detection and reduction of emi noises in an emc ...

DETECTION AND REDUCTION OF EMI NOISES IN AN EMC COMPLIED SMPS AS PER IEC/CISPR STANDARDS D.Anita priyadarshini, UG student/ECE Rajalakshmi institute of technology, Kuthampakkam,thiruvallur dist.,Tamil nadu, India. E-mail: [email protected] Abstract – Switched Mode Power Supply (SMPS) is an electronic power supply that incorporates a switching regulator to produce a regulated DC output voltage. The problem of Electro Magnetic Interference (EMI) plays an important role in the design of an SMPS. This paper detects the EMI noises that interferes the SMPS performance before and after the (Electro Magnetic Compatibility (EMC) compliance and also includes some EMI filters for the EMI noise suppression in the SMPS which needs to be complied with the EMC. The proposed approach allow us to measure the noise level in the SMPS without interfere its normal operation and also to design the EMI filters required to reduce the EMI noises within the SMPS. These investigations are achieved by means of different test methodologies with proper test setup calibration required for the IEC/CISPR (International Electro technical Committee/International Special Committee on Radio interference) standards.

K.Senthilkumar, Associate professor/ECE, Rajalakshmi institute of technology, Kuthampakkam,thiruvallur dist.,Tamil nadu, India. E-mail: [email protected] Radio electriques (CISPR), or Committee on Radio Interference.

International

Special

II.BASICS OF SMPS CIRCUIT DIAGRAM AND IT‟S WORKING PRINCIPLE An S.M.P.S. can be a fairly complicated circuit, as can be seen from the block diagram shown in Fig. 1. (This configuration assumes a 50/60Hz mains input supply is used.) The ac supply is first rectified, and then filtered by the input reservoir capacitor to produce a rough dc input supply. This level can fluctuate widely due to variations in the mains.

Key words- EMC Compliance, EMI filters, EMI Noise, IEC & CISPR Standards, SMPS. I.INTRODUCTION or many years the world of power supply design has seen F a gradual movement away from the use of linear power supplies to the more practical switched mode power supply(SMPS). Furthermore, by employing high switching frequencies, the sizes of the power transformer and associated filtering components in the SMPS are dramatically reduced in comparison to the linear. This is now an essential requirement for the majority of electronic systems. When designing switch mode power supplies (SMPS), undesirable noise and Electromagnetic Interference (EMI) are always present. Their effects are even more severe as the switching frequency increases, especially in applications requiring the use of small size transformer and capacitors. This investigation describes the nature and sources of EMI noise, and the design techniques used to reduce their shortcomings. The EMI noise in power converters generally can be associated with the layout and design. For a cost-effective and timesaving approach to design, the EMI noises in switch-mode power supply (SMPS) need to be investigated in this project. EMC aims to ensure that equipment or SMPS will not interfere with or prevent each other's correct operation through spurious emission and absorption of EMI. The unified standards required to prove the performance limits of our equipment are International Electro Technical Commission (IEC), and Comit‟e International Special des Perturbations

Fig. 1. Basic switched mode power supply block diagram In the SMPS first stage AC input is converted to DC. The inverter stage converts this high voltage DC, to AC by running it through a power oscillator, whose output transformer is very small having few windings at a frequency of tens or hundreds of kilohertz (kHz). The inverted AC is used to drive the primary winding of a high frequency transformer, if the output is required to be isolated from the input, as is usually the case in mains power supplies. This transformer converts the voltage up or down to the required output level on its secondary winding. A feedback circuit monitors the output voltage and compares it with a reference voltage, which is set manually or electronically to the desired output. If there is an error in the output voltage, the feedback circuit compensates by adjusting the timing with which the MOSFETs are switched on and off. This part of the power supply is called the switching regulator. III. EMI NOISES OCCURRED IN AN SMPS While a number of topologies exist for SMPS, the causes of electromagnetic noise are similar in all of them. Since most of the noise is caused by parasitic components in the circuit, one highly critical factor for the reduction of EMI noise is the layout geometry of the boost circuit. When designing switched mode power supplies, undesirable noise and Electromagnetic Interference are always present. Their effects are even more severe as the switching frequency

