Conventional technology generates AC with variable frequency by using Pulse-Width Modulation, (PWM). All competitors use PWM-technology in all competing products. With PWM, the voltage is rapidly switched into short pulses with variable width in such a way that the average of the voltage will approximately be equal to what the motor recieve from a sinus curve. This leads to several drawbacks.
NFO Drives AB is the only company that uses patented technology to generate a pure sinusoidal voltage output directly, without any filters.
Complete absence of radio interference
With a pure sinusoidal voltage, problems with radio interference and ground currents are completely eliminated. The risk for insulation break-through and damage to bearings from electro-erosion are reduced to a minimum. Switching losses in the cables are completely eliminated. The only limitation to cable length is set by its resistance.
PWM-pulses are reflected at the end of cables. Such reflections may cause voltage spikes with a voltage up to twice the DC link voltage 1130V in 400 v system. The cable insulation and the stator winding may be damaged, especially in old cables not designed to withstand this kind of over-voltage. Older motors may not have sufficient insulation. In some motors, the bearings may rapidly be damaged by electro-erosion.
PWM systems will cause severe interference with radio / TV, mobile phones, wireless networks and similar systems. To avoid this, external filters and shielded cables will be required whenever conventional frequency converters are used. A shielded cable will increase the load, and the converter shall have to be placed near the load, not where the user might prefer to have it, for instance together with other electrical installations in the basement.
NFO’s Natural Field Orientation (NFO) makes it possible to control the speed of an asynchronous motor exactly to the required rpm, which otherwise would require an additional sensor and extra control electronics. With NFO, the motor will deliver its rated torque from start and at any speed. In many applications this will make it possible to select a smaller and less expensive motor than when PWM is used.
Certified EMI performance
Mobile phones, personal computers, the Internet, Satellite-TV and wireless local area networks are becoming ubiquitous. To safeguard the proper function of such devices, the European CE-mark, the EMC-Directive (EMC- Electromagnetic Compatibility) and the U.S. FCC regulations were adopted. They define the maximum amount of Electromagnetic Interference, EMI, electronic equipment is allowed to emit, and also how much EMI the equipment must withstand without impeding its functionality.
NFO’s frequency converters are interference-free. The NFO Sinus Inverter G2 are the only converters that are certified according to the Medical Directive for hospital equipment. Most manufacturers are not even certified for use in office buildings or light industry. In contrast to NFO devices, additional measures to reduce interference become mandatory.
