Arquivos Mensais: maio 2018

Scalar and Vector Inverters

The inverters can be classified into two types: scalar inverter and vector inverter. Both have the same operating structure, differing only in the way the torque is controlled.

In the scalar inverter, the V / f curve is fixed (parameterized) based on the type of working regime in which the inverter will operate. There is, however, a problematic condition, which is precisely the critical point of any AC drive system: low rotations.

The AC system does not achieve satisfactory torque at low speeds due to the AC motor’s own performance. To compensate for this phenomenon, the vector frequency inverter was developed, which, although much more expensive and complex than the scalar, does not work with a preset V / f curve (parameterized).

In fact, it varies voltage and frequency in order to optimize the torque for any rotation condition (low or high). And as if every millisecond a new V / f curve was parameterized for each new situation. The vector inverter controls V / f by means of the magnetizing and rotoric currents of the motor. Generally, a tachometer or an encoder are used as speed sensors, forming a “closed loop” of speed control.

The Transformers

A transformer is a device that modifies a sinusoidal alternating current with a certain voltage, in a sinusoidal electric current, with a generally different voltage, this transformation being done through the action of a magnetic flux.

It is therefore something that transforms electric energy into electrical energy (with different characteristics), maintaining electrical independence – there is no point of electrical connection – between the two voltages of the transformer.

We also observe the principle of energy conservation, it is clear that the same power (P = W / t) is maintained on both sides of the transformer, which causes changes in voltage to cause changes in terms of current, keeping the energy that “enters” equal to the energy that “comes out”.

The creation of the magnetic flux is made with a coil of wire through which an electric current that is variable in time is passed (Lenz-Faraday’s law). The different tension value is achieved by placing a second coil of wound wire around the same iron part.              730473-001-15748

The first coil, where the voltage source is connected, is called the primary coil, and the second coil, where the different voltage is drawn, is called the secondary coil.