JPH0595698A - DC brushless motor drive - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to prevent a large short-circuit current from flowing through a switching element even at a low temperature. [Structure] A detection circuit 30 for detecting a timing at which a switching element of a lower arm switches, and a switching circuit of an upper arm switching element from an off state to an on state for a certain period of time after the switching of the switching element of the lower arm is detected. A prohibition circuit 40 for prohibiting is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC brushless motor drive device for driving a DC brushless motor used in, for example, a washing machine.

[0002]

2. Description of the Related Art As a conventional DC brushless motor drive device, there is one shown in FIG. 6, for example.

The DC brushless motor drive device is composed of a three-phase full-wave bridge type inverter circuit 10 using six NPN bipolar transistors as switching elements and a control circuit section for controlling the same. In the three-phase full-wave bridge type inverter circuit 10, 2 is a diode bridge for rectification, 3 is a smoothing capacitor,
AC voltage from commercial AC power supply 1 is diode bridge 2
After being rectified by, the capacitor 3 is smoothed to obtain a DC voltage. Then, this DC voltage is converted into a three-phase AC in the three-phase full-wave bridge portion. That is, in the three-phase full-wave bridge part,
Six transistors u ₁ , u ₂ , v ₁ , v ₂ , which are switching elements, are provided on three pairs of arms corresponding to three phases.
w ₁ and w ₂ are connected. Where transistor u
_The three arms on the side to which ₁ , v ₁ and w ₁ are connected are called upper arms, and the three arms on the other side to which the other transistors u ₂ , v ₂ and w ₂ are connected are called lower arms. .. 6
The free wheel diode 4 is connected in parallel to each of the transistors u _{1 to} w ₂ , and the three connection points of the upper arm and the lower arm are connected to the driven DC brushless motor 20.
Are connected to the three-phase armature windings u, v, and w.

The DC brushless motor 20 includes, in addition to the armature windings u, v, and w, a rotor (not shown) formed of permanent magnets, and three Hall elements for detecting the rotational position of the rotor. 5a, 5b, 5c are provided. The rotor position detection signals of the Hall elements 5a, 5b, 5c are given to the motor control circuit 6. The output of the motor control circuit 6 is given as a drive signal to the bases of the transistors u ₁ , v ₁ and w ₁ of the upper arm via the chopper circuit 7 and the drive circuits 8a, 8b and 8c, and the output of the lower arm. For the transistors u ₂ , v ₂ and w ₂ , the drive circuit 8d,
It is given as a drive signal to the base through only 8e and 8f. The rotor position detection signals of the Hall elements 5a, 5b, 5c are logically converted by the motor control circuit 6, and corresponding to the rotor position, for example, the transistor u ₁ in the upper arm and the transistor v ₂ in the lower arm, similarly the transistor v. ₁ and w ₂ , transistors w ₁ and u ₂
A drive signal for sequentially turning on the transistors of each combination is output. The DC voltage is converted into a three-phase AC by switching the transistor ON, and the DC brushless motor 2
The DC brushless motor 20 is rotationally driven in one direction by sequentially flowing a current through the zero armature windings u-v, v-w, and w-u. The forward and reverse rotations of the DC brushless motor 20 are performed by reversing the order of the currents flowing through the armature windings u, v, and w. The forward and reverse control is performed by a normal rotation / reverse control from a microcomputer (not shown). It is performed via the motor control circuit 6 by the inversion signal.

Further, a PWM oscillator (pulse width modulation signal generator) 9 is provided to change the rotation speed of the DC brushless motor 20. The PWM on-duty setting signal from the microcomputer causes the PWM oscillator 9 to output a PWM signal with a variable on / off duty. This PWM signal is output by the chopper circuit 7 and the drive circuits 8a, 8b,
8c through the upper arm three transistors u ₁ ,
DC is given to v ₁ and w ₁ and its ON period is changed.
The rotation speed of the brushless motor 20 is variable. That is, the shorter the on-duty of the transistors u ₁ , v ₁ , w ₁ , for example, the lower the rotation speed of the DC brushless motor 20.

FIG. 7 (a) shows the internal structure of the drive circuit. In order to shorten the turn-off time of the transistor in the three-phase full-wave bridge section, the drive circuit has an inverse structure between the base and emitter of the transistor. It has a circuit for applying a bias. This circuit charges the capacitor 11 with the electric charge due to the base current when the transistor is on,
A reverse bias voltage is applied between the base and the emitter by discharging this charge when the transistor is off. An electrolytic capacitor is used because a capacitor having a relatively large capacity is required to apply this reverse bias.

