Abstract:
An information output apparatus includes: a first switching element joined through a solder part, and forming one arm of a power conversion apparatus; a second switching element connected in series with the first switching element, and forming the other arm of the power conversion apparatus; a smoothing capacitor; a measuring unit configured to measure a temperature of the first switching element to output a measured value; an applying unit configured to apply two or more continuous pulses in a state where a potential difference across the smoothing capacitor is greater than or equal to a predetermined value, the pulses causing the first switching element and the second switching element to simultaneously turn on; an adjusting unit configured to adjust pulse widths of the pulses; and an output unit configured to output information indicating a deterioration of the solder part based on a manner of a change in measured values.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The disclosure is related to an information output apparatus. 
     2. Description of the Related Art 
     A technology is known, in which a service-life measuring pulse with its pulse width of around 10 μs is applied only once to upper and lower IGBT (Insulated Gate Bipolar Transistor) switching element to detect deterioration in a solder joint (for example, Japanese Laid-open Patent Publication No. 2009-19953). 
     However, actually, the deterioration in the solder joint cannot be detected in high precision since the IGBT is not heated enough by the short-circuiting current generated by applying only once the service-life measuring pulse with its pulse width of around 10 μs. 
     RELATED ART DOCUMENT 
     Patent Document 
     [Patent Document 1]: Japanese Laid-open Patent Publication No. 2009-19953 
     SUMMARY OF THE INVENTION 
     An object of the present disclosure is to provide an information output apparatus capable of outputting information precisely indicating a deterioration state of solder for jointing a switching element. 
     The following configuration is adopted to achieve the aforementioned object. 
     In one aspect of the embodiment, there is provided an information output apparatus comprising: a first switching element joined through a solder part to a surface of a substrate cooled by a refrigerant, and forming one arm of a power conversion apparatus; a second switching element connected in series with the first switching element, and forming the other arm of the power conversion apparatus; a smoothing capacitor disposed in parallel with the first switching element and the second switching element; a measuring unit configured to measure a temperature of the first switching element to output a measured value corresponding to the measured temperature; an applying unit, achieved by a process performed by a processing device, configured to apply two or more continuous pulses to the first switching element and the second switching element in a state where a potential difference across the smoothing capacitor is greater than or equal to a predetermined value, the pulses causing the first switching element and the second switching element to simultaneously turn on; an adjusting unit, achieved by a process performed by the processing device, configured to adjust pulse widths of the pulses so that a difference between a temperature of the first switching element before having the pulses applied and a temperature of the first switching element after having the pulses applied becomes greater than or equal to a predetermined temperature; and an output unit, achieved by a process performed by the processing device, configured to output information indicating a deterioration of the solder part based on a manner of a change in measured values, the measured values being output from the measuring unit when the pulses are applied. 
     Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram for illustrating configuration of an information output apparatus  1 . 
         FIG. 2  is a diagram for illustrating an example of a mounted first switching element  10 ; 
         FIG. 3  is a flowchart for illustrating an example of a solder deterioration determination process performed by the processing device  100 ; 
         FIG. 4  is a diagram illustrating an example of a circuit including the first switching element  10 ; 
         FIG. 5  is a diagram for showing an example of the heat/release curve; 
         FIG. 6  is a diagram for showing an example of the heat/release curve according to a deterioration of a solder part with relatively small loss; 
         FIG. 7  is a diagram for showing another example of the heat/release curve according to a deterioration of a solder part with relatively large loss; 
         FIG. 8A  is a diagram for illustrating change of short-circuiting current in a case where the pulse width of the test drive pulse is 5 μs; 
         FIG. 8B  is a diagram for illustrating change of short-circuiting current in a case where the pulse width of the test drive pulse is 5.1 μs; 
         FIG. 9  is a diagram for illustrating an example of variance of temperature of the solder part  50  and the like when applying the test drive pulse; and 
         FIG. 10  is a diagram for illustrating contribution rate of the solder part  50  in the variance of temperature of the first switching element  10 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, embodiments are described in detail with reference to appended drawings. 
