KR101244843B1 - Counter electromotive force detector circuit of sensorless bldc motor and method thereof - Google Patents

Abstract

PURPOSE: A counter electromotive force detection circuit of a sensorless BLDC(Brushless DC) motor and a method thereof are provided to improve the efficiency of the motor by detecting an accurate counter electromotive force even when the motor operates in a low RPM. CONSTITUTION: A three phase full bridge circuit drives a three phase sensorless BLDC motor. A first LPF(Low Pass Filter) unit filters the signal of an angular in the output of the motor. A second LPF unit changes a reference value toward the counter electromotive force level of the angular in the output of the motor. A comparator unit outputs the signal of the counter electromotive force to a pulse wave. The comparator unit compares the voltage of the first LPF unit and the second LPF unit.

Description

Counter electromotive force detector circuit of Sensorless BLDC motor and method

The present invention relates to a back electromotive force detection circuit and method for a sensorless BLDC motor, and more particularly, to a low back electromotive force that can detect an accurate back electromotive force even when the sensorless BLDC motor is driven at a low RPM. An RPM back electromotive force detection circuit and a method thereof are provided.

In general, BLDC motor is a kind of DC motor and is known to be smaller and more efficient than AC motor.

The rotor of the BLDC motor rotates in synchronization with a rotating magnetic field in which a magnet installed in the rotor is formed in the stator. Accurate position detection of the rotor is required for synchronizing the magnetic field formed in the magnet and the stator of the rotor. In order to detect the position of the rotor, a position detecting device such as a hall sensor is used.

The schematic driving circuit of the BLDC motor is as shown in FIG.

In FIG. 1, the power supply unit 21 converts an AC voltage, which is a commercial power supply 20, into a DC voltage, and the pulse width modulator 23 receives a converted DC voltage from the power supply unit 21 to generate a switching control signal. In response to the switching control signal, the switching element 24 converts the DC voltage applied from the power supply unit 21 into a three-phase voltage and applies it to the motor 10. Due to this three-phase voltage, the winding of the motor 10 generates a magnetic field so that the rotor of the motor rotates.

The counter electromotive force is output to the winding as the motor rotor rotates. The counter electromotive force detection unit 27 detects the counter electromotive force and applies it to the microcomputer 25. In response to the detection of the counter electromotive force, the microcomputer 25 controls the pulse width modulator 23 so that the motor operates correctly. In addition, the microcomputer 25 receives a current value applied to the motor 10 from a current detector 26 that detects a current at an output terminal of the switching element 24, and a voltage detector that detects a voltage of the power supply unit 21. When the voltage applied to the microcomputer is detected from (22) and an excessively high voltage or current is applied to the motor, the power supply of the power supply unit is cut off to achieve stable operation of the motor.

At this time, the motor generates counter electromotive force during rotation, and the magnitude of the counter electromotive force increases as the rotation speed of the motor increases. The position detector 25a calculates the position of the motor rotor based on the current applied to the motor 10 detected by the current detector 26 and the counter electromotive force detector 27 at the output terminal of the switching element 24. The speed controller 25b controls the rotational speed of the motor based on the position of the rotor, the output current and the counter electromotive force.

In general, the driving stage of the BLDC motor can be divided into three sections such as an initial positioning section, an open loop section and a close loop section. The initial position setting section is a section in which the rotor starts to rotate in a stopped state and moves the rotor to a preset position.The open loop section is a low section in which no back EMF is detected after the initial position of the rotor is set. Is a section in which normal electromechanical control of the rotor is performed since the back EMF can be detected.

In order to start the BLDC motor, the 180-degree energization method initially applied a certain amount of current for a certain period of time on the U phase to align the rotor of the BLDC motor to the U phase and immediately started it through a senseless control. That is, it is assumed that the position of the rotor is 0 while the rotor of the BLDC motor is aligned on the U phase, and the speed of the motor is controlled through the position of the rotor through the senseless using this position as a reference position.

As described above, the control method of the sensorless BLDC motor detects the back EMF of the motor using three phase voltages, finds a zero-crossing point of the detected signal, and switches each phase to match the position of the rotor. I'm using the method.

