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Constant Frequency Unified Power Quality Conditioner Engineering Essay

The purpose of this paper is to show a changeless frequence unified power quality conditioning system which consists of an incorporate power quality conditioner ( UPQC ) extended by adding a frequence modifier in between the shunt active filter and series active filter. The series active filter and shunt active filters chiefly used to counterbalance the electromotive force, current instability and harmonics. The frequence convertor is used to counterbalance the supply frequence when it varies beyond the power quality bound. The proposed constellation all convertors are connected back to endorse on the dc side and portion the common District of Columbia nexus capacitance. The simulation consequences are presented to corroborate that the new attack has better public presentation than the traditional UPQC.

Uunifed power quality conditioner is an advanced constructs in the country of power quality control. The basic working rule of incorporate power quality conditioner is based on series and parallel power convertors that portion a common District of Columbia nexus [ 1 ] .Unified power quality conditioner is used to counterbalance electromotive force droop, electromotive force crestless wave [ 2 ] , current harmonics [ 3 ] it is besides creates an impact on the reactive power [ 4 ] through shunt electromotive force beginning inverter and series electromotive force beginning inverter. In order to avoid the switching oscillation, a inactive filter is applied at the end product of each inverter. At the end product of shunt inverter a high base on balls 2nd order LC filter is allocated and the end product of series inverter low base on balls 2nd order LC resonance filter is allocated. UPQC accountant provides the compensation electromotive force through the UPQC series inverter and conditioning the current through the shunt inverter by instantaneous sampling of burden current and beginning electromotive force. The mention current are compared with the shunt inverter end product current ( , ) and are fed to hysteresis type

( PWM ) current accountant. There are some jobs with UPQC. As the supply frequence changes the UPQC will non

Fig.1: Basic Configuration of Changeless Frequency Unified Power Quality Conditioner ( CFUPQC )

counterbalance the electromotive force droop and crestless wave and current harmonics

decently. This happens due to the presence of LC filters at the

Inverters end product terminuss. It is straight affected by the fluctuation of supply frequence

Fig 1 shows the proposed improved constellation of changeless Frequency unified power quality conditioner. This modified incorporate power quality conditioner constructs enables the PWM convertor to execute non merely active filtrating intent, besides the map of frequence modifier. The compensation rule of the CFUPQC will be described in the approaching subdivisions. The proposed incorporate power quality conditioner has to fulfill the undermentioned demands. Reactive power is maintained at minimal value. The burden electromotive force should be maintained at the rated supply electromotive force. Keep the input current with really low harmonic content. Guarantee the supply frequence is allowable within the power quality limits.The simulations result will be presented to formalize the proposed CFUPQC.

frequence quality indices

In order to qualify the power system frequence under normal runing status the undermentioned indices are used

Where Fr is the rated frequence ( 50 or 60 ) Hz and degree Fahrenheit is the existent frequence.

The comparative frequence divergence

( 2 )

The built-in divergence during the hold required to guarantee appropriate of clock synchronized to the electrical web frequence

( 3 )

Harmonizing to the criterion En 50160/2006rated frequence of supply electromotive force is 50Hz.Under normal operation conductivity the average value of the cardinal frequence measured over loss stay within the undermentioned scope.

50 Hz+ 1 % .ie 49.5-50.5Hz for 99.5 % of the twelvemonth

50 Hz+ 4 % .ie 47-52Hz for 100 % of the clip.

But as power frequence may non be precisely 50Hz within the clip interval. The cardinal frequence end product is the ratio of the figure of integer rhythm counted uncluttering 10s clip interval divided by the cumulative value of the whole number value. The measure taken to keep the frequence with in needed bounds render divergence from the normalized value really rate phenomena. In this manner an analysis is of the influence of frequence fluctuation on the concluding client is merely for a decreased interval about +3Hz of the rated value and for instead short period. Within the decreased fluctuation field ( 40 % ) a considerable figure of inactive clients are non affected by the system fluctuation ( rectifier, opposition, ovens, electric discharge ECT ) but 60 % of the consumers ( fans, motors ect ) affected by the frequence fluctuations. The asynchronous and synchronal driving motors connected the supply web used extensely in single acceleration have the power frequence alterations. Depending on the mechanical characteristic velocity of the motor and besides depends on the supply frequence [ 13 ] .The velocity of asynchronous motors or synchronal motor unlimited retarding forces to the electric power supply fluctuations s relative to the applied electromotive force frequence. The frequence fluctuation leads to the correspond alteration of the procedure production clip throughout the supply with a decreased frequence dejecting the supply frequence capacitive circuit, transformer, relay spiral are affected

