CN106059407A - Current control method for reducing torque ripple of brushless DC motor - Google Patents

Abstract

The invention discloses a current control method for reducing the torque ripple of a brushless DC motor. The control method comprises the steps that (1) current control for a reference waveform, which is calculated by taking a calculation formula as reference, is carried out; and (2) a current hysteresis compared PWM method is used, and a discrete current reference value is written in a brushless DC motor program according to the reference waveform value obtained in the step 1. The current control method can ensure that the motor torque is not decreased in the whole rotation process of the brushless DC motor; the operationality is high, and the control method is simple and convenient to popularize and use; and the control method can satisfy requirements for low-speed operation and high-precision motion control of a servo system, and provides basic technical conditions for present motor servo systems.

Description

A kind of current control method reducing brushless direct current motor torque ripple

Technical field

The present invention relates to X in brushless DC motor control field, particularly relate to a kind of reduction brushless direct current motor torque The current control method of fluctuation.

Background technology

Brushless direct current motor is the one of dc motor, uses permanent magnet excitation, with position sensor and electronic cutting Close circuit and replace the brush of dc motor and slip ring, there is the simple in construction of ac motor, reliable, easy to maintenance etc. Series of advantages, the operational efficiency possessing again dc motor is high, without the plurality of advantages such as excitation loss and good speed adjustment features, leads to Cross servo-controlled brushless direct current motor and be widely used in the motor control systems such as electric automobile, robot, Digit Control Machine Tool In the middle of system.

The common control electric current in brushless direct current motor winding is square wave, and position sensor uses Hall element, Or use the control technology (being applied to the electric drive system that position control is the highest) of position-sensor-free.Motor generally uses The working method of star three-phase six state, armature supply every 60 ° of electrical angle commutations once, thus causes rotor often to turn over 60 ° Electrical angle armature field spatially changes once along direction of rotation saltatory, has distinctive turn during the energising of motor winding Square fluctuates.The existence of torque ripple is a big defect of this motor, especially low speed occasion, and torque ripple is the most prominent, It is difficult to the speed controlling of more accurate position control and higher performance, thus limits it and further apply.Now need one Plant Control Method of Brushless DC Motor, to overcome the problems referred to above.

Summary of the invention

Technical problem solved by the invention is to provide a kind of control method, it is achieved and meet servosystem low cruise A kind of current control method reducing brushless direct current motor torque ripple controlled with high-precision motion, to solve above-mentioned background Practical problem in technology.

Technical problem solved by the invention realizes by the following technical solutions:

The present invention provides a kind of three-phase brushless DC motor to control the reference waveform of electric current, and uses according to reference waveform The PWM that Hysteresis Current compares realizes reducing brushless direct current motor torque ripple.

Reference waveform is as follows:

(1) described current control reference waveform be wave crest shape two ends exceed, middle recessed.

(2) described reference waveform wave crest is shaped as smooth curved section；

(3) current maxima I of described reference waveform_max, minima I_minCurrent amplitude I when controlling with square wave_mCompare, There is equation below:

$\frac{I_{\max }+I_{\min }}{2}=I_m---\left(1\right)$

(4) in the brshless DC motor current control mode using reference waveform to be the straight square wave in top, at winding During the commutation of twice adjacent 60 ° electrical angle of electric current, magnetomotive force F that armature supply produces_aSpace and amplitude keep Constant, that permanent magnet produces magnetomotive force F_mAmplitude is constant, but it is with armature magnetomotive force F_aAngle theta become 60 ° from 120 ° of electrical angles Electrical angle.The torque that motor produces is

T=k_TF_aF_m sinθ (2)

Wherein: T is torque；k_TFor the constant determined by motor；F_aFor armature magnetomotive force；F_mMove for permanent magnet magnetic Gesture；θ is angle；

Owing to the change of θ causes torque T fluctuation during 60 ° of electrical angle armature supply conductings.

Described reference waveform, during θ is become 60 ° of electrical angles from 120 ° of electrical angles, smoothly regulation armature magnetomotive force F_a Size so that motor produce torque T keep constant.

The torque T=Ta (Ta is definite value) making motor produce keeps constant, magnetomotive force F that armature supply produces_a, can push away Derive F_aRelation equation below with θ:

$F_a=\frac{T_a}{k_T{F}_m}\frac{1}{sin\mathrm{\θ}}---\left(3\right)$

Wherein F_aWith armature supply I, there is linear relationship.In conjunction with formula (1), I=h (θ) can be derived as reference waveform Current control reference numerical value.

Calculate θ ∈ [θ₀+ 60 °, θ₀+ 120 °] in I value (θ₀For the electricity that winding current conducting moment rotor magnetic pole is corresponding Angle), and as form table [I1, I2, I3 ... I256], the interior interval to 60 ° of form is divided into 256 values, As resolution, respectively θ 1, θ 2 ... θ 255, θ 256.256 values h (θ 1), h (θ 2) ... h (θ corresponding in form 255), h (θ 256) obtains the discrete reference value that electric current controls.

The invention has the beneficial effects as follows:

1, the present invention proposes a kind of current control method reducing brushless direct current motor torque ripple, and guarantees whole Motor torque in brushless direct current motor rotation process does not declines；

2, the present invention is workable, and control method is simple, it is simple to promote the use of；

3, the present invention meets servosystem low cruise and the needs of high-precision motion control, for motor servo system now The fundamental technical specifications of system.

Accompanying drawing explanation

Fig. 1 is the square-wave waveform schematic diagram that the present invention is traditional；

Fig. 2 is the reference waveform schematic diagram of the present invention；

Fig. 3 is the reference waveform three-phase current application schematic diagram of the present invention；

Fig. 4 is the hysteretic loop current control control figure of brushless direct current motor.