increases, especially in applications requiring the use of small size transformer and capacitors. This application note describes the nature and sources of EMI noise, and the design techniques used to reduce their shortcomings. The most effective way to handle EMI is to minimize its source, and then use filters to filter away the remaining noise. Therefore understanding the noise sources will greatly help to reduce the effects of EMI. IV. EMC COMPLIANCE SOLUTION FOR AN SMPS The goal of EMC is the correct operation of different equipment in the same electromagnetic environment, with the same electromagnetic phenomena, and the avoidance of any interference effects within the equipment. In order to achieve this, EMC pursues two different kinds of issues: 1. Emission issues are related to the unwanted generation of electromagnetic energy by some source, and the avoidance any remaining energies from source to the external environment. 2. Susceptibility or immunity issues, refers to the correct operation of the equipment, in the presence of unplanned electromagnetic disturbances. In order to comply with EMC, the below mentioned tests are needed to be performed: Emission like, Conducted Emission Test, Radiated Emission Test and Harmonics Emission Test. Susceptibility like, Surge Immunity Test and Electro static discharge immunity Test. At first it is necessary to investigate the EMI noises that is generated, transmitted and also recepted by the SMPS. A. SMPS complied EMC Tests: EMC Testing is required to confirm that a particular device meets the required standards. It divides broadly into emissions testing and susceptibility testing. B.Emissions Testing: Emissions are typically measured for radiated emissions and conducted emissions along cables and wiring. Typically a spectrum analyzer is used to measure the emission levels of the SMPS across a wide band of frequencies. In our testing methods, EMI Test Receivers or EMI Analyzers which is specialized spectrum analyzers for EMC testing are used. These incorporate bandwidths and detectors as specified by international EMC standards. These receivers are used with specified transducers. Conducted Emission test: The purpose of conducted emissions testing is to measure noise currents that exit the product under test‟s (SMPS) ac power cord and make sure these currents are within the regulated limit. It is not sufficient to measure the noise currents on the power cord with a current probe. Instead, the SMPS is connected to a LISN, which stabilizes the impedance seen by the product looking out the ac power cord. Radiated Emission test: Radio frequency emissions tests are used to ensure that other users are protected from the emissions generated when the product is used in their neighborhood. All commercial products will be tested against the standards which are mostly based on CISPR tests. Semi anechoic Chamber: This type of chamber yields ambient-free RF environments and reduces unwanted reflections that are encountered in shielded enclosures. Harmonics Emission test: In today‟s environment, all computer systems use SMPS that convert utility AC voltage to regulated low voltage DC for internal electronics. These non-linear power supplies draw current in high amplitude short pulses. These current

pulses create significant distortion in the electrical current and voltage wave shape.This is referred to as a harmonic distortion and is measured in Total Harmonic Distortion (THD). C.Susceptibility Testing: Transient immunity is used to test the immunity of the SMPS against power line disturbances which includes surges, lightning strikes and switching noise. Electrostatic discharge test: Electrostatic discharge testing is typically performed with an "ESD pistol" which is a piezo spark generator. Electrostatic discharge (ESD) flows between two objects at different electrical potentials. When ESD flows between that objects, the sudden and momentary electric current is caused by direct contact or induced by an electrostatic field. The main causes of ESD events are static electricity. ESD is one of the major causes of device failures in the semiconductor industry. Lightning Surge: It is unfortunate, but a fact of life, that SMPS environments can be damaged by high-voltage surges and spikes. Such power surges and spikes are most often caused by lightning strikes.Conceptually, lightning protection devices are switches to ground. Once a threatening surge is detected, a lightning protection device grounds the incoming signal connection point of the equipment being protected. Thus, redirecting the threatening surge on a path-of-least resistance (impedance) to ground where it is absorbed.

Fig: 2: Surge Coupling Components V.TEST SETUP AND METHODOLOGIES TO DETECT AND ANALYSE EMI NOISES A. Test Methodology Adopted for Conducted Emission: Table 1:Test Specifications for CE Test CISPR 22 Class A Limit in dBµV Frequency (MHz) Quasi- peak Average 0.15 to 0.5

79

66

0.5 to 30 73 60 The Conduction test was carried out in both Quasi Peak and Average mode in the frequency range of 150 kHz to 30MHz. Table 2: Calibration Details of Conducted Emission Test Test Equipment

Location

Model No.

