JP2017175819A - Motor drive device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce vibrations in a radial direction without largely increasing d-axis current which contributes little to torque.SOLUTION: The motor drive device modulates a d-axis current, by using a frequency of 6 times of a drive current frequency of a motor 1, between a d-axis maximum current flow rate, which has a large absolute value as a maximum value in a magnetic field direction weaker than the d-axis current flow rate at which the motor efficiency gets maximum, and a d-axis current value smaller than the d-axis maximum current value as an actual d-axis current value. With this, the magnitude of the attraction force in a radial direction can be restricted by using a drive current, mean value or effective value of which is smaller than the d-axis maximum current value. Thus, vibrations in a radial direction can be reduced.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a motor drive device in a machine that converts electrical energy into mechanical energy and performs desired work.

  Conventionally, this type of motor drive device is driven and controlled by a semiconductor circuit in order to obtain an arbitrary rotation speed. Among these, a motor having a permanent magnet in a rotor is used, so that it is small and highly efficient. Things can be realized. In particular, a highly efficient motor can be realized by employing a stronger permanent magnet containing a rare earth element.

  However, when a strong permanent magnet is used, rotational torque can be obtained by the attractive / repulsive force between the permanent magnet and each phase of the stator. On the other hand, when each stator phase and the permanent magnet are at the same angle, However, a suction force is generated in the radial direction. This attractive force increases regardless of polarity, and increases at a high magnetic force, and is not a uniform value depending on the rotation angle. As a result, at one point of the stator, radial vibration is caused at a frequency twice the electrical frequency (electrical secondary frequency). On the other hand, a technique for reducing radial vibration by intentionally flowing a d-axis current that hardly contributes to torque has been proposed in consideration of home appliances and electric vehicles (for example, Patent Documents). 1).

Japanese Patent Laid-Open No. 2015-211561 JP 2008-17642 A

  However, the conventional technique has a problem that the d-axis current that hardly contributes to the torque needs to flow constantly, so that the drive current increases and the copper loss of the motor increases. On the other hand, a technique for suppressing an increase in loss by changing the d-axis current has been proposed (see, for example, Patent Document 2). However, the technique disclosed in Patent Document 2 experimentally obtains a variable frequency component, and when adjustments such as modulation amplitude and phase are included, it takes a lot of man-hours to determine parameters of the modulation. become.

  The present invention solves the above-described conventional problems, and an object of the present invention is to provide a motor driving device that can easily suppress radial vibration while suppressing increase in copper loss of the motor. .

  In order to solve the above-described conventional problems, the motor driving device of the present invention swings the d-axis current at a frequency that is six times the electrical frequency.

  This increases the effect of weakening the attractive force with a large d-axis current in the rotational phase where the radial attractive force is maximum in all phases of the stator, and reduces the d-axis current in other areas, Since the suction force cannot necessarily be weakened, the amplitude of the change in the suction force can be reduced, and the radial vibration can be weakened.

  The motor drive device of the present invention can suppress radial vibration while suppressing an increase in loss.

Control block diagram of motor drive device in Embodiment 1 of the present invention Waveform diagram in the same control block

1st invention is a motor drive device provided with the power converter which can output the alternating current of variable frequency and variable current, and the controller which carries out drive control of the synchronous motor connected to the said power converter at arbitrary rotation speeds There,
The controller has a d-axis maximum current amount having a maximum absolute value in the field-weakening direction than the d-axis current amount at which the motor efficiency is maximum at a frequency six times the drive current frequency; This is modulated as an actual d-axis current value between the d-axis current value smaller than the d-axis maximum current value.

  As a result, the suction force is weakened in the period in which the radial suction force is large, and conversely, the suction force is not weakened in the period in which the radial suction force is small. The vibration in the radial direction can be reduced while keeping the increase in loss due to the current smaller than the method of increasing the current.

  According to a second aspect of the invention, in particular, in the first aspect of the invention, the phase at which the modulated actual d-axis current becomes the maximum d-axis current is a radial magnetic attraction in at least one phase coil of the synchronous motor. The phase where the force is maximum.

  The magnetic attractive force in the radial direction becomes maximum when the phase is in a phase where no torque is generated, and becomes small when the phase is in a phase where torque can be generated.

  In a third aspect of the invention, particularly in the first or second aspect of the invention, the torque of the synchronous motor is calculated from the power of the power converter and the motor rotation speed, and the actual d-axis current is modulated according to the calculated torque. It defines the amplitude and phase of the modulation information.

  In a so-called IPM motor with a permanent magnet built into the rotor, the fluctuation phase and magnitude of the radial attractive force change due to the reluctance torque, so the phase fluctuation amount and magnitude change in each torque are obtained in advance. In addition, by detecting the torque and adjusting the modulation phase and modulation width of the d-axis current, it is possible to always obtain the optimum vibration reduction effect.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 shows a circuit block configuration of a motor drive device according to an embodiment of the present invention.

