KR20040065426A - Control apparatus and method for brushless dc motor - Google Patents

Abstract

PURPOSE: An apparatus and a method for controlling BLDC motor are provided to minimize torque ripple generated in a phase commutation section of the BLDC motor. CONSTITUTION: A BLDC motor(110) comprises a power converter(104), a current sensor(112), and a controller(114). The power converter converts AC power(102) to polyphase AC power and supplies the polyphase AC power to the BLDC motor. The current sensor detects a phase current of the BLDC motor. The controller calculates an ideal phase converting time of the BLDC motor and a real phase converting time of the phase current and controls the BLDC motor in such a manner that the real phase converting time follows the ideal phase converting time.

Description

CONTROL APPARATUS AND METHOD FOR BRUSHLESS DC MOTOR}

The present invention relates to a control apparatus and method of a motor, and more particularly, to a control apparatus and a method for minimizing torque ripple of a brushless DC motor.

Brushless DC motors use commutation circuits consisting of switching elements instead of mechanical elements such as brushes and commutators. The brushless DC motor does not require replacement of the brush due to wear, and features low electromagnetic interference and low driving noise.

Brushless DC motors are powered by a power converter that converts commercial AC power into pulsed, multiphase AC power (generally three-phase). The control device for controlling the speed of the brushless DC motor is based on the phase current information of the multiphase AC power supplied from the power converter to the brushless DC motor, the position and speed information of the rotor, and the rotation speed of the brushless DC motor. To control. The control device controls the rotational speed of the brushless DC motor to follow the speed command input from the outside.

Such a conventional brushless DC motor control device generates a counter electromotive force detection signal by comparing the counter electromotive force generated in each phase of the brushless DC motor with a reference voltage, and controls the power converter based on the counter electromotive force detection signal. However, when the electric time constant (L / R) of the winding of the brushless DC motor increases, such as when the load of the brushless DC motor is very large or operates at high speed, the phase is applied to the current flowing through the winding. May be delayed. When the phase delay of the current flowing through the winding of the brushless DC motor is accumulated, excessive current is supplied to the brushless DC motor, thereby increasing the amount of heat generated by the brushless DC motor, which causes a decrease in the efficiency of the brushless DC motor.

An object of the present invention is to provide a control apparatus and method for a brushless DC motor for controlling the phase difference of the phase current flowing through the winding of the brushless DC motor to be in phase with the counter electromotive force.

1 is a block diagram showing a control device of a brushless direct current motor according to the present invention.

2 is a waveform diagram showing characteristics of a voltage and a current associated with driving a brushless DC motor.

3 is a view showing a case where the phase current is the true or ground.

4 and 5 are views for explaining a method of determining the phase / phase of the phase current in the control device of the brushless DC motor according to the present invention.

6 is a flowchart illustrating a control method of a brushless DC motor according to the present invention.

Figure 7 is a block diagram showing another embodiment of a control device of a brushless direct current motor according to the present invention.

* Description of the symbols for the main parts of the drawings *

102: commercial AC power

104: Converter

106: inverter

108: direct current capacitor

110: brushless DC motor

112, 712: current detector

114: control unit

114a: memory

The control device for a brushless DC motor according to the present invention for such a purpose includes a power converter for converting commercial AC power into a polyphase AC power and providing the same to a brushless DC motor. The current detector detects the phase current of the brushless DC motor. The control unit calculates the ideal phase switching time of the brushless DC motor and the actual phase switching time of the phase current, and controls the actual phase switching time to follow the ideal phase switching time.

The control method of the brushless DC motor according to the present invention calculates the ideal phase switching time of the brushless DC motor, calculates the actual phase switching time of the phase current, and controls the actual phase switching time to follow the ideal phase switching time. do.

In addition, the control device of the brushless DC motor according to the present invention includes a power conversion device for converting commercial AC power into a multi-phase AC power for providing to the brushless DC motor. The position detector detects the zero crossing point of the counter electromotive force of the brushless DC motor. The current detector detects the phase current of the brushless DC motor. The control unit calculates the ideal phase switching time of the brushless DC motor and the actual phase switching time of the phase current, and extends the actual phase switching time when the phase current is forward and shortens the actual phase switching time when the phase current is ground. Control the phase changeover time to follow the ideal phase changeover time.

