Abstract:
The present invention provides a power converter which, while ensuring safety, implements control for the flow of a constant current in a specified switching element, more accurately determines the lifetime of a switching element, and reduces the number of temperature detectors. The power converter is provided with a mechanism which causes a brake device to operate or which confirms that a brake mechanism is operating. The power converter supplies current to the d-axis and the q-axis of a rotational coordinate system, within the range of the braking torque of the brake mechanism, and passes the desired current to the desired element. Furthermore, temperature detectors are attached only in chips in sections where a crack readily develops in the upper solder layer or peeling is readily generated in the wire bonding, and in chips where a crack readily develops in the lower solder layer.

Description:
TECHNICAL FIELD 
     The present invention relates to a power converter, and more particularly to a power converter that motor drives a moving body. 
     BACKGROUND ART 
     The power converter described in Patent Literature 1 drives the power transistor so that a predetermined value of current is supplied to the motor for a predetermined period of time before driving a vehicle in order to determine the lifetime of the power semiconductor device of the power converter mounted on a hybrid vehicle. In addition, the power converter calculates the thermal resistance value of the power transistor and, based on the calculated thermal resistance value, determines the lifetime. 
     CITATION LIST 
     
         
         PATENT LITERATURE 1: JP-A-2003-9541 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, according to the description in Patent Literature 1, because the lifetime is determined by supplying current (d-axis current), which does not generate torque, as the current command, a measurable switching element varies according to the magnetic pole position of the motor and, therefore, it is difficult to supply a constant current to a particular switching element. In addition, because the state of the magnetic pole position is indeterminate, some switching elements can hardly be evaluated depending upon the condition. It is also described that current is supplied to an element in the fixed coordinate system (UVW phase), selected by the magnetic pole position, using a command composed only of the d-axis in the rotational coordinate system. However, it is difficult to constantly supply a constant value of current under the condition in which the state of the magnetic pole position is indeterminate, sometimes with a result that an error in evaluation determination will become serious. In addition, a temperature detector must be installed on all switching elements to allow a measurable switching element to be selected according to the magnetic pole position, this configuration generates the problem that the cost will increase and that the device installation will become more complex. 
     It is an object of the present invention to provide a power converter that performs control so that a constant current is supplied to a particular switching element while ensuring safety, determines the lifetime of a switching element more accurately, and reduces the number of temperature detectors. 
     Solution to Problem 
     To achieve the problems described above, the present invention is characterized in that a power converter comprises an inverter main circuit; a motor driven by the inverter main circuit; a brake device that puts brake on the motor; a control circuit that calculates a command value for driving the inverter main circuit; a mechanism that causes the brake device to operate or confirms that the brake device is in operation; and a temperature detector that detects a temperature of a switching element mounted in the inverter main circuit wherein, with the brake device in operation, a command for supplying a predetermined current to a particular phase is given from the control circuit to the inverter main circuit, a current is supplied from the inverter main circuit to the motor, and a lifetime of the switching element is evaluated based on temperature information detected by the temperature detector. 
     In addition, the present invention provides the power converter characterized in that the predetermined current supplied to a particular phase with the control device in operation is a current in which a field system current component and a torque current component are mixed and in that a torque generated by the motor using the mixed current is smaller than a braking torque of the brake device. 
     In addition, the present invention provides the power converter characterized in that the temperature detector is composed of two chips, one is a chip in the center and the other is a chip on an outermost periphery, in modules configuring the inverter main circuit. 
     In addition, the present invention provides the power converter characterized in that the phase to which the predetermined current is supplied is a phase that includes a chip where the temperature detector detects temperature and in that an amount of the predetermined current is a constant value for all phases. 
     In addition, the present invention provides the power converter characterized in that an element module configuring the inverter main circuit is a six-in-one mode module in which all switching elements of three phases of the inverter are mounted and in that an operation of the power converter is controlled so that almost equal losses are generated in the phases in a steady state. 
     In addition, the present invention provides the power converter characterized in that, if a detected temperature value or temperature rise value becomes larger by at least a predetermined amount as compared with normal-time history or exceeds a predefined reference temperature value or reference temperature rise value, information is displayed on a display device or notified to a management center. 
