Power management in distributed generation systems becomes challenging under unbalanced grid conditions, as the negative sequence voltage generate power oscillations at twice the fundamental grid frequency. Grid unbalance can be mitigated through sequence current control, which also enables the regulation of active and reactive power oscillations. This paper presents an analysis of the generated active and reactive oscillating power under different unbalanced grid conditions. In addition, a reference generation methodology is introduced to share power oscillations and reduce the amplitude of the reactive power oscillations. The performance of this strategy is evaluated through switched EMT simulations.

Impedance-based stability analysis techniques are increasingly used to assess the stability of power converter-dominated power systems. Among these techniques, the Generalized Bode Criterion (GBC) has emerged as a robust method, combining the strengths of the Nyquist Stability Criterion (NSC) with the ease of application of the Bode criterion. However, the GBC requires knowledge of the phase derivative at 0 Hz, which can be challenging to obtain when the system transfer function is analytically unknown. This paper proposes and proves a mathematical relation to eliminate the need for the phase derivative in the GBC. Consequently, all necessary information required for the GBC can be directly obtained from the system Bode plot, enabling the application of the GBC to power systems represented by black-box models with no detailed internal information. The proposed approach is validated by analyzing the stability of a DC-DC converter connected to a DC grid and comparing the results with time-domain simulations.

As electrical grids integrate increasing shares of renewable energy, the role of power electronic converters, particularly grid-forming (GFM) inverters, becomes increasingly critical. However, GFM inverters introduce new challenges in self-protection due to their synchronization mechanisms being tightly coupled with power dynamics. This paper proposes a layered self-protection scheme for GFM inverters, inspired by classical grid-following (GFL) strategies. The scheme comprises three hierarchical layers: (1) setpoint saturation, (2) control / software limitation, and (3) hardware limitation. Special emphasis is placed on adapting the first layer to the GFM context. The third layer remains largely applicable without significant changes. Additionally, hardware-imposed operational boundaries due to voltage and current constraints are examined and validated by simulation in order to define feasible inverter operation under fault conditions or setpoint misconfigurations.

The increased grid configuration variability and, among others, the massive integration of renewable energies, have created a challenging scenario for power converters. Due to this fact, active impedance estimation is an interesting characteristic that will allow power converter online control tuning and/or stability analysis. Pseudo Random Binary Sequence (PRBS) injection is one the most interesting and proposed methods in the literature to obtain this impedance estimation. Many papers use impedance estimation on dedicated power converters, or they often overlook the digital and power hardware constraints that power converters must meet. This is especially important in high-power converters, where low switching and control frequencies are used. This paper defines and proposes an implementation and design method for PRBS injection considering the abovementioned constraints. The proposed method is aimed to be implemented in an already operating converter, thus adding the impedance estimation as one additional functionality of the converter. Therefore, no dedicated power converter to estimate the grid frequency is required. Multi-harmonic and multi-sequence impedance estimation is also analyzed, thus demonstrating the ability of the proposed method to operate under highly variable and demanding grid conditions. The analysis is validated via simulation results in different case scenarios.

High penetration of renewable energy resources in the power system results in various new challenges for power system operators. One of the promising solutions to sustain the quality and reliability of the power system is the integration of energy storage systems (ESSs). This article investigates the current and emerging trends and technologies for grid-connected ESSs. Different technologies of ESSs categorized as mechanical, electrical, electrochemical, chemical, and thermal are briefly explained. Especially, a detailed review of battery ESSs (BESSs) is provided as they are attracting much attention owing, in part, to the ongoing electrification of transportation. Then, the services that grid-connected ESSs provide to the grid are discussed. Grid connection of the BESSs requires power electronic converters. Therefore, a survey of popular power converter topologies, including transformer-based, transformerless with distributed or common dc-link, and hybrid systems, along with some discussions for implementing advanced grid support functionalities in the BESS control, is presented. Furthermore, the requirements of new standards and grid codes for grid-connected BESSs are reviewed for several countries around the globe. Finally, emerging technologies, including flexible power control of photovoltaic systems, hydrogen, and second-life batteries from electric vehicles, are discussed in this article.

Publisher Copyright: © 2022 IEEE.

