JP5045003B2 - Motor control device - Google Patents

Description

  The present invention relates to a motor control device, and more particularly to a motor control device used for a battery-mounted electric vehicle such as a hybrid vehicle.

  Conventionally, when it is determined that a battery cannot be charged in a battery-equipped electric vehicle such as a hybrid vehicle, or in the case of a battery-less electric vehicle, the braking of the motor is performed using a dynamic brake that short-circuits the motor terminal. . As what performs such a braking of a motor, the "emergency stop circuit of a rotary motor" (refer patent document 1) is known.

Japanese Patent Laid-Open No. 08-149870

However, since the conventional “emergency stop circuit for a rotary motor” is configured to turn on all three upper or lower arms of the semiconductor switch element, current flows only to the switch element of one arm. As a result, it is inevitable that only one arm is rapidly deteriorated.
An object of the present invention is to provide a motor control device capable of suppressing heat from flowing only through a specific switch element.

To achieve the above object, a motor control device according to the invention, there is provided a driving force control apparatus for vehicles, and a heat engine, a generator driven by the heat engine, the electric power generated by the generator supply by being, an AC motor for driving the driving wheels, an inverter provided between the generator and the AC motor, is configured to include a controller for controlling the inverter and the generator and the AC motor The controller determines that a predetermined condition is satisfied, and controls the inverter to apply a braking force to the AC motor while continuing the load fixing control / rectangular wave control for fixing the PWM duty. Brake control is performed, the generated power of the generator is reduced to zero, and the generated switching pattern calculation processing signal is sent to the inverter And the inverter is controlled to make the utilization rate of the voltage applied to the AC motor constant, and to make the phase command value of the motor voltage larger than the point where the generated voltage becomes zero .

According to the present invention, when it is determined that the predetermined condition is satisfied and the controller controls the inverter to apply the braking force to the AC motor, the load fixing control and the rectangular wave control for fixing the PWM duty are continued. Motor brake control is performed so that the power generated by the generator drops to zero, and the generated switching pattern calculation processing signal is input to the inverter to control the inverter, so that the usage rate of the voltage applied to the AC motor is constant. In addition, since the phase command value of the motor voltage is made larger than the point at which the generated voltage becomes zero, the switching element of the inverter is ON / OFF controlled, so that the ON state does not occur continuously. . For this reason, it can suppress that an electric current flows into only a specific switch element, and generate | occur | produces heat | fever.

The best mode for carrying out the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a motor 4WD system according to an embodiment of the present invention. As shown in FIG. 1, the vehicle 10 includes a motor 4WD (4-wheel drive) system that drives a front wheel (main drive wheel) 11 with an engine 12 and a rear wheel (secondary drive wheel) 13 with a motor 14. ing.

A generator 15 mounted on the engine 12 has a rotating shaft 15 a connected to the engine rotating shaft 12 a via a belt 16 and rotates at a rotational speed proportional to the rotational speed of the engine 12. The generator 15 has a configuration in which the field current is controlled by the 4WD control circuit 17, and the magnitude of the generated power is determined by the generator speed and the magnitude of the field current.
On the other hand, a motor 14 and a speed reducer 18 for driving the sub drive shaft 13a are installed on the sub drive shaft (in this case, a rear shaft because it is an FF (Front engine Front drive) vehicle). The motor 14 is, for example, a three-phase AC synchronous motor that uses an electromagnet with a winding field instead of a permanent magnet as a rotor magnet. The inverter 19 converts the DC power of the generator 15 into three-phase AC and sends it to the motor 14.

That is, the vehicle 10 is driven via the inverter 19 based on the main drive shaft 11 a driven by the engine 12, the generator 15 that generates power using the driving force from the engine 12 as a power source, and the generated power of the generator 15. An AC motor 14 that generates force is included.
This motor 4WD system is controlled by a 4WD control circuit 17. For example, a 4WD switch (SW) signal is input to the 4WD control circuit 17, and the generator 15, the inverter 19, the motor 14, and the speed reducer are input from the 4WD control circuit 17. Control signals are sent to 18 and a warning lamp (not shown).

