JPS60121991A - Inverter controlled air conditioner - Google Patents

Abstract

PURPOSE:To enhance the workability even if slight capacity is sacrificed. by providing a thermistor in a heat sink unit of an output transistor and inputting the temperature of a heat sink unit to a controller. CONSTITUTION:When a comparator 13 judges that the signal from a heat-sensitive element 15 becomes the first set value 14a due to the temperature rise of a heat sink unit 4 during the operation of an inverter, the inverter is not immediately stopped, but the operating frequency F is decreased to continue the operation. Further, when the temperature of the unit 4 rises to increase to the value corresponding to the second set value 14b, an output drive signal 12 is controlled to become the minimum frequency in order to protect the output transistor 3 in the inverter device against the thermal damage.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention converts alternating current power into direct current, and further converts this direct current into alternating current power whose frequency can be changed, thereby controlling a compressor motor. The present invention relates to an inverter-controlled air conditioner.

[Prior art]

FIG. 1 is an f diagram showing -fu of a conventional inverter device. In the figure, 1 is a rectifier circuit, 2 is a smoothing capacitor,
3 is an output transistor, 4 is a heatsink for the output transistor, 5 is a compressor motor that becomes the negative side of the inverter, 6 is a drive signal generation circuit provided in the heatsink 4 to generate a piezo, and 1o is a determination circuit. , 11 is an overcurrent detection circuit that inputs a signal from the thermal detector 6 and detects whether or not an overcurrent has flowed;
This is an output drive signal from the 12-digit drive MB signal generation circuit 9 to the output transistor 3.

The inverter device that controls the conventional air leg kimono Ult is configured as described above, and drives the output transistor 3 using a sine wave approximation method, a pulse width f modulation method, etc., and changes the output frequency to control the load. The rotation speed of the compressor motor 5 is controlled.

As shown in FIG. 3, V/F/'' is generally determined in advance so that when the operating frequency F increases, the output voltage V also increases and V/F becomes approximately constant. The output current also increases as the operating frequency F increases.This output current causes the output transistor to generate heat, and there is naturally an upper limit to the current that can flow.

Generally, the temperature of the transistor case Tc1 The surrounding temperature Ta
There is fi1 between the internal 4% loss P of one transistor and each thermal resistance.
There is a relationship like a formula.

Tc Ta≦P(θ.f〇fa) ・・・・・・［
11 Here, θfa: Thermal resistance between the transistor case and the heatsink θfa: Thermal resistance between the heatsink and the surroundings. These values depend on the inherent characteristics of the transistor, the shape of the heatsink, and heat radiation conditions such as self-cooling and narrowness. Therefore, f
The i1 formula can be replaced by 1 as shown in formula 21.

To≦P (I)・(θcf + θfa) + Ta...
...(2) Here, PCI) : ) Transistor internal loss (function of output current) During inverter operation, the temperature KTo of the output transistor case will never exceed the specified upper limit value under any circumstances. It's impossible.

In the conventional device shown in Fig. 1, during inverter operation,
The compressor motor current is detected by the current detector 7, and when a predetermined current level is reached, the operating frequency F is decreased by a certain amount, so-called stall operation is executed, and the current is further increased to reach the next current level. A heat-sensitive detector 6' that operates at a temperature close to the temperature Tc of the output transistor case, which is allowed 8'G in addition to protection! The operation of the thermal detector 6 is detected by the overcurrent detection circuit 0, and the output drive signal 12 is completely cut off to protect the output transistor. However, in the above-mentioned device, as is clear from equation (2), the temperature T of the output transistor case is determined only by the output current. cannot be determined, and the temperature of the surrounding area 'f'as increases due to the increase in thermal resistance θf between the radiator and the surroundings due to the blockage of the air path of the radiator of the output transistor. The disadvantage is that it takes a considerable amount of time until the heat sensitive detector 6 is restored and operation can be resumed because the temperature rises to the allowable upper limit value.

