JP2017079525A - Motor driving device and driving system using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor driving device capable of increasing the maximum value of a motor torque without enlarging the physical size of a motor under restriction of average input current.SOLUTION: An operation determining unit 61 of a motor driving device 30 determines whether the operation state of a motor 20 is in a first operation state or in a second operation state. A first calculating unit 62 calculates a duty according to a target motor rotational speed when the operation state of the motor 20 is in the first operation state. A second calculating unit 63 calculates the duty according to a target motor torque when the operation state of the motor 20 is in the second operation state. A command unit 64 outputs the command signal Spwm corresponding to the final duty calculated by the first calculating unit 62 or the second calculating unit 63. A driving unit 32 switches energization and non-energization of the motor 20 according to the command signal Spwm. The second calculating unit 63 reduces the duty when the target motor torque is larger than the present motor torque.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a motor drive device and a drive system using the same.

2. Description of the Related Art A motor driving device that drives an electric motor by PWM control is known. The motor drive device controls a voltage applied to the motor by changing a duty that is a ratio of a time during which the motor is energized in one cycle of PWM control (hereinafter, PWM cycle).
In Patent Document 1, in order to avoid a motor failure caused by heat generation during energization, an average value of current input to the motor during the PWM period (hereinafter, average input current) is set to a predetermined limit value or less. A limiting motor drive is disclosed. In addition, the motor drive device increases the motor rotation speed by vector control in an operation state where the motor torque is relatively high.

JP 2012-139105 A

  The motor driving device disclosed in Patent Document 1 can increase the motor rotation speed in an operation state where the motor torque is relatively high, but cannot increase the maximum value of the motor torque. In order to increase the maximum value of the motor torque under the limit of the average input current, it is necessary to increase the wire diameter of the coil or increase the number of turns, and there is a disadvantage that the physique of the motor becomes large.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a motor drive device capable of increasing the maximum value of motor torque without increasing the physique of the motor under the limitation of the average input current. Is to provide.

  The present invention is a motor drive device that drives an electric motor by PWM control, and includes an operation determination unit, a first calculation unit, a second calculation unit, a command unit, and a drive unit. In the following, the motor operating state when the average input current is smaller than a predetermined limit value is referred to as a first operating state, and the motor operating state when the average input current is limited to the limit value is referred to as a second operating state. The target value of the motor speed is set as the target motor speed, and the target value of the torque generated by the motor is set as the target motor torque.

  The operation determination unit determines whether the operation state of the motor is the first operation state or the second operation state. The first calculation unit calculates the duty according to the target motor rotation speed when the operation state of the motor is the first operation state. A 2nd calculation part calculates a duty according to a target motor torque, when the operation state of a motor is the 2nd operation state. The command unit outputs a command signal corresponding to the duty calculated by the first calculation unit or the second calculation unit. The drive unit switches between energization and non-energization of the motor according to the command signal.

Here, when the rotational speed of the motor decreases, the electromotive force of the motor decreases. Therefore, when the rotational speed of the motor is relatively low, a large current can flow even at a low voltage, that is, a small duty, compared to when the motor is relatively high.
In the present invention, when the motor operating state is the second operating state, motor torque control is performed in which the duty is calculated according to the target motor torque. When the target motor torque is greater than the current motor torque, the duty is decreased. Is done. If the duty is reduced in a state where the motor torque, which has been the maximum value in the past, is output, the motor speed decreases, and the average input current is limited, but the current flowing to the motor when energized increases. Since the motor torque is proportional to the current flowing through the motor, the motor torque is increased as a result.
Therefore, according to the present invention, the maximum value of the motor torque can be increased without increasing the size of the motor under the limitation of the average input current.

1 is a block diagram showing a drive system to which a motor drive device according to a first embodiment of the present invention is applied. It is sectional drawing of the reduction gear of FIG. It is a figure which shows the operation | movement area | region map which the operation | movement determination part of the control part of FIG. 1 uses for determination. It is a circuit diagram explaining the drive part of FIG. It is a flowchart explaining the process which the control part of FIG. 1 performs. It is a figure which shows the motor torque characteristic map which the control part of FIG. 1 uses. It is a figure which shows the relationship between the efficiency at the time of forward rotation of the reduction gear of FIG. 1, and a motor torque, and the relationship between the efficiency at the time of reverse rotation, and a motor torque. It is a block diagram which shows the drive system with which the motor drive device by 2nd Embodiment of this invention was applied. It is a flowchart explaining the process which the control part of FIG. 8 performs. FIG. 8 is a diagram showing the relationship between the motor torque of the motor of FIG. 8 and the output torque output to the driven body by the drive system. An example of the fluctuation range of the motor torque in the first embodiment and the motor in the second embodiment It is a figure which overlaps and shows an example of the fluctuation range of a torque.

