KR101251906B1 - Counter electromotive force detector circuit of sensorless bldc motor and method thereof - Google Patents

Abstract

The present invention relates to a reverse electromotive force detection circuit and a method thereof, comprising: a three-phase full bridge circuit for driving the motor unit, a signal and a motor of each phase at an output of the motor unit, as a reverse electromotive force detection circuit for a phase sensorless brushless DC (BLDC) motor unit; A multiplier for multiplying a phase modulated signal of a PWM (pulse width modulation) control signal for driving, a low pass filter (LPF) unit for first filtering each output signal output from the multiplier, and the LPF unit And a comparator configured to perform a second filtering on the first filtered signal and the first filtered signal, and compare a reference voltage value changed with respect to the counter electromotive force level at each phase output to output a pulse signal according to the rotor position. Prepare.
By using the counter electromotive force detection circuit and the method as described above, the present invention provides a phase modulated signal of each phase output signal and PWM control signal even if a flyback pulse is generated due to the influence of the load applied to the motor when the motor is driven under high load. By multiplying and multiplying the multiplied output signal by primary and secondary filtering, a pulse signal can be output through a comparator whose reference voltage value fluctuates to accurately detect the rotor position of the motor.

Description

COUNTER ELECTROMOTIVE FORCE DETECTOR CIRCUIT OF SENSORLESS BLDC MOTOR AND METHOD THEREOF

The present invention relates to a back electromotive force detection circuit and a method of a sensorless BLDC motor, and more particularly to a sensorless BLDC capable of detecting accurate back electromotive force even when the sensorless BLDC motor is driven under high load. A back electromotive force detection circuit of a motor 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.

Here, accurate position detection of the rotor is required for synchronization between the magnet of the rotor and the rotor field formed in the stator.

Accordingly, a position detecting device such as a hall sensor is used to detect the position of the rotor in the BLDC motor.

1 is a schematic driving circuit diagram of a BLDC motor.

In FIG. 1, the power supply unit 1 converts a commercially available wheel power source into a direct current power source, and the pulse width modulator 2 receives the converted direct current power source from the power supply unit 1 to generate a switching control signal. In accordance with the switching control signal, the DC power applied from the power supply unit 1 is converted into a three-phase voltage and applied to the motor 4. Due to this three-phase voltage, the winding of the motor 4 generates a magnetic field so that the rotor of the motor 4 rotates.

As the motor rotor rotates, the counter electromotive force is output to the winding, and the counter electromotive force detection unit 5 detects the counter electromotive force and applies it to the microcomputer 6. In response to the detection of the counter electromotive force, the microcomputer 6 controls the pulse width modulator 2 so that the motor 4 is operated correctly.

In addition, the microcomputer 6 receives a current value applied to the motor 4 from the current detection unit 7 which detects a current at the output terminal of the switching element 3, and detects the voltage of the power supply unit 1 ( When the voltage applied to the microcomputer 6 from 8) is detected and excessively high voltage or current is applied to the motor 4, the power supply of the power supply unit 1 is cut off, thereby achieving stable operation of the motor 4.

At this time, the motor 4 generates counter electromotive force during rotation, and as the rotation speed of the motor 4 increases, the magnitude of the counter electromotive force also increases.

The position detector 6a calculates the position of the motor rotor based on the current applied to the motor 4 detected by the current detector 7 and the counter electromotive force detector 5 at the output terminal of the switching element 3.

The speed controller 6b controls the rotation speed of the motor 4 based on the position of the rotor, the output current and the counter electromotive force.

In general, the driving stage of the BLDC motor may be divided into three sections such as an initial positioning section, an open-loop section, and a close-loop section.

The initial positioning section is a section in which the rotor starts to rotate in a stationary state and moves the rotor to a preset position. The open loop section is a low speed section in which no counter electromotive force is detected after the initial position of the rotor is set. The closed loop section is a section in which the normal control of the rotor is performed since the back EMF can be detected.

In order to start the BLDC motor, the 180 ° 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 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 senseless control with this position as the 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.

FIG. 2 is a diagram illustrating a configuration of a conventional counter electromotive force detection circuit, FIG. 3 is a diagram illustrating a phase voltage signal of the motor unit illustrated in FIG. 2, and FIG. 5 is a diagram illustrating a pulse signal obtained by passing a counter electromotive force component shown in FIG. 4 through a comparator, and FIG. 6 is a diagram illustrating a state in which a distortion occurs in a pulse signal due to a flyback pulse at a high load. to be.

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

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, the switching signal as shown in FIG. 3 is output.

