CN203251262U - Brushless DC motor power conversion circuit - Google Patents

Abstract

The utility model provides a brushless DC motor power conversion circuit used for reducing the torque ripple of a brushless DC motor. The circuit is formed by a DC/DC chopper circuit, an inversion main circuit, and transfer switches. Before the commutation of a motor winding controlled by the inversion main circuit, a transfer switch S3 is switched on, transfer switches S2 and S4 are switched off, and through the collected motor real-time speed value and duty ratio controlled by a switch S1 of the DC/DC chopper circuit, the output voltage following of the DC/DC chopper circuit is controlled and a certain proportional relationship is formed between the output voltage and a motor back electromotive force value. After the commutation is completed, the S3 is switched off, and the S2 and S4 are switched on, which is equivalent to that the DC/DC chopper circuit works before the commutation of a winding in every time. By employing the method and the circuit, the current rise and decrease slopes of windings of switch-on and switch-off phases in the commutation can be the same, the current and torque ripple are small, the noise is reduced accordingly, and the application of this kind of motor systems is raised.

Description

A kind of brshless DC motor power conversion circuit

Technical field

The utility model relates to a kind of brshless DC motor power conversion circuit, the power conversion circuit of the torque pulsation that produces in the time of can suppressing the commutation of brshless DC motor winding.

Background technology

The torque pulsation problem of brshless DC motor is to hinder bottleneck that it is used in some field always, also is focus both domestic and external in recent years about the research and practice of its torque pulsation always.The torque pulsation that wherein produces during commutation between the different windings of motor is the most obvious.

The basic reason that torque pulsation produces during the winding commutation, be turn-off with two electric currents opening phase descend with raise asynchronous, slope is different, thereby has caused the current waveform that synthesizes to produce herein fluctuation, the output torque that affects motor is pulsed.

On correlation theory, if make shutoff synchronous with the curent change of opening phase, must to allow the inverter main circuit dc power supply voltage of its power inverter become the fixed proportion relation with motor winding back electromotive force, and general counter electromotive force of motor size and rotating speed proportion relation, that is to say the power supply size to follow motor speed and change, and satisfy certain proportion relation, the torque pulsation problem in the time of then commutation can being suppressed.

Summary of the invention

Based on above background, the utility model proposes a kind of new power conversion main circuit form based on the DC/DC chopper circuit, can realize the inhibition of brshless DC motor commutation torque pulsation when cooperating certain control mode.

The technical scheme that its technical problem that solves the utility model adopts is:

This new power translation circuit comprises DC/DC chopper circuit, inverter main circuit, change over switch S2, S3, S4, and power supply and brshless DC motor winding.The commutation of inverter main circuit control brshless DC motor three phase windings, before commutation, control change over switch S2 and S4 disconnect, S3 is closed simultaneously, constant dc current source U _sDirect voltage U by the output of DC/DC chopper circuit ₀Be the power supply of motor winding as inverter main circuit, voltage U ₀Size depend on the velocity amplitude of motor, regulate the switch S 1 of DC/DC chopper circuit according to the velocity amplitude that transducer gathers, and then regulated U ₀Value; After commutation finished, the closed simultaneously S3 of S2 and S4 disconnected, and inverter main circuit is by constant-current source U _sDirectly power supply.

The beneficial effects of the utility model are, at commutation period, adopt after this circuit and the control model, opening of commutation period will be along identical slope rise and fall with the electric current that turn-offs phase, the fluctuation of resultant current will reduce greatly, become to be similar to proportional relation under the certain condition and satisfy between winding current and the torque, thereby also just suppressed torque pulsation.

Description of drawings

When Figure 1 shows that between the brshless DC motor winding commutation, the different resultant current waveform that different supply power voltages and back electromotive force Relations Among obtain.

Wherein: i _a, i _b, i _cExpression is turn-offed phase, is opened phase and resultant current respectively; t ₁And t ₂Expression is turn-offed the phase turn-off time and is opened mutually service time respectively; E represents back electromotive force; U _dBe the power supply phase voltage.

