阅读说明：本技术 一种永磁直流无刷电机的反电动势过零点检测电路 (Back electromotive force zero-crossing detection circuit of permanent magnet brushless direct current motor ) 是由 李先虎 于 2019-08-05 设计创作，主要内容包括：本发明公开了一种永磁直流无刷电机的反电动势过零点检测电路,包括：浮地电源电路、过零点比较电路、逻辑电平平移电路；所述浮地电源电路,与所述过零点比较电路、逻辑电平平移电路连接,用于给所述过零点比较电路、逻辑电平平移电路提供电能；所述过零点比较电路,用于判断是否存在过零时点,若存在,则输出浮地逻辑电平；所述逻辑电平平移电路,与所述过零点比较电路连接,用于将过零点比较电路输出的浮地逻辑电平转换成以控制系统地GND为参考的逻辑电平输出。本发明无衰减地取得悬浮相的反电动势输入到电压比较器,实现准确的过零时点的检测,适用于无位置传感器120°方波的永磁直流无刷电机的驱动系统。(The invention discloses a counter electromotive force zero-crossing detection circuit of a permanent magnet brushless DC motor, which comprises: the circuit comprises a floating power circuit, a zero crossing point comparison circuit and a logic level translation circuit; the floating power circuit is connected with the zero crossing point comparison circuit and the logic level translation circuit and is used for providing electric energy for the zero crossing point comparison circuit and the logic level translation circuit; the zero crossing point comparison circuit is used for judging whether a zero crossing point exists or not, and if yes, outputting a floating logic level; and the logic level translation circuit is connected with the zero-crossing point comparison circuit and is used for converting the floating logic level output by the zero-crossing point comparison circuit into a logic level output by taking the control system ground GND as a reference. The invention obtains the counter electromotive force of the suspension phase without attenuation and inputs the counter electromotive force to the voltage comparator, realizes accurate detection of zero-crossing time point, and is suitable for a driving system of a permanent magnet direct current brushless motor without 120-degree square waves of a position sensor.)

1. a counter electromotive force zero-crossing detection circuit of a permanent magnet brushless DC motor is characterized by comprising: the circuit comprises a floating power circuit, a zero crossing point comparison circuit and a logic level translation circuit;

The floating power circuit is connected with the zero crossing point comparison circuit and the logic level translation circuit and is used for providing electric energy for the zero crossing point comparison circuit and the logic level translation circuit;

the zero crossing point comparison circuit is used for judging whether a zero crossing point exists or not, and if yes, outputting a floating logic level;

And the logic level translation circuit is connected with the zero-crossing point comparison circuit and is used for converting the floating logic level output by the zero-crossing point comparison circuit into a logic level output by taking the control system ground GND as a reference.

2. A back emf zero-crossing detection circuit of a permanent magnet brushless dc motor according to claim 1, wherein the floating power supply circuit comprises a diode D1, a diode D2, a capacitor C1; one end of the diode D1 is connected with a low-voltage direct-current power supply VCC, and the other end of the diode D1 is connected with one end of a capacitor C1; the other end of the capacitor C1 is connected with one end of a diode D2; the other end of the diode D2 is connected with a phase line of the motor; the low-voltage direct-current power supply VCC is referenced to a system ground GND and is used for providing electric energy.

3. A back electromotive force zero-crossing detecting circuit of a permanent magnet brushless dc motor according to claim 1 or 2, wherein the zero-crossing comparing circuit includes a resistor R1, a resistor R2, a resistor R3, a comparator; the resistor R1 and the resistor R2 are connected, and the common connection point of the resistor R1 and the resistor R2 is connected with the negative input end of the comparator; the positive input end of the comparator is connected with one end of a resistor R3; the other end of the resistor R3 is connected with a phase line of the motor; the comparator is used for comparing the signal voltage of the positive input end and the negative input end of the access comparator.

4. A back electromotive force zero-crossing detection circuit of a permanent magnet brushless dc motor according to claim 1 or 2, wherein the logic level shift circuit comprises a photo coupler, and a signal inputted from the photo coupler is derived from a floating logic level outputted from the zero-crossing point comparison circuit; the output signal of the photoelectric coupler is a logic level taking the ground GND of the control system as a reference.

