Characterization of Conducted Electromagnetic Interference (EMI) Generated by Switch Mode Power Supply (SMPS)

Transcription

1 Revue des Sciences et de la Technologie - RST- Volume 5 N 1 / janvier 2014 Characterization of Conducted Electromagnetic Interference (EMI) Generated by Switch Mode Power Supply (SMPS) M. Miloudi*, A. Bendaoud**, H. Miloudi***, S. Nemmich*, M. Oukli* *Department of Electrical Engineering, Djilali Liabes University, mil_milmed@yahoo.fr **Department of Electrical Engineering, Djilali Liabes University, babdelber22@yahoo.fr ***Department of Electrical Engineering, Djilali Liabes University, al_houssaine@yahoo.fr Abstract Since the efficiency of Switched Mode Power Supply (SMPS) is much higher than that of linear power supplies. This type of supply has gained favour among designers and manufacturers. Switching frequencies extend from ten to hundred kilohertz with the result that conducted from circuits carrying switched current is becoming more of a problem. This work addresses the analysis of the conducted EMI characteristics of Switched Mode Power Supply. This paper introduces an efficient method to predict the conducted EMI of Flyback converter. Keywords EMI, EMC, LISN, Differential Mode (DM), Common Mode (CM), Switched Mode Power Supply (SMPS), Flyback converter. I. INTRODUCTION In the field of power electronics, there is a trend for pushing up switching frequencies of Switched Mode Power Supplies to reduce volume and weight. This trend inevitably contributes to an increasing level of Electro Magnetic Interference (EMI) emissions. It leads to a general Electromagnetic Compatibility (EMC) degradation for electronic devices. Electromagnetic Interference (EMI) problems in Switching Power Supplies have been traditionally treated with cut and try approaches. In recent years, advancement has been made to better understand the problems and minimize the cut-and-try portion of the design process. The Flyback converter belongs to the primary switched converter family, which means there is isolation between in and output [1]. Flyback converter has a remarkably low number of components compared to other SMPSs, they also have the advantage that several isolated output voltages can be regulated by one control circuit (Fig.1). Fig.1. Flyback Converter 1

2 M. Miloudi, A. Bendaoud, H. Miloudi, S. Nemmich, M. Oukli II. LISN MODEL Conventionally, the total conducted EMI noise is caused by two mechanisms, the Differential Mode (DM) and Common Mode (CM) Noise. Generally, the Differential Mode (DM) noise is related to switching current and the Common Mode (CM) noise is related to capacitive coupling of switching voltage into Line Impedance Stabilizing Network (LISN), which is used in standard conducted EMI measurement. Fig.2 shows the typical setup for conducted EMI measurement. The LISN contains inductors, capacitors and 50 resistors. The inductors are basically shorted; the capacitors are open and the power passes through to supply the Equipment Under Test (EUT). For EMI noise frequency, the inductors are essentially open, the capacitors are shorted and the noise sees 50 resistors. The noise voltage measured across the 50 input impedance of a Spectrum [2, 3]. Fig.2. Measurement Setup for Conducted EMI Noise III. EMI TYPES IN SMPS Standards have been established to fix a limit below which SMPS will not disturb the surrounding equipment sharing the same line or outlet (e.g. CISPR22, FCC15 etc.). International standards have defined reference impedance on which the measurements will be made. This impedance is guaranteed by a Line Impedance Stabilization Network (LISN) and precisely defined by CISPR16 document. Fig.2 portrays how this device is made. The LISN offers a 50 impedance over the frequency of interest (e.g. 150 khz - 30 MHz for CISPR22) and shields the measurement against unwanted incoming noises. The high values of some capacitors connected between Live and Earth require the adjunction of an isolating transformer between mains and the LISN. Conducted noise consists of two categories commonly known as Differential Mode noise (DM) and Common Mode noise (CM) [3]. EN and CISPR 22 [4] are the standards relevant to the conducted EMI noise limits in the input of the converter. The former describes the limits and test conditions under which the Characterization of Conducted Electromagnetic Interference (EMI) Generated by Switch Mode Power Supply (SMPS) 2