The counter electromotive force detection circuit and its operation will be described with reference to FIGS. 2 to 4.

2 is a diagram illustrating a configuration of a conventional counter electromotive force detection circuit, and FIGS. 3 and 4 are views illustrating a switching signal of the counter electromotive force detection circuit shown in FIG. 2.

As shown in FIG. 2, the counter electromotive force detection circuit includes a three-phase full bridge circuit A for driving a motor, a motor B, a low pass filter (LPF), and a reference voltage. A reference voltage setting unit (D) having an input / output terminal and a resistor and a voltage comparator (F) are provided.

The counter electromotive force detection circuit shown in FIG. 2 operates as follows.

First, when the switching PWM signal for driving the motor is applied to the motor in the three-phase full bridge circuit A, a phase voltage signal as shown in ① of FIG. 3 is output.

3 shows the phase voltage and the counter electromotive force that appear when the BLDC motor is driven at 1500 RPM or more.

When the back EMF component is extracted by passing through the LPF (Low Pass Filter) in the ① waveform of FIG. 3, a trapezoidal voltage as shown in ③ of FIG. 3 is output.

When passing through the comparator with reference voltage fixed (mostly 1/2 level of motor voltage) as in ② of FIG. 3, the pulse as shown in ④ of FIG. Done.

On the other hand, when the motor is driven at a low RPM of 500 RPM or less as shown in Figure 4, the waveform as shown in ① of Figure 4 appears and the back EMF component of this waveform is so low that it is invisible.

The reason why the counter electromotive force varies depending on the RPM in FIGS. 3 and 4 is that the counter electromotive force (e) is proportional to the angular velocity (ω), as can be seen in Equation 1 below.

[Formula 1]

In Equation 1, e is the counter electromotive force, λ is the magnetic flux, θ is the position of the rotor, ω is the angular velocity.

When RPM is low by Equation 1, a voltage waveform having a low back EMF is generated as shown in ① of FIG.

When the back EMF component is extracted by passing through the LPF (Low Pass Filter) in the ① waveform of FIG. 4, a trapezoidal voltage having a low level as in ③ of FIG. 4 is output.

That is, when the counter electromotive voltage such as ③ in FIG. 4 passes through the comparator F having a constant reference voltage such as ②, the comparison target voltage is lower than the reference voltage. Is output.

In addition, when the position of the rotor is determined by the forced alignment, the BLDC motor is started to operate in an open-loop to obtain a BEMF signal. To determine the position of the rotor from the back EMF signal, a signal such as a Hall signal must be extracted from the back EMF signal. A circuit as shown in FIG. 5 is generally used to detect a position signal from a back EMF signal. 5 is a diagram illustrating an example of a conventional counter electromotive force detection circuit.

As shown in the circuit of FIG. 5, one input of the comparator is applied by filtering to remove the PWM signal from the back EMF signal on the A, B or C phase, and on the other side, the reference voltage is distributed by appropriately distributing the power supply voltage of the comparator. It is made and approved. In such a circuit, if the reference voltage is reduced, the rotor position can be detected even at a low RPM of the motor. However, if the RPM is high, the duty of the position detection signal may change, causing a malfunction. On the contrary, if the reference voltage is increased, the minimum RPM of the motor is increased. That is, the higher the rotational speed of the motor, the more the duty changes and causes a malfunction.

In addition, Patent Document 1 discloses that when the rotor of the motor is aligned to the initial position for starting, the motor fails to start even when the motor is under high load or the position of the motor rotor is aligned near the reference position and is not perfectly aligned. A device and a method for starting a sensorless BLDC motor for preventing a load are disclosed. Patent Document 2 below discloses a load applied to a sensorless BLDC motor and a torque of a BLDC motor even when a load applied to the sensorless BLDC motor is large during synchronous acceleration. Disclosed is a control method of a sensorless BLDC motor driving device which prevents start-up failure due to a synchronization error between a magnet of a rotor and a rotor magnetic field of a stator due to a deviation maintaining an equilibrium state.