Sl No.

EMI Receiver

HCL Lab

ESIB26

100360

LISN

HCL Lab

ESH2-Z5

100150

Fig.3: Test Setup for Conducted Emission Test Photographs of CE Test setup

B. Test Methodology Adopted for RADIATED EMISSION: Table 3: Test Specifications for RE test- CISPR 22 Class A Frequency (MHz)

Quasi Peak Limit for 10 meter distance (dBV/m)

30 -230

40

230 -1000 47 The measurement was carried out inside the shielded semi anechoic chamber. The EUT placed over the turntable and energized by 230V AC 50Hz. The distance between the EUT and the ultra log antenna was 10m. Radiated Emission from the EUT was picked up by the ultra log antenna in the frequency range of 30MHz to 1GHz. The EUT was rotated from 0° to 360° and the antenna height varied from 1 to 4meter to maximize the emission. Table 4:Calibration Details of Radiation Emission Test Test Equipment 10mSemiAnechoic chamber

Location

Sl No.

Manufacturer ETS Lindgren

HCL Lab

AP871

EMI Receiver

HCL Lab

100360

R&S

Ultra Log Antenna

HCL Lab

100287

R&S

Fig.4: Test Setup for Radiated Emission Test Photograph of Radiation Emission Test Setup:

C. Test Methodology Adopted for HARMONIC EMISSION: Table 5: Calibration Details of Harmonic Emission Test Test Equipment

Location

ESD Simulator with Gun

HCL Lab

Three phase power source

Three phase harmonics analyser

Model No. ESS2002

Manufacturer Noise ken

SMPS

Fig.5: Test Setup for Harmonics Current Emission Test Photograph of Harmonics Emission Test

D. Test Methodology Adopted for ESD Test: During the test the SMPS was placed on the ground reference plane with 10cm insulation support. Contact Discharges were injected with increasing amplitude from ±2kV to ±4kV on all conductive points of the EUT. Air discharges were injected with increasing amplitude from ±2kV to ±8kV on all non- conductive user accessible parts of the SMPS. Table 6:Test Specifications for ESD as per IEC 61000- 4-2 No. of Severi Type of Huma dischar ty Discharge Discharg n body ge per Voltag points e model test e point Indirect Discharg Level 4 sides of 2: +/e the EUT HCP 4kV &VCP Level All Direct accessible /Contact 2: +/conductive Discharg 4kV 330 Ω 10 +ve points of the e /150pF & 10-ve EUT. pulses All accessible Level non Air conductive Discharg 3: +/points of the 8kV e EUT.(LED‟ s)

Table 7:Calibration Details of Electrostatic Discharge Test Test Locatio Model Manufactur Equipment n No. er ESD HCL ESSSimulator Noise ken Lab 2002 with gun

Fig.6: Test Setup for Electro Static Discharge Test Photograph of ESD Test setup

Graph 2: Conducted Emission in Neutral at 230V AC 50Hz Le v e l i n d B µ V 80 C IS P R 2 2 V o l ta g e o n M a i n s Q P C l a s s A 70

C IS P R 2 2 V o l ta g e o n M a i n s A V Cl a s s A 60

50

40

30

20

10

0 150 k

300

400

500

800

1M

2M

3M

4M

5M

6

8

10M

20M

30M

F r e q ue nc y i n H z

Blue Trace ◊-Quasi peak Detector, Green trace ◊-Average Detector E. Test methodology adopted for Lightning Surge immunity: SMPS was energized by 230V AC 50Hz.During the test the SMPS was placed above the metallic ground plane with 10cm insulating support. The Surge test was conducted up to level 3 (±2.0kV). Table 8:Surge Test Specifications as per IEC 61000-4-5:2005 Test Parameters Specifications 1.2/50 µs (open circuit Voltage); Pulse form 8.0/20 µs (Short circuit current) for power line Pulse Amplitude ±2.0kV Output Impedance 2 Ω – Differential mode(±1.0kV) (Power Line) 12 Ω – Common mode(±2.0kV) Repetition 60s Number of Pulses 5 Positive, 5 Negative Phase positioning 0º, 90º , 180º, 270º Coupling Mode L-N, L-PE, N-PE, L N-PE

