JPH0284011A - Temperature protection for power converter - Google Patents

Abstract

PURPOSE:To protect a semi-conductor element against temperature ripple by operating the temperature ripple based on the effective current and frequency obtained from current commands. CONSTITUTION:A current command is detected through a current command detecting section 31 then temperature ripple is operated at a temperature ripple operating section 32 based on the effective current and frequency. A temperature ripple judging section 35 judges whether the temperature ripple exceeds over an allowable level, and a protector 37 functions if the temperature ripple exceeds over the allowable level. A junction average temperature operating section 33 operates the junction average temperature of a semi-conductor element based on the detected current command, and a junction temperature operating section 34 operates the junction temperature in which the temperature ripple is considered. A junction temperature judging section 36 judges whether the operation result exceeds over a predetermined level, and a protector 37 functions according to the judgement result.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention provides a method for controlling the current of a power conversion device configured by mounting a semiconductor element on a cooling fin, in which the semiconductor element is damaged due to temperature. The present invention relates to a temperature protection method for a power conversion device that can prevent the above.

[Prior Art] Power conversion devices such as inverters and choppers perform desired power conversion by turning on and off current using semiconductor elements such as GTO silice.
-a, since the semiconductor element cannot effectively dissipate the heat generated by this current, and the semiconductor element will be damaged if the junk temperature of the semiconductor element exceeds a predetermined value, a material with good thermal conductivity is used, This semiconductor element is attached to a cooling fin that has a large heat dissipation area, and the generated heat is transferred to the cooling fin.

As described above, while dissipating the heat generated by the semiconductor element, the junk temperature of the semiconductor element is monitored, and if this temperature reaches a dangerous value, the operation of the power converter is stopped to prevent damage due to overheating. However, it is extremely difficult to measure junkidine temperature. Therefore, in practice, the junction temperature is estimated and the protection device is operated in the following manner. For example, a temperature detection means is attached to the cooling fin, and a protection device is activated when the detected temperature exceeds a certain value. Alternatively, the output current of the power converter can be detected, the magnitude of this current can be divided into several categories, and the energization time can be determined for each current category, so that once a predetermined period of time has elapsed, the junk temperature reaches a dangerous value. It is assumed that the target has been reached and a protective device is activated.

However, the former of the above protection methods is
For example, if an excessive current suddenly flows through a semiconductor element, and the loss of ti in the semiconductor element suddenly and dramatically increases, the thermal time constant of this element is sufficient compared to the thermal time constant of the cooling fins. Since the temperature is small, only the junk temperature of this semiconductor element will rise rapidly, causing a situation where the temperature of the cooling fins will be about -1:,d.
Merely monitoring the temperature of the cooling fins has the disadvantage that it is not possible to detect the increase in junk temperature due to the above-mentioned phenomenon, and therefore the semiconductor element cannot be reliably protected.

In addition, in the latter protection method, if the size of the output current of the power conversion device is widened, the temperature limit to be protected becomes rougher, so the current carrying capacity of the semiconductor element used is reduced to 1.
Since the power cannot be utilized at 00%, the capacity of the power conversion device will be reduced. Therefore, if the current resolution is improved by narrowing the width of the current division, the current carrying capacity of the semiconductor element can be utilized almost completely, but at the cost of this, the protection circuit is It has the disadvantage of being complicated and expensive.

Therefore, an idea to eliminate the above-mentioned drawbacks was developed in ``Jetgan Sho 62-1.
No. 65507”.

FIG. 6 is a flowchart showing a conventional example of temperature protection of a power conversion device, and is a flowchart showing a conventional example of temperature protection of a power conversion device, and is described in [Utility Application No. 165507/1989]
This is the proposal in ``No.

The outline of the operation of the flowchart shown in FIG. 6 is as follows. In other words, when a large current suddenly flows through a semiconductor device, there is a temperature difference between the junction part of the semiconductor device and the cooling fin, a temperature difference between the cooling fin and its surroundings, and Since the cooling fins have a large thermal time constant, the temperature difference between the cooling fins and the surroundings changes from moment to moment. Therefore, if these temperature differences and their temporal changes can be detected, indirect This method focuses on the fact that the average junction temperature TJ" can be detected at Read the value and calculate the loss occurring in the semiconductor element in process 12,
Based on this loss and the thermal resistance of the semiconductor element, in process 13, the temperature difference between the junction part and the cooling fin T J-F
Also, based on the above current command value, calculate the generated loss on the cooling fin (process 15), and from this generated loss, the thermal resistance and thermal time constant of the cooling fin, calculate the distance between the cooling fin and the surroundings. The temperature difference T r −a that changes from moment to moment is determined (process 15.16.17). Then, the junction section and
By adding the temperature difference T1-1 between the cooling fins and the temperature difference T, -1 between the cooling fins and the surrounding amount that changes over time, the junk-sitting average temperature TJ'' of the semiconductor element is detected (1718), If this detected temperature exceeds a predetermined value, the flowing current is reduced (judgment 20. Processing 2).
1) This prevents the power converter from being damaged by overheating.

