Electric Power Systems Research 79 (2009) 759765

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Electric Power Systems Research

journa l homepage: www.e lsev ier .co

New di unpower s

Mohame a, Sa Groupe de Rec eb Laboratoire d ancy U

a r t i c l

Article history:Received 21 DReceived in reAccepted 13 OAvailable onlin

Keywords:Active lterHarmonics isoDistorted voltage conditionsSelf-tuning lterModulated hysteresis current control

comproporrentonicy of th genACE pbyus

an analogue card. The use of STF instead of classical extraction lters allows extracting directly the voltageand current fundamental components in the axis without phase locked loop (PLL). The performancesare good even under distorted voltage conditions. First, the effectiveness of the new proposed method ismathematically studied and veried by computer simulation. Then, experimental results are presentedusing a DSPACE system associatedwith the analogue current controller for a real shunt active power lter.

2008 Elsevier B.V. All rights reserved.

1. Introduc

Generallpower convin domesticthe sourceas heatingcontrol equ

Many socompensatehybrid) witphase, thre[1]. These ssource inve

The passcurrents. Hothem and hwith the symances depand shunt)

CorresponE-mail add

philippe.poure

0378-7796/$ doi:10.1016/j.etion

y, harmonic currents aremostly generatedby theAC/DCersion units and the power electronic equipments, usedand industry applications. The harmonic currents are

of adverse effects for many types of equipments suchin distribution transformer, perturbation of sensitiveipments and resonances with the grid.lutions are proposed and studied in the literature tothe harmonics such as ltering (passive, active, and

h various topologies (shunt, series) for two-wire single-e-wire three-phase and four-wire three-phase systemsolutions have been proposed using current and voltagerters to improve the mains power quality.ive ltering is a simple way to eliminate the harmonicwever, it does not allow to completely eliminate all of

as many drawbacks such as series or parallel resonancestem impedance. Moreover, the compensation perfor-end on the mains impedance. The active lters (serieswere also developed and widely used to overcome the

ding author. Tel.: +33 3 83 68 41 31; fax: +33 3 83 68 41 33.resses: Mohamed.Abdusalam@green.uhp-nancy.fr (M. Abdusalam),@lien.uhp-nancy.fr (P. Poure).

drawbacks of the passive lters and improve power quality. Aswell known, the parallel active lters are controlled to generate inreal time the harmonic currents produced by the non-linear loads[2].

The performances of an active lter mainly depend on the ref-erence current generation strategy. Several papers studied andcompared the performances of different reference current genera-tion strategies under balanced, sinusoidal, unbalanced or distortedalternating current (AC) voltages conditions [35]. In all of them,authors demonstrated that under balanced and sinusoidal AC volt-ages conditions, the strategies such as the so-called pq theory andSynchronous Reference Frame Theory (SRF) provide similar per-formances. Differences arise when one works under distorted andunbalanced AC voltages. In real conditions, the mains voltages aredistorted, which decreases the lter performances [6]. In this case,the pq theory performances are poor, from the harmonics point ofview, and the best results are obtained with the SRF. However, theSRF theory requires a phase locked loop (PLL) which increases thecomplexity of the control system: an additional card is usually usedand the controller implementation is more complex. In this paper,we theoretically and experimentally studied a new reference cur-rent generation suitable for shunt active power lter control underdistorted voltage conditions byusing self-tuninglters (STF) for thereference current generation and amodied version of the classicalpq theory.

see front matter 2008 Elsevier B.V. All rights reserved.psr.2008.10.009gital reference current generation for shlter under distorted voltage condition

d Abdusalama, Philippe Poureb,, Shahram Karimiherche en Electrotechnique et Electronique de Nancy (GREEN), CNRS UMR 7037, FrancInstrumentation Electronique de Nancy (LIEN), EA 3440, Universit Henri Poincar N

e i n f o

ecember 2007vised form 30 July 2008ctober 2008e 19 December 2008

lator

a b s t r a c t

In this paper, a new reference currentunder distorted voltage conditions is ptuning lters (STF) for the reference cuThis active lter is intended for harmdistorted voltage conditions. The studdeals with the harmonic isolator whicimplemented in a DS1104 card of a DSPof the switchingpattern of the inverterm/locate /epsr

t active

hahrokh Saadatea

niversit, B.P. 239, 54506 Vandoeuvre ls Nancy Cedex, France

utation method suitable for shunt active power lter controlsed. The active power lter control is based on the use of self-generation and on a modulated hysteresis current controller.compensation of a diode rectier feeding a RL load underhe active lter control is divided in two parts. The rst oneerates the harmonic reference currents and is experimentallyrototyping system. The second part focuses on the generationing amodulatedhysteresis current controller, implemented in

