JP2004260919A - Apparatus and method for controlling motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a method for controlling a motor which stabilizes the estimation of a rotor position even when a control for lowering the applied voltage to the motor is performed. <P>SOLUTION: The apparatus for controlling the motor estimates the position of the rotor 31 based on the induced voltage of non-energizing phase of a brushless DC motor 29 to be driven by an inverter 32, outputs a PWM switching signal pulse-width-modulated based on this estimated result to the inverter 32, and controls the applied voltage to the brushless DC motor 29. When the switching signal having the duty ratio corresponding to the applied voltage is generated, the apparatus includes a controller 34 for regulating the carrier frequency of the PWM switching signal so that the pulse width of the switching signal becomes a predetermined pulse width or more. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a motor control device and a motor control method, and more particularly to a motor control device and a motor control method for estimating a rotor position.
[0002]
[Prior art]
Conventionally, a rotor position is estimated based on an induced voltage of a non-energized phase of a motor driven by an inverter, and a pulse width modulated switching signal is output to the inverter based on a result of the estimation to reduce a voltage applied to the motor. 2. Description of the Related Art A motor control device for controlling is known (for example, see Patent Document 1).
[0003]
As the above motor, a brushless DC motor is known, and a control method (sensorless control method) of detecting an induced voltage and estimating the position of the rotor without providing a sensor for detecting the position of the rotor is generally adopted. ing. In the motor control device, for example, a 120-degree energized rectangular wave drive system that controls the inverter so as to apply a three-phase AC voltage to the motor at 120 degrees is employed, and appears in a non-energized phase on the output side of the inverter. The position of the rotor is estimated by detecting the induced voltage.
[0004]
As means for estimating the position of the rotor based on the induced voltage, the detected induced voltage is compared with a reference voltage by a rotor position detection circuit including a comparator. The position is estimated.
[0005]
The induced voltage appears as a pulse-like voltage corresponding to the switching signal, and the rotor position detection circuit compares the pulse-like voltage with a reference voltage based on the voltage value of the pulse-like voltage during the ON period.
[0006]
In this type of motor control device, the carrier frequency of the switching signal is fixed in order to reduce the voltage applied to the motor when the DC voltage applied to the inverter increases due to poor power supply conditions or when the rotation speed of the motor is reduced. Control that shortens the pulse width of the switching signal, that is, control that lowers the duty ratio of the switching signal, is performed.
[0007]
[Patent Document 1]
JP-A-2002-186274
[0008]
[Problems to be solved by the invention]
However, in the above-described motor control device, when the pulse width of the switching signal is reduced to reduce the duty ratio in order to reduce the voltage applied to the motor, the pulse width of the pulse-like induced voltage corresponding to the switching signal is also reduced. If the pulse width of the induced voltage is too short, there is a problem that it is impossible to respond to an input due to the characteristics of the rotor position detection circuit and estimation of the rotor position becomes impossible.
[0009]
An object of the present invention has been made in consideration of the above circumstances, and a motor control device and a motor control that stabilize the estimation of the rotor position even when performing control to reduce the voltage applied to the motor. It is to provide a method.
[0010]
[Means for Solving the Problems]
In order to solve the above problem, the position of the rotor is estimated based on the induced voltage of the non-energized phase of the motor driven by the inverter, and a pulse width modulated switching signal is output to the inverter based on the estimation result, In the motor control device for controlling an applied voltage to the motor, when generating the switching signal having a duty ratio corresponding to the applied voltage, the switching may be performed such that a pulse width of the switching signal becomes a predetermined pulse width or more. A frequency adjusting means for adjusting a carrier frequency of a signal is provided.
[0011]
Further, the position of the rotor is estimated based on the induced voltage of the non-energized phase of the motor driven by the inverter, and a switching signal pulse-width modulated based on the estimation result is output to the inverter, and the switching signal is applied to the motor. In a motor control device that controls voltage, a setting unit that sets a threshold value for a duty ratio of the switching signal, and when generating the switching signal having a duty ratio corresponding to the applied voltage, the duty ratio of the switching signal is Frequency adjusting means for adjusting the carrier frequency such that the pulse width of the switching signal becomes equal to or larger than a predetermined pulse width when the switching signal falls below the threshold value.
