JPH0519067B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a refrigerator that changes the rotation speed of a compressor based on the refrigeration load, and particularly relates to a refrigerator that uses a frequency conversion device.

Conventional configuration and its problems The amount of heat that must be removed per unit time during cooling operation in order to keep the air inside the refrigerator in the required state is called refrigeration load. This refrigeration load can be roughly determined by measuring the difference between the internal temperature and the temperature setting value.

On the other hand, the refrigerating capacity of a refrigerator can be varied over a wide range by controlling the rotation speed of the compressor.

Therefore, by changing the rotational speed of the compressor based on the refrigeration load, it is possible to perform the minimum necessary cooling operation, which can significantly improve the operating efficiency and greatly contribute to energy saving. In addition, it is possible to always operate the compressor at the optimum rotation speed so that the temperature inside the refrigerator reaches the set temperature value, and smooth temperature control within the refrigerator can be realized.

Conventional control systems that change the rotation speed of the compressor based on the refrigeration load use a voltage-frequency converter, etc. to perform linear control based on the difference between the internal temperature and the temperature setpoint, as shown in Figure 1. The control method used was a so-called linear circuit, which linearly controlled the rotation speed of the compressor by changing the frequency to the compressor.
The drawback was that the circuit was too complex. In addition, when performing motion control with the temperature inside the refrigerator, the frequency is set using an analog signal, so there is a large fluctuation or error in the frequency, which has the disadvantage of a large error in performance. Another disadvantage was that the frequency slightly fluctuated in response to slight changes in the temperature inside the refrigerator, producing a harsh fluctuating sound. Furthermore, since the compressor rotation speed is controlled linearly, it may be stable at any rotation speed from low rotation to high rotation, but it has the disadvantage of causing noise and vibration due to resonance of the compressor and cooling system piping. Ta.

Purpose of the Invention The present invention has been made in view of the above points, and provides a refrigerator that simplifies the control circuit, suppresses fluctuations or errors in the rotation speed of the compressor, and suppresses the discomfort of noise and vibrations. For the purpose of providing.

Structure of the Invention In order to achieve this object, the present invention compares the difference between the internal temperature and the temperature setting value with a preset threshold value at predetermined time intervals, and generates a multi-stage digital signal, that is, a frequency setting signal. The signal is sequentially sent to a frequency conversion device, and the rotational speed of the compressor is changed in multiple stages.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings.

2 and 3, an alternating current voltage 1' from a power source 1 is converted into a direct current 2' by a rectifier circuit 2 and applied to a frequency converter 3. In FIGS. This frequency converter 3 converts a digital signal, that is, a frequency setting signal a
A pulse width modulation signal generator 4 generates a pulse width modulation signal, which is amplified and switched by a power element 5 and converted into an alternating current pulse width modulation voltage 3' of variable voltage and variable frequency. The output frequency of the frequency converter 3 can be changed continuously in the range of approximately 30 to 90 Hz, and thereby the rotation speed of the compressor 6 is 1600.
Varies in the range of ~5300rpm.

On the other hand, the digital signal, that is, the frequency setting signal a, applied to the frequency conversion device 3 is the output of the comparison control device 7.
Alternatively, the microcomputer 11 performs logical operations based on a preset program based on the inputs from the defrosting operation switch 8, the internal temperature sensor 9, and the temperature setting device 10, and controls the control valves, fan motors, etc. The load 12 is activated and a frequency setting signal a is applied to the frequency conversion device 3. Further, the internal configuration of the comparison control device 7 is mainly composed of a microcomputer 11, which creates various timers based on the oscillation frequency input from the oscillator 13. The input of the internal temperature sensor 9 and the temperature setting device 10 are sent from the memory 14 in which preset programs are stored through the central processing unit 15 to the data latch 16.
Digital data is sent to the D/A converter 17
The comparator 18 compares the digital data with a reference voltage corresponding to the digital data. The compared results are returned to the central processing unit 15, and this operation is
By repeating the process while changing the digital data, data b corresponding to the internal temperature value and data c corresponding to the temperature set value are obtained. A temperature difference value can be obtained by calculation. Next, data corresponding to a preset threshold value is retrieved from the memory 14 and compared with the temperature difference value at predetermined timer intervals in the central processing unit 15. As a result, a digital signal corresponding to the frequency is set in the data latch 19. The frequency converter 3 is sent out through the frequency converter 3.
Here, the memory 14, central processing unit 15, and data latches 16 and 19 are constituted by a one-chip microcomputer 11.

