[Communication] Inconsistency on the connection/disconnection of modules using duty cycle ramping

[analuhaas]

While implementing "Software fix 1 : changing the way CVB switch modules IN or OUT" to reduce oscillations generated on the stack voltage, we identified that often the modules would not connect or disconnect when expected, causing the stack voltages to be deformed. This inconsistency of connection/disconnection appeared only by adding the duty cycle ramping mechanism.

The origin of this problem is not yet diagnosed.

Software fix 1 : changing the way CVB switch modules IN or OUT

We tried to add an up and down ramp of duty cycle to make reduce the oscillations generated by one module connection. The width of the steps tested were equal to 1 or 3 critical tasks periods.

Figure 1: Duty cycle ramp up and down idea.

This helped us to reduce the oscillation amplitude significantly which is summarized in the table. The oscillations was even more reduced by increasing the width of the duty cycle steps.

Table 1: Oscillations reduction by adding duty cycle ramp.

Figure 2: Oscillations during connection of one module without ramp

Figure 3: Oscillations during disconnection of one module without ramp

Figure 4: Oscillations during connection of one module adding duty cycle ramp (width of 1 critical task).

Figure 5: Oscillations during disconnection of one module adding duty cycle ramp (width of 1 critical task).

Figure 6: Oscillations during connection of one module adding duty cycle ramp (width of 3 critical task).

Figure 7: Oscillations during disconnection of one module adding duty cycle ramp (width of 3 critical task).

However, some inconsistencies on the connection and disconnection appeared during the individual module and stack tests. We don't have yet a diagnosis why this happens so I will open an individual issue about it and it happend for both 1 and 3 critical task widths.

Figure 8: Inconsistencies on the connection (rose) and disconnection (green) of one module (width of 1 critical task).

Figure 9: Inconsistencies on the connection (rose) and disconnection (green) on one stack (width of 1 critical task).

Figure 10: Inconsistencies on the connection (rose) and disconnection (green) of one module (width of 3 critical task).

Figure 11: Inconsistencies on the connection (rose) and disconnection (green) of one stack (width of 3 critical task).

Software fix 2 : changing the way CVB inserts and de-inserts multiple modules at once

We can change the CVB algorithm to only connect/disconnect $\Delta N$ modules at a time:

Figure 12: Possible CVB strategy to reduce multiple modules connections/disconnections.

Originally posted by @analuhaas in #2