Richard Bloch

Estimation of Induction Motor Operating Power Factor From Measured Current and Manufacturer Data

Three-phase induction (asynchronous) motors (IM) are industrial work-horses, making the protection of IM a very important topic. IM protection devices typically monitor the motor current and/or voltage to provide the motor protection functionalities like current overload, over/under voltage, etc. One of the interesting parameters to monitor is the operating power factor (PF) of the IM, which provides better underload protection compared to the motor current-based approaches. Traditionally, PF estimation would require both the voltage and the current measurements in order to apply the displacement method. In this paper, we present a method of determining the operating PF of the IM using only the measured current and the manufacturer data that are typically available from the nameplate and/or datasheet. Experimental results are presented to substantiate the feasibility of the proposed method, validated alongside the state of the art PF estimation methods. Operational PF can be effectively used for underload detection, like in a pump application, or PF compensation for improving the power quality.

A study on IGBT junction temperature (Tj) online estimation using gate-emitter voltage (Vge) at turn-off

Abstract A novel method is presented for online estimation of the junction temperature (Tj) of semiconductor chips in IGBT modules, based on evaluating the gate-emitter voltage (Vge) during the IGBT switch off process. It is shown that the Miller plateau width (in the Vge waveform) depend linearly on the junction temperature of the IGBT chips. Hence, a method can be proposed for estimating the junction temperature even during converter operation – without the need of additional thermal sensors or complex Rth network models. A measurement circuit was implemented at gate level to measure the involved time duration and its functionality was demonstrated for different types of IGBT modules. A model has been proposed to extract Tj from Vge measurements. Finally, an IGBT module with semiconductor chips at two different temperatures has been measured using Vge method and this method was found to provide the average junction temperature of all the semiconductor chips.