Short-circuit protection for an IGBT with detecting the gate voltage and gate charge

This paper proposes a new short-circuit protection method for an IGBT. The proposed method is characterized by detecting not only gate charge but also gate voltage of the IGBT. This results in a shorter protection time, compared to the previous method that detects only the gate charge. A real-time monitoring system using an FPGA, A/D converters, and a D/A converter is used for the proposed protection method. Experimental results verify that the proposed method achieves a protection time of 390 ns, which is reduced by 68% compared to the previous method. In recent years, current density of Insulated-Gate Bipolar Transistors (IGBTs) is getting higher as their market share grows [1–3]. One of the key issues in reliability of IGBTs is protection from a short circuit in the inverter [2–8]. The higher current density results in higher heat density in the IGBTs, so that temperature rising gets faster in the short-circuit condition. This paper proposes a new short-circuit protection method with sensing the gate charge and gate voltage of the IGBT using a digitally controlled real-time monitoring system. The method is characterized by putting a short-circuit detection curve to the characteristic of the gate charge vs. gate voltage of an IGBT. This results in a significantly short protection time of 390 ns for a 600-V 10-A IGBT. 2. Short-circuit protection for IGBTs 2.1. Protection method with detecting the collector current or collector-emitter voltage Many kinds of protection method based on the collector current or collector-emitter voltage sensing has been proposed [4,5]. They detect overcurrent at the collector or de-saturation collector-emit-ter voltage. They need additional hardware installation to the IGBT, which brings higher initial cost. IGBT modules having short-circuit protection have been used, which employ a current-sense emitter to detect the collector current [6,7]. This method, however, has a delay time of 5 ls for sensing the collector current because a low-pass filter is embedded in the module to filter noise components. 2.2. Protection method with detecting the gate charge The authors have addressed a short-circuit protection method with gate-charge sensing [2,3], namely, previous method. In the normal condition, Q G rapidly increases when V GE exceeds its threshold voltage V TH because a miller current flows into the collector terminal. On the other hand, Q G in the short circuit condition is lower than that in the normal condition because the miller current does not flow. The previous method detects the …