1. A synchronous motor control device (1) comprising: a synchronous motor (2) having a rotor using a permanent magnet; an inverter configured to drive the synchronous motor (2); current conversion means (11) configured to convert a three-phase current (iU, iV, iW) of the 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); 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); current command intermediate value calculation means (14) configured to calculate a d-axis current command intermediate value (idref1) from a motor speed; and current command value calculation means (15) configured to calculate a d-axis current command value (idref) and a q-axis current command value (iqref) from the d-axis current command intermediate value (idref1), the synchronous motor control device (1) is configured to perform output from the inverter to the synchronous motor (2) based on the three-phase voltage command value (VUref, VVref, VWref), when the synchronous motor (2) is stopped, to input the d-axis current command value (idref) and the q-axis current command value (iqref) to the current feedback control calculation means (12), and to set output torque of the synchronous motor (2) to zero so as to stop an operation of the synchronous motor (2).

2. The synchronous motor control device (1) as claimed in claim 1, wherein the current command value calculation means (15) comprising: a d-axis current command value calculation step of comparing the d-axis current command intermediate value (idref1) with a d-axis current command previous value and determining the d-axis current command value (idref); and a q-axis current command value calculation step of setting, as the q-axis current command value (iqref), a value obtained by multiplying the d-axis current command value (idref) by a predetermined coefficient, and the d-axis current command value calculation step calculates the d-axis current command value (idref) according to following conditions A and B, wherein the condition A: when the d-axis current command intermediate value (idref1) is greater than or equal to the d-axis current command previous value, the d-axis current command previous value is set as the d-axis current command value (idref) the condition B: when the condition A is not satisfied, the d-axis current command intermediate value (idref1) is set as the d-axis current command value (idref).

3. The synchronous motor control device (1) as claimed in claim 2, wherein the predetermined coefficient is set to a positive value smaller than 1, a positive sign is assigned to the predetermined coefficient when the rotor is rotated in a forward direction, and a negative sign is assigned to the predetermined coefficient when the rotor is rotated in a reverse direction.

Description:TECHNICAL FIELD
[0001]
The present invention relates to a synchronous motor control device operated by vector control, and more particularly, to a control device that realizes torque-free control in which a motor does not run away when the motor is stopped as being torque-free (output torque is zero) by a fail-safe operation at the time of failure determination or a command from a host controller in the middle of driving or generating power of the synchronous motor.

RELATED ART
[0002]
A synchronous motor is an electric motor that rotates in synchronization with an input AC voltage, and while a rotor of the synchronous motor is attracted by a rotating magnetic field formed by an input AC current, the synchronous motor performs a rotation operation thereof following the magnetic field. The synchronous motor is generally driven and controlled by a control system by a control device connected thereto.
[0003]
FIG. 4 illustrates a conventional example of a motor control system. 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 motor.
[0005]
Here, in order to realize the torque-free control, it is known to set the q-axis current command value (iqref) proportional to the output torque to 0, for example, as described in JP 2014-233109 A (Patent Literature 1).
[0006]
On the other hand, the d-axis current command value (idref) needs to cause a negative current corresponding to the rotation speed to flow even in the torque-free control in order to avoid the control device from being damaged by the induced voltage of the motor.
[0007]
A problem in the conventional motor control system will be described with reference to FIG. 5. Normally, the d-axis current (id) and the q-axis current (iq) are caused to flow on the basis of the motor position. However, in a case where the motor position is shifted from the actual magnetic axis of the motor by Δθ, even if the q-axis current command value (iqref) is zero for torque-free, a current flows in the q-axis current (iqreal) based on the actual magnetic axis.
[0008]
Accordingly, if the torque in the acceleration direction is output, the rotation speed of the motor further increases. Furthermore, if the d-axis current increases as the rotation speed increases, the output torque also increases, leading to runaway.

CITATION LIST
PATENT LITERATURE
[0009]
Patent Literature 1: JP 2014-233109 A

SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0010]
An object of the present invention is to provide a control device for realizing torque-free control that avoids runaway when a synchronous motor is stopped.

