UBC Theses and Dissertations
Adaptive active damping methods for DC-AC power-electronic-based systems with constant-power loads Qu, Zhi
Many electronic loads in fast-developing power systems behave as constant-power loads (CPLs) which are known to exhibit negative incremental impedance and have a destabilizing effect in the system. To improve the stability of modern power systems with CPLs, research efforts have been focused on impedance-based and small-gain stability criterion, the design of advanced controllers, and passive or active damping solutions. Some disadvantages for most of the existing solutions include unnecessary energy losses in their passive elements, requirements of beforehand knowledge of the system characteristics, and inadaptability to the change in system operating conditions. This thesis presents new methods for stabilizing power systems with CPLs using tunable active damping based on an auxiliary converter circuit. Therein, the load bus voltage is monitored and an active damper is used to stabilize the system once an instability is detected. The methodologies are first developed in DC power systems and later extended for three-phase AC power systems as well. The proposed methodologies are less conservative than traditional methods and its damping characteristics are established “on-the-fly” in real-time to achieve effective stabilization under various CPLs and different operating conditions that may be unknown a priori. The proposed methodologies are verified under three different power systems: a simplified version of an aircraft power system with two sources, a 48/24 VDC telecom system consisting commercially available converters, and a three-phase AC power system. It has been shown that the proposed methodologies can detect instability and damp the unstable oscillations in all three systems when the CPL power level becomes high.
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