A preferred embodiment of the apparatus and method for controlling a brushless DC motor according to the present invention will be described with reference to FIGS. 1 to 7. First, Figure 1 is a block diagram showing a control device of a brushless DC motor according to the present invention. As shown in FIG. 1, the power converter including the converter 104, the capacitor 108, and the inverter 106 converts the AC power supplied from the AC power supply 102 into a three-phase AC power in the form of a pulse. Supply to the brushless DC motor (110). The U-phase and V-phase currents of the three-phase AC powers U, V, and W supplied from the inverter 106 to the brushless DC motor 110 are detected through the current detector 112. Information on the U-phase and V-phase currents detected by the current detector 112 is provided to the controller 114 to form the basis of the inverter control signal. The position and speed of the rotor of the brushless DC motor 110 are detected by the position detector 116, and the detected position information of the rotor is also provided to the controller 114 to form the basis of the inverter control signal. The position detector 116 detects a zero crossing point of the counter electromotive force induced by the phase voltage of the brushless DC motor 110 and obtains the position information of the rotor through the zero crossing point. The controller 114 controls the rotation speed of the brushless DC motor 110 with reference to the phase current information input from the current detector 112 and the position information of the rotor input from the position detector 116. The controller 114 outputs an inverter control signal for controlling the phase commutation timing and the magnitude of the phase current of the three-phase AC power sources U, V, and W output from the inverter 106 to output the brushless DC motor. The rotational speed of 110 follows the speed command. The controller 114 internally includes a memory 114a, which is a data storage device, which detects within the phase switching time of the current brushless DC motor 110 and an electric angle of 0 ° to 60 °. Two or more phase current values are stored. The controller 114 corrects the phase difference between the counter electromotive force and the phase current with reference to the phase switching time and the phase current values stored in the memory 114a.

2 is a waveform diagram illustrating voltage and current characteristics associated with driving a brushless DC motor, and illustrates a driving voltage 202, a counter electromotive force 204, and a phase current 206 of the brushless DC motor 110, respectively. . As shown in FIG. 2, there is a phase transition period of time between the time 208 at which the back EMF 204 passes the zero point 208 and the time 210 at which the supply of the new phase current 206 begins. do. In the case of 120 ° energization, the ideal phase switching time is a section corresponding to 30 ° before and after the electric angle of 0 °. In the control device of the brushless DC motor according to the present invention, in order to determine the phase difference between the counter electromotive force and the phase current, and to calculate the phase switching time therefrom, the firing point of the firing phase current after the electric angle of 0 ° is detected. In FIG. 2, the phase switching period t ₃₀ ° from the electrical angle 0 ° to the firing point of the firing phase current corresponds to the electrical angle 30 °, which is an ideal case. The time corresponding to the electric angle section of 0 ° to 30 ° may be calculated through the frequency of the driving voltage 202. The controller 114 converts the electric angle 30 ° into time and stores it in the memory 114a as an ideal phase switching time t _{30 °} .

If the electric time constant (L / R) of the winding of a brushless DC motor increases, such as when the load of a brushless DC motor is very large or is driven at high speed, the phase is ideal for the current flowing in the winding according to the applied voltage. You can escape from the case. That is, the phase of the phase current can be advanced or ground relative to the phase of the counter electromotive force. In order to optimize the driving efficiency of the brushless DC motor 110, it is important to match the phase of the counter electromotive force and the phase current. If the phase of the phase current is positive or relative to the phase of the counter electromotive force, the optimum driving efficiency cannot be obtained. Therefore, in order to obtain the optimum driving efficiency of the brushless DC motor 110, it is desirable to determine whether the phase current is reversed / grounded relative to the counter electromotive force and compensate for the phase difference.

3 is a diagram illustrating a case where the phase current is a true phase or a ground. 3A is a diagram showing a phase current 302 which is in phase, and the point of time of the phase current 302 being fired is preceded by an electric angle of 30 °. In this case, since the phase switching time t _C1 is shorter than the ideal phase switching time t _{30 °} , the phase switching time t _C1 needs to be extended to match the phase of the phase current 302 with the counter electromotive force. 3B is a diagram showing the phase current 304 which is the ground, in which the firing time of the phase current 304 to be fired is lag behind the electric angle of 30 °. In this case, since the phase switching time t _C2 is longer than the ideal phase switching time t _{30 °} , the phase switching time t _C2 must be shortened to match the phase of the phase current 304 and the counter electromotive force.