When the phase voltage signal shown in FIG. 3 passes through the LPF (C), the counter electromotive force component of the motor appears as a trapezoidal voltage as shown in FIG. 4.

When the counter electromotive force component is passed through the voltage comparator F having a fixed reference voltage (mostly 1/2 level of the motor voltage), the pulse signal as shown in FIG. 5 is a signal similar to that of the hall sensor output of the sensored BLDC motor. This signal is used to detect the position of the rotor using this signal to drive the sensorless motor.

On the other hand, when the sensorless BLDC motor is driven at a high load, a fly back pulse (a of FIG. 3) that is output while the current stored in the motor coil is drawn out becomes large.

The flyback pulse causes signal distortion as shown in FIG. 6 when the counter electromotive force is detected so that the position of the rotor cannot be determined. In other words, when the BLDC motor is applied at high power and high load, the flyback pulse increases, and thus the rotor is not accurately located, causing malfunction.

Accordingly, in the case of applying a BLDC motor to a high output and a high load, a sensored type to which a hall sensor is added must be used as shown in ⓒ of FIG. 6.

In Patent Document 1, when the rotor of the motor is aligned to an initial position for starting, even if the motor is under high load or the position of the motor rotor is aligned near the reference position, the motor fails to start. Disclosed are an apparatus and a method for starting a sensorless BLDC motor.

In addition, Patent Document 2 discloses a rotor magnetic field and a stator rotor magnetic field due to a deviation between the load of the sensorless BLDC motor and the torque of the BLDC motor even when the load on the sensorless BLDC motor is large during synchronous acceleration. Disclosed is a control method of a sensorless BLDC motor driving device which prevents start failure due to synchronization error.

In addition, Patent Document 3 discloses a method for detecting a counter electromotive voltage of a sensorless BLDC motor which shortens the cycle of the driving signal by confirming whether the counter electromotive voltage is detected and then shortening the period of the driving signal for detecting the counter electromotive voltage only when the counter electromotive voltage is not detected. 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, when the sensorless BLDC motor is driven under high load, the signal back occurs due to the flyback pulse output as the current stored in the motor coil escapes, so that the position of the rotor cannot be accurately determined. There was a problem that became impossible.

Accordingly, when the BLDC motor is applied at a high load, there is a problem that the flyback pulse becomes large and causes a malfunction.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to detect the counter electromotive force of a sensorless BLDC motor capable of calculating the position of the rotor by detecting the counter electromotive force even when the flyback pulse increases when the motor is driven under high load. It is to provide a circuit and a method thereof.

According to a feature of the present invention for achieving the above object, the present invention is a three-phase sensorless BLDC (backward electromotive force detection circuit of the motor unit), a three-phase full bridge circuit for driving the motor unit, the motor unit A multiplier for multiplying a phase modulated signal of a phase-modulated signal of each phase and a PWM (pulse width modulation) control signal for driving a motor at an output, and a low pass filter (LPF) for first filtering each output signal output from the multiplier Second filtering the first filtered signal and the first filtered signal from the filter unit and the LPF unit, and comparing the reference voltage value changed for the counter electromotive force level at each phase output to output a pulse signal according to the rotor position. It includes a comparison unit.

The multiplier includes three multipliers for multiplying each phase output signal of the motor unit and the phase modulated signal, and the phase modulated signal is a signal obtained by modulating a phase by a predetermined angle θ of the PWM control signal Asinωt. (sin (ωt + θ)).

The output signal of the multiplier is a signal (-A / 2 {cos (2ωt + θ) -cos (-θ)}) multiplied by PWM + θ to the flyback pulse generated by the load during motor driving. do.

The output signal frequency of the multiplier is characterized in that twice the output signal frequency of each phase in the interval from the point where the PWM control signal of the motor is switched from the off state to the off state again.

The LPF unit may include three first LPFs which respectively filter output signals of the multipliers and extract DC components of the output signals.

The comparison unit compares a second LPF for filtering the DC component signal extracted from the LPF unit to a cutoff frequency lower than the cutoff frequency of the first LPF, and a reference voltage value that is a signal filtered from the DC component signal and the second LPF. It is characterized by including three comparators.

The second LPF includes an adder for adding voltages of each phase output from the three first LPFs, and a capacitor coupled to the adder. The adder includes three resistors each connected to each phase of the motor. The same voltage is supplied to the second input terminal of the first comparator.

The three comparators are provided with first and second input terminals, respectively, and output signals of the three first LPFs are supplied to the first input terminals of the comparators, and output signals of the second LPFs are respectively provided. It is characterized by being supplied to two input terminals.

According to another feature of the invention, the present invention is a method for detecting the back electromotive force of the three-phase sensorless brushless DC (BLDC) motor unit, (a) driving the motor unit using a three-phase full bridge circuit, (b) the motor Multiplying an output signal of each negative phase by a phase modulated signal of a PWM control signal, (c) first filtering the output signal output in step (b), and (d) first filtering in step (c) Filtering the extracted signal to a cutoff frequency lower than the cutoff frequency during the first filtering to vary the reference voltage value for the counter electromotive force of each phase at the output of each phase; and (e) the first filtered in the step (c). And comparing the signal with the reference voltage value varied in step (d) to output a pulse signal based on the position of the motor rotor.

Each phase output signal of step (b) is characterized in that it is distorted by the flyback pulse generated due to the load applied to the motor when the motor is driven at a high load.

The phase modulated signal of step (b) is a signal (sin (ωt + θ)) obtained by modulating a phase of the PWM control signal Asinωt by a predetermined angle θ.

In the step (e), if the primary filtered signal is greater than the reference voltage value, a high signal is output, and if the primary filtered signal is less than the reference voltage value, a low signal is output.

As described above, the present invention multiplies the output signal of each phase and the phase modulated signal of the PWM control signal even if a flyback pulse occurs due to the influence of the load applied to the motor when the motor is driven at high load, and multiplies the multiplied output signal by one. It is possible to accurately detect the rotor position of the motor by outputting a pulse signal through a comparator in which the reference voltage value is varied by differential and secondary filtering.

Accordingly, the present invention has an effect that can accurately control the rotational speed of the motor by accurately calculating the rotor position of the motor according to the pulse signal according to the rotor position of the comparator.

In addition, the present invention also has the effect of reducing the production cost of the product by removing the Hall (Hall) sensor and its peripheral circuit to be applied when driving the BLDC motor at high load.

1 is a schematic driving circuit diagram of a BLDC motor;
2 is a diagram showing the configuration of a conventional counter electromotive force detection circuit;
3 is a view illustrating a phase voltage signal of a motor unit illustrated in FIG. 2;
4 is a diagram illustrating a counter electromotive force component of a motor in which a phase voltage signal shown in FIG. 3 is passed through an LPF;
5 is a diagram illustrating a pulse signal passing a counter electromotive force component shown in FIG. 4 through a comparator;
6 is a diagram illustrating a state in which distortion occurs in a pulse signal due to a flyback pulse at a high load;
7 is a counter electromotive force detection circuit according to a preferred embodiment of the present invention;
8 is a phase voltage waveform graph when high load is applied to the motor unit shown in FIG.
9 is a graph of an output signal multiplied by a multiplier and outputting a phase voltage waveform and a PWM control signal for driving a motor;
10 is an output signal graph of a first LPF receiving an output signal of a multiplier;
11 is a rotor position detection signal output from the comparator,
12 is a flowchart illustrating a step-by-step electromotive force detection method according to a preferred embodiment of the present invention.

Hereinafter, a counter electromotive force detection circuit and a method of a sensorless BLDC motor according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 7 is a circuit diagram of a counter electromotive force detection according to a preferred embodiment of the present invention. FIG. 8 is a phase voltage waveform graph when a high load is applied to the motor unit shown in FIG. 7, and FIG. 9 is a phase voltage waveform and a PWM control signal for driving a motor. Is a graph of the output signal multiplied by the multiplier.

10 is an output signal graph of the first LPF receiving the multiplier output signal, and FIG. 11 is a rotor position detection signal output from the comparator.

The counter electromotive force detection circuit according to the preferred embodiment of the present invention is a three-phase full bridge circuit for driving a three-phase sensorless BLDC motor unit (hereinafter, abbreviated as a motor unit) 20 as shown in FIG. 7. 10), the multiplier 30 for multiplying the signal of each phase and the PWM control signal for driving the motor at the output of the motor unit 20, filtering to extract the DC component of each output signal output from the multiplier 30 The output signal of the LPF unit 40 and the LPF unit 40 and the output signal of the LPF unit 40 are filtered to compare the reference voltage value that is varied with respect to the counter electromotive force level of each phase at the output of the multiplier 30 to pulse the pulse. Comparing unit 50 for outputting a signal.

That is, in the counter electromotive force detection circuit according to the preferred embodiment of the present invention, the reference voltage input / output terminal and the resistor having a reference voltage input / output terminal and a resistor, and a peripheral circuit thereof are removed in comparison with the conventional counter electromotive force detection circuit shown in FIG. 2. do.

