I have had experience with systems like this, probably smaller in horsepower but otherwise the same in theory. One centrifugal booster pump per plunger injector pump would be what I would favour, especially if the booster is not on a VFD and has a somewhat flat characteristic to a little bit past BEP. The idea is to keep the suction header pressurized with enough water flow available to meet the volumetric demand of the injector throughout its speed range. The "plug and chug" mentality would be to somewhat oversize the booster so that it could be expected to run a bit left of BEP most of the time.
Two centrifugal boosters in parallel in front of the plungers is another way to flatten out the effective characteristic, but one needs to pay attention to control and shutdown logic to deal with a case in which one of the boosters cuts out.
If indeed the injectors are plunger type, then they might be equipped with belt drive speed reduction between the electric motor and the pump. It takes time - and a certain number of revolutions - to ramp down to zero speed when such a pump trips out. Meanwhile, it continues to demand water from the booster / suction header. Regardless of what else is done, I would be inclined to put a time delay on the booster pump trip for the case when the plunger pump trips; otherwise, the booster will stop first and the plunger will continue to ramp down and create a significant pressure reduction in its suction piping. The subsequent start-up of the booster pump can hammer the system and do serious damage to plungers and cranks. It's better to dead-head the booster for a few seconds before tripping it to avoid this.
Regards,
SNORGY.