In addition, Patent Literature 3 below detects the counter electromotive voltage and detects the counter electromotive voltage of the sensorless BLDC motor which shortens the cycle of the drive signal by shortening the cycle of the drive signal for the counter electromotive voltage detection only when the counter electromotive voltage is not detected. A method is disclosed.

Republic of Korea Patent Publication No. 2010-0070223 (published June 25, 2010) Republic of Korea Patent Publication No. 2009-0064980 (Published June 22, 2009) Republic of Korea Patent Publication No. 2004-0034827 (2004.04.29 published)

However, in the conventional technology as described above, when the RPM is low, there is a problem that the sensorless motor cannot be driven because the position of the rotor is not detected. In addition, there is a problem that if a circuit for detecting a case where the RPM is low, malfunction occurs when the RPM rises.

That is, in the related art, there is a problem in that the reference value supplied to the comparator is fixed so that the counter electromotive force cannot be detected due to the change in RPM.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems as described above, and to provide a counter electromotive force detection circuit and a method of the sensorless BLDC motor that detects the position of the rotor even when the RPM is low due to the change in RPM.

In order to achieve the above object, the counter electromotive force detection circuit according to the present invention is a counter electromotive force detection circuit of a three-phase sensorless BLDC (Brushless DC) motor, a three-phase full bridge circuit for driving the three-phase sensorless BLDC motor, the three phase A first low pass filter (LPF) unit for filtering signals of each phase at the output of the sensorless BLDC motor, and a second LPF unit arranged to vary a reference value with respect to the counter electromotive force level of each phase at the output of the three-phase sensorless BLDC motor. And a comparator unit for comparing the voltages of the first LPF unit and the second LPF unit to output the counter electromotive force as a pulse wave.

In the counter electromotive force detection circuit according to the present invention, the first LPF unit and the second LPF unit are connected in parallel.

In the counter electromotive force detection circuit according to the present invention, the comparator unit includes three comparators corresponding to three phases of the three-phase sensorless BLDC motor, and the first LPF unit is respectively configured to provide the three-phase sensorless BLDC motor. Three LPFs corresponding to the three phases are provided, and the second LPF unit comprises an adder and a capacitor coupled to the adder.

In the counter electromotive force detection circuit according to the present invention, the three comparators of the comparator unit include a first input terminal and a second input terminal, and the output signals of the three LPFs of the first LPF unit are respectively three. It is characterized in that it is supplied to the first input terminal of the two comparators, the output of the second LPF unit is commonly supplied to the second input terminal of the three comparators.

In the counter electromotive force detection circuit according to the present invention, the adder is composed of three resistors connected to each of A, B and C phases of the three-phase sensorless BLDC motor, and a second input terminal of each comparator of the comparator unit. It is characterized by supplying the same voltage.

In addition, a method for detecting back EMF according to the present invention for detecting the back EMF of a three-phase sensorless BLDC (Brushless DC) motor to achieve the above object, (a) a three-phase full bridge circuit to the three-phase sensorless BLDC motor (B) filtering the output signals of each phase of the three-phase sensorless BLDC motor with a first low pass filter (LPF) and a second LPF, respectively, (c) the three-phase sensorless BLDC motor And varying and outputting a reference voltage with respect to the counter electromotive force level of each phase at the output of the output.

In the counter electromotive force detection method according to the present invention, the step (c) is characterized in that when the output of the three-phase sensorless BLDC motor is high, the reference voltage is increased, and if the output is low, the reference voltage is lowered and output.

In the counter electromotive force detection method according to the present invention, the step (c) is characterized in that it outputs a constant output value regardless of the RPM of the three-phase sensorless motor.

As described above, according to the counter electromotive force detection circuit and the method of the sensorless BLDC motor according to the present invention, the effect that the accurate counter electromotive force can be detected even if the sensorless BLDC motor is driven at a low RPM.

