Suppression of Short-circuit Current in Halt Sequence to StopTwo-level Inverter connected to PMSM during Regeneration Mode

Transcription

1 Suppression of Short-circuit Current in Halt Seuence to StopTwo-level Inverter connecte to PMSM uring Regeneration Moe Tsuyoshi Nagano an Jun-ichi Itoh Dept. of Electrical Engineering Nagaoka University of Technology Niigata, Japan Toba Akio Fuji Electric Co., Lt. Tokyo, Japan Abstract This paper iscusses an approach to suppress the rise of the short-circuit current in a halt seuence which is name Flux-weakening Short-circuit halt seuence (FSHS). When a back-to-back system with a small capacitor is stoppe by gri faults uring regeneration, the capacitor increases rapily ue to regeneration current. FSHS stops the regeneration operation an suppresses the rise of the capacitor without a ynamic brake circuit. However, FSHS cannot suppress the rise of short-circuit current cause by the -axis current which rises uring the short-circuit moe when the regeneration current is low or PMSM with small synchronous inuctance is riven. The improve FSHS suppresses the rise of the short-circuit current in low-loa region by maintaining the -axis current aroun zero until before the moe is change to Seuence II at zero-crossing point of the current. In the experiment, it is confirme that the improve FSHS suppresses to 85% of the short-circuit current when the regeneration current is low. Keywors Permanent magent synchoronous motor, Halt seuence, Short-circuit I. INTRODUCTION Recently, power converters are reuire to reuce the volume an to improve long life time in ajustable rive systems with regeneration moe such as elevator, crane, flywheel energy storage system an so on [1-5]. A back-toback (BTB) system which consists of a PWM rectifier an an inverter is wiely use for this kin of regeneration system. In orer to achieve the improvement of long life time, a film capacitor is use as a capacitor [6]. However, the capacitor with small capacitance causes over problems of the part with gri faults. That is, when the BTB system is stoppe by the gri faults uring regeneration, the increases rapily. Conseuently, the switching evice will be broken when the capacitor becomes higher than the rating of them. Therefore, it is necessary to suppress the rise of the capacitor when system accients occur. In one of conventional methos to suppress increasing, a brake chopper circuit is connecte in parallel to the capacitor, i.e. a ynamic brake circuit [7]. When the capacitor excees the threshol, the regeneration power is consume by the resistance in the brake chopper circuit. However, the ynamic brake circuit reuires aitional switching evice an components. Several methos to reuce the volume of the ynamic brake circuit have been reporte in Ref. [8]. However, the cost an volume of the ynamic brake circuit is not esirable in the power conversion system, even it is operate only for the halt seuence uring the system failures. The authors have propose a halt seuence that shorts the terminal of the motor accoring to the motor current when the gri is cutoff uring the regeneration moe in orer to avoi the over of the capacitor, an also prevents the overcurrent [9-1]. This halt seuence, which is name Fluxweakening short-circuit halt seuence (FSHS), can be also applie to the regeneration system such as flywheel energy storage systems. In aition, it is possible to ownsize the BTB system because the ynamic brake circuit is not reuire in the fux-weakening short-circuit halt seuence. However, the fluxweakening short-circuit halt seuence cannot suppress the rise of short-circuit current cause by the -axis current which rises uring the short-circuit moe when the regeneration current is low or PMSM with small synchronous inuctance is riven. Therefore, it is necessary to suppress the rise of the shortcircuit current cause by the -axis current. This paper proposes an improve FSHS to suppress the rise current of the short-circuit in low-loa region. In the improve FSHS, the -axis current is maintaine aroun zero by applying the lagging an leaing to PMSM epening on the -axis current from the en of Seuence I to the beginning of Seuence II in orer to suppress the rise of the -axis current which causes the rise of the short-circuit current. This paper is organize as follows; Firstly, the principle of FSHS is iscusse. Secon, its problem in the low-loa region is iscusse. Next, the principle of the improve FSHS to solve

