A Novel Control Method for Direct Interface Converters used for DC and AC Power Supplies

Transcription

1 A Noel Control Method for Direct Interface Conerters sed for DC and AC Power Spplies Koji Kato, Jn-ichi Itoh Nagaoka Uniersity of Technology Kamitomioka-cho Nagaoka city Niigata, Japan Tel./FAX: +81/ (258) URL: Keywords «Matrix conerter», «Conerter control», «Power factor correction», «Energy conerters for HEV» Abstract This paper proposes a noel control method for a direct interface conerter for management of the energy flow in either an AC or DC spply. The proposed conerter is constrcted based on an indirect matrix conerter. Therefore a proposed control strategy is based on an indirect control method with a trianglar carrier wae. This paper proposes two control methods, sing a boost p and a step down type DC/DC conerter. The basic operation of the proposed control method is confirmed by simlation and experimental reslts. In addition, this paper also proposes a commtation error compensation method for an otpt oltage error and an inpt error for an indirect matrix conerter. In the proposed method, the otpt oltage and inpt error by the commtation can be compensated at the same time, becase the PWM plse of each switch is directly compensated. The alidity of the proposed method is confirmed by experimental reslts. Those reslts proe that the proposed compensation method can decrease total harmonic distortion (THD) of the inpt and otpt. I. Introdction Recently, interface power conerters for renewable energy and hybrid electric ehicle (EV) systems hae been stdied intensely. Power sorces can different types; AC power sorces sch as wind power, and DC power sorces sch a photooltaic cells, a batteries, and fel cells. Therefore, a conentional power conerter system composed of AC/DC, DC/DC and DC/AC conerters reqires a large energy bffer, sch as an electrolytic capacitor. Howeer, the electrolytic capacitor in a conentional system interferes with down sizing, long-life time and low costs. On the other hand, there is an AC/AC direct conerter with a DC link, known as an indirect matrix conerter [1-1]. The indirect matrix conerter, which does not hae a large energy bffer sch as an electrolytic capacitor, can sole these problems. This conerter is sitable to realize direct interface conerters with mlti-port for seeral power spplies. Howeer, it is difficlt to be added a DC/DC conerter, becase the conentional control method for the indirect matrix conerter ses the space ector modlation [1], which is expressed by three dimensions. This paper proposes tri-port conerters sing a simple control method based on the indirect control method with a trianglar carrier wae [11]. By sing a trianglar carrier, the PWM plse can be generated withot relationship to the nmber of phases. As a reslt, the proposed control system can be easy added to a DC/DC conerter. In addition, this paper proposes the commtation error compensation method for the otpt oltage error and the inpt error of the indirect matrix conerter. The commtation cases the otpt oltage error and the inpt error, sch as the dead-time in a conentional inerter. In the proposed method, the otpt oltage and inpt error are compensated at the same time, becase the PWM plse of each switch is directly EPE 27 - Aalborg ISBN : P.1

2 compensated. As a reslt, the inflence of the commtation for the inpt and otpt can be decreased by the proposed commtation method. Experimental reslts with an AC power grid, a motor, and a battery are also proide. The basic operation and alidation of the proposed method are confirmed by simlation and experimental reslts. As a reslt, inpt, otpt and DC otpt total harmonics distortion (THD) are 1.4, 1.8%, 2.3%, were confirmed. In addition, an inpt power factor of oer 99% and an efficiency of 95.4% were obtained. II. Circit topology Figre 1 shows the proposed direct interface conerters for the energy management system. This system consists of two AC power sorces or loads and the DC power sorce withot a large energy bffer, sch as an electrolytic capacitor. In case of a hybrid EV system, the energy flow of the interface conerter mst be maintained in three directions, as shown Fig. 1. Figre 2 shows the main circits of the proposed system. There are two operation methods in this system. The first operation method is to operate the inerter side conerter as a for-phase oltage sorce inerter, inclding the DC/DC conerter. For this operation, the DC link oltage becomes higher than the DC power spply. Therefore, it is referred to as a boost type AC/DC/AC direct conerter. The second operation method is to operate the rectifier side conerter as the for-phase sorce rectifier, inclding the DC/DC conerter. In this case, DC link oltage becomes lower than DC power spply, and ths, is referred to as a step down type AC/DC/AC direct conerter in this paper. The proposed control strategy, which is based on an indirect control method with the trianglar carrier wae, easily realizes the addition of a DC/DC conerter. The conentional indirect control Wind power Engine generator etc. G AC/DC Conerter Energy Flow No energy bffer DC/AC Conerter Load or Power line Photooltaics Fel cell Battery etc. DC/DC conerter Fig. 1. Block diagram of AC and DC power spply interface system. Crrent sorce rectifier DC/DC conerter Voltage sorce inerter Srp Ssp Stp Sbp Sp Sp Swp Crrent sorce rectifier DC/DCVoltage sorce conerter inerter Srp Ssp Stp Sbp Sp Sp Swp Inpt filter R S T U V W M Inpt filter R S T U V W M Srn Ssn Stn Sbn Sn Sn Swn Srn Ssn Stn Sn Sn Swn Bn Bp Lb batt Battery batt Battery Bp Bn (a)boost type AC/DC/AC direct conerter. (b) Step down type AC/DC/AC direct conerter. Fig. 2. Proposed circits. EPE 27 - Aalborg ISBN : P.2

