IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 30, NO. 5, MAY SeHwan Kim, Student Member, IEEE, andjul-kiseok, Senior Member, IEEE

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1 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 30, NO. 5, MAY Induction Moto Contol With a Small DC-Link Capacito Invete Fed by Thee-Phase Diode Font-end Rectifies SeHwan Kim, Student Membe, IEEE, andjul-kiseok, Senio Membe, IEEE Abstact This pape pesents a small film capacito invetebased induction moto contol appoach to enhance with eliability and powe density of thee-phase vaiable speed dive applications. A obust hybid moto contolle is developed to pevent pefomance degadation caused by the electolytic capacito-less invete fed by font-end diode ectifies. The stuctue of the contolle combines a model-based contolle (MBC) and a hexagon voltage manipulating contolle (HVC). The MBC detemines the command output voltage with the intesection of the toque and oto flux linkage command. In the HVC mode, the command voltage vecto is detemined simply by the toque command and the hexagon-shaped invete voltage bounday. Successful application of the contol appoach is cooboated by a gaphical and analytical means that natually lead to a single voltage selection ule. This pape also examines the opeation sensitivity unde moto paamete difts to detemine how to decouple its effect using a voltage distubance state-filte design. Index Tems Font-end diode ectifies, hexagon voltage manipulating contolle (HVC), model-based contolle (MBC), small film capacito invete, thee-phase vaiable speed dive. I. INTRODUCTION IN low-cost thee-phase vaiable speed dive applications, such as heating-ventilating-ai-conditioning (HVAC) systems, diode ectifies ae commonly used as the font-end cicuit fo nonegeneative ac dc convesion because of thei lowe cost and highe eliability [1]. In these types of low-cost ac dive systems, aluminum electolytic capacitos ae commonly used to balance the diffeence between the instantaneous input and output powe as well as suppess the voltage spikes caused by leakage inductance and switching opeations, as shown in Fig. 1 [2], [3]. On the othe hand, the dc-bus capacito is not only bulky and heavy but it is also one of the least eliable components on vaious powe electonic topologies. Futhemoe, the paasitic lead inductance can cause voltage spikes, which ae a majo facto in the failue of powe electonic devices. A failue suvey of switch mode powe supplies epoted that electolytic capacitos ae esponsible fo moe than half of the beakdowns of an invete [4]. Theefoe, thee is inceasing Manuscipt eceived Mach 31, 2014; evised June 18, 2014; accepted July 28, Date of publication July 31, 2014; date of cuent vesion Decembe 23, This wok was suppoted by the National Reseach Foundation of Koea gant funded by the Koea govenment (MSIP) ( ). Recommended fo publication by Associate Edito D. O. Neacsu. The authos ae with the School of Electical Engineeing, Yeungnam Univesity, Gyeongbuk , Koea ( ksh8508@ynu.ac.k; doljk@ ynu.ac.k). Colo vesions of one o moe of the figues in this pape ae available online at Digital Object Identifie /TPEL Fig. 1. Thee-phase diode ectifie and PWM invete fo IM dive. inteest in the monitoing lifetime of electolytic capacitos fo eliable and safe opeation [4] [7]. On the othe hand, offline monitoing techniques [4], [5] equie additional measuements as well as apioidata fo the efeence model, which makes monitoing pocess complicated and difficult. A peviously epoted online method [6] fo estimating the capacitance cannot be applied to invetes fed by diode ectifies. In this egad, a ange of egeneative convetes and contol methods have been poposed in ode to minimize o educe these passive components on a dc bus. The focus of most studies has been on how to educe the dc-bus capacito of thee-phase pulse width modulation (PWM) ectifies and single-phase diode ectifies [7] [11]. All pevious studies wee equipped with a conventional closed-loop cuent contolle to egulate the ai-gap toque and flux linkage of ac motos. Howeve, instantaneous cuent contol in a small dc-bus capacito invete with the diode ectifie font-end is not staightfowad because the dc-link voltage and output powe to the moto decease peiodically due to the absence of enegy stoage. This apid dc voltage eduction dives the moto to be opeated fequently in the field-weakening egion below a based speed. Theefoe, the cuent contol stategy becomes moe complicated unde voltage-limited conditions because multipleobjective subcontolles, such as field-weakening, antiwindup contol, and ovemodulation scheme, should be designed caefully based on the complex tadeoff between the subcontol actions and cuent contol dynamics [12], [13]. Futhemoe, ealization of the maximum voltage utilization fails because a cicula voltage limit is consideed an opeation bounday instead of a hexagonal limit [8]. This pape pesents a position sensoless vecto-contolled induction moto (IM) dive system integated into HVAC applications. The moto powe is supplied by a small dc-link film capacito invete fed by a thee-phase diode font-end ectifie. A PI moto-cuent-egulato-fee contol stategy is poposed to meet the afoementioned challenges by combining IEEE. Pesonal use is pemitted, but epublication/edistibution equies IEEE pemission. See standads/publications/ights/index.html fo moe infomation.

