Parallel inverters are commonly adopted in high-power applications, for instance wind energy systems, smart transformers, and power conditioners. Meanwhile, interleaved pulse width modulation is usually considered as an optimal approach to reduce the current ripple and harmonics of the parallel inverters. However, in the case of a common dc link, the problem of circulating current emerges and leads to performance degradation. This paper aims at investigating the influence of different modulation techniques on the circulating current of two neutral-point-clamped (NPC) inverters under interleaved operation. Two modulation techniques, phase disposition (PD) and alternative phase opposite disposition (APOD), have been studied and compared in terms of current ripple, spectrum quality, and circulating current. Though the PD modulation was regarded as the optimum solution in most of the single-NPC cases, it offers worse performance in the two parallel NPC applications due to higher circulating current. Simulation and experimental validations are provided and show that the APOD leads to much lower circulating current and similar current ripple as well as spectrum quality compared to the PD.

The More Electric Aircraft (MEA) concepts aims at increasing the amount and the power of the electrical subsystems on the next generation of aircrafts. One of the major challenges in this framework is that the electric power is generated by means of electrical generators connected to the jet turbine shaft. In order to satisfy the peak power demand and overload conditions, the generators are oversized, increasing weight and total cost of operation. Possible solutions to this problem is to decrease the size of the generator and to provide the peak power with storage systems. As an alternative, load disconnection during peak demand (load-shedding) can be enforced with solid-state switches. This paper presents a different approach: by modifying the DC voltage of the distribution, the load can be controlled. In order to achieve this objective, a precise on-line identification algorithm is proposed. Theoretical analysis is performed and simulation results on a study-case distribution system are reported, highlighting how the proposed load identification and control method effectively manages a power curtailment condition without load-shedding or storage systems.

Large-scale integration of renewable generation interfaced to the network through power electronic converters has led to drastic changes in power system dynamics. In islanded microgrids or weak grids, different control concepts for the synchronization of converters have been proposed to provide virtual inertia and improve their resilience against transient events, ensuring safe operation without heavy redundant design. The complexity of these power-related control algorithms and their interaction with the inner control loops causes problems in frequency components above the range of traditional studies which calls on modeling techniques with a wider bandwidth. This work aims to provide an outline of modeling methods for grid-connected converter dynamics from subsynchronous to switching sideband frequency range and relevant analyzing tools. The major contributions of this work are: 1. Theoretical foundations and the derivation processes are discussed for each of the modeling methods within the time domain, frequency domain and harmonic domain. 2. Similarities and differences between these methods are highlighted and recommendations are given regarding different grid situations. 3. A case study with an active front end converter is shown and the analysis results are validated by simulation and Hardware-in-the-Loop (HiL) test, illustrating the effectiveness of these methods.

Knowledge of the frequency depending grid impedance is necessary for adequate grid integration, including setting of standards, of renewable energy sources. It is also essential for the design of power converters for renewable energy sources. In this paper wide frequency range measurements of the positive sequence grid impedance in public low voltage grids with high proportion of renewable energy generation systems are presented and analyzed. This case study shows, that the impedance of a point of connection strongly depends on the low voltage grid including its sources and loads. Moreover, the impedance varies strongly during the day but shows similar recurring pattern from day to day. The used measuring system is briefly described.

Dual-active-bridge-based (DAB-based) input-series output-parallel (ISOP) converters have become increasingly popular due to their promising features made up of the advantages of the modular power electronics and the DAB converter. The modeling of the DAB converter and the DAB-based ISOP converter has been widely explored for control design in order to analyze the stability and improve the performance of the converter itself, such as the voltage balancing and power sharing of DAB submodules. However, the modeling on the impedance of the DAB-based ISOP converter, which can be quite useful for system-level stability analysis and optimization, has not been addressed sufficiently so far. To solve this issue, this article presents comprehensive impedance modeling of the DAB-based ISOP converter, where the output voltage control and the input voltage balancing control are applied to the converter to achieve the equal power sharing of the submodules. The proposed input impedance model and output impedance model of the DAB-based ISOP converter are validated through the frequency-domain sweep in simulation and experiment. With the validated impedance models, the instability phenomenon and the frequency of the main harmonic component in oscillating waveforms can be accurately predicted at the source side and at the load side of the converter respectively.

To enhance the power density and increase the efficiency of electrical power distribution systems, the concept of multiple active bridge (MAB) converters has been developed. The conventional MAB control method utilizes PI voltage controllers for each DC port without decoupling, facing the drawbacks of slow dynamic responses and limited power transfer capability. This paper proposes a Newton iteration based decoupling algorithm combined with a current decoupling control algorithm to realize the voltage controls for the multiport electric vehicle (EV) charger applications. This control strategy composes of the DC reference current generators and the current to phase shifts decoupling algorithm, which divides the MAB converter with n ports, into n - 1 virtual dual active bridge (DAB) sub-branches. Generalized phase shift (GPS) modulation was utilized in the decoupling algorithm to quantitatively characterize the relationship between the phase shift and the port average current, aiming at achieving the ‘modular’ switching of the fundamental modulations. The complexity and accuracy of the proposed online offline Newton decoupling (O ² ND) algorithm have been evaluated and compared with Newton decoupling (ND) algorithm and simplified Newton decoupling (SND) algorithm. The effectiveness and flexibility of the O ² ND algorithm and the performance of the O ² ND current decoupling control are verified through a comparative assessment by means of simulation and experimental results.