FIG. 2 is an explanatory diagram of a motor control block provided in the 4WD control circuit of FIG. As shown in FIG. 2, the 4WD control circuit 17 includes a power generation control unit 20 that controls the generator 15 and a motor control unit 21 that controls the motor 14. The inverter 19 has three switch elements 19a on each of the upper and lower arms, and a free-wheeling diode (not shown) corresponding to each of the switch elements 19a.
The power generation control unit 20 outputs a power generation control signal to the field coil 15b of the generator 15 based on the torque command value signal and the engine speed signal. Based on the torque command value signal and the motor rotation speed signal of the motor 14 from the resolver 22, the motor control unit 21 outputs a switching control signal for the three-phase power element to the inverter 19 and sends the motor to the field coil 14 a of the motor 14. Outputs a field current signal. The generator 15 is provided with a voltage sensor 23 and a current sensor 24, and a small capacitor 25 is connected in parallel to the inverter 19.

  FIG. 3 is a block diagram illustrating the configuration of the motor control unit of FIG. As shown in FIG. 3, the motor control unit 21 includes a motor voltage phase control unit 26, a motor field current command value calculation unit 27, a motor field magnetic flux command value calculation unit 28, a d-axis voltage (Vd) and a q-axis voltage. (Vq) A command value calculation unit 29 and a motor field current control unit 30 are provided. The motor voltage phase control unit 26 that controls the motor voltage phase includes a motor brake control unit 31 and a load fixing control / rectangular wave control unit 34.

  The motor brake control unit 31 calculates a Vd command value (Vd2 *) and a Vq command value (Vq2 *) based on the motor rotation number signal, and outputs the calculated command values to the load fixing control / rectangular wave control unit 34. To do. The motor field current command value calculation unit 27 calculates a motor field current command value (Ifm1 *) based on the motor rotation number signal, and uses the calculated command value as the motor field magnetic flux command value calculation unit 28 and Output to the motor field current control unit 30. The motor field flux command value calculation unit 28 calculates a motor field flux command value (Φ *) based on the motor field current command value (Ifm1 *), and uses the calculated command value as a Vd / Vq command. The value is output to the value calculation unit 29. The Vd / Vq command value calculation unit 29 is based on the motor rotational speed signal, the torque command value signal, and the motor field magnetic flux command value output from the motor field magnetic flux command value calculation unit 28, and provides a Vd command value (Vd1 *). The Vq command value (Vq1 *) is calculated, and these command values are output to the load fixing control / rectangular wave control unit 34.

  Based on the torque command value, the load fixing control / rectangular wave control unit 34 receives a command value (Vd2 *, Vq2 *) from the motor brake control unit 31 or a command value (Vd1 *, Vd1 *, Vq1 *) is selected, and U, V, and W phase switch pulse signals are calculated based on the selected command value. Based on the torque command value, the motor field current control unit 30 receives either the command value (Ifm2 *) from the motor brake control unit 31 or the command value (Ifm1 *) from the motor field current command value calculation unit 27. Based on the selected command value, the duty ratio output to the field coil 14a of the motor 14 is calculated.

  FIG. 4 is a block diagram illustrating the load fixing control by the load fixing control / rectangular wave control unit 34 of FIG. As shown in FIG. 4, the torque command value determination unit 101 includes command values (Vd1 *, Vq1 *) from the Vd / Vq command value calculation unit 29, and command values (Vd2 *, Vq2) from the motor brake control unit 31. *) And torque command value are input. The torque command value determination unit 101 determines whether the torque is positive or negative based on the input torque command value, and if positive (powering side), the command value (Vd1 *, Vq1 *) from the Vd / Vq command value calculation unit 29 is used. If it is negative (braking side), command values (Vd2 *, Vq2 *) from the motor brake control unit 31 are selected and output to the dq / uvw conversion unit 35. Further, the torque command value determination unit 101 determines the command value (Vd1 *, Vq1 *) from the Vd / Vq command value calculation unit 29 and the command from the motor brake control unit 31 when the sign of the torque command value is reversed. The command value is calculated so that the values (Vd2 *, Vq2 *) are switched smoothly and output to the dq / uvw conversion unit 35.

  The dq / uvw conversion unit 35 to which the command value from the torque command value determination unit 101 is input generates a dq / uvw conversion signal based on the input command value, and generates the generated dq / uv to the modulation factor fixing unit 36. The uvw conversion signal is output. The modulation rate fixing unit 36 generates a modulation rate fixed signal based on the input dq / uvw conversion signal, and outputs the generated modulation rate fixed signal to the triangular wave comparison & dead time compensation unit 37. The triangular wave comparison & dead time compensation unit 37 generates U, V, and W switch pulse signals, which are triangular wave comparison & dead time compensation processing signals, based on the input modulation rate fixed signal, and outputs them to the inverter 19. The dq / uvw converter 35 feeds back the rotor magnetic pole position signal of the motor 14 detected by the resolver 22.

