JP2020018138A - Motor control device and motor control method - Google Patents

Abstract

To reduce calculation resources required to execute a 120-degree conduction method.SOLUTION: The motor control device includes: a power conversion unit having upper and lower arms of U, V, and W phases; U, V, W phase coils receiving an output of the power conversion unit; a rotor for rotating by receiving magnetic flux from each coil; a control unit; and a current detection unit capable of acquiring a current value flowing through each of the coils. For each of six modes of a 120-degree conduction method, combinations of on and off of upper and lower arms are switched. The control unit performs mode switching by using a current value obtained by the current detection unit.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a motor control device and a motor control method.

  As a driving method of the rotary motor for three-phase driving, a 120-degree energization method in which there is an open phase in which both the upper and lower arms of one phase are off, and a 180-degree energization in which one of the upper and lower arms is on in any phase The method is known. While the 120-degree energization method enables position estimation, torque ripple is likely to occur, and the efficiency is relatively low. On the other hand, the 180-degree energization method is easy to achieve high efficiency where position estimation is difficult.

  As a position estimating method using the 120-degree energization method, a rotor position detecting means using an open-phase back electromotive voltage is known, for example, as disclosed in Patent Document 1 (0035). More specifically, for example, a configuration is provided in which a resistance element is arranged between each phase coil and the ground, and a change in voltage at the resistance is measured.

    In Patent Document 1, the time change rate ΔI ′ of the current becomes smaller when the timing is later than the pattern switching at the appropriate energization timing, and the time change rate ΔI ′ becomes larger when the timing is advanced. After pointing out (0068), there is disclosed a control for changing the energization switching timing by a time depending on a difference between the set value of the current time change rate and the measured value (0069, FIG. 13).

JP-A-9-9668

  In a low-speed rotation region such as when a rotary motor is started, it is particularly preferable to obtain position information from the viewpoint of step-out suppression and the like. Therefore, a 120-degree energization method is relatively used, and in a high-speed rotation region, high efficiency can be achieved by 180 degrees. The energization method is often used. However, in the case of the 120-degree conduction method, if a resistance element that obtains open-phase back electromotive voltage information is provided as in Patent Document 1, energy consumption due to the resistance element occurs. On the other hand, many rotary motors are provided with one to three shunt resistors used for current measurement of each phase, separately from a resistance element for obtaining back electromotive force information.

    In Patent Document 1, since the energization timing for each phase of the motor is executed using the time change rate of the current, the current change rate is calculated every time the energization pattern is switched. This algorithm requires a high computation load on the microcomputer and requires a lot of computational resources.

The first present invention made in view of the above circumstances,
A power conversion unit having upper and lower arms of U, V, and W phases;
U, V, W phase coils receiving the output of the power converter;
A rotor that rotates by receiving a magnetic flux from each of the coils;
A control unit;
A current detection unit capable of acquiring a current value flowing through each of the coils,
Switching the on / off combination of the upper and lower arms corresponding to each of the six modes of the 120-degree conduction method,
The control unit is a motor control device that switches the mode using a current value obtained by the current detection unit.

In addition, the second present invention made in view of the above circumstances,
A power conversion unit having upper and lower arms of U, V, and W phases;
U, V, W phase coils receiving the output of the power converter;
A rotor that rotates by receiving a magnetic flux from each of the coils;
A current detection unit capable of acquiring a current value flowing through each of the coils,
A motor control method for switching a combination of on and off of the upper and lower arms corresponding to each of six modes of a 120-degree energization method,
The switching of the mode is performed using a current value of the current detection unit.

2 is an example of a circuit configuration of the motor control device according to the first embodiment. FIG. 3 is a schematic diagram of DC current detection according to the first embodiment. FIG. 4 is a schematic diagram illustrating a switching method at the time of 120-degree conduction according to the first embodiment. 4 is an example of a motor operation state at the time of 120-degree energization of the first embodiment. 7 is an example of a method of switching a current-carrying phase at 120-degree current-carrying according to the first embodiment. 7 is an example of a method of switching a current-carrying phase at 120-degree current-carrying according to the first embodiment. 7 is an example of a description of a control state in FIG. 6. 9 is an example of a circuit configuration of a motor control device according to a second embodiment. 14 is an example of a winding current waveform according to a load torque value according to the third embodiment. 13 illustrates an example of a method for switching a conduction phase at the time of 120-degree conduction according to the load torque value according to the third embodiment. 13 illustrates an example of a load torque determination method according to the third embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[overall structure]
FIG. 1 is an example of a circuit configuration diagram of the motor control device according to the first embodiment. The motor control device includes a DC power source, an inverter 1 that outputs an AC voltage, a motor 2 connected to the inverter 1, a controller 3 that outputs a pulse width modulation signal to the inverter 1 to control the inverter 1, And a shunt resistor 4 as an example of a current detection unit. The motor 2 includes an armature having a coil through which each of three-phase AC currents from the inverter 1 flows, and a field element having a permanent magnet, and the armature and the field element rotate relative to each other. be able to.

