JP2000050678A - Dc brushless motor drive gear - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the efficiency of a motor in a high-revolution range by detecting the rotor position of the motor with a position detecting means, based on an induced voltage constituent which passed a low-pass filter, and by controlling the motor with PWM in the first half of conduction period for each winding of the motor in its high-revolution range. SOLUTION: Induced voltages A, B, C inputted to a position detecting means 4 are outputted as induced voltage components VA, VB, VC after high harmonic constituents were removed with low-pass filters 4a, 4b, 4c which attenuate the signals of the chopping frequency band in PWM. The position detecting means 4 detects the position of a rotor, by comparing the virtual neutral point potential VN generated by resistors 4R with the induced voltage components VA, VB, VC with comparators 4p, 4q, 4r. Also the motor is driven with PWM in the first half of conduction period for each winding only in the high-revolution range of the motor. As a result, this structure can improve the efficiency of the motor in the high-revolution range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for detecting a position of a rotor based on an induced voltage generated in a driving winding of a motor,
The present invention relates to a DC brushless motor drive device that calculates the number of rotations of a motor from a detected rotor position of the motor and performs PWM control on the motor.

[0002]

2. Description of the Related Art A DC brushless motor includes a rotor composed of a permanent magnet and a stator having a three-phase winding. An AC voltage having a predetermined frequency is applied to each winding from an inverter composed of a switching element. By controlling the on / off duty ratio of the switching element,
The motor is controlled to a target rotation speed by controlling a current value supplied to the motor. FIG. 7 is a diagram showing a configuration of a DC brushless motor driving device described in, for example, Japanese Patent Application Laid-Open No. H10-174484. In FIG. 7, inverters 2 are connected in series.
Arm 2a, 2 comprising two switching elements
b, 2c, the upper transistor of one arm and the lower transistor of the other arm are turned on, so that the two windings (for example, U
Phase and V phase), and the motor 3 rotates. At this time, an induced voltage is induced in the winding (W phase) that is not energized with the rotation of the rotor 3R of the motor 3.
In a DC brushless motor having no means for directly detecting the position of the rotor 3R, the position detecting means 4 detects the position of the rotor 3R from the induced voltage, and the microcomputer 5 detects the position of the rotor 3R. From the motor 3 is calculated. The microcomputer 5 determines the commutation timing from the position of the rotor 3R, calculates the on / off duty ratio of the switching element to control the rotation speed to the target rotation speed, and sets a preset duty ratio. Each winding U, V, W is energized according to an energization pattern, and the number of rotations of the motor 3 is controlled.

[0003]

The induced voltage is accompanied by generation of noise. This noise generation period (return current period)
The energy accumulated in the winding continues to flow for a while after the commutation. Therefore, the position detection must be interrupted during the return current period, and the commutation timing is delayed, so that accurate position detection cannot be performed. Therefore, Japanese Patent Application Laid-Open
In Japanese Patent No. 2847873, PWM control is performed in the latter half 60 degrees of the switching element energization period 120 degrees, thereby shortening the return current period, reducing the delay of commutation timing, and performing stable position detection. Performing techniques are disclosed. However, during the reflux current period, the energy accumulated in the windings continues to flow for a while after the commutation and applies torque to the motor. Therefore, performing the PWM control at the latter half of 60 degrees as in the above example is optimal for motor efficiency. However, there is a problem that the motor efficiency deteriorates particularly in a high rotation range where the motor current is large. In Japanese Patent Application Laid-Open No. H10-174484, the applicant provides a low-pass filter for attenuating a signal in a PWM chopping frequency band in the position detecting means 4 to reduce noise and to adjust the rotation frequency of the motor 3 according to the rotation frequency. A method of optimizing the commutation timing by performing commutation at the timing of the phase delay has been proposed. However, there is no mention of control in consideration of the timing of the PWM control during the energization period.

SUMMARY OF THE INVENTION The present invention has been made in view of the conventional problems, and provides a DC brushless motor driving device capable of performing accurate position detection and improving motor efficiency in a high rotation speed range. With the goal.

[0005]

According to a first aspect of the present invention, there is provided a DC brushless motor driving apparatus, wherein a low pass filter for attenuating a signal in a PWM chopping frequency band is provided in a position detecting means, and the low pass filter passes through the low pass filter. The rotor position of the motor is detected based on the induced voltage component, and the PWM control is performed in the high rotation range of the motor in the first half of the energization period for each winding of the motor.

