KR930004030B1 - Torque riffle improving method of brushless dc motor - Google Patents

Abstract

The method is for improving the torque ripple caused by the wow/ flutter or drift of the variation of the capstan motor speed. In the linear voltage driving method, the slew rate of the inverter (2) is controlled by the deviation (delta) which minimises the harmonic element (I) of the phase current to maximise the average torque and minimise the torque ripple. Then the turn-on angle and the slope of the phase current wave at the switching time is controlled.

Description

Torque Ripple Improvement Method of Brushless DC Motors

1 is a driving circuit diagram of a general brushless DC motor.

Figure 2 is a perspective view showing the shape of the rotor and stator of a general brushless DC motor.

3 is an explanatory diagram showing a driving method and a current waveform of a general brushless DC motor.

4 is an explanatory diagram of the conduction angle and the switching slope of the phase current waveform.

* Explanation of symbols for main parts of the drawings

1: switching logic unit 2: inverter

3: position detecting element 4: position detecting unit

Q1-Q6: Transistor

The present invention relates to a method for improving the torque ripple of a brushless DC motor, and in particular, the torque ripple represented by W / F (Wow / Flutter) or drift due to the rotational change of the capstan motor for moving the tape of V-Cal. The present invention relates to a method for improving the torque ripple of a brushless DC motor, which is improved by the optimum driving method and is suitable for the control of the capstan motor of VRC.

In general, the rotational variation of the capstan motor that moves the VCA tape is expressed as W / F or drift. The rotational variation of the motor is representative of the torque ripple and the disturbance of the motor itself. Toe ripple is generally caused by:

Due to the mechanical precision, the shift of the switching point and the shift of the magnetic field of each phase may occur, and the distribution of the rotor field is caused by the armature current which is structurally uneven, so in recent years, the field (permanent magnet) is improved in consideration of the armature current. And minimizing the torque ripple by optimizing the magnetization state has been developed.

Therefore, as a method for improving the rotational nonuniformity, first, the feedback control of the drive current by the control circuit technology to average the torque and the servo mechanism control using the speed detector (FG) or the phase control (PLL) technique. The method of improving or arbitrarily processing the drive current waveform by using a microcomputer has been proposed, but it is possible to remove the pulsation elaborately, but the control cost is high.

Secondly, by the method of magnetic circuit analysis, the finite element method is used to diversify the structure of the motor by multipolarization (deformation of shape and shape of magnets or windings), or to install auxiliary windings or auxiliary slots, etc. And a method of improving the magnetic circuit by installing a magnetic distribution correction member in the air gap, but this has a disadvantage in that it costs a lot of money to realize the structure of the motor.

Third, there is a method of adjusting the conduction angle and the direction of energization of the constant and armature currents by the driving method, which are divided into sine wave driving and linear voltage driving when a voltage source is used for classification by a driving source, and constant current driving when a current source is used. Various switching methods have been proposed in law.

However, due to the inductive load of the armature coil generated by applying the armature current as a square wave in the conventional constant current driving method, there is a problem of influence of spike voltage and rotational unevenness due to switching harmonics.

To solve this problem, the present invention proposes a method for improving torque ripple using a linear voltage driving method which gives a slight inclination at the switching moment, which minimizes the driving current in the linear voltage driving method and thus the torque pulsation index. By minimizing the rotation of the motor and adjusting the slope of the conduction angle and the switching moment, that is, the slew rate of the active amplifier in the inverter stage, to maximize the average torque as much as possible, To solve the torque ripple of the brushless DC motor to drive the drive to the optimum drive current to improve the torque ripple, the invention is described in detail with reference to the accompanying drawings as follows.

FIG. 1 is a driving circuit diagram of a general brushless DC motor. As shown in FIG. 1, the energization control signals C1, C2 and C3 and C4 of each phase are provided by the switching logic unit 1 receiving the direction command signal P1. And (C5, C6) are output to control transistors (Q1, Q2), (Q3, Q4), (Q5, Q6) of inverter 2 to control each phase U, V, W. In addition, the position detecting unit 3 is configured to apply the signal P2 according to the rotor position detection to the switching logic unit 4 to control energization timing through the position detecting element 3.

2 is a perspective view showing the shape of a stator and a rotor of a general flat brushless DC motor. As shown therein, the rotor is fixed to the spindle 15 so that the permanent magnet 14 formed of 8 poles in a donut shape is fixed to the spindle 15. 6 bobbin tescoils 12 are fixed on the substrate 11 and two coils facing each other are paired to form a pair (U, V, W) and Y-connected. It is configured to detect the magnetic pole change according to the rotation of the dipole permanent magnet 14 between the bobbin tescoil 12 through the Hall element 13 to output to the position detection unit (4). Here, reference numeral 16 in the drawings denotes rotor yoke.

