Method for controlling a brushless DC motor and device for controlling a brushless DC motor

Abstract

To provide a method for controlling a brushless DC motor that can suppress current ripple, reduce noise, and control the speed of the brushless DC motor with square wave drive.SOLUTION: A brushless DC motor control method uses an inverter circuit 30 configured to be able to switch the energized phase of a brushless DC motor 10, and drives the brushless DC motor 10 in a square wave at a target rotational speed vr using discrete time system control, and executes a target current value setting step ST2 of setting a target current value Is for tracking the target rotational speed vr, a current value measurement step ST3 of measuring energized phase current values Iu, Iv, Iw of the brushless DC motor 10 during square wave drive, a gate signal generation step ST4 of generating a gate signal such that the energized phase current values Iu, Iv, Iw track the target current value Is, and an energized phase switching step ST5 of switching the energized phase on the basis of the gate signal.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method for controlling a brushless DC motor and a device for controlling a brushless DC motor. [Background technology]

[0002] Brushless DC motors are widely used in various fields such as industrial products and computer peripherals, taking advantage of their features such as small size, high efficiency, long life, and low noise, and in recent years, higher standards of noise reduction are being demanded. The noises of brushless DC motors are known to be mechanical noise caused by vibration of bearings and scratches on parts, and electromagnetic noise caused by electromagnetic torque ripple and cogging torque. Generally, to drive brushless DC motors, sine wave drive control (180 degree control) is used, in which the voltage is changed to a sine wave to rotate the rotor, or square wave drive control (120 degree control) is used, in which the direction of the current is changed every 60 electrical degrees to rotate the rotor. In particular, as a square wave drive control, PWM (Pulse Width Modulation) speed control (hereinafter referred to as "PWM control") is often used, which controls the output power by repeatedly switching ON / OFF. In PWM control, the ON / OFF duty ratio is changed and the effective value of the voltage is adjusted to follow the target rotation speed. Compared to sine wave drive control, square wave drive control has the advantage of being able to configure a control system more simply and at lower costs, but it tends to produce relatively loud noise due to electromagnetic torque ripple during switching.Therefore, various proposals have been made to reduce the noise of brushless DC motors driven by square wave drive control (for example, Patent Document 1 and Patent Document 2).

[0003] The control device (motor control device) disclosed in Patent Document 1 starts a motor and controls its rotation speed so that it coincides with a target rotation speed. Specifically, a control calculation unit outputs a q-axis current command value according to the rotation speed deviation so that the rotation speed of the motor coincides with the target rotation speed, and a drive circuit unit outputs a PWM voltage control signal generated based on this q-axis current command value to an inverter circuit (see paragraph

[0006] in Patent Document 1).

[0004] The control device (driver for a brushless DC motor) disclosed in Patent Document 2 has a trapezoidal wave generating means, a triangular wave oscillation circuit that oscillates a triangular wave, a PWM modulation circuit that generates a PWM modulated wave from the trapezoidal wave and the triangular wave, and a drive circuit that generates a control signal based on the PWM modulated wave, and drives a brushless DC motor based on the control signal output to an inverter circuit (see paragraph

[0006] of Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2007-295672 A [Patent Document 2] JP 2006-006067 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the PWM control adopted in the control devices disclosed in Patent Documents 1 and 2, when the duty ratio changes drastically, current pulsation called current ripple occurs, and the resulting vibration becomes a cause of electromagnetic noise. In PWM control, voltage is adjusted by ON / OFF switching, so it is difficult to suppress the current ripple.

[0007] In view of the above, the main object of the present invention is to propose a control method for a brushless DC motor that can suppress current ripples, reduce noise, and control the speed of the brushless DC motor by square wave drive. Another object of the present invention is to propose a control device for a brushless DC motor to which this control method is applied. [Means for solving the problem]

[0008] [1] In order to solve the above problems, a method for controlling a brushless DC motor according to the present invention uses an inverter circuit configured to be able to switch the energized phase of a brushless DC motor based on a gate, and drives the brushless DC motor in a rectangular wave at a target rotational speed by discrete time system control, and executes a target current value setting step of generating a target current value for tracking the target rotational speed, a current value measurement step of measuring an energized phase current value of the brushless DC motor during rectangular wave drive, a gate signal generation step of generating a gate signal so that the energized phase current value tracks the target current value, and an energized phase switching step of switching the energized phase based on the gate signal.

[0009] [2] In the control method for a brushless DC motor according to the present invention, it is preferable to further execute a rotational speed calculation step of calculating the rotational speed from rotational speed information obtained by measuring the brushless DC motor during rectangular wave drive, and in a target current value setting step, generate a target current value from the difference between the target rotational speed and the rotational speed calculated in the rotational speed calculation step.

