POWER CONVERSION DEVICE

Abstract

A power conversion device including a main circuit unit that performs power conversion by turning on / off a semiconductor switching element (3a - 3f), and comprising: a temperature setting unit configured to set a temperature of the semiconductor switching element (3a - 3f) based on a frequency characteristic of a current flowing in the main circuit unit, wherein the temperature setting unit setting a temperature of the semiconductor switching element (3a - 3f) based on a frequency at which a slope of decrease of the current in the frequency characteristic of the current changes from 20 to 40 dB / dec.

Description

Technical area

[0001] The present invention relates to a power conversion device including a temperature measuring function of a semiconductor switching element. Technical background

[0002] A power conversion device such as an inverter is used in various fields for motor control, solar power generation, wind power generation, etc. The service life of the power conversion device (five to ten years) is short compared to the service life of a motor, a solar power panel, a wind power generator, etc. (twenty years or more) associated with the power conversion device. Therefore, there is a demand for extending the service life of the power conversion device.

[0003] A major factor determining the service life of the power conversion device is a failure of a power semiconductor switching element that configures a main circuit of the power conversion device, such as an insulated gate bipolar transistor (IGBT, hereinafter referred to as insulated gate bipolar transistor).

[0004] The emitter electrode of the IGBT is connected to the emitter wiring of a component by wire bonding using aluminum or copper. Meanwhile, the collector electrode of the IGBT is connected to the collector wiring of the component by soldering. A large current of 100 A / cm2 flows through it. 2or more to the emitter electrode and the collector electrode of the IGBT. Therefore, a temperature change often occurs between the wire and the emitter electrode or between the solder and the collector electrode in response to the IGBT's operating pattern. Due to the temperature change, cracks due to metal fatigue are generated in the wire and emitter electrode junction or the solder and collector electrode junction, causing the IGBT to fail.

[0005] The relationship between the magnitude of temperature change and the number of cycles of temperature change to failure is provided by IGBT manufacturers as an experimental formula (described in a reliability manual, application manual, or the like). Accordingly, if the temperature of the IGBT can be measured, the lifetime of the IGBT can be predicted. Then, by reviewing the driving method of the power conversion device or systematically replacing the IGBT in response to a predicted lifetime of the IGBT, an extension of the lifetime of the power conversion device can be expected.

[0006] As the prior art for measuring the temperature of an IGBT, technologies described in Patent Document 1 and Patent Document 2 are known.

[0007] In the technology described in Patent Document 1, a temperature detection diode is provided on a semiconductor substrate of an IGBT chip, which detects a temperature of the IGBT by using the temperature dependence of the forward voltage of the diode.

[0008] In the technology described in Patent Document 2, during an off-state of an IGBT device, the temperature of the IGBT is detected by using the temperature dependence of the duration of a Miller plateau state of the gate-emitter voltage.

[0009] Patent Document 3 relates to a power converter computing unit that determines an average temperature from a power loss, a thermal resistance, and a thermal time constant of a semiconductor device of the power converter, extracts therefrom a pulsation envelope temperature that exceeds the maximum value of a pulsation temperature depending on the average power loss and a pulsation frequency, and estimates a temperature change in the semiconductor device by adding the average temperature and the pulsation envelope temperature. Prior Art Document patent document Patent document 1: JP H09 - 36 356 A Patent document 2: JP 2013 - 142 704 A Patent document 3: US 8 926 174 B2 Summary of the inventionProblems to be solved by the invention

[0010] In the technology described in Patent Document 1, since a sensor is provided in an IGBT chip, the manufacturing process of the IGBT is complicated and the chip size increases. This leads to an increase in the size and cost of the power conversion device.

[0011] In the technology described in Patent Document 2, when the IGBT is switched at high speed, the temperature measurement accuracy deteriorates because the Miller Plateau period decreases.

[0012] Therefore, the present invention provides a power conversion device that can detect the temperature of a semiconductor switching element such as an IGBT with high accuracy without resulting in an increase in size and an increase in cost of the device. Means of solving the problem

[0013] The above-described problem is solved by the subject matter of claim 1. Preferred embodiments are described in the dependent claims. In particular, the power conversion device according to the present invention includes a main circuit unit that performs power conversion by turning a semiconductor switching element on / off, and includes a temperature setting unit that sets a temperature of the semiconductor switching element based on a frequency characteristic of a current flowing in the main circuit unit. Effects of the invention

[0014] According to the present invention, by setting the temperature of the semiconductor switching element based on the frequency characteristic of an electric current, the detection accuracy of the semiconductor switching element can be improved without resulting in an increase in size and an increase in cost of the device.