Hereinafter, a plurality of embodiments of the present invention will be described with reference to the drawings. In the embodiments, substantially the same components are denoted by the same reference numerals and description thereof is omitted.
<First Embodiment>
The motor drive apparatus according to the first embodiment of the present invention is applied to the drive system shown in FIG. The drive system 10 is a system that rotationally drives the driven body 90. In the present embodiment, the driven body 90 is, for example, an engine camshaft (not shown).

(Drive system)
First, the configuration of the drive system 10 will be described with reference to FIGS. 1 and 2.
As shown in FIG. 1, the drive system 10 includes an electric motor 20, a motor drive device 30 that drives the motor 20 by PWM control, and a speed reducer that decelerates the rotation of the motor 20 and outputs it to the driven body 90. 40. The load torque transmitted from the driven body 90 to the motor 20 through the speed reducer 40 varies depending on the operating state of the engine.

  The motor drive device 30 includes a control unit 31 and a drive unit 32. The control unit 31 calculates a duty based on an externally input signal or the like, and outputs a command signal Spwm corresponding to this duty. The “external” includes, for example, sensors such as the rotation speed sensor 50 that detects the rotation speed of the motor 20, the engine control device 91, and the like. The duty is a ratio of time during which the motor 20 is energized during the PWM cycle. The drive unit 32 switches between energization and non-energization of the motor 20 in accordance with the command signal Spwm.

  In the present embodiment, the current input to the motor drive device 30 is limited in order to avoid a motor failure due to heat generation during energization, and the average of the current input to the motor 20 during the PWM period The value (hereinafter, average input current) is limited to a predetermined limit value or less.

  As shown in FIG. 2, the speed reducer 40 includes a differential gear device, and includes a housing 41, an input shaft 42, a differential gear 43, and an output shaft 44. The housing 41 has a large-diameter internal gear 45 provided integrally with the inner wall. The input shaft 42 is rotatably supported by the housing 41. The input shaft 42 has an eccentric portion 46 that is eccentric with respect to the rotational axis. The differential gear 43 is rotatably supported by the eccentric portion 46 and has a large diameter gear portion 47 and a small diameter gear portion 48. The large diameter gear portion 47 meshes with the large diameter internal gear 45. The output shaft 44 is rotatably supported by the housing 41. The output shaft 44 has a small-diameter internal gear 49 that meshes with the small-diameter gear portion 48.

  When the input shaft 42 rotates, the differential gear 43 makes a planetary motion so as to revolve around the rotation axis while rotating around the eccentric axis. The rotation speed of the differential gear 43 is reduced with respect to the rotation speed of the input shaft 42. Further, when the differential gear 43 moves in a planetary motion, the output shaft 44 is transmitted with rotation decelerated with respect to the rotation speed of the differential gear 43. The speed reducer 40 transmits the rotation between the input shaft 42 and the output shaft 44 by reducing the rotation by two stages.

(Motor drive device)
Next, the configuration of the motor drive device 30 will be described with reference to FIGS. 1, 3, and 4.
Hereinafter, the operation state of the motor 20 when the average input current is smaller than the limit value is referred to as a first operation state. Further, the operation state of the motor 20 when the average input current is limited to the limit value is defined as a second operation state. Further, a target value of the rotation speed of the motor 20 (hereinafter referred to as motor rotation speed) is set as the target motor rotation speed. In addition, a target value of torque generated by the motor 20 (hereinafter referred to as motor torque) is set as a target motor torque.

As illustrated in FIG. 1, the control unit 31 includes an operation determination unit 61, a first calculation unit 62, a second calculation unit 63, and a command unit 64.
The operation determination unit 61 determines whether or not the operation state of the motor 20 is the first operation state, and determines whether or not the operation state of the motor 20 is the second operation state. In the present embodiment, the motion determination unit 61 performs determination using the motion region map shown in FIG. 3 stored in the storage unit. The operation area map stores the operation area A1 of the motor 20 when in the first operation state and the operation area A2 of the motor 20 when in the second operation state in the coordinate system of the motor torque and the motor rotation speed. doing. The operating point of the motor 20 in the operating area map is obtained from the current duty and the motor rotational speed. The operation determination unit 61 determines that the operation state of the motor 20 is the first operation state when the operation point is within the operation region A1, and the motor 20 when the operation point is within the operation region A2. Is determined to be the second operating state.

