- Email: [email protected]
Interference source analysis and EMC design for All-SiC power module in EV charger
Microelectronics Reliability xxx (xxxx) xxxx
Contents lists available at ScienceDirect
Microelectronics Reliability journal homepage: www.elsevier.com/locate/microrel
Interference source analysis and EMC design for All-SiC power module in EV charger Zhijun Lia, Tiancong Shaoa, , Trillion Q. Zhenga, Hong Lia, Bo Huangb ⁎
a b
School of Electrical Engineering, Beijing Jiaotong University, Beijing, China Global Power Technology Co., Ltd., Beijing, China
ABSTRACT
Silicon carbide (SiC) power devices suitable for high-frequency, high-power density and high-temperature applications, and thus gain a broad prospect in the electric vehicle (EV) charger area. However, the high-frequency switching of SiC devices under high-power application challenges the electromagnetic compatibility (EMC) of the power module. Noises generated from high-frequency switching need to be analyzed and suppressed. This paper introduces the configuration of a 30 kW AllSiC power module designed for EV charger, then reveals the interference source analysis. Based on the interference analysis, a double π electromagnetic interference (EMI) filter is added, intended for this All-SiC power module. Experimental results show that the All-SiC power module achieves excellent efficiency over a wide power range. Meanwhile, the conducted EMI measurement is reported to verify the effectiveness of EMC design.
1. Introduction Electric vehicles (EVs) release no tailpipe air pollutants at the place where they are operated [1]. Many governments offer incentives to promote the use of electric vehicles, with the goals of reducing air pollution and oil consumption [2]. In China, The annual EV production and sales are planned to be 200 million with total ownership of EVs expected to reach 500 million by 2020, in the meantime, it was planned to construct 4.3 million charging points and build 2397 public charging stations before 2020 [3]. As the growing market demand for EVs, the research for silicon carbide (SiC) power devices in the power module of EV chargers gains great attention [4–7]. Owing to the intrinsic material advantages of SiC over silicon (Si), SiC power devices can operate at a higher voltage, higher switching frequency, and higher temperature [8–10]. Hence SiC power devices are very suitable for high-frequency, high-power-density and hightemperature applications, such as EV chargers [11,12,15]. However, the higher switching frequency and higher operating voltages enabled by SiC devices challenge the EMC of the power module. Research in [16] shows that the very high switching frequency has a significant influence on the power converter common mode voltage spectrum, focusing on the frequency range of 150 kHz to 30 MHz. In [17], the
⁎
trade-off between switching losses and the high-frequency spectral amplitude is quantified experimentally for all-Si, Si-SiC, and all-SiC device combinations. Results show that the high switching frequency causes an increase in the high-frequency spectral amplitude. Poorly designed EMI filters would ruin the power density advantage by using SiC devices. In [18], an EMI filter designed to comply with EMC standards for an All-SiC motor drive operating at 200 kHz. Research shows that it is significantly larger and heavier than its counterpart designed for 20 kHz operation. Commercial power electronics usually have a compact and complex two-stage structure. For the power conversion between different voltage levels, the power module for EV chargers adopts two-stage structure with cascaded converters. The EMI mechanism is still not well understood. This paper analyses the interference sources in an All-SiC power module topology composed by the cascaded four quadrant converter (4QC) and LLC converter. Then a double π EMI filter is designed intended for this topology. Finally, the experimental efficiency test and conducted interference test are presented. The analysis and design methodology provides a reference for the suppression of the noises generated from high-frequency-switching SiC power devices. The research of this paper has positive significance for the development of
Corresponding author. E-mail address: [email protected] (T. Shao).
https://doi.org/10.1016/j.microrel.2019.113458 Received 15 May 2019; Received in revised form 15 July 2019; Accepted 19 July 2019 0026-2714/ © 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: Zhijun Li, et al., Microelectronics Reliability, https://doi.org/10.1016/j.microrel.2019.113458
Microelectronics Reliability xxx (xxxx) xxxx
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Fig. 1. The All-SiC power module in EV charger.
