Power Quality is an of import job a Power System has to manage to supply its consumers a dependable and economical supply. Three-phase four-wire distribution systems have been widely used in commercial and industrial installings. In the three-phase four-wire distribution systems, the impersonal current carries the nothing sequence current due to the imbalanced burden among the stage music directors. Due to the presence of power electronics load a triplen ( 3rd, 9th, etc ) harmonics are introduced in the system.
This undertaking uses a new harmonic suppression strategy for the impersonal music directors of three-phase four-wire distribution systems. This new strategy consists of a series active filter, which is connected in series with the impersonal music director to stamp down the harmonics in the impersonal music director. This new filtrating engineering strategy consists of a electromotive force beginning inverter in series with the series connected inductance and capacitance set. This strategy is implemented for a system feeding a non-linear tonss and its public presentation is tested. The consequences show that the proposed strategy is suited for practical applications.
Electric Power becomes a most basic demand in our daily life. Electric utilities purpose is to supply a consumer a good quality of dependable uninterrupted power supply at economical cost. In three-phase four-wire distribution system, due to utilize of non-linear tonss, inordinate current will flux in the impersonal music director. In most three-phase power systems providing single-phase tonss, there will be some phase current instability and some impersonal current. Under normal runing conditions with moderately balanced burden, the current in the impersonal is expected to be 20 % of the normal stage currents. Particularly on three-phase four-wire distribution systems, the third-harmonic currents are increased. The inordinate 3rd harmonic currents cause overheating of the impersonal music directors. Hence, electromotive force deformation on public-service corporation mercantile establishments and inordinate impersonal current on distribution lines have arisen and lead to a figure of serious jobs in the distribution system. These impersonal currents are basically 3rd harmonics and uneven multiples of 3rd due to non-linearity of tonss.
The followers are the Potential jobs are straight related to inordinate harmonic currents in the impersonal music director are
Wiring failure due to improper size of the impersonal music director.
Over warming of the transformer due to harmonic currents and insularity amendss and failure.
Intermittent electrical noise from connexions loosened by thermic cycling.
Excessive impersonal to land electromotive force due to a electromotive force bead caused by the impersonal current. This common manner potency can ensue in the malfunction of sensitive electronic constituents.
Due to the presence of non-linear tonss, the other tonss connected to a Point of Common Coupling ( PCC ) besides affected by harmonics shown in fig.1. Harmonicss are injected to a line by usage of non-linear tonss. Harmonicss is defined as “ the current or electromotive force wave forms holding frequences that are whole built-in multiplies of cardinal frequence i.e. multiplies of 50Hz or 60Hz ” .
These harmonics can be eliminated by utilizing Passive filters ( Combination of L and C ) . These types of filters have disadvantages of series resonance, parallel resonance, tuning of inactive elements is hard, etc.
Recently, harmonics suppression installations based on Power Electronics techniques have proved to be of import. This harmonics suppression can be done with the aid of new emerging SERIES ACTIVE POWER FILTERS. This Series Active Filters ( SAF ) is connected in series with the impersonal line to cut down the harmonics in the impersonal line. This has more advantages when compared to the other constellations. The followerss are the advantages of linking series active filters in series with the impersonal line.
It is really less complexness and less economical
It has little evaluation usually 4 % of the burden KVA
It acts as a harmonic isolator between the supply and the burden
It is more economical for harmonic compensation of the big no-linear tonss
It prevents supply-load interaction and resonance job
It can accommodate to altering the burden status
Figure 1. Point of common yoke
II. CONTROL STRATEGY OF THE ACTIVE FILTER
By utilizing, the most efficient method of pulse Width Modulation ( PWM ) Control with in the inverter can command the end product electromotive force of the inverter. The normally used engineerings are
Single Pulse Width Modulation
Multi Pulse Width Modulation
Sinusoidal Pulse Width Modulation
Modified Sinusoidal Pulse Width Modulation
The most normally used method is Sinusoidal Pulse Width Modulation ( SPWM ) . In this method, the end product Voltage is controlled by bring forthing the gating signal by comparing a sinusoidal mention signal with triangular bearer moving ridge.
