JP7645914B2 - Method for controlling a brushless DC motor and device for controlling a brushless DC motor - Google Patents

Description

The present invention relates to a method for controlling a brushless DC motor and a control device for a brushless DC motor.

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 have been required. The noise of brushless DC motors is 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 a brushless DC motor, sine wave drive control (180 degree control) is performed, in which the voltage is changed into a sine wave to rotate the rotor, or square wave drive control (120 degree control) is performed, 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 voltage value 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 the control system simply and at low cost, 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).

The control device (motor control device) disclosed in Patent Document 1 starts a motor and controls its rotation speed so that it matches 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 motor rotation speed matches 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] of Patent Document 1).

The control device (driver of 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).

JP 2007-295672 A JP 2006-006067 A

However, in the PWM control employed 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. With PWM control, voltage is adjusted by ON/OFF switching, making it difficult to suppress current ripple.

In view of these circumstances, the main object of the present invention is to propose 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. In addition, the object of the present invention is to propose a control device for a brushless DC motor that applies this control method.

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

[2] In the brushless DC motor control method according to the present invention, it is preferable to further execute a rotational speed calculation step in which the rotational speed is calculated from rotational speed information obtained by measuring the brushless DC motor during rectangular wave drive, and in the 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.

[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.

[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 the current value of the energized phase in the positive current direction with a target current value, and generate a gate signal so that the energized phase is switched depending on the magnitude of the comparison.

[5] In the control method for a brushless DC motor according to the present invention, in the gate signal generation step, it is preferable to generate a gate signal so as to change the number of transistors that are simultaneously opened in the inverter circuit to switch the current-carrying phase.

[6] In the control method for a brushless DC motor according to the present invention, in the gate signal generation step, if the current value of the energized phase is smaller than the target current value, a gate signal is generated to open 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 if the current value of the energized phase is larger than the target current value, a gate signal is preferably generated to close the gate of the transistor that causes current to flow into the coil and to open the gate of the transistor that causes current to flow out of the coil.

[7] The 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 rotation speed by discrete time system control, and includes an inverter circuit configured to control the switching of the energized phase of the brushless DC motor by switching of a gate signal, a target rotation speed input unit that receives an input of the target rotation 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 a target current value of the energized phase current value of each phase in order to make the rotation speed of the brushless DC motor follow the target rotation speed received by the target rotation speed input unit, and a gate signal generation unit that generates a control command to make the energized phase current value 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.

[8] The brushless DC motor control device 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 generating unit generates a target current value based on the target rotational speed and the rotational speed.

[9] In the brushless DC motor control device according to the present invention, it is preferable that the discrete-time system control is discrete-time system PI control, and the target current value generating unit generates the target current value (Is[z]) using the above formula 1.

[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.

The present invention makes it possible to suppress current ripple, reduce noise, and control the speed of a brushless DC motor using square wave drive.

1 is a block diagram showing a configuration of a brushless DC motor system according to a first embodiment. FIG. 2 is a block diagram showing a control concept in the brushless DC motor system of the first embodiment. 5 is a graph showing current tracking control of the brushless DC motor system of the first embodiment. 4 is a flowchart showing a control method for the brushless DC motor according to the first embodiment. 4 is a schematic diagram showing 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. 4 is a schematic diagram showing 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. 13 is a schematic diagram showing a current conduction phase switching step in the control method for a brushless DC motor according to the second embodiment (rotor rotation angle 0° to 180°). FIG. 13 is a schematic diagram showing a current conduction phase switching step in the control method for a brushless DC motor according to the second embodiment (rotor rotation angle 180° to 360°). FIG. 13 is a graph showing motor rotation speeds in experimental results. 13 is a graph showing motor current waveforms in experimental results. 13 is a graph showing motor electromagnetic torque waveforms in experimental results. FIG. 13 is a diagram showing the spectral intensity of the motor electromagnetic torque waveform in the experimental results. FIG. 13 is a diagram showing a cumulative amplitude spectrum of a motor electromagnetic torque waveform in an experimental result.

Below, a brushless DC motor system 1 as an embodiment to which the present invention is applied will be described 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 velocity". 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 equipment for controlling the brushless DC motor are generally the same as in the past, and the same parts as in the past will be described briefly or omitted.

[Embodiment 1]
(1-1. Configuration of Brushless DC Motor System of First Embodiment)
Fig. 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. 1 .

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, discrete-time control also includes IP control (Integral-Proportional control), in which the P control calculation is performed on the output rather than the deviation, and IP control may be used as the discrete-time control. In the second and other embodiments described below, the case where discrete-time PI control is used as the discrete-time control will also be described, but IP control may be used instead of PI control as in the first embodiment.