[0015] The problems, configuration, and advantageous effects other than those described above will become clear from the following description of embodiments. Brief description of the drawings Fig. 1 illustrates a configuration of a power conversion device of a first embodiment. Fig. 2 is a gate voltage waveform, an emitter current waveform, and a current frequency characteristic after an off time in the first embodiment. Fig. 3 is a flowchart illustrating a setting process of a temperature of an IGBT in the first embodiment. Fig. 4 illustrates a configuration of a power conversion device of a second embodiment. Fig. 5 is a flowchart illustrating a setting process of a temperature of an IGBT in the second embodiment. Fig. 6 illustrates a configuration of a power conversion device of a third embodiment. Fig. 7 illustrates a gate voltage waveform, a DC bus current waveform, and a current frequency characteristic of the detection current in the third embodiment. Fig. 8 illustrates a configuration of a power conversion device of a fourth embodiment. Fig. 9 illustrates a gate voltage waveform, a current waveform detected by a current sensor, and a current frequency characteristic of the detection current in the fourth embodiment. Fig. 10 illustrates a configuration of a power conversion device of a fifth embodiment. Fig. 11 illustrates a configuration of a power conversion device of a sixth embodiment. Fig. 12 is a flowchart illustrating a setting process of a temperature of an IGBT in the sixth embodiment. Fig. 13 schematically illustrates sample data of a current waveform in the sixth embodiment. Modes for carrying out the invention

[0016] An embodiment of the present invention will be described below with reference to the drawings. In the figures, like reference numerals denote like components or components that perform like functions. First embodiment

[0017] Fig. 1 illustrates a configuration of a power conversion device of a first embodiment of the present invention.

[0018] The power conversion device of the first embodiment receives three-phase AC power (R, S, and T), converts the received three-phase AC power into three-phase AC power of variable voltage and variable frequency, and outputs the resulting three-phase power to a three-phase AC motor (U, V, and W). The three-phase AC power to be received is three-phase AC power of fixed voltage and fixed frequency, supplied, for example, from a commercial power supply.

[0019] First, a main circuit unit provided in the power conversion device will be described.

[0020] Diodes 1a to 1f configure a rectification circuit formed of a three-phase diode bridge circuit. The anode of diode 1a and the cathode of diode 1b are connected to an R-phase input of the power input side. Similarly, the anode of diode 1c and the cathode of diode 1b are connected to an S-phase input, and the anode of diode 1e and the cathode of diode 1f are connected to a T-phase input. The received three-phase AC power is full-wave rectified by the rectification circuit configured of diodes 1a to 1f and is further converted into DC power by removing its ripple components through a smoothing capacitor 2.

[0021] The IGBTs 3a to 3f configure a three-phase inverter circuit. The cathodes of the diodes 4a to 4f are connected to the collectors of the IGBTs 3a to 3f, respectively, and the anodes of the diodes 4a to 4f are connected to the emitters of the IGBTs 3a to 3f, respectively. Accordingly, the diodes 4a to 4f act as so-called freewheeling diodes. The collectors of the IGBTs 3a, 3c, and 3e are connected to the high-potential side of the opposite ends of the smoothing capacitor 2, together with the cathodes of the diodes 1a, 1c, and 1e. Furthermore, the emitters of the IGBTs 3b, 3d, and 3f are connected to the low-potential side of the opposite ends of the smoothing capacitor 2, together with the anodes of the diodes 1b, 1d, and 1f. The gates of the IGBTs 3a to 3f are connected to gate driver circuits which are not shown (5a to 5f in Fig. 4). The emitter of IGBT 3a and the collector of IGBT 3b are connected to the W phase of a three-phase AC motor 5. Similarly, the emitter of IGBT 3c and the collector of IGBT 3d are connected to the V phase of the three-phase AC motor 5, and the emitter of IGBT 3e and the collector of IGBT 3f are connected to the U phase of the three-phase AC motor 5.