4 and 5 are diagrams for explaining a method for determining the phase / phase of the phase current in the control device of the brushless DC motor according to the present invention, Figure 4 is a case where the phase current is the lead (lead), 5 is the case where the phase current is lag. As shown first in FIG. 4, the basic phase transition of one phase starts at an electrical angle of 0 °. The control device of the brushless DC motor according to the present invention periodically measures the value of the phase current 404 within the electric angle of 0 ° to 60 °, and compares the magnitude of the measured values to improve the phase current 404. Determine if ground is present. If the current values (I ₁ , I ₂ , I ₃ ) measured at the time points t ₁ , t ₂ , t ₃ in the 0 ° to 60 ° period of the phase current 404 as shown in FIG. It can be seen that I ₁ > I ₂ > I ₃ ) phase current 404 is true. On the contrary, as shown in FIG. 5, current values I ₄ , I ₅ , and I ₆ measured at the time points t ₄ , t ₅ , and t ₆ in the 0 ° to 60 ° intervals of the phase current 504 increase. It can be seen that the backside I ₄ <I ₅ <I ₆ is the current 504 on the ground. In the 0 ° to 60 ° sections of the phase currents 404 and 504, the denser the current value detection interval is, the more precisely the phase / ground status can be measured. 4 and 5, when the phase currents 404 and 504 are in phase or ground, the DC terminal currents 402 and 502 are also the same as phase or ground. Accordingly, the phase / ground of the phase currents 402 and 502 may be determined from the DC current 402 and 502 instead of the phase currents 404 and 504.

FIG. 6 is a flowchart illustrating a method for controlling a brushless DC motor according to the present invention, and is a view illustrating a method of correcting a phase difference by determining whether or not phase current is present. As shown in FIG. 6, the ideal phase switching time t _{30 °} is calculated from the frequency of the drive voltage 202 of the current brushless DC motor 110 (602). The zero crossing point 208 of the counter electromotive force 204 is detected, and the actual phase switching time t _C , which is the time from the zero crossing point 208 to the firing time point 210 of the firing phase current 206, is calculated. (604). When the actual phase switching time t _C is calculated, a phase for determining the phase / phase of the phase current is detected (606). Two or more phase current values I ₁ , I ₂ , I ₃ , or I ₄ at regular intervals within the electrical angle of 0 ° to 60 ° of the phase currents 404, 504, as shown in FIGS. 4 and 5. , I ₅ , I ₆ ) and the phase current progression by determining whether the detected phase current values I ₁ , I ₂ , I ₃ , or I ₄ , I ₅ , I ₆ are decreasing or increasing. Determine the ground. If the detected phase current values I ₁ , I ₂ , I ₃ , or I ₄ , I ₅ , I ₆ are declining, it is true, and if it is increasing, it is ground. In addition, if the detected phase current values I ₁ , I ₂ , I ₃ , or I ₄ , I ₅ , I ₆ are constant, the counter electromotive force and the phase current are in phase.

If the phase of the phase current 404 with respect to the counter electromotive force is positive (see 608, Fig. 4), the currently calculated actual phase switching time t _C1 is extended by β to reset the phase switching time t _C1 . 610. If the phase of the phase current 404 with respect to the counter electromotive force is positive, the phase of the counter electromotive force and the phase current 404 by extending the actual phase switching time t _C1 and delaying the start of the supply of the new phase current 604 which is interlocked. To match. Therefore, while extending the actual phase switching time t _C1 by β, it finally matches the ideal phase switching time t _{30 °} .

If the phase of the phase current 504 with respect to the counter electromotive force is above the ground (see 612 and FIG. 5), the currently calculated actual phase switching time t _C2 is shortened by β to reset the phase switching time t _C2 . (614). That is, if the phase of the phase current 504 with respect to the counter electromotive force is above the ground, the actual phase switching time t _C2 is shortened to advance the starting point of supply of the new phase current 504 to be fired. ) To match the phase. The match of the phases of the back EMF and the phase currents 404, 504 means that the actual phase switch time t _C is equal to the ideal phase switch time t _{30 °} .

When the counter electromotive force and the phase current are in phase, the brushless DC motor 110 is driven by applying the currently calculated phase switching time t _C as it is (616). When the phase change time is corrected to the ideal value t _{30 °} as described above, the phase change is performed at the time when the phase change time t _{30 °} elapses from every zero crossing point of the counter electromotive voltage (614).

Figure 7 is a block diagram showing another embodiment of a control device of a brushless DC motor according to the present invention. As illustrated in FIG. 7, the current detector 712 detects the DC stage current appearing at the cathode of the DC stage capacitor 108 and provides the value to the controller 114. As shown in Figs. 4 and 5 described above, if the phase currents 404 and 504 are the phase or the ground, the DC terminal currents 402 and 502 are also the same as the phase or the ground. Therefore, the phase / ground of the phase currents 402 and 502 can be determined from the DC stage currents 402 and 502 instead of the phase currents 404 and 504 of the brushless DC motor 110.

The control device of the brushless DC motor according to the present invention is generated in the phase commutation section of the brushless DC motor by correcting the phase difference between the counter voltage and the phase current of the brushless DC motor. Minimize torque pulsation.