  Returning to FIG. 1, when the operation state of the motor 20 is the first operation state, the first calculation unit 62 calculates the target motor rotation speed and calculates the duty according to the target motor rotation speed. That is, the motor drive device 30 performs the rotational speed control for controlling the rotational speed of the motor 20 when the operational state of the motor 20 is the first operational state.

  When the operation state of the motor 20 is the second operation state, the second calculation unit 63 calculates a target motor torque and calculates a duty according to the target motor torque. That is, the motor drive device 30 performs torque control for controlling the motor torque when the operation state of the motor 20 is the second operation state. At this time, the second calculation unit 63 sets the duty to be small when the target motor torque is larger than the current motor torque. Thereby, the motor rotation speed is lowered.

  The command unit 64 outputs a command signal Spwm corresponding to the duty calculated by the first calculation unit 62 or the second calculation unit 63 to the drive unit 32. Assuming that the reciprocal of the PWM period is the drive frequency, in this embodiment, the command unit 64 sets the drive frequency in the second operation state to a predetermined frequency f1 that is the same value as the drive frequency in the first operation state.

  In the present embodiment, the control unit 31 is configured by, for example, a microcontroller. The processing in each functional unit included in the control unit 31 is software processing by executing a program stored in advance by the CPU, but may be hardware processing by a dedicated electronic circuit.

  As shown in FIG. 4, the drive unit 32 includes a power source 71 and a changeover switch 72 connected in series to the motor 20, a diode 73 connected in parallel to the motor 20 and the changeover switch 72, This is a drive circuit having a motor 20, a changeover switch 72, and a capacitor 74 connected in parallel to the diode 73.

  The changeover switch 72 is composed of, for example, a transistor or the like, and switches between a connection state and a cutoff state between the power source 71 and the motor 20 in accordance with a command from the control unit 31. The diode 73 is a free wheel diode that causes the motor 20 to return an inertial current when the changeover switch 72 is cut off. The capacitor 74 is a power storage unit that stores electric power when the motor 20 is not energized and discharges electric power toward the motor 20 when the motor 20 is energized. The resonance frequency of the electric circuit constituted by the coil 21 and the capacitor 74 of the motor 20 is set to coincide with the drive frequency in the second operation state.

(Processing executed by the control unit)
Next, processing executed by the control unit 31 will be described with reference to FIGS. In FIG. 5, the symbol “S” means a step. A series of routines shown in FIG. 5 are repeatedly executed at predetermined time intervals from when the motor drive device 30 is started until it is stopped.

  In S1 of FIG. 5, various signals are read. The signals include detection signals from various sensors that detect the vehicle state, information signals from the engine control device 91, and signals indicating control targets for the driven body 90. The control target is information indicating whether the rotational speed of the driven body 90 is increased, decelerated, or maintained. After S1, the process proceeds to S2.

In S2, a load torque acting on the motor 20 is calculated. In the present embodiment, for example, the load torque is calculated based on information from the engine control device 91 (for example, engine torque, engine speed). After S2, the process proceeds to S3.
In S3, input power required to achieve the control target acquired in S1 is calculated. After S3, the process proceeds to S4.

  In S4, it is determined whether or not the operation state of the motor 20 is the first operation state. When it is determined that the operation state of the motor 20 is the first operation state (S4: YES), the process proceeds to S5. When it is determined that the operation state of the motor 20 is not the first operation state (S4: NO), the process proceeds to S8.

In S5, the target motor speed is calculated, and the basic duty is calculated according to the target motor speed. After S5, the process proceeds to S6.
In S6, the feedback amount is calculated from the feedback gain based on the deviation between the target motor rotation speed and the current motor rotation speed. After S6, the process proceeds to S7.
In S7, the sum of the basic duty and the feedback amount is calculated as a final duty (hereinafter referred to as a final duty) that is a basis for generating the command signal Spwm. After S7, the process proceeds to S12.

