Smart Resistor: Trajectory Control of Constant Power Loads in DC Microgrids

Application areas such as electric vehicles, data centers and microgrids increasingly rely on power electronic converters and electric motor drives to control loads. These tightly regulated converters act as Constant Power Loads (CPLs) in the context of the entire system. The negative incremental impedance of a CPL causes inherent instability which may lead to a grid collapse. This paper reviews the operating principles of the Smart Resistor concept wherein a bi-directional current compensation circuit and energy storage are attached at the point-of-load to stabilize the system. This decentralized control allows the equivalent load to behave as a linear resistor, which is inherently stable during either voltage or power perturbations. These adaptive resistors can work with smart sources to realize ultimate smart power networks. This paper then details the full control strategy needed to realize the concept. Smart Resistor voltage and current trajectory control principles are analyzed and validated using a hardware test setup. Energy management strategies are discussed and verified in simulation to ensure uninterrupted operation.