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1. Using input regulation alone means that no output voltage regulation is required, but it is still needed as the maximum output voltage should not exceed the maximum charge voltage of the battery. Thus, a secondary feedback loop needs take over from the MPPT loop to limit the output voltage after it surpass set point by forcing it to operate below MPP. This control loop should not saturate the MPPT loop, otherwise it may fail to find the MPP when it is needed. Current regulation is built in to the DCDC controller so it is not something we need to add.

2. Investigate methods to prevent saturation of MPP controller 9409801.pdf (hindawi.com)

3. Investigate load current sensing to eliminate the need for a multiplier. Since a battery keeps the output voltage at nearly a constant voltage (in the timescales relevant to the control loop), the output power can be sensed by measuring the output current, which can be used to find dP/dV instead of multiplying panel input voltage and current.

This is the simulation we have so far, that you can add to for these next steps:

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Pros

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Input voltage regulation

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• No obvious way to limit the output voltage

• Relatively large # of external components

• Large input perturbations (2-3%)

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Pros

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Voltage regulation

Input vs output voltage regulation? How to limit output when using input regulation?

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Power Stage

Function

Array configuration

Seems boost only MPPTs are sufficient for MS15, as even with the lowest battery pack voltage the boost ratio is at the minimum of 1.1. It is possible for Vmpp to be slightly higher if the irradiance is above 1000W/m2, but I don’t think that’s too much of a concern.

Since pack voltage can’t go any higher (limited by motors), a buck-boost topology will be needed for MS16 since array area is increasing to 6m2, or the array will need to be split into 3 strings.

Topology

Since we only need boost mode for now, we will stick with that as it is the simplest option. The same controller can be used in a SEPIC configuration if step-up/down is desired in the future.

Primary FETs

GSFN6982 Good-Ark Semiconductor | Discrete Semiconductor Products | DigiKey

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Expand
title Gate Charge Loss

Other things we need:

• Inductor: AGP4233-473ME (100khz) or -683 (50khz), larger

  • Lower frequency → higher efficiency (less switching loss), more mass (larger coils)

• Other simpler components in spreadsheet, seem feasible.

• ~4 mOhm at 7.5V

Current Progress:

MPPT with output regulation:

updated preadsheet with boost converter specs:

To investigate: not using a multiplier

• Potentially via output current sensing?

  • Battery should keep (in a short timeframe) stable voltage, so sensing the output current would give us a proxy for power

Next steps:

Create schematic

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