3 strategy, which ses space ector control, mst calclate the PWM plse width to inclde a DC/DC conerter. In addition, it is difficlt to define the otpt oltage command ector to inclde a DC otpt. Howeer, the proposed control system can inclde a DC/DC conerter by sing a command for the comparison of the carrier wae and the oltage. This chapter describes two types of control method for the DC/DC conerter. A. Boost type AC/DC/AC direct conerter Figre 3 shows a block diagram of the boost type DC/DC conerter with the indirect matrix conerter. This conerter operates the inerter side conerter as a for-phase oltage sorce inerter inclding the DC/DC conerter. The relation between the inpt oltage [ r s t ] t and the otpt oltage [ w b ] t can be expressed as sp sn r sp sn srp ssp stp = s (1), w swp swn srn ssn stn t b ' sbp sbn where S xy is the switching fnction of the switch S xy in Fig. 2. S xy = 1 when S xy is trned on, and S xy = when S xy is trned off. The otpt oltage b is the battery oltage batt based on that the motor netral point. The rectifier side conerter ses single-phase modlation, as shown in Ref. [11]. Ths, the DC link oltage contains the ripple, which contains sixth order component of a power spply freqency. The otpt oltage commands of the inerter side conerter inclding the DC/DC conerter mst compensate for this ripple. Moreoer, the otpt oltage commands of the for-phase oltage sorce inerter are based on the netral point of the motor. In contrast, the DC/DC conerter otpt oltage commands are based on the point B n, as shown in Fig. 2. Therefore, the DC/DC conerter oltage command bot is conerted by the following eqation: 2 1 (2). batt = batt Rectifier side plse commands ( type) DC/DC conerter side plse commands Inerter side plse commands (oltage type) PWM rectifier Plse pattern conersion DC/DC conerter Inerter Carrier DC link ripple cal dc_rip + - Single leg modlation Carrier generator 1/X + - Dty conersion Inpt commands Chopper comands Otpt oltage commands Fig. 3. Control block diagram of boost type AC/DC/AC direct conerter. B. Step down type AC/DC/AC direct conerter Figre 4 shows a block diagram of the step down type AC/DC/AC direct conerter. This conerter operates the rectifier side conerter as a for-phase sorce rectifier inclding the DC/DC conerter. The relation between the inpt oltage [ r s t b ] t and the otpt oltage [ w ] t can be expressed as: r sp sn srp ssp stp sbp = s sp sn (3), s rn ssn stn sbn t w swp swn b ' EPE 27 - Aalborg ISBN : P.3

4 where the inpt oltage b is the battery oltage batt based on the inpt oltage netral point. To aoid short circit of the power spply, the rectifier side conerter and DC/DC conerter mst be switched separately. Figre 5 shows the relation of the carrier signals between the inerter and the rectifier. Usally, a type rectifier is controlled nder the constant DC link. Howeer, the DC link mst be zero when the inerter selects zero oltage ectors. In the proposed method, this is achieed by controlling the slope of the inerter carrier signal as shown in Figre 5. By adopting this method, the zero period of the DC link is distribted by the same ratio as each inpt, as described in Eq. (4). Tr Ts Tb Tr + Ts + Tb = = = (4). T T T T + T + T Rectifier side plse commands ( type) DC/DC conerter plse pattern Inerter side plse commands (oltage type) PWM rectifier Carrier dc_rip DC link ripple cal Plse pattern conersion Single leg modlation DC/DC conerter Inerter Carrier generator 1/X Inpt commands Chopper comands Otpt oltage commands Fig. 4. Control block diagram of step down type AC/DC/AC direct conerter. T Rectifier side carrier and commands i b i rec T 1 Rectifier side plse Inpt S rp S sp S tn S bp i r i s i t i b T 2 /2 T 2 /2 T 3 /2 T 3 /2 T r T s /2 T s /2 T b /2 T b /2 Dc link Inerter side carrier and commands w Fig. 5. Relation between inerter carrier and rectifier plse. EPE 27 - Aalborg ISBN : P.4

