JP2008278698A - Motor driving apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor driving apparatus capable of reducing a shock caused by decelerating a brushless motor by means of a short brake, and performing smooth and rapid deceleration. <P>SOLUTION: A gate inputting unit 4 converts a braking instruction signal from a controller 1 to a signal expressed by an exponential function f2(t)=e<SP>(-1/bt)</SP>with a sign opposite to the exponential function f1(t) to feed the signal to a PWM comparator 7, when the deceleration curve of a motor is approximated by the exponential function f1(t)=-e<SP>(-1/at)</SP>. The PWM comparator 7 generates a PWM braking signal with its on-duty cycle gradually expanding for speed-up to input it to gates in switching devices Q2, Q4, Q6. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a motor driving device that shorts and brakes motor coils of a DC brushless motor, for example.

  In a motor drive device that drives a DC brushless motor, it is necessary to apply braking when the motor reduces the speed from a high-speed rotation operation to an arbitrary rotation speed.

  For example, FIG. 6 shows an example of a drive circuit that drives a three-phase DC brushless motor at 120 ° rectangular wave. A three-phase bridge circuit 52 that constitutes the output stage of the drive circuit is connected to the three-phase motor coil 51. The three-phase bridge circuit 52 is provided with switching elements (transistors) Q1 to Q6. Note that flywheel diodes and resistors connected in parallel to the respective switching elements are omitted. A buffer 53 is connected to the three-phase bridge circuit 52, and the switching elements (transistors) Q1 to Q6 are on / off controlled.

In order to reduce the rotational speed of the motor, it is necessary to apply braking, but a so-called short brake is used. For example, in FIG. 6, braking can be applied by short-circuiting all of the motor coils 51. In FIG. 6, a buffer command from the controller 54 causes the buffer 53 to turn off the transistors Q1, Q3, and Q5 and to turn on the transistors Q2, Q4, and Q6 to short-circuit the motor coil 51 (Patent Document 1).
Japanese Patent Laid-Open No. 9-149684

When the motor is driven to rotate normally, back electromotive force V _bemf = N × Ke (N: motor rotation speed, Ke: back electromotive force constant) is generated in coils U, V, W. During braking, the motor coil 51 is short-circuited by the resistor Ra and the on-resistance R _on of each transistor, so that a brake current I _bk = V _bemf / (Ra + R _on ) that is proportional to the back electromotive force flows through the motor coil 51. The brake current I _bk reaches about twice the normal drive current. For this reason, the braking force is excessive, and the load device and the motor itself may be damaged.

  FIG. 7 is a graph showing a deceleration curve when the motor is not braked. Waveform A shows the RUN signal and stops on the H side. Waveform B is a sensor signal and outputs H / L according to the rotor rotation. Waveform C shows the motor speed detected by the frequency voltage converter of the sensor signal.

FIG. 8 is a graph showing a deceleration curve until the motor is stopped by applying a short brake. Waveform A shows the RUN signal and stops on the L side. Waveform B is a sensor signal and outputs H / L according to the rotor rotation. Waveform C is a brake signal and the brake is applied on the H side. Waveform D shows the motor speed detected by the frequency voltage converter of the sensor signal. In FIG. 8, it can be seen that the motor rotation speed decreases suddenly with the start of braking (see waveform C), and the deceleration decreases gradually as the speed decreases (see waveform D). The deceleration curve of the motor rotation speed at this time is represented by an exponential function f (t) = − e ^{(−1 / at)} . The motor stop time when the brake in FIG. 7 is not applied is 5 seconds, but the motor stop time when the short brake is applied is shortened to about 0.22 seconds.
However, since a shock accompanying sudden deceleration occurs at the start of braking, a gradual deceleration is required.

  The present invention has been made to solve these problems, and an object of the present invention is to provide a motor drive device that can reduce a shock when braking a brushless motor with a short brake and can perform braking gently and quickly. There is.

In order to achieve the above object, the present invention comprises the following arrangement.
A motor driving device that controls driving of a brushless motor by selecting an excitation phase to be energized to a motor coil and performing gate input to a switching element through a gate input unit. The motor is applied to a gate input unit according to a brake command from a controller. A brake control unit for braking the motor while turning on all the high side or low side of all the switching elements constituting the bridge circuit connected to the coil while the motor coil is short-circuited, and the motor deceleration curve has an exponential function f1 ( When approximated by t) = − e ^{(−1 / at)} , the gate input unit outputs the brake command signal from the controller, and the exponential function f2 (t) = e ⁽ with the opposite sign to the exponential function f1 (t). ^{-1 / bt) (b;} shake into a brake command signal given by the coefficient) defining a deceleration or braking time To key control unit performs input, brake control unit is characterized in that the braking force by receiving it performs gate input to the switching element to generate a brake signal that gradually increases.
The gate input unit integrates a brake command signal and converts the rectangular wave into an exponential function wave given by an exponential function f2 (t), a sawtooth wave generation circuit that generates a sawtooth wave, and an integration circuit. A PWM comparator is provided that compares the input exponential wave with the sawtooth wave input from the sawtooth wave generation circuit to generate a PWM brake signal whose on-duty gradually increases.