SOLUTION TO PROBLEM
[0011]
The present invention made to solve the above-described problems is a synchronous motor control device includes: a synchronous motor having a rotor using a permanent magnet; an inverter configured to drive the synchronous motor; current conversion means configured to convert a three-phase current of the 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; 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; current command intermediate value calculation means configured to calculate a d-axis current command intermediate value from a motor speed; and current command value calculation means configured to calculate a d-axis current command value and a q-axis current command value from the d-axis current command intermediate value,
the synchronous motor control device is configured to perform output from the inverter to the synchronous motor based on the three-phase voltage command value,
when the synchronous motor is stopped, to input the d-axis current command value and the q-axis current command value to the current feedback control calculation means, and to set output torque of the synchronous motor to zero so as to stop an operation of the synchronous motor.
[0012]
In the present invention, in a case where the current command value calculation means includes:
a d-axis current command value calculation step of comparing the d-axis current command intermediate value with a d-axis current command previous value and determining the d-axis current command value; and a q-axis current command value calculation step of setting, as the q-axis current command value, a value obtained by multiplying the d-axis current command value by a predetermined coefficient, and
the d-axis current command value calculation step has an advantage in that an absolute value of the d-axis current command value does not increase during the torque-free control when the d-axis current command value is calculated under the following conditions A and B.
The condition A: when the d-axis current command intermediate value is greater than or equal to the d-axis current command previous value, the d-axis current command previous value is set as the d-axis current command value.
The condition B: when the condition A is not satisfied, the d-axis current command intermediate value is set as the d-axis current command value.
[0013]
In the present invention, in a case where when the predetermined coefficient is set to a positive value smaller than 1, a positive sign is assigned to the predetermined coefficient when the rotor is rotated in a forward direction, and a negative sign is assigned to the predetermined coefficient when the rotor is rotated in a reverse direction, torque in the deceleration direction is easily output even if the motor position is shifted, and runaway can be prevented.

ADVANTAGEOUS EFFECTS OF INVENTION
[0014]
According to the present invention, it is possible to realize torque-free control that avoids runaway when a synchronous motor is stopped.

BRIEF DESCRIPTION OF DRAWINGS
[0015]
FIG. 1 is a functional block diagram illustrating an outline of a control system in a synchronous motor control device according to the present invention;
[0016]
FIG. 2 is an explanatory diagram illustrating current vectors of a d-axis current and a q-axis current in the present invention;
[0017]
FIG. 3 is a flowchart illustrating processing contents by current command value calculation means in the present invention;
[0018]
FIG. 4 is a functional block diagram illustrating an outline of a control system in a synchronous motor control device of a conventional example; and
[0019]
FIG. 5 is an explanatory diagram illustrating current vectors of a d-axis current and a q-axis current in the control system of the conventional example.

DESCRIPTION OF EMBODIMENTS
[0020]
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0021]
In the following description, "torque-free control" refers to control for setting the output torque of the synchronous motor to zero, and "torque-free state" refers to a state in which the output torque of the synchronous motor is zero.
[0022]
FIG. 1 is a block diagram illustrating a configuration of a synchronous motor control device of the present invention. In a control device 1 that executes the drive control of a synchronous motor 2, a synchronous motor control device uses a three-phase current (iU, iV, iW) of the synchronous motor detected or estimated from a current sensor or is represented by an axis synchronized with the estimated motor position, thereby being converted into a d-axis current (id) and a q-axis current (iq) by current conversion means 11.
[0023]
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).
[0024]
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 a switching element of an inverter. As the control device 1, for example, a computer such as an in-vehicle ECU can be used.
[0025]
In the present embodiment, when the synchronous motor is stopped by performing a fail-safe operation at the time of failure determination or torque-free control according to a command from a host controller while the synchronous motor 2 is driven or generating power, current command intermediate value calculation means 14 and current command value calculation means 15 are included in order to calculate the d-axis current command value (idref) and the q-axis current command value (iqref) used in the current feedback control described above.
[0026]
Specifically, in the present embodiment, the current command intermediate value calculation means 14 sets a d-axis current command calculation result in a conventional example as a d-axis current command intermediate value (idref1), and then the current command value calculation means 15 calculates the d-axis current command value (idref) and the q-axis current command value (iqref).
[0027]
FIG. 2 is an explanatory diagram illustrating current vectors of a d-axis current and a q-axis current in the present invention.
[0028]
In the conventional torque-free control, the q-axis current command is set to zero, but in the present invention, calculation is performed based on the d-axis current (id).