760 M. Abdusalam et al. / Electric Power Systems Research 79 (2009) 759765

The STFdirectly fro referenresponses oThe major a

operating no phase no PLL req easy to im

In this pactive powephase parapresented.phase moduthe systemter controlharmonic elters (LPF)ematical ancontroller isexperiment

2. System

Fig. 1 prephase voltaparallel witinductors LDC terminarectier supin the supp

The proprst part isconsists in ginstead of Hby Akagi etinto a DSPAsecond parttroller genethe inverterthe experimlogue card.lter system

trol

nera

ordinthe

stemof thng ppute Lc La Lb scvsa + vsb). Then,weapplyamodiedversionof thepq theoryction 3.3) developed in our laboratory for generating thet references i

fa, i

fband i

fc(see Fig. 2).

se digital references are the outputs of the DSPACE systeme converted into analogue signals by Digital-to-Analogueters. By using an analogue card developed in our laboratory,erate the switchingpattern for the inverter by implementinglogue modulated hysteresis current controller (see Section

lf-tuning lterFig. 1. Power system conguration.

is dedicated to extract the fundamental componentm electrical signals (distorted voltage and current) ince frame. In the following, the frequency and dynamicf the STF are mathematically analyzed and discussed.dvantages of the STF are cited hereby:

adequately in steady state and transient condition;delay and unity gain at the fundamental frequency;uired;plement in digital or analogue control system.

aper, we validated the STF performances in a real shuntr lter. A theoretical and experimental study of a three-llel active lter for harmonic compensation (Fig. 1) isImproved harmonic isolator based on STF and three-lated hysteresis current control are used. In Section 2,conguration is presented. Then, in Section 3, the l-strategy is discussed. We used STF instead of classicalxtraction based on high pass lters (HPF) or low pass. A focus is made on the STF performances by math-alysis under distorted voltage conditions. The currentalso presented [7]. In Sections 4 and 5, simulation andal results are presented, respectively.

conguration

sents the shunt active lter topology based on a three-ge source inverter, using IGBT switches, connected inh the AC three-phase three-wire system through threeF. The capacitor C is used in the DC side to smooth the

3. Con

3.1. Ge

AcciLb, andwire syinputssampliis comvsc =((see Securren

Theand arconverwegenthe ana3.4).

3.2. Se

l voltage. The non-linear load is a three-phase diodeplying a RL load. This load generates harmonic currentsly system.osed control strategy can be divided in two parts. Thethe harmonic isolator (reference current generation). Itenerating theharmonic current references anduses STFPF or LPF usually used in the pq theory rst proposedal. [8]. This harmonic isolator will be implemented

CE system (DS1104 card) in the experimental study. Theis the current control of the power converter. This con-rates the suited switching pattern to drive the IGBTs ofby using a modulated hysteresis current controller. Inental study, this controller is implemented into an ana-Fig. 2 shows the schematic diagram of the active power.

3.2.1. PrinciHong-so

erence fram

Vxy(t) = ej

whereUxy aand after invious equatafter Laplac

H(s) = Vxy(Uxy(Fig. 2. Active lter system.

strategy

l control principle

g to Fig. 2, the voltage vdc , the load currents iLa andsource voltages vsa and vsb of the three-phase three-are acquired and converted into digital signals at the

eDSPACEsystembyAnalogue-to-Digital converters. Theeriod for acquisition is equal to 30s. The current iLcd by i =(i + i ) and the voltage v is calculated byple and frequency response of the STFck Song studied the integration in the synchronous ref-e [9]. He demonstrated that:

t

ejtUxy(t)dt (1)

ndVxy are the instantaneous signals, respectively beforetegration in the synchronous reference frame. The pre-ion can be expressed by the following transfer functione transformation:

s)s)

= s + js2 + 2 (2)

M. Abdusalam et al. / Electric Power Systems Research 79 (2009) 759765 761

Fig. 3. Self-tuning lter tuned to the pulsation c .

