Low Voltage DC Distribution System Research Articles

Various Feature-Based Series Direct Current Arc Fault Detection Methods using Intelligence Learning Models and Diverse Domain Exclusion Techniques

The expansion of DC electrical distribution systems necessitates advancements in detecting and mitigating DC arc events, a significant contributor to fire accidents in low-voltage DC distribution systems. Detecting DC arc faults poses considerable challenges, making them a major safety concern in DC power lines. Conventional approaches mainly rely on arc current, which can vary during normal operation, potentially leading to false alarms. Moreover, these methods often require manual adjustment of detection thresholds for different systems, introducing the risk of malfunction. This study proposes an advanced arc fault recognition procedure that extracts and utilizes various key features for the DC arc detection. This work investigated new various features, which are the square average, the average, the median, the rms, the peak-to-peak, and the variance values, to find out which one can be the most effective features to detect the DC arc failure. The results of this detection process show good evidence for the effectiveness and reliability of the proposed malfunction detecting plan.

Low-Voltage ac and Low-Voltage dc Distribution Systems: An Assessment of Losses and Power Capacity considering the Penetration of Renewable Energy Sources

Low-Voltage ac and Low-Voltage dc Distribution Systems: An Assessment of Losses and Power Capacity considering the Penetration of Renewable Energy Sources

A DCM-Based Non-Isolated Step-Down DC Transformer

DC transformers have emerged as essential devices for medium voltage DC (MVDC)-low voltage DC (LVDC) distribution systems. However, conventional step-down single-level converters have limits on the voltage level of the MVDC-LVDC distribution system. This paper proposes a non-isolated step-down (NISD) DC transformer based on discontinuous conduction mode (DCM). The proposed structure can withstand high voltage levels by sharing voltages between energy storage modules dividing voltage levels. The proposed NISD DC transformer determines operational modes based on energy storage modules and performs the voltage conversion process. The effectiveness of the proposed NISD DC transformer is verified based on a case study using a power system computer-aided design and electromagnetic transient simulation engine including DC (PSCAD/EMTDC™).

A Review on Topological Advancement and Performance of Low Voltage DC Distribution System

A Review on Topological Advancement and Performance of Low Voltage DC Distribution System

A Simplified Current Feature Extraction and Deployment Method for DC Series Arc Fault Detection

DC series arc fault (DSAF) is one of the main causes of low-voltage DC (LVDC) distribution system fire accident. Traditional methods use time-frequency domain features to make judgments directly or use machine learning to further classify them. In this paper, a method is proposed to simplify the feature extraction process while ensuring accuracy. Firstly, a fully automated process is used to establish DC arc datasets. A composite bandpass filter (CBF) is designed to extract the typical frequency segment of DC arc. Besides, an arc detection neural network (ArcNN) based on temporal convolution network (TCN) is proposed to extract current waveform features. Principal component analysis (PCA) is used to process these features to reduce correlation. Finally, a single hidden layer neural network (SHLNN) is used as classifier. The database is collected from different scenarios and working conditions. By measuring the DC raw current, the arc fault detector (AFD) can achieve a test set accuracy of 99.88% at a sampling rate of 250 kHz. The model is also deployed on Jetson Nano with an average real-time detection of 0.15 s/sample.

Research on Dynamic and Thermal Effects Based on the Calculation of the Short-Circuit Current in Low-Voltage DC Distribution Systems for Civil Buildings

The verification of short-circuit effects is very important for ensuring the safety of equipment and power systems. Compared with that in alternating current (AC) systems, research on this issue in direct current (DC) systems is scarce, and it is urgently necessary to develop an accurate verification method for applications in DC systems. This research establishes an equivalent model of a pole–pole cable short-circuit according to the characteristics of low-voltage DC distribution systems in civil buildings. Through theoretical analysis and numerical simulation, the development process of a short circuit is summarized, and the methods of verifying dynamic and thermal effects based on the time-domain characteristics of the short-circuit current are specified. By calculating the peak value and Joule integral of the short-circuit current, in comparison with those in the IEC 61660 (1997) standard, this research points out that the method in the IEC 61660 (1997) standard is insufficient. Finally, the short-circuit peak current is greatly affected by the DC-link capacitance, the steady-state current is directly related to the filter inductance of the AC-link; and the verification of the thermal effect requires the calculation of the Joule integral in the transient and steady state.