When the motor driving apparatus described above is used, when the motor deceleration curve is approximated by an exponential function f1 (t) = − e ^{(−1 / at)} , the gate input unit outputs the brake command signal from the controller to the exponential function f1. The sign is opposite to that of (t) and is converted into a brake command signal given by an exponential function f2 (t) = e ^{(−1 / bt)} (b: a coefficient that defines deceleration acceleration or braking time) and is sent to the brake controller. In response to the input, the brake controller generates a brake signal in which the braking force gradually increases, and performs gate input to the switching element that short-circuits the motor coils. As a result, since the brake command signal is zero at the start of braking, no inflection point is generated, and the braking force gradually increases thereafter, so that the brakes are gradually and quickly applied without rapidly decreasing the motor speed. Is possible.
In particular, when the PWM comparator compares the exponential wave given by the exponential function f2 (t) input from the integration circuit and the sawtooth wave input from the sawtooth wave generation circuit to generate a PWM brake signal whose on-duty gradually increases. The rotation speed of the motor does not have an inflection point at the start of braking, and the braking shock does not occur. Further, by adjusting the coefficient b, which is the time constant of the integration circuit, to be optimal, it is possible to realize a gentle and quick braking operation without increasing the motor stop time.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a preferred embodiment of a motor drive device according to the invention will be described with reference to the accompanying drawings. The present invention can be widely applied to a motor drive device that drives a brushless motor including a permanent magnet rotor and a stator.

Below, the motor drive device which drives a 3-phase DC brushless motor is demonstrated.
In FIG. 1, the motor driving apparatus includes a controller 1 that linearly drives (or PWM drives) a three-phase DC brushless motor. The controller 1 selects an excitation phase to be energized to the three-phase motor coil 2 and performs gate input to the switching elements Q1 to Q6 constituting the three-phase bridge circuit 3 according to a control sequence.

  The motor drive device also includes a brake control unit (a PWM comparator 7 described later). The brake control unit turns on all the high side or low side of all the switching elements Q1 to Q6 constituting the three-phase bridge circuit 3 connected to the motor coil 2 through the gate input unit 4 according to the brake command from the controller 1 ( In FIG. 1, the low-side switching elements Q2, Q4, and Q6 are turned on), and braking (short brake) is applied to the motor while the motor coil 3 is short-circuited.

Braking force when applying the short brake as described above is proportional to the brake current _{I bk,} a brake current _{I bk = N × Ke / (} Ra + R on) (N; motor speed, Ke; counter electromotive force constant ). As the motor speed decreases, the brake current I _bk also decreases. The braking force at this time decreases exponentially and the deceleration curve is represented by an exponential function f1 (t) = − e ^{(−1 / at)} (a: coefficient of deceleration curve caused by the motor). At the start of braking, braking begins to act at once from zero braking force, so an inflection point occurs in the deceleration curve and appears as a braking shock of the motor.

The deceleration curve of the motor rotation speed at this time draws a logistic curve as shown in FIG. 2, and is considered to approximate the sigmoid function P (t) = 1 / (1 + e ^at ). FIG. 2 shows a deceleration curve of the motor rotation speed when braking is started from the origin 0 with the rotation speed N on the vertical axis and the elapsed time t on the horizontal axis. Even if a weak brake command having a duty of 50%, for example, is given as a rectangular wave input (step input) with respect to a normal full brake command, the braking shock at the start of braking does not disappear. Further, when the brake command signal is given by a ramp wave input (ramp input) by a linear function, the braking shock is improved compared to the rectangular wave input, but an inflection point still occurs and the stop time becomes longer. Therefore, when a brake command is given with an exponential function f2 (t) = e ^{(−1 / bt)} (b: a coefficient that defines deceleration acceleration or braking time) whose sign is opposite to that of the braking force at the start of braking, This makes it possible to stop the motor in a short time without the inflection point.

That is, the gate input unit 4 converts the brake command signal from the controller 1 into a brake command signal given by an exponential function f2 (t) = e ^{(−1 / bt)} whose sign is opposite to that of the exponential function f1 (t). The PWM comparator 7 generates a PWM brake signal whose on-duty gradually increases and inputs the gate to the low-side switching elements Q2, Q4, and Q6 in FIG. Thus, by using PWM control for the brake command signal, it is possible to reduce circuit loss and simplify the circuit configuration.

  An example of the circuit configuration of the gate input unit 4 is shown in FIG. In FIG. 1, the gate input unit 4 includes an integration circuit 5, a sawtooth wave generation circuit 6, and a PWM comparator 7 (brake control unit). The integration circuit 5 integrates the brake command signal input from the controller 1 and converts the square wave into an exponential function wave given by the exponential function f2 (t). The sawtooth wave generating circuit 6 generates a sawtooth wave that serves as a reference signal. An exponential function wave is input from the integration circuit 5 to the + side terminal of the PWM comparator 7, and a sawtooth wave (reference signal) from the sawtooth wave generation circuit 6 is input to the − side terminal. The PWM comparator 7 compares these input signals and outputs one of two values (H / L) determined in advance depending on the magnitude. In this embodiment, since the signal input to the + side terminal employs an exponential function wave, a PWM brake signal whose on-duty gradually increases is generated.