[0012]
In this case, the setting means sets the threshold value to a range of a duty ratio in which a pulse width when adjusting a pulse width of the switching signal while keeping a carrier frequency of the switching signal constant is equal to or larger than a predetermined pulse width. You may make it set within.
[0013]
Further, the frequency adjusting means may continuously decrease the carrier frequency according to the decrease in the duty ratio.
[0014]
Further, the frequency adjusting means may decrease the carrier frequency stepwise according to the decrease in the duty ratio.
[0015]
Furthermore, the frequency adjusting means changes the carrier frequency from the first frequency to a second frequency lower than the first frequency, and changes the carrier frequency from the second frequency to the first frequency. Hysteresis may be provided so that the duty ratio differs from time to time.
[0016]
Further, the position of the rotor is estimated based on the induced voltage of the non-energized phase of the motor driven by the inverter, and a switching signal pulse-width modulated based on the estimation result is output to the inverter, and the switching signal is applied to the motor. In the method of controlling a motor for controlling a voltage, when generating the switching signal having a duty ratio corresponding to the applied voltage, a carrier frequency of the switching signal is set such that a pulse width of the switching signal is equal to or larger than a predetermined pulse width. Is adjusted.
[0017]
Further, the position of the rotor is estimated based on the induced voltage of the non-energized phase of the motor driven by the inverter, and a switching signal pulse-width modulated based on the estimation result is output to the inverter, and the switching signal is applied to the motor. In a motor control method for controlling a voltage, a threshold value is set for a duty ratio of the switching signal, and when the switching signal having a duty ratio corresponding to the applied voltage is generated, the duty ratio of the switching signal is set to When the frequency is lower than the threshold value, the carrier frequency is adjusted so that the pulse width of the switching signal becomes equal to or larger than a predetermined pulse width.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[1] First Embodiment
FIG. 1 is an electric circuit diagram showing a first embodiment of the motor control device according to the present invention. FIG. 2 is a refrigerant circuit diagram showing an air conditioner including a compressor having the motor of FIG. 1 built therein.
[0019]
As shown in FIG. 2, the air conditioner 10 includes an outdoor unit 11 and an indoor unit 12, and an outdoor refrigerant pipe 14 of the outdoor unit 11 and an indoor refrigerant pipe 15 of the indoor unit 12 are connected to a connection pipe 24, 25.
[0020]
The outdoor unit 11 is arranged outdoors. A compressor 16 is disposed in the outdoor refrigerant pipe 14, an accumulator 17 is disposed on a suction side of the compressor 16, and a four-way valve 18 is disposed on a discharge side of the compressor 16. An outdoor heat exchanger 19 is provided on the 18 side. An outdoor fan 20 that blows air from the outdoor heat exchanger 19 to the outside is disposed adjacent to the outdoor heat exchanger 19. The outdoor fan 20 is driven by an indoor fan motor 20A. The outdoor fan 20 is, for example, a propeller fan. The compressor 16 is an inverter-driven compressor. The compressor 16 incorporates a brushless DC motor 29 as a motor driven by an inverter.
[0021]
The indoor unit 12 is installed indoors, and an indoor heat exchanger 21 and an electronic expansion valve 22 are sequentially arranged in the indoor refrigerant pipe 15. An indoor fan 23 that blows air from the indoor heat exchanger 21 into the room is disposed adjacent to the indoor heat exchanger 21. The indoor fan 23 is driven by an indoor fan motor 23A. The indoor fan 23 is, for example, a cross flow fan.
[0022]
By switching the four-way valve 18 of the outdoor unit 11, the air conditioner 10 is set to the cooling operation or the heating operation. In other words, when the four-way valve 18 is switched to the cooling side, the refrigerant flows as shown by the solid line arrow, the outdoor heat exchanger 19 becomes a condenser, the indoor heat exchanger 21 becomes an evaporator, and enters a cooling operation state. Twelve indoor heat exchangers 21 cool the room. When the four-way valve 18 is switched to the heating side, the refrigerant flows as indicated by the dashed arrow, the indoor heat exchanger 21 functions as a condenser, the outdoor heat exchanger 19 functions as an evaporator, and the heating operation state is established. Twelve indoor heat exchangers 21 heat the room.
[0023]
As shown in FIG. 1, the brushless DC motor 29 built in the compressor 16 includes a stator (stator) 30 having stator windings 30u, 30v and 30w, and a rotor (rotor) having permanent magnets. 31 is a three-phase motor. The brushless DC motor 29 is driven by a motor control device 100 including an inverter 32, a rotor position detection circuit 33, and a control unit 34 including a microcomputer. Normally, the rotation speed of the brushless DC motor 29 of the compressor 16 is controlled according to the air conditioning load.
[0024]
The inverter 32 is, for example, a three-phase bridge-connected transistor 38u, 38v, 38w, 38x, 38y, and 38z as six switching elements. A flywheel diode 42 is connected between each emitter terminal 39 and each collector terminal 40 of these transistors 38u, 38v, 38w, 38x, 38y and 38z.
[0025]
The inverter 32 converts the pulse width modulated switching signal (hereinafter, referred to as “PWM switching signal”) output from a PWM (Pulse Width Modulation) terminal 35 of the control unit 34 into transistors 38u, 38v, 38w, 38x. , 38y and 38z are operated by being inputted to the respective base terminals 41.
[0026]
By the operation of the inverter 32, the DC power obtained by converting the AC power of the AC power supply (not shown) is converted into three-phase AC power that has been subjected to pulse width modulation and has a predetermined frequency and voltage. The voltages Vu, Vv, Vw are applied to the stator windings 30u, 30v, 30w of the brushless DC motor 29. Here, Vu indicates a U-phase voltage, Vv indicates a V-phase voltage, and Vw indicates a W-phase voltage.
[0027]
In the present embodiment, the motor control device 100 drives the brushless DC motor 29 by a 120-degree energized rectangular wave driving method that controls the inverter 32 so that the three-phase AC voltage is energized to the brushless DC motor 29 by 120 degrees. I have.
[0028]
Here, the transistors 38u, 38v, and 38w are referred to as an upper-arm transistor group of the inverter 32, and the transistors 38x, 38y, and 38z are referred to as a lower-arm transistor group of the inverter 32. The transistors 38u and 38x, the transistors 38v and 38y, and the transistors 38w and 38z form a pair, respectively, and their connection points are connected to the stator windings 30u and 30v of the starless brushless DC motor 29, respectively. 30w respectively.
[0029]
The rotor position detection circuit 33 detects the induced voltage of the non-energized phase of the input terminal voltage of the brushless DC motor 29 and outputs a signal indicating the position of the rotor 31 to the control unit 34.
[0030]
The rotor position detection circuit 33 includes a comparator 51 and a photo coupler 52. The input terminal 51a of the comparator 51 is connected to the U-phase, V-phase, and W-phase input terminals of the brushless DC motor 29 (the U-phase, V-phase, and W-phase output terminals of the inverter 32) via the respective resistors 53, 54, and 55. Connected. In addition, a reference voltage power supply 56 that generates a DC reference voltage Vref is connected to the input terminal 51b. An output terminal 51c of the comparator 51 is connected to an input terminal 52a of the photocoupler 52 via a resistor 57, and an output terminal 52b of the photocoupler 52 is connected to the input terminal 36 of the control unit 34.
[0031]
The comparator 51 compares the input signal indicating the induced voltage detected via the resistors 53, 54, and 55 with the reference voltage Vref. If the input signal is higher than the reference voltage Vref, the comparator 51 goes to the H level (for example, 5 V ]), And outputs an L level (eg, 0.6 [V]) signal when the signal is low.
[0032]
The photocoupler 52 is provided to protect the control unit 34, which is a microcomputer, and outputs an H level or L level signal output from the comparator 51 to the control unit 34.
[0033]
The control unit 34 compares the current rotational speed of the brushless DC motor 29 with the target rotational speed, obtains an applied voltage to be applied to the brushless DC motor 29 and a frequency of the applied voltage based on the result of the comparison. The duty ratio of the switching signal is determined.
[0034]
Further, the control unit 34 estimates the position of the rotor based on the output signal from the rotor position detection circuit 33, and obtains the phase of the applied voltage of each phase to be applied to the brushless DC motor 29 based on the estimation result. I have.
[0035]
Then, the control unit 34 generates a PWM switching signal based on the obtained frequency of the applied voltage, the duty ratio of the PWM switching signal, and the phase of the applied voltage, and outputs the PWM switching signal to the inverter 32 through the PWM terminal 35.
[0036]
FIG. 3 is a schematic waveform diagram showing the phase voltage at the input terminal of brushless DC motor 29. 3A illustrates a U-phase voltage waveform, FIG. 3B illustrates a V-phase voltage waveform, FIG. 3C illustrates a W-phase voltage waveform, and FIG. 3D illustrates a three-phase induced voltage waveform.
[0037]
For example, with reference to FIG. 3A, in one cycle of the U-phase voltage Vu, a PWM switching signal is input to the inverter 32 to apply a voltage to the brushless DC motor 29. There are provided non-conducting periods Tb and Td with an electrical angle of 60 degrees in which Ta and Tc and a PWM switching signal are not input to the inverter 32 and are in a non-conducting phase. In these non-energized periods Tb and Td, an induced voltage corresponding to the position of the rotor 31 is generated. The V-phase voltage Vv has a phase shift of 120 degrees from the U-phase voltage Vu as shown in FIG. 3B, and the W-phase voltage Vw has a V-phase voltage as shown in FIG. The phase is shifted by 120 degrees from Vv. Then, the total induced voltage of the three phases, that is, the voltage waveform generated at the input terminal 51a of the comparator 51 of the rotor position detection circuit 33 becomes a pulse-shaped triangular wave as shown in FIG.
[0038]
The carrier frequency and pulse width of the PWM switching signal output from the control unit 34 to the inverter 32 are substantially the same as the frequency and pulse width of the pulse-like voltage appearing as the induced voltage. Therefore, if the carrier frequency of the PWM switching signal changes, the frequency of the pulse-like voltage appearing as the induced voltage also changes, and if the pulse width of the PWM switching signal changes, the pulse width of the induced voltage also changes. . For example, if the pulse width of the PWM switching signal is reduced, the pulse width of the induced voltage is also reduced.
[0039]
When the input pulse width becomes shorter than a predetermined pulse width (for example, 5 [μs]), the rotor position detection circuit 33 having the comparator 51 and the photocoupler 52 receives the input to the input terminal 51a due to the response characteristic of the circuit. It cannot follow the signal. That is, the rotor position detection circuit 33 can respond to the input when the pulse width of the input signal to the input terminal 51a, that is, the PWM switching signal is shorter than a predetermined pulse width (for example, 5 [μs]). Instead, the output signal may be unstable. Therefore, in order for the control unit 34 to accurately estimate the position of the rotor 31, the input signal (pulse) to the rotor position detection circuit 33 must be equal to or more than a predetermined pulse width (for example, 5 [μs]).
[0040]
In the present embodiment, when generating the PWM switching signal having the duty ratio corresponding to the voltage applied to the brushless DC motor 29, the control unit 34 sets the pulse width of the PWM switching signal to a predetermined pulse width (for example, 5 [μs ]) The carrier frequency of the PWM switching signal is adjusted so as to be as described above.
[0041]
Specifically, referring to an explanatory diagram showing a carrier frequency corresponding to the duty ratio and an applied voltage of the brushless DC motor 29 shown in FIG. 4, first, the control unit 34 sets the duty ratio of the PWM switching signal to a threshold value A. Is set.
[0042]
Here, the threshold value A is set to a predetermined pulse width (for example, 5 [kHz]) when adjusting the pulse width of the PWM switching signal while keeping the carrier frequency B of the PWM switching signal constant (for example, 5 [kHz]). [Μs]) is set within the range of the duty ratio which is equal to or larger than [μs]).
[0043]
For example, when the carrier frequency B of the PWM switching signal is 5 [kHz] and the duty ratio of the PWM switching signal is 5 [%], the pulse width is 10 [μs]. %].
[0044]
When generating a PWM switching signal having a duty ratio corresponding to the applied voltage (line voltage or phase voltage) C of the brushless DC motor 29, the control unit 34 sets the duty ratio of the PWM switching signal to a threshold value A. If it is less than the predetermined value, the carrier frequency B is adjusted so that the pulse width of the PWM switching signal becomes equal to or larger than the predetermined pulse width in order to prevent the pulse width from being shorter than the predetermined pulse width (for example, 5 [μs]). I have.