The Conducted RF emission from the SMPS was observed for the specified limits of CISPR 22 Class A. Graph 3&4 shows the CE in 230V AC, 50Hz Line and Neutral (CISPR22 Class A) passed Plots(with EMI Filter). Table 10:Test Results for CE Test 230V AC50Hz Test Parameter

Standard

Date of test

Conducted Emission

CISPR22, Class A

30-12-2012

Result

p

P: Meets the requirements F: Does not meet the requirement Graph 3: Conducted Emission in Line at 230V AC 50Hz Le v e l i n d B µ V 80 C IS P R 2 2 V o l ta g e o n M a i n s Q P C l a s s A 70

C IS P R 2 2 V o l ta g e o n M a i n s A V Cl a s s A 60

50

40

Photographs of Surge Test Setup

30

20

10

0 150 k

300

400

500

800

1M

2M

3M

4M

5M

6

8

10M

20M

30M

F r e q ue nc y i n H z

Blue Trace ◊-Quasi peak trace ◊-Average 10Detector, cm Green Insulation Detector Support Graph 4: Conducted Emission in Neutral at 230V AC 50Hz Le v e l i n d B µ V 80 C IS P R 2 2 V o l ta g e o n M a i n s Q P C l a s s A 70

C IS P R 2 2 V o l ta g e o n M a i n s A V Cl a s s A 60

50

VI. RESULT ANALYSIS OF EMI NOISES IN AN SMPS WITH AND WITHOUT EMC COMPLIANCE

40

30

20

10

0 150 k

A. TEST RESULTS for CE TEST: The Conducted RF emission from the EUT was observed below the specified limits of CISPR 22 Class A. Plot 1, 2 shows the CE in 230V AC, 50Hz Line and Neutral (CISPR22 Class A) failed Plots (without filters) Table 9:Test Results for CE Test 230V AC50Hz Test Date Standard Result Parameter of test Conducted CISPR22, 30-Oct-2012 F Emission Class A P: Meets the requirements F: Does not meet the requirement Graph 1: Conducted Emission in Line at 230V AC 50Hz Le v e l i n d B µ V 80 C IS P R 2 2 V o l ta g e o n M a i n s Q P C l a s s A 70

C IS P R 2 2 V o l ta g e o n M a i n s A V Cl a s s A 60

50

40

30

20

10

0 150 k

300

400

500

800

1M

2M

3M

4M

5M

6

8

10M

20M

30M

F r e q ue nc y i n H z

Blue Trace ◊-Quasi peak Detector, Green trace ◊-Average Detector

300

400

500

800

1M

2M

3M

4M

5M

6

8

10M

20M

30M

F r e q ue nc y i n H z

Blue Trace ◊-Quasi peak Detector, Green trace ◊-Average Detector B. TEST RESULTS FOR RE TEST: The emission radiated from the SMPS without the EMI filter was observed to be below the specified limits of CISPR 22 Class A standards in both the horizontal and vertical polarization of the antenna. (WITHOUT FILTER) Table11:Test Results for RE Test 230V AC 50Hz Test Standard Date of test Result Parameter Radiated CISPR22, 15-Nov-2012 F Emission Class A P: Meets the requirements F: Does not meet the requirement

Graph 5: Radiated Emission in Vertical polarization:

Graph 6: Radiated Emission in Horizontal polarization:

The emission radiated from the SMPS with EMI filter design was observed to meet the specified limits. Table 12:Test Results for RE Test 230V AC 50Hz Test Parameter Radiated Emission

Standard

Date of test

CISPR22, Class A

Result

20-01-2013

p

P: Meets the requirements F: Does not meet the requirement Graph 7:RE in Vertical polarization (with filter) 80

70

Le vel in dBµ V/m

60

50

C IS P R 2 2 E l e c tri c F i e ld

S tre n g th 1 0 m

QP

Cla s s

3

2.30

5

1.14

7

0.77

9

0.40

11

0.33

13 15 ≤ n ≤ 39 Odd harmonics only Even Harmonics

0.21

2

1.08

4

0.43

6

0.30

0.15*15/n

0.23*8/n 8 ≤ n ≤ 40 TEST RESULTS for Electro Static Discharge: Table 15:Test specifications for Electro Static Discharge: Test Date of Standard Result Parameter testing Electrostatic IEC 6100015-Nov-12 P Discharge Test 4-2:2008 P: Meets the requirements F: Does not meet the requirement Table 16:Test Observations for Electrostatic Discharge Test Indirect Discharge Observations:

