link for **power** exchange between converters. The method of **power** exchange in DPFC is based on **power** theory of non-sinusoidal components [9]. Non- sinusoidal voltage and current can be presented as the sum of sinusoidal components at different frequencies. It is the main result of Fourier analysis. The product of voltage and current components provides the **active** **power**. Since the integral of some terms with different frequencies are zero, so the **active** **power** equation is as follow:

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R ecently to eliminate the **harmonics** and improve the **power** factor of the **power** networks, much attention has been attracted to **active** filters. The advantages of these filters are lower volume and their better compensating characteristics than the passive filters. In conventional sliding mode controllers, the source current waveform is fluctuated in near to zero values. In this paper, **using** a new sliding technique, lower Total Harmonic Distortion (THD) in source current is obtained and the current waveform is improved. As well as, two novel control strategies for two types of **active** filters, VSI and CSI is proposed and then these two types of filters are compared to reduce THD value of source current.The proposed controlled strategies are simulated by MATLAB/Simulink. The Simulation results confirm that the proposed strategies reduce the THD of source current more than other strategies, and **active** **filter** based on CSI has a better performance than **active** **filter** based on VSI with a dead time area (for avoiding short circuit of the source) in high powers.

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Abstract — **Active** **Power** Filters (APFs) are the up-to-date solution to **power** quality problems. Shunt **active** filters (the most common type) allow the compensation of current **harmonics**, unbalance, together with **power** factor correction, and can be much better solution than the conventional approach. This paper discusses four different control strategies applied to shunt **active** **power** **filter**, the four control strategies are time-domain based strategies which are instantaneous reactive **power** theory (IRPT), synchronous reference frame (SRF), synchronous detection method (SDM), and a proposed method which presents a positive sequence detector that is used with an improved ABC reference frame formula based upon the p-q theory to solve the problem of non-ideal mains. The improved formula needs fewer calculations than the conventional p-q theory. Moreover, it is very easy to implement this algorithm on a digital signal processor (DSP).

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A nine-switch **power** converter having two sets of output terminals was recently proposed in place of the traditional back-to-back **power** converter that uses 12 switches in total. The nine-switch converter has already been proven to have certain advantages, in addition to its component saving topological feature. Despite these advantages, the nine-switch converter has so far found limited applications due to its many perceived performance tradeoffs like requiring an oversized dc-link capacitor, limited amplitude sharing, and constrained phase shift between its two sets of output terminals. Instead of accepting these tradeoffs as limitations, a nine- switch **power** conditioner is proposed here that virtually ―converts‖ most of these topological short comings into interesting performance advantages. Aiming further to reduce its switching losses, **Harmonics**, Voltage Sag & Swell an appropriate discontinuous modulation scheme is proposed and studied here in detail to doubly ensure that maximal reduction of commutations is achieved. With an appropriately designed control scheme with PI and ANN with Hysteresis controller then incorporated, the nine-switch converter is shown to favorably raise the overall **power** quality in Simulation, hence justifying its role as a **power** conditioner at a reduced cost.

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System performance can be achieved by **using** a controller to convert and control **power** to nonlinear loads. The non-uniform sinusoidal current waveform was obtained by **harmonics** generated in the voltage source. The distortion in voltage and current will af- fect the total system efficiency. These will lead to damage to the system components and failure of the system. Non-linear loads create harmonic distortion. These harmonic distortions can be eliminated **using** harmonic filters. There are three types of harmonic filters; they are passive, **active** and hybrid filters. The selection of **filter** is based upon the problem.

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In this paper, the impacts of harmonic distortions on the electric drives in Delta paper mill, Vendra, West Godavari(Dist), Andhra Pradesh, India, which is major supplier of different kinds of paper to most of the industries/organizations in south India, is investigated. The harmonic measurement is done with Fluke 434 **power** quality analyzer. A large diversity of solutions exists to reduce the harmonic emission of Adjustable Speed Drives in order to fulfill the requirements of the international harmonic standards. In recently **active** **power** filters gained an increased attention due to their good harmonic reduction. In this paper an **active** **power** **filter** has been designed for minimization of the **harmonics** and results are presented in terms of % THD without and with **active** **power** **filter**, which is implemented in Matlab/Simulink based on real time measurement of the harmonic data.

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The increased use of nonlinear loads, such as switch mode **power** supply in computers, rectifier devices in TVs, ovens and telecommunication **power** supplies and commercial lighting systems cause excessive neutral currents, harmonic injection and reactive **power** burden in the **power** system. They result in poor **power** factor, lower efficiency and interference to adjacent communication systems. In the past L-C filters were employed to reduce **harmonics** and **power** capacitors were used to improve the **power** factor of the AC mains, however, they have the demerits of fixed compensation level, large size and resonance. In the last two decades, a device generally named as **active** **power** **filter** (APF) has been investigated to provide an appropriate solution to most of these problems. Elimination of current **harmonics**, reactive **power** compensation and voltage regulation are the main functions of **active** **power** filters for the improvement of **power** quality. T. C. Author is with the Electrical Engineering Department, University of Colorado, Boulder, CO 80309 USA, on leave from the National Research Institute for Metals, Tsukuba, Japan (e-mail: author@nrim.go.jp).

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Many configurations such as shunt, series, hybrid (a combination of shunt and series **active** filters), and unified **power** quality conditioner (UPQC, a combination of series and shunt **active** filters) have been introduced and improved [3]. The UPQC can compensate not only harmonic currents and unbalances of a non-linear load, but also voltage **harmonics** and unbalances of the **power** sup-ply. The latter improves the **power** quality offered for other harmonic sensitive loads.

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The basic simulation model as well as the experimental small scale platform shows very good results in filtering the current of a nonlinear load with a shunt **active** **filter** based on indirect control. This method has the advantage of **using** only two transducers: one for voltage and one for current. Experimental results were unexpected good even if the controllers used in the control algorithm allow stationary error on the controlled signal. Further analysis could consider some better controllers, with better dynamic characteristics.

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This paper deals with a Unified **Power** Quality Conditioner (UPQC) for load balancing, **power** factor- correction, voltage regulation, voltage and current **harmonics** **mitigation**, **mitigation** of voltage sag, swell and voltage dip in a three-phase three-wire distribution system for different combinations of linear and non- linear loads.The unified **power** quality conditioner (UPQC) is a combination of back to back connected shunt and series **active** **power** filters (APFs) to a common DC link voltage, which compensates voltage and current based distortions, independently.Using instantaneous **active** and reactive **Power** theory ,harmonic detection, reactive **power** compensation, voltage sag and swell have been simulated and the results are analyzed. The operation and capability of the proposed system was analyzed through simulations with MATLAB / SIMULINK.

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