JP3258037B2 - Air conditioner inverter control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air conditioner having a compressor in which irregular load fluctuation occurs, and more particularly to an inverter control device for driving a motor of the compressor.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram showing an example of a conventional air conditioner driving apparatus, wherein 1 is a commercial AC power supply, 2 is a rectifier circuit, 3 is a smoothing capacitor, 8 is a current detector, and 5 is a current detector. An inverter, 6 is an electric motor, and 7 is an inverter control circuit.

In FIG. 1, an AC voltage from a commercial AC power supply 1 is rectified by a rectifier circuit 2 and smoothed by a smoothing capacitor 3 to become a DC voltage. This DC voltage is applied to the inverter 5. The inverter 5 is supplied with a PWM (Pulse Width Modulation) signal from the inverter control circuit 7 and supplies a three-phase drive current having a magnitude corresponding to the applied DC voltage and a pulse width corresponding to the duty ratio of the PWM signal. appear.
The motor 6 of the compressor in the refrigeration cycle is driven by this drive current, and rotates at a rotation speed according to the DC voltage and the duty ratio of the PWM signal.

By the way, the load applied to the compressor fluctuates at a regular short cycle, and the rotation speed of the motor fluctuates with the fluctuation, resulting in vibration and noise. In order to prevent this, conventionally, various methods have been proposed, but as an example, the winding current of the motor changes with the change of the load, and thus the rotation speed of the motor changes. There is known a technique in which a change in current is detected, and the applied voltage of the winding is changed in accordance with the change to compensate for a variation in voltage drop in the winding due to the current change ( JP-A-61-214787).

As another method, there is a technique in which the output torque of the electric motor is changed so as to be substantially equal to the fluctuating load torque per one rotation applied to the compressor (Japanese Patent Laid-Open No. 2-797).
No. 93). This detects the rotor position of the motor,
A current pattern corresponding to the detection result is generated to control the winding current and change the output torque of the electric motor.

[0006]

However, in the prior art described in Japanese Patent Application Laid-Open No. 61-214787, when the DC voltage applied to the inverter 5 in FIG. 7 fluctuates, the voltage applied to the motor 6 fluctuates. As a result, the winding current fluctuates. The output torque of the motor 6 is proportional to this winding current, but since the motor 6 tries to keep the output torque constant,
The rotation speed fluctuates. The acceleration / deceleration rate of the motor 6 is proportional to the applied voltage. Therefore, if the applied voltage fluctuates, the acceleration / deceleration rate (change in rotation speed per time)
Fluctuates. The commercial AC voltage is allowed to fluctuate ± 15%, and if there is a fluctuation in the commercial AC voltage, the DC voltage obtained from the smoothing capacitor 3 also fluctuates.

[0007] If the rotation speed of the electric motor fluctuates, stable operation of the air conditioner cannot be performed. In addition, if the acceleration / deceleration rate fluctuates, for example, if the acceleration rate is large, vibration or noise will increase in transient times such as at startup or when the set temperature is changed, and if the acceleration rate is small, the startup characteristics of the driving will deteriorate. However, operation at the set temperature cannot be performed. In such prior art, no consideration has been given to the problem of fluctuations in the rotation speed and acceleration / deceleration rate of the electric motor with respect to such fluctuations in the voltage applied to the inverter.

In the prior art described in Japanese Patent Application Laid-Open No. 2-79793, the rotational position of the rotor of the electric motor is detected to generate a predetermined current pattern, and the rotational speed of the electric motor accompanying a load change is detected. It is effective if this load fluctuation is regular, but when driving a scroll compressor, etc., it is effective against irregular load fluctuation due to sudden change of the set temperature. Cannot immediately respond to this. That is, it is not possible to cope with an unpredictable instantaneous load change, and even if the rotation speed is reduced, the winding current of the electric motor is controlled to the current value immediately before the rotation speed is reduced. For this reason, especially at the time of low-speed rotation of a compressor, torque shortage arises and inverter tolerance falls, and it becomes impossible to maintain a compressor at low-speed rotation state.

