JP2017017996A - DC brushless motor control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC brushless motor control device in which a generation period of a spike signal is not overlapped with a zero-cross point even when rotation number of a DC brushless motor accelerates.SOLUTION: A DC brushless motor control device comprises: an inverter for converting DC power into AC power based on driving of a plurality of switching elements, energizing winding of a stator of a DC brushless motor and rotating a rotor; electromotive voltage detection means for detecting electromotive voltage generated in the winding with rotation of the rotor of the DC brushless motor; and a control circuit for detecting a zero-cross point of the electromotive voltage from the electromotive voltage detected by the electromotive voltage detection means, detecting a rotational position of the rotor, and switching energization to the plurality of switching elements after prescribed delay time from detection of the zero-cross point. The control circuit prevents a generation period of the spike signal generated just after energization pause of the switching element from being overlapped with the zero-cross point by using a wide band gap semiconductor for the plurality of switching elements.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a DC brushless motor control device that controls a DC brushless motor.

  In a hand-drying device that dries hands with a high-pressure air flow ejected from an air nozzle, the drying time is generally determined by the static pressure of the high-pressure air flow blown from the air nozzle x the air volume, and the larger the product, the shorter the time The hand can be dried. The static pressure is proportional to the square of the wind speed. The high-pressure airflow of the hand dryer is generated by a blower motor, and a commutator motor or a DC brushless motor that has a longer life than the commutator motor is employed as the blower motor.

  When a DC brushless motor is used for the blower motor, the motor drive circuit must be compact and inexpensive, so that the DC brushless motor is not equipped with a rotor position detection means (sensor element) such as a hall element, and the motor rotates. A sensorless driving method is adopted in which the zero cross point generated in response to the change in the magnetic pole of the rotor (the boundary between the magnetic poles) is detected in the counter electromotive voltage generated by the above, and the rotational position of the rotor is detected (for example, Patent Document 1). reference).

  In addition, as a sensorless drive method using a back electromotive voltage, the back electromotive voltage cannot be detected correctly during the spike signal generation period immediately after the switching element that drives the DC brushless motor is de-energized. There is one that detects the position of the rotor while avoiding it (see, for example, Patent Document 2).

Japanese Patent No. 3208641 (page 5-6) JP-A-01-234086 (Claims)

  In a hand-drying apparatus of the type that blows off water adhering to the hand with a high-pressure air flow, the drying time is generally determined by the wind speed × the air volume of the high-pressure air flow. When obtaining a predetermined drying performance, the air passage that sends the high-pressure air flow from the motor to the air nozzle can be downsized by increasing the air speed and reducing the air volume, and when the heater that warms the high-pressure air flow is installed, There is an advantage that the capacity is small.

  Increasing the motor speed can increase the speed of the jet wind. However, in the sensorless drive system based on the detection of the rotor rotation position using the back electromotive force, the spike signal is generated when the DC brushless motor is rotated at a high speed. The zero cross point will be reached during the occurrence period, making it impossible to detect the rotational position of the rotor. Therefore, the number of revolutions of the motor can be increased only to the number of revolutions at which the spike signal generation period does not overlap with the zero cross point.

  That is, since the rotational speed of the DC brushless motor is limited, an air volume is required to obtain the drying performance, which hinders downsizing of the air passage and the capacity of the heater.

  The present invention has been made to solve the above-described problems, and provides a DC brushless motor control device in which the generation period of a spike signal does not overlap with the zero cross point even if the rotational speed of the DC brushless motor is increased. With the goal.

  A DC brushless motor control device according to the present invention converts an DC power into an AC power based on driving of a plurality of switching elements, and an inverter that rotates a rotor by energizing a winding of a stator of the DC brushless motor, and a DC brushless The counter electromotive voltage detecting means for detecting the counter electromotive voltage generated in the winding due to the rotation of the rotor of the motor, and the rotation of the rotor by detecting the zero cross point of the counter electromotive voltage from the counter electromotive voltage detected by the counter electromotive voltage detecting means. And a control circuit that switches energization to a plurality of switching elements after a predetermined delay time after detecting a position and detecting a zero cross point, and the control circuit uses a wide band gap semiconductor for the switching elements and performs switching. If the generation period of the spike signal that occurs immediately after the element is de-energized and the zero cross point overlap It was strange.

