JP4016835B2 - Motor control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a motor control device for controlling an electric motor.
[0002]
[Prior art]
For example, in a power steering device that assists the operation of a steering wheel by supplying hydraulic oil from an oil pump to a power cylinder coupled to a steering mechanism, a three-phase brushless motor is used as a drive source of the oil pump. The driving power supplied to the three-phase brushless motor is controlled so that the three-phase brushless motor is rotated at a target rotational speed corresponding to the steering angular speed of the steering wheel.
[0003]
As a driving method for a three-phase brushless motor, a 120-degree energization method and a 180-degree energization method are generally known. In a power steering device, a large rotational speed is required for a three-phase brushless motor even though the on-board battery, which is a constant voltage generation source, is used as a power source. The 180 degree energization method is adopted. However, depending on the rotational speed of the three-phase brushless motor, the 120-degree energization method may be more efficient than the 180-degree energization method, and it can be said that driving with the 180-degree energization method alone is optimal in terms of efficiency. Absent.
[0004]
Therefore, it is conceivable to switch the driving method of the three-phase brushless motor between the 120-degree energization method and the 180-degree energization method according to the target rotation speed of the three-phase brushless motor. For example, in a state where the rotational speed of a three-phase brushless motor driven by a 120-degree energization method is saturated, in response to the setting of a target rotational speed larger than the saturated rotational speed, the driving method of the three-phase brushless motor is changed. Switch from the 120 degree energization method to the 180 degree energization method. As a result, the three-phase brushless motor can be driven with high efficiency by the 120-degree energization method in the low and medium-speed rotation range of the three-phase brushless motor. This can be achieved by driving a three-phase brushless motor in an energized manner.
[0005]
[Patent Document 1]
JP-A-2001-352777 [0006]
[Problems to be solved by the invention]
However, when the drive method of the three-phase brushless motor is switched from the 120-degree energization method to the 180-degree energization method, the motor rotation speed changes abruptly at that moment, so the peak current due to the energy that increases the motor rotation speed is three-phase. Since the three-phase brushless motor suddenly accelerates due to this peak current flowing through the brushless motor, there is a problem that mechanical impact is applied to the steering mechanism.
[0007]
SUMMARY OF THE INVENTION An object of the present invention is to provide a motor control device that can prevent a sudden change in the rotational speed of an electric motor when switching from a 120-degree energization method to a 180-degree energization method.
[0008]
[Means for Solving the Problems and Effects of the Invention]
In order to achieve the above-mentioned object, the invention according to claim 1 is a motor control for rotating the electric motor at a target rotational speed by PWM controlling the supply of the drive current from the drive circuit (2) to the electric motor (1). The driving method switching means (35) for switching the driving method of the electric motor from the 120-degree energization method to the 180-degree energization method, and when driving the electric motor in the 120-degree energization method, according to the target rotational speed, 120 degree energization duty setting means (33) for setting the duty of the PWM pulse signal to be given to the drive circuit during the 120 degree energization period, and the 180 degree energization period when the electric motor is driven in the 180 degree energization method, Dividing into a middle period and a later period, and setting the duty of the PWM pulse signal to be given to the drive circuit in each period based on the target rotational speed And setting means (34), seen including a rotational speed calculating means (32) for calculating the rotational speed of the electric motor, the 180 ° conduction when the duty setting means is computed as the target rotational speed by the rotational speed calculating means A medium period duty that performs a PI control calculation based on the deviation from the rotation speed, obtains a control voltage value to be applied to the electric motor, and sets a duty corresponding to the control voltage value as a duty of the PWM pulse signal in the middle period After the drive method of the electric motor is switched from the 120-degree energization method to the 180-degree energization method by the setting means (341) and the drive method switching means, the duty of the PWM pulse signal in the previous period and the subsequent period is changed to the intermediate period. From the value smaller than the duty set by the duty setting means, the intermediate period duty setting means A motor control device, wherein the front and rear set to gradually increase until set duty period is intended to include a duty setting means (342, 343).
[0009]
In addition, the alphanumeric characters in parentheses represent corresponding components in the embodiments described later. The same applies hereinafter.