  In FIG. 1, a motor drive device includes a power converter capable of outputting an alternating current of variable frequency and variable current, a motor 1 connected to the power converter, and a controller for driving and controlling the motor 1 at an arbitrary rotation number. It has. The motor 1 is a three-phase permanent magnet synchronous motor having three coils.

The rotation status of the motor 1 is detected by the current sensors 3u, 3v, 3w, and coordinate conversion is performed by the coordinate conversion means 4 using the information of the rotation phase θ or the estimation information θ ^, and d-axis current information Id, q-axis current Convert to information Iq. Here, the d-axis current is an exciting current and hardly contributes to the motor torque. Conversely, the q-axis current is a current that greatly contributes to the motor torque.

  The d-axis current Id is input to the comparator 12, compared with the d-axis current command value Id *, and the error is input to the current compensation means 14 to equivalently convert the d-axis voltage command information into voltage information. Obtain Vd *.

  Similarly, the q-axis current Iq is input to the comparator 10, compared with the q-axis current command value Iq *, the error is input to the current compensation means 13, and the q-axis is converted into voltage information equivalently. Voltage command information Vq * is obtained.

  The current compensation means 13 and 14 are means for causing each current control to operate stably at high speed. For example, well-known PI (proportional / integral) control is used. The d-axis voltage command information Vd * and the q-axis voltage command information Vq * obtained in this way are sent to the coordinate conversion means 5, and the rotational phase information θ information or the estimation information θ ^ is used. , Converted into three-phase voltage command information Vu *, Vv *, Vw *.

  The obtained three-phase voltage command information Vu *, Vv *, Vw * is sent to the three-phase AC power supply 2 and converted into a voltage at which power can appear to drive the motor 1. Thus, a control system for driving the motor 1 with desired currents Id * and Iq * is configured.

  Next, the rotational phase estimation information θ ^ of the motor 1 will be described. The rotational phase estimation means 6 estimates the rotational phase of the motor 1 from the current information Id and Iq of the motor 1 and the drive voltage information Vd * and Vq *. If the inductance and winding resistance of the motor 1 are known, the rotational phase θ and the rotational speed ω can be estimated using these. For example, if it is a permanent magnet synchronous motor of the motor 1, the voltage equation shown by the following formula (1) is established using the motor parameters Ra, Ld, Lq, and Ψa.

  If there is a slight error “Δθ” in this rotational phase estimation, an error substantially proportional to the error “Δθ” appears in the d-axis voltage component of the voltage equation, as shown in the following equation (2).

Therefore, if the rotational phase estimation is corrected so that the error “Δθ” does not appear in the d-axis component while stabilizing Vd, Vq and Id, Iq by current control, the estimated phase is correct. become. The estimated speed ω can be obtained as differential information of the phase. Note that the method of rotational phase estimation is not limited to this method.

  The estimated phase information θ ^ obtained in this way is sent to the coordinate conversion means 4, 5 and the 6-times multiplication means 19, and the estimated speed information ω ^ is sent to the speed comparison means 7 to realize rotational speed control.

  On the other hand, the speed comparison means 7 compares the target rotational speed ω * to be realized by the motor drive device with the estimated rotational speed information ω ^ and inputs the difference to the speed compensation means 8. The speed compensation means 8 is a means for operating the speed control stably at high speed, and a well-known technique such as PI control is used as in the current control system.

  The output of the speed compensation means 8 is equivalent to a current command Ia * corresponding to torque. The torque equivalent current command Ia * is obtained by the distribution means 9 as a q-axis current command Iq * and a d-axis current provisional command Id0 *. The q-axis current command Iq * is compared with the q-axis current Iq obtained as a result of the current detection by the comparator 10 to constitute a q-axis current control system. The distribution ratio of the d-axis and q-axis currents in the distribution means 9 is a value obtained by dividing power information obtained from the three-phase AC power source 2 as power information and dividing by the rotational speed command ω *, that is, an amount corresponding to torque. To be optimal.

  On the other hand, the provisional command Id0 * for the d-axis current is added to the information δId * from the multiplication unit 18 by the adding unit 11 to obtain the d-axis current command Id *. A d-axis current control system is configured by comparing with Id.

  Next, the process of obtaining information δId * from the multiplication means 18 will be described. The estimated phase information θ ^ of the rotational phase estimation means 6 is obtained via the 6-times multiplication means 19 as 6-fold estimated phase information 6θ ^. The 6-fold estimated phase information θ ^ is sent to the adding means 20 and added to the modulation phase offset information “Δ” obtained from the second conversion table 17 to be 6 times the estimated phase information θ ^. Is estimated phase information “6θ ^ + Δ”.