2 its problem is iscusse. Next, the operation of short-circuit current suppression seuence is confirme in simulation. Finally, the effectiveness of the short-circuit current suppression seuence is evaluate in experiments. II. FLUX-WEAKENING SHORT-CIRCUIT HALT SEQUENCE A. Principle of short-circuit halt seuence Fig. 1 shows the system configuration of the power conversion system. This system uses a two-level PWM inverter an rectifier in orer to control an Interior Permanent Magnet Synchronous Machine (IPMSM). A capacitor with small capacitance is use to absorb the switching ripples. The regeneration power P from the motor epens on the rotating spee an braking torue as (1). P T P i 3 L L (1) n e where is the rotational spee, T is torue of the PMSM, L an L are the -axis an -axis inuctance, e is the linkage magnetic flux of armature by permanent magnet, i an i are the - an -axis current, P n is the number of the pairs of poles. From (1), the negative torue will cause the increase of the if the -axis current is not controlle to zero. Thus, in orer to prevent the over at the, the -axis current shoul be zero immeiately. In [9], the flux-weakening short-circuit halt seuence prevents the over at the capacitor by shorting the terminal of motor when the relay is cutoff. The Fluxweakening short-circuit halt seuence consists of two seuences; in Seuence I, the -axis current is controlle to become zero by the reactive power without a current regulator while the is maintaine within a certain range by selecting the switching patterns between the charge moe an ischarge moe. After the -axis current becomes zero, Seuence II is implemente in orer to conuct the shortcircuit moe until the -axis current becomes zero. In a matter of fact, Seuence II alone can achieve this halt seuence an preventing the capacitor from over, since the motor currents are circulating in the inverter uring this halt seuence. However, the motor current will be increase rastically in high spee region because of the electromotive force in the motor. As a result of the short circuit conition, the large motor current causes the irreversible flux loss in the magnet of PMSM. In aition, the inverter is reuire to implement with high current rating switching evices. Therefore, Seuence I is introuce to prevent the occurrence of large current. The motor is typically esigne in a matter that the maximum current is allowe up to 2.5 to 3.7 p.u. of the rate current [11-14]. By implementing Seuence I, the maximum current in the flux-weakening short-circuit halt seuence is suppresse to less than three times of the rating current. Fig. 2 shows the relationship between the comman vector an the motor current vector in Seuence I. The instantaneous power p out becomes zero when the motor current vector crosses the inverter at the right angles as shown in Fig. 2. However, the instantaneous power p out cannot always become zero because there are only eight space i Generator Parallel-off Others PWM rectifier (STOP) Regeneration current C DC V C PWM inverter (STOP) Fig. 1. System configuration of the motor rive system connecte to the grring the motor regeneration. Charging (11) Discharging Motor current (1) (1) (11) p inv > p inv < (11) (1) Fig. 2. Relation between space an current vector of motor in Phase I. The two-level inverter has the switching patterns to charge an ischarge the capacitor. Charge Discharge Table 1. Switching pattern of Phase I. Direction of current State of switch of inverter S pu S pv S pw S nu S nv S nw ON OFF ON OFF ON OFF OFF OFF ON ON ON OFF OFF ON ON ON OFF OFF OFF ON OFF ON OFF ON ON ON OFF OFF OFF ON ON OFF OFF OFF ON ON OFF OFF ON ON ON OFF OFF ON ON ON OFF OFF OFF ON OFF ON OFF ON ON ON OFF OFF OFF ON ON OFF OFF OFF ON ON ON OFF ON OFF ON OFF vectors incluing zero s in two-level inverter. The two-level inverter has the switching patterns to charge an ischarge the capacitor. Therefore, in Seuence I, the switching pattern to maintain the capacitor is selecte accoring the current polarity while the instantaneous power p out is arrange to become zero by charging an ischarging the capacitor. Accoringly, the -axis current achieves zero at the very short time because the active current is change into a reactive current. Table 1 illustrate the switching table that is implemente in the inverter that is epening on the capacitor in subjects to the charge an ischarge moes. The comman vector becomes a lag of 3-9 egrees with respect to the motor current vector uring the ischarge moe. Similarly, the comman vector becomes the lea of 9-15 egrees with respects to the motor current vector uring the charge moe. As a result, the comman vector becomes the lagging phase of 6-12 egree with respects to the motor current vector. Seuence I operation ens when the -axis current becomes zero. PM