According to the above configuration, for example, in the low-medium speed rotation range of the electric motor, the electric motor can be driven with high efficiency by the 120-degree energization method. This can be achieved by driving the electric motor by the 180-degree energization method.
[0010]
Further, when the electric motor is driven by the 180-degree energization method, the 180-degree energization period is divided into a previous period, a middle period, and a later period, and the duty of the PWM pulse signal to be given to the drive circuit (PWM duty) in each period Set individually. For example, immediately after the drive method of the electric motor is switched from the 120-degree energization method to the 180-degree energization method, the PWM duty in the previous period and the subsequent period is set to be smaller than the PWM duty in the middle period, and then the drive of the electric motor is performed. If the PWM duty in the previous period and the subsequent period is gradually increased as the control proceeds, the generation of peak current at the time of switching from the 120-degree energization method to the 180-degree energization method can be suppressed. Can prevent overcurrent destruction of the switching elements (UH, UL, VH, VL, WH, WL) in the drive circuit. In addition, it is possible to prevent a sudden change in the rotation speed of the electric motor due to the peak current, and it is possible to prevent the occurrence of a mechanical shock due to a sudden change in the rotation speed of the electric motor.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a diagram showing a configuration of a motor control device according to an embodiment of the present invention. This motor control device targets an electric motor 1 composed of a three-phase brushless motor, and includes a drive circuit 2 that generates drive power for the electric motor 1 and a control unit 3 that controls the drive circuit 2. And.
[0013]
In the electric motor 1, a stator having a U-phase field coil 11U, a V-phase field coil 11V, and a W-phase field coil 11W, and a permanent magnet that receives a repulsive magnetic field from these field coils 11U, 11V, and 11W are fixed. And the rotational position of the rotor is detected by the rotational position sensor 12. The rotational position sensor 12 can detect the rotational position of the rotor with a resolution of 30 deg / 360 deg (= 1/12) or more, and the detection signal is input to the control unit 3.
[0014]
The drive circuit 2 is a three-phase bridge inverter circuit, and a series circuit of a pair of field effect transistors UH and UL corresponding to the U phase of the electric motor 1 and a series of a pair of field effect transistors VH and VL corresponding to the V phase. A circuit and a series circuit WH and WL of a pair of field effect transistors corresponding to the W phase are connected in parallel between the DC power supply 4 and the ground 5. The U-phase field coil 11U of the electric motor 1 is connected to a connection point between the field effect transistors UH and UL, and the V-phase field coil 11V is connected to a connection point between the field effect transistors VH and VL. The W-phase field coil 11W is connected to a connection point between the series circuits WH and WL of the field effect transistor.
[0015]
The control unit 3 includes a microcomputer, and is based on a target rotation speed setting unit 31 that sets a target rotation speed of the electric motor 1 and a detection signal of the rotation position sensor 12 by program processing executed by the microcomputer. A rotation speed calculation unit 32 for calculating the rotation speed of the electric motor 1, a 120-degree energization calculation unit 33 for performing calculations necessary for driving the electric motor 1 by a 120-degree energization method, and a 180-degree energization method for the electric motor 1. 180-degree energization calculation section 34 for performing calculations necessary for driving at a drive system, drive system switching section 35 for switching the drive system of the electric motor 1 between a 120-degree energization system and a 180-degree energization system, and a 120-degree energization calculation section 33 or Based on the calculation result of the 180-degree conduction calculation unit 34, the field effect transistor UH of the drive circuit 2 is used to achieve the target rotation speed. UL, realized VH, VL, WH, the functions of the drive signal generator 36 for generating a drive signal to be applied to WL.
[0016]
When this motor control device is used to control an electric motor (an electric motor for driving an oil pump or an electric motor as a source of steering assist force) provided in the power steering device, it is included in the control unit 3 The microcomputer may be a microcomputer provided in an electronic control unit (ECU), and the target rotational speed setting unit 31 is based on the steering angular speed and the vehicle speed of the steering wheel. A rotational speed may be set.
[0017]
The drive signal generation unit 36 gives, for example, a signal to turn on the electric field effect transistors UH, VH, and WH of the drive circuit 2 sequentially in a period corresponding to 120 degrees or 180 degrees in electrical angle. A drive signal composed of a PWM (Pulse Width Modulation) pulse is applied to the effect transistors UL, VL, WL.