The equivalent circuit of the electrolytic capacitor includes a resistance component and an induction component in series with the capacitance as shown in FIG. 7 (b).
This induction component increases as the temperature decreases. Therefore, when the transistor is turned on and off at a high frequency when the temperature is low, the impedance increases due to the inductive component.

Here, consider a case where the combination of the upper arm transistor u ₁ and the lower arm transistor v ₂ is turned on. Now, according to the PWM signal from the PWM oscillator 9, when the transistor u ₁ of the upper arm is in the off state, a current flows through the free wheel diode of the transistor u ₂ of the lower arm (FIG. 8). Subsequently, when the lower arm transistor v ₂ is switched to w ₂ , the transistor v ₂
A reverse bias current flows to turn off (FIG. 9). At this time, at low temperature, a voltage drop occurs due to the impedance of the large inductive component of the capacitor. At this time, when the transistor v ₁ is turned on, a short circuit current flows (see FIG.
0), which may lead to destruction of the transistor. FIG. 11 is a timing chart showing this state, and FIG.
Is an example when a large short-circuit current is flowing in the upper arm transistor.

[0009]

In the conventional DC brushless motor driving device, a reverse bias is applied between the base and emitter of the transistor in order to shorten the turn-off time of the transistor in the three-phase full-wave bridge section. , With a circuit equipped with an electrolytic capacitor. The electrolytic capacitor contains a resistance component and an induction component in series with the capacitance, and the induction component increases as the temperature decreases. Therefore, when the transistor in the lower arm is switched at a low temperature, a reverse bias current flowing at that time causes a voltage drop due to impedance due to a large inductive component of the capacitor. At this time, when a transistor in the upper arm corresponding to the transistor in the lower arm is turned on, a short-circuit current flows due to the voltage drop, which may cause damage to the element itself.

Therefore, according to the present invention, even at low temperature, DC
Without almost reducing the drive output to the brushless motor,
An object of the present invention is to provide a DC brushless motor drive device capable of preventing a large short-circuit current from flowing through a switching element.

[0011]

In order to solve the above problems, the present invention comprises switching elements of an upper arm and a lower arm, and a DC voltage is driven by these switching elements to periodically switch a DC voltage. A full-wave bridge type inverter circuit for obtaining a drive output of a motor, a pulse width modulation signal generator for generating a pulse width modulation signal for varying an on / off ratio of a switching element of the upper arm, and switching of the lower arm A detection circuit that detects the timing at which the element switches, and prohibits the switching element of the upper arm from turning on from the off state for a certain period of time after the switching circuit detects switching of the switching element of the lower arm. The gist is to have a prohibition circuit.

[0012]

When the transistor in the lower arm is switching and the reverse bias current is flowing, the transistor in the upper arm is prohibited from being turned on from the off state for a certain period of time. This prevents a large short-circuit current from flowing through the switching element without reducing the drive output to the DC brushless motor.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS.

In FIG. 1, the same or equivalent components as the circuit devices and elements in FIG. 6 are designated by the same reference numerals as those described above, and the duplicated description will be omitted.

In the DC brushless motor drive device of this embodiment, the transistor u _{2 of the} lower arm is added to the circuit of FIG.
Hall signal down edge detection circuit 30 for detecting the timing at which ~ w ₂ switches, and the switching of the lower arm transistors u _{2 to} w ₂ from when the detection circuit 30 detects switching of the lower arm transistors u _{2 to} w _2. A PWM signal prohibiting circuit 40 for prohibiting the corresponding upper arm transistor from being turned on from the off state for a certain period of time is added.

The transistors u _{2 to} w ₂ of the lower arm switch because any one of the three Hall signals (rotor position detection signals) from the Hall elements 5a, 5b, 5c is H level.
It is time to transit from the level to the L level. Therefore, if the down edge of the Hall signal is triggered, the switching of the transistors u _{2 to} w _{2 in} the lower arm is known. The hall signal down edge detection circuit 30 does this. The down edge signal detected by the detection circuit 30 is sent to the PWM signal prohibition circuit 40, and the PWM signal prohibition circuit 40
The PWM signal is prohibited from changing to turn on the upper arm transistor for a certain period of time.

FIG. 2 shows the internal structure of the hall signal down edge detection circuit 30. A combination circuit of three D flip-flops 31, 32, 33 and one OR gate 34 catches the down edge of the Hall signal and outputs the down edge signal from the OR gate 34.

FIG. 3 shows the internal structure of the PWM signal prohibiting circuit 40. 3 inputs N to which the down edge signal is input
AND gate 41, counter 42, NOR gate 43,
It is composed of an AND gate 44 and a D flip-flop 45.

