JPS6074967A - Inverter device - Google Patents

Abstract

PURPOSE:To raise the workability of an inverter device by providing a thermal sensitive element in a heat sink unit of an output transistor, and lowering the operating frequency of an inverter when the temperature of the unit becomes the prescribed value or higher, thereby continuing the operation. CONSTITUTION:A thermal sensitive element 15 such as a thermistor is mounted in a heat sink unit 4 of an output transistor 3 to continuously detect the temperature of the unit 4. The output of the element 15 is inputted to a comparator 13, and when the output reaches the first discriminated value, the operating frequency is reduced by the prescribed frequency during the predetermined or prescribed certain time, thereby continuing the operation. When the temperature of the unit 4 further rises so that the output of the element 15 becomes the second discriminated value, an output drive signal 12 is completely interrupted to protect the transistor 3, thereby stopping the inverter.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an inverter device that converts alternating current into direct current, and further converts this direct current into alternating current with variable frequency to control the variable speed of an alternating current motor.

[Prior art]

FIG. 1 is a diagram showing an example of a conventional inverter device.
In the figure (11 is the rectifier circuit, (2) is the smoothing capacitor, (3) is the output transistor, (4) is the heat sink for the output transistor, (5) is the motor that is the load of the inverter, and (6) is the heat sink mentioned above. A heat-sensitive switch, such as a bimetallic or thermal reed switch, mounted on a device, (7)
is a current detector, (8) is a control circuit, (9) is a drive signal generation circuit for operating the output transistor, tlo
) is a determination circuit that determines whether the heat-sensitive switch is activated, (11+ is an overcurrent detection circuit that receives a signal from the current detector and detects whether an overcurrent has flowed, and 02 is from the drive signal generation circuit) This is the output drive signal to the output transistor.

A conventional inverter device is configured as described above.

The output transistor (3) is driven by a sine wave approximation PWM method, etc., and the rotation speed of the load motor (5) is controlled by changing the output frequency.

As shown in Fig. 3, when the operating frequency F increases, the output voltage V is also increased to keep the frequency constant at 'J/F.
Hatan has been decided. 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.

In general, the case temperature T of a transistor. The relationship between the ambient temperature Ta, the internal loss P of the transistor, and each thermal resistance is (1)
5/There is a labor relationship.

Tc ”a≧P(12of10fa) ---・--
(1) Here θ. f is the thermal resistance of the transistor case heatsink, and θfa is the thermal resistance around the heatsink, which is a constant that is uniquely determined once the transistor model name, the shape of the heatsink, and the heat radiation conditions such as natural cooling or external cooling are determined. It is a value.

Furthermore, the internal loss P of the transistor depends on the output current (2). Therefore, equation (1) can be rewritten as equation (2).

To≧P(1)・(θcf+θfa) + Ta −
・= −−12JP (1) Transistor internal loss Function of current T During inverter operation, transistor case temperature T in any case. cannot exceed a certain upper limit.

In the conventional device shown in Fig. 1, during inverter operation,
The motor output current is detected by the current detector (7), and when the current level reaches a certain level, the operating frequency is reduced, so-called stall operation, or when the current increases further and reaches the next judgment label (l ■The output drive signal of
~ or disconnected to protect the transistor. In addition to this current protection, a heat-sensitive switch (6) that operates at a temperature close to the permissible transistor case temperature is provided, and the operation of this heat-sensitive switch is detected by the judgment circuit ([) and the output drive signal of α is detected. However, in the above-mentioned device, as can be seen from equation (2), the transistor case temperature T changes only from the current.

1.Thermal resistance θf between the surroundings of the heatsink due to the ambient temperature Ta and the blockage (blockage) of the ventilation path for heat radiation of the transistor
Due to the increase in a, the transistor case temperature rises to the allowable upper limit, the heat-sensitive switch (6) is activated, and the inverter operation is completely stopped.The heat-sensitive switch (6) returns to its original state and operation resumes. The drawback was that it took a considerable amount of time to complete.

