you have 24 slots on your stator.. unless its 4 poles, and then you have 48.
it will all go away if you put a 20-60uF capacitor across the 240v output of your generator.
a 5kw generator will have about a 10vac increase in its no load output voltage with a 60uF cap across its 240v output.
if you want to improve the voltage regulation of your system, add capacitors at each load sized for the load. for example a refrigerator might only be 100 watts but it could draw 3 amps of reactive current, so the voltage drops even though the load isn't that much. keep in mind though that capacitors and switches don't go together. NTC resistors are your friend here... don't go overboard with the capacitors, and don't use them to compensate for resistive loads, no point in doing that.