JP3333552B2 - Air conditioner - 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 which determines the occurrence of a compressor lock by detecting an inverter input current.

[0002]

2. Description of the Related Art When performing variable speed control of a compressor motor by V / f control of an inverter device, a so-called locking phenomenon occurs in the compressor due to insufficient rotation torque of the motor or overload of a refrigeration cycle. When such a compressor lock occurs, it is necessary to temporarily stop the operation of the compressor. However, whether or not the compressor has locked has conventionally been determined as follows.

That is, FIG. 6 is a characteristic diagram showing the relationship between the inverter output frequency f and the inverter input current I. The straight line (a) is a straight line (b) when operating at the maximum load.
Is the straight line (c) when compressor lock starts to occur
Is a case where the operation is continued in the compressor locked state. As shown in the figure, since the current values in the respective straight lines are different, it is possible to determine whether or not the compressor lock is currently occurring by detecting the current value at a certain frequency.

In this case, in a region where the frequency is high to some extent, the difference between the current values between the straight lines (a) and (b) is large, so that it is easy to determine the occurrence of lock. Since the difference between the current values is small in the region, it is difficult to determine the occurrence of lock.

Therefore, conventionally, as shown in FIG. 7, in a low frequency region, the inverter output voltage V is set to a level higher than the original level (the dotted line portion in FIG. 7). According to this, even in the low frequency region, FIG.
, The difference between the current values between the straight lines (a) and (b) can be increased, and the occurrence of lock can be easily determined.

[0006]

However, as described above, if the level of the inverter output voltage V is constantly increased in the low frequency range, the compressor is driven with the motor efficiency lowered. This results in increased power loss.

Therefore, in order to minimize such power loss, the voltage V is set to a low level, and the inverter output frequency f is set to a predetermined value (for example, every 10 to 20 minutes). 30 Hz) or more so that the difference in current between the straight lines (a) and (b) in FIG.

However, increasing the output frequency of the inverter in order to determine the occurrence of compressor lock increases the capacity which is originally unnecessary,
From the viewpoint of reduction of power loss and comfort of indoor air conditioning, there is still room for improvement.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an air conditioner capable of effectively reducing power loss without impairing the comfort of indoor air conditioning.

[0010]

According to a first aspect of the present invention, there is provided an air conditioner for controlling a variable speed of a compressor motor by controlling an inverter output voltage and an inverter output frequency of an inverter device. A low frequency region discriminating means for comparing the value of the inverter output frequency with a predetermined set value to determine whether or not the value is within a low frequency region; and When the means is determined to be within the low frequency range, the inverter output voltage is increased so that the compressor motor is over-excited every predetermined time, and the detected value of the inverter input current at that time is predetermined. Compare with a certain set value, if this detection value is greater than or equal to this set value, output a command to stop the operation of the inverter device, On the other hand, when the detected value is lower than the set value, the V / f control means for outputting a command for operating the inverter device for at least a predetermined time with the inverter output voltage at a lower level than at the time of the comparison is provided. It is characterized by having.

In a second aspect based on the configuration of the first aspect, the V / f control means continuously or step-wise controls the inverter output voltage when the detected value is lower than the set value. The minimum value or a value near the minimum value of the detected value of the inverter input current is obtained by increasing or decreasing the inverter input current, and the operation of the inverter device is controlled by the inverter output voltage corresponding to the minimum value or the value near the minimum value. An air conditioner, which outputs a command to be performed only for a predetermined time.

[0012]

In the structure of the first invention, the low frequency region determining means compares the value of the inverter output frequency with the set value to determine whether or not the value is within the low frequency region. If it is determined that it is within the low frequency range, V /
The f control means increases the inverter output voltage so that the compressor motor is over-excited. This allows
Even in the low frequency range, the level of the inverter input current is increased, so that it is easy to determine the occurrence of lock.

The V / f control means compares the detected value of the inverter input current at this time with a set value, and if the detected value is equal to or greater than the set value, determines that a lock has occurred, Outputs an inverter operation stop command.

On the other hand, if the detected value is lower than the set value,
Since it is considered that the lock has not occurred, the operation in the low frequency region is continued as it is. However, the level of the inverter output voltage after the discrimination is set at least lower than the level at the time of the discrimination in order to reduce the power loss.

In the first invention, the level of the output voltage of the inverter after the lock determination is completed is at least lower than the level at the time of the determination. Control is performed so that the voltage level is the minimum necessary level.

That is, when the inverter output voltage is continuously increased or decreased, the inverter input current also changes continuously, so that a minimum value of the detected value of the inverter input current can be found. However, when increasing or decreasing the inverter output voltage in a stepwise manner, the change in the inverter input current also becomes stepwise, so that it is not always possible to find the minimum value, and the value is near the minimum value.

