Minimization of EMC Filter for Interconnection Inverter by High Switching Frequency

Transcription

1 Minimization of EMC Filter for Interconnection Inverter by High Switching Frequency Takuya Kataoka, Masakazu Kato Nagaoka University of Technology Nagaoka, Niigata,Japan Jun-ichi Itoh Nagaoka University of Technology Nagaoka, Niigata,Japan Abstract This paper proposes a esign metho of a commonmoe current feeback type EMC filter in an interconnection system. First, the relationship between the switching frequency of the PWM inverter, the common-moe feeback current an the volume of the filter reactor is theoretically estimate. Moreover, the switching frequency an the current capacity of switching evices which are necessary in orer to estimate the volume of the EMC filter is etermine by this relationship. Secon, the inverter loss is calculate base on the experimental result. After that, the relationship between the cut-off frequency of the EMC filter an volume of the cooling system is calculate. As a result, the minimum total volume of the EMC filter estimation an the esign metho of the cooling system are clarifie. From the experimental result, the esign point of the maximum power ensity is clarifie. Moreover, the conuction noise of the switching frequency component suppresses below the prescribe by CISPR. Keywors EMC Filter; High-Frequency Switching; Wie Ban-Gap evice I. INTRODUCTION Recently, attentions are focuse on miniaturization of the power conversion for interconnection system. In particular, it is necessary to reuce volume of an EMC filter because the EMC filter accounts for a consierable proportion of the power conversion system. The EMC filter comprise of a normal-moe filter an a common-moe filter. Furthermore, by increasing the switching frequency, passive components in the normal-moe filter are ownsize an consequently the volume is reuce. Besies, in orer to achieve a high frequency switching operation, the inverter requires fastswitching evices to be use because slow-switching evices cause a large switching loss an a ea time error. Thereby, the switching evice using a wie ban-gap semiconuctor such as gallium nitrie (GaN) or silicon carbie (SiC) is use to the PWM inverter, instea of the silicon base switching evice [-3]. However, the performance an the miniaturization effect have not been iscusse in previous stuies when wie ban-gap semiconuctors are applie to the PWM inverter for an interconnection system. Moreover, when the switching loss is increase by consiering a high switching frequency, the volume of a cooling system becomes large. Therefore, there is a trae-off relationship between the EMC filter volume an cooling system volume. In orer to solve this problem, the esign metho for minimization by using Pareto front curve has been iscusse [4]. On the other han, when the switching frequency is increase, electromagnetic noise is also increase. Therefore, a common-moe filter increases in volume in orer to avoi incorrect operation of peripheral equipment by the conuction noise [5]. Furthermore, in orer to solve this problem, the common-moe current feeback type EMC filter has been propose [6-7]. In the past work, the normal-moe filter an the common-moe filter for PWM inverters are iscusse [6]. Ref.[6] consiers the esign metho of the normal-moe an common-moe filters an the effect of the harmonics suppression by experiments. Moreover, Ref.[6] clarify a esign metho of the common-moe reactor. The commonmoe current which flows between the PWM inverter an the EMC filter becomes small an to be negligible ue to increase the inuctance of the filter reactor. When the switching frequency is larger than the cut-off frequency, the commonmoe current is etermine by the inuctance of the filter reactor. In aition, the volume of the filter reactor accounts for a consierable proportion of the volume of the EMC filter because the energy ensity of the filter inuctor is lower than one of the filter capacitor. Thus, it is important to consier the relationship between the common-moe current an the filter reactor from a viewpoint of a miniaturization. On the other han, etail analyzes of a LC filter an simple esign proceures along with a esign example are presente in [7]. Furthermore, Ref.