3 S up S vp S wp C c S un S vn S wn (a) State 1 (short moe) S up S vp S wp IPMSM Start Relay is open Open of relay Detecting the irection of current Short moe (All upper/lower arms is shut own) is etecte? Seuence 2 Single phase moe (correspon switch arm is open) C c IPMSM S un S vn S wn (b) State 2 (single-phase moe) i = Generation of switching pattern is etecte? All gate off moe S up S vp S wp C c S un S vn S wn IPMSM (c) State 3 (all gate-off moe) Fig. 3. Operational moes in Phase II. Phase II avois the regeneration current flowing into capacitor to prevent its from increase. In aition, Phase II interrupts the three-phase current. Fig. 3 shows the short circuit operation moe that intens to prevent the capacitor from rising by circulating the regenerating current insie the inverter. In Seuence II, the switching states create a short conition to prevent the from increasing. The following shows the switching states of the inverter, first, all of upper or lower sie arms of the inverter are short-circuite as shown in Fig. 3(a). This switching state can avoi the motor current flows into the capacitor because it is a short-circuit conition. Then, when the zero-crossing current is etecte, the correspone switch arm is opene seuentially as shown in Fig. 3(b). Thus, the inverter becomes a conition of a single phase operation. Finally, the remaining two switching arms are opene when the zero-crossing current are etecte, respectively as shown in Fig. 3(c). Therefore, the suppression of the circulating current an the rising of the can be achieve. Fig. 4 shows the operation flow chart in Seuence I. Once the relay is opene, the current polarity is recore then the - axis current signal is comparing in the system to ecie the operation between Seuence I an Seuence II. Then, the - axis current is change into reactive current by changing the s in the inverter. Fig. 5 shows the experimental waveform of the output current an the DC link capacitor which are obtaine by gate interruption. In the experiment, a relay is opene an all switches are turne off by interrupting the gate signal at the same time. The DC link capacitor is increase by approximately 14 V after the relay is opene an all switches are turne off. Fig. 6 shows the experimental result of the output current an the capacitor which are obtaine by the V c >V upper_limit V c <V lower_limit Output of signal flux-weakening short-circuit halt seuence. In Fig. 6, once the relay is opene at 4 ms. At approximately 6 ms, the -axis current reaches zero, then Seuence II begins to be operate. From the result, the output current can be suppresse to less than 2.5 p.u of the rate current by applying the fluxweakening short-circuit halt seuence. In aition, the fluctuation of the capacitor is suppresse to less than.7 p.u. (= 22V) of the rate, which is sufficiently small. En charge moe ischarge moe V upper_limit : upper limit V lower_limit : lower limit Fig. 4. Operation flow chart of Short-circuit halt seuence. E DC 5V/iv 2,, 4A/iv i, i 2p.u./iv Gate interruption Dynamic braking i i t 1 t 2 14V Seuence 1 2ms/iv 2ms/iv 2ms/iv Fig. 11. Experimental results when all gate signals are interrupte as the halt seuence. the capacitor rises by approximately 14 V after the relay is opene an all switches are turne off.

4 Phase 1 Phase 2 Seuence 1 Seuence 2 E DC 2 5V/iv,, 4A/iv i, i 2p.u./iv Flag for etecting the -axis current i i 22V t 1 t 2 t p.u. 2ms/iv B. Problem of flux-weakening short-circuit halt seuence Fig. 7 shows the simulation result when the flux-weakening short-circuit halt seuence cuts low regeneration current (.5 p.u.) off. In Fig. 7, the -axis current increase rastically uring short-circuit moe of Seuence II. The -axis euation, when the seuence is change to Seuence 2, is shown in (2). 8V 2ms/iv Detecting the -axis current 2ms/iv Fig. 6. Experimental result when the system is applie with the fluxweakening short-circuit halt seuence. i reaches zero, then Phase II begins to be operate. The output current can be suppresse to less than 2.5 p.u of the rate current. Table 3. Simulation conitions. Rate motor power 3 kw Rate current 16.9 A rms Rate spee 72 rpm Number of poles 12 Wining resistance -axis inuctance -axis inuctance.127 W.389 mh 5.56 mh Back-electromotive force 58 V Rate DC 2 V Threshol DC over- 33 V,, [p.u.] i, i [p.u.] E DC [V] i i State 1 State 2 Fig. 7. Simulation result in PMSM which has low inuctance. If the high back electromotive force, the cross term of the -axis current an the - an - axis inuctance, the -axis current flows rastically in the negative irection uring short-circuit moe. (11) Discharging (11) (1) (11) (1) Discharging (1) (11) (1) p inv> p inv< (11) i L L i e (2) re t te that, the rop cause by the resistance is neglecte because it is very small. As shown in (2), the -axis current variation of negative irection is ecie by back electromotive force (back-emf), the cross term of the -axis current an the - an - axis inuctance. In Fig. 7, the -axis current flows in the negative irection uring short-circuit moe. When the regeneration current is low in high spee region or PMSM with low inuctance is riven, the -axis current flows rastically in the negative irection uring the short-circuit moe of