The V / f control means outputs a command to operate the inverter device for a predetermined time based on the inverter output voltage corresponding to the minimum value of the inverter input current or a value near the minimum value thus found. .

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram showing the configuration of the embodiment of the present invention.

In FIG. 1, in a heating mode, a refrigerant discharged from a compressor 1 is sent to an indoor heat exchanger 3 through a four-way valve 2 where heat is exchanged. The refrigerant exiting the indoor heat exchanger 3 is sent to the outdoor heat exchanger 5 through the expansion valve 4, where the heat is exchanged again. The refrigerant that has exited the outdoor heat exchanger 5 is circulated through the four-way valve 2 to the suction port of the compressor 1. In addition, 7 is an indoor fan and 8 is an outdoor fan.

The compressor 1 includes a compressor motor 9
The compressor motor 9 is controlled by an inverter device 10 at a variable speed. The inverter device 10 includes a converter unit 11, a smoothing capacitor 12, and an inverter unit 13,
Converter unit 11 is supplied with AC power from AC power supply 14 .

An inverter control device 14 for controlling the inverter device 10 includes an inverter frequency determining means 16 and V /
An f control unit 17, a low frequency region determination unit 18, and a timer 19 are provided. The inverter frequency determining means 16 receives the room temperature Ta from the room temperature sensor 20 attached to the indoor unit and the room set temperature Ts from the room temperature setter 21. Further, the V / f control unit 17 receives a detection value I of the input current of the inverter device 10 from the current sensor 22.

Next, the operation of the present embodiment configured as described above will be described with reference to the flowcharts of FIGS.

During the operation of the compressor 1, the inverter frequency determining means 16 inputs the room temperature Ta and the set temperature Ts to calculate a deviation (Ts-Ta), and based on the calculation result, a determination signal relating to the inverter output frequency f. To V / f
The data is output to the control means 17 and the low frequency area determination means 18 (step 1). The low frequency region determining means 18 determines whether the frequency f is in the low frequency region by comparing the frequency f with a predetermined set value Fs (step 2). The signal is output to the V / f control means 17. Then, the V / f control means 17
The inverter 13 is controlled so that the frequency f and the standard inverter output voltage V corresponding to the frequency f are obtained (step 3).

If it is determined in step 2 that f is equal to or less than Fs, that is, if it is determined that f is within the low frequency range, the V / f control means 17 performs the following operations as shown in FIG. The inverter 13 is controlled so that the frequency f and the maximum inverter output voltage Vmax corresponding to the frequency f are obtained ( step 4 ). The V / f control means 17 reads the detected value of the inverter input current I at this time from the current sensor 22 (step 5) and compares this current I with the set value Is to determine whether or not the compressor 1 is locked. Is determined (step 6). If I ≧ Is, it is determined that the lock has occurred, and the operation of the inverter device 10 is stopped (step 7).

On the other hand, if it is determined in step 6 that I <Is, the V / f control means 17 changes the inverter output voltage V from the maximum Vmax to the standard V0 (step 8), and reads the current I at that time. At the same time (step 9), it is set in its own memory (step 10). Then, the inverter output voltage V is increased by one step,
(Step 11) The current I at that time is read (Step 12).

Here, the relationship between the inverter output voltage V and the inverter input current I will be described. The relationship between the air conditioning load and the output voltage V and the input current I of the inverter fluctuates according to the load of the refrigeration cycle as shown in FIG. For example,
When the load of the refrigeration cycle is heavy, the highest efficiency point is the current I1 voltage V0 point where the current is the smallest, as shown by the curve A. On the other hand, when the load of the refrigeration cycle is light, the highest efficiency point is the point of the current I1 'and the voltage V-2 as shown by the curve B.

Therefore, the voltage V closest to the highest efficiency point
Can be achieved by taking the following steps.

First, the current I is detected by increasing the current voltage V by one step. If the current I becomes higher than the current before the voltage was increased, the current I is located on the left side of the center of the curve. When the current value decreases, it is found that the current value is on the right side of the center of the curve. Therefore, if the current increases when the voltage is increased, the lower the voltage has the highest efficiency point,
If the current decreases, the highest voltage has the highest efficiency point. Therefore, when the current increases when the voltage is increased, the voltage is decreased by one step until the current changes from the decrease to the increase, and the voltage obtained by increasing the one-step voltage from the point at which the current changes to the increase is the highest efficiency point. Is the voltage V closest to

On the other hand, if the current decreases when the voltage is increased, the voltage is reduced by 1 until the current changes from the decrease to the increase.
The voltage obtained by increasing the voltage step by step and decreasing the voltage by one step from the point where the voltage changes to the increased voltage becomes the voltage V closest to the highest efficiency point.

Steps 13 to 18 and Step 1 in FIG.
Reference numerals 3 to 23 denote steps for finding a minimum point using such a characteristic curve indicating the relationship between V and I.