2 2714 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 30, NO. 5, MAY 2015 At the steady state, the moto ai-gap toque and the oto flux linkage of the oto flux-oiented-contolled (RFO) IM can be expessed as Fig. 2. Poposed IM contol stategy fo small capacito invetes. a model-based contolle (MBC) and a hexagon voltage manipulating contolle (HVC). The MBC finds the command output voltage with the intesection of the toque and oto flux linkage command. In the HVC mode, the command voltage vecto can be detemined simply by the toque command and the hexagon voltage bounday. The MBC is pefomed unde nonlimited conditions and moto contol is handed automatically ove to the poposed HVC in the voltage shotage egion. These voltage selection ules allow fo the choice of an objective voltage vecto in the absence of PI contol gains, subcontolles, and obseves fo closed-loop contol. The contol stategy was implemented on a 1.5-kW IM dive that was equipped with a 20-μF film capacito to confim its feasibility. II. MOTOR CONTROLLER DESIGN WITH SMALL DC-LINK CAPACITOR INVERTER A. Design and Analysis of a Moto Contolle Fig. 2 shows a block diagam of the poposed contol stategy fo an IM using a complex vecto epesentation. Hee, v abcs and ae the stato voltage commands in the abc-efeence fame and the synchonous efeence fame, espectively, and V dc denotes the measued dc-link voltage. When stating (Mode I), the scala Volts/Hz o V/f open-loop contol is intoduced to avoid the lack of obsevability of the moto back-emf voltage at low speeds. This featue pemits the dive system to satisfy the stating speed equiement of the back-emf tacking-based position sensoless opeation, of which the theshold begins in the vicinity of 10% of the ated speed. The contol authoity is then handed ove to model-based contol (MBC, Mode II) o hexagon voltage manipulating contol (HVC, Mode III), depending on the amount of available dc-link voltage. The moto stato voltage and flux linkage equation can be expessed using a complex vecto epesentation: vdqs e vdqs e = R s i e di e dqs dqs σl s Jω e σl s i e dqs dt L m dλ e dq J L m ω e λ e dq (1) L dt L whee i e dqs is the d q axis stato cuent vecto in the synchonous efeence fame, J =, R [ ] s is the stato esistance, ω e is the synchonous angula velocity, σl s is the stato tansient leakage inductance, and λ e dq epesents the d q axis stato and oto flux linkage vecto. L m and L epesent the magnetizing and oto inductance, espectively. T e = 3 P L m λ e 2 2 L di e qs λ e d = L m i e ds whee P is the numbe of poles. The stato voltage equation can be also simplified as vds e = R s i e ds ω e σl s i e qs vqs e = R s i e qs ω e L s i e ds. (2a) (2b) (3a) (3b) By combining (2a), (2b), (3a), and (3b), the toque and oto flux linkage command can be obtained as a function of the oto speed: Te = 3 ( P L m v λ e e ds R si e ) ds d (4) 2 2 L ω e σl s λ e vqs e R s i e qs d = L m. (5) ω e L s Fig. 3(a) pesents a gaphical epesentation of the toque and oto flux between (4) and (5) in the synchonously otating dq volt plane. The desied toque of (4) foms a vetical line in the complex dq plane and is shown in blue. The oto flux linkage line is shown in ed, which is paallel to the d-axis. When the voltage solutions emain within V dc / 3 (cicula voltage bounday), which is called the MBC opeation, they become feasible voltage vectos at the next sampling time. The stato voltage command vdqs e MBC can be obtained simply as ( ) vds e Te MBC = ω e σl s R s i e ds (6a) 3 P L m 2 2 L λ e d vqs e λ e d MBC = ω e L s R s i e L qs. (6b) m Fig. 3(b) shows a zoomed view of the stato voltage solutions between (6a) and (6b) in the dq volt plane. At low speeds, the d-axis voltage solution vds