Online Thermal Monitoring Method for Converter System Based on Extraction of DC Bus Leakage Current

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 (I_leakDC) is selected as an indicator for converter thermal monitoring. Theoretical analysis and offline experiments prove I_leakDC is quasi-exponential to temperature. Then, temperature-related parameters (T_CONU and T_CONL) are defined corresponding to I_leakDC, respectively, to characterize thermal state of converters. Next, an extraction method for I_leakDC is proposed based on state-delay converter control method. Using online extracted I_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.