       FIG. 1  is a diagram for illustrating a configuration of an information output apparatus  1 .  FIG. 2  is a diagram for illustrating an example of a mounted first switching element  10 . 
     The information output apparatus  1  includes the first switching element  10 , a second switching element  12 , a smoothing capacitor  20 , a temperature sensor  40 , and a processing device  100 . 
     In this example, the first switching element  10  is an IGBT (Insulated Gate Bipolar Transistor). The first switching element  10  may be formed by another switching element such as a MOSFET (Metal Oxide Semiconductor Field-Effect Transistor) instead of the IGBT. As shown in  FIG. 1 , a FWD (Free Wheeling Diode) may be disposed with the first switching element  10 . An emitter electrode of the first switching element  10  is connected with a negative electrode line  32  while a collector electrode of the first switching element  10  is connected to a positive electrode line  30  through the second switching element  12 . 
     As shown in  FIG. 2 , the first switching element  10  is mounted on a substrate  60  through a solder part  50 . The substrate  60  is mounted on the heat sink  70 . A lower surface (opposite to the substrate  60 ) of the heat sink  70  is in contact with a refrigerant. Fins  70   a  may be formed in the lower surface of the heat sink  70 . Additionally, although a configuration of the substrate  60  is optional, the substrate  60  is formed by disposing aluminum plates  62  and  66  at both sides of a ceramic substrate  64  such as aluminum nitride, in  FIG. 2 . Also, the substrate  60  may be formed by disposing copper plates at both sides of the ceramic substrate or may be formed only of a copper plate (heat spreader). In a case where the substrate  60  is formed only of a copper plate, the substrate  60  is mounted on the heat sink  70  through an insulation layer such as an insulation film. 
     In this example, although the second switching element  12  is an IGBT, the second switching element may be formed of another switching element. As shown in  FIG. 1 , a FWD may be disposed with the second switching element. As shown in  FIG. 1 , the first switching element  10  and the second switching element.  12  are connected in series between the positive electrode line  30  and the negative electrode line  32 . An emitter electrode of the second switching element  12  is connected with the collector electrode of the first switching element  10  while a collector electrode of the second switching element  12  is connected with the positive electrode line  30 . 
     Similarly to the first switching element  10 , the second switching element  12  is mounted on a substrate. Additionally, the substrate on which the second switching element  12  is mounted is electrically insulated from the substrate  60  on which the first switching element  10  is mounted. 
     The smoothing capacitor  20  is disposed between the positive electrode line  30  and the negative electrode line  32  in parallel with the first switching element  10  and the second switching element  12 . For example, a capacitance of the smoothing capacitor  20  is 1 mF. 
     The temperature sensor  40  measures a temperature of the first switching element  10 . The temperature sensor  40  may be formed in a chip including the first switching element  10 . 
     The processing device  100  includes an applying unit  102 , an adjusting unit  104  and a determination output unit  106 . The processing device  100  includes a microcomputer having a CPU. Functions of the processing device  100  (for example, respective functions of the applying unit  102 , the adjusting unit  104  and the determination output unit  106 , described below) may be achieved by arbitrary hardware, software, firmware or a combination thereof. For example, the functions of the processing device  100  may be achieved by an ASIC (application-specific integrated circuit) or an FPGA (Field Programmable Gate Array) for a specific use. Also, the processing device  100  may be achieved by a plurality of processing devices (including a processing device formed in a sensor). 
     The applying unit  102  applies two or more continuous test drive pulses for simultaneously switching on the first switching element  10  and the second switching element  12  to the first switching element  10  and the second switching element  12 , wherein a potential difference VH between both sides of the smoothing capacitor  20  is greater than or equal to a predetermined value VHth. The predetermined value VHth may be determined so that a temperature variance ΔT (described below) of the first switching element  10  in response to having the test drive pulse applied becomes greater than or equal to a predetermined temperature Tth. 
