JPH0353534B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to a variable capacity air conditioner.

<Prior art> In general, in air conditioners whose capacity is variable by changing the frequency (hereinafter referred to as output frequency) of the three-phase power supply to the electric compressor, the electric compressor changes the refrigerant compression cycle (discharge pressure) in response to changes in the output frequency. ) is slow to follow, and there is no problem when the output frequency is gradually increased, but when it is decreased, the refrigerant compression cycle is almost overloaded because the discharge pressure follows slowly. Normally, if the refrigerant compression cycle is stabilized, the output frequency and discharge pressure will have a relationship as shown in FIG. Note that A in the figure indicates the starting frequency. When both the output frequency and the discharge pressure are high and there is an overload condition, if the output frequency is significantly lowered, there is a risk that the discharge pressure will not be able to follow the decrease in the output frequency and an overload condition will occur.

In addition, in order to maintain high efficiency of the motor over the variable range of the output frequency, the ratio of the fundamental wave effective value of the output voltage to the output frequency (hereinafter referred to as the voltage/frequency ratio V/Hz)
In an electric compressor that is controlled so as to maintain a constant constant value, the maximum torque of the electric compressor decreases slightly at low output frequencies, as shown in Fig. 3. Therefore, in this low frequency band, as the overload condition progresses, the torque of the electric compressor will no longer be able to follow the load, and the electric compressor will become locked. If this lock state occurs, a lock current several times the normal flow will flow through the electric compressor, causing heat generation and large current in the electric compressor, which may damage the switching transistor, as well as subjecting the electric compressor to abnormal force. In addition, it becomes a factor that causes eccentricity of mechanical parts.

<Objective> In view of the above, it is an object of the present invention to provide an air conditioner that can suppress abnormalities in an electric compressor by suppressing the decrease in output frequency per unit time in relation to the increase in output frequency. .

<Example> Hereinafter, an example of the present invention will be explained based on FIGS. 1 to 4. This will be explained based on FIG. 1 to FIG. 4. An electric compressor 4 to which the AC voltage converted by the inverter 3 is applied compresses and discharges refrigerant, and a control device 5 that controls the inverter 3. It is growing. An indoor heat exchanger 6 is connected to the electric compressor 4 via piping, an outdoor heat exchanger 8 is connected to the indoor heat exchanger 6 via a pressure reducer 7, and an electric compressor is connected to the outdoor heat exchanger 8. 4 are connected to form a refrigerant compression cycle 9.

Further, as shown in FIG. 1, the control device 5 determines the output voltage and output frequency based on the temperature input signals from the room temperature detector 5A and the room temperature setting board 5B, and controls the inverter 3.
A microcomputer (hereinafter referred to as a microcomputer) that outputs a pulse width modulation signal (PWM waveform) to the side
11, and an inverter drive section 12 that drives and controls the inverter 3 based on the PWM signal from the microcomputer 11. That is, as shown in FIG. 5, the control device 5 has a room temperature detector 5A that detects the room temperature, a room temperature setting board 5B that sets the room temperature, and a temperature signal of the room temperature detector 5A and a set temperature of the room temperature setting board 5B. Comparison means 5a for comparison, and comparison means 5a
An operating frequency determining means 5b determines whether to raise or lower the operating frequency to the inverter 3 than the current operating frequency based on the comparison result, and as a result of the determination by the operating frequency determining means 5b, when increasing the operating frequency, the unit time The operating frequency increasing means 5c outputs a signal to the inverter to sequentially increase the operating frequency by a predetermined increase width, and as a result of the judgment of the operating frequency determining means 5b, when lowering the operating frequency, the operating frequency is lowered per unit time. and operating frequency reduction means 5b for outputting a signal to the inverter that is smaller than the increase width when the operating frequency is sequentially increased and is lowered to an extent that does not cause overload of the compressor. .

Figure 4 shows the time required to greatly reduce the output frequency from 90Hz to 30Hz when both the output frequency and discharge pressure are high and there is an overload condition.The time required to do so is 25 seconds (dotted chain line) and 100 seconds. FIG. 3 is a diagram showing the relationship between time (solid line) and discharge pressure. In this figure, the dash-dotted line indicates an overload state where the output frequency drops to 30Hz after 25 seconds, but the discharge pressure remains almost unchanged. On the other hand, in the case of the solid line, when 100 seconds have passed and the output frequency reaches 30Hz, the discharge pressure has decreased considerably and no overload condition occurs.

