| Abstract |
Frequency inverter induction motor drives with direct stator flux and torque control as the Direct Self Control (DSR) of Depenbrock [1] or the method of Takahashi and Noguchi [2] have very short torque response times. A typical feature of these control methods is the irregular switching sequence of the inverter legs within a cycle of the stator frequency. Since the average switching frequency does not consider this, it is not a measure for the thermal stress of the power devices. To protect them against thermal destruction, a method of on-line monitoring is proposed based on a so called "temperature index" and a "window frequency." By observing the values of temperature index and window frequency for each switching element, an overloading is prevented, including possible cases of fault. When temperature index or window frequency are reaching their limits, the inverter can be turned off in time. This ensures a safe operation of the drive. In addition, digital simulation results show an improved operational performance, which can be achieved by this method. |