     The adjusting unit  104  adjusts a pulse width of the test drive pulse so that a temperature variance (difference) ΔT between before and after applying the test drive pulse to the first switching element  10  becomes greater than or equal to a predetermined temperature Tth. A specific example of method for adjusting by the adjusting unit  104  will be described below. 
     The determination output unit  106  outputs information indicating a deterioration of the solder part  50  based on the change of sensing values from the temperature sensor  40  when the two or more test drive pulses whose pulse widths are adjusted by the adjusting unit  104  are applied. The information indicating the deterioration of the solder part  50  indicates the deterioration of the solder part  50  directly or indirectly. For example, the determining unit  106  may output sensing values (change of the sensing values) sequentially (chronologically) output from the temperature sensor  40  when the two or more test drive pulses whose pulse widths are adjusted by the adjusting unit  104  are applied, thereby outputting the information indirectly indicating the deterioration of the solder part  50 . In this case, for example, an inspector in a dealer shop may determine the deterioration of the solder part  50  with reference to the sensing values sequentially output from the temperature sensor  40 . Also, the determination output unit  106  may determine the deterioration of the solder part  50  based on the change of the sensing values output from the temperature sensor  40  when the two or more test drive pulses whose pulse widths are adjusted by the adjusting unit  104  are applied, and output the determination result (an example of the information directly indicating the deterioration of the solder part  50 ). A specific example of a method for determining by the determination output unit  106  will be described below. Additionally, an output destination is optional, and it may be, for example, an onboard display, a terminal device in a dealer shop, an external server or the like. 
     Additionally, in  FIG. 2 , a pump  80  for providing the refrigerant to a flow passage of the refrigerant, which is formed in the lower surface side of the heat sink  70 , is schematically shown. The pump  80  forms a flow (circulation) of the refrigerant, which flows in a flow passage  82  thereby passing between the fins  70   a  of the heat sink  70 . The refrigerant is optional and may be air, or liquid such as LLC (Long-Life Coolant). In this example, the refrigerant is water and the pump  80  is a water pump. 
       FIG. 3  is a flowchart for illustrating an example of a solder deterioration determination process performed by the processing device  100 . Here, the description is given assuming that the first switching element  10 , the second switching element  12  and the smoothing capacitor  20  shown in  FIG. 1  are included in the electric circuit  2  shown in  FIG. 4 . The electric circuit  2  shown in  FIG. 4  is a circuit for a driving motor used in a hybrid vehicle or an electric vehicle and includes a DC power supply VL. The first switching element  10  and the second switching element  12  form a converter in cooperation with an inductor Id connected at a central point P 0  between the first switching element  10  and the second switching element  12 , thereby performing a voltage stepping-up operation and a voltage stepping-down operation. The driving motor (not shown) is connected to an inverter circuit  3 . 
     For example, the process shown in  FIG. 3  may be started when turning on an ignition switch or when turning off the ignition switch, and also may be started when receiving a certain test signal from a mobile device or the like in the dealer shop. Here, the description is given assuming that the process shown in  FIG. 3  is started when turning on the ignition switch. 
     In step S 300 , the processing device  100  stops the pump  80  (W/P). Additionally, in a case where the pump  80  has been stopped, it is kept being stopped. In a case where the pump  80  is not included, the process of step S 300  may be omitted. 
     In step S 302 , the adjusting unit  104  of the processing device  100  sets the pulse width of the test drive pulse to be an initial value. The initial value may correspond to a minimum value among the settable pulse widths. For example, the initial value may be 5 μs. 
     In step S 304 , the processing device  100  switches on the switch SW 1  (see  FIG. 4 ). Thus, the DC power supply VL (see  FIG. 4 ) is connected to the inverter circuit  3  (see  FIG. 4 ) through the converter. 
