Patent ID: 7954334

Claim:
An inverter system, comprising: a semiconductor device; a control circuit for on/off control of said semiconductor device; first and second temperature detectors for detecting temperature at first and second sites, respectively; and circuitry operatively associated with the first and second temperature detectors that calculates the temperature at the second site that is at or in said semiconductor device based on: an actual temperature value detected by said first temperature detector at the first site adjacent said semiconductor device and a temperature calculation parameter, being one of a cooling air velocity, a vehicle velocity, and a cooling water velocity, so as to capture with periodic sampling over a selected period of time a trend of a differential value between said calculated temperature and the actual temperature value detected by said second temperature detector, wherein the trend of the differential value is being given as an approximate curve formed by the plurality of differential values corresponding to a plurality of loss values in the inverter system, and that determines that an error exists in the inverter system when a difference between the captured trend and an initial predetermined trend or on a change in the captured trend over the selected period of time exceeds a predetermined value.