KR20040035358A - Control apparatus and method for brushless dc motor - Google Patents

Abstract

PURPOSE: An apparatus and a method for controlling a brushless DC motor are provided to supply the compensation voltage during a phase commutation period by detecting a starting point and an ending point of the phase commutation period. CONSTITUTION: An apparatus for controlling a brushless DC motor includes a power conversion unit and a control unit(214). The power conversion unit converts the commercial AC power to the multi-phase AC power. The control unit(214) detects a phase commutation period by using the position information of a rotor and an extinction point of the arc extinction phase current applied to a cathode of the power conversion unit. In addition, the control unit(214) controls the power conversion unit to supply the compensation voltage for maintaining the average voltage of non-commutation phases during the phase commutation period. The power conversion unit includes a converter(204) for converting the commercial AC power to the DC power, an inverter(206) for converting the DC power to the multi-phase AC power, and a DC terminal capacitor(208) for connecting the converter(204) to the inverter(206).

Description

CONTROL APPARATUS AND METHOD FOR BRUSHLESS DC MOTOR}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for controlling a motor, and more particularly to an apparatus and method for controlling a brushless DC motor for minimizing torque ripple.

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 is characterized by low electromagnetic interference and noise. The structure of such a brushless DC motor control apparatus will be described with reference to FIG. 1 as follows.

1 is a block diagram showing a conventional brushless DC motor control apparatus. 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). Each phase current of the three-phase alternating current (U, V, W) supplied from the inverter 106 to the brushless DC motor 110 is detected through the current sensors 112a and 112b. Information of the detected phase current is provided to the controller 114 to form a basis for generating an inverter control signal. The position and speed of the rotor of the brushless DC motor 110 are detected by the position / speed detection unit 116, and the detected position information of the rotor is provided to the control unit 114 to generate the inverter control signal. Becomes The controller 114 controls the rotation speed of the motor 110 to meet the demand of the speed control signal by referring to the speed control signal, phase current information, and the position of the rotor input from the outside. The inverter control signal is 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.

In driving such a conventional brushless DC motor 110, torque pulsation occurs due to the temporary decrease in the phase current at the time when the phase change of the three-phase AC power source (U, V, W) is made. The torque of the brushless DC motor can be expressed as the product of the induced voltage and the current. In the phase switching section, the phase current temporarily decreases, causing torque pulsation. Since this torque pulsation causes noise and vibration, a control device and a method for minimizing it are required.

In order to minimize torque pulsation of brushless DC motors, it is necessary to accurately detect the phase switching period and compensate for the insufficient voltage. Inaccurate detection of phase transitions is critical for minimizing torque pulsations, since it can lead to undercompensation or overcompensation of current. Conventional methods used to detect the phase switching period of a brushless DC motor include detecting a phase current using a current sensor. However, the use of two current sensors to detect each phase current as shown in FIG. 1 causes a rise in manufacturing cost, which is a great burden for both producers and consumers.

The present invention accurately predicts and detects phase switching timing and period of a three-phase AC power source in order to minimize torque pulsation caused by a temporary decrease in phase current occurring in a phase switching period of a three-phase current supplied to a brushless DC motor. The purpose of the present invention is to compensate for the decrease in current in the phase shift period.

1 is a block diagram showing a conventional brushless DC motor control device.

Figure 2 is a block diagram showing a brushless DC motor control apparatus according to the present invention.

3 is a block diagram showing a configuration of a control unit of the brushless DC motor control apparatus according to the present invention shown in FIG.

4 is a block diagram illustrating a configuration of a control signal converter of FIG. 3.

5 is a circuit diagram showing the configuration of an inverter of the brushless DC motor control device according to the present invention shown in FIG.

6 is a diagram illustrating a rear end unipolar pulse width modulation method of a brushless DC motor control device.

7A to 7D are diagrams showing current flow inside an inverter in a phase switching period.

