Control the input voltage of a unidirectional boost converter

Hi all,


I have a boost converter of a PV system. The output voltage of the boost converter is regulated by another element (storage) at some value. The boost converter controller is supposed to control the input voltage at some value in order to extract the max. power from the PV.

My question is how I control the input voltage of the boost converter and how to verify if it is really controlling the input voltage a reference value.


Thanks,

Think about how a voltage regulated and current limited bench power supply operates.

Voltage feedback from the output controls the power regulator, to fix the output voltage to the required voltage.
If the output current then exceeds some limit, current feedback overrides the output voltage control to turn the supply into a current limited source.

What you need for a maximum peak power tracking PV regulator is very similar in how it works.

There will be the usual voltage feedback loop from the output that compares a fraction of the output voltage to some voltage reference. This is the conventional output voltage regulator with which we are all very familiar.

The trick is to add a second control loop that senses the solar panel voltage.
The idea is to override the output voltage control loop with the second control loop that senses solar panel voltage.

If the solar panel voltage tries to fall BELOW the peak power voltage, we want this to override the output voltage control loop (similar in concept to a current limit override) so that the power regulator cannot then overload the solar panels.

To do this, we must first invert the solar panel voltage, and scale it to some workable range with an op amp. Solar panel voltage maybe 0 to +45v
corresponding output of our op amp inverter/scaler +10v to 0v (for example).

The gain is reduced, and the output inverted.

If the solar panel voltage tries to fall below the peak power voltage, the output of our inverter/scaler rises above a fixed reference voltage. We then use that as a power limiting circuit to override the main output voltage regulator.

Its an extremely effective and simple MPPT control system, and very fast acting.

Thanks Tony for your reply.

Since you have only one control variable (the duty cycle), switching from controlling the output voltage to controlling the input voltage means we lose control of the output voltage of the boost converter.

If this is the case, then we must have some regulation on the load side (for example a storage or a capacitor) to regulate the output voltage, is that right?

If your 2Kw solar panel array is only outputting fifty watts on a very cloudy day, that is all there is....

What that means is the output voltage control loop will regulate to the set output voltage, right up to a fifty watt load.

Any more load than that, and the output voltage will be pulled down out of regulation.
But you will still get the full fifty watts of available output power which is the best the system can do under the circumstances, and no possible way to improve on it.

If you have a battery load, the output voltage will be pretty much fixed by the battery terminal voltage, and the PWM will self adjust to maintain fifty watts, or whatever power is available into the battery in the most efficient way.

The output voltage control loop will then set the maximum charge voltage the battery can reach.