Inverter – Frequency Variator Drive (VFD)

Normally, both nomenclatures are used when we talk about equipment capable of changing frequency.

However, Inverter is a technology associated with the conversion of DC Voltage to AC Voltage.

Inverters are used in diverse equipment: Frequency Variators; Unit power supply (UPS); Air conditioning equipment; etc.

We are only talking about VFD from a power perspective for a motor – scalar control.

 It is extremely important to change the speed of a motor – this allows you to have control over the speed of machines, like controlling the tension in a fabric, for example. But we can think of a fan or a pump.

On the other hand, engine power is related to the 3rd power of angular velocity

This means that when reducing speed, power is greatly reduced and so is energy cost.

Frequency variators are increasingly complicated as the vector VFD that allows high precision in speed synchronization in systems with feedback by coupling encoders or resolvers or other type.

Finally, to mention that with a simple filter can transform AC (rectangular wave with sinusoidal shape) into a perfect AC sine wave (for example necessary in a UPS).

I will go present the concept of frequency Inverter applied to motors that work perfectly with a sin wave formed by rectangular impulses with a T variable and with impulse variable with a sinusoidal envelope.

Basically there are two stages:

i)                    Convert AC for DC 

ii)                   Convert DC to AC with frequency control and making constant the relation V/f to have a torque constant (pumps for example).

This issue ii) is the most important – essentially, is in this stage that stands out all complex software to program the switching and the hundreds of configuration parameters.

The power hardware consists in Diodes, capacitor for rectification and Thyristors for switching.

Summarizing:

Scalar control: simpler and cheaper: for fans, pumps… equipment does not require great precision.

Vector control: very complicated and extremely expensive: high precision in speed regulation; High-performance dynamics; High torque control even at low speeds and different loads.

#Inverter