  FIG. 5 is a block diagram illustrating rectangular wave control by the load fixing control / rectangular wave control unit 34 of FIG. As shown in FIG. 5, the torque command value determination unit 101 includes command values (Vd1 *, Vq1 *) from the Vd / Vq command value calculation unit 29, and command values (Vd2 *, Vq2) from the motor brake control unit 31. *) And torque command value are input. The torque command value determination unit 101 determines whether the torque is positive or negative based on the input torque command value, and if positive (powering side), the command value (Vd1 *, Vq1 *) from the Vd / Vq command value calculation unit 29 is used. If it is negative (braking side), command values (Vd2 *, Vq2 *) from the motor brake control unit 31 are selected and output to the voltage phase (θv) calculation unit 38.

Further, the torque command value determination unit 101 determines the command value (Vd1 *, Vq1 *) from the Vd / Vq command value calculation unit 29 and the command from the motor brake control unit 31 when the sign of the torque command value is reversed. The command value is calculated so that the values (Vd2 *, Vq2 *) are switched smoothly and output to the voltage phase (θv) calculation unit 38. The voltage phase (θv) calculation unit 38 to which the command value from the torque command value determination unit 101 is input performs θv calculation (θv = tan ⁻¹ Vq / Vd) based on the input command value, and the θv calculation result The signal is output to the switching pattern calculation unit 39. The switching pattern calculation unit 39 generates U, V, and W phase switch pulse signals that are switching pattern calculation processing signals based on the input θv calculation result signal, and outputs them to the inverter 19. The rotor magnetic pole position signal of the motor 14 detected by the resolver 22 is fed back to the θv calculator 38.

FIG. 6 is an explanatory diagram showing, in a graph, output characteristics of the generator when the generated magnetic field current for each power generation speed is constant. As shown in FIG. 6, the characteristics of the output voltage and output current of the generator 15 are determined by the generator rotation speed (4000 rpm, 8000 rpm, and 12000 rpm are exemplified) and the generated field magnetic current (Ifg).
FIG. 7 is an explanatory diagram showing the locus of the operating point when the phase is changed in the load fixing control and the rectangular wave control at a certain motor rotation speed. As shown in FIG. 7, in load fixing control and rectangular wave control, since the duty (ratio of ON and OFF) of PWM (Pulse Width Modulation) is fixed, the operating point P changes when the motor current or the motor voltage is changed. (P1 → P2). If the generated voltage Vdc is 0 V (Vdc = 0), the motor terminal is short-circuited to generate a braking force.

It should be noted that Ifg1 to Ifg4 are constant lines of generated magnetic field magnetic current, and θv1 to θv4 (θv increases from 1 to 4) are loci of operating points of the motor / inverter at the time of phase change.
Now, assume that the operating point is at P1 (Ifg1, θv1) and a braking force is to be applied. If the motor voltage phase is set to θv2 or more, the operating point moves to P2, Vdc = 0, and a braking force can be generated.

Therefore, in order to move the operating point from P1 to P2, the motor voltage phase may be set from θv1 to θv2 or more. Since the operating point P2 is Vdc = 0, the motor terminal is short-circuited and generates a braking force. The magnitude of the braking force is determined by the magnitude of the motor field current (Ifm).
FIG. 8 is a block diagram illustrating the configuration of the motor brake control unit of FIG. As shown in FIG. 8, the motor brake control unit 31 includes an Idc0 calculation unit 40, a motor voltage phase command value (θv *) calculation unit 41, a vd / vq command value calculation unit 42, a motor rotation speed determination unit 43, and θv *. = 180 deg (vd * = 1, vq * = 0) fixing unit 44 and motor field current command value calculation (including limiter) unit 45.