Note that since a digital signal is applied to the frequency conversion device 3, it is possible to provide a detailed correspondence between the predetermined timer time and the compressor rotation speed, but in this embodiment, this correspondence is partially It has been changed to make it easier to explain.

Hereinafter, an example of the correspondence between the internal temperature and the temperature setting value and the frequency setting signal a will be shown, and the operating state will be explained with reference to FIGS. 4 to 6.

Figure 4 shows the operating status during cooling operation, with the temperature difference value where the internal temperature is 0.5degC higher than the temperature setting value set as the threshold value, and the temperature difference value 0.5degC lower than the temperature set value set as the threshold value. The zone where the temperature difference value is above the threshold is defined as the α zone, the zone between the threshold and the threshold is defined as the β zone, and the zone below the threshold is defined as the γ zone. The operating conditions are made to correspond to the zones divided by these threshold values as shown in FIG.

In the left diagram of Figure 4, at the start of cooling operation, the temperature inside the refrigerator is in the α zone, which is higher than the threshold value relative to the temperature set value, so the upper limit frequency of the frequency set value is [90Hz].
At this time, the comparison control device 7 outputs a frequency setting signal a corresponding to the upper limit frequency [90 Hz] to the frequency conversion device 3, and the compressor 6 is operated. At time A, when A time has elapsed after the start of operation, the temperature difference between the internal temperature and the temperature set value (hereinafter referred to as temperature difference) is still in the α zone, so the frequency setting signal a is about to increase by one step, but it has already reached the upper limit frequency. has been reached, so operation continues at that upper limit frequency [90Hz]. After time B has elapsed, the temperature difference reaches the β zone, so operation continues at that frequency [90Hz]. Further, the temperature difference is detected by the comparison control device 7 every time B time elapses, and at the time C when the temperature difference reaches the γ zone, the frequency setting signal a is lowered by one step to [80 Hz]. After this, the same control is repeated every time B time elapses. In the right diagram of Fig. 4, when the temperature difference between the internal temperature and the temperature setting value is between the threshold value and the β zone at the start of the cooling operation,
At this time, the intermediate frequency as the frequency setting value [53Hz]
The compressor 6 starts operating. At point 2, when time A has elapsed, the temperature difference is in the γ zone, so the operating frequency is lowered by one step to [37Hz]. At time E, after B time has elapsed, the temperature difference is still in the γ zone, so the frequency is further lowered by one step to [30Hz]. Further, at the point in time when B time has elapsed, since the temperature difference is still in the γ zone, the frequency is further lowered by one step [0 Hz], that is, the compressor 6 is stopped. Then, at the time B time elapses, when the temperature difference reaches the β zone, the compressor 6 continues to operate in that state and is stopped. Thereafter, the temperature difference is detected by the comparison control device 7 every time B time elapses, and when the temperature difference reaches the α zone, a restart is performed after [0Hz], and the intermediate frequency is [37Hz]
Drive with. After that, the same control is repeated every time B time elapses, so that the temperature difference between the internal temperature and the temperature set value is within the temperature range of the threshold value.
It controls the operating frequency, that is, the rotation speed of the compressor 6.

FIG. 6 shows the comparison control device 7 showing the above control operation.
This is a flowchart. The cooling operation is continuously controlled by the flow of signals shown in this flowchart. In this embodiment, the operating frequency is set in seven stages from 30Hz to 90Hz. First, at the start of the cooling operation, a subroutine for detecting the temperature zone in the refrigerator is called, and the subroutine is executed from point b to detect whether it is the α zone, the β zone, or the γ zone. Based on this result, the frequency at the start of operation is determined, and the operation is performed for A time to reach point c. Thereafter, the subroutine is called and if the room temperature is in the α zone, the frequency is increased by one step, if the room temperature is in the β zone, operation continues at that frequency, and if the room temperature is in the γ zone, the frequency is decreased by one step.
Furthermore, as shown at point d, even if the current is 0Hz, when the power is increased by one step, the operation stalls from 37Hz. If the cooling operation does not stop, a timer process is performed for the passage of time B at point e, and then the process returns to point c and the same process is performed thereafter. If the cooling operation is stopped, the process goes to point f and stops the operation. It is controlled as described above, but when the compressor 6 in the refrigerator is operated at around 45Hz, the compressor 6
Since the noise and vibration increase due to the resonance phenomenon of pipes, etc., we avoided setting the frequency between 45Hz±5Hz and set it to 37Hz and then 53Hz.