  According to the present invention, a wide band gap semiconductor is used for a plurality of switching elements energized in the stator winding of a DC brushless motor, and the generation period of a spike signal generated immediately after the energization of the switching element is interrupted and the zero cross point overlap. I tried not to be. Therefore, the switching speed is increased, the generation period of the spike signal immediately after the switching element is deenergized is shortened, and the period during which the back electromotive voltage cannot be detected correctly by the spike signal is also shortened. You can increase the number.

It is sectional drawing which cut | disconnects and shows the right side of the hand-drying apparatus which concerns on embodiment. It is sectional drawing which shows the structure of the high pressure air generator mounted in the hand dryer of FIG. FIG. 3 is a circuit diagram for driving a DC brushless motor of the high-pressure air generator of FIG. 2. FIG. 4 is a waveform diagram of a motor drive signal when the rotational speed of a DC brushless motor is set to 20000 per minute, for example, and a waveform diagram showing a back electromotive voltage signal and a spike signal induced in a stator winding in the prior art. It is a wave form diagram which shows a counter electromotive voltage signal and a spike signal when the rotation speed of a DC brushless motor is 30000 per minute, for example. It is a wave form diagram which shows a counter electromotive voltage signal and a spike signal when the rotation speed of the DC brushless motor in a prior art is 30000 / min, for example.

  Hereinafter, an embodiment of a hand dryer according to the present invention will be described in detail. In addition, this invention is not limited by this embodiment.

FIG. 1 is a cross-sectional view showing the right side of the hand dryer according to the embodiment.
In FIG. 1, the external appearance of the hand drying device is a box-shaped casing 1 having a hand insertion port 3 and a hand drying chamber 6 that is recessed downward from the hand insertion port 3 and open on both sides. The casing 1 is composed of a base 5 that forms the outline of the back surface, a front panel 7 that forms the outline of the front surface, and side panels that form the outline of both sides. The front and back wall surfaces of the hand-drying chamber 6 are impregnated with a water-repellent coating such as silicon or fluorine, or a hydrophilic coating such as titanium oxide, or an antibacterial agent to reduce the adhesion of dirt to the surface. And bacterial growth is reduced.

  The casing 1 is generated by the hand detection device 8 installed on the front and back walls of the hand drying chamber 6, the high pressure air generator 2 installed below the hand drying chamber 6, and the high pressure air generator 2. The air flow path 15 that divides the high-pressure air flow into the front side and the back side of the hand drying chamber 6, the drain container 13 that can be inserted and removed in the front-rear direction at the bottom, and the drainage that is provided at the bottom of the hand drying chamber 6 A drain pipe 12 connected to the port 11 for guiding water to the drain vessel 13 and a circuit board 10 installed in the vicinity of the high-pressure air generator 2 are provided. In addition, an air intake port 17 in which an air filter 14 is detachably mounted is provided at the bottom of the casing 1.

  The hand detection device 8 includes an infrared light emitting unit and an infrared light receiving unit, and inputs a hand detection signal to the control circuit of the circuit board 10 when the infrared light between the infrared light emitting unit and the infrared light receiving unit is interrupted. As will be described later, the high-pressure air generator 2 includes a DC brushless motor and a fan that sucks outside air from the suction port 16 by rotation of the DC brushless motor and sends a high-pressure air flow into the blower passage 15.

  The air passage 15 is divided into the front side and the back side of the hand drying chamber 6 as described above, and is connected to the air nozzles 4 provided on the front and back wall surfaces near the hand insertion port 3. ing. A high-speed air flow is jetted from these air nozzles 4 into the hand drying chamber 6, and water attached to the hand inserted into the hand insertion port 3 is blown off into the hand drying chamber 6. The blown water falls to the bottom of the hand drying chamber 6 and is stored in the drain container 13 from the drain port 11 through the drain pipe 12. A heater 9 that uses the high-pressure air flow from the high-pressure air generator 2 as warm air is installed in the air passage 15 described above.