     In addition, the present invention provides the power converter characterized in that, if a detected temperature value or temperature rise value becomes larger by at least a predetermined amount as compared with normal-time history or exceeds a predefined reference temperature value or reference temperature rise value, an output power of the inverter main circuit is limited. 
     In addition, the present invention provides the power converter characterized in that a lifetime evaluation of the switching element is performed before a moving body is operated, or in a stopped state after a predetermined operation is performed, or at a predetermined time. 
     To achieve the problems described above, the present invention is characterized in that a power converter comprises an inverter main circuit; a motor driven by the inverter main circuit; a brake device that puts brake on the motor; a control circuit that calculates a command value for driving the inverter main circuit; a mechanism that causes the brake device to operate or confirms that the brake device is in operation; and a voltage detector provided between terminals of switching elements mounted in the inverter main circuit wherein, with the brake device in operation, a command for supplying a predetermined current to a phase, to which the voltage detector is connected, is given from the control circuit to the inverter main circuit, a current is supplied from the inverter main circuit to the motor, and a lifetime of the switching element is evaluated based on voltage information detected by the voltage detector. 
     In addition, the present invention provides the power converter characterized in that the predetermined current supplied to a particular phase with the control device in operation is a current in which a field system current component and a torque current component are mixed and in that a torque generated by the motor using the mixed current is smaller than a braking torque of the brake device. 
     In addition, the present invention provides the power converter characterized in that the predetermined current supplied to a particular phase with the control device in operation is a current in which a field system current component and a torque current component are mixed and in that a torque generated by the motor using the mixed current is smaller than a braking torque of the brake device. 
     In addition, the present invention provides the power converter characterized in that a thermal resistance value is calculated using a voltage detected by the voltage detector and, if the calculated thermal resistance value becomes larger by at least a predetermined amount as compared with normal-time history or exceeds a predefined reference thermal resistance value, information is displayed on a display device or notified to a management center. 
     In addition, the present invention provides the power converter characterized in that a thermal resistance value is calculated using a voltage detected by the voltage detector and, if the calculated thermal resistance value becomes larger by at least a predetermined amount as compared with normal-time history or exceeds a predefined reference thermal resistance value, an output power of the inverter main circuit is limited. 
     In addition, the present invention provides the power converter characterized in that a lifetime evaluation of the switching element is performed before a moving body is operated, or in a stopped state after a predetermined operation is performed, or at a predetermined time. 
     Advantageous Effects of Invention 
     The present invention provides a power converter that performs control so that a constant current is supplied to a particular switching element while ensuring safety, determines the lifetime of a switching element more accurately, and reduces the number of temperature detectors. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a configuration diagram showing a first embodiment of the present invention. 
         FIG. 2  is a diagram showing an example of the chip arrangement in an element module in the first embodiment. 
         FIG. 3  is a cross sectional diagram of the dotted part in  FIG. 2 . 
         FIG. 4  is a diagram showing an example of the junction temperature and the chip bottom temperature with respect to a speed command. 
         FIG. 5  is a diagram showing an example of the cycle lifetime characteristics of a semiconductor device. 
         FIG. 6  is a block diagram showing the main circuit inverter control in the first embodiment. 
         FIG. 7  is a flowchart showing lifetime evaluation in the first embodiment. 
         FIG. 8  is a diagram showing an example of lifetime determination in the first embodiment. 
         FIG. 9  is a configuration diagram showing a second embodiment of the present invention. 
         FIG. 10  is a flowchart showing lifetime evaluation in the second embodiment. 
         FIG. 11  is a diagram showing an example of lifetime determination in the second embodiment. 
         FIG. 12  is a diagram showing an example in which the first embodiment or the second embodiment is used in an elevator. 
         FIG. 13  is a diagram showing an example in which the first embodiment or the second embodiment is used in an electric vehicle. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention are described below with reference to the drawings. 