[7] have analyze a single phase equivalent circuit of the LC filter. However, common-moe equivalent circuit an the effect of the power loss of the inverter by the filter current have not been iscusse. Moreover, the miniaturization effect an the effect of reucing conuction noise have not been iscusse in previous stuies. In this paper, a esign metho for miniaturization of the common-moe current feeback type EMC filter with high switching frequency is propose. First, the switching frequency an the current capacity of switching evices which are necessary in orer to estimate the volume of the EMC filter are etermine. These factors are etermine by consiering ) the current flowing between the inverter an the EMC filter, an 2) the relationship between the switching frequency an the volume of the filter inuctor. Secon, the inuctance of the filter inuctor is varie, an the relationship between the volume of the EMC filter an the cooling system

2 is consiere. Next, the minimum value of the total volume of the EMC filter an the cooling system is erive ue to the trae-off relationship between the volume of the filter inuctor an the inverter losses. Finally, experiments with a prototype of the GaN-FET inverter are conucte to verify the valiity of the propose esign metho. As a result, the esign point of the maximum power ensity is clarifie. Thus the valiity of the propose esign metho is confirme. V in GaN-FET Inverter LC filter gri II. SYSTEM CONFIGURATION Fig. shows the circuit configuration of an Three-phase inverter with the common-moe current feeback type EMC filter. The natural point of a Y-type capacitor in the commonmoe current feeback-type EMC filter is connecte to the natural point of the DC link bus because it is possible to increase the allowable current i c in comparison with connecting to the groun case. In this paper, the current i c flowing between the inverter an the EMC filter is calle as the filter current. Furthermore, the volume of the filter inuctor accounts for the majority of the EMC filter volume because the energy ensity of the filter inuctor is lower than one of the filter capacitor. Hence, the filter inuctor volume is iscusse with a special emphasis in this paper. III. ESTIMATION OF VOLUME AND POWER LOSS A. Volume of reactor In this paper, the reactor volume is focuse because the energy ensity of the filter inuctor is lower than one of the filter capacitor. In aition, the reactor of the EMC filter is esigne by the Area prouct concept using a winow area an a cross-sectional area [8]. Then volume of the reactor is given by () W vol L K v () Ku Bm J where K v is the constant value epening on the shape of a use reactor core. W is the maximum power of the reactor. K u is the occupancy of the winow area of core. B m is the maximum flux ensity of the core. J is the current ensity of the wire which is use to the reactor. From (), the volume of reactor is proportional to the power of 3/4 of maximum energy of the reactor. B. Power loss of Inverter an Volume of Cooling system A power loss of the inverter is separate into the conuction loss an the switching loss of the switching evices. Generally, the conuction loss of the switching evices is calculate by the on-state resistance R on an the switching loss is calculate by turn-on loss P on an turn-off loss P off accoring to the atasheet. In this paper, loss analysis is base on the experimental results of the simplify estimation of volume of the cooling system. Table shows the circuit parameters on experiment. The GaN-FETs (V DSmax = 6 V, I D_max = A) are use for the PWM inverter in orer to achieve the 3-kHz switching frequency. The PWM signals are generate by comparing the output voltage comman with the triangle wave. Fig.2 shows the measure power loss of the GaN-FET inverter in Fig.. The conuction loss is given by y-intercept of approximation formula b because it is not relate to the switching frequency. On the other han, the switching loss of PWM inverter is given by slope of the approximation formula. As a result, the conuction loss an the switching loss on arbitrary output power are calculate by (2) an (3). P SW VDC _ calc I out _ calc afsw (2) V I DC _ test out _ test L C y Fig.. Three-phase inverter system with the commonmoe current feeback type EMC filter. Table. Conitions of Experimental for measurement the power loss of GaN-FET inverter with RL loa. Input voltage V in 4 V Moulation ratio Output frequency f out 2 Hz Loa impeance Z loa 5 Power factor cos.99 Ambient temperature T a 25 Dea time T ns Total loss Ptotal [W] Carrier frequency f sw [khz] i c P total =.47-5 f sw Fig. 2. Measurement result of relationship between switching frequency an power loss of GaN-FET inverter.