[0022] The three-phase inverter circuit converts DC power input from the rectifier circuit side into three-phase AC power of variable voltage and variable frequency by controlling its IGBTs 3a to 3f on / off through the gate drive circuits, and outputs the resulting three-phase AC power to the U-phase, V-phase, and W-phase of the three-phase AC motor 5. The three-phase AC motor 5 is thereby driven at a variable speed.

[0023] Now, a temperature setting section provided in the power conversion device will be described.

[0024] A current sensor 10 is provided for the emitter of the IGBT 3b of the lower W-phase arm. The emitter current of the IGBT 3b is detected by the current sensor 10. A signal from the current sensor 10 is input to an A / D converter 11. An output from the A / D converter 11 is input to a frequency converter 12. The frequency converter 12 calculates a frequency characteristic of the detected emitter current based on a digital signal output from the A / D converter 11 and indicating an emitter current. Furthermore, data indicating a relationship between the frequency characteristic of a current flowing to the IGBT 3b and the temperature of the IGBT 3b is accumulated in a storage device 14.A calculator 13 compares the frequency characteristic of an emitter current of the detected IGBT 3b output from the frequency conversion device 12 and the data accumulated in the storage device 14 to calculate the temperature of the IGBT 3b.

[0025] According to research by the inventor of the present invention, the frequency characteristic of a current flowing to an IGBT has a temperature dependence, as described below. Accordingly, according to the first embodiment, by detecting the temperature of the IGBT based on the frequency characteristic, the temperature of the IGBT can be measured with a higher degree of accuracy without particularly changing the element configuration of the IGBTs or the circuit configuration of the power conversion device, and accordingly without causing an increase in the size of the device or an increase in cost.

[0026] Now, an operation of the first embodiment will be described with reference to Fig. 2 and Fig. 3 described.

[0027] Fig. 2 illustrates a gate voltage waveform, an emitter current waveform, and a current frequency characteristic after a turn-off time of the IGBT 3b in the first embodiment. When the gate voltage exceeds a threshold voltage therefor, the IGBT 3b turns on, and the emitter current begins to flow. In an initial state after turn-on, a recovery current of the diode 4a of the upper W-phase arm is superimposed on a W-phase current of the three-phase AC motor 5, and therefore, the emitter current waveform has a peak. After a turn-off time, when the gate voltage becomes lower than a threshold voltage therefor, the IGBT 3b turns off, and the emitter current decreases.

[0028] Emitter current waveforms found in Fig. 2, the waveform indicated by a solid line is an emitter current waveform when the temperature of the IGBT 3b is Ta, and the waveform indicated by a broken line is an emitter current waveform when the temperature of the IGBT 3b is Tb (> temperature Ta). As shown in Fig. 2, the off-time (fall time) tf at temperature Ta < off-time (fall time) ft' at temperature Tb.

[0029] The current frequency characteristics that Fig. 2 are obtained by frequency conversion (e.g. Fourier transformation) of the emitter currents, which are Fig. 2. Such a frequency conversion is carried out by the frequency conversion device 12 ( Fig. 1). If the period during which the emitter current is fixed is represented by tp, the current value (dB) of the emitter current when the IGBT 3b turns off has a fixed value from DC up to a frequency of 1 / (πtp), but decreases at frequencies higher than 1 / (πtp) with a slope of 20 dB / dec (a 20 dB change at ten times the frequency) in frequency response. Furthermore, according to the research of the present inventor, in the case of a temperature Ta where the frequency is equal to or higher than 1 / (πtf), the current value (dB) decreases at a slope of 40 dB / dec (a 40 dB change at ten times the frequency) in frequency response. Furthermore, in case of temperature Tb (> Ta) where the frequency is equal to or higher than 1 / (πtf') (< 1(πtf)), the current value (dB) decreases with a slope of 40 dB / dec in a frequency response.

[0030] Thus, according to the research of the inventor of the present invention, the frequency characteristic of an emitter current after the off-time of an IGBT has such a temperature dependence as described above. Therefore, in the first embodiment, a relationship between the frequency and temperature at which the slope of the decrease in the current value in a frequency characteristic changes from 20 dB / dec to 40 dB / dec is determined in advance by measurement or the like and stored as data in the storage device 14 ( Fig. 1) accumulated. The computer 13 ( Fig. 1) calculates a frequency at which the slope of the decrease of the detection current value changes from 20 dB / dec to 40 dB / dec from the frequency characteristic of the detection current supplied by the frequency converting device 12 ( Fig. 1) and compares the calculated frequency with the data stored in the memory device 14 ( Fig. 1) are accumulated to establish a temperature corresponding to the calculated frequency.