[Problem to be solved by the invention]

For example, if the power conversion device is a variable voltage/variable frequency (hereinafter abbreviated as VVVF) inverter for driving an induction motor at variable speed, the current that flows when the induction motor is operated at low speed is used to drive a semiconductor element. However, if the current is constant, this temperature ripple increases as the frequency decreases.

However, the conventional temperature protection method described above does not take such temperature ripple of the semiconductor element into consideration, and therefore has the disadvantage that it cannot protect the power cycle life of the semiconductor element in the 6H range where the output frequency is low.

Furthermore, since the influence of this temperature ripple is excluded when calculating the junction temperature, there is also the drawback that reliable junction temperature control cannot be performed.

Therefore, an object of the present invention is to provide protection against temperature ripples of semiconductor elements constituting a power conversion device that operates according to current commands, and protection against junction temperatures of the semiconductor elements in consideration of this temperature ripple. It is something to be done.

[Means to solve the problem]

In order to achieve the above object, the temperature protection method of the present invention comprises a power i which is made up of a semiconductor element attached to a cooling fin and is equipped with a current control loop through which a current matching a current command value flows. In the 1A device, the 'rt
The current command value is used to calculate the temperature difference between the junction of the semiconductor element and the cooling fin, and the current command value is also used to calculate the temperature difference between the cooling fin and the surroundings, taking into account a thermal time constant. , the ambient temperature is added to the sum of these two temperature differences to obtain the average temperature of the junction of the semiconductor element, while the current command value and the frequency of this current are used to find that these have a predetermined functional relationship. Determine the temperature ripple of the semiconductor element,
When this temperature ripple is greater than or equal to the first predetermined value, or
When the junction temperature calculated from this temperature ripple and the junction average temperature is equal to or higher than a second predetermined value, the electric current flowing through the power converter is decreased.

[Effect]

In this invention, since the power conversion device is equipped with a current control loop, the current command value and the output type [(a' are equal, so the temperature ripple is calculated using the current effective value and frequency obtained from the current command value. is calculated, and if this temperature ripple exceeds a first predetermined value, protection is provided by cutting off the current, etc., and the junction temperature calculated by taking this temperature ripple into account is added to the junction average temperature of this semiconductor element. However, even if the second predetermined value is exceeded, protection is attempted by cutting off the current or the like.

[Embodiment] FIG. 1 is an 81-function block diagram showing an embodiment of the present invention.

In a power conversion device that performs current control, the magnitude of the output current of the device and the current command value match, so this current command value is detected by the current command value detection unit l,
Based on this current command value, the temperature ripple is calculated from the effective value and frequency of this current in the temperature ripple calculating section 32, and the temperature ripple determining section 35 determines whether this value exceeds the allowable value. If the value exceeds the allowable value, the protection device 37 operates to prevent the power converter from being damaged by cutting off the current or the like.

Further, using the detected current command value, the junk-sign average temperature calculating section 33 calculates the junk-sign average temperature of the semiconductor element. Since it is as described in No. j, the explanation of this part will be omitted.

The junction temperature calculation unit 34 calculates the junction temperature average temperature obtained in this way, taking into account the temperature ripple described above,
The junk silane temperature determining section 36 determines whether or not this calculation result exceeds a predetermined value, and depending on the determination result, the protection device 37 is activated.

FIG. 2 is a circuit diagram showing an example in which the functions of the embodiment shown in FIG. It's raining.

In this FIG.
The position detector 50, the speed setter 41, and the speed regulator 42 constitute a speed control loop, and the speed il1 moderator 42
The torque current command signal outputted by the torque ti limiter 4
3 to the microcomputer 44.

The microcomputer 44 calculates and outputs a current command signal corresponding to the external load from the input torque current command signal. Therefore, the microcomputer 44 that outputs the current command signal, the current transformer 48, and the current regulator 45 control the current. ■This current forms a loop! j1
The output of the moderator 45 is connected to VV via the gate drive circuit 46.
By applying it to the gate of the GTO Sirisk that constitutes the VF inverter 47, the induction motor III 49 is driven at a desired speed.

FIG. 3 is a flow chart showing the operation of the microcomputer used in the application example circuit shown in FIG.

In FIG. 3, first, the frequency r and the effective current value i of the output current are read from the current command value (processing 1), and the temperature ripple ΔTJ of the semiconductor element is calculated as a function of the effective current value i and the frequency f. (processing 2).

Figure 4 is a graph showing the relationship between current frequency and temperature ripple ΔT when current effective value i is constant, and Figure 5 is a graph showing the relationship between output current effective value I and temperature ripple ΔT when current frequency f is constant. , and in the calculation in process 2 described above, the temperature ripple ΔT is calculated using the relationship shown in FIGS. 4 and 5.

The temperature ripple ΔT obtained in process 2 in FIG. 3 is
Preset maximum allowable temperature ripple value ΔT J
This maximum permissible temperature ripple value ΔT J@@X, which is compared with a (judgment 3), becomes the protection level of the power cycle life of the semiconductor element against the temperature ripple. As a result of the judgment in judgment 3, if the temperature ripple ΔT1 exceeds the protection level, a gate cutoff signal or a torque current command limit signal is output (process 4) to protect the semiconductor element.

Also, if the temperature ripple does not exceed the protection level,
Using the current command value read in process 1, the junction average temperature T, 11 is calculated (process 5).
The calculation of this junction average temperature T,'' has already been described in "Utility Application No. 165507/1982" as mentioned above, so the explanation thereof will be omitted.

This junk silane average temperature TJ” and the temperature ripple Δ
From TJ, the junction temperature T is calculated in process 6, and this calculation is performed using the following equation (13).

T, −・ΔT, +T J
(1) Compare and judge the junction temperature T1 obtained in process 6 with the maximum allowable jump junction temperature T Jaa & set in advance as a protection level (7), and if the junction temperature TJ exceeds the protection level, a gate cutoff signal or torque A current command value limit signal is issued (process 8) to prevent junk silane of the semiconductor element from being damaged by overheating.

〔Effect of the invention〕

According to the present invention, when the frequency of the current flowing through the semiconductor element constituting the power conversion device is low, the temperature ripple generated by this current cannot be ignored. In addition to protecting against the power cycle life of the semiconductor device, by taking this temperature ripple into account, what was previously the average junction temperature of the semiconductor device can now be detected as a more precise junction temperature, making it possible to reliably detect the semiconductor device. Great protection can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a functional block diagram showing an embodiment of the present invention.
2 is a circuit diagram showing an example of applying the functions of the embodiment shown in FIG. 1, FIG. 3 is a flowchart showing the operation of the microcomputer used in the applied example circuit shown in FIG. Figure 4 is a graph showing the relationship between current frequency f and temperature ripple ΔT when current effective value i is constant, and Figure 5 is a graph showing the relationship between output current effective value i and temperature ripple ΔTJ when current frequency f is constant. FIG. 6 is a flowchart showing a conventional example of temperature protection of a power conversion device. 1, 2. 4. 5. 6. 8.11.12.13
．． 14.15°16, 17.18.19.21... Processing, 3, 7.20... Judgment, 31... Current command value detection unit, 32... Temperature ripple calculation unit, 33... - Junction average temperature calculation unit, 34... Junction temperature calculation unit, 35... Temperature ripple determination unit, 36...
・Janfusibon temperature determination section, 37...protective device, 4
1...Speed setter, 42...Speed adjuster, 43...
・Torque current limiter, 44...Microcomputer, 45...Current! j1 node, 46...gate drive circuit, 47...VVVF inverter, 48...current transformer, 49...induction motor, 50...speed diagram 31 was constructed Out 77 next day: Go (H) in the L equation

Claims (1)

[Claims] 1) In a power converter device configured with a semiconductor element attached to a cooling fin and equipped with a current control loop that passes a current matching a current command value, bonding of the semiconductor element is performed using the current command value. Similarly, using the current command value, calculate the temperature difference between the cooling fin and the surroundings considering the thermal time constant, and add the ambient temperature to the sum of these two temperature differences. Then, the average temperature of the junction of the semiconductor element is determined, and the temperature ripple of the semiconductor element, which has a predetermined functional relationship with the current command value and the frequency of this current, is determined. is greater than or equal to a first predetermined value, or when a junction temperature calculated using this temperature ripple and the average junction temperature is greater than or equal to a second predetermined value, the current flowing through the power converter is reduced. Temperature protection method for power conversion equipment.