e MBC is positive because the stato esistance dop is dominant. As ω e inceases, vds e MBC shifts to the left half-plane. On the othe hand, the q-axis voltage solution vqs e MBC of (6b) shifts downwad along the q-axis diection as the flux deceases at a cetain oto speed o the oto speed deceases fo a given flux. The moto speed elevation o the dc-link voltage eduction dives vdqs e MBC to appoach V dc/ 3. Once vdqs e MBC neas the cicula voltage bounday, the contol switches to the poposed HVC that geneates the desied ai-gap toque as closely as possible, while simultaneously egulating the flux linkage magnitude unde a field-weakening opeation. In pactice, the MBC dominates the contol action at low speeds, wheeas the HVC opeation dominates at high speeds. In this sense, it is easonable to assume that the stato esistance voltage dop can be negligible in the HVC mode, which does not jeopadize the moto contol pefomance. Theefoe, in the

3 KIM AND SEOK: INDUCTION MOTOR CONTROL WITH A SMALL DC-LINK CAPACITOR INVERTER FED BY THREE-PHASE DIODE 2715 Fig. 3. Voltage command selection in the MBC mode. The coesponding hexagon bounday (shown in blue) and the toque command cuve of (9) can povide two possible stato voltage solutions that poduce the desied output toque, as shown in Fig. 5. Hee, the command voltage vecto vdqs e is chosen as a feasible solution because it is the only voltage to satisfy the desied stato flux magnitude. A selected voltage vecto at the intesection can be uniquely expessed as vds e HVC = B n Bn 2 4M n γ 2M n vqs e HVC = M n vds e HVC B n (10a) (10b) Fig. 4. Voltage command selection in the HVC mode. HVC mode, the stato voltage equation can be simplified as vds e = ω e σl s i e qs vqs e = ω e L s i e ds. (7) Combining (2a) and (7) povides a command toque equation with espect to the d q command voltage as follows: Te = 3 P L 2 ( )( m v e ds v e ) qs (8) 2 2 L ω e σl s ω e L s whee the toque command tajectoy foms a hypebolic cuve in the dq volt plane. Fig. 4 gives a schematic epesentation of the stato voltage solutions between the toque cuves and otating hexagon, which shinks with the invete dc-bus voltage. In the poposed HVC method, the intesection (maked as a black dot) of the toque line and the shinking hexagon becomes the command voltage vecto at the next sampling instant. The bounday of each otating hexagon secto can be modeled as a staight line in the dq volt plane as follows [12]: v e qs (k) =M n v e ds (k)b n (9) whee M n and B n ae constant values given by the bounday of each hexagon secto. whee γ = T e 3 P L 2 m L ω e 2 L s σls. Using this algoithm, the moto toque is egulated aound a desied toque line in the pesence of apid voltage vaiations. How the HVC pefoms the field-weakening opeation duing the invete voltage eduction peiod should be investigated. As shown in Fig. 4, the possible voltage solutions fo a given command toque tajectoy ae detemined on the otating hexagon with the dc-link voltage fluctuation. The voltage solution natually moves to a downwad q-axis diection (fom vdqs1 e to vdqs4 e ) as the hexagon shinks. The voltage vecto ve dqs4 has a lowe q-axis voltage component than that of vdqs1 e. It can be noticed fom (7) that vdqs4 e leads to the deceased d-axis cuent which causes a lowe flux linkage at a given oto speed. This suggests that an automatic field-weakening opeation and maximum voltage utilization can be achieved simultaneously without equiing an exta contol function. In addition, a apid mode tansition between MBC and HVC is possible without contol manipulations because no integatos ae involved fo moto ai-gap toque egulations. This featue is beneficial to small capacito invete applications that ae subject to an unexpected gid voltage dip, fequent dc voltage fluctuation, and vaiable dc voltage ipples esulted fom the gid-side impedance. B. Compensation of Effects of Paamete Difts In pactice, the oto flux level is not maintained popely in the MBC and HVC modes because the machine paametes of

