I am trying to implement the simulation of a dual stage grid tied photovoltaic system. But I am a bit confused as to how the boost converter can output a constant voltage, as well as limit the current flowing from the solar panel. For instance up to certain input voltage level, output a constant voltage independent of the input voltage by using limited current flowing from the solar panel.
Dear Özgür,
there is a misunderstanding, I think.
Using the boost converter to work as MPP-Tracker will lead to a change in DC-link voltage of the following inverter.
To hit the MPP, you have to adapt the U/I-point of operation in the solar cells, thus a fixed voltage is not an option.
The trick is to boost the DC-link voltage to most accurately achieve maximum power delivered from the cell field.
At constant power, this can be achieved at different combinations of voltage and current, depending on radiation levels.
The output from the grid-connected inverter is then controlled by adapting the modulation index to inject the proper current into the grid.
Dear Martin Schulz,
First thank you very much for your interest. I was thinking like you, however I saw a data sheet and related design paper of a widely used inverter. In there, they noticed that between specific input voltage values, the dc dc boost converter limiting the current flowing from the solar panel and producing a constant voltage at the output. Therefore I am a bit confused, as far as I know the task of providing proper dc link voltage related with controlling inverter.
Impossible to do both by the boost.
In the case of PV grid connected, Usually , the boost is tracking the MPP and the inverter (grid side obviously) is controlling the DC bus voltage.
By tracking the MPP Martin Shultz explained it well (reaching the MPP by ontrolling the current or the voltage at the boost input, depending of the choosen strategy : P&O, mapping...)
see the free access paper :
Bratcu, A. I., Munteanu, I., Bacha, S., & Raison, B. (2008). Maximum power point tracking of grid-connected photovoltaic arrays by using extremum seeking control. Journal of Control Engineering and Applied Informatics, 10(4), 3-12.
All the best
The boost converter can do only one thing at a time either maintain MPPT or Voltage mode Control (const. Vdc ). Generally in grid connected applications the boost converter is used to track the MPP and the dc-link voltage is regulated by the inverter by controlling the real power injected to the grid.
Agreed with Bacha Seddik and Nishant Bilakanti. In a two-stage grid-connected inverter, the boost converter is responsible for tracking the MPP of PV arrays. The dc-link voltage is stabled by the inverter. That is to say, the input voltage of boost converter is regulated by the MPPT controller then generate corresponding PWM signal. Meanwhile, the output voltage of boost converter is clamped by the inverter as the output voltage of inverter is clamped by the AC grid.
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