Controlled rectifier

The controlled rectifier represents a form of rectifier in electronics , which achieves its rectifying effect through the precise timing by means of a control voltage . The primary function is to convert an AC voltage into a DC voltage .

Controlled rectifiers are usually implemented in the form of electronic switches which are controlled by a control circuit in such a way that a rectifying effect occurs. In contrast to uncontrolled rectifiers, which change between the switching states due to differences in potential , controlled rectifiers also allow DC voltage to be converted into AC voltage by changing the control. In this case, the assembly is called an inverter in the field of energy technology .

The meaning of the term varies depending on the area of ​​application.

Applications

Energy Technology

Controlled rectifiers in the converter hall of an HVDC transmission system

Controlled rectifiers today consist of electronic switching elements such as insulated gate bipolar transistors (IGBT), thyristors or special MOSFETs . There used to be controlled rectifiers with mechanical contacts similar to relays that switched AC voltage synchronously. Furthermore, were the realization of phase controls , among other thyratrons a special form of in use electron tube .

In a thyristor, the flow of current begins when the component is "ignited" by a voltage pulse on a control electrode. The current flows in the thyristor until it crosses zero. Thyristors are increasingly being replaced by IGB transistors in power electronics, as these, like GTO thyristors, can not only be switched on at will, but can also be switched off at any time. The electrical power can be controlled by shifting the switch-on and switch-off times in relation to the course of the alternating voltage over time .

Typical applications of controlled rectifiers in power engineering are converter stations for high-voltage direct current (HVDC) transmissions and HVDC close couplings .

measuring technology

Results with controlled rectification

For comparing two DC voltages can be a moving coil - voltmeter or corresponding digital meter easily determine if their difference is negative, zero or positive. This is necessary , for example, for the targeted setting of a Wheatstone bridge . Accordingly, the comparison of the instantaneous values ​​of two alternating voltages is necessary when balancing the AC voltage bridge. It is not possible with simple laboratory measuring devices, because the usual devices with rectified value or rms value formation do not change the sign. However, this feature can provide phase sensitive or controlled rectification . An additional control or carrier frequency voltage is required for this.

Circuits such as demodulation are suitable for this type of rectification , e.g. B. ring modulator , electronic chopper or amplifier with a switchable gain factor (type AD 630).

The operation with an amplifier is shown in the picture with a sinusoidal input voltage , an output voltage and a control voltage . The sign of the gain factor is the same as for . ${\displaystyle u_{e\,}}$ ${\displaystyle u_{a}}$ ${\displaystyle u_{s\,}}$ ${\displaystyle V}$ ${\displaystyle u_{s\,}}$

• If and are synchronous (in phase), it is positive. ${\displaystyle u_{e}}$ ${\displaystyle u_{s}}$ ${\displaystyle u_{a}}$
• If and are shifted by 180 ° (out of phase), it is negative. ${\displaystyle u_{e}}$ ${\displaystyle u_{s}}$ ${\displaystyle u_{a}}$

The equivalence of the output voltage or the display of a moving-coil measuring device is proportional to the amplitude of the input voltage.

• If and are shifted by an angle in the general case , then is ${\displaystyle u_{e}}$ ${\displaystyle u_{s}}$ ${\displaystyle \varphi }$

${\displaystyle {\overline {u}}_{a}={\frac {2}{\pi }}{\hat {u}}_{e}\,\cos \varphi ={\overline {|u_{e}|}}\cos \varphi \ .}$

In a phase shift between a voltage and a current , this means that if the control voltage is derived, and the input voltage across a measurement resistor of , it is of measured that component which is in phase with the voltage in the normal range also active current mentioned. The reactive current rotated by 90 ° has no influence on the measured value. ${\displaystyle {\underline {U}}}$ ${\displaystyle {\underline {I}}}$ ${\displaystyle {\underline {U}}}$ ${\displaystyle {\underline {I}}}$ ${\displaystyle {\underline {I}}}$ ${\displaystyle -\pi /2<\varphi <\pi /2}$

literature

• Dieter Anke: Power electronics . 2nd Edition. Oldenbourg Wissenschaftsverlag, 2000, ISBN 978-3-486-22634-8 .