Here, the phase voltage waveform Asinωt output from each phase output terminal of the motor unit 20 is a flyback pulse generated by the influence of the load applied to the motor when the motor is driven at a high load, as shown in FIG. 8. Because of the distortion.

The multiplier 30 includes three multipliers for multiplying a phase modulated signal of each phase output signal and a PWM control signal.

That is, the three multipliers multiply the signal output from each phase output terminal and the PWM control signal by a phase-modulated signal (hereinafter referred to as a 'phase modulated signal') (sin (ωt + θ)). As shown in Fig. 9, an output signal (-A / 2 {cos (2ωt + θ) -cos (-θ)}) multiplied by PWM + θ is output.

Here, the frequency of the signal output from the three multipliers is twice the frequency of each phase output signal in the interval from the point where the PWM control signal of the motor is switched from the off state to the off state again.

The LPF unit 40 includes three first LPFs 41 that pass only the cut-off frequency of the first frequency band preset through the output signal output from each multiplier of the multiplier 30.

The three first LPFs 41 filter the output signals output from the respective multipliers to extract the DC component A / 2cosθ as shown in FIG. 10.

The comparator 50 is connected to the output terminals of the three first LPFs 41 provided in the LPF unit 40 and adds one second LPF 51 and each phase to add a DC component signal outputted from the first LPF unit. Three comparators 52 for comparing the DC component signal with the reference voltage value output from the second LPF 51 are provided.

The second LPF 51 passes only the cut-off frequency band of the preset second frequency band to change the reference voltage value with respect to the DC component signal of each phase.

The second LPF 51 is composed of an adder consisting of three resistors connected to the three first LPFs 41 and one capacitor coupled to the adder, and the output of the second LPF 51 has three comparators 52. It is supplied to the second input terminal.

The adder is composed of three resistors connected to the output terminals of the three first LPFs 41, respectively, and supplies the same voltage to the second input terminals of the three comparators 52.

Here, the DC component signals extracted from the three first LPFs 41 are supplied to each of the first input terminals of the three comparators 52 provided in the comparator 50 and the three second LPFs 51.

The second frequency band is set to a lower frequency band than the first frequency band.

For example, in the present embodiment, the first frequency band is set to about 10 Hz to 15 Hz, and the second frequency band is set to about 10 Hz to 1 Hz.

The reference voltage value output from the second LPF 51 is supplied to each second input terminal of the three comparators 52.

The three comparators 52 change the output signal output from the LPF unit 40 into a pulse signal according to the rotor position of the motor to output the rotor position detection signal shown in FIG.

That is, the three comparators 52 output a high signal when the DC component signal input from the LPF unit 40 through the first input terminal is higher than the reference voltage value input through the second input terminal. If it is lower than the reference voltage value, a low signal is output.

Thus, since the reference voltage values input to the three comparators 52 in the circuit of FIG. 7 fluctuate by the second LPF 51, the outputs of the three comparators 52 exhibit duty ratios of substantially constant values.

Accordingly, the present invention can accurately control the rotational speed of the motor by accurately calculating the rotor position of the motor according to the pulse signal output from the comparator.

Next, a back electromotive force detection method according to a preferred embodiment of the present invention will be described in detail with reference to FIG. 12.

12 is a flowchart illustrating a step-by-step electromotive force detection method according to a preferred embodiment of the present invention.

In this embodiment, it should be noted that the output signal of each phase is distorted due to the flyback pulse generated by the influence of the load applied to the motor when the motor is driven at a high load.

When the motor of the motor unit 20 is driven (S10), the multiplier 10 is a phase modulated signal (sin (ωt + θ) whose phase is modulated by θ to the three-phase output signal Asinωt and the PWM control signal of the motor. ) Are respectively multiplied (S11) to output the output signal (-A / 2 {cos (2ωt + θ) -cos (-θ)}) multiplied by PWM + θ as shown in FIG. 9. do.

At this time, the signals output from the three multipliers are doubled in frequency at the portion where the PWM control signal of the motor is switched.

Then, the first LPF 41 of the LPF unit 40 first filters the output signal output from each multiplier to pass only the cut-off frequency of the first frequency band set in advance (S12), and extracts the DC component of the output signal. .

The second LPF 51 of the comparator 50 performs the second filtering so that only the cut-off frequency of the second frequency band set lower than the first frequency band is passed through the DC component signal extracted by the first filtering. The reference voltage value is varied with respect to the component signal (S13).

Subsequently, each comparator 52 compares a DC component signal input from the LPF unit 40 through the first input terminal with a reference voltage value varied by the second LPF 51 (S14).

