Kiril Karagiozov @ edn.com has a circuit idea that is able to deliver constant power to a load. This is done by generating energy pulses, independent of resistance of the load.
If you have a load with a variable or poorly specified resistance and want to regulate the power applied to it (a heater for example), merely controlling the voltage or current will not work, as in both cases the power P = I2R = V2/R depends on R.
Instead, let us generate pulses with constant energy Epulse, independent of the resistance of the load RL. Then by changing the frequency f of the pulses we can conveniently and precisely control the load power (P = f·Epulse), from 0 to a known maximum level.
Circuit delivers constant power to a load – [Link]