Integrating feedforward, average output voltage and transient response into the voltage control loop. ARG...
This has always been a "last 10%" tweaking function of the SMPS engineer. Maximizing input regulation while providing good output regulation, especially in a multiple output voltage condition requires a lot of attention. Transient response is not only a trait of the analog compensation loop, but could be treated as a hardware override subcircuit. Getting all these circuits to play nicely together can be a great challenge.
Perhaps, I should elaborate. Traditionally, feedforword, within the analog control domain, is when a small current through a high-value resistor from the DC input voltage is summed (or subtracted) to the input to the voltage error amp. Add to that, a possible multiple output cross-sensing circuit can be the other part of the voltage feedback circuit, it can become a bit of a problem to have tightly regulated and accurate output voltage(s) with a wide input voltage range. It is more a bit of time allocation. Modeling would be difficult, Playing with the physical circuit might be more expeditious.
There are several new philosophies, within the digital domain, is to handle transient increases in output load currents may be handled by an association of new hardware design and new software triggers. Within the analog domain it may be a high-speed comparator and an override of the output PWM with extra on-time to be better than only the analog feedback loop, this is important for the lower output voltages, (MCUs and ASICs). This is a problem for the analog Si designers.
In short, as analog SMPS designers, selecting an analog controller is as involved as selecting an MCU for a best product performance.