     In step S 306 , the processing device  100  generates a voltage stepping-up instruction to perform the voltage stepping up operation. For example, the voltage stepping-up instruction may indicate an output voltage of the converter (potential difference VH between P 1  and P 2 ) of 500 V. Also, for example, only the first switching element  10  in a lower arm may be switched on/off according to the voltage stepping-up instruction. Thus, the voltage supplied from the DC power supply VL is stepped-up and output to the inverter circuit  3 , while charge for generating potential difference VH (greater than “0”) is accumulated in the smoothing capacitor  20 . 
     In step S 308 , the processing device  100  determines whether the potential difference VH is greater than or equal to the predetermined value VHth. The predetermined value VHth may be slightly lower than a target value (for example, 500 V) of the output value of the converter. In a case where the potential difference VH is greater than or equal to the predetermined value VHth (YES in S 308 ), the process proceeds to step S 310 . In a case where the potential difference VH is not greater than or equal to the predetermined value VHth, the process waits until the potential difference VH becomes greater than or equal to the predetermined value VHth (while the voltage stepping-up operation is continued). 
     In step S 310 , the processing device  100  switches off the switch SW 1  and stops performing the voltage stepping-up operation. Thus, the first switching element  10  (and the second switching element  12 ) is switched off. 
     In step S 312 , the applying unit  102  of the processing device  100  continuously outputs the test drive pulses (see “PL” in  FIG. 4 ) and applies them to the first switching element  10  and the second switching element  12 . A frequency of the output test drive pulses is defined by a frequency of a carrier signal for generating the pulses. For example, the frequency of the carrier signal may be 50 kHz. The applying unit  102  applies the test drive pulses so that the first switching element  10  and the second switching element  12  are switched on at the same time. The applying unit  102  continuously outputs the test drive pulses within a certain period T 1 . For example, the certain period T 1  is a period from 3 ms to 110 ms, preferably, is a period from 5 ms to 100 ms, and more preferably, is a period from 5 ms to 20 ms. Also, the certain period T 1  may be a time it takes the potential difference VH to be a predetermined value (for example 0 V). In this case, the applying unit  102  continuously outputs the test drive pulses until the potential difference VH becomes a certain value. When passing the certain period T 1 , the process proceeds to step S 314 . 
     In step S 314 , the adjusting unit  104  of the processing device  100  determines, based on the sensing values of the temperature sensor  40 , whether a temperature of the first switching element  10  increases greater than or equal to the predetermined temperature Tth, that is, determines whether the temperature variance ΔT of the first switching element  10  is greater than or equal to the predetermined temperature Tth. The temperature variance ΔT may be a difference between a temperature of the first switching element  10  just before having the test drive pulses applied and that after having applied the test drive pulses applied. Or it may be a difference between a temperature of the first switching element  10  just before the test drive pulses are applied and a peak (highest) temperature of the first switching element  10  while the test drive pulses are being applied. A measured temperature of the refrigerant may be used, instead of the sensing value of the temperature sensor  40 , as the temperature of the first switching element  10  just before the test drive pulses are applied, since the temperature of the refrigerant just before the test drive pulses are applied is assumed to be almost the same as the temperature of the first switching element  10  just before the test drive pulses are applied. In a case where the temperature variance ΔT of the first switching element  10  is greater than or equal to the predetermined temperature Tth, the process proceeds to step S 320 . In a case where the temperature variance ΔT of the first switching element  10  is not greater than or equal to the predetermined temperature Tth, the process proceeds to step S 316 . 
     In step S 316 , the adjusting unit  104  of the processing device  100  expands the pulse width of the test drive pulse. For example, the adjusting unit  104  expands the pulse width of the test drive pulse by 12.5 ns. Therefore, when the process of step S 312  is performed next time, the applying unit  102  of the processing device  100  outputs the test drive pulses whose pulse widths are expanded in step S 316 . Additionally, the adjusting unit  104  expands the pulse width of the test drive pulse as long as the pulse width does not exceed a certain upper limit. The certain upper limit depends on short-circuiting tolerance of the first switching element  10 , and may be, for example, several dozen μs. 
