JP3274903B2 - Current control method of brushless motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current control method for a brushless motor. More particularly, the present invention controls a command current by comparing it with zero volts by digital processing to stabilize the current and reduce the speed of the motor by a back electromotive current. New improvement for preventing

[0002]

2. Description of the Related Art As a current control method for a brushless motor of this type which has been conventionally used, for example, a configuration shown in FIG. 4 is employed. That is, in FIG. 4, those indicated by reference numerals 1, 2, and 3 are drive coils composed of a U-phase, a V-phase, and a W-phase. Transistors UH, UL and V
H, VL and WH, WL are connected.

Each of the transistors VH to WL has a P (Pulse Width Modulation) signal from the comparators 4, 5, and 6 provided by PWM.
The WM signals 4a, 5a, 6a are supplied directly or inverted through an inverter 7. Each of the comparison circuits 4,
Triangular wave pulses 8 are input to 5, 6 and command currents iu *, iv *, and iw * are input via a subtractor 9 and a constant unit 10 having a gain K.

The actual currents iu, i flowing through the output sides of the transistors UH to WL, ie, the drive coils 1, 2, 3, respectively.
The signals v and iw are input to the respective subtracters 9 via the current detector 11 as feedback signals.

Next, in the above configuration, first, the difference between the U-phase command current iu * and the actual current iu of that phase is multiplied by a gain K, and the output 10a of the real constant 10 and the level of the triangular wave 8 are obtained. Are compared by a comparison circuit 4 comprising an analog comparator to form a PWM signal 4a. The PWM signal 4a is input to each of the U-phase transistors UH and UL to turn on and off. The other V-phase and W-phase are controlled by the same operation as described above so that the actual current of each phase becomes equal to the command current.

[0006]

Since the conventional brushless motor current control method is configured as described above,
The following issues existed. That is, when an induced voltage is generated in each drive coil, a counter-electromotive current flows in a direction to stop the rotation of the motor, which may reduce the rotation of the motor.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems. In particular, the present invention compares a command current with zero volts and controls the current by digital processing to stabilize the current.
It is an object of the present invention to provide a current control method for a brushless motor that prevents deceleration of the motor due to a back electromotive current.

[0008]

According to the current control method for a brushless motor according to the present invention, a command current (iu) is supplied to a three-phase drive coil (1, 2, 3) via a pair of transistors (UH to WL). *, iv *, iw *), in the current control method of the brushless motor which controls the actual current (iu, iv, iw), the command current (iu *, iv *, iw *) is set to zero V. Comparison, the comparison result is latched at the rise of the clock (28), and one of the transistors (UH to WL) of the phase is turned on, and the command current (iu *, iv
*, iw *) and the actual current (iu) through the transistors (UH to WL) become equal when the transistor (any of UH to WL) is turned off, thereby realizing the actual current of each phase. (iu, i
v, iw) to stop the current from flowing to the drive coil (1, 2, 3) beyond the command current (iu *, iv *, iw *) ,
This is a method of controlling the actual current (iu, iv, iw) of each phase to be constant .

[0009]

In the current control method for a brushless motor according to the present invention, the command current is compared with zero (0) V, the comparison result is latched at the rising edge of the clock, and one of the transistors of the phase is turned on. By turning off the transistor when the command current becomes equal to the actual current passing through the transistor, the current is controlled to be substantially constant by controlling the current so as not to flow through the drive coil beyond the command current. Is done. Therefore, when the transistors connected to the two-phase drive coils are turned off, only the transistors connected to the remaining one-phase drive coil maintain the on state. Motor deceleration can be prevented.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a current control method for a brushless motor according to the present invention will be described below in detail with reference to the drawings. The same or equivalent parts as those in the conventional example will be described with the same reference numerals. 1 to 3 show a current control method for a brushless motor according to the present invention. FIG. 1 is a block diagram, FIG. 2 is a waveform diagram of a main part of FIG. 1, and FIG. It is a waveform diagram.

In FIG. 1, reference numerals 1, 2, and 3 denote first, second, and third drive coils of U, V, and W phases, respectively. Phase drive circuit 20,
It is configured to be driven by a V-phase drive circuit 21 and a W-phase drive circuit 22.

Each of the drive circuits 20, 21, 22 has the same configuration, and only the U-phase drive circuit 20 will be described here. Current command iu * and each transistor UH, U
The actual current iu detected by the current detector 11 provided on the output side of L is input to the first and second comparators 23 and 24, and the comparison outputs a and b from the comparators 23 and 24 are , Are input to a pair of first and second gate circuits 25 and 26.

The output e1, of each of the gate circuits 25, 26,
e2 passes through the third gate circuit 27 and becomes a gate output e,
The clock 28 from the outside is input to the reset terminal RST of the second flip-flop FF2 of the first and second flip-flops FF1 and FF2. At the same time, the comparison output a is input to the data terminal D of the first flip-flop FF1.

The FF outputs c and d of the flip-flops FF1 and FF2 are input to fourth and fifth gates 29 and 30 connected to the transistors UH and UL, respectively.

Next, a case where the driving coils 1, 2, 3 of each phase are actually driven in the above-described configuration will be described.
The driving circuits 20, 21, 22 perform the same operation. Only the U-phase drive circuit 20 will be described as the representative side. First, the comparison output a is iu *> 0 = 1, iu * <0 =
0, the comparison output b is iu> iu * = 1, iu <i
Output as u * = 0. That is, the comparison output a becomes a polarity signal through which the command current iu flows, and iu becomes positive (flows out) when it is 1, and negative (flows in) when it is 0. Yuo, the positive and negative flow directions are shown in FIG.

The comparison output b is a comparison output of the command current iu and the actual current iu *, and is a logical product of the comparison output a (FIG. 2).
), A gate output e (iu> iu *) is obtained.

Next, as shown in FIG. 3, at the rising edge of the clock 28, the flip-flops FF1 and FF2 are simultaneously set, and the FF outputs c and d are synchronized.
The output c is used as a polarity signal of the actual current iu. Further, the transistors UH or UL on the high arm or low arm side are turned on by the FF outputs c and d, and the actual current i
u starts to flow. In this case, when iu> iu *, the gate output e becomes 0, and the second flip-flop F
Since F2 is reset and the FF output d becomes zero (0),
The transistors UH and UL are turned off, and the actual current iu is stopped.

Therefore, the above-described control is applied to the other drive circuits 21 and
By applying the same to 22, control can be performed so that current does not flow more than the command current iu *, and the actual current iu can be controlled to be substantially constant. When the transistors of two phases of each of the elements U, V, W are turned off based on the comparison between the command currents iu * .iv *, iw * and the actual currents iu, iv, iw, the remaining one phase is turned off. Does not newly increase the actual currents iu, iv and iw, only the transistors in that phase continue to be in the ON state, and no reverse current flows due to the induced voltage of the motor. Can be prevented.

Accordingly, the above-described control is summarized as follows. That is, the command currents iu *, iv of each phase
In accordance with * and iw *, it is determined whether to turn on the high-arm side transistor or the low-arm side transistor of the phase, and turn off all the transistors other than the selected one. At the start of one cycle of driving by the well-known PWM (pulse width modulation) method, all the selected transistors are turned on. The actual current iu,
When iv and iw become equal to the flow command current, the on-state transistor of the phase is turned off. By performing the above operation in each cycle of the PWM method, the actual current i
u, iv, iw can be controlled to be substantially constant.

[0020]

The current control method for a brushless motor according to the present invention is configured as described above, so that the following effects can be obtained. That is, when the transistors of the two phases are turned off by comparing the actual current and the command current, the current does not newly increase in the remaining one phase,
Since only the transistors in that phase remain on, no reverse current flows due to the induced voltage of the motor, and the motor can be prevented from decelerating. In addition, since the control circuit for turning on / off each transistor has a digital configuration, stable driving can be achieved without being affected by temperature drift or the like.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a current control method for a brushless motor according to the present invention.

FIG. 2 is a waveform diagram of a main part of FIG.

FIG. 3 is a waveform diagram of a main part of FIG.

FIG. 4 is a block diagram showing a conventional current control method.

[Explanation of symbols]

 1,2,3 drive coil UH ~ WL transistor iu * command current iu actual current 28 clock

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02P 6/08

Claims (1)

(57) [Claims] A command current (iu *, iv *, iv *, iv *, iv *, iv *) for each of three-phase drive coils (1, 2, 3) via a pair of transistors (UH to WL).
iw *), in the current control method of the brushless motor configured to control the actual current (iu, iv, iw), the command current (i
u *, iv *, iw *) to zero V, and
Latch at the rise of (28) to turn on any of the transistors (UH to WL) of the phase, the actual current passing through the command current (iu *, iv *, iw *) and the transistor (UH to WL). By turning off the transistor (any of UH to WL) when (iu) becomes equal to each other, the actual current (iu, iv, iw) of each phase is stopped.
Is, the command current (iu *, iv *, iw *) as above no current flows to the driving coils (1, 2, 3), the actual electric of the phase
A current control method for a brushless motor, characterized in that current (iu, iv, iw) is controlled to be constant .