JP2016100997A - Control device of electric motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a problem in which, when a large reluctance torque is generated, an unstable state is brought about caused by a slight variation of a torque or speed.SOLUTION: The electric motor is treated by being converted to an equivalent circuit having a d-axis armature on a d-axis in a direction of a field magnet flux and a q-axis armature on a q-axis perpendicular to the d-axis. The energization control means sets a limit value lower than a maximum value of a q-axis current, which is a current flowing through the q-axis armature and controls so that the q-axis current does not exceed the limit value.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a drive device for an embedded magnet type synchronous motor, and relates to a control technique for expanding an operation range by magnetic flux weakening control.

  FIG. 1 shows a vector diagram represented on an orthogonal coordinate system in which the magnetic pole direction of the rotor is d-axis and the direction orthogonal thereto is q-axis in the embedded magnet type synchronous motor. Here, ψa is a magnetic flux generated by a permanent magnet. Further, the armature current vector i is decomposed into dq-axis components, the d-axis component is set as the excitation current id, and the q-axis component is set as the torque component current iq.

  When id and iq flow during operation, magnetic fluxes Ldid and Lqiq are generated by the dq axis components Ld and Lq of the winding inductance, and a magnetic flux ψ0 obtained by combining these becomes the magnetic flux inside the motor. When the rotor rotates at an angular velocity ω, induced voltages ωψa, ωLdid, and ωLqiq are generated for each magnetic flux. A voltage vo obtained by synthesizing these becomes an induced voltage generated in the motor, and a voltage v Ra applied to the winding resistance is added to the voltage v applied to the motor.

  The torque T generated by the embedded magnet type synchronous motor includes a magnet torque ψaiq based on an electromagnetic force and a reluctance torque (Ld−Lq) idq generated when the magnetic field attracts the iron core. Here, p is the number of pole pairs.

  It can be seen that magnet torque is generated by flowing iq, and reluctance torque is generated by flowing id in the negative direction.

  As the rotational speed ω increases, the electromotive force vo increases. However, since the output voltage v of the inverter that drives the motor is limited, it is necessary to limit the induced voltage to a value vom that is smaller than the inverter output limit. Therefore, as shown in FIG. 2, the flux weakening control is used in which the exciting current id is passed in the negative direction and the induced voltage vo is reduced to the limit value vom. Here, since the magnitude of the induced voltage vo is expressed by Equation 2, when id is solved with vo = vom, the current id for the flux weakening control is obtained as Equation 3 and Equation 4 (for example, Patent Documents). 1).

JP 2008-43030 A (paragraphs 0098 to 0100)

  FIG. 3 shows a current vector locus (hereinafter referred to as a voltage limit ellipse) when the induced voltage is limited to vom by the magnetic flux weakening control at each rotational speed. As the load increases, id is increased in the negative direction so as to generate a larger reluctance torque. Therefore, the current vector moves to the left in the figure on the voltage limit ellipse. The center coordinate of the voltage limiting ellipse is (−ψa / Ld, 0), and the excitation current id is calculated using Equation 3 in the right region in the figure, with id = −ψa / Ld as the boundary, and in the left region. The excitation current id is calculated using Equation 4.

  However, it may operate near the boundary depending on the operating conditions. At this time, the calculation of Formula 3 and the calculation of Formula 4 are frequently switched due to slight fluctuations in torque and speed, which may result in an unstable state. There is a problem that.

  In view of the above problems, an object of the present invention is to provide a control device for an electric motor that does not cause the above problems.

  In order to solve the above-mentioned problems, an electric motor control apparatus according to the present invention controls the operation of an embedded magnet type synchronous motor in which a rotor having a plurality of fields by permanent magnets is arranged concentrically around a rotating shaft. An electric motor control device that converts a DC voltage supplied from a DC power source into a multiphase AC voltage and applies it to an armature of the electric motor, and an electric motor via the inverter in accordance with a predetermined torque command Including an energization control means for controlling a phase current that is a vector sum of currents flowing through armatures of respective phases of the motor, wherein the electric motor is connected to a d-axis electric machine on a d-axis that is a magnetic flux direction of a field. Treated by converting into an equivalent circuit having a q-axis armature on the q-axis orthogonal to the d-axis and the energization control means is lower than the maximum value of the q-axis current that is the current flowing through the q-axis armature Set the limit value, Axis current and the controller controls so as not to exceed this limit.

