Constant power loads in AC distribution systems: An investigation of stability

The effects of constant power loads (CPLs) has been for long time the focus of research in isolated power systems such as automotive systems, electric ships and spacecrafts, with main focus on DC-systems. Due to the instability effect of the negative incremental resistance phenomena of CPLs, several criteria have been investigated to ensure system stability in the presence of large amount of CPLs. With an increasing share of CPLs, the same negative incremental resistance phenomena can be the source of instability in AC distribution systems, especially in the event of voltage disturbances. The literature on AC systems has not yet addressed this problem in a comprehensive way, and more research effort will be required around the topic. This paper investigates the effect of the negative incremental resistance phenomena in AC distribution systems with large share of CPLs, and proposes an approach for mitigation of instability in presence of large signal disturbances based on injection of reactive current by active rectifiers interfacing the CPLs. Results from a simulation study with Matlab suggest how stability can be improved by reactive compensation and that distributed injection of reactive current by the CPLs might be more effective than a centralized compensation by a STATCOM.