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

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

210: brushless DC motor

212: current sensor

214: control unit

302, 306: adder

308: current controller

310: control signal conversion unit

316: phase change detection unit

The brushless DC motor control apparatus according to the present invention for this purpose comprises a power converter and a control unit. The power converter converts a commercial AC power source into a polyphase AC power source. The control unit detects the phase switching section based on the position information of the rotor of the brushless DC motor and the extinction point of the sub-phase current flowing through the cathode of the power converter, and compensates for maintaining a constant average voltage of the non-switching phase during the phase switching section. The power conversion device is controlled to supply a voltage.

In addition, the control method of the brushless DC motor according to the present invention, which is supplied with power through a power converter for converting commercial AC power into a polyphase AC power, first supplies a non-switched phase current to drive the motor, The starting point of phase change is detected by the position information of the rotor. When the phase change starts, the compensation voltage for minimizing the torque pulsation caused by the phase change is supplied, and the end point of the phase change is detected by detecting the extinction phase current appearing at the negative pole (-) of the power converter. Stop supply and resume supply of non-switched phase current.

A preferred embodiment of the apparatus and method for controlling a brushless DC motor according to the present invention will be described below with reference to FIGS. 2 to 8. 2 is a block diagram showing a brushless DC motor control apparatus according to the present invention. As shown in FIG. 2, the power conversion device including the converter 204, the capacitor 208, and the inverter 206 converts AC power supplied through the AC power supply 202 into DC power, and then converts the power into three phases. It is converted into AC power (U, V, W) and supplied to the brushless DC motor 210. The converter 204 converts AC power into DC, and the inverter 206 converts DC power into pulsed three-phase AC power U, V, and W to supply the brushless DC motor 210.

The current flowing through the cathode (-) of the DC-link capacitor 208 between the converter 204 and the inverter 206 is detected by the single current sensor 212, and the detected current information is stored in the controller ( 214). The position / speed detector 216 detects the speed and position of the rotor of the brushless DC motor 210 and provides the information to the controller 214. The controller 214 controls the rotation speed of the DC motor 110 to follow the value of the speed control signal input from the outside based on the current amount information and the position / speed information provided in this way. To this end, the inverter 206 generates an inverter control signal to control the phase commutation timing and the current of each phase of the three-phase AC power sources U, V, and W output from the inverter 206. The biggest feature of the brushless DC motor control apparatus according to the present invention shown in FIG. 2 is the detection of current at the cathode (-) of the DC stage capacitor 208 using a single current sensor 212.

3 is a block diagram showing the configuration of the control unit 214 of the brushless DC motor control apparatus according to the present invention shown in FIG. As shown in FIG. 3, the speed control signal and the current speed information are added by the adder 302 and provided to the speed control unit 304. The speed controller 304 generates a current command so that the rotational speed of the brushless DC motor 210 follows the value of the speed control signal. This current command and current information detected by the current sensor 212 are added by the adder 306 and provided to the current controller 308. The current controller 308 generates a first current control signal A for causing the phase current of the brushless DC motor 210 to follow the current command. The phase change detection unit 316 detects a phase change section based on the position information detected by the position / speed detector 216 and the current information detected by the current sensor 212 to generate a phase change detection signal D. . The phase change detection signal D is input to the control signal converter 310 together with the first current control signal A generated by the current controller 308.

The control signal converter 310 internally generates the second current control signal B (not shown) by converting the first current control signal A generated by the current controller 308. The phase change detection signal D of the phase change detection unit 316 causes one of the first current control signal A and the second current control signals A and B to be output as the third current control signal C. The third current control signal C output from the control signal converter 310 determines the pulse width of the inverter control signal generated by the inverter controller 314.

