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ISOLATED IGBT TEMPERATURE MEASUREMENT

IP.com Disclosure Number: IPCOM000248405D
Publication Date: 2016-Nov-25
Document File: 7 page(s) / 388K

Publishing Venue

The IP.com Prior Art Database

Related People

Antti Kekki: AUTHOR [+2]

Abstract

An isolated temperature-measurement solution for an IGBT module. The solution is based on a simple temperature to a pulsed signal conversion. In the solution a voltage over an NTC is compared to a PWM ramp generating a pulsed signal with a duty ratio relative to the temperature. The pulsed signal is fed to a digital controller, where the duty ratio is recognized and the temperature is calculated using a predetermined equation or a look-up table between the duty ratio and the temperature. The measurement system is referred to the same potential as the IGBT gate driver and utilizes the same isolation barrier as the IGBT control signal. A digital isolator or an optocoupler with a return channel is a possible solution minimizing the component count.

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ISOLATED IGBT TEMPERATURE MEASUREMENT

The disclosure relates to an isolated temperature-measurement solution for an IGBT module.

An electric converter, for example, may comprise one or more IGBT (Insulated-Gate Bipolar Tansistor) modules, their gate drivers and related control electronics. Such IGBT modules typically consist of one or more IGBTs and an NTC thermistor for temperature measurement. The temperature has been measured by using the thermistor in a voltage division circuit with a known reference voltage and a resistor(s). The thermistor voltage is AD-converted and converted to resistance and thereafter to a temperature value according to a thermistor temperature vs. resistance characteristics. The control electronics are typically referred to a different potential than the IGBT requiring isolation between the control signal and the IGBT gate driver. The isolation distance between the NTC and the IGBT may not meet the safety requirements of a high-voltage converter or the IGBT switching introduces excess noise on control electronics, when the NTC resistance is determined with a circuit referred to the same potential as the control electronics. This document proposes an isolated temperature-measurement circuit for an IGBT module to overcome these problems.

Fig. 1.Isolated IGBT module temperature measurement with a non-linear PWM ramp.

The disclosed solution is generally based on a simple temperature to a pulsed signal conversion. A duty-ratio-based signal is fed back to the control board using a digital isolator return channel used to control the IGBT. In the solution the voltage over the NTC is compared to a PWM ramp generating a pulsed signal with a duty ratio (D) relative to

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the temperature (T). The pulsed signal is fed to a digital controller, where a duty ratio is recognized and a temperature is calculated using a predetermined equation or a look-up table between the duty ratio and the temperature as shown in Fig. 1. The measurement system is referred to the same potential as the IGBT gate driver and utilizes the same isolation barrier as the IGBT control signal. A digital isolator or an optocoupler with a return channel is a possible solution minimizing the component count.

When comparator A1 output is high (uo = uo,h), capacitor C1 is charged through R4. When PWM ramp voltage uramp reaches comparator hysteresis high voltage limit (uh = uh,h), comparator output goes low (uo = uo,l). Now capacitor C1 is discharged through R4 until comparator hysteresis low voltage limit (uh = uh,l) is reached and the ramp cycle starts over. Comparator output voltages uo,h and uo,l depend on comparator and its supply voltage(s). High and low hysteresis voltage limits are given by


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