[0031] It should be noted that the frequency characteristic of the current value (dB), with the exception of the temperature dependence, corresponds to a frequency spectrum of a so-called trapezoidal wave.

[0032] Fig. 3 is a flowchart illustrating a setting process of a temperature of an IGBT in the first embodiment.

[0033] After the process has been started (step (1)), the current waveform after the current switching of the IGBT 3b is converted into a voltage signal by the current sensor 10 (step (2)).

[0034] A voltage signal from the current sensor 10, namely an analog signal representing a current, is converted into a digital signal by the A / D converter 11 (step (3)).

[0035] A current waveform indicated by the digital signal from the A / D converter 11 is converted into a frequency characteristic of the current by the frequency converting device 12 (step (4)).

[0036] Then, the calculator 13 refers to the relationship between the frequency characteristic of the current and the temperature accumulated in the storage device 14, the relationship between the frequency and the temperature at which a current value decrease starts with the slope of 40 dB / dec in the first embodiment (step (5)), and calculates the frequency at which a current value decrease starts with the slope of 40 dB / dec in the frequency characteristic of the detection current calculated by the frequency converting device 12 (step (6)).

[0037] Then, the calculator 13 compares the data accumulated in the storage device 14 and the frequency characteristic of the detection current, the calculation value of the frequency at which a current value decrease starts with the slope of 40 dB / dec in the first embodiment, and sets the temperature of the IGBT in response to a result of the comparison (step (7)).

[0038] As described above, according to the first embodiment, the temperature of an IGBT can be measured with high accuracy without resulting in an increase in device size and cost. Note that, although in the first embodiment, the temperature of an IGBT is set based on the current frequency characteristic after the off-time, the temperature of an IGBT may be set in another way based on the current frequency characteristic after the on-time. In this case, it is sufficient if the fall time tf described above is replaced by a rise time tf.

[0039] It should be noted that, although in the first embodiment, the temperature is set with the IGBT 3b as a representative of the IGBTs configuring the inverter circuit, each of the other IGBTs 3a and 3c to 3f may be set as a representative. Alternatively, a current sensor may be provided in each of the IGBTs 3a to 3f to individually set the temperature. Since this makes it possible to replace only an IGBT that is likely to fail, an extension of the service life of the power conversion device can be achieved easily or at low cost. Furthermore, the temperature of an IGBT can be set based on the frequency characteristic of a collector current of the IGBT.

[0040] Furthermore, the parallel connection of an IGBT and a diode in the upper and lower arms can be a parallel connection of multiple IGBT chips and multiple diode chips connected in parallel. For example, the upper and lower arms can be configured by a so-called IGBT module. In the case of an IGBT module, the temperature of a representative IGBT is determined, and if the period (time) until the IGBT failure becomes lower than a predetermined value, the IGBT module is replaced. Second embodiment

[0041] Now, a second embodiment of the present invention will be described with reference to Fig. 4 and Fig. 5. Note that a description will mainly be given of differences from the first embodiment.

[0042] Fig. 4 illustrates a configuration of a power conversion device of the second embodiment of the present invention.

[0043] In the second embodiment, a microcomputer 6 generates a PWM signal to drive the IGBTs 3a to 3f based on a torque command value (not shown) from the outside (e.g., a host controller) and motor current information detected by the current sensors 8a and 8b. The PWM signal is transmitted from the microcomputer 6 to gate drive circuits 5a to 5f via photocouplers 7a to 7f. The gate drive circuits 5a to 5f output gate drive voltage signals in response to the PWM signal to the gates of the IGBTs 3a to 3f. Thus, the IGBTs 3a to 3f are on / off controlled. In other words, the microcomputer 6 functions as a control unit for generating gate drive voltage signals for on / off controlling the IGBTs 3a to 3f.

[0044] It should be noted that photocouplers 7a to 7f are provided to electrically isolate the microcomputer 6 side and the gate drive circuits 5a to 5f from each other while transmitting the PWM signal.