Changeless Frequency Unified Power Quality Conditioner ( CFUPQC )

CFUPQC construction

Fig.3: Proposed Configuration

Modified constellation of UPQC consist of shunt active filter, series active filter, electromotive force beginning inverter and electromotive force beginning convertor shown in Fig ( 3 ) .CFUPQC similar to the UPQC expect the frequence altering subdivision. UPQC has the possible drawbacks in the intercrossed filtering public presentation. Since its filter in features depends on load electric resistance and supply frequence. CFUPQC series active filter is used for compensation the electromotive force harmonics and electromotive force instability In add-on the electromotive force beginning convertor supplies the AC to DC power and is fed to common DC nexus. The CFUPQC consists of parallel active filter ( PAF ) that eliminates load harmonics and compensates load reactive power. The control equation is

Ipf=G.IL ( 4 )

Where g is the control map, is cardinal frequency.IL is the burden current, Ipf is the parallel filter input current constituents for compensation are extracted from burden current and burden electromotive forces utilizing theory while the convertor is a current controlled device utilizing 20 kilohertz clocked hysteresis set.

Series active filter ( SAF ) that compensates supply harmonics spark, electromotive force sag/swell, imbalance and rectifying tube + capacitance type burden harmonics to flux in to the parallel filter. Control equation is

comp ( 5 )

Where K is regulator addition, Usf is the series filter electromotive force, Ish are harmonic supply current and Ucomp is compensation electromotive force needed to take supply electromotive force imperfectness. Ish are extracted to theory.

Active rectifier ( AR ) for existent power transportation to/from common DC coach and for DC coach control. Switch overing losingss and power received from the District of Columbia nexus capacitances through the series inverter can diminish the mean value of District of Columbia coach. Other deformations such as imbalanced conditions and sudden alterations in burden current can ensue in oscillation in District of Columbia coach electromotive force.In order to work out the fluctuated District of Columbia electromotive force the three stage rectifier is used.DC coach electromotive force is maintained changeless utilizing three-phase rectifier convertor for bi-directional power flow and is controlled in such a manner that it is insensitive to provide voltage imperfectnesss.

Rms value of the end product electromotive force Vorms=0.9558Vml

Rms value of the end product current Iorms=0.9558Iml

Where milliliter is maximal value of line current. Multi phase 48 pulse electromotive force beginning inverter ( VSI ) supplies the changeless power frequence when the supply frequence will alter. Here multilevel electromotive force beginning inverter is used, to extinguish the harmonic constituent of the end product. The frequence convertor is placed in between the series and shunt active filters. Normally the electromotive force beginning convertors ( rectifiers ) generate the current harmonics. In order to avoid the harmonics and reactive power the rectifier is placed at the center of the two active filters. Similarly if the burden is increased electromotive force dip may happen in forepart of electromotive force beginning inverter. At the same clip series active filter compensate the electromotive force jobs.

Control system of the CFUPQC shunt Part

Fig.4: Control System of the Shunt CFUPQC

1 ) CFUPQC shunt inverter control system:

In the Fig ( 4 ) shows the shunt inverter commanding block diagram of CFUPQC utilizing synchronal mention frame theory where the sensitive tonss current are. The mensural currents of burden are transferred in to border utilizing sinusoidal maps through synchronal mention frame transition. The sinusoidal maps are obtained through the grid electromotive force utilizing stage lock cringle ( PLL ) . Here the currents are divided in to ac and dc constituents

( 6 )

( 7 )

The equation ( 6 ) and ( 7 ) and are the existent and reactive constituents and dc elements can be derived by low base on balls filter.are the District of Columbia constituents and are the ac constituents of. The control algorithm corrects the systems power factor and compensates all the current mouth organ constituent by bring forthing the mention currents given in equation

= ( 8 )

= ( 9 )

The mention current is transferred in to border through rearward transition of synchronal mention frame. Resulted mention current ( ) and the end product current of shunt inverter ( ) are fed to the hysteresis set accountant. Now the needed controlling pulsations are generated and the needed compensation current is generated by the inverter using these signals to shunt inverters power switch Gatess.

