JP3818082B2 - Inverter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an inverter having a semiconductor element as a main circuit switch element, and more particularly to a protection device for air-cooling a semiconductor element by on / off control of a fan.
[0002]
[Prior art]
FIG. 4 shows a configuration example of an inverter provided with this kind of protection device. The inverter main body converts alternating current power into direct current by the rectifier 1, smoothes it by the electrolytic capacitor 2, obtains an alternating current output in which the voltage and frequency are controlled from the direct current by the inverse converter 3, and supplies the alternating current output to the motor 4 as a load. The PWM control circuit 5 compares the motor speed command with the detection signal of the speed detector 6 of the motor 4, and further obtains the gate signal of the inverse converter 3 with a PWM waveform.
[0003]
The protective device 7 monitors the voltage and current in the operation of the inverter, and obtains a protective output such as output limitation of the inverter and circuit breaker disengagement by detecting overcurrent, overvoltage, and undervoltage. The protection device 7 is provided with a temperature protection function of a semiconductor element provided in the inverse converter 3 as another protection function.
[0004]
This temperature protection function will be described. The inverse converter 3 is equipped with a plurality of (for example, 6 arms) semiconductor elements 9 mounted on the heat sink 8 and is turned on / off by the gate signal. The element 9 is prevented from being thermally destroyed. An air cooling fan 10 is provided around the heat sink 8. Further, the thermistor 11 as a temperature detector is brought into contact with the heat sink 8.
[0005]
The protection device 7 monitors the temperature Th of the heat sink 8 detected by the thermistor 11, and protects the semiconductor element from overheating by controlling the fan 10 to turn on when the temperature Th exceeds the on-condition temperature Ton of the fan 10. Then, when the temperature Th is equal to or lower than the off-condition temperature Toff of the fan 10, the fan 10 is controlled to be turned off to suppress the power consumption of the fan.
[0006]
[Problems to be solved by the invention]
(1) Problems of the temperature cycle In the conventional temperature protection system, the fan is controlled only based on the detected temperature of the heat sink 8 without considering the ambient temperature Ta of the inverter. Therefore, the temperature of the heat sink 8 is low when the ambient temperature Ta is low. Even if the increase value (ΔT = Th−Ta) increases, the fan is not controlled to be turned on. For example, when Ton = 60 ° C. and Ta = 0 ° C., the fan is not controlled to turn on until ΔT = 60 ° C.
[0007]
For this reason, for example, when the inverter repeats intermittent operation and acceleration / deceleration operation of the motor 4 and the temperature of the heat sink 8 repeats the temperature cycle of 0 ° C. → 60 ° C. → 0 ° C., the semiconductor element 9 attached to the heat sink 8 There is a risk of destruction due to thermal fatigue.
[0008]
(2) Problem of thermistor abnormality In the conventional temperature protection method, the control of the fan 10 depends on the detected temperature of the thermistor 11, so that if an abnormality occurs in the temperature detection circuit of the thermistor, ΔT exceeds the allowable value. In this case, the fan cannot be turned on, which causes thermal destruction of the semiconductor element 9.
[0009]
As a countermeasure, in the conventional apparatus, when the circuit of the thermistor 11 is opened or short-circuited, it is determined that the abnormality is detected, and a protective operation such as operation stop is obtained. However, when an abnormality occurs in which the circuit of the thermistor 11 is neither open nor short-circuited, for example, a defective attachment of the thermistor 11 to the heat sink 8 occurs, the temperature abnormality cannot be detected and the semiconductor element 9 is thermally destroyed.
[0010]
The objective of this invention is providing the inverter which solved the said subject.
[0011]
[Means for Solving the Problems]
The present invention predicts the ambient temperature of the heat sink from the detected temperature history of a temperature sensitive element such as a thermistor, and controls the fan so that the detected temperature falls within the temperature difference between the on and off conditions of the fan, thereby controlling the temperature cycle. Is to prevent thermal fatigue of the semiconductor element due to, and is characterized by the following configuration.
[0012]
(1) In an inverter provided with a protective device that protects a semiconductor element from thermal destruction by using a semiconductor element mounted on a heat sink as a main circuit switch element, and controlling the heat sink by on / off control of an air cooling fan.
The protection device obtains a deviation ΔT between a minimum temperature within a set time and a current temperature detection value among temperature detection values of a semiconductor element detected by a temperature sensing element attached to the heat sink, and the deviation ΔT is calculated as the fan ΔT. Protective means for controlling the fan to turn on when the temperature difference is larger than the on-condition difference temperature ΔTon of the fan and to turn off the fan when the deviation ΔT is smaller than the fan-off condition difference temperature ΔToff. To do.
