Method of controlling synchronous electric motor with permanent magnets

Abstract

An invention relates to synchronous electric motors, in particular, to a method of controlling a synchronous electric motor with permanent magnets, utilized as a linear drive for an electric submersible pump unit. A technical result achieved from a method embodiment consists in increasing an accuracy of a torque control of the electric motor and improving an energy efficiency of the electric motor, as well as in achieving an increase in an operation speed of control systems by minimizing settings and eliminating complex calculations of motor parameters. An essence of the claimed method consists in an implementation of an algorithm of the control system of the synchronous electric motor with permanent magnets, utilized, in particular, as a linear drive for an electric submersible pump unit.

Claims

1. A method for controlling a synchronous electric motor with permanent magnets, comprising: connecting via a cable line the electric motor with a surface control unit, said surface control unit including a control device, defining values characterizing applied voltage and phase via the control device; measuring phase currents of a stator winding of the electric motor via current sensors and converting obtained current values into a d-q fixed reference system, wherein said obtained current values are measured for every instance of a moving part of the electric motor, the surface control unit forming signals of Ud, Uq voltage from the obtained current values, the surface control unit forming signals for setting U.sub.A, U.sub.B, and U.sub.C phase voltages by converting Ud, Uq voltage signals into U, U, wherein the control device performs said converting, supplying the signals for setting U.sub.A, U.sub.B, and U.sub.C phase voltages a pulse generating unit of the surface control unit, detecting a reactive current value, Iq, and a voltage value, Uq, via the control device, setting a standard reactive current value and a standard voltage value via the control device, defining alterations of the reactive current value relative to the standard reactive current value via the surface control unit, generating correction signals for voltage according to the defined alterations via the surface control unit, and the surface control unit transmitting the correction signals for voltage to the control device, said control device being in communication with the electric motor, thereby enabling a direct control of the electric motor's torque.

2. The method of claim 1, wherein the control device generates the correction signals taking into account: a return voltage signal from a proportional-and-integral controller of the Iq current, and a specification of the reactive voltage value, said specification being formed on a basis of parameters of the controlled synchronous electric motor.

3. The method of claim 2, wherein the control device sets the alterations to reactive current signal to zero when generating a specification for the proportional-and-integral controller provided that the voltage signal from the proportional-and-integral controller is generated based on: a value of an angle between an output phase voltage and a phase current of the stator winding, and a nominal voltage value of the electric motor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The essence of the claimed invention is explained, but is not limited to the following drawings:

(2) FIG. 1 shows a diagram of a linear electric submersible pump unit;

(3) FIG. 2 shows a control-flow chart of controlling the synchronous electric motor with permanent magnets.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(4) The described method can be implemented in control systems of the synchronous electric motors of various purposes and designs.

(5) An example of a control system of synchronous electric motors with permanent magnets of linear electric submersible pump unit 1 is shown schematically on FIG. 1 as one of the embodiments of the claimed methods and contains submersible linear electric motor 2 (FIG. 1, 2) with permanent magnets, connected with cable line 3 to surface control unit 4 which includes control device 4.1.

(6) The control system of the electric motor is implemented by software-based methods of controlling power sources 5 of U.sub.A, U.sub.B, U.sub.C voltage (FIG. 2), such as IGBT transistors. Said control system, connected to control device 4.1, comprises I.sub.A, I.sub.B, I.sub.cphase current conversion block 6; I, Ito Id, Iq current conversion block 7; PI regulators of Iq current 8 and Id current 9 generating the Uq, Ud voltages; block 10 setting .sub.zad speed; block 11 generating angle signals and main Uq.sub.OCH, Ud.sub.OCH voltage signals; block 12 generating Uq..sub.KOP , Ud.sub.KOP correction signals; block 13 of conversion Ud, Uq to U, Uvoltages; current sensors 14.