     First Embodiment 
       FIG. 1  is a diagram showing a power converter in a first embodiment of the present invention. The power converter comprises an inverter main circuit  101 , a motor  102  driven by the inverter main circuit  101 , a brake device  103  for putting brake on the motor  102 , a rotary encoder  104  that detects the magnetic pole position and the rotational speed of the motor  102 , a current detector  105  that detects the current outputting from the inverter main circuit  101  to the motor  102 , a control circuit  106  that carries out operation for controlling the inverter main circuit  101  using the magnetic pole position signal received from the rotary encoder  104  and the current signal received from the current detector  105 , a brake circuit  107  that activates/deactivates the brake device  103 , and a lifetime evaluation circuit  108  that evaluates the lifetime of a switching element based on the switching element information output from the inverter main circuit  101 . The inverter main circuit  101  uses an element module  109 . In the first embodiment, the inverter main circuit  101  uses the so-called six-in-one module in which the six switching elements, corresponding to the three phases (UVW phases) of the output, are mounted in one module. 
       FIG. 2  is a diagram showing an example of the chip arrangement in the element module  109  shown in  FIG. 1 . Each phase of the inverter main circuit has the configuration in which the switching elements, each composed of the switch part, such as an IGBT, transistor, and MOS-FET, and the diode part, are connected in series. For example, a U-phase positive pole side switching element  109 UP shown in  FIG. 1  is configured by a substrate, on which the switch part chip Tup and the diode part chip Dup are mounted, as shown by the dotted line in  FIG. 2 . This substrate and the similarly configured U-phase negative pole side substrate, on which the switch part chip Tun and the diode part chip Dun are mounted, are electrically connected in series. Similarly, the V-phase positive pole side substrate, on which the switch part chip Tvp and the diode part chip Dvp are mounted, and the V-phase negative pole side substrate, on which the switch part chip Tvn and the diode part chip Dvn are mounted, are connected in series. Also, the W-phase positive pole side substrate, on which the switch part chip Twp and the diode part chip Dwp are mounted, and V-phase negative pole side substrate, on which the switch part chip Twn and the diode part chip Dwn are mounted, are connected in series.  FIG. 2  shows an example of the configuration in which the U phase is arranged on the left side, the V phase in the center, and W phase on the right side. 
       FIG. 3  shows an example of the cross section of the dotted-line part in  FIG. 2  (substrate part on which the switch part chip Tup and the diode part chip Dup are mounted). In this example, a metal pattern  111   a  is connected below the switch part chip Tup and the diode part chip Dup via an upper solder layer  114   a . In addition, the laminated structure is built in which the metal pattern  111   a  is connected to a metal pattern  111   b  via an insulating substrate  112   a  and the metal pattern  111   b  is connected to a metal base plate  113  via an insulating substrate  112   b , which connects to all substrates, and an lower solder layer  114   b . In addition, the switch part chip Tup and the diode part chip Dup are connected to the metal pattern by a metal conducting wire  115 . 
     The switching element is deteriorated in most cases when a crack develops in the lower solder layer  114   b  as shown in  FIG. 3 . This crack develops when the temperature is changed as the inverter is started and stopped repeatedly and, as a result, stress is generated between the metal base plate  113  and the lower solder layer  114   b  because of a difference in the coefficient of thermal expansion between the metals. Similarly, due to a change in the temperature on the chip, a crack develops as shown in the upper solder layer  114   a  in  FIG. 3  or peeling occurs on the metal conducting wire  115 . This crack or the peeling deteriorates the radiation efficiency and further increases the temperature change, leading to chip destruction. 
       FIG. 4  shows an example of the junction temperature and the chip bottom temperature with respect to the speed command. Here, the junction temperature refers to the temperature of a chip, and the chip bottom temperature refers to the temperature of the metal base plate  113  directly under the chip. Because the time constant of the junction temperature for a heat change is small, the temperature increases in an acceleration area where the speed increases (area where the output torque is high and a relatively large current flows) and the temperature decreases in a constant-speed area and a deceleration area. On the other hand, because the bottom of a chip is connected to a radiation part such as a heat sink that has a large heat capacity, the thermal time constant of the chip bottom temperature is large and the temperature gradually increases during the operation. A large time constant indicates that the temperature gradually increases and that the temperature gradually decreases when the operation is stopped. Therefore, when the operation is started and then stopped frequently and continuously, the chip bottom temperature starts increasing before the temperature decreases to the initial temperature at a stopped time, meaning that the temperature increases over time. In addition, this increased temperature is added to the junction temperature with the result that the peak value of the junction temperature is increased. In general, the change ΔTj in the junction temperature affects a crack in the upper solder layer  114   a  and a peeling of the metal conducting wire, and the change ΔTc in the chip bottom temperature affects the lower solder layer  114   b .  FIG. 5  is a diagram showing an example of the cycle life characteristics of a semiconductor device. The lifetime of a switching element is shortened inversely proportional to the change ΔTj in the junction temperature and the change ΔTc in the chip bottom temperature. 