Fig. 2. The configuration of the All-SiC power module for EV charger.
high-reliability power module in EV charger and can promote the development of the third generation semiconductor industry to a certain extent.
end of each module are connected in parallel to share the output current. The configuration of one All-SiC power module is shown in Fig. 2. Fig. 2 shows the topology and outlook of the All-SiC power module. This technical scheme is proposed based on 1200 V SiC MOSFETs and 1200 V SiC Schottky diodes. The 30 kW All-SiC power module adopts the two-stage structure, and the first stage is two-level and six-switch four quadrant converter (4QC). Its primary function is to realize active power factor correction
2. The configuration of All-SiC power module The EV charger is in a multi-module parallel structure, as shown in Fig. 1, with multiple All-SiC power modules. The input end and output
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Fig. 3. Interference sources in the All-SiC power module.
3. Analysis of the significant interference sources It is generally believed that the common mode interference of the topology, 4QC series with LLC, mainly comes from the parasitic capacitor between the power devices and the protection ground (PE), while the difference mode interference source is equivalent to the AC-side inductors of 4QC (La~Lc) and LLC resonance inductor (Lr). The distribution of main interference sources is illustrated in Fig. 3. The 4QC adopts Space Vector Pulse Width Modulation (SVPWM), and hence all the power devices in 4QC are of high-frequency switching action. When the 4QC is in operation, take PE as the reference potential, then the input voltage is the three-phase 220 V/50 Hz waveform, but the switch devices conduct and make the positive bus (VbusL), and negative bus (VbusN) show ± 400 V high-frequency switching waveform. In the whole circuit, the stray capacitors of the positive and negative bus cannot be avoided. The stray capacitors charged and discharged with the ± 400 V high-frequency switching waveform, resulting in interference current. Similarly, when the switching devices of the LLC is conducted alternately, the positive bus (VoutL) and the negative bus (VoutN) would generate a high-frequency alternating voltage, valued ± 400 V. This high-frequency alternating voltage would charge the stray capacitors and result in interference. The authors measured the drain-to-source voltage of the SiC MOSFETs, in the 4QC and the LLC. The waveforms are saved in the CSV file with oscilloscope Tektronix MDO3024. Then the saved CSV data is processed with MATLAB 2017 in the Simulink by the Spectrum Analyzer. The spectrums are given in Fig. 4(a) and (b). The switching frequency of 4QC is 30 kHz and the one of LLC is about 133 kHz. It can be seen that, the SiC MOSFETs provide abundant interference at the switching frequency and their harmonic frequencies. Especially the SiC MOSFETs in LLC, their interference between 0.1 MHz and 10 MHz is significant. Also, since the switching speed of SiC MOSFET is dozens of times higher than that of the conventional Si device, the interference from the All-SiC power module shows a substantial impact on the ACside input. The LLC is not directly connected to the AC input. Although the DM disturbance path can be easily established, identifying the CM disturbance path is not straightforward. The impact of the LLC interference on the AC side conducted EMI measurement needs further investigation. In [19], the transfer function is introduced to compute the output
Fig. 4. Spectrums of the SiC MOSFETs drain-to-source voltage: (a) MOSFET of 4QC, (b) MOSFET of LLC.
and stabilize the intermediate DC bus voltage. Input three-phase fourwire system (no zero lines), input voltage 220 V phase voltage, output voltage 800 V dc bus. The output stage uses a two-level LLC resonance converter, whose primary function is to achieve electrical isolation and output voltage conversion, where the input from the intermediate DC bus is 800 V, and the output DC ranges from 750 V to 300 V.
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Fig. 5. High-frequency interference model of a power module connected to a LISN.
Fig. 6. The double π EMI filter for 30 kW All-SiC power module in EV charger.