Next, the operation of the DC brushless motor drive device constructed as described above will be described with reference to the control timing chart of FIG.

Now, the case where the combination of the upper arm transistor u ₁ and the lower arm transistor v ₂ is turned on and the lower arm transistor is switched from v ₂ to w ₂ will be described.

When the down edge of the hall signal is detected by the hall signal down edge detection circuit 30 (see FIG. 4).
(A)), it is detected that the down edge signal is output and the transistor v _{2 of the} lower arm is switched to w ₂ (FIG. 4 (b)). The down edge signal is sent to the PWM signal prohibiting circuit 40, and the counter 4 starts from the time when this signal is input.
2 starts the counter operation (FIG. 4C), and the PWM signal is prohibited from changing to turn on the upper arm transistor v ₁ for a certain period of time (FIG. 4D).
(E)). As a result, while the reverse bias current is flowing to the transistor v ₂ of the lower arm, the transistor v _{1 of the} upper arm is prohibited from being turned on from the off state for a certain period of time, and the drive output to the DC brushless motor 20 is almost eliminated. A large short-circuit current is prevented from flowing in the transistor v ₁ without dropping (FIG. 4 (f)). FIG. 5 shows changes in the collector current of the upper arm transistor v ₁ when the changes in the PWM signal are prohibited.

In a normal case, the PWM signal from the PWM oscillator 9 changes so as to turn on the upper arm transistor v ₁ after a certain time has passed since the lower arm transistor v ₂ was switched to w _2. The PWM signal inhibition operation by the signal inhibition circuit 40 is not performed (FIG. 4).
(G), (h)). Also, the lower arm transistor v ₂
Is detected to be switched to w ₂ , the next upper arm transistor v ₁ is not turned on while the PWM signal for turning on the upper arm transistor u ₁ is being output. Even at this time, the PWM signal prohibiting operation by the PWM signal prohibiting circuit 40 is not performed (FIG. 4).
(J) to (k)).

[0023]

As described above, according to the present invention,
Since the switching element of the upper arm is prohibited from being turned on from the off state for a certain period of time after the switching of the switching element of the lower arm is detected,
Even when the temperature is low, it is possible to prevent a large short-circuit current from flowing due to the presence of the capacitor of the reverse bias circuit in the switching element, with almost no drop in the drive output to the DC brushless motor.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a DC brushless motor drive device according to the present invention.

FIG. 2 is a diagram showing a configuration of a Hall signal down edge detection circuit in FIG.

FIG. 3 is a diagram showing a configuration of a PWM prohibiting circuit in FIG.

FIG. 4 is a control timing chart for explaining the operation of the embodiment.

FIG. 5 is a diagram showing a change in collector current of an upper arm transistor when a change in a PWM signal is prohibited in the embodiment.

FIG. 6 is a circuit diagram of a conventional DC brushless motor drive device.

FIG. 7 is a diagram showing a reverse bias circuit provided in a conventional DC brushless motor drive device.

FIG. 8 is a diagram showing a partial current flow when a lower arm transistor is switched in a conventional example.

FIG. 9 is a diagram showing a reverse bias current flow when a lower arm transistor is switched in a conventional example.

FIG. 10 is a diagram for explaining a problem at a low temperature in a conventional example.

FIG. 11 is a timing chart for explaining the operation of the conventional example.

FIG. 12 is a diagram showing an example of a large short-circuit current flowing through an upper arm transistor in a conventional example.

[Explanation of symbols]

9 PWM oscillator (pulse width modulation signal generator) 10 3-phase full-wave bridge type inverter circuit 20 DC brushless motor 30 Hall signal down edge detection circuit 40 PWM signal inhibition circuit u ₁ , v ₁ , w ₁ Upper arm transistor (switching) Element) u ₂ , v ₂ , w ₂ lower arm transistor (switching element)

Claims (1)

[Claims] 1. A full-wave bridge type inverter circuit comprising switching elements for an upper arm and a lower arm, wherein a DC voltage is periodically switched by these switching elements to obtain a drive output of a driven DC brushless motor, A pulse width modulation signal generator for generating a pulse width modulation signal for varying the on / off ratio of the upper arm switching element, a detection circuit for detecting the timing of switching of the lower arm switching element, and the detection circuit A DC brushless motor drive device, comprising: a prohibition circuit for prohibiting the switching element of the upper arm from being switched from the OFF state to the ON state for a certain period of time after the switching of the switching element of the lower arm is detected. ..