1. A synchronous motor control device (1) comprising: an inverter including a plurality of switching elements; a current conversion means (11) that converts a three-phase current or a motor position of a synchronous motor into a d-axis current and a q-axis current represented by vectors synchronized with a magnetic field direction of a rotor of the synchronous motor; a current feedback control calculation means (12) that calculates a d-axis voltage command value and a q-axis voltage command value from the d-axis current and the q-axis current by using current feedback control; and a voltage command value conversion means (13) that converts the d-axis voltage command value and the q-axis voltage command value into three-phase voltage command values, the synchronous motor control device (1) being configured to perform, on a basis of the three-phase voltage command values, output to the synchronous motor while controlling the switching elements to be turned on and off, and to correct an output vector of a d-axis voltage that causes the d-axis current to flow so as to generate a magnetic field matching the magnetic field direction, and an output vector of a q-axis voltage orthogonal to the d-axis voltage, using a correction coefficient determined in advance for reducing an angle at which the output vector of the d-axis voltage deviates from the magnetic field direction, wherein while reducing the correction coefficient according to an increase in a rotation speed of the synchronous motor, the synchronous motor control device (1) performs control to output a voltage later than the d-axis voltage and the q-axis voltage that generate the magnetic field matching the magnetic field direction, and suppresses oscillation of a current during high-speed rotation.

2. The synchronous motor control device (1) according to claim 1, wherein the correction coefficient is decreased by adding a predetermined negative value to the correction coefficient when it is detected that an electrical angular velocity of the synchronous motor exceeds a predetermined threshold.

Description:BACKGROUND
TECHNICAL FIELD
[0001]
The present invention relates to a synchronous motor control device, and in particular, to a synchronous motor control device having a function of correcting a deviation generated between an actual magnetic axis position in a synchronous motor and an output vector of a voltage.
Related Art
[0002]
A synchronous motor is an electric motor that rotates in synchronization with an input AC voltage. A rotor is attracted by a rotating magnetic field formed by an input AC current and rotates following the magnetic field. The synchronous motor is generally driven and controlled by a control system by a control device connected to the rotor.
[0003]
FIG. 3 shows such a synchronous motor control system in a functional block diagram. In this system, three-phase currents (iU, iV, iW) of a motor detected or estimated from a current sensor are converted, on the basis of motor positional information detected or estimated, into a d-axis current (id) and a q-axis current (iq) expressed by axes (vectors) synchronized with a magnetic field direction of a rotor of the synchronous motor. 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 and the q-axis current respectively match a d-axis current command value (idref) and a q-axis current command value (iqref). These voltages are converted into three-phase voltage command values (VUref, VVref, VWref) of the synchronous motor, and a switching element of an inverter is controlled to be turned on and off, so that the three-phase voltage command values are output to the synchronous motor.
[0004]
FIG. 4 is a vector diagram illustrating three-phase voltages, a d-axis voltage, and a q-axis voltage of the synchronous motor as viewed in electrical angles in the synchronous motor control system. The three-phase voltages are axes fixed to each other at intervals of 120° in a stator of the synchronous motor, and the d-axis and the q-axis are axes following the position of the rotor. A permanent magnet is provided in the rotor, a current that generates a magnetic field in the same direction as the magnetic field of the magnet is referred to as d-axis current, a current that generates a magnetic field in a direction orthogonal to the d-axis current is referred to as q-axis current, a voltage in a direction in which the d-axis current flows is referred to as d-axis voltage, and a voltage in a direction in which the q-axis current flows is referred to as q-axis voltage.
[0005]
However, since the directions in which the d-axis voltage command and the q-axis voltage command obtained as described above are output are calculated using the detected or estimated positions, while the synchronous motor operates at a high rotation speed, as illustrated in FIG. 5, a deviation occurs between the d-axis voltage (Vdreal) and the q-axis voltage (Vqreal) that generate the magnetic field matching the actual magnetic field direction of the stator. For example, the present position and the next position after a sampling time Ts seconds are deviated by ωΦTs using a motor electrical angular velocity ωΦ. Therefore, in order to reduce the average deviation for Ts seconds, a method of outputting a voltage to a position advanced by 0.5 ωΦTs from the present position has widely been adopted. Here, the voltage output axis is corrected by multiplying ωΦTs with a correction coefficient αV = 0.5.
[0006]
However, in such a conventional synchronous motor control system, although it is possible to output the d-axis voltage command value and the q-axis voltage command value so that the deviation between the actual d-axis voltage and q-axis voltage becomes small during normal operation, the current tends to oscillate in a high rotation region, and thus there is a problem in that it is difficult to increase the current to a desired rotation speed or higher.
[0007]
On the other hand, JP 2009-183022 A proposes a method of performing position/speed control including proportional-integral control by matching a reference magnetic pole command position given to a synchronous motor with a magnetic pole detection position, and performing control in a direction of reducing an error torque of the synchronous motor by adding a magnetic pole position error estimation value according to a positive or negative moving direction of a rotor to an electrical angle position of the motor to update a magnetic pole position on control. However, when the inertia of the synchronous motor greatly changes, the gain adjustment time for optimally adjusting a position/speed control gain becomes long, so that the position/speed control gain band needs to be set wide, and the operation becomes unstable.
[0008]
On the other hand, JP 2022-020905 A proposes a method of using a control device that estimates an actual magnetic pole position of a synchronous motor on the basis of a movement amount of a rotor when a predetermined drawing current is applied to an armature winding of the synchronous motor to draw a magnetic pole of the rotor. The control device uses a control angle position obtained by calculating a predetermined variable gain for the movement amount and performs coordinate conversion for feeding back the drawing current to calculate an electrical angle phase offset to be added to the movement amount of the synchronous motor during normal operation.
[0009]
However, in this method, the control procedure in the synchronous motor control device is complicated and processing load tends to be excessive, and it is difficult to suppress the oscillation tendency of the current generated in the high rotation region of the synchronous motor as described above. Therefore, it has been desired to develop a synchronous motor control system capable of performing stable control in all rotation regions by a simple method.
[0011]
The present invention has been made to solve the above problems, and an object of the present invention is to enable a synchronous motor control device to stably perform current control in any rotation region.

