Overview of the Controllers Used for Mitigation of Harmonics Injected Due to Nonlinear Loads

This paper presents the skin effect impact on the active power losses in the sheathless single-core cables/wires supplying nonlinear loads. There are significant conductor losses when the current has a distorted waveform (e.g., the current supplying diode rectifiers). The authors present a new method for active power loss calculation. The obtained results have been compared to the IEC-60287-1-1:2006 + A1:2014 standard method and the method based on the Bessel function. For all methods, the active power loss results were convergent for small-cable cross-section areas. The proposed method gives smaller power loss values for these cable sizes than the IEC and Bessel function methods. For cable cross-section areas greater than 185 mm2, the obtained results were better than those for the other methods. There were also analyses of extra power losses for distorted currents compared to an ideal 50 Hz sine wave for all methods. The new method is based on the current penetration depth factor calculated for every considered current harmonics, which allows us to calculate the precise equivalent resistance for any cable size. This research is part of our work on a cable thermal analysis method that has been developed.

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Configurations, Power Topologies and Applications of Hybrid Distribution Transformers

Energies ◽

10.3390/en14051215 ◽

2021 ◽

Vol 14 (5) ◽

pp. 1215

Author(s):

Alvaro Carreno ◽

Marcelo Perez ◽

Carlos Baier ◽

Alex Huang ◽

Sanjay Rajendran ◽

...

Keyword(s):

Distribution Systems ◽

Power Converter ◽

Operating Conditions ◽

Distribution Transformer ◽

Nonlinear Loads ◽

Electric Vehicle Charging ◽

Distribution Transformers ◽

Alternative Systems ◽

Charging Stations ◽

Hybrid Distribution

Distribution systems are under constant stress due to their highly variable operating conditions, which jeopardize distribution transformers and lines, degrading the end-user service. Due to transformer regulation, variable loads can generate voltage profiles out of the acceptable bands recommended by grid codes, affecting the quality of service. At the same time, nonlinear loads, such as diode bridge rectifiers without power factor correction systems, generate nonlinear currents that affect the distribution transformer operation, reducing its lifetime. Variable loads can be commonly found at domiciliary levels due to the random operation of home appliances, but recently also due to electric vehicle charging stations, where the distribution transformer can cyclically vary between no-load, rated and overrated load. Thus, the distribution transformer can not safely operate under highly-dynamic and stressful conditions, requiring the support of alternative systems. Among the existing solutions, hybrid transformers, which are composed of a conventional transformer and a power converter, are an interesting alternative to cope with several power quality problems. This article is a review of the available literature about hybrid distribution transformers.

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Dual Two-Level Voltage Source Inverter Virtual Inertia Emulation: A Comparative Study

Energies ◽

10.3390/en14041160 ◽

2021 ◽

Vol 14 (4) ◽

pp. 1160

Author(s):

Mohammad Ali Dashtaki ◽

Hamed Nafisi ◽

Amir Khorsandi ◽

Mojgan Hojabri ◽

Edris Pouresmaeil

Keyword(s):

Harmonic Distortion ◽

Synchronous Generator ◽

Voltage Source ◽

Small Signal ◽

Voltage Source Inverter ◽

Nonlinear Loads ◽

Virtual Inertia ◽

The Stability ◽

Stability Enhancement ◽

Oscillation Damping

In this paper, the virtual synchronous generator (VSG) concept is utilized in the controller of the grid-connected dual two-level voltage source inverter (DTL VSI). First, the topology of the VSG and the DTL VSI are presented. Then, the state-space equations of the DTL VSI and the grid-connected two-level voltage source inverter (TL VSI), regarding the presence of the phase-locked loop (PLL) and the VSG, are given. Next, the small-signal modeling of the DTL VSI and the TL VSI is realized. Eventually, the stability enhancement in the DTL VSI compared with the TL VSI is demonstrated. In the TL VSI, large values of virtual inertia could result in oscillations in the power system. However, the ability of the DTL VSI in damping oscillations is deduced. Furthermore, in the presence of nonlinear loads, the potentiality of the DTL VSI in reducing grid current Total Harmonic Distortion (THD) is evaluated. Finally, by using a proper reference current command signal, the abilities of the DTL VSI and the TL VSI in supplying nonlinear loads and providing virtual inertia are assessed simultaneously. The simulation results prove the advantages of the DTL VSI compared with the TL VSI in virtual inertia emulation and oscillation damping, which are realized by small-signal analysis.

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