I would like to start out saying that I think boost converters are generally a bad idea. I had someone from Europe inquiring with an array of 120V. Their water heater had a 2,000W 230V element and there was no lower resistance replacement for it. In that case using a 48 power supply to increase the voltage was justified. It was not an issue of efficiency, but accomplishing a goal.
A boost converter can not be totally turned off. Input voltage always flows from the input to the output thru the diode and inductor. Only the amount of boost is controlled. The lower panel power is just passed thru. One has to accept that the lower wattages are just lost. I give this example which can control a boost or buck converter only for educational purposes.
Every switching converter has an IC pin which is a reference which is connected to the output to regulate voltage. The reference is typically 1.2 or 2.5 volts. That connection is easiest to find by either measuring the lowest voltage or resistance. Pot pins are easiest to solder to. When the reference pin goes above the reference voltage the switching regulator will turn off. A 12K resistor can usually supply enough current thru the diode to that pin. Less than 1mv increase is more than enough. The diode is there only to affect the circuit in turn off mode. When the FET, TL431, or opamp pulls the 12K resistor to - common, the added control circuit has no effect,
and the switching regulator operates normally. A FET is used in this example for simplicity, and it is a power FET because these are common. It is also not linear having a sharp turn on between 2.5 and 4V with a high impedance that will not load down a voltage divider. There is some drift with temperature. Everything to the right of the diode are switching module components. The 12V can be obtained from the regulator of the switching module.
As PV voltage drops below the power point voltage, added current feeds to the reference pin. This adds to the current from the output voltage divider. This action does not completely turn off the switching controller. Rather it reduces the amount of boost till the PV voltage stabilizes near power point.
This circuit helps a little preventing a boost converter from putting the panels in a death spiral by drawing more and more panel current. It turns off the boost converter and makes it the same as direct connect. Boost converters are just a bad bad bad idea. To be efficient the panel should feed into a capacitor bank and be pulsed from that maintain a constant voltage from the panel near power point.