- Power Electronics Definition: Power electronics is defined as a field combining power engineering, analog electronics, semiconductor devices, and control systems to regulate electrical energy.
- Switching Function: Power electronic devices act as switches, operating in either ON or OFF modes to control electrical power flow.
- Historical Development: The field advanced significantly with the introduction of silicon controlled rectifiers (SCRs) by General Electric in 1958.
- Types of Circuits: Major power electronic circuits include rectifiers, choppers, inverters, voltage regulators, and cycloconverters.
- Applications: Power electronics is widely used in applications like motor speed control, where it regulates electrical power to achieve desired performance.
Power electronics is a modern branch of electrical engineering that has advanced significantly and impacts many areas of our lives. We use many power electronic applications daily without even realizing it. But what exactly is power electronics?
Power electronics is defined as a field that combines power engineering, analog electronics, semiconductor devices, and control systems. It takes principles from each area to regulate electrical energy. Electrical energy becomes useful when converted into forms like motion, light, sound, or heat. By regulating electrical energy, we can control these different forms efficiently.
We can trace the overwhelming advancement in the subject back to the development of commercial thyristors or silicon controlled rectifiers (SCR) by General Electric Co. in 1958. Before this the control of electrical energy was mainly done using thyratrons and mercury arc rectifiers which works on the principle of physical phenomena in gases and vapours.
After the SCR, many power electronic devices like GTO, IGBT, SIT, MCT, TRIAC, DIAC, IEGT, and IGCT emerged. These devices can handle hundreds of volts and amperes, unlike signal level devices that operate at only a few volts and milliamperes.
In order to achieve the purpose of power electronics, the devices are made to work as nothing more than a switch. All the power electronic devices act as a switch and have two modes, i.e. ON and OFF.
For example, a BJT (Bipolar Junction Transistor) has three regions of operation in its output characteristics cut-off, active and saturation. In analogue electronics where the BJT is supposed to work as an amplifier, the circuit is so designed to bias it in active region of operation. However in power electronics BJT will work in cutoff region when it is OFF and in saturation region when it is ON.
Now that the devices are required to work as a switch, they must follow the basic characteristic of a switch, i.e. when the switch is ON, it has zero voltage drop across it and carries full current through it, and when it is in OFF condition, it has full voltage drop across it and zero current flowing through it. The figure below depicts the above statement-
Now since in both the mode either of the quantity V or I is zero, the switch power also turns out to be zero always. This characteristic is easy to visualize in a mechanical switch and the same has to be followed in power electronic switch also.
However practically there always exists a leakage current through the devices when in OFF condition, i.e Ileakage ≠ 0 and there is always a forward voltage drop in ON condition, i.e Von ≠ 0. However the magnitude of Von or Ileakage is very less and hence the power across the device is also very less, in order of few millwatts.
This power is dissipated in the device and hence proper heat evacuation from the device is an important aspect. Apart from this ON state and OFF state losses, there are switching losses also in power electronic devices. This is mainly while the switch toggles from one mode to another and V and I across the device changes. In power electronics both the losses are important parameters of any device and essential in determining its voltage and current ratings.
Power electronic devices need additional circuits and components to be useful in practical applications. These components act like decision-makers, controlling the power electronic switches to achieve the desired output. This includes the firing and feedback circuits.
The Control Unit takes the output feedback from sensors and compares it with references and accordingly gives input to the firing circuit. Firing circuit is basically a pulse generating circuit which gives pulse output in a fashion so as to control the power electronic switches in the main circuit block.
The net result is that the load receives the desired electrical power and hence delivers the desired result. A typical example of the above system would be speed control of motors. You can learn more about power electronics by studying our basic electronics questions.
Majorly there are five types of power electronic circuits, each having different purpose-
- Rectifiers – converts fixed AC to variable DC (such as half wave rectifiers or full wave rectifiers)
- Choppers – converts fixed DC to variable DC
- Inverters – converts DC to AC having variable amplitude and variable frequency
- Voltage Regulators – converts fixed AC to variable AC at same input frequency
- Cycloconverters – converts fixed AC to AC with variable frequency
There is a common misconception about the term converter. Converter is basically any circuit that converts electrical power from one form to another. Above we have explorerd the five different types of converters.
