Hello,
We are designing a 7.4kW offline LLC battery charger for EV. The (lithium) battery is 300-410VDC.
As you know, We are closing the feedback loop on the output current (into the battery).
Do you believe that this presents a tricky dynamic situation for us?
I am used to closing the loop in previous SMPS’s on output voltage, with a resistance type load. In other words, there is a load pole of 1/(2.pi.R.C)…
Where
R is the load
C is the SMPS output capacitance.
As you know, in output voltage regulated SMPS’s the addition of an enormous load capacitance often brings about instability in an SMPS…due to the big decrease in phase margin that it causes.
Our huge lithium battery is obviously an enormous output capacitance, and we are somewhat concerned about this situation of decreased phase margin.
We are wondering, that instead of using an analog feedback loop, comprising an error amplifier, with feedback compensation R’s and C’s, perhaps we would instead be more advised to implement a very slow “try it and see”, incremental type of feedback loop? That is, we could set up for a very low initial charge current, and then just bit-by-bit, reduce the frequency of the LLC converter, until the output current is the right value, and then just continually monitor the current from there on. This would be handled by a microcontroller. Obviously we would have an overcurrent shutdown comparator ‘overseeing’ the whole process.
Which type of feedback loop would you advise for this?
To give an example, the attached Ltspice simulation shows that slightly reducing the LLC switching frequency from 60.2khz to 58.8hz results in an increase in charging current of 10 Amps
We are designing a 7.4kW offline LLC battery charger for EV. The (lithium) battery is 300-410VDC.
As you know, We are closing the feedback loop on the output current (into the battery).
Do you believe that this presents a tricky dynamic situation for us?
I am used to closing the loop in previous SMPS’s on output voltage, with a resistance type load. In other words, there is a load pole of 1/(2.pi.R.C)…
Where
R is the load
C is the SMPS output capacitance.
As you know, in output voltage regulated SMPS’s the addition of an enormous load capacitance often brings about instability in an SMPS…due to the big decrease in phase margin that it causes.
Our huge lithium battery is obviously an enormous output capacitance, and we are somewhat concerned about this situation of decreased phase margin.
We are wondering, that instead of using an analog feedback loop, comprising an error amplifier, with feedback compensation R’s and C’s, perhaps we would instead be more advised to implement a very slow “try it and see”, incremental type of feedback loop? That is, we could set up for a very low initial charge current, and then just bit-by-bit, reduce the frequency of the LLC converter, until the output current is the right value, and then just continually monitor the current from there on. This would be handled by a microcontroller. Obviously we would have an overcurrent shutdown comparator ‘overseeing’ the whole process.
Which type of feedback loop would you advise for this?
To give an example, the attached Ltspice simulation shows that slightly reducing the LLC switching frequency from 60.2khz to 58.8hz results in an increase in charging current of 10 Amps
Attachments
Last edited: