SHUNT HYBRID ACTIVE POWER FILTER USED FOR …joics.org/gallery/ics-1589.pdf · In this paper, Shunt Hybrid APF’s are designed to mitigate harmonic components; a passive filter combination

SHUNT HYBRID ACTIVE POWER FILTER

USED FOR COMPENSATION OF

HARMONIC CURRENTS WITH

MODIFIED DQ THEORY

G.Spurthi (P.G.Schlor), CH.SeshagiriRao(Asst professor)

Department of Electrical and Electronics Engineering Sreenidhi Institute

of Science and Technology, Hyderabad

E-mail: [email protected], [email protected]

Abstract

In these days, power quality has become the serious issue. Hybrid Filter is

used for the reduction of harmonics. In this paper, Shunt Hybrid APF’s

are designed to mitigate harmonic components; a passive filter

combination is used which is tuned for reduction of 5th order harmonics. A

3ɸ, 4wire voltage source inverter is taken, which consists of 6 IGBT’s and

a dc capacitor which acts as active filter and used with the combination of

passive filter. DQ theory with modified Phase Locked Loop is designed to

use as a control algorithm. PI controller is used here for the conversion of

dc component of voltage to direct form of current and to maintain dc-link

capacitor voltage regulation. The reference current can be generated

using DQ theory which is given to hysteresis band controller block, where

the gate pulses are generated, that are given to IGBTs in hybrid filter

which produces the compensating currents. The modified PLL technique is

used to suppress the double frequency, present in –ve sequence of non-

ideal voltage source. The results show the value of harmonics in terms of

THD by taking different types of source voltages i.e., balanced source,

unbalanced source, unbalanced distorted source and distorted source by

taking induction motor as load. This technique is performed in MATLAB

SIMULINK.

Keywords: Harmonics, PQ, SHAPF, PLL, PI controller

1. Introduction

In power systems, power quality is the most major notable factor. In

Electrical power systems, among generation, transmission and

distribution, Distribution plays the vital role regarding power quality [1],

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Volume 9 Issue 10 - 2019

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[2]. Because of the existence of nonlinear varying loads the harmonics are

being injected into the voltages and currents waveforms. Harmonics is

one of the sensitive and important factors. Mostly loads which are present

in distribution side are nonlinear loads. For ex in residential sector air

conditioners, washing machines etc.; in industrial sector compressors,

lasers, furnaces etc.; in telecommunication sector chargers, UPS etc.;

which has power electronic components injecting harmonics into the

system which leads to the distortion of the fundamental wave. The other

loads which are connecting at the same point can be affected due to the

presence of harmonics.

Harmonics leads to numerous problems in the system. Harmonics

results in severe effects like overheating of equipment, overheating

of transformers, malfunctioning of switching devices, interference of

telecommunication lines, insulation failure, unnecessary tripping of

circuit breakers etc. so elimination of harmonics should be done to

avoid these type of problems.

In case of single phase transformer third order harmonics are

present while in three phase transformer third, fifth and seventh

order harmonics are present. Because of the presence of these

harmonics there may be malfunction of breakers and insulation

failure due to overheating of equipment. Due to the presence of third

harmonics, neutral currents will also be increased because of the

sharp rise of zero sequence currents.

In the early days for elimination of harmonics, isolation

transformers, dynamic voltage regulators are used. And then after

passive filters are used only for the elimination of particular order of

harmonics and active filters are efficient when compared to passive

filters. To remove the drawbacks of these types of filters, hybrid

filters are used. Hybrid Filters even has a combined design of active

and passive filters. Passive filter is tuned accordingly to mitigation

of 5th order harmonics. Different control techniques have been

evolved such as discrete Fourier Transforms, Fast Fourier

Transform, direct testing and calculation method etc. here we are

using Synchronous Reference Form (SRF) theory with modified

PLL.

Hybrid active filters are installed at the PCC adjusted near to the

load side. The harmonics at load side are eliminated by counter

harmonics produced by active filter which are of same magnitude

but opposite in direction.