     In step S 318 , the processing device  100  determines whether the potential difference VH is greater than or equal to the predetermined value VHth. In a case where the potential difference VH is greater than or equal to the predetermined value VHth, the process proceeds to step S 312 . In a case where the potential difference VH is not greater than or equal to the predetermined value VHth, the process returns to step S 304 . 
     In step S 320 , the determination output unit  106  of the processing device  100  acquires (latches) a heat/release curve while applying the test drive pulses.  FIG. 5  is a diagram for showing an example of the heat/release curve. In  FIG. 5 , the heat/release curve is shown where the horizontal axis shows time and the vertical axis shows the temperature (sensing value of the temperature sensor  40 ) of the first switching element  10 . In  FIG. 5 , the temperature of the first switching element  10  rapidly increases from timing T 0  at which the test drive pulse is started to be applied and reaches its peak at timing t 1  from which the temperature gradually decreases. The reason the temperature rapidly increases from timing T 0  is that a great short-circuiting current flows at timing T 0  since the potential difference VH is great, and transfer of heat generated by the first switching element  10  to the substrate  60  is temporarily shut off by the solder part  50 . The reason the temperature gradually decreases from timing t 1  is that the potential difference VH gradually becomes smaller. 
     In step S 322 , the determination output unit  106  of the processing device  100  determines, based on the heat/release curve, the deterioration of the solder part  50  and outputs the determination result. The method for determining based on the heat/release curve is optional. 
     The heat/release curve varies according to the deterioration of the solder part  50 .  FIG. 6  is a diagram for showing another example of the heat/release curve in a case where the test drive pulses are continuously applied within 10 ms (a certain period T 1 ) to cause loss corresponding to 800 W in the first switching element  10 . In  FIG. 6 , a curved line A shows a case of a non-deteriorated (non-defective) solder part  50 , while a curved line B shows a case of a deteriorated solder part  50 . As shown in  FIG. 6 , in a case where the solder part  50  is deteriorated, the peak temperature TP in the curve becomes higher in comparison to a case where the solder part  50  is not deteriorated. This is caused by the deterioration of the solder part  50  which causes shutting off the transfer of heat to the substrate  60 . Therefore, the determination output unit  106  of the processing device  100  may determine the deterioration of the solder part  50  based on the peak temperature TP in the heat/release curve.  FIG. 7  is a diagram for showing another example of the heat/release curve in a case where the test drive pulses are continuously applied within 10 ms to cause loss corresponding to 1600 W in the first switching element  10 . In  FIG. 7 , a curved line A shows a case of non-deteriorated (non-defective) solder part  50 , while a curved line B shows a case of deteriorated solder part  50 . Similarly to  FIG. 6 , as shown in  FIG. 7 , in a case where the solder part  50  is deteriorated, the peak temperature TP in the curve becomes higher in comparison to a case where the solder part  50  is not deteriorated. Also, as shown in  FIG. 6  and  FIG. 7 , the difference between the respective peak temperatures Tp becomes greater when the loss becomes greater. For example, in  FIG. 7 , the difference between the respective peak temperatures TP is more than two times greater than that in  FIG. 6 . This shows that the deterioration of the solder part  50  can be more precisely determined when the loss generated in the first switching element  10  becomes greater. Additionally, the predetermined temperature Tth (threshold with respect to temperature variance ΔT) referred to in step S 314  may be set taking this into account. That is, since the temperature variance ΔT depends on the loss in the first switching element  10 , the deterioration of the solder part  50  can be precisely determined by setting the predetermined temperature Tth to be a large value. Although depending on precision of the temperature sensor  40 , a required determination precision or the like, in a case where the deterioration is determined when the difference between the respective peak temperatures Tp becomes greater than or equal to 10% of the peak temperature Tp of non-defective product, for example, the predetermined temperature Tth may be set so that the 10% of the peak temperature Tp is greater than or equal to 5° C. 
