JPS6159076B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drive device for a brushless DC motor, and in particular, it is concerned with thermal insulation breakdown of the stator windings of the motor, which occurs when the brushless DC motor is locked in the commutation position, and The purpose is to prevent thermal damage to the drive power transistor.

Conventionally, as a countermeasure against the rise in temperature of the stator windings or motor drive power transistor when the motor is locked due to overload, etc., methods have been used to detect abnormalities by attaching a temperature sensor to the motor itself, or by designing sufficient heat dissipation. Methods are being taken to prevent increases in the temperature of the motor and drive power transistors.

In such conventional examples, the method employing a temperature sensor has the disadvantage that the cost increases due to an increase in the number of parts and the number of installation steps. Furthermore, systems that provide sufficient heat dissipation design generally have the disadvantage that the motor becomes large or the heat dissipation plate of the power transistor becomes large. What further complicates heat dissipation design is the case where the motor is locked at the commutation position. In other words, DC motors generally have no dead center (position where the generated torque is zero) and need to start no matter what position the rotor is in. Therefore, during the commutation period, current is applied to the stator windings of multiple phases. It needs to flow. The heat generated during locking differs greatly between when locked at the commutation position and at other positions, and the specific difference in heat generated will be described below using a brushless DC motor. Note that in order for a brushless DC motor to start automatically, a stator winding consisting of at least two phases (m=2) is required.
Here, an example using a more commonly used three-phase stator winding will be explained.

FIG. 1 is a principle diagram of a full-wave drive circuit for a three-phase brushless DC motor. In the figure, 1' is a stator winding group consisting of stator windings L ₁ , L ₂ , and L ₃ that are commonly connected at one end. Q ₁ , Q ₂ , and Q ₃ are NPN type transistors, and Q ₁ ′, Q ₂ ′, and Q ₃ ′ are switch elements consisting of PNP type transistors. Here, Q ₁ , Q ₂ , and Q ₃ are switch elements having the same polarity on one side regarding the current supplied to the stator windings L ₁ , L ₂ , and L ₃ , and Q ₁ ′, Q ₂ ′, Q ₃ ′ is the other switch element of the same polarity. 2′ is Q ₁ , Q ₂ , Q ₃ , Q ₁ ′, Q ₂ ′,
This is a switch means consisting of Q ₃ ′. transistor
The emitters of Q ₁ , Q ₂ , and Q ₃ are connected to each other, and the collectors of each are connected to the collectors of transistors Q ₁ ′, Q ₂ ′, and Q ₃ ′, as well as the stator windings L ₁ , L ₂ , and L _{3 .}
is connected to one terminal of the Further, the emitters of the transistors Q ₁ ', Q ₂ ', and Q ₃ ' are connected to the positive terminal of a DC voltage source E whose negative terminal is grounded.

Next, referring to FIG. 1, the power consumed by the stator winding group 1' and the switch means 2' when the motor is locked is determined. Here stator winding L ₁ ,
Let the resistance values of L ₂ and L ₃ be R (Ω).

First, transistors Q ₁ , Q ₂ , Q ₃ , Q ₁ ′, Q ₂ ′,
If Q ₃ ' is used as a switching transistor, the power dissipation in these transistors is generally ignored (V _CE(SAT) <0; however, V _CE(SA
T) is the collector-emitter saturation voltage of the transistor. Therefore, when locked in the normal position (a position other than the commutation point), for example, when Q ₁ and Q ₂ ' are on and the other transistors are off, the stator windings L ₁ and L ₂ The total power consumption P _D is expressed by the following equation (1).

P _D = E ² /2R (1) In addition, when the commutation position is locked, for example, transistors Q ₁ , Q ₂ ′, and Q ₃ ′ are turned on (stator winding
(the point where the current switches from L ₂ to L ₃ ), the power consumption P _D in the stator windings L ₁ , L ₂ , and L ₃ at that time is
_C is expressed by the following equation (2).

