I raise you the output of an inverter/ups/vfd:most good powersupplies have inlet surge protection.maybe you need a double-online UPS feeding a subpanel? also - have you asked the power company to troubleshoot it? I had a light flickering issue that resulted in getting a new pole transformer, and a substation repair. they installed a datalogging meter and traced it back to the source.
1/8/18 at 3:59pm