Search

A decentralized control approach is introduced in this paper that utilizes passivity-based control for two DC-distributed energy sources supplying the power of a load. Considering the concept of passivity, if each distributed generator exhibits passivity, this property will be maintained when these generators are connected in series or parallel. Thus, the stability of the entire system is guaranteed through the implementation of an interconnection and damping assignment passivity-based control (IDA-PBC). Additionally, droop voltage control is employed to achieve current sharing among the two power sources. If the model used is not an accurate representation of the original system, the controlled system may experience steady-state errors. To address these modeling errors, a compensation term is employed as the desired output voltage. The effectiveness of the proposed methodology is confirmed via results from simulation in three cases in which the performance of the system is investigated in start-up and load resistance or nominal load current change. With PBC, the system maintains stable operation. Experimental results validate the simulation results. Moreover, the proposed method guarantees global stability without knowing the parameters to prove global stability with local control.

Small-signal stability and dynamic interactions among power electronic converters (PECs) and electrical grids are widely analyzed using the impedance-based approach. To reduce such interactions, a desirable feature of PECs is that their admittance exhibits dissipative behavior. Due to control delays, the PEC admittance usually exhibits non-dissipative zones around and above the crossover frequency of the inner control loop, possibly reducing the stability margins of the contemporary electrical grids. This paper proposes the double-sampling asymmetric dual-edge digital pulse-width modulator (ADE-DPWM) as an effective way to improve the passivity properties of the PEC admittance. Even in the digital implementation, the ADE-DPWM features zero delay and almost unity magnitude up to half of the switching frequency. Moreover, this paper examines the influence of ADE-DPWM on the PEC admittance even at higher frequencies, where destabilization of poorly damped grid resonances may be influenced by sampling and pulse-width modulation sidebands. Due to an operating point dependent ADE-DPWM small-signal model, the high-frequency passivity properties highly depend on the steady-state operating point. The analytical predictions are shown to be in excellent agreement with the experimental admittance measurements up to twice the switching frequency for all tested steady-state operating points.

Harmonic resonance is a kind of oscillatory instability phenomenon occurring in the electric railway. To investigate this problem, the frequency-domain model of the single-phase voltage source converter for locomotives is derived based on the transfer function of the current control loop. The equivalent circuit of the traction network is also included in this frequency-domain model. Particularly, the time delay and zero-order-holder effect of the digital pulse width modulation are taken into consideration in order to obtain more accurate a model of the digital controller. After that, the harmonic resonance of the locomotive-network system is assessed through the passivity properties of the interacted frequency-domain impedance model. Finally, the effectiveness of the theoretical analysis is demonstrated by simulations and experiments. As a result, the harmonic resonance can be predicted before a new electric railway is put into use so that some mitigation measures can be taken in advance.

In this study, a new non‐linear dynamic controller is proposed for regulating the output voltage of a DC/DC boost power converter in a stand‐alone photovoltaic (PV) system. The controller provides directly the duty‐ratio input of the converter, bounded in the permitted range, and as it is proven it achieves the desired voltage regulation independently from the PV source voltage, the converter parameters and the kind of the load. An appropriate mathematical analysis is used to indicate that the proposed control scheme guarantees closed‐loop system stability with the state trajectories converging to the desired equilibrium. Particularly, using as generic concept the fundamental property of passivity of the original system, the proposed controller scheme results in a closed‐loop system wherein (i) the passivity and damping properties are maintained and (ii) the conditions which exploit these properties in a manner that guarantees stability are met. Extended simulation and experimental results verify effectiveness of the controller for the case of a DC/DC boost converter with resistance‐inductance load. The system performance, operating with the proposed non‐linear (voltage) controller is compared with that obtained by implementing conventional cascaded (voltage–current) controllers under input voltage step disturbances or load variations. Finally, some experimental resuts for the case of a non‐linear load consisted of a three‐phase voltage source inverter and a three‐phase resistance–inductance load are illustrated. [ABSTRACT FROM AUTHOR]