P _DC = E ² / (R + RR) = 2E ² / 3R … (2) As is clear from the above equations (1) and (2), the amount of energy consumed in the stator winding group when locked at the commutation position is Power is increased by 33% compared to locking in other locations. (Although this example shows the case of full-wave drive,
The above ratio during half-wave driving is the ratio of the resistance value R to the resistance value R/2, so it increases by 100%. ) That is, the heat dissipation design of the motor must take into consideration the power consumption at the commutation position, making it difficult to downsize the motor.

Next, as a method of preventing an increase in power consumption in the stator windings when the stator windings are locked at the commutation position as described above, a method of limiting the maximum current flowing to the motor using a circuit is often adopted. For example, if this limit current value I _linit is set as I _linit = E/2R (3), then no matter what point the motor is locked, the power consumption in the stator winding group is expressed by equation (1). It becomes constant. And transistors Q ₁ , Q ₂ , Q ₃ ,
_The power consumption when _{Q 1} ′, Q _{2 ′ , and Q 3 ′} are locked is as follows. It becomes saturated and the power consumption of the transistor is ignored. However, at the commutation position, for example, Q ₁ , Q ₂ ′,
If Q ₃ ' is in a conductive state and the collector currents of Q ₂ ' and Q ₃ ' are each I _linit/2 , then the transistors Q ₁ ,
The power P _Q consumed by Q ₂ ′, Q ₃ ′ is P _Q = E ² /8R (4), and the transistors Q ₁ , Q ₂ , Q ₃ .Q ₁ ′, Q ₂ ′,
It becomes necessary to sufficiently dissipate the heat of Q ₃ ′. That is, it is necessary to attach a large heat sink to the drive transistor, which increases the cost and increases the size of the motor drive section.

The present invention solves the above-mentioned problems by detecting the commutation period of the brushless DC motor, detecting the lock of the motor at the commutation point, and stopping the power supply to the motor. .

The present invention will be explained below based on the illustrated embodiments. In Fig. 2, 1 is the stator winding L ₁ ,
The stator winding group of the brushless DC motor includes L ₂ and L ₃ , and one end of L ₁ , L ₂ , and L ₃ is connected to the power terminal 14 . 2 is a switch means for supplying current to the stator windings L ₁ , L ₂ , L ₃ , which is an identical switch whose collector is connected to one end of each stator winding L ₁ , L ₂ , L ₃ . It consists of transistors Q ₁ , Q ₂ , and Q ₃ which are polar semiconductor switch elements.
3 is a driving means for driving transistors Q ₁ , Q ₂ , Q ₃ , and this is a driving means for driving transistors Q ₄ , Q ₅ , Q 3 .
It consists of Q ₆ and resistors 4, 5, and 6.
7 is a position signal generating means that detects the rotational position of the rotor (rotor magnet) with respect to the stator windings L ₁ , L ₂ , and L ₃ and outputs a position signal for each phase _. , Q ₅ , and Q ₆ to control the conduction period of transistors Q ₁ , Q ₂ , and Q ₃ . Reference numeral 8 denotes a two-phase conduction state detection means, which detects a state in which two transistors Q ₁ , Q ₂ , and Q ₃ are conductive at the same time. 9 is a two-phase conduction state determination means, which includes transistors Q ₇ and Q ₈ and resistors 12 and 1.
3. It includes a capacitor C and a comparator 10 that compares the charging voltage of the capacitor C with the reference voltage of the reference power source Er. Reference numeral 11 denotes a storage means that is set by the output of the two-phase conduction state determining means 9.