A

40

30

20

10

0 30M

50

60

80

100 M

200

300

400

500

800

1G

F r e q ue nc y i n H z

Graph 8:RE in Horizontal polarization(with filter) 80

Test levels(kV)

Vertical coupling plane (VCP),All conductive and Non-conductive parts of the SMPS

+2 ±4

No malfunction was Observed in the EUT during and after the test

70

Le vel in dBµ V/m

60

50

C IS P R 2 2 E l e c tri c F i e ld S tre n g th 1 0 m QP C l a s s

A

40

E. TEST RESULTS FOR SURGE TEST:

30

20

10

0 30M

50

60

80

100 M

200

300

400

500

800

1G

F r e q ue nc y i n H z

Table 13:Harmonic Current Emission Test Result Date of Test Parameter Standard Result testing Harmonic Current IEC 61000-330-01-2013 P Emission test 2:2009 P: Meets the requirements F: Does not meet the requirement Graph 9:Spectrum 230V AC 50Hz

The Harmonic Current Emission from the SMPS AC mains input 230V AC 50Hz was measured using Harmonic Analyzer.

Table 17:Calibration Details of Surge Test Test Equipment Surge Generator

Location

Manufacturer

Calibration status

HCL Lab

Keytek

10-Feb-2013

Table 18:Test observation of Surge 230V AC 50Hz Test Levels

Coupling mode

Observation

+0.5kV to+2kV

L-N, L-PE, NPE, L N-PE

No malfunction was Observed in the EUT during and after the test

±1.0kV

L-N, L-PE, NPE, L N-PE

No malfunction was Observed in the EUT during and after the test

±2.0kV

L-PE, N-PE, L N-PE

No malfunction was Observed in the EUT during and after the test

Table 14:Harmonic Current Emission Test Specifications Harmonic order N Odd Harmonics

Maximum permissible harmonic current A

VII. CONCLUSION An SMPS which produces a regulated 24V DC output has been tested for EMC compliance. After the completion of

every test, the appropriate results for the corresponding tests are also reported by means of various plots and graphs. The conducted emissions presented in the SMPS can be controlled by the use of special EMI filters (Snubbers, MOV and special capacitors) in the SMPS. The Radiated emissions are arrested by the use of Ferrites in the input and output power cords to meet the limit line mentioned in the CISPR 22 standard. Harmonic emission tests are found to be produce pass result with our specially designed SMPS. ESD test was conducted and the SMPS was grounded properly to withstand the standard requirement of 8kV as per IEC61000-4-2. Surge immunity test and Harmonics emission test from the SMPS are also has to be observed as per IEC 61000-3-2. To overcome this problems we have initiate the MOV to clamp the spike voltage coupling through a power line. Then only the EMC requirement of both Emission and Immunity of the SMPS is complied and we can self certify this product for CE certification.

X. REFERENCES [1]

[2]

[3]

[4]

VIII.APPLICATION SMPS have applications in various areas. A switchedmode supply is chosen for an application when its weight, efficiency, size, or wide input range tolerance make it preferable to linear power supplies. Initially the cost of semiconductors made switch-mode supplies a premium cost alternative, but current production switch-mode supplies are nearly always lower in cost than the equivalent linear power supply. 1. Personal computers 2. Battery chargers 3 .Central power distribution 4 .Vehicles 5 .Consumer electronics 6 .Lighting 7 .Space station

[5]

[6]

[7] [8]

[9]

[10]

IX. ACKNOWLEDGEMENT I would pay my sincere devotion to The Almighty, My Parents and My Mentor, who filled me with wisdom and knowledge and rendered me good health and make me to finish this project successfully, the satisfaction and delight that accompany the successful completion of any task would be incomplete without mentioning the people who are responsible for the completion of this project. Last but not the least I thank to all my friends for their moral support and technical discussions in doing the project.

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