4 2716 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 30, NO. 5, MAY 2015 Fig. 5. Feasible voltage vecto selection stategy. Fig. 6. Stato cuent deviation by moto paamete difts at 0.6 p.u. of the ated speed. Fig. 7. State-filte design fo decoupling the paamete dependence. TABLE I RATINGS AND KNOWN PARAMETERS OF THE IM UNDER TEST Ratings and paametes Value Unit Rated powe output 1.5 kw Rated voltage 220 V Rated speed 1500 /min R s /R at 25 C 2.47 / 0.7 Ω L m /σl s 134 /12.6 mh (6a), (6b), (10a), and (10b) dift due to magnetic satuation and initial eos. The voltage eos of (6a), (6b), (10a), and (10b) also esult in an incoect actual stato cuent, which might esult in high coppe o ion losses fo a given toque condition. In HVAC applications, the main opeation is pefomed in the speed ange fom 50% up to 90% of the ated moto speed. Fig. 6 shows the stato cuent deviation tajectoies of a tested IM, as shown in Table I, at 60% of the ated speed and 67% of the ated toque. The stato esistance eo has little impact on the cuent deviation at this speed. In pactical applications, an online compensation fo model eos is believed to be moe effective in achieving accuate moto contol. This pape poposes a voltage distubance statefilte [14] to decouple the paamete dependence of MBC and HVC modes. Fig. 7 pesents a block diagam of the distubance voltage estimation stategy using a complex vecto epesentation in the synchonous efeence fame. A familia PI-type Luenbege-style model-cuent obseve contolle was adopted to estimate the voltage distubance esulting fom paamete vaiations, whee the estimated output cuent î e dqs follows the stato cuent i e dqs. Because the command voltage vecto vdqs e is fed-fowad to the obseve, the voltage distubance eo Δˆv dqs e D can be estimated at the output of the obseve contolle. Hee, the stato cuent has a cetain amount of hamonics with six times the synchonous and gid fequency due to the manipulated voltage on the hexagon bounday and fluctuating dc-bus voltage. A esonant-type filte is intoduced to eject these ipple components of i e dqs, which achieves enomously high gains at esonant fequencies of concen. This stuctue can estimate and compensate fo voltage deviation esulting fom distubances and uncetainties [14].

5 KIM AND SEOK: INDUCTION MOTOR CONTROL WITH A SMALL DC-LINK CAPACITOR INVERTER FED BY THREE-PHASE DIODE 2717 The estimated distubance voltage and stato cuent in the s-domain ae given by as (11) and (12) shown at the bottom of the page, whee K p and K i epesent the PI gains. ω h 6fg, ω f 6fe, ω cut, and K epesent the gid fequency, concened synchonous fequency, 3-dB cut-off fequency, and esonant filte gain, espectively. In this pape, supescipt ˆ epesents the coesponding vaiables ae estimated. Substituting (12) into (11) yields TF ct (s)δˆv e dqs D =(ˆR s sσ ˆL s Jω e σ ˆL s )i e dqs s ˆL m ˆL ˆλ e dq whee TF ct (s) =1 J ˆL m ˆL ω eˆλ e dq v e dqs (13a) ( K p sk i s ˆR s sσ ˆL s Jω e σ ˆL s K ω cut s s 2 ω cut sω 2 h 6 fg K ω cut s s 2 ω cut sω 2 h 6 fe ). (13b) At the steady-state (s 0), the estimated d q-axis distubance voltage can be obtained by substituting (1) into (13a) ( ) ˆLm Δˆv ds e D = ΔR s i e ds ω e ΔσL s i e qs ω e ˆλ ˆL e q L m λ e q L ( ) ˆLm Δˆv qs e D = ΔR s i e qs ω e ΔσL s i e ds ω e ˆλ ˆL e d L m λ e d L whee ΔR s = ˆR s R s and ΔσL s = σ ˆL s σl s. Fo the RFO IM, (14) can be ewitten as (14) Fig. 8. Inductance compensation esults. (a) 15% ΔL s.