JP3198543B2 - Inverter switching element temperature rise detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for detecting a temperature rise of an inverter main circuit switching element which is used for overheating protection of the element.

[0002]

2. Description of the Related Art A conventional temperature rise detection signal of an inverter switching element of this type includes a cooling element which is considered to have a certain temperature difference relationship with a junction temperature of the element, which is a final protection target temperature. A signal for detecting a rise in body temperature from a predetermined value is used. Therefore, as a circuit for detecting a rise in temperature of the switching element, a circuit for detecting and calculating only the temperature of the cooling body is known.

[0003]

The switching elements of the upper and lower arms of each phase of the inverter main circuit in a bridge configuration are usually paired on the same cooling body for each of the upper and lower arms of each phase. The two elements do not conduct and generate heat at the same time, and conduction occurs in one of the elements alternately every positive and negative half cycles of the output waveform of the inverter. Therefore, if the output frequency of the inverter falls within a low range of, for example, 10H or less, and its cycle approaches the heat conduction time constant of the cooling body, the difference in heat generation time between the two switching elements becomes relatively large, and the two switching elements become large. The temperature rises and falls repeatedly according to the heat conduction time constant of the cooling body, and the pulsation becomes remarkable.

However, the temperature detected by the cooling body temperature detector is such that the pulsating fluctuation as described above is averaged through the thermal resistance of the cooling body. Even when the maximum value of the actual value of the junction temperature is shorter than the upper limit set value determined by a predetermined value lower than the absolute maximum rated value of the junction temperature of each element, its absolute maximum rated value is reduced. There was a risk of exceeding. Therefore, in order to reliably perform overheating protection of the switching element using the detection signal of the cooling body temperature detector, it is necessary to set the upper limit set value for the cooling body temperature rise determination sufficiently low.
A wide range of operations regarding the output current or the output frequency of the inverter may be restricted.

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide a temperature rise detection circuit for an inverter switching element which can accurately estimate the element junction temperature and can stably operate a wide range of the inverter. It is.

[0006]

In order to achieve the above object, a temperature rise detection circuit for an inverter switching element according to the present invention is a junction temperature rise detection circuit for a main circuit switching element having a bridge configuration in an inverter. The average value of the output current of the inverter is input, and the value of the saturation voltage between the main electrodes of the element corresponding to the average value of the output current is calculated in accordance with the preset current characteristics, and the saturation voltage value is calculated. Voltage loss calculator for calculating and outputting the product of the average of the output current and the average value of the output current as a saturation voltage average loss, and a preset current ratio with the input of the output current average value and the carrier frequency for PWM calculation as input. Calculating an average loss per switching cycle of the switching element corresponding to the output current average value according to the characteristic; A switching loss calculator for calculating and outputting the product of the value of the carrier frequency as a switching average loss, and a junction cable of the switching element for which the sum of the outputs of the two loss calculators is input and the sum of the losses is set in advance. -Junction thermal resistance
An average value of the temperature difference between the cases is calculated, and a conversion coefficient corresponding to the output frequency of the inverter is calculated in accordance with a preset output frequency characteristic with respect to the inverter. A temperature difference calculator for calculating and outputting the instantaneous maximum value of the temperature difference between the junction case by multiplying by a coefficient, a cooling body temperature detector for the switching element such as a thermistor, and a reader for output data thereof;
The instantaneous maximum value of the calculated junction temperature of the switching element, which is given as the sum of the instantaneous maximum value of the temperature difference calculated by the temperature difference calculator and the cooling body temperature detected by the cooling body temperature detector, is the element. And a comparator that generates an output when the temperature becomes larger than the upper limit set value determined from the absolute maximum rated value of the junction temperature, and the output signal of the comparator is used as a required temperature rise detection signal. And

[0007]

A power transistor will be described below as an example of a switching element of the inverter. Now, the junction temperature T _j Tosureba which the switching element is the sum of the temperature difference between the element cooling of the junction-of the element ΔT and _(jc) and the temperature T _c of the cooling body. The temperature difference between the case of the element and the cooling body is an extremely small value, and is omitted. Here, the aforementioned temperature T _c
Is an object to be detected as an average value, and the temperature difference ΔT _(jc) changes every moment depending on the operation state of the output current or the output frequency of the inverter, and cannot be directly measured, and is estimated. Subject to.

