CN1555130A

CN1555130A - Pulse width modulation method for permanent magnet brushless DC motor

Info

Publication number: CN1555130A
Application number: CNA2003101229096A
Authority: CN
Inventors: 张仲超; 韦鲲
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2003-12-26
Filing date: 2003-12-26
Publication date: 2004-12-15
Anticipated expiration: 2023-12-26
Also published as: CN1269304C

Abstract

This invention discloses a pulse width modulation method used in permanent magnetic brush-less DC motor, which is put forward against the shortage of the current PWM method. The PWM-ON-PWM method is suitable for the pulse width modulation when a brush-less DC motor works at 120deg. electric angle, each switch tube is in 120deg. trigger pulse width, the front 30deg. interval modulates the pulse width, the mid 60deg. interval keeps constant conduction and the rear 30deg. interval modulates the pulse width, which can eliminate the continuous current on non-conductive phase in the period of non-phase switch to increase the smooth operation of the motor.

Description

Be applied to the pulse-width modulation method of permanent-magnet brushless DC electric machine

Affiliated technical field

The present invention relates to a kind of pulse-width modulation method that is applied to permanent-magnet brushless DC electric machine.

Background technology

Existing PWM (Pulse WidthModulation) modulation technique that is used for permanent-magnet brushless DC electric machine (stator winding Y-connection), when motor uses the three-phase half-bridge inverter to drive and worked in for 120 degree conduction mode following times, can be at non-commutation period, make the terminal voltage of non-conduction phase be higher than DC bus-bar voltage or be lower than no-voltage, and then cause the non-conduction freewheel current that produces mutually, aggravate the motor electromagnetic torque pulsation.

Summary of the invention

The objective of the invention is to deficiency at above-mentioned existing PWM modulator approach existence, a kind of pulse-width modulation method that is applied to permanent-magnet brushless DC electric machine is provided, it is PWM_ON_PWM (pulse-width modulation _ perseverance is led to _ pulse-width modulation) modulator approach, eliminate the non-conduction freewheel current that goes up mutually of non-commutation period, increase the motor traveling comfort, the electromagnetic torque pulsation problem when reducing the motor operation.

In order to achieve the above object, the technical solution used in the present invention is as follows:

Permanent-magnet brushless DC electric machine with trapezoidal wave back emf waveform adopts three-phase semibridge system main circuit to drive, and machine operation is under 120 degree electrical degree modes; Three of last brachium pontis, three of following brachium pontis are that each switching tube trigger pulse width is 120 ° of electrical degrees in six switching tubes, 60 ° of electrical degrees of phase place mutual deviation, promptly once every 60 ° of electrical degree commutations; Commutation signal is by the square-wave signal decision that is installed in the Hall element output on the motor; For each switching tube, its trigger pulse width is 120 ° of electrical degrees, trigger impulse preceding 30 ° promptly 0～30 ° carry out pulse-width modulation, be the non-conduction back electromotive force zero-crossing of going up mutually of a correspondence in the time of 30 °; 30～90 ° keep permanent logical, are the non-conduction back electromotive force zero-crossing of going up mutually of another correspondence in the time of 90 °; Carry out pulse-width modulation in 90～120 ° of intervals; Pulse-width modulation _ perseverance on Here it is the switching tube is logical _ forming process of pulse duration modulation method; The modulator approach of other 5 switching tubes is identical with it.

The present invention compared with prior art, the useful effect that has is: it adopts pulse-width modulation _ perseverance to lead to _ pulse-width modulation (PWM_ON_PWM) modulator approach, eliminate the non-conduction freewheel current that goes up mutually of non-commutation period, increase the motor traveling comfort, the electromagnetic torque pulsation problem when reducing the motor operation.

Description of drawings

The invention will be further described below in conjunction with drawings and Examples.

Fig. 1 is the PWM_ON_PWM modulator approach schematic diagram that the present invention proposes;

Fig. 2 be the phase current waveform that emulation obtains when adopting the PWM_ON_PWM modulator approach that traditional PWM_ON modulator approach and the present invention propose (on) and electromagnetic torque waveform (descending);

Fig. 3 is an actual testing of electric motors phase current waveform when adopting the PWM_ON_PWM modulator approach that traditional PWM_ON modulator approach and the present invention propose.

Embodiment

The PWM_ON_PWM modulator approach schematic diagram that Fig. 1 proposes for the present invention.Wherein dash area is the zone of carrying out the PWM modulation.T1～T6 represents the trigger waveform of corresponding switching tube respectively among the figure; Thick dashed line PA, PB, PC represent the position signalling of brshless DC motor Hall rotor-position sensor output respectively; e _A, e _CRepresent the back emf waveform that A and C go up mutually respectively; For every switching tube trigger impulse, modulation areas is preceding 30 degree and back 30 degree, and middle 60 degree are not modulated, and keep permanent logical.With the T3 pipe is the method that the example explanation realizes, other switching tube trigger impulses realize that principle is identical with it.