(7) The claimed method involves generating setting for the voltage .sub.zad circular frequency within block 10 at the moment of a start of the linear electric motor. The main Uq, Ud voltage signals are generated and the angle of a permissible deviation of a magnetic field of the stator from a magnetic field of a movable part is determined within block 11 on the basis of the set value of the .sub.zad circular frequency, while the angle is limited within a range of 0 to 2.

(8) In the next stage, the Ud voltage value are determined by means of the U.sub.HOM nominal voltage values and PI controller 9 of the Id current, taking into account the Uq.sub.oc return signal from PI controller 8 of the set Uq.sub.zad value, generated on the basis of the controlled electric motor parameters, containing values of the angle between the output phase voltage and the phase current.

(9) Next, the main signals of the Uq.sub.OCH, Ud.sub.OCH voltages and the signal with the angle value, corrected in block 12 considering with Ud, Uq signals formed by blocks 8, 9, are supplied from block 11 to Ud, Uq to U, U voltage conversion block 13. The U, U voltage signals resulting from the conversion are applied to U, U to U.sub.A, U.sub.B, U.sub.C voltage conversion block. The received U.sub.A, U.sub.B, U.sub.C phase voltage signals constitute the setting for controllable voltage sources 5, in which the phase voltage signals are generated by means of pulse width modulation (PWM), while the mentioned signals supply the linear electric motor of the pump unit, thereby provide a progressive motion to its movable part.

(10) Next, the I.sub.A, I.sub.B, I.sub.C phase currents begin to flow through stator windings with the progressive motion of the movable part of the linear motor, while the mentioned phase currents are recorded in sensor block 14 at every instant.

(11) The received signals from the I.sub.A, I.sub.B, I.sub.C phase current fixation sensors are supplied to the phase current conversion block 6, where they are converted into a stationary - coordinate system. The converted signals are fed to block 7 of transforming the coordinates - to d-q and generating the Id, Iq signals, taking into account the angle.

(12) The Iq signal is used as a feedback in the PI regulator 8 of Iq current, where it is subtracted from the generated Iq.sub.zad (standard reactive current) signal, which is set to zero. The said PI controller is connected operatively with the control device 4.1, due to which the Iq.sub.zad (standard reactive current), Uq.sub.zad (standard voltage value) are set, as well as the .sub.zad circular frequency value.

(13) The Uq.sub.KOP, Ud.sub.KOP signals, received at an output of blocks 8, 9, are fed to block 12 in order to perform correction of the Uq.sub.OCH, Ud.sub.OCH main voltage. The signals corrected in block 12 serve as the setting for the Ud, Uq to U, U voltage generation and transformation blocks.

(14) Consequently, an adjustment of the Iq reactive current is performed during the operation of the linear submersible electric motor with permanent magnets. In addition, an adjustment of the Id active current is performed, while obtaining the Ud, Uq voltage signals at the output of the PI regulators 8, 9, which provides the necessary correction of the Ud.sub.OCH, Uq.sub.OCH main voltage signals, generated in block 11, thereby enabling the direct control of the electric motor torque.

(15) Herewith, the position of the stator magnetic field is determined relatively to the magnetic field of the moving part of the electric motor at every instant by measuring the phase current signals with their subsequent conversion in blocks 6, 7, 8, 9, while determining the changes in the Iq reactive current relatively to the Iq.sub.zad setting, according to which the Uq.sub.KOP, Ud.sub.KOP voltage correction signals are formed, which lead to the values necessary to form the set value of the Iq.sub.zad reactive current.

(16) The described control method allows to increase and decrease rapidly the voltages and the currents of the SM under load surges and reliefs.

(17) The implementation of the claimed invention contributes to the achievement of the claimed technical result, providing the increase in the energy efficiency of the electric motor, as well as improving the operational speed of the control system by minimizing the settings and eliminating the complex calculations of the electric motor parameters. This method can be used to control various types of electric motors, taking into account the change in the setting signals of the PI regulators.