Variable Speed Drive

For a three phase motor, six, two for each leg. A high DC voltage is created by rectifying and filtering the AC line, such as 380 or 560 volts, etc. ( or more with a power-factor controller), and a pulse-width modulation (PWM) signal is applied to the control gates of the two IGBTs to create a sine wave of the desired amplitude and frequency.

Discrete IGBTs may come as small surface-mount parts, like the D2Pak shown, or in larger TO-220 or TO-247 packages that can have a heat sink attached.

Larger motors use IGBT modules in place of individual IGBTs. For modest currents, the module will have the required six IGBTs, but at higher currents and voltages, the modules may have only two IGBTs each, so three modules are required. In addition to handling higher currents and voltages, the modules also offer a large metal plate to bolt to a heat sink, that's insulated from the IGBT terminals. They also offer captive nut connection for the terminals.

It's interesting to discover, if one takes apart a module, that they are made up from dozens of individual discrete IGBTs glued to the metal plate and wired in parallel.

This part is an older Powerex CM200DY-12H. It's rated at 600V and 200A, which is fairly modest as these parts go. You can see three bolt-hole terminals. E2 and C1 are bussed to the DC power rails, and C2E1 is your sine-wave PWM output. The small tab terminals G1, E1 and G2, E2 at the right side provide two control-gate connections.

These modules cost $162 each at Newark, which is also a modest price for a module. You'd need three of these modules for a three-phase VSD motor controller.

Yes Windfield is correct, however you can also connect two VSD's together in parallel and therefore you've doubled your IGBT count.

Question?

How does one get the gate drivers from two independent VSD's connected in parallel to synchronise their firing order to the IGBT's in order to ensure phase angle alignment at the motor terminals.

good question... can I get back to you on that later, with a FULL answer, I'm not in my office so I cannot look at my drawings. I'm tempted to say, the controllers are are joined, but that is VERY vague.