IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 32, NO. 12, DECEMBER LC-coupling hybrid active power filter (TCLC-HAPF),

Transcription

1 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 32, NO. 12, DECEMBER Selecte Compensaton of Dstorton, Unbalanced and Reacte Power of a Thyrstor-Controlled LC-Couplng Hybrd Acte Power Flter (TCLC-HAPF) Le Wang, Ch-Seng Lam, Senor Member, IEEE, and Man-Chung Wong, Senor Member, IEEE Abstract When the load generated harmonc, unbalanced, and reacte power s beyond the lmted capacty of a thyrstorcontrolled LC-couplng hybrd acte power flter (TCLC-HAPF), the TCLC-HAPF wth the conentonal control methods cannot prode satsfactory compensaton performance. In ths paper, a selecte compensaton control method of harmonc dstorton, unbalanced and reacte power of the TCLC-HAPF s proposed, whch can functon een at dfferent oltage condtons (e.g., oltage dp, oltage fault, etc.). Frst, the proposed control method decomposes the load power nto fundamental poste-sequence reacte power, fundamental negate-sequence power (unbalanced power), and harmonc power. Then, the decomposed reacte, unbalanced, and harmonc power can be selectely or fully compensated based on the capacty of the TCLC-HAPF. Fnally, smulaton and expermental results are proded to erfy the effecteness of the proposed selecte compensaton control method for the TCLC- HAPF. Index Terms Negate-sequence acte power, postesequence, reacte power, selecte compensaton, thyrstorcontrolled LC-couplng hybrd acte power flter (TCLC-HAPF), unbalance power, oltage dp, oltage fault. I. INTRODUCTION THE smart grd, regarded as the next-generaton power grd, s consdered as a promsng soluton for energy crss. Howeer, the smart grd s nterconnected wth dfferent power grds, so that the dfferent power qualty problems can easly occur n weak grd areas such as harmonc dstorton, lower power factor (PF), unbalanced problem, oltage dp, oltage fault, Manuscrpt receed October 10, 2016; resed December 11, 2016; accepted January 10, Date of publcaton January 23, 2017; date of current erson August 2, Ths work was supported n part by the Macau Scence and Technology Deelopment Fund (FDCT 109/2013/A3) and n part by the Research Commttee of the Unersty of Macau (MYRG AMSV, MYRG FST, MRG012/WMC/2015/FST). Recommended for publcaton by Assocate Edtor S. Golestan. (Correspondng author: C.-S. Lam.) L. Wang s wth the Department of Electrcal and Computer Engneerng, Faculty of Scence and Technology, Unersty of Macau, Macao, Chna. C.-S. Lam s wth the State Key Laboratory of Analog and Mxed Sgnal VLSI, Unersty of Macau, Macao, Chna (e-mal: C.S.Lam@eee.org; cslam@umac.mo). M.-C. Wong s wth the Department of Electrcal and Computer Engneerng, Faculty of Scence and Technology and the State Key Laboratory of Analog and Mxed Sgnal VLSI, Unersty of Macau, Macao, Chna. Color ersons of one or more of the fgures n ths paper are aalable onlne at Dgtal Object Identfer /TPEL etc. The contnuous deelopment of the dfferent power qualty compensators has faored the deelopng progress of the smart grd. At the early stage, the passe power flters (PPFs) and statc ar compensators (SVCs) are used to sole the power qualty problems. The PPFs are desgned for the harmonc current and fxed reacte power compensaton. And, the SVCs are desgned for the dynamc reacte current and unbalanced power compensaton 1]. Howeer, both PPFs and SVCs are ery senste to the oltage araton, and suffer from the resonance problem. The acte power flters (APFs) can be used for solng the dfferent power qualty problems. Howeer, ther ntal and operatonal costs are hgh. To reduce the power capacty of the acte nerter part, hybrd APFs (HAPFs) hae been proposed whch combne the PPFs or SVCs n seres/parallel wth the APFs (PPF APFs 2] 6], PPF//APFs 7], 8], SVC//APFs 9] 12], and SVC APFs 13] 17]). Among the dfferent hybrd structures, the thyrstor-controlled LC-couplng HAPF (TCLC-HAPF) 13] 17] has the dstncte characterstcs of a much wder compensaton range than the seres-connected structures of PPF APFs and a lower dc-lnk oltage than the parallel-connected structures of PPF//APFs and SVC//APFs. The aboe-mentoned APFs and HAPFs are normally desgned as the global flters to compensate all the noneffcent power that s reacte, unbalanced, and harmonc power. Howeer, due to the loads contnuous expanson and the smultaneous operaton of dfferent loads, the global flters cannot prode satsfactory compensaton performance f the targeted noneffcent power s beyond the desgned capacty of the power flters. Therefore, t s suggested to selectely compensate the noneffcent power components (reacte, unbalanced, and harmonc power) when they are more than the compensaton range of the power flters 18] 26]. In 18] 20], dfferent harmonc selecte compensaton technques are proposed. Howeer, the reacte and unbalanced power has not been taken nto consderaton among those works. In 21], a selecte compensaton technque s proposed n dstrbuted generators by nsertng negate- and zero-sequence rtual mpedances. Howeer, the harmonc component compensaton s not taken nto account 21]. Steps beyond, the selecte compensaton of the noneffcent power components for the APF has been proposed by usng the current decomposton approach 22], 23], equalent con IEEE. Personal use s permtted, but republcaton/redstrbuton requres IEEE permsson. See standards/publcatons/rghts/ndex.html for more nformaton.