(b)15% ΔL s. Δˆv e ds D = ΔR s i e ds ω e ΔσL s i e qs Δˆv e qs D = ΔR s i e qs ω e ΔL s i e ds (15) whee ΔL s = ˆL s L s. Fom (15), the inductance values used in (6a), (6b), (10a), and (10b) can be identified by neglecting the stato esistance voltage dop ΔσL s = Δˆv e ds D ω e i e qs Δˆv ΔL s qs e D = ω e i e. (16) ds Fig. 8 shows the simulated compensation esults of the paamete vaiation effect at 60% of the base speed and 67% of the load toque. In Fig. 8(a), L s was set to be 15% of its nominal value and (16) was deliveed at t = 1 s. Afte 1 s, the deviation of the stato cuent and oto flux linkage was educed to almost zeo. The same test was epeated at 15% of ΔL s,asshownin Fig. 8(b). These test esults indicate that the stato cuent and oto flux linkage wee contolled pecisely against paamete mismatch because the poposed compensation method povides a concuent estimation of the magnetic satuation and initial eo. Theefoe, this design can be effective in accuately estimating and compensating fo the MBC and HVC modes while educing the computational complexity. Fig. 9 pesents an oveall block diagam of the contol system augmented to include the poposed algoithm to compensate fo the paamete vaiation effects in eal time. A simple back-emf tacking-based position sensoless method was employed fo a moto position estimation [15]. ( Δˆv dqs e D = ˆR s î e dqs sσ ˆL s î e dqs Jω e σ ˆL s î e dqs s ˆL m ˆλ ˆL e dq J ˆL ) m ω eˆλ ˆL e dq v e dqs (11) î e dqs = i e dqs ( K p sk i s 1 K ω cut s s 2 ω cut sω 2 h 6 fg K ω cut s s 2 ω cut sω 2 h 6 fe )Δˆv e dqs D (12)

6 2718 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 30, NO. 5, MAY 2015 Fig. 9. Oveall contol block diagam. III. SIMULATION AND EXPERIMENTAL RESULTS Validation of the theoetical developments pesented ealie was pefomed on a 1.5-kW IM dive with a 20-μF film capacito fed by a thee-phase diode ectifie though a simulation and eal test. A 4096 pulses-pe-evolution encode was mounted to one end of the IM to monito the oto speed. The othe end of the shaft was coupled to a 1.5-kW dc geneato to contol the extenal load. The algoithm was implemented in the invete with a constant PWM switching fequency of 5 khz. The nominal input line-to-line voltage was set to 210 V and the advent of flux weakening occus at appoximately 1500 /min. The online distubance state-filte was pefomed evey 100 μs and the bandwidth of the state-filte and PI speed contolle was set to 600 ad/s. The gain (K ) of the esonant contolle and 3-dB cut-off fequency (ω cut ) ae fixed to 3 and 50 Hz, espectively. In all expeimental tests, the unning conditions wee identical to those in the simulation. Fig. 10 pesents a simulated esult in the motoing opeation, whee the dc-link voltage, flag signal, ai-gap toque, and oto flux linkage ae illustated fom top to bottom. The mode_hvc is 1 if the HVC mode activates and 0 othewise (MBC mode). In this test, the IM dive was opeated with 90% of the base speed while the ated load toque was applied. The dc-link voltage fluctuates with six times the input gid voltage fequency. The wavefom of the flag signal and ai-gap toque show a smooth and apid tansition occus between the MBC and HVC opeation. This is because the poposed MBC and HVC wee designed without integatos fo cuent contol and with the same voltage selection ule. This stuctue leads to a single contol law in the entie opeating egion, which avoids seconday upsets by the contol mode switching and complexity of having an additional contol function o gain to be adjusted. Fig. 11 shows the expeimental esults in the same test scenaio, whee the measued dc-link voltage, flag signal, estimated Fig. 10. Simulated esults of the poposed contol method.