FIG. 3 shows the signal waveforms of each part in FIG. 2, and the symbols I to I in FIG. 3 and I to I in FIG. 2 correspond to each other. The operation will be explained below with reference to FIGS. 2 and 3. The brushless DC motor switches transistors Q4 and _{Q1 to t3 during} the period from time _t1 to _{time t4} according to the output of the position signal generating means 7.
The stator windings L 1 , L 2 , L ₃ are driven by sequentially driving each transistor, such as transistors Q ₅ and Q ₂ during _the period up to t ₆ and transistors Q _{6 and} Q ₃ after t _5. Rotation is maintained by sequentially passing current through the motors. And transistors Q ₄ , Q ₅ ,
The base potential of _Q6 represents the signal waveforms A, B, and C in Fig. 3. By inputting the signals indicated by A, B, and C to the two-phase conduction state detection means 8,
As an output, a signal as shown in FIG. 3D is obtained. Normally, the storage means 11 is in a reset state,
Therefore, transistor _Q8 is in an off state. Therefore, charging and discharging of capacitor C is done by transistor.
Since the ON/OFF state of the transistor Q ₇ is determined by the output of the two-phase conduction state detection means 8, the charging voltage waveform of the capacitor _C becomes as shown in FIG. That is, 2
During the periods of time _t1 to _t2 , _t3 to _t4 , and _t5 to _t6 when the phase is in a conductive state, it is charged through the resistor 12, and during the time period _t2 to _t3 , when the single phase is in a conductive state. During _t4 to _t5 and _t6 to _t7 , the transistor _Q7 is turned on, so the potential is zero. As long as this condition continues, capacitor C
Since the charging potential of is lower than the reference power supply Er, the output of the comparator 10 maintains a low level, and the storage means 11
remains in the reset state. In other words, the brushless DC motor continues to rotate.

Next, when the brushless DC motor is instantaneously locked due to overload at time _t7 , the capacitor C continues to be charged so that the position signal generating means 7 generates a signal to turn on the transistors _Q4 and _Q6 . , its potential reaches Er at time _t8 . Therefore time
At _t8 , the comparator 10 inverts its output and outputs a high level as shown in FIG. The storage means 11 is set by the output of the comparator 10 at time _t8 , and its output outputs a high level at time _t8 , as shown in FIG. Then, the output of the storage means 11 disables the operation of the position signal generation means 7, stops the supply of current to the drive means 3, stops the supply of power to the stator winding group 1, and also stops the supply of electric power to the stator winding group 1.
Turn on _Q8 and discharge the charge in capacitor C. By keeping the capacitor C in the discharge state while the storage means 11 is in the set state in this manner, the motor can be restarted promptly by resetting the storage means 11 from the outside.

FIG. 4 shows a specific circuit configuration of the two-phase conduction state detection means 8. In the same figure, Q ₁₁ , Q ₁₂ , Q ₁₃ are
It is an NPN type transistor. 104,10
5 and 106 are resistors, and transistors Q _{11 and 106} are resistors, respectively.
Connected between the emitter terminals of Q ₁₂ and Q ₁₃ and ground. The collectors of transistors Q ₁₁ , Q ₁₂ , Q ₁₃ are connected to the power supply terminal 14 via resistors 101, 102, 103, and are also connected to the emitter terminals of PNP transistors Q ₁₄ , Q ₁₅ , Q ₁₆ . There is.

The base terminals of the transistors Q ₁₄ , Q ₁₅ , and Q ₁₆ are gathered together and grounded through a resistor 108, and are connected to the power supply terminal 14 through diode-connected transistors Q ₁₇ , Q ₁₈ , and Q ₁₉ . has been done. In addition, the collectors of transistors Q ₁₄ , Q ₁₅ , and Q ₁₆ are combined together and grounded via a resistor 107, and are also grounded via diode-connected transistors Q ₂₀ and Q ₂₁ and a resistor 109. . Resistors 104, 105, 106
R ₁ and resistors 101, 102, 1
The value of resistor 107 is R ₂ , the value of resistor 107 is R ₃ , and R ₂
>2R ₁ , R ₂ = R ₃ .

