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DC technologies constitute essential components within the scope of DC distribution networks. All DC networks confront inherent threats, such as DC short‐circuit faults, necessitating robust protective measures. Utilizing DC circuit breakers (DCCBs) emerges as a pivotal strategy for safeguarding these networks. Among the available topologies, z‐source solid‐state circuit breakers (Z‐SSCBs) prove to be optimal for protecting low‐ and medium‐voltage distribution networks and DC equipment due to their straightforward structure, uncomplicated control mechanisms, and cost‐effectiveness. This paper comprehensively explores various Z‐SSCB topologies. The study commences with a comprehensive overview of recent research on circuit breakers and subsequently delves into specific aspects of Z‐SSCB structures. It thoroughly evaluates proposed methodologies and configurations pertaining to these structures. Each structure's merits and drawbacks are utterly analyzed and compared in detail. The analysis categorizes these structures into directional and bidirectional types, offering detailed comparative tables for reference. Finally, the paper addresses the future challenges confronting Z‐SSCB technology, shedding light on existing research gaps. This nuanced exploration contributes valuable insights to the field, paving the way for future advancements in DC distribution network protection. [ABSTRACT FROM AUTHOR]

This manuscript presents a comprehensive review of recent advancements in electrical distribution networks, with a specific focus on the incorporation of direct current (DC) applications. The research aims to comprehensively address the current and future aspects of DC, spanning from the distribution level to the utilization level. The renewed interest in DC power systems has led to the investigation of several transitional challenges in recent years. A significant portion of these efforts has been dedicated to determining the feasibility of applying DC to specific use cases. Additionally, the literature has explored design considerations such as system architecture and voltage levels, the integration of DC into existing distribution networks, load flow (LF) computations, and the distinct safety concerns associated with DC power systems. In this paper, the various research endeavors are categorized, evaluated, and scrutinized to assess the current state of the transition from a purely alternating current (AC) distribution system to a solely DC or hybrid AC/DC distribution system. A bibliometric analysis is conducted, constructing a network of co-occurrence based on author-provided keywords, which reveals the primary research foci in this domain. The barriers hindering the widespread adoption of DC distribution systems and potential solutions are also discussed. Moreover, this article synthesizes ongoing efforts to address these obstacles and delineates future research directions by emphasizing the existing knowledge gaps. [ABSTRACT FROM AUTHOR]

Conventional strategies are not effective in addressing the complex protection challenges in medium-voltage DC distribution networks (MVDCDN). The main challenge in MVDCDN is the high-rising DC fault current, requiring a robust and fast protection strategy. This paper proposes the use of an Extended Kalman filter (EKF) to detect various types of DC faults using only the current signal in the MVDCDN. In the first stage, current signals from the positive and negative poles corresponding bus are obtained. The EKF is then applied to the measured DC-current signals to generate two fault detection indices. The first index is the cumulative residuals (CR), calculated using the EKF iterative differencing process with updated current estimated state and noisy measurement. The second index is the modified DC version of total harmonic distortion, known as DC distortion factor (DCDF). The fault classification/zone identification (FCZI) unit is activated if changes in CR and DCDF are detected within the observation window of the relay. In the second stage, the FCZI unit calculates the Extended Kalman filter-based predicted energy (EKFBPE) for the faulty DC line section at both ends. The polarity of EKFBPE is used for fault classification and localization decisions. The proposed protection strategy requires low-band wireless communication capability in the smart grid. Extensive simulations using MATLAB Ⓡ Simulink 2022b are conducted on a ±2.5 kV MVDCDN with three feeders, considering various fault scenarios. The results demonstrate that the proposed scheme achieves 99.9% accuracy, under radial, looped, and meshed topology and is highly resilient to different types of faults with time of operation 1 msec. The scalability of proposed method and its effectiveness in handling higher voltage levels and associated fault uncertainty will investigate in future research.