Seuence II in Fig. 7. Accoringly, the short-circuit current which is more than 2.4 times of the regeneration current flows because the -axis current to cancel the back-emf is insufficient. In orer to prevent the rise of the -axis current, it is necessary to shorten the perio of the shortcircuit moe i.e. the perio between the start of the short circuit an the first current zero-crossing point. III. IMPROVED SHORT-CIRCUIT HALT SEQUENCE In the improve the flux-weakening short-circuit halt seuence, the the short-circuit suppression seuence maintains the -axis current of zero after the -axis current reaches zero in Seuence I. After that, the seuence is change to Seuence II at first current zero-crossing point. Fig. 8 shows the vector iagrams of lagging an leaing moe in the short-circuit current suppression seuence. p inv> p inv< (1) Charging vector (11) (a)lagging moe (i <) Charging (1) (b)leaing moe (i >) Fig. 8. Vector iagrams of lagging an leaing. When the - axis current is negative, the inverter applies the lagging to PMSM. On the other han, when the -axis current is positive, the inverter applies the leaing to PMSM uring the short-circuit current suppression seuence

5 When the two-level inverter applies the lagging to PMSM, the -axis current is rotate in the anticlockwise irection. When the inverter applies the leaing to PMSM, the -axis current is rotate in the clockwise irection. The short-circuit current suppression seuence maintains the -axis current aroun zero by applying the lagging an leaing to PMSM epening on the -axis current. Fig. 9 shows the flowchart of the improve short-circuit halt seuence with the short-circuit suppression seuence. The green line in Fig. 8 is the short-circuit current suppression seuence. Fig. 1 shows the simulation result when the improve FSHS applie with the short-circuit current suppression seuence acts to stop the inverter. After the -axis current reaches zero in Seuence I, the short-circuit current suppression seuence maintain the -axis current aroun zero until just before V-phase current crosses zero because the inverter applies the lagging an leaing to PMSM epening on the -axis current irection. From Fig. 1, the -axis current is maintaine aroun zero by applying the lagging an leaing epening on the -axis current irection. After that, the inverter short-circuits PMSM. IV. EXPERIMENTAL RESLUTS Fig. 11 shows the experimental result when FSHS (without the short-circuit current suppression seuence) stops the inverter. In Fig. 6, -axis current flows in negative irection. When the regeneration current is low in high spee region or PMSM with low inuctance is riven, the -axis current flows rastically in negative irection uring short-circuit moe of Seuence II in Fig. 11. As a result, the short-circuit current which is more than 5 times of the regeneration current flows because the -axis current to cancel the back-emf is insufficient. Fig. 12 shows the experimental result when the improve FSHS (with the short-circuit current suppression seuence) stops the inverter. After the -axis current reaches zero in Seuence I, the short-circuit current suppression seuence maintains the -axis current aroun zero until just before W- phase current crosses zero because the inverter applies the lagging an leaing to PMSM epening on the -axis current irection. After that, the inverter short-circuits PMSM. The fluctuation of the capacitor uring the charge an ischarge by the lagging an leaing is suppresse within 5V. In Fig. 12, the shortcircuit current which is more than four times the regeneration current flows. On the other han, the short-circuit current is suppresse to 85% of the shirt-circuit current in Fig. 11 because the -axis current is maintain aroun zero until just before the W-phase current reaches zero. As a result, it is confirm that the improve FSHS with the suppression seuence stops the regeneration operation an suppress the rise of the capacitor an the short-circuit current without the ynamic brake system when the regeneration current is low. Start Relay is open Open of relay Detecting the irection of current i = i > V c>v upper_limit V c<v lower_limit Output of signal etection (Lagging volage) Charge moe (Lag) (Leaing ) V c>v upper_limit V c<v lower_limit Discharge moe (Lag) Short moe (All upper/lower arms is shut own) Single phase moe (correspon switch arm is open) Charge moe (Lea) V upper_limit : upper limit V lower_limit : lower limit etection etection All gate off moe En Seuence 2 Discharge moe (Lea) Seuence 1 Fig. 9. Flowchart of the improve halt seuence with the short-circuit suppression seuence.,, [p.u.] i, i [p.u.] E DC [V] Short-circuit current suppression seuence Seuence 1 Seuence 2 i i Fig. 1. Simulation result when the short-circuit halt seuence with the suppression seuence is applie in PMSM which has low inuctance.

