Introduction
How do we ensure that all the different modules in a product receive the right voltages and therefore work as intended? We use power electronics!
Power electronics is the branch of electrical engineering concerned with processing voltages and currents to deliver power that supports a variety of needs. This covers everything from household electronics to equipment for space applications.
The purpose of power electronics is to produce stable, reliable electrical power with the desired specifications.
Feedback Chain
In electricity generation, particularly renewable energy, the power produced must be processed to meet the grid’s voltage specifications. For example, a solar cell generating direct current does not produce a constant voltage, so it is important to maximise and use all the energy from the solar cells. The aim is to extract the maximum power available at their output and transfer it further through the system as efficiently as possible.
To avoid wasting energy when working with solar cells, rechargeable batteries are often used to store energy. This stored energy can then be used later in the system as needed, improving efficiency.
This is often achieved by establishing a feedback chain, or feedback loop, in the circuit. A feedback chain measures specific voltages around the circuit to check whether they have the desired values at those points. When they do not, calculations are made in the circuit to correct these errors. The faster the corrections are calculated and acted upon, the more responsive the feedback control. Figure 1 below shows a block diagram of a typical power electronics system.
Figure 1: Block diagram of a typical power electronics system. In our solar-cell example, the power they generate would be the input. The input would vary rather than remain constant, but we often want a constant output without fluctuations. A feedback chain is used to determine and correct the error. The correction method depends on the particular application, but the error is almost always the difference between the desired reference value and the measured output.
The primary element in a power electronics system is a switching power converter. A switch can be seen as a link between different circuits and subcircuits. When the switch is closed, it connects one subcircuit to another, and when it is open, there is no connection. Since system efficiency is very important in power electronics, it makes sense to discuss the losses a circuit experiences when switching occurs.
Switching Losses
Switching losses occur when a switch opens and closes. For example, when a switch turns on, the voltage across it falls from the blocked voltage towards a low value. At the same time, current through the device goes from zero to the load-current level (or to whatever the switch connects). Since this process is not instantaneous and takes some time, power losses occur. These are switching losses. Whenever subcircuits/circuits are connected or disconnected, the system therefore experiences switching losses because the action of a switch is not instantaneous.
Types of Power Electronics Circuits
Depending on the purpose of the circuit being worked on, we may need to convert the input to a particular type of output. Perhaps we want the voltage to rise or fall, or change from DC to AC or vice versa. Converters can be used for this.
Figure 2: Different types of power converters.
Many different converters can convert inputs to the outputs shown in Figure 2. Let’s go through one for each conversion.
A rectifier, also mentioned in this blog about analogue circuits, can convert an AC signal to DC.
A buck converter is used, for example, to convert a DC voltage to a lower DC voltage. The boost converter, as you may have guessed, boosts the voltage so the output is higher than the input.
Finally, for AC to AC conversion, a cycloconverter, also called a frequency changer, can be used.
The Importance of Power Electronics
As we use more and more electricity, demand for this energy source is growing rapidly. We use incredible amounts of electrical energy today, so it is important to make the most of it. This energy needs to be converted into a form usable in different applications.
To sum up, an electrical product can consist of many different modules. Each module in the system has its own input- and output-voltage requirements for optimal operation. There are therefore typically criteria for the voltage across both the module’s input and output. Methods for meeting these requirements while maintaining high efficiency with the available energy are exactly what power electronics is about.