5. The back electromotive force zero-crossing detection circuit of a permanent magnet brushless dc motor according to claim 3, wherein the resistors R1 and R2 are resistors with the same resistance.

6. A back electromotive force zero-crossing detection circuit of a permanent magnet dc brushless motor according to claim 3, wherein the zero-crossing comparison circuit further comprises a clamping element, both ends of the clamping element are connected to the positive and negative input terminals of the comparator; the clamping voltage of the clamping element is lower than the maximum allowable differential input voltage of the comparator.

7. The back electromotive force zero-crossing detection circuit of a permanent magnet brushless dc motor according to claim 6, wherein the clamping element employs a TVS transient suppression diode, a schottky barrier diode.

Technical Field

The invention relates to the technical field of sensorless direct current brushless motor driving, in particular to a back electromotive force zero-crossing detection circuit of a permanent magnet direct current brushless motor.

Background

To drive a three-phase permanent magnet brushless direct current motor, BLDC for short, a rotating magnetic field with a proper phase is established on a stator to drive permanent magnet electrons to rotate, and the real-time position of the magnetic field direction angle of a permanent magnet rotor needs to be accurately known. In the simplest method, the position of the rotor is detected directly by a hall sensor. But requires increased cost and structural complexity and even in some applications cannot be realized due to the limitations of the operating environment. In view of the various drawbacks of position sensor driving schemes, the industry is continuously pursuing position sensor-less driving schemes.

The instantaneous position of the permanent magnet rotor when rotating is the phase of the ac waveform relative to the stator back emf of the brushless dc motor. The zero crossing point of the alternating current waveform is the characteristic point of the waveform, and if the zero crossing point can be accurately grasped, the accurate real-time position of the permanent magnet rotor can be obtained.

Generally, any phase voltage of the motor is reduced through a voltage dividing resistor, and then is directly supplied to a hardware voltage comparator circuit to be compared with the neutral point voltage of the motor, so that the zero crossing point of a certain suspended phase voltage can be grasped. The neutral point voltage of the motor can be obtained virtually by three resistors with the same resistance value in star connection, the common end of the three resistors is the virtually obtained motor neutral point, and the other end of each resistor is connected with the three-phase line of the motor respectively. As shown in fig. 1.

For a low-speed low-voltage motor, the method is reliable, and the zero crossing point of the counter electromotive force of the motor can be accurately detected. However, for a high-voltage high-speed motor, the detection method has extremely low resolution, because the comparator circuits are all low-voltage electronic circuits, the signal voltage which can be borne by the comparator circuits is very low, for the phase line voltage modulated by the high-voltage PWM, a voltage division circuit with a large proportion is needed to attenuate the phase voltage, and then the phase voltage can be input into the signal comparator, meanwhile, the amplitude of the counter electromotive force included in the phase voltage is also greatly attenuated, the signal to noise ratio is greatly reduced, and the counter electromotive force value of the high-speed motor is very low relative to the direct-current bus voltage VDC when the high-speed motor runs at medium and low speeds, so that the detection difficulty is further increased.

Specific contradictions and problems are clarified as follows:

When the 120-degree square wave is used for driving the permanent magnet brushless direct current motor, the terminal voltage of one phase is always in a suspension state relative to a system ground GND at any time, namely the upper bridge arm and the lower bridge arm of the power driving bridge circuit of the phase are in a cut-off state, no current flows through the phase, the opposite electromotive force is generated by cutting a stator winding of the permanent magnet rotor through a rotating magnetic field of the permanent magnet rotor, and the current angular position of the permanent magnet rotor can be known by detecting the zero-crossing time point of the back electromotive force of the suspension phase. In order to be able to accurately detect the zero crossing point of the back emf of the suspended phase, the sampling decay of this voltage should be as small as possible. In the conventional method, the sampling and comparing circuit and the control system are grounded, so that the phase voltage cannot be directly input into the comparing circuit, because the phase line terminal voltage comprises PWM pulse width modulation, and the maximum amplitude value is equal to the high-voltage direct current bus VDC and far exceeds the input voltage range which can be borne by the comparator circuit, as shown in fig. 2, the phase line terminal voltage must be greatly attenuated. Thus creating a contradiction.