According to the present invention, the output current average value I of the inverter is obtained.
The I _av from _av and its PWM control carrier frequency f _c
And a switching average loss corresponding to both the saturation voltage (V _{CE (sat)} ) and the sum of the two losses is divided by the junction-case thermal resistance of the switching element to obtain the ΔT. an average value [Delta] T _{(jc) av} of _(jc), obtained in advance from the further maximum value [Delta] T _{(jc) max} and the average value [Delta] T _{(jc) av} and the conversion coefficient K of the output frequency f _m of the [Delta] T _(jc) the maximum value determined by _{ΔT (jc) max = K ·} ΔT (jc) av the relationship, sought as _{T j = T c + ΔT (} jc) max by the specification and determines according to the functional relation that is and with a T _j are those that form its protected temperature as required of the switching element junction temperature. That indirect by the upper limit set value the temperature T _c conventional, such as by forming a direct comparison object value of the expected maximum value of the operational temperature T _j is in determining that corresponds to the junction temperature absolute maximum rating The purpose is to improve the accuracy and responsiveness of the temperature rise protection as compared with the comparison.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the block diagram of FIG. 1 and the characteristic diagrams shown in FIGS. The following description is for the case where the switching element is a power transistor. First, in FIG.
Is a V _CE loss calculator which receives the average value I _av of the output current of the inverter as an input and obtains a collector saturation voltage V _{CE (sat)} corresponding to the I _av according to a preset current characteristic. As a product of the two, the saturation voltage average loss corresponding to the _Iav is calculated and output. The 2 is the switching loss calculator, the I _av and the inverter - switching of the switching element corresponding to the I _av accordance-current characteristic which is set in advance as input and PWM calculation carrier frequency f _c of the data in which it calculates the average loss per cycle operation output the product of the f _c and the average loss per the cycle as the switching average loss. Reference numeral 3 denotes a temperature difference calculator which receives the sum of the outputs of the two loss calculators 1 and 2 as an input and divides the sum of the losses by a preset thermal resistance between the junction case and the switching element. and the element junction to case and - as well as calculating the mean value ΔT _{(jc) av} of rce temperature difference, inverter pairs is preset - data output frequency f _m characteristic conversion from the inverter output frequency f _m coefficients according K _Is calculated and the instantaneous maximum value ΔT _{(jc) max} of the junction-case temperature difference obtained by multiplying the average temperature difference ΔT _{(jc) av} by the conversion coefficient K is output. 4 is a thermistor for detecting the cooling body temperature Tc of the switching element, and 5 is a thermistor.
It is a reader for the output data of the mister.

Next, the comparator 6 determines the instantaneous maximum value Δ of the temperature difference.
T _{(jc) max} and the calculated junction temperature T of the switching element, which is given as the sum of the cooling body temperature _Tc.
j is a comparator which emits its output if it becomes larger than the upper limit set value T _ju which is determined from the junction temperature absolute maximum rating of the device, the comparator 7 is the cooling body temperature T _c is the upper limit a comparator which emits its output if it becomes larger than the set value T _cu, required temperature rise detection signal with a output signal S _h of the OR element 8 for calculating the logical sum receives the output of both said comparators and No. As shown in the figure, the detection of the temperature rise related to the cooling body temperature _Tc using the comparator 7 is as follows.
This is supplementary to use the output signal of the comparator 6 as a required temperature rise detection signal, and the comparator 7 and the OR element 8 associated therewith can be omitted.

[0011] Next Fig. 2, the inverter - a collector current of the switching element corresponding to the average value I _av of the motor output current and I _c, the collector saturation voltage V as being a linear relationship with said I _c FIG. 4 is an example of a characteristic diagram in a case where _{CE (sat)} is approximately displayed, and shows characteristics previously set in the V _CE loss calculator 1. FIG. 3 is an example of a characteristic diagram when the average loss E _{sw of} each switching cycle of the switching element is approximately displayed assuming a linear relationship with the I _c, and is set in the switching loss calculator 2 in advance. It shows the characteristic which is. FIG. 4
Is the instantaneous maximum value ΔT of the junction case temperature difference of the switching element from the average value ΔT _{(jc) av} of the junction case temperature difference of the switching element.
_(jc) versus about conversion coefficient K for calculating the _max inverter - are those preset in the data output frequency f _m characteristics are illustrative of the temperature difference calculator 3.

