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Goals
Goals
- Isolate ADC
- Interface with the RaceMax meter board connecter pinoutsInterface with Nomura MPPTConnect to the STM32F072CBT6 microcontroller
- Record voltage and temperature per-module and current per-string
Background and strategic fit
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Interfacing with the RaceMax board will allow for solar array diagnostics.
Assumptions
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We're planning on using Nomura MPPTs. Each MPPT is designed to connect to a smaller number of cells and output up to around 30V. A few of these MPPTs are then put in series. Theoretically, this should maximize the performance of our array in non-optimal conditions.
We're like to record data on the array to optimize our strategy and charging.
Assumptions
- Our MPPTs will output around 30V at max
- Our array should generate around 1kW at max
- Our MPPTs will be integrated into the array modules
- We will need to deal with communications over 1m+ cables
Requirements
| # | Title | User Story | Importance | Notes |
|---|---|---|---|---|
| 1 |
| Work with |
- STM32F0 ADC, 3.3v (min: 2.4v and max:3.6v)
Interface with Nomura MPPT
Multiple Nomura MPPTs connect in series with the array, while before there was just one MPPT connected in parallel with the array. The Nomura MPPT's setup allows for greater power output.
Research must be done on voltage and current sensing.
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| Nomura MPPTs | We're using 10 Nomura MPPTs, 5 in series for 2 strings total. They don't have any public way of interfacing with them, but we'd like to collect data on our array. | Must Have | Using a master board for current sensing and LIN slaves for each MPPT | |
| 2 | Record voltage and temperature per-module | We'd like to know the voltage and temperature of each module so we can tell how each module is performing and any potential hotspots. | Must Have | |
| 3 | Record current per-string | We'd like to know the current provided by each string so we can calculate the overall power of the solar array. | Must Have | We will probably use a dedicated current slave to record the current of the string. |
| 4 | Isolated | We want to make sure that our analog measurement is isolated from the rest of the car. | Must Have | Look into analog isolation using a class D amplifier + digital isolator |
| 5 | Low-cost/Simple | We'd like to make these boards as simple as possible to reduce development time. | Must Have | Once the LIN stack is written, we can use the built-in ADC to record voltage and temperature. |
Questions
Below is a list of questions to be addressed as a result of this requirements document:
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| Question | Outcome |
|---|---|
| Can we use the Nomura Multi Display Meter to interface with the MPPT? (It has voltage and current sensing) | n/a |
Not Doing
| What kind of architecture are we using? | Master node with controller board living in the roof enclosure Slave nodes (LIN) attached to each MPPT |
| How will our boards communicate? | Originally, we were planning on using differential I2C. However, after doing a cost analysis, we have decided to use LIN instead, with low-cost LIN slave controllers on each board. See Solar Slave - System Architectures for a comparison between the two. |
| What's powering the boards? | The MCUs and LIN transceiver will be powered from as 12V rail provided by the solar master node. To save on costs, we plan on using LDOs since our MCUs are relatively low-power. On the isolated side, we will likely use an LDO to convert the MPPT output to a voltage usable by our isolator. |