[0013]
The protection device controls the fan to turn on when the temperature detection value Th of the temperature sensing element is larger than the fan on-condition temperature setting value Ton, and the temperature detection value Th is the off-condition temperature of the fan. It is preferable to provide protection means for controlling the fan to be turned off when it is smaller than the set value Toff.
[0014]
Further, the present invention associates the integral value of the load current of the inverter with the detected temperature of the temperature sensing element, thereby enabling the detection of an abnormality such as a contact failure of the thermistor circuit and further eliminating the need for the thermistor circuit. Features the configuration.
[0015]
(2) In an inverter provided with a protection device that protects a semiconductor element from thermal destruction by using a semiconductor element mounted on a heat sink as a main circuit switch element, and the heat sink is controlled by on / off control of an air cooling fan.
The protection device includes protection means for obtaining a protection output by determining that the temperature sensing element is abnormal when the integral value I within the set time of the load current i of the inverter is greater than the temperature sensing element abnormality determination value THErr. It is characterized by.
[0016]
The temperature-sensitive element abnormality determination value THerr is such that the temperature deviation ΔT in the operation pattern in which the temperature rise of the semiconductor element is the smallest among the load current patterns within the set time coincides with the fan on-control difference temperature ΔTon. The current integral value is preferable.
[0017]
The protection device controls the fan to turn on when the temperature detection value Th of the temperature sensing element is larger than the fan on-condition temperature setting value Ton, and the temperature detection value Th is the fan off-condition temperature. It is preferable to provide protection means for controlling the fan to be turned off when it is smaller than the set value Toff.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
FIG. 1 is a protection processing flow according to the first embodiment, which is a protection method that solves the above-described temperature cycle problem when the protection device 7 has a software configuration of a microprocessor.
[0021]
The protection device 7 periodically reads the detected temperature Th of the thermistor 11 (S1), and repeats recording and updating the minimum temperature Tmin within a set time (for example, the past 4 hours) for this temperature Th (S2). In the process S2, the minimum temperature Tmin is obtained as the current ambient temperature of the semiconductor element or the heat sink.
[0022]
Next, every time the protection device 7 reads the detection temperature Th of the thermistor 11, it obtains a deviation ΔT (= Th−Tmin) between the detection temperature Th and the minimum temperature Tmin (S3), and this ΔT is the ON condition of the fan 10. It is determined whether or not the temperature is higher than the difference temperature ΔTon (for example, 15 ° C.) (S4). When the temperature is higher than ΔTon, the fan 10 is turned on (S5).
[0023]
When ΔT is smaller than ΔTon, it is determined whether ΔT is larger than an OFF condition difference temperature ΔToff (for example, 15 ° C.) of the fan 10 (S6), and when it is smaller than ΔToff, the fan 10 is turned off ( S7).
[0024]
Therefore, when the heat sink temperature (temperature of the semiconductor element 9) Th detected by the thermistor 11 does not reach the fan on-condition temperature Ton or the off-condition temperature, the fan on / off control is not conventionally performed. Fan control is performed when the upper limit is equal to or higher than the differential temperature ΔTon, or the lower limit is equal to or lower than the differential temperature ΔToff, thereby preventing the semiconductor element from causing a thermal cycle in a wide temperature range and causing thermal fatigue of the semiconductor element. Lifetime can be greatly improved.
[0025]
(Embodiment 2)
FIG. 2 shows a protection processing flow according to the second embodiment, in which a semiconductor element is protected by detecting an abnormality in the thermistor circuit.
[0026]
The protection device 7 periodically reads the output current detection signal of the inverter for overcurrent protection as a load current i (S11), and calculates an integral value I for a set time (for example, 16 minutes) for this load current i. Update (S12). This integrated current value I corresponds to the average value of the load current at the set time, and the magnitude of this load current has a correlation with the heat generation amount of the semiconductor element, and therefore corresponds to the detection signal of the thermistor 11. It is calculated as a quantity.
[0027]
Next, the protection device 7 determines whether or not the current integral value I is larger than the set value THErr (S13). If the current integration value I is larger, it is determined that the thermistor circuit is abnormal, and a protection operation is performed with the output (S14). ). On the other hand, if it is smaller, the thermistor circuit is normal and the process returns to the next protection process.
[0028]
Here, the calculation of the set value THerr will be described. If the current integrated value I matches the set value THerr, it will be erroneously detected unless ΔT> ΔTon. In view of this, the inverter operation is performed with a pattern in which the temperature rise is the smallest among the current patterns of the set time, and an average current at which ΔT = ΔTon at this time is obtained and set as THerr.