     When considering a crack in the lower solder layer  114   b , the crack tends to propagate from the periphery to the center of the lower solder layer  114   b  because of the stress-strain relation. Therefore, the radiation efficiency is decreased beginning with the chips near the periphery (corresponding to Dup, Dun, Dwp, and Dwn in the example in  FIG. 2 ), with the temperature largely increased in those chips. On the other hand, when considering a crack in the upper solder layer  114   a  and a peeling of the metal conducting wire  115 , the crack and the peeling are generated more easily in the chips in the center. This is because, though a heat loss generally occurs evenly in the phases of the inverter main circuit, the temperature of the central part of the metal base plate  113  becomes highest in the chip arrangement shown in  FIG. 2  because the central part is affected by thermal interference caused by the heat generation in the other phases. As a result, a crack in the upper solder layer  114   a  and a peeling of the metal conducting wire  115  are conspicuous in the chips in the center (corresponds to Tvp and Tvn in the example in  FIG. 2 ). When a crack develops in the upper solder layer  114   a , the radiation efficiency is decreased, as in the lower solder layer  114   b , with the temperature increased in the corresponding chips. The peeling of the metal conducting wire  115  also increases the resistance and therefore increases the temperature of the corresponding chips. Therefore, temperature detectors  110   a  and  110   b , such as a temperature-detecting diode or a thermo-couple, are connected only to the chips in the center and the chips in the outmost chips as shown in  FIG. 2  for evaluating the temperature. Connecting the temperature detectors in this way makes it possible to detect the most conspicuous part of the deterioration in the lower solder layer  114   b  and the most conspicuous part of the deterioration and most-peeled-off part of the metal conducting wire  115  in the upper solder layer  114   a.    
     Next, the following describes the control of the inverter main circuit  101  in the first embodiment.  FIG. 6  is a block diagram showing the control of the main circuit inverter in the first embodiment. In  FIG. 6 , the current signal of each phase (u, v, w phase) in the fixed coordinate system, obtained from a current detector  5 , is converted to the signal (Idf, Iqf) in the rotational coordinate system (dq phase) by a 3-phase/2-phase conversion unit  116 . The d-axis and the q-axis in the rotational coordinate system cross at right angles and, in general, the d-axis is an axis for motor field-system components, and the q-axis is an axis for motor torque components. That is, in controlling the motor  102 , the coordinate system is converted to the rotational coordinate system to allow the field system and the torque to be controlled independently. The difference between the signal (Idf, Iqf) in the rotational coordinate system described above and the current command value (Id*, Iq*) is input to a d-axis current control system  117   d  and the q-axis current control system  117   q  respectively to make the signal (Idf, Iqf) follow the current command value (Id*, Iq*). In addition, the output result (voltage command in the rotational coordinate system) is input to a 2-phase/3-phase conversion unit  118  to convert the value to a value in the fixed coordinate system. The converted value is then input to a pulse width modulation conversion unit  119  that outputs the voltage command of each element of the inverter main circuit  101 . 
     To perform the temperature evaluation accurately, it is necessary to constantly supply a constant current to a particular switching element for evaluation. That is, it is important to decide how to determine the current command value (Id*, Iq*) in the rotational coordinate system for supplying a constant current to the semiconductor switch of a particular phase in the fixed coordinate system. The relational expression of the rotational coordinate system and the fixed coordinate system is shown in [Expression 1]. 