The Idc0 calculation unit 40 outputs a calculation result signal to the θv * calculation unit 41 by receiving the generated magnetic field magnetic current signal Ifg and the generator rotational speed (Ng) signal. The motor rotation speed determination unit 43 determines whether or not the motor rotation speed (Nm) is greater than a predetermined value. If the motor rotation speed (Nm) is smaller, the motor rotation speed is input to the θv * calculation unit 41. Output.
The θv * calculation unit 41 outputs the calculation result signal to the vd / vq command value calculation unit 42 when the calculation result signal from the Idc0 calculation unit 40 and the motor rotation number from the motor rotation number determination unit 43 are input. . The vd / vq command value calculation unit 42 receives the calculation result signal from the θv * calculation unit 41 and outputs a vd command value (vd2 *) and a vq command value (vq2 *) as calculation results. The θv * = 180 deg fixing unit 44 outputs the vd command value (−1) and the vq command value (0), which are θv * = 180 deg fixed values, when the motor rotation number from the motor rotation number determination unit 43 is input. To do. The motor field current command value calculation (including limiter) unit 45 outputs a motor field current command value (Ifm2 *) that is a calculation result signal in response to the input of the motor rotation speed and the torque command value.

  That is, the motor brake control unit 31 controls the inverter 19 to increase the motor voltage phase (θv *) and determine the motor field current command value (Ifm2 *). In order to determine the voltage phase (θv *) of the motor in the θv * calculation unit 41, the electric field magnetic current (Ifg) is detected, and Idc0 is determined from the previously determined generator characteristics (see FIG. 6). The calculation unit 40 obtains the value of Idc0 at the operating point P2. If the sensor for measuring Ifg cannot be installed due to lack of space, the generated voltage and generated current are measured, and Ifg is obtained in advance. Θv * is determined from the generated current Idc0 at the operating point P2. The determination method is performed as follows.

The locus of the operating point (see FIG. 7) at the time of load fixing / rectangular wave control is obtained by a mathematical expression.
The voltage-current equation (steady state) of a synchronous motor is
v _d = R i _d −ωL _q i _q (1)
v _q = Ri _q + ωL _d i _d + ωφ (2)
It can be expressed. here,
v _d , v _q : d, q-axis voltage [V]
i _d , i _q : d, q-axis current [motor control device]
L _d , L _q : d, q axis inductance [H]
R: Winding resistance [Ω]
ω: Motor rotation angular velocity [rad / sec]
φ: Field magnetic flux [Wb]

It is. The instantaneous input power P _i to the synchronous motor is
P _i = v _d i _d + v _q i _q (3)
And substituting Equations (1) and (2) into Equation (3),
^{_{P i = R (i d 2}} + i q 2) + ωφi q + ω (L d -L q) i d i q ......... (4)
It can be seen that this is the sum of copper loss and shaft output.
The output power P _g of the generator is
P _g = V _dc I _dc (5)
It is.

Ignoring switching loss and iron loss now,
P _g = P _i (6)
It becomes.
Substituting equations (3) and (5) into equation (6),
V _dc I _dc = v _{di d} + v _q i _q (7)
It becomes.

Where v _d v _q is
v _d = (v _d ² + v _q ² ) ^1/2 cos θ _v = v _m cos θ _v (8)
v _q = (v _d ² + v _q ² ) ^1/2 sin θ _v = v _m sin θ _v (9)
Here, theta _v a is defined as the motor voltage phase based on the d-axis positive direction.
Also, the relationship between the magnitudes of V _dc and v _m is as follows:
v _m = kV _dc ......... (10)
k = α / 2 (2/3) ^1/2
There is a relationship.

Substituting equations (8), (9), and (10) into equation (7) and solving for I _dc ,
_{I dc = kv m (i d} cosθ v + i q sinθ v) / v m
_{= K (i d cosθ v +} i q sinθ v) ......... (11)
It becomes.

となり、式（１０）を代入すると、

となり、式（１１）に式（１４），（１５）を代入し、まとめると、

と算出することができる。 Also, from equations (1) and (2), solving for i _d i _q

And substituting equation (10),

Substituting the equations (14) and (15) into the equation (11)

Can be calculated.

FIG. 9 is an explanatory diagram showing, in a graph, the operating point locus during load fixing / rectangular wave control obtained from the mathematical expression. That is, the VI characteristic when a parameter is substituted into Expression (16) is shown.
Although the motor voltage phase command value (θv *) is obtained from the current electromagnetic field current (Ifg), θv * may be set to a value larger than that.
FIG. 10 is an explanatory diagram showing the relationship between the motor voltage phase and Vd, Vq in a graph. Figure 11 shows a Idc-theta _v characteristics obtained from equation (17) in a graph, illustrates the case of (a) is omega> 0, (b) is an explanatory view of a case of omega <0.