3 is an explanatory diagram showing a driving method and waveforms of a general brushless DC motor.

First, the classification by the number of phases and the energization direction is classified according to the coil utilization conduction of the phase current. The classification is based on the bipolar (propagation) method and the unipolar (half wave) method. It is classified according to the degree of conduction angle, which is classified into 90 °, 120 °, and 180 °, and the classification by the driving source consists of current driving, which is the collector-side output, and voltage driving, which is the emitter-side output, of a typical N-type power transistor. The voltage drive is classified into linear drive and sinusoidal drive.

During this classification, current driving can improve torque pulsation or W / F because it directly controls the current, but care must be taken for parasitic oscillation, etc., and a surge absorption circuit is needed because the current flows in proportion to the command value. In the servo state, the current corresponding to the load is output to suppress the current consumption.

The voltage drive is relatively stable because the output is emitter follower, and the response is good because it absorbs the energy induced in the coil when the output changes, and the spike current can be absorbed during phase switching, but the current consumption of the circuit increases compared to the current drive. Tend to.

Accordingly, the present invention uses Fourier analysis to determine the optimum current. Since the brushless motor applied to the cap grenade motor does not have a caulking effect that greatly affects the torque pulsation, the torque pulsation largely depends on the pulsation of the current.

Therefore, Fourier analysis of the driving current of the linear voltage driving method is performed to obtain a current waveform that minimizes the magnitude of harmonics that generate the current pulsation.

The definition of the slope of the conduction angle and the switching instant of FIG. 3 is as follows.

Fourier expansion to find the harmonic content of the current using equation (1),

From here, π / 20 I _u (θ) Sin nθ dθ (n = 1, 3, 5,…)

In Fig. 3, since the phase current waveform is half-symmetric, the integration is performed only up to? / 2. If the coefficient of the harmonic term obtained at this time is I _un ,

Here, only the first, fifth, and seventh harmonic terms are considered in terms of the magnitude of the harmonic components, and if the harmonic magnitude of the current is ni,

To minimize this If you find the condition

Where X = 0.008-0.008 * Cos2

-1.018 * 10 ^-5 Cos10

-2.53 * 10 ^-8 Cos14

X '= 0.016 × Sin2

+ 1.018 * 10 ^-4 Sin10

+ 3.54 * 10 ^-7 * Sin14

Solving this best satisfies the above formula (5) in the vicinity of Δ = 6 ° (each constant at this time is a theoretical value).

Therefore, considering the performance evaluation of the motor, if the rotational speed of a small brushless DC motor is N _P ,

If the speed of the rotor is Wm,

P: Number of stimulus

f: frequency of current

Using this, the magnetic flux distribution waveform of the permanent magnet of a brushless DC motor is approximated by an exponential function.

Equation (8) is symmetric with respect to π / 2 and is designated as a negative value in the interval π≤θ <2π.

In addition, as shown in Equation (8), the closer to r → 0, the closer to the square wave, and the closer to r → ∞, the closer to the triangle wave.

As described above, the present invention minimizes the torque pulsation index of the linear voltage drive method and maximizes the average torque as much as possible to obtain the optimum magnetic flux distribution of the permanent magnet as a method for improving the torque characteristics of the brushless DC motor. When adjusting the slope, there is an effect that can significantly improve the torque characteristics at △ = 6 °.

Claims (3)

In the linear voltage driving method of the brushless DC motor, the inverter stage 2 is controlled according to the change rate value (△) at which the harmonic component (I) of the phase current waveform is minimized to minimize the torque pulsation index and maximize the average torque. A method of improving the torque ripple of a brushless DC motor, characterized by adjusting the slew rate of the performance amplifier and controlling the slope of the phase current waveform of the energization angle and the switching moment. The harmonic component (I) of the phase current waveform obtained by Fourier analysis, and then the magnitude of the harmonic component (I). So that the derivative is A method of improving torque ripple in a brushless DC motor, characterized by obtaining a rate of change (Δ) of a condition where?) Becomes zero ("0"). 2. The method of improving torque ripple of a brushless DC motor according to claim 1, wherein the phase current waveform slope at the switching moment is adjusted by setting the change rate value? To 6 degrees.