JPH0389887A - Drive circuit for brushless motor - Google Patents

Abstract

PURPOSE:To reduce the noise and torque ripple by changing the amplitude of the output voltage of the position detecting element of each phase, in inverse proportion to the magnitude of the voltage or current applied to the driving coil. CONSTITUTION:An inverter amplifier 10 generates a signal being in inverse proportion to an amplitude control signal input S, which is in proportion to the amplitude of driving signals applied to driving coils L1, L2, L3. And, this signal is used as a multiplier for multiplying the output voltages H1, H2, H3 of the Hall elements of multiplying devices 9a, 9b, 9c, or a gain for the output voltages H1, H2, H3 of the Hall elements. And, the gain is changed in inverse proportion to the amplitude of the driving signals. As result, the input waveforms of limiters 4a, 4b, 4c come to have large amplitude as the gain becomes high in time of low-speed revolution, and have small amplitude as the gain becomes low in time of high-speed revolution or under a heavy load. When the waveforms are clipped at constant voltage V1, the inclination of the waveforms of coil driving signals becomes steep and low torque ripple is maintained in time of low-speed revolution, and the inclination becomes gentle and the noise reduces in time of high-speed revolution or under a heavy load.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention drives a DC brushless motor in a semi-linear manner, thereby reducing torque ripple and noise to the best possible value under the conditions of use where each characteristic is required. This invention relates to a drive circuit for a brushless motor.

[Summary of the Invention] The present invention provides a brushless motor drive circuit that adds or subtracts all or part of the output voltages of a plurality of position detection elements of a rotor to semi-linearly synthesize the voltage or current applied to the coil. By changing the amplitude of the output voltage of the position detection element in inverse proportion to the magnitude of the voltage or current applied, clipping the output voltage, and changing the slope of the drive waveform of the voltage or current applied to the coil, At low speed rotations where torque ripple is a problem, the slope is increased to maintain low torque ripple, and at high speed rotations or high loads where noise is a problem, the slope is flattened to smoothly switch the coil current and reduce noise. By doing so, torque ripple and noise can be optimized under the conditions of use where each characteristic is required.

[Prior Art] Conventionally, DCC brushless motors have been known in which magnets are disposed on the rotor and the rotor is rotated by switching voltages or currents applied to drive coils of multiple phases on the stator side. When driving the C brushless motor in this manner, it is necessary to sequentially switch the current flowing through each drive coil according to the rotation angle. Normally, this switching is performed by shaping the output of a Hall element that detects the leakage flux of the rotor's magnet and throat into a rectangular wave. However, sudden switching is undesirable because it causes electrical and acoustic noise. Furthermore, in that case, the torque ripple is large, so when used in a capstan motor for a VTR (video tape recorder) or the like, sufficient wow and flutter characteristics may not be obtained.

Therefore, a semi-linear drive was devised and used that linearly amplifies the waveform of the Hall element, performs waveform synthesis to smoothly switch the coil current, and further corrects the torque ripple by overlapping energization. There is.

FIG. 5 is a block diagram of a conventional semi-linear drive circuit for a brushless motor. This brushless motor has a three-phase configuration and includes drive coils L, , L, , L, each having a three-phase configuration. la, lb, and IC are three Hall elements that detect the magnet glue and cage flux of the rotor (not shown) corresponding to each of the three phases, 2 is a power supply for the detection, and 3a, 3b, and 3c are each Hall elements 1a, lb, l
This is a Hall element amplifier that amplifies the output of c. 4a+4
b, 4c are limiters, Hall element amplifiers 3a,
The outputs of the Hall elements 1a+lb, lc amplified by 3b, 3c are clipped at a constant voltage (V, ). In this way, the clipped waveform is transferred to the adders 5a, 5b, 5c.
The added waveforms are added between each phase by the other limiters 5a, 5b, and 5c, respectively, at a constant voltage (■,).
clip and synthesize the waveforms necessary for driving. 7
a, 7b, 7C are multipliers, limiters 6a, 5b
, 6c, the clipped drive waveform is multiplied according to the amplitude control signal input S. Each of the multiplied drive waveforms is amplified by power amplifiers 8a, 8b, and 8c, respectively, and is applied to the drive coil L1+ Tjt+ as a drive voltage or drive current.
Applied to L3. The part of this drive waveform that is related to acoustic noise is the slope, and the flatter the slope, the lower the sound/noise can be.

Further, the portion related to the torque ripple is a portion where the drive waveforms of each phase overlap, and the amount of correction of the torque ripple is determined by the amount of overlap.

[Problems to be Solved by the Invention] However, in the semi-linear drive circuit of the brushless motor in the conventional technique described above, when the slope of the drive waveform is flattened to reduce acoustic noise, the overlapping part becomes smaller and torque ripple worsens. On the other hand, if a sloped section is erected to improve torque ripple, there is a problem in that acoustic noise increases.

The present invention was devised to solve the above problems, and an object of the present invention is to provide a brushless motor drive circuit that reduces noise and torque ripple.