DC Transformers in DC Distribution Systems

With the rapid development of power electronics technology and its successful application, many demonstration projects of medium/low-voltage DC (M-LVDC) distribution systems have been constructed. The DC transformer (DCT) is the key equipment in the M-LVDC distribution system for interconnecting the MVDC and LVDC buses. In this paper, the characteristics of DCTs are summarized. The existing topologies of DCTs are analyzed, and the relevant control strategies are researched, including steady-state control, transient control, and cascaded control. The engineering application examples of DCTs are introduced by interpreting the medium and low-voltage DC distribution system demonstration project in Wujiang City, Suzhou. Finally, the challenges faced by the DCT are given, and the future development trend is predicted. This perspective provides a constructive basis for DCTs and an important reference for M-LVDC distribution systems.

Intelligent Short-Circuit Protection with Solid-State Circuit Breakers for Low-Voltage DC Microgrids

Fault current limiting (FCL) for short-circuit protection of DC microgrids is a challenging task due to the influence of power electronic converters on the fault characteristics. To overcome these challenges, a protection scheme needs to be developed which is capable of limiting the fault current, provides continuous power to the unfaulted sections in the network, and coordinates between the downstream and upstream protection devices. For the above-mentioned reasons, this paper analyzes the problems related to the protection of low voltage (LV) and to propose a solid-state circuit breaker (SSCB) based short-circuit protection methodology that provides FCL. To improve the action of the proposed approach, the conventional threshold-based fault detection approaches (FDAs) are replaced with an intelligent technique where decision trees (DTs) are used to learn the fault characteristics of the system. To evaluate the development of the proposed approach, numerical simulations are performed with a notational LV DC distribution system representing a . The simulation results and analysis proved the effectiveness of the proposed approach, and the FDA improves the operation of the SSCB and FCL with an accuracy of 98.3%. Further, the action of FCL function is tested on the reliability of the SSCB by analyzing the thermal characteristics of the device under both normal operating mode and the FCL mode.

Protection Scheme Based on Fault Area Estimation in Loop-Type Low Voltage DC Distribution System with Photovoltaic System using Derivative of Current and Power at Tie Switch

Protection Scheme Based on Fault Area Estimation in Loop-Type Low Voltage DC Distribution System with Photovoltaic System using Derivative of Current and Power at Tie Switch

A Low-Voltage AC, Low-Voltage DC, and High-Voltage DC Power Distribution System with Grid: Design and Analysis

Low-voltage (LV) and high-voltage (HV) DC distribution systems are being investigated as alternatives due to the growth of DC distribution energy resources (DER), DC loads such as solar and wind power systems, and energy storage sources (ESSs). Furthermore, an HV/LV DC distribution system offers various advantages, including lower conversion losses, an easier connecting strategy for DC DERs, and less complex power management techniques. As renewable energy sources are increasingly incorporated into the electrical grid, it is important to create novel, effective approaches for connecting such sources and loads. It would hence be effective to merge DC distribution with AC distribution to fulfill the energy demands of both DC and AC consumers. To this end, this study proposes a multizone design with four buses: low-voltage direct current (LVDC), high-voltage direct current (HVDC), low-voltage alternating current (LVAC), and an electrical grid. A model of this system that covers crucial elements, including power systems, DER systems, and power electronic devices, to serve as a foundation for the analysis and design of this architecture is proposed. MATLAB/Simulink is used to conduct a simulation study to verify the performance of the proposed design. In this study, a hybrid electrical grid with an LVDC, HVDC, and LVAC distribution network test is used and implemented. Additionally, a transient and steady-state characteristic analysis of the test system is performed.

Power and Voltage Control Based on DC Offset Injection for Bipolar Low-voltage DC Distribution System

Power and Voltage Control Based on DC Offset Injection for Bipolar Low-voltage DC Distribution System

A comprehensive evaluation method of DC voltage sag in medium–low voltage DC distribution system