We think of introducing a constant K in the transfer function H(s),to obtain a STF with a cut-off frequency c so the previous transferfunction H(s) becomes:

H(s) = Vxy(s)Uxy(s)

= K (s + K) + jc(s + K)2 + 2c

(3)

By introducing the parameter K in H(s), the transfer function mag-nitude is liMoreover, tc. By replasignals Vxy(

x(s) = K(s +

x(s) =(s +

where x(srespectively

Eqs. (4) a

x(s) = Ks [x

x(s) =K

s[x

The blocdepicted insus differenthat no disp

Fig. 4. Bode deter K (fc =50H

sation. One can see that small value of K increases lter selectivity.Dynamic response consideration is studied in the following section.Thus, by using a STF, the fundamental component can be extractedfrom distorphase delay

3.2.2. DynaA three-

Fourier seri

xa(t) = X1 s

xb(t) = X1si

xc(t)=X1 sin

This three-preference fr

=

8a)(32

lacin) andlowied:

32

[s

mited and more particularly equal to one for =c.he phase delay is equal to zero for the cut-off frequencycing the input signals Uxy(s) by x(s) and the outputs) by x(s), the following expressions can be obtained:

(s + K)K)2 + 2c

x(s) Kc(s + K)2 + 2c

x(s) (4)

Kc

K)2 + 2cx(s) + K(s + K)

(s + K)2 + 2cx(s) (5)

) and x(s) can either be a current or a voltage signal,before and after ltering (see Fig. 4).nd (5) can be expressed as follows:

(s) x(s)] cs x(s) (6)

(s) x(s)] +cs

x(s) (7)

k diagram of the STF tuned at the pulsation c isFig. 3. Fig. 4 shows the frequency responseof theSTFver-t values of the parameter K for fc =50Hz. One can noticelacement is introduced by this lter at the system pul-

[xx

]

From (

x(t) =

x(t) =

By repEqs. (4the folobtain

x(t) =

x(t) =iagram for the STF versus pulsation for different values of the param-z).

[c

with Ah = (1From the

response anmances. Thtransient tiSTF is stable

Also, theis approximted electrical signals (voltage or current) without anyand amplitude changing.

mic response of the STF under distorted conditionsphase distorted electrical signal x(t) can be expressed ines by Eqs. (8a)(8c) as follows:

in(t + 1) +n

h=2Xhsin(ht + h) (8a)

n(

t + 1 23

)+

nh=2

Xh sin(

ht + h 23

)(8b)

(t + 1+

23

)+

nh=2

Xh sin(

ht + h +23

)(8c)

hase signal canbe transformed into the two-phaseame by using the Concordia transformation:

23

1 12 12

0

32

32

[

xaxbxc

](9)

8c) and (9), we obtained:

X1 sin(t + 1) +

32

nh=2

Xh sin(ht + h) (10)

32

X1 cos(t + 1)

32

nh=2

Xh cos(ht + h) (11)

g Eqs. (10) and (11) after Laplace transformation into(5) and by applying the inverse Laplace transformation,ng instantaneous expressions for the STF outputs are

X1(1 eKt) sin(t + 1) +

32

nh=2

Xh1 + Ah2

in(ht+h + arctan Ah)eKtsin(t + h + arctan Ah)](12)

32

X1(1 eKt)cos(t + 1)

32

nh=2

Xh1 + Ah2

os(ht + h+arctan Ah)eKtcos(t + h + arctan Ah)](13)

h)/K.analytical Eqs. (12) and (13),we examined thedynamicd the inuence of the parameter K on the STF perfor-e time constant of the STF is equal to1/K. Therefore, theme is increased when K is decreased. Additionally, thefor any positive value of the parameter K.phasedelay for the fundamental component is zero andately equal to 90 for the other harmonics. Moreover,

762 M. Abdusalam et al. / Electric Power Systems Research 79 (2009) 759765

d harm

the STF redugain equal t

Gh =1

1 +In Eq. (14),(fundamenis illustrate

3.3. Harmo

The loadsystem are

[ii

]=

As knowdecompose

i = i + ii = i + i

Then, thsation c di harmosubtracting(see Fig. 3).which correiLa, iLb and i

For thetransforme

[vv

]=

Then,weponents. Thof the distothe harmon

After co

harmonic c

p = iv + i

i

pq

, q: fupowrrent[

vv

r ad, pc,p (si

, a

v+ v2v+ v2

ubstiFig. 5. Block diagram of the new STF-base

ces the amplitude of the harmonic components with ao:

