Friday, June 11, 2010

Eloads are great for outdoor Photovoltaic test but where is the MPPT capability?

Eloads have become a popular solution for outdoor testing of higher power photovoltaic (PV) devices, like PV panels and concentrated PV. The main reason for this is eloads can sink a lot of current at a low cost compared to 2 and 4 quadrant power supplies. The testing is usually of the design verification variety and one of the main roles of the eload is max power point tracking (MPPT) on the output of the PV device. One request of end users of eloads for this application is does the eload have MPPT capability or can you put built-in MPPT capability in the eload? Currently there are no general purpose eloads (that I know of) that have built-in MPPT capabilities. This means it is up to the test engineer to implement an MPPT algorithm in software. This adds time and complexity to the test engineer’s job. Also since the algorithm is in the software it has to deal with IO latency between the computer and the eload which lowers the test systems MPPT speed. To help test engineers out with this challenge I wrote an article entitled “A Photovoltaic MPPT Algorithm for DC Electronic Loads” that was published by Electronic Design and can be found at the link below. The article introduces an ideal algorithm for performing MPPT with an eload. It is ideal because of its low complexity and it keeps IO transactions to a minimum to reduce the affects of IO latency.

A Photovoltaic MPPT Algorithm for DC Electronic Loads

4 comments:

  1. Hi Neil,

    Clearly, an eload is useful for capturing the I-V curve of a PV device in order to confirm parameters such as Voc, Isc, Pmp, etc. Can you explain the reason you would want to subject a PV device to a simulated MPPT algorithm? What are the test criteria? What are the test results expected to show?

    Thanks,

    Gary

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  2. It is basically a design verification/durability type test. You want to simulate the conditions the panel or CPV will experience in real world use (having its MPP tracked by a inverter). This type of testing could last for days or months. You want to see if the PV device catches on fire, if a part begins to degrade, and most of all you want to ensure it maintains its rated efficiency or power output specs over an extended period of time.
    Besides MPPT, other conditions are simulated with the eload such as short circuit conditions to see if the conductor runs can hold up to high current. Open circuit conditions to see if the PV device can stand up to high heat.

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