[0045] A trigger signal is input from the microcomputer 6 to the frequency conversion device 12 as a trigger to start the frequency conversion. The trigger signal is output at a time when the IGBT is to turn on or off in response to the PWM signal. Specifically, the frequency conversion device 12 starts calculating a frequency characteristic of a frequency conversion, namely an emitter current of the IGBT 3b, in synchronization with the gate drive voltage signal.

[0046] Fig. 5 is a flowchart illustrating a setting process of a temperature of an IGBT in the second embodiment.

[0047] In the second embodiment, in response to a trigger signal from the microcomputer 6 (step (8)), an inrush current waveform or an off-current waveform indicated by a digital signal from the A / D converter 11 is converted into a frequency characteristic of a current by the frequency converting device 12 (step (4)).

[0048] As a result, the frequency conversion device 12 can determine which of the power-on waveforms and the power-off waveforms to retrieve and perform a conversion process for one of the current waveforms. Therefore, the processing load of the frequency conversion device 12 or the A / D converter 11 is reduced. Accordingly, the processing time is reduced, or the frequency conversion device 12 or the A / D converter 11, which are cheaper, can be used. Third embodiment

[0049] Now, a third embodiment of the present invention will be described with reference to Fig. 6 and Fig. 7. Note that a description will mainly be given of differences from the second embodiment.

[0050] Fig. 6 illustrates a configuration of a power conversion device of the third embodiment of the present invention.

[0051] In the third embodiment, the current sensor 10 is provided between the low-potential end of the smoothing capacitor 2 and the emitter of the IGBTs 3b, 3d, and 3f on the lower arm side, namely, the low-potential side of a DC input of the inverter circuit. Accordingly, the current sensor 10 effectively detects a DC bus current.

[0052] Fig. 7 illustrates a gate voltage waveform of the IGBT 3b, a DC bus current waveform detected by the current sensor 10, and a current frequency characteristic of the detection current in the third embodiment.

[0053] At the time of the gate voltage rise, namely when the IGBT 3b turns on, a recovery current flows and current flows transiently through a parasitic capacitance of the IGBT 3b. The currents flow into the rectifier circuit side via a parasitic wiring capacitance, the parasitic capacitance of the IGBT 3b, and a parasitic capacitance of the wiring. As shown in Fig. Therefore, as shown in Figure 7, the detection current through the current sensor 10 oscillates transiently. Furthermore, at the time the gate voltage drops, namely after the turn-off time of the IGBT 3b, a current flows transiently through the parasitic capacitances, and therefore the detection current through the current sensor 10 oscillates similarly to the turn-on time.

[0054] Furthermore, the frequency characteristic of the DC bus current detected by the current sensor 10 indicates a peak value at some frequencies along with the transient oscillation of the current. According to the research of the present inventor, the frequency at which a peak value is displayed has such a temperature dependence that as the temperature rises (Ta → Tb (> Ta)), the frequency is shifted to the low-frequency side, as shown in Fig. 7 is shown.

[0055] Here, if the parasitic capacitance is represented by Cs and the collector / emitter voltage change of an IGBT after the on-time or off-time is represented by dV / dt, the current flowing transiently is represented as Cs × (dV / dt). This (dV / dt) decreases as the temperature increases and the current fluctuation becomes moderate. Therefore, as can be seen by comparing the frequency characteristic (solid line) at temperature Ta and the frequency characteristic (broken line) at temperature Tb (> Ta) in Fig. 7, in both cases the peak value in the case of temperature Tb (> Ta) is shifted to the decreasing side of the frequency with respect to the peak value in the case of temperature Ta.

[0056] In the third embodiment, such a relationship between the frequency characteristic and the temperature as described above, namely the relationship between the temperature and the frequency at which a current peak value is displayed, is acquired in advance by actual measurement or the like and is stored in the storage device 14. Then, through the above-described temperature setting process, which is shown in Fig. 5, a temperature can be determined from the detection current by the current sensor 10.

