Turning-On behavior of high voltage optically and electrically triggered thyristors

Abstract

1a.Usage of LTTs in high voltage switching applications like HVDC and SVC simplifies/avoids the control circuitry and thereby offers robust power systems with lower production cost. 1b. Integration of protection against all possible fault triggering mechanisms (including reapplied dv/dt) is possible. Therefore, LTTs offer a genuine alternative to ETTs in very high voltage switching applications.2a.Dynamic punch-through reduces turn-on delay in symmetrical thyristors. Kirk effect displaces the hot spot during triggering from cathode side to anode side in asymmetrical thyristors2b. Tandem 13kV thyristor offers an increase of 5kV in blocking voltage with only doubling the on-state losses, without any significant difference in switching losses compared to an 8kV thyristor.2c. Anode shunting is the better alternative solution for the problem of blocking at high temperatures in Tandem 13kV thyristors. A weak anode shunting density, which causes only a negligible increase in the on-state losses, is sufficient to ensure blocking at high temperatures. 3a. An integrated lateral resistance is necessary to protect the inner AGs and thereby to increase the di/dt capability of a thyristor. However, heat distribution across the integrated lateral resistance shall be homogeneous.3b. Homogeneous heat distribution is achieved by a non-linear resistance structure which also provides an enhanced protection to the inner AGs without increasing the minimum triggering voltage and therefore results in a higher di/dt capability.3c. Negative resistance (Snap-back) phase of the non-linear resistor is forbidden. A method to eliminate snap-back is investigated.4a. Several novel gate structures with the aim of increasing the di/dt capability of thyristors are investigated.-Reducing the p emitter efficiency or completely eliminating the p emitter in the AG1 region.-Reduced Current Gain (RCG) AG-Self Turn Off (STO) AG-Capacitive ballastingThese novel gate structures are submitted at the German patent office for patent rights.4b. A concept of using an LTT as a pilot thyristor with a segmented n emitter to trigger a main ETT is investigated with the aim of achieving protection against fault reapplied dv/dt triggering.