When the electric motor 1 is driven by the 120-degree energization method, the duty of the PWM pulse signal (PWM duty) given from the drive signal generator 36 to the field effect transistors UL, VL, WL is calculated by the 120-degree energization calculator 33. The That is, the 120-degree energization calculation unit 33 includes a duty setting unit 331 that sets a PWM duty according to the target rotation speed set by the target rotation speed setting unit 31 when the electric motor 1 is driven by the 120-degree energization method. Yes. The duty setting unit 331 performs PI (Proportional-Integral) control calculation based on the deviation between the target rotation speed set by the target rotation speed setting unit 31 and the rotation speed calculated by the rotation speed calculation unit 32, A control voltage value to be applied to the electric motor 1 is obtained, and a PWM duty corresponding to the control voltage value is set.
[0018]
As long as the 120-degree energization calculation unit 33 sets a PWM duty of less than 100%, the PWM duty set by the 120-degree energization calculation unit 33 is given to the drive signal generation unit 36. Then, the drive signal generator 36 generates a drive signal according to the 120-degree energization method based on the PWM duty given from the 120-degree energization calculator 33 and the rotational position of the rotor detected by the rotational position sensor 12. For the field effect transistors UH, VH, and WH, drive signals that are turned on over a period of 120 degrees in electrical angle are provided with phases shifted by 120 degrees. On the other hand, the PWM pulse signal of the PWM duty set by the 120-degree energization calculating unit 33 is given to the field effect transistors UL, VL, WL. As a result, a drive voltage corresponding to the PWM duty is applied from the drive circuit 2 to the electric motor 1, and the electric motor 1 is driven at the target rotational speed set by the target rotational speed setting unit 31.
[0019]
When the 120-degree energization calculating unit 33 sets a PWM duty of 100% and the energization by PWM control in the 120-degree energization method is saturated, the target rotation is larger than the rotation speed (saturation rotation speed) of the electric motor 1 at that time. When the target rotational speed setting unit 31 sets the speed, the drive method switching unit 35 switches the drive method of the electric motor 1 from the 120 degree energization method to the 180 degree energization method, and the PWM duty set by the 180 degree energization calculation unit 34. Is provided to the drive signal generator 36.
[0020]
In the PWM control in the 180-degree energization method, the target rotation speed set by the target rotation speed setting unit 31 is a drive signal that turns on the field effect transistors UH, VH, and WH over a period of 180 degrees in electrical angle. Is applied to the field effect transistors UL, VL, WL by applying a PWM pulse signal having a constant PWM duty according to the target rotation speed during the energization period of 180 degrees. Can be achieved. However, immediately after switching from the 120-degree energization method to the 180-degree energization method, if a PWM pulse signal having a PWM duty corresponding to the target rotation speed is applied to the field effect transistors UL, VL, WL during the energization period of 180 degrees. Since an excessively large current (peak current) flows instantaneously in the electric motor 1 and the three-phase brushless motor is accelerated rapidly by this peak current, there is a possibility that mechanical shock is applied to the electric motor 1. Further, such a peak current may cause overcurrent breakdown of the field effect transistors UH, UL, VH, VL, WH, WL.
[0021]
Therefore, in this embodiment, as shown in FIG. 2, the energizing period of 180 degrees includes a middle period corresponding to an electrical angle of 120 degrees, a preceding period corresponding to an electrical angle of 30 degrees before and after the middle period, and The PWM duty in each period is individually set by being divided into subsequent periods.