Ah2

= KK2 + (1 h)22

for h 1 (14)

Gh denotes the harmonic gain. When h is equal to 1tal component), this gain is equal to 1. This performanced by the frequency response of the STF shown in Fig. 4.

nic isolator

currents, iLa, iLb and iLc of the three-phase three-wiretransformed into the axis (see Fig. 5) as follows:

23

1 12 12

0

32

32

[

iLaiLbiLc

](15)

n, the currents in the axis can be respectivelyd into DC and AC components by

(16)

e STF extracts the fundamental components at the pul-rectly from the currents in the axis. After that, thenic components of the load currents are computed bythe STF input signals from the corresponding outputs

q = iv

where

p = p +q = q +

with pThe

and cu[pq

]=

Aftevoltagepower,frame,

i =v2

i = v2With s

The resulting signals are the AC components, i and i,spond to theharmonic components of the load currentsLc in the stationary reference frame.source voltage, the three voltages vsa, vsb and vsc ared to the reference frame as follows:

23

1 12 12

0

32

32

[vsavsbvsc

](17)

applied self-tuning ltering to these voltage com-is lter allows suppressing of any harmonic componentrted mains voltages and consequently leads to improveic isolator performance.mputation of the fundamental component v and theurrents i, we calculate the p and q powers as follows:

v (instantaneous activepower) (18)

i = i +v2

i = i + v2Current

terms, theand the secwith the supower is abregulate thethe abc c

ifai

fb

ifc

=

onic isolator.

v (instantaneous reactivepower) (19)

(20)

ndamental components, p, q: alternative componentser components p and q related to the same voltagess can be written as follows:

v v

][ii

](21)

ding the active power required for regulating DC busto the alternative component of the instantaneous realee Fig. 5), the current references in the referencere calculated by

(p + pc) v

v2 + v2q (22)

(p + pc) + vv2 + v2

q (23)

tution of (21) into (22) and (23), we obtained:

v

+ v2

pc (24)

v+ v2

pc (25)

references obtained from Eqs. (24) and (25) include tworst term contains the harmonic current componentsond one is a fundamental current component in phasepply voltage. Consequently, a small amount of activesorbed from or released to the DC capacitor so as toDC bus voltage. Then, the lter reference currents in

oordinates are dened by

23

1 012

32

12

32

[

i

i

]. (26)

M. Abdusalam et al. / Electric Power Systems Research 79 (2009) 759765 763

Fig. 6. Modulated hysteresis current controller.

3.4. Modulated hysteresis current controller

Consider now the current controller. With linear controllersusing pulse width modulation (PWM) techniques, a constantswitching frequency can be achieved and a well-dened harmonicspectrum can be obtained, but with limited dynamic proper-ties. Compared with linear controllers, non-linear ones based onhysteresis strategies allows faster dynamic response and betterrobustness with respect to the variation of the non-linear load[7]. Nevertheless, with non-linear current controllers, the switch-ing frequency is not constant and this technique generates a largeside harmonics band around the switching frequency. To x theswitching frequency, one solution could consist in using a variablehysteresis bandwidth [7]. This solution which implies the knowl-edge of the systemmodel and its parameterswith enoughprecisionis difcult to implement experimentally. Here, we implemented anon-linear current controller, so-called modulated hysteresis cur-rent controller [10].

Fig. 6 presents the modulated hysteresis current controller. Theprinciple of this controller consists in adding to the error signalX (X = i

f

Fig. 7. Reference and measured current.

and period (T). The carrier frequency is chosen equal to the desiredswitching frequency for the voltage inverter. The resulting signal(H) constitutes then the new reference of a classical hysteresis con-troller with a bandwidth of 2Bh. The outputs of the hysteresis blockare the switching pattern.

In order to set the switching frequency in steady state, itshould exist during each switching period T, only two intersectionsbetween the error X and the triangular signal: the rst onewith thehigher limit of the hysteresis controller and the second onewith itslower limit (Fig. 7).

To control theactivelter atxedswitching frequency, the trian-gular signal amplitude Atr and the hysteresis bandwidth Bh for themodulated hysteresis current controllermust be carefully selected.If these parameters are notwell chosen, the effective switching fre-quencywould be either higher or lower than the desired one set bythe triangular signal as illustrated in Fig. 8.

