A Novel Engine Generator System with Active Filter and UPS Functions

Transcription

1 A Novel Engine Generator Sytem with Active Filter and UPS Function Uing a Matrix Converter A Novel Engine Generator Sytem with Active Filter and UPS Function Uing a Matrix Converter Jun-ichi Itoh, Shunuke Tamada Nagaoka Univerity of Technology Kamitomioka-cho Nagaoka city Niigata, Japan Tel./FAX: +81/ (58) itoh@vo.nagaokaut.ac.jp URL: Keyword Matrix converter, Active filter, Regenerating power, Uninterruptible power upplie (UPS), Converter control Abtract Thi paper propoe the application of a matrix converter to a PM generator for power quality compenation, uch a reactive power compenation, harmonic current and power interruption. The novel point of thi work i that the matrix converter provide reactive power with harmonic current. Simulated and experimental reult confirm that the matrix converter can maintain high performance a ame a a conventional active filter and an uninterruptible power upply (UPS). I. Introduction Recently, renewable reource upplie, uch a fuel cell, photovoltaic cell, wind power and engine generator, for ditributed power ytem have been tudied intenely. Ue of uch power upplie mean that power quality compenator, uch a active filter, reactive power compenator, and uninterruptible power upplie (UPS) are becoming more important for maintenance of a high quality power grid. Power quality compenator with witching device are contructed baed on a voltage ource inverter uing ix arm. Therefore, conventional power quality compenator require a large electrolytic capacitor in the dc link part of the equipment. The ue of a large capacitor hinder downizing effort and the lowering of equipment cot. In addition, the high reliability i required for the power compenator and a ditributed power ytem. Therefore the life time of the electrolytic capacitor caue trouble. On the other hand, ac to ac direct converter have been tudied, uch a a matrix converter for motor drive application. Direct converter, which do not have a large electrolytic capacitor and an initial charge circuit, can be ued to realize downizing and lowering of equipment cot, when compared with conventional converter. In thi cae, the input current of the matrix converter i controlled by only a unity power factor inuoidal waveform. Thi paper propoe the application of a matrix converter to a permanent magnet (PM) generator with power quality compenation. The input current control repone of a matrix converter i higher than the conventional voltage type converter, becaue the input current control work a ame a a current type converter. A control trategy i alo propoed for an active filter with UPS function. The propoed control trategy i baed on a virtual indirect control method [4], which can clearly eparate an input ide control and an put ide control, uch a an indirect matrix converter. Thu, thi paper lead a relation between the input and put current. A compenation capacity of thi propoed ytem i alo mentioned. EPE 7 - Aalborg ISBN : P.1

2 A Novel Engine Generator Sytem with Active Filter and UPS Function Uing a Matrix Converter Furthermore, imulated and experimental reult are provided for reactive power compenation, UPS operation and active filter operation, uing the propoed control method. A a reult, the propoed engine generator ytem ha been validated. II. Sytem Configuration Figure 1 how a block diagram of the propoed engine generator ytem with the matrix converter to compenate power quality. The reactive power and the harmonic in the power grid are compenated by the matrix converter, which generate the ame reactive power and harmonic a the load. Auming that a matrix converter i applied to one type of ditributed power upply with a PM generator, then the matrix converter can upply not only the active power, but alo compenate the harmonic current in the power grid, which will realize the maintenance of high power quality with the ue of other active filter equipment. The energy buffer of the matrix converter i ued a a PM generator, intead of a large volume capacitor. In the cae of compenating active power, uch a for power interruption and an unbalanced voltage, a conventional compenator, which conit of a witching device bridge with ix arm, require a large volume capacitor. However, electrolytic capacitor can not be applied to high voltage ytem, becaue there are no high-voltage rated electrolytic capacitor. v i il i c v g v cf i c v g Fig. 1. Block diagram for the engine generator ytem with a matrix converter. III. Control trategy A. Virtual indirect control method The propoed control trategy i baed on a virtual indirect control method with a triangular carrier wave for power grid ide control and generator ide control, repectively. A feature of thi method i that variou control method for a conventional inverter or rectifier can be applied to a matrix converter. The control algorithm i provided by the inverter part (the generator ide), the rectifier part (the power grid ide) and a compoite pule width modulation (PWM) generator, which generate the PWM pattern for the matrix converter, a hown in Figure 1. The PWM pattern for the matrix converter i obtained by the witching function of the inverter and rectifier part. Figure and 3 how a model of the indirect matrix converter and the matrix converter, repectively. In thi cae, the relation between the input voltage and the put voltage of the indirect matrix converter i expreed a v u v = v v w up vp wp un rp vn rn wn p n vr tp v tn v t (1) EPE 7 - Aalborg ISBN : P.