[0057] Here, the waveform of the DC bus current detected by the current sensor 10 changes as shown by a current waveform shown in Fig. 7 at the time of turning off and turning on each of the IGBTs 3a to 3f. Accordingly, by generating a trigger signal at the time when the gate drive signal for each of the IGBTs configuring the inverter circuit turns on or off, it is possible to determine from which of the IGBTs 3a to 3f an inrush current waveform or an off-current waveform is obtained. Accordingly, the temperatures of the IGBTs can be determined by the individual current sensor 10.

[0058] For example, a shunt resistor is used as the current sensor 10. It should be noted that the current sensor 10 can also serve as a DC bus current detection sensor, which is used to detect motor current using a so-called shunt method. Fourth embodiment

[0059] Now, a fourth embodiment of the present invention will be described with reference to Fig. 8 and Fig. 9. Note that a description will mainly be given of differences from the third embodiment.

[0060] Fig. 8 illustrates a configuration of a power conversion device of the fourth embodiment of the present invention.

[0061] In the fourth embodiment, an X-capacitor 20, as a filter for removing noise, is connected at one end to the low-potential side (N-side) of a DC input of the inverter circuit. The X-capacitor 20 is connected at its other end to ground via the current sensor 10. Accordingly, noise, namely transient oscillation components after the on-time and off-time of each IGBT, is removed from a DC bus current by the X-capacitor 20. The transient oscillation components flow to ground via the X-capacitor 20 and are detected by the current sensor 10.

[0062] Fig. 9 illustrates a gate voltage waveform of the IGBT 3b, a current waveform detected by the current sensor 10, and a current frequency characteristic of the detection current in the present fourth embodiment.

[0063] As in Fig. 9, the frequency characteristic of a current detected by the current sensor 10 has such a temperature dependency that it displays a peak value at some frequencies, and furthermore, as the temperature becomes high (Ta → Tb (> Ta)), the frequency at which a peak value is displayed is shifted to the low frequency side, similarly to Fig. 7 (Third Embodiment). Accordingly, the temperature of each IGBT can be set similarly to the third embodiment described above.

[0064] Furthermore, as can be seen from the current waveforms and frequency characteristics of Fig. 7 and Fig. As can be seen from Figure 9, in the fourth embodiment, a DC component of the DC bus current, namely, a current component flowing in response to the motor current, is removed from the detection current of the current sensor 10. Accordingly, as a behavior exhibited by the current sensor 10, a detectable maximum current value can be reduced. In other words, the size and cost of the current sensor 10 can be reduced. Fifth embodiment

[0065] Now, a fifth embodiment of the present invention will be described with reference to Fig. 10. Note that a description will mainly be given of differences from the fourth embodiment.

[0066] Fig. 10 illustrates a configuration of a power conversion device of the fifth embodiment of the present invention.

[0067] In the fifth embodiment, to remove common-mode noise from the DC bus current, Y capacitors 21a and 21b are connected as filter capacitors to the DC input side of the inverter circuit. The Y capacitor 21a has one end connected to the low-potential side (N side) of the DC input of the inverter circuit and the other end connected to one end of the Y capacitor 21b. The Y capacitor 21b has the other end connected to the high-potential side (P side) of the DC input of the inverter circuit. Furthermore, the connection point between the Y capacitors 21a and 21b is grounded. Accordingly, common-mode noise, namely, oscillation components, are removed from a DC bus current after the off-time and the on-time of each IGBT by the Y capacitors 21a and 21b.The transient oscillation components flow to ground and are detected by the current sensor 10.

[0068] In addition, in the fifth embodiment, since the frequency characteristic of the current detected by the current sensor 10 has a temperature dependence similar to that in Fig. 7 (the third embodiment) or Fig. 9 (the fourth embodiment), the temperature of each IGBT is similar to the third and fourth embodiments described above (referring to Fig. 5).

[0069] In addition, in the fifth embodiment, the size and cost of the current sensor 10 can be made similar to the fourth embodiment ( Fig. 8) described above. Sixth embodiment

[0070] Now, a sixth embodiment of the present invention will be described with reference to Fig. 11 and Fig. 12. Note that a description will mainly be given of differences from the fifth embodiment.

[0071] Fig. 11 illustrates a configuration of a power conversion device of the sixth embodiment of the present invention.

