1. A synchronous motor axis error estimation method serving as a control method of driving a synchronous motor (2) including an inverter formed of a plurality of switching elements by sensorless vector control, the synchronous motor axis error estimation method comprising: defining that a magnetic axis of a permanent magnet of the synchronous motor (2) is a d-axis, a direction orthogonal to the d-axis is a q-axis, a designated magnetic axis of the synchronous motor (2) is a γ-axis, and a direction orthogonal to the γ-axis is a δ-axis; defining that a current for generation of a magnetic field in a d-axis direction is a d-axis current (id), a voltage in a direction in which the d-axis current (id) flows is a d-axis voltage (vd), a current for generation of a magnetic field in a q-axis direction is a q-axis current (iq), and a voltage in a direction in which the q-axis current (iq) flows is a q-axis voltage (vq); estimating that a d-q axis and a γ-δ axis coincide with each other without an error when expression of the following Equation (1) is satisfied; and estimating an amount of error from a difference between a left side and a right side when the expression of the Equation (1) is not satisfied, [Mathematical Formula 1] here, 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 number of motor poles, R represents a resistance value per motor phase [Ω], ωR represents a motor electric angular velocity [rad/s], and ΦM represents a magnet magnetic flux [wb].

2. The synchronous motor axis error estimation method as claimed in claim 1, wherein the resistance value R on the right side of the Equation (1) is derived using the following Equation (2). [Mathematical Formula 2]

3. A synchronous motor control device (1) comprising an inverter formed of a plurality of switching elements, current conversion means (11) configured to convert a three-phase current of a detected or estimated synchronous motor (2) into a d-axis current (id) and a q-axis current (iq), current feedback control calculation means (12) configured to calculate, by using current feedback control, a d-axis voltage command value (vdref) and a q-axis voltage command value (vqref) from the d-axis current (id) and the q-axis current (iq), and voltage command value conversion means (13) configured to convert the d-axis voltage command value (vdref) and the q-axis voltage command value (vqref) into a three-phase voltage command value (VUref, VVref, VWref), wherein the synchronous motor (2) is driven by sensorless vector control while the switching elements are controlled to be turned on and off based on the three-phase voltage command value (VUref, VVref, VWref), the synchronous motor control device (1) comprising a synchronous motor axis error estimation method, wherein the synchronous motor axis error estimation method comprises: defining that a magnetic axis of a permanent magnet of the synchronous motor (2) is a d-axis, a direction orthogonal to the d-axis is a q-axis, a designated magnetic axis of the synchronous motor (2) is a γ-axis, and a direction orthogonal to the γ-axis is a δ-axis; defining that a current for generation of a magnetic field in a d-axis direction is the d-axis current (id), a voltage in a direction in which the d-axis current (id) flows is a d-axis voltage (vd), a current for generation of a magnetic field in a q-axis direction is the q-axis current (iq), and a voltage in a direction in which the q-axis current (iq) flows is a q-axis voltage (vq); estimating that a d-q axis and a γ-δ axis coincide with each other without an error when expression of the following Equation (1) is satisfied; and estimating an amount of error from a difference between a left side and a right side when the expression of the Equation (1) is not satisfied, [Mathematical Formula 3] here, 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 number of motor poles, R represents a resistance value per motor phase [Ω], ωR represents a motor electric angular velocity [rad/s], and ΦM represents a magnet magnetic flux [wb].

4. The synchronous motor control device (1) as claimed in claim 3, wherein the resistance value R on the right side of the Equation (1) is derived using the following Equation (2). [Mathematical Formula 4]

Description:TECHNICAL FIELD
[0001]
The present invention relates to a method of estimating an error of a magnetic shaft in a synchronous motor to enable stable current control, and a synchronous motor control device including the axis error estimation method.