[Means for Solving the Problems] The configuration of the brushless motor drive circuit of the present invention to achieve the above object is to clip the output voltage of the position detection element of each phase and add or subtract all or part of the output voltage. In a brushless motor drive circuit that synthesizes the voltage or current applied to the drive coil by controlling it to a predetermined magnitude after addition or subtraction, the amplitude of the output voltage of the position detection element of each phase is converted into the voltage or current applied to the drive coil. The present invention is characterized by providing means for changing the current in inverse proportion to the magnitude of the current.

[Operations] In the present invention, noise is relatively less of a problem when rotating at low speeds, but torque ripple is a problem, and torque ripple is relatively less of a problem when rotating at high speeds or under high loads, but acoustic noise is a problem. The amplitude of the output voltage of the position detection element is changed in inverse proportion to the magnitude of the voltage or current applied to the coil, and the output voltage is clipped to create the drive waveform of the voltage or current applied to the coil. By changing the slope of the coil current, it is possible to maintain low torque ripple by increasing the slope during low speed rotations where torque ripple becomes a problem, and by flattening the slope during high speed rotations or high loads where noise is a problem. Switch smoothly to reduce noise.

[Example] Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In FIG. 1, members having the same functions as those in FIG. 5 are given the same reference numerals. This embodiment shows an example in which the present invention is applied to a three-phase DC brushless motor. D of this example
CC brushless morph, 3-phase drive coils L, L, L3 are arranged on the stator side, and magnetized poles facing the drive coils L, L, L, on the rotor side, although not shown in the figure. It is equipped with a magnet. D.C.C.
Brushless morph, drive coil L for each phase, L□ L3
The rotor is rotated by controlling the magnitude and polarity of the voltage or current applied to it to obtain a predetermined rotational speed and torque.

First, a configuration example of a means for changing the slope of the rising and falling slopes of the driving waveform of the driving coils L, , L, , L will be described. la, lb, and lc are Hall elements as position detection elements that detect the magnet glue and cage flux of the rotor corresponding to each of the three phases, 2 is the power supply for detection, and 3a, 3b + 3c are each hole Element 1a
, lb, and lc. 9a.

9b and 9c are multipliers that multiply the output voltages of the Hall elements la, lb, and lc amplified by the Hall element amplifiers 3a+3b+3c by a predetermined value, and the predetermined value is applied to the drive coils L, L, L3. An amplitude control signal for controlling the magnitude of the applied driving voltage or driving current is set to a value inversely proportional to the human power S. That is, the amplitude control signal human power S is inverted by an inverting amplifier IO to create an output inversely proportional to the amplitude control signal human power S, and is connected to the input of each multiplier 9a, 9b, 9c through a limiter 1l.

Next, the configuration of the means for synthesizing the drive waveforms of the drive coils Ll+Lx and L- will be described. Limiters 4a, 4b, and 4c clip the respective outputs of the multipliers 9a, 9b, and 9C to a constant voltage V1. Each limiter-4a
, 4b, 4c are non-inverted outputs HIC, Hff as outputs.
1c + H3 (and inverted output Hlc + H1°, H, c, and these phase outputs are mutually added m5a, 5b, 5c
Connect to to synthesize waveforms. That is, tr, c and Hjc are connected to the input of the adder 5a, Htc and Hlc are connected to the input of the adder 5b, and H is connected to the input of the adder 5c.
Connect 2C and “=.

The combined waveform of each phase of adders 5a+5b, 5c is sent out via limiters 6a, 6b, 6c. These limiters 6a, 5b, and 6c are for determining the amount of overlap of the composite waveform between each phase, and each clips at a constant voltage (V).

The coil driving signal waveform synthesized in this way is sent to the multiplier 7
a, 7b, and 7c are multiplied by the amplitude control signal S to control its magnitude, and the power amplifiers 8a, 8b,
8c, it is applied to the drive coils L, , L, , L3 as a drive voltage or drive current.

In the above, the amplitude control signal human power S is given from a control means (not shown) to obtain the necessary torque or rotational speed depending on the usage state of the brushless motor, and is input to each multiplier 7a, 7b, 7C. connected to.

The operation and effect of the embodiment configured as above will be described.

FIG. 2 is a waveform diagram showing the operation of this embodiment, and in the figure (
(a) shows the output voltage H,, H□H1 of the Hall element amplified by the Hall element amplifiers 3a, 3b, and 3C, and (b) shows the non-inverted output HIC clipped at a constant voltage V1 in the limiter 4a. , (C) shows the inverted output H3C clipped by the constant voltage V1 in the limiter 40, (d) shows the composite waveform of H1c+H5c added by the adder 5a, and (e) shows the waveform of each phase U, V, The signal waveform for driving the coil of W is shown. In semi-linear drive, (a)
The amplified output voltage of the Hall element shown in is clipped at a constant voltage V1, and as shown in (d), the inverted output and non-inverted output are added between each phase, and the waveforms of each phase are synthesized. . Furthermore, 2 after addition as shown in (d)
The synthesized waveform with an amplitude of v is transmitted to limiters 6a, 6b, 6
A constant voltage V t (V + < V t <
2V l) Tick') to obtain the coil drive signal waveform necessary for driving each phase U, V, and W shown in (e).