5 III. Improement of waeform for boost type AC/DC/AC direct conerter Figre 6 shows a part of the plse pattern and behaior of the oltage error for the proposed indirect conerter. In an indirect matrix conerter, the rectifier side conerter can achiee the zero switching when the inerter generates the zero oltage ectors [4]. In other words, the dc-link mst be zero when the inerter selects the zero oltage ectors. Howeer, the dc-link flows in the proposed circit when the inerter generates the zero oltage ectors of the pper (P) arms. Therefore, the proposed circit has to choose only lower (N) arms zero oltage ectors. It is shold be note that the conentional dead-time is applied for the commtation of the inerter side. A. Analysis of the commtation error In order to realize the low harmonics inpt and otpt, the oltage error by the commtation is important as a conentional inerter. At first, this paper analyzes the commtation error of the indirect matrix conerter. The relation between inpt oltage and otpt oltage of the indirect matrix conerter can be expressed as Eq. (5) sing "D mn ",which is dty ratio for switch S mn. Dp Dn r Drp Dsp Dtp = Dp Dn s (5). Drn Dsn Dtn w Dwp Dwn t As shown in Figre 4, the error by the dead time occrs to the inerter side and rectifier side dty ratio. In this case, the dty ratio considering the dead time error can be expressed by Eq. (6). D 1 - D ΔD r + Δ + Δ Drp Drp Dsp Dsp = D 1 - D ΔD s Dtn tn + Δ Δ w D w Dw 1 - Dw Dw t ( D ) ( D ) (1- D ΔD ) rp rp s sp tn tn r = ( D ) ( D ) (1- D ΔD ) (6), rp rp s sp tn tn s ( D ) ( D ) (1- D ΔD ) w w rp rp w w s sp w w tn tn t where ΔD mn represents the dty error by the dead time, and the sffix represents the command. From Eq. (6), the otpt oltage can be determined by Eq. (7). = ( D + D D ) ( ΔD ΔD ) rp r sp s tn t rp r sp s tn t (7). + { D ( ΔD ) + (1 - D ) ΔD } rp r sp s tn t Fig. 6. Commtation example. EPE 27 - Aalborg ISBN : P.5

6 The second term in the right side of Eq. (7) means the oltage error directly affected by the inerter dead time, the third term means the inflence of the inpt side, and the forth term means mixed error between the inpt and otpt side. On the other hand, the relation between the inpt and otpt of the indirect matrix conerter can be expressed as Eq. (8). It shold be noted that Eq. (8) is the transposed matrix of Eq. (6). i r ( D )( Drp rp) ( D rp rp) ( Dw w rp rp) i rs = ( D s sp) ( D s sp) ( Dw w s sp) i (8). i t (1- D Δ + Δ Δ + Δ Δ + Δ D)( Dtn Dtn) (1- D D tn Dtn) (1- Dw Dw tn Dtn) i w From Eq. (8), for example, the inpt i r can be determined by Eq. (9). i = i ( D i + D i + D i ) ( ΔD i i i ) ( D i + D i + D i ) (9). r r rp w w rp In the conentional compensation methods, the otpt oltage error is compensated by Eq. (7). That is, the oltage error adds to the oltage commands of the inerter. From Eq. (7), the compensation dty ratio D comp can be determined by Eq. (1) becase dty factor is obtained by diiding the dty ratio by the DC-link oltage. In the indirect matrix conerter, the compensation ales contain not only the inerter oltage error ΔD bt also the inflence error ΔD rcomp of the inpt side. Similarly, other compensation dty ratio can be calclated. { D ( ΔD ΔD ) + (1 - D ΔD } D = ΔD + ) e comp rp r sp s tn dc (1). = ΔD rcomp This method can compensate the otpt oltage, howeer, the inpt can not compensate becase the compensation ales is decided withot consideration for the inpt. In this case, the inpt i r can be expressed by Eq. (11). { D i + D i + D i } ir = ir rp w w (11). ΔDrcomp ( Drp i ΔDrpi) ΔDrcomp ( Drp i ΔDrpi ) ΔDrwcomp ( Drp iw ΔDrpiw ) The additional inpt error occrs to Eq. (11) since the otpt oltage is compensated by Eq. (1). Moreoer, the commtation error of the rectifier side can not compensate becase the commtation error of the rectifier side does not depend on the inerter side dty ratio. Therefore, the inpt error remains as shown in Eq. (11). B. Proposed compensation method In this paper, the oltage error is directly compensated by the PWM plse. The inpt and otpt oltage error can compensate at the same time becase the PWM plse of each switch is directly compensated. Figre 7 shows the proposed commtation error compensation method. The inerter side and DC/DC conerter side plse commands are compensated directly based on the load direction in Commtation compensator as shown Fig. 7(a). Figre 7(b) shows behaior of the commtation compensator. In case of load direction is w rp rp rp w Rectifier side plse commands Inerter and DC/DC conerter side plse commands Load direction signal Commtation time i i i w i b T d FPGA Commtation compensator Commtation generator 2 Inerter side plse commands Inerter side plse with compensation S p S p (I load >) (I load <) T d increasing (a) Configration of proposed commtation (b) Behaior of compensator error compensation. Fig. 7. Proposed commtation error compensation method. T d decreasing EPE 27 - Aalborg ISBN : P.6

