US-12620923-B2 - Variable speed drive control

US12620923B2US 12620923 B2US12620923 B2US 12620923B2US-12620923-B2

Abstract

Examples include a method for controlling a variable speed drive driving a three-phase electric motor. The method includes measuring current signals in the windings of the electric motor, and determining a current parameter associated to the electric motor based on the current signals. The current parameter includes either a current offset of at least one winding of the electric motor in relation to a zero-current value, or a current misbalance between windings of the electric motor. The method further includes determining an amended control law of the electric motor for decreasing the determined current parameter, and applying pulse width modulation signals on insulated gate bipolar transistors of the inverter based on the amended control law.

Inventors

Emmanuel Frappé
Thomas Devos
Al Kassem Jebai
François Malrait

Assignees

SCHNEIDER TOSHIBA INVERTER EUROPE SAS

Dates

Publication Date: 20260505
Application Date: 20231211
Priority Date: 20221216

Claims (17)

1 . A method for controlling a variable speed drive driving a three-phase electric motor, the variable speed drive comprising 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 three windings of the electric motor, each of the three legs being connected on a first side to a positive bus of the significantly continuous voltage and on a second side to a negative bus of the significantly continuous voltage, each of the three legs comprising a top switch and a bottom switch; wherein each of the top switch and the bottom switch comprises two components, a first component being an Insulated Gate Bipolar Transistor (IGBT) controlled by a PWM signal output 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; and the method comprising: measuring current signals in the three windings of the electric motor; determining a current parameter associated with the electric motor based on the current signals, wherein the current parameter comprises a current offset of at least one of the three windings of the electric motor in relation to a zero-current value; or wherein the current parameter comprises a current misbalance between at least two windings of the electric motor; determining an amended control law of the electric motor for decreasing the current parameter, wherein the determining comprises determining a proportional factor and an integral factor of a proportional-integer (PI) regulator for canceling the current parameter; and outputting PWM signals to at least one of the IGBTs based on the amended control law.
2 . The method according to claim 1 , wherein determining the current parameter comprises determining the current offset and the current misbalance.
3 . The method according to claim 2 , wherein determining the current misbalance comprises: determining 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.
4 . The method according to claim 3 , 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 I ⁢ 1 a ⁢ b ⁢ c in the Clarke representation, wherein {circumflex over (θ)} corresponds to an estimation of the current vector angle in αβ frame, wherein Î ƒ e j{circumflex over (θ)} 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 ˆ 1 r corresponds to an estimation of the real part of the reverse component of the measured current signals, and wherein I ˆ 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 ˆ 1 r and imaginary part I ˆ 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 ˆ 1 r and imaginary part I ˆ 2 r of the reverse component of the measured current signals.
5 . The method according to claim 4 , wherein the current vector angle {circumflex over (θ)} in αβ frame is estimated based on a Phase-Locked Loop (PLL) or is determined based on a magnetic flux vector angle of the electric motor determined by the variable speed drive.
6 . The method according to claim 4 , 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 ˆ a ⁢ β f I ˆ I r I ˆ 2 r ) = K p ⁢ ( ( cos ⁢ θ ˆ sin ⁢ θ ˆ cos ⁢ θ ˆ - s ⁢ in ⁢ θ ˆ sin ⁢ θ ˆ cos ⁢ θ ˆ ) ⁢ ( I α I β ) - ( 1 cos ⁢ ( 2 ⁢ θ ˆ ) sin ⁢ ( 2 ⁢ θ ˆ ) cos ⁢ ( 2 ⁢ θ ˆ ) 1 0 sin ⁢ ( 2 ⁢ θ ˆ ) 0 1 ) ⁢ ( I ˆ a ⁢ β f I ˆ 1 r I ˆ 2 r ) ) wherein I ^ αβ 1 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 ƒ 0 with ƒ 0 being the selected gain frequency, wherein {circumflex over (θ)} corresponds to an estimation of the current vector angle in αβ frame, wherein Iα corresponds to a first component of the current in the Clarke representation determined based on the measured current signals in the windings, and wherein Iβ corresponds to a second component of the current in the Clarke representation determined based on the measured current signals in the windings.
7 . The method according to claim 1 , wherein the current offset of the at least one of the three windings comprises a respective current offset for each of the three windings of the electric motor.
8 . The method according to claim 1 , wherein the current offset of the at least one of three windings comprises a current offset of a specific winding of the electric motor, and the method further comprising determining the current offset of the specific winding by determining an average value of the current signal of the specific winding.
9 . The method according to claim 1 , wherein the current offset comprises a current offset of a specific winding of the electric motor, and the method further comprising determining the current offset of the specific winding by applying a digital low-pass filter on the measured current signal of the specific winding of the electric motor.
10 . The method according to claim 1 , 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.
