EP-4387080-B1 - CONTROL METHOD FOR VARIABLE SPEED DRIVE AND PROCESSING SYSTEM COMPRISING VARIABLE SPEED DRIVE

EP4387080B1EP 4387080 B1EP4387080 B1EP 4387080B1EP-4387080-B1

Inventors

Frappé, Emmanuel
DEVOS, THOMAS
JEBAI, Al Kassem
Malrait, François

Dates

Publication Date: 20260513
Application Date: 20221216

Claims (14)

A method for controlling a variable speed drive (3) driving a three-phase electric motor (4), the variable speed drive (3) comprising electric measuring means adapted to measure current signals, a pulse width modulation, PWM, controller (PWM), an inverter (33) and a DC-link (32) adapted to supply the inverter (33) with a significantly continuous voltage, wherein: the inverter (13) comprises three legs connected to the three windings of the electric motor, each leg being connected on one side to a positive bus of the significantly continuous voltage and on another side to a negative bus of the significantly continuous voltage, each leg comprising a top switch (131t) and a bottom switch (131b); whereby each switch (131) comprises two components, a first component being an Insulated Gate Bipolar Transistor, IGBT, controlled by a PWM signal emitted by the PWM controller based on a control law of the electric motor, and a second component being a freewheeling diode (FD) connected in parallel with the IGBT; the method comprising: measuring (110) current signals in the windings of the electric motor (4); the method is characterised by determining (120) a current parameter associated to the electric motor based on the current signals, wherein the current parameter comprises a current offset of at least one winding of the electric motor in relation to a zero-current value; or wherein the current parameter comprises a current misbalance between windings of the electric motor; determining (130) an amended control law of the electric motor for decreasing the determined current parameter; and applying (140) PWM signals on the IGBTs of the inverter based on the amended control law.
The method according to the preceding claim, wherein determining a current parameter comprises determining a current offset of at least one winding of the electric motor and a current misbalance between windings of the electric motor.
The method according to the preceding claim, wherein determining the current misbalance between windings of the electric motor comprises: determining the current offsets of the current signals in the windings of the electric motor; removing the current offsets from the current signals for obtaining centered current signals; and determining a reverse component of the measured current signals based on a current observer and on the centered current signals.
The method according to the preceding claim, wherein the centered current signals are defined in the current observer as: I ^ αβ 1 = I ^ f e j θ ^ + I ^ 1 r + j I ^ 2 r e − j θ ^ wherein I ^ αβ 1 corresponds to an estimation of the centered current signals I abc 1 in the Clarke representation, wherein θ̂ corresponds to an estimation of the current vector angle in αβ frame, wherein Î f e j θ̂ corresponds to an estimation of the forward component of the measured current signals, wherein I ^ 1 r + j I ^ 2 r e − j θ ^ corresponds to an estimation of the reverse component of the measured current signals, wherein I ^ 1 r corresponds to an estimation of the real part of the reverse component of the measured current signals, and wherein I ^ 2 r corresponds to an estimation of the imaginary part of the reverse component of the measured current signals; wherein determining the reverse component of the measured current signals comprises determining the estimated real part I ^ 1 r and imaginary part I ^ 2 r of the reverse component of the measured current signals; and wherein the amended control law of the electric motor is determined for decreasing the estimated real part I ^ 1 r and imaginary part I ^ 2 r of the reverse component of the measured current signals.
The method according to the preceding claim, wherein the current vector angle θ̂ in αβ frame is estimated based on a Phase-Locked Loop, PLL, or is determined based on the magnetic flux vector angle of the electric motor determined by the variable speed drive.
The method according to the claims 4 or 5, wherein the estimated real part I ^ 1 r and imaginary part I ^ 2 r of the reverse component of the measured current signals I ^ αβ 1 are estimated based on the following equation: d dt I ^ αβ f I ^ 1 r I ^ 2 r = K p cos θ ^ sin θ ^ cos θ ^ − sin θ ^ sin θ ^ cos θ ^ I α I β − 1 cos 2 θ ^ sin 2 θ ^ cos 2 θ ^ 1 0 sin 2 θ ^ 0 1 I ^ αβ f I ^ 1 r I ^ 2 r wherein I ^ αβ f corresponds to an estimation of the forward component of the measured current signals in the Clarke representation, wherein I ^ 1 r corresponds to an estimation of the real part of the reverse component of the measured current signals, wherein I ^ 2 r corresponds to an estimation of the imaginary part of the reverse component of the measured current signals, wherein K p = 2 π f 0 with f 0 being the selected gain frequency, wherein θ̂ corresponds to an estimation of the current vector angle in αβ frame, wherein I α corresponds to the first component of the current in the Clarke representation determined based on the measured current signals in the windings, and wherein I β corresponds to the second component of the current in the Clarke representation determined based on the measured current signals in the windings.
The method according to any one of the preceding claims, wherein the current parameter comprises a current offset of each winding of the electric motor.
The method according to any one of the preceding claims, wherein the current parameter comprises a current offset of a specific winding of the electric motor and wherein determining a current offset of the specific winding comprises determining an average value of the current signal of the specific winding.
The method according to any one of the preceding claims, wherein the current parameter comprises a current offset of a specific winding of the electric motor and wherein determining a current offset of the specific winding comprises applying a digital low-pass filter on the measured current signal of the specific winding of the electric motor.
The method according to any one of the preceding claims, wherein determining (130) an amended control law comprises determining a proportional factor and an integral factor of a proportional-integer, PI, regulator for canceling the determined current parameter.
The method according to any one of the preceding claims, wherein a transformer is disposed between the variable speed drive and the electric motor such that the variable speed drive drives the electric motor through the transformer.
A computer-readable storage medium comprising instructions which, when executed by at least one controller, cause the at least one controller to carry out a method of any one of the claims 1 to 11.
A computer program product comprising instructions which, when the program is executed by at least one controller, cause the computer to carry out a method of any one of the claims 1 to 11.
A processing system comprising a variable speed drive (3), the variable speed drive comprising electric measuring means adapted to measure current signals and a pulse width modulation controller (PWM); wherein the processing system is adapted to implement a method of any one of the claims 1 to 11.

