This paper examines high-frequency disturbances in interconnected converters within dc microgrids, focusing on the effects of electromagnetic interference (EMI) filters and long interconnection cables. Understanding these phenomena is essential for systems with multiple power converters as it facilitates the identification and mitigation of voltage and current oscillations. The study investigates the beating effect in dc microgrids, providing an analytical derivation of the oscillation amplitudes at the beat frequency. It also explores how interactions between long cables inductive impedance and EMI filter capacitors can influence the system performance, distinguishing it from previous works. The study examines a dc microgrid consisting of two connected cascaded buck converters. Two scenarios are analyzed: one considers no filters between the two converters, while the other includes a low-pass filter (LPF), an EMI filter, and a cable feeder between them. The proposed theoretical models are validated using a 2 kW experimental prototype comprising two interconnected buck converters. In addition, the paper presents various strategies to mitigate the beating effect in dc microgrids, discussing their effectiveness and the associated implementation challenges.

This work presents a droop-based control strategy for a dc nanogrid designed to operate under the Net Zero Energy (NZE) concept, enabling seamless transitions between grid-connected and islanded modes. The nanogrid integrates photovoltaic (PV) generation, a fast electric vehicle charging station (EVSE), and a battery energy storage system (BESS) into a $700~$V dc bus interfacing with the ac grid via a bidirectional three-phase AC-DC converter. An isolated DC-DC converter establishes a secondary $48~$V dc bus for powering dc loads. An energy management system (EMS) defines an optimal day-ahead power dispatch for the BESS to meet NZE objectives. At the primary control level, a modified power-to-voltage droop strategy ensures accurate power tracking and parallel operation with the AC-DC converter. This approach enables continuous voltage regulation of the main bus under instantaneous power imbalances caused by schedule deviations or operational mode transitions. Additionally, the proposed strategy eliminates the need for secondary control or high-bandwidth communication. The system is validated through hardware-in-the-loop (HIL) simulations using the Typhoon HIL 604 platform, with the control strategy implemented on a DSP. Real-time simulation results confirm stable performance under various operating conditions, including transitions between modes.

This paper presents the validation of a voltage balancing converter for a bipolar DC microgrid designed to ensure reliable operation in both grid-connected and islanded modes. This microgrid includes unipolar constant power loads (CPL), a unipolar Battery Energy Storage System (BESS), and local PV generation. The BESS converter employs a V–I droop strategy using only inductor current feedback, reducing sensing requirements while maintaining plug-and-play capability and ensuring smooth transitions between connected and islanded modes. In such a microgrid, the voltage balancing converter regulates the differential voltages under severe unbalanced load conditions and during transients caused by changes in unipolar loads and sources. The experimental results validate the voltage balancing strategy across various scenarios in a small-scale prototype. The results show tight voltage regulation under unbalanced conditions, and smooth transitions during load transients and unintentional islanding, even if there is no dc voltage source in one of the poles of the bipolar dc bus. For both conditions, the imbalance between the unipolar voltages is less than 0.5% of the total bipolar voltage.

This paper investigates beat frequency oscillations in dc microgrids, which occur due to switching frequency mismatches between cascaded converters. These oscillations can be aggravated by non-synchronized sampling in control systems, leading to stability and performance issues. The study introduces a simplified transfer function model that relates beat frequency disturbances to output voltage oscillations. Unlike previous methods, this approach allows for systematic analysis using Bode diagrams, providing a clear understanding of the mechanisms behind these disturbances. The analysis evaluates three configurations—ranging from a baseline setup to one including EMI filters and long cable feeders—using a 4.75 kW experimental prototype. The proposed model demonstrates high accuracy, with a maximum magnitude deviation of less than 2 dB up to 20 kHz. Furthermore, the model successfully predicts a critical resonance at 19.4 kHz, which amplifies oscillations by 8 V peak-to-peak. The results confirm that beat-frequency gain remains near 0 dB for frequencies below 1 kHz, while high-frequency attenuation exceeds 40 dB. Ultimately, this work offers a computationally efficient tool for stability assessment and effective filter parameter tuning in dc microgrids.

A dc microgrid comprises distributed energy sources and loads interconnected through a common dc bus via dc–dc converters. Their inherent switching behavior necessitates input filters to attenuate high-frequency components. However, interactions between cable impedances and converter filters can lead to high-frequency resonance, degrading bus voltage quality and system performance. This paper proposes a design-oriented mitigation approach for high-frequency resonance in dc microgrids. The method is based on a detailed analysis of the interaction between cable feeders and EMI filters, considering converter dynamic behavior and switching frequency effects. A damping strategy based on the optimal placement of an R–C branch is developed to suppress resonance and improve stability while ensuring compliance with voltage ripple limits derived from MIL-STD-704F. A key contribution of this work is establishing a direct relationship between cable length and the grid-forming converter switching frequency, providing practical design guidelines. This reveals that higher switching frequencies reduce the critical cable length required to trigger resonance, imposing more stringent constraints on dc microgrid layouts. The proposed approach is validated through analytical modeling, simulation results, and experimental tests on a 2 kW dc microgrid prototype, demonstrating significant reduction in high-frequency distortion and compliance with power quality limits.

This article discusses the anachronism, insufficiency, and imprecision of the formulation and definitions of power factor (PF) in several regulatory texts. For consumer units in distribution networks, analyses are presented of how ANEEL defines this figure of merit. In the case of individual equipment, INMETRO's measurement procedures employ formulas that, depending on the tested device's operating principle, may yield technically erroneous results. For example, the results of LED luminaires, which are supposedly designed to have a high power factor, are analyzed and it is concluded that the solution for the errors in single-phase case is straightforward, and are achieved by using the correct formulation of the power factor, defined as the ratio between active and apparent power, with a sufficiently high sampling rate to capture the possible high-frequency spectral components of the current. Modern digital measuring instruments can easily obtain such quantities and do not incur errors that may arise from using quantities such as distortion factors or fundamental displacement.