VLT ® 2000 Series I The Danfoss VVC principle VLT 2000 Series frequency converters use an inverter control system known as the Voltage Vector Control (VVC) developed by Danfoss. The VVC principle is superior to the traditional PWM (Pulse Width Modulation) principle used in most modern frequency converters in the following ways: − Full-rated motor voltage at rated motor frequency. − Near perfect resemblance to the sinusoidal mains supply. − Extremely low switching losses, resulting in high converter efficiency. The features are obtained through a special switching pattern:
the switching intervals are very short, which means high switching frequency, and the six semiconductors of the inverter section are alternately held inactive in pairs, throughout a 60 ° sine period. The current wave form of the motor current closely resembles that obtained on mains operation. The switching pause in 60 ° of the sine period also means that full-rated motor voltage can be obtained - and inverter switching losses are reduced by about one third. How the VLT works The figures below show the switching pattern and maximum motor voltage according to the VVC principle and the traditional PWM principle respectively.
The full-rated motor voltage and the perfect current wave form mean that the Danfoss VLT 2000 Series allows full motor performance without any derating - just like running the motor on the mains. Section 1 Section 2 Section 3 Motor voltage and simplified switching pattern according to the Danfoss VVC principle 1,00 U-V U-W W-U U-V V-W W-U 0,50 0,00 0 360 -0,50 -1.00 Motor voltage and simplified switching pattern according to the traditional PWM principle 1,00 0,866 U-V V-W W-U 0,50 0,00 0 60 120 180 360 -0,50 -1.00 Switching pattern for phase U Single phase voltage Phase-phase voltage for motor MG.20.B6.02 – VLT is a registered Danfoss trademark 23 6 0 18 2 40 300 2 40 300