一种基于门极电压阈值检测的SiC MOSFET结温在线监测方法

A Novel On-line Method for Monitoring the Junction Temperature of SiC MOSFET Based on Threshold Voltage

碳化硅(silicon carbide,SiC)金属–氧化物半导体场效应晶体管(metal-oxide-semiconductorfield-effect transistor,MOSFET)作为第三代功率器件的代表,已被广泛用于小容量高频领域,其可靠性问题备受关注。结温过高是制约SiC MOSFET可靠性的重要因素。然而,碳化硅器件高开关频率增大了动态参数测量的难度和成本。与硅基器件相比,其导通压降和导通电阻等稳态参数对结温的敏感性较低。因此,主流的热敏电参数法无法有效地在线监测结温。已有研究表明:门极阈值电压与结温密切相关,但这种通过门极阈值电压监测结温的方法易受电流震荡影响且测量电路复杂,故监测效果差强人意。为此,文中提出一种新型的基于门极电压阈值检测的SiC MOSFET结温监测方法。首先,理论推导结温与门极阈值电压之间的解析表达式,发现其呈线性关系。其次,提出一种多项式拟合门极阈值电压测量方法,并设计与之匹配的电流采样测量电路。最后,通过基于H桥单相逆变电路的在线监测试验证明该方法的有效性。研究表明:新型结温监测方法具有以下突出优势:1)不易受开关过程震荡的影响,监测精度高;2)测量电路简单可靠,仅用采样电路和滤波器即可,毋需复杂的捕捉电路;3)对采样频率具有一定的容差性。

As the representative of wide band gap power devices, silicon carbide MOSFET has become the future development direction due to its application in small capacity high frequency converter. As a result, its reliability has gradually attracted attention. Among all the factors restricting reliability of SiC MOSFET, excessive junction temperature matters the most. However, the high switching frequency of SiC devices increases the difficulty and cost of dynamic parameter measurement. Compared with silicon devices, the sensitivity of steady-state parameters such as on-voltage drop and on-resistance to junction temperature is greatly reduced. Therefore, the mainstream thermistor parameter method(TSEP method) cannot effectively monitor the junction temperature online. Compared with other TESPs, the threshold voltage is more sensitive and relatively easier to measure. However, the accuracy of conventional method based on threshold voltage is disturbed by the switch oscillation, and the measurement circuit is complex. To solve these problems, this paper proposed a novel on-line method for monitoring the junction temperature of SiC MOSFET based on threshold voltage. Firstly, the relationship between junction temperature and threshold voltage was theoretically derived, which is proved highly linear. Then an algorithm of threshold voltage based on polynomial fitting was proposed and the matching measurement circuit was designed. Finally, the effectiveness of this method was proved by the on-line monitoring experiment based on an H-bridge single-phase inverter. This method has the following advantages: 1) it is less affected by the switch oscillation and improves the monitoring accuracy;2) it greatly simplifies the measuring circuit and only needs a simple sampling circuit and a filter;3) it has certain tolerance on the the change of sampling frequency.