[Summary of the invention]

This invention was made with the aim of improving such drawbacks, and it involves attaching a heat-sensitive element such as a thermistor to the radiator and continuously detecting the temperature of the radiator. When the radiator temperature reaches the judgment value of 1-, the operating frequency of the inverter is lowered and operation is continued with the inverter capacity somewhat reduced.

Even in this state, the present invention proposes a device that cuts off the output drive signal and stops the inverter operation only when the temperature continues to rise and reaches a second judgment value set close to the allowable upper limit.

[Embodiments of the invention]

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

+1) to (51, +71 to (91, at), α2 are exactly the same as the above conventional device. (13 is a comparison circuit, (14a) is the first judgment value, (14b) is the second judgment value The judgment value, R!9, is a heat sensitive element such as a thermistor attached to the heat sink (4).

In the inverter device configured as above, (7
) When no overcurrent is detected by the current detector and the radiator is operating normally, the temperature of the radiator will naturally gradually rise to 1.

The temperature rise of the radiator is sent to the comparator circuit Q3 in the control board (8) by a heat sensitive element α9 attached to the radiator.

Comparison circuit 0 (there are two, each with a separate judgment value (14a) (1
4b) is given. The judgment value (14a) corresponds to a value several times before the transistor allowable temperature rise value, and the 1 judgment fit (14b) is set to a value corresponding to the transistor allowable temperature rise value.

While the inverter is operating under such conditions, if it is determined that the radiator temperature has risen and the signal from the heat-sensitive element has reached the first judgment value, the inverter does not stop operating immediately, but instead stops at a predetermined time. During a certain period of time, the operating frequency is reduced by a certain amount and operation continues. Of course, this method will reduce the rotation speed of the motor by a certain number of rotations, but if the load is a compressor motor for a refrigerator or a blower motor, this is much more useful than completely stopping the operation.

During operation with one frequency reduced in this way, when the radiator temperature further increases from 1 to 1, the signal from the heat sensitive element α increases until it corresponds to the second judgment value (14b).

In order to protect the transistor (4) of the inverter device from thermal damage, the output drive signal of Q'IJ is completely cut off to stop the inverter.

In the above embodiment, a transistor was used as the output semiconductor, but the same applies even if the transistor is used as the output semiconductor.

〔Effect of the invention〕

As explained above, the present invention provides an inverter device in which a heat sensitive element such as a nermistor is provided in the heat sink of an output transistor, the temperature of the heat sink is sent to a control circuit, and the heat sink temperature is set as a first and a second judgment value. When the first judgment value is reached, the operating frequency is reduced for a certain period of time and the operation is continued.

It is very useful because it has the effect of increasing the operating rate even if it sacrifices some capacity.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a conventional inverter device, FIG. 2 is a diagram showing an embodiment of the present invention, and FIG. 3 is a diagram showing the relationship between the operating frequency, voltage, and current of the inverter. In the figure, (1) is a rectifier circuit, (2) is a smoothing capacitor, (3) is an output transistor, (4) is a heat sink, (
5) is a motor, (6) is a thermal switch, (7) is a current detector, (8) is a control circuit, (9) is a drive signal generation circuit,
+IQ is a judgment circuit, aυ is an overcurrent detection circuit, 02 is an output drive signal, o is a comparison circuit, (14a), (14
b) is a judgment value, (19 is a heat-sensitive element. Note that the same reference numerals in Figure 1 indicate the same - or corresponding parts. Agent Masuo Oiwa Figure 1 Figure 21'-1

Claims (1)

[Claims] In an inverter device that controls the variable speed of an AC motor using a variable frequency power supply, a semiconductor temperature is detected by a heat sensitive element attached to a heat radiator of an output semiconductor, and the semiconductor temperature reaches a first judgment value. When I did. The operation is continued by reducing the operating frequency and reducing the inverter capacity, and when the second judgment value is reached, the drive signal of the output semiconductor is completely cut off and the operation of the inverter device is stopped. Inverter device 1゜ characterized by being configured to protect the inverter device from destruction.