[0072] In the sixth embodiment, a trigger circuit 30 is provided that generates a trigger signal in response to a gate drive signal generated by the microcomputer 6. The trigger signal generated by the trigger circuit 30 is provided to the A / D converter 11. Further, a setting circuit 40 and a memory 50 are provided between the A / D converter 11 and the frequency conversion device 12. The memory 50 accumulates digital data of a current output from the A / D converter 11 in time series. In other words, the memory 50 accumulates current waveform data. Note that the A / D converter 11 in the sixth embodiment samples a current value at predetermined time intervals in a predetermined period of time to retrieve current waveform data. Then, such current waveform retrieval is repeated a plurality of times within the predetermined period of time, as described below.

[0073] Fig. Fig. 12 is a flowchart illustrating a setting process of a temperature of an IGBT in the sixth embodiment. A process similar to the setting process ( Fig. 5) of the fifth embodiment by the trigger circuit 30, the setting circuit 40 and the memory 50 in the sixth embodiment is as follows.

[0074] A sampling trigger for the A / D converter 11 is generated by the trigger circuit 30 in synchronism with a gate drive signal generated by the microcomputer 6 (step (9)).

[0075] Further, it is determined by the determination circuit 40 whether the repetition number of sampling in a predetermined period for such current wavelength retrieval, namely, the current wavelength retrieval time number, reaches a predetermined number of times (step (10)).

[0076] Then, when the sampling repetition number reaches the predetermined number of times (Yes at (10)), namely, when the retrieval of the current wavelength data is carried out the predetermined number of times, the frequency converting device 12 calculates a frequency characteristic of a current from the current waveform data (digital signal) accumulated in the memory 50 (step (4)).

[0077] Then, when the sampling repetition number does not reach the set number of times (No in step (10)), data of a current A / D-converted by the A / D converter 11 is accumulated in the memory 50 (step (11)), and the sampling trigger start time is delayed by a predetermined period Δt shorter than the sampling interval (step (12)), and a sampling trigger is generated again by the trigger circuit 30 (step (9)), after which the current detection signal of the current sensor 10 is A / D-converted by the A / D converter 11.

[0078] Fig. 13 schematically illustrates sample data of a current waveform in the sixth embodiment.

[0079] In Fig. 13, graphic representations of a black circle indicate sampling data for the first time; graphic representations of a black square indicate sampling data for the second time; and graphic representations of a black triangle indicate sampling data for the third time.

[0080] As in Fig. As shown in Figure 13, by acquiring waveform data multiple times with the sampling trigger start time delayed by the predetermined period Δt shorter than the sampling interval, the detection accuracy of the current waveform is improved. At this time, waveform data substantially equivalent to those obtained by sampling at a sampling rate higher than the sampling rate of the A / D converter 11 is obtained. Accordingly, even when an inexpensive A / D converter is used, accurate waveform data is obtained.

[0081] Here, the motor speed is generally equal to or less than about 100 Hz, and the switching carrier frequency of an IGBT is equal to or higher than 1 kHz, while noise (a transient oscillation component) is a high-frequency current (about 1 MHz or more). Since noise is generated after the IGBT is switched on, it is generated at a frequency equal to or higher than ten times that of a change in the motor's current. Since the temperature of the IGBT is related to the current flowing to the main circuit of the power conversion device, namely the motor current, the temperature change frequency here is equal to or less than 1 / 10 of the noise generation frequency. In other words, the temperature is almost fixed, while a noise current waveform is retrieved multiple times.Accordingly, with the sixth embodiment, the temperature of the IGBT can be set with high accuracy because accurate waveform data is obtained by fetching waveform data multiple times.

[0082] It should be noted that the present invention is not limited to the above-described embodiments, but includes various modifications. For example, the above-described embodiments are explained in detail to describe the present invention in an easy-to-understand manner, and it is not necessarily limited to including all of the above-described configurations. Furthermore, it is possible to add, delete, and replace various components to, from, and with a part of the components of the embodiments.

[0083] For example, in the second to fifth embodiments ( Fig. 4, Fig. 6, Fig. 8 and Fig. 10), the A / D converter 11, the frequency conversion device 12, the computer 13 and the memory device 14 are integrated into a semiconductor chip with the microcomputer 6. Furthermore, in the sixth embodiment ( Fig. 11) the A / D converter 11, the frequency conversion device 12, the calculator 13, the storage device 14, the trigger circuit 30, the setting circuit 40, and the memory 50 are integrated into a semiconductor chip with the microcomputer 6. Through such integration, a reduction in the size and cost of the control unit of the power conversion device can be achieved.

