The majority of converter failures are caused by overheating and temperature fluctuation. Therefore

online thermal monitoring methods for converters are necessary to enhance reliable operation capacity. Conventional thermal monitoring methods mainly focus on a single semiconductor device. Monitoring cost is high

and measuring circuits are difficult to integrate. Moreover

converter structure must be adjusted in industrial applications for these methods. To solve these problems

a novel online thermal monitoring method for IGBT-based converter systems is proposed. The aim is to obtain an overall temperature evaluation of the converter. First

leakage current in DC bus <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(I_{\text{leakDC}})$ is selected as an indicator for converter thermal monitoring. Theoretical analysis and offline experiments prove <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$I_{\text{leakDC}}$ is quasi-exponential to temperature. Then

temperature-related parameters (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$T_{\text{CONU}}$ and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$T_{\text{CONL}}$) are defined corresponding to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$I_{\text{leakDC}}$

respectively

to characterize thermal state of converters. Next

an extraction method for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$I_{\text{leakDC}}$ is proposed based on state-delay converter control method. Using online extracted <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$I_{\text{leakDC}}$

a novel thermal monitoring strategy is developed. Online experiments validate effectiveness of the proposed strategy in different operating conditions. The proposed method gains advantages in low cost

easy integration

feasible and convenient implementation for system-level thermal management.