In other words, the 180-degree energization calculation unit 34 includes a middle period duty setting unit 341 that sets the PWM duty in the middle period, a previous period duty setting unit 342 that sets the PWM duty in the previous period, and after setting the PWM duty in the subsequent period. A period duty setting unit 343. The intermediate period duty setting unit 341 performs PI control calculation based on the deviation between the target rotation speed set by the target rotation speed setting unit 31 and the rotation speed calculated by the rotation speed calculation unit 32 and should be applied to the electric motor 1. A control voltage value is obtained, and a PWM duty corresponding to the control voltage value is set. The pre-period duty setting unit 342 and the post-period duty setting unit 343 immediately after the drive method switching unit 35 switches the drive method of the electric motor 1 from the 120-degree energization method to the 180-degree energization method. Is set to a value smaller than the PWM duty set by the middle period duty setting unit 341 (for example, a value half that of the PWM duty set by the middle period duty setting unit 341). As the drive control of the electric motor 1 proceeds, the PWM duty in the previous period and the subsequent period is gradually increased, and finally the PWM duty in the previous period and the subsequent period is made to coincide with the PWM duty in the middle period. In this way, by controlling the PWM duty in the previous period and the subsequent period, the occurrence of peak current can be suppressed when switching from the 120-degree energization method to the 180-degree energization method, and a sudden change in the rotation speed of the electric motor 1 can be prevented. Can be prevented.
[0022]
Note that switching from the 180-degree energization method to the 120-degree energization method is performed by, for example, rotating the electric motor 1 at the time when the target rotation speed is switched from the 120-degree energization method to the 180-degree energization method by the target rotation speed setting unit 31. It is performed in response to being set to a speed (the above-mentioned saturation rotational speed) or less.
As described above, according to this embodiment, the electric motor 1 can be driven with high efficiency by the 120-degree energization method in the low / medium-speed rotation region of the electric motor 1, and cannot be achieved by this 120-degree energization method. A high rotation speed can be achieved by driving the electric motor 1 by a 180-degree energization method.
[0023]
Further, when switching from the 120-degree energization method to the 180-degree energization method, the generation of the peak current can be suppressed, and a sudden change in the rotation speed of the electric motor 1 can be prevented, so that the field effect transistor UH, There is no possibility of causing mechanical shock due to overcurrent destruction of UL, VH, VL, WH, WL or a sudden change in the rotational speed of the electric motor 1.
As mentioned above, although one Embodiment of this invention was described, this invention can also be implemented with another form. For example, in the above embodiment, the energization period of 180 degrees is divided into a middle period corresponding to an electrical angle of 120 degrees and a previous period and a rear period corresponding to electrical angles of 30 degrees before and after the middle period. The widths of the preceding period, the middle period, and the subsequent period can be arbitrarily set. For example, each of the widths may be set to a width corresponding to an electrical angle of 60 degrees.
[0024]
In addition, various design changes can be made within the scope of matters described in the claims.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a motor control device according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining division of a 180-degree energization period.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electric motor 2 Drive circuit 3 Control part 31 Target rotational speed setting part 32 Rotational speed calculating part 33 120 degree energization calculating part 34 180 degree energization calculating part 35 Drive system switching part 36 Drive signal generation part 331 Duty setting part 341 Medium period duty Setting unit 342 Previous period duty setting unit 343 After period duty setting unit

Claims (1)

A motor control device that PWM-controls the supply of drive current from the drive circuit to the electric motor and rotates the electric motor at a target rotational speed,
Drive method switching means for switching the drive method of the electric motor from the 120-degree energization method to the 180-degree energization method;
120 degree energization duty setting means for setting the duty of the PWM pulse signal to be given to the drive circuit during the 120 degree energization period according to the target rotational speed when driving the electric motor in the 120 degree energization method;
When the electric motor is driven by the 180-degree energization method, the 180-degree energization period is divided into the previous period, the middle period, and the later period, and the duty of the PWM pulse signal to be given to the drive circuit in each period is determined based on the target rotation speed. 180 degree energization duty setting means for setting ;
And rotational speed calculating means for calculating a rotational speed of the electric motor <br/> seen including,
The 180 degree energization duty setting means is:
PI control calculation is performed based on the deviation between the target rotation speed and the rotation speed calculated by the rotation speed calculation means, a control voltage value to be applied to the electric motor is obtained, and the duty corresponding to this control voltage value is set to the middle period PWM during the previous period and the subsequent period after the drive method of the electric motor is switched from the 120 degree energization method to the 180 degree energization method by the medium period duty setting means for setting the duty of the PWM pulse signal in It includes a period duty setting means for setting the duty of the pulse signal so as to gradually increase from a value smaller than the duty set by the middle period duty setting means to a duty set by the middle period duty setting means. A motor control device.

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