For example, for a 40 MVAR DSTATCOM, what are the di/dt limitation of transistors and flywheel diodes? In other words, what limits such devices in the compensation of very fast changing disturbances?
Dear Amin,
if your device is built using IGBTs as a power semiconductor, then the limiting factor is not the semiconductor but the grid's inductance. Considering the mains as a source with an inductive character in a mH-regime, the current change rate is dictated by the voltage level your compensator is attached to and the grid's inductance.
Assuming a device in the medium voltage level of 20kV, an inductance in the mH-regime will allow for a maximum di/dt of 20kA/ms.
The fact that typical IGBTs today can safely handle current change rates of several kA/µs substantiates my statement that the semiconductors are not the limiting factor here.
Dear Martin,
Thanks for your complete response. Would you please explain a little bit more about your example? How could one calculate the maximum allowable di/dt by knowing the voltage level? If there are some articles available on this matter, it would be very much appreciated if you could share them.
Bests,
Amin
It may varry from 20-500 KA/ms depending on the devices used and its internal configuration.Usually snubber circuits are used for protection of this di/dt.
Der Amin,
my example just relates to the law of inductance.
A di/dt in an induktive load L has to be driven by a voltage acc.to U=L*di/dt.
The grid as an entity has an inductance in a mH regime, thus at 20kV the di/dt can reach no more than some 20kA/ms.
For current high voltage IGBTs check a typical piece like the FZ1500R33HE3, a single switch capable to handle 1500A at 3300V maximum blocking voltage.
- Badges
- Science topic
- Similar topics
- Engineering
- Control Theory
- Control Systems
- Control Systems Engineering