  A removable lid is attached to the drain container 13. The drain container 13 and the lid are formed of a chemical-resistant PP or ABS resin, and can be cleaned and cleaned using a neutral detergent and alcohol. As will be described later, on the circuit board 10, for example, a control circuit composed of a microcomputer, a DC power supply circuit, an inverter for driving the high-pressure air generator 2, a back electromotive voltage detection means, and the like are mounted.

  When the hand detection signal from the hand detection device 8 is input, the control circuit described above energizes the high-pressure air generator 2 to generate a high-speed air flow, and when the input of the hand detection signal is interrupted, After the delay time, the power supply to the high-pressure air generator 2 is cut off and stopped. Further, the control circuit energizes the heater 9 installed in the air passage 15 during operation of the high-pressure air generator 2 so that a warm high-pressure air flow is injected from the air nozzle 4.

Next, the configuration of the high-pressure air generator 2 will be described with reference to FIG.
FIG. 2 is a cross-sectional view showing the configuration of the high-pressure air generator mounted on the hand dryer shown in FIG.
In FIG. 2, the high-pressure air generator 2 is constituted by the DC brushless motor 2a and the fan 2b that rotates with the rotating shaft 22c of the DC brushless motor to generate a high-pressure air flow, as described above.

  The DC brushless motor 2a is an inner rotor type sensorless DC brushless motor. The DC brushless motor 2a is disposed with a gap inside the stator 21 and the stator 21, and is rotatably supported by the bearing 23 via an integrated rotating shaft 22c. And the rotor 22 made. The stator 21 has an iron core tooth portion 21a protruding radially inward and a winding 21b wound around the iron core tooth portion 21a. The stator 21 is composed of three phases of a U phase, a V phase, and a W phase, which are constituted by windings 21b. The rotor 22 includes a cylindrical rotor core 22a and a plurality of permanent magnets 22b embedded in the circumferential direction on the outer periphery of the rotor core 22a. In the DC brushless motor 2a described above, a rotating magnetic field is generated in the winding 21b of the stator 21 based on a current from an inverter described later, and the rotor 22 rotates at the same cycle as the rotating magnetic field.

Next, a circuit configuration for driving the DC brushless motor 2a will be described with reference to FIG.
FIG. 3 is a circuit diagram for driving a DC brushless motor of the high-pressure air generator of FIG.
In FIG. 3, a DC power supply circuit 31 that rectifies and smoothes AC current and converts it into DC current, DC power from the DC power supply circuit 31 is converted into AC power, and current is supplied to the windings 21 b of the respective phases of the stator 21. The inverter 32 to be supplied, the counter electromotive voltage detecting means 33 for detecting the counter electromotive voltage generated in the winding 21b by the rotation of the rotor 22, and the rotational position of the rotor 22 from the counter electromotive voltage detected by the counter electromotive voltage detecting means 33. And a control circuit 34 that outputs a motor drive signal to the inverter 32 based on the rotational position thereof, and these are mounted on the circuit board 10 described above.

  The inverter 32 includes six switching elements 51 to 56 (UH, VH, WH, UL, VL, WL). In the present embodiment, wide band gap semiconductors are used for the switching elements 51 to 56. This band gap semiconductor has a large energy bandwidth compared to a conventional silicon (silicon: Si) based semiconductor, and for example, silicon carbide (SiC), gallium nitride (GaN) based material, or diamond is used. ing. Since the switching elements 51 to 56 made of a band gap semiconductor have a switching speed twice to several times faster than that of a Si-based semiconductor switching element, the generation period of a spike signal described later is shortened (for example, 1/2).

  The control circuit 34 monitors the counter electromotive voltage generated in the winding 21b of the stator 21 by the counter electromotive voltage detection means 33, and generates it corresponding to the change of the magnetic pole of the rotor 22 (boundary between the N pole and the S pole). The rotational position of the rotor 22 is detected by detecting the zero cross point, and the energization to the switching elements 51 to 56 is switched after a predetermined delay time (sensorless drive method). When the energization to the switching elements 51 to 56 is switched, a spike signal is generated due to the return of the motor current.