[0084] Furthermore, various AC motors such as induction machines and synchronous machines can be used as the three-phase AC motor 5.

[0085] Furthermore, the load driven by the inverter circuit is not limited to a three-phase AC motor, but can be a variety of AC loads. List of reference symbols 1a to 1f diode 2 smoothing capacitor 3a to 3f IGBT 4a to 4f diode 5a to 5f Gate driver circuit 5 three-phase AC motor 6 microcomputers 7a to 7f photocouplers 10 Current sensor 11 A / D converters 12 Frequency conversion device 13 computers 14 Storage device 20 X-capacitor 21a, 21b Y-capacitor 30 trigger circuit 40 Fixing circuit 50 storage

Claims

[1] A power conversion device including a main circuit unit that performs power conversion by turning on / off a semiconductor switching element (3a - 3f), and comprising: a temperature setting unit configured to set a temperature of the semiconductor switching element (3a - 3f) based on a frequency characteristic of a current flowing in the main circuit unit, wherein the temperature setting unit setting a temperature of the semiconductor switching element (3a - 3f) based on a frequency at which a slope of decrease of the current in the frequency characteristic of the current changes from 20 to 40 dB / dec. [2] The power conversion device according to claim 1, wherein the temperature setting unit detects a current flowing in the main circuit unit, a frequency characteristic of the detected current is calculated and sets a temperature of the semiconductor switching element based on the calculated frequency characteristic. [3] The power conversion device according to claim 1, wherein the current is a current flowing from the semiconductor switching element (3a - 3f). [4] The power conversion device according to claim 1, wherein the temperature setting unit includes: A current sensor (10) configured to detect the current, an A / D converter (11) configured to convert an output signal of the current sensor (10) into a digital signal, a frequency conversion device (12) configured to calculate a frequency characteristic of the current based on the digital signal output from the A / D converter (11), a storage device (14) configured to accumulate data indicating a relationship between the frequency characteristic of the current and the temperature of the semiconductor switching element (3a - 3f), and a calculator (13) configured to compare the frequency characteristic of the current, the frequency characteristic being calculated by the frequency conversion device (12), and the data accumulated in the frequency conversion device (12) to determine a temperature of the semiconductor switching element (3a - 3f). [5] The power conversion device according to claim 2, wherein the temperature setting unit starts a calculation of the frequency characteristic of the current in synchronization with a drive signal for controlling the turning on / off of the semiconductor switching element (3a - 3f). [6] The power conversion device according to claim 4, wherein the frequency conversion device (12) calculates the frequency characteristic of the current in synchronism with a drive signal for controlling the turning on / off of the semiconductor switching element (3a - 3f). [7] The power conversion device according to claim 1, wherein the current is a DC bus current measured between a smoothing capacitor (2) and an emitter of the semiconductor switching element (3a - 3f) of the main circuit unit. [8] The power conversion device according to claim 7, wherein the temperature setting unit sets a temperature of the semiconductor switching element (3a - 3f) based on a frequency at which a current peak value appears in response to a transient oscillation component of the DC bus current at a turn-on time or a turn-off time of the semiconductor switching element (3a - 3f) in the frequency characteristic. [9] The power conversion device according to claim 7, wherein the current is a transient oscillation component of the DC bus current at an on-time or an off-time of the semiconductor switching element (3a - 3f). [10] The power conversion device according to claim 9, wherein the temperature setting unit sets a temperature of the semiconductor switching element (3a - 3f) based on a frequency at which a current peak value appears in response to the transient oscillation component in the frequency characteristic. [11] The power conversion device according to claim 9, wherein the temperature setting unit detects the transient oscillation component flowing between a filter capacitor for removing noise of the DC bus current and ground. [12] A power conversion device according to claim 4, wherein a waveform of the current is obtained by sampling the current multiple times at predetermined time intervals by the A / D converter (11). [13] The power conversion device according to claim 4, wherein the A / D converter (11), the frequency conversion device (12), the memory device (14) and the calculator (13) are integrated into a semiconductor chip that configures a control unit that generates a drive signal for controlling the switching on / off of the semiconductor switching element (3a - 3f).

Images