In S8, it is determined whether or not the operation state of the motor 20 is the second operation state. When it is determined that the operation state of the motor 20 is the second operation state (S8: YES), the process proceeds to S9. When it is determined that the operation state of the motor 20 is not the second operation state (S8: NO), the process proceeds to S13.
In S9, a target motor torque is calculated. After S9, the process proceeds to S10.

In S10, the torque priority duty is calculated from the motor torque characteristic map by the duty variable control in the second operation state shown in FIG. As shown in FIG. 6, as the duty is reduced from the maximum motor torque T ₁₀₀ at a duty of 100% under the limit of the average input current, the motor rotational speed is decreased and the motor torque is increased. Such a motor torque characteristic is due to the fact that the electromotive force of the motor 20 decreases as the motor speed decreases. This can be understood from the equation (1) showing the relationship among the resistance R, inductance L, electromotive force V0, current i, and applied voltage V in the equivalent electric circuit of the motor 20.
V = Ri + L (di / dt) + V0 (1)
That is, when the motor speed is relatively low, a large current can flow even at a low voltage (that is, a small duty) as compared to when the motor speed is relatively high.

In S11, the torque priority duty is calculated as the final duty. After S11, the process proceeds to S12.
In S12, a command signal Spwm corresponding to the final duty is generated and output to the drive unit 32. After S12, the process exits the routine of FIG.
In S13, an alarm is output that the motor 20 is overloaded. After S13, the process exits the routine of FIG.

(effect)
As described above, in the first embodiment, the motor drive device 30 includes the operation determination unit 61, the first calculation unit 62, the second calculation unit 63, the command unit 64, and the drive unit 32. The operation determination unit 61 determines whether the operation state of the motor 20 is the first operation state or the second operation state. When the operation state of the motor 20 is the first operation state, the first calculation unit 62 calculates the duty according to the target motor rotation speed. The second calculator 63 calculates the duty according to the target motor torque when the operation state of the motor 20 is the second operation state. The command unit 64 outputs a command signal Spwm corresponding to the final duty calculated by the first calculation unit 62 or the second calculation unit 63. The drive unit 32 switches between energization and non-energization of the motor 20 in accordance with the command signal Spwm.

In the motor drive device 30 configured as described above, when the operation state of the motor 20 is the second operation state, motor torque control for calculating the duty according to the target motor torque is performed, and the target motor torque is set to the current motor torque. If it is greater than the torque, the duty is reduced. If the duty is reduced in a state where the motor torque T ₁₀₀ that has been the maximum value is being output, the motor rotation speed is decreased, and the average input current is limited, but the current flowing to the motor 20 is increased while energizing. . Since the motor torque is proportional to the current flowing through the motor 20, the motor torque is increased as a result. Therefore, the maximum value of the motor torque can be increased without increasing the size of the motor 20 under the limitation of the average input current.

In the first embodiment, the second calculation unit 63 reduces the duty when the target motor torque is larger than the current motor torque.
Thus, the duty in if conventional outputs a motor torque T ₁₀₀ was the maximum value state is smaller motor speed is lowered.

In the first embodiment, the drive system 10 includes a gear-type speed reducer 40 provided between the motor 20 and the driven body 90.
Here, the efficiency η1 of the speed reducer 40 during the normal rotation of the motor 20 is expressed by Expression (2) when expressed using the input work X, the output work Y, and the loss A due to friction inside the speed reducer 40. The forward rotation is when the motor 20 overcomes the load torque and rotationally drives the driven body 90. On the other hand, the efficiency η2 of the speed reducer 40 at the time of reverse rotation of the motor is expressed by Expression (3). The reverse rotation is when the motor 20 is rotated by the load torque.
η1 = Y / X = Y / (Y + A) (2)
η2 = X / Y = (YA) / Y (3)
Therefore, for example, when X = 100, Y = 60, and A = 40, the efficiency η1 is 0.6, whereas the efficiency η2 is about 0.33. That is, as shown in FIG. 7, the speed reducer 40 is more efficient at the time of forward rotation than at the time of reverse rotation. Therefore, even when the load torque is relatively high, the driven body 90 can be reliably rotated forward while suppressing reverse rotation.

Second Embodiment
In the second embodiment, as shown in FIG. 8, the command unit 82 of the control unit 81 sets the drive frequency f2 in the second operation state to be smaller than the drive frequency f1 in the first operation state. In other words, the command signal Spwm is generated so that the drive frequency f2 is smaller than the drive frequency f1.

