1. A power converter (18) adapted to convert input direct-current power or
alternating-current power into desired alternating-current power according to a
switching operation of a switching element (57) to output the desired alternating-
current power, said switching element (57) cooled by using a cooling apparatus
(50) that makes use of a boiling phenomenon of a coolant (54) incorporated
therein, the power converter (18) comprising:
a control unit (17) controlling an operation of the power converter (18) based on a deviation between a temperature (Tf) of the switching element (57) or an attachment surface of the switching element and a temperature (Ta) of cooling air sucked by the cooling apparatus (50) ,
wherein the control unit (17) includes a detecting unit (16) generating and outputting a cooling performance deterioration detection signal (RLD) representing performance deterioration of the cooling apparatus (50) when the deviation exceeds a predetermined threshold.
2. The power converter according to claim 1, wherein the detecting unit
includes a threshold generating unit generating the threshold based on
temperature of the cooling air, and
wherein the threshold generating unit generates the threshold that is smaller when the temperature of the cooling air is high than when the temperature of the cooling air is low.
3. The power converter according to claim 1, wherein the detecting unit
includes a threshold generating unit generating the threshold based on a loss of
the switching element, and
wherein the threshold generating unit generates the threshold that is smaller when the loss of the switching element is large than when the loss of the switching element is small.
4. The power converter according to claim 1, wherein the detecting unit
includes a threshold generating unit including a calendar function and configured
to generate the threshold based on season information by the calendar function,
and

wherein the threshold generating unit generates the threshold that is smaller when outdoor temperature predicted based on the season information is high than when the outdoor temperature is low.
5. A power converter (18) adapted to convert input direct-current power or
alternating-current power into desired alternating-current power according to a
switching operation of a switching element (57) to output the desired alternating-
current power, said switching element (57) cooled by using a cooling apparatus
(50) that makes use of a boiling phenomenon of a coolant (54) incorporated
therein, the power converter (18) comprising:
a control unit (17) controlling an operation of the power converter (18) based on a deviation between a temperature during operation and a temperature before an operation start of the switching element (57) or an attachment surface of the switching element,
wherein the control unit (17) includes a detecting unit (16) generating and outputting a cooling performance deterioration detection signal (RLD) representing performance deterioration of the cooling apparatus (50) when the deviation exceeds a predetermined threshold, and
wherein the detecting unit (16) includes a threshold generating unit that generates the threshold based on a loss of the switching element (57) such that the threshold is smaller when the loss of the switching element is large than when the loss of the switching element is small.
6. A power converter (18) adapted to convert input direct-current power or
alternating-current power into desired alternating-current power according to a
switching operation of a switching element (57) to output the desired alternating-
current power, said switching element (57) cooled by using a cooling apparatus
(50) that makes use of a boiling phenomenon of a coolant (54) incorporated
therein, the power converter (18) comprising:
a control unit (17) controlling an operation of the power converter (18) based on a deviation between a temperature during operation and a temperature before an operation start of the switching element or an attachment surface of the switching element,
wherein the control unit (17) includes a detecting unit (16) generating and outputting a cooling performance deterioration detection signal (RLD) representing performance deterioration of the cooling apparatus (50) when the deviation exceeds a predetermined threshold,

wherein the detecting unit (16) includes a threshold generating unit generating the threshold based on season information by a calendar function contained therein, and
wherein the threshold generating unit generates the threshold that is smaller when outdoor temperature predicted based on the season information is high than when the outdoor temperature is low.
7. The power converter according to claim 1, 5, or 6, wherein the control unit performs control of stopping the power converter when the deviation exceeds the predetermined threshold.
8. The power converter according to claim 1, 5, or 6, wherein, when the deviation exceeds the predetermined threshold, the control unit performs control of reducing a switching frequency for causing the switching element to operate.
9. The power converter according to claim 1, 5 or 6, wherein, when the deviation exceeds the predetermined threshold, the control unit performs control of limiting an electric current applied to the switching element.
10. The power converter according to claim 1, 5, or 6, wherein at least one of a transistor element and a diode element included in the switching element is formed of a wide band gap semiconductor.
11. The power converter according to claim 10, wherein the wide band gap semiconductor is a semiconductor formed using silicon carbide, a gallium nitride material, or diamond.