voltage of a bridge leg. Meanwhile, such an approach is complicated in a commercial power module, which has many bridge legs, such as the object of study of this paper given in Fig. 2. A general high-frequency noise model of a three-phase system is given in Fig. 5, where the line impedance stabilization network (LISN) is modeled as three 50 Ω resistors. The voltages v1, v2 and v3 are measured to generating the conducted EMI test results by the computer for spectrum calculation. Separation of common mode interference and differential mode interference in three-phase systems with two stages is not easily possible. Regardless of the intended three-phase system and its noise sources, the CM current can be defined as the current flowing out through the phases and returning via earth. Reference [20] shows the common mode interference passes through the bus to cabinet stray capacitors. Here in Fig. 5, Cp1 and Cp2 are stray capacitors of the bus to PE. The CM current is the sum of all three-phase currents iCM = i1 + i2 + i3. The DM currents can be defined as the currents flowing out through one phase and returning through the two other phases, which mostly comes from the ripple on the inductors La, Lb, Lc
(represented by ZDM1 in Fig. 5) and Lr (represented by ZDM2 in Fig. 5). Although the source of DM currents comes from the switching of power devices, researchers often treat components full of ripple currents as the source of DM interference. This model implies that the propagation paths of the DM and CM currents can be separated, which may not be true in every case. For better understanding, the model sets a virtual middle point (M) on the DC voltage bus between 4QC and LLC. Through this point, the interference from LLC passes into the LISN. It should be noticed that the interference path analysis with this model can explain how the LLC interference, together with the 4QC interference impacts the LISN voltages. 4. Suppression for the interference Fig. 6 shows the double π EMI filter used in the All-SiC power module. For simplification, Fig. 6 only illustrates one phase of the EMI filter to explain its composition. When the filter added, it is equivalent to add a large impedance for the high-frequency current loop, forming a
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Fig. 7. The EMI filter in an All-SiC power module.
Fig. 8. The All-SiC power module under test.
low impedance path between the AC-side power supply and PE. This EMI filter would reduce the high-frequency current flows through the stray capacitors, thus suppress the current flowing through LISN, and reduce the input common-mode current of the power supply. The two common mode inductors of the double π EMI filter are different in design. Common mode inductor (Lcm1) aims at the lowfrequency ripple current suppression (1 MHZ - 3 MHZ), common mode inductor (Lcm2) aims at the medium frequency ripple current suppression (3 MHZ - 10 MHZ), and the common mode capacitors (Ccm1 - Ccm8) and differential mode capacitors aims at the high-frequency current suppression (10 MHZ - 30 MHZ), so as to reduce the high-frequency current emitted by conduction.
Table 1 Critical parameters of the All-SiC power module. Parameter
Value
Units
Input voltage Output voltage Maximum output current Maximum output power 4QC switching frequency LLC switching frequency Maximum output power Power density
320–450 250–750 50 30 42 120–400 30 2.48
V AC V DC A kW kHz kHz kW kW/L
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is more significant than 96% over 60% load range. According to the Chinese inspection and test specifications for electric vehicle charging requirement NB/T 33008–2013, when the power module operates under 50%~100% rated power, the efficiency should larger than 92%; when the power module operates under 20% ~50% rated power, the efficiency should be higher than 86%. Hence, the efficiency of the All-SiC power module passed the efficiency requirement. During the efficiency test, the converter equipped with EMI filter. The EMI filter didn't impact efficiency. The All-SiC power module has been tested according to the requirements of the EMC standards. As required, the converter has been connected to a stabilized voltage source through a LISN, and spectrum of the input current has been measured in the range from 150 kHz to 30 MHz. The result of the conducted EMI measurement is shown on the left of Fig. 10. As a comparison, the EMI measurement of an All-Si power module counterpart is given on the right side. As can be seen, the noise of the All-SiC power device is larger than the All-Si power module. It is mainly because of the high-frequency switching of SiC devices. However, owing to the double π EMI filter, the All-SiC power module's noise at the whole frequency range reaches the requirement, the noise is smaller than the required value in NB/T 33008–2013, marked with a red line. Although it satisfies the requirement, the noise above 1 MHz still has room for improvement. The filter's parasitic parameters significantly influence the noise at these higher frequencies [21]. However, the parameter extraction and simplification processes are design and application specific that usually require engineering experiences and prior knowledge of the EMI problem. We are working to secure accuracy.
Fig. 9. Experimental result: efficiency under different output power.
After repeated experiments and tests, the capacitance and inductance in the double π EMI filter are determined. Common mode inductance Lcm1 = 3 mH, Lcm2 = 1.3 mH; Differential mode inductance Ldm1 = 30 μH, Ldm2 = 14 μH; Common mode capacitance Ccm1~Ccm4 = 4.7 nF, Ccm5~Ccm8 = 1 nF; Differential mode capacitance Cdm1~Cdm4 = 4.7 μF. The EMI filter area in the power module is shown in Fig. 7. The weight is about 0.553 kg, which is 3.57% of the total weight of the All-SiC power module.