  FIG. 3 shows the result of the brake operation of the motor to which the brake command signal given by the exponential function f2 (t) is given. FIG. 3 is a graph showing a deceleration curve until the motor is stopped by applying a short brake. Waveform A shows the RUN signal and stops on the L side. Waveform B is a sensor signal and outputs H / L according to the rotor rotation. Waveform C is a brake signal and the brake is applied on the H side. The brake command signal is PWM-controlled from the start of braking, and the PWM control time is about 0.1 second. Waveform D shows the motor speed detected by the frequency voltage converter of the sensor signal.

  In FIG. 3, since the brake command signal is zero at the start of braking, the inflection point does not occur, and then the braking force gradually increases, and eventually the brake command signal approaches the convergence value. It becomes a curve. As a result, it can be seen that the motor speed starts to decrease gradually with the start of braking (see waveform C), and the deceleration gradient also becomes gentle, following a change approximating a sigmoid function curve (see waveform D). . Immediately after the start of braking, the inversion point at the start of braking does not occur in the deceleration curve of the motor speed, and no braking shock occurs. Further, the motor stop time is about 0.27 seconds, which is shorter than the conventional one (see FIG. 8), and can be stopped quickly without being so long.

The coefficient b of the exponential function f2 (t) = e ^{(−1 / bt)} input as a brake command signal corresponds to the time constant of the integrating circuit 5 shown in FIG. The value of the coefficient b of the brake command signal can be arbitrarily adjusted. For example, if the value of the coefficient b is decreased, an increase in braking force is suppressed, the deceleration acceleration is decreased, and the stop time is increased. On the other hand, if the value of the coefficient b is increased, the braking force is rapidly increased, the deceleration acceleration is increased, and the stop time is shortened. Thus, if the coefficient b of the brake command signal is set as necessary, the optimum deceleration acceleration and braking time can be obtained.

  FIG. 4 is a graph showing a deceleration curve when the PWM control time (time constant of the integration circuit 5) is approximately doubled. The time by PWM control is about 0.2 seconds. Also in FIG. 4, it can be seen that the motor rotational speed starts to decrease gradually with the start of braking (see waveform C), and the deceleration gradient further decreases (see waveform D). Since the deceleration acceleration was reduced, the effect of the braking command appeared up to the low speed range, and ideal characteristics were obtained. The motor stop time is 0.372 seconds, which is slightly longer than that in FIG.

  FIG. 5 is a graph showing an enlarged waveform at the start of braking in FIG. It can be seen that the on-duty of the PWM waveform of the brake signal shown in waveform C gradually increases. Further, it can be seen from the motor rotation speed waveform of waveform D that no shock is generated at the start of braking.

  In the above-described embodiment, the brake control unit is configured to generate a brake signal in which the braking force gradually increases by PWM control and perform gate input to the switching element. However, the present invention is not limited to this. For example, the brake control unit may generate a linear brake signal in which the braking force gradually increases by linear driving and input the gate to the switching element.

It is a circuit block diagram of a motor drive device. It is a graph which shows the exponential function with which a brake command is approximated. It is a graph which shows the signal waveform at the time of the motor stop at the time of a brake operation. It is a graph which shows the signal waveform at the time of the motor stop which doubled the time constant of FIG. It is the graph which expanded the signal waveform at the time of the brake start of FIG. It is a circuit block diagram of the conventional motor drive device. It is a graph which shows the signal waveform at the time of a motor stop when not applying a brake. It is a graph which shows the signal waveform at the time of a motor stop at the time of applying a short brake.

Explanation of symbols

1 Controller
2 Motor coil 3 Three-phase bridge circuit
4 Gate input section
5 Integration circuit
6 Sawtooth wave generation circuit
7 PWM comparator

Claims (2)

A motor drive device that selects the excitation phase to be energized to the motor coil and performs gate input to the switching element through the gate input unit to control the drive of the brushless motor,
Brake control that applies braking to the motor while the motor coil is short-circuited by turning on the high side or low side of all switching elements that constitute the bridge circuit connected to the motor coil in response to the brake command from the controller at the gate input section Part
When the motor deceleration curve is approximated by an exponential function f1 (t) = − e ^{(−1 / at)} , the gate input unit outputs a brake command signal from the controller, and the sign is opposite to that of the exponential function f1 (t). It is converted into a brake command signal given by an exponential function f2 (t) = e ^{(−1 / bt)} (b: a coefficient that defines deceleration acceleration or braking time) and input to the brake control unit. In response to this, a motor drive device that generates a brake signal in which the braking force gradually increases and inputs the gate to the switching element.   The gate input unit is input from an integration circuit that integrates the brake command signal and converts the square wave into an exponential wave given by an exponential function f2 (t), a sawtooth wave generation circuit that generates a sawtooth wave, and an integration circuit. 2. The motor drive device according to claim 1, further comprising: a PWM comparator that compares the exponential wave and the sawtooth wave input from the sawtooth wave generation circuit to generate a PWM brake signal whose on-duty gradually increases.

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