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Frequency Converter SD4M

Standard converters in the higher power classes typically use the well-known technology of two-level pulse width modulation (PWM) with max. 8 kHz switching frequency. In most high-speed applications, this requires additional components such as LC filters or chokes to minimize the additional losses in the engine. SIEB & MEYER frequency converters of series SD4M are specially designed for high-speed applications and use the innovative three-level technology – also called multi-level technology.

The SD4M devices follow the successful SD2M series and are designed for stationary use in control cabinets of turbo compressors as well as for applications such as ORC, gas expansion and flywheel.

The Top Booster

The three-level technology is of great advantage in these applications because in most cases the SD4M converters do not require motor filter elements. This additional value is achieved by the three-level technology, as well as the PWM switching frequency of up to 16 kHz as standard and optionally up to 32 kHz for dedicated versions. The combination leads to a considerably improved motor current quality, which significantly reduces the undesired rotor losses – by up to 90 %!

Three-level PWM
Standard converter
Two-level PWM with motor choke
Standard converter
Two-level PWM with LC filter
Low weight X X
Small installation space X X
No risk of resonance effects X
Total costs X X



  • Three-Level Technology

    The output stages of SD4M Turbo are based on a three-level technology and provide rotating field frequencies up to 2,000 Hz with switching frequencies of 16 kHz.

    Reduced motor losses combined with minimum efforts for motor filters and motor chokes as well as low interfering radiation and insulation stress.

    Low system costs over the whole product life cycle.

  • Efficiency

    The devices reach efficiencies of up to 98 %.

    The high efficiency of the devices ensures optimal system efficiencies and reduces cooling requirements.

    Maximum system output and lower environmental footprint due to lower energy consumption.

  • DC Supply

    Active emergency braking and maintenance of voltage supply in case of power supply failure.

    No separate voltage supply for the magnetic bearings needed.

    Protection of the magnetic bearings in case of power failure as well as cost savings.

Our Experience in High-speed Technology - Your Advantage!

Up to 60 % reduced installation space for the required electrical components

Improved availability due to the reduced number of components

Up to 50 % reduced weight for the required electrical component

Reduced environmental footprint due to lower energy consumption

Significantly less wiring- and assembly work

Connectivity for the future Ethernet/web server/EtherCAT/Modbus

Cost reduction for IPM the drive chain

Maximum performance of IPM motors through dynamic operating point control

Improved efficiency of the overall system

Motor Currents by Comparison

Good to Know

  • Currently available power classes from 100 to 500 kVA, with up to 800 Aeff rated current.
  • Liquid cooling as standard (water-based), air cooling on request
  • NRTL/CSA certified
  • Very low insulation stress on the motor winding - even with long motor cables - due to 50 % smaller PWM switching amplitudes (see graphic below)
  • Optional DC power supply for active magnetic bearings, via internally fused DC link terminals
  • Designed for 100 % utilisation 24/7
  • All power components designed for 10 years continuous operation at rated load
  • Designed for worldwide 3-phase supply networks - also potential-free IT
  • Powerful parameterisation and diagnostic software drivemaster4
  • Customer-specific solutions can be realised
  • 3C3 protective coating of the printed circuit boards for operational safety in aggressive environments

The Interfaces of Frequency Converter SD4M

  1. Mains voltage
  2. Logic board
  3. Motor connection
  4. Liquid cooling

Drive Functions and Safety Functions


Simulation, commissioning, monitoring: drivemaster4


  • Electrical operating points
  • Influence of PWM frequency/inverter topology
  • FFT analysis including THDi/THDu calculation
  • Export of simulation data


  • Parameterisation of the motor data/interfaces
  • Optimisation by means of oscilloscope
  • Commissioning tool


  • Data logger
  • Real-time clock
  • Error memory
  • Operating hours counter

Technical Specifications of Frequency Converter SD4M
with 3-phase AC Mains Voltage without Brake Chopper

Device type Nominal power1 Nominal current Max. Output voltage1 HxBxT (mm) Weight Cooling
Compact units - 3 x 200...480 VAC mains voltage


120 kVA 165 Arms 3 x 410 VAC 685 x 388 x 188 30 kg Water 2) 4)
180 kVA 255 Arms 3 x 410 VAC 771 x 439 x 207 43 kg Water 2) 4)
228 kVA 310 Arms 3 x 410 VAC 771 x 439 x 207 43 kg Water 2) 4)
342 kVA 480 Arms 3 x 410 VAC 1317 x 326 x 489 94 kg Water 2) 3)
438 kVA 630 Arms 3 x 410 VAC 1317 x 326 x 489 94 kg Water 2) 3)
500 kVA 800 Arms 3 x 410 VAC 1478 x 353 x 596 136 kg Water 2) 3)

1) Rated power and max. output voltage with mains voltage/supply voltage printed in italics.
2) Cooling tubes aluminium
3) Copper cooling tubes
4) Air-cooled variants and variants with other cooling tube materials on request.    


  • In the field of turbomachines, the system's efficiency can be continuously improved by increasing the system speed or omitting the gear. 


  • Due to their design, a large number of technologies in the field of waste energy usage or mechanical energy storage require high-speed motors and generators


  • Rotary atomization processes, e.g. applied for the production of milk powder or flue gas treatment, require high circumferential speeds. Therefore, it is necessary to use matching high-speed motors instead of low-speed standard motors.


  • Refrigeration units with turbo or centrifugal compressors with higher power ranges operate with high speeds. Frequency converters by SIEB & MEYER easily provide the required speeds and their control method ensures an exceptionally low rotor heating.



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