Is it possible to harvest maximum power point tracking for getting constant voltage?
Here are some of my understanding,
The open circuit voltage of a solar cell is ususlly proportional to the logarithm of the incident light intensity, for a PV module I think the similar, the voltage would drop slowly as the light intensity decrease. That is to say, the output voltage and output current of PV array have strong nonlinear response upon the change of external environment or load. So it's the intrinsic property of PV cells or modules and arrays and we can only optimize it through external variable.
For your situation, voltage stabilizer may help but probably with limited capacity. Making some complement by sacrificing a few PV devices to guarantee the output stability of the system may be also a choice worth considering.
I am not sure I understand what are you trying to do, but I'll try to answer...
Are you connecting a PV array to a DC bus without any DC-DC converter in between? If yes, I don't see how we can talk about MPPT...
If you are using a DC-DC converter between your PV array and the DC bus, then there is no problem to have constant voltage at the input of your converter, which is equal to your PV array voltage (assuming there is enough irradiance for your PV panels to generate something). For that your DC-DC converter must be controlled in such a way as to keep the input voltage constant. This is doable, but then for most of the time you will not be harvesting maximum power. The reason is, that the MPP of the PV panels (and the entire array) varies with time as the conditions of the PV panels change constantly (irradiance, temperature, and shading of the panels). As the conditions change, so does the operating VI-curves of the PV panels. This is why the front-end converter (DC-DC or DC-AC, depending on the system) in a PV system has some sort of MPPT algorithm implemented in its control system.
In short, you can force your PV array to operate at constant voltage, but if you do that you will not harvest maximum power.
A simple approach taken by some mppt battery charge ICs is to use the Vmp of the panel used as a set point and make an algorithm that throttles back the current to the DC bus if the panel voltage falls below the set point. If the panel voltage increases above the set point then increase the current. This system does not guarantee maximum power output as stated by Konstantin Kostov but would give a constant panel voltage with adequate solar irradiance available. A mppt charge IC that uses this principle is the BQ24650 from Texas Instruments although they allow the panel voltage to increase above the set point not below to maintain a constant output current.
Thank you all for your valuable replies.
Sir Konstantin Kostov, I am simulating the system using MATLAB, and I have used boost converter in between solar array and dc bus.
Can anyone suggest any reference of control strategy for generating pulses for switching system of boost converter, so that I may get constant dc voltage at dc bus.
Hi,
You can try the concept in the paper:
C. S. Chiu, "T-S Fuzzy Maximum Power Point Tracking Control of Solar Power Generation Systems," in IEEE Transactions on Energy Conversion, vol. 25, no. 4, pp. 1123-1132, Dec. 2010.doi: 10.1109/TEC.2010.2041551
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5437312&isnumber=5635301
You can read my papers regarding this subject. It is a complex subject to control both mppt and bus voltage when the load, irradiation and temperature changes.
it is possible to get the constant voltage output from the PV array at different radiation and temperature levels by using the Buck & Boost Converter at the output side with a predefined control loop.
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