  Next, processing executed by the control unit 81 will be described with reference to FIG. In S21 to S27 of FIG. 9, the same processing as S1 to S7 of FIG. 5 is executed. In S28 of FIG. 9, the same process as S12 of FIG. 5 is executed. Further, in S29 to S32 and S34 of FIG. 9, the same processing as S8 to S11 and S13 of FIG. 5 is executed. In S33 of FIG. 9, a command signal Spwm corresponding to the final duty is generated and output to the drive unit 32 so that the drive frequency f2 is smaller than the drive frequency f1. After S33, the process exits the routine of FIG.

(effect)
In the second embodiment, the drive frequency f2 is set smaller than the drive frequency f1. Therefore, the number of operations of the changeover switch 72 is relatively reduced in the second operation state, and the power consumption due to the resistance when the switch is turned on and the power consumption due to the counter electromotive force of the coil 21 are reduced.

  Further, in combination with the fact that the drive frequency f2 and the resonance frequency are set to coincide with each other, the applied voltage and current ripple when the duty is ON are increased. As shown in FIG. 10, when PWM control is performed at a relatively large drive frequency f1 in the second operation state as in the first embodiment, there is a case where the fluctuation range of the motor torque is small and the output torque does not change. come. On the other hand, when PWM control is performed at a relatively low drive frequency f2 in the second operation state as in the second embodiment, the fluctuation range of the motor torque becomes large and the output torque can be changed. Become. At this time, since there is a difference in efficiency between the forward rotation and the reverse rotation of the speed reducer 40, the forward rotation of the driven body 90 can be reliably performed while suppressing the reverse rotation.

<Other embodiments>
In another embodiment of the present invention, the operation determination unit determines the operation state of the motor based on information from a sensor that detects an input current to the motor, for example, without determining the operation state of the motor from the operation region map. May be.
In another embodiment of the present invention, the reduction gear may be another gear type reduction gear instead of the differential gear device. The reduction gear may be one that performs one-stage deceleration or three or more stages.

In other embodiments of the present invention, the drive system may not include a speed reducer. That is, the motor and the driven body may be directly connected.
In another embodiment of the present invention, the driven body may be a rotating body other than the camshaft of the engine.
The present invention is not limited to the embodiments described above, and can be implemented in various forms without departing from the spirit of the invention.

DESCRIPTION OF SYMBOLS 10 ... Drive system 20 ... Motor 30 ... Motor drive device 32 ... Drive part 61 ... Operation | movement determination part 62 ... 1st calculation part 63 ... 2nd calculation part 64,82 ... Command section

Claims (6)

A motor driving device for driving an electric motor (20) by PWM control,
An average value of currents input to the motor during the PWM period is defined as an average input current, and an operation state of the motor when the average input current is smaller than a predetermined limit value is defined as a first operation state. The operating state of the motor when the current is limited to the limit value is set as the second operating state, the target value of the motor speed is set as the target motor speed, and the target value of the torque generated by the motor is set as the target Assuming motor torque,
An operation determination unit (61) for determining whether the operation state of the motor is the first operation state or the second operation state;
When the motor operating state is the first operating state, a first calculating unit (62) that calculates a duty, which is a ratio of a time during which the motor is energized in the PWM cycle, according to the target motor rotation speed When,
A second calculator (63) that calculates the duty according to the target motor torque when the motor operating state is the second operating state;
A command unit (64, 82) for outputting a command signal corresponding to the duty calculated by the first calculation unit or the second calculation unit;
A drive unit (32) for switching between energization and de-energization of the motor according to the command signal;
A motor drive device comprising:   The motor driving apparatus according to claim 1, wherein the second calculation unit reduces the duty when the target motor torque is larger than a current motor torque. When the reciprocal of the PWM period is a drive frequency,
The command unit outputs the command signal so that the drive frequency (f2) in the second operation state is smaller than the drive frequency (f1) in the first operation state. The motor drive device described. The drive unit includes a capacitor (74) that stores electric power when the coil (21) of the motor is de-energized and discharges electric power toward the coil when the coil is energized;
4. The motor drive device according to claim 3, wherein a resonance frequency of an electric circuit including the coil and the capacitor is set to coincide with the drive frequency in the second operation state. The motor drive device according to any one of claims 1 to 4,
The motor;
A gear-type speed reducer (40) for reducing the rotation of the motor;
A drive system comprising:   The drive system according to claim 5, wherein the speed reducer is a differential gear device.

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