[0045]
More specifically, when generating a PWM switching signal having a duty ratio corresponding to the applied voltage (line voltage or phase voltage) C of the brushless DC motor 29, the control unit 34 determines the duty ratio of the generated PWM switching signal. Is less than the threshold value A (for example, 5 [%]), that is, the duty ratio of the generated PWM switching signal is within the duty ratio range X smaller than the threshold value A (for example, 5 [%]). In this case, in order to prevent the pulse width of the PWM switching signal from becoming shorter than a predetermined pulse width (for example, 5 [μs]), the pulse width is continuously increased according to the decrease of the duty ratio so as to be equal to or more than the predetermined pulse width. The carrier frequency B is lowered.
[0046]
For example, when the duty ratio of the generated PWM switching signal is lower than the threshold value A, the control unit 34 sets the pulse width of the PWM switching signal to a pulse width (for example, 5 [μs]) or more. 10 [μs]), and the carrier frequency B is continuously reduced according to the decrease in the duty ratio. At this time, it is preferable to set the pulse width to be constant to be the same as the pulse width at the duty ratio of the threshold value A (for example, 5 [%]).
[0047]
Here, even if the duty ratio is the same, when the carrier frequency B decreases, the pulse width of the PWM switching signal increases. For example, when generating a PWM switching signal with a duty ratio of 5 [%], when the carrier frequency B 'is 5 [kHz], the pulse width is 10 [μs], but the carrier frequency B' is 2.5 [kHz]. ], The pulse width is 20 [μs]. That is, the pulse width of the PWM switching signal becomes longer as the carrier frequency B ′ decreases.
[0048]
Therefore, according to the first embodiment, when the DC voltage applied to the inverter 32 increases or when the rotation speed of the brushless DC motor 29 is reduced, the control unit 34 When the duty ratio of the PWM switching signal is controlled to a value lower than the threshold value A in order to lower the applied voltage, the pulse width of the input signal indicating the induced voltage input to the rotor position detection circuit 33 has a predetermined pulse width. Since it does not fall below, the rotor position can be stably estimated even if the control to reduce the voltage applied to the brushless DC motor 29 is performed.
[0049]
When generating a PWM switching signal having a duty ratio corresponding to the applied voltage C of the brushless DC motor 29, the control unit 34 sets the duty ratio of the PWM switching signal to a threshold value A (for example, 5 [%]). If it exceeds, that is, if the duty ratio of the PWM switching signal to be generated is within the duty ratio range Y larger than the threshold value A (for example, 5%), the pulse width of the switching signal becomes a predetermined pulse width (for example, , 5 [μs]), the carrier frequency B is fixed (for example, 5 [kHz]).
[0050]
Here, when driving the brushless DC motor 29, the control unit 34 controls so that the rotation speed does not become zero. That is, the control unit 34 provides the lowest applied voltage to be applied to the brushless DC motor 29 in order to avoid the applied voltage from becoming close to 0 [V]. Control is performed so as not to fall below the minimum applied voltage. Therefore, since the applied voltage does not become 0 [V] or near 0 [V], the carrier frequency is prevented from being extremely lowered. Therefore, the rotor position can be stably estimated.
[2] Second embodiment
In the first embodiment, the case where the control unit 34 continuously lowers the carrier frequency B in accordance with the decrease in the duty ratio has been described. However, in the second embodiment, the control unit 34 , The carrier frequency is reduced stepwise according to the reduction of the duty ratio. Note that the configuration of the system is the same as that of FIGS. 1 and 2 of the first embodiment, and a description thereof will be omitted.
[0051]
FIG. 5 is an explanatory diagram illustrating a carrier frequency corresponding to a duty ratio.
[0052]
First, the control unit 34 sets a threshold value A (for example, 5 [%]) for the duty ratio of the PWM switching signal, as in FIG. 4 of the first embodiment.