  Further, it is characterized in that a decrease in torque that is reduced by limiting the q-axis current to a limit value is compensated by an increase in reluctance torque by increasing a d-axis current that is a current flowing in the d-axis armature. To do.

  Further, when the q-axis current is limited to a limit value, a wind-up phenomenon in which the rotation speed becomes unstable by correcting the rotational speed deviation of the electric motor according to the reduction amount of the q-axis current due to the limitation. It is characterized by suppressing.

  As the load increases, the operating point shifts on the voltage limit ellipse and reaches the boundary point between the region where Formula 3 is applied and the region where Formula 4 is applied, and the torque current iq is vom / (ωLq). Is the largest. If a current command iq_ref corresponding to a torque larger than this maximum value is given, the square roots of Equations 3 and 4 are negative, and the excitation current id cannot be calculated.

  Therefore, iq_ref is limited to a value (iq_lim) smaller than the maximum value vom / (ωLq). When a current command iq_ref greater than iq_lim is given, iq is limited as shown in Equation 5, and thus the torque is insufficient by ΔT in Equation 6.

  The insufficient torque ΔT is compensated with reluctance torque as shown in Equation 7. The exciting current Δid necessary for generating the reluctance torque is expressed by Equation 8, and by adding this to the equation id, the magnetic flux control can be achieved even under heavy load.

  FIG. 4 shows a voltage limit ellipse according to Equation 3 and Equation 4, and a current vector locus when the flux-weakening control is performed according to Equation 9. Until the q-axis current is limited, the operating point moves on the voltage limit ellipse of Equation 3. When the q-axis current is limited to iq_lim, the operating point shifts inside the voltage limit ellipse. Here, in order to compensate for the insufficient torque, the d-axis current is increased in the negative direction by Δid, so that id can be calculated using Equation 3 even in the region on the left side of the boundary of −Ψa / Ld. Thereby, the unstable phenomenon which generate | occur | produces by switching the calculation by Numerical formula 3 and the calculation by Numerical formula 4 can be prevented.

  In a system having a speed control system, the q-axis current command iq_ref is generally generated by a speed PI controller. When the output of the PI controller is limited, the speed and current may behave in an oscillating manner due to the windup phenomenon. Therefore, when iq_ref is limited, the limited amount Δiq is fed back to the input of the PI controller, and the vibration is suppressed by correcting the speed deviation Δω (= ωref−ω) as shown in Equation 10. Here, Kp is a proportional gain of the speed PI controller. FIG. 5 shows the configuration of the PI controller considering the limitation of iq_ref.

  As is apparent from the above description, according to the present invention, the torque current iq is limited in the high-speed rotation region where the flux-weakening control of the embedded magnet type synchronous motor is required, and the insufficient torque is compensated with the reluctance torque. Determine the excitation current id. Accordingly, the excitation current command can be determined continuously using one equation without switching between the two equations that calculate the excitation current, Equation 3 and Equation 4, resulting from the switching of the equation. Phenomena such as vibration and oscillation can be suppressed.

Vector diagram of voltage, current and magnetic flux when operating an embedded magnet type synchronous motor Vector diagram of voltage, current, and magnetic flux when flux-weakening control is performed with an embedded magnet type synchronous motor Diagram showing the relationship between the current vector locus (voltage limit ellipse) and the excitation current calculation formula during flux-weakening control The figure showing the electric current vector locus (voltage limit ellipse) at the time of the flux weakening control by this invention Block diagram of a technique to suppress the effects of torque current limitation Block diagram showing an example of a drive system for an embedded magnet type synchronous motor Block diagram of extended induced voltage observer used for speed estimation

  Hereinafter, an embodiment in which the present invention is applied to a sensorless drive system of an embedded magnet type synchronous motor will be described with reference to the drawings.

  FIG. 6 shows a sensorless drive system of an embedded magnet type synchronous motor. This system includes a speed control unit 1, an excitation current command calculation unit 2, a current control unit 3, a non-interference control unit 4, a coordinate conversion unit 5, a speed estimation unit 6, a PWM modulation unit 7, and a three-phase inverter 8. The

  The detected motor currents iu and iw are coordinate-transformed into a γ-δ rotating coordinate system based on the estimated magnetic pole position (electrical angle) θ to obtain iγ and iδ. The motor currents iγ and iδ and the motor voltage command values vγ1_ref and vδ1_ref are input to the speed estimation unit 6.