     
       
         
           
             
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     In [Expression 1], θ is the magnetic pole position of the motor  102 . When a constant current amount Iconst is supplied to the V phase output assuming that the element in the V phase in  FIG. 2  is evaluated, the following is obtained by substituting −Iconst/2, which is the current that returns to the U phase and W phase, in [Expression 1]. 
                   [     MATH   .           ⁢   2     ]     ⁢           ⁢     
     ⁢           [     Expression   ⁢           ⁢   2     ]     ⁢     
     [         Id           iq         ]     =       2   3     ⁢     Iconst   ⁡     [               -     1   2       ⁢   cos   ⁢           ⁢   θ     +     cos   ⁡     (     θ   -       2   3     ⁢   π       )       -       1   2     ⁢     cos   ⁡     (     θ   +       2   3     ⁢   π       )                         1   2     ⁢   sin   ⁢           ⁢   θ     -     sin   ⁡     (     θ   -       2   3     ⁢   π       )       +       1   2     ⁢     sin   ⁡     (     θ   +       2   3     ⁢   π       )                 ]               
Therefore, a desired current may be supplied to the V phase by setting the current command value (Id*, Iq*) in  FIG. 6  based on [Expression 2]. A desired current may also be supplied to the U phase or the W phase by carrying out the similar calculation.
 
     However, because the current is supplied also to the torque axis (q-axis) according to [Expression 2], there is a possibility that the motor will rotate to operate the moving body. Therefore, in the present invention, the brake circuit  107  shown in  FIG. 1  is used to operate the brake device of the motor  102  or to confirm that the brake mechanism is in operation and, under the condition that the brake device is in operation, the command indicated by [Expression 2] is given to supply a desired current. This achieves the effect that a desired current may be supplied to the element of a desired phase while ensuring safety. Of course, the torque generated by the current given by [Expression 1] and [Expression 2] is within the range of the braking torque of the brake device  103 . 
     Next, the following describes the current flowing in the chips in each phase in  FIG. 2 . The output current in the V phase can be controlled by [Expression 2]. However, for example, when current flow is set up so that the current flows from the inverter main circuit  101  to the motor  102 , the current flows to the chip Tvp of the positive pole side switch part or to the chip Dwp of the negative pole side switch part/diode part. This is distributed according to the duty factor of the voltage command value given by the pulse width. In the first embodiment, because the motor  102  is locked by the brake device  103 , the induced voltage is not generated in the motor. That is, the brake device  103  puts brake on the motor to make the amplitude of the command voltage extremely small with the result that the duty factor is almost 50%. That is, an effective current of Iconst/2 flows through the chip Tvp of the positive pole side switch part and the chip Dwp of the negative pole side switch part/diode part (strictly speaking, though the duty factor varies slightly according to the magnetic pole position θ, the effect on the lifetime estimation is very small). 
     Next, the following describes a sequence of operation of lifetime evaluation with reference to the lifetime evaluation flowchart in the first embodiment shown in  FIG. 7 . First, after starting the operation, the brake device  103  is driven in step  120 . In this step, the brake circuit  107  in  FIG. 1  is used to surely drive the brake device or to confirm that the drive device is in operation. Next, in block  121 , the magnetic pole position of the motor  102  is confirmed. The magnetic pole position can be detected by the rotary encoder  104  shown in  FIG. 1 . Next, in step  122 , the current command value is calculated by carrying out calculation using [Expression 1] and [Expression 2] and, in step  123 , the current is supplied to the corresponding phase. The phase, to which the current is supplied, is the V phase if the evaluation indicates that a crack in the upper solder layer  114   a  or a peeling of the metal conducting wire  115  is found, and is the phase in which the temperature detector  110   a  is mounted (W phase in the example in  FIG. 2 ) if the evaluation indicates that a crack is detected in the lower solder layer  114   b . Next, in step  124 , the temperature detector  110   a  or temperature detector  110   b  is used to detect the temperature and, in step  125 , the lifetime evaluation circuit  108  in  FIG. 1  determines the lifetime. 