Claims (20)

A power converter for converting commercial AC power into a multiphase AC power and providing the same to a brushless DC motor; A current detector for detecting a phase current of the brushless DC motor; And a control unit for calculating an ideal phase switching time of the brushless DC motor and an actual phase switching time of the phase current, and controlling the actual phase switching time to follow the ideal phase switching time. The method of claim 1, A position detector for detecting a zero crossing point of counter electromotive force of the brushless DC motor; The ideal phase switching time is a time corresponding to a section between 0 ° and 30 ° of the electrical angle of the phase current; And the actual phase switching time is a time from the zero crossing point to the firing point of the firing phase current. The method of claim 1, wherein the control unit, Brushless DC motor control device for extending the actual phase switching time when the phase current is fast, and shortening the actual phase switching time when the phase current is above ground. The method of claim 1, The phase current detection unit detects at least two phase current values in the electrical angle of 0 ° to 60 ° of the phase current, and compares magnitudes of two or more detected phase current values to determine the phase / ground of the phase current. Brushless DC motor control device to determine. The method of claim 4, wherein Determine the phase current as the true phase when the detected two or more phase current values are in decreasing trend; Brushless DC motor control device for determining the phase current to the ground when the detected two or more phase current value is increasing trend. The method of claim 1, And the phase current detection unit detects the phase current of the multi-phase AC power supplied from the power converter to the brushless DC motor. The power converter of claim 1, wherein A converter for converting the commercial AC power into direct current; An inverter for converting the DC power into the multiphase AC power; It comprises a direct current stage capacitor for connecting the converter and the inverter; And a phase current detection unit detects a phase current appearing at a cathode of the DC terminal capacitor. The method of claim 1, Brushless DC motor control device wherein the multi-phase AC power supply is a pulse-shaped three-phase AC power supply. In the control method of a brushless DC motor, Calculate an ideal phase change time of the brushless direct current motor; Calculate an actual phase switching time of the phase current; And controlling the actual phase change time to follow the ideal phase change time. The method of claim 9, A position detector for detecting a zero crossing point of counter electromotive force of the brushless DC motor; The ideal phase switching time is a time corresponding to a section from 0 ° to 30 ° of the electrical angle of the phase current; And the actual phase switching time is a time from the zero crossing point of the counter electromotive force to the firing point of the firing phase current. The method of claim 9, And extending the actual phase switching time when the phase current is fast and shortening the actual phase switching time when the phase current is above ground. The method of claim 9, Brushless DC motor which detects at least two phase current values in the electric angle range of 0 ° to 60 ° of the phase current and compares magnitudes of two or more detected phase current values to determine the phase / ground of the phase current. Control method. The method of claim 12, Determine the phase current as the true phase when the detected two or more phase current values are in decreasing trend; And controlling the phase current to the ground when the detected two or more phase current values increase. A power converter for converting commercial AC power into a multiphase AC power and providing the same to a brushless DC motor; A position detector for detecting a zero crossing point of counter electromotive force of the brushless DC motor; A current detector for detecting a phase current of the brushless DC motor; Calculating the ideal phase switching time of the brushless DC motor and the actual phase switching time of the phase current, extending the actual phase switching time when the phase current is true and the actual phase switching time when the phase current is ground And a controller configured to shorten the control unit to control the actual phase switching time to follow the ideal phase switching time. The method of claim 14, The ideal phase switching time is a time corresponding to a section between 0 ° and 30 ° of the electrical angle of the phase current; And the actual phase switching time is a time from the zero crossing point to the firing point of the firing phase current. The method of claim 14, The phase current detection unit detects at least two phase current values in the electrical angle of 0 ° to 60 ° of the phase current, and compares magnitudes of two or more detected phase current values to determine the phase / ground of the phase current. Brushless DC motor control device to determine. The method of claim 16, Determine the phase current as the true phase when the detected two or more phase current values are in decreasing trend; Brushless DC motor control device for determining the phase current to the ground when the detected two or more phase current value is increasing trend. The method of claim 14, And the phase current detection unit detects the phase current of the multi-phase AC power supplied from the power converter to the brushless DC motor. The power conversion device of claim 14, wherein A converter for converting the commercial AC power into direct current; An inverter for converting the DC power into the multiphase AC power; It comprises a direct current stage capacitor for connecting the converter and the inverter; And a phase current detection unit detects a phase current appearing at a cathode of the DC terminal capacitor. The method of claim 14, Brushless DC motor control device wherein the multi-phase AC power supply is a pulse-shaped three-phase AC power supply.