SUMMARY
[0012]
The present invention is characterized in that a synchronous motor control device includes: an inverter including a plurality of switching elements; a current conversion means that converts a three-phase current or a motor position of a synchronous motor into a d-axis current and a q-axis current represented by vectors synchronized with a magnetic field direction of a rotor of the synchronous motor; a current feedback control calculation means that calculates a d-axis voltage command value and a q-axis voltage command value from the d-axis current and the q-axis current by using current feedback control; and a voltage command value conversion means that converts the d-axis voltage command value and the q-axis voltage command value into three-phase voltage command values, the synchronous motor control device being configured to perform, on the basis of the three-phase voltage command values, output to the synchronous motor while controlling the switching elements to be turned on and off, and to correct an output vector of a d-axis voltage that causes the d-axis current to flow so as to generate a magnetic field matching the magnetic field direction of the rotor, and an output vector of a q-axis voltage orthogonal to the d-axis voltage, using a correction coefficient determined in advance for reducing an angle at which the output vector of the d-axis voltage deviates from the magnetic field direction, in which, while reducing the correction coefficient according to an increase in a rotation speed of the synchronous motor, the synchronous motor control device performs control to output a voltage later than the d-axis voltage and the q-axis voltage that generate the magnetic field matching the magnetic field direction of the rotor, and suppresses oscillation of a current during high-speed rotation.
[0013]
As described above, by using a relatively simple method in which the control device executes a control method in which a phase of the voltage is output later than the d-axis voltage and the q-axis voltage that generate the magnetic field matching the magnetic field direction of the rotor while reducing the predetermined correction coefficient for reducing the angle of deviation from the magnetic field direction of the rotor according to the increase in the rotation speed of the synchronous motor, stable current control can be executed in any rotation region while suppressing the oscillation of a current during high-speed operation.
[0014]
In addition, in the synchronous motor control device, in a case where the reduction of the correction coefficient is performed by adding a predetermined negative value to the correction coefficient when it is detected that the electrical angular velocity of the synchronous motor exceeds the predetermined threshold, it is possible to execute more stable control without excessively increasing the burden on the control device.
[0015]
According to the present invention adopting a method in which a voltage is output later than the d-axis voltage and the q-axis voltage that generate the magnetic field matching the magnetic field direction of the rotor while reducing the correction coefficient for reducing the deviation from the magnetic field direction of the rotor according to an increase in the rotation speed of the synchronous motor, stable current control can be performed in any rotation region.