4 is a block diagram illustrating a configuration of the control signal converter 310 of FIG. 3. As shown in FIG. 4, the control signal converter 310 may include one of the first current control signal A generated by the current controller 308 and the second current control signal B generated internally. Is input to the limiter 412 via < RTI ID = 0.0 > 3/4 signal of the first current control signal A produced by the amplifier 402 and 1/2 signal of A _max produced by the second amplifier 404, K produced by the signal generator 406 _{The e} ω / 2V _DC signal is added through the adder 408 to produce a second current control signal B. The A _max signal input to the second amplifier 404 is the maximum value that the first current control signal A can have, and in this embodiment, has a value of 1.

The switch 410 for selecting one of the first and second current control signals A and B is switched by the phase change detection signal D generated by the phase change detection unit 316. During the phase shift period, the phase shift detection unit 316 causes the contact of the switch 410 to be connected to the S1 terminal, so that the first current control signal A is transmitted as the third current control signal C through the limiter 412. To be printed. In contrast, the phase change detection unit 316 allows the contact of the switch 410 to be connected to the S2 terminal during the phase change period so that the second current control signal B is used as the third current control signal C through the limiter 412. To be printed. The third current control signal C is input to the inverter controller 314 to be the basis of the inverter control signal. The limiter 412 limits the size of the third current control signal C to less than a predetermined size (for example, 1).

The first current control signal A is for generating a normal phase current, and the second current control signal B is for generating a compensation current so that the average voltage of the non-switched phase does not decrease in the phase switching period. The average voltage V1 applied to the phase energized by the first current control signal A in the two-phase energization period when using the rear end unipolar pulse width modulation method is expressed as follows.

(One)

In the above Equation (1), V _DC is the voltage across the capacitor 208 of the DC terminal, and A has a value of 0 <A <1 as the magnitude of the first current control signal.

In addition, when using the rear-end unipolar pulse width modulation scheme, the average voltage V2 applied to the non-switched phase during the phase switching period is expressed as follows.

(2)

In Equation (2), K _e is the counter electromotive force constant, ω is the rotational speed, V _DC is the voltage across the capacitor 208 of the DC terminal, A is the magnitude of the first current control signal, and a value of 0 <A <1. Have

In order that the average voltage of the non-switched phase does not change, a condition of V1 = V2 must be established. The magnitude B of the second current control signal B that satisfies this condition can be expressed as follows.

(3)

In Equation (3), the size of B has a value of 0 <B <1.

The second current control signal B must be supplied only during the phase shift period correctly to achieve accurate compensation of the average voltage. If the supply of the second current control signal B is stopped before the end of the phase switching period, undercompensation is performed. If the second current control signal B is still supplied even after the phase switching period is terminated, overcompensation is performed. Torque pulsation cannot be minimized. In the brushless DC motor control apparatus and method according to the present invention, the starting point of the phase switching section is detected from the position information of the rotor, and the end time of the phase switching section is detected from the disappearance of the sub-phase current appearing at the cathode of the DC stage capacitor. The torque pulsation is minimized by supplying a compensating current only during this phase transition period. Such a method for detecting a phase end point ending time point according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 5 is a circuit diagram showing the configuration of the three-phase full-bridge inverter 206 of the brushless DC motor control apparatus according to the present invention shown in FIG. 2, and each of the three-phase AC signals of FIG. The switching elements, that is, the transistors Q1 to Q6 are controlled to switch the phase current.

FIG. 6 is a diagram illustrating a rear end unipolar pulse width modulation scheme of the brushless DC motor controller, and illustrates an inverter control signal for driving the inverter 206. In the rear-end unipolar pulse-width modulation method, the pulse width is modulated by the on / off of a single switching element in the 60-degree section of the out-going phase in the 120-degree conduction section as shown in FIG. do.

6, the point of time of the firing of the phase current supplied through the transistor Q2 and the first pulse of the pulse width modulation phase current supplied through the transistor Q1 are not synchronized with each other. Since the average voltage of the non-switched phase may fluctuate due to this asynchronous, in order to minimize torque pulsation, the firing point of the firing phase current and the start point of the first pulse of the pulse width modulation phase current are synchronized.