2 9066 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 32, NO. 12, DECEMBER 2017 II. CIRCUIT CONFIGURATION OF TCLC-HAPF Fg. 1 shows the crcut confguraton of the TCLC-HAPF, where x stands for phases a, b, and c n the followng analyss. sx and x are the source and couplng pont oltages, sx, Lx, and cx are the source, load, and compensatng currents, respectely. L s s the transmsson lne mpedance. The TCLC-HAPF conssts of a TCLC part and an acte nerter part. The TCLC part s composed of a couplng nductor L c,a parallel capactor C PF, and a thyrstor-controlled reactor wth L PF. The TCLC part prodes a wde and contnuous fundamental reacte power and unbalanced power compensaton range, whch s controlled by trggerng the frng angles α of the thyrstors 14]. The acte nerter part s a oltage source nerter whch conssts of a dc-lnk capactor C DC and power swtches nsulated gate bpolar transstors (IGBTs). The small capacty of the acte nerter part s used to compensate the harmonc power, aod mstunng of the frng angles, and preent the resonance problem of the TCLC part. III. POWER ANALYSIS OF THE PROPOSED SELECTIVE COMPENSATION Accordng to IEEE Std ], the defnton of threephase total effecte apparent load power S L n terms of the fundamental component and harmonc component can be expressed as S 2 L S 2 L1 S 2 Lh (3 V L1 I L1 ) 2 (3 V L1 I Lh ) 2 Fg. 1. Crcut confguraton of the TCLC-HAPF. ductance approach 24], IEEE Std based approach 25], and lnear matrx nequaltes approach 26]. Howeer, all the aboe selecte compensaton methods 18] 26] are deeloped for the APFs only. The selecte compensaton technques for HAPFs especally for the SVC APFs and the SVC//APFs stll lack study. Moreoer, the compensaton performances under dfferent oltage condtons such as oltage fault and oltage dp are not beng consdered too 18] 26]. Therefore, ths paper ams to deelop a selecte compensaton control method for the TCLC-HAPF to selectely or fully compensate the harmonc dstorton, unbalanced and reacte power components based on ts desgned capacty. And the proposed method can functon well een under oltage dp or oltage fault condton. In the followng, the crcut confguraton of the three-phase three-wre TCLC-HAPF s proded n Secton II. And, the basc power analyss of the proposed selecte compensaton s llustrated n Secton III. Then, the proposed selecte compensaton control method for the TCLC-HAPF s presented n Secton IV. To erfy the proposed selecte control method, smulaton case studes and representate expermental results are presented n Secton V. Fnally, concluson wll be drawn n Secton VI. (3 V Lh I L1 ) 2 (3 V Lh I Lh ) 2] (1) where S L1 and S Lh are the fundamental and harmonc components of the load apparent power. V L1,I L1,V Lh, and I Lh are the fundamental and harmonc components of the load oltage and load current, respectely. The fundamental load apparent power S L1 n (1) can be decomposed nto poste-sequence component and unbalanced (negate) component 26], 27] as S 2 L1 ( S L1) 2 (SU 1 ) 2 (2) where S L1 s the poste-sequence component and S U 1 s the unbalanced component of the apparent power. Furthermore, the poste-sequence component S L1 n (2) can be decomposed nto the acte power and reacte power as ( ) S 2 ( ) L1 P 2 ( L1 Q 2 L1) (3) where P L1 and Q L1 are the fundamental load acte power and reacte power. Based on (1) (3), the load apparent power can be expressed as S 2 L ( P L1 ) 2 ( Q L1) 2 (SU 1 ) 2 (S Lh ) 2. (4) In (4), the noneffcent power terms Q L1,S U 1, and S Lh are supposed to be compensated by the TCLC-HAPF. If those terms (Q L1,S U 1, and S Lh ) are fallng wthn the TCLC-HAPF compensaton range, the TCLC-HAPF can perform full compensaton and only P L1 wll be left n the system source sde. Howeer, f the desgned capacty (S TCLC HAPF ) of the TCLC- HAPF cannot fully compensate all the noneffcent power components, the selecte compensaton s needed to be performed, the expresson of the TCLC-HAPF capacty s gen as ) 2 (ku S U 1 ) 2 (k H S Lh ) 2 STCLC HAPF 2 ( k Q Q L1 (5) where k Q,k U, and k H are the compensaton rato of Q L1,S U 1, and S Lh, respectely. After the TCLC-HAPF compensaton, the apparent power at the system source sde can be expressed as S 2 S ( P L1) 2 (1 kq ) Q L1 (1 k U ) S U 1 ] 2 (1 k H ) S Lh ] 2. (6) ] 2