7 KIM AND SEOK: INDUCTION MOTOR CONTROL WITH A SMALL DC-LINK CAPACITOR INVERTER FED BY THREE-PHASE DIODE 2719 Fig. 12. HVMC opeation duing the gid voltage tansients. Fig. 11. Test esults of the poposed contol method. ai-gap toque, and estimated oto flux linkage ae, espectively, illustated fom top to bottom. The desied toque was well egulated with the aveage value because the poposed state-filte povides a concuent compensation. Although a sufficient contol voltage magin is essential to the cuent egulato-based stategy fo feedback coections, the poposed method is immune to a lack of available voltage because it manipulates the output voltage instead of contolling the moto cuent. A close match was obseved between simulation and test esult. The x y locus shows that the esulting contolle can achieve the maximum voltage utilization at the peiodic voltage dopping egion. Paticula attention should be paid to the field-weakening opeation of the poposed HVC mode because a sudden gid voltage dop foces the dive to ente the field-weakening egion. Fig. 12 shows the field-weakening opeation esults, whee the thee-phase souce voltage suddenly dops by 15% of its nominal value at 90% of the ated speed. The line-to-line gid voltage, measued dc-bus voltage, the estimated oto velocity, and oto flux linkage ae depicted fom top to bottom. In the wavefom of the dc-bus voltage and the oto flux, it can be noticed that an automatic and apid tansition occus between nonlimited opeation and field-weakening Fig. 13. Load test esult of the poposed method. mode without any subcontol functions used in the cuent contol stategy. This featue is beneficial fo achieving the ability to maintain the invete opeation duing the gid voltage tansients. Fig. 13 shows the test esult at the base speed, wheeas the extenal load was inceased stepwise fom 0% to the ated value. This load toque test can be thought to be as being moe sevee than would be encounteed in pactical situations. The estimated/contolled oto speed, actual oto speed fo monitoing, measued amatue cuent of the dc geneato, and q-axis stato cuent of the tested IM ae illustated fom top to bottom. Distotions wee aely found duing the velocity tansition of each contol mode. The dive does not lose its contol capability in the pesence of the full load toque, which means that the moto geneates the desied ai-gap toque with easonable accuacy that is compaable to that of commecial ac dive systems. With the poposed algoithm, the invete equiements of a long lifetime, high eliability, and high powe density can be achieved without sacificing the system pefomance.

8 2720 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 30, NO. 5, MAY 2015 IV. CONCLUSION This pape addesses the contolle design of a position sensoless vecto-contolled IM dive system supplied fom a small dc-link film capacito invete fed by a thee-phase diode fontend ectifie. The poposed appoach focuses on the contolle pefomance when enteing o leaving the infeasible voltage domain. The PI moto-cuent-egulato-fee contol stuctue pesents a smooth tansition fom the MBC unde the unconstained voltage egion to the HVC when the voltage limit is encounteed. The analytical solution leads to the dynamic voltage modification at each time step with espect to the available dc-bus voltage. The algoithm can povide adequate esults ove a numbe of potential seconday upsets found in the cuent egulato-based contol stuctue. The opeation sensitivity unde moto paamete difts is also examined to decouple its influence using a voltage distubance state filte. The test esults clealy show that the poposed method can impove the invete eliability without sacificing the moto contol pefomance. REFERENCES [1] Altiva 21 Use s Manual, Schneide Electic Industies S.A.S., Rueil