(2022 - 2024) Design Implementation:

Refer here for the general documentation: [WIP] High Voltage System

Understanding how the battery charges and discharges:

1. All contactors stay close while the car is in operation with the exception of BPS fault states (when triggered) and when the battery begins to overheat at 40 degrees C.
2. The arrays will always be charging the battery because the MPPT can be treated like a current source, or an array of PN junctions driving a forward current.
3. While the battery overheats, it discharges to the motor.
4. Regenerative braking can also charge the motor. (When the battery overheats and the arrays pre-charge contactor is opened, regenerative braking is toggled off by Controls in the motor controller.)

Understanding how the motors work (limitations and functionality relative to HV System):

1. There is no recovery state implemented in either Controls or BPS to reset the motor.
2. The motor cannot be powered while it is faulting.

(2024 - 2026) Design and Considerations:

What are areas of improvement?

1. Since we cannot connect to the arrays and thus are NOT charging the battery, the power generated by the arrays is wasted.
   
   1. BPS no longer has fine-tuned control over the arrays (switching them on and off to charge)
   2. Arrays are always on, leading to excess power captured with MPPT.
2. We can utilize excess power from the arrays to power the motor!
   1. Manthan claims that BEFORE THE FAULT STATE (when the battery hits 45 degrees C), BPS will turn off the contactor (HVARR contactor) allowing the battery to charge.
      1. Refer to Integration Test Plan for when something should connect or disconnect (in Appendix)
      2. Adding another contactor and diode will help discharge the battery and draw power from the arrays to the motor simultaneously.

Solutions:

1. Creating a new current regulating board
2. Adding another contactor and diode
   1. Simple design that has similarities to the Fig. 2a in Energy Management Power Converters in Hybrid Electric and Fuel Cell Vehicles | IEEE Journals & Magazine | IEEE Xplore
   2. Equal voltage between the battery and arrays allows for connection to the load in parallel. 

Impact on other systems and received inputs:

Ideally, there are no significant impact on other systems. We must also be careful of integrating with other systems, what of kind of inputs we're taking (voltage and current wise).

1. Regenerative Braking (Controls)
   1. Would regenerative breaking be affected by this rearrangement?
      1. In the current implementation (2022-2024), while the battery is overheating, Controls disables regenerative breaking in conjunction with the arrays contactor being opened.
      2. In the new design, the arrays contactor is opened, and the diode will prevent reverse current regardless of whether or not the regenerative breaking is enabled/disabled.
         1. When the arrays contactor is closed (the new one that BPS will control), regenerative breaking will have no issues with the HV design.
         2. Refer to microcontroller for how regenerative breaking is managed: ENGR - Longhorn Racing - WaveSculptor22 Users Manual.pdf - All Documents (sharepoint.com)
2. MPPT Output (Power Gen)
   1. Can we assume that the arrays behave like a current source?
      1. MPPT helps the arrays get the maximum power from the solar cells
         1. Arrays can generate high output voltage (open circuit voltage) and little current
         2. On the other side, arrays can generate high output current and no voltage (short circuit)
         3. MPPT ensures max power are obtained from the solar arrays (see Sunscatter (MPPT))
      2. The Arrays themselves output ~60 V, which is consistently lower than the battery voltage so that you can always boost your voltage instead of having to determining whether you need to boost or step down the voltage relative to the voltage of the battery.
      3. The reason for why arrays act like a current source is because photovoltaic cells are PN junctions, and current goes only one way in the forward bias (small reverse bias current)
3. Fault States (BPS)
   1. Theoretically, if we're planning to open the contactor that allows the battery to charge when the battery reaches 40 degrees C (before the fault state at 45 degrees C), there should be no issue with the new design since the battery will still be forced to discharged.

Tentative New Design:

Appendix:

Integration Test Plan:

• CAN Bus not overflowing 
• Data Acquisition Reading all CAN messages 
• Turning ignition to LV enable: 

• • BPS contactors close 
  • Pre-charge contactors are open 

• Turning Ignition to Charge Enable: 

• • BPS Contactors Close 
  • Array pre-charge contactor closes 

• Turning ignition to motor enable: 

• • Motor Pre-charge contactor closes 

• BPS temperature exceeds 40 degrees C: 

• • BPS Array contactor closes: 
  • Controls pre-charge contactor opens 

• BPS fault for: 

• • Overcurrent charging 
  • Overcurrent discharging 
  • Overtemperature charging 
  • Overtemperature discharging 
  • Overvoltage 

• • Ensure that Data Acquisition display shows correct fault every single time 
  • Ensure controls stops running 
  • Ensure all contactors open every single time 

• Controls motor fault: try simulating by disconnecting a connector and then connecting again. 

• Data Acquisition: should send proper message on its display 

• Power Systems: 

• • Supplemental Battery -> DC-DC power handoff works properly 

• • None of the systems undervolted during handoff 

• Pressing the Kill Switch: 

• • Ensure BPS shuts off 
  • Ensure other systems stop running 
  • Ensure pre-charge contactors turn off