7 pls, the compensator adds the dead-time period to the plse command, becase actal plse is decreased by the dead-time period. In case of load direction is mins, the compensator sbtracts the dead-time period to the plse command, becase actal plse is increased by the deadtime period. IV. Simlation and experimental reslts Figre 8 shows the simlation reslts of the proposed control strategy. In the simlation, an ideal sorce load and a main circit are sed to check the proposed strategy. Good sinsoidal waeforms are obtained for the inpt and the otpt oltage. The THD of the inpt and the otpt are less than 1%, respectiely. In addition, a good DC waeform, withot low freqency ripple, is obtained for the DC otpt oltage. Table 1 proides the experimental parameters. The operation of a boost type DC/DC conerter with indirect matrix is shown by the experimental reslts. This conerter has six operation modes as follows. (P: power grid, B: battery, M: motor) I: P: generation, B: charge, M: motoring II: P: generation, B: charge, M: generating III: P: generation, B: discharge, M: motoring IV: P: regeneration, B: charge, M: generating V: P: regeneration, B: discharge, M: motoring VI: P: regeneration, B: discharge, M: generating r [V] 2-2 i r [A] (LPF) 1-1 [V] (LPF) 2-2 i [A] 1-1 batt [V] (LPF) 2 1 i batt [A] (a) boost mode r [V] 2-2 i r [A] (LPF) 4-4 [V] (LPF) 2-2 i [A] 1-1 batt [V] 4 2 i batt [A] (LPF) [sec] [sec] Fig. 8. Simlation reslts. (b) step down mode Table1 Experimental parameter. Inpt oltage 2[V] 2 [mh] LC filter Inpt freqency 5[Hz] 6.6 [μf] Carrier freqency 1[kHz] Ct-off freqency 1.3[kHz] Otpt freqency 4[Hz] DC load R-L AC load 1.5[kW]motor DC sorce DC power spply Commtation time 2.5[μs] EPE 27 - Aalborg ISBN : P.7

8 Figre 9 shows the waeforms for operation modes I, II, and VI, as typical modes. Good sinsoidal and dc waeforms were obtained for the inpt and otpt. The other operation modes were also confirmed. As a reslt, generation and regeneration of a power grid, the charge and discharge of a battery, and motoring and generating operations are obtained for each operation waeform. Figre 1 shows the efficiency and the inpt power factor when the dc/dc conerter leg is stopped in the proposed conerter. The inpt power factor of oer 99% and the high efficiency of 95.4% were obtained. It shold be noted that the efficiency of a conentional AC/DC/AC interface conerter with a large electrolytic capacitor is approximately 9%. Therefore, the proposed conerter can decrease the conerter loss of 1/2. (a) Mode I 1 [ms/di] Inpt oltage (phase) 2 [V/di] Inpt 1 [A/di] AC Otpt 1 [A/di] DC Otpt 5 [A/di] (b) Mode III Inpt oltage (phase) 2 [V/di] 1 [ms/di] Inpt oltage (phase) 2 [V/di] Inpt 5 [A/di] AC Otpt 1 [A/di] DC Otpt 5 [A/di] Inpt 5 [A/di] 1 [ms/di] (c) Mode VI Fig. 9. Experimental reslts. AC Otpt 1 [A/di] DC Otpt 5 [A/di] Fig. 1. Efficiency and inpt power factor. EPE 27 - Aalborg ISBN : P.8