     The determination result of the deterioration of the solder part  50  may be output in an arbitrary manner. For example, two types of determination result merely indicating presence or absence of the deterioration may be output, or three or more types of determination result may be output. The two types of determination result may be expressed by outputting an alarm only when the presence of deterioration is determined. Also, the determination output unit  106  of the processing device  100  may output the difference between the respective peak temperatures Tp (difference of the peak temperatures between the tested product and the non-defective product), or the heat/release curve itself, as the determination result of the deterioration of the solder part  50 . In this case, for example, an inspector in a dealer shop may determine the deterioration of the solder part  50  with reference to the difference value or the heat/release curve. 
     In this example, the determination output unit  106  of the processing device  100  detects the peak temperature Tp based on the heat/release curve, thereby determining the presence of the deterioration in a case where the detected peak temperature Tp is higher than a reference temperature by a value greater than or equal to a predetermined threshold while determining the absence of the deterioration in a case where the detected peak temperature Tp is not higher than the reference temperature by a value greater than or equal to the predetermined threshold. The reference temperature may be set based on data acquired through an experiment. For example, the data acquired through an experiment may indicate the peak temperature Tp of a non-defective product having the test drive pulses applied in the same condition (the pulse width or the certain period T 1 ). Or, the reference temperature may be set to be another peak temperature Tp which is detected based on a heat/release curve of the second switching element  12 . The second switching element  12  is disposed in the upper arm and a frequency of driving the second switching element  12  is significantly lower than that of the first switching element  10 . Therefore the heat/release curve of the second switching element  12  is used since the second switching element  12  is likely to remain non-defective. 
     According to the process shown in  FIG. 3 , the deterioration of the solder part  50  can be determined based on the variance of temperature of the first switching element  10  when applying the test drive pulses to it, which is indicated by the heat/release curve. Also, the deterioration of the solder part  50  is determined based on the heat/release curve in which the temperature variance ΔT of the first switching element  10  is greater than or equal to the predetermined temperature Tth. Therefore, the precision of the determination result can be improved. 
       FIG. 8A  and  FIG. 8B  are diagrams for illustrating change of short-circuiting current when applying the test drive pulses.  FIG. 8A  is a diagram for illustrating change of short-circuiting current in a case where the pulse width of the test drive pulse is 5 μs.  FIG. 8B  is a diagram for illustrating change of short-circuiting current in a case where the pulse width of the test drive pulse is 5.1 μs. 
     As shown in  FIG. 8A  and  FIG. 8B , in a case where the pulse width of the test drive pulse is 5 μs, a period in which the short-circuiting current flows becomes longer although a peak value of the short-circuiting current becomes lower in comparison to the case where the pulse width of the test drive pulse is 5.1 μs. As a consequence, the temperature variance ΔT of the first switching element  10  becomes 50° C. in a case where the pulse width of the test drive pulse is 5 μs while it becomes 19° C. in a case where the pulse width of the test drive pulse is 5.1 μs. In a case where the pulse width of the test drive pulse is 5 μs, the loss in the first switching element  10  becomes greater, which causes the determination result to be in higher precision, in comparison to the case where the pulse width of the test drive pulse is 5.1 μs. This means that since energy is consumed in the smoothing capacitor  20  in response to an instantaneously large current flow when the test drive pulses with longer pulse widths are applied, the loss in the first switching element  10  becomes smaller. Meanwhile, if the pulse width of the test drive pulse is too short, the required loss cannot be generated since the short-circuiting current is small or does not substantially flow. Thus, there is an appropriate value of the pulse width for maximizing the loss. However, the appropriate value of the pulse width varies according to individual difference (the individual difference of the first switching element  10  or that of the driving circuit). 
