This paper presents a study of the GaN HEMT as a bidirectional switch. The considerations were conducted for the purpose of application of bidirectional switch in a matrix converter. Semi-soft 4-step commutation method was analysed and laboratory tested on the 2-phase to 1-phase converter to verify all the possible commutation processes which occur in a matrix converter. The problem of wrong sign of current detection and output current interruption has also been raised.
Słowa kluczowe: matrix converter, bidirectional switch, GaN, semisoft commutation
Artykuł przedstawia badania GaN HEMT jako łącznika dwukierunkowego. Rozważania były prowadzone w celu zastosowania łącznika dwukierunkowego w przekształtniku matrycowym. Metoda 4-krokowej półmiękkiej komutacji została przeanalizowana i przebadana laboratoryjnie na przekształtniku 2-fazowym na 1-fazowy, który odwzorowuje wszystkie procesy komutacyjne w przekształtniku matrycowym. Został również poruszony problem błędnej detekcji znaku prądu wyjściowego oraz jego przerwania.
Keywords: przekształtnik matrycowy, łącznik dwukierunkowy, GaN, półmiękka komutacja
In power electronics, bidirectional (four-quadrant) switches (BDS) are a necessary part of all matrix converters which allow to convert AC voltage directly (without a DC link) to AC voltage with controllable amplitude and frequency. BDS are capable to conduct current in both directions and block voltage of both polarities. There are several configurations of BDS but the most commonly used is antiparallel connection of two RB-IGBT and its main advantage is that the current is passing only through one semiconductor . Nowadays, GaN BDS begin to appear as a single package device with dual gate and are used in matrix converters (MC), e.g. [2, 3], but they are still not available on the market. GaN HEMT could be a competition for RB-IGBT due their lower switching and conduction losses, their high frequency operation which could increase the power density of MCs . GaN HEMT connected in series has not yet been tested as a BDS which was the main reason to conduct the research. I. Four-step semisoft current commutation method A. Analysis The 4-step semisoft current commutation method for BDS was firstly proposed in . It is called semisoft, because half of the commutation process is soft switching and half is hard switching . There are many other modifications of that method, e.g. 3-step, 2-step.  which are the modification of the 4-step method. To analyse all the commutation processes in a 3-phase MC it is enough to consider only a 2-phase to 1-phase (2f/1f) converter with a DC voltage source and RL load (Fig.1). RC snubbers added to each GaN HEMT significantly reduce the voltage ripple , (it is worth mentioning that in  for GaN BDS an RCD snubber with 4 diodes, resistor and capacitor is proposed, which could be compared in future work). Control strategy of the 4-step current commutation method is shown in Table 1. For example, if we want to switch from conducting TAa to open TBa BDS and the current of the RL [...]
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