3 2 I out _ calc P CON b (3) I out _ test where I out_calc is the output current on arbitrary output power, I out_test is the output current when the power loss is measure in experiment, V DC_calc is the DC link voltage on arbitrary output power, an V DC_test is the DC link voltage when the power loss is measure in experiment. Thus, the power loss is given by the following equation. P loss P P (4) SW CON The switching evices that use for the PWM inverter is heate by the loss of the conuction loss an the switching loss. The rising in temperature causes a breaking the switching evice. Hence, the PWM inverter requires a cooling system such as heatsinks an fans. In this paper, consieration of the cooling system is the heatsinks only. Generally, a thermal resistance is use in orer to evaluate the cooling system performance. However, it is not enough because the evaluation base on thermal resistance oes not consier the volume of the cooling system. In this paper, CSPI (Cooling System Performance Inex), which is a reciprocal of the prouct of the volume an the thermal resistance, is introuce for the volume of the cooling system estimation. The CSPI inicates the cooling performance per unit volume of the cooling system. Thereby, it means that a high CSPI shows a high performance cooling system. Therefore, in orer to ownsize a cooling system, PWM inverter nees a cooling system which has high CSPI. The volume of the cooling system is given by the relationship between the power loss an the rise in temperature by the following equation [9]. vol cooling R th CSPI Ploss T T CSPI where R th is the thermal resistance of the cooling system, T j is the junction temperature of switching evices, T a is the ambient temperature, P loss is the power loss of the switching evices that use for PWM inverter. IV. DESIGN CONSIDERATION OF EMC FILTER Fig. 3 shows the part of common-moe equivalent circuit of GaN-FET inverter an the EMC filter in Fig.. The filter current i c flows between the GaN-FET inverter an the EMC filter. The filter current i c an cut-off frequency of the EMC filter are given by the following equations. 3C y vinv 2 2 L / 33 C ( c)( L / 3) y j a (2) j ic (5) 2 c (6) L C y whereis the switching angular frequency, c is the cut-off angular frequency of the EMC filter, L is the Table 2. Simulation an calculation parameters. Input voltage V in 282 V Output voltage v out 2 V Output frequency f out 5 Hz Loa resister R loa Loa reactor L loa mh Switching frequency f sw 6 khz Moulation Ratio CSPI 3 Ambient temperature T a 2 C Junction temperature T j C Slope in Fig.2 a.47-5 y-intercept in Fig.2 b 4.67 To input inuctance of the filter reactor an v inv is the common-moe voltage of the inverter. When the switching frequency is much larger than the cutoff frequency of the EMC filter, ( c ) can be approximate to. Therefore, the changes of the filter current ue to the effect of resonant is negligibly small. Hence, the approximation formula of the film current i c is given by the following equation. ic vinv (7) ( L / 3) v inv L /3 3C y Fig. 4 shows the relationship between the filter current an the volume of the filter inuctor from (7), when the switching frequency is varie. Table 2 shows the calculation conition for the esigne EMC filter. In orer to eliminate the effect of resonant of the EMC filter, the cut-off frequency is set as / of the switching frequency. As a result, when the switching frequency is high, the volume of the filter inuctor is small. Moreover, the relationship between the filter current an the filter reactor volume is a trae-off relationship. Therefore, the switching frequency an power loss of the switching evices are necessary in orer to estimate the volume of the EMC filter an it is etermine by this relationship. i c To output Fig. 3. Interconnection system with the common-moe current feeback type EMC filter. The filter current is calculate by use of the filter reactor L, the filter capacitor C y an the common-moe voltage v inv.

4 Fig. 5 shows the relationship between the cut-off frequency of the EMC filter an the power loss of the GaNinverter, when the filter capacitor is nf, an the switching frequency is 6 khz. Fig. 5 is base on the simulation results by referring to (3) an (4). When the cut-off frequency increases, the filter current becomes large ue to the ecreasing of the inuctance of the filter reactor; therefore, the power loss of the inverter becomes large. Fig. 6 shows the relationship between the cut-off frequency of the EMC filter an total volume of the filter inuctor an the cooling system, when the switching frequency is 6 khz. In this paper, the total volume is sum of the volume of the heatsink an the filter reactor. When the cut-off frequency ecreases, the inuctance of the filter inuctor becomes large, an the volume of the filter inuctor also becomes large. On the other han, when the cut-off frequency increases, the filter current becomes small, whereas the volume of the cooling system becomes large ue to the increasing of the inverter losses. As a result, the relationship between the cut-off frequency an total volume is establishe as a ownwar convex function. Therefore, the minimum value of total volume is clarifie. V. EXPERIMENTAL RESULTS Fig. 7 shows the relationship between the cut-off frequency of the EMC filter an total volume at 3-kHz switching frequency. In the simulation, the EMC filter is esigne base on switching frequency of 6-kHz. However, switching frequency is 3-kHz in experiment. Therefore, the EMC filter nees to be reesigne. As a result, the relationship between the cut-off frequency an total volume is establishe as a ownwar convex function an similar to Fig. 6. Therefore, the minimum value of total volume is clarifie. At this point, total volume can be estimate at minimum point when the percentage of an impeance of the filter inuctor %Z is.8% as the cut-off frequency is 5-kHz. Fig. 8 shows the circuit iagram for conucting experiment. From the experiment setup, in orer to simplify experiment, the loa resister is use, instea of the gri. Furthermore, in orer to reuce the conuction noise, the EMC filter is connecte to the earth via groune capacitor C yg. Moreover, the RL loa is connecte to the earth via capacitor C s. The capacitor C s imitates stray capacitance. Table 3 shows the experimental conition. In the experiment, the GaN-FET inverter is operate at 3-kHz switching frequency. The inverter is controlle by an openloop control system. The conuction noise which be generate by control circuit is eucte to evaluate the conuction noise by main circuit. Fig. 9 shows output waveforms of the inverter. The loa current has low istorte sinusoial waveform. The reactor current has large ripple current comparing to the loa current because the reactor current is compose from the loa current an the filter current. When the filter current is large, the reactor current ripple become large; thereby, the inverter loss an conuction loss of the filter reactor is increase. The maximum value of the filter current is 3.32A in the experiment. However, in the simulation, the maximum value of the filter Volume of filter reactor[p.u.] [p.u.]