3 WANG et al.: SELECTIVE COMPENSATION OF DISTORTION, UNBALANCED AND REACTIVE POWER OF A TCLC-HAPF 9067 Lx (t)] xa,b,c T 2 Lx (t)] xa,b,c T 1 D Lx(t) ] xa,b,c Lx (t) ] xa,b,c T 2 Lx (t)] xa,b,c T 1 D Lx(t) ] xa,b,c (8) (9) Fg. 2. HAPF. Power flow of the proposed selecte compensaton of the TCLC- In (5) and (6), k Q,k U, and k H 0 1]. Howeer, f S TCLC HAPF 2 (Q L1 )2 (S U 1 ) 2 (S Lh ) 2, the TCLC-HAPF can perform full compensaton wth k Q k U k H 1and S S P L1. On the other hand, f S2 TCLC HAPF < (Q L1 )2 (S U 1 ) 2 (S Lh ) 2, the selecte compensaton s needed wth the tradeoff consderaton among k Q,k U, and k H. Based on the aboe-mentoned dscussons, the power flow of the proposed selecte compensaton of the TCLC-HAPF s llustrated n Fg. 2. IV. PROPOSED SELECTIVE COMPENSATION CONTROL STRATEGY OF THE TCLC-HAPF The TCLC-HAPF conssts of the TCLC part and acte nerter part. The TCLC part s controlled to prode a wde and contnuous fundamental reacte power (Q L1 ) and unbalanced power (S U 1 ) compensaton range 14]. The low capacty acte nerter part s manly used to compensate the harmonc power (S Lh ) and also help to mproe the performance of the TCLC part by enlargng ts power compensaton range. In the followng, the control strategy of the TCLC-HAPF wll be dscussed n four parts: A. acte nerter part control, B. TCLC part control, C. compensaton prorty selecton among k Q,k U, and k H, and D. the oerall control block. A. Acte Inerter Part Control The compensaton prncple of the acte nerter part s to generate a reference compensatng current cx to the controller, whch ncludes the components of k Q Q L1,k U S U 1, and k H S Lh. By lmtng the compensatng current cx to track ts reference alue cx, the TCLC-HAPF can cancel the harmonc current, balance the system, and compensate the reacte power to certan degree. For the unbalanced three-phase three-wre system, the nstantaneous x and Lx can be decomposed nto the poste- and negate components by usng the notch flter 28] as x (t) ] xa,b,c T 2 x (t)] xa,b,c T 1 x D (t) ] xa,b,c (7) where x (t) and Lx (t) are the three-phase load oltage and load current. x D (t) and D Lx (t) can be obtaned by delayng x(t) and Lx (t) by 90 o. x (t) and Lx (t) are the poste sequence of the load oltage and current of each phase, Lx (t) s the negate sequence of the load current. T 1 and T 2 can be expressed as T (10) T (11) After obtanng x (t), Lx (t), and Lx (t), the three-phase poste sequence and negate sequence acte powers and reacte powers can be calculated as ] ] ] p α β Lα (12) q ] p q β β α α α β Lβ ] ] Lα. (13) In (12) and (13), the poste and negate sequences of the oltage and current n the α β plane are transformed from the a-b-c frames by ] ] a α 1 1/2 1/2 b (14) 0 3/2 3/2 β ] Lα Lβ Lβ Lβ ] 1 1/2 1/2 0 3/2 3/2 ] ] Lα 1 1/2 1/2 0 3/2 3/2 c La Lb Lc La Lb Lc (15) (16) where x (t) and Lx (t) are obtaned from (7) to (9). Referrng to Fg. 2, k Q Q L1,k U S U 1, and k H S Lh can be obtaned as k Q Q L1 k Q ( q) (17) k U S U 1 k U ( p) ] 2 ( q) ] 2 (18) k H S Lh ( k H ( p) ] 2 ( q) ] 2 ( p) ] 2 ( q) ] 2).(19) rms

4 9068 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 32, NO. 12, DECEMBER 2017 The detaled selecton compensaton among k Q,k U, and k H wll be explaned n Secton IV-C. By addng the scale factors (k Q,k U, and k H ) nto the reference current calculaton, the poste and negate compensatng currents n α β plane can be gen as ] cα cβ ] cα cβ 1 ( ) ( ) 2 2 α β α β β α ] 1 ( ) ( ) 2 2 α β β α k H ( p) k Q ( q) k H ( q) ] (20) ] ] α ku ( p) k H ( p) k U ( q) k H ( q). (21) β The fnal reference compensatng currents n the a-b-c plane are transformed from the α β plane by ca cb cc 1 0 ] 2 3 cα cα 1/2 3/2 1/2 cβ 3/2. (22) cβ The acte nerter part s used to mproe the TCLC part compensaton performance by lmtng the compensatng current cx to track wth ts reference alue cx. cx s calculated by the aboe proposed method and t s ald for dfferent oltage and current condtons. B. TCLC Part Control The purpose of the TCLC part s to prode the reference compensatng reacte power q cx for each phase n order to compensate the reacte and unbalanced powers (k Q Q L1 and k U S U 1 ) of the loadng 14]. From the preous calculated reference compensatng current cx whch conssts of the load reacte power, unbalanced and harmonc current components (k Q Q L1,k U S U 1, and k H S Lh ), wth the help of sngle-phase nstantaneous p-q theory 29], x and cx, the nstantaneous reference compensatng reacte power q cx n each phase can be calculated as q ca q cb q cc b D ca a D ca b D cb D b cb (23) c D cc c D cc where x, cx, x D, and cx D are the load oltage, reference compensatng current, and ther alues delay by 90 o. Then, the reference compensatng reacte power Q cx q cx/2 can be obtaned by usng q cx n (23) and three low pass flters (LPFs). Wth the calculated reference q cx, the requred TCLC part mpedance can be calculated as (24) shown at the bottom of ths page, where V x s the