Differential and common mode passive motor filters Dennis Kampen, EWG [email protected] Tel. +49 (0)4231 678 178

Agenda • Differential mode and Common Mode • Differential mode filters – Topologies – effects

• Common mode filter – Topologies – Effects

• Materials • Summary

Differential and Common Mode definition Differential mode voltage

inverter

uab  t   ua0  t   ub0  t   

 

 

load grid

Common mode voltage uM0  t   

The inverter generates no pure symmetrical voltage system. A common mode voltage remains.



ua0  t   ub0  t   uc0  t   

 

3

 

Distribution of disturbances Differential mode and common mode HF-disturbances are not damped by line reactors or harmonic filters.

Differential mode path Grid impedance

Line inductor

Differential mode path

Common mode path

parasitic motor/ cable capacitance

The motor side inverter generates differential mode disturbances between the phases on motor and line side. Common mode currents are driven over the motor and cable capacitances to Earth and back over the line side to the input rectifier and the DC link.

Distribution of disturbances conducted emissions>150kHz

Differential mode

Common mode

The grid can be safely protected against disturbances of all frequencies with a line inductor or a hamonic filter and in addition an EMI-Filter.

Motor filter

Motor terminal voltage

Inverter output voltage

wave forms without filter

Motor current

Motor starpoint – Earth voltage

cable

grid

motor

Motor leakage current

Line leakage current

Motor phase voltage

Differential mode motor filters motor choke, dv/dt-filter

Inverter output current

Motor current Motor terminal Leiter Leiter Spannungvoltage am Motor

Spannung / V

800 400 200 0 -200 -400 -800 40.00m

50.00m Zeit /s

60.00m

Motor starpoint – Earth voltage

grid

Cable motor

Motor leakage current

Reduction of differential mode dv/dt