1 is a view showing a driving circuit of a conventional BLDC motor;
2 is a diagram showing the configuration of a conventional counter electromotive force detection circuit;
3 and 4 are views illustrating a phase voltage signal of the counter electromotive force detection circuit shown in FIG.
5 is a view showing another configuration of a conventional counter electromotive force detection circuit;
6 is a counter electromotive force detection circuit according to an embodiment of the present invention;
7 is a view illustrating a phase voltage signal of the counter electromotive force detection circuit shown in FIG. 6;
8 is an operation flowchart of the counter electromotive force detection circuit shown in FIG. 6;

These and other objects and novel features of the present invention will become more apparent from the description of the present specification and the accompanying drawings.

Hereinafter, the structure of this invention is demonstrated according to FIG.

6 is a back EMF detection circuit according to an embodiment of the present invention.

As shown in FIG. 6, the counter electromotive force detection circuit according to the present invention includes a three-phase full bridge circuit for driving the three-phase sensorless BLDC motor such that the three-phase sensorless BLDC motor detects the counter electromotive force even when driven at a low RPM. Not shown), the first LPF unit (C) for filtering the signals of each phase at the output of the three-phase sensorless BLDC motor, to vary the reference voltage with respect to the counter electromotive force level of each phase at the output of the three-phase sensorless BLDC motor A second LPF unit (D) is provided, and a comparator unit for comparing the output voltage of the first LPF unit and the second LPF unit to output the signal of the counter electromotive force as a pulse wave.

In addition, as shown in FIG. 6, the first LPF unit C has three LPFs connected to output terminals of respective phases of a three-phase sensorless BLDC motor and passing only a frequency band capable of detecting back EMF. The output of each of the first LPF units C is supplied to the first input terminal of each comparator of the comparator unit.

The second LPF unit D is connected in parallel to the first LPF unit C at an output terminal of each phase of a three-phase sensorless BLDC motor and supplies a reference voltage to the first LPF unit. It consists of one LPF unit that adds the voltage of each three phases. That is, as shown in FIG. 6, the second LPF unit D is an adder made up of three resistors connected in parallel to each of three LPFs of the first LPF unit C, and the adder. Consisting of a capacitor coupled to the output of this second LPF portion D is supplied to a second input terminal of each comparator of the comparator portion.

That is, when the signal input to the first input terminal is higher than the reference voltage input to the second input terminal, the comparator outputs a 'HIGH' signal, and the signal input to the first input terminal is a second input signal. If the input voltage is lower than the input voltage of 2, 'LOW' is output.

However, in the present invention, since the second LPF unit D is provided to vary the reference voltage, for example, when the motor of the three-phase sensorless BLDC motor B is driven at a low RPM of 500 RPM or less, the second LPF unit D is provided. Since the reference voltage output from the LPF unit (D) is also lowered, the counter electromotive force can be detected according to the reference voltage supplied from the second LPF unit (D).

In the circuit of Fig. 6, since the reference voltage input to the comparator is changed by the second LPF unit D, the output of the comparator shows a duty ratio of a substantially constant value.

That is, the present invention relates to the counter electromotive force level of each phase at the output of the first LPF unit C and the output of the three-phase sensorless BLDC motor in FIG. 6 that filter signals on A, B and C of the three-phase sensorless BLDC motor. Accordingly, a second LPF unit D for outputting a reference voltage is provided.

Thus, for example, since the second LPF unit D supplies a reference voltage that varies according to the output of the three-phase sensorless BLDC motor, the reference voltage is lowered when the motor is driven at a low RPM, thereby reducing the counter electromotive force. Can be detected.

As described above, the counter electromotive force detection circuit according to the present invention can detect the counter electromotive force regardless of the driving speed of the motor.

In addition, as shown in FIG. 6, the second LPF unit D is composed of three resistors connected to A, B, and C of the three-phase sensorless BLDC motor and a capacitor commonly connected to the resistors. A variable reference voltage is supplied to the second input terminal of each comparator of the comparator section.

Next, the operation of the counter electromotive force detection circuit according to the present invention shown in Fig. 6 will be described with reference to Figs.

FIG. 7 is a diagram illustrating a phase voltage signal of the counter electromotive force detection circuit shown in FIG. 6, and FIG. 8 is an operation flowchart of the counter electromotive force detection circuit shown in FIG. 6.

When the three-phase sensorless motor is driven (S10), the three-phase output is filtered for each phase in the first LPF unit (C) and the second LPF unit (D) (S20, S30).