[0053]
When generating a PWM switching signal having a duty ratio corresponding to the applied voltage (line voltage or phase voltage) C of the brushless DC motor 29, the control unit 34 sets the duty ratio of the PWM switching signal to the threshold A. If the pulse width is lower than the threshold value, that is, if the duty ratio of the generated PWM switching signal is within the duty ratio range X smaller than the threshold value A (for example, 5 [%]), the pulse width of the PWM switching signal is set to a predetermined pulse width. (For example, 5 [μs]), the carrier frequency B ′ is reduced stepwise according to the reduction of the duty ratio so as to be equal to or more than a predetermined pulse width.
[0054]
Specifically, the control unit 34 changes the carrier frequency B ′ from the first frequency B1 (for example, 5 [kHz]) to a second frequency B2 (for example, 2.5 [kHz]) lower than the first frequency B1. [KHz]) in a stepwise manner as the duty ratio decreases. For example, when the duty ratio of the PWM switching signal is lower than the threshold A, the carrier frequency B 'is changed from the first frequency B1 (for example, 5 [kHz]) to the first frequency B1 with the threshold A as a boundary. The second frequency B2 is lower than the second frequency B2 (for example, 2.5 [kHz]).
[0055]
Therefore, when the DC voltage applied to the inverter 32 increases or when the rotation speed of the brushless DC motor 29 is reduced, the duty ratio of the PWM switching signal is set to a threshold value so as to reduce the voltage applied to the brushless DC motor 29. When controlling to a value lower than A, the pulse width of the PWM switching signal is increased by decreasing the carrier frequency B ′ stepwise, so that the pulse of the input signal indicating the induced voltage input to the rotor position detection circuit 33 is controlled. Since the width does not fall below the predetermined pulse width, the rotor position can be stably estimated even when the control for reducing the voltage applied to the brushless DC motor 29 is performed.
[0056]
Here, the control unit 34 determines when the carrier frequency B ′ changes from the first frequency B1 to a second frequency B2 lower than the first frequency B1, and when the carrier frequency B ′ changes from the second frequency B2 to the first frequency B1. Is controlled so as to have a hysteresis (differential) Δ so that the duty ratio is different from when the duty ratio changes.
[0057]
Specifically, the control unit 34 determines that the duty ratio A when changing from the first frequency B1 to the second frequency B2 is greater than the duty ratio A ′ when changing from the second frequency B2 to the first frequency B1. Is controlled so as to have a hysteresis Δ so as to be lower.
[0058]
This prevents hunting from occurring at the boundary where the carrier frequency B 'is switched stepwise. This makes it possible to more stably estimate the rotor position.
[0059]
At this time, the hysteresis Δ between the duty ratio A and the duty ratio A ′ is such that the applied voltage at the duty ratio A ′ is smaller than the applied voltage (line voltage or phase voltage) at the duty ratio A. It is set to be a predetermined multiple (for example, 1.5 times) that does not occur.
[0060]
In order to avoid the applied voltage from becoming close to 0 [V], the lowest applied voltage to be applied to the brushless DC motor 29 is provided. When the brushless DC motor 29 is driven, the lowest applied voltage is set. , The pulse width does not become extremely short, and the rotor position can be stably estimated.
[0061]
In the above description, the threshold A is used as control for stepwise decreasing the carrier frequency B ′ from the first frequency B1 to the second frequency B2 lower than the first frequency B1 according to the decrease in the duty ratio. Has been described in which the carrier frequency B ′ is reduced by one step from the first frequency B1 to the second frequency B2 at the boundary. However, as shown in FIG. May be reduced by a plurality of stages (for example, two stages). In this case, in FIG. 6, when the duty ratio is lower than A ″, the carrier frequency B ′ is reduced from the frequency B2 to the frequency B3. At this time, B2 is the first frequency and B3 is the second frequency. It is. Furthermore, the duty ratio A ″ when changing from the first frequency B2 to the second frequency B3 is lower than the duty ratio A ′ ″ when changing from the second frequency B3 to the first frequency B2. May be controlled so as to have hysteresis.
[0062]
In the above description, the case where the motor control device drives the motor of the compressor has been described. However, any motor may be used as long as the motor position is estimated based on the induced voltage by the sensorless control method. It is possible to do. For example, the present invention can be applied to a case where an outdoor fan motor or an indoor fan motor is driven.
