Patent ID: 8761957

Claim:
A method of controlling a transition time through a speed range that is unsafe for an integrity of a first expander, by automatically biasing a speed of a second expander that receives a fluid flow output from the first expander, the method comprising: setting the speed of the second expander to be larger than a current speed of the first expander, when (a) the current speed of the first expander is within a bias application range, and (b) the current speed of the first expander increases and is smaller than a first speed value, or decreases and is smaller than a second speed value; and setting the speed of the second expander to be smaller than the current speed of the first expander, when (a) the current speed of the first expander is within the bias application range, and (c) the current speed of the first expander increases and is larger than the first speed value, or decreases and is larger than the second speed value.