3 A Novel Engine Generator Sytem with Active Filter and UPS Function Uing a Matrix Converter where witching function i defined that =1 mean witch S i turned on, = mean witch S i turned off. Likewie, the relation between the input voltage and the put voltage of the matrix converter i expreed a vu = vv v w ru rv rw u v w tu vr tv v tw vt Therefore, the PWM pattern for the matrix converter can be converted by ru rv rw u v w tu tv = tw up vp wp un vn wn rp rn p n tp tn A a reult, control performance of a matrix converter i exactly ame a an indirect matrix converter becaue the relation between the input voltage and the put voltage i the ame. It hould be noted that the relation between the input current and the put current i alo the ame. (). (3). r Sru Srv Srw Input filter t Su Sv Sw Stu Stv Stw u v w Fig.. Indirect converter Fig. 3. Matrix converter B. Active filter control with UPS function Figure 4 how a control block diagram for rectifier control. Thi ytem ha two operation mode for harmonic current compenation uch a an active filter, and power interruption compenation uch a UPS. Detection of power interruption i ued in the ame way a the conventional method, which detect the magnitude of the input voltage. When a power interruption ha occurred, the matrix converter work a the voltage power ource. The elector hown in Figure 1 elect the current command for UPS mode and active filter mode. Selector Load current i La i Lb i Lc v cfa v cfb v cfc p-q tranform Capacitor voltage p-q tranform θ v cfp v cfq HPF i cq HPF HPF i cp i ap + +? + Kd Active power command of generator? Kd i cp i cq invere p-q tranform Fig. 4. Block diagram for rectifier control. Fig. 5. Block diagram for reactive power compenation with damping control for the input current. i ca i cb i cc Current command of matrix converter Figure 5 how a control block diagram for the active filter function. The input current command are calculated uing the load current. It hould be noted that the control method of the rectifier part i EPE 7 - Aalborg ISBN : P.3

4 A Novel Engine Generator Sytem with Active Filter and UPS Function Uing a Matrix Converter the ame a a current type converter. In thi controller, the load current i converted to a p-q frame, which i a rotating frame baed on the voltage vector of the power grid. Therefore, the value of the p- axi repreent the active current and thoe of the q-axi repreent the reactive current. There are two difference point for application of the control method to a conventional power grid compenator, decribed a follow: 1) Active power command of the PM generator i added to the active current command. ) Damping control [5] of the input current i applied to the active and reactive current command calculation, a hown in Figure 5. The current command with damping control are obtained uing equation (4). A high pa filter (HPF) i ued to extract the harmonic current from the capacitance voltage. The cut off frequency of the HPF depend on the harmonic extraction frequency. c i = i c K d ST v 1+ ST cf (4) where, ic i the compenated current command, ic i the original current command, T i the time contant, Vcf i the capacitor voltage, and Kd i the damping gain. C. Input current control method of matrix converter In thi chapter, we dicu the input current control method for the matrix converter baed on the indirect matrix converter. The theorie of the indirect converter are entirely equivalent to the matrix converter becaue the matrix converter i controlled baed on the virtual indirect control method in thi propoed ytem. In thi cae, for example, when Srp, Stn, Sup, Svp, and Swn are turned on in the indirect matrix converter a hown in Figure, R phae i connected to U, V phae, and T phae i connected to W phae. Likewie, when Sru, Srv, Stw are turned on, R phae i alo connected to U, V phae, and T phae i alo connected to W phae in the matrix converter. Thu, the connection between the input terminal and the put terminal of the matrix converter i the ame a converter indirect matrix converter. Figure 6 indicate power flow of the indirect matrix converter. The input ide converter operate a a current ource rectifier, and the put ide converter operate a a voltage ource inverter in the indirect matrix converter. Therefore, the maximum value of the input current depend on magnitude of the DC link current. i dc u r t e dc v w PM Current ource rectifire active power Voltage ource inverter reactive power Fig. 6. Power flow of AC/DC/AC converter. The reactive power of the load ide doe not affect the DC link tage becaue the reactive power i generated by free wheeling mode. In addition the DC link tage only tranmit the active power on the load. It i imilar to control a matrix converter with the virtual indirect control method. The indirect matrix converter doe not have an energy buffer. Therefore, the DC link current i determined by the put current and the load power factor of the voltage ource inverter. The load power factor i EPE 7 - Aalborg ISBN : P.4