     According to the process shown in  FIG. 3 , certain precision of the determination result can be kept since the pulse width for generating more than a certain loss (the temperature difference ΔT greater than or equal to the predetermined temperature Tth) is searched for while slightly varying the pulse width (see step S 314  and S 316 ). 
     Additionally, in the process shown in  FIG. 3 , the pulse width for causing the maximum temperature difference ΔT is not searched for. However, the pulse width for causing the maximum temperature difference ΔT may be searched for and the deterioration of the solder part  50  may be determined based on the heat/release curve with the pulse width for causing the maximum temperature difference ΔT. 
       FIG. 9  is a diagram for illustrating an example of variance of temperature of the solder part  50  and the like when the test drive pulses are applied.  FIG. 10  is a diagram for illustrating a contribution rate of the solder part  50  in the variance of temperature of the first switching element  10  shown in  FIG. 9 . 
     In  FIG. 9 , a curved line shown as “ΔT” indicates the temperature variance of the first switching element  10 , a curved line shown as “δTsn” indicates the temperature variance of the solder part  50 , a curved line shown as “δTal 1 ” indicates the temperature variance of the aluminum plate  62  (see  FIG. 2 ), a curved line shown as “δTal 2 ” indicates the temperature variance of the aluminum plate  66  (see  FIG. 2 ), a curved line shown as “δTaln” indicates the temperature variance of the ceramic substrate  64  (see  FIG. 2 ), a curved line shown as “δTplt” indicates the temperature variance of the heat sink  70  (see  FIG. 2 ), and a curved line shown as “δTfin” indicates the temperature variance of the fins  70   a  (see  FIG. 2 ). 
     As shown in  FIG. 9 , the temperature of the solder part  50  is saturated relatively quickly. In  FIG. 9 , the temperature of the solder part  50  is saturated in around 10 ms. When the temperature of the solder part  50  is saturated, the heat generated by the first switching element  10  is likely to be transferred to the substrate  60  disposed in the lower layer with respect to the solder part  50 . Thus, as shown in  FIG. 10 , the contribution rate of the solder part  50  to the temperature of the first switching element  10  decreases relatively quickly. The contribution rate of the solder part  50  to the temperature of the first switching element  10  expresses that how much the solder part  50  shuts off the transfer of the heat from the first switching element  10  to the substrate  60 . Therefore, the deterioration of the solder part  50  can be precisely determined in a case where the temperature variance of the first switching element  10  with the high contribution rate is used. In  FIG. 10 , the contribution rate of the solder part  50  reaches at its peak (approx. 40%) in several ms, then it significantly decreases to reach approx. 4% in 1 s. 
     Additionally, according to the process shown in  FIG. 3 , as described above, the determination output unit  106  of the processing device  100  determines the deterioration of the solder part  50  based on the peak temperature Tp. If a timing at which the peak temperature Tp is generated is coincident with a timing at which the contribution rate of the solder part  50  reaches its peak, the deterioration of the solder part  50  can be precisely determined. Therefore, the adjusting unit  104  of the processing device  100  may adjust the pulse width so that the peak temperature Tp is generated in a short period (for example, within 10 ms). Thus, the deterioration of the solder part  50  can be precisely determined. 