=.337m 3 (5kHz,i c =.5p.u.) 4.3A(rate current) Smaller an Lower loss khz 5kHz khz 3kHz 6kHz Common-moe filter current i c [p.u.] Fig. 4. Relationship between the filter current i c an the volume of the filter inuctor, when the switching frequency is varie. Power Loss[%] i c =.2 p.u. i c =.38 p.u. i c =.42 p.u. [p.u.]=4.33a rms,c y =nf Conuction loss Switching loss Rate power of inverter:.5kw=% L :small Cut-off frequency [khz] Fig. 5. Relationship between the cut-off frequency of the EMC filter an a power loss of the inverter. Total volume an Heatsink volume [m 3 ] Total volume Volume of heatsink Volume of reactor Cut-off frequency [khz] Fig. 6. Relationship among the cut-off frequency of the EMC filter an volume of reactor, heatsink an total. The relationship is establishe as a ownwar convex. Therefore, the minimum value of total volume is clarifie. current is 2.9A. The ifference between experiment an simulation has occurre. The possible cause of the ifference is the effect of the groune capacitor. However, this paper oes not consier this matter in etails. Fig. shows the measurement result of the relationship between the cut-off frequency an the efficiency. In this case, volume of reactor[m 3 ]

5 the capacitance of the filter capacitor is kept at a constant value. Therefore, the cut-off frequency is varies by changing the inuctance of the filter inuctor. The efficiency inclues total efficiencies of both the inverter an the EMC filter an it measure by the power meter of Yokogawa, WT8. When the filter inuctor is small, the loss of the inverter becomes large ue to the increasing of the filter current i c. In contrast, when the filter inuctor is large, the core loss of the filter inuctor becomes large. As a result, the efficiency can be represente into an upwar convex function in experiment. Therefore, the maximum point of efficiency is clarifie. Hence, the efficiency is clarifie at the maximum point when the inuctance of the filter inuctor is 5-H as the cut-off frequency is 49-kHz. Fig. shows the Pareto front curve of the relationship between power ensity an efficiency. The total volume is calculate as sum of volumes of the EMC filter an the cooling system. In particular, the volume of the inverter is calculate from the measurement results of inverter losses by using CSPI. The volume of the filter reactor is calculate from the inuctance of the filter reactor which using is experiment by (). From these results, the maximum point of power ensity of the interconnection system with the common-moe current feeback-type EMC filter is clarifie. At this point, the power ensity can be clarifie at the maximum point when the inuctance of the filter inuctor is 5-H as the cut-off frequency is 49-kHz. Fig. 2 shows the measurement result of the conuction noise of the prototype circuit of the inverter with the commonmoe current feeback-type EMC filter. As a result, the conuction noise of the funamental component of the switching frequency an the high-frequency components are less than 2MHz is generate by the main circuit an it mostly suppresse accoring to the regulation value of CISPR. In orer to suppress fully accoring to the regulation, the revising of cut-off frequency is neee. However, the conuction noise in the range of more than 2MHz has exceee the limit of CISPR. This problem occurs ue to the evice mounting such as a stray capacitor. However, this problem is not consiere in this paper. Base on these results, the valiity of the propose esign metho for the common-moe current feeback-type EMC filter is confirme. VI. CONCLUSION This paper proposes a esign metho of the common-moe current feeback type EMC filter in an interconnection system. In this paper, the relationship between the cut-off frequency of the EMC filter an the total volume of the GaN-FET inverter an the EMC filter is iscusse base on a simulation an an experiment results. As a result, the esign point of the minimum volume of the sum of the EMC filter an the cooling system is clarifie. In the experiment, the esigne point of the maximum power ensity is clarifie. In aition, the loa current has low istorte sinusoial waveform. Furthermore, the conuction noise of the funamental component of the switching frequency an the high-frequency components are less than 2MHz is generate by the main circuit an it suppresse accoring to the regulation value of CISPR by esigne EMC filter. These results, the propose esign Total volume [m 3 ] Switching frequency : 3 khz Output power :.5 kw C y : nf(%y =.6%) L = H (%Z =.8%) f c = 5 khz Cut-off frequency f c [khz] Fig.7. Relationship between the cut-off frequency of the EMC filter an total volume. 2V 5Hz LISN Carirrer 3kHz Controll V ref circuit 6 LC filter Dioe rectifier GaN-FET inverter heatsink i c C y RL loa =nf C yg =4.7nF Fig. 8. Circuit iagram for the conuction noise evaluation. Table 3. Experimental conitions. Input voltage v in 2 V Input frequency 5 Hz Moulation Ratio.866 Loa resister R loa 75 Loa reactor L loa mh Switching frequency f sw 3 khz Moulation Ratio Dea time T ns U-phase Loa current (Green) [A] U-phase filter reactor current (blue)[a] 3.32[A] Filter current [A] C s =nf Inverter output voltage(line to line) [V] 5[V/iv] 2[A/iv] 2[A/iv] 4[ms/iv] Fig. 9. Output waveform of the GaN-FET inverter at 3- khz switching frequency. The loa current obtains low istorte sinusoial waveform.