Next, the operation of the two-phase conduction state detection circuit 8 shown in FIG. 4 will be explained with reference to FIG. 2. As is clear from Fig. 2, the high level of input signals A, B, and C corresponds to the forward base-emitter voltage V _BE (0.7V) of transistors Q ₄ , Q ₁ , Q ₅ , Q ₂ , Q ₆ , and Q ₃ ), each with 2V _BE . Also, transistor Q ₁₁ ~
Since the base-emitter forward voltage drop in the forward direction of Q ₂₀ is V _BE , in a two-phase conduction state, for example, when current is flowing in stator windings L ₁ and L ₂ , resistors 105 and 106 Voltage V _BE is applied, transistors Q ₁₅ and Q ₁₆ are cut off, and resistor 1
07 is supplied with current through the transistor _Q14 , and a voltage of 2V _BE is generated. As a result, no voltage is generated in the resistor 109 and the potential is zero. Also,
In other states, that is, a state in which current is flowing only to one phase of the stator windings among stator windings L ₁ , L ₂ , and L ₃ , for example, a state in which power is flowing only to stator winding L ₁ . In this case, the voltage of V _BE is applied only to the resistor 106, the transistor Q ₁₆ is cut off, and current is supplied to the resistor 107 through the transistors Q ₁₄ and Q ₁₅ , so the voltage of 4 V _BE is applied to the resistor 107. Occur. As a result, resistor 109 has
A voltage of 2V _BE is output.

As described above, the high level in the two-phase conduction state,
Outputs a low level signal in other states.

As described above, the present invention detects the time during which current flows through the stator windings of multiple phases that occur during commutation of a brushless DC motor, and when this state continues for a certain period of time, the power to the motor is reduced. By stopping the supply, it is possible to prevent the temperature of the motor or the drive switch means from rising when the motor is locked in the commutation position, thereby preventing their thermal damage and significantly reducing the size of the motor and drive unit. It is something that contributes.

In the above-described embodiments of the present invention, a half-wave drive method (a method in which current flows in only one direction to the stator windings to drive the motor) was used as an example, but a full-wave drive method (a method in which the motor is driven by passing current in only one direction to the stator windings) was used as an example. Even in the case of a method in which a motor is driven by passing current in two directions through the windings, the method is essentially the same by simultaneously detecting the two-phase conduction period of the switch element that causes current to flow in the opposite direction to the stator windings. , is included in the present invention.

[Brief explanation of the drawing]

Fig. 1 is a basic configuration diagram of a half-wave drive circuit for a three-phase brushless DC motor, Fig. 2 is a circuit configuration diagram of an embodiment of the present invention, and Fig. 3 is a signal waveform diagram of each part of Fig. 2. FIG. 4 is a diagram showing a specific example of the circuit configuration of the two-phase conduction state detection means shown in FIG. Q ₁ ~ _{Q 8} , Q ₁₁ ~ Q ₂₁ ...transistor, L ₁ ~ _{L 3}
... Stator winding, C ... Capacitor, Er ... Reference power supply, 1 ... Stator winding group, 2 ... Switch means, 3 ... Drive means, 4 to 6 ... Resistor, 7 ...
Position signal generation means, 8... Two-phase conduction state detection means, 9... Two-phase continuity state determination means, 10... Comparator, 11... Storage means, 12, 13, 101-1
09...Resistor.

Claims (1)

[Claims] A stator winding of 1 m (however, m≧2) phase, a rotor including a permanent magnet, and a positional relationship of the rotor with respect to the stator winding are detected. A brushless DC motor has a position signal generating means for generating a position signal for controlling energization to the stator winding of each phase, and is connected to each terminal of the stator winding to supply power to the brushless DC motor. a switch means comprising a switch element that operates, a switch drive means for driving the switch means by the output of the position signal generating means, and a switch means having the same polarity with respect to the current supplied to the stator winding. A two-phase conduction state detection means detects the state in which two of the constituent switch elements are conductive at the same time, and the time of the two-phase conduction state is measured by the output of the two-phase conduction state detection means, and the measured time is A two-phase conduction state determining means whose output state changes when a predetermined time has elapsed, and a function of maintaining the switch means in a non-operating state by being set by the output of the two-phase conduction state determining means. A drive device for a brushless DC motor, comprising a storage means. 2. The brushless DC motor according to claim 1, further comprising means for resetting the two-phase conduction state time measurement of the two-phase conduction state determination means by the set output of the storage means. Drive device.