Malmaison, Fance, [2] K. W. Lee, M. Kim, J. Yoon, S. B. Lee, and J. Y. Yoo, Condition monitoing of dc-link electolytic capacitos in adjustable-speed dives, IEEE Tans. Ind. Appl., vol. 44, no. 5, pp , Sep./Oct [3] M. L. Gaspei, Life pediction modeling of bus capacitos in AC vaiable fequency dives, IEEE Tans. Ind. Appl., vol. 41, no. 6, pp , Nov./Dec [4] A. Layhani, P. Venet, G. Gellet, and P. J. Vivege, Failue pediction of electolytic capacitos duing opeation of a switchmode powe supply, IEEE Tans. Powe Electon., vol. 13, no. 6, pp , Nov [5] A. M. Imam, T. G. Habetle, R. G. Haley, and D. M. Divan, Real-time condition monitoing of the electolytic capacitos fo powe electonics applications, in Poc. IEEE Appl. Powe Electon. Conf.,2007,pp [6] D. C. Lee, J. K. Seok, and J. W. Choi, Online capacitance estimation of DC-link electolytic capacitos fo thee-phase AC/DC/AC PWM convetes using ecusive least squaes method, Poc. Inst. Elect. Eng. Elect. Powe Appl., vol. 152, no. 6, pp , Nov [7] L. Malesani, L. Rossetto, P. Tenti, and P. Tomasin, AC/DC/AC PWM convete with educed enegy stoage in the DC link, IEEE Tans. Ind. Appl., vol. 31, no. 2, pp , Ma./Ap [8] A. Yoo, S. K. Sul, H. Kim, and K. S. Kim, Flux-weakening stategy of an induction machine diven by an electolytic-capacito-less invete, IEEE Tans. Ind. Appl., vol. 47, no. 3, pp , May/Jun [9] K. Inazuma, H. Utsugi, K. Ohishi, and H. Haga, High-powe-facto single-phase diode ectifie diven by epetitively contolled IPM moto, IEEE Tans. Ind. Electon., vol. 60, no. 10, pp , Oct [10] H. S. Jung, S. J. Chee, S. K. Sul, Y. J. Pak, H. S. Pak, and W. K. Kim, Contol of thee phase invete fo AC moto dive with small DC-link capacito fed by single phase AC souce, in Poc. IEEE Enegy Conves. Cong. Expo. Conf., 2012, pp [11] W. J. Lee, Y. Son, and J. I. Ha, Single-phase active powe filteing method using diode-ectifie-fed moto dive, in Poc. IEEE Enegy Conves. Cong. Expo. Conf., 2013, pp [12] C. H. Choi, J. K. Seok, and R. D. Loenz, Wide-speed diect toque and flux contol fo inteio PM synchonous motos opeating at voltage and cuent limits, IEEE Tans. Ind. Appl., vol. 49, no. 1, pp , Jan./Feb [13] S. H. Kim and J. K. Seok, Finite-settling steps diect toque and flux contol (FSS-DTFC) fo toque-contolled inteio PM motos at voltage limits, IEEE Tans. Ind. Appl., vol. 50, no. 5, Sep./Oct., [14] S. H. Kim, C. H. Choi, and J. K. Seok, Voltage distubance state-filte design fo pecise toque-contolled inteio pemanent magnet synchonous motos, in Poc. IEEE Enegy Conves. Cong. Expo. Conf., 2011, pp [15] H. Kim, M. C. Hake, and R. D. Loenz, Sensoless contol of inteio pemanent-magnet machine dives with zeo-phase lag position estimation, IEEE Tans. Ind. Appl., vol. 39, no. 6, pp , Nov./Dec SeHwan Kim (S 10) eceived the B.S. degee fom Yeungnam Univesity, Gyeongsan, Koea, in 2010, whee he is cuently woking towad the combined M.S./Ph.D. degee in the Powe Convesion Laboatoy. His cuent eseach inteests include high pefomance electical machine dives, battey voltage maximum utilization fo EVs/HEVs, and pecise toque contol of PM synchonous motos. Jul-Ki Seok (S 94 M 98 SM 09) eceived the B.S., M.S., and Ph.D. degees fom Seoul National Univesity, Seoul, Koea, in 1992, 1994, and 1998, espectively, all in electical engineeing. Fom 1998 to 2001, he was a Senio Enginee with the Poduction Engineeing Cente, Samsung Electonics, Suwon, Koea. Since 2001, he has been a membe of the faculty of the School of Electical Engineeing, Yeungnam Univesity, Gyeongsan, Koea, whee he is cuently a Pofesso. His specific eseach aeas ae moto dives, powe convete contol of offshoe wind fams, and nonlinea system identification elated to the powe electonics field. D. Seok seves as an Associate Edito of the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS.