JP2002125362A - Method for improving main circuit element life time in semiconductor power converting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve life time of a main circuit element, without deteriorating its controllability. SOLUTION: In a PWM power converting device, the state of a load is monitored. When the load is light, a carrier frequency for PWM is increased, the switching frequency of a main circuit element is increased, the switching loss is increased, and a junction temperature of the element is increased. When the load is heavy, however, the carrier frequency is decreased, the switching frequency of the main circuit element is decreased, the switching loss is decreased and the junction temperature of the element is decreased. The difference in the junction temperatures in the case of a light load and in the case of a heavy load becomes small, so that the power cycle and thermal fatigue life time are improved. The carrier frequency may be changed only when the load is light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for improving the life of a main circuit element in a semiconductor power conversion device.

[0002]

2. Description of the Related Art FIG. 9 shows an example of improving the life of a conventional inverter main circuit element. This inverter main circuit 82 is IGBTa
To IGBTf are the switching elements. The motor drive signal output from the motor control circuit 83 is pulse width-modulated by a PWM generation circuit 84 and drives the bases of the main circuits IGBTa to IGBTf via an IGBT drive circuit 85. It is converted to a three-phase AC and output to the motor 88. Timer set circuit 8
6 and an IGBT heat retention circuit 87 are circuits for extending the life of the IGBT, and a timer setting circuit 86 is provided for the IGBT of the main circuit 82 based on a preset start start time of the motor 88.
The heat retention start time of Ta to IGBTf is calculated. IGBT
When the calculated heat retention start time comes, the heat retention circuit 87 outputs a signal for keeping the IGBT of the main circuit warm, using the PWM generation circuit 8.
4 and the IGBTs are alternately turned on and off at a timing when the IGBTs are not output to the motor 88 to keep the IGBTs Ta-f. As a result, each IGB is
T can be warmed, and the temperature of the IGBT does not rise rapidly even after the motor 88 is operated. Therefore, the temperature change of the IGBT before and after the start of the motor operation can be suppressed to a predetermined range, so that the life of the IGBT is improved. (Japanese Patent Application Laid-Open No. Hei 8-186905).

FIG. 10 shows another conventional example of improving the life of an inverter main circuit element. This inverter device has a power supply 91
The three-phase alternating current is converted to direct current by the forward converter 92, and the direct current smoothed by the capacitor 93 is converted to three-phase alternating current by the inverse converter 94 controlled by the PWM control signal to drive the motor 99.
The carrier signal from the carrier signal generator 95 is input to the carrier frequency variable setting unit 96, and the PWM generation circuit 97 performs pulse width modulation on the voltage command signal with the carrier signal output from the carrier frequency variable setting unit 96 to perform inverse conversion. It is a PWM signal for driving the base of the switching element S 94.

The inverting section 94 is provided with a thermistor 98 for detecting the temperature of the switching element S. The carrier frequency variable setting section 96 compares the temperature detected by the thermistor 98 with a predetermined temperature. The carrier frequency is reduced at a predetermined ratio with respect to the detected temperature and output to the PWM generation circuit 97. When the carrier frequency decreases, the inverse conversion unit 9
4, the number of times of switching of the switching element S is reduced, and the temperature rise of the switching element S is reduced, so that the destruction and deterioration of the switching element S are avoided. (Japanese Patent Laid-Open No. 11-
No. 69836).

[0005]

The main circuit semiconductor element is constructed as shown in FIG. The loss generated in the main circuit element used in the forward conversion unit and the inverse conversion unit of the variable speed device includes a steady loss and a switching loss. The steady loss is determined by the voltage Vce and the current Ic flowing when the main circuit element is turned on.
And the product of The switching loss is determined by the product of the number of switching times (the carrier frequency in PWM), and the loss E _SW per switching is determined by the current Ic flowing through the element. FIG. 8 shows an example of Vce-Ic characteristics of the main circuit element.

Due to these losses (steady-state loss + switching loss), a temperature rise (ΔTj−c) occurs between the case of the main circuit element and the junction.

ΔTj−c = Rth (j−c) × loss Rth (j−c): Thermal resistance between junction and case The time constant varies depending on the applied element, or approximately 0.2 to 0.
Saturates in 3 seconds, 0.5-1 second.

There are "power cycle" and "thermal fatigue" as parameters of the life of the main circuit element. In the power cycle, the junction temperature Tj repeatedly rises and falls due to the above-mentioned loss from the temperature equilibrium state. This is a characteristic in which the number of times the temperature rises and falls until the element is destroyed is determined from the temperature change width ΔTj at this time (FIG. 6).

When the temperature change width ΔTj is large, the allowable number of repetitions of temperature rise / fall decreases, and when ΔTj is small, the allowable number of repetitions of temperature rise / fall increases. This is mainly because mechanical expansion is applied to the bonding portion between the silicon chip 13 and the bonding wire 15 in the semiconductor power conversion device shown in FIG. I do.

[0010] Thermal fatigue is also mechanical stress due to repetition of temperature rise and fall like a power cycle. However,
The stressed part is between the cooling part of the module (generally, the copper base plate 11) and the insulating substrate 12 or the insulating substrate 1
The main part is a soldered portion between the silicon chip 2 and the silicon chip 13.
This occurs because the thermal expansion coefficient differs between the cooling section of the module and the insulating substrate. As for the thermal fatigue, as in the case of the power cycle, the allowable number of repetitions increases if the variation width of the case temperature is small, and the allowable number of repetitions decreases if the increase / decrease width increases.

In order to extend the life due to the above factors, the temperature change width may be reduced. Usually, for this purpose, under the condition that a large amount of current flows and the loss increases, the carrier frequency is lowered to reduce the loss, or a method of adopting a large-capacity element to reduce the loss and reduce the temperature change width is adopted. Can be

A decrease in the carrier frequency causes a deterioration in current control performance, an increase in noise, a deterioration in current waveform, and a rise in motor temperature. Further, when the element capacity is increased, the cost increases, the element size increases, and the device becomes larger.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a semiconductor power conversion device capable of extending the life of an element without increasing the element capacity or reducing control performance. An object of the present invention is to provide a method for improving the life of a circuit element.

[0014]

A method for improving the life of a main circuit element in a semiconductor power conversion device according to the present invention includes the steps of:
In a power converter using a semiconductor device having a power cycle life or a thermal fatigue life such as a GBT, a carrier frequency for pulse width modulation is increased at a low load to increase a switching loss of the semiconductor device, thereby increasing a junction of the semiconductor device. It is characterized in that the difference from the junction temperature under a high load is reduced by increasing the temperature.

Alternatively, the gate resistance of the semiconductor element is increased at a low load to increase the switching loss of the semiconductor element and the junction temperature of the semiconductor element is increased to reduce the difference from the junction temperature at a high load. It is characterized by the following.

These methods can be used in combination.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 An example of a method of changing a carrier frequency according to a load state according to the present invention will be described with reference to FIGS. FIG. 1 shows a configuration of a power conversion device that controls the speed of the motor 9. PWM operation unit 1
Is configured such that a carrier frequency used for pulse width modulation can be adjusted by a frequency command. A frequency command and a voltage command are input to the PWM operation unit 1, and the output PWM signal drives the gate of the switching element S of the main circuit 3 via the gate drive circuit 2, and the frequency command and the voltage are output from the inverter main circuit 3. The motor 9 outputs an alternating current according to the command.

The carrier frequency is adjusted by monitoring the load condition of the inverter as shown in FIG. 2, and increasing the carrier frequency when the load is light and increasing the carrier frequency when the load is heavy. For monitoring the load state, for example, the power or current output from the inverter main circuit 3 to the motor 9 or the temperature of the switching element S is detected and compared with a predetermined value to reduce the light load,
Determine heavy load.

When the carrier frequency at the time of light load is increased, the number of times of switching of the switching element increases, the loss of the element increases, and the junction temperature Tj increases. Further, when the carrier frequency under heavy load is reduced, the number of times of switching is reduced, the loss of the element is reduced, and the junction temperature Tj is lowered. As a result, the difference between the junction temperature Tj at the time of light load and the junction temperature Tj at the time of heavy load becomes small, and the life of the switching element becomes longer.

In the above description, the carrier frequency is changed under both a light load and a heavy load. However, by increasing the carrier frequency only under a light load, the life of the switching element can be extended. Second Embodiment An example of a method of switching a gate resistance according to a load state according to the present invention will be described with reference to FIGS.
FIG. 3 shows a gate circuit of the inverter main circuit element. Between the output terminal 23 of the gate drive circuit 21 and the gate terminal G of the main circuit element S, a series circuit of a resistor R1, a resistor R2 and a gate resistance changeover switch SW is connected in parallel.
When W is turned off, the gate resistance becomes only R1 and the gate resistance (value) increases, and when the switch SW is turned on, the gate resistances R1 and R2 become parallel to reduce the gate resistance.

Then, as shown in FIG. 4, the load state of the inverter is monitored. When the load is light, the switch SW is turned off to increase the gate resistance, and when the load is heavy, the switch SW is turned on to reduce the gate resistance. . When the gate resistance increases, the loss of the main circuit element increases, and when the gate resistance decreases, the loss of the main circuit element S decreases. Therefore, the difference between the main circuit element junction temperature Tj under light load and under heavy load decreases.

In the above description, the gate resistance is switched between large and small at light load and heavy load. However, the life of the switching element can be extended by increasing the gate resistance only at light load. FIG. 7 shows an example of gate resistance and switching characteristics.

In the above-described method of the present invention, the loss of the element is increased at light load, but the loss is not greater than at heavy load, so that the method can be carried out without enhancing the cooling capacity. Hereinafter, an example of the improvement of the element lifetime by the method of switching the gate resistance will be described.

[0024]

[Table 1]

The normal circuit characteristics, switching loss characteristics, power cycle life, thermal resistance, and the like of the main circuit element vary depending on the applied element. Element loss is determined under the conditions shown in Table 1. The carrier frequency is set at 6 KHz. The thermal resistance between the junction and the case of the element is set to 0.1 [° C./W].

The loss under high load is 170 + 0.016 × 6000 = 266 W Therefore, the temperature rise between the junction and the case is 2
It will be 6.6 ° C.

If the above measures are not taken, the loss at low load is 33 + 0.005 × 6000 = 63 W. Therefore, the difference in temperature rise between the junction and the case is:
6.3 ° C.

As a result, the difference in temperature rise between when the load is low and when the load is high is as follows. 20.3 ° C.

In the power cycle characteristics shown in FIG. 6, the power cycle life at a temperature change width ΔTj = 20 ° C. is about 18.5 million times. Here, if ΔTj is reduced by 1 ° C., the power cycle becomes about 19.6 million times, and the life can be extended by 5 to 6%. Here, to increase the temperature rise under light load by 1 ° C., the loss may be increased by 10 W. When this is performed by the method of changing the carrier frequency in the first embodiment,
The carrier frequency at light load may be changed from 6 KHz to 8 KHz.

In the above example, even if only the gate resistance is switched, the difference can be reduced only by 0.43 ° C., but can be realized by selecting a larger gate resistance.

The methods of Embodiments 1 and 2 can be used together, and the portion compensated by the gate resistance can be covered by increasing the carrier frequency.

[0032]

Since the present invention is configured as described above, the following effects can be obtained. (1) Since the junction temperature difference between the main circuit element under light load and heavy load can be reduced, the life of the main circuit element is improved. (2) Although the loss of the main circuit element is increased at light load, the loss is not larger than at heavy load, so that the life of the main circuit element can be improved without strengthening the cooling capacity. (3) Since it is only necessary to monitor the load state and change the carrier frequency or the gate resistance, it can be easily implemented. (4) By using both the method of changing the carrier frequency and the method of changing the gate resistance, the junction temperature difference between the light load and the heavy load of the main circuit element can be further reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of an inverter according to a first embodiment.

FIG. 2 is a diagram illustrating a method according to the first embodiment.

FIG. 3 is a block diagram of an inverter according to a second embodiment;

FIG. 4 is a diagram illustrating a method according to the second embodiment.

FIG. 5 is a schematic side view showing an example of the internal configuration of a semiconductor element for a main circuit.

FIG. 6 is a graph showing an example of power cycle characteristics of a switching element.

FIG. 7 is a graph showing an example of a gate resistance-switching loss characteristic of an IGBT.

FIG. 8 is a graph showing an example of a collector-emitter saturation characteristic of a switching element.

FIG. 9 is a block diagram showing a conventional example.

FIG. 10 is a block diagram showing another conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... PWM calculation part 3 ... Main circuit 21 ... Gate drive circuit S ... Main circuit element R1, R2 ... Gate resistance SW ... Gate resistance changeover switch

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference)

Claims (3)

[Claims] In a power converter using a semiconductor element having a power cycle life or a thermal fatigue life such as an IGBT for a main circuit, a switching frequency of the semiconductor element is increased by increasing a carrier frequency for pulse width modulation at a low load. And increasing the junction temperature of the semiconductor element to reduce the difference from the junction temperature under a high load. 2. In a power converter using a semiconductor element having a power cycle life or thermal fatigue life such as an IGBT in a main circuit, a gate resistance of the semiconductor element is increased at a low load to increase a switching loss of the semiconductor element. A method for improving the life of a main circuit element in a semiconductor power conversion device, wherein the difference from the junction temperature under high load is reduced by increasing the junction temperature of the semiconductor element. 3. A method for improving the life of a main circuit element in a semiconductor power conversion device, wherein the method according to claim 1 and the method according to claim 2 are used together.