As shown in Figure 1, the brushless DC motor system 1 includes a brushless DC motor 10 that outputs rotational power, a rotary encoder 20 that detects the 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 that data can be sent and received, 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.

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 has 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 to form a rotor. The multiple coils 12 can switch between generating a magnetic force of the S pole, generating a magnetic force of the 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 with 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).

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 the DSP unit 70 (described later) and outputs an angle signal to the DSP unit 70 as rotation speed information.

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.

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 the DSP unit 70 described below.

The motor drive power supply 50 is electrically connected to the inverter circuit 40 and supplies drive power to the energized phases of the brushless DC motor 10 via the three-phase bridge 42 of the inverter circuit 40.

The current sensor 60 is a sensor that can measure the current value flowing where it is installed in real time, and is installed in the 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 the DSP unit 70 described below, and outputs the measured current value to the DSP unit 70.

The DSP unit 70 is a processing unit having a memory element for storing a control program and temporary storage 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 digital signal input/output processing according to the control program stored in the memory element. The DSP unit 70 includes a target rotation speed input unit 71, a current-carrying phase current value acquisition unit 72, a target current value generation unit 73, a gate signal generation unit 74, a rotation speed information input unit 75, and a magnetic sensor signal input unit 76, and executes control processing of the brushless DC motor 10.

The target rotational speed input unit 71 accepts input of the target rotational speed vr when driving the brushless DC motor 10 from the computer device 80 described below.

The energized phase current value acquisition unit 72 acquires the energized phase current values Iu, Iv, and Iw of the brushless DC motor 10 during rectangular wave drive measured by the current sensor 60.

なお、式１では、伝達関数における積分の近似法として前進矩形近似を用いたが、他の近似法、例えば、後退矩形近似、台形近似（双一次変換）などを用いてもよい。 The target current value generation unit 73 generates a target current value Is of the energized phase current values Iu, Iv, Iw of the respective phases 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.

In addition, 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.

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 current, 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.

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

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

The computer device 80 is, 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.

(1-2. Control Concept of the Brushless DC Motor System of the First Embodiment)
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.

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

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

More specifically, in the brushless DC motor system 1, as shown in FIG. 2, a target current value Is for 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 the energized phase switching control process is performed based on the gate signal.

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

The brushless DC motor control method in the brushless DC motor system 1 uses an inverter circuit 40 configured to be able to switch the energized phase of the brushless DC motor 10 based on a gate signal, and drives the brushless DC motor 10 with a rectangular wave at a target rotation speed vr by discrete-time PI control. This brushless DC motor control method executes a target rotation speed setting step ST1, a target current value setting step ST2, a current value measurement step ST3, a gate signal generation step ST4, an energized phase switching step ST5, and a rotation speed calculation step ST6, which are repeated until the drive control is stopped.

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

なお、式１では、伝達関数における積分の近似法として前進矩形近似を用いたが、他の近似法、例えば、後退矩形近似、台形近似（双一次変換）などを用いてもよい。 In the 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 the rotation speed calculation step ST6. Specifically, forward rectangular approximation is used in the integration approximation method, and the target current value (Is[z]) is generated using the following formula 1.

In addition, 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.

In the current value measurement step ST3, the energized phase current values Iu, Iv, and Iw of the brushless DC motor 10 during square wave drive are measured.

In the gate signal generation step ST4, a gate signal is generated to make 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. Also, a gate signal is generated to change the number of transistors that are simultaneously opened in the inverter circuit 40 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.

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

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

If 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 steps from the target current value setting step ST2 to the rotation speed calculation step ST6 are performed again.

The above is the procedure for the control method of the brushless DC motor of embodiment 1. The switching of the energized phase, which is a feature of this control method, will be further explained below.

5A and 5B are schematic diagrams showing the energization phase switching in energization phase switching step ST5 in the control method for the brushless DC motor of embodiment 1. With reference to FIG. 5A and FIG. 5B, the state of the energization phase switched in energization phase switching step ST5 based on the gate signal generated in gate signal generation step ST4 will be described in more detail.

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.

First, when the electrical angle (rotation angle) of the rotor 11 is in the range of 0° to 60°, it is necessary to pass 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), current flows from the power supply to the U-phase and 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, the phase to which current is applied must be changed each time the electrical angle of the rotor 11 advances by 60°, but because control is based on a similar concept, the specific control for other electrical angles is not described here and should be referred to in Table 1 and Figure 5A or Figure 5B.

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, and the current value is made to follow the target current value Is.

(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 as to make 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. In addition, in the control method for the brushless DC motor of the first embodiment, current ripples are unlikely to occur because the current phases are 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 control device 30 for brushless DC motor 10 of embodiment 1, control processing 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 brushless DC motor 10 with square wave drive.

In addition, in the brushless DC motor control method of embodiment 1, a gate signal is generated to change the number of transistors that are simultaneously open in the inverter circuit 40 to switch the energized phase. Specifically, when the energized phase current values Iu, Iv, and Iw are greater than the target current value Is, a gate signal is generated to close the previously open transistor on the side where the current flows into the brushless DC motor 10. According to the brushless DC motor control method of embodiment 1, the gate signal generated in this manner is used to simply deenergize one energized phase, so that it is not affected by the timing deviation of simultaneous processing as occurs when deenergizing and then energizing another phase at the same time, and current ripple can be further suppressed.

[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.

6A and 6B are schematic diagrams showing the energization phase switching in energization phase switching step ST5 in the control method for a brushless DC motor of embodiment 2. With reference to FIG. 6A and FIG. 6B, the state of the energization phase switched in energization phase switching step ST5 based on the gate signal generated in gate signal generation step ST4 will be described in more detail.

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

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 flow the current from the V-phase to the U-phase, and the current value Iu decreases. Thereafter, the phase to which current is applied must be changed each time the electrical angle of the rotor 11 advances by 60°, but because control is based on a similar concept, specific control for other electrical angles should be referred to in Table 2 and Figure 6A or Figure 6B, and explanations will be omitted.

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 according to the result, thereby performing feedback control to increase or decrease the supply current, and the current value is made to follow the target current value Is.

According to the brushless DC motor control method of the second embodiment, similarly to the brushless DC motor control method of the first embodiment, the target current value setting step ST2, the current value measurement step ST3, the gate signal generation step ST4, and the current phase switching step ST5 are executed, so that, similarly to the brushless DC motor control method of the first embodiment, the current ripple can be suppressed, noise can be reduced, and the brushless DC motor can be speed-controlled by square wave drive.

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

(1) The number of components, the manner of connection, etc. described in the above embodiment are examples and can be changed without impairing the effects of the present invention.

(2) In the above embodiment, the brushless DC motor control device is described as a device that integrates an inverter circuit, a motor drive power supply, a current sensor, and a DSP unit, 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.

(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 with eight magnetic poles arranged on the rotor 11 (divided into eight at 45°).

(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 from a magnetic sensor.

An experiment was conducted in which the brushless DC motor 10 was subjected to current tracking control (hereinafter referred to as "current tracking control using the present invention") using the brushless DC motor control device 30 of embodiment 1. 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 in which the brushless DC motor 10 was subjected to 120-degree PWM control (hereinafter referred to as "conventional PWM control") using a conventional control device. The results of the experiment are described below.

Figure 7 is a graph showing the motor rotation speed in the experimental results. Figure 8 is a graph showing the motor current waveform in the experimental results. Figure 9 is a graph showing the motor electromagnetic torque waveform in the experimental results. Figure 10 is a diagram showing the spectral intensity of the motor electromagnetic torque waveform in the experimental results. The spectral intensity shown in Figure 10 is the result of determining the frequency components of the motor electromagnetic torque. Figure 11 is a diagram showing the cumulative amplitude spectrum of the motor electromagnetic torque in the experimental results. The cumulative amplitude spectrum shown in Figure 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.

As a result of the experiment, as shown in Figure 7, it was found that while 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. On the other hand, as shown in Figure 8, it was confirmed that the motor current waveform was closer to a square wave with the current tracking control using the present invention, with the current ripple suppressed more than with the conventional PWM control.

As for the motor electromagnetic torque, as shown in FIG. 9, it was confirmed that the current tracking control using the present invention had less overall swell and a smaller fluctuation range than the conventional PWM control, and vibrations were suppressed. Looking at the spectrum intensity of this motor electromagnetic torque, as shown in FIG. 10, the current tracking control using the present invention suppressed vibration components in all frequency bands, and no extreme increase in spectrum intensity was observed between 2 kHz and 3 kHz in the conventional PWM control. Furthermore, as shown in FIG. 11, the cumulative amplitude spectrum of the motor electromagnetic torque was approximately 39 N·m in the conventional PWM control, whereas it was approximately 24 N·m in the current tracking control using the present invention, confirming that the current tracking control using the present invention reduced vibration components by approximately 39% compared to the conventional PWM control.

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...Electrified 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...(Electrical ... (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 (9)

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. 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. 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. 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. 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. A control device for a brushless DC motor that drives the brushless DC motor at a target rotation speed by a rectangular wave through 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. 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. 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. 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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