JPH01300076A - Air conditioner - Google Patents

Abstract

PURPOSE:To distinguish a high load time from a lock time to protect a motor at the high load time of motor and lock time of compressor by increasing the output frequency of inverter at a time until the difference appears in the input currents of inverter. CONSTITUTION:The output frequency of inverter 6 is controlled at a controller 20 outside a room according to air conditioning load obtained by a controller 10 inside the room and a motor 7 is operated to drive a compressor. The control ler 20 inputs voltages of both ends of shunt resistor 5 and detects that the input voltage of inverter 6 is excessive. The controller 10 drives a power relay 3 to nonexcitation conditions at a circuit 11 to open a contact 3a. In this case, an operation frequency changing means 22 is added to the part 20. Until the difference in input currents of inverter 6 appears at high load time of motor 7 and lock time of compressor, the output frequency of inverter 6 is raised at a time.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) This invention operates a compressor at variable speed by controlling the output frequency of an inverter, and also detects the input terminal of the inverter. This invention relates to an air conditioner that cuts off human power to the inverter when the input current exceeds a predetermined value.

(Prior Art) FIG. 5 is a block diagram showing the configuration of a conventional air conditioner of this type. In the figure, the AC side of a converter 4 is connected to a plug 1 connected to a commercial power outlet via a fuse 2 and a contact 3a of a power relay 3. This converter 4 consists of 4 diodes and 2
A voltage doubler rectifier circuit is formed with two capacitors, and further,
The rectified voltage is smoothed by another capacitor, and a stable DC voltage is output from the DC side. The DC side of the converter 4 is connected to the DC side of an inverter 6 via a shunt resistor 5, and the compressor drive motor 7 is connected to the AC side of the inverter. Here, the inverter 6 is made up of six transistors each having a diode connected in antiparallel in a Graetz connection, and is sequentially turned on and off by an outdoor control section to be described later.
Variable voltage, variable frequency alternating current is supplied to the compressor drive motor 7 ◎ It also inputs signals from various sensors, switches, setting devices, etc. to control the indoor fan motor, adjust room temperature and settings. An indoor control section 10 that displays modes and the like on a display, and an outdoor control section 20 that controls the outdoor fan motor and inverter 6 are connected so that signals can be exchanged. Then, the outdoor control unit 20 controls the output frequency of the inverter 6 according to the air conditioning load determined by the indoor control unit 10 to operate the compressor under capacity control, while the dry operation command lowers the output frequency of the inverter 6 to the lowest Perform the so-called lowest frequency operation. The outdoor control unit 20 also includes an overcurrent detection circuit 21 that detects when the input current of the inverter 6 becomes excessive by manually controlling the voltage across the shunt resistor 5, and the indoor control unit 10 receives an overcurrent detection signal. A relay drive circuit 11 is provided which de-energizes the power relay 3 and opens the contact 3a when the power relay 3 is received. Therefore, when the compressor is locked and the motor stops, an excessive current flows through the inverter 6. In this case, the overcurrent detection circuit 21 detects this, and the relay drive circuit 11 disables the power relay 3. The compressor drive motor 7 is protected by being in an excited state.

(Problems to be Solved by the Invention) In the air conditioner described above, even when the air conditioner is operated at the lowest frequency, if the compressor is in a locked state, the number of input terminals of the inverter increases as a matter of course. However, this value is not much different from the current of the compressor drive motor during high frequency, high load operation, and if you try to continue operation under high load conditions, the compressor drive motor will The problem was that it was not possible to protect the

This invention was made to solve the above problems, and provides an air conditioner that can reliably protect the compressor drive motor from compressor locking even when the compressor is operated at a low frequency. The purpose is to obtain.

[Structure of the invention]

(Means for Solving the Problems) This invention provides that during low frequency operation of the compressor, there is a difference in the input current of the inverter between when the compressor drive motor is in a high load state and when the compressor is in a locked state. Until the value that appears,
The compressor is equipped with a frequency changing means for temporarily increasing the output frequency of the inverter, and cuts off the input to the inverter when the input current of the inverter exceeds a value corresponding to a locked state of the compressor.

(Function) In this invention, during low frequency operation of the compressor, up to a value at which a difference appears at the input terminal of the inverter between when the compressor drive motor is in a high load state and when the compressor is in a locked state, Since overcurrent is detected by temporarily increasing the output frequency of the inverter, when the compressor becomes locked, it can be distinguished from overload operation, and the compressor drive motor can be reliably protected.

(Embodiment) FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, the same reference numerals as in FIG. The difference from FIG. 5 is that an operating frequency changing means 22 is provided. Originally, this outdoor control unit 20 included a microcomputer, and the operating frequency changing means 22 was a new function added by changing the software.

Here, the operating frequency changing means 22 is for increasing the operating frequency for a short period of time at predetermined time intervals when the compressor is operating at the lowest frequency. This will be explained below.

First, when the air conditioner is operated in a dry manner, the output frequency of the inverter 6 gradually increases at the start of operation and is maintained at approximately 30 Hz, as shown by the broken line B in FIG. In this state, there is no significant difference between the current when the compressor is locked and the current when the compressor is under high load, so it is difficult to detect whether the compressor is locked. The operating frequency changing means 22 temporarily increases the operating frequency to approximately 60 Hz during the lowest frequency operation, as shown by the solid line A in FIG. 2, and maintains this frequency for approximately 15 to 20 seconds.
Furthermore, when 60 minutes have passed since the time when the frequency returned to 30 Hz, the same frequency change is performed for a total of 40 seconds. The operating frequency of 60 Hz in this case was selected as a value at which a difference appears in the input current of the inverter 6 when the compressor drive motor is in an overload state and when the compressor is in a locked state. FIG. 2 shows that such frequency changes are performed approximately every 60 minutes.

FIG. 3 shows the input current of the inverter 6 and the overcurrent detection state of the overcurrent detection circuit 21 due to the frequency change. That is, if the compressor is not in the locked state, the input current to the inverter 6 changes slightly depending on the frequency, as shown by the broken line, but the magnitude is less than IOA. However, when operating at the lowest frequency with the compressor locked, the input terminal of the inverter 6 increases proportionally as the frequency increases, as shown by solid line C.
When the magnitude exceeds 16A, the overcurrent detection circuit 21
sends an overcurrent detection signal to the indoor control unit 10. At this time, the relay drive circuit 11 receives the overcurrent detection signal and de-energizes the power relay 3 to cut off the input current, so the input current drops to zero.

FIG. 4 shows the overcurrent detection circuit 21 and the operating frequency changing means 2.
2 is a flowchart showing the processing procedure of the microcomputer related to the second embodiment. In the figure, if dry operation is started in step 101, a frequency change is performed in step 102 to increase, maintain, and decrease the frequency for 40 seconds. In step 103, it is determined whether or not the human power of the inverter 6 has caused an overcurrent due to this frequency change. If it is determined that an overcurrent has occurred, an operation stop command is output to the indoor control unit 10 in step 107.

If no overcurrent is detected, the frequency is set to 30Hz in step 104.
Dry operation is performed at step 105, and a 60-minute timer is activated. Then, in step 106, it is determined whether or not this timer has timed up. If it is determined that the timer has timed up, the frequency is changed again for 40 seconds in step 102, and the same process is repeated thereafter.

Thus, according to this embodiment, even when the compressor is operated at the lowest frequency, if the compressor is in a locked state, the compressor drive motor 7 can be protected by overcurrent detection of the inverter 6.

In the above embodiment, protection of the compressor drive motor against the locked state of the compressor has been explained. However, even when the compressor drive motor 7 does not rotate due to an open phase of the inverter 6, it can be protected by appropriately selecting the operating frequency. , the compressor drive motor 7 can be protected in the same way.

Furthermore, in the above embodiment, protection of the electric motor during dry operation at the lowest frequency was explained, but it is clear that protection can also be provided when the compressor is operated at low speed during air conditioning control.
The present invention can also be applied to devices that operate at a so-called low frequency other than the lowest frequency operation.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, during low frequency operation of the compressor, the input terminal of the inverter is Overcurrent is detected by temporarily increasing the inverter's output frequency to a value where a difference appears, so when the compressor locks up, it can be distinguished from high-load operation, and this allows the compressor drive motor to operate reliably. It has the effect of being able to protect the

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of an embodiment of Hoko's invention, Figs. 2 and 3 are time charts for explaining the operation of the embodiment, and Fig. 4 is an explanation of the operation of the embodiment. FIG. 5 is a block diagram showing the configuration of a conventional air conditioner. 3...Power relay, 4...Converter, 5...
Shunt resistor, 6... Inverter, 7... Compressor drive motor, 10... Indoor control section, 11... Relay drive circuit, 20... Outdoor control section, 21... Overcurrent detection circuit , 22... Operating frequency changing means. Applicant's agent Sato -O Time (minutes) Figure 2 Time minutes Figure 3 Proceedings amendment band June 24, 1988 1 Indication of the case 1988 Patent application No. 128779 2 Name of the invention Air conditioner 3 Relationship with the amended person case Patent applicant (307) Toshiba Corporation (and 1 other person) 4 agents

Claims (1)

[Claims] In the air conditioner, the compressor is operated at variable speed by controlling the output frequency of the inverter, and the input current of the inverter is detected, and when the input current exceeds a predetermined value, the input of the inverter is cut off. During low frequency operation of the compressor, the output frequency of the inverter is temporarily increased to a value that causes a difference in the input current of the inverter between when the compressor drive motor is in a high load state and when the compressor is in a locked state. An air conditioner comprising a frequency changing means for increasing the frequency, and cutting off input to the inverter when the input current to the inverter exceeds a value corresponding to a locked state of the compressor.