Distribution networks feature distinct topologies than transmission networks, such as radial or weakly meshed structures with tens of thousands of nodes. They have more points of power injection owing to the integration of distributed generators and high R/X ratios. Furthermore, there has recently been a surge of interest in DC distribution networks. In the planning and operation of modern distribution systems, load flow needs to be executed in series considering short intervals of time in the order of minutes or even less. Hence, these networks require a load flow solver that can converge fast with low computational burden. In this paper, we propose a unique iterative power flow solver based on graph theory for DC distribution networks. The proposed formulation is flexible and can handle both radial and mesh configurations with just one connectivity matrix. To validate the proposed method, we used the IEEE 33 bus test feeder and compared the results with an existing methodology. Results suggest that the proposed method is robust and possesses fast convergence.

This manuscript presents a comprehensive review of recent advancements in electrical distribution networks, with a specific focus on the incorporation of direct current (DC) applications. The research aims to comprehensively address the current and future aspects of DC, spanning from the distribution level to the utilization level. The renewed interest in DC power systems has led to the investigation of several transitional challenges in recent years. A significant portion of these efforts has been dedicated to determining the feasibility of applying DC to specific use cases. Additionally, the literature has explored design considerations such as system architecture and voltage levels, the integration of DC into existing distribution networks, load flow (LF) computations, and the distinct safety concerns associated with DC power systems. In this paper, the various research endeavors are categorized, evaluated, and scrutinized to assess the current state of the transition from a purely alternating current (AC) distribution system to a solely DC or hybrid AC/DC distribution system. A bibliometric analysis is conducted, constructing a network of co-occurrence based on author-provided keywords, which reveals the primary research foci in this domain. The barriers hindering the widespread adoption of DC distribution systems and potential solutions are also discussed. Moreover, this article synthesizes ongoing efforts to address these obstacles and delineates future research directions by emphasizing the existing knowledge gaps.

Direct current (dc) distribution networks are rapidly growing, but they still face serious challenges of severe converter damage due to low inertia, short fault duration, and fast-growing dc fault currents. In this regard, a data-driven fault detection scheme for dc distribution networks is presented using machine learning techniques. To have a good fault detection capability of dc distribution networks, the fault characteristics of the faulted and healthy dc lines are analyzed with lots of fault data. After preprocessing, the fault feature vector is constructed to identify the faulted line using multi-dimensional fault features. Additionally, the adaptive boosting technique, which is a kind of machine learning, is used for the data-driven fault detection scheme. It is yielded with the abilities of fault identification and fault pole discrimination, tolerance to fault location, transition resistance, and noise interference. Further, a large amount of fault data is obtained by PSCAD/EMTDC to verify the proposed detection scheme. Test results demonstrate that the proposed fault detection scheme can achieve sensitive and accurate fault identification and fault pole selection within 2.5 ms. The proposed scheme is immune to noise interference and effectively adapts to changes in voltage level and topology with high accuracy. • A data-driven fault detection scheme using the adaboost technique for dc distribution networks is proposed. • A fault feature screening and a fault data preprocessing strategy are proposed to improve detection performance. • A fault identification model is designed, in which fault judgment, fault pole discrimination, and adaptability are considered. [ABSTRACT FROM AUTHOR]

In DC distribution networks, the uncertainties of renewable energies and loads cause frequent voltage fluctuations. In this paper, a voltage regulation strategy based on the combined coordination of centralized optimal control (COC) and adaptive droop control (ADC) is proposed for droop-controlled DC distribution networks. In the COC strategy, the operation reference power of voltage source converters (VSCs) is optimized using the bus injection power measurements to improve the voltage profile and balance the power loading rates of different VSCs. The VSC capacity margin constraint is established to ensure that the capacity margin of each VSC is sufficient to cope with the unexpected fluctuation of loads and renewable energies. Then, an ADC strategy is adopted to handle voltage fluctuation between adjacent two COCs. In the ADC strategy, the operation reference power of the VSCs is further adjusted to recover the voltages. The voltage regulation is achieved based on the relationship among the VSC voltages and the minimum/maximum voltages of the whole network, which does not depend on the information of each nodal voltage and thus real-time network communication is avoided. The simulation results show that the proposed voltage regulation strategies can effectively improve the voltage profile under various uncertain environments. [ABSTRACT FROM AUTHOR]