2 ) CFUPQC Series Inverter Control System

Fig.5: Control System of the Series CFUPQC

2 ) CFUPQC series inverter control system:

Fig ( 5 ) shows the CFUPQC series inverter commanding block diagram utilizing synchronal mention frame theory. In this method the coveted value of load stage electromotive forces in vitamin D axis and Q axis is compared with the burden electromotive force and the consequence is consider as the mention signal. The supply electromotive force detected is detected and transformed in to the synchronal mention frame utilizing

( 10 )

The counterbalancing mention electromotive force in the synchronal mention frame is defined as

( 11 )

The counterbalancing mention electromotive force in ( 11 ) is so transformed back into the mention frame.Resulted mention electromotive force ( ) and the end product current of shunt inverter ( ) are fed to the hysteresis set accountant. The needed controlling pulsations are generated and the needed compensation electromotive force is generated.

3 ) Control system of 48 pulse electromotive force beginning inverter:

48-pulse electromotive force beginning convertor consists of four 3-phase, multi-level inverters and four phase-shifting transformers presenting stage displacement of +/- 7.5 & A ; deg ; grade. This transformer agreement eleminates all uneven harmonics up to the forty-fifth harmonic. Eight 6-pulse inverters are combined to obtain a 48-pulse with the intent of cut downing harmonic content. Table 1 shows the values of stage displacements which are applied to the inverter electromotive forces in two stairss, viz. in firing pulsations and in Zig-zag transformers, to make a 48-pulse wave form at the end product.

Table 1:48 Pulse electromotive force beginning Inverter

Matching transformer

Gate pulsation form

Phase switching transportation


+11.25 & A ; deg ;

-11.25 & A ; deg ;






















content in the order of n= 48m±1, where m= 0, 1, 2. The main-inverter intermediate-circuit capacitances together have an energy storage capacity of merely 15 J/kVA. An end product exchanging frequence of 1 kilohertz is chosen, which is reasonably sensible for this convertor. Input is a frequence mention, which is passed through a rate clipper in order to be within the bounds of maximal acceleration.

Fig.6: Control System of the Frequency modifier CFUPQC

Except for the 23rd and 25th harmonics, this transformer agreement eleminates all uneven harmonics up to the forty-fifth harmonic. Y and D transformer secondary ‘s natural harmonics 5+12n ( 5, 17, 29, 41, … ) and 7+12n ( 7, 19, 31, 43, … ) . In add-on, the 15 & A ; deg ; phase switch between the two groups of transformers ( Tr1Y and Tr1D taking by 7.5 & A ; deg ; , Tr2Y and Tr2D lagging by 7.5 & A ; deg ; ) allows cancellation of harmonics 11+24n ( 11, 35, … ) and 13+24n ( 13, 37, … ) . Sing that all 3n harmonics are non transmitted by the transformers, the first harmonics that are non canceled by the transformers are hence the 23rd, 25th, 47th and 49th harmonics. By taking the appropriate conductivity angle for the three-level inverter ( ? = 172.5 & A ; deg ; ) , the 23rd and 25th harmonics can be minimized. The first important harmonics generated by the inverter will so be 47th and 49th. Using a bipolar DC electromotive force, the electromotive force beginning inverter therefore generates a 48-step electromotive force come closing a sine moving ridge. The secondary sides of the yoke transformers are connected in series to sum the end product electromotive forces of single VSIs and consequences in a multi-pulse stage electromotive force which can be expressed mathematically as follow

( 12 )

( 13 )

Both equations ( 12 ) and ( 13 ) which are phase-to-phase and phase-to-neutral electromotive force representations, severally, show that harmonics up to 47th order are inherently filtered. The signalisation of the 48-pulse inverter are generated for the inverter holding -41.25 of gate pulse stage and straight fed to the corresponding inverter. PWM signals for the staying inverters are obtained by using relevant stage displacements to the set of PWM signals generated. For illustration, in order to obtain the pulsations for the inverter holding -11.25o of gate pulse +30o of stage displacement is applied to the closed cringle current accountant ‘s end product. In pattern, the stage shifting of the pulsations is realized by using a hold in the first rhythm. The generated set of pulsations is the earliest set looking at the time-line and since it is non possible to use a negative hold the earliest appearance set is generated and the remainder are delayed consequently. When the supply frequence is exceeded beyond the power quality limit the changeless frequence electromotive force beginning inverter control system change the burden from beginning power supply to the changeless frequence inverter power supply.