    FIG. 2 is a schematic diagram of the detection timing of the direct current. The voltage of each phase of the motor 2 has a three-phase AC waveform, and is always divided into a maximum phase, an intermediate phase, and a minimum phase. When the voltage level of each phase of the motor is in a state as shown in FIG. 2A, the DC current appearing in the shunt resistor 4 changes as shown in the figure during one PWM cycle. With this DC current, the current of the maximum phase and the current of the minimum phase can be detected. The direct currents are Idc1 and Idc2, and are detected by the arithmetic unit 3 on the uphill and downhill of the PWM carrier wave. On the uphill slope of the PWM carrier wave, the current flowing in each phase can be known by detecting Idc1 as the minimum voltage phase and Idc2 as the maximum voltage phase and treating them as motor reproduction currents. On the downhill of the PWM carrier wave, Idc1 is detected as the maximum voltage phase and Idc2 is detected as the minimum voltage phase. The detected Idc1 and Idc2 are distributed to the current of each phase in a pattern as shown in FIG. For example, in the section A0, Idc2 is assigned to the U-phase current and Idc1 is assigned to the V-phase current on the uphill of the PWM carrier wave, and Idc1 is assigned to the U-phase current and Idc2 is assigned to the minimum-phase current on the downhill of the PWM carrier wave. . The W-phase current, which is an intermediate phase voltage, is obtained by Idc1−Idc2 according to Kirchhoff's law. The current detection method and the current reproduction method are effective for both 120-degree conduction and 180-degree conduction.

  The controller 3 receives the inverter DC current Idc detected using the shunt resistor 4 as an input, and performs a 120-degree conduction method or a 180-degree conduction method according to these inputs, thereby switching each switching element of the inverter 1. Drive.

[120 degree conduction]
FIG. 3 is a schematic diagram relating to the switching system at the time of 120 ° conduction in the first embodiment. In the 120-degree conduction control method, a switching operation is performed on two phases of the three-phase upper and lower arms of the inverter 1. Since the switching is performed for a period of 120 degrees during a phase of 180 degrees in electrical angle, it is called a 120-degree conduction control method.

  There are several switching methods, and for example, any one of the methods shown in FIG. 3 may be used. FIG. 4 conceptually shows gate signals of the upper and lower arms in one cycle of the electrical angle. In the figure, Gp indicates an upper arm gate signal, and Gn indicates a lower arm gate signal. These upper and lower arm drive signals are output from the controller 3 to the inverter 1.

  When driving the motor 2 by the 120-degree conduction method, two phases to be supplied are selected from the three-phase windings of the motor 2 and a pulse voltage is applied to generate a torque. There are six possible combinations of two phases to be energized, each of which is defined as energization mode 1 to energization mode 6.

[Relationship between rotor position and current]
FIG. 4 is an example of the motor operation state at the time of 120-degree energization according to the first embodiment. The current Iu flowing in the U-phase winding of the motor when the rotation angle position of the rotor is changed by one electrical angle is the magnitude in the energization mode 1, the U-phase motor terminal voltage is Vu, the U-phase induced voltage Can be expressed by Equation 1 where Eu, the resistance and inductance of the U-phase and V-phase windings are respectively Ru, Rv, Lu, Lv, and the motor rotational angular velocity is ω.
Iu = (Vu−Eu) / (Ru + Rv + ω (Lu + Lv)) (1)
From Equation 1, since the motor induced voltage Eu changes on a sine wave depending on the rotation angle with respect to the U-phase terminal voltage Vu, the U-phase winding current Iu changes.

  FIG. 5 is an example of the energized phase switching method at the time of 120-degree energization according to the first embodiment. In FIG. 5, the solid line indicates the U-phase coil current, and the dotted line indicates the U-phase induced voltage. The same can be said for the V and W phases. The current flowing in each phase of the motor 2 increases and decreases due to the potential difference between the output voltage of the inverter 1 and the induced voltage generated in the coil in the motor 2 when the motor 2 rotates. Therefore, as the motor induced voltage approaches the maximum point, the potential difference between the inverter output voltage and the induced voltage decreases, and the motor current decreases. When the motor induced voltage passes through the maximum point, the motor induced voltage goes to the minimum point, so the potential difference between the inverter output voltage and the induced voltage increases, and the motor current increases. For example, the U-phase induced voltage becomes maximum and the U-phase winding current becomes minimal at a point at a rotation angle of 270 degrees from a state in which energization is started in energization mode 1 started at a rotation angle of 210 degrees. Thereafter, the U-phase induced voltage decreases and the U-phase winding current tends to increase. Thus, it can be seen that the current value of the U-phase winding changes depending on the rotation angle position.

[How to switch the energized phase]
In order to perform the 120-degree energization method, it is necessary to sequentially switch the energization phase according to the rotational angle position of the rotor. In the present embodiment, as shown in FIG. 5, the energized phase before switching (for example, in mode 2, U-phase upper arm switched at the end of mode 2; in mode 5, U-phase lower arm switched at the end of mode 5) Observe the winding current of the arm.). In the modes 2 and 5, the U-phase current is observed, and the description will be given with reference to FIG. As shown in FIG. 5, the energized phase switching thresholds A and B are set on the + and-sides, respectively, of the observed current, and the energized phase is switched when the observed current exceeds each threshold. As the thresholds A and B, values that do not cause overcurrent are set in advance through tests.

