| Abstract |
During the last couple of years, the introduction of power electronic semi-conductors into electrical apparatus has greatly improved its dynamic performances. This change, beyond a simple substitution, creates new functions. This paper presents the study of an "intelligent" contactor used with an induction motor. The switching module has a GTO-MOS cascade structure. It is controlled by an 8-bit microcontroller which integrates driving, protection and communication functions. The driving module analyses the electrical characteristics of the load before its connection to the power supply. Thus, it provides preventive protection for the motor and reduces the electrical and thermal stresses during starting. Short circuit protection is realized in a few hundreds of nanoseconds by the close drive of the contactor. The overload protection is based on a thermal image representation. The microcontroller calculates in real time the junction temperature of the static switches and the thermal state of the load. In order to provide a continuous protection during power failures, an autonomous numerical circuit registers the failure duration and initializes the microcontroller at the next power-on. |