As shown in FIG. 10, the motor voltage phase (θv) is defined as positive in the counterclockwise direction with the d-axis positive direction as a reference. What should be noted here is an overcurrent of the generated current (Idc).
The generated current (Idc0) at P2 is obtained from the generated magnetic field current (Ifg), and motor brake control is performed when Idc0 <Idcmax (current limit). If Idc0 ≧ Idcmax, motor brake control is not performed. In that case, ifg is lowered until Idc0 <Idcmax, and motor brake control is performed.

The motor voltage phase command value for (.theta.v *) may be set to a value which is obtained by substituting the power generation current (Idc0) at the operating point P2 in equation (17), but the function to Fig 11 (theta _v as can be seen from the Idc0), higher the rotation speed increases, the negligible second term of the equation (17), so theta _v is Idc0 are around 180deg the maximum value, | omega | when large, the motor The voltage phase command value θv * is not calculated and may be fixed at 180 deg.

FIG. 12 is an explanatory diagram showing the relationship between the rotational speed and the braking force in a graph using the motor field as a parameter. FIG. 13 is an explanatory diagram showing, in a graph, changes in motor current when the motor field is changed.
As shown in FIG. 12, it can be seen that the greater the motor field, the greater the braking force. However, if the motor rotational speed is large (| ω | large), the motor current (Im) flowing through the stator winding also becomes large, which may cause overcurrent (see FIG. 13). It is necessary to provide a limit on the magnetic current command value (Ifm2 *).

FIG. 14 is an explanatory diagram showing a gate pulse waveform during three-phase short-circuit control. FIG. 15 is an explanatory diagram showing a gate pulse waveform during control according to the present embodiment.
As shown in FIG. 14, only one arm (lower arm in FIG. 14) is used during the three-phase short-circuit control. For this reason, since heat concentrates on the switch element of one arm, the motor field current is limited to suppress the motor current, and the braking force is weakened.
On the other hand, in the case of the present embodiment, as shown in FIG. 15, since the motor brake control is performed while continuing the PWM control, since all the switch elements are used, the motor field that has been restricted during the three-phase short-circuit control is used. The limit value of the magnetic current is increased, and it becomes possible to flow a motor current twice that in the three-phase short-circuit control.

FIG. 16 is a diagram illustrating simulation results of the d-axis current, the q-axis current, and the motor rotation speed during the three-phase short-circuit control. FIG. 17 is a diagram illustrating simulation results of the d-axis current, the q-axis current, and the motor rotation speed during control according to the present embodiment.
In the case of three-phase short-circuit control, the ON / OFF of the gate pulse is steep, so that a large transient phenomenon occurs in the d-axis current and the q-axis current as shown in FIG. On the other hand, in the case of braking according to the present embodiment, since the switch element is turned ON / OFF, there is almost no transient phenomenon in the d-axis current and the q-axis current as shown in FIG. Therefore, it is not necessary to perform the control for dropping the brake force, and it is possible to quickly shift to the braking control. That is, in the present embodiment, since there is almost no transient phenomenon in switching between power running control and motor brake control, seamless control switching is possible without dropping the field of the motor.

  Further, in the present embodiment, since a current can flow through each switch element of the upper and lower arms, a motor field current can flow more than in the three-phase short-circuit control, and a large braking force can be obtained. In the above-described embodiment, the generation of the braking force during the motor forward rotation (forward direction) has been described. However, the present invention is not limited thereto, and the braking force can be generated similarly during the motor negative rotation (reverse direction).

Thus, in the above embodiment, when the motor voltage phase is controlled, the operating point of the generator is operated by controlling the voltage phase of the motor, and the generator output voltage is reduced (FIG. 7, P1, P2). See), the braking force is generated in the motor by short-circuiting the terminals of the motor.
That is, when controlling the motor voltage phase, the voltage utilization factor is made constant, the generated magnetic field current Ifg is detected (estimated), and the generated voltage Vdc becomes zero (that is, the generated current Idc becomes maximum). ) Is larger than the motor voltage phase command value (θv *). For example, when the motor rotation speed is large, the motor voltage phase command value (θv *) is set to 180 degrees.
As a result, since the switch element uses both upper and lower arms, the heat generation is dispersed and the heat concentration can be eliminated. In addition, since there is room for heat generation, the motor field current can be further passed to increase the braking force. For example, it is possible to generate a braking force that is approximately twice that of the three-phase short-circuit control. In addition, it is possible to seamlessly switch to normal power running control.