BRIEF DESCRIPTION OF DRAWINGS
[0016]
FIG. 1 is a functional block diagram illustrating an outline of a control system by a synchronous motor control device according to an embodiment of the present invention;
FIG. 2 is a flowchart showing a calculation procedure in the control system of FIG. 1;
FIG. 3 is a functional block diagram illustrating an outline of a control system by a conventional synchronous motor control device;
FIG. 4 is a vector diagram of three-phase voltages, a d-axis voltage, and a q-axis voltage of a synchronous motor as viewed in electrical angles in the control system of FIG. 3; and
FIG. 5 is a vector diagram illustrating deviation of vectors of the d-axis voltage and the q-axis voltage in the control system of FIG. 3 and correction of the deviation.

DETAILED DESCRIPTION
[0017]
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0018]
FIG. 1 is a functional block diagram functionally illustrating processing contents of a control system by a synchronous motor control device 1 according to the present embodiment. The control device 1 includes an inverter (not illustrated) including a plurality of switching elements, a current conversion means 11 that converts a detected or estimated three-phase current or motor position information of a synchronous motor into a d-axis current and a q-axis current represented by vectors synchronized with a magnetic field direction of a rotor of the synchronous motor, a current feedback control calculation means 12 that calculates a d-axis voltage command value and a q-axis voltage command value from the d-axis current and the q-axis current by using current feedback control, and a voltage command value conversion means 13 that converts the d-axis voltage command value and the q-axis voltage command value thus obtained into three-phase voltage command values.
[0019]
On the basis of the three-phase voltage command values obtained in this manner, output is performed to the synchronous motor (not illustrated) while the switching elements are controlled to be turned on and off, and an output vector of a d-axis voltage that causes the d-axis current to flow so as to generate a magnetic field matching the direction of the magnetic field generated by the rotor of the synchronous motor, and an output vector of a q-axis voltage orthogonal to the d-axis voltage, are corrected using a correction coefficient determined in advance for reducing an angle at which the output vector of the d-axis voltage deviates from the magnetic field direction of the rotor detected or estimated, and the configuration described above is the same as that in the conventional example.
[0020]
The synchronous motor control device 1 according to the present embodiment employs a control method in which, while reducing the correction coefficient determined in advance in order to reduce the deviation according to an increase in the rotation speed of the synchronous motor, the voltage command value conversion means 13 performs control to output a voltage later than the d-axis voltage and the q-axis voltage that generate the magnetic field matching the magnetic field direction of the rotor, and suppresses the oscillation of a current during high-speed rotation. This point is the largest feature of the present invention.
[0021]
That is, a change of the control system by the control device 1 according to the present embodiment from the conventional example lies in a method of determining the correction coefficient αV with which the deviation ωΦTs of the motor electrical angular velocity is multiplied, and in that processing of reducing the correction coefficient αV is performed in accordance with an increase in the rotation speed. The correction coefficient αV has normally been fixed to 0.5 in the conventional example.
[0022]
FIG. 2 is a flowchart illustrating a procedure for determining the correction coefficient αV in the present embodiment. In the calculation of αVave, when it is detected that the present motor electrical angular velocity ωΦ exceeds a predetermined threshold ωΦH, processing according to an expression including a negative value as illustrated in the drawing is performed, and a value obtained by adding 0.5, which is similar to that of the conventional control system, to the calculated αVave is set as the correction coefficient αV.
[0023]
According to the synchronous motor control device 1 of the present embodiment characterized by executing such a control procedure, it is possible to suppress the oscillation of a current during high-speed rotation of the synchronous motor, and it is possible to realize a rotation speed higher than that of the conventional control system. The reason will be described below.
[0024]
The following Expressions 1 and 2 are current voltage equations on the d-axis and the q-axis of the synchronous motor. Here, the equations are described with R as a motor resistance value [Ω] for one phase, L as a motor inductance value [H] for one phase, ωΦ as a motor electrical angular velocity [rad/s], and Φm as a motor induced voltage constant [V/(rad/s)]. Expression 1 is a general current-voltage equation of a synchronous motor, and Expression 2 is a modification of Expression 1. Here, since the voltages caused by the d-axis current and the q-axis current are the actual d-axis voltage and q-axis voltage, respectively, Vdreal and Vqreal are used instead of Vdref and Vqref.
[Expression 1]