At the rising edge of Hall rotor-position sensor output PB signal, i.e. t ₁Constantly, the T1 switching tube turn-offs, and the T3 switching tube is opened and carried out the PWM modulation, and it is permanent logical that the T2 switching tube still keeps; When rotor-position arrives t ₂Constantly, promptly during A phase back electromotive force zero passage, the T3 switching tube stops the PWM modulation, keeps permanent logical state, and the T2 switching tube begins to carry out the PWM modulation simultaneously; Arrive t ₃Constantly, i.e. commutation is (PA trailing edge) constantly, and T2 manages shutoff, and the T4 pipe is opened and carried out the PWM modulation simultaneously, and the T3 pipe still keeps permanent logical; Arrive t ₄Constantly, i.e. back electromotive force e _CDuring zero passage, the T4 pipe stops the PWM modulation, keeps permanent logical, and the T3 pipe is beginning PWM modulation by the logical state-transition of original perseverance simultaneously; This state lasts till next commutation t constantly always ₅, promptly the rising edge of PC signal arrives constantly, and T3 manages shutoff, and the T5 pipe is opened and is carried out the PWM modulation, and it is permanent logical that the T4 pipe still keeps; Arrive this, formed the complete trigger impulse of T3 pipe one time.

According to above-mentioned principle, other the trigger impulse of 5 switching tubes is carried out same processing, just can realize purpose of the present invention.

Compare with existing PWM modulator approach, modulator approach of the present invention can be under identical switch power consumption, during stable state, at non-commutation period, non-conduction phase winding terminal voltage can not be higher than DC bus-bar voltage and be lower than no-voltage, eliminates non-conduction diode phase afterflow phenomenon fully, reduces electromagnetic torque pulsation.According to brshless DC motor commutation period electromagnetic torque pulsation analysis and research are shown, commutation period is opened pipe and is carried out commutation electromagnetic torque pulsation that the PWM modulation produces to carry out the commutation electromagnetic torque pulsation that the PWM modulation produces than non-commutation pipe little; And the invention belongs to the situation that pipe carries out PWM modulation of opening.In general, the present invention can eliminate the afterflow of the non-conduction phase of non-commutation period fully, reduces the electromagnetic torque pulsation of non-commutation period, belongs to the less class modulator approach of commutation period electromagnetic torque pulsation again, reduces the commutation torque pulsation; Therefore, the present invention is a kind of modulator approach more excellent than traditional PWM modulator approach, and the motor runnability is significant for improving, and has very high using value.

Actual effect is as described below:

Fig. 2 be the phase current waveform that emulation obtains when having chosen the modulator approach that a kind of traditional PWM modulator approach (PWM_ON) and the present invention propose (on) and electromagnetic torque waveform (descending).A) emulation obtains when adopting traditional PWM_ON (preceding 60 degree PWM modulation, back 60 degree are permanent logical) phase current waveform (last figure) and the electromagnetic torque waveform (figure below) of correspondence among the figure.The place of drawing a circle in the phase current waveform is exactly the place with freewheel current; The place of drawing a circle in the electromagnetic torque waveform is exactly the place of the electromagnetic torque pulsation that causes owing to freewheel current; When Fig. 2 b) being depicted as the PWM_ON_PWM modulator approach that adopts the present invention's proposition, phase current waveform that emulation obtains (last figure) and corresponding electromagnetic torque waveform; The place of drawing a circle in the phase current waveform does not have the freewheel current as shown in a) as figure; And also little a lot of than in a) of the degree of pulsatility of electromagnetic torque waveform.

Figure 3 shows that actual testing of electric motors phase current waveform under two kinds of modulator approaches.A) be the phase current waveform that records when adopting traditional PWM_ON modulator approach, the place of drawing a circle among the figure is exactly the place with afterflow; B) phase current waveform that actual test obtains when adopting the PWM_ON_PWM modulator approach that the present invention proposes a) is compared with figure, and the place of drawing a circle among the figure does not have the afterflow generation.

Claims

1 one kinds of pulse-width modulation methods that are applied to permanent-magnet brushless DC electric machine is characterized in that: have the permanent-magnet brushless DC electric machine of trapezoidal wave back emf waveform, adopt three-phase semibridge system main circuit to drive, machine operation is under 120 degree electrical degree modes; Three of last brachium pontis, three of following brachium pontis are that each switching tube trigger pulse width is 120 ° of electrical degrees in six switching tubes, 60 ° of electrical degrees of phase place mutual deviation, promptly once every 60 ° of electrical degree commutations; Commutation signal is by the square-wave signal decision that is installed in the Hall element output on the motor; For each switching tube, its trigger pulse width is 120 ° of electrical degrees, trigger impulse preceding 30 ° promptly 0～30 ° carry out pulse-width modulation, be the non-conduction back electromotive force zero-crossing of going up mutually of a correspondence in the time of 30 °; 30～90 ° keep permanent logical, are the non-conduction back electromotive force zero-crossing of going up mutually of another correspondence in the time of 90 °; Carry out pulse-width modulation in 90～120 ° of intervals; Pulse-width modulation _ perseverance on Here it is the switching tube is logical _ forming process of pulse duration modulation method; The modulator approach of other 5 switching tubes is identical with it.