The development of the DC distribution system (DCDS) has attracted increasing attention, due to its technological superiorities in integrating new energy sources and DC power loads more friendly and effectively. In this paper, a comprehensive evaluation method is proposed for the medium–low​ voltage DCDS to handle the voltage sag assessment problem. Firstly, the topology structure and control strategy of the DCDS are stated, and the pragmatic characteristics of DC voltage sag on the medium-voltage and low-voltage sides based on the dual active bridge (DAB) converter are analyzed. Then, considering the difference in the evaluation indexes of the low-voltage and medium-voltage sides of the DCDS, a comprehensive evaluation system is established. Further, the analytic hierarchy process (AHP) and criteria importance through intercriteria correlation (CRITIC) weighting method are applied to achieve comprehensive weighting, and the TOPSIS model is used to describe the severity of DC voltage sag. Using MATLAB, a 10 kV/ 750 V DCDS with the DAB is built, and comparative assessments are performed. The results show that the proposed method can reasonably evaluate the DC voltage sag of the low-voltage and medium-voltage sides. Compared to the evaluation schemes based on the single index, the proposed method can more effectively reflect the waveform features of the DC voltage sag, and it is very appropriate for the voltage dip evaluation of the medium–low voltage DCDS.

Modified Three-Port DAB Converter Employing Voltage Balancing Capability for Bipolar DC Distribution System

To construct the bipolar low-voltage dc distribution system, a dual-active-bridge (DAB) converter and a voltage balancer are needed. However, this conventional two-stage circuit is bulky and shows low efficiency. Besides, when a short circuit fault occurs at one of the bipolar dc poles, the conventional topology cannot balance the other normal dc pole voltage due to its single closed circuit, which eventually loses the high reliability of the bipolar system. To mitigate those issues, a modified three-port DAB converter is proposed. The proposed converter is an enhanced topology of the three-port DAB converter, which can balance the bipolar voltage levels without additional voltage balancers. In addition, each bipolar output has an independent closed circuit to balance the normal dc pole under the short circuit fault at one of the dc poles, thereby improving the system reliability. Moreover, constant duty-cycle modulation and magnetizing inductance design are proposed to obtain full-range zero voltage switching (ZVS) of all switches. Since the proposed ZVS modulation uses a constant duty-cycle value, its control can be easily implemented in a digital signal processor. Finally, a 2-kW prototype is developed to validate the effectiveness of the proposed converter.

Modular modeling method and power supply capability evaluation for integrated hydrogen production stations of DC systems

Low-voltage DC distribution system has many advantages, such as facilitating the access of DC loads and distributed energies and improving the network’s stability. It has become a new idea for integrated hydrogen production stations. Power supply capacity and small-signal stability are important indexes to evaluate a low-voltage DC integrated system. Based on the master–slave control mode, this paper selects the typical star structure as the research object, constructs the system transfer function through the scalable modular modeling method, and further evaluates the impact of the high-order DC hydrogen production station integrated system on the hydrogen production capacity under the changes of the line length and master station position. The results show that the hydrogen production capacity of the system decreases gradually with the main station moving from side to inside. Finally, a practical example is analyzed by MATLAB/Simulink simulation to verify the accuracy of the theory. This study can provide an effective theoretical method for the structure optimization and integrated parameter design of low-voltage DC system.

LVDC Bipolar Balance Control of I-M2C in Urban AC/DC Hybrid Distribution System

With the high proportional renewable energy integration and rapid increase in the DC loads, such as the electric vehicle and distributed energy storage, the DC distribution system becomes a prospective solution for the urban power grid enhancement for its high-efficiency and eco-friendly nature. In most DC distribution systems, power interfaces are applied to connect low-voltage DC (LVDC) distribution systems with multiple medium-voltage (MV) systems in order to improve the operating reliability and economy. Compared to other types of multiports power interfaces, the three-port-isolated modular multilevel converter (I-M2C) has shown many advantages, including low cost, high power density, and low control complexity. However, the I-M2C cannot handle the power imbalance at the bipolar LVDC port like the other MMC-based three-port power interfaces, which limits the operating range and decreases the stability of the I-M2C in bipolar LVDC application. In order to solve the bipolar imbalance problems, a novel balance control method is proposed in this article. The proposed balance control method is based on symmetrical decomposition. By decoupling the MV power control and the LV bipolar power compensation control, the proposed method can eliminate the bipolar voltage deviation under different working conditions. The simulation results prove the validity and good control performance of the proposed method.

