The power electronics is a branch of the electrical engineering which deals with the transformation of electrical energy with switching electronic employs components. Typical applications are converters or frequency converters in the field of electrical drive technology, solar inverters and converters for wind turbines for feeding renewable energy into the grid or switching power supplies .
The conversion of electrical energy with converters , that is, rotating sets of machines consisting of an electric motor and generator, or power transformers are not counted as part of power electronics. Even transmitter power amplifiers or audio amplifier not part of the power electronics, though here too the electric power can be substantial and although, for example, class D audio amplifiers operate on similar principles to drive.
Power electronics began with the invention of the first rectifier in 1902, but was only given this name later. The rectifier was a gas discharge vessel with liquid mercury - cathode . These mercury vapor rectifiers were able to rectify alternating currents of up to a few kiloamperes and withstand voltages of over 10 kV . From 1930 these mercury converters were equipped with a grid control analogous to tube technology , and so a controllable direct current could be generated ( ignitron , thyratron ). Due to the very high forward voltage of around 20 V, which multiplied by the forward current means a very high loss of electrical power , as well as the complex construction and the resulting high acquisition and operating costs, these converters were not used to the same extent as today's power electronics. The first semiconductors for current direction were selenium and copper oxide rectifiers .
In 1957 General Electric developed the first controllable power semiconductor and later referred to as a thyristor . The following development resulted in a multitude of other controllable and passive power semiconductors that are used today in large parts of drive technology.
Types and areas of application
Above all, power electronics enable the conversion of electrical energy in terms of voltage form, the level of voltage and current, and frequency . The arrangements for this conversion are called converters . Depending on their function, they are divided into rectifiers, inverters and converters.
There are also power electronic components and assemblies that only serve to switch electrical consumers on and off . In addition to the switching function, these often include additional protection and monitoring functions. They differ from relays and contactors in that they work without moving parts.
- Conversion of AC voltage to DC voltage by a rectifier
- Conversion from DC voltage to AC voltage by an inverter
- Conversion of direct voltage into a higher or lower direct voltage by means of a direct voltage converter (DC / DC converter)
- Conversion of AC voltage to AC voltage with a different frequency or amplitude z. B. by AC power controller or frequency converter
Advances in microelectronics have also led to further improved control and regulation options in the field of power electronic components and have made power electronics even more important.
In the drive technology of electric drives , the control options of the power electronics allow the operating points of electric machines to be set very flexibly. Today, even large machine drives and electric locomotives are equipped with power electronic controls.
Power electronics are also finding ever greater areas of application in the areas of energy generation and transmission. In systems with lower output or systems with conditions under which the classic synchronous generator cannot be used as an energy generator, frequency converters are used to feed the generated electrical energy into the power grid. In energy transmission, the power electronics are used in so-called HVDC close couplings for frequency decoupling between interconnected networks. The same technology is used for high-voltage direct current transmission (HVDC, also called long coupling). Substations for traction power - and tram - Oberleitungs -Excitation work with power electronics.
Power electronics are also used in the area of targeted control in high-voltage networks with three-phase alternating current as part of the Flexible AC Transmission System (FACTS). By means of a Unified Power Flow Controller (UPFC), power flows can be set on individual lines in meshed interconnected networks , so that transmission lines can be optimally used in their transport capacity.
Power electronics are becoming increasingly important in automotive engineering. A large number of electrical consumers are switched and controlled here with power electronic components. One of the first applications in motor vehicles was the alternator regulator, which, among other things, made it possible to use more effective, smaller and less maintenance three-phase alternators instead of direct current generators . Further applications are electronic ignition (thyristor ignition) and electronic intake manifold injection .
In hybrid vehicles (e.g. Toyota Prius ), part of the drive power in electric vehicles (forklifts, "e-cars") is generated with an electric motor. The electrical energy must be converted to the right voltage and frequency for the electric drive motor by means of power electronics. Powerful DC choppers and inverters are used for this, which in hybrid vehicles also process the energy when the motor is in generator mode for intermediate storage in accumulators or double-layer capacitors ("SuperCaps").
In high-frequency technology , power electronics are gradually replacing the slowly obsolete tube technology . At very high frequencies and power levels, electron tubes ( klystrons , magnetrons ) are still used. With induction heating , thanks to power electronics, there are now small, effective, maintenance-free and durable devices.
Other examples are welding - inverters for arc welding and medium frequency inverters for resistance welding .
