Axis error estimating method for synchronous motor and control device for synchronous motor

Abstract

To provide a method for estimating an axis error between a d-q axis and a γ-δ axis in a synchronous motor.SOLUTION: In a control method for driving a synchronous motor by sensorless vector control, a magnetic axis of a permanent magnet of the synchronous motor is defined as a d-axis, a direction orthogonal to the d-axis is defined as a q-axis, a designated magnetic axis of the synchronous motor is defined as a γ-axis, and a direction orthogonal to the γ-axis is defined as a δ-axis, and when vγ iγ+vδ iδ=P / 2 ωR ΦM iδ+R (iδ^2+iγ^2) is established, it is estimated that the d-q axis and the γ-δ axis coincide with each other without an error, and when the above expression is not established, an amount of the error is estimated from a difference between the left side and the right side. vγ represents a γ-axis voltage [V], iγ represents a γ-axis current [A], vδ represents a δ-axis voltage [V], iδ represents a δ-axis current [A], P represents a motor pole number, R represents a motor one-phase resistance value [Ω], ωR represents a motor electrical angular speed [rad / s], and ΦM represents a magnet flux [wb].SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for estimating an error in the magnetic axis of a synchronous motor to enable stable current control, and to a control device for a synchronous motor equipped with the axis error estimation method. [Background technology]

[0002] Vector control is known as one of the control methods for synchronous motors. Vector control considers the current component that generates torque and the current component that generates magnetic flux in the rotor separately, and controls each current component independently.

[0003] First, a conventional synchronous motor control system and the d-axis voltage and q-axis voltage related to the present invention will be described. In this system, the three-phase current (i U ,i V ,i W ) is expressed as the d-axis current (i d ),q-axis current(i q )

[0004] This d-axis current (i d ),q-axis current(i q ) are the d-axis current command values ​​(i dref ),q-axis current command value (i qref ) is obtained by using current feedback control to obtain the d-axis voltage command value (v dref ), d-axis voltage command value (v qref ) is calculated. This voltage is used as the motor's three-phase voltage command value (v Uref ,v Vref ,v Wref ) and output to the synchronous motor.

[0005] This will be explained using Figure 1. This figure is a vector diagram of the motor's three-phase voltages and d-axis and q-axis voltages, viewed in terms of electrical angles, in a conventional synchronous motor control system. The three-phase AC voltages (U-phase, V-phase, and W-phase) are axes fixed to the motor's stator and offset by 120°, while the d-axis and q-axis are axes that follow the rotor's position. The rotor is equipped with a permanent magnet, and the current that generates a magnetic field in the same direction as the magnetic field of this magnet is called the d-axis current, while the current that generates a magnetic field in the perpendicular direction is called the q-axis current. The voltage in the direction that this d-axis current flows is called the d-axis voltage, and the voltage in the direction that the q-axis current flows is called the q-axis voltage.

[0006] However, in the conventional motor control system, the axis to which the calculated shaft voltage command is output is calculated using a detected or estimated position (defined as the γ-δ axis), and an error may occur between the γ-δ axis and the dq axis of the actual synchronous motor. If this error becomes large, it may cause abnormalities in the motor control.

[0007] In response to this, for example, in a sensorless inverter control device described in Japanese Patent Laid-Open No. 2009-100600 (Patent Document 1), a method is known in which an axial error calculator calculates a phase difference Δθ by calculating an arctangent function using an induced voltage estimated value estimated by an induced voltage estimator. However, there has been a demand for estimating the axial error using fewer parameters. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-100600 Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a method for estimating the axis error between the dq axes and the γ-δ axes of a synchronous motor. [Means for solving the problem]

[0010] The present invention, which has been made to solve the above problems, provides an axis error estimation method for a synchronous motor, which is a control method for driving a synchronous motor having an inverter consisting of a plurality of switching elements by sensorless vector control, comprising: The magnetic axis of the permanent magnet of the synchronous motor is defined as the d-axis, the direction perpendicular to the d-axis is defined as the q-axis, the designated magnetic axis of the synchronous motor is defined as the γ-axis, and the direction perpendicular to the γ-axis is defined as the δ-axis, The current that generates the magnetic field in the d-axis direction is the d-axis current, the voltage in the direction that the d-axis current flows is the d-axis voltage, the current that generates the magnetic field in the q-axis direction is the q-axis current, and the voltage in the direction that the q-axis current flows is the q-axis voltage, If the following formula is true, it is estimated that the dq axis and the γ-δ axis coincide without error. If the equation does not hold, estimate the amount of error from the difference between the left and right sides. It is characterized by:

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[0011] A synchronous motor control device according to another aspect of the present invention includes an inverter including a plurality of switching elements, current conversion means for converting detected or estimated three-phase currents of the synchronous motor into d-axis currents and q-axis currents, current feedback control calculation means for calculating d-axis voltage command values ​​and q-axis voltage command values ​​from the d-axis currents and q-axis currents using current feedback control, and voltage command value conversion means for converting the d-axis voltage command values ​​and q-axis voltage command values ​​into three-phase voltage command values, and the synchronous motor control device drives the synchronous motor by sensorless vector control while controlling on / off of the switching elements based on the three-phase voltage command values, The synchronous motor includes an axis error estimation method, The method for estimating an axis error of a synchronous motor comprises: The magnetic axis of the permanent magnet of the synchronous motor is defined as the d-axis, the direction perpendicular to the d-axis is defined as the q-axis, the designated magnetic axis of the synchronous motor is defined as the γ-axis, and the direction perpendicular to the γ-axis is defined as the δ-axis, The current that generates the magnetic field in the d-axis direction is the d-axis current, the voltage in the direction that the d-axis current flows is the d-axis voltage, the current that generates the magnetic field in the q-axis direction is the q-axis current, and the voltage in the direction that the q-axis current flows is the q-axis voltage, If the following formula is true, it is estimated that the dq axis and the γ-δ axis coincide without error. If the equation does not hold, estimate the amount of error from the difference between the left and right sides. It is characterized by:

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[0012] In the present invention, when the resistance value R on the right side of the above formula is derived using the following formula, it is derived based on the three-phase current and three-phase voltage measured when the motor is actually rotating at a constant speed, making it possible to derive the resistance value including the inverter.

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[0013] According to the present invention, it is possible to estimate the axis error between the dq axes and the γ-δ axes with a relatively small number of parameters. [Brief explanation of the drawings]

[0014] [Figure 1] Vector diagram of the motor's three-phase voltage, d-axis voltage, and q-axis voltage in terms of electrical angle. [Figure 2] 1A and 1B are diagrams illustrating the relationship between the dot product of a current vector and a voltage vector. [Figure 3] 1 is a diagram showing the configuration of a control device for a synchronous motor that executes a method for estimating an axis error of a synchronous motor according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0016] First, an explanation will be given with reference to Figures 1 and 2. Figure 1 is a vector diagram of the three-phase voltages, d-axis voltage, and q-axis voltage of a motor in terms of electrical angles. The three-phase AC voltages (U-phase, V-phase, and W-phase) are axes fixed to the stator of a synchronous motor and are offset by 120°, while the d-axis and q-axis are axes that follow the position of the rotor. The magnetic axis of the synchronous motor is defined as the d-axis, the direction perpendicular to the d-axis is defined as the q-axis, the designated magnetic axis of the synchronous motor is defined as the γ-axis, and the direction perpendicular to the γ-axis is defined as the δ-axis. The current that generates a magnetic field oriented in the d-axis direction is defined as the d-axis current, the voltage in the direction that causes the d-axis current to flow is defined as the d-axis voltage, the current that generates a magnetic field oriented in the q-axis direction is defined as the q-axis current, and the voltage in the direction that causes the q-axis current to flow is defined as the q-axis voltage.

[0017] In the axis error estimation method for a synchronous motor of the present invention, as shown in FIG. 2, the inner product of a current vector and a voltage vector is the same regardless of the coordinate plane from which it is calculated, and this is utilized to estimate the error of the magnetic axis.

[0018] Since the dot product of the current vector and voltage vector in the dq plane and the γ-δ plane is equal, i d v d +i q v q =i γ v γ +i δ v δ Also, from the voltage equation in the following formula (1), the inner product i d v d +i q vq When this is executed, the following formula (2) is obtained.

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[0019] However, v d is the d-axis voltage [V], i d is the d-axis current [A], v q is the q-axis voltage [V], i q is the q-axis current [A], v γ is the γ-axis voltage [V], i γ is the γ-axis current [A], v δ is the δ-axis voltage [V], i δ is the δ-axis current [A], L is the inductance value of one motor phase [H], P is the number of motor poles, R is the resistance value of one motor phase [Ω], ω R is the motor electrical angular velocity [rad / s], Φ M indicates the magnetic flux [wb].

[0020] Then, the result of the following equation (3) can be derived from the inner product and the voltage equation.

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[0021] When the value of the dot product is equal to the value calculated from the voltage equation, in other words, when the following equation (4) is established, the following equation (5) is obtained, and it can be estimated that the dq axes and the γ-δ axes are aligned without error.

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[0022] On the other hand, when the formula (4) does not hold, the degree of error between the dq axes and the γ-δ axes can be estimated from the difference between both sides of the formula (4).

[0023] Now, let us consider the above formula (4). The term R(i δ 2 +i γ 2) can be ignored when the resistance value R is small, but must be derived when it is large. However, since the resistance value R includes the inverter resistance, it is difficult to measure with an ohmmeter.

[0024] Therefore, we will show a method to derive the resistance value R using the inner product. During rotation speed control, the γ-axis current i γ1 and δ-axis current i δ1 Under the same load conditions, the γ-axis current is assumed to be i γ2 When there is an error between the dq axis and the γ-δ axis, the δ axis current is i δ2 This becomes:

[0025] For each, take the dot product of the current vector and the voltage vector. The dot product is the active power, which is the sum of the power and copper loss. The power is equal, i δ1 2 +i γ1 2 ≠i δ2 2 +i γ2 2 Therefore, we obtain the following formulas (6) and (7).