5 A Novel Engine Generator Sytem with Active Filter and UPS Function Uing a Matrix Converter calculated uing the voltage command and the put current of the inverter. A a reult, the DC link current i given by i img _ dc = i _ max coθ v i + v i a α β β = i (5) _ max ( v + v )( i + i ) α β α β where v α and v β are the put voltage command of the inverter, i α and i β are the put current, i _max i the peak value of the put current, and uffix α and β mean on a ret frame. The control range of the input current i contrained by 3 / time of the DC link current becaue the DC link current ha ripple between 3 /iimg_dc and i img_dc. The current ource rectifier ue a triangular carrier in order to generate PWM pule. Thu, the input current command are normalized by 3 / time of the DC link current. Finally, the modulation index of the input current i obtained by i c = 3 i c i img _ dc i ( v + v )( i + i ) c α β α β = 3 i v i + v i _ max a α β β where i c i the modulation index of the input current, i c i the input current command. (6) By uing the virtual current ource type rectifier with the modulation index a hown in Equation (6), the input current of the matrix converter i able to be controlled by an open loop controller though there i no auto current regulator for the input ide. IV. Reactive Power Compenation range The power factor of the input ide of the matrix converter deteriorate according to magnitude of compenated reactive power, becaue the input current of the matrix converter not only contain the active power but alo the reactive power to compenate the power grid. A decribed in previou chapter, a behavior of a matrix converter can be baically dicued a ame a an indirect matrix converter. In cae of an indirect matrix converter, if the input power factor become low, then a DC voltage would decreae. That i, the matrix converter can not control the motor connected to the put ide becaue the put voltage of the inverter i contrained by the DC link voltage. Accordingly, we have to carefully chooe the reactive power compenated in a load including the put voltage of the matrix converter. In thi chapter, we examine the relation between the maximum compenated reactive power and the put voltage of the matrix converter. The maximum put voltage of the matrix converter i obtained uing 3 V = V coθ (7) in where V i the power grid voltage, coθ in i the input power factor of the matrix converter. In cae of the indirect matrix converter, the input current of the matrix converter i alo depended on the put power factor and the magnitude of the put current becaue the input current i determined by the DC link current. Therefore, when the matrix converter compenate reactive power, the input apparent power i obtained uing Equation (8). S = V I coθ (8) in where I i the put current(rms), coθ i the put power factor of the matrix converter. EPE 7 - Aalborg ISBN : P.5