6. Conclusion
5. Experimental results
Because of the fast switching of the SiC power devices, All-SiC power converters face the challenge of EMI issue. For solving the EMI issue in a 30 kW All-SiC power module for the EV charger, this paper analyzed the interference sources in the power module. Then this paper introduces a double π EMI filter to suppress the noises. Experiment results show that the efficiency and power density are not influenced after adding this filter, and the EMI measurement test verifies the effectiveness of the EMI filter design. The technique reported in this paper has been used in the 30 kW All-SiC power module and realized the commercial application. The research would provide a valuable reference for the implementation of SiC power devices for EV charger. Future work would focus on the optimization of the parasitic parameters to further reduce the EMI onward 1 MHz.
The 30 kW All-SiC power module embedded with the aforementioned double π EMI filter is tested to verify the efficiency and EMC performance. Fig. 8 shows the test platform. The critical parameters listed in Table 1. The input voltage is 50 Hz, 320–450 V AC voltage, and the output voltage is 250–750 V DC voltage. The SiC power devices in the 4QC operate under 42 kHz, and the ones in the LLC operate under 120–400 kHz. The power density is 2.48 kW/L (L is liter), which is reasonable for a power module for an EV charger. Fig. 9 gives the efficiency test result. The output range varies from 6 kW to 30 kW, three conditions of the output voltage are considered, which are Vout = 550 V, 650 V and 750 V. As given in Fig. 9, the peak efficiency is 96.7%, full load efficiency is 96%, in a word, the efficiency
Fig. 10. Experimental result: conducted EMI measurement. 6
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Acknowledgments
and their applications, IEEE Trans. Ind. Electron. 64 (2017) 8193–8205. [9] A.K. Morya, M.C. Gardner, B. Anvari, L. Liu, A.G. Yepes, J. Doval-Gandoy, H.A. Toliyat, Wide bandgap devices in AC electric drives: opportunities and challenges, IEEE Transactions on Transportation Electrification 5 (2019) 3–20. [10] J. Wang, V. Veliadis, J. Zhang, Y. Alsmadi, P.R. Wilson, M.J. Scott, IEEE ITRW working group position paper-system integration and application: silicon carbide: a roadmap for silicon carbide adoption in power conversion applications, IEEE Power Electronics Magazine 5 (2018) 40–44 2018-01-01. [11] J. Shao, A. Barkley, Y. Hu, T.S. Ong, B. Agrawal, SiC MOSFET based bi-directional 3-phase AC/DC converter, 2018 IEEE Energy Conversion Congress and Exposition (ECCE), 2018, pp. 2890–2895. [12] Q. Feng, W. Miao, X. Longya, Investigation and review of challenges in a high temperature 30kVA 3-phase inverter using SiC MOSFETs, IEEE Trans. Ind. Appl. 54 (2018) 2483–2491. [15] P. Johnson, K. Bai, A dual-DSP controlled SiC MOSFET based 96%-efficiency 20kW EV on-board battery charger using LLC resonance technology, 2017 IEEE Symposium Series on Computational Intelligence (SSCI), 2017, pp. 1–5. [16] D. Han, S. Li, Y. Wu, W. Choi, B. Sarlioglu, Comparative analysis on conducted CM EMI emission of motor drives: WBG versus Si devices, IEEE Trans. Ind. Electron. 64 (2017) 8353–8363. [17] N. Oswald, P. Anthony, N. McNeill, B.H. Stark, An experimental investigation of the tradeoff between switching losses and EMI generation with hard-switched All-Si, SiSiC, and All-SiC device combinations, IEEE Trans. Power Electron. 29 (2014) 2393–2407. [18] D. Han, C.T. Morris, W. Lee, B. Sarlioglu, Comparison between output CM chokes for SiC drive operating at 20- and 200-kHz switching frequencies, IEEE Trans. Ind. Appl. 53 (2017) 2178–2188. [19] D. Labrousse, B. Revol, F. Costa, Switching cell EMC behavioral modeling by transfer function, Emc Europe, 2011. [20] R. Zhang, X. Wu, T. Wang, Analysis of common mode EMI for three-phase voltage source converters, IEEE Power Electronics Specialist Conference, 2003. [21] S. Wang, F.C. Lee, J.D.V. Wyk, A study of integration of parasitic cancellation techniques for EMI filter design with discrete components, IEEE Trans. Power Electron. 23 (2008) 3094–3102.