The following components are characteristic of power electronics:
- Diac (for controlling thyristors)
- bipolar power transistor (switching power supplies and DC / DC converters)
- Power MOSFET (switching power supplies and DC / DC converters)
- GTO ( Integrated Gate-Commutated Thyristor, IGCT ) thyristor (high-performance converter)
- IGBT (switched-mode power supplies, motor controls, converters)
- Thyristor (converters, semiconductor relays, pulse current sources)
- Triac ( dimmer , semiconductor relay)
- Diodes for rectification and as freewheeling diodes ( Schottky diodes for low voltages up to about 200 V, silicon diodes for voltages up to a few kilovolts)
- Power capacitors
Rectifiers are used to generate direct current from alternating current . They consist of several non-controlled diodes or actively controlled components such as thyristors or IGBTs , which, when connected together, become rectifiers. In power electronics, three-phase rectifiers such as the six-pulse circuit or the twelve-pulse circuit are used in particular .
Controlled power converters are rectifier circuits that work with thyristors , GTO thyristors or IGBT and allow the output voltage to be continuously adjusted. Here a phase control shifts the switching on of the electronic switches within the period by an adjustable angle. They are often able to feed the current back into the grid from the direct current side (four-quadrant operation).
Inverters (also known as inverters) can convert direct voltage into alternating voltage .
DC choppers are in DC power supply with up-converters (English-up converters. Step up converter, boost converter ) and buck converters (down converters, buck knob step down converter ). The so-called “active PFC” ( power factor correction) also works with a step-up converter connected downstream of the mains rectifier. These DC choppers work with bipolar transistors , MOSFET or IGBT . With DC converters, synchronous rectifiers are often implemented instead of diodes, so that in principle it is also possible to feed back current.
AC power controller
When AC power controller circuits with thyristors or triacs referred to with which the brightness control of lamps ( dimmer ), temperature control of heating resistors or actuations of the magnet coil are realized or motors. Two thyristors connected in parallel in opposite directions or a triac also switch through both half oscillations of the alternating current at a certain phase angle with a phase control .
Solid-state relays (Engl. Solid state relay ) are electronic AC switches and also use thyristors or triac, they have a built-in potential separation between power and signal circuit and switch either to prevent immediately or always at the zero crossing of the AC voltage so as spurious emissions.
Switching power supplies
Switching power supplies convert the mains voltage into isolated, regulated DC voltages and work with a controlled inverter, which first generates an AC voltage of high frequency from the rectified mains AC voltage, which is then transformed and rectified. Switching power supplies work with bipolar transistors , MOSFET or IGBT .
Power consumption and efficiency
The efficiencies of power electronic systems are often very high (around 70 to over 95%) and, for example, exceed those of network transformers. Nevertheless, power electronic assemblies lead to interference emissions and often to reactive power and distortions (harmonics) in the power grid. The non-sinusoidal curve of the current consumption causes reactive power, it is called distortion reactive power .
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- Arendt Wintrich, Ulrich Nicolai, Werner Tursky, Tobias Reimann: Application Manual 2010 . 1st edition. ISLE Verlag, 2010, ISBN 978-3-938843-56-7 ( PDF version ). ; English version: Arendt Wintrich, Ulrich Nicolai, Werner Tursky, Tobias Reimann: Application Manual Power Semiconductors . 1st edition. ISLE Verlag, 2011, ISBN 978-3-938843-66-6 ( PDF version in the web archive ( Memento from February 1, 2014 in the Internet Archive )).
- Arendt Wintrich, Ulrich Nicolai, Werner Tursky, Tobias Reimann: Application Manual 2015 . Ed .: Semikron International GmbH. 2nd Edition. ISLE Verlag, Ilmenau 2015, ISBN 978-3-938843-66-6 , pp. 464 ( semikron.com [PDF]).
- Simulation tool for power calculation and for designing power electronic components
- Interactive Power Electronics Seminar (iPES)
- Bosch Power Electronics, Bosch Mobility Solutions, 2015 on YouTube
- E-car or hybrid drive, power electronics, Continental Automotive Germany, 2015 on YouTube
- Interview: Gerd Griepentrog - Professor for Power Electronics, etit darmstadt, 2016 on YouTube
- Power Electronics - Electrical Engineering - Prof. Dr.-Ing. Dr. hc Hans-Eberhard Schurk, Augsburg University of Applied Sciences, 2018 on YouTube