According to a second aspect of the present invention, there is provided a DC brushless motor driving device, wherein the DC brushless motor is a motor for driving a compressor of an air conditioner.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described.
A description will be given based on the drawings. FIG. 1 shows an embodiment of the present invention.
Shows the configuration of the DC brushless motor drive device related to
In the figure, 1 is a DC power supply, 2 is a switching element (T_U~
T_Z) And commutation diode (D_U~ D_Z) And the above
An inverter that converts DC voltage to AC voltage, and 4 is a DC
Induction induced in each winding U, V, W of the brushless motor 3
A position for detecting the position of the rotor 3R of the motor 3 from the voltage.
The position detecting means 5 is the rotation detected by the position detecting means 4.
When calculating the rotation speed of the motor 3 from the position of the child 3R,
First, each switching element (T_U~
T_Z) Is turned on and off to control the motor by PWM
Control means. The control means 5 includes the position detection means.
4 to the actual rotational speed N of the motor 3_kSpeed to calculate
From the calculation means 6 and information such as the load state of the motor 3, the target
Number of turns N₀Target speed setting means 7 for setting
Each switching element (T_U~ T _Z) Driving due
Rotation speed control means 8 for calculating and setting the tee ratio;
Each of the above switchings based on a command from the number control means 8
Element (T_U~ T_ZSignal output means for outputting a control signal to
9 and the actual rotation speed N of the motor 3_kIs the above target speed
N₀Each switching element (T_U~ T_Z)
Calculate the drive duty ratio of each switching element
(T_U~ T_ZA) control signal to drive the inverter
2 is output.

Further, as shown in FIG. 2, the position detecting means 4 generates induced voltages A, B, C inputted to the position detecting means 4.
Are induced voltage component voltages VA, VB, from which high-frequency components have been removed by low-pass filters 4a, 4b, 4c for attenuating signals in the PWM chopping frequency band, respectively.
Output as VC. The position detecting means 4 generates a virtual neutral point potential (the induced voltage component V
A, VB, VC) VN and each induced voltage component V
The position of the rotor 3R is detected by comparing A, VB, and VC with the comparators 4p, 4q, and 4r. As shown in FIG. 3A, the low-pass filters 4a, 4b, and 4c (hereinafter abbreviated as filters) have a motor 3
It has a frequency-gain characteristic such that it is substantially flat up to an induced voltage frequency of 200 Hz corresponding to the maximum rotation speed of 6000 rpm, and decreases at a predetermined attenuation rate (in this case, 20 dB / Oct.) Above 200 Hz. Signal in the chopping frequency band (2 kHz to 5 kHz) can be sufficiently attenuated. As shown in FIG. 3B, the low-pass filters 4a, 4b, and 4c have a small phase delay up to the intermediate rotation speed of the motor 3, and thereafter, the phase delay increases as the rotation speed increases. 3 has a frequency-phase characteristic such that the phase lag is approximately 90 degrees near the maximum rotation speed. Therefore, the induced voltages induced in the windings U, V, W are filtered by the filters, and as a result, the induced voltage components (VA, VB, VC in FIG. 2) in which the chopping frequency components during PWM control are attenuated. ), The position of the rotor 3R can be detected, so that the position can be accurately detected.
In particular, in the high rotation range where the rotation speed is about 2000 rpm or more,
The effect of reducing noise is greater than in the low rotation range. Therefore, in the present embodiment, as described later, the PWM control is performed only in the high rotation range of the motor in the first half of the energization period for each winding.

Next, the operation of the DC brushless motor driving device having the above configuration will be described in detail with reference to the flowchart of FIG. The rotation speed control means 8 first checks whether or not the current energization pattern is the latter half PWM (step S1). 5 (a) is a diagram showing a part of the energization pattern in _{FIG, T U, T Z, T} Y each switching element _{T U,} T Z, a diagram showing the on-off state of the _{T Y} , The solid line indicates P in the first half 60 ° of the conduction period 120 °.
In the case of performing WM control, the broken line indicates the energization period of 120 °.
In this case, the PWM control is performed in the latter half 60 °. FIG. 5B is a diagram showing the W-phase current at that time. When the energization pattern is switched from two-phase energization by the U-phase and the W-phase to two-phase energization by the U-phase and the V-phase, it is indicated by a broken line. Shown second half P
In the WM control, since the return current period is shorter than that in the first half PWM control of the solid line, torque cannot be applied to the motor 3 and motor efficiency is poor. In step S1, if the energization pattern is the latter half PWM, the rotation speed controller 8 sets the actual rotation speed _Nk input from the rotation speed calculator 6 to the preset reference rotation from the latter half PWM to the former half PWM. Number N ₁
(For example, N ₁ = 2500 rpm) (Step S2), and the actual rotation speed _Nk is changed to the switching reference rotation speed N _1.
Is exceeded, it is determined that the motor 3 has entered the high rotation range, and the energization pattern is switched from the latter half PWM to the former half PWM (step S3). Thereby, as shown in FIG.
Further, in step S2, if the actual rotational speed N _k is equal to or less than the switching reference rotational speed N ₁ is the second half of the current P
The WM control is continued. On the other hand, when the energization pattern is the latter half PWM in step S1, the rotation speed controller 8 sets the actual rotation speed _Nk input from the rotation speed calculator 6 to the preset first half PWM to the latter half PWM. The reference rotation speed N ₂ (for example, N ₂ = 2000 rpm) is compared with the reference rotation speed N ₂ (step S4). If the actual rotation speed _Nk is lower than the reference rotation speed N ₁ , the motor 3 is switched to the low rotation speed range. Is determined, the energization pattern is switched from the first half PWM to the second half PWM (step S5). Further, in step S4, when the actual rotational speed N _k is the switching reference rotational speed N ₂ or more, it is determined that the motor 3 is still in the high speed range, to continue the first half PWM control of current. Thus, the energization of the DC brushless motor is performed at the actual rotational speed N.
_k is the first half of PWM when it exceeds the switching reference rotational speed N ₁ rises, so when the actual rotational speed N _k falls below the switching reference rotational speed N ₂ descends is set as the second half PWM In addition, the motor efficiency can be improved in a high rotation range, and stable operation can be performed in a low rotation range.