This work was supported in part by the Excellent Youth Scholars of National Natural Science Foundation of China under Grant 51822701; the Key Project of National Natural Science Foundation of China under Grant U1866211. References [1] S. Habib, M.M. Khan, F. Abbas, S. Lei, M.U. Shahid, H. Tang, A comprehensive study of implemented international standards, technical challenges, impacts and prospects for electric vehicles, IEEE Access (2018) 1. [2] M.F.M. Sabri, A review on hybrid electric vehicles architecture and energy management strategies, Renew. Sustain. Energy Rev. 53 (2016) 1433–1442. [3] C. Ming, T. Minghao, Development status and trend of electric vehicles in China, Chinese Journal of Electrical Engineering 3 (2017) 1–13. [4] R. Maeno, H. Omori, H. Michikoshi, N. Kimura, T. Morizane, A 3kW single-ended wireless EV charger with a newly developed SiC-VMOSFET, 2018 7th International Conference on Renewable Energy Research and Applications (ICRERA), 2018, pp. 1–6. [5] Z. Li, X. Yang, Y. Li, J. Li, B. Zhang, T. Lei, Design and implementation of a highefficiency DC/DC converter for EVs charging basing on LLC resonant topology and silicon-carbide devices, 2018 IEEE International Power Electronics and Application Conference and Exposition (PEAC), 2018, pp. 1–6. [6] Z. Li, X. Yang, Y. Li, N. Wang, S. Zhang, H. Chen, J. Ma, A high-efficiency DC/DC converter with SiC devices and LLC topology for charging electric vehicles, 2018 Asian Conference on Energy, Power and Transportation Electrification (ACEPT), 2018, pp. 1–7. [7] A. Taylor, J. Lu, L. Zhu, K.H. Bai, M. McAmmond, A. Brown, Comparison of SiC MOSFET-based and GaN HEMT-based high-efficiency high-power-density 7.2 kW EV battery chargers, IET Power Electron. 11 (2018) 1849–1857. [8] S. Xu, A.Q. Huang, O. Lucia, B. Ozpineci, Review of silicon carbide power devices
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Contents lists available at ScienceDirect
Microelectronics Reliability journal homepage: www.elsevier.com/locate/microrel
Interference source analysis and EMC design for All-SiC power module in EV charger Zhijun Lia, Tiancong Shaoa, , Trillion Q. Zhenga, Hong Lia, Bo Huangb ⁎
a b
School of Electrical Engineering, Beijing Jiaotong University, Beijing, China Global Power Technology Co., Ltd., Beijing, China
ABSTRACT
Silicon carbide (SiC) power devices suitable for high-frequency, high-power density and high-temperature applications, and thus gain a broad prospect in the electric vehicle (EV) charger area. However, the high-frequency switching of SiC devices under high-power application challenges the electromagnetic compatibility (EMC) of the power module. Noises generated from high-frequency switching need to be analyzed and suppressed. This paper introduces the configuration of a 30 kW AllSiC power module designed for EV charger, then reveals the interference source analysis. Based on the interference analysis, a double π electromagnetic interference (EMI) filter is added, intended for this All-SiC power module. Experimental results show that the All-SiC power module achieves excellent efficiency over a wide power range. Meanwhile, the conducted EMI measurement is reported to verify the effectiveness of EMC design.