  Here, the generation period of the spike signal will be described with reference to FIGS. The generation period of the spike signal varies depending on the specification of the winding 21b of the DC brushless motor 2a and the motor current. It is assumed that a DC brushless motor 2a having 4 poles is used.

  4 is a waveform diagram of a motor drive signal when the rotational speed of the DC brushless motor is, for example, 20000 per minute, and a waveform diagram showing a back electromotive voltage signal and a spike signal induced in the stator winding in the prior art, FIG. FIG. 6 is a waveform diagram showing a counter electromotive voltage signal and a spike signal when the rotational speed of the DC brushless motor is 30000 per minute, for example. FIG. 6 is a reverse diagram when the rotational speed of the DC brushless motor in the prior art is 30000 per minute, for example. It is a wave form diagram which shows an electromotive voltage signal and a spike signal.

  When the DC brushless motor 2a is rotated at 20000 rpm, the cycle of the motor drive signal and the counter electromotive voltage signal is 1.5 msec (= 1 s / ((20000 rpm / 60 s) × 4 poles / 2)). In this example, the time from when the zero cross point 18 of the back electromotive voltage signal is detected to when the motor drive signal is switched is set to 15 ° of the cycle, which is 62.5 μsec at the cycle of 1.5 msec. This value is set individually in considering the drive sequence. The time of the spike signal 19 varies depending on the amount of current flowing in the motor and the speed of the switching element. If the spike signal 19 is generated for 125 μsec in a conventional switching element using a Si-based semiconductor, the generation period of the spike signal 19 is The period from the completion of the process to the zero cross point 18 is 62.5 μsec, and the back electromotive voltage signal can be detected.

  From this state, when the rotational speed of the DC brushless motor 2a is increased to 30000 revolutions per minute, the cycle of the back electromotive voltage signal is about 1.0 msec (= 1 s / ((30000 rpm / 60 s) × 4 poles / 2)). The time from the detection of the zero cross point 18 of the voltage signal to the switching of the motor drive signal is 41.7 μsec (= 1.0 msec × 15 ° / 360 °). Since the interval between the zero cross points is 166.7 μsec (= 1.0 msec / 6), if the spike signal 19 is generated for 125 μsec, which is the same as that in FIG. 4, then 41.7 μsec + 125 μsec = 166.7 μsec, and as shown in FIG. The 19 period and the zero cross point 18 overlap. Therefore, the zero cross point 18 does not appear as a signal, and the back electromotive voltage signal cannot be normally detected.

  Here, the switching elements 51 to 56 using the wide band gap semiconductor are driven, and the DC brushless motor 2a is rotated at 30000 revolutions per minute as in FIG. In this example, it is assumed that the generation period of the spike signal 19 is 62.5 μsec (= 125 μsec / 2) which is ½ of those in FIGS. 4 and 6. Then, the period from the completion of the generation period of the spike signal 19 to the zero cross point 18 is 62.5 μsec (= 166.7 μsec-41.7 μsec-62.5 μsec), which is a switching element using a conventional Si-based semiconductor. The detection of the rotational position of the rotor 22 has the same stability when rotated 20000 times.

  As described above, also in the sensorless driving method, the DC brushless motor 2a can be rotated at a high speed by shortening the generation period of the spike signal 19.

  In a hand dryer that blows off water adhering to the hand with a high-pressure air flow, the drying performance is generally determined by the static pressure x air volume of the high-pressure air flow blown from the air nozzle 4, and the larger the product, the shorter the time. Hands can be dried.

