VLT ® 2000 Series How the VLT works I How the VLT is built up A frequency converter is an electronic unit for infinite speed control of a.c. motors. The frequency converter controls the motor speed by converting the fixed volt- age and frequency of the supply mains, e.g. 400 V/ 50 Hz, to variable values. The frequency converter does this by rectifying a.c. voltage to DCvoltage and converting this to a.c. voltage with variable amplitude and frequency. Saved energy Energy is saved when the motor runs at a speed which is continually matched to the momentary requirement.
An example is a pump and ventilating plant, where a frequency converter can reduce energy consumption by the cube of the speed. Improved process Matching the speed to the production process has several advantages: an increase in production and a decrease in the consumption of materials and the scrapping rate. The variable voltage and frequency supplying the motor make infinite speed control of standard three-phase, asynchronous motors possible.Today the a.c. motor controlled by a frequency converter is a natural part of all automised plants. Apart from utitilizing the good fea- tures of the a.c. motor, the infinite speed control gives the user a multitude of additional advantages:
Improved quality The number of starts and stops is reduced. This avoids unnecessarily hard treatment of machine parts. Less maintenance The frequency converter requires no maintenance. In water supply plants there are no pressure surges which might damage the water pipes. 1. Mains supply 1 Ч 220/230/240 V AC, 50/60 Hz 3 Ч 208/220/230/240 V AC, 50/60 Hz 3 Ч 380/400/415/440/460 V AC, 50/60 Hz 6. Inverter Converts DC voltage to variable a.c.voltage and variable frequency. 7. Motor coils (as module) Advantages of motor coils: − You can use long motor cables. − Unlimited switching at the output of the frequency converter (trip may occur). 2.
Rectifier Three-phase rectifier bridge rectifies AC to DC. 3. Intermediate circuit DC voltage = √ 2 Ч supply voltage 8. Output Variable a.c. voltage,10-100% of the supply voltage. Variable frequency: 0-120/0-500 Hz. 4. Coils in the intermediate circuit (not all VLT 2000 units) Smoothen DC voltage and limit mains supply interference (mains harmonics). 9. Control card The integrated computer controls the inverter, which generates the pulse pattern by means of which DC voltage is converted to variable a.c. voltage and variable frequency. 5. Capacitors in the intermediate circuit Smoothen the voltage of the intermediate circuit (energy store).
22 MG.20.B6.02 – VLT is a registered Danfoss trademark