With this configuration, during cooling operation, it is possible to control the refrigerating capacity by changing the rotation speed of the compressor 6 according to the refrigerating load, that is, the temperature inside the refrigerator.
Moreover, since this refrigerator is comprised of a frequency conversion device 3 controlled by a digital signal a and a comparison control device 7 mainly composed of a microcomputer 11, complex control can be performed with a simple circuit configuration. Furthermore, since the frequency is set using the digital signal a, fluctuations or errors in the rotational speed of the compressor 6 can be kept extremely low. Furthermore, since the temperature inside the refrigerator is controlled to be maintained between the threshold value and the frequency continues at the same value between this threshold value, the frequency will be slightly affected by slight fluctuations in the temperature inside the refrigerator. It is possible to eliminate the occurrence of unpleasant fluctuating noise without causing any fluctuation. Also, since the frequency is changed in multiple stages,
By setting the frequency in advance to avoid resonance or resonant sound of the compressor 6 or the cooling system piping, noise and vibration can be kept extremely low. Furthermore, at the start of cooling operation, operation with a good start-up is possible, and operation can be started at an appropriate frequency from the start of operation. Furthermore, by making time A and time B longer than time A, the first temperature comparison can be performed after stable operation has started, thereby making it possible to avoid detection of an unstable state at the beginning of operation.

Although not shown in the example, the threshold value is set to 2.
With this configuration, control that increases or decreases the frequency by one step each time the temperature difference between the internal temperature and the temperature set value falls below the threshold value can also be realized with this configuration. control is possible.

Effects of the Invention As is clear from the above explanation, the refrigerator of the present invention includes a digitally controlled frequency converter that changes the rotation speed of the compressor into multiple stages using a frequency setting signal, and a difference between the internal temperature and the temperature setting value. and a preset threshold value, and the frequency setting signal sequentially increases, decreases, or maintains the current speed of the compressor at predetermined time intervals depending on whether the rotation speed is above or below the threshold value. The circuit configuration is simple, and fluctuations or errors in the rotation speed of the compressor can be kept extremely low, and resonance in the compressor and cooling system piping can be avoided. By setting the rotation speed, vibration and noise can be extremely reduced.

In addition, by configuring two or more thresholds to be set in advance, the rotation speed of the compressor will not change between these thresholds, and the rotation speed will slightly fluctuate in response to slight fluctuations in the temperature inside the refrigerator. It is possible to prevent the occurrence of unpleasant fluctuating noise without causing any noise.

Furthermore, by determining the frequency at the start of operation according to the zone divided by the threshold value, the start-up operation characteristics are improved and operation can be started at an appropriate frequency from the start of operation.

Furthermore, since the predetermined time interval for detection is changed depending on when the temperature inside the refrigerator fluctuates and when the temperature inside the refrigerator is stable, it is possible to avoid detection and control in unstable conditions at the beginning of operation. This has the effect of improving performance.

[Brief explanation of the drawing]

Fig. 1 is a control system diagram of a conventional refrigerator, Fig. 2 is a block diagram of a refrigerator according to an embodiment of the present invention, Fig. 3 is a control circuit diagram of the same refrigerator, Fig. 4 is an explanatory diagram of the operation of the same refrigerator, FIG. 5 is a correspondence diagram of operating conditions at each temperature difference value, and FIG. 6 is an operation flowchart. 3... Frequency converter, 6... Compressor, 7...
Comparison control device, a...frequency setting signal.

Claims (1)

[Claims] 1. A digitally controlled frequency converter that changes the number of revolutions of a compressor in multiple stages using a frequency setting signal, and a preset threshold value that is determined by the difference between the internal temperature and the temperature setting value. A comparison control device that sends out the frequency setting signal to sequentially increase, decrease, or maintain the current speed of the compressor at predetermined intervals depending on whether the frequency is above or below the threshold value. . 2 At least two or more threshold values are set in advance, and it is determined at predetermined time intervals in which zone the difference between the temperature inside the refrigerator and the temperature set value is divided by the thresholds. The refrigerator according to claim 1, further comprising a comparison control device that sends out a frequency setting signal. 3 Claims that constitute a comparison control device that determines in which zone divided by threshold values the difference between the internal temperature and the temperature set value is in at the start of operation, and sends out a frequency setting signal of a predetermined frequency. Refrigerator according to paragraph 2. 4. The refrigerator according to claim 2, further comprising a comparison control device that changes the time interval of a predetermined time period for determining which zone the refrigerator is in when the internal temperature is stable.