RELATED ART
[0002]
Vector control is known as one of synchronous motor control methods. This vector control is considered to be divided into a current component that generates torque and a current component that generates magnetic flux in a rotor, and each of the current components is independently controlled.
[0003]
First, a conventional synchronous motor control system and a d-axis voltage and a q-axis voltage according to the present invention will be described. In this system, three-phase currents (iU, iV, iW) of a motor detected or estimated from a current sensor are converted into a d-axis current (id) and a q-axis current (iq) represented by axes synchronized with a detected or estimated motor position.
[0004]
A d-axis voltage command value (vdref) and a q-axis voltage command value (vqref) are calculated using current feedback control such that the d-axis current (id) and the q-axis current (iq) become a d-axis current command value (idref) and a q-axis current command value (iqref), respectively. This voltage is converted into a three-phase voltage command value (vUref, vVref, vWref) of the motor and is output to the synchronous motor.
[0005]
A description will be given with reference to FIG. 1. This diagram is a vector diagram of three-phase voltages, d-axis voltages, and q-axis voltages of a motor as viewed in an electrical angle in a conventional synchronous motor control system. The three-phase AC voltage (U-phase, V-phase, and W-phase) is an axis that is fixed to a stator of the motor and is shifted by 120°, while the d-axis and the q-axis are axes that follow the position of a rotor. A permanent magnet is attached to the rotor, and a current that generates a magnetic field in the same direction as a magnetic field of the magnet is referred to as a d-axis current, and a current that generates a magnetic field in an orthogonal direction is referred to as a q-axis current. A voltage in a direction in which the d-axis current flows is defined as the d-axis voltage, and a voltage in a direction in which the q-axis current flows is defined as the q-axis voltage.
[0006]
However, an axis that outputs an axis voltage command calculated in a conventional motor control system is calculated using the detected or estimated position (this is defined as a γ-δ axis), and an error may occur between the d-q axis and the γ-δ axis of an actual synchronous motor. An increase in this error may cause an abnormality in the control of the motor.
[0007]
On the other hand, for example, in a sensorless type inverter control device described in JP 2009-100600 A (Patent Literature 1), known is a method of calculating a phase difference Δθ by an arc tangent function calculation using an induced voltage estimation value estimated by an induced voltage estimator as an axis error calculator, but it has been required to estimate an axis error with fewer parameters.

Citation List
Patent Literature
[0008]
Patent Literature 1: JP 2009-100600 A

SUMMARY OF INVENTION
Technical Problem
[0009]
An object of the present invention is to provide a method of estimating an axis error between the d-q axis and the γ-δ axis of a synchronous motor.
Solution to Problem
[0010]
A synchronous motor axis error estimation method according to the present invention made to solve the above-described problem is a control method of driving a synchronous motor including an inverter formed of a plurality of switching elements by sensorless vector control, the synchronous motor axis error estimation method characterized by including:
defining that a magnetic axis of a permanent magnet of the synchronous motor is a d-axis, a direction orthogonal to the d-axis is a q-axis, a designated magnetic axis of the synchronous motor is a γ-axis, and a direction orthogonal to the γ-axis is a δ-axis;
defining that a current for generation of a magnetic field in a d-axis direction is a d-axis current, a voltage in a direction in which the d-axis current flows is a d-axis voltage, a current for generation of a magnetic field in a q-axis direction is a q-axis current, and a voltage in a direction in which the q-axis current flows is a q-axis voltage;
estimating that a d-q axis and a γ-δ axis coincide with each other without an error when expression of the following Equation is satisfied; and
estimating an amount of error from a difference between a left side and a right side when the expression of the Equation is not satisfied.
[Mathematical Formula 1]

Here, 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 the number of motor poles, R represents a resistance value per motor phase [Ω], ωR represents a motor electric angular velocity [rad/s], and ΦM represents a magnet magnetic flux [wb].
[0011]
A synchronous motor control device according to another aspect of the present invention includes an inverter formed of a plurality of switching elements, current conversion means configured to convert a three-phase current of a detected or estimated synchronous motor into a d-axis current and a q-axis current, current feedback control calculation means configured to calculate, by using current feedback control, a d-axis voltage command value and a q-axis voltage command value from the d-axis current and the q-axis current, and voltage command value conversion means configured to convert the d-axis voltage command value and the q-axis voltage command value into a three-phase voltage command value, wherein the synchronous motor is driven by sensorless vector control while the switching elements are controlled to be turned on and off based on the three-phase voltage command value, the synchronous motor control device characterized by including a synchronous motor axis error estimation method,
wherein the synchronous motor axis error estimation method includes:
defining that a magnetic axis of a permanent magnet of the synchronous motor is a d-axis, a direction orthogonal to the d-axis is a q-axis, a designated magnetic axis of the synchronous motor is a γ-axis, and a direction orthogonal to the γ-axis is a δ-axis;
defining that a current for generation of a magnetic field in a d-axis direction is the d-axis current, a voltage in a direction in which the d-axis current flows is a d-axis voltage, a current for generation of a magnetic field in a q-axis direction is the q-axis current, and a voltage in a direction in which the q-axis current flows is a q-axis voltage;
estimating that a d-q axis and a γ-δ axis coincide with each other without an error when expression of the following Equation is satisfied; and
estimating an amount of error from a difference between a left side and a right side when the expression of the Equation is not satisfied.
[Mathematical Formula 2]

Here, 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 the number of motor poles, R represents a resistance value per motor phase [Ω], ωR represents a motor electric angular velocity [rad/s], and ΦM represents a magnet magnetic flux [wb].
[0012]
In the present invention, when the resistance value R on the right side of the Equation is derived using the following Equation, a resistance value including the inverter can be derived because the resistance value R is derived based on the three-phase current and the three-phase voltage actually measured when the motor is in the constant rotation state.
[Mathematical Formula 3]

ADVANTAGEOUS EFFECTS OF INVENTION
[0013]
According to the present invention, it is possible to estimate an axis error between the d-q axis and the γ-δ axis with a relatively small number of parameters.