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[0026] Then, by calculating the difference between the above formula (6) and formula (7), the following formula (8) is obtained, which can derive the resistance value R. This resistance value R is derived based on the three-phase current and three-phase voltage actually measured when the motor is rotating at a constant speed, so it is possible to derive the resistance value including the inverter.

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[0027] FIG. 3 is a functional block diagram showing a control system for the synchronous motor 2. In this system, a control device 1 that executes drive control of the synchronous motor 2 detects or estimates the three-phase current (i U ,i V ,i W) or by expressing it as an axis synchronized with the estimated motor position, the current conversion means 11 converts the d-axis current (i d ),q-axis current(i q )

[0028] The d-axis current (i d ), q-axis current (i q ) is the input d-axis current command value (i dref ), q-axis current command value (i qref ) by the current feedback control calculation means 12. dref ), q-axis voltage command value (V qref ) is calculated. The voltage command value conversion means 13 converts this voltage into a three-phase voltage command value (V Uref ,V Vref ,V Wref ) and outputs the three-phase voltage command value to the synchronous motor 2 by controlling the on / off of the inverter's switching elements.

[0029] And the three-phase current of the synchronous motor (i U ,i V ,i W ) is converted into a d-axis current (i d ),q-axis current(i q ), and before being input to the current feedback control calculation means 12, the axis error estimation means 20 estimates the axis errors of the dq axes and the γ-δ axes.

[0030] The details of the method for estimating the axis error of a synchronous motor executed by the axis error estimating means 20 are omitted since they are the same as the above-mentioned method for estimating the axis error of a synchronous motor. Note that the control device 1 can be, for example, a computer such as an ECU in the case of an automobile. [Explanation of symbols]

[0031] 1 control device, 2 synchronous motor, 11 current conversion means, 12 current feedback control calculation means, 13 voltage command value conversion means, 20 axis error estimation means

Claims

1. A control method for driving a synchronous motor having an inverter consisting of a plurality of switching elements by sensorless vector control, comprising: The magnetic axis of the permanent magnet of the synchronous motor is defined as the d-axis, the direction perpendicular to the d-axis is defined as the q-axis, the designated magnetic axis of the synchronous motor is defined as the γ-axis, and the direction perpendicular to the γ-axis is defined as the δ-axis, The current that generates the magnetic field in the d-axis direction is called the d-axis current, the voltage in the direction that the d-axis current flows is called the d-axis voltage, the current that generates the magnetic field in the q-axis direction is called the q-axis current, and the voltage in the direction that the q-axis current flows is called the q-axis voltage, If the following formula (1) is satisfied, it is estimated that the d-q axes and the γ-δ axes coincide without error. If the formula (1) does not hold, the amount of error is estimated from the difference between the left and right sides. A method for estimating an axis error of a synchronous motor, comprising: [Equation 1] However, v γ is the γ-axis voltage [V], i γ is the γ-axis current [A], v δ is the δ-axis voltage [V], i δ is the δ-axis current [A], P is the number of motor poles, R is the motor resistance value for one phase [Ω], ω Ｒ is the motor electrical angular velocity [rad / s], Φ Ｍ indicates the magnet magnetic flux [wb].

2. 2. The method for estimating an axis error of a synchronous motor according to claim 1, wherein the resistance value R on the right side of the formula (1) is derived using the following formula (2): [Equation 2]

3. a current feedback control calculation means for calculating a d-axis voltage command value and a q-axis voltage command value from the d-axis current and the q-axis current using current feedback control; and a voltage command value conversion means for converting the d-axis voltage command value and the q-axis voltage command value into three-phase voltage command values, wherein the synchronous motor control device drives the synchronous motor by sensorless vector control while controlling on / off of the switching elements based on the three-phase voltage command values, The synchronous motor includes an axis error estimation method, The method for estimating an axis error of a synchronous motor comprises: The magnetic axis of the permanent magnet of the synchronous motor is defined as the d-axis, the direction perpendicular to the d-axis is defined as the q-axis, the designated magnetic axis of the synchronous motor is defined as the γ-axis, and the direction perpendicular to the γ-axis is defined as the δ-axis, The current that generates the magnetic field in the d-axis direction is called the d-axis current, the voltage in the direction that the d-axis current flows is called the d-axis voltage, the current that generates the magnetic field in the q-axis direction is called the q-axis current, and the voltage in the direction that the q-axis current flows is called the q-axis voltage, If the following formula (1) is satisfied, it is estimated that the d-q axes and the γ-δ axes coincide without error. If the formula (1) does not hold, the amount of error is estimated from the difference between the left and right sides. A control device for a synchronous motor. [Equation 3] However, v γ is the γ-axis voltage [V], i γ is the γ-axis current [A], v δ is the δ-axis voltage [V], i δ is the δ-axis current [A], P is the number of motor poles, R is the motor resistance value for one phase [Ω], ω Ｒ is the motor electrical angular velocity [rad / s], Φ Ｍ indicates the magnet magnetic flux [wb].

4. 4. The synchronous motor control device according to claim 3, wherein the resistance value R on the right side of the formula (1) is derived using the following formula (2). [Equation 4]

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