[0010] [3] In the control method for a brushless DC motor according to the present invention, it is preferable that the discrete-time control is discrete-time PI control, and in the target current value setting step, the target current value (Is[z]) is generated using the following equation 1. TIFF0007645914000001.tif43170

[0011] [4] In the control method for a brushless DC motor according to the present invention, in the gate signal generation step, it is preferable to compare a current value of an energized phase having a positive current direction with a target current value, and generate a gate signal so that the energized phase is switched depending on whether the current value is larger or smaller.

[0012] [5] In the method for controlling a brushless DC motor according to the present invention, in the gate signal generating step, it is preferable to generate gate signals so as to change the number of transistors that are simultaneously opened in the inverter circuit to switch the energized phase.

[0013] [6] In the control method for a brushless DC motor according to the present invention, in the gate signal generation step, when the energized phase current value is smaller than a target current value, a gate signal is generated for opening both the gate of the transistor that causes current to flow into the coil of the energized phase and the gate of the transistor that causes current to flow out of the coil, and when the energized phase current value is greater than the target current value, a gate signal is generated for closing the gate of the transistor that causes current to flow into the coil and for opening the gate of the transistor that causes current to flow out of the coil.

[0014] [7] A brushless DC motor control device according to the present invention is a brushless DC motor control device that drives a brushless DC motor in a rectangular wave at a target rotational speed by discrete time system control, and includes an inverter circuit configured to control switching of current-carrying phases of the brushless DC motor by switching of a gate signal, a target rotational speed input unit that accepts an input of the target rotational speed, an energized phase current value acquisition unit that acquires an energized phase current value of the brushless DC motor during rectangular wave drive measured by an external or built-in current sensor, a target current value generation unit that generates target current values ​​for the energized phase current values ​​of each phase in order to make the rotational speed of the brushless DC motor follow the target rotational speed accepted by the target rotational speed input unit, and a gate signal generation unit that generates a control command for making the energized phase current values ​​acquired by the energized phase current value acquisition unit follow the target current, and outputs the control command to the inverter circuit as a gate signal for switching the energized phase by the inverter circuit.

[0015] [8] The control device for a brushless DC motor according to the present invention preferably further includes a rotational speed information input unit that accepts input of measured rotational speed information of the brushless DC motor during rectangular wave drive, and the target current value generation unit generates a target current value based on the target rotational speed and the rotational speed.

[0016] [9] In the brushless DC motor control device of the present invention, it is preferable that the discrete-time control is discrete-time PI control, and the target current value generation unit generates the target current value (Is[z]) using the above equation 1.

[0017]

[10] In the control device for a brushless DC motor according to the present invention, it is preferable that the gate signal generating unit generates a gate signal for opening both the gate of the transistor that causes current to flow into the coil of the energized phase and the gate of the transistor that causes current to flow out of the coil when the energized phase current value is smaller than the target current value, and generates a gate signal for closing the gate of the transistor that causes current to flow into the coil and opening the gate of the transistor that causes current to flow out of the coil when the energized phase current value is greater than the target current value. Effect of the Invention

[0018] According to the present invention, it is possible to suppress current ripples, reduce noise, and control the speed of a brushless DC motor by square wave drive. [Brief description of the drawings]

[0019] [Figure 1] 1 is a block diagram showing a configuration of a brushless DC motor system according to a first embodiment. [Diagram 2] FIG. 2 is a block diagram showing a control concept in the brushless DC motor system of the first embodiment. [Diagram 3] 5 is a graph showing current tracking control of the brushless DC motor system of the first embodiment. [Figure 4] 4 is a flowchart showing a method for controlling the brushless DC motor of the first embodiment. [Figure 5A] 4 is a schematic diagram showing current conduction phase switching in a current conduction phase switching step in the control method for the brushless DC motor of the first embodiment (rotor rotation angle 0° to 180°). FIG. [Figure 5B] 4 is a schematic diagram showing current conduction phase switching in a current conduction phase switching step in the control method for the brushless DC motor of the first embodiment (rotor rotation angle 180° to 360°). FIG. [Figure 6A] 10 is a schematic diagram showing current conduction phase switching in a current conduction phase switching step in a control method for a brushless DC motor according to a second embodiment (rotor rotation angle 0° to 180°). FIG. [Figure 6B] 10 is a schematic diagram showing current conduction phase switching in a current conduction phase switching step in a control method for a brushless DC motor according to a second embodiment (rotor rotation angle 180° to 360°). FIG. [Figure 7] 13 is a graph showing motor rotation speeds in experimental results. [Figure 8] 13 is a graph showing motor current waveforms in experimental results. [Figure 9] 13 is a graph showing motor electromagnetic torque waveforms in experimental results. [Figure 10] FIG. 13 is a diagram showing the spectral intensity of the motor electromagnetic torque waveform in the experimental results. [Figure 11] FIG. 13 is a diagram showing a cumulative amplitude spectrum of a motor electromagnetic torque waveform in an experimental result. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] A brushless DC motor system 1 as an embodiment to which the present invention is applied will be described below with reference to the drawings. Note that each drawing does not necessarily strictly reflect all of the actual configuration. In addition, in this specification, the rotation of the rotor of the brushless DC motor is described using the term "rotational speed", but this term may be replaced with the term "angular speed". In this specification, the structure of the brushless DC motor, the driving principle of the brushless DC motor using an inverter circuit, and the peripheral devices for controlling the brushless DC motor are generally the same as in the conventional case, and the description of the same parts as in the conventional case will be simplified or omitted.