3 Characterization of Conducted Electromagnetic Interference (EMI) Generated by Switch Mode Power Supply (SMPS) converter must comply with regulations. The quasi-peak limit spectrum in the voltage across the LISN resistors for Class A, Group 1 and Class B, Group 1 of the apparatuses is presented in Fig.3. Fig.3. EMI Noise Standard (EN 55022) Determination of Common Mode and Differential Mode noise in SMPS, EMI filter design for both Common Mode (CM) and Differential Mode (DM) noise, Filter termination impedance. Design for Electromagnetic Compatibility (EMC) has become a requirement. EMC s is the absence of EMI. Electromagnetic Compatibility (EMC) is a system level consideration. This topic attempts to describe the more significant causes of EMI in power supplies and offer design techniques to minimize their impact. Discuss about the sources and paths of Common Mode (CM) and Differential Mode (DM) noise, which is due the rapid frequency changes. Discuss about the equivalent circuit of noise source for Switched Mode Power Supplies and design an EMI Filter [5] IV. CONDUCTED EMI IN SMPS Switched Mode Power Supplies (SMPS) are usually a part of a complex electronic system. The system operates with electric signals with much lower amplitude and energy compared to those on a SMPS. It means that usually the SMPS is the strongest electrical noise generator in the whole system. Especially the power switches with their high dv/dt and di/dt switching slopes are the sources of EMI. The source of Differential Mode (DM) Interferences is the current switched by a MOSFET or a diode. High rates of dv/dt and parasitic capacitors to the ground are the reasons for Common Mode Interferences [6]. There are three essential elements in EMI problem: source, coupling path and receiver, as illustrated in Fig.4. A source (culprit) generates the emission, and a coupling path (transfer), transfers the emission energy to a receiver (victim). A. Differential Mode noise (DM) Fig.4. Essential Elements of the EMI Coupling Problem It is measured between each power line and ground. Differential Mode (DM) is due to magnetic coupling. It is otherwise called as Normal-Mode or Transverse-Mode Noise. Current path of Differential Mode is shown in Fig.5 Differential Mode (DM) noise attempts to dissipate its energy M. Miloudi, A. Bendaoud, H. Miloudi, S. Nemmich, M. Oukli 3

4 M. Miloudi, A. Bendaoud, H. Miloudi, S. Nemmich, M. Oukli along any path from line to neutral. If the Normal-Mode noise has sufficient voltage (or energy), damage could first occur to the SMPS and then to the computer circuitry [6]. The P-N junction of the rectified diodes can breakdown due to excessive biasing. The capacitors may degrade if the noise is opposite in polarity or exceeds operating limits. Transformer insulation may breakdown if the noise peaks are excessively high. The transmission of the Differential Mode (DM) noise is through the input line to the utility system and through the dc-side network to the load on the power converter. Differential Mode (DM) noise is presents on both the input and output lines. B. Common Mode noise (CM) Fig.5. Differential Mode (DM) Path (CM) noise is measured between line and ground. Common Mode (CM) noise is due to stray capacitance. Common Mode (CM) noise may be coupled through the high frequency transformer or along paths that have parasitic capacitance. It consists of high frequency impulses, there is a high probability that the noise will see the high frequency transformer just as a coupling capacitor and pass through unobstructed. Stray Capacitor paths may exist within SMPS because they are smaller in physical size and more densely packaged as compared to other types of power supplies. Common Mode (CM) noise is present on both input and output lines [6]. The current path of CM is shown in Fig.6. The transmission of CM noise is entirely through parasitic or stray capacitors and stray electric and magnetic fields. Fig.6. Common Mode (CM) Path V. NOISE SEPARATOR FOR CONDUCTED EMI EMI diagnosis and EMI filter design need accurate DM and CM noise separation and measurement. Noise separator is a powerful tool to separate and measure EMI noise. Since all EMI standards are based on the noise voltage drop on 50 resistance, the noise separator must have 50 input impedances under any conditions. Furthermore, the noise separator should accurately finish the calculation to separate DM and CM noise. The noise rejection ratio should also be good enough to reject the unwanted noise mode [7]. A noise separator is using transmission line transformer, which can cancel the effects of winding capacitance and leakage inductance of the windings. 50 input impedance is also guaranteed under any conditions. The rejection ratio is good to efficiently prevent the interference of unwanted EMI mode in the measurement. The noise separator integrates both CM and DM separators, so it is easy to measure both noise at the same time without switching connectors [6, 7]. Characterization of Conducted Electromagnetic Interference (EMI) Generated by Switch Mode Power Supply (SMPS) 4