  The speed estimation unit 6 estimates the expansion induced voltages eγ and eδ from the motor voltage commands vγ1_ref and vδ1_ref and the motor currents iγ and iδ. FIG. 7 shows the configuration of an observer for estimating the extended induced voltage. From the obtained extended induced voltage, an estimation error θe of the magnetic pole position is obtained as in Expression 11.

  PI calculation is performed so that the estimated error θe calculated by Expression 11 becomes 0, and the output is set to an estimated speed (mechanical angular speed) ωm. This ωm is integrated and the estimated magnetic pole position θm is obtained. ωm is used for speed control and non-interference control. Further, θm is converted into an electrical angle θ by the number of pole pairs P and used for coordinate conversion 5.

  The speed control unit 1 performs PI control so that the speed command value ω_ref and the estimated speed ωm coincide. The output of this PI controller is a torque current command iq. When iq_ref becomes larger than the limit value iq_lim in the area where the flux-weakening control is necessary, iq_ref is limited by iq_lim. At this time, in order to prevent a wind-up phenomenon, as shown in FIG. 5, a limited amount Δiq is obtained, the speed deviation Δω is corrected, and the integral calculation is recalculated.

  The excitation current command calculation unit 2 determines the excitation current command id_ref. In an area where the rotational speed is low and the flux-weakening control is not necessary, id_ref is determined according to the “maximum torque / current control” curve shown in FIG. 3 so that torque is efficiently generated with as little current as possible. An arithmetic expression at this time is shown in Expression 12.

  When the rotational speed increases and the induced voltage vo becomes larger than the limit value vom, the flux-weakening control is required. Therefore, id_ref is determined by Equation 3. Here, when iq_ref is limited by iq_lim, an excitation current Δid for compensating for the insufficient torque with the reluctance torque is obtained from Equation 8, and id_ref is calculated by Equation 9.

  The current control unit performs PI control so that the current commands id_ref and iq_ref and the motor currents iγ and iδ match, and outputs the PI controller as voltage commands vγ_ref and vδ_ref. Non-interference control is performed on the voltage commands vγ_ref and vδ_ref to determine the voltage commands vγ1_ref and vδ1_ref. Here, vγ1_ref and vδ1_ref are obtained by Expression 13 and Expression 14.

  The PWM modulation unit determines an inverter switching command by space vector modulation from the voltage commands vγ1_ref and vδ1_ref, operates the inverter, and drives the embedded magnet type synchronous motor.

  In addition, this invention is not limited to an above-described form, You may add a various change in the range which does not deviate from the summary of this invention.

DESCRIPTION OF SYMBOLS 1 Speed control part 2 Excitation current command calculating part 3 Current control part 4 Non-interference control part 5 Coordinate conversion part 6 Speed estimation part 7 PWM modulation part 8 Three-phase inverter

Claims (3)

A control device for an electric motor for controlling the operation of an embedded magnet type synchronous motor in which a rotor having a plurality of magnetic fields by permanent magnets is arranged concentrically around a rotating shaft, and a DC voltage supplied from a DC power source Is converted to a multiphase AC voltage and applied to the armature of the electric motor, and a phase current that is a vector sum of currents flowing through the armature of each phase of the electric motor via the inverter according to a predetermined torque command And a power supply control means for controlling
The electric motor is handled by converting it into an equivalent circuit having a d-axis armature on the d-axis that is the magnetic flux direction of the field and a q-axis armature on the q-axis that is orthogonal to the d-axis. The means sets a limit value lower than the maximum value of the q-axis current, which is a current flowing through the q-axis armature, and controls so that the q-axis current does not exceed the limit value. .   The decrease in torque that is reduced by limiting the q-axis current to a limit value is supplemented by an increase in reluctance torque by increasing the d-axis current that is a current flowing in the d-axis armature. Item 4. A control device for an electric motor according to Item 1.   When the q-axis current is limited to a limit value, the rotational speed of the electric motor is corrected in accordance with the amount of decrease in the q-axis current due to the limitation, thereby suppressing the occurrence of a windup phenomenon in which the rotational speed becomes unstable. The control apparatus for an electric motor according to claim 1, wherein the control apparatus is an electric motor.

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