[0029]
When a q-axis current actual value (iqreal) in the acceleration direction is generated (becomes a value larger than zero), runaway occurs. To avoid this, the q-axis current command value (iqref) is set to a negative value during forward rotation and a positive value during reverse rotation.
[0030]
The q-axis current command value (iqref) is a value obtained by multiplying the d-axis current (id) by a coefficient (K).
[0031]
Here, considering that the d-axis current command value (idref) is always a negative value, it is assumed that the coefficient (K) is a small positive value of about 0.1, and a large current does not flow by adjusting a sign applied to the coefficient (K) with positive or negative.
[0032]
As a result, even if the motor position deviates, torque in the deceleration direction is easily output, and runaway can be prevented.
[0033]
Further, when the rotation speed increases even during the torque-free control, the d-axis current command value is normally increased, but when the d-axis current command value is larger than a previous value, the previous value is output as it is.
[0034]
FIG. 3 is a flowchart illustrating processing contents by current command value calculation means in the present invention. The current command value calculation means includes: a d-axis current command value calculation step of comparing the d-axis current command intermediate value and a d-axis current command previous value to determine a d-axis current command value; and a q-axis current command value calculation step of setting a value obtained by multiplying the d-axis current command value by a predetermined coefficient as the q-axis current command value.

[0035]
The d-axis current command value calculation step calculates the d-axis current command value according to the following conditions A and B.
The condition A: when the d-axis current command intermediate value is greater than or equal to the d-axis current command previous value, the d-axis current command previous value is set as the d-axis current command value.
The condition B: when the condition A is not satisfied, the d-axis current command intermediate value is set as the d-axis current command value.
By performing this processing, an absolute value of the d-axis current command value does not increase during the torque-free control.
[0036]
Thereafter, the q-axis current command value is calculated by multiplying a predetermined coefficient based on the rotation direction of the motor and the d-axis current. The predetermined coefficient is a positive value smaller than 1, and is about 0.1 in the present embodiment.
[0037]
A positive sign is assigned to the predetermined coefficient when the rotor is rotated in the forward direction, and a negative sign is assigned to the predetermined coefficient when the rotor is rotated in the reverse direction.
[0038]
This makes it possible to avoid runaway in the torque-free state even if the motor position is shifted.

REFERENCE SIGNS LIST
1 control device
2 synchronous motor
11 current conversion means
12 current feedback control calculation means
13 voltage command value conversion means
14 current command intermediate value calculation means
15 current command value calculation means
, Claims:1. A synchronous motor control device (1) comprising:
a synchronous motor (2) having a rotor using a permanent magnet;
an inverter configured to drive the synchronous motor (2);
current conversion means (11) configured to convert a three-phase current (iU, iV, iW) of the 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);
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);
current command intermediate value calculation means (14) configured to calculate a d-axis current command intermediate value (idref1) from a motor speed; and
current command value calculation means (15) configured to calculate a d-axis current command value (idref) and a q-axis current command value (iqref) from the d-axis current command intermediate value (idref1),
the synchronous motor control device (1) is configured to perform output from the inverter to the synchronous motor (2) based on the three-phase voltage command value (VUref, VVref, VWref),
when the synchronous motor (2) is stopped, to input the d-axis current command value (idref) and the q-axis current command value (iqref) to the current feedback control calculation means (12), and
to set output torque of the synchronous motor (2) to zero so as to stop an operation of the synchronous motor (2).

2. The synchronous motor control device (1) as claimed in claim 1, wherein
the current command value calculation means (15) comprising:
a d-axis current command value calculation step of comparing the d-axis current command intermediate value (idref1) with a d-axis current command previous value and determining the d-axis current command value (idref); and
a q-axis current command value calculation step of setting, as the q-axis current command value (iqref), a value obtained by multiplying the d-axis current command value (idref) by a predetermined coefficient, and
the d-axis current command value calculation step calculates the d-axis current command value (idref) according to following conditions A and B, wherein
the condition A: when the d-axis current command intermediate value (idref1) is greater than or equal to the d-axis current command previous value, the d-axis current command previous value is set as the d-axis current command value (idref)
the condition B: when the condition A is not satisfied, the d-axis current command intermediate value (idref1) is set as the d-axis current command value (idref).

3. The synchronous motor control device (1) as claimed in claim 2, wherein
the predetermined coefficient is set to a positive value smaller than 1,
a positive sign is assigned to the predetermined coefficient when the rotor is rotated in a forward direction, and
a negative sign is assigned to the predetermined coefficient when the rotor is rotated in a reverse direction.