5 Characterization of Conducted Electromagnetic Interference (EMI) Generated by Switch Mode Power Supply (SMPS) Fig.7. Noise Separation VI. SYSTEM MODEL All of the part models described here was combined to form a system model. The system model can be used to predict the conducted EMI. There are many standard power converter topologies available to choose from, each with its advantages and disadvantages [8]. After careful consideration, taking into account factors such as low power, simplicity, isolation, input and output ripple currents, and low cost, the Flyback converter configuration was chosen. The basic system model topology is shown in Fig.8. The design procedure is based on a frequency domain model described in other work [4, 8]. It is based on both a complete representation of possible propagation paths for differential and common mode disturbances and a frequency domain representation of conducted EMI sources present in the converter (existing in both types of propagation paths). The propagation path model takes into account CISPR 16-2 test conditions (ground plane, LISN, etc ) and a high-frequency model representation of the converter, including parasitic. By accounting for the effects of the test conditions in the filter design, the iterations in the design process are minimized [8]. Fig.8. System Model VII. EMI CONTROL The results of the simulation are shown below. These results were achieved by using the FFT analysis option of LTSPICE sofware. Fig.9 shows the MOSFET model which includes two parts. One part is the model of the DC transfer-function characteristics. The other part is the model of the diode and the parasitic capacitances. The DC transfer-function model of MOSFET realizes the characteristic of turn-on M. Miloudi, A. Bendaoud, H. Miloudi, S. Nemmich, M. Oukli 5

6 M. Miloudi, A. Bendaoud, H. Miloudi, S. Nemmich, M. Oukli and off. The parasitic capacitance model of MOSFET is an important factor because the parasitic capacitances make resonant oscillations with system inductances. Drain to source capacitance is modeled as the junction capacitance of the diode. In general, gate to source capacitance can be modeled as a constant value capacitance. Gate to drain capacitance characteristic curve is nonlinear and discontinuous. Fig.9. Scheme of MOSFET Model The simulation method is divided in two cases. We use IRF530 MOSFET in case 1 and IRF510 MOSFET. in case 2. Table 1 summarizes the model parameters and their values for the IRF530 and IRF510 MOSFET. R G ) R D (m ) TABLE I MODEL PARAMETERS R S (m ) C GD (nf) C GS (nf) I (pa) (IRF530) V (V) (IRF510) A. Case 1 The MOSFET (the source of disturbance) is the power component most commonly spread in power electronics. It is commonly used for its ability to operate at high frequency. Low voltage and low gate drive current, ease of paralleling and the absence of secondary effects from the parasitic bipolar junction. As the diode junction doesn t control, its parasitic components are smaller and insignificant. Fig.10. Simulated CM Spectrum for Flyback Converter for IRF530 MOSFET Characterization of Conducted Electromagnetic Interference (EMI) Generated by Switch Mode Power Supply (SMPS) 6

7 Characterization of Conducted Electromagnetic Interference (EMI) Generated by Switch Mode Power Supply (SMPS) Fig.11. Simulated DM Spectrum for Flyback Converter IRF530 MOSFET Fig.12. Conducted EMI Emission of Flyback Converter IRF530 MOSFET We see clearly on these surveys, the lobes from the noise behavior. Overall, the level of Differential Mode (MD) noise is much lower than the standard EN Class A and B over the entire frequency range, but the level of Common Mode (CM) noise is higher (exceeding of 14 dbµv) to the standard class B on a small part of the range of frequencies (0.15 MHz MHz). Beyond 0.5 MHz, it fell rapidly and falls below the template. This significant reduction is partly due to the effects of the filter capacity still present on the structure, but with a very significant overshoot of class A. Differential Mode noise is negligible compared with those of Common Mode. The filtering effect becomes more prominent if the length of the path of the noise is longer. B. Case 2 The MOSFET is used most of its high integration capability and for its manufacture easier. This section presents the results of simulation disturbances EM lines including EMC model of the system overall (the Flyback) with the IRF510 MOSFET. M. Miloudi, A. Bendaoud, H. Miloudi, S. Nemmich, M. Oukli 7

8 M. Miloudi, A. Bendaoud, H. Miloudi, S. Nemmich, M. Oukli Fig.13. Simulated CM Spectrum for Flyback Converter IRF510 MOSFET. Fig.14. Simulated DM Spectrum for Flyback Converter IRF510 MOSFET. Fig.15. Conducted EMI Emission of Flyback Converter IRF510 MOSFET. With à long path, the equivalent capacitance of the CM increases, this decreases the equivalent impedance CM, over the spectrum of the modulus of CM current is high. In high frequency, the best path longer reduces the module currents, this can be explained by the fact that it acts as a lowpass filter that will reduce the voltage and current CM and DM. Characterization of Conducted Electromagnetic Interference (EMI) Generated by Switch Mode Power Supply (SMPS) 8