BRIEF DESCRIPTION OF DRAWINGS
[0014]
FIG. 1 is a vector diagram of a three-phase voltage, a d-axis voltage, and a q-axis voltage of a motor viewed in terms of an electrical angle.
[0015]
FIG. 2 is a diagram for description of a relationship between an inner product of a current vector and a voltage vector.
[0016]
FIG. 3 is a diagram illustrating a configuration of a synchronous motor control device that executes a synchronous motor axis error estimation method according to the present invention.

DESCRIPTION OF EMBODIMENTS
[0017]
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0018]
First, a description will be given with reference to FIGS. 1 and 2. FIG. 1 is a vector diagram of a three-phase voltage, a d-axis voltage, and a q-axis voltage of a motor viewed in terms of an electrical angle. The three-phase AC voltage (U-phase, V-phase, and W-phase) is an axis that is fixed to a stator of a synchronous motor and is shifted by 120°, while the d-axis and the q-axis are axes that follow the position of a rotor. A magnetic axis 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, a direction orthogonal to the γ-axis is defined as a δ-axis, a current for generating a magnetic field in the d-axis direction is defined as a d-axis current, a voltage in a direction in which the d-axis current flows is defined as a d-axis voltage, a current for generating a magnetic field in the q-axis direction is defined as a q-axis current, and a voltage in a direction in which the q-axis current flows is defined as a q-axis voltage.
[0019]
In the synchronous motor axis error estimation method according to the present invention, as illustrated in FIG. 2, an error of a magnetic axis is estimated by using a fact that an inner product of a current vector and a voltage vector is the same regardless of which coordinate plane is used for calculation.
[0020]
Since the inner product of the current vector and the voltage vector on the d-q plane and the γ-δ plane is equal, idvd + iqvq = iγvγ + iδvδ is satisfied. When the inner product idvd + iqvq is executed from the voltage equation of the following Equation (1), the following Equation (2) is obtained.
[Mathematical Formula 4]

[0021]
Here, vd represents a d-axis voltage [V], id represents a d-axis current [A], vq represents a q-axis voltage [V], iq represents a q-axis current [A], 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], L represents a motor one-phase inductance value [H], P represents the number of motor poles, R represents a resistance value per motor phase [Ω], ωR represents a motor electric angular velocity [rad/s], and ΦM represents a magnet magnetic flux [wb].
[0022]
Then, the result of the following Equation (3) can be derived from the inner product and the voltage equation.
[Mathematical Formula 5]

[0023]
When the value of the inner product is equal to the value obtained from the voltage equation, that is, when the following Equation (4) is satisfied, the following Equation (5) is obtained, so that it can be estimated that the d-q axis and the γ-δ axis coincide with each other without an error.
[Mathematical Formula 6]

[0024]
On the other hand, when the Equation (4) is not satisfied, a degree of error between the d-q axis and the γ-δ axis can be estimated by a difference between both sides of the Equation (4).
[0025]
Here, the Equation (4) is considered. The term R (iδ2+iγ2) on the right side can be ignored when a resistance value R is small, but needs to be derived when the resistance value R is large. However, since the resistance value R includes an inverter resistance, it is difficult to measure the resistance value R with a resistance meter.
[0026]
Therefore, a method of deriving the resistance value R using the inner product will be described. It is assumed that the γ-axis current iγ1 and the δ-axis current iδ1 are flowing during execution of rotation speed control. The γ-axis current is changed to iγ2 under the same load condition. When there is an error between the d-q axis and the γ-δ axis, the δ-axis current becomes iδ2.
[0027]
For each, the inner product of the current vector and the voltage vector is obtained. The inner product is active power, and is the sum of power and copper loss. Since the power is equal and iδ12 + iγ12 ≠ iδ22 + iγ22, the following Equations (6) and (7) are obtained.
[Mathematical Formula 7]

[0028]
Then, by calculating a difference between the Equation (6) and the Equation (7), the following Equation (8) is derived, and the resistance value R can be derived. Since the resistance value R is derived based on the three-phase current and the three-phase voltage actually measured when the motor is in the constant rotation state, it is possible to derive the resistance value including the inverter.
[Mathematical Formula 8]