SUMMARY OF THE INVENTION It is an object of the present invention to solve such a problem, to reduce fluctuations in rotation speed and acceleration / deceleration rate due to fluctuations in a DC voltage applied to an inverter, and to prevent a compressor from being subjected to irregular load fluctuations. An object of the present invention is to provide an air conditioner inverter control device capable of stabilizing the low-speed rotation of the air conditioner.

[0010]

In order to achieve the above object, the present invention provides a commercial AC voltage obtained by rectifying and smoothing the AC voltage.
A DC voltage and a PWM signal are supplied, and the DC voltage and the PWM signal are supplied.
Generates a motor drive current according to the pulse width of the WM signal
DC voltage in an air conditioner equipped with an inverter
To obtain an average value of the detected DC voltage, and the average value
Is compared with the detected instantaneous value of the DC voltage, and the instantaneous value is
When larger than the average value, the pulse width of the PWM signal is reduced.
Control in the small direction, when the instantaneous value is smaller than the average value
The pulse width of the PWM signal is controlled in the enlargement direction.
Things.

[0011]

[Function] A commercial AC voltage is rectified and smoothed.
The average value and the instantaneous value of the DC voltage supplied to the motor are compared with each other, and the duty ratio of the PWM signal is changed according to the comparison result, so that the change in the rotation speed due to the change in the DC voltage is reduced. .

Since the motor is driven by the DC voltage and the PWM signal, if the rotation speed suddenly drops due to irregular load fluctuations, the induced voltage of the motor decreases, and the winding current increases. The output torque of the electric motor increases in proportion to this. For this reason, the rotation speed instantaneously increases and returns. For this reason, even if there is an irregular load change during low-speed rotation, the rotation speed is stable, and the inverter resistance does not decrease.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an inverter control device for an air conditioner according to the present invention. Reference numeral 4 denotes a DC voltage detector, and portions corresponding to those in FIG. Is omitted.

In FIG. 1, a DC voltage detector 4 applies a DC voltage Ve applied to an inverter 5 obtained by a smoothing capacitor 3.
And supplies the detection output to the inverter control circuit 7. The inverter control circuit 7 generates a PWM signal having a duty ratio according to the supplied detection output and supplies the PWM signal to the inverter 5.

The rotation speed of the electric motor 6 depends on the applied voltage, and the applied voltage is proportional to the DC voltage Ve applied to the inverter 5 and the duty ratio of the PWM signal. The acceleration / deceleration of the motor 6 is performed by changing the duty ratio of the PWM signal. Therefore, when the DC voltage Ve fluctuates, the rotation speed and the acceleration / deceleration rate of the electric motor 6 fluctuate.

In this embodiment, if the DC voltage Ve fluctuates, the fluctuation is compensated by changing the duty ratio of the PWM signal, whereby the fluctuation of the rotation speed and the acceleration / deceleration rate of the motor 6 is reduced. Is suppressed.

Further, when a PWM signal having a certain DC voltage Ve and a certain duty ratio is supplied to the inverter 5, the load applied to a compressor such as a scroll compressor fluctuates irregularly. Assuming that the speed, that is, the rotation speed of the electric motor 6, suddenly decreases, the induced voltage of the winding of the electric motor 6 decreases with the decrease of the rotation speed, and the winding current rapidly increases. Since the output torque of the motor is proportional to the winding current, the output torque of the motor 6 increases as the winding current sharply increases, and the rotation speed increases instantaneously. As a result, the compressor is in a stable state even at a low rotation speed, and the tolerance of the inverter is improved.

FIG. 2 shows the inverter control circuit 7 shown in FIG.
9 is a block diagram showing one specific example, 9 is a reference voltage generator, 10 is an arithmetic circuit, 11 is a PWM signal generator, 12
Is Doiba.

