What are different control (decision) variables of maximum power point tracking (MPPT) systems in PV's (other than duty cycle of boost converters)?
Commonly the Vpv and Ipv should be controlled to push operation at the knee of teh P-V characteristic curve of PV module.
The control is such that given certain load resistance and output voltage at the output of the DC to DC converter, the duty ratio of the converter must be adjusted to operate the photo voltaic array at its maximum power point Pom, Which implies that the input current to the converter is Ipvm and Its input voltage is Vpm.
Dear Ahmad
The control unit of the PV energy conversion system must have a MPPT process for the operation of PV at the point of maximum power generation.
However, the MPPT methods also involves electrical parameters of PV system and is affected by
- Uncertainty in electrical parameter values of installed PV modules because of the measurement errors during an experimental characterization process.
- Electrical parameters deviation in the individual PV modules supplied by a manufacturer due to non-idealities of the manufacturing process.
- Drift of the PV module electrical characteristics during the operational lifetime period of a PV system i.e., 20-25 years.
- Quantitative impact of this feature on the energy production performance of a PV system also depends on the magnitude and duration of the short-term variability of solar irradiation and ambient temperature at each particular installation site under consideration.
i hope it will help you.
As far as MPPT is concerned, many MPPT techniques are developed and implemented from simple P&O to Artificial Intelligence based MPPT. Each MPPT differs one from another by means of Input and output parameters.
Input variables are T, G, Vpv, Ipv, dP, dV or dI and the the output of MPPT can be Vref, Pref, delD or D. But, ultimately the operation of DC-DC converter is to be controlled where the control variable id duty cycle.
So, the duty cycle corresponding to the output variable of MPPT should be determined. This is done using PI or some other controllers.
Read review papers of MPPT techniques for more information.
Good Luck.
The more simple way to control a DC-DC converter to perform MPPT requires the measurement of the current and voltage of the PV module (Ipv and Vpv) in order to estimate the required value of the duty cycle D (Using PWM with constant frequency). Another way to perform MPPT is obtained by using a hysteresis comparator to control the DC-DC converter through is input conductance (G) having that G=Ipv/Vpv, in that case the same measurements are required.
Yo can see details of an approach of this kind of methods in my Ph.D. thesis entitled "Contribution to the DC-AC conversion in photovoltaic systems: Module oriented converters".
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