Disclosure of Invention

The invention aims to provide a counter electromotive force zero-crossing detection circuit of a permanent magnet brushless direct current motor, aiming at the defects of the prior art. The back electromotive force of the suspension phase is obtained without attenuation and is input into a voltage comparator, so that the accurate detection of the zero-crossing time point is realized.

in order to achieve the purpose, the invention adopts the following technical scheme:

A back electromotive force zero-crossing detection circuit of a permanent magnet brushless DC motor includes: the circuit comprises a floating power circuit, a zero crossing point comparison circuit and a logic level translation circuit;

the floating power circuit is connected with the zero crossing point comparison circuit and the logic level translation circuit and is used for providing electric energy for the zero crossing point comparison circuit and the logic level translation circuit;

The zero crossing point comparison circuit is used for judging whether a zero crossing point exists or not, and if yes, outputting a floating logic level;

And the logic level translation circuit is connected with the zero-crossing point comparison circuit and is used for converting the floating logic level output by the zero-crossing point comparison circuit into a logic level output by taking the control system ground GND as a reference.

Further, the floating power circuit comprises a diode D1, a diode D2, a capacitor C1; one end of the diode D1 is connected with a low-voltage direct-current power supply VCC, and the other end of the diode D1 is connected with one end of a capacitor C1; the other end of the capacitor C1 is connected with one end of a diode D2; the other end of the diode D2 is connected with a phase line of the motor; the low-voltage direct-current power supply VCC is referenced to a system ground GND and is used for providing electric energy.

Further, the zero-crossing point comparison circuit comprises a resistor R1, a resistor R2, a resistor R3 and a comparator; the resistor R1 and the resistor R2 are connected, and the common connection point of the resistor R1 and the resistor R2 is connected with the negative input end of the comparator; the positive input end of the comparator is connected with one end of a resistor R3; the other end of the resistor R3 is connected with a phase line of the motor; the comparator is used for comparing the signal voltage of the positive input end and the negative input end of the access comparator.

Further, the logic level translation circuit comprises a photoelectric coupler, and a signal input by the photoelectric coupler is from the floating logic level output by the zero-crossing point comparison circuit; the output signal of the photoelectric coupler is a logic level taking the ground GND of the control system as a reference.

Further, the resistor R1 and the resistor R2 are resistors with the same resistance.

furthermore, the zero-crossing point comparison circuit further comprises a clamping element, and two ends of the clamping element are connected to the positive and negative input ends of the comparator; the clamping voltage of the clamping element is lower than the maximum allowable differential input voltage of the comparator.

further, the clamping element adopts a TVS transient suppression diode and a Schottky barrier diode.

Compared with the prior art, the invention obtains the back electromotive force of the suspension phase without attenuation and inputs the back electromotive force to the voltage comparator, realizes accurate detection of the zero-crossing time point, and is suitable for the driving system of the permanent magnet direct current brushless motor without 120-degree square waves of the position sensor.

drawings

FIG. 1 is a prior art circuit topology diagram providing common zero crossing points;

FIG. 2 is a diagram illustrating a waveform of a phase voltage provided by the prior art;

fig. 3 is a schematic diagram of a back-emf zero-crossing detection circuit of a permanent-magnet brushless dc motor according to an embodiment;

FIG. 4 is a connection topology diagram of a power circuit of a driver and a three-phase permanent magnet DC brushless motor according to an embodiment;

Fig. 5 is a topology diagram of a back electromotive force zero crossing detection circuit of a permanent magnet brushless dc motor according to an embodiment.

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It is to be noted that the features in the following embodiments and examples may be combined with each other without conflict.

The invention aims to provide a counter electromotive force zero-crossing detection circuit of a permanent magnet brushless direct current motor, aiming at the defects of the prior art.