Low switching frequency modulation techniques such as Selective Harmonic Elimination - Pulse Width Modulation (SHE-PWM) or Optimal Pulse Pattern (OPP) are commonly used in medium voltage - high power multilevel converters to improve their efficiency. These techniques require solving non-linear equations in order to calculate the firing angles. These equations can be solved by meta-heuristic optimization algorithms, which depend on a set of hyperparameters that must be properly adjusted to ensure their effectiveness. This paper presents a methodology to tune different meta-heuristic algorithms to fairly compare them and select the best algorithm to solve SHE-PWM/OPP formulation. The methodology is applied considering different meta-heuristic algorithms such as genetic algorithm, differential evolution, harmony search and simulated annealing. It has been validated in SHE-PWM and OPP techniques with different number of firing angles.

Medium-voltage high-power converters are usually modulated using low switching frequency techniques such as Selective Harmonic Elimination - Pulse Width Modulation (SHE-PWM) in order to improve their efficiency. To calculate the firing angles, SHE-PWM transcendental equations are usually solved by offline calculation methods, whose computational burden depends on the number of firing angles or eliminated harmonics and the required accuracy in the solutions. Consequently, with the aim of reducing this computational burden, this paper presents an analysis that estimates the maximum accuracy required in the calculated SHE-PWM solutions considering the main non-idealities of the converter. In this sense, a systematic methodology to evaluate the error in the harmonic amplitudes due to control and dead time effects has been developed, providing an optimal error tolerance for the calculation methods that solve the SHE-PWM problem.

This paper analyzes and compares the reactive power limits of single- and three-phase configured dc-link Voltage Source Converter (VSC) structures for Static Synchronous Compensator (STATCOM) to operate with negative-sequence voltage and current. The three-level Neutral Point Clamped (3L NPC) is used as an example of a three-phase dc-link topology. Likewise, the Cascaded H-Bridge (CHB) is used as a single-phase dc-link case, in both star and delta configurations. Modular Multilevel Converter is also considered as a combination of both dc-link configurations. The conclusions drawn are generic whichever the Power Electronics Building Block (PEBB) used in each VSC structure.

The evolution of self-commutated semiconductor devices, development of fast digital controllers and the emergence of new multilevel converter topologies have allowed to increase the voltage and power ratings of power electronic equipment. This has accelerated the use of these devices in MV levels. As multilevel Voltage-Source Converter (VSC) topology-based equipment prevails in MV applications, the operating range of these converters is getting increasingly wider. A common choice to increase the power rating is to combine basic Power Electronics Building Blocks (PEBB). There is a demand of new operating requirements for power converters, such as unbalances in the grid or fault operation. This paper presents a methodology to evaluate different MV multilevel VSC structures working under any operating scenario. The methodology is integrated into a software-based tool. This tool enables to obtain valuable information to compare, select and design the converter PEBB combination that better suits certain operating requirements. In order to evaluate the potential, the proposed methodology is applied in two operating case studies.

This paper presents a pulse width modulation variation in order to overcome any drawback in the sampled reference signal due to its discretization. This discretization can be a problem in low switching frequency power converters; for instance, in Medium Voltage applications. This effect is amplified with interleaved power converter structures. The proposal is based on the polynomial linearization of the reference sampled point, instead of maintaining the reference constant in the whole switching update period. The graphical analysis is applied into three-phase, three-level power converter case study, but the conclusions can be extrapolated to any number of levels or any type of converter structure. The performance in one single and two interleaved power converters scenario scenarios is simulated in order to prove its superiority compared to the existing literature.

The serialization of semiconductors arises as an attractive solution at the time of engineering high voltage and high power Variable Speed Drive equipments. The voltage balancing is the main concern, as the maximum blocking voltage of the components can be exceeded during the turn off process. In this paper auxiliary low-loss circuitry for Medium Voltage modules series-connection is presented for a 3-Level NPC topology 6.6kV output voltage inverter. They are considered both the gate control for possible asymmetries during turn-off and a passive clamp circuit to match the stationary unbalances generated by the Ices (Leakage Current) and Qrr (Recovered Charge) differences between the serialized modules. The analysis criteria is justified, and experimental results in a real high-power medium-voltage (6.6kV and 10MW) converter are served.

This paper presents an analysis of the reactive power injection limits of Medium Voltage STATCOM with harmonic active filtering capability. In order to obtain those limits, voltage and current requirements for the active filter application are estimated for a simplified case. In the same way, evolving the same analysis, some hardware and system issues, such as transformers de-rating and the impact of the phase angle of the compensated harmonic, are also addressed. Those limits are evaluated for a real full-scale power converter.