This paper introduces the concept, theory of operation and applications of soft open points for direct current networks (DCSOPs). The DCSOP is based on a bidirectional DC–DC converter actively controlled to behave like a normal conductor. Unlike the normal conductor, the DCSOP can transfer the electric power between nodes at different voltage levels. With this advantage, the DCSOP can effectively control the power flow direction. Thus, DCSOPs can play a vital role in the reconfiguration of DC distribution networks. The operation and control of the DCSOP device was investigated, both in transient and steady-state conditions. Then, a DCSOP was integrated into a DC microgrid model to validate its ability to change the power flow through the modelled feeders. In addition, a set of reliability indicators was calculated for the DC microgrid under different reconfiguration scenarios. It was shown that reliability is improved when the DCSOP device implements network reconfiguration. Finally, an agent-based framework for controlling the DCSOP in a DC microgrid is presented. A fundamental implementation was created for reconfiguring a DC microgrid with a DCSOP controlled by an agent, proving that the agent-based system can effectively control the DCSOP device for reconfiguration and voltage regulation. [ABSTRACT FROM AUTHOR]

• An improved active injection method is proposed to inject a detection signal to strengthen the fault characteristics with a lesser negative impact on the system during the injection process. • A ZPI algorithm is proposed to calculate the feeder length, and the faulty feeder is selected based on the polarity of the calculated length. • The waveform, frequency, amplitude, and duration of the detection signal are analyzed based on the requirements of the faulty feeder selection method and system constraints. • Simulations verify the feasibility of the proposed method under conditions of up to 5000 Ω transient resistance and 20 dB noise. Identifying single-line-to-ground faults in non-effectively grounded DC distribution networks is challenging because the fault current is fleeting in the transient stage and negligible in the fault steady stage. First, an active signal injection method is proposed to inject signals into the DC network after the fault occurs. And the fault characteristics of the zero-mode fault circuit including the injected signal are analyzed. Second, a zero-mode parameter identification algorithm is proposed to calculate the length of each feeder based on the injected signal in the fault steady stage. It is found that the calculated length of the healthy feeder corresponds to its actual length, but the calculated result of the faulty feeder is the opposite of the total length of all healthy feeders. Finally, a faulty feeder selection method based on the polarity of the calculated length is proposed. The simulation results shown that the method can select faulty feeders under conditions of up to 5000 Ω transient resistance and 20 dB noise. [ABSTRACT FROM AUTHOR]

The new millennium has witnessed a pervasive shift of trend from AC to DC in the residential load sector. The shift is predominantly due to independent residential solar PV systems at rooftops and escalating electronic loads with better energy saving potential integrated with diminishing prices as well as commercial availability of DC-based appliances. Comprehensive sensitivity analysis considering the real load profile is missing in the present body of knowledge. In order to fill that gap, this paper is an attempt to include a comprehensive sensitivity analysis of the DC distribution system and its simulation-based comparison with its AC counterpart, considering the real load profile. The paper uses the Monte Carlo technique and probabilistic approach to add diversity in residential loads consumption to obtain an instantaneous load profile. Various possible scenarios such as variation of standard deviation from 5% to 20% of mean load value, PV capacity variation from 1000 W to 9000 W, and variation in power electronic converter (PEC) efficiencies are incorporated to make the system realistic as much as possible maintaining a fair comparison between both systems. The paper concludes with the baseline efficiency advantage of 2% to 3% during the day for the case of the DC distribution system as compared to the AC distribution system. [ABSTRACT FROM AUTHOR]

