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Posted on 25 April 2019

Power Electronic Switches: Neutral Switches

 

 

 

 

 

 

 

A commutation process is started or ended by neutral turn-on or turn-off of a neutral switch. At the moment of switching, the voltage and current at the switch are both zero. These switching properties are inherent in diodes. Neutral switches can also be implemented using actively switchable power semiconductors (e.g. IGBT), provided a suitable intelligent driver circuit is used to lend them diode-like properties.

Figure 1. Circuits with neutral switches

 

Figure 1  shows commutation circuits with neutral switches, as well as a diode rectifier topology, as examples of typical circuits for neutral switches. The table below shows a summary of the basic types of power semiconductor switches with the aforementioned turn-on and turn-off operations. Switches fitting in the blank fields of the table would be modifications of the switches shown. Such modified switches are common in applications.

Table 1. Switch types. Subscript S denotes switch;  abbrevitations are - H=Hard, S=Switch, C=Current, V=Voltage, Z=Zero, M=Modified, R=Resonant; other quantities are as shown in Figure 1.

 

If the resonant or commutation conditions in circuits with soft or resonant switches are not met at certain operating points, the switches will have to perform as hard switches in addition to their main function (modified ZVS = MZVS; modified ZCS = MZCS) in order to ensure that the entire circuit continues to work.

Normally, switches are operated in this deviating operating mode for a brief period only. In the case of hard active turn-off of a ZVS or active turn-on of a ZCS, the switches are operated as ZVHS or ZCHS switches, respectively.

 

For more information, please read:

Four Types of Switching Processes

 Power Electronic Switches: Zero Voltage Switching and Zero Voltage Resonant Switches

An Advantage of Hard Switching

 

 

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