rms alue of poste sequence phase oltage whch can be nstantaneous calculated by / / V x 3 a 2 2 b c 2 3. (25) Moreoer, the expresson of the TCLC mpedances (X af,x bf, and X cf ) can also be expressed n terms of the TCLC part passe components and frng angles (α x ) X af (α a ) X bf (α b ) X cf (α c ) πx L PF X C PF X L X C PF 2π 2α a sn(2α a )] πx c L PF πx L PF X C PF X L X C PF 2π 2α b sn(2α b )] πx c L (26) PF πx L PF X C PF X L X C PF 2π 2α c sn(2α c )] πx c L PF where X LPF,X CPF,X Lc are the reactance of L PF,C PF, and L c, respectely. The requred X xf n (24) s obtaned by controllng the frng angle through (26). Howeer, (26) does not hae a closed-form soluton. A look up table has been nstalled to drectly obtan the frng angle α x wth known X xf. By comparng the frng angle α x wth the phase angle ϕ Vxf Vnf of the oltage between TCLC part (V x V nf ), the trgger sgnals to control the thyrstors of the TCLC part can be obtaned. The phase angle of the oltage between the TCLC part (V x V nf ) X af X bf X cf 3 V x 2 (Q cc Q cb Q ca) 1 (Q cb Q ca Q cc) 1 (Q ca Q cb Q cc) 1 (Q cb Q ca Q cc) 1 (Q cc Q cb Q ca) 1 3 V x 2 (Q ca Q cb Q cc) 1 (Q cc Q cb Q ca) 1 (Q ca Q cb Q cc) 1 (Q cb Q ca Q cc) 1 (Q cc Q cb Q ca) 1 3 V x 2 (Q ca Q cb Q cc) 1 (Q cb Q ca Q cc) 1 (Q ca Q cb Q cc) 1 (Q cb Q ca Q cc) 1 (Q cc Q cb Q ca) 1 (24)

5 WANG et al.: SELECTIVE COMPENSATION OF DISTORTION, UNBALANCED AND REACTIVE POWER OF A TCLC-HAPF 9069 TABLE I POWER QUALITYSTANDARDS,EFFECTS ANDPENALTY OFHARMONIC,UNBALANCED ANDREACTIVEPOWER PROBLEMS Harmonc power (k H S Lh ) Unbalanced power (k U S U 1 ) Reacte power (k Q Q L 1 ) Related Standards Internatonal IEEE Std ] IEEE Std ] N/A Chna GB/T ] GB/T ] GB ] Regulaton of power factor adjustng charge 35] Requrements THD < 5% UF < 0.5 2% PF > 0.8 THD < 5 20% UF < 10% Effects 1) Damage to senste loads, 1) Reduce the transmsson effcency, 2) Resonance problem, 2) Increase power loss and temperature of transformer, etc. 3) Increase power loss, etc. 1) Increase ratng of transformer and generator, and ncrease power loss, 2) Cause the oltage drop, etc. Penalty (GB standards) Termnate electrcty supply Termnate electrcty supply Extra charge/cost can be expressed as ϕ Vaf Vnf ϕ Vbf Vnf ϕ Vcf Vnf ( ) θ a tan 1 Xcf X bf 3(Xbf X cf ) ( ) θ b tan 1 Xaf X cf 3(Xaf X cf ) ( ) θ c tan 1 Xbf X af 3(Xbf X af ) tan 1 θ 90 o,90 o ] (27) where θ x s phase angle of the load oltage V x, whch can be obtaned by usng the phase lock loop. By comparng α x wth ϕ Vxf Vnf, the trgger sgnals to control the thyrstors of the TCLC part can be obtaned. C. Compensaton Prorty Selecton Among k Q,k U, and k H In (17) (19), k Q Q L1,k U S U 1, and k H S Lh can be calculated. If the load reacte, unbalanced, and harmonc powers fall wthn the desgned capacty of the TCLC-HAPF, the dfferent power qualty standards as shown n Table I can be satsfed smultaneously. Howeer, f the desgned capacty of the TCLC-HAPF s nsuffcent, the power qualty standards may not be satsfed, and the compensaton prorty selecton among reacte power, unbalanced, and harmonc currents can be done by changng the gans (k Q,k U, and k H ). The compensaton prorty manly depends on 1) power qualty standards 30] 35], 2) ther effects, and 3) ther correspondng penalty. Table I summarzes the power qualty standards, effects and penalty of harmonc, and unbalanced and reacte power problems. Based on Table I, f the harmonc current leel s hgh, the harmonc senste loads can easly get damaged. And the resonance problem can also be caused by the harmonc current. Moreoer, Fg. 3. k H. Flowchart of the compensaton prorty assgnments of k Q,k U,and f the harmonc current leel of the customer loads cannot satsfy the Chnese standard GB/T ], the electrcty company has the rght to termnate the electrcty supply for that customer. In addton, the unbalanced oltage and current can reduce the transmsson effcency and ncrease the power loss and temperature of the transformer, etc. Accordng to the Chnese standards GB/T ] and GB ], the same penalty can be ssued for unbalanced problem. On the other hand, the penalty of the reacte power problem n Chna s the extra charge, whch s not as strct as the harmonc and unbalanced problems. Based on the aboe-mentoned analyss, the compensaton prorty has been assgned to the gan of the harmoncs k H frst,

