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温安凌
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1 开关电源电磁兼容设计的几个问题 Some key EMC design techniques in SMPS 报告人 : 和军平 (Dr.) Shenzhen City hejunping@hitsz.edu.cn

2 内容一. 开关电源主要 EMC 性能及其改善技术二. 开关电源 EMI 滤波器的协调设计三. 降低 EMI 发射的抖频参数设计四. 温升引起的发射波动及改善五. 瞬态过电压抑制设计的要点六. 结束语

3 一. 开关电源主要 EMC 性能与设计技术传导测试测试 5uH L G N.1uF 5 Ohm 5 Ohm.1uF 5uH SMPS LISN EMI receiver Flyback total

4 辐射发射测试 Chamber SMPS 8cm EMI receiver L1 Input cable 45uH D1 Output cable Rload icm2.47uf M 22μF icm1 PFC

5 雷击浪涌测试信号电缆用的耦合解耦网络接辅助设备接电网 EUT 与发生器或耦合器之间的电缆小于 2 米保护地线要能够承受浪涌电流 ESD 测试

6 EMI Reduction Techniques for Power Electronic Systems EMI Reduction Filter Control Topology Structure Passive Active Drive Circuit Soft Switching Snubber shielding Frequency Forward Feedback modulation Balancing Grounding

7 二. 开关电源 EMI 滤波器的协调设计 Topologies : How to design the filter in a short design cycle? & How to improve the filter performance?

8 Input Filter Design Improve the Design Program ( <1MHz ) Input the Filter Spec Noise Impedance : Filter Spec : C ps C sg C y C sum f stop := 1 p (F) := 15 p (F) := 47 p (F) := 135 p (F) := 195 k (Hz) IL need := 2 (db) Program needs further optimize! Inductors_sum vs. Filter Topology Calculate the Total Inductance of Each Topology Inductor sum.1 LL n, Select the Suitable One IL Curve Analysis L = Total Inductance LL n, Filter Topology.5 1? ? ? ? ? ? -3 IL(dB) 2 IL4( f, L 4 ) Insertion Loss Evaluation k f 3M [Hz] 1

9 Output Filter Design Give the Noise Model ( >1MHz ) L/N 1 2 L line Input Filter Noise Source Output Filter Case 1 L CM_Out ZL CM_Out <<ZC S_G G L line Chassis CM Noise doesn t changed much. C S_G Ground L/N 1 2 L line Input Filter Noise Source Output Filter Case 2 ZC Y_Out <<ZC S_G G L line Chassis C Y_Out CM Noise is decreased. C S_G Ground

10 Output Filter Design L/N 1 2 L line Input Filter Noise Source Output Filter L CM_Out Case 3 ZL CM_Out <<ZC S_G G L line Chassis C Y_Out The same as Case 2. C S_G Ground L/N 1 2 L line Input Filter Noise Source Output Filter Case 4 L CM_Out CM Noise is decreased more. G L line Chassis C Y_Out This is the best. C S_G Ground

11 Experimental Results The test results come from the former debug on 22v-3kw UPS. Better Best Cy_out removed Cy_out restored Cy_out restored Lcm_out shorted Lcm_out shorted Lcm_out restored

12 三. 降低 EMI 发射的抖频参数设计 Frequency jitter can lower EMI in SMPS To exactly predict the noise reduction and optimize the parameters of frequency jitter, the effect of EMI receiver must be considered Amplitude [db] 12.9dB 3.9dB f [Hz] Spectrum of modulated signal in EMI test Original sin signal with fsw=5khz Calculated spectrum of modulated signal without consider the effect of EMI receiver

13 Sin carrier signal S1(t) F(t) S1(t) S S1(t) S2(t) d(s2(t))/dt S1( t) = V 1 sin(2π f t) 1 m Sin modulating signal S2(t) S2( t) = β sin(2π f t) 1 fmax 1/ fmin fc t c m /(2fm) t FM Modulated signal F(t) f ( t) = f ( t) = Frequency of F(t) 1 d 2π f + β c Δf Δf pk pk [ 2πf t + S2( t) ] = [ 2 f t S2( )] F( t) = V 1 sin π t m c + f f c = β m max dt cos 2 f m f ( 2π f t) Peak frequency deviation Δfpk min m

14 Amplitude [db] 4 8 F( t) = V 1 sin(2π f t + β sin(2π f t) m c B B B fc=1khz Modulated signal F(t) Carrier signal S1(t) f [khz] fm f [khz] fm f [khz] m fm=1h & β=2.5 fm=1hz & β=1 fm=4hz & β=2.5 The effective bandwidth (B) of modulated signal B = 2( β + 1) B = ( Δf + f ) f m 2 pk m

15 β: maximum phase angle shift in modulated signal and amplitude of modulating signal Δfpk: peak frequency derivation and amplitude of derivate of modulating signal fm: frequency of modulating signal B: effective bandwidth of modulated signal S1( t) = V 1 sin(2π f t) m S2( t) = β sin(2π f t) c m F( t) = V 1 sin(2π f t + β sin(2π f t)) m c m Δf = β pk f m B = 2( β + 1) f m

16 Sinusoidal signal modulated by three modulating signal Triangular Sinusoidal Exponential Amplitude [db] 1 Peak amplitude reduction f [khz] fc=5khz fm=1hz β = f [khz] fc f [khz] Triangular modulated signal has the maximum flat side-band harmonics spectrum