Description

FIELD OF THE INVENTION This invention relates to a method for controlling a variable speed drive driving a three-phase electric motor. BACKGROUND Numerous electric motors connected to an electric network are driven by a variable speed drive. A variable speed drive allows modifying a frequency, amplitude and/or phase of an electric signal provided by an electric network in order to control an electric motor. The variable speed drive usually comprises a rectifier stage, a DC-link stage and an inverter stage. The inverter stage may comprise six switches controlled using a pulse width modulation, PWM, function. The PWM function is determined based on a control law enabling to drive the electric motor at a desired operating point while seeking to balance the voltages applied on the different windings of the electric motor for reducing component aging and thermal problems of the electric motor. The present description aims at improving operation of electric motor, in particular with regards to aging of components. Document CN208656661 discloses an inverter circuit, wherein the inverter circuit includes three pairs of bridge arms and three output phase lines, and a protection circuit connected to each output phase line. The protection circuit includes a current sampling circuit, a control switch and a controller. The sampling circuit samples the current of the output phase line, the control switch is connected in parallel with the inverter lower arm power switch, the controller is connected to the current sampling circuit, the lower arm power switch and the control switch, and the controller outputs the current according to the phase line. The value and the PWM signal of the lower arm power switch and the lower arm power switch collector voltage control the on and off of the control switch. The proposed solution in this document results in increased system reliability, and increased IGBT's lifetime. SUMMARY An object of the present disclosure is to propose a method for controlling a variable speed drive driving a three-phase electric motor, the variable speed drive comprising electric measuring means adapted to measure current signals, a pulse width modulation, PWM, controller, an inverter and a DC-link adapted to supply the inverter with a significantly continuous voltage, wherein: the inverter comprises three legs connected to the three windings of the electric motor, each leg being connected on one side to a positive bus of the significantly continuous voltage and on another side to a negative bus of the significantly continuous voltage, each leg comprising a top switch and a bottom switch; wherebyeach switch comprises two components, a first component being an Insulated Gate Bipolar Transistor, IGBT, controlled by a PWM signal emitted by the PWM controller based on a control law of the electric motor, and a second component being a freewheeling diode connected in parallel with the IGBT;the method comprising: measuring current signals in the windings of the electric motor;determining a current parameter associated to the electric motor based on the current signals, wherein the current parameter comprises a current offset of at least one winding of the electric motor in relation to a zero-current value; orwherein the current parameter comprises a current misbalance between windings of the electric motor;determining an amended control law of the electric motor for decreasing the determined current parameter; andapplying PWM signals on the IGBTs of the inverter based on the amended control law. The PWM signals applied based on an amended control law therefore allows reducing a current offset in relation to a zero-current of at least one winding of the electric motor or reducing a current misbalance between the windings of the electric motor. Reducing a current offset in relation to a zero-current value in a specific winding of an electric motor allows reducing inductance saturation probability of the specific winding of the electric motor, therefore reducing the torque ripple of the electric motor. Reducing a current misbalance between the windings of the electric motor allows mitigating the electric motor overheating and therefore reducing the electrical and/or mechanical damages induced by an undesired overheating. Optionally, determining a current parameter comprises determining a current offset of at least one winding of the electric motor and a current misbalance between windings of the electric motor. Optionally, determining the current misbalance between windings of the electric motor comprises: determining the current offsets of the current signals in the windings of the electric motor;removing the current offsets from the current signals for obtaining centered current signals; anddetermining a reverse component of the measured current signals based on a current observer and on the centered current signals. Optionally, the centered current signals are defined in the current observer as: wherein I^αβ1 corr