6 9070 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 32, NO. 12, DECEMBER 2017 Fg. 4. Control block of the proposed selecte compensaton control strategy of TCLC-HAPF. then to the gan of the negate sequence k U, and the fnally the gan of the reacte component k Q n ths paper. Certanly, users can also defne ther own compensaton prorty and compensaton porton of each noneffcent power by themseles. The flowchart dagram to determne the gans (k Q,k U, and k H )of the TCLC-HAPF s gen n Fg. 3. In Fg. 3, f k H,k U, and k Q are equal to 1, the harmonc, unbalanced, and reacte powers are fully compensated. In contrast, f k H,k U, and k Q are equal to 0 (no compensaton), the harmonc, unbalanced, and reacte powers are not compensated. As shown n Fg. 3, f the TCLC-HAPF capacty S TCLC HAPF can compensate the load harmonc, unbalanced, and reacte powers smultaneously, k H 1,k U 1, and k Q 1.IfS TCLC HAPF can fully support the harmonc and unbalanced powers compensaton only, k H 1,k U 1, and k Q < 1 (partal compensaton). And f S TCLC HAPF can fully support the harmonc power compensaton only, k H 1,k U < 1, and k Q 0.Otherwse,fS TCLC HAPF cannot fully support the harmonc power compensaton, k H < 1, k U 0, and k Q 0. Based on Fg. 3, the gans k Q,k U, and k H can be obtaned correspondngly. D. Control Block of the TCLC-HAPF Fg. 4 shows the TCLC-HAPF oerall control block dagram wth the proposed selecte compensaton control strategy. Based on Fg. 4, t can be seen that the proposed selecte

7 WANG et al.: SELECTIVE COMPENSATION OF DISTORTION, UNBALANCED AND REACTIVE POWER OF A TCLC-HAPF 9071 TABLE II SIMULATION AND EXPERIMENTAL SYSTEM PARAMETERS FOR THE TCLC-HAPF POWER QUALITY COMPENSATION Parameters Physcal alues System parameters V x,f 110 V, 50 Hz TCLC-HAPF parameters L c,l PF,C PF 5 mh, 30 mh, 160 µf C DC,V DC 5mF,80V compensaton control strategy conssts of the acte nerter part control and the TCLC part control. The major connecton between these two control loops s the calculated reference compensatng current cx. The reference current cx s calculated wthn the acte nerter part control loop. And the target of the acte nerter part nstantaneously lmts the compensatng current cx to track wth ts reference alue cx, whch ncludes the unwanted components of the loadng fundamental reacte power (k Q Q L1 ), unbalanced power (k U S U 1 ), and harmonc power (k H S Lh ). The trgger sgnals for the acte nerter part are generated by comparng cx and cx through the hysteress current pulse wdth modulaton method. On the other hand, the TCLC part control loop extracts the fundamental reacte power component from the reference current cx. Wth the extracted reference compensatng reacte power of each phase, the requred TCLC part mpedance can be calculated. Then, the correspondng trgger sgnals for the TCLC part n each phase can be generated based on the calculated TCLC part mpedance. Fg. 5. power. Relatonshp between the frng angle and the compensatng reacte V. SIMULATION AND EXPERIMENTAL VERIFICATIONS To erfy the proposed selecte compensaton control method among dstorton, unbalanced, and reacte powers of the TCLC-HAPF, power systems computer aded desgn (PSCAD) smulaton erfcatons are carred out to nestgate the system performance under dfferent oltage and current condtons. Moreoer, a laboratory-scaled hardware prototype s also constructed to obtan the expermental results. The smulaton and expermental system parameters for the TCLC- HAPF power qualty compensaton are shown n Table II. The TCLC part s used to prode the k Q Q L1 and k U S U 1 compensaton. Therefore, the total amount of k Q Q L1 and k U S U 1 proded by the TCLC part s gen by S TCLCf 3 Q cx TCLCf (α x )3 3 V 2 x V 2 x X TCLC (α x ) πx L PF X C (28) PF X C PF 2π 2α x sn(2α x )] πx L X L c PF where V x s the rms alue of the load oltage, X L c, X L PF, and X C PF are the reactance of L c,l PF, and C PF, respectely. When both thyrstors are turned OFF for the whole fundamental perod (frng angle α x 180 ), the TCLC part can prode the maxmum capacte compensatng reacte power Q cx(maxcap). On the other hand, when one of the thyrstors s alternately turned ON for half of the fundamental perod (frng angle α x 90 ), the TCLC part can prode the max- Fg. 6. Smulated dstorton, unbalanced and reacte power compensaton performances by usng the conentonal control strategy 14] of the TCLC- HAPF. mum nducte compensatng reacte power Q cx(maxind) as α x 90. Wth the system parameters as shown n Table II and (28), the fundamental compensatng reacte power range can be plotted n Fg. 5. From Fg. 5, the maxmum k Q Q L1 and k U S U 1 powers proded by the TCLC part are S TCLCf max ar 1.89 kar for nducte loadng compensaton and S TCLCf max ar 1.80 kar for capacte loadng compensaton. Based on the capacty of the hardware components, the acte nerter part s desgned to be S Act 0.6 kva, whch s manly used for the harmonc current compensaton and enlargng the k Q Q L1 and k U S U 1 compensaton range. In the followng smulaton and expermental case studes, the maxmum capacty of the TCLC-HAPF s S TCLC HAPF STCLCf 2 max S2 Act. (29)