       FIG. 8  shows an example of lifetime determination in the first embodiment. When a predetermined output phase current is supplied, the temperature increases according to the conduction interval. When an abnormal condition occurs, the radiation efficiency deteriorates as described above and therefore the temperature is much higher than at the normal time. The difference between the normal time and the abnormal time is larger as the amplitude of the output current is larger or as the conduction interval is longer. By setting the current amplitude as large as possible within the range in which the torque, generated by the command value, is equal to lower than the braking torque of the brake device as shown in  FIG. 8 , the evaluation time can be shortened. The lifetime evaluation circuit  108  in  FIG. 1  determines that an abnormal condition is detected if the temperature or temperature rise becomes a temperature or temperature rise larger than at least a predetermined amount as compared with the history of the normal-time temperature or temperature rise value measured when a current of predetermined amplitude is given for a predetermined time. Alternatively, the lifetime evaluation circuit  108  determines that an abnormal condition is detected if the temperature or temperature rise value, detected by the temperature detector, exceeds a pre-set reference temperature or reference rise in temperature. If it is determined that an abnormal condition is detected, the abnormal indication signal is output and, as shown in  FIG. 1 , the abnormal state is displayed on the display device or the abnormal indication signal is issued to the management center. After that, the processing is performed, for example, by imposing limitations on the control circuit (for example, the output current is limited to a predetermined value or lower). 
     Although the six-in-one module in which the switching elements of all phases are mounted in one module, is described in the first embodiment, the similar method may be used for lifetime determination in one-in-one module or two-in-one module in which the switching elements are connected in parallel in one module. 
     In this case, because the chips in the center and the chips in the most outer periphery are in the same phase, the processing of the flowchart in  FIG. 7  may be performed for the phases to be evaluated to perform the evaluation of a crack in the upper solder layer  114   a  and a peeling of the metal conducting wire  115  and the evaluation of a crack in the lower solder layer  114   b  at the same time. According to the present invention, lifetime determination may be made extremely accurately using a minimum of two temperature detectors per module. 
     Although the rotary encoder  104  is used to detect the magnetic pole position of the motor  102  in the first embodiment, the present invention may of course be applied, for example, to a system that does not use the rotary encoder  104  but uses the position sensor-less method in which the magnetic pole position is estimated from the motor current information using the saliency of the inductance of the motor  102 . 
     Second Embodiment 
       FIG. 9  is a diagram showing a power converter in a second embodiment of the present invention. This power converter has the configuration in which, in the inverter main circuit  101  in the first embodiment, a voltage detector  126 , provided for detecting the collector-emitter voltage, is connected to a switching element to be measured (in  FIG. 9 , to the V-phase positive pole side switching element positioned in the center where the deteriorated is most conspicuous as indicated in the first embodiment). In the configuration of the second embodiment, the evaluation of a crack in the upper solder layer  114   a  and a peeling of the metal conducting wire  115  may be performed without using the temperature detector  110   b  used in the first embodiment.  FIG. 10  is a flowchart showing the lifetime evaluation in the second embodiment. First, the brake device  103  is driven in block  127  as in the first embodiment shown in  FIG. 7 , and the magnetic pole position of the motor is confirmed in block  128 . [Expression 1] and [Expression 2] are used to calculate the current command value. Note that the current command value given in the second embodiment is a square wave current as shown in the example of lifetime evaluation in the second embodiment shown in  FIG. 11  (In  FIG. 11 , a small current is first supplied and, after supplying a pulse-shaped large current for a predetermined time, the current is switched to a small current). This can be implemented by temporally changing the value of Iconst in [Expression 1] and [Expression 2]. Next, in block  130 , the inverter main circuit is activated to flow the above-described current command, and the voltage is detected by the voltage detector  126  in block  131 . In this case, the detected voltage increases with the large current flowing as in  FIG. 11 . Next, in the lifetime determination block in block  132 , the lifetime evaluation circuit  108  calculates the thermal resistance component from the difference ΔVce in the detected voltage. That is, if a crack develops in the upper solder layer  114   a  or a peeling of the metal conducting wire  115  occurs, the thermal resistance component increases and the difference ΔVce in voltage increases. The lifetime evaluation circuit  108  determines that an abnormal condition is detected if the thermal resistance becomes a thermal resistance value higher by at least a predetermined amount as compared with the history of thermal resistance value measured when a predetermined current is given for a predetermine time. Alternatively, the lifetime evaluation circuit  108  determines that an abnormal condition is detected if the calculated thermal resistance value exceeds a pre-set reference thermal resistance value. If it is determined that an abnormal condition is detected, the abnormal indication signal is output as in the first embodiment to display the abnormal state is displayed on the display device or the abnormal indication signal is issued to the management center. In addition, the processing is performed, for example, by imposing limitations on the control circuit. This invention achieves an effect that lifetime evaluation may be performed, not by using temperature detectors, but by detecting the voltage. 