6 metho achieves minimization of interconnection system which inclue the EMC filter. In future work, the effect of suppression of conuction noise will be improvement. REFERENCES [] M. Roriguez, Y. Zhang an D. Maksimovic : High-Frequency PWM Buck Converters Using GaN-on-SiC HEMTs, IEEE Transactions on Power Electronics, Vol.29, No.5, pp (24) [2] T. Funaki, J. C. Bala, J. Junghans, A. S. Kashyap, H. A. Mantooth, F. Barlow, T. Kimoto an T. Hikihara : Power Conversion With SiC Devices at Extremely High Ambient Temperatures, IEEE Transactions on Power Electronics, Vol.22, No.4, pp (27) [3] F. Xu, T. J. Han, D. Jiang, L. M. Tolbert, F. Wan, J. Nagashima, S. J. Kim an F. Barlow : Development of a SiC JFET-Base Six-Pack Power Moule for a Fully Integrate Inverter, IEEE Transactions on Power Electronics, Vol.23, No.3, pp (23) [4] J. Itoh, T. Araki, K. Orikawa: "Experimental Verification of an EMC Filter Use for PWM Inverter with Wie Ban-Gap Devices", The 24 International Power Electronics Conference, No. 2J3-4, pp (24) [5] J. Itoh, T. Araki: "Volume Evaluation of a PWM Inverter with Wie Ban-Gap Devices for Motor Drive System", 5th IEEE Annual International Energy Conversion Congress an Exhibition, Vol., No , pp (23) [6] H.Hasegawa, T.Doumoto, H.Akagi, A Three-phase Voltage-source PWM Inverter System Characterize by Sinusoial Output Voltage with Neither Common-moe Voltage nor Normal-moe Voltage Design an Performance of a Passive EMI filter-, IEEJ Trans. Vol.22-D, No.8, pp (22) [7] C.Vastrup, X.Wang, F.Blaabjerg LC Filter Design for Wie Ban Gap Device Base Ajustable Spee Drives, IEEE PEAC, pp (24) [8] Wm T Mclyman: Transformer an inuctor esign hanbook Marcel Dekker Inc.(24) [9] U. Drofenik et al.:"theoretical Converter Power Density Limits for Force Convection Cooling", Proc. Int. PCIM Eur., pp (25) Efficiency [%] i c:small L :large Filter loss large f c = 3 khz L = 26 H f c = 39 khz L = 5 H Carrier frequency : 3 khz Output power : 22 W i c:large L :small Inverter loss large f c = 46 khz L = H Cut-off frequency f c [khz] Fig.. Measurement result of the relationship between the cut-off frequency an the efficiency. In conition, the filter capacitor is kept at constant value, whereas the filter inuctor is varie. The efficiency is represente into an upwar convex function. Therefore, a maximum point of efficiency is clarifie. Efficiency [%] Carrier frequency : 3 khz Output power : 22 W C y : nf f c = 39 khz L = 5 H (.4 m 3 ) High power ensity f c = 3 khz L = 26 H (.4 m 3 ) f c = 46 khz L = H (.24 m 3 ) Power ensity[kw/m 3 ] Fig.. Calculation result of the Pare to front curve of the relationship between the power ensity an the efficiency. Conuction noise[bv] CISPR Class.A (QP) (f sw ) frequency[mhz] Fig. 2. Measurement result of the conuction noise of the prototype circuit with propose EMC filter.