Development of compact inverter power supply for microwave oven
Kako, H.; Nakagawa, T.; Narita, R.
Consumer Electronics, IEEE Transactions on
Volume 37, Issue 3, Aug 1991 Page(s):611 - 616
Digital Object Identifier 10.1109/30.85575
Summary: The development of a novel inverter power supply for a microwave oven is described. Due to its operation at a high frequency using a fast switching device, an IGBT (insulated-gate bipolar transistor), the power supply has been made light and compact. It weighs about one-fifth of the conventional ferro-resonant unit. Adopting the inverter power supply with a new control IC has made it possible to realize a new microwave oven featuring a power control function and high output power.
(If you want a copy, let me know.)
I assume it hasn't been used on most consumer microwave ovens simply because it's more expensive than switching the tube on or off.
Cheers,
Scott.