[0012]

According to the present invention, inverter - relates junction temperature rise detecting circuit of the main circuit switching device which forms the bridge structure in the data, inverter - pairs of the element as an input the mean value I _av of the motor output current saturation A saturation voltage loss calculator for calculating and outputting a voltage average loss, the _Iav and PWM
A switching average loss calculator that inputs the carrier frequency f _c for the calculation computes outputs switching average loss of the device, the output sum of the both losses calculator junction to case of the device - dividing rce thermal resistance temperature by multiplying the output frequency f _m by the conversion coefficient K which is defined in the characteristics of the data to the average value of the temperature difference - the inverter as well as calculating an average value of rce temperature difference - the junction to case and A temperature difference calculator for calculating and outputting the instantaneous maximum value of the difference, a cooling body temperature detector such as a thermistor and a reader for reading the output data thereof, and the calculated instantaneous maximum value of the temperature difference is detected. By providing a comparator for comparing the calculated junction temperature of the element given as the sum with the cooling body temperature and its upper limit set value, and using the output signal of the comparator as a required temperature rise detection signal, , The calculated junction temperature itself of the switching element, which is estimated every moment according to the operating state of the inverter, can be compared with a predetermined temperature upper limit set value. The accuracy and responsiveness of the temperature rise protection can be improved as compared with the indirect comparison via temperature, and therefore, the inversion is also possible.
It is possible to expand the operating range related to the output current or output frequency of the motor.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a switching element collector saturation voltage vs. collector current characteristic applied to FIG.

FIG. 3 is a graph showing switching loss vs. collector current characteristics of the switching element applied to FIG. 1;

FIG. 4 is a graph showing an instantaneous maximum value of a temperature difference between a switching element junction case and a conversion coefficient between the average values thereof and an inverter output frequency characteristic applied to FIG. 1;

[Explanation of symbols]

1 V _CE loss calculator 2 Switching loss calculator 3 Temperature difference calculator 4 Thermistor 5 Thermistor data reader 6 Comparator 7 Comparator 8 OR element

Claims (1)

(57) [Claims] 1. A junction temperature rise detection circuit of a main circuit switching element having a bridge configuration in an inverter, wherein an average value of the output current of the inverter is input and the average temperature of the output current is determined according to a preset current characteristic. A saturation voltage loss calculator that calculates a value of the saturation voltage between the main electrodes of the element corresponding to the output current average value and calculates and outputs a product of the saturation voltage value and the output current average value as a saturation voltage average loss; Receiving the output current average value and the carrier frequency for PWM calculation as input, calculating an average loss per switching cycle of the switching element corresponding to the output current average value in accordance with a preset current characteristic, and calculating the cycle. A switching loss calculator that calculates and outputs the product of the average loss for each and the value of the carrier frequency as a switching average loss, Junction of the switching element which is set in advance the loss sum as input the sum of the outputs of both loss calculator,
The junction temperature is calculated by dividing the average value of the temperature difference between the junction and the case by dividing by the thermal resistance between the cases and calculating the conversion coefficient corresponding to the output frequency of the inverter in accordance with the preset output frequency characteristic with respect to the inverter. Multiplying the average value of the temperature difference between the cases by the above conversion coefficient to obtain a junction;
A temperature difference calculator for calculating and outputting the instantaneous maximum value of the temperature difference between the cases; a cooling body temperature detector for the switching element such as a thermistor; and a reader for reading output data thereof; The instantaneous maximum value of the calculated junction temperature of the switching element, which is given as the sum of the calculated instantaneous maximum value of the temperature difference and the cooling element temperature detected by the cooling element temperature detector, is the absolute maximum junction temperature rating of the element. And a comparator for generating an output when the upper limit set value determined from the value is larger than the upper limit set value, wherein an output signal of the comparator is used as a required temperature rise detection signal. Element temperature rise detection circuit.