9 Characterization of Conducted Electromagnetic Interference (EMI) Generated by Switch Mode Power Supply (SMPS) VIII. STUDY OF THE COMPARISON Fig.16 shows the spectra of the level of noise in CM for both types of MOSFET (IRF530 and IRF510). We note that the spectrum of the MOSFET type IRF510 is much less than the spectrum of the MOSFET type IRF530, this difference is much greater in the frequency range (100 khz - 1 MHz), the disturbances are the predominant type MOSFET IRF530. These significant results are partly due to the effects of parasitic components that are low in the MOSFET type IRF510 compared to those of the MOSFET type IRF530. Both spectra have the same shape. Levels of disturbance type IRF510 MOSFET is much lower than the standard EN class A and B, but the level of disruption to the MOSFET type IRF530 is higher (14 dbµv) with standard Class B a small part of the range of frequencies (0.15 MHz MHz). We find that the results were the same trend, that is to say, with the new type of MOSFET type IRF510, the spectra are reduced with increasing frequency. The spectra are quite similar in HF. Fig.16. Simulated CM Spectrum for Flyback Converter Fig.17. Simulated DM Spectrum for Flyback Converter These results are significant in part due to the effects of parasitic components that are low in the MOSFET type IRF510 compared to those of the MOSFET type IRF530. Both spectra are at the same pace. Levels of disruption for both types of MOSFETs are much lower than the EN standard. M. Miloudi, A. Bendaoud, H. Miloudi, S. Nemmich, M. Oukli 9

10 M. Miloudi, A. Bendaoud, H. Miloudi, S. Nemmich, M. Oukli IX. CONCLUSION This paper introduces an efficient method of predicting the conducted EMI of an SMPS through LTSPICE simulation that takes the SMPS as a noise source to model. The research results indicate that this method of SMPS modelling is reasonable and efficient. The combined system model accurately predicts the conducted EMI. This simulation method can be helpful to designers in several respects, including filter design and optimization of external filters for SMPS, quantification of the filter s suppression effect, and analysis of conducted EMI problems through simulations rather than experimental procedures and iterations. This method is especially suitable for situations in which many types of SMPS modules are used. A time domain approach to predict of conducted EMI from Flyback converter has been presented. Followed by Fast Fourier Transformation (FFT) analysis, the perturbation level and the global envelope of the spectrum are superior to the standard CISPR, Publication 22: class A, The conducted noise reduction must be gotten with the help of an optimization of filtering to the entry of the converter, the next application of this work is the EMI filter optimization. X. REFERENCES [l] F. Tsai, P. Markowski, and E. Whitcomb, Off-Line Flyback Converter With Input Harmonic Correction IEEE International Telecommunications Energy Conf., pp , [2] Christophe Basso Conducted EMI Filter AND, France, April, [3] P. Khamphakdi, Junichiro Urabe, W. Khan-ngern, C. U-yaisom, V. Tarateeraseth, Katsumi Fujii, Yasushi Matsumoto and Akira Sugira The Comparison of Conducted EMI Measurement between the Small Loop Antenna and a Conventional LISN EMC 04/Sendai [4] Sergio Busquets-Monge, Application of Optimization Techniques to the Design of a Boost Power Factor Correction Converter, master of science in Electrical Engineering, Blacksburg, Virginia [5] R. Dhanasekaran, M. Rajaram and S.N.Sivanandam Mixed Mode EMI Noise Level Measurement in SMPS American Journal of Applied Sciences 3 (5): , [6] M. Miloudi Interférences Electromagnétiques Conduites Dans les Alimentations à Découpage mémoire de magister, Université de Sidi-bel-Abbes, Algérie ; [7] Ting Guo, Dan Y. Chen and Fred C. Lee Diagnosis of Power Supply conducted EMI Using a Noise Separator IEEE, pp , 2005 [8] Hongyu Li, David Pommerenke, Weifeng Pan, Shuai Xu, Huasheng Ren, Fantao Meng "Conducted EMI Simulation of Switched Mode Power Supply" IEEE, pp , Characterization of Conducted Electromagnetic Interference (EMI) Generated by Switch Mode Power Supply (SMPS) 10