I want to ask if there is resistive load and inductive load so in which condition we have to use IGBT and Thyristor. Or my question is wrong? Please explain?
Tourist or us the generic name for ANY 3 terminal device but mostly just refers to current controlled devices. I’m assuming you are referring to medium voltage.
When we get into power stacks in medium voltage there are many choices, all with drawbacks. A very old design is the cycloconverter. The easiest way to visualize it is if we took a 60 Hz waveform and cut out every other pulse. This gives us 30 Hz. Fundamentally we can’t exceed 30 Hz but various firing patterns make nearly any frequency from 0 to 30 Hz possible. This is ideal for SCRs. An SCR can be made to block up to 10s of kV blocking. If it wasn’t for the fact that it can’t shut off without a current zero, it’s the perfect device. You can easily stack them to go to 15 kV and they are cheap. This is also ideal for soft starts.
So to get to a full 60 Hz the old design is a load commutated inverter. So in this design we rely quite a bit on the reactance of the load to force commutation. A gate commutated thyristor is effectively an SCR but if you put a huge negative current pulse in the gate it can be forced back open. This was the first “real” VFD but they aren’t terribly efficient with the current control and they are sensitive to load changes. Ultimately these issues lead to equipment that has to be built to order leading to very long lead times.
Then we get to IGBTs. At low voltages it has high current handling, very fast turn on/off times (to a fault), and voltage control instead of current. In every respect it is the perfect device except two (one). The first is that switching consumes a lot of current and being silicon based causes thermal limitations. Fortunately newer wide band gap materials are largely solving this. The second more serious problem is it has an inherent low blocking voltage. The vast majority of IGBTs are limited to 1500 V blocking. Although there are “high voltage” 3300 V IGBTs the yields, prices, and availability make it less expensive to use low voltage IGBTs and just deal with the consequences. 5, 7, or 9 level cascaded H bridges or tapped transformer designs are most common. Every VFD manufacturer has a slight twist on things. There is no “standard” design like we see with 6 pulse mass produced 600 V drives.
Even if a better device existed no market would exist. 600 V inverters rely on the fact that wiring is rated to at least 200% of rated plus 1 kV or 1800 V so little transient protection is required. At medium voltage the same spec exists but now at say 5 kV with a 6 kV DC bus voltage and cable limited to 11 kV a 200% transient will rip through the insulation. 5 level switching is a bare minimum.
At low voltage IGBTs are used almost exclusively down to around 25-30 A. At that point simple MOSFETs have lower losses and are cheaper so they dominate the micro drive market.