In FIG. 1, the DC voltage detector 4
Assuming that the value of the DC voltage detected in FIG. 1 is Ve, the arithmetic circuit 10 performs the following operation using the DC voltage value Ve and the value Vs of the reference voltage from the reference voltage generator 9, and A pulse increase / decrease coefficient Ce for the voltage value Ve is generated.
Ce = Cs × Vs / Ve where Cs is the PW during acceleration / deceleration.
This is a reference pulse increase / decrease coefficient of the M signal, and is used to set the duty ratio of the PWM signal so that a designed acceleration / deceleration rate is obtained when the DC voltage Ve is equal to the reference voltage Vs. This reference pulse increase / decrease coefficient Cs is obtained experimentally. The reference voltage value Vs is equal to the DC voltage value Ve when the commercial AC voltage is 100 (V). PW
The M signal generator 11 corrects the duty ratio of the output PWM signal with the pulse increase / decrease coefficient obtained by the arithmetic circuit 10,
The PWM signal is transmitted to the inverter 5 via the driver 12.
(Figure 1).

As described above, by changing the duty ratio of the PWM signal in accordance with the detected DC voltage Ve during acceleration / deceleration, the acceleration / deceleration rate does not change even if the DC voltage Ve changes. The increase / decrease of the pulse width (duty ratio) of the PWM signal during acceleration / deceleration will be described with reference to FIG. Now, Ve = Vs (input = A
When the change in pulse width at C100 (V) is indicated by a solid line, when Ve <Vs (input <100 (V)), that is, when the commercial AC voltage becomes smaller than 100 (V), the pulse increase / decrease coefficient Increase Ce and as shown in the figure,
Increase / decrease the width of the pulse width of the PWM signal. Conversely, V
e> Vs (input> AC100 (V)), that is, when the commercial AC voltage becomes greater than 100 (V), the pulse increase / decrease coefficient Ce is decreased, and as shown in the figure, the PWM is increased.
Reduce the increase / decrease width of the signal pulse width. As a result, the acceleration / deceleration rate increases / decreases to match the designed acceleration / deceleration rate regardless of whether the commercial AC voltage is lower or higher than 100 (V). Of course, the acceleration / deceleration rate is different depending on the difference between the set temperature and the current temperature.However, the design acceleration / deceleration rate is set according to the temperature difference. A corresponding design acceleration / deceleration rate can be obtained.

FIG. 4 shows the experimental results of the fluctuation of the acceleration / deceleration rate with respect to the fluctuation of the commercial AC voltage. The broken line a is the one without the conventional correction, and the solid line b is the one according to this embodiment. As shown, the commercial AC voltage is 100
(V) If fluctuated ± 15% relative, whereas the variation acceleration and deceleration rate of about 45min ~ ¹ / sec in the prior art, in this embodiment only variation in half following about 20min ~ ¹ / sec It is clear that the fluctuation of the acceleration / deceleration rate is greatly reduced.

FIG. 5 is a block diagram showing another specific example of the inverter control circuit in FIG. 1, wherein 13 is an averaging circuit, 14 is a comparison circuit, 15 is a PWM signal generator, 16
Is a pulse width expansion circuit, 17 is a pulse width reduction circuit, 18 is an increase / decrease determination circuit, and 19 is a driver. FIG. 6 is a waveform chart showing signals of respective parts in FIG.

In FIGS. 5 and 6, the detection output Ve of the DC voltage detector 4 (FIG. 1) is supplied to an averaging circuit 13, and the average voltage Vo is detected. The comparison circuit 14 compares the detection output Ve with the average voltage Vo, and supplies the comparison result to the increase / decrease determination circuit 18.

On the other hand, a PWM generator 15 outputs a PWM signal e, and a pulse width expansion circuit 16 and a pulse width reduction circuit 17
To supply. The pulse width expanding circuit 16 widens the pulse width of the PWM signal e by a predetermined ratio, and the pulse width reducing circuit 17 narrows the pulse width by a predetermined ratio. When the voltage Ve is lower than the average voltage Vo according to the comparison result of the comparison circuit 14, the increase / decrease determination circuit 18
And when the voltage Ve is higher than the average voltage Vo, the output of the pulse width reducing circuit 17 is selected. The PWM signal f output from the increase / decrease determination circuit 18 is supplied to the inverter 5 (FIG. 1) via the driver 19.