     The lifetime evaluation in the first embodiment or the second embodiment is performed in the stopped state before a moving body is operated or after a predetermined operation is performed on the moving body. This prevents the operation of the moving body from being affected. It is also possible to perform the processing when a predetermined fixed time arrives (for example, a midnight time at which the moving body is not used) on a daily or weekly basis. 
       FIG. 12  is a diagram showing an example in which the first embodiment or the second embodiment is used in an elevator driving system. A sheave  133  is connected to the motor  102  to elevate a car  134  and a balance weight  135 . In this case, the brake circuit  107  is used to confirm that the brake device  103  is in operation, and the control circuit  106  gives a command to supply a predetermine current to the inverter main circuit  101 . In addition, the lifetime evaluation circuit  108  determines the lifetime of the elements in the inverter main circuit  101  and, if an abnormal condition is detected, issues the abnormal indication signal to the management center. Because the brake device  103  is in operation in the case shown in  FIG. 12 , the car  134  is not operated even if current is supplied to the inverter main circuit  101  for evaluation. In the case of an elevator, the lifetime evaluation processing may be performed in a time zone such as a midnight during which few users uses the elevator. The processing may also be performed as a remote diagnostic operation. In addition, the embodiment may be applied not only to an elevator but also to a system such as a crane. 
       FIG. 13  is a diagram showing an example in which the first embodiment or the second embodiment is used in an electric vehicle. An electric vehicle  136  has the configuration in which a power converter is used as the drive system and a tire  137  is connected to the motor  102 . In this case, the brake circuit  107  is used to force the brake device  103  to operate or to confirm that the brake device  103  is in operation. The brake device in this case gives a braking torque in the same manner as a foot brake  138  does when operated. And, on the premise that brake device  103  is in operation, the control circuit  106  gives a command to supply a predetermined current to the inverter main circuit  101 . In addition, the lifetime evaluation circuit  108  determines the lifetime of the elements in the inverter main circuit  101 . If an abnormal condition is detected, it is possible to cause the display monitor to display a message to prompt the user to make repairs, to issue the abnormal indication signal wirelessly to the management center of the electric vehicle, or to perform operation with limitations imposed on the control circuit. Because the brake device  103  is in operation also in  FIG. 13 , the electric vehicle  136  does not operate even if current is supplied to the inverter main circuit  101  for evaluation. In the case of the electric vehicle  136 , evaluation may also be performed before the operation. Although an example of an electric vehicle is shown in  FIG. 13 , the present invention may of course be applied to a hybrid vehicle, a cart, or an electric construction machine. 
     While the embodiments of the present invention have been described, it is to be understood that the present invention is not limited to the embodiments above and that further modifications may be made without departing from the spirit of the present invention. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to a general power converter for industrial use and, more particularly, to a power converter that drives the motor of a moving body. 
     REFERENCE SIGNS LIST 
     
         
           101  Inverter main circuit 
           102  Motor 
           103  Brake device 
           104  Rotary encoder 
           105  Current detector 
           106  Control circuit 
           107  Brake circuit 
           108  Lifetime evaluation circuit 
           109  Element module 
           109 UP U-phase positive pole side switching element 
           110   a ,  110   b  Temperature detector 
           111   a ,  111   b  Metal pattern 
           112   a ,  112   b  Insulating substrate 
           113  Metal base plate 
           114   a  Upper solder layer 
           114   b  Lower solder layer 
           115  Metal conducting wire 
           126  Voltage detector 
           133  Sheave 
           134  Car 
           135  Balance weight 
           136  Electric vehicle 
           137  Tire 
           138  Foot brake