[0021] [Embodiment 1] (1-1. Configuration of Brushless DC Motor System of Embodiment 1) 1 is a block diagram showing the configuration of a brushless DC motor system 1 according to embodiment 1. First, the configuration of the brushless DC motor system 1 according to embodiment 1 will be described with reference to FIG.

[0022] In the first embodiment, the following description will be given taking as an example a case where discrete-time PI control (Proportional-Integral control) is used as the discrete-time control. In addition to PI control, the discrete-time control also includes IP control (Integral-Proportional control) in which the P control calculation is performed on the output instead of the deviation, and IP control may be used as the discrete-time control. In the second embodiment and other embodiments described below, the case where discrete-time PI control is used as the discrete-time control will also be described, but as in the first embodiment, IP control may be used instead of PI control.

[0023] 1, the brushless DC motor system 1 includes a brushless DC motor 10 that outputs rotational power, a rotary encoder 20 that detects a rotation angle, and a control device 30 that drives the connected brushless DC motor 10 in a rectangular wave at a target rotation speed using discrete-time PI control. The brushless DC motor system 1 also includes a computer device 80 that is connected to the control device 30 so as to be able to send and receive data, so that data can be set in the control device 30 and data can be acquired from the control device 30. Each component of the brushless DC motor system 1 will be described in detail below.

[0024] The brushless DC motor 10 includes a stator (not shown), a rotor 11 having multiple magnetic poles and rotatable relative to the stator, multiple coils 12 fixed to the stator at equal intervals in the circumferential direction, and magnetic sensors 13 fixed to the stator at equal intervals in the circumferential direction. The rotor 11 includes an output shaft and a permanent magnet with an S pole and a permanent magnet with an N pole aligned at equal intervals in the circumferential direction on the output shaft, forming a rotor. The multiple coils 12 can switch between generating a magnetic force of an S pole, generating a magnetic force of an N pole, and no magnetic force depending on the presence or absence of a current supplied from an inverter circuit 40 described later and the direction of the current. The multiple magnetic sensors 13 are, for example, Hall sensors, and detect the magnetic poles of the rotor 11 that they face. The stator, the multiple coils 12, and the multiple magnetic sensors 13 form a stator. The brushless DC motor 10 is a three-phase motor having U-phase, V-phase, and W-phase, with two magnetic poles (divided into two at 180°) arranged on the rotor 11, three coils 12 (120° pitch), and three magnetic sensors 13 (120° pitch).

[0025] The rotary encoder 20 is mechanically connected to the output shaft of the rotor 11, and detects the rotation angle of the rotor 11. The rotary encoder 20 is also electrically connected to a DSP unit 70 (described later), and outputs an angle signal to the DSP unit 70 as rotation speed information.

[0026] The control device 30 includes an inverter circuit 40, a motor drive power supply 50, a current sensor 60, and a DSP unit 70 (Digital Signal Processor unit 70). The control device 30 also includes other components such as an AD converter, but these other components are well known and will not be described here.

[0027] The inverter circuit 40 is formed as a circuit including a gate driver 41 and a three-phase bridge 42. In the inverter circuit 40, each coil 12 of the brushless DC motor 10 is connected to each line of each phase of the three-phase bridge 42, and the gate driver 41 can switch the energized phase of the brushless DC motor 10 based on a control command (gate signal) from a DSP unit 70 described later.

[0028] The motor driving power supply 50 is electrically connected to the inverter circuit 40 and supplies driving power to the current-carrying phases of the brushless DC motor 10 via the three-phase bridge 42 of the inverter circuit 40 .

[0029] The current sensor 60 is a sensor that can measure in real time the value of a current flowing where it is installed, and is installed in a power supply line from the inverter circuit 40 to each coil 12 of the brushless DC motor 10. The current sensor 60 is also electrically connected to a DSP unit 70 (described later), and outputs the measured current value to the DSP unit 70.

[0030] The DSP unit 70 is a processing unit having a memory element for storing a control program and temporary stored data, a calculation element for performing calculation processing, and an input / output interface for inputting and outputting data to and from the outside, and executes digital signal processing and input / output processing of digital signals according to the control program stored in the memory element. The DSP unit 70 includes a target rotational speed input unit 71, an energized phase current value acquisition unit 72, a target current value generation unit 73, a gate signal generation unit 74, a rotational speed information input unit 75, and a magnetic sensor signal input unit 76, and executes control processing of the brushless DC motor 10.

[0031] The target rotation speed input unit 71 receives an input of a target rotation speed vr when the brushless DC motor 10 is driven from a computer device 80 described later.

[0032] The energized phase current value acquisition unit 72 acquires energized phase current values ​​Iu, Iv, and Iw of the brushless DC motor 10 during square wave driving measured by the current sensor 60.

[0033] The target current value generation unit 73 generates a target current value Is of the energized phase current values ​​Iu, Iv, Iw of each phase in order to make the rotation speed v of the brushless DC motor 10 follow the target rotation speed vr received by the target rotation speed input unit 71. The target current value generation unit 73 generates the target current value Is based on the target rotation speed vr and the rotation speed v. For example, the target current value generation unit 73 generates the target current value Is from the difference between the target rotation speed vr and the rotation speed v. Specifically, the target current value generation unit 73 uses forward rectangular approximation in the integration approximation method, and generates the target current value (Is[z]) using the following Equation 1. TIFF0007645914000002.tif43170 Note that in equation 1, forward rectangular approximation is used as an approximation method for the integral in the transfer function, but other approximation methods, such as backward rectangular approximation and trapezoidal approximation (bilinear transformation), may also be used.

[0034] The gate signal generating unit 74 generates a control command for making the energized phase current values ​​Iu, Iv, Iw acquired by the energized phase current value acquiring unit 72 follow the target currents, and outputs the control command to the inverter circuit 40 as a gate signal for switching the energized phase by the inverter circuit 40. When the energized phase current values ​​Iu, Iv, Iw are smaller than the target current value Is, the gate signal generating unit 74 generates a gate signal for opening both the gate of the transistor that causes current to flow into the coil 12 of the energized phase and the gate of the transistor that causes current to flow out of the coil 12, and when the energized phase current values ​​Iu, Iv, Iw are larger than the target current value Is, the gate signal generating unit 74 generates a gate signal for closing the gate of the transistor that causes current to flow into the coil 12 and opening the gate of the transistor that causes current to flow out of the coil 12.

[0035] The rotational speed information input unit 75 receives an input of an angle signal that is measured rotational speed information of the brushless DC motor 10 during square wave driving from a rotational speed information measuring device such as the rotary encoder 20.

[0036] The magnetic sensor signal input unit 76 receives an input of a magnetic sensor signal detected by the magnetic sensor 13 of the brushless DC motor 10 in order to determine the timing for switching the energized phase.

[0037] The computing device 80 may be, for example, a personal computer, a tablet terminal, a mobile terminal, a control switch, or a display panel, and exchanges data with the DSP unit 70, instructs the DSP unit 70 on the control content to be executed, displays data obtained from the DSP unit 70, and performs analysis using that data.

[0038] (1-2. Control Concept in Brushless DC Motor System of Embodiment 1) Fig. 2 is a block diagram showing a control concept in the brushless DC motor system 1 of embodiment 1. Fig. 3 is a graph showing current tracking control in the brushless DC motor system 1 of embodiment 1. Next, the control concept in the brushless DC motor system 1 of embodiment 1 will be described with reference to Figs. 2 and 3.

[0039] In brushless DC motor system 1, the current supplied to each current-carrying phase is controlled by opening and closing transistors in inverter circuit 40 based on gate signals so that brushless DC motor 10 follows a given target rotation speed vr, and feedback control is performed using the rotation angle of brushless DC motor 10.

[0040] In the brushless DC motor system 1, unlike conventional PWM control, a current tracking control (see FIG. 3) is performed in which the measured energized phase current values ​​Iu, Iv, and Iw of the brushless DC motor 10 are made to track a target current value Is corresponding to a target rotation speed vr, and a control process different from the conventional one is performed.

[0041] 2, in the brushless DC motor system 1, a target current value Is for performing discrete-time PI control is set from the difference between a given target rotation speed vr and a rotation speed v calculated and fed back from an angle signal as rotation speed information output by a rotary encoder 20. Then, the current sensor 60 is used to measure the energized phase current values ​​Iu, Iv, Iw of the brushless DC motor 10, and a gate signal is generated as a control command to make the energized phase current values ​​Iu, Iv, Iw follow the target current value Is at the timing obtained from the magnetic sensor signal, and control processing for switching the energized phase is performed based on the gate signal.

[0042] (1-3. Control method of brushless DC motor in embodiment 1) 4 is a flowchart showing a method for controlling the brushless DC motor according to embodiment 1. Next, a method for controlling the brushless DC motor for performing the above-mentioned current tracking control will be described with reference to FIG.

[0043] The method for controlling the brushless DC motor in the brushless DC motor system 1 is a method for driving the brushless DC motor 10 with a square wave at a target rotation speed vr by discrete-time PI control using an inverter circuit 40 configured to be able to switch the energization phase of the brushless DC motor 10 based on a gate signal. This method for controlling the brushless DC motor executes a target rotation speed setting step ST1, a target current value setting step ST2, a current value measuring step ST3, a gate signal generating step ST4, an energization phase switching step ST5, and a rotation speed calculating step ST6, which are repeated until the drive control is stopped.

[0044] In the target rotation speed setting step ST1, the target rotation speed vr is set.

[0045] In target current value setting step ST2, in order to follow the target rotation speed vr, a target current value Is is generated and set from the difference between the target rotation speed vr and the rotation speed v calculated in rotation speed calculation step ST6. Specifically, forward rectangular approximation is used in the integral approximation method, and the target current value (Is[z]) is generated using the following equation 1. TIFF0007645914000003.tif43170 Note that in equation 1, forward rectangular approximation is used as an approximation method for the integral in the transfer function, but other approximation methods, such as backward rectangular approximation and trapezoidal approximation (bilinear transformation), may also be used.

[0046] In the current value measuring step ST3, the energized phase current values ​​Iu, Iv, and Iw of the brushless DC motor 10 during square wave driving are measured.

[0047] In the gate signal generating step ST4, gate signals are generated so that the energized phase current values ​​Iu, Iv, Iw follow the target current value Is. Specifically, the energized phase current values ​​Iu, Iv, Iw in the positive current direction are compared with the target current value Is, and a gate signal is generated depending on the magnitude of the compared values. Also, a gate signal is generated so that the number of transistors simultaneously opened in the inverter circuit 40 is changed to switch the energized phase. More specifically, when the energized phase current values ​​Iu, Iv, Iw are smaller than the target current value Is, a gate signal is generated to open both the gate of the transistor that causes current to flow into the coil 12 of the energized phase and the gate of the transistor that causes current to flow out of the coil 12, and when the energized phase current values ​​Iu, Iv, Iw are larger than the target current value Is, a gate signal is generated to close the gate of the transistor that causes current to flow into the coil 12 and to open the gate of the transistor that causes current to flow out of the coil.

[0048] In the energized phase switching step ST5, the energized phase is switched based on the gate signal.

[0049] In rotation speed calculation step ST6, the rotation speed v is calculated from rotation speed information obtained by measuring the brushless DC motor 10 during square wave driving.

[0050] When the drive control is to be continued, the rotation speed v calculated in the rotation speed calculation step ST6 is fed back to the target current value setting step ST2, and the steps from the target current value setting step ST2 to the rotation speed calculation step ST6 are performed again.

[0051] The above is the procedure of the control method for the brushless DC motor of the first embodiment. The switching of the energized phase, which is a feature of this control method, will be further explained below.

[0052] 5A and 5B are schematic diagrams showing the switching of energized phases in energized phase switching step ST5 in the control method for the brushless DC motor of embodiment 1. The state of the energized phases switched in energized phase switching step ST5 based on the gate signal generated in gate signal generating step ST4 will be described in more detail with reference to Figs. 5A and 5B.

[0053] In the first embodiment, in the gate signal generating step ST4, a gate signal is generated based on Table 1 below so as to open and close the gate of a transistor. [Table 1]

[0054] First, when the electrical angle (rotation angle) of the rotor 11 is in the range of 0° to 60°, it is necessary to pass a current from the U-phase coil to the V-phase coil. At this time, if the current value Iu supplied to the U-phase measured in the current value measurement step ST3 is lower than the target current value Is, the gate of the P-type transistor UP for the U-phase and the gate of the N-type transistor VN for the V-phase are opened. Then, as shown in FIG. 5A (a1), a current flows from the power supply to the U-phase and a current flows from the V-phase to the power supply, and the current value Iu increases. On the other hand, if the current value Iu increases too much and the current value Iu measured in the current value measurement step ST3 exceeds the target current value Is, the gate of the P-type transistor UP for the U-phase is closed and only the gate of the N-type transistor VN for the V-phase is opened. Then, as shown in FIG. 5A (a2), no current flows from the power supply to the U-phase, and the current value Iu decreases. Thereafter, it is necessary to change the phase to which current is applied each time the electrical angle of rotor 11 advances by 60°. However, since control is performed using a similar concept, the specific control for other electrical angles shall refer to Table 1 and FIG. 5A or FIG. 5B, and description thereof shall be omitted.

[0055] In this way, in the first embodiment, the current value is constantly measured, the magnitude of the measured current value relative to the target current value Is is determined, and the gate of the transistor is opened and closed based on the gate signal generated according to the result, thereby performing feedback control to increase or decrease the supply current, thereby making the current value follow the target current value Is.

[0056] (1-4. Actions and Effects of the First Embodiment) The control method for the brushless DC motor of the first embodiment includes a target current value setting step ST2 for setting a target current value Is for following the target rotation speed, a current value measuring step ST3 for measuring current values ​​Iu, Iv, Iw of the brushless DC motor 10 during square wave drive, a gate signal generating step ST4 for generating gate signals so that the current values ​​Iu, Iv, Iw follow the target current value Is, and a current phase switching step ST5 for switching the current phase based on the gate signal. That is, in the control method for the brushless DC motor of the first embodiment, the current phase is switched based on the gate signal, and current tracking control is performed so that the current value of the current phase follows the target current value Is corresponding to the target rotation speed, and the brushless DC motor 10 is speed-controlled to the target rotation speed by square wave drive. Also, in the control method for the brushless DC motor of the first embodiment, current ripples are unlikely to occur because the current phase is switched so that the current values ​​Iu, Iv, Iw follow the target current value Is, and noise associated with the current ripples is reduced. Therefore, according to the control method for a brushless DC motor of embodiment 1, it is possible to suppress current ripples, reduce noise, and control the speed of the brushless DC motor with square wave drive. Also, according to the control device 30 for the brushless DC motor 10 of embodiment 1, the control process is executed using the control method for the brushless DC motor, and therefore the effects of the control method are enjoyed, so that it is possible to suppress current ripples, reduce noise, and control the speed of the brushless DC motor 10 with square wave drive.

[0057] In the control method for the brushless DC motor of the first embodiment, a gate signal is generated so as to change the number of transistors that are simultaneously opened in the inverter circuit 40 to switch the energized phase. Specifically, when the energized phase current values ​​Iu, Iv, Iw are greater than the target current value Is, a gate signal is generated so as to close the transistor that was previously open on the side where current flows into the brushless DC motor 10. According to the control method for the brushless DC motor of the first embodiment, one energized phase is simply deenergized using the gate signal generated in this manner, so that it is not affected by the timing deviation of simultaneous processing as occurs in the case where one energized phase is deenergized and then another phase is energized at the same time, and current ripple can be further suppressed.

[0058] [Embodiment 2] The brushless DC motor system of the second embodiment is similar to the brushless DC motor system 1 of the first embodiment in terms of basic configuration, control concept, and flow of the control method, but differs only in the gate signal generated in gate signal generating step ST4 and the state of the energized phase switched in energized phase switching step ST5 based on the gate signal. Therefore, in the following description, only the different control contents will be described, and other descriptions will be omitted. Note that Figures 1 to 4 can also be applied to the second embodiment.

[0059] 6A and 6B are schematic diagrams showing the switching of energized phases in energized phase switching step ST5 in the control method for a brushless DC motor of embodiment 2. The state of the energized phases switched in energized phase switching step ST5 based on the gate signal generated in gate signal generating step ST4 will be described in more detail with reference to Figs. 6A and 6B.

[0060] In the second embodiment, in the gate signal generating step ST4, gate signals are generated to switch the transistors based on Table 2 below. [Table 2]

[0061] First, when the electrical angle (rotation angle) of the rotor 11 is in the range of 0° to 60°, it is necessary to pass a current from the U-phase coil to the V-phase coil. At this time, if the current value Iu supplied to the U-phase measured in the current value measurement step ST3 is lower than the target current value Is, the gate of the P-type transistor UP for the U-phase and the gate of the N-type transistor VN for the V-phase are opened as in the first embodiment. Then, as shown in FIG. 6A (a1), a current flows from the power supply to the U-phase and a current flows from the V-phase to the power supply, and the current value Iu increases. On the other hand, if the current value Iu increases too much and the current value Iu measured in the current value measurement step ST3 exceeds the target current value Is, the gate of the P-type transistor VP for the V-phase and the gate of the N-type transistor UN for the U-phase are opened. Then, as shown in FIG. 6A (a2), a force acts to pass a current from the V-phase to the U-phase, and the current value Iu decreases. Thereafter, it is necessary to change the phase to be energized each time the electrical angle of rotor 11 advances by 60°. However, since control is performed using a similar concept, the specific control for other electrical angles shall refer to Table 2 and FIG. 6A or FIG. 6B, and description thereof shall be omitted.

[0062] In the second embodiment, as in the first embodiment, the current value is constantly measured, the magnitude of the measured current value relative to the target current value Is is determined, and the gate of the transistor is opened and closed based on the gate signal generated in response to the result, thereby performing feedback control to increase or decrease the supply current, and causes the current value to track the target current value Is.

[0063] According to the control method for a brushless DC motor of embodiment 2, similarly to the control method for a brushless DC motor of embodiment 1, target current value setting step ST2, current value measuring step ST3, gate signal generating step ST4, and current conduction phase switching step ST5 are executed. Therefore, similarly to the control method for a brushless DC motor of embodiment 1, it is possible to suppress current ripples and reduce noise, and to control the speed of the brushless DC motor by square wave drive.

