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This paper proposes an active switching harmonic current reduction method within the dc-link capacitor of two-level, three-phase, back-to-back converters. This method is based on the derived analytical solution for switching harmonic currents in the dc-link. It is shown that by controlling the pulse width modulation carrier waveform's phase angles, the harmonics in the second carrier band of the rectifier and the inverter can be synchronized such that cancellation occurs in the dc-link capacitor. This synchronization is provided by harmonic phase feedback control. The feasibility of the proposed approach has been verified experimentally and results are presented in this paper. [ABSTRACT FROM PUBLISHER]

It is known that, when tightly regulated, actively controlled power converters behave as constant power loads (CPLs). These loads can significantly degrade the stability of their feeder system. The loop-cancelation technique has been established as an appropriate methodology to mitigate this issue within dc–dc converters that feed CPLs. However, this has not yet been applied to uncontrolled rectifier based ac–dc converters. This paper therefore details a new methodology that allows the loop-cancelation technique to be applied to uncontrolled rectifier based ac–dc converters in order to mitigate instability when supplying CPLs. This technique could be used in both new applications and easily retrofitted into existing applications. Furthermore, the key contribution of this paper is a novel adaptive stabilization technique, which eliminates the destabilizing effect of CPLs for the studied ac–dc power system. An equation, derived from the average system model, is introduced and utilized to calculate the adaptable gain required by the loop-cancelation technique. As a result, the uncontrolled rectifier based ac–dc feeder system is always stable for any level of CPL. The effectiveness of the proposed adaptive mitigation has been verified by small-signal and large-signal stability analysis, simulation, and experimental results. [ABSTRACT FROM AUTHOR]

Droop control has been widely applied in dc microgrids (MGs) due to its inherent modularity and ease of implementation. Among the different droop control methods that can be adopted in dc MGs, two options have been considered in this paper: I–V and V–I droop. I–V droop controls the dc current depending on the dc voltage while V–I droop regulates the dc voltage based on the output current. The paper proposes a comparative study of V–I/I–V droop control approaches in dc MGs focusing on steady-state power-sharing performance and stability. The paper presents the control scheme for current-mode (I–V droop) and voltage-mode ( V–I droop) systems, derives the corresponding output impedance of the source subsystem, including converters dynamics, and analyzes the stability of the power system when supplying constant power loads. The paper first investigates the impact on stability of the key parameters including droop gains, local control loop dynamics, and number of sources and then performs a comparison between current-mode and voltage-mode systems in terms of stability. In addition, a generalized analytical impedance model of a multisource, multiload power system is presented to investigate stability in a more realistic scenario. For this purpose, the paper proposes the concept of “global droop gain” as an important factor to determine the stability behaviour of a parallel sources based dc system. The theoretical analysis has been validated with experimental results from a laboratory-scale dc MG. [ABSTRACT FROM AUTHOR]

The dynamic phasor (DP) concept has been widely used in modeling electrical power systems. So far, the DP concept has been restricted to modeling systems with one single electrical source at a fixed fundamental frequency, either one generator or an ideal three-phase AC source. This paper aims to extend the DP modeling methodology to a wider application area. Two major achievements have been introduced: 1) application of DPs for multi-source, multi-frequency systems; 2) modeling of systems with time-varying frequencies. These two techniques enable the use of DPs to study nearly all types of electrical power systems (EPS). The developed theory is validated using a twin-generator system from the More Open Electrical Technologies (MOET) project. The accuracy and effectiveness of the developed models is confirmed by comparing the simulation results of detailed switching models and DP models under both balanced and unbalanced conditions. [ABSTRACT FROM AUTHOR]