Modelling Constant Power Loads: Accounting for Power Losses in Power Converters

A constant power load (CPL) refers to an electrical load that maintains constant power consumption regardless of variations in the supply voltage. Many power electronics devices and converters exhibit such characteristics from the point of view of their DC link due to their control mechanisms and design configurations that aim to regulate output power despite changes in input voltage. This CPL characteristic is often modelled as a constant negative resistance. However, this modelling approach is inaccurate and may not represent the worst-case scenario because it neglects losses of power converters. In this paper, the effect of power losses in converters on the modelling of CPLs is studied, demonstrating that a lossy model of a power converter can present a more critical situation than a lossless one. The results of the mathematical study are verified using multi-domain offline and real-time simulations of a single buck converter with control characteristics of a CPL. In addition, to further show the aforementioned effect, a multi-converter system has been simulated which its results support the mathematical analysis.