6 A Novel Engine Generator Sytem with Active Filter and UPS Function Uing a Matrix Converter The input power factor of the matrix converter i given uing the apparent power leaded by Equation (8), and reactive power compenated in a load. A the reult, the input power factor i obtained uing Equation (9). coθ = in ( V I S in Q S in coθ load ) Q load = (9) V I coθ where S in i the input apparent power of matrix converter, Q load i reactive power for compenation. Finally, the relation among the put voltage V, the reactive power of the load Q load and the load power factor co θ for compenation i expreed uing Equation (1). Q load = I coθ ( V + V )( V V ) (1) 3 3 Figure 7 how the compenation range of reactive power, uing Equation (1) under contant put current I and contant input voltage V. The ability a a reactive power compenator increae in the domain of low put voltage and high power factor. 1 V = V I =5A coθ V [V] Fig. 7. Compenation range of reactive power. V. Simulation reult Table 1 how the imulation parameter ued to confirm the baic operation of the propoed ytem. The imulation aume that the commutation of the matrix converter i the ideal, that i, the commutation time i zero. In thi ytem, the active power i divided between the power grid and the PM generator. The ratio of the active power (power ditribution ratio) between the power grid and the PM generator i et to almot 7:3. Table. 1. Simulation parameter. Power grid voltage [V] Power grid frequency 5[Hz] Carrier frequency 1[kHz] Power ditribution ratio 7:3 (Power grid :PM generator) LC filter Cut of frequency 1.6[kHz] LC filter Damping factor. Load (UPS, Active filter operation) Diode bridge (R=75Ω, DCL= mh) (reactive power compenation) R=5Ω,L=5 mh EPE 7 - Aalborg ISBN : P.6

7 A Novel Engine Generator Sytem with Active Filter and UPS Function Uing a Matrix Converter Figure 8 how the imulation reult for reactive power compenation. At the middle of the horizontal axi, reactive power compenation i initiated and the unity input power factor can then be obtained. The erving active power of the power grid i decreaed, becaue the PM generator i upported by the active power. It hould be noted that we alo confirmed that the propoed ytem can compenate the power factor of the power grid for capacitor load. Figure 9 how the reult for active filter operation, which mean harmonic current compenation of the power grid. The harmonic current caue a diode rectifier. The harmonic compenation i tarted in the middle of the horizontal axi. A a reult, a good inuoidal current waveform i obtained in the power grid. In addition, the imulation reult confirm that the damping control can uppre the ocillation of the LC filter to the input current of the matrix converter. However, the ocillation depend on LC filter in the grid current i lightly remaining. Figure 1 how the UPS operation with active filter, which repreent power interruption compenation by the PM generator ytem. The put voltage i moothly changed from the power grid to the PM generator. The put voltage i controlled by a proportion and integration (PI) controller during the power interruption. That i, the put voltage regulator i immediately applied when the power interruption occur. A good inuoidal voltage waveform i alo obtained in thi cae. Fig. 8. Simulation reult of reactive power compenation with an R-L load Fig. 9. Simulation reult for active filter operation. EPE 7 - Aalborg ISBN : P.7

8 A Novel Engine Generator Sytem with Active Filter and UPS Function Uing a Matrix Converter Power grid voltage [V] Power grid current [A] Load voltage [V] Load current [V] Power of power grid[w] Interruption time [] Fig. 1. Simulation reult for UPS operation. VI. Experimental reult Figure 11 how the experimental reult for reactive power compenation uing the propoed ytem and RL load. The experimental condition are almot the ame a the imulation, except for the direction of the power flow, the LC filter deign of the matrix converter, and the commutation method according to the polarity of the input voltage [3]. The experimental etup contrain the operation mode, which i motoring. The input current of the matrix converter controlled a lead phae for the power grid voltage. A a reult, the power factor of the power grid current wa corrected a unity. Figure 1 how the experimental reult for active filter operation for a diode rectifier load. In figure 1(a), a good inuoidal waveform i obtained for the input current of the matrix converter. However, the power grid current contain the ditortion due to the input current generate the harmonic component. On the other hand, in Figure 1(b), the power grid current i compenated by the matrix converter. A a reult, the power grid current become a inuoidal waveform. However, a few ditortion remain in the load current. One of the reaon for the ditortion i the influence of voltage error by commutation. Fig. 11. Experimental reult of reactive power compenation with RL load. EPE 7 - Aalborg ISBN : P.8

