EMC Output Filter Solutions

Compared to the various concepts for output filters, the new SineFormer is both technically and economically the superior solution.

Concept with dv/dt choke

Advantages and disadvantages

• + Reduces dv/dt peaks significantly
• + Low cost solution
• - Motor cable is limited to approx. 100m
• - No reduction of noise
• - Shielded cable necessary

Concept with sine-wave filter

Advantages and disadvantages

• + Reduces dv/dt peaks significantly
• + Forms a sinusoidal wave between the phases
• + Reduces noise
  
• - Reduces eddy currents
  
• - Relatively expensive solution because shielded cables still have to be used
  

Concept with SineFormer

Advantages

• + Motor size can be reduced
  
• + Motor operating life can be significantly increased
  
• + Unshielded motor cables can be used, thus reducing assembly expenditures, increasing the operating life and reducing cable costs
  
• + Longer motor cables possible (ub to 1000 m unshielded measured)
  
• + No maintenance costs, as the Sine Former is built without forced ventilation
  
• + Compact filter solution (not modular system) with lower volume and weight
  
• + Reduced requirements for the power line filter
  
• + Increased equipment availability
  
• + Also suitable as a retrofitting set
  

Advantages of a SineFormer solution compared with other output filter solutions using examplary measurements

Frequency converter without output filter

Measurements

High-frequency interference requires a shielded motor cable.

Figure 1:

Phase-to-phase voltage

Figure 2:

dv/dt

Frequency converter with dv/dt choke

Measurements

Steep current and voltage rises at the output of the frequency converter are evened out by the inductance, while the parasitic capacitances of the motor cable are charged and discharged less powerfully. Motor chokes are used mainly for protecting motor windings against voltage spikes.

Figure 3:

dv/dt

Frequency converter with sine-wave filter

Measurements

Sine-wave filters are designed as LC filters. Unlike motor chokes, however, their limit frequency, lies between the output frequency and the converter clock speed. As the sine-wave filter mainly suppresses the symmetrical interference between the lines, the interference acting on the phase-to-ground voltage is hardly reduced at all. Therefore, the motor leads still require shielding. Sine-wave filters reduce the motor noise and the eddy current losses and permit the use of motor leads much longer than 100 m.

Figure 4:

Phase-to-phase voltage

Figure 5:

Phase-to-ground voltage

Frequency converter with SineFormer

Measurements

Figure 6:

Phase-to-phase voltage

Figure 7:

Phase-to-ground voltage

Comparison of bearing currents in the various output filter solutions

High frequency common-mode interference is generated by the switching behavior of IGBTs. This interference propagates over the motor cable and is conducted to ground via the parasitic capacitance of the cable and the motor. Currents flow through the bearings in the motor, which can lead to increased wear and tear and premature damage of the motor bearings.

Bearing currents without output filters

Measurements

Bearing currents with sine-wave filter

Measurements

The series inductor of the sine-wave filter mainly has a symmetrical effect and only to a small degree asymmetrical. For this reason the high-frequency interference continues to flow through the motor cable, meaning that it is still necessary to use a shielded motor cable. Moreover, bearing currents are only slightly reduced.

Bearing currents with SineFormer

Measurements

Motor chokes for drives B86301U*R000/S000

Motor chokes reduce the voltage stress at the motor and the dv/dt increase at the frequency converter output.

Features

• 4 to 1500 A / 520 V
• 1% impedance reactor
• Easy to install
• Low weight
• Compact design
• Design complies to IEC 60076-6
• UL approved isolation system class F (155 °C)

Sine-wave output filter series B84143V*R227/R229/R230

Features

• Complete design from 4 A up to 720 A / 520 V (R227/R230)
• 690 V version: R230 up to 204 A
• Designed for motor cables up to 1000 m
• Slim design unique in the market
• UL approved isolation system

SineFormer^®: Best output filter solution

Features

• Complete design
  from 6 A up to 180 A / 520 V (-R127 series)
  and 95 A up to 320 A / 760 V (-R290 series)
• Commercial advantages
  System-cost savings due to the use of unshielded cables
  • Automatic cost savings from a motor-cable length of approx. 100 m
• Technical benefits
  Longer life cycle of the motor, motor noise reduction, substantial compensation of bearing currents and eddy current losses, no forced ventilation necessary
  • Maintenance-free (fan would have a life cycle of 2 to 4 years only), no feedback to the DC link needed
  • Reduction of all kinds of radiation sources by easy installation
• Installation advantage
  Unshielded cables are lighter and more flexible
  • Cost savings during installation
• Logistics advantage
  Unshielded cables are standard products