VFDs for induction motors use power electronics switching technologies to supply AC power of variable frequencies to motors. This allows direct control of motor speed and improves efficiency. The output voltage waveform of a typical VFD is based on pulse-width modulation (PWM). The amplitude, duty cycle, and periodicity of the PWM waveform decide the effective voltage and frequency of the VFD output. The voltage and frequency output from the VFD, together with the motor load, are the most important factors that determine the operating point of a VFD-driven motor. VFDs have become the preferred way to achieve variable speed operation as they are relatively inexpensive and very reliable.
ENEVO Group provides a wide range of VFD applications, from 100 kW up to 3 MW. The drive cabinet are designed according to EMC regulations. DC chokes are used to reduce current harmonics in order to comply with the IEC standards. DC choke when used with a passive filter can reduce THDI to 5-10%, while maintaining the motor torque in relation to the line inductance. DC chokes are used for drives in which the line current is more than 16A and less than 75A.
Line chokes are used to provide improved protection against over-voltages on the line supply and to reduce harmonic distortion of the current produced by the drive. They are in line with standard IEC 61800-5-1 (VDE 0160 level 1 high-energy over-voltages on the line supply). The choke values are defined for a phase-to-phase voltage drop of between 3% and 5% of the nominal supply voltage.