9 Figre 11 shows the comparison among the THD of the proposed circit withot oltage and error compensation, with the conentional compensation, which only add the oltage error to the otpt oltage command, and proposed compensation methods, as described in chapter III. In the inpt THD, the conentional compensation methods is not effectie, becase the conentional compensation method only compensates the otpt oltage withot consideration for the inpt. In contrast, the THD for the inpt is improed by approximate 5%, sing the proposed compensation method. On the other hand, the conentional compensation method decreases the otpt THD by approximate 5%. In addition, the proposed compensation method also decrease the inpt THD by approximate 6%. Howeer, almost same THD are obtained in the DC otpt. This cases that an ato reglator is sed in the DC/DC conerter control. In the proposed compensation, low THD is obtained for the inpt and otpt s. These experimental reslts confirm that the alidity of the proposed circit and commtation error compensation method. 1 Inpt with conentional compensation( ) 5 Inpt withot conentional compensation( ) Inpt with proposed compensation( ) Otpt Power[W] (a) THD of inpt. AC otpt THD [%] (b) THD of AC otpt. (c) THD of DC otpt. Fig. 11. THD of inpt and otpt sing a R-L load. EPE 27 - Aalborg ISBN : P.9

10 V. Conclsion This paper proposes a noel control strategy for the energy management of an AC and DC power spply direct interface conerters. The proposed control strategy, which is based on an indirect control method with a trianglar carrier wae, is easy to expand to the mlti-phase system. This paper proposes the two control methods sing a boost p and step down type DC/DC conerters. Moreoer the compensation method for the otpt oltage and the inpt error by the commtation were also proposed. The proposed compensation method can be sed in the indirect matrix conerter. The proposed compensation methods compensate directly the PWM plse of each switch. The alidity of the proposed strategy was confirmed by both the simlation and experimental reslts. As a reslt, it is confirmed that the AC inpt, otpt, and the DC otpt THD are 1.4%, 1.8%, 2.3%, respectiely, and the inpt power factor is oer 99% and the maximm efficiency is 95.4%. Moreoer, the inflence of the commtation for the inpt and otpt can be decreased by the proposed commtation method. In addition, three directions of energy flow in this circit are confirmed. This stdy was spported by Indstrial Technology Grant Program in 25 from New Energy and Indstrial Technology Deelopment Organization (NEDO) of Japan. References [1] J.W.Kolar, M.Bamann, F.Schafmeister, H.Ertl: "Noel Three Phase AC-DC-AC Sparse Matrix Conerter", IEEE APEC 22 [2] L.Wei, Y.Matsshita, T.A.Lipo: "Inestigation of Dal-bridge Matrix Conerter Operating nder Unbalanced Sorce Voltage" IEEE PESC23, 1293(23) [3] K. Iimori, K. Shinohara, O. Tarmi, Z. F, and M. Mroya, New -controlled PWM rectifier- oltage sorce inerter withot DC link components, Proc. Conf. Rec. PCC, 1997, ol. 2, pp [4] K. Iimori, K. Shinohara, K. Yamamoto,:" Stdy of Dead Time of PWM Rectifier of Voltage-Sorce Inerter Withot DC-Link Components and Its Operating Characteristics of Indction Motor" IEEE Trans. on Indstry Applications Vol. 42, No. 2, pp , 26. [5] S. Mariethoz. A new control scheme for an hybrid two-stage matrix conerter with improed efficiency. Proc. IEEE IECON 6.. [6] S.Kim, S.K.Sl, T.A.Lipo:" AC/AC Power Conersion Based on Matrix Conerter Topology with Unidirectional Switches" IEEE Trans. on Indstry Applications Vol. 36, No. 1, pp , 2. [7] Jin Aijan, Li Hangtian, Li Shaolang:" A New High-Freqency AC Link Three-Phase For-Wire Power Electronic Transformer " ICIEA26 [8] L. Wei and T. A. Lipo, A Noel Matrix Conerter Topology with Simple Commtation, IAS21, Vol. 3, pp , 21 [9] M.Jssila, M.Eskola, H.Tsa,:" Analysis of Non-Idealities in Direct and Indirect Matrix Conerters Eropean Conference on Power Electronics and Applications 25 [1] S.Rond, F.Schafmeister, M.Heldwein, E.Pereira, L.Serpa, J. Kolar,:" Comparison of Performance and Realization Effort of a Very Sparse Matrix Conerter to a Voltage DC Link PWM Inerter with Actie Front End " The 25 International Power Electronics Conference, pp , 25 [11] J.Itoh, I.Sato, A.Odaka, H.Ohgchi, K.Kodachi:" A Noel Approach to Practical Matrix Conerter Motor drie System with RB-IGBT" Power Electronics Specialists Conference 24 EPE 27 - Aalborg ISBN : P.1