1 is a schematic configuration diagram of a motor 4WD system according to an embodiment of the present invention. It is explanatory drawing of the motor control block provided in the 4WD control circuit of FIG. It is a block diagram explaining the structure of the motor control part of FIG. It is a block diagram explaining the load fixing control of FIG. 3 or the load fixing control by a rectangular wave control part. FIG. 4 is a block diagram illustrating rectangular wave control by the load fixing control or rectangular wave control unit of FIG. 3. It is explanatory drawing which shows the output characteristic of a generator at the time of the electric field magnetic current for every power generation rotation speed with a graph. It is explanatory drawing which shows the locus | trajectory of the operating point when changing the phase in load fixing control and rectangular wave control at a certain motor rotation speed. It is a block diagram explaining the structure of the motor brake control part of FIG. It is explanatory drawing which shows the operating point locus | trajectory at the time of load fixed and rectangular wave control calculated | required from numerical formula with a graph. It is explanatory drawing which shows a motor voltage phase with a graph. Indicates Idc-theta _v characteristics obtained from equation (17) in the graph is an explanatory diagram of the case of (a) is omega> explanatory diagram of the case of 0, (b) is omega <0. It is explanatory drawing which shows the relationship between a rotation speed and braking force with a motor field as a parameter with a graph. It is explanatory drawing which shows the change of the motor electric current when changing a motor field with a graph. It is explanatory drawing which shows the gate pulse waveform at the time of three-phase short circuit control. It is explanatory drawing which shows the gate pulse waveform at the time of control by this Embodiment. It is explanatory drawing which shows the simulation result of d-axis current at the time of three-phase short circuit control, q-axis current, and motor rotation speed in a graph. It is explanatory drawing which shows the simulation result of the d-axis current at the time of control by this Embodiment, q-axis current, and a motor rotation speed with a graph.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Vehicle 11 Front wheel 11a Main drive shaft 12 Engine 12a Engine rotation shaft 13 Rear wheel 13a Sub drive shaft 14 Motor 14a Field coil 15 Generator 15a Rotation shaft 15b Field coil 16 Belt 17 4WD control circuit 18 Reducer 19 Inverter 19a Switch Element 20 Power generation control unit 21 Motor control unit 22 Resolver 23 Voltage sensor 24 Current sensor 25 Small capacitor 26 Motor voltage phase control unit 27 Motor field current command value calculation unit 28 Motor field magnetic flux command value calculation unit 29 Vd / Vq command value Calculation unit 30 Motor field current control unit 31 Motor brake control unit 34 Load fixing control / rectangular wave control unit 35 dq / uvw conversion unit 36 Modulation rate fixing unit 37 Triangular wave comparison and dead time compensation unit 38 θv calculation unit 39 Switching pattern calculation Part 40 Id c0 computing unit 41 θv * computing unit 42 vd / vq command value computing unit 43 motor rotation speed judging unit 44 θv * = 180 deg fixed unit 45 motor field current command value computing (including limiter) unit 101 torque command value judging unit

Claims (2)

In vehicles of the driving force control device,
A heat engine,
A generator driven by the heat engine;
By electric power generated by the generator is supplied, and an AC motor for driving the driving wheels,
An inverter provided between the generator and the AC motor;
A controller that controls the generator, the AC motor, and the inverter;
The controller determines that a predetermined condition is satisfied, and controls the inverter to apply a braking force to the AC motor while continuing the load fixing control / rectangular wave control to fix the PWM duty. Control is performed so that the generated power of the generator is reduced to zero , the generated switching pattern calculation processing signal is input to the inverter, the inverter is controlled, and the utilization rate of the voltage applied to the AC motor And a phase command value of the motor voltage is made larger than the point at which the generated voltage becomes zero . Said controller, when the rotation speed of the AC motor is greater than a predetermined value, by controlling the inverter, driving force according to claim 1, characterized in that the phase command value of the motor voltage to 180 degrees Control device.

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