17 Peak Amplitude Reduction vs. β Amplitude reduction [db] 1 2 tri exp sin β=4 fc=65khz fm=2hz β The reduction increases as β increases Tri modulated signal has the maximum reduction especially when β>4

18 fc=65khz Amplitude reduction [db] fm=1hz fm=1hz fm=2hz fc=1khz fm=2hz fm=5hz fm=5hz The reduction is only the function of β β tri exp sin

19 EMI Receiver s Effect on FM The most impotent parts in EMI receiver s model are intermediatefrequency (IF) filter and detector IF filter has a resolution bandwidth RBW, when spectral components closer in frequency than RBW of IF filter will create a beat note AV detector takes an envelope detected signal and passes it through a low-pass filter IF filter AV detector

20 Equivalent IF Filter The equivalent low pass approximation of IF filter is defined as below: 1 IF( ω) = π ω = B 2 ( ω + jω ) 6, 2*ω B ω 2 = 9kHz 2 IF(w).5 Resolution bandwidth (RBW) of IF filter is 9kHz 9kHz f [Hz] Amplitude [db] 5 sin( 2 π k t) Spectrum of signal: + sin 2 π Spectrum of the signal output of IF filter 2 k t π f [khz]

21 EMI Receiver s Model 2 cos(2πf t) V(t) IF(ω) IF(ω) Vd(t) Vq(t) vd + 2 ( t) vq( t ) 2 VIF(t) VIF( t) dt 2 sin(2πf t) V(t) s frequency response of EMI analyser at frequency of f

22 RBW of EMI Receiver and fm When fm>rbw, the peak amplitude reduction is only the function of β When fm<rbw, the B is more active in lower EMI than β, and the reduction level is the function of both β and fm. In switching power supply as the limit of the minimum operating frequency, fm is usually several hundred or kilo Hz less than RBW

23 Bandwidth of Modulated Signal In SMPS noise signal is almost trapezoid Spectrum of a trapezoid signal Spectrum of modulated trapezoid signal Amplitude [db] 5 Amplitude [db] f [khz] The bandwidth of modulated signal at n-order harmonic (Bn) is : B = 2 ( n β + 1) n f m f [khz] Modulated signal at higher harmonics will have larger bandwidth and more peak amplitude reduction when overlap doesn't happens

24 Optimum Parameters Selection Peak amplitude reduction at third-order harmonic of a square signal Δfp k [Hz] fm [Hz] 2k k k k k k k Max reduction and max fm at 1selected 8 Δfpk 5 2 1k 13. ß=4 2k 1. 9 Test condition: carrier signal is a square wave and fc=65khz modulating signal is triangular

25 Optimum Parameters Selection When fm is selected, the amplitude reduction increases with β (or Δfpk ) increases; When Δfpk is selected and B > RBW, the lower fm the larger reduction When Δfpk is selected and B < RBW, the amplitude reduction is not inverse proportion with fm, there is a trade-off between maximum reduction and maximum fm. The optimal fm can be selected in the look-up table of the experimental results

26 ADP-65JP: 65W flyback adapter, PWM controller is DAP8 DAP8 is Delta s specific device ordered from ON Semi, it has built-in frequency jitter for lower EMI Parameters of jitter in DAP8 Δfpk=3kHz fm =1Hz

27 In order to keep the second-order harmonic of the noise out of the conducted EMI measurement range (.15-3MHz), Δfpk has to be limit as: B k < 15k 2 B 2 = 2 (2 Δf + 1) Δf pk B = 4 f 2 9k pk f m < 5.5k } f 2 2 m m Another limit on Δfpk is the minimum operating frequency of the power supply Δfpk is slected about 4kHz, and fm is selected equal to1khz B2 65kHz 13kHz

28 The EMI noise reduction is about 1dB with AV detector

29 四. 温升引起的发射波动及改善 LC 温度的影响 Z Z T rise T rise ideal Normal 居里点 f fact f f f

30 五. 瞬态过电压抑制设计的要点瞬态干扰对设备的威胁静电放电静电放电静电放电浪涌电快速脉冲电源端口信号端口电快速脉冲浪涌

31 瞬态干扰抑制器件压敏电阻钳位不紧浪涌电压瞬态抑制二极管电流容量不大气体放电管有跟随电流

32 气体放电管的跟随电流寄生电容小电流容量大跟随电流不可用在直流的场合!

33 多级浪涌抑制电路 Z ΔV I 2P V 1 V 2 V V 1 V 2 = 额定工作电压 I 2 = 第二级额定峰值电流 V 2 V + 电压偏差 2 V V 1 V 2 + 电压偏差 1+ 电压偏差 2 ΔV =V 1MAX -V 2MIN V Z ΔV / I 1 2P V 2 V MAX 浪涌一级二级

34 地线反弹与对策 V Z V Z +V G V G 设施地设备参考地若电流为 5kA, 地线阻抗为.5Ω, 则反弹电压达到 25V!

35 六. 结束语 1: 开关电源 EMI 滤波器设计需要综合考虑输入输出侧干扰的传播 2: 抖频需要考虑 EMI 接收机的带宽, 使抖频参数合适, 才能达到预期的降噪效果 3: 开关电源的温升对 EMI 发射性能有影响, 具体趋势取决于温升的高低 4: 过压钳位和过流保护器件合理结合, 可以达到良好的抗瞬态干扰和安全的目的

36 谢谢大家! Thanks for your attention!

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