[0063]
【The invention's effect】
According to the present invention, the position of the rotor can be stably estimated even when control is performed to reduce the voltage applied to the motor.
[Brief description of the drawings]
FIG. 1 is an electric circuit diagram showing a first embodiment of a motor control device according to the present invention.
FIG. 2 is a refrigerant circuit diagram showing an air conditioner including a compressor in which the motor of FIG. 1 is built.
3A and 3B are schematic waveform diagrams showing phase voltages at input terminals of a motor, wherein FIG. 3A is a U-phase voltage waveform, FIG. 3B is a V-phase voltage waveform, FIG. 3C is a W-phase voltage waveform, and FIG. It is a three-phase induced voltage waveform.
FIG. 4 is an explanatory diagram illustrating a carrier frequency corresponding to a duty ratio and a voltage applied to a motor according to the first embodiment.
FIG. 5 is an explanatory diagram illustrating a carrier frequency corresponding to a duty ratio according to the second embodiment.
FIG. 6 is an explanatory diagram showing a carrier frequency corresponding to a duty ratio as a modification.
[Explanation of symbols]
10 Air conditioner
29 Brushless DC motor (motor)
31 rotor
32 inverter
34 control unit (frequency adjustment means, setting means)
100 Motor control device

Claims (8)

Estimating the position of the rotor based on the induced voltage of the non-energized phase of the motor driven by the inverter, outputting a pulse width modulated switching signal based on the estimation result to the inverter, and applying the applied voltage to the motor. In the motor control device to control,
When generating the switching signal having a duty ratio corresponding to the applied voltage, a frequency adjustment unit that adjusts a carrier frequency of the switching signal so that a pulse width of the switching signal is equal to or greater than a predetermined pulse width. A motor control device characterized by the above-mentioned. Estimating the position of the rotor based on the induced voltage of the non-energized phase of the motor driven by the inverter, outputting a pulse width modulated switching signal based on the estimation result to the inverter, and applying the applied voltage to the motor. In the motor control device to control,
Setting means for setting a threshold value for the duty ratio of the switching signal;
When generating the switching signal having a duty ratio corresponding to the applied voltage, when the duty ratio of the switching signal is lower than the threshold, so that the pulse width of the switching signal is equal to or greater than a predetermined pulse width, A motor control device comprising: a frequency adjusting unit that adjusts the carrier frequency. The motor control device according to claim 2,
The setting means sets the threshold value within a range of a duty ratio where a pulse width when adjusting a pulse width of the switching signal while keeping a carrier frequency of the switching signal constant is equal to or larger than a predetermined pulse width. A motor control device characterized by the above-mentioned. The motor control device according to any one of claims 1 to 3,
The motor control device according to claim 1, wherein the frequency adjusting means continuously reduces the carrier frequency in accordance with a decrease in the duty ratio. The motor control device according to any one of claims 1 to 3,
The motor control device, wherein the frequency adjusting unit decreases the carrier frequency stepwise in accordance with the decrease in the duty ratio. The motor control device according to claim 5,
The frequency adjustment unit is configured to determine when the carrier frequency changes from a first frequency to a second frequency lower than the first frequency and when the carrier frequency changes from the second frequency to the first frequency. A motor control device having a hysteresis so that the duty ratios are different. Estimating the position of the rotor based on the induced voltage of the non-energized phase of the motor driven by the inverter, outputting a pulse width modulated switching signal based on the estimation result to the inverter, and applying the applied voltage to the motor. In the control method of the motor to be controlled,
When generating the switching signal having a duty ratio corresponding to the applied voltage, a carrier frequency of the switching signal is adjusted such that a pulse width of the switching signal is equal to or greater than a predetermined pulse width. Control method. Estimating the position of the rotor based on the induced voltage of the non-energized phase of the motor driven by the inverter, outputting a pulse width modulated switching signal based on the estimation result to the inverter, and applying the applied voltage to the motor. In the control method of the motor to be controlled,
Setting a threshold value for the duty ratio of the switching signal, and generating the switching signal having a duty ratio corresponding to the applied voltage, when the duty ratio of the switching signal is lower than the threshold value, A motor control method comprising: adjusting the carrier frequency so that a pulse width is equal to or greater than a predetermined pulse width.

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