[Expression 2]

[0025]
Next, the development of the stability theory in current feedback control will be described using Expressions 3 to 7. In the proportional control of current feedback, control is performed by multiplying a current feedback gain KA such that a deviation obtained by subtracting the d-axis current from the d-axis current command value and a deviation obtained by subtracting the q-axis current from the q-axis current command value become small. However, when the command values are constant, the stability is not affected, and thus the d-axis current command value and the q-axis current command value are not included in Expression 3.
[Expression 3]

[0026]
When this Expression 3 is substituted into Expression 3-2 in FIG. 5, the following Expression 4 can be derived.
[Expression 4]

[0027]
When this is substituted into Expression 2 described above, a differential equation of the d-axis current and the q-axis current as in the following Expression 5 is obtained.
[Expression 5]

[0028]
In order to obtain the stability of this expression, the underlined portion in Expression 5 is set to A and the eigenpolynomial is obtained, so that the following Expression 6 can be derived.
[Expression 6]

[0029]
From the viewpoint of the stability theory, it can be seen that by setting the correction coefficient αV to a negative value and reducing the zero-order term, the attenuation coefficient increases, and thus the oscillation of a current can be suppressed. Furthermore, when ωΦ ≥ ωΦH is satisfied with the electrical angular velocity [rad/s] of a normally controllable synchronous motor immediately before oscillation as the threshold ωΦH, the value of the zero-order term does not increase if the correction coefficient αV is set by the following Expression 7, so that the synchronous motor can be stably controlled even at high rotation.
[Expression 7]

[0030]
As described above, the present invention enables a synchronous motor control device to perform stable current control in any rotation region.
, Claims:1. A synchronous motor control device (1) comprising: an inverter including a plurality of switching elements; a current conversion means (11) that converts a three-phase current or a motor position of a synchronous motor into a d-axis current and a q-axis current represented by vectors synchronized with a magnetic field direction of a rotor of the synchronous motor; a current feedback control calculation means (12) that calculates a d-axis voltage command value and a q-axis voltage command value from the d-axis current and the q-axis current by using current feedback control; and a voltage command value conversion means (13) that converts the d-axis voltage command value and the q-axis voltage command value into three-phase voltage command values, the synchronous motor control device (1) being configured to perform, on a basis of the three-phase voltage command values, output to the synchronous motor while controlling the switching elements to be turned on and off, and to correct an output vector of a d-axis voltage that causes the d-axis current to flow so as to generate a magnetic field matching the magnetic field direction, and an output vector of a q-axis voltage orthogonal to the d-axis voltage, using a correction coefficient determined in advance for reducing an angle at which the output vector of the d-axis voltage deviates from the magnetic field direction, wherein
while reducing the correction coefficient according to an increase in a rotation speed of the synchronous motor, the synchronous motor control device (1) performs control to output a voltage later than the d-axis voltage and the q-axis voltage that generate the magnetic field matching the magnetic field direction, and suppresses oscillation of a current during high-speed rotation.

2. The synchronous motor control device (1) according to claim 1, wherein the correction coefficient is decreased by adding a predetermined negative value to the correction coefficient when it is detected that an electrical angular velocity of the synchronous motor exceeds a predetermined threshold.