방사상 LVDC 배전계통에서 고장전류의 극성을 이용한 보호 방법

The low-voltage DC (LVDC) distribution system is attracting attention due to the increase in DC-based distributed generation and the development of power conversion technology. This technology has various advantages by reducing power consumption through high-efficiency conversion that reduces the number of AC/DC power conversions. In this paper, a new protection method for the stable operation of LVDC distribution system is proposed. The change of fault current according to fault location in LVDC distribution system is analyzed. Based on this, a new protection method using the polarity of the fault current is proposed. The proposed method determines the fault location and transmits a trip signal of circuit breaker (CB) accordingly. For verification of the proposed method, the LVDC distribution system and the proposed method are modeled using Electro Magnetic Transient Program (EMTP). Simulations are performed according to the fault location and fault resistance, and the results are analyzed. The simulation results show that the fault location is accurately determined and the trip signal of CB is transmitted according to the proposed method.

Fault Section Estimation in Radial LVDC Distribution System Using Wavelet Transform

The demand for low voltage DC (LVDC) distribution systems is increasing due to the rapid development of power conversion technology, the increase of DC-based digital loads, and the expansion of DC-based distributed generation (DG). For the stable operation of the LVDC distribution system, it is necessary to develop a protection method. In this paper, the fault section is estimated using wavelet transform (WT) in LVDC distribution system. The fault section is classified into a DC line and a DC bus. The characteristics of fault current at each fault section part are analyzed in simple and actual LVDC system. Based on this analysis, the algorithm for fault section estimation is proposed using the detail component after performing WT. The results of fault section estimations are verified through various simulations using EMTP and MATLAB. The fault section estimation can be utilized in the development of protection schemes in LVDC distribution system.

Energy saving potential through artificial lighting system in PV integrated smart buildings

Artificial lighting in buildings is accountable for a remarkable portion of overall energy consumption. It is thus necessary to reduce especially for zero energy buildings (ZEBs). Daylight harvesting holds the immense potential of reducing energy consumption but it can disturb the occupants' optical preferences if harvested in excess. A semi-transparent building integrated photovoltaic (BIPV) module which can generate clean energy at the building site and allows the reduced daylight harvesting through, has been proposed as the envelope of the building facade . Hence, to minimize energy consumption and enhancing occupants' visual preferences, a smart lighting system with daylight harvesting through BIPV for an office building is proposed in this paper. The advantages associated with a low-voltage DC (LVDC) distribution system for the proposed system in ZEB is highlighted. Moreover, the opportunity of energy-saving across the proposed artificial lighting system with BIPV as the envelope of the building is investigated with occupants’ visual preference levels in different sky conditions. Results show that the proposed lighting system can be fully energized by the energy generated from the BIPV module. Moreover, a significant amount of surplus energy was also reported. Further, the economic and environmental footprint analysis of the BIPV as a building envelope is presented. The result indicates a competent levelized cost of energy (LCOE) when comparing with the existing utility grid. • Building-integrated photovoltaic module is proposed as an envelope of the building. • Low voltage DC distribution system for the building is highlighted with BIPV. • Coupled energy analysis of smart lighting systems and BIPV are addressed. • The economic and environmental footprint analysis of the BIPV is also included. • Smart lighting system is energized by the energy generated from the BIPV module.

The Coordination Control of SMES and PV in LVDC Distribution System

This paper presents a coordination scheme of superconducting magnetic energy storage (SMES) and photovoltaic (PV) generation system for regulating the DC bus voltage in the low voltage direct current (LVDC) distribution systems. Firstly, the effect of AC grid faults on LVDC distribution system is analyzed. Then, the PV is designed to operate as the backup power of SMES by adjusting the control mode automatically according to the residual energy of SMES. The proposed scheme can regulate DC bus voltage in milliseconds and maintain the bus voltage during the whole fault process by taking use of both SMES and PV. A LVDC distribution system is modelled in PSCAD/EMTDC. Simulation results have demonstrated the feasibility and effectiveness of the proposed scheme.

Fault identification of medium and low voltage DC distribution system based on high frequency fault component

The protection technology of medium and low voltage DC distribution system is still in its infancy, and its accuracy is not high in the process of practical application. Therefore, a fault identification method of medium and low voltage DC distribution system based on high-frequency fault component is proposed, and the topology, grounding mode, protection equipment Fault type and fault transient characteristics are closely related to the design of protection scheme. Based on the high-frequency fault component, the fault identification algorithm of medium and low-voltage DC distribution system is optimized, and different fault categories of AC and medium and low-voltage DC distribution system are divided, so as to achieve the research goal of accurate positioning of different fault types. Finally, it is confirmed by experiments. The fault identification method of medium and low voltage DC distribution system based on high frequency fault component has high accuracy and fully meets the research requirements.