A known voltage converter and a known inverter have been used when driving a three-phase motor. The voltage converter boosts an input voltage to a predetermined voltage. The inverter changes a frequency of an output of the voltage converter. Meanwhile, plural switching elements are provided at the voltage converter and the inverter. The switching elements self-heat by energization, and electrical characteristics and a rating are specified in response to an ambient temperature level of the switching elements. Here, the ambient temperature is desired to be considered upon the use of the switching elements. The technology in which the switching elements are used under the consideration of the ambient temperature is disclosed in JP2013-48515A (hereinafter referred to as Patent reference 1).
An electric automobile disclosed in Patent reference 1 is provided with an inverter supplying electric power to a three-phase motor. The inverter includes plural switching elements. The electric automobile is provided with a temperature sensor, a current sensor, and a voltage sensor. The temperature sensor measures a temperature level of a refrigerant cooling the switching elements. The current sensor measures an output current of the inverter. The voltage sensor measures an input voltage inputted to the inverter. A temperature correction value is calculated based on a measurement data of the current sensor per switching element, a measurement data of the voltage sensor per switching element, and a duty ratio of the switching element. The temperature correction value is added to a measurement result of the temperature level of the refrigerant to estimate the temperature level of the switching elements.
According to a device disclosed in Patent reference 1, detection results of the plural sensors are used to estimate the temperature level of the switching elements. In this case, because the detection results include errors of measurement, the errors of measurement included in the estimate results of the temperature levels of the switching elements may be increased. Accordingly, when the switching elements are energized, the electric characteristics and the rating are desired to include margins. Accordingly, the device disclosed in Patent reference 1 may not be able to fully use a capability of the switching elements.
A need thus exists for an energization control system and a sensor unit which is not susceptible to the drawback mentioned above.