The modular multilevel high-frequency DC transformer (MDCT) plays an important role in the bus connection, voltage conversion, power transmission and electrical isolation in the DC distribution networks. During practical operation, the mismatch between high-frequency-link (HFL) voltages and HFL transformer voltage ratio caused by the variation of DC bus voltages occurs, resulting in the increased reactive power, larger current stress and decreased efficiency in MDCT. To solve this problem, an adaptive modulation strategy (AMS) is proposed in this paper. The proposed AMS adjusts HFL voltages by varying the number of inserted sub-modules adaptively, ensuring the HFL voltages match HFL transformer voltage ratio. Compared with the conventional phase-shift strategies, the proposed strategy obtains higher transmission power capacity and HFL power factor, and it maintains the ideal efficiency of MDCT under light load situation. Besides, the proposed strategy avoids the optimal phase-shift angle calculation containing numerous parameters, reducing computing burden and improving practicality for MDCT. Moreover, the hybrid-wave modulation in proposed strategy makes HFL voltages compose of quasi-square-wave and square-wave, addressing the $\text{d}v/\text{d}t$ stress problem and ensuring the higher DC voltage utilization and power transmission capability simultaneously. The mathematical model, operation principle and control architecture of proposed AMS are investigated, and the experimental results in a MDCT prototype verify the correctness and effectiveness of the analysis and proposed strategy.

This paper introduces the concept, theory of operation and applications of soft open points for direct current networks (DCSOPs). The DCSOP is based on a bidirectional DC–DC converter actively controlled to behave like a normal conductor. Unlike the normal conductor, the DCSOP can transfer the electric power between nodes at different voltage levels. With this advantage, the DCSOP can effectively control the power flow direction. Thus, DCSOPs can play a vital role in the reconfiguration of DC distribution networks. The operation and control of the DCSOP device was investigated, both in transient and steady-state conditions. Then, a DCSOP was integrated into a DC microgrid model to validate its ability to change the power flow through the modelled feeders. In addition, a set of reliability indicators was calculated for the DC microgrid under different reconfiguration scenarios. It was shown that reliability is improved when the DCSOP device implements network reconfiguration. Finally, an agent-based framework for controlling the DCSOP in a DC microgrid is presented. A fundamental implementation was created for reconfiguring a DC microgrid with a DCSOP controlled by an agent, proving that the agent-based system can effectively control the DCSOP device for reconfiguration and voltage regulation.

Due to the promising development of direct current (dc) distribution networks, we focus on the demand-side management (DSM) problems which aim at the minimization of operational costs in dc distribution networks. Based on the established voltage model of power electronic loads, we formulate a DSM optimization problem that coordinates the bus voltage by minimizing the system cost, and the underlying optimization problem is nonconvex. In order to solve this nonconvex problem, we first reformulate it as a difference of convex programming problem, and then propose a novel algorithm based on branch and bound to implement the optimal solution. It is shown that the system is guaranteed to converge to the global optimum under the proposed method. As demonstrated with numerical examples, we analyze the convergence and global optimality of the proposed method, and discuss the computational complexity and scalability with respect to the size of distribution networks. Moreover, in case each of individual loads can make its own decisions by itself, the underlying optimization problem is implemented in the context of the noncooperative game. The existence of the Nash equilibrium is verified and demonstrated through simulation results. [ABSTRACT FROM AUTHOR]

The concept of DC power distribution has gained interest within the research community in the past years, especially due to the rapid prevalence of solar PVs as a tool for distributed generation in DC microgrids. Various efficiency analyses have been presented for the DC distribution paradigm, in comparison to the AC counterpart, considering a variety of scenarios. However, even after a number of such comparative efficiency studies, there seems to be a disparity in the results of research efforts, wherein a definite verdict is still unavailable. Is DC distribution a more efficient choice as compared to the conventional AC system? A final verdict is absent primarily due to conflicting results. In this regard, system modeling and the assumptions made in different studies play a significant role in affecting the results of the study. The current paper is an attempt to critically observe the modeling and assumptions used in the efficiency studies related to the DC distribution system. Several research efforts are analyzed for their approach toward the system upon which they have performed efficiency studies. Subsequently, the paper proposes a model that may alleviate the shortcomings in earlier research efforts and be able to give a definite verdict regarding the comparative efficiency of DC and AC networks for residential power distribution.

In this study, an interval arithmetic‐based method