In this coil drive signal waveform', the parts related to acoustic noise are the rising and falling slopes, and the flatter the slope, the smoother the switching of the coil current can be, so the noise can be lowered. can do. On the other hand, the part related to torque ripple is the part where the coil drive signal waveform overlaps between phases.
The amount of torque ripple correction can be determined based on the amount of overlap. In the coil drive signal waveform (e), if the timing at which the voltages become equal in the overlapped portion between phases is tl, and the voltage value at that time is V, then the amount of overlap is determined by Vs/Vt. V
3, the other side's waveform to be added at time t is V
If it is clipped by l, it becomes v1V3, and the amount of overlap is determined by V, /V, so it is not affected by the output of the Hall element. In this way, the semi-linear drive method uses the linear portion of the output of the Hall element to create a smoothly changing drive waveform, while being unaffected by variations in the output of the Hall element. However, recently, demands regarding acoustic noise have increased, and motors with lower noise have been required. In order to realize a low-noise motor, it is necessary to further reduce the slope of the slope. However, if the slope is gradually lowered, the waveform of the other side that is added at time tl will no longer be clipped at Vl, and the overlap will no longer be maintained, leading to worsening of torque ripple. Therefore, in this example,
Multipliers 9a, 9b, and 9c are used to change the slope of the slope depending on the usage state of the brushless motor, that is, the rotational speed and load state.

FIG. 3 is an explanatory diagram of the operation at low speed rotation in this embodiment, and FIG. 4 is an explanatory diagram of the operation at high speed rotation and high load in this embodiment. When using a brushless motor,
Low torque ripple is required at low speeds, and noise becomes a problem at high speeds or high loads. The amplitude of the drive signal applied to the drive coils L, , L□L is controlled to a small amplitude by the amplitude control signal S during low speed rotation, and is controlled to a large amplitude during high speed rotation and high load.

Therefore, in this embodiment, a signal that is inversely proportional to the amplitude control signal human power S that is proportional to the drive signal amplitude is created by the inverting amplifier 10, and this is applied to the Hall element output voltage H, , H of the multiplier 9 a + 9 b + 9 C. , , H, the gain for the Hall element output voltage is changed in inverse proportion to the drive signal amplitude.

As a result, the input waveforms of limiters 4a, 4b, and 4c are as follows:
During low speed rotation, the gain increases and the amplitude becomes large, as shown in Figure 3 (a), and during high speed rotation and high load, the gain decreases and the amplitude becomes small, as shown in Figure 4 (a). . If this is clipped at a constant voltage V1, the slope of the coil drive signal waveform becomes steeper during low speed rotation, as shown in Figure 3 (b).
), the amount of overlap is maintained and low torque ripple is maintained, and the slope of the coil drive signal waveform is flattened during high speed rotation and high load, resulting in a smooth coil as shown in Figure 4(b). This becomes a driving signal waveform, and noise is reduced. At this time, if the slope of the drive signal waveform is too steep, the motor efficiency will drop, so limiter 1
1 prevents the gain with respect to the Hall element output voltage from becoming less than a certain gain.

It is clear that the present invention is applicable not only to brushless motors with a three-phase configuration but also to other multi-phase configurations. Multipliers 9a, 9b, and 9C are Hall element amplifiers 3a and 3b, respectively.

3c, and the gains of the Hall element amplifiers 3a, 3b, and 3c may be controlled by the output of the limiter 11 instead. Further, in waveform synthesis, adders 5a and 5b.

The waveform shown in the embodiment can be synthesized by using a subtracter instead of 5C and using only the non-inverted output of the previous stage. As described above, the present invention can be applied in various ways and can take various embodiments in accordance with its gist.

[Effects of the Invention] As is clear from the above explanation, the brushless motor drive circuit of the present invention changes the amplitude of the output voltage of the position detection element in inverse proportion to the magnitude of the voltage or current applied to the drive coil. The torque ripple is optimized when the voltage or current applied to the drive coil is small, and the acoustic noise is minimized when the voltage or current applied to the drive coil is large. It can be made into the best possible condition under the conditions of use.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing one embodiment of the present invention, Fig. 2 is a waveform diagram showing the operation of this embodiment, Fig. 3 is an explanatory diagram of the operation of this embodiment at low speed rotation, and Fig. 4 is the main FIG. 5 is a block diagram of a drive circuit of a conventional brushless motor. la, lb, 1c---Hall element, 3a, 3b.

Claims (1)

[Claims] (1) A brushless motor that clips the output voltage of the position detection element of each phase, adds or subtracts all or part of it using an adding/subtracting means, and then controls it to a predetermined magnitude to synthesize the voltage or current applied to the drive coil. A drive circuit for a brushless motor, characterized in that the drive circuit is provided with means for changing the amplitude of the output voltage of the position detection element of each phase in inverse proportion to the magnitude of the voltage or current applied to the drive coil.