1. Introduction Electric vehicles (EVs) release no tailpipe air pollutants at the place where they are operated [1]. Many governments offer incentives to promote the use of electric vehicles, with the goals of reducing air pollution and oil consumption [2]. In China, The annual EV production and sales are planned to be 200 million with total ownership of EVs expected to reach 500 million by 2020, in the meantime, it was planned to construct 4.3 million charging points and build 2397 public charging stations before 2020 [3]. As the growing market demand for EVs, the research for silicon carbide (SiC) power devices in the power module of EV chargers gains great attention [4–7]. Owing to the intrinsic material advantages of SiC over silicon (Si), SiC power devices can operate at a higher voltage, higher switching frequency, and higher temperature [8–10]. Hence SiC power devices are very suitable for high-frequency, high-power-density and hightemperature applications, such as EV chargers [11,12,15]. However, the higher switching frequency and higher operating voltages enabled by SiC devices challenge the EMC of the power module. Research in [16] shows that the very high switching frequency has a significant influence on the power converter common mode voltage spectrum, focusing on the frequency range of 150 kHz to 30 MHz. In [17], the
⁎
trade-off between switching losses and the high-frequency spectral amplitude is quantified experimentally for all-Si, Si-SiC, and all-SiC device combinations. Results show that the high switching frequency causes an increase in the high-frequency spectral amplitude. Poorly designed EMI filters would ruin the power density advantage by using SiC devices. In [18], an EMI filter designed to comply with EMC standards for an All-SiC motor drive operating at 200 kHz. Research shows that it is significantly larger and heavier than its counterpart designed for 20 kHz operation. Commercial power electronics usually have a compact and complex two-stage structure. For the power conversion between different voltage levels, the power module for EV chargers adopts two-stage structure with cascaded converters. The EMI mechanism is still not well understood. This paper analyses the interference sources in an All-SiC power module topology composed by the cascaded four quadrant converter (4QC) and LLC converter. Then a double π EMI filter is designed intended for this topology. Finally, the experimental efficiency test and conducted interference test are presented. The analysis and design methodology provides a reference for the suppression of the noises generated from high-frequency-switching SiC power devices. The research of this paper has positive significance for the development of
Corresponding author. E-mail address: [email protected] (T. Shao).
https://doi.org/10.1016/j.microrel.2019.113458 Received 15 May 2019; Received in revised form 15 July 2019; Accepted 19 July 2019 0026-2714/ © 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: Zhijun Li, et al., Microelectronics Reliability, https://doi.org/10.1016/j.microrel.2019.113458
Microelectronics Reliability xxx (xxxx) xxxx
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Fig. 1. The All-SiC power module in EV charger.
Fig. 2. The configuration of the All-SiC power module for EV charger.
high-reliability power module in EV charger and can promote the development of the third generation semiconductor industry to a certain extent.
end of each module are connected in parallel to share the output current. The configuration of one All-SiC power module is shown in Fig. 2. Fig. 2 shows the topology and outlook of the All-SiC power module. This technical scheme is proposed based on 1200 V SiC MOSFETs and 1200 V SiC Schottky diodes. The 30 kW All-SiC power module adopts the two-stage structure, and the first stage is two-level and six-switch four quadrant converter (4QC). Its primary function is to realize active power factor correction
2. The configuration of All-SiC power module The EV charger is in a multi-module parallel structure, as shown in Fig. 1, with multiple All-SiC power modules. The input end and output
2
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Fig. 3. Interference sources in the All-SiC power module.