11 . A non-transitory computer-readable storage medium comprising instructions which, when executed by at least one hardware processor, cause the at least one hardware processor to perform a method for controlling a variable speed drive driving a three-phase electric motor, the variable speed drive comprising 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 three windings of the electric motor, each of the three legs being connected on a first side to a positive bus of the significantly continuous voltage and on a second side to a negative bus of the significantly continuous voltage, each of the three legs comprising a top switch and a bottom switch; wherein each of the top switch and the bottom switch comprises two components, a first component being an Insulated Gate Bipolar Transistor (IGBT) controlled by a PWM signal output 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; and the method comprising: measuring current signals in the three windings of the electric motor; determining a current parameter associated with the electric motor based on the current signals, wherein the current parameter comprises a current offset of at least one of the three windings of the electric motor in relation to a zero-current value; or wherein the current parameter comprises a current misbalance between at least two windings of the electric motor; determining an amended control law of the electric motor for decreasing the current parameter, wherein the determining comprises determining a proportional factor and an integral factor of a proportional-integer (PI) regulator for canceling the current parameter; and outputting PWM signals to at least one of the IGBTs based on the amended control law.
12 . The non-transitory computer-readable storage medium according to claim 11 , the method further comprising determining the current misbalance by: determining 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.
13 . The non-transitory computer-readable storage medium according to claim 11 , wherein the current offset of the at least one of three windings comprises a current offset of a specific winding of the electric motor, and the method further comprising determining the current offset of the specific winding by determining an average value of the current signal of the specific winding.
14 . The non-transitory computer-readable storage medium according to claim 11 , wherein the current offset comprises a current offset of a specific winding of the electric motor, and the method further comprising determining the current offset of the specific winding by applying a digital low-pass filter on the measured current signal of the specific winding of the electric motor.
15 . A system comprising: a variable speed drive configured to drive a three-phase electric motor having three windings; an inverter comprising three legs connected to the three windings of the electric motor, each of the three legs being connected on a first side to a positive bus of a significantly continuous voltage and on a second side to a negative bus of the significantly continuous voltage, each of the three legs comprising a top switch and a bottom switch, each of the top switch and the bottom switch comprises two components, a first component being an Insulated Gate Bipolar Transistor (IGBT) controlled by a pulse width modulation (PWM) signal output by a 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; a DC-link adapted to supply the inverter with the significantly continuous voltage; and the PWM controller configured to execute a method comprising: measuring current signals in the three windings of the electric motor; determining a current parameter associated with the electric motor based on the current signals, wherein the current parameter comprises a current offset of at least one of the three windings of the electric motor in relation to a zero-current value; or wherein the current parameter comprises a current misbalance between at least two windings of the electric motor; determining an amended control law of the electric motor for decreasing the current parameter, wherein the determining comprises determining a proportional factor and an integral factor of a proportional-integer (PI) regulator for canceling the current parameter; and outputting PWM signals to at least one of the IGBTs based on the amended control law.
16 . The system according to claim 15 , the method further comprising determining the current misbalance by: determining 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.
17 . The system according to claim 15 , further comprising a transformer disposed between the variable speed drive and the electric motor such that the variable speed drive is configured to drive the electric motor through the transformer.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This patent claims priority under 35 U.S.C. § 119 to European Patent Application No. 22306903.0, filed on Dec. 16, 2022, and titled “VARIABLE SPEED DRIVE CONTROL.” 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. 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 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; or wherein 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: I^αβ1=I^f⁢ej⁢θ^+(I^1r+j⁢I^2r)⁢e-j⁢θwherein I^αβ1 corresponds to an estimation of the centered current signals Iabc1 in the Clarke representation,wherein {circumflex over (θ)} corresponds to an estimation of the current vector angle in αβ frame,wherein Îƒ ej{circumflex over (θ)} corresponds to an estimation of the forward component of the measured current signals,wherein (I^1r+j⁢I^2r)⁢e-j⁢θ^ corresponds to an estimation of the reverse component of the measured current signals,wherein I^1r corresponds to an estimation of the real part of the reverse component of the measured current signals, andwherein I^2r 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