III. OVERALL BLOCK DIAGRAM AND THE DESIGN OF SERIES ACTIVE FILTERING TECHNOLOGY
Due to the development of Power Electronics engineering, more and more Power Electronics contraptions are widely used, which leads to the serious harmonic pollutions.
Figure 2. Overall block diagram
These sorts of harmonics can be eliminated by utilizing Series Active Filtering engineering. The development of new Series Active Filtering engineering is presented in this chapter. The Series Active Filter is connected in series with the impersonal music director to stamp down the harmonics, which frequently suppress the harmonics in the stage music director as good. The construct of proposed Series Active Filtering engineering, and its operating Principle, Control theory are besides discussed in this chapter
IV. OVERALL BLOCK DIAGRAM OF THE SYSTEM
The overall block diagrams and the system constellation of the proposed series active filter are shown in the fig 2 and 3.
It consists of a three-phase beginning, which is connected to a three-phase non-linear rectifying tube span rectifier circuit. The Series Active Power Filter is connected in series with the impersonal music director. It consists of the electromotive force beginning inverter in series with the inductance and capacitance. The triping for the inverter circuit is given through the control circuit. The inverter can be implemented by IGBTs runing in difficult switched Pulse-Width Modulation ( PWM ) manner to supply sufficient bandwidth for the filtering map.
Figure 3.Proposed series active filter
The proposed series active filter system can forestall overloading of the impersonal music director and the distribution transformer with one installing.
V. OPERATING PRINCIPLE
Three stage span rectifier with RC tonss ( non-linear tonss ) are connected to the three stage four wire distribution system as shown in fig 3. Due to the nature of the non-linear tonss, harmonics are injected in to the system through the impersonal currents. This harmonics can shoot in to the stage music directors besides every bit good.
Series Active Power Filter is connected in impersonal music director to stamp down the harmonics. The Voltage Source Inverter ( VSI ) generates a compensating harmonics currents in to the impersonal music director through the inductance and capacitance sets connected in series with it.
The generated harmonic currents and the harmonic currents flows in the impersonal music director cancel each other without impacting the cardinal portion of the impersonal current.
VI. EQUIVALENT CIRCUIT OF THE SYSTEM
Fig. 4 shows the tantamount circuit diagram of a proposed series active filter
Figure 4. Equivalent circuit diagram
Vsa, Vsb, Vsc are the beginning electromotive force of the stage A, stage B, and stage C Respectively
VAF, represents the series active filter inverter end product electromotive force
VLa, VLb, VLc are modelled load electromotive force beginning ( Balanced or unbalanced )
ZL Load electric resistance
Zs Source electric resistance
Iowa, ib, Intelligence Community and in are the stage currents and impersonal current severally
VAF = Kh.G.In, ( 1 )
Kh is a addition
G = 0.0 for cardinal frequence
1.0 for harmonic frequences
The relationship of currents and Voltages can be expressed as
Vsa-ZsIa-ZLIa-VLa+VAF+ZnIn = 0 ( 2 )
Vsb-ZsIb-ZLIb-VLb+VAF+ZnIn = 0 ( 3 )
Vsc-ZsIc-ZLIc-VLc+VAF+ZnIn = 0 ( 4 )
By adding above equations
Vsa+Vsb+Vsc-Zs ( Ia+Ib+Ic ) -ZL ( Ia+Ib+Ic ) –
VLa-VLb-VLc+3VAF+3ZnIn = 0 ( 5 )
Since ( Ia+Ib+Ic = In )
Vsa+Vsb+Vsc = 0 for balanced conditions ( 6 )
– ( Ia+Ib+Ic ) ( Zs+ZL ) -VLa-VLb-VLc+3VAF+3ZnIn=0 ( 7 )
Where, VAF = Kh.G.In
In = – ( VLa+VLb+VLc ) / ( Zs+ZL+3Zn+3KhG ) ( 8 )
VII. DESIGN OF CONTROLLER FOR SERIES ACTIVE FILTER
Fig.5 shows the control block diagram of the proposed Active Power Filter. An active filter is placed in series connexion with the impersonal music director of the three-phase four-wire system. A Hall-Effect detector provides the measuring of the impersonal current in the system accountant.
The mensural impersonal current In from the system incorporating both harmonics and cardinal constituents is multiplied by wickedness ( I‰ot ) and cos ( I‰ot ) severally, to pull out the cardinal constituents of In, where I‰o is the frequence of the public-service corporation grid.
