Patent ID: 7558699

Claim:
A method of measuring the performance of a centrifugal pump for extracting fluid from a subterranean wellbore, said centrifugal pump being directly coupled to an electrical motor, wherein both the centrifugal pump and the electrical motor are disposed near the bottom of the wellbore, and wherein said motor receives electrical power through a motor cable extending from the motor to a point above the surface of the earth, the method comprising the steps of: determining a value of speed input to the centrifugal pump; determining a value of pump flow rate; and using the value of speed input and the value of pump flow rate to calculate one or more values representing the performance of the centrifugal pump, wherein the values of speed input and pump flow rate are derived without the use of any sensor disposed within the wellbore and without having any sensing lines extending to the motor through the wellbore; and also wherein the step of determining the speed input to the centrifugal pump comprises the steps of: measuring values of electrical voltages applied to the motor cable and currents drawn by the motor cable; using the values of electrical voltages applied to the motor cable and currents drawn by the motor cable to determine values of a stator voltage vector, a stator current vector and a rotor flux vector; using the values of the stator voltage vector, the stator current vector, the rotor flux vector and a model of the motor, the model being executed by a controller, to calculate a value for the motor speed.