6 V. CONCLUSION This paper propose the improve FSHS to suppress the rise current of the short-circuit in low-loa region. The improve FSHS stops the regeneration operation an suppresses the rise of the capacitor without the ynamic brake circuit as well as FSHS. Moreover, the improve FSHS suppresses the rise current of the short-circuit in low-loa region by maintaining the -axis current aroun zero with the leaing an lagging until before the moe is change to Seuence II at zero-crossing point of the motor current. In the experiment, it is confirme that the improve FSHS with the suppression seuence suppresses to 85% of the short-circuit current when the regeneration current is low. In aition, the rise in the capacitor is maintaine within 5V. In future work, the improve FSHS will be constructe on the harware in terms of the reliability. REFERENCES [1] M.Uno, K.Tanaka: Accelerate Charge-Discharge Cycling Test an Cycle Life Preiction Moel for Supercapacitors in Alternative Battery Applications IEEE Trans on inustrial electronics, Vol.6,.6, pp (213) [2] Jime nez, H., Calleja, H., Clauio, A.: The Lifetime/Volume Ratio as an Inex to Assess the Reliability of Power Converters Energy Conversion Congress an Exposition (ECCE), pp (21) [3] Ryoh Saitoh, Yuki Makaino, an Takumi Ohnuma, "Aaptive Signal Injection Metho Combine with EEMF-base Position Sensorless Control of IPMSM Drives", IEEJ Journal of Inustry Applications, Vol.4,.4, pp (215) [4] Toshiki Suzuki, Masaru Hasegawa, Mutuwo Tomita, an Shinji Doki, "Initial Position Estimation for IPMSMs Using Comb Filters an Effects on Various Injecte Signal Freuencies", IEEJ Journal of Inustry Applications, Vol.4,.3, pp (215) [5] Koai Abe, Hitoshi Haga, Kiyoshi Ohishi, an Toshio Hiraie, "Harmonics Reuction Control for the Input Current of Electrolytic Capacitor-less High-Power-Factor Inverter for IPMSM", IEEJ Journal of Inustry Applications, Vol.4,.3, pp (215) [6] Jorge O. Estima an Antonio J. Marues Caroso: "A Time- Coorination Approach for Regenerative Energy Saving in Multiaxis Motor-Drive Systems", IEEE Transactions on Power Electronics Vol. 27,. 2, pp (212) [7] Jorge O. Estima an Antonio J. Marues Caroso: " Efficiency Analysis of Drive Train Topologies Applie to Electric/Hybri Vehicles", IEEE Transactions on Vehicular Technology Vol. 61,. 3, pp , (212) [8] W. Aoki, G.T.Chiang, J. Itoh, A. Toba: " Suppression Metho of Rising DC Voltage for the Halt Seuence of an Inverter in the Motor Regeneration ", Energy Conversion Congress an Expo (ECCE), pp (213) [9] T. Nagano, K. Orikawa, J. Itoh, A. Toba: "Simplification of Halt Seuence to Suppress Increase of Voltage uring Motor Regeneration", 9th International Conference on Power Electronics, pp (215) [1] G. Pellegrino, A. Vagati, P. Guglielmi, an B. Boazzo: Performance Comparison Between Surface-Mounte an Interior PM Motor Drives for Electric Vehicle Application IEEE Transactions on Inustrial Electronics, Vol. 59,. 2, pp , (212) [11] A. Nishio, M. Hirano, Y. Kato, T. Irie, T. Baba: Development of Small Size, Light Weight an High Power IPM Motor for Electric Vehicle Mitsubishi Heavy Inustries, Lt. Technical Review Vol.4.5, (23) Table 4. Experimental conitions. Rate motor power Rate motor Rate current Rate spee Number of poles Wining resistance -axis inuctance -axis inuctance Back-electromotive force Rate DC Threshol DC over- E DC [5 V/iv],, [1 A/iv] 2 iu i i, i [.5 p.u./iv] i 5.5 kw 2 V rms 2 A rms 15 rpm 6 poles.215 W 4.3 mh 1.2 mh 164 V 2 V 33 V Seuence 1 Seuence 2 15V 36A (Rise : 41%) 2 [ms/iv] t 1 t 2 t 3 Fig. 11. Experimental result with the short-circuit halt seuence without the flux-weakening short-circuit current suppression seuence. E DC [5 V/iv],, [1 A/iv] i, i [.5 p.u./iv] 2 Short-circuit current suppression seuence Seuence 1 Seuence 2 i i 5V 3A (Rise : 325%) t 1 t 2 t 3 t 4 2 [ms/iv] Fig. 12. Experimental result with the improve short-circuit halt seuence with the short-circuit current suppression seuence.