[0029]
By adopting this method, even when the thermistor abnormality is detected, it is possible to reliably protect the semiconductor element within the guaranteed operating temperature range.
[0030]
Therefore, according to the present embodiment, it is possible to detect abnormality of the thermistor circuit based on the integrated value of the load current at the set time, and it is possible to reliably detect abnormality such as contact failure of the thermistor circuit, As a result, protection of the semiconductor element is ensured.
[0031]
Instead of obtaining the load current from the output current, the DC current of the inverter may be detected.
[0032]
(Embodiment 3)
FIG. 3 shows a protection processing flow according to the third embodiment, which is a system that enables protection even when the thermistor circuit is abnormal when the protection device 7 has a software configuration of a microprocessor.
[0033]
Similarly to the second embodiment, the protection device 7 periodically reads the current detection signal of the inverter DC circuit as the load current i (S21), and uses the integrated value I for a set time (for example, 16 minutes) for the load current i. Calculate and update (S22).
[0034]
Next, every time the protection device 7 calculates the current integral value I, it determines whether or not the integral value I is larger than the on-condition current setting value Ion of the fan 10 (S23). The fan 10 is turned on (S24).
[0035]
When I is smaller than Ion, it is determined whether I is larger than the off-condition current setting value Ioff of the fan 10 (S25). When I is smaller than Ioff, the fan 10 is controlled to be turned off (S26).
[0036]
Here, the current set value Ion is calculated by performing inverter operation using a pattern in which the temperature rise is the largest in the current pattern at the set time, and setting the current integrated value where ΔT = ΔTon is Ion. Similarly, the current set value Ioff is calculated by performing inverter operation with a pattern in which the temperature rise is the largest in the current pattern at the set time, and setting the current integral value where ΔT = ΔToff is Ioff.
[0037]
Therefore, instead of the fan control based on the heat sink temperature (temperature of the semiconductor element 9) Th detected by the thermistor 11, the fan control based on the average value I of the load current i can be performed. Detection is not necessary.
[0038]
In addition, although each embodiment until the above shows the temperature protection system of the reverse converter 3, when replacing with the rectifier 1 and providing the forward converter of a semiconductor element structure, it applies to protection of this forward converter, and is equivalent The effect can be obtained. Although the protection device has a software configuration, it is needless to say that these can be replaced with a hardware configuration. Further, each embodiment is used in combination with a conventional protection method, so that the protection of the semiconductor element becomes more effective. Although the thermistor is shown as the temperature detection element, it can be replaced with another temperature sensing element, and the inverter control method is not limited to the PWM method. Furthermore, the load is not limited to the motor.
[0039]
【The invention's effect】
As described above, according to the present invention, the ambient temperature of the heat sink is predicted from the detected temperature history of the temperature sensing element, and the fan is controlled so that the detected temperature falls within the fan ON / OFF condition differential temperature. It is possible to prevent the element from being destroyed by thermal fatigue due to a temperature cycle applied to the element.
[0040]
In addition, according to the present invention, since the integral value of the load current of the inverter is protected in correspondence with the detected temperature of the temperature sensing element, it is possible to detect abnormality such as contact failure of the thermistor circuit, and thermistor circuit Is no longer necessary.
[Brief description of the drawings]
FIG. 1 is a protection processing flow according to a first embodiment of the present invention.
FIG. 2 is a protection processing flow according to the second embodiment of the present invention.
FIG. 3 is a protection processing flow according to a third embodiment of the present invention.
FIG. 4 is a configuration example of an inverter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Rectifier 2 ... Electric field capacitor 3 ... Inverter 4 ... Motor 5 ... PWM control circuit 7 ... Protection apparatus 8 ... Heat sink 9 ... Semiconductor element 10 ... Fan 11 ... Thermistor

Claims (2)

In an inverter equipped with a protection device that protects the semiconductor element from thermal destruction by turning on and off the air cooling fan as a main circuit switch element, the semiconductor element mounted on the heat sink.
The protection device obtains a deviation ΔT between a minimum temperature within a set time and a current temperature detection value among temperature detection values of a semiconductor element detected by a temperature sensing element attached to the heat sink, and the deviation ΔT is calculated as the fan ΔT. Protective means for controlling the fan to turn on when the temperature difference is larger than the on-condition difference temperature ΔTon of the fan and to turn off the fan when the deviation ΔT is smaller than the fan-off condition difference temperature ΔToff. To inverter. The protection device includes protection means for obtaining a protection output by determining that the temperature sensing element is abnormal when the integral value I within the set time of the load current i of the inverter is greater than the temperature sensing element abnormality determination value THErr. The inverter according to claim 1 .

Images