4. Power Supply Finite State Machine

The behaviour of the power unit output is determinated by a Finite State Machine (FSM).

The Output Finite State Machine is the following:

../_images/Output_FSM.png

The three FSM states are:

  • OFF State: in this state the output drivers and PID controller are disabled. This is the default state at machine startup.

  • ON State: in this state the output drivers and PID controller are enabled and the unit can accepts a new setpoint. The default setpoints are:

    • 0A in CC Mode

    • 0V in CV Mode.

  • Wait for Off State: in this state the unit performs a ramp-down to 0A in CC mode (or 0V in CV mode) and waits until the output current reaches 0A. When the current is about 0A, the FSM evolves automatically to OFF State.

Tip

The Wait for Off State is useful with superconducting magnets, when the output needs a longer amount of time to reach the 0A. In this case the unit ramps down in a controlled way and switch off the power stage only once the 0A are reached.

The transition between the states are the following:

  • Command-related transitions (in blue): that are defined by software commands (see OUT Command)

  • Fault-related transitions (in red): that are defined by a Fault condition. When a fault occurs, the machine starts a transaction to a “save state”, this is the OFF State in which the power stage is disabled.
    There are two types of Fault conditions:

    • Soft Fault: faults that does NOT impact the functionality of the power unit (for example a temperature fault). In this case it is possible to switch-off the unit in a controlled way and so the FSM evolves in the Wait for Off State.

    • Hard Fault: faults that impact directly the correct functionality of the power unit (for example a crowbar fault). In such case the FSM evolves directly in the Off State in which the power stage is immediately disabled.

  • Internal transitions (in green): there is only one internal transition that is related to the output current. This transition is used only when the OUT FSM is in OUT Wait for Off State and the output current is close to 0A, at this point the OUT FSM automatically evolves to OUT OFF State.