8 9072 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 32, NO. 12, DECEMBER 2017 Fg. 7. Smulated dstorton, unbalanced and reacte power compensaton performances by usng the proposed selecte compensaton control strategy of the TCLC-HAPF. TABLE III SIMULATION COMPENSATION RESULTS OF THE PROPOSED SELECTIVE COMPENSATION METHOD FOR THE TCLC-HAPF Phase Q sx (ar) PF THD sx (%) UF (%) Before Compensaton a b c Conentonal Method 14] a b c Proposed Method Harmonc Compensaton (k H 1,k U 0,k Q 0) Proposed Method Harmonc and Unbalanced Compensaton (k H 1,k U 1,k Q 0) Proposed Selecte Compensaton (k H 1,k U 1,k Q 0.85) Proposed Selecte Compensaton durng Voltage Dp a b c a b c a b c a b c Based on (29) and the aboe-mentoned analyss, the maxmum capacty of the TCLC-HAPF s desgned to be S TCLC HAPF 1.98 kva for nducte loadng compensaton and S TCLC HAPF 1.90 kva for capacte loadng compensaton. In ths paper, wth reference to the IEEE standard ], the oltage THD x s requred to be lower than 8% for the laboratory-scaled low-oltage applcaton n ths paper (<1 kv). For the IEEE standard ], the acceptable total demand dstorton (TDD) 12% wth I SC /I L n 50 < 100 scale (a small capacty of solated transformer used n the

9 WANG et al.: SELECTIVE COMPENSATION OF DISTORTION, UNBALANCED AND REACTIVE POWER OF A TCLC-HAPF 9073 Fg. 8. Waeforms of x, ts poste sequence x, and source current by usng the proposed selecte compensaton control strategy of the TCLC-HAPF durng oltage dp. laboratory and a small ratng 110 V-5 kva expermental prototype). The nomnal rated current s assumed to be equal to the fundamental load current at the worst-case analyss, whch results n THD TDD 12%. Therefore, ths paper ealuates the TCLC-HAPF current harmoncs compensatng performance by settng an acceptable THD sx 12%. A. PSCAD Smulatons The purpose of the smulaton studes s to erfy the conentonal method 14] cannot prode satsfactory compensaton results f the load generated noneffecte powers are beyond the lmted capacty of the TCLC-HAPF (n Fg. 6). Wth the same load, the proposed selecte compensaton control method for the TCLC-HAPF can selectely compensate dstorton, unbalanced and reacte power components wth the satsfactory results (n Fg. 7). Also, the proposed selecte compensaton method s erfed under the oltage dp condton (n Fg. 8). The detaled compensaton results are summarzed n Table III. In Fg. 6 and Table III, the TCLC-HAPF wth the conentonal method 14] can compensate the reacte power to 154, 64, and 44 ar from the orgnal 756, 809, and 346 ar, and the source PF has been mproed to 0.96 from the orgnal 0.57 for the worst phase. Howeer, the compensated THD sx are 21.1%, 27.2%, and 13.3%, whch cannot satsfy the IEEE standard ]. Ths s due to the load noneffecte powers are beyond the lmted capacty of the TCLC-HAPF. On the other hand, from Fg. 7 and Table III, t can be seen that the proposed selecte compensaton method for the TCLC-HAPF can selectely compensate dstorton, unbalanced and reacte power components. For harmonc compensaton (k H 1,k U 0,k Q 0), the source acte power and reacte power before and after the TCLC-HAPF compensaton are bascally keepng the same leel. And the current unbalanced factor (UF ) s stll larger than >40% after compensaton. Howeer, the source current THD sx has been compensated to 2.8% from the orgnal 24.5% (worse phase among phases a, b, and c). For both harmonc and unbalanced compensaton (k H 1,k U 1,k Q 0), UF Fg. 9. Expermental setup of the TCLC-HAPF hardware prototype and ts testng enronment. Fg. 10. Expermental waeforms of x and sx before and after the TCLC- HAPF compensaton wth the proposed selecte compensaton method (k H 1, k U 1,k Q 0.85). s reduced to 1.2% from the orgnal 41.6%. And the source reacte power (Q sx ) and acte power (P sx ) of each phase become the same. Meanwhle, THD sx has been compensated to be lower than 5%. For the proposed selecte compensate method (k H 1,k U 1,k Q 0.85), the source PF and UF are mproed to 0.98 and 1.1, respectely. And, THD sx s compensated to 5.9% (worst phase). In addton, there s stll remanng Q sx alue whch s due to the gan k Q 0.85 nstead of k Q 1. From Fg. 8 and Table III, t can be seen that the poste sequence of the load oltage x can be nstantaneously extracted by usng (7). The source PF and THD sx can be compensated to 0.99 and 2.7% (worse phase) een durng the oltage dp condton.

