• UFRJ Nautilus

Power Electronics

Updated: May 7, 2021

Power electronics has as a main objective the conversion and control of electrical energy through the use of electronic components such as transistors, DIACs, TRIACs, among others, being found at high levels of energy such as power plants and in factories or at low levels as in computing and robotics.

The main parameters for this control are voltage, current and frequency. Voltage and current would be reasonably easy to control, but there are problems such as heat dissipation or magnetic losses. In this case, power electronics are more viable because avoid these problems with switching systems, controlling electrical pulses, consequently controlling the frequency of the signal.


The main applications are:


Rectifier circuits are circuits that convert an AC signal to a DC signal and are divided into two categories: controlled and uncontrolled.

Uncontrolled circuits are composed of only diodes, with the possibility of having a single one, featuring a half wave output (where only half the cycle is used due to the diode polarization), or 4 diodes (known as diode bridge), resulting in a full wave rectification (where the distribution of the components takes advantage of the whole AC signal at the input). Since the output ends up as a pulsating continuous signal, it is interesting to use capacitors in parallel to the circuit to try to use the peak voltage as a continuous signal, this is due to the fact that the capacitor works as an open circuit when it is fully charged.

Circuito retificador não controlado UFRJ Nautilus
Uncontrolled rectifier circuit

Controlled rectifiers, unlike uncontrolled ones, are made up of SCRs (Silicon Controlled Rectifier), where, in addition to having positive and negative poles, it has a gate that is responsible for determining the current flow at the main terminals. At each semicycle, the gate switches allowing the current to pass in a certain polarity. The circuit starts to be controlled when the moment of switching is determined in relation to the phase of the input signal (which may delay or advance the current in the SCR).

Circuito retificador controlado num sistema trifásico UFRJ Nautilus
Rectifier circuit controlled in a three-phase system


The chopper is a circuit that converts a DC signal with a fixed intensity to a DC signal with a different voltage. Better known as a linear voltage regulator, it is most commonly used in systems that have a single power supply and several elements with different input voltage.

This system consists of power semiconductors, operating as passive elements and switches (inductor and capacitor). The output voltage is controlled by an active switch (usually with transistors) and a passive switch (usually with diodes). The intensity of the output signal is a result of the frequency in the switching, this technique is called PWM (Pulse Width Modulation) and the output has a filter to prevent voltage variation.

Exemplo de um circuito chopper UFRJ Nautilus
Example of a chopper circuit


Inverter circuits are used to convert a DC input signal to an AC signal. A very common application is at the entrance of substations that receive a direct current transmission line allowing the distribution to be made in alternating current.

This system consists of 3 parts: Oscillator, Transformer, and Regulator.

Diagrama de blocos de um inversor UFRJ Nautilus
Block diagram of an inverter

The power oscillator is responsible for transforming the continuous input signal into a pulsating signal. It can be done through the LM380 CI (integrated circuit) and filters to eliminate noise. This process is necessary, as the transformer does not operate with continuous signals.

The transformer is a device with two coils (insulated copper cable winding with enamel), where the difference in cable turns between the coils determines the relationship between the input voltage and the output voltage. When a pulsating current is injected into the primary coil, a variant magnetic field is induced in the transformer, this magnetic flux in the secondary coil induces an electromotive force that allows the emergence of a current, respecting Ohm's Law.

And lastly, the regulator works as a kind of filter, as there is a very high chance of surges at the output, so the regulator is necessary.

From this, it is possible to understand the importance of power electronics in any system that needs an electrical power supply, whether with batteries or with an alternating source.

Written by Lucas Alexandre


Recent Posts

See All