Is throttle position control enough for frequency stability on a generator?
No. Frequency is directly tied to engine speed through the relation f = (speed x pole count) / 120; a 4-pole alternator needs 1500 rpm for 50 Hz, a 2-pole one 3000 rpm. Holding the throttle lever position fixed does not hold the speed fixed, because the speed drops when load is applied. Frequency stability requires speed feedback; on the GS740 this can only be provided by the optional active-feedback speed stabilisation module.
On an alternator the relation between frequency and speed is physical, not optional. When the speed drops, the frequency drops as well.
The standard GS740 kit works open loop: it holds the throttle lever where the potentiometer says, it does not measure at what speed the engine is turning. When load is applied the engine speed drops, and since the lever stays in the same place the kit does not compensate for it. On engines with a mechanical governor the no-load speed is typically higher than the full-load speed by the equivalent of 2-3 Hz; this drop (droop) is inherent in the nature of a mechanical governor.
- Droop mode: the speed drops somewhat as the load increases. This is what provides load sharing on generators running in parallel.
- Isochronous mode: zero droop, speed constant from no load to full load. It is preferred on stand-alone sets and requires an electronic governor.
Conclusion: if grid quality matters, throttle position control alone is not enough. This job requires a sensor that reads engine speed and a control chain that corrects according to that sensor. The GS740-3P's closed loop is also on actuator position; it does not provide frequency stability.
Full article: Why is constant speed important on a generator?