The detailed theory of SHAPF is mentioned below sections as



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follows.

2. Shunt hybrid Active Power Filter topology

The preferred shunt hybrid active power filter design is shown in Figure

below. It contains the passive power filter & an active power filter in

shunt combination that creates a hybrid active power filter respectively

and a 3-leg converter with two capacitors serves as the APF and which is

designed to connect in parallel with varying loads, in this case

asynchronous machine (induction motor) load is used in 3-Ø, 4-wire

distribution network. Here all elements which are present inside the

inverter are joined to the system with an inductor i.e. utilized to reduce

the ripples present in the inverter. The passive filter is tuned to reduce 5 th

order harmonic frequency i.e. associated in parallel with the electrical

lines at the loads and also low impedance path for the harmonic currents

is created simultaneously, helps to decrease the rating of the APF.

Figure1. Proposed shunt hybrid active filter



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Figure 2: SRF method based control block diagram

3. Proposed control technique

3.1. Modified Phase Locked Loop (PLL) operation

To extract the clear and detailed values of the maximum voltage

at instant phases, in the unbalanced voltage case, it needs to convert

the 3ɸ unbalanced voltage to the two dimensional stationary axis (αβ

axis). In balanced case, if we assume the converted form of voltage

vectors are plotted on a DQ frame then a round vector is formed

which rotates at the speed equivalent to the frequency. In the same

manner, if the converted unbalance voltage vectors are plotted, an

eclipse formation is created as a result of both positive and negative

sequences present in the vector. Considering the frequency & the

phase details that are previously obtained and by taking an

imaginary frame which rotates in the direction of positive sequence

vector with the speed equivalent to frequency. At that point the

positive sequence vector shows up like stationary and negative

sequence vector rotates at the double speed of the frequency. For

secure and predictable working of APF with the unbalanced and

distorted voltage sources, the frequencies and the phase

information’s of +ve sequence elements of the source voltage must

be achieved rapidly & exactly. Regular Phase Lock Loop of DQ

method working strategy was unable to provide adequate solutions at

unbalanced voltage sources due to the presence of the dynamic

characteristics. The improvised Phase locked loop is created in this

project which can be seen in Figure3. Therefore the working of PLL

is to find the positive sequence elements in not optimal voltage



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sources:

Figure 3: modified PLL block

Vsabc= [

𝑉𝑎𝑉𝑏𝑉𝑐

]=[

𝑉𝑎+

𝑉𝑏+

𝑉𝑐+

]+[

𝑉𝑎−

𝑉𝑏−

𝑉𝑐−]+[

𝑉𝑎0𝑉𝑏0𝑉𝑐0

]………… (1)

=𝑉+ [

𝑠𝑖𝑛𝜃

sin[𝜃 −2𝜋

3]

sin[𝜃 +2𝜋

3]

] + 𝑉− [

𝑠𝑖𝑛𝜃

sin [𝜃 +2𝜋

3]

sin[𝜃 −2𝜋

3]

] + 𝑉0……………… (2)

Considering αβ transforms, the voltage vectors are

𝑉𝛼𝛽 = [𝑉𝛼𝑉𝛽] = [𝑇𝛼𝛽]𝑉𝑎𝑏𝑐…………. (3)

Where

[𝑇𝛼𝛽] = 2/3 [1 −1/2 −1/2

0 √3/2 −√3/2]

So,

𝑉𝛼𝛽 = [𝑉𝛼𝑉𝛽] = [ 𝑉+𝑠𝑖𝑛𝜃+ + 𝑉−𝑠𝑖𝑛𝜃−

−𝑉+𝑐𝑜𝑠𝜃+ + 𝑉−𝑐𝑜𝑠𝜃−]……………… (4)

