Solar Test Plans - Rev. 1.0

SEE BOTTOM OF PAGE FOR VALIDATION RESULTS (FOR SOME OF THE TESTS)

This page will go over the test plans for the solar sense board and all the unit/integration tests for each subsystem implemented. It will be written out based on what to populate, then subsequently what to test so we populate only the subsystems we need to.

It will be ordered based on what to test/populate first.

As a side note so that things can be done in parallel: there will need to be firmware written or at least set up to read values in SPI from the Nomuras (which Arshan has), and code to read from the thermistors, set the chip select lines for the SPI communication, control the relay and read voltage measurements from the ADCs. See schematics on my branch for details.

Part 1: Digital Communication Unit testing

This testing will be done by Liam during the Spring 2020 term, and will verify the ability to communicate over SPI, I2C and read using the controller board ADCs for each of the sense measurements.

SPI Communication

The SPI communication is used for the input voltage sense measurements to the MPPTs, indicating the amount power generated by each segment of the array. The SPI communication from the MPPTs will give indication of the input voltage, input current and MPPT temperature as it will internally go into a fault state for an OVP, OCP and OTP conditions.

This validation can be done with the SPI smoke test, and would ideally look at the signal integrity through the isolators and to controller board. But for now, let’s just test for functionality. We will test reading one mppt, and then string two in series.

Populate the following components, we will be testing the channel outlined

• U22, U27, C35, C34, C54, C53, R38, R39, R24, C18, C20, U9, U14, C25, R25, U2, C5, C6, P1

The above components will allow for us to validate the SPI interface. Note, U2 is a decoder that must output the CS to the 6th line for the highlighted channel. For this test, the input of the MPPT must be connected to a power supply and the output to an Eload. Then, the SPI header from the MPPT must be soldered to the spi header on this board. Note; the nomura MPPTs have a trace that must be cut so the SPI header is not all grounded and is useable → see the other validation pages in this space.

We want to make sure we are able to see the MPPT give us information about the voltage, current and temp parameters. To make it accurate to what we expect in the car, use this page to configure the potentiometers on the MPPT (follow the one for the 6 MPPTs): Potentiometer Configuration

Use the following space to record findings:

<insert test table>

Output Voltage sense

We take our own measurements for output voltage sense, and to do so for this test we will connect one MPPT output to the 6th channel as done in the above SPI testing. The MPPT also has to be connected to an E-load, and will basically have taps that go to this board. We will want to vary the voltage input of the power supply so that we get the expected stable output each time from the MPPT when the input is within operation range.

Make sure you have the same parts populated as in the above SPI testing, as it includes the parts needed for the voltage sense.

Use the following space to record findings:

<insert test table>

Temperature sense

We take our own thermistor measurements from the panels for each section. If you have a spare 10k ntc, that would be ideal to connect, otherwise we can just use a resistor and make sure that the voltage divider and internal ADC work. Make sure you connect it from pin 1 and 4 on P15, and populate C42 and R46.

Use the following space to record findings:

<insert test table>

Part 2: HV/Series MPPT Testing

Ideal Diode

The ideal diode design was taken from the typical applications in the LTC4359 Ideal Diode Controller Datasheet and was used in the ideal diodes purchased from Nomura for MS12. The implementation uses Zener diodes to clamp the reference of the input to 12V wrt Vss. The remainder of the 200V drops across R1, allowing the IC to stay at a LV reference. The purpose of this ideal diode is to implement diode features (near ideal) in which all current in a forward bias is conducted, while it is isolated in reverse bias.

To test the ideal diode, first, populate the following components in the order from first to last:

U2,D5,D4,D6,C66,Q3,D7,R51,C9,R54,C10,Q2,R19,P2

The following is a list of the tests that need to be run and instructions to do so. Make sure YOU ARE ALWAYS CAREFUL AND CONFIDENT IN WHAT YOU’RE DOING, else seek help from an EE lead:

• General connectivity

  • You’ll want to test all the nets (refer to schematic diagram) at each node. Simply use a DMM on ohm mode and turn on the sound with the sound button (if the probes make noise when they touch each other its the right mode). This is just a quick test after population to make sure everything seems right.

The following tests will be conducted with 1 mppt connected to the 6th slot on the board (the slot on the right side) with a jumper going from the ground pin of the mppt to the “to battery terminal”.

• Voltage drop across diode all cases

Measure the voltage difference across the diode for each of the following cases.

• LV Conduction forward bias

Test from a range of 10V - 50V at a dc load drawing from 1A to 6A (check the specs of the load if this is possible). Most likely with the load we have, we will only be able to have a current limit of 6A at low voltages for the power rating, and so to test the current limit of 6A that the diode could see, we will test that limit in this test case.

Make sure you are only using probes with alligator clips for the multimeter readings of voltage. Use the really nice and not sketchy looking alligator clip probes and attach to the P2 terminal closer to the ideal diode section for the “out” node of the ideal diode, and the slot in the relay close to the ideal diode section as the “in” node on the diode. Find the ground as the other terminal on the batter connector.

Make a table below, and fill it out with all the data points from these ranges.

• HV Conduction forward bias

• LV isolation reverse bias

• HV isolation reverse bias

• Voltage drop across diode all cases

• Thermals (shouldn't be anything significant)

The following will outline my testing of the ideal diode:

• I populated everything as instructed above

• I first wanted to ensure the forward bias works. The following table outlines the drop across (everything without load btw) the diode based on the output and input. Note, the table only has forward bias testing, where no power supply was loaded onto the cathode.

• Now I want to test the reverse bias protection to make sure that when i put a supply on the cathode, it will not conduct to the anode. The following table summarizes my results, and note that once again there is no load.

The ideal diode works!! that was the smoothest validation so far → ideally id test with higher potentials, but considering that this testing was above the rating of the zener diodes already, it’s safe to say it operates as intended. Of course, double checking with a potential of over 100V would be ideal before integration testing (in which case I can finish filling out these tables).

The following will outline my testing of the relay and relay driver:

• I have populated everything necessary and rerouted the relay as per the schematic issue of placing it low side instead of high side.

• When I toggle a GPIO for enabling the DRV120APWR, I notice that if it is a low or a high value of GPIO, the contacts on the relay still close. Need to still investigate this, but it seems like the relay is always pulling the output low. This is also probably a fault with the rerouting because it seems to just turn on no matter the code and just when 12V is present. Also, the LED doesnt ever turn on.

• I can also hear a high pitch hum as noise from the driver → might want to adjust the resistor/cap to adjust the PWM.