Simulation Consequences

The proposed system, shown in Fig.1 with parametric quantity values presented in table II, is simulated by MATLAB package.

Table II





Electric resistance

R=0.001I? , L=0.01mH

DC Link


C1=15µf, c2=15µf

Mention electromotive force


Non linear burden

Normal power



L, C


Inverter power


Fig 7Current harmonic minimisation when the supply frequence is normal

In the above simulation some capablenesss of UPQC to work out power quality jobs are shown. The nonlinear burden which is produced harmonic current to the web. Fig. 7 shows that the shunt portion of UPQC compensates these harmonics

Components when the supply frequence is normal.

Now assume that a deep and unbalance electromotive force droop, as occurs at t = 0.2 s to 0.25 s and electromotive force crestless wave occurred 0.26 and stopping points for 0.3 2nd.

Fig.8. Sag swell status when the supply frequence is normal

In Fig ( 8 ) the UPQC inject the compensation electromotive force via series inverter and counterbalance expeditiously at 0.2 2nd sag status and electromotive force crestless wave status at supply frequence normal ( 60Hz )

Fig.9.Series UPQC when the frequence exceed the power quality bound

In fig 9 shows the operation of UPQC when the supply frequence exceeds the power quality limits the end product was non found satisfactory.The supply beyond the power quality bound ( greater than 63 Hz ) at 0.25 2nd the burden electromotive force wave form varies. The frequence addition quickly the electromotive force wave form extremely distorted as shown in the simulation consequences Fig 9.

Based on the simulation consequence Fig 10 it is intended that if the supply frequence varies greater than power quality limit the burden current moving ridge signifier is distorted. If the frequence increases the moving ridge signifier besides distort quickly as shown in fig10.

Fig 11. CF- UPQC Operated when Frequency greater than the Power quality bounds

Fig 11showsthe proposed CFUPQC theoretical account was simulated for a period of 0.01 sec to 0.5 sec from the consequences in fig 11, it was seen that at 0.28 sec the supply frequence crossed the power quality bound at 0.29.

Fig.12. CF-UPQC ‘s inverter providing current under over frequence status

The above simulation shows the 48 pulsation inverter carries the burden current when the supply frequence varied beyond the power quality bound. When the frequence exceed the bounds at 0.28 sec. the electromotive force beginning convertor supply the power.

Fig.13. UPQC connected asynchronous motor under over frequence status

The above simulation consequence Fig ( 13 ) clearly shows when the frequence changes the asynchronous motor velocity besides alterations and the UPQC besides non present the electromotive force sinusoidal. In this instance the burden connected in to paper Millss, relays are affected.

Fig.14. CFUPQC connected asynchronous motor under over frequence status

The proposed theoretical account simulation fig 14 shows when the supply frequence change the motor velocity non changed and the CFUPQC besides work satisfactory

Fig.15.harmonic analysis of inverter

Fig 15 shows the CF UPQC ‘s inverter entire harmonic deformation is 0.87.

Table I11


Power quality jobs





Frequency Hz


& A ; gt ; 62Hz- & A ; lt ; 58


& A ; gt ; 60- & A ; lt ; 58

Voltage crestless wave


Not counterbalance



Voltage droop


Not counterbalance



Current harmonics


Not counterbalance



Frequency control

Not counterbalance

Not counterbalance



In this paper, incorporate system of UPQC and variable Frequency convertor was developed and the control system for each VSC was introduced. By utilizing the proposed system, the CFUPQC has performed good when the supply frequence exceeds the power quality bounds. Therefore, we could pull off power delivering of changeless power frequence to the load side. . By the proposed system, we need no alteration in the manner of control system. Simulation consequences by MATLAB package showed advantageous characteristics of the proposed system.

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