The signal filtered in the first LPF unit C is supplied to the first input terminal of each comparator of the comparator unit, and the signal filtered in the second LPF unit D is the first comparator of each comparator unit of the comparator unit. It is supplied to the input terminal of 2 as the reference voltage.

Accordingly, the comparator compares the signal input to the first input terminal and the second input terminal according to a preset condition (S40), and outputs the output signal of the first LPF unit C input to the first input terminal. Is higher than the reference voltage (S50), and outputs a 'HIGH' signal in accordance with a preset condition, thereby determining the position of the current rotor to switch each phase (S70).

On the other hand, as shown in Figure 7, when the three-phase sensorless motor is driven at a low RPM, for example 500 RPM or less in the back EMF detection circuit according to the present invention, the waveform as shown in ① of Figure 7 is output, the second LPF unit (D) of the outputs the reference voltage as shown in ② by the adder and capacitor.

That is, as shown in Fig. 7, when the output signal filtered by the first LPF unit C is low (S60), the output of the second filter unit D is fluctuated, so that the comparator The same waveform can be output to detect back EMF.

Meanwhile, in the description of FIG. 8, the output of the motor unit is described as being low RPM, but the present invention is not limited thereto.

That is, according to the present invention, by providing the second LPF unit (D), when the reference voltage fluctuates, that is, the RPM increases, the reference voltage increases as the counter electromotive force increases, and when the RPM decreases, the reference voltage decreases. Since the comparator supplies an output signal as ④ of FIG. 7 regardless of the change in RPM, the comparator can detect the counter electromotive force.

Although the present invention has been described in detail with reference to the above embodiments, it is needless to say that the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention.

The counter electromotive force detection circuit and the method of the sensorless BLDC motor according to the present invention are applied to the field of detecting the accurate back electromotive force even when the sensorless BLDC motor is driven at a low RPM.

Claims (8)

As a counter electromotive force detection circuit of 3-phase sensorless brushless DC (BLDC) motor,
A three phase full bridge circuit for driving the three phase sensorless BLDC motor,
A first low pass filter (LPF) unit for filtering a signal of each phase at an output of the three-phase sensorless BLDC motor;
A second LPF unit arranged to vary a reference value with respect to the counter electromotive force level of each phase at the output of the three-phase sensorless BLDC motor;
Comparing unit for comparing the voltage of the first LPF unit and the second LPF unit for outputting the signal of the counter electromotive force as a pulse wave,
The comparator unit includes three comparators corresponding to three phases of the three-phase sensorless BLDC motor,
The first LPF unit includes three LPFs corresponding to three phases of the three-phase sensorless BLDC motor, and the second LPF unit includes an adder and a capacitor coupled to the adder. . The method of claim 1,
And the first LPF unit and the second LPF unit are connected in parallel. delete The method of claim 2,
The three comparators of the comparator unit include a first input terminal and a second input terminal,
The output signals of the three LPFs of the first LPF unit are respectively supplied to the first input terminals of the three comparators,
And the output of the second LPF unit is commonly supplied to the second input terminals of the three comparators. The method of claim 1,
The adder is composed of three resistors each connected to A, B, and C phases of the three-phase sensorless BLDC motor, and supplies the same voltage to the second input terminal of each comparator of the comparator unit. Detection circuit. As a method of detecting back EMF of a 3-phase sensorless BLDC (Brushless DC) motor,
(a) driving the three-phase sensorless BLDC motor with a three-phase full bridge circuit;
(b) filtering output signals of each phase of the three-phase sensorless BLDC motor with a first low pass filter (LPF) and a second LPF, respectively;
(c) varying and outputting a reference voltage with respect to the counter electromotive force level of each phase at the output of the three-phase sensorless BLDC motor,
Step (c) is a method for detecting back electromotive force, characterized in that for outputting a constant output value regardless of the RPM of the three-phase sensorless motor. The method according to claim 6,
In the step (c), when the output of the three-phase sensorless BLDC motor is high, the reference voltage is increased, and when the output is low, the counter electromotive force detection method is characterized in that the output is lowered. delete

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