Performing DQ transform



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𝑉𝑑𝑞 = [𝑉𝑑𝑉𝑞] = [𝑇𝑑𝑞]𝑉𝛼𝛽

=[ 𝑐𝑜𝑠𝜃 𝑠𝑖𝑛𝜃−𝑠𝑖𝑛𝜃 𝑐𝑜𝑠𝜃

] [ 𝑉+𝑠𝑖𝑛𝜃+ + 𝑉−𝑠𝑖𝑛𝜃−

−𝑉+𝑐𝑜𝑠𝜃+ + 𝑉−𝑐𝑜𝑠𝜃−]…………….. (5)

=[𝑉+ sin(𝜃+ − 𝜃) + 𝑉− sin(𝜃− + 𝜃)

−𝑉+ cos(𝜃+ − 𝜃) + 𝑉− cos(𝜃− + 𝜃)]

The approx. phase angle=𝜃;

Phase angle of +ve sequence voltages =𝜃+;

Phase angle of -ve sequence voltages =𝜃−;

Let, 𝜃=ωt, successfully the PLL spots the phase at𝜃 = 𝜃+ = 𝜃−.

So,

[VdVq]=[

𝑉− sin(2𝜃)

−𝑉+ + 𝑉− cos(2𝜃)]……………….(6)

Now the doubled frequency should be removed off, where this is the

main motto of the design of modified phase locked loop. By elimination

of 2θ frequency, it provides the positive sequence elements. The PLL

network utilizes park and Clarke transformation in which 3ɸ unbalanced

voltages is changed over the synchronous rotating frame voltages to

recognize the maximum voltage of +ve sequence. Then the second order

resonant filters are utilized rather than the respected low pass filter to

eliminate the double(2θ) frequency which are produced due to unbalance

of the system. The rate limiter serves to eliminate the ripples present in

the voltage.

3.2. Generation of reference Currents

In active power filter, the load currents used to be estimated by the use of

the Hall Effect current sensor and transformed to dq0 with the help of

rotational frames that are constant with the positive sequence voltages in

the system. Currents are

[

𝑖𝑑𝑖𝑞𝑖0

] = 2/3 [

sin(𝜔𝑠𝑡) sin(𝜔𝑠 𝑡 − 2𝜋/3) sin(𝜔𝑠 𝑡 + 2𝜋/3)cos(𝜔𝑠 𝑡) cos(𝜔𝑠 𝑡 − 2𝜋/3) cos(𝜔𝑠𝑡 + 2𝜋/3)

1/√2 1/√2 1/√2

] ×

[𝐼𝑙𝑎𝐼𝑙𝑏𝐼𝑙𝑐

]……(7)



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𝜔𝑠𝑡 Is assumed as angle of +ve sequence voltage source and this is

output of PLL.

The observation here is with the help of PLL output the currents are

converted into id and iq form. Then the values of id and iq load

currents are permitted to supply through the LPF to isolate the

alternate & direct current parts thus the LPF allows only DC

components and stops AC components as per its nature and in this

currents the AC parts are responsible for harmonics so, Later the AC

harmonic components will remains as an output because of the

difference operation (subtraction) between the output of LPF and id-

iq currents. The both idAC and iqAC currents that have been filtered

from the below equations are utilized in the production of the exact

reference currents which given as input to the hysteresis loop

controller. The DC components of the currents are removed by the

LPF to produce the harmonic elements which to be referred.

[𝑖𝑑𝐴𝐶𝑖𝑞𝐴𝐶

] = [𝑖𝑑𝑖𝑞] − [

𝑖𝑑𝐷𝐶𝑖𝑞𝐷𝐶

]………….. (8)

The abc reference currents:

[𝑖𝑎𝑟𝑖𝑏𝑟𝑖𝑐𝑟

] = [

sin(𝜔𝑠 𝑡) cos(𝜔𝑠𝑡)sin(𝜔𝑠 𝑡 − 2𝜋/3) cos(𝜔𝑠𝑡 −2𝜋/3)sin(𝜔𝑠𝑡 + 2𝜋/3) cos(𝜔𝑠𝑡 + 2𝜋/3)

] [𝑖𝑑𝐴𝐶𝑖𝑞𝐷𝐶

]………….. (9)

3.3 DC link capacitor voltage control:

In the SAPF, the value of DC link capacitor voltage can be detected by

the senor known as Hall Effect voltage sensor then compares with the

reference DC voltage.