The number of rotations of the motor is set mainly based on the operating state of the motor load. When the load is an air conditioner, the motor is a motor that operates a compressor of the air conditioner. FIG. 6 is a diagram schematically illustrating a configuration of an air conditioner capable of switching between cooling and heating. The air conditioner includes a compressor 10 driven by a motor 3, a condenser 11, an evaporator 12, and a four-way valve 13. Prepared,
At the time of heating, the gas (refrigerant) compressed by the compressor 10 is heated and condensed by a condenser 11 provided with an indoor heat exchanger for heating, and the heated air is sent as hot air to be sent into the room. It is. On the other hand, at the time of cooling, the refrigerant compressed by the compressor 10 is cooled and condensed by the condenser 11 provided with the outdoor heat exchanger for heating, and evaporated from the expansion valve 14 to the evaporator provided with the indoor heat exchanger for cooling. It is sent to the vessel 12 and expands into a low-temperature low-pressure refrigerant to cool the air. Compressor 10
The rotation speed of the motor 3 in the steady state is about 3500 rpm during cooling and about 5000 rpm during heating. In any case, the rotation speed of the motor 3 is in the high rotation range described above. During the operation of the air conditioner,
The motor 3 that operates the compressor 10 can be controlled by the first half PWM, and the air conditioner can be operated efficiently.

In the present embodiment, the first half PWM control is performed only in the high rotation range, and the second half PWM control is performed in the low rotation range where the noise reduction effect of the low-pass filters 4a, 4b and 4c is small. This is because it is not necessary to consider the deterioration of the motor efficiency because the motor current is small at the time of low rotation of the motor. Further, the switching reference rotation speeds N ₁ and N ₂ are set to 2500 rpm and 2000 rpm, respectively.
The value of N ₁ and N ₂ is not limited to this, but is determined as appropriate based on the chopping frequency, the accuracy of the rotation speed control, and the like.

[0012]

As described above, according to the first aspect of the present invention, the position detecting means controls the motor based on the induced voltage component that has passed through the low-pass filter that attenuates the signal in the PWM chopping frequency band. Since the rotor position is detected and the PWM control is performed in the first half of the energization period for each winding of the motor in the high rotation range of the motor, the motor efficiency can be improved in the high rotation range.

According to the second aspect of the present invention, the DC brushless motor is a motor for driving the compressor of the air conditioner, so that the first half PWM control is performed in each of the cooling and heating steady states of the air conditioner. Can be performed, and the air conditioner can be operated efficiently.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a DC brushless motor according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a position detector of the DC brushless motor.

FIG. 3 is a diagram illustrating frequency characteristics of gain and phase of a low-pass filter provided in a position detector of a DC brushless motor.

FIG. 4 is a flowchart for explaining an energization method according to the embodiment of the present invention.

FIG. 5 is a diagram for explaining an energization method according to the embodiment of the present invention.

FIG. 6 is a diagram showing a configuration of an air conditioner according to an embodiment of the present invention.

FIG. 7 is a diagram showing a configuration of a conventional DC brushless motor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 DC power supply, 2 inverters, 3 DC brushless motors, 4 position detection means, 5 control means, 6 rotation speed calculation means, 7 target rotation speed setting means, 8 rotation speed control means, 9 signal output means, 10 compressor, 11 Condenser,
12 evaporator, 13 four-way valve, 14 expansion valve.

Claims (2)

[Claims] 1. A position detecting means for detecting a position of a rotor of the DC motor based on an induced voltage induced in each winding of the DC brushless motor, and calculating a rotational speed of the motor from the detected rotor position. In a DC brushless motor drive device comprising: a control unit for performing PWM control on the motor, a low-pass filter for attenuating a signal in a PWM chopping frequency band is provided in the position detection unit, and the induced voltage component passing through the low-pass filter is provided. , The rotor position is detected based on the PW, and in the high rotation range of the motor, PW
A DC brushless motor drive device characterized by performing M control. 2. The DC brushless motor driving device according to claim 1, wherein the DC brushless motor is a motor that drives a compressor of an air conditioner.