JP2022190437A - Motor drive method and motor drive device - Google Patents

Abstract

To provide a motor drive method capable of detecting the position of a rotor.SOLUTION: A motor drive method includes: a q-axis current command value acquisition step of driving an AC motor by controlling current flowing through a coil provided in a stator of the AC motor on the basis of an orthogonal vector coordinate system of a d-axis in a direction of a field magnetic flux generated by a permanent magnet provided in a rotor of the AC motor and a q-axis orthogonal to the d-axis and acquiring a current command value of q-axis current that is a current component in a q-axis direction as a q-axis current command value; a coil current detection step of detecting current flowing through the coil as coil current by an energization instruction based on the q-axis current command value; a drive current operation step of operating drive current on the q-axis on the basis of a result of detection of the coil current as q-axis drive current; a difference calculation step of calculating the difference between the q-axis current command value and the q-axis drive current; and an estimation step of estimating the position of the rotor on the basis of the difference.SELECTED DRAWING: Figure 2

Description

The present invention relates to a motor driving method and a motor driving device for driving an AC motor.

Conventionally, AC motors are used. As a method of driving such an AC motor, there is a method of driving by controlling the current flowing through the coils provided in the stator. In order to control the current flowing through such coils, it is desired to appropriately grasp the position of the rotor of the AC motor. Therefore, techniques for driving an AC motor while detecting the position of the rotor have been studied (for example, Patent Document 1).

Patent Literature 1 describes a motor drive system. This motor drive system is provided with a motor having a rotor, and the rotor of this motor is provided with permanent magnets for generating torque and permanent magnets for position detection. A motor drive system detects the position (angle) of a rotor by using changes in the magnetic field of a permanent magnet for position detection caused by the rotation of the rotor.

JP 2014-103809 A

In the technique described in Patent Document 1, as described above, the permanent magnet for torque generation and the permanent magnet for position detection are separately provided. For this reason, it becomes a factor of an increase in cost. It is also conceivable to detect the position of the rotor based on the back electromotive force caused by the current flowing through the coil without providing a permanent magnet for position detection. is difficult to detect.

Therefore, there is a demand for a low-cost technology that can detect the position of the rotor even when the rotor rotates at a low speed.

A characteristic configuration of the motor driving method according to the present invention is that the d-axis, which is the direction of the field magnetic flux generated by the permanent magnet provided in the rotor of the AC motor, and the q-axis, which is orthogonal to the d-axis, are arranged in an orthogonal vector coordinate system. A motor driving method for controlling a current flowing in a coil provided in a stator of the AC motor to drive the AC motor, wherein the current command value of the q-axis current, which is the current component in the q-axis direction, is set to a q-axis current command value acquisition step for acquiring a q-axis current command value; a coil current detection step for detecting a current flowing through the coil as a coil current in response to an energization instruction based on the q-axis current command value; a drive current calculation step of calculating the drive current on the q-axis as the q-axis drive current based on the detection result; a difference calculation step of calculating a difference between the q-axis current command value and the q-axis drive current; and an estimating step of estimating the position of the rotor based on the difference.

With such a characteristic configuration, the q-axis drive current calculated based on the detection result of the coil current includes pulsation caused by the cogging torque generated between the permanent magnet and the coil. Rotor position can be estimated based on torque-induced pulsations. Moreover, there is no need to provide a dedicated permanent magnet for detecting the position of the rotor, and a permanent magnet for rotating the rotor can also be used. Therefore, it is possible to detect the position of the rotor at low cost and even if the rotational speed of the rotor is low.

In the coil current detection step, it is preferable to perform detection in a state in which field strengthening control is performed by applying a current to the coil according to an energization instruction based on a current command value of the d-axis current, which is the current component in the d-axis direction. is.

With such a configuration, the field magnetic flux of the permanent magnet can apparently be increased by supplying the d-axis current. Therefore, it becomes possible to amplify the cogging torque and make it easier to detect the pulsation.

Further, a rotational speed estimation step of estimating the rotational speed of the rotor based on the estimated position of the rotor is preferably provided, and the current command value of the d-axis current preferably increases as the rotational speed increases. is.

With such a configuration, the cogging torque caused by the d-axis current can be increased even when the rotational speed increases. Therefore, even when the rotational speed increases, it is possible to appropriately estimate the position of the rotor.

Further, the estimation of the position of the rotor in the estimation step drives the AC motor based on the orthogonal vector coordinate system without performing estimation based on the difference between the q-axis current command value and the q-axis drive current. In this case, it is preferable that the detection is performed in a low speed region in which the rotor position cannot be detected.

With such a configuration, the position of the rotor can be estimated even when the rotational speed is extremely low.

A motor driving device according to the present invention is characterized in that the AC motor is driven using any one of the motor driving methods described above.

Even with such a characteristic configuration, it is possible to realize an AC motor that exhibits the effects described above.

1 is a block diagram showing the configuration of a motor drive device that drives an AC motor; FIG. 4 is an example of a current waveform used for estimating the control state of the AC motor, the behavior of the rotor, and the position of the rotor when the AC motor is started.

A motor driving method according to the present invention is configured to estimate the position of a rotor of an AC motor. The motor driving method of this embodiment will be described below.

FIG. 1 shows a block diagram of a motor driving device 1 that drives an AC motor M according to the motor driving method of this embodiment. A motor driving device 1 drives an AC motor M by controlling an inverter 10 interposed between a three-phase AC motor M and a power source V. FIG. The motor driving device 1 is based on an orthogonal vector coordinate system of the d-axis, which is the direction of the field magnetic flux generated by the permanent magnet provided in the rotor of the AC motor M, and the q-axis, which is orthogonal to the d-axis. The AC motor M is driven by controlling the current flowing through the coils provided in the M stator. In order to perform control (vector control) based on such an orthogonal vector coordinate system, the motor drive device 1 includes a target current setting section 21, a current control section 22, a PWM control section 20, a current detection section 23, a conversion 24 and a rotational state calculation unit 25. Each functional unit is constructed of hardware and/or software with a CPU as a core member in order to perform processing related to rotor position estimation. there is The motor drive device 1 performs PWM control of a high-side switching element QH and a low-side switching element QL of an inverter 10, which will be described later, based on a target torque and rotation speed for the AC motor M, thereby supplying a three-phase AC power to the AC motor M. Provides drive current. As a result, the AC motor M is powered according to the rotation speed and the target torque.

The inverter 10 includes a high-side switching element QH and a high-side switching element QH connected in series between the first power supply line 2 and the second power supply line 3 connected to a potential lower than the potential of the first power supply line 2. 3 sets of arm portions A each having a low-side switching element QL. The first power supply line 2 is a cable connected to the power supply V. As shown in FIG. The second power supply line 3 connected to a potential lower than the potential of the first power supply line 2 is a cable to which a potential lower than the output voltage of the power supply V is applied. It is connected to the other terminal of resistor R which is grounded.

In this embodiment, the high-side switching element QH is constructed using a P-MOSFET, and the low-side switching element QL is constructed using an N-MOSFET. The high-side switching element QH has a source terminal connected to the first power supply line 2 and a drain terminal connected to the drain terminal of the low-side switching element QL. A source terminal of the low-side switching element QL is connected to the second power supply line 3 . The high-side switching element QH and the low-side switching element QL connected in this manner form an arm portion A, and the inverter 10 includes three sets of the arm portions A. As shown in FIG. Gate terminals of the high side switching element QH and the low side switching element QL are connected to the driver 15 . Also, the drain terminal of the high-side switching element QH of each arm portion A is connected to three terminals of the AC motor M, respectively.

The PWM control unit 20 generates a PWM signal and PWM-controls the high-side switching element QH and the low-side switching element QL of the inverter 10 . Specifically, the PWM control unit 20 is different from the high-side switching element QH included in a predetermined first arm portion among the three arm portions A and the first arm portion in the three arm portions A. The low-side switching element QL of the second arm of the other two sets of arms is closed, and current flows between two of the three terminals of the AC motor M by PWM control.

For ease of understanding, if the three sets of arm portions A are respectively referred to as a first arm portion A1, a second arm portion A2, and a third arm portion A3, the above "out of the three sets of arm portions A A high-side switching element QH included in a predetermined first arm portion, and a low-side switching element QL included in a second arm portion among the other two sets of arm portions different from the first arm portion in the three sets of arm portions A. ” is, for example, the high side switching element QH of the first arm portion A1 and the low side switching element QL of one of the second arm portion A2 and the third arm portion A3. Therefore, when the high-side switching element QH and the low-side switching element QL are closed at the same time, the switching element is such that a so-called through current does not flow from the first power supply line 2 to the second power supply line 3. is closed.

The three terminals that AC motor M has are a U-phase terminal, a V-phase terminal, and a W-phase terminal that AC motor M has. For example, when the high-side switching element QH of the first arm portion A1 and the low-side switching element QL of the second arm portion A2 are closed, a current is generated from the U-phase terminal of the AC motor M to the V-phase terminal by PWM control. flows. Further, for example, when the high-side switching element QH of the second arm portion A2 and the low-side switching element QL of the first arm portion A1 are closed, the PWM control is performed from the V-phase terminal of the AC motor M to the U-phase terminal. current flows.

When driving the AC motor M, the PWM control unit 20 sequentially switches the coils (not shown) of the AC motor M to supply current. Therefore, while the AC motor M is being driven, two of the three terminals of the AC motor M are sequentially switched to flow a current. In the present embodiment, a state in which the PWM control unit 20 energizes a current having a preset current value while sequentially switching between two terminals is referred to as a "three-phase energized state." On the other hand, a state in which the PWM control unit 20 supplies a current having a preset current value only between two terminals for a predetermined time is called a "single-phase conduction state."

For example, it is possible to input the PWM signal output from the PWM control unit 20 to the driver 15 so that the driver 15 improves the drive capability of the PWM signal and inputs it to the inverter 10 .

In vector control, the motor current flowing in each of the three phases of the stator coils of the AC motor M is controlled by the vector of the d-axis, which is the direction of the magnetic field generated by the permanent magnets arranged on the rotor, and the q-axis, which is orthogonal to the d-axis. Feedback control is performed by transforming coordinates into components. A target current setting unit 21 sets target currents for the d-axis and the q-axis for driving the AC motor M based on the rotation speed and the target torque of the AC motor M. FIG. The target current setting unit 21 acquires target torque information indicating the target torque required for the AC motor M from the host system, and based on the target torque based on this target torque information and the rotation state such as the rotation speed of the AC motor M to calculate the target current value. The rotation state of the AC motor M is calculated by the rotation state calculator 25 .

The rotation state calculation unit 25 detects the position of the rotor of the AC motor M based on the motor current flowing through the AC motor M. As shown in FIG. In this embodiment, as shown in FIG. 1, a resistor R is provided between the second power supply line 3 to which the source terminal of the low-side switching element QL of each arm portion A is connected and the ground potential. The rotational state calculator 25 detects the motor current based on the potential across the terminals of the resistor R, and detects (calculates) the position of the rotor. Since detection of the position of the rotor is known, the description thereof will be omitted.

The current control unit 22 calculates drive currents on the d-axis and q-axis by current control using proportional control (P control), proportional integral control (PI control), etc. and the drive voltage on the q-axis. The current control unit 22 calculates drive currents on the d-axis and the q-axis based on the target currents on the d-axis and the q-axis set by the target current setting unit 21 and the two-phase currents fed back. The two-phase current to be fed back is obtained by converting the detection result of the three-phase current flowing in the stator coil detected by the current detection unit 23 into two-phase current of the d-axis and the q-axis by the conversion unit 24 . After calculating the drive current, the current control unit 22 substitutes the determined value of the drive current into the voltage equation and calculates the d-axis voltage and the q-axis voltage, which are two-phase drive voltages.

The PWM control unit 20 converts the two-phase drive voltage determined by the current control unit 22 into a three-phase drive voltage that is a drive voltage for causing a drive current to flow through the three-phase stator coil, and performs the three-phase drive. A drive signal for driving and controlling the inverter 10 is generated based on the voltage. DC power is supplied to the inverter 10 from the power source V, and switching of the switching elements QH and QL of the inverter 10 is controlled by the PWM control unit 20 to convert the output of the power source V into AC power, which is supplied to the AC motor M. be.

According to the motor drive device 1, the current flowing through the three-phase coils of the AC motor M is detected in this way, and the detected current is fed back to perform vector control of the AC motor M. FIG.

Here, as described above, the motor drive device 1 sets the target current value based on the position of the rotor when driving the AC motor M by vector control. Such detection of the rotor position is not easy when the rotation speed of the rotor is extremely low, such as immediately after the AC motor M is started. Therefore, the motor driving device 1 is configured so that when the AC motor M is driven based on the orthogonal vector coordinate system, the rotor position can be estimated appropriately even in a low-speed region in which the rotor position cannot be detected. be done.

Cogging torque generated between the permanent magnets of the rotor and the coils of the stator is used to estimate the position of the rotor when the rotation speed of the AC motor M is in the low speed region. First, the current control unit 22 acquires the current command value of the q-axis current, which is the current component in the q-axis direction, as the q-axis current command value. As described above, the drive currents on the d-axis and q-axis are calculated by the current controller 22 . Therefore, the current control unit 22 calculates and acquires the drive current on the q-axis as the q-axis current command value. The step of obtaining the current command value of the q-axis current, which is the current component in the q-axis direction, as the q-axis current command value is called the q-axis current command value obtaining step in the motor driving method.

Based on this q-axis current command value, the PWM control unit 20 drives the inverter 10 and current flows through the coils of the AC motor M. FIG. The current detection unit 23 detects the current flowing through the coil as a coil current in response to an energization instruction based on the q-axis current command value. As described above, the resistor R is provided between the ground potential and the second power supply line 3 to which the source terminal of the low-side switching element QL of each arm portion A is connected. A coil current is detected based on the potential across terminals of R. The step of detecting the current flowing through the coil as the coil current in accordance with the energization instruction based on the q-axis current command value is called a coil current detection step in the motor driving method.

Based on the detection result of the coil current detected in the coil current detection step, the conversion unit 24 calculates the drive current on the q-axis as the q-axis drive current. The step of calculating the drive current on the q-axis as the q-axis drive current based on the detection result of the coil current is called a drive current calculation step in the motor drive method.

The rotational state calculator 25 calculates the difference between the q-axis current command value and the q-axis drive current. The q-axis current command value is acquired from the current control section 22 and the q-axis drive current is acquired from the conversion section 24 . Therefore, the rotational state calculator 25 calculates the difference between the q-axis current command value obtained from the current controller 22 and the q-axis drive current obtained from the converter 24 . Since the q-axis current command value is a theoretical indicated value, the current waveform does not include pulsation caused by, for example, cogging torque. On the other hand, since the q-axis drive current is actually measured while the AC motor M is actually rotating, the current waveform includes pulsation caused by cogging torque. Therefore, the difference between the q-axis current command value and the q-axis drive current includes pulsation caused by cogging torque. The step of calculating the difference between the q-axis current command value and the q-axis drive current is called a difference calculation step in the motor driving method.

Next, the rotational state calculator 25 estimates the position of the rotor based on the difference. As described above, the difference between the q-axis current command value and the q-axis drive current includes pulsation caused by cogging torque. The rotational state calculator 25 estimates the position of the rotor based on such a pulsation period. The process of estimating the position of the rotor based on such differences is called the estimation step in the motor drive method.

Here, in the coil current detection step, it is preferable to perform detection in a state in which field intensifying control is performed by applying a current to the coil according to an energization instruction based on a current command value of the d-axis current, which is a current component in the d-axis direction. . As a result, by passing a d-axis current in the same direction as the field magnetic flux generated by the permanent magnet, the cogging torque that strengthens the field magnetic flux from the permanent magnet can be emphasized. Therefore, it is possible to more easily estimate the position of the rotor.

Further, the rotational state calculator 25 can also estimate the rotation speed of the rotor based on the estimated position of the rotor. As described above, the position of the rotor is estimated based on the period of pulsation caused by the cogging torque, and it is possible to estimate the rotation speed of the rotor based on the change in the period of this pulsation. At this time, it is preferable to increase the current command value of the d-axis current in the coil current detection step as the rotational speed increases. The step of estimating the rotation speed of the rotor based on the estimated rotor position is called a rotation speed estimation step in the motor driving method.

Next, a method of driving the motor will be described using behavior of the rotor and current waveforms. FIG. 2A shows the control state when the AC motor M is started, and FIG. 2B shows the behavior of the rotor. (C) shows the current waveform and the difference when the AC motor M is started. In addition, in order to facilitate understanding, one permanent magnet is illustrated as the rotor in (B), but a plurality of permanent magnets may be provided.

Before the AC motor M is started (#1), the state of the rotor is illustrated in (B), but the actual position of the rotor is unknown. Therefore, the motor drive device 1 energizes the U-phase coil (one-phase energization) so that the N pole of the permanent magnet faces the U-phase coil (#2). At this time, as shown in (C), along with energization based on the d-axis current command, energization based on the q current command value is also performed. Such energization of the U-phase coil for making the N pole of the permanent magnet face the U-phase coil is called U-phase alignment. As a result, the N pole of the permanent magnet faces the U-phase coil, as indicated by #2 in (B).

In this state, the motor driving device 1 applies the d-axis current to the coil as described above (#3). At this time, as shown in (C), the q-axis current is stopped. In (B), the magnetic field generated in the coil by energization of the d-axis current is indicated by the white arrow. Since the direction of the magnetic field generated by the coil due to this d-axis current application coincides with the direction of the magnetic field of the N pole, the magnetic field of the N pole is strengthened. Then, a q-axis current is applied to the coil, and the difference between the q-axis current command value and the q-axis drive current is calculated (#4). The position of the rotor is estimated based on the calculated difference between the q-axis currents. #4 in (C) shows the difference between the q-axis current command value and the q-axis drive current. This difference includes pulsation synchronized with the cogging torque period, that is, pulsation (waveform) with a period corresponding to the position of the permanent magnet. Therefore, it is possible to estimate the position (angle) and rotation speed of the rotor based on the period of this pulsation. Since the period of such pulsation corresponds to the number of permanent magnets and coils (least common multiple), it can be easily estimated based on the number of permanent magnets and coils.

When the AC motor M is started, the rotor position is estimated by the above-described estimation step without performing estimation based on the difference between the q-axis current command value and the q-axis drive current. When driven based on the vector coordinate system, it is difficult to detect the position of the rotor. Therefore, the rotor position is estimated by the estimation step when the AC motor M is driven based on the orthogonal vector coordinate system without performing estimation based on the difference between the q-axis current command value and the q-axis drive current. It is preferable to perform this operation in a low speed region where the rotor position cannot be detected.

[Other embodiments]
In the above embodiment, the coil current detection step is described as detecting in a state in which field intensifying control is performed by applying a current to the coil according to an energization instruction based on the current command value of the d-axis current, which is the current component in the d-axis direction. However, it is also possible to detect the coil current without performing field-strengthening control in the coil current detection step.

In the above embodiment, the rotation speed estimation step of estimating the rotation speed of the rotor based on the estimated position of the rotor is provided, but it is also possible to configure so as not to estimate the rotation speed. Further, although it has been described that the current command value of the d-axis current increases as the rotation speed increases, the current command value of the d-axis current can be configured regardless of the rotation speed.

In the above embodiment, the rotor position is estimated by the estimation step when the AC motor M is driven based on the orthogonal vector coordinate system without performing estimation based on the difference between the q-axis current command value and the q-axis drive current. , described as being performed in a low-speed region where the rotor position cannot be detected, but the estimation of the rotor position by the estimation step can be performed in a state different from the low-speed region. .

In the above embodiment, FIG. 1 shows the functional units of the motor drive device 1 and the functions of the respective functional units have been described, but the configuration and functions of the functional units can be changed as appropriate.

INDUSTRIAL APPLICABILITY The present invention can be used for a motor driving method and a motor driving device for driving an AC motor.

M: AC motor 1: Motor drive device

Claims (5)

Based on the orthogonal vector coordinate system of the d-axis, which is the direction of the field magnetic flux generated by the permanent magnet provided in the rotor of the AC motor, and the q-axis, which is orthogonal to the d-axis, the stator of the AC motor A motor driving method for driving the AC motor by controlling current flowing through a coil,
a q-axis current command value acquiring step of acquiring a current command value of the q-axis current, which is the current component in the q-axis direction, as a q-axis current command value;
a coil current detection step of detecting the current flowing through the coil as a coil current in accordance with the energization instruction based on the q-axis current command value;
a drive current calculation step of calculating the drive current on the q-axis as the q-axis drive current based on the detection result of the coil current;
a difference calculation step of calculating a difference between the q-axis current command value and the q-axis drive current;
an estimating step of estimating the position of the rotor based on the difference;
A motor driving method comprising: 2. The coil current detecting step further detects the coil current in a state in which a strong field control is performed by applying a current to the coil according to an energization instruction based on a current command value of the d-axis current, which is the current component in the d-axis direction. The motor driving method described in . further comprising a rotational speed estimation step of estimating the rotational speed of the rotor based on the estimated position of the rotor;
3. The motor driving method according to claim 2, wherein the current command value of the d-axis current increases as the rotation speed increases. When the position of the rotor is estimated by the estimation step, the AC motor is driven based on the orthogonal vector coordinate system without performing estimation based on the difference between the q-axis current command value and the q-axis drive current. 4. The motor driving method according to any one of claims 1 to 3, wherein the rotor is rotated at a rotational speed at which the position of the rotor cannot be detected. A motor driving device that drives the AC motor using the motor driving method according to any one of claims 1 to 4.

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