This article presents a vector fitting (VF) algorithmbased robust circuit and controller parameters identification method for grid-connected voltage source converters (VSCs). The dq-domain impedance frequency responses (IFRs) of the VSCs are first measured using frequency scanning method, based on which the corresponding measured phasor-domain IFRs are calculated. Then, polynomial transfer functions are generated by applying the VF algorithm on the measured phasor-domain IFRs, from which the circuit and controller parameters, i.e., LCL filter parameters, digital sampling time, current controller parameters, and phase-locked loop parameters, are identified. Influence of measurement noise on parameters identification accuracy and corresponding countermeasure to mitigate the adverse influence are also theoretically investigated. The proposed method is able to identify the circuit and controller parameters, when detailed parameters are missing due to industrial secrecy or parameters variation caused by operating condition change, temperature fluctuation, or aging. Effectiveness of the proposed circuit and controller parameters identification method is validated by theoretical demonstration, OPAL-RT-based real-time simulation, and experimental validation.Index Terms-Impedance frequency responses, parameters identification, polynomial transfer function, vector fitting algorithm, voltage source converter.
I. INTRODUCTIONRenewable energy sources, such as wind power and solar power, have been increasingly penetrating into conventional
One of the main challenges of decentrally operated islanded microgrids has been proper harmonic sharing for parallel connected inverters. This is largely affected by differences in the feeder impedances of the inverters. Virtual impedances are able to improve the harmonic current sharing, at the cost of deteriorating the power quality at the outputs of the inverters. This paper proposes a method for minimally setting the virtual impedances based on an optimization algorithm and estimation of the feeder impedances. The scheme ensures proper sharing between the units, while the power quality at the inverter terminals are minimally affected. The scheme is verified by numerically simulating a test microgrid.
Droop control has shown promising results for decentralized power sharing in microgrids. However, the basic scheme can suffer from unequal reactive power sharing power due to differing line impedances between converters and due to the predominantly resistive nature of low voltage networks. Virtual impedances are able to mitigate these drawbacks, and are mostly implemented using a quasi-stationary approach. This approach replicates an impedance in steady state, but transients of the load current are only partly reproduced. This paper discusses the effect of including the transient term of the virtual impedance. A state-space small-signal model is derived in order to show the effect of including the transient virtual impedance. Simulations of a two-inverter microgrid are also shown to test the model and offer a numerical example. Both modal analysis on the small-signal model and the results from the simulation indicate improved damping when including the transient virtual impedance.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.