Shamsi et al. investigated a high frequency averagemodel of thecontroller to dene the suited parameters [10]. Thanks to a limitorbit analysis, they demonstrated that with appropriate values ofAtr and Bh, irregular orbits can be avoided. For any value of the

rameters, it has been shown that the current waveform is

Fig. 8. Examp an thif ) a triangular carrier signal (Tr) with amplitude (Atr) load pa

les of bad design of control parameters leading to: (a) switching frequency larger thFig. 9. Simulation results for the phase 1 under sinusoidal voltage conditions: (a) loae desired one; (b) switching frequency lower than the desired one.d current; (b) supply current after compensation.

764 M. Abdusalam et al. / Electric Power Systems Research 79 (2009) 759765

Table 1Power system parameters.

System frequency 50HzSystem voltage 130VmaxInductor: LF 3mHInductor: LC 0.8mHDC bus voltage 400VCapacitor: Cd 1100FResistor: Rd 48.6Inductor: Ld 40mH

T-periodic (stable one-periodic orbit) when the parameters Atr andBh are correctly chosen [10].

3.5. DC bus voltage control

A DC bus controller is required to regulate the DC bus voltagevdc and to compensate for the active lter losses. The measuredDC bus voltage vdc is compared with its reference value vdc . Theresulting error is applied to aproportional integral (PI) regulator. So,the active lter can build up and regulate the DC capacitor voltagewithout any

4. Simulat

Fig. 9 shFig. 2 undereters are deparametersis equal to 2(K=80 for tin Fig. 9 betand the supnentof thethe DC busdistorted vosinusoidal aThe THD ofafter lterinperformancvoltage con

5. Experim

The expIt consists ipower sem

Fig. 11. Experimental waveforms for the harmonic reference currents ifa, i

fband i

fc

(5A/div, 10ms/div).

Experimental results for the phase a, from top to bottom: load current iLr current iF (A) and source current iS (A) (5A/div, 10ms/div).

ed in the Section 3. The IGBTs are controlled by switchingproduced by the modulated hysteresis current controller.

n-linear load is a diode rectier feeding a RL load and thethe supply voltage is equal to 3.7%. The harmonic isolatoremented by using a DSPACE DS1104 development board. Ittes the harmonic current references. Fig. 11 shows the three-harmonic current references generated at the output of theE system.switching frequency of the power semiconductors is set atby choosing a suited triangular carrier signal at the sameexternal power supply.

ion results

ows the simulation results for the system depicted insinusoidal voltage conditions. The simulation param-ned in Table 1. They correspond to the experimental. The total harmonic distortion (THD) of the load current8.08%. The THDof the supply currents is reduced to 2.3%he STF) after compensation. A difference can be noticedween the fundamental component of the load currentply current. It is justied by the fundamental compo-lter current inphasewith the supplyvoltage to regulatevoltage. Fig. 10 illustrates the simulation results underltage conditions. In this case the supply voltage is notnd includes a 5th harmonic component (THD=9.96%).the supply current under this condition is equal to 2.4%g. The simulation results verify the effectiveness andes of the proposed harmonic isolation under distortedditions.

ental results

erimental active lter was realized according to Fig. 2.n a three-phase source voltage inverter based on IGBTiconductors. The harmonic isolator uses STFs and was

Fig. 12.(A), lte

describpatternThe noTHD ofis implgeneraphaseDSPAC

The20kHzFig. 10. Simulation results for the phase 1 under distorted voltage conditions: (a) supply voltage; (b) supply current after compensation.

M. Abdusalam et al. / Electric Power Systems Research 79 (2009) 759765 765

compe

Fig.