10 9074 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 32, NO. 12, DECEMBER 2017 Fg. 11. Expermental results of dynamc performance before and after the TCLC-HAPF compensaton wth the proposed selecte compensaton method (k H 1,k U 1,k Q 0.85): (a)p sx and (b) Q sx. Fg. 12. Expermental phasor dagrams of x and sx : (a) before compensaton (b) after the TCLC-HAPF compensaton wth the proposed selecte compensaton method (k H 1,k U 1,k Q 0.85). Fg. 13. Expermental current harmonc spectrums of sx : (a) before compensaton (b) after the TCLC-HAPF compensaton wth the proposed selecte compensaton method (k H 1,k U 1,k Q 0.85). VI. EXPERIMENTAL RESULTS An 110 V-5 kva expermental prototype of the three-phase three-wre TCLC-HAPF s constructed n the laboratory as shown n Fg. 9. The control system has the samplng frequency of 25 khz. The swtchng deces for the acte nerter part are Mtsubsh IGBTs PM300DSA060. And, the swtchng deces for the TCLC part are thyrstors SanRex PK110FG160. Moreoer, the expermental parameters of the TCLC-HAPF and the test loads are approxmately the same as the smulaton studes

11 WANG et al.: SELECTIVE COMPENSATION OF DISTORTION, UNBALANCED AND REACTIVE POWER OF A TCLC-HAPF 9075 TABLE IV EXPERIMENTAL COMPENSATION RESULTS OF THE PROPOSED SELECTIVE COMPENSATION METHOD FOR THE TCLC-HAPF Phase Q sx (ar) PF THD x (%) THD sx (%) UF (%) Before Compensaton (see Fg. 10) a b c Proposed Selecte Compensaton (k H 1,k U 1,k Q 0.85) a b c Before Compensaton (see Fg. 14) a b c Proposed Selecte Compensaton (k H 1,k U 1,k Q 1) a b c Fg. 14. Expermental waeforms of sx, cx, CPFx, LPFx,andV DC by usng the proposed selecte compensaton method before and after TCLC-HAPF compensaton. n Table II. In addton, durng the TCLC-HAPF expermental testng n the laboratory, a small capacty of solated step-down transformer s used to reduce grd oltage from 230 to 110 V. Fg. 10 shows the expermental waeforms of the load oltage and source current before and after the TCLC-HAPF compensaton wth the proposed selecte compensaton control method (k H 1,k U 1,k Q 0.85). Fgs show the expermental results of the source power (P sx and Q sx ), phasor dagrams, and source current harmonc spectrum, respectely. Table IV also summarzes the correspondng expermental results. From Fg. 10, t can be seen that after the TCLC-HAPF compensaton wth the proposed selecte compensaton method, sx and x are bascally n phase wth each other. The source PF can be compensated to 0.98 from the orgnal 0.80, 0.86, and From Fg. 11, P sx and Q sx n each phase are compensated to about the same (790 W and 160 ar) from the orgnal 900, 530, and 780 W for P sx and 730, 800, and 460 ar for Q sx. And, the remanng Q sx s due to k Q 0.85 settng. Fg. 12 shows that the magntude of sx and phase angle between x and sx of each phase become approxmately the same. From Fg. 13, t can be seen that THD sx s mproed from 20.1% to 10.5% for the worst phase. From Table IV, UF s reduced to 1.3% from the orgnal 32.2%. Fg. 14 shows the more detaled expermental waeforms of the source currents sx, compensatng currents cx, capactor (C PF ) currents CPFx, nductor (L PF ) currents LPFx, and dclnk oltage V dc by usng the proposed selecte compensaton method before and after TCLC-HAPF compensaton. Table IV summarzes the correspondng expermental results. Fgs. 15 and 16 prode the dynamc compensaton waeforms by applyng the proposed selecte compensaton method for the TCLC-HAPF durng oltage dp and oltage fault condtons. From Fgs. 15 and 16, they clearly llustrate that the source current can keep snusodal and n phase wth the load oltage een durng the oltage dp and oltage fault condtons. Comparng the smulaton results as n Table III wth the expermental results as n Table IV, there are dfferences between

12 9076 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 32, NO. 12, DECEMBER 2017 REFERENCES Fg. 15. Dynamc compensaton waeforms of x and sx by usng the TCLC- HAPF compensaton wth the proposed selecte compensaton method durng oltage dp. Fg. 16. Dynamc compensaton waeforms of x and sx by usng the TCLC- HAPF compensaton wth the proposed selecte compensaton method durng oltage fault. the smulaton and expermental results, whch are actually due to the dfference of the component parameters, the resoluton of the transducers, the dgtal computaton error, and the nose n the experments. In addton, the small capacty of solated step-down transformer used n the laboratory also causes larger oltage dstorton than the smulaton case, whch deterorates the compensaton results. Therefore, those factors wll affect the TCLC-HAPF compensaton performance durng experments. VII. 