[0064] [Other formats] Although the present invention has been described based on the above embodiment, the present invention is not limited to the above embodiment. The present invention can be embodied in various forms without departing from the spirit of the present invention, and for example, the following modifications are also possible.

[0065] (1) The number of components, the manner of connection, and the like described in the above embodiment are merely examples and may be changed without impairing the effects of the present invention.

[0066] (2) In the above embodiment, the brushless DC motor control device is described as a device in which the inverter circuit, the motor drive power supply, the current sensor, and the DSP unit are integrated, but the present invention is not limited to this. For example, some components may be configured as separate devices electrically connected to the control device.

[0067] (3) In the above embodiment, the brushless DC motor is described as a three-phase motor with two magnetic poles arranged on the rotor, three coils, and three magnetic sensors, but the present invention is not limited to this. For example, the brushless DC motor may be one in which the rotor 11 has eight magnetic poles (divided into eight at 45°).

[0068] (4) In the above embodiment, the rotation speed information to be fed back is described as an angle signal obtained from the rotary encoder 20, but the present invention is not limited to this. For example, the rotation speed information may be calculated from a signal of a magnetic sensor. EXAMPLES

[0069] An experiment was conducted using brushless DC motor control device 30 of embodiment 1 to perform current tracking control of brushless DC motor 10 (hereinafter referred to as "current tracking control using the present invention"). This experiment was conducted under conditions of a target rotation speed vr of 2000 (rpm), a load torque of 0.2 (N·m), and a sampling time of 20 (μs). For comparison, an experiment was also conducted using a conventional control device to perform 120-degree PWM control of brushless DC motor 10 (hereinafter referred to as "conventional PWM control"). The results of the experiment are described below.

[0070] FIG. 7 is a graph showing the motor rotation speed in the experimental results. FIG. 8 is a graph showing the motor current waveform in the experimental results. FIG. 9 is a graph showing the motor electromagnetic torque waveform in the experimental results. FIG. 10 is a diagram showing the spectral intensity of the motor electromagnetic torque waveform in the experimental results. The spectral intensity shown in FIG. 10 is the result of determining the frequency components of the motor electromagnetic torque. FIG. 11 is a diagram showing the cumulative amplitude spectrum of the motor electromagnetic torque in the experimental results. The cumulative amplitude spectrum shown in FIG. 11 is the result of quantitatively determining the vibration energy of the frequencies of sounds audible to humans (20 Hz to 20 kHz) from the spectral intensity of the motor electromagnetic torque.

[0071] As a result of the experiment, it was found that, although there was a slight difference in the time it took to reach the target rotation speed between the current tracking control using the present invention and the conventional PWM control, no difference in tracking was confirmed, as shown in Fig. 7. On the other hand, it was confirmed that, as for the motor current waveform, the current ripple was more suppressed in the current tracking control using the present invention than in the conventional PWM control, and the waveform was closer to a square wave, as shown in Fig. 8.

[0072] As for the motor electromagnetic torque, as shown in Fig. 9, in the current tracking control using the present invention, it was confirmed that the overall swell was less, the fluctuation width was smaller, and vibration was suppressed compared to the conventional PWM control. Looking at the spectrum intensity of this motor electromagnetic torque, as shown in Fig. 10, in the current tracking control using the present invention, vibration components were suppressed in all frequency bands, and the extremely high spectrum intensity seen in the 2kHz to 3kHz range in the conventional PWM control was not confirmed. Furthermore, as shown in Fig. 11, in the conventional PWM control, the cumulative amplitude spectrum of the motor electromagnetic torque was about 39N·m, whereas in the current tracking control using the present invention, it was about 24N·m, and it was confirmed that in the current tracking control using the present invention, the vibration components were reduced by about 39% compared to the conventional PWM control. [Explanation of symbols]

[0073] 1...brushless DC motor system, 10...brushless DC motor, 11...rotor, 12...coil, 13...magnetic sensor, 20...rotary encoder, 30...control device, 40...inverter circuit, 41...gate driver, 42...three-phase bridge, 50...motor drive power supply, 60...current sensor, 70...DSP unit, 71...target rotation speed input section, 72...energized phase current value acquisition section, 73...target current value generation section, 74...gate signal generation section, 75...rotation speed information input section, 76...magnetic sensor signal input section, 80...computer equipment, Is...target current value, Iu...(transmission (energized phase) current value (U phase), Iv...(energized phase) current value (V phase), Iw...(energized phase) current value (W phase), v...rotation speed, vr...target rotation speed, ST1...target rotation speed setting step, ST2...target current value setting step, ST3...current value measurement step, ST4...gate signal generation step, ST5...energized phase switching step, ST6...rotation speed calculation step, UN...N-type transistor for U phase, UP...P-type transistor for U phase, VN...N-type transistor for V phase, VP...P-type transistor for V phase, WN...N-type transistor for W phase, WP...P-type transistor for W phase