7A to 7D are diagrams showing the current flow inside the inverter in the phase inversion period, in which the current flow from the UV phase (0 ° to 60 ° section) to the UW phase (60 ° 120 ° section) is gradually It is shown as. 7A shows the current flow in the inverter 206 on the U-V phase (0 to 60 degrees). In this section, the transistors Q1 and Q6 are turned on so that the U-V phase current flows.

In this state, the transistor Q6 is turned off and the transistor Q2 is turned on to start the phase transition from the U-V to the U-W phase as shown in FIGS. 7B and 7C. 7B and 7C show the flow of the phase current 702 to be arced and the phase current 704 to be arced in the phase switching section. In the case of FIG. 7B, the transistors Q1 and Q2 are both turned on. In this case, the current 704 of the newly-burned phase W appears at the cathode (−) of the DC-stage capacitor 208. In the case of FIG. 7C, the transistor Q1 is turned off and the transistor Q2 is still turned on. In this case, the current 706 of the phase V which is extinguished to the negative electrode (-) of the DC-stage capacitor 208. Only appear, and the current 708 of the phase W being fired flows through the diode D4 without reaching the cathode (-) of the capacitor 208. This flow of current is similar in the case of bipolar pulse width modulation, which simultaneously turns on and off two energized switching elements. Therefore, if both current unipolar pulse width modulation method and bipolar pulse width modulation method are installed at the cathode of the inverter DC stage, the current sensor can be detected during phase switching period, and the time of extinction of the phase current being extinguished can be detected. By detecting, the completion time of a phase change section can be detected correctly. In this case, since only the current appearing on the negative electrode (-) of the DC-stage capacitor 208 is detected, only a single current sensor can detect the phase change completion time. The torque pulsation caused by the variation of the average voltage of the non-switched phase in the phase switching period is supplied by supplying the second control signal B to the inverter controller 314 instead of the first current control signal A during the phase switching period thus obtained. It can be minimized.

FIG. 7D is a diagram showing the current flow of the inverter 206 in the phase switching completed state, in which the transistors Q1 and Q2 are both turned on. At this time, the non-switched phase current in which the phase change is completed appears on the negative electrode (-) of the DC stage capacitor 208.

8 is a flowchart illustrating a control method of a brushless DC motor according to the present invention. As shown in FIG. 8, the non-switched phase current is supplied to drive the motor 210 (802). The position information of the rotor is monitored to determine if phase switching is started (804), and the supply of non-switched phase current is continued until phase switching begins. Once the phase shift is initiated (806), a compensation voltage is provided (808) to minimize torque pulsation following the phase shift. When the end point of phase switching is detected through the disappearance of the sub-phase current appearing at the cathode (-) of the DC stage capacitor 208 (810), the supply of the compensation voltage is stopped and the supply of the non-switched phase current is resumed (812). ).

The brushless DC motor control apparatus and method according to the present invention detects the starting point of the phase switching section from the position information of the rotor and detects the end point of the phase switching section from the disappearance of the sub-phase current appearing at the cathode of the DC stage capacitor. By supplying a compensation voltage only during the phase transition period, torque pulsations that can occur during phase transition of the three-phase AC power source of the brushless DC motor are minimized.