frequency.0.15A and t

Fig. 12 sthe studied26% while i

Fig. 13 psource curreffectivenes

Fig. 14 shvoltage vdcaround its r

With theactive lterreferences pdirectly afteto isolate thguarantees

6. Conclus

This papshunt activhardware immisation ofversionof thin two part

he reue calate-tunrsionass ats. Thrformdistod thewitchsimunfortsis cposetion

ncesFig. 13. Harmonic spectrum of the source current: (a) before

14. Experimental voltage vdc on the DC side of the inverter.

The amplitude Atr of this triangular signal is xed athe bandwidth Bh is equal to 0.05A [10].hows the experimental waveforms for the currents of

erate tanaloga modu

Selfed ve(high pcurrentory peundermentexed s

Theand cohysterethe proinstalla

Referesystem. The THD of the non-linear load iL is equal tot is equal to 2.5% for the source current iS after ltering.resents, for the phase 1, the harmonic spectrum of theent before and after active ltering. It demonstrates thes and the efciency of the proposed control scheme.ows experimental results for the DC bus controller. Theon the DC side of the inverter is stable and regulatedeference.modulated hysteresis current controller (Atr, Bh), thegenerates the suited currents to efciently track theroduced by the harmonic isolator. The use of the STFr transformation in the control system allows use fundamental component of the supply voltages andhigh performances to extract the AC components.

ion

er has discussed the control and performances of ae power lter under distorted voltage conditions. Theplementation has been performed based on the opti-

the reference current generation and using a modiedepq theory. The control of the activelterwasdivideds, the rst one realized by the DSPACE system to gen-

[1] B. Singh,ity impro(1999) 96

[2] S.A. Gonznique suElectronic

[3] G.W. Chanter controApplicatio

[4] S. Georgeunder nonon Power

[5] M.Monteactive poPower Ele

[6] T.C. Greenings Elect

[7] M.P. Kazmvoltage sotronics 45

[8] H. Akagi,reactive pElectronic

[9] S. Hong-Stion algorPower El533537.

[10] M. Nejad,rent contrPower Elensation; (b) after compensation.

ference currents and the second one achieved by anrd for the switching pattern generation, implementingd hysteresis current controller.ing lters have been introduced in the proposed modi-of the pq theory instead of classical extraction ltersnd/or low pass lters) for both grid voltages and loade use of this lter experimentally leads to satisfac-ances since it perfectly extracts the harmonic currents

rted conditions. For the current controller, we imple-modulated hysteresis current controller to obtain aing frequency for the IGBTs.lation and the experimental results have demonstrateded the major advantages of using STF and modulatedurrent controller in the lter control. In conclusion,d control for shunt active power lter is effective inon an actual power system under distorted conditions.

K. Al-Haddad, A. Chandra, A review of active lters for power qual-vement, IEEE Transactions on Industrial Electronics 46 (October (5))0971.alez, R. Garcia-Retegui, M. Benedetti, Harmonic computation tech-itable for active power lters, IEEE Transactions on Industrials 54 (October) (2007) 27913279.g, C.M. Yeh, Optimisation-based strategy for shunt active power l-l under non-ideal supply voltages, IEE Proceedings Electric Powerns 152 (March (2)) (2005) 182190., V. Agarwal, A DSP based optimal algorithm for shunt active ltersinusoidal supply and unbalanced load conditions, IEEE TransactionsElectronics 22 (March) (2007) 593601.ro, E.R. Cadaval, F.Gonzalez, Comparisonof control strategies for shuntwer lters in three-phase four-wire systems, IEEE Transactions onctronics 22 (January) (2007) 229236., J.H. Marks, Control techniques for active power lters, IEE Proceed-ric Power Applications 152 (March (2)) (2005) 369381.ierkowski, L. Malesani, Current control techniques for three-phaseurce PWM converters: a survey, IEEE Transactions on Industrial Elec-(5) (1998) 691703.Y. Kanazawa, A. Nabae, Generalized theory of the instantaneous

ower in three-phase circuits, in: Proceedings of International Powers Conference, Tokyo, Japan, 1983, pp. 13751386.eok, P. Hyun-Gyu, N. Kwanghee, An instantaneous phase angle detec-ithm under unbalanced line voltage condition, in: IEEE 30th Annualectronics Specialist Conference PESC99, vol. 1, August, 1999, pp.

S. Pierfederici, J.P. Martin, F. Meibody-Tabar, Study of an hybrid cur-oller suitable for DCDC or DCAC applications, IEEE Transactions onctronics 22 (November) (2007) 21762186.

New digital reference current generation for shunt active power filter under distorted voltage conditionsIntroductionSystem configurationControl strategyGeneral control principleSelf-tuning filterPrinciple and frequency response of the STFDynamic response of the STF under distorted conditions

Harmonic isolatorModulated hysteresis current controllerDC bus voltage control

Simulation resultsExperimental resultsConclusionReferences