The cardinal constituents of In is converted in to DC and the harmonics are converted in to AC after the generation procedure. Sin ( I‰ot ) and Cos ( I‰ot ) are synchronized to the public-service corporation by a Phase-Lock-Loop ( PLL ) circuit.
Low Pass Filter ( LPF ) cut off at 5Hz is applied to pull out the DC constituents. The end product of the Low Pass Filter is a DC constituents, which are multiplied by wickedness ( I‰ot ) and cos ( I‰ot ) severally and so summed to synthesise the cardinal constituents of In ( represents by In, degree Fahrenheit ) . The Scaling factor of 2 is for standardization.
The ab initio measured current In is subtracted with the cardinal constituents of In. i.e. In, degree Fahrenheit.
Then the harmonic constituent of impersonal current is obtained. The Voltage bid of the active filter inverter is generated by
Vinv=Kh. ( In-In, degree Fahrenheit ) =Kh.In, H ( 9 )
Figure 5. Accountant of series active filter
Where In, H represents the harmonic constituents.
Vinv represents a high addition ( Kh ) for the current harmonics in the impersonal music director, hence will be suppressed by the active filter inverter while the cardinal constituents In, degree Fahrenheit is non affected. The staying In, degree Fahrenheit will non overload the impersonal music director which is normally sized the same as stage music director.
The Voltage bid Vinv is compared to the triangular bearer to bring forth the PWM gating pulsation. The active filter inverter switches at 20 KHz to supply sufficient bandwidth for the coveted filtering features.
Figure 6. End product wave forms without filter
Depends upon the PWM gating pulsations, the inverter circuit will shoot the negative harmonic currents to the impersonal line, as a consequence merely cardinal constituents of the impersonal current will flux through the line.
VIII. CIRCUIT DIAGRAM AND SIMULATION RESULT
The Circuit diagram for with filter is shown in fig 8. In this active filter is connected in series with the impersonal line. The burden taken for the simulation is parallel RC burden. Simulation is done for both balanced and imbalanced conditions.
IX. SIMULATION RESULTS FOR THE PROPOSED FILTER
The system chosen is 230V, 50Hz distribution system feeding a rectifying tube rectifier with parallel R and C tonss. The Simulation is carried out for a period of 200ms.
The end product wave forms of the stage currents and impersonal currents for both balanced and imbalanced conditions without filter for R and RC tonss are shown in fig.6. Form the figure, evidently shown that the impersonal current wave forms without filters are distorted because of the harmonic and stage current are in imbalanced status.
Figure 7. End product wave forms with filter
The wave forms of the stage currents and the impersonal currents for both balanced and imbalanced conditions with filter for R and RC tonss are shown in fig.7. It clearly shows that the impersonal current deformations are much reduced.
Figure 8.The simulation theoretical account of the proposed system
Ten. EFFECTIVENESS OF THE FILTER
The Total Harmonic Distortion ( THD ) of the end product wave forms without and with filter is analyzed utilizing Fast Fourier Transform. From the fig 9 it is clearly shown that THD of the impersonal current is 24.29 % .
Figure 9. FFT Analyses for Neutral current wave form without filters.
After the series active filter is connected in the impersonal music director the THD are much reduced to 1.24 % and it ‘s shown in fig 10.
Figure 10. FFT Analyses for Neutral current wave form with filters
[ 6 ] M.Aredes, J. Hafner, and k.Heumann, “ Three-phase four wire shunt active filter control schemes, ” IEEE Transactions on Power Electronics. , vol. 12, no.2.pp.311/318.March 1997.
[ 7 ] P.T.Cheng, C.C.Hou, and Y.F.Huang, “ Overload Prevention, ” IEEE Transactions on Industry Applications, vol.10, no.6, pp.26-34, Nov/Dec.2004
The theoretical account of the proposed new Series Active Power Filter is realized. The developed new Series Active Power Filtering engineering is implemented for a system feeding a non-linear burden. It is simulated utilizing the extremely developed in writing tool SIMULINK available in MATLAB. The consequences reveal that the proposed new Series Active Filtering engineering is simple and effectual and is suited for practical applications.