Fig 4: DC link voltage control loop

The DC link capacitor voltage equation is

𝐶𝑑𝑉𝑑𝑐

𝑑𝑡= 𝐼𝑑𝑐………… (10)

Where 𝐼𝑑𝑐is dc-link current

Using LT



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𝐶𝑆𝑉𝑑𝑐(𝑠) = 𝐼𝑑𝑐(𝑠)………… (11)

So

G(S) =𝑉𝑑𝑐(𝑠)

𝐼𝑑𝑐(𝑠)=

1

𝑐𝑠…………. (12)

The output which is the error of the voltage at the nth sampling

moment, the error = 𝑉𝑑𝑐𝑟𝑒𝑓 − 𝑉𝑑𝑐 is fed through to PI controller by

means of this transfer function to create the necessary reference

current.

3.4. Harmonic current generator

Generally, hysteresis comparators are utilized for the fast operation and

proper sinusoidal waveforms tracing ability. However the reference

current𝐼𝑎𝑟𝑒𝑓, and the compensating current 𝐼𝑎𝑐𝑜𝑚are compared and

analyzed. The switching concept is mentioned below:

If the current𝐼𝑎𝑟𝑒𝑓 ≺ (𝐼𝑎𝑐𝑜𝑚) hysteresis band first S1 is OFF and

then S6 is ON of leg (a) in APF.

If the current𝐼𝑎𝑟𝑒𝑓 ≻ (𝐼𝑎𝑐𝑜𝑚) hysteresis band first S1 switch is ON

and then S6 switch is OFF of leg (a) in Active power filter.

Similarly, in leg (b) and (c) the switching process is used with the

help of using hysteresis band controller. The hysteresis bands are

planned by considering the limits of switching frequency of device.

4. Result Analysis

In MATLAB Simulink, the utilization of the 3ɸ, 4wire power system

network blocks with using the shunt hybrid active power filter

combination of passive power filter is done. The induction motor

draws high starting currents which are 6to8 times of rated current

and also reduces within seconds to normal values. The values of

simulation outputs are achieved for the four cases balanced,

unbalanced, distorted and unbalanced distorted sources in the system

network. The utilized parameter values of SHAPF are shown below.

4.1. Balanced voltage source condition

By the consideration of proposed control technique under balanced

voltage source with induction load, it gives effective outputs for

compensation of harmonic currents present in load current. In this case it

reduces the starting high currents of induction motor in source current of

the power system by providing compensation currents and make source

currents in sinusoidal waveform with below 5% of THD according to the

IEEE format as shown in below figures waveforms of Vs, IL,Is and



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THDs of IL and Is.

Fig 5: After injection of compensating currents

a)Voltage source b)Load current c) source current



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Fig 6: a) THD of load current=13.07% b)THD of source

current=2.64%

Fig 7: DC voltage



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4.2. Unbalanced source condition

In unbalanced source case the phases of voltage are uneven,

magnitude of phases are not equal. So the control technique under

this condition is also effective and output waveforms and THDs are

shown below.

.

Fig 8: a) Voltage source, b) Load current, c) source current.



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Fig 9:THD of load current=20.54% THD of source

current=1.31%

Fig10 :DC Voltage

4.3. Distorted source condition

In this case we are injecting 5 th order harmonics in the source

voltage for distortions and observing weather control technique is

satisfactory working or not, the output waveforms and THD are

shown in below figures.



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Fig 11: a) Voltage source, b) Load current, c) Current source.



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Fig 12: THD of load currents=24.40% THD of source

current=1.30%

Fig 13: DC voltage

4.4. Unbalanced distorted source condition

In this case both unbalanced and distortions are present the output

waveforms and THDs are shown below.