[0029]
FIG. 3 is a functional block diagram illustrating a control system of a synchronous motor 2. In this system, in the control device 1 that executes the drive control of the synchronous motor 2, three-phase currents (iU, iV, iW) of the synchronous motor detected or estimated from the current sensor are used, or represented by axes synchronized with the estimated motor position, so that the three-phase currents are converted into a d-axis current (id) and a q-axis current (iq) by current conversion means 11.
[0030]
Current feedback control calculation means 12 calculates a d-axis voltage command value (Vdref) and a q-axis voltage command value (Vqref) by current feedback control such that the d-axis current (id) and the q-axis current (iq) respectively match an input d-axis current command value (idref) and a q-axis current command value (iqref). This voltage is converted into a three-phase voltage command value (VUref, VVref, VWref) of the synchronous motor by the voltage command value conversion means 13, and the three-phase voltage command value is output to the synchronous motor 2 by performing on/off control of switching elements of an inverter.
[0031]
After the three-phase currents (iU, iV, iW) of the synchronous motor are converted into the d-axis current (id) and the q-axis current (iq) by the current conversion means 11, axis error estimation means 20 estimates an axis error between the d-q axis and the γ-δ axis before the three-phase currents are input to the current feedback control calculation means 12.
[0032]
Details of the synchronous motor axis error estimation method executed by the axis error estimation means 20 are the same as those of the synchronous motor axis error estimation method described above, and thus the details thereof are omitted. It is noted that, as the control device 1, for example, a computer such as an ECU can be used in the case of an automobile.

Reference Signs List
[0033]
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 synchronous motor axis error estimation method serving as a control method of driving a synchronous motor (2) including an inverter formed of a plurality of switching elements by sensorless vector control, the synchronous motor axis error estimation method comprising:
defining that a magnetic axis of a permanent magnet of the synchronous motor (2) is a d-axis, a direction orthogonal to the d-axis is a q-axis, a designated magnetic axis of the synchronous motor (2) is a γ-axis, and a direction orthogonal to the γ-axis is a δ-axis;
defining that a current for generation of a magnetic field in a d-axis direction is a d-axis current (id), a voltage in a direction in which the d-axis current (id) flows is a d-axis voltage (vd), a current for generation of a magnetic field in a q-axis direction is a q-axis current (iq), and a voltage in a direction in which the q-axis current (iq) flows is a q-axis voltage (vq);
estimating that a d-q axis and a γ-δ axis coincide with each other without an error when expression of the following Equation (1) is satisfied; and
estimating an amount of error from a difference between a left side and a right side when the expression of the Equation (1) is not satisfied,
[Mathematical Formula 1]

here, 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 number of motor poles, R represents a resistance value per motor phase [Ω], ωR represents a motor electric angular velocity [rad/s], and ΦM represents a magnet magnetic flux [wb].

2. The synchronous motor axis error estimation method as claimed in claim 1, wherein
the resistance value R on the right side of the Equation (1) is derived using the following Equation (2).
[Mathematical Formula 2]

3. A synchronous motor control device (1) comprising an inverter formed of a plurality of switching elements, current conversion means (11) configured to convert a three-phase current of a detected or estimated synchronous motor (2) into a d-axis current (id) and a q-axis current (iq), current feedback control calculation means (12) configured to calculate, by using current feedback control, a d-axis voltage command value (vdref) and a q-axis voltage command value (vqref) from the d-axis current (id) and the q-axis current (iq), and voltage command value conversion means (13) configured to convert the d-axis voltage command value (vdref) and the q-axis voltage command value (vqref) into a three-phase voltage command value (VUref, VVref, VWref), wherein the synchronous motor (2) is driven by sensorless vector control while the switching elements are controlled to be turned on and off based on the three-phase voltage command value (VUref, VVref, VWref), the synchronous motor control device (1) comprising a synchronous motor axis error estimation method,
wherein the synchronous motor axis error estimation method comprises:
defining that a magnetic axis of a permanent magnet of the synchronous motor (2) is a d-axis, a direction orthogonal to the d-axis is a q-axis, a designated magnetic axis of the synchronous motor (2) is a γ-axis, and a direction orthogonal to the γ-axis is a δ-axis;
defining that a current for generation of a magnetic field in a d-axis direction is the d-axis current (id), a voltage in a direction in which the d-axis current (id) flows is a d-axis voltage (vd), a current for generation of a magnetic field in a q-axis direction is the q-axis current (iq), and a voltage in a direction in which the q-axis current (iq) flows is a q-axis voltage (vq);
estimating that a d-q axis and a γ-δ axis coincide with each other without an error when expression of the following Equation (1) is satisfied; and
estimating an amount of error from a difference between a left side and a right side when the expression of the Equation (1) is not satisfied,
[Mathematical Formula 3]

here, 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 number of motor poles, R represents a resistance value per motor phase [Ω], ωR represents a motor electric angular velocity [rad/s], and ΦM represents a magnet magnetic flux [wb].

4. The synchronous motor control device (1) as claimed in claim 3, wherein
the resistance value R on the right side of the Equation (1) is derived using the following Equation (2).
[Mathematical Formula 4]