Patent ID: 8155915

Claim:
A method for determining temperature of a delivery fluid of a centrifugal pump driven by a permanent magnet motor, whose rotor runs within a fluid-filled can, the method comprising: receiving in a controller a plurality of electrical values from the permanent magnet motor; determining in the controller a magnetic flux of the rotor based on the electrical values; determining in the controller the temperature of the rotor based on the determined magnetic flux of the rotor, wherein the rotor temperature is determined during operation by way of electrical power taken up by the motor, a phase current, and by way of the frequency of the voltage prevailing at the motor, and wherein the rotor temperature Tm is determined by way of the following equations: T M = ⁢ f 1 ⁡ ( I rms , T m ) = ⁢ 3 ⁢ ⁢ λ m ⁢ ⁢ 0 ⁡ ( 1 + β m ⁡ ( T m - T m ⁢ ⁢ 0 ) ) ⁢ I r ⁢ ⁢ m ⁢ ⁢ s T M = f 2 ⁡ ( P 1 , I rms , f , T s ) = P 1 - ( 3 ⁢ ⁢ R s ⁢ ⁢ 0 ⁡ ( 1 + α s ⁡ ( T s - T s ⁢ ⁢ 0 ) ) ⁢ I rms 2 + k F ⁢ f + k Iron ⁢ fI r ⁢ ⁢ m ⁢ ⁢ s + P I ⁢ ⁢ 0 ) 2 ⁢ ⁢ π ⁢ ⁢ f T s = ⁢ f 3 ⁡ ( I rms , T m ) = ⁢ 1 B m ⁢ 3 ⁢ ⁢ R s ⁢ ⁢ 0 ⁡ ( 1 + α s ⁡ ( T s - T s ⁢ ⁢ 0 ) ) ⁢ I rms 2 + T m , in which T M is a motor moment, λ m0 is a magnetic flux of the rotor at temperature T m0 , β m is a temperature coefficient of the magnet(s), T m0 is a temperature at which the magnetic flux of the rotor is λ m0 , I rms is an effective value of the phase current, P 1 is a power taken up by the motor, R s0 is a stator resistance at temperature T s0 , α s is a temperature coefficient of the stator resistance, T s is a stator temperature, T s0 is a stator temperature, at which the resistance is R s0 , k F is intrinsic losses of the rotor, f is a frequency of current supply of the motor k Iron is iron losses of the stator, P 10 is losses of the frequency converter, B m is thermal transfer resistance between the stator and fluid; and configuring the centrifugal pump such that the temperature of the delivery fluid is determinable from the temperature of the rotor.