That is, if the current state is on the curve A where the load of the refrigeration cycle is heavy in FIG.
The current value I1 at the standard voltage V0 is stored as I0 in steps S10 to S10.
The current value I = I2 when the voltage is changed to V1 increased by one step from is read.

Then, in step 13, the standard voltage V
0 at current 0 (= I1) and current I at voltage V1
(= I2). If the current increases, the process branches to step 14, and if the current decreases, the process branches to step 19.

In the state of the curve A, since I1 <I2, the routine proceeds to step 14, where the current value I2 is stored as I0, and the voltage is changed from the current voltage V1 to V0 lower by one step. Here, the current is read again in step 16, and
In step 17, the current value I = I1 at this time and the current value I
Compare 0 = I2. In this comparison, since I <I0, the process returns to step 14 again to decrease the voltage by one step, and the comparison result in step 17 indicates that (storage current I0) <
This is repeated until (detection current I) is reached. In the state of the curve A, the voltage V-1 is a voltage that satisfies (storage current I0) <(detection current I).

If the result of the comparison in step 17 is (storage current I0) <(detection current I), it is determined that the voltage closest to the highest efficiency point is too high by one step, and the voltage is increased by one step in step 18. Let me go step 2
Then, the process proceeds to step 4, and the voltage change is completed. As a result, curve A
In this case, the voltage V0 returned by one step from the voltage V-1 is determined to be the voltage closest to the highest efficiency point.

On the other hand, in step 13 (the storage current I
0) ≧ (detection current I), it is determined that the highest efficiency point is in the voltage direction higher than the reference voltage V0, and in this case, steps 19 to 23 are executed.

As described above, the V / f control means 17 finds the value of the inverter output voltage V that can minimize the inverter input current I, and outputs the voltage signal V and the frequency signal f to the inverter section 13. The timer 19 starts measuring (step 24). When it is determined that a predetermined time (for example, 10 to 15 minutes) has elapsed (step 25), the operation from step 1 onward is repeated again.

As described above, in the configuration of FIG. 1, when operating in the low frequency range, the output voltage of the inverter is increased every 10 to 15 minutes to determine whether or not compressor lock has occurred. However, most of the time, since the inverter is operated at the inverter output voltage that minimizes the inverter input current, power consumption can be reduced,
Power loss can be effectively reduced. Also, since the inverter output frequency is not unnecessarily increased,
The comfort of indoor air conditioning is not impaired.

Although the above embodiment has been described with reference to the case where the voltage V in FIG. 5 is changed stepwise, the voltage V may be changed continuously.

[0039]

As described above, according to the present invention, when operating in the low frequency range, control is performed with the inverter output voltage so that the inverter input current is minimized to determine whether or not compressor lock has occurred. Since the inverter output voltage is increased every predetermined time, power loss can be effectively reduced without impairing the comfort of indoor air conditioning.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation of FIG. 1;

FIG. 3 is a flowchart for explaining the operation of FIG. 1;

FIG. 4 is a characteristic diagram for explaining the operation of FIG. 1;

FIG. 5 is a characteristic diagram for explaining the operation of FIG. 1;

FIG. 6 is a characteristic diagram for explaining a conventional example.

FIG. 7 is a characteristic diagram for explaining a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Compressor 9 Compressor motor 10 Inverter device 16 Inverter frequency determination means 17 V / f control means 18 Low frequency area determination means V Inverter output voltage f Inverter output frequency I Inverter input current

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F25B 49/02 570 F24F 11/02 102 F25B 1/00 361

Claims (2)

(57) [Claims] 1. An air conditioner for controlling a variable speed of a compressor motor by controlling an inverter output voltage and an inverter output frequency of an inverter device, wherein a value of the inverter output frequency is compared with a predetermined set value. By this means, a low frequency region determining means for determining whether or not the value is in the low frequency region, and, when the low frequency region determining means determines that the value is in the low frequency region, the compressor for every predetermined time Increase the inverter output voltage so that the motor is over-excited
Then, the detected value of the inverter input current at that time is compared with a predetermined set value, and when the detected value is equal to or greater than the set value, a command to stop the operation of the inverter device is output. V / f control means for outputting, when the detected value is lower than the set value, a command for operating the inverter device for at least a predetermined time with an inverter output voltage of a lower level than at the time of the comparison. An air conditioner characterized by the following. 2. The air conditioner according to claim 1, wherein the V / f control means increases or decreases the inverter output voltage continuously or stepwise when the detected value is lower than the set value. Thus, a minimum value or a value near the minimum value of the detected value of the inverter input current is obtained, and the inverter device is operated for a predetermined time by an inverter output voltage corresponding to the minimum value or a value near the minimum value. An air conditioner characterized by outputting a command.