T
treez
Guest
Hello,
We are designing a 3kw PFC stage (part of a battery charger) which must have its vout variable so that it can feed the downstream LLC converter with that voltage which allows the LLC stage to operate at its resonant frequency.
This means we would like to be able to set the PFC output voltage all the way up to 435V. however, the PFC output caps are 450V rated so we would have to set the PFC overvoltage limit at 445V.
But 445V is far too close to the PFC’s nominal output voltage of 435V. PFC’s are naturally “slow” and wandering as they attempt to get into regulation, and if the PFC was set up for 435VDC output nominal , then the PFC would in fact never get properly into regulation, -instead it would just keep “bouncing” up and down from the 445V overvoltage limit.
Therefore, with an overvoltage limit of 445VDC, the highest that we would be able to set the nomnal PFC output voltage to would be 405VC.
We could possibly go a little higher than 405VDC , but then that places more constraints on the setting of the feedback loop, ie it has to be faster if the nominal output voltage is too near to the overvoltage limit.
So do you agree, that if the PFC overvoltage limit is set to 445V, then it is very unadviseable to have the nominal PFC output voltage set to 435VDC?
By the way in the above I am assuming enough output capacitance to ensure no more than 12V pk-to-pk output voltage ripple.
We are designing a 3kw PFC stage (part of a battery charger) which must have its vout variable so that it can feed the downstream LLC converter with that voltage which allows the LLC stage to operate at its resonant frequency.
This means we would like to be able to set the PFC output voltage all the way up to 435V. however, the PFC output caps are 450V rated so we would have to set the PFC overvoltage limit at 445V.
But 445V is far too close to the PFC’s nominal output voltage of 435V. PFC’s are naturally “slow” and wandering as they attempt to get into regulation, and if the PFC was set up for 435VDC output nominal , then the PFC would in fact never get properly into regulation, -instead it would just keep “bouncing” up and down from the 445V overvoltage limit.
Therefore, with an overvoltage limit of 445VDC, the highest that we would be able to set the nomnal PFC output voltage to would be 405VC.
We could possibly go a little higher than 405VDC , but then that places more constraints on the setting of the feedback loop, ie it has to be faster if the nominal output voltage is too near to the overvoltage limit.
So do you agree, that if the PFC overvoltage limit is set to 445V, then it is very unadviseable to have the nominal PFC output voltage set to 435VDC?
By the way in the above I am assuming enough output capacitance to ensure no more than 12V pk-to-pk output voltage ripple.