This paper studies the design of a Maximum Power Point Tracker (MPPT) for low power portable solar array applications. The discussion will compare different digital and mixed signal implementation approaches of the same Perturb and Observe algorithm, in particular: simple P&O algorithm on the duty cycle, P&O algorithm using an analog inner voltage control loop and finally using a digital voltage control loop programmed into the microcontroller. This research shows that the method of implementation (analog, digital) has an influence on the robustness of the MPPT particularly in suddenly changing illumination conditions. Solar Panels have been used for decades to generate electricity in various applications: small electronics, spacecrafts, remote locations… However, the little efficiency of solar panels has limited their use. As the efficiency is limited, harvesting the maximum amount of energy from the panel is of prime interest. Recently, the arrival on the market of several types of flexible and lightweight solar panel has unlocked many applications as they can deliver power where no other source is available. However, these solar panels have lower efficiency than average solar cells (although increasing). This emphasizes the need for maximum power extraction even more.Maximum power is produced by the solar panel at a specific point on the I-V curve of the solar panel. That maximum power point fluctuates with temperature and light intensity. To deliver the maximum amount of power to a load, a DC-DC converter is placed between the solar panel and the load. Different control methods exist to achieve maximum power point tracking. Some rely on the open circuit voltage of the solar panel or short circuit current and then control the voltage to be a fixed fraction of that value [1]. Another widely used method is the "Perturb and Observe" method in which the duty cycle of the converter is modified and the power generated measured [2,3]. If the power increased following that modification of the duty cycle, then the duty cycle will be again be changed in the same direction. If the power generated by the solar panel has reduced, the duty cycle will be changed in the other direction. That will cause the duty cycle to drift and eventually oscillate around the maximum power point of the solar panel. That method has proven to be efficient in optimizing the power output [4].
This paper proposes a method for extracting power from several solar panel modules with different characteristics using one single current sensor. This method can prove useful to reduce the board size and to increase the variety of controllers (microcontrollers or FPGAs) that are suitable for that application.
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