Fig 14: a) Voltage Source, b) Load current, c) Current source



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Fig 15: THD .of load current=32.42% THD of source

current=3.83%

Fig 16: DC voltage



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Table 1.Comparison of THD analysis

Algorith

m

Balanced Unbalanced distorted Unbalanced

distorted

THD(R

L-load)

3.82% 3.16% 3.32% 3.85%

THD(in

duction

motor)

2.64% 1.31% 1.30% 3.83%

Table 2.Simulation parameters

Parameters Values

Source voltage 415v, 50hz

Shunt APF R=1ohm, L=2mh, two DC-link

capacitors=2000UF,

Vdc=700v

Passive power

filter

Fifth harmonic tuned,

R=0.01ohm,L=5mH, C=80UF

Induction motor 5.4HP(4KW),400v,50Hz,

1430rpm



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5. Conclusions

In this paper the main aspect is to improve power quality of a

system with SHAPF. It is achieved by using SRF strategy and a

modified PLL is created which is successfully utilized as per the grid

voltage synchronization by fulfilling all the four conditions. The

Total Harmonic Distortion values of four different conditions are

found below 5%. In this way, to achieve high quality harmonics

compensation and reliable reduction of harmonics with quick action,

the modified SRF method is used.

6. References

1. H.Akagi,(1996), “New trends in active filters for power

conditioning”, IEEE Transactions on Industry Application, Vol.32,

pp1312- 1322

2. S. K. Jain and P. Agarwal, "Design Simulation and Experimental

Investigations, on a Shunt Active Power Filter for Harmonics, and

Reactive Power Compensation," Electric Power Components and

Systems, vol. 31,pp.671-692, 2003

3. Ambrish Chandra, Bhim Singh, B. N. Singh, and Kamal Al-

Haddad,(20000), “An Improved Control Algorithm of Shunt Active

Filter for Voltage Regulation, Harmonic Elimination, Power-Factor

Correction, and Balancing of Nonlinear Loads”Vol.15,No.3,pp.495-

507

4. A. F. Zobaa, "Letter to the Editor: Optimal Sizing of the Passive Filter's

Elements in Hybrid Active Filters," Electric Power Components and

Systems, vol. 35, pp. 483-488, 2007.

5. S. S. Patnaik and A. K. Panda, "Real-time performance analysis and

comparison of various control schemes for particle swarm optimization-

based shunt active power filters," International Journal of Electrical

Power &Energy Systems, vol. 52 pp. 185-197, 2013.

6. Kesler, M., Ozdemir, E.: ‘Synchronous-reference-frame-based control

method for UPQC under unbalanced and distorted load conditions’,

IEEE Trans. Ind. Electron., 2011, 58, pp. 3967–3975

7. Sinha, R.K., Sensarma, P.: ‘A pre-filter based PLL for three-phase grid

connected applications’, Electric Power Syst. Res., 2011, 81, pp. 129–

137

8. Salmeron, P., Litrán, S.P.: ‘A control strategy for hybrid power filter to

compensate four-wires three-phase systems’, IEEE Trans. Power

Electron., 2010, 25, pp. 1923–1931



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9. A. Nasiri, A. E. Amac, and A. Emadi, "Series-Parallel Active

Filter/Uninterruptible Power Supply System," Electric Power

Components and Systems, vol.32, pp. 1151-1163, 2004.

10. De, D., Ramanarayanan, V.: ‘An active shunt compensator for reactive,

unbalanced and harmonic loads under balanced and unbalanced grid

voltage conditions’. 2010 Joint Int. Conf. on Power Electronics, Drives

and Energy Systems (PEDES) & 2010 Power India, 2010, pp. 1–6

11. Lam, C.-S., Wong, M.-C., Han, Y.-D.: ‘Hysteresis current control of

hybrid active power filters’, IET Power Electron. 2012, 5, pp. 1175–

1187



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