When we apply constant power load across the open loop DC converters the response of inductor current and capacitor voltage will remains oscillated, reflecting the limit cycle behavior. Physically what is the effect of this behavior on the converter operation and stability in general?
Dear researcher
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https://www.researchgate.net/publication/312573195_Development_circumstances_of_four_recycling_industries_used_motor_oil_acidic_sludge_plastic_wastes_and_blown_bitumen_in_the_world
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Article Development circumstances of four recycling industries (used...
More information on the details is required: what is the converter topology (active clamp forward, perhaps?). By "open loop" I presume that you mean there is no feedback control of the the output voltage, but is there an inner current control loop, such as constant frequency peak current control? An instability implies some form of feedback somewhere.
Dear Bruce Carsten
thanks for your answer, I meant is a simple Buck converter without closed loop voltage control connected in cascade to constant power load. this connection makes the buck converter oscillate.
Physically a constant power load is an actively controlled component and every constant power load has a finite bandwidth. I am not sure if you have a load such as that. However, a constant power load would make the ripple on the output capacitor relatively higher. From stability point of view, a constant power load exhibits negative incremental resistance which makes it relatively more difficult to design a stable controller. Depending on the actual bandwidth of the constant power load, it will show negative incremental resistance over a frequency range. If there is any disturbance in your system in that range, the negative resistance nature of the load will amplify that disturbance, eventually leading to an unstable situation unless your controller can provide sufficient damping. For an ideal constant power load this frequency range is infinite.
M A Awal has a valid point about the negative impedance of a constant power load, which slipped my mind (I must be getting senile in my old age).
Even the input to any efficient power converter with a fixed load has the same negative dynamic impedance characteristic, and can cause an L-C input filter to oscillate when the negative impedance becomes greater than the filter impedance, which typically is at the L-C resonance frequency of the filter.
If you have a constant power load on a converter with a fixed voltage conversion ratio, it may be that it is an input filter to the converter that is driven into oscillation, or the constant power load may be driving the converter's output filter into oscillation, or it could even be the converter's input and output filters combined, as the converter would couple the two together.
I have attached an extract from my seminar "SMPS Circuit Design Tricks" on designing an optimum (minimal) input filter damping circuit for switchmode converters which may be of help.
There are some difference between negative incremental resistance and negative resistance itself, the first one imply the slope is negative and the resistance is actually positive (Not negative), but how can I getting negative incremental resistance ???? as I am thinking, constant power load is negative incremental resistance with a very high dynamic resistance according to this equation
dr=delta(V)/delta(I)
according to a constant power load V-I characteristic, if the voltage is increase the current will decrease, and if the rate of change of current is greater than the rate of change of the voltage the result is getting high dynamic resistance making the system working with less damming and will tend to oscillate.
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