Detailed description of the invention

A kind of current control method reducing brushless direct current motor torque ripple to the present invention below with reference to accompanying drawings Embodiment be described in detail.

The present invention provides a kind of three-phase brushless DC motor to control the reference waveform of electric current, and uses according to reference waveform The PWM that Hysteresis Current compares realizes reducing brushless direct current motor torque ripple.

As it is shown in figure 1, three-phase brushless DC motor controls the square-wave waveform reference waveform of electric current, square wave current controls ripple The wave crest shape of shape is straight, and armature supply every 60 ° of electrical angle commutations once, thus causes rotor often to turn over 60 ° of electric angles Degree armature field spatially changes once along direction of rotation saltatory, there is distinctive torque ripple during the energising of motor winding Dynamic.

The current control method step reducing brushless direct current motor torque ripple that the present invention provides is as follows:

(1) reference waveform is derived

Reference waveform, the difference square wave that to be embodied in wave crest shape different, traditional compared with traditional square-wave waveform It is straight that electric current controls the wave crest shape of waveform.The current control reference waveform of the present invention be wave crest shape two ends exceed, in Between recessed.

Two ends exceed, middle recessed reference waveform uses smooth curved section, and electric current exists maximum I_max, minima I_min, current amplitude I when controlling with square wave_mCompare, there is following relation:

$\frac{I_{\max }+I_{\min }}{2}=I_m---\left(1\right)$

In the brshless DC motor current control mode using reference waveform to be the straight square wave in top, at winding current Twice adjacent 60 ° electrical angle commutation during, armature supply produce magnetomotive force F_aSpace and amplitude keep constant, Magnetomotive force F that permanent magnet produces_mAmplitude is constant, but it is with armature magnetomotive force F_aAngle theta become 60 ° of electric angles from 120 ° of electrical angles Degree.The torque that motor produces is

T=k_TF_aF_m sinθ (2)

Wherein: T is torque；k_TFor the constant determined by motor；F_aFor armature magnetomotive force；F_mMove for permanent magnet magnetic Gesture；θ is angle；

Owing to the change of θ causes armature supply fluctuation of torque T during 60 ° of electrical angle conductings.

Reference waveform, during θ is become 60 ° of electrical angles from 120 ° of electrical angles, smoothly regulation armature magnetomotive force F_aBig Little so that the torque T that motor produces keeps constant.

(2) PWM using Hysteresis Current to compare realizes

The torque T=Ta (Ta is definite value) that motor is produced keeps constant, can derive F_aThe most public with the relation of θ Formula:

$F_a=\frac{T_a}{k_T{F}_m}\frac{1}{\sin \mathrm{\θ}}---\left(3\right)$

Wherein F_aWith armature supply I, there is linear relationship.In conjunction with formula (1), I=h (θ) can be derived, such as Fig. 2, Fig. 3 institute Show.

(θ 0 turns on, for winding current, the electricity that moment rotor magnetic pole is corresponding to calculate the I value in θ ∈ [θ 0+60 °, θ 0+120 °] Angle), and as form table [I1, I2, I3 ... I256], the interior interval to 60 ° of form is divided into 256 values, As resolution, respectively θ 1, θ 2 ... θ 255, θ 256.256 values h (θ 1), h (θ 2) ... h (θ corresponding in form 255), the discrete reference value that h (θ 256) controls as electric current.

It is illustrated in figure 4 the PWM hysteretic loop current control block diagram of brushless direct current motor (BLDCM), the three-phase electricity calculated Scattered reference value of wandering about as a refugee write brshless DC motor controls program, compares with the real-time measurement values of winding current, is passed through stagnant chain rate relatively Device produces pwm control signal, it is achieved control.

The foregoing is only embodiments of the invention, not in order to limit the present invention, all spirit in the present invention and Any amendment, equivalent and the improvement etc. made within principle, should be included within the scope of the present invention.

Claims (2)

1. the current control method reducing brushless direct current motor torque ripple, it is characterised in that:

The reference waveform of electric current have (1) current control reference waveform be wave crest shape two ends exceed, middle recessed；(2) described Current maxima I of reference waveform_max, minima I_minCurrent amplitude I when controlling with square wave_mCompare, there is equation below:

$\frac{I_{max}+I_{min}}{2}=I_m---\left(1\right)$

(3) torque that brushless direct current motor produces is:

T=k_TF_aF_msinθ (2)

Wherein: T is torque；k_TFor the constant determined by motor；F_aFor magnetomotive force；F_mFor magnetomotive force；θ is angle；

Described reference waveform, during θ is become 60 ° of electrical angles from 120 ° of electrical angles, meets following condition between θ and electric current: order The torque T=Ta (Ta is definite value) that motor produces keeps constant, magnetomotive force F that armature supply produces_a, derive F_aPass with θ It is equation below:

$F_a=\frac{T_a}{k_T{F}_m}\frac{1}{sin\mathrm{\θ}}---\left(3\right)$

Wherein F_aWith armature supply I, there is linear relationship, derive the I=h (θ) the current control reference calculating as reference waveform Formula.

A kind of current control method reducing brushless direct current motor torque ripple the most according to claim 1, its feature Being: rate-determining steps is divided into two steps, (1) calculates the electric current of described reference waveform and controls, and calculates reference with reference to computing formula Waveform；(2) use the method for PWM that Hysteresis Current compares, the reference waveform numerical value calculated according to the first step, to brushless directly Stray currents reference value in stream motor program writes.