  This information is input to the sine wave calculation means 21, “sin (6θ ^ + Δ)” is calculated, input to the multiplication means 18, and multiplied by the modulation amount information obtained from the first conversion table 16. Thus, the modulation amount δId * of the d-axis current command is obtained. Here, the input information to the first conversion table 16 and the second conversion table 17 is the output of the block 15, that is, the amount corresponding to the torque, and the modulation amount which is the first value according to the torque, The modulation phase offset which is the second value is read and corresponds to the non-linear characteristic generated by the torque of the motor 1.

  With the configuration of FIG. 1, the d-axis current can be fluctuated at a frequency six times the electrical frequency.

  FIG. 2 is a waveform diagram showing the relationship between the induced voltage, d-axis current, and radial attractive force in the rotational phase. FIG. 2 (a) shows the change in attractive force caused by constantly and constantly flowing the d-axis current as in the conventional example. FIG. 2 (b) shows the magnitude of the d-axis current in the present embodiment. Modulation is performed at 6 times the electrical frequency. In the case of general driving in which the d-axis current hardly flows in the lower suction force waveform, the radial suction force fluctuates greatly at twice the electrical frequency as shown by the broken line. It becomes an excitation force and causes vibration noise. In FIG. 2 (a), since a large d-axis current always flows constantly, the action of weakening the attractive force works in all phases. As a result, the change of the attractive force is reduced, the excitation force is reduced, and the vibration is reduced. Noise can be reduced.

On the other hand, in FIG. 2B, the magnitude of the d-axis current is fluctuated. The point is that the d-axis current is increased when the radial attractive force is the largest (T0, T6), and the d-axis current is decreased when the radial attractive force is the smallest (T3, T9). It is what you want to do.

  This is an example focusing on the suction force change in one phase, but since a general motor is driven by a three-phase alternating current, the suction force changes appear to be shifted from each other by 120 degrees. For this reason, even if the radial attractive force in the other phase is the largest (T2, T4, T8, T10), the d-axis current is increased and the attractive force is the smallest (T1, T5, T7). However, the d-axis current is reduced. That is, the magnitude of the d-axis current is modulated at a frequency three times the frequency of the attractive force change, that is, a frequency six times the electrical frequency.

  The suction force waveform at this time is shown by a solid line in the lower part of FIG. That is, large suppression is performed in the phase with the largest suction force, and almost no suppression is performed in the phase with the smallest suction force. For this reason, the amplitude of the suction force change is reduced, the excitation force is reduced, and vibration noise can be reduced. In addition, since the average value or effective value of the d-axis current used for suppressing the attractive force decreases, the increase in copper loss can also be reduced. Moreover, the same effect can be obtained in all three-phase coils by modulating at a frequency six times the electrical frequency.

  In the case of a so-called IPM motor having a magnet built in the rotor, it is known that the d-axis current also flows according to the torque to improve the efficiency. In this case, the phase at which the attractive force is maximized The optimum current amount for reducing the suction force change is also shifted, but it can be corrected by the first conversion table 16 and the second conversion table 17 in FIG. If an experiment is performed, it can be obtained in advance.

  As described above, in the present embodiment, the amplitude of change in attractive force can be reduced by modulating the magnitude of the d-axis current at a frequency six times the electrical frequency, so that the excitation force is reduced and the copper loss is reduced. It is possible to suppress radial vibration noise while reducing the amount of increase.

  In the embodiment, an example in which the rotational phase of the motor is estimated is shown. However, it is apparent that the present invention can be used even when a rotational phase detector is provided.

  As described above, the motor drive device according to the present invention can reduce the vibration noise in the radial direction while suppressing an increase in loss, and the relationship between the modulation frequency of the d-axis current and the rotation speed is fixed. Therefore, since the determination of related parameters is also simplified, it can be easily applied to uses such as household appliances, electric compressors for refrigeration and air-conditioning equipment, and motor driving of electric vehicles.

DESCRIPTION OF SYMBOLS 1 Motor 2 Three-phase alternating current power supply 3u, 3v, 3w Current sensor 4 Coordinate conversion means 5 Coordinate conversion means 6 Rotation phase estimation means 19 6 Multiplication means

Claims (3)

A power converter capable of outputting AC of variable frequency and variable current;
A motor driving device comprising a controller that controls driving of the synchronous motor connected to the power converter at an arbitrary rotational speed;
The controller has a d-axis maximum current amount having a maximum absolute value in the field-weakening direction than the d-axis current amount at which the motor efficiency is maximum at a frequency six times the drive current frequency; A motor drive device that modulates an actual d-axis current value between a d-axis current value smaller than the d-axis maximum current value. The phase where the actual d-axis current to be modulated becomes the maximum value of the d-axis current is a phase where the magnetic attractive force in the radial direction is maximum in at least one phase coil of the synchronous motor. The motor drive device described. The torque of the synchronous motor is calculated from the power of the power converter and the motor rotation speed, and the modulation amplitude of the actual d-axis current and the phase of the modulation information are determined according to the calculated torque. Motor drive device.