As a result of the comparison, the comparator 52 outputs a high signal when the DC component signal is higher than the reference voltage value, and outputs a low signal when the DC component signal is lower than the reference voltage value.

Accordingly, the comparator 52 outputs a pulse signal according to the position of the rotor as shown in FIG.

Through the above process, the present invention multiplies the output signal of each phase and the phase modulated signal of the PWM control signal even if a flyback pulse occurs due to the load applied to the motor when the motor is driven at a high load, and the multiplied output. The primary and secondary filtering signals can be used to output a pulse signal through a comparator whose reference voltage value fluctuates to accurately detect the rotor position of the motor.

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 of the sensorless BLDC motor and the method thereof according to the present invention are applied to the field of detecting the correct back electromotive force even when a flyback pulse occurs due to the load of the motor when the sensorless BLDC motor is driven at a high load.

10: three-phase full bridge circuit 20: motor portion
30: multiplication part 40: LPF part
41: first LPF 50: comparison unit
51: second LPF 52: comparator

Claims (12)

As a counter electromotive force detection circuit of 3-phase sensorless BLDC (Brushless DC) motor unit,
A three-phase full bridge circuit for driving the motor unit;
A multiplier for multiplying a phase modulated signal of a phase modulated signal of each phase signal and a PWM (pulse width modulation) control signal for driving a motor at an output of the motor unit;
A low pass filter (LPF) unit for first filtering each output signal output from the multiplier;
And a second comparator for filtering the first filtered signal and the first filtered signal from the LPF unit to compare the reference voltage value changed for the counter electromotive force level at each phase output to output a pulse signal according to the rotor position. A counter electromotive force detection circuit, characterized in that. The method of claim 1,
The multiplier includes three multipliers for multiplying each phase output signal and the phase modulated signal of the motor unit,
And the phase modulated signal is a signal (sin (ωt + θ)) obtained by modulating the phase of the PWM control signal (Asinωt) by a predetermined angle (θ). 3. The signal of claim 2 wherein the output signal of the multiplier is
A counter electromotive force detection circuit, characterized in that the signal (-A / 2 {cos (2ωt + θ) -cos (-θ)}) multiplied by PWM + θ is generated by the flyback pulse generated by the load during motor driving. 4. The frequency converter of claim 3, wherein the output signal frequency of the multiplier is
A counter electromotive force detection circuit, characterized in that twice the output signal frequency of each phase in the interval from the point where the PWM control signal of the motor is switched from the off state to the off state again. The LPF unit according to any one of claims 2 to 4, wherein the LPF unit
And three first LPFs each filtering output signals of the multipliers to extract a DC component of the output signal. The method of claim 5, wherein the comparison unit
A second LPF filtering the DC component signal extracted from the LPF unit to a cutoff frequency lower than the cutoff frequency of the first LPF;
And three comparators for comparing the DC component signal with a reference voltage value which is a signal filtered from the second LPF. The method according to claim 6,
The second LPF is an adder for adding the voltage of each phase output from the three first LPF
A capacitor coupled to the adder,
The adder comprises three resistors each connected to each phase of the motor, and supplies the same voltage to the second input terminals of the three comparators. The method according to claim 6,
The three comparators are provided with first and second input terminals, respectively,
Output signals of the three first LPFs are supplied to first input terminals of the comparators,
And an output signal of the second LPF is supplied to second input terminals of the comparators. As a method of detecting the back electromotive force of a three-phase sensorless BLDC (Brushless DC) motor unit,
(a) driving the motor unit using a three-phase full bridge circuit;
(b) multiplying an output signal of each phase of the motor unit by a phase modulated signal of a PWM control signal;
(c) first filtering the output signal output in step (b);
(d) performing second filtering on the first filtered signal in the step (c) with a cutoff frequency lower than the cutoff frequency during the first filtering to vary the reference voltage value with respect to the counter electromotive force of each phase at the output of each phase; and
(e) comparing the first filtered signal in step (c) with a reference voltage value that is varied in step (d) and outputting a pulse signal based on the position of the motor rotor. Detection method. 10. The method of claim 9, wherein each phase output signal of the step (b)
A method of detecting back electromotive force, characterized in that it is distorted by a flyback pulse generated due to a load applied to a motor when the motor is driven at a high load. The method of claim 9 or 10, wherein the phase modulated signal of step (b)
And a step (sin (ωt + θ)) of modulating a phase of the PWM control signal (Asinωt) by a predetermined angle (θ). The method of claim 11, wherein step (e)
If the first filtered signal is greater than the reference voltage value, and outputs a high signal,
And outputting a low signal when the first filtered signal is smaller than the reference voltage value.

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