Therefore, when the output frequency is high and there is an overload condition, the control device 5 prevents the compressor from locking by reducing the amount of decrease in the output frequency per unit time to 0.8 (Hz/sec) or less, and also increases the output frequency. If you go, 3
(Hz/sec) or less. The actual frequency increase/decrease is done digitally over time. Therefore, if the amount of decrease or increase is large, the torque fluctuation will be large at the frequency change, and there is a high possibility that the compressor will lock up. Therefore, the amount of decline and the amount of increase are suppressed as described above. Also 3 (Hz/sec)
If it is increased above this level, mechanical problems such as oil circulation will occur.

In addition, in the present invention, since there is a difference in the decrease and increase widths depending on the capacity of the compressor, etc., when the output frequency is increased sequentially, the upper output frequency per unit time is F1 (Hz/second), and the width is lowered sequentially. When the reduction width is F2 (Hz/sec), the ratio of F1 and F2 is 3F2.
Compressor lock can be prevented by controlling the inverter 3 so that ≦F1≦5F2 (however, F2≦3Hz/sec).

Next, the control method of the present invention will be explained with reference to the flowchart shown in FIG.
The microcomputer 11 compares the temperature signal received from the room temperature with the room temperature set value, and if the temperature has increased, the output frequency up timer in the microcomputer 11 is activated and after a certain period of time, the temperature is increased by a predetermined amount (e.g.
2.0Hz/sec) to increase the output frequency. In addition, if the output frequency is decreasing, the output frequency down timer in the microcomputer 11 is activated, and after a certain period of time has elapsed, the output frequency is decreased by a predetermined amount (e.g.
0.5Hz/sec) to lower the output frequency. By controlling in this manner, it is possible to prevent the electric compressor 4 from being overloaded and to prevent the electric compressor from locking.

<Effects> As is clear from the above description, the present invention provides an air conditioner including an inverter that controls the output frequency and output voltage to an electric compressor, and a control device that controls the inverter. teeth,
a room temperature detector for detecting the room temperature; a room temperature setting board for setting the room temperature; a comparison means for comparing the temperature signal from the room temperature detector and the set temperature of the room temperature setting board; and an inverter based on the comparison result of the comparison means. an operating frequency determining means for determining whether to raise or lower the operating frequency than the current operating frequency; and as a result of the determination by the operating frequency determining means, when increasing the operating frequency, the operating frequency is sequentially increased by a predetermined increase width per unit time. As a result of the determination by the operating frequency increasing means for outputting a signal to the inverter and the operating frequency determining means, when lowering the operating frequency, the amount of decrease in the operating frequency per unit time is determined by the operating frequency when increasing the operating frequency sequentially. and operating frequency down means for outputting to the inverter a signal that is smaller than the increase and is within a degree of decrease that does not overload the compressor.

Therefore, according to the present invention, for example, when the room temperature setting is increased during cooling operation, the load becomes smaller and the operating frequency is lowered. At this time, the operating frequency is gradually lowered. Since the inverter is controlled so that the amount of decrease in the operating frequency per unit time is smaller than the amount of increase when the operating frequency is increased sequentially, the refrigerant compression cycle ( (discharge pressure) can be sufficiently followed, the refrigerant compression cycle can be prevented from becoming overloaded, and the electric compressor can be prevented from locking up.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an air conditioner showing an embodiment of the present invention, FIG. 2 is a control flowchart, and FIG. 3 is a diagram showing the relationship between discharge pressure and electric compressor maximum torque with respect to the same output frequency. FIG. 4 is a diagram showing the relationship between discharge pressure and output frequency over the same period of time, and FIG. 5 is a functional block diagram of the air conditioner control device according to the present invention. 1: AC power supply, 2: converter, 3: inverter, 4: electric compressor, 5: control device, 6: indoor heat exchanger, 7: pressure reducer, 8: outdoor heat exchanger, 9: refrigerant compression cycle, 11 : microcomputer,
12: Inverter drive unit.

Claims (1)

[Scope of Claims] 1. An air conditioner including an inverter that controls the output frequency and output voltage to an electric compressor, and a control device that controls the inverter, wherein the control device includes: a room temperature detection device that detects the room temperature. a room temperature setting board for setting the room temperature; a comparison means for comparing the temperature signal of the room temperature detector with a set temperature of the room temperature setting board; an operating frequency determining means for determining whether to raise or lower the operating frequency; and a signal to the inverter to sequentially increase the operating frequency by a predetermined increase amount per unit time when increasing the operating frequency as a result of the determination by the operating frequency determining means. As a result of the determination by the operating frequency increasing means to output and the operating frequency determining means, when lowering the operating frequency, the amount of decrease in the operating frequency per unit time is smaller than the amount of increase when increasing the operating frequency sequentially, and An air conditioner comprising an operating frequency reduction means for outputting a signal to the inverter to reduce the frequency to an extent that does not cause overload of the compressor.