PWM Motor Drives and EMC in installations and systems

Transcription

1 PWM Motor Drives and EMC in installations and systems Mart Coenen

2 PWM Motor Drives and EMC in installations and systems Intro Problem definition Why What How Problem solutions Application results Conclusions

3 Intro

4 Problem definition With large systems and installations, the EMC- requirements are primary determined by: the needed functionality (#1) and the needed reliability (#2) of the (end-) system.

5 Problem definition

6 Problem definition; why? Need for measures to: Handle fast switching (power efficiency) Minimize external RF emission/ noise Cost effective integral solutions; drive, filter(s), cable, motor sensor/encoder Overvoltage reduction lacking reference to PE in -systems Bearing erosion reduction

7 Problem definition, what? PWM drive: hard/soft switching w/o di/dt limiter Output filter(s), Cable: shielded/non-shielded Motor(s): DC, 3-phase, multi-phase/stepping

8 Problem definition, what? PWM drive output impedance determined by drive s output topology: Break-before-make (typical) Clamp diodes Capacitances at output di/dt limiter; typ. 3-phase reactor or single inductors often driven, so floating from PE

9 Problem definition, what? Output filters: 2-phase 3-phase 4-phase Sine-wave Power losses and efficiency shall be considered in drive, filter, cable and motor

10 Problem definition, what? Cable(s) Shielded/ non-shielded Cross-sectional symmetry Characteristic impedance Length, propagation delay Number of wires

11 Problem definition, what? Motor(s): Phase winding inductance Phase winding capacitance Phase winding to enclosure capacitances

12 Problem solution, how? Determine equivalent drive characteristics; impedance, dv/dt, di/dt Determine cable characteristics Determine equivalent motor characteristics

13 Problem solution, how?

14 Problem solution, how? Current confinement to ensure that i n (t) = 0 within the shielded cable for all frequencies Reduce RF on motor lines by filtering over various decades of frequency Terminate electrically long cable(s) to avoid standing waves/ resonances Add all measures together

15 Current confinement I I R S ( Z ( Z G G R R j ( M w j ( L Rw M T L )) RT )) Plot1 IDB(IR24), IDB(IR23) in db(amperes) 1 IDB(IR23) 2 IDB(IR24) I S = Source current I R = Return path current Z G = Shield and/or frame impedance M W = Mutual coupling between wire and return wire M T = Mutual coupling due to the CM-choke R R = Resistance of the return wire L RW = Inductance of the return wire L RT = Inductance of the CM-choke k 10k 100k 1Meg 10Meg 100Meg FREQUENCY in hertz

16 RF (di/dt) filtering V5 V X7 SSWITCH X8 SSWITCH D7 40EPS16 D8 40EPS16 R4 1 IR4 16 R7 30 L4 6u V17 17 C4 10n IR1 2 IR X9 SSWITCH D9 40EPS16 R5 1 R8 30 L5 6u V21 Plot1 IR1, IR4 in amperes 0 21 V X10 SSWITCH D10 40EPS C5 10n R u 466.0u 466.4u 466.8u 467.2u TIME in seconds V X11 SSWITCH X12 SSWITCH D11 40EPS16 D12 40EPS16 R L6 6u V25 25 C6 10n Series reactor in combination with cable and motor capacitance may cause resonances

17 Avoid cable resonances Plot1 VDB(V4), VDB(V8), VDB(V16) in db(volts) Ov e rshoot 50 [%] u Se rie s Inductance [uh] 10u 100u Paralle l Resistance [Ohm] 1000u 1 1k 10k 100k 1Meg 10Meg FREQUENCY in hertz 1 VDB(V4) 2 VDB(V8) 3 VDB(V16)

18 Application results Ref 0 dbm Att 10 db 0-10 SWT 5 s 100 khz Ma rker 1 [T1 ] 1 MHz dbm MHz Hz Ref 0 dbm Att 10 db A 0-10 SWT 5 s Hz 100 khz Marker 1 [ T1 ] 1 MHz dbm MHz A 1 SA MAXH SA MAXH SA CLRWR SA CLRWR DB -60 3DB Center 100 khz Sp an 990 khz -100 Cente r 100 khz Span 990 khz 2 Measured common-mode current through motor cable before (left) and after (right) modifications

19 Conclusions Concept is in use for more than 5 years in low and high power applications Common-mode currents on cables can be reduced by 40 db (100 x) in less volume and less power losses!! Overvoltages/ bearing currents can be effectively reduced by factor 10 Spice analyis possible on MoR circuit topology Most components needed are of-the-shelf available Easy to apply in existing installations

20 Conclusions Applying the combined measures eliminate cable screen currents: NO current = NO crosstalk ALL cables can then be routed adjacent to one another with minimum separation (when thermally allowed)