     Additionally, in the process shown in FIG.  3 , although the determination output unit  106  of the processing device  100  determines the deterioration of the solder part  50  based on the peak temperature Tp, the deterioration of the solder part  50  may be determined based on other parameters instead of or in addition to the peak temperature Tp. For example, the other parameters may include a temperature variance ΔT up to the peak temperature Tp, a speed of temperature rise to the peak temperature Tp, a time taken to reach a predetermined temperature (for example, 100° C.), a speed (change rate against time) of temperature drop from the peak temperature Tp, and the like. The speed of temperature rise to the peak temperature Tp may be defined based on a time taken to raise the temperature to the peak temperature Tp (time t 0 -t 1  in  FIG. 5 ), or it may be defined based on the temperature of the first switching element  10  after passing a certain time (for example, 5 μs) from applying the test drive pulse. The speed of temperature drop from the peak temperature Tp may be defined, for example, as shown in  FIG. 5 , based on a temperature of the first switching element  10  when a certain time (for example, 5-20 μs) passes from timing t 1  at which the temperature reaches its peak temperature Tp, or based on a time (time t 1 -t 2  in  FIG. 5 ) taken to drop the temperature to a predetermined temperature from timing t 1  at which the temperature reaches its peak temperature Tp. These parameters may be used as an arbitrary combination thereof. In this case, the determination output unit  106  of the processing device  100  may determine the deterioration of the solder part  50  taking into account of the following. The temperature variance ΔT up to the peak temperature Tp is likely to increase as the degree of the deterioration of the solder part  50  increases. The speed of temperature rise to the peak temperature Tp is likely to increase as the degree of the deterioration of the solder part  50  increases. The time taken to reach a predetermined temperature is likely to decrease as the degree of the deterioration of the solder part  50  increases. The speed of temperature drop from the peak temperature Tp is likely to decrease as the degree of the deterioration of the solder part  50  increases. The transfer of the heat from the first switching element  10  to the substrate  60  is more shut off as the degree of the deterioration of the solder part  50  increases, which causes the aforementioned tendencies. 
     Also, the determination output unit  106  of the processing device  100  may determine the deterioration of the solder part  50  by comparing a waveform (pattern) of the heat/release curve of the first switching element  10  with a reference pattern. The reference pattern may be set based on data acquired through an experiment (for example, a heat/release curve of a non-defective product when the test drive pulses are applied in the same condition). Or, the reference pattern may be set based on a heat/release curve of the second switching element  12 . The second switching element  12  is disposed in the upper arm and a frequency of driving the second switching element  12  is significantly lower than that of the first switching element  10 . Therefore the heat/release curve of the second switching element  12  is used since the second switching element  12  is likely to remain non-defective. In this case, the determination output unit  106  of the processing device  100  may compare the pattern of the heat/release curve in a term where the contribution rate of the solder part  50  is relatively high (for example, a term of 0-20 μs). 
     Herein above, although the invention has been described with respect to a specific embodiment, the appended claims are not to be thus limited. It should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the claims. Further, all or part of the components of the embodiments described above can be combined. 
     For example, although in the embodiment described above, mainly, the first switching element  10  and the second switching element  12  shown in  FIG. 1  respectively form the lower arm and the upper arm of the converter (an example of a power conversion apparatus), the present technology can be applied to a case where the first switching element  10  and the second switching element  12  shown in  FIG. 1  respectively form a lower arm and a upper arm (or a upper arm and a lower arm) of the inverter circuit  3  (another example of the power conversion apparatus.) 
     Further, although in the embodiment described above, in step S 312  shown in  FIG. 3 , the pulse widths of the output pulses are fixed, the pulse widths may be variable. 
     Also, in the embodiment described above, as shown in  FIG. 3 , the adjusting unit  104  sets the initial value of the pulse width to be a minimum value among the settable pulse widths (see step S 302 ), and gradually expands the pulse width until the temperature variance ΔT of the first switching element  10  caused by applying pulses becomes greater than or equal to the predetermined temperature Tth (step S 316 ). However, the adjusting unit  104  may set the initial value of the pulse width to be a maximum value among the settable pulse widths, and gradually diminishes the pulse width until the temperature variance ΔT of the first switching element  10  caused by applying pulses becomes greater than or equal to the predetermined temperature Tth. 
     The present application is based on Japanese Priority Application No. 2014-144421, filed on Jul. 14, 2014, the entire contents of which are hereby incorporated by reference.