Claims

1. A method for controlling a brushless DC motor, using a full-wave bridge type inverter circuit configured to be able to switch a current-carrying phase of the brushless DC motor based on a gate signal, for square-wave driving the brushless DC motor at a target rotation speed by discrete time system control, comprising: a target current value setting step of generating a target current value for following the target rotation speed; a current value measuring step of measuring a current value of a current-carrying phase of the brushless DC motor during the rectangular wave drive; a gate signal generating step of generating a gate signal so as to cause the energized phase current value to follow the target current value; a phase switching step of switching the phase based on the gate signal; Run In the gate signal generating step, when the energized phase current value is smaller than the target current value, generating the gate signal for opening both the gate of a transistor that causes a current to flow into the energized phase coil and the gate of a transistor that causes a current to flow out of the energized phase coil, generating a gate signal for closing a gate of a transistor that causes a current to flow into the coil and for keeping a gate of a transistor that causes a current to flow out of the coil open when the energized phase current value is greater than the target current value; A method for controlling a brushless DC motor.

2. In the gate signal generating step, generating the gate signal for closing the gate of the transistor that causes a current to flow into the coil and for leaving the gate of the transistor that causes a current to flow out of the coil open when the energized phase current value is greater than the target current value, instead of generating the gate signal for instantly switching the transistor that causes a current to flow into the coil and the transistor that causes a current to flow out of the coil so as to reverse the direction of the current flowing into the coil; 2. A method for controlling a brushless DC motor according to claim 1.

3. Furthermore, a rotation speed calculation step is executed to calculate a rotation speed from rotation speed information obtained by measuring the brushless DC motor during the rectangular wave drive.

3. The method for controlling a brushless DC motor according to claim 1, wherein in said target current value setting step, said target current value is generated from a difference between said target rotation speed and said rotation speed calculated in said rotation speed calculation step.

4. 4. The method for controlling a brushless DC motor according to claim 3, wherein the discrete-time control is discrete-time PI control, and the target current value (Is[z]) is generated using the following equation 1 in the target current value setting step.

5. 5. The method for controlling a brushless DC motor according to claim 4, wherein in said gate signal generating step, a current value of a current-carrying phase having a positive current direction is compared with said target current value, and said gate signal is generated so that the current-carrying phase is switched depending on whether the current value is larger or smaller.

6. A control device for a brushless DC motor that drives the brushless DC motor in a rectangular wave at a target rotation speed by discrete time system control, a full-wave bridge type inverter circuit configured to switch a current-carrying phase of the brushless DC motor by switching a gate signal; a target rotation speed input unit that receives an input of the target rotation speed; a current-carrying phase current value acquisition unit that acquires a current-carrying phase current value of the brushless DC motor during the rectangular wave drive measured by an external or built-in current sensor; a target current value generation unit that generates a target current value for a current-carrying phase current of each phase so that the rotation speed of the brushless DC motor follows the target rotation speed received by the target rotation speed input unit; a gate signal generating unit that generates a control command for causing the energized phase current value acquired by the energized phase current value acquiring unit to follow the target current, and outputs the control command to the inverter circuit as the gate signal for switching the energized phase by the inverter circuit; Equipped with The gate signal generating unit when the energized phase current value is smaller than the target current value, generating the gate signal for opening both the gate of a transistor that causes a current to flow into the energized phase coil and the gate of a transistor that causes a current to flow out of the energized phase coil, generating a gate signal for closing a gate of a transistor that causes a current to flow into the coil and for keeping a gate of a transistor that causes a current to flow out of the coil open when the energized phase current value is greater than the target current value; A control device for a brushless DC motor.

7. The gate signal generating unit: generating the gate signal for closing the gate of the transistor that causes a current to flow into the coil and for leaving the gate of the transistor that causes a current to flow out of the coil open when the energized phase current value is greater than the target current value, instead of generating the gate signal for instantly switching the transistor that causes a current to flow into the coil and the transistor that causes a current to flow out of the coil so as to reverse the direction of the current flowing into the coil; 7. The control device for a brushless DC motor according to claim 6.

8. a rotation speed information input unit that receives an input of measured rotation speed information of the brushless DC motor during the rectangular wave drive, 8. The control device for a brushless DC motor according to claim 6, wherein the target current value generating unit generates the target current value based on the target rotation speed and the rotation speed.

9. 9. The brushless DC motor control device according to claim 8, wherein the discrete-time control is discrete-time PI control, and the target current value generating unit generates the target current value (Is[z]) using the following equation 1:

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