System and method for mode transition for a two-stage series sequential turbocharger

A method of controlling an engine comprising:

• opening the high pressure turbine bypass valve of a turbocharging system;
• for a first position of a variable geometry turbine of the high pressure turbocharger, determining a first predicted boost pressure when the high pressure turbine bypass valve is in an open position;
• for a second position of the variable geometry, determining a second boost pressure when the high pressure turbine bypass valve is in the open position;
• determining a desired boost;
• and
• when the desired boost signal is between the first predicted boost pressure and the second predicted boost pressure, closing the high pressure turbine bypass valve.

A control system comprising:

• a boost determination module that determines a first predicted boost pressure for a first position of a variable geometry turbine when a high pressure turbine bypass valve is in an open position, and that determines a second boost pressure for a second position of the variable geometry when the high pressure turbine bypass valve is in the open position;
• a desired boost module that determines a desired boost;
• a comparison module that determines when the desired boost signal is between the first predicted boost pressure and the second predicted boost pressure;
• and
• a bypass valve control module that closes the high pressure turbine bypass valve when the desired boost signal is between the first predicted boost pressure and the second predicted boost pressure.