3. Analysis of the significant interference sources It is generally believed that the common mode interference of the topology, 4QC series with LLC, mainly comes from the parasitic capacitor between the power devices and the protection ground (PE), while the difference mode interference source is equivalent to the AC-side inductors of 4QC (La~Lc) and LLC resonance inductor (Lr). The distribution of main interference sources is illustrated in Fig. 3. The 4QC adopts Space Vector Pulse Width Modulation (SVPWM), and hence all the power devices in 4QC are of high-frequency switching action. When the 4QC is in operation, take PE as the reference potential, then the input voltage is the three-phase 220 V/50 Hz waveform, but the switch devices conduct and make the positive bus (VbusL), and negative bus (VbusN) show ± 400 V high-frequency switching waveform. In the whole circuit, the stray capacitors of the positive and negative bus cannot be avoided. The stray capacitors charged and discharged with the ± 400 V high-frequency switching waveform, resulting in interference current. Similarly, when the switching devices of the LLC is conducted alternately, the positive bus (VoutL) and the negative bus (VoutN) would generate a high-frequency alternating voltage, valued ± 400 V. This high-frequency alternating voltage would charge the stray capacitors and result in interference. The authors measured the drain-to-source voltage of the SiC MOSFETs, in the 4QC and the LLC. The waveforms are saved in the CSV file with oscilloscope Tektronix MDO3024. Then the saved CSV data is processed with MATLAB 2017 in the Simulink by the Spectrum Analyzer. The spectrums are given in Fig. 4(a) and (b). The switching frequency of 4QC is 30 kHz and the one of LLC is about 133 kHz. It can be seen that, the SiC MOSFETs provide abundant interference at the switching frequency and their harmonic frequencies. Especially the SiC MOSFETs in LLC, their interference between 0.1 MHz and 10 MHz is significant. Also, since the switching speed of SiC MOSFET is dozens of times higher than that of the conventional Si device, the interference from the All-SiC power module shows a substantial impact on the ACside input. The LLC is not directly connected to the AC input. Although the DM disturbance path can be easily established, identifying the CM disturbance path is not straightforward. The impact of the LLC interference on the AC side conducted EMI measurement needs further investigation. In [19], the transfer function is introduced to compute the output
Fig. 4. Spectrums of the SiC MOSFETs drain-to-source voltage: (a) MOSFET of 4QC, (b) MOSFET of LLC.
and stabilize the intermediate DC bus voltage. Input three-phase fourwire system (no zero lines), input voltage 220 V phase voltage, output voltage 800 V dc bus. The output stage uses a two-level LLC resonance converter, whose primary function is to achieve electrical isolation and output voltage conversion, where the input from the intermediate DC bus is 800 V, and the output DC ranges from 750 V to 300 V.
3
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Fig. 5. High-frequency interference model of a power module connected to a LISN.
Fig. 6. The double π EMI filter for 30 kW All-SiC power module in EV charger.
voltage of a bridge leg. Meanwhile, such an approach is complicated in a commercial power module, which has many bridge legs, such as the object of study of this paper given in Fig. 2. A general high-frequency noise model of a three-phase system is given in Fig. 5, where the line impedance stabilization network (LISN) is modeled as three 50 Ω resistors. The voltages v1, v2 and v3 are measured to generating the conducted EMI test results by the computer for spectrum calculation. Separation of common mode interference and differential mode interference in three-phase systems with two stages is not easily possible. Regardless of the intended three-phase system and its noise sources, the CM current can be defined as the current flowing out through the phases and returning via earth. Reference [20] shows the common mode interference passes through the bus to cabinet stray capacitors. Here in Fig. 5, Cp1 and Cp2 are stray capacitors of the bus to PE. The CM current is the sum of all three-phase currents iCM = i1 + i2 + i3. The DM currents can be defined as the currents flowing out through one phase and returning through the two other phases, which mostly comes from the ripple on the inductors La, Lb, Lc
(represented by ZDM1 in Fig. 5) and Lr (represented by ZDM2 in Fig. 5). Although the source of DM currents comes from the switching of power devices, researchers often treat components full of ripple currents as the source of DM interference. This model implies that the propagation paths of the DM and CM currents can be separated, which may not be true in every case. For better understanding, the model sets a virtual middle point (M) on the DC voltage bus between 4QC and LLC. Through this point, the interference from LLC passes into the LISN. It should be noticed that the interference path analysis with this model can explain how the LLC interference, together with the 4QC interference impacts the LISN voltages. 4. Suppression for the interference Fig. 6 shows the double π EMI filter used in the All-SiC power module. For simplification, Fig. 6 only illustrates one phase of the EMI filter to explain its composition. When the filter added, it is equivalent to add a large impedance for the high-frequency current loop, forming a
4
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Fig. 7. The EMI filter in an All-SiC power module.
Fig. 8. The All-SiC power module under test.
low impedance path between the AC-side power supply and PE. This EMI filter would reduce the high-frequency current flows through the stray capacitors, thus suppress the current flowing through LISN, and reduce the input common-mode current of the power supply. The two common mode inductors of the double π EMI filter are different in design. Common mode inductor (Lcm1) aims at the lowfrequency ripple current suppression (1 MHZ - 3 MHZ), common mode inductor (Lcm2) aims at the medium frequency ripple current suppression (3 MHZ - 10 MHZ), and the common mode capacitors (Ccm1 - Ccm8) and differential mode capacitors aims at the high-frequency current suppression (10 MHZ - 30 MHZ), so as to reduce the high-frequency current emitted by conduction.
