Observer Based Fault Detection for D-STATCOM Systems
Xiangyu Ding with advisor A. Dominguez-Garcia
The two-level inverter (six-pulse) circuit is one of the most widely used power electronics circuits for three-phase rectification or inversion. Applications range from inverter systems and motor drives to high voltage direct current (HVDC) systems and flexible ac transmission systems (FACTS). One application is in D-STATCOM systems. D-STATCOM is a lower-voltage distribution-level controller often tied to highly nonlinear loads to reduce their disturbance to the grid or to custom power loads that require very strict power quality control. Several large industrial users have reported large financial losses as a result of even minor lapses in electricity supply quality, so the reliability of the DSTATCOM systems is extremely importance to these users. For this reason, effective fault detection and isolation are necessary.
In this research, we propose the use of piecewise-linear observers for power electronics health monitoring. In the absence of faults, the proposed detection filter asymptotically converges to the state variable actual values. When a fault occurs, the estimated values diverge from the state variable actual values, and the filter residual errors accurately determine the location and extent of the fault(s). Initial simulations for high power FACTS devices were very promising. Recent work has been focused on the D-STATCOM system. A circuit model
of a D-STATCOM was constructed using Simulink and the electrical circuit simulation (PLECS) toolbox. Various component faults/degradation were injected into the model to study their overall system effects. Simulation results show that the detection filter was able to accurately detect the fault/degradation and determine the extent
as well as the location of the fault. Figure 24 shows the results of a 50% drop in dc link capacitance. While systems seem to be completely normal based on voltage and current measurements, the detection filter was able to clearly identify the fault. Figure 25 shows the detection filter output after a resistance increase in phase C, which also shows a very clear fault signal. To verify the feasibility of the detection filter, a prototype D-STATCOM with an observer filter was built using a modular inverter and control using a TI F2812 DSP. Initial experimental results show convergence of all detection filter states. Additional work is needed to minimize sensor noise.
This research was supported by NSF CAREER award ECCS-CAR-0954420.