9 A Novel Engine Generator Sytem with Active Filter and UPS Function Uing a Matrix Converter (a) With harmonic compenation. Input voltage [5V/DIV] Input current of matrix converter [5A/DIV] Grid current [1A/DIV] Output current of matrix converter [1A/DIV] (b) With harmonic compenation. 1m/DIV Fig. 1. Experimental reult of active filter operation. Fig. 13. Harmonic analyi reult of the power grid current. Figure 13 how the analyi reult of harmonic under the diode rectifier load a hown in Figure 1. The frequency component of 3 rd, 5 th, 7 th and 11 th are decreaed by applying the propoed harmonic compenation. However the frequency component of even number are higher becaue the ocillation of the input current depend on the LC filter caue the current ditortion. EPE 7 - Aalborg ISBN : P.9

10 A Novel Engine Generator Sytem with Active Filter and UPS Function Uing a Matrix Converter Fig. 14. Relation between power factor and THD. Figure 14 how the relation between the power factor of the PM motor connected ide and the total harmonic ditortion (THD) of the power grid. When the power factor of the PM motor increae, THD of the power grid become low. Thi mean that the compenation i effective according to increaing the power factor of the PM motor. Thi reaon can be explained a follow. The large power factor increae the virtual DC link current. A a conequence the input current control range i widened a dicued in chapter IV. The validity of the analyi i proved becaue thi experimental reult agree with equation (6). Concluion Thi paper propoe a new application of the AC/AC direct converter. Reactive power, harmonic current and power interruption can be compenated by the propoed input current control method of matrix converter. In addition, thi paper decribed the range of the reactive power compenation, clearly. The propoed compenation trategy i not only applicable to conventional matrix converter, but it can alo be ued for an indirect matrix converter with a dc link. Thi tudy wa upported by Indutrial Technology Grant Program in 5 from New Energy and Indutrial Technology Development Organization (NEDO) of Japan. Reference [1] H. Akagi, New trend in active filter for power conditioning, IEEE Tran. Indutry Application, vol.3, no. 6, Nov/Dec 1996, pp [] Pichai Jintakoonwit, Hideaki Fujita, Yaufumi Akagi: Conideration of a Fully-Digital controlled Active Filter for Intallation on Power Ditribution Sytem T.IEE Japan, Vol.11-D, No.3 1 (in Japanee) [3] P. W. Wheeler, J. Rodriguez, J. C. Clare, L. Empringham: Matrix Converter: A Technology Review IEEE Tranaction on Indutry Electronic Vol. 49, No., pp74-88, [4] J. Itoh, I. Sato, H. Ohguchi, K. Sato, A. Odaka and N. Eguchi: A Control Method for the Matrix Converter Baed on Virtual AC/DC/AC Converion Uing Carrier Comparion Method, Tran. IEEJ, Vol.14-D, No.5 p457 (4) [5] Ikuya Satou, Jun-ichi Itoh, Hideki Ohguchi, Akihiro Odaka, Hironori Mine: An Improvement Method of Matrix Converter Drive Under Input Voltage Diturbance International Power Electronic Conference, Niigata, , 5 [6] Junnouke Haruna, Jun-ichi Itoh A Conideration ab the Voltage Utilization Ratio of the Matrix Converter Connected a Generator to the Input Side, Annual Conference of IEEJ, No.4-1, 7(in Japanee) [7] Jun-ichi Itoh, Koji Kato: Improvement of Commutation Method in Matrix Converter JIASC6, 1-O4-1 [8] J.Itoh, I.Sato, A.Odaka, H.Ohguchi, K.Kodachi: A Novel Approach to Practical Matrix Converter Motor drive Sytem with RB-IGBT Power Electronic Specialit Conference 4 [9] Yauhiro Tamai, Sunt Srianthumrong, Hirofumi Akagi: Comparion Between a Hybrid Shunt Active Filter and a Pure Shunt Active Filter, IEEJ Tran. IA, Vol.14, No.5, 4 EPE 7 - Aalborg ISBN : P.1