  The static pressure is proportional to the square of the wind speed, and the wind speed is proportional to the square of the rotational speed ratio of the DC brushless motor 2a. Therefore, if the rotation speed is increased 1.5 times, the wind speed is 2.25 times and the static pressure is 5.06 times. Therefore, when the drying performance of the hand dryer is maintained, the air volume can be reduced to 1/5 if the static pressure is 5.06 times. In addition, since the area of the air passage 15 is Q = AP (A: duct area, Q: air volume, P: air speed), if the air volume is 1/5 and the air speed is 2.25 times, The area can be reduced to 1 / 11.25. As shown in FIG. 1, the air passage 15 greatly contributes to the product size. Therefore, by reducing the air passage 15, it is possible to reduce the size of the hand dryer and relax the product structure constraints.

  In the present embodiment, a wide band gap semiconductor is used for switching elements 51 to 56 for switching energization to winding 21b of stator 21 of DC brushless motor 2a, and a spike signal generated immediately after energization of the switching element is stopped. The generation period of 19 is shortened. For this reason, the DC brushless motor 2a can be rotated at a high speed even in the sensorless drive system, and the volume of the air passage 15 can be reduced by reducing the air volume to 1/5 while maintaining the hand drying performance. The size of the device can be reduced.

  Further, the capacity of the heater 9 for warming the high-pressure air flow is ΔT = W / KQ (ΔT: temperature rise, W: heater heat generation, Q: air volume, K: coefficient). If it can be reduced, the capacity of the heater 9 can be reduced to 1/5. For example, when a 500 W heater 9 is conventionally used, if the air volume can be reduced to 1/5, the same warm air can be obtained with the 100 W heater 9, and significant energy saving can be realized.

  In addition, since the switching elements 51 to 56 using the wide band gap semiconductor have high heat resistance, it is possible to reduce the size of the radiation fins (not shown) necessary for cooling the switching elements 51 to 56. The drying apparatus can be downsized.

  Furthermore, since the power loss is low, the switching elements 51 to 56 can be highly efficient, and further, the efficiency of the hand dryer can be increased.

  Further, since the switching elements 51 to 56 are rotated at a high speed, the transition period from the start of the DC brushless motor 2a to the steady rotation can be shortened, so the air nozzle is inserted after the hand is inserted into the hand drying chamber 6. Since the time until the high-pressure air flow blown from 4 becomes steady can be shortened, the hand can be dried in a shorter time and the usability is good.

  1 Hand dryer casing, 2 High pressure air generator, 2a DC brushless motor, 2b Fan, 3 Hand insertion port, 4 Air nozzle, 5 Base, 6 Hand drying chamber, 7 Front panel, 8 Hand detector, 9 Heater, DESCRIPTION OF SYMBOLS 10 Circuit board, 11 Drain port, 12 Water distribution pipe, 13 Drain container, 14 Air filter, 15 Air passage, 16 Suction port, 17 Air intake port, 18 Zero cross point, 19 Spike signal, 21 Stator, 21a Iron core part, 21b Winding, 22 rotor, 22a rotor core, 22b permanent magnet, 22c rotating shaft, 23 bearing, 31 DC power supply circuit, 32 inverter, 33 counter electromotive voltage detection means, 34 control circuit, 51-56 switching element.

Claims (3)

An inverter that converts DC power into AC power based on driving of a plurality of switching elements, energizes the windings of the stator of the DC brushless motor, and rotates the rotor;
Back electromotive voltage detection means for detecting a back electromotive voltage generated in the winding by rotation of the rotor of the DC brushless motor;
From the back electromotive voltage detected by the back electromotive voltage detecting means, a zero cross point of the back electromotive voltage is detected to detect the rotational position of the rotor, and after the predetermined time delay, A control circuit for switching energization to the switching element,
The control circuit uses a wide band gap semiconductor for the plurality of switching elements so that a generation period of a spike signal generated immediately after the energization of the switching elements is stopped does not overlap with the zero cross point. Brushless motor control device.   2. The control circuit according to claim 1, wherein the total of the predetermined delay time and the generation period of the spike signal generated immediately after the energization of the switching element is stopped is shorter than the interval of the zero cross points. DC brushless motor control device.   3. The DC brushless motor control device according to claim 1, wherein the wide band gap semiconductor is silicon carbide, a gallium nitride material, or diamond.

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