  As shown in FIG. 6, for each energization mode, the phase switched at the end of the mode is the maximum phase (maximum phase) and the minimum phase (minimum phase) of the motor current. For example, in the mode 2 in which the U + phase is switched, the U-phase current goes to the maximum value. Therefore, the threshold value A, which is the threshold value of the U-phase current positive value, is set in advance and compared. Further, in the mode 5 in which the U-phase is switched, the U-phase current goes to the minimum value. Therefore, the threshold value B which is the threshold value of the U-phase current negative value is set in advance and compared. In this way, the phase in which the absolute value of the current tends to increase in each energization mode is determined. FIG. 6 shows a switching operation when the V phase and the W phase are also considered. The thresholds for the V-phase and W-phase currents are thresholds C, D, E, and F, respectively. As shown in FIG. 7, the three-phase winding currents are compared with the thresholds according to each energization mode, and the energization phase can be sequentially switched. I just need.

  As described above, according to the present embodiment, mode switching can be performed by comparing the threshold value and the current value of the energized phase, and thus mode switching can be performed with a small amount of calculation.

  FIG. 8 shows an example of a drive circuit when three shunt resistors 5, 6, and 7 for detecting a current are used. Shunt resistors 5 to 7 are arranged on the lower arm side of U, V and W of inverter 1. By using Idc detected from the shunt resistors 5 to 7 as an input of the arithmetic unit and an input of the current reproducer 6, it is possible to reproduce a winding current equivalent to that of a single shunt resistor. According to the present embodiment, since the current value of each phase can be acquired with higher accuracy, the switching timing can be determined more accurately.

  Since the amplitude of the winding current changes due to the influence of the load torque applied to the motor, the threshold values AF are affected by the load torque. FIG. 9 shows an example of the motor current waveform when the load torque changes. When the load torque increases, the current required to drive the motor increases, and the winding current amplitude increases. In order to cope with the change in the winding current amplitude due to the change in the load torque, the energized phase switching thresholds A and B are changed according to the load torque.

  FIG. 10 shows a conduction phase switching pattern corresponding to a change in load torque. In the figure, the absolute values of A to F are smaller than the absolute values of A 'to F'. When the load torque is small, a comparison with the winding current is performed by a determination formula using the thresholds A to F, and when the load torque is large, a comparison with the winding current is performed by the determination formula using the thresholds A ′ to F ′, and the energized phase is switched. I do. Which of A to F and A 'to F' to use can be determined, for example, as follows.

FIG. 11 shows a method for determining the load torque. When the value of the difference A or B between the actual rotation frequency and the command rotation frequency estimated inside the microcomputer exceeds a preset load torque determination threshold value, the energized phase switching threshold value is changed to a load torque large threshold value A ′. To F '. Further, when the value of the difference A or the difference B between the actual rotation frequency and the command rotation frequency falls below a preset threshold value for load torque determination, the threshold value for switching the energized phase is switched to threshold values A to F for small load torque. .
The motor control device according to the present embodiment can be applied to a rotary motor and various devices including the rotary motor.

[effect]
According to the present embodiment, since control can be performed using the shunt resistor 4 in both the 180-degree conduction method and the 120-degree conduction method, the necessity of a voltage dividing resistor and the like used for measuring the open-phase voltage is reduced. Can be reduced. Further, since the comparison between the threshold value and the current value may be performed, the calculation amount can be reduced.

1 ... Inverter 2 ... Motor 3 ... Controller 4 ... Shunt resistor (one or three may be used, and the current value of each of the three-phase coils can be obtained)

Claims (5)

A power conversion unit having upper and lower arms of U, V, and W phases;
U, V, W phase coils receiving the output of the power converter;
A rotor that rotates by receiving a magnetic flux from each of the coils;
A control unit;
A current detection unit capable of acquiring a current value flowing through each of the coils,
Switching the on / off combination of the upper and lower arms corresponding to each of the six modes of the 120-degree conduction method,
The motor control device, wherein the control unit switches the mode using a current value obtained by the current detection unit.   The motor control device according to claim 1, wherein the current detection unit includes three resistance elements provided on a DC side of the power conversion unit.   The control unit acquires and monitors the current value of the phase to which the arm to be switched at the end of the mode belongs to at least one of the six modes of the 120-degree conduction method, and the absolute value of the current value of the phase has exceeded the threshold value. 3. The motor control device according to claim 1, wherein switching of the mode is performed in such a case.   4. The motor control device according to claim 3, wherein the control unit acquires a load torque of a motor to be controlled, and increases the absolute value of the threshold according to the increase in the load torque. 5. A power conversion unit having upper and lower arms of U, V, and W phases;
U, V, W phase coils receiving the output of the power converter;
A rotor that rotates by receiving a magnetic flux from each of the coils;
A current detection unit capable of acquiring a current value flowing through each of the coils,
A motor control method for switching a combination of on and off of the upper and lower arms corresponding to each of six modes of a 120-degree energization method,
Switching the mode using a current value of the current detection unit.

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