Claims (21)

In the control device of a brushless DC motor, A power converter for converting commercial AC power into a polyphase AC power; Compensation for maintaining a constant average voltage of the non-switched phase during the phase switching period by detecting the phase switching period based on the position information of the rotor of the brushless DC motor and the extinction time of the sub-phase current flowing through the cathode of the power converter. And a control unit for controlling the power conversion device to supply a voltage. 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; Control device for a brushless DC motor comprising a DC stage capacitor for connecting the converter and the inverter. The method of claim 2, And a single current sensor for detecting a current appearing at the cathode of the inverter DC stage and providing the detected current information to the controller. The method of claim 1, A control device for a brushless DC motor, wherein the inverter is a three-phase full-bridge inverter. The method of claim 1, wherein the control unit, A phase change detector for detecting a phase change section; Brushless DC motor including a control signal converter for generating a first current control signal for supplying the non-switched phase current in the non-switching period, and a second current control signal for supplying the compensation current in the phase switching period Control device. The method of claim 5, wherein And the second current control signal B is defined as follows. (Where B has a magnitude of 0 <B <1, A has a value of 0 <A <1 as magnitude of the first current control signal, K _e is a counter electromotive force constant, ω is a rotational speed of the rotor, V _DC is the voltage at both ends of DC capacitor) The method of claim 1, wherein the control unit, A speed controller configured to generate a current command so that the rotational speed of the brushless DC motor follows the value of the speed control signal based on the speed control signal input from the outside and the current speed information; A current controller for generating the first current control signal for causing the phase current of the brushless DC motor 210 to follow the current command based on the current command and current information detected by the current sensor; A control signal converter configured to input the first current control signal and generate the second current control signal to output one of the first and second current control signals according to the phase change detection signal generated by the phase change detection unit Wow; And an inverter controller configured to generate a control signal for controlling the inverter according to the current control signal output from the control signal converter. The method of claim 7, wherein the control signal converter, A switch configured to input the first and second current control signals at both ends thereof and to be controlled by a phase change detection signal generated by the phase change detection unit to output one of the first and second current control signals; And a limiter for limiting a magnitude of a current control signal output through the switch to a predetermined size or less. The method of claim 1, A control device for a brushless DC motor, wherein the multi-phase AC power output from the power converter is a three-phase AC power. The method of claim 1, And the power converter operates in one of a rear end unipolar pulse width modulation method and a bipolar pulse width modulation method. In the phase change detection device of the brushless DC motor control device having a power converter for converting commercial AC power into a multi-phase AC power, Phase switching start point is detected from the position information of the rotor of the brushless DC motor, and phase switching end of the brushless DC motor control device is detected from the extinction time of the sub-phase current flowing through the cathode of the power converter. Detection device. The power converter of claim 11, wherein A converter for converting the commercial AC power into direct current; An inverter for converting the DC power into the multiphase AC power; Phase change detection device of a brushless DC motor including a DC stage capacitor for connecting the converter and the inverter. The method of claim 12, And a single current sensor for detecting a current appearing at the cathode of the inverter DC terminal and providing the detected current information to the control unit. The method of claim 11, Phase change detection device of a brushless DC motor, wherein the inverter is a three-phase full-bridge inverter. The method of claim 11, The phase change detection device of the brushless DC motor, wherein the multi-phase AC power output from the power converter is a three-phase AC power. The method of claim 11, And a phase conversion detection device of a brushless DC motor in which the power converter operates in one of a rear end unipolar pulse width modulation method and a bipolar pulse width modulation method. In the control method of a brushless DC motor supplied with power through a power converter for converting commercial AC power into a multi-phase AC power, Driving a motor by supplying a non-switched phase current; Detecting a phase change start point through position information of the rotor; Supplying a compensating current for minimizing torque pulsation caused by phase switching when phase switching starts; And stopping the supply of the compensation current by detecting an end point of the phase change from disappearance of the extinguishing phase current appearing at the cathode (-) of the power converter. The method of claim 17, A control method for a brushless DC motor, wherein the inverter is a three-phase full-bridge inverter. The method of claim 17, The control method of the brushless DC motor which detects the electric current which appears in the cathode of the said power converter using a single current sensor. The method of claim 17, The control method of the brushless DC motor whose polyphase AC power output from the said power converter is 3-phase AC power. The method of claim 17, And the power converter operates in one of a rear end unipolar pulse width modulation method and a bipolar pulse width modulation method.