Here, assuming that the pulse width of the PWM signal e output from the PWM signal generator 15 is d0 , this becomes d1 (> d0) in the pulse width expansion circuit 16, and d2 (<d0) in the pulse width reduction circuit 17. ). Therefore, the pulse width of the PWM signal f output from the increase / decrease determination circuit 18 is d1 when the voltage Ve is lower than the average voltage Vo.
And d2 when high.

FIG. 6C shows the winding current of the motor 6 (FIG. 1). Assuming that the solid line is the current based on the PWM signal e output from the PWM signal generator 15, the above-described inverter control circuit 7 shown in FIG. By the operation, the width of the winding current C changes as indicated by the broken line in accordance with the fluctuation of the DC voltage Ve. According to this, when the DC voltage Ve increases, the time width of the winding current c decreases, and when the DC voltage Ve decreases, the time width of the winding current c increases, and the fluctuation of the rotation speed of the electric motor 6 decreases.

[0027]

As described above, according to the present invention,
Even if the commercial AC voltage fluctuates, at the time of acceleration / deceleration, the pulse width of the PWM signal is increased / decreased in accordance with this fluctuation to control the voltage applied to the motor, so that the fluctuation of the acceleration / deceleration rate can be greatly reduced. Characteristics such as pressure protection at the time of load and instantaneous heating effect at the time of start-up are stabilized, and the pulse width of the PWM signal is corrected according to the relationship between the instantaneous value and the average value of the DC voltage. Because it controls the applied voltage,
The fluctuation of the rotation speed is greatly reduced, and the generation of vibration and noise of the compressor accompanying the fluctuation of the commercial AC voltage can be reduced, and the electric current of the electric motor is stabilized, so that the efficiency of the electric motor is improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of an inverter control device for an air conditioner according to the present invention.

FIG. 2 is a block diagram showing a specific example of the inverter control circuit in FIG.

FIG. 3 is a diagram showing an operation of the specific example shown in FIG. 2;

FIG. 4 is a diagram comparing the variation of the acceleration / deceleration rate with respect to the variation of the commercial AC voltage between the embodiment shown in FIG. 1 and the conventional air conditioner.

FIG. 5 is a block diagram showing another specific example of the inverter control circuit in FIG. 1;

FIG. 6 is a waveform chart showing signals of respective units in FIG.

FIG. 7 is a configuration diagram illustrating an example of a conventional air conditioner.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Commercial AC power supply 2 Rectifier circuit 3 Smoothing capacitor 4 DC voltage detector 5 Inverter 6 Motor 7 Inverter control circuit 9 Reference voltage generator 10 Operation circuit 11 PWM generation circuit 13 Averaging circuit 14 Comparison circuit 15 PWM signal generator 16 pulse Width expansion circuit 17 Pulse width reduction circuit 18 Increase / decrease determination circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-114387 (JP, A) JP-A-63-224675 (JP, A) JP-A-58-103875 (JP, A) JP-A-62 181676 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M 7/48 F24F 11/02 F25B 1/00 H02P 7/63

Claims (1)

(57) [Claims] An AC voltage obtained by rectifying and smoothing a commercial AC voltage.
A DC voltage and a PWM signal are supplied, and the DC voltage and the PWM signal are supplied.
Generates a motor drive current according to the pulse width of the WM signal
In the air conditioner equipped with an inverter, the DC voltage is detected, and an average value of the detected DC voltage is calculated.
And comparing the average value with the instantaneous value of the detected DC voltage.
And when the instantaneous value is greater than the average value, the PWM signal
Is controlled in the decreasing direction, and the instantaneous value is
Smaller than the pulse width of the PWM signal in the enlargement direction.
Inverter control device of an air conditioner which is characterized in that control.