Power Electronics!

Introduction

How do we ensure that all the different modules in a product get the right voltages and thereby work as intended? We use power electronics!
Power electronics is the branch of electrical engineering that deals with the processing of voltages and currents to deliver power that supports a variety of needs. This includes everything from household electronics to equipment in space applications.
The purpose for power electronics is to construct stable and reliable electric power with the desired specifications

 

Feedback-chain

In power generation, especially in renewable energy, the generated power must be processed to meet the voltage specification of the power grid. For instance, a solar cell which generates DC power isn’t producing a constant voltage, so to maximize and utilize all the energy from the solar cells is vital. It is important to extract the maximum power available at the output of the cell and transfer it to the grid with the highest possible efficiency. To not waste any energy when working with solar cells, renewable batteries are often used to store energy that isn’t needed at the moment to then be used later on, and thereby uilize the energy effeciently. This increases the efficiency of the power generation and is one example of how to effectively utilize energy from renewable energy sources. This is often done by creating a feedback chain in the circuit. A feedback chain works by measuring certain voltages around the circuit, to check if voltages are as wanted. If they aren’t then calculations are made in the circuit to correct those errors. The faster the corrections are calculated and reacted to, the more sensitive the feedback control is. Below on Figure 1 is a block diagram of a typical power electronic system.

Figure 1: Block diagram of a typical power electronic system. So if we think about our situation with the solar cells then the power generated from them would be the input. The input would be varying and not a constant, but we want a constant output with no fluctations. This is typical for electronics. So we use a feedback-loop to determine and correct for the error. The method for the correction depends on the specefic application, but the error is nearly always the difference between our input and our desired output.

The primary element in a power electronic system is a switching power converter. A switch is like a connector between different sub-circuits. When the switch is closed it connects one sub-circuit to another and when it is closed there’s no connection between the sub-circuits. As the efficiency of a system is very important for power electronics, it makes sense to discuss the loss a circuit experiences when a switch occurs.

Switching Losses
The switching losses occur during the turn on (closed) and off (open) for a switch. For instance, when a switch turns on, the voltage across the switch goes to a low value from the voltage that was being blocked when it was in the off state. At the same time, the current through the device goes from zero to the load current level, or to whatever the switch is connecting. Since this process doesn’t happen instantly and takes finite time and the voltage and current are transitioning, power loss takes place. These losses constitute the switching losses. So everytime we connect or disconnect sub-circuits to each other, we experience switching losses because we can't switch instantly

Types of Power Electronic Circuits

All depending on the purpose of a given circuit, we might need to convert the input to a certain kind of output. Maybe we want the voltage to increase or decrease or transition from a DC voltage to an AC voltage or vice versa. For this we use converters.

 

 
Figure 2: Basic types of power converters.

There many different converters that can be used to convert all the inputs to the outputs seen in figure 2. Let's go through one for each type of converter:

A buck converter for example is used to convert a DC voltage to a smaller DC voltage. The boost converter, as you might have guessed, boosts the voltage so the output is higher than the input.
A rectifier, which also is mentioned in this [blog] can be used to convert an AC signal to DC, and an inverter for DC to AC.
And lastly from AC to AC a cycloconverter, also called a frequency changer, can be used.

The Importance of Power Electronics

The drive towards more electrification has resulted in the need for more electric power. We use a lot of electrical energy in today's world, so it is important to waste as little as possible. Therefore apart from power generation, power processing plays a key role in efficient utilization of the available power. It is important that the raw power is converted to a form that is usable in different applications. Power electronics are important for providing power based on the desired specifications. So to sum up an electrical product might consist of many different modules, which each needs different voltages to function optimally, and this is what power electronics is all about.  

 

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