Table 1 Critical parameters of the All-SiC power module. Parameter
Value
Units
Input voltage Output voltage Maximum output current Maximum output power 4QC switching frequency LLC switching frequency Maximum output power Power density
320–450 250–750 50 30 42 120–400 30 2.48
V AC V DC A kW kHz kHz kW kW/L
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is more significant than 96% over 60% load range. According to the Chinese inspection and test specifications for electric vehicle charging requirement NB/T 33008–2013, when the power module operates under 50%~100% rated power, the efficiency should larger than 92%; when the power module operates under 20% ~50% rated power, the efficiency should be higher than 86%. Hence, the efficiency of the All-SiC power module passed the efficiency requirement. During the efficiency test, the converter equipped with EMI filter. The EMI filter didn't impact efficiency. The All-SiC power module has been tested according to the requirements of the EMC standards. As required, the converter has been connected to a stabilized voltage source through a LISN, and spectrum of the input current has been measured in the range from 150 kHz to 30 MHz. The result of the conducted EMI measurement is shown on the left of Fig. 10. As a comparison, the EMI measurement of an All-Si power module counterpart is given on the right side. As can be seen, the noise of the All-SiC power device is larger than the All-Si power module. It is mainly because of the high-frequency switching of SiC devices. However, owing to the double π EMI filter, the All-SiC power module's noise at the whole frequency range reaches the requirement, the noise is smaller than the required value in NB/T 33008–2013, marked with a red line. Although it satisfies the requirement, the noise above 1 MHz still has room for improvement. The filter's parasitic parameters significantly influence the noise at these higher frequencies [21]. However, the parameter extraction and simplification processes are design and application specific that usually require engineering experiences and prior knowledge of the EMI problem. We are working to secure accuracy.
Fig. 9. Experimental result: efficiency under different output power.
After repeated experiments and tests, the capacitance and inductance in the double π EMI filter are determined. Common mode inductance Lcm1 = 3 mH, Lcm2 = 1.3 mH; Differential mode inductance Ldm1 = 30 μH, Ldm2 = 14 μH; Common mode capacitance Ccm1~Ccm4 = 4.7 nF, Ccm5~Ccm8 = 1 nF; Differential mode capacitance Cdm1~Cdm4 = 4.7 μF. The EMI filter area in the power module is shown in Fig. 7. The weight is about 0.553 kg, which is 3.57% of the total weight of the All-SiC power module.
6. Conclusion
5. Experimental results
Because of the fast switching of the SiC power devices, All-SiC power converters face the challenge of EMI issue. For solving the EMI issue in a 30 kW All-SiC power module for the EV charger, this paper analyzed the interference sources in the power module. Then this paper introduces a double π EMI filter to suppress the noises. Experiment results show that the efficiency and power density are not influenced after adding this filter, and the EMI measurement test verifies the effectiveness of the EMI filter design. The technique reported in this paper has been used in the 30 kW All-SiC power module and realized the commercial application. The research would provide a valuable reference for the implementation of SiC power devices for EV charger. Future work would focus on the optimization of the parasitic parameters to further reduce the EMI onward 1 MHz.
The 30 kW All-SiC power module embedded with the aforementioned double π EMI filter is tested to verify the efficiency and EMC performance. Fig. 8 shows the test platform. The critical parameters listed in Table 1. The input voltage is 50 Hz, 320–450 V AC voltage, and the output voltage is 250–750 V DC voltage. The SiC power devices in the 4QC operate under 42 kHz, and the ones in the LLC operate under 120–400 kHz. The power density is 2.48 kW/L (L is liter), which is reasonable for a power module for an EV charger. Fig. 9 gives the efficiency test result. The output range varies from 6 kW to 30 kW, three conditions of the output voltage are considered, which are Vout = 550 V, 650 V and 750 V. As given in Fig. 9, the peak efficiency is 96.7%, full load efficiency is 96%, in a word, the efficiency
Fig. 10. Experimental result: conducted EMI measurement. 6
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Acknowledgments
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