Fig. 2 is the brshless DC motor new power inverter main circuit that the utility model proposes.

Wherein: VT1-VT6 is six switching tubes; BLDCM is the abbreviation of brshless DC motor; Be respectively DC/DC chopper circuit and inverter main circuit in two dotted line frames.

Embodiment

(a) of Fig. 1 be (c) three subgraphs (b), have characterized the resultant current situation when different supply power voltages and four times of back electromotive force concern.If U _d≠ 4E, when the switching tube conducting state of inverter main circuit changes and enters commutation during the stage, because the impact of armature winding inductance, electric current can not suddenly change, and turn-offs mutually and open the phase current rate of change not to be both the basic reason that causes the commutation torque pulsation.

(1) works as U _dDuring=4E, t ₁=t ₂, the commutation period torque is constant;

(2) work as U _dDuring＞4E, t ₁＞t ₂, the commutation period torque increases;

(3) work as U _dDuring＜4E, t ₁＜t ₂, the commutation period torque reduces.

Current changing rate is by DC side supply power voltage U _dE determines jointly with back electromotive force, and E is directly proportional with rotating speed, by detecting the real-time speed value of motor, can hold comparatively accurately the E value; Generally, dc voltage U _dOften remain unchanged, and the velocity variations of motor impels E to change, and can not satisfy all the time Ud during speed governing ₌4E, therefore the torque pulsation when commutation is just apparent in view.

And in the new power inverter main circuit of Fig. 2, having increased the DC/DC chopper circuit, this chopper circuit can under the constant prerequisite of input direct voltage, by the duty cycle of switching of control S1, change output dc voltage U ₀Size, if this moment, S3 was closed again, U then ₀=U _dBe exactly inverter voltage.

Input/output relation according to the DC/DC chopper circuit

$U_0=\frac{\mathrm{\α}}{1-\mathrm{\α}}{U}_S---\left(1\right)$

α is DC/DC chopper circuit duty ratio in the formula, is controlled by S1.The pass of back electromotive force E and motor speed is

E＝C _eΦn (2)

C in the formula _eTo prop up way relevant with the number of pole-pairs of motor and winding parallel, is constant; Because brshless DC motor is magnet structure, its magnetic flux phi also is constant; Thereby basic linear approximate relationship between E and the n, obtain can obtain after the value of n the value of E.

At commutation period, so that U _d=U ₀=4E can get according to formula (1) and (2)

$\mathrm{\α}=\frac{4C_e\mathrm{\Φn}}{U_S+4C_e\mathrm{\Φn}}---\left(3\right)$

If supplying DC voltage U in the formula _SKeep constant, the real-time speed signal that gathers of Negotiation speed feedback transducer then, the switch of S1 switching tube that can real time altering DC/DC chopper circuit changes duty ratio, so that U _d=U ₀It is stable that=4E keeps, and cut the DC/DC chopper circuit in commutation temporarily, thereby suppress the generation of commutation torque pulsation.After commutation finished, S3 disconnected, and S2 and S4 are closed.

Claims (1)

1. a brshless DC motor power conversion circuit comprises the DC/DC chopper circuit, inverter main circuit, change over switch S2, S3, S4 is characterized in that: the commutation of brshless DC motor three phase windings of inverter main circuit control, before commutation, S2 and S4 disconnect, S3 is closed, constant dc current source U _sDirect voltage U by the output of DC/DC chopper circuit ₀Be the power supply of motor winding as inverter main circuit, voltage U ₀Size depend on the velocity amplitude of motor, regulate the switch S 1 of DC/DC chopper circuit according to the velocity amplitude that transducer gathers, and then regulated U ₀Value; After commutation finished, the closed simultaneously S3 of S2 and S4 disconnected, and inverter main circuit is by constant-current source U _sDirectly power supply.

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