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Sngh, Generalzed sngle-phase p-q theory for acte power flterng: smulaton and DSP-based expermental nestgaton, IET Power Electron., ol. 2, pp , Jan ] IEEE Recommended Practces and Requrements for Harmonc Control n Electrcal Power Systems, IEEE Standard , Jun ] IEEE Recommended Practce for Montorng Electrc Power Qualty, IEEE Std , Jun ] Standardzaton Admnstraton of the People s Republc of Chna, GB/T Power Qualty Harmoncs n Publc Supply Network. Bejng, Chna: Electr. Power Press, ] Standardzaton Admnstraton of the People s Republc of Chna, GB/T Power Qualty Three-Phase Voltage Unbalance. Bejng, Chna: Electr. Power Press, ] Standardzaton Admnstraton of the People s Republc of Chna, GB Rotatng Electrcal Machnes Ratng and Performance. Bejng, Chna: Electr. Power Press, ] Mnstry of Water Resources and Electrc Power of Chna, Regulaton of power factor adjustment charge, Bejng, Chna, Le Wang receed the B.Sc. degree n electrcal and electroncs engneerng from the Unersty of Macau (UM), Macao, Chna, n 2011, the M.Sc. degree n electroncs engneerng from the Hong Kong Unersty of Scence and Technology, Hong Kong, Chna, n 2012, and the Ph.D. degree n electrcal and computer engneerng from UM, Macao, Chna, n Currently, he s a Postdoctoral Fellow n the Power Electroncs Laboratory, UM. Hs research nterests nclude power electroncs, power qualty and dstrbuton flexble ac transmsson system, power qualty compensaton, and renewable energy. Dr. Wang receed the champon award n the Schneder Electrc Energy Effcency Cup, Hong Kong, Ch-Seng Lam (S 04 M 12 SM 16) receed the B.Sc., M.Sc., and Ph.D. degrees n electrcal and electroncs engneerng from the Unersty of Macau (UM), Macao, Chna, n 2003, 2006, and 2012 respectely. From 2006 to 2009, he was an E&M Engneer n UM. In 2009, he smultaneously worked as a Laboratory Techncan and started to work toward the Ph.D. degree, and completed the Ph.D. degree wthn 3 years. In 2013, he was a Postdoctoral Fellow n the Hong Kong Polytechnc Unersty, Hong Kong, Chna. He s currently an Assstant Professor n the State Key Laboratory of Analog and Mxed-Sgnal VLSI, UM. He has co-authored 2 books: Desgn and Control of Hybrd Acte Power Flters (Sprnger, 2014) and Parallel Power Electroncs Flters n Three-Phase Four-Wre Systems - Prncple, Control and Desgn (Sprnger, 2016), 1 US patent, 2 Chnese patents, and more than 50 techncal journals and conference papers. Hs research nterests nclude ntegrated power electroncs controllers, power management ntegrated crcuts, power qualty compensators, smart grd technology, renewable energy, etc. Dr. Lam receed the Macao Scence and Technology Inenton Award (Thrd-Class) and the R&D Award for Postgraduates (Ph.D.) n 2014 and 2012, respectely, the Macao Goernment Ph.D. Research Scholarshp n , the Macao Foundaton Postgraduate Research Scholarshp n , and the 3rd RIUPEEEC Mert Paper Award n In 2007, 2008, and 2015, he was the GOLD Offcer, a Student Branch Offcer, and the Secretary of IEEE Macau Secton. He s currently the Vce-Char of IEEE Macau Secton and the Secretary of IEEE Macau PES/PELS Jont Chapter. He was the Local Arrangement Char of IEEE TENCON 2015 and ASP-DAC Man-Chung Wong (SM 06) receed the B.Sc. and M.Sc. degrees n electrcal and electroncs engneerng from the Unersty of Macau (UM), Macao, Chna, n 1993 and 1997, respectely, and the Ph.D. degree n electrcal engneerng from Tsnghua Unersty, Bejng, Chna, n He was a Vstng Fellow n Cambrdge Unersty, Cambrdge, U.K., n He s currently an Assocate Professor n the Department of Electrcal and Computer Engneerng, UM. He has co-authored 2 Sprnger books, more than 100 journal and conference papers, and 6 patents (Chna and USA). Recently, an ndustral power flter platform was deeloped and nstalled n a practcal power system based on hs research results. Hs research nterests nclude power electroncs conerters, pulse wth modulaton, acte power flters, hybrd acte power flters, and hybrd power qualty compensator for hgh-speed ralway power supply system. Dr. Wong receed the Macao Young Scentfc Award from the Macau Internatonal Research Insttute n 2000, the Young Scholar Award of UM n 2001, Second Prze for the Tsnghua Unersty Excellent Ph.D. Thess Award n 2003, and the Macao Scence and Technology Inenton Award (Thrd- Class) n 2012 and He supersed seeral students to recee mert paper awards n conferences and champons n student project compettons. He was seeral conference commttee members and the General Char of IEEE TEN- CON 2015 n Macau. In , he was the IEEE Macau Secton Char. Currently, he s the North Representate of IEEE Regon 10 Power and Energy Socety and the IEEE Macau PES/PELS Jont Chapter Char.