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[!UPDATE] {docsify-updated}

Temperature Control

Concepts

The climate control integrated in pev-controller application is taking temperature channels as input and realise actions as output in reaction to the measured temperatures.

The inputs are:

  • PTC 1000 analog inputs from the board connectors
  • Temperature signals reported over CAN
  • System temperatures (CPU and SoM)

The output actions are:

  • Add current derating
  • Stop the charge
  • Monitor (ie. distribute measurements over the charger interface)

To draw the line between an input measurement and an output action, a list of actions can be configured. That list of actions is defined in a "functional" group, that can be associated to various temperature channels.

Example: A temperature channel is associated to a functional group (eg. "cable"). That functional group list the actions that should be invoked for every measurement (1 sample per second) (eg. "cable_current_derate", "charge_stop", "monitor"). Each action implements the reaction it wants and acts on the rest of the system.

Temperature channels configuration

Temperature channels are configured in the /srv/config.cfg file under [temperature] section.

  • [temperature] can be a multi-line entry
  • Each line has the following format: <CHANNEL> = <FUNCTION>
  • <FUNCTION> has to correspond to another section of the config file named [temperature:<FUNCTION>]. Several sensible default functions are already provided (see below).
  • <CHANNEL> corresponds to a temperature channel available on the controller.
Example temperature channels configuration 
[temperature]

ptc0 = monitor
ptc1 = cable
ptc2 = monitor

Channel functions configuration

A [temperature:<FUNCTION>] section has only one possible entry, the action list.

  • actions can be a multi-line entry of possible <ACTION>
  • Each <ACTION> has to correspond to another section of the config file named [temperature_action:<ACTION>]. Several sensible default actions are already provided (see below).
Example temperature function configuration 
[temperature:cable]
actions =
		cable_derate_current
		cable_stop_threshold
		monitor

Default functions provided
Function Actions Purpose
cable cable_derate_current
cable_stop_threshold
monitor		 Derates the current as temperature goes up. And stop the charge once passed a certain threshold. Also report the temperature over CAN.
monitor monitor Just for reporting a temperature channel over CAN.

Actions configuration

Each [temperature_action:<ACTION>] section is providing parameters to actual action classes hard-coded in the pev-controller application.

  • mode is the entry corresponding to an actual action class (list below)
  • target is an entry common to all modes. It defines what the action will act upon. It can also be a comma or space separated list of target.

Monitor mode

The monitor mode is simply storing the value of the measured temperature into the internal datastructure that will be passed on to the charger interface for reporting. It is then up to the charger interface to actually emit the information on its bus according to its own encoding.

  • target parameter can only be monitor.
Example (actually, only valid way) of writing a monitor action 
[temperature_action:monitor]
target = monitor
mode = monitor

A default monitor action is already provided (as in the example). And you would most likely just use it as-is as there is nothing particular to configure here.

On the generic interface, these measurements are reported in ADM_CS_EVCC_Inputs.

Encoding of temperature signals in the generic CAN interface

All temperature signals in the generic interface (ie. input and output ones) are encoded in the same way:

  • Length of 8 bits
  • Slope of 1 (ie. 1°C/bit)
  • Offset of -40
  • Minimum: -40°C (encoded as 0x00)
  • Maximum: 215°C (encoded as 0xFF)
  • Default value of -40°C means "not provided" or "not connected"

Threshold mode

The threshold mode is triggering its target when its configured limit is crossed.

  • Currently, the available target is charge_stop.
  • limit is a float.
Example cable temperature action for stopping charge at a threshold (as per CCS standard) 
[temperature_action:cable_stop_threshold]
target = charge_stop
mode = threshold
limit = 90

Default threshold actions provided
Action Target Limit Note
cable_stop_threshold charge_stop 90 As per CCS standard

Derate interpolate modes

The derate_interpolate mode is suitable to derate the charging current as a measured temperature goes up.

The derate_interpolate mode sets the result of a linear interpolation function defined by setpoints into the target parameter. This actually defines a "response curve" in function of the measured temperature.



  • setpoints is a multi-line list of input temperature to output result. A linear interpolation of the output is applied for input temperature values that are in between the setpoints.

Warning

Because internally the setpoint list ends up being stored in a dictionary data-type, you cannot have duplicated input values in your list. However, the input values are converted to float. So, it is fine to use two different values with a small (eg. 0.1) difference.

Tip

The best way to define the behaviour of the response curve at the boundaries (low or high temperatures) is to use the special -inf and +inf float values.

Warning

When a sensor is disconnected or shorted to ground, it is interpreted as -inf.

Example setpoints configuration 
setpoints =
		-inf = 0%   # For any temperature below 20°C, have a null response
		20   = 0%   # Corner at 20°C to ramp-up
		50   = 40%  # Ramp-up to 40% from 20°C to 50°C
		50.1 = 70%  # Brick wall response, jump from 40% to 70% at 50°C
		70   = 70%  # Plateau at 70% between 50°C and 70°C
		90   = 50%  # Ramp down to 50% up to 90°C
		+inf = 50%  # Flat end of the curve after 90°C
Resulting response curve 
   Response                                                   
       ^                                                      
  100% |                                                      
       |                                                      
   80% |                                                      
       |                   |---------\                        
   60% |                   |          ---\                    
       |                   |              ----------------    
   40% |                  -|                                  
       |               --/                                    
   20% |            --/                                       
       |         --/                                          
    0% +---+----/--+---+---+---+---+---+---+---+---+---+--> Temperature  
      0°C    20°C    40°C    60°C    80°C    100°C   120°C



  • Currently, the only available target is max_charging_current.

Note

When several derating are active at the same time on the same target (from different temperature channels and/or accross different actions), the highest derating value is used.

  • setpoints is the definition of the response curve

Note

The output quantity expressed by this response curve is the amount of derating applied to the target in percent. Ie. 0% means no derating, and 100% is full derating.

Note

Therefore, the formula is akin to target_value *= 1 - max(target_deratings)

Example of a derate interpolate action 
[temperature_action:cable_derate_current]
target = max_charging_current
mode = derate_interpolate
setpoints =
    -inf = 0%
    60 = 0%
    90 = 50%
    +inf = 50%
Default derate interpolate actions provided
Action Target Setpoints Note Comment
cable_derate_current max_charging_current -inf = 0%
60 = 0%
90 = 50%
+inf = 50%		 Gradual increase of derating from 60°C to 90°C.
Plateau at 50% derating beyond 90°C.		 To be used with a charge stop threshold action above 90°C.