[Summary of the invention]

This invention was made with the aim of improving such drawbacks, and the radiator is provided with a heat-sensitive element such as a Leemister, and the temperature of the radiator is continuously detected. When the temperature of the radiator reaches the set value, the inverter's operating frequency is lowered and operation continues with the inverter's operating capacity somewhat reduced.Even in this state, the radiator's temperature still rises. However, we are proposing a device that ensures only the minimum amount of operation by setting the second set value for the first and second soil limit values to the minimum frequency.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 2 is a diagram showing an embodiment of the present invention.

The forward numbers 1-5, 7-9, 11 and 12 are completely the same as those in the conventional device. 10 is a judgment circuit, 13
14a is a first set value, 14b is a second set value, and 15 is a heat sensitive element such as a thermistor provided in the heat radiator 4.

In the inverter device configured as described above, the temperature of the radiator 4 naturally rises gradually during normal operation without the current detector 7 detecting overcurrent or overcurrent. The increased temperature value of the heat radiator 4 is input to the comparison circuit 13 in the control circuit 8 by the heat sensitive element 15 provided in the heat radiator 4.

There are two comparison circuits 13, each with a different setting value 14a.
, 14b are given. The first setting value 14a corresponds to a value several degrees below the allowable temperature rise value in the output transistor 3, and the second setting value 14bH
It is set to a value corresponding to the allowable temperature rise value in .

In the above state, when the comparator circuit 13 determines that the temperature of the heat radiator 4 has risen and the signal from the heat sensitive element 15 has reached the first set value 14aK while the inverter is operating, the inverter operation is immediately stopped. Instead of stopping, the operating frequency 1 is maintained at a constant frequency for a preset period of time.
Continue driving by lowering i''. In this way,
Of course, the rotational speed of the compressor motor 5 will decrease by a certain amount, but if the load is a compressor motor or blower motor (not shown), it is much more useful than completely stopping operation. is. During operation with the frequency reduced in this way, the temperature of the radiator 4 further increases and the second set value 1
4b, when the Q value from the thermal element 15 increases, the output transistor 3 in the inverter device increases.
In order to protect the output drive signal 12 from thermal damage, the output drive signal 12 is controlled to the minimum frequency, and the output drive signal 12 is operated with the output Ik sufficiently reduced.

〔Effect of the invention〕

As explained above, in the inverter device, a heat sensitive element such as a thermistor is provided in the heat sink of the output transistor, and the temperature of the heat sink is inputted to the control circuit, and the temperature ta1 of the heat sink and the second set value are set. The useful effect is that it is possible to increase the operating rate even if some capacity is sacrificed by continuing the operation with the operating frequency reduced by a fixed frequency for a fixed period of time.

[Brief explanation of drawings]

Figure 1 is a block diagram showing a conventional inverter device, Figure 2 is a block diagram showing a conventional inverter device.
The figure is a block diagram showing an inverter device according to an embodiment of the present invention, and FIG. 3 is a graph showing the relationship between the operating frequency, voltage, and current of the inverter. 1... Rectifier circuit, 2... Smoothing capacitor, 3...
Output transistor, 4... Heat sink, 5... Compressor motor, 6... Heat sensitive detector, 7... Current detector, 8...
...Control circuit, 9...Drive signal generation circuit, 10...
Judgment circuit, 11... Overcurrent detection circuit, 12... Output drive signal, 13... Comparison circuit, 14a, 14b...
Setting value, 15... Heat sensitive detection element, 16... AC power supply. In the figures, the same reference numerals indicate the same or corresponding parts. Agent Masu Yumi Oiwa 1 Figure 2

Claims (1)

[Claims] +n In an inverter device having means for variably controlling an AC motor using a variable frequency power supply, and means for detecting the temperature of the semiconductor using a heat-sensitive element provided in a heat radiator of the output semiconductor, When the comparator circuit determines that the set value has been reached, the operating frequency is lowered to the predetermined value, and the input current of the inverter is reduced to a smaller value, A<L, jl(
The inverter-controlled air conditioner is characterized in that the inverter-controlled air conditioner operates at the minimum value of the operating frequency when the comparison 1i; .