Patent Document ID: 20010033147
Application ID: 09764667
Patent Flag: 0

Claim One:
1. An apparatus for providing a constant fluid flow comprising: a induction motor having at least one rotor, and at least one variable frequency drive; at least one fluid impeller attached to said at least one rotor wherein said at least one fluid impeller is constrained to rotate with an angular velocity equal to an angular velocity of said at least one rotor; electronic components capable of storing and manipulating electrical signals wherein said electronic components are in electrical communication with said at least one variable frequency drive; selector means in electrical communication with said electronic components wherein said selector means are configured to provide electrical signals which represent a desired fluid flow rate; a zeroth data set stored as electrical signals in said electronic components comprising estimated initial values of stator frequency and stator voltage as a function of said desired fluid flow rate; at least one set of system current constant values stored as electrical signals in said electronic components; at least one set of system voltage constant values stored as electrical signals in said electronic components; a first data set stored as electrical signals in said electronic components comprising target DC bus current values as a function of said desired fluid flow rate, a stator frequency and said at least one set of system current constants; a second data set stored as electrical signals in said electronic components comprising root mean square voltage values for a stator voltage as a function of said stator frequency and said at least one set of system voltage constants; a current sensor disposed in functional proximity to a DC bus of said variable frequency drive and in electrical communication with said electronic components wherein said current sensor provides electrical signals to said electronic components which represent a measured DC bus current value; electrical signals comprising a program stored in said electronic components wherein said program causes said electronic components to: read said desired fluid flow rate; read an estimated stator frequency value and an estimated stator voltage value from said zeroth data set as a function of said desired fluid flow rate; write said estimated stator frequency value and said estimated stator voltage values as inputs to said at least one variable frequency drive; allow a system specific settle time to elapse during which said motor and fluid impeller reach a steady state in response to said inputs and an ambient fluid pressure; read a target DC bus current value from said first data set as a function of said stator frequency value, said desired flow rate value, and a set of said at least one set of system current constants; read a measured DC bus current value from said current sensor; compare said target DC bus current value with said measured DC bus current value and determine a DC bus current error value wherein said DC bus current error value is a difference between said target DC bus current value and said measured DC bus current value; calculate an updated stator frequency value as a function of said DC bus current error value using a PI controller; read a root mean square stator voltage value from said second data set as a function of said updated stator frequency value and a set of said at least one set of system voltage constants; write said updated stator frequency value and said root mean square stator voltage value as updated inputs to said variable frequency drive; allow a system specific settle time to elapse during which said motor and fluid impeller reach an updated steady state in response to said updated inputs and ambient fluid pressure; read an updated desired fluid flow rate from said selector means; perform a next iteration of said program beginning at reading a target DC bus current from said first data set.