Magnum inverter, Yamaha Generator

Technology covered by a patent is proprietary, but is not by any means secret, because it's published in excruciating detail. Speaking for the USA, all modern patents can be searched for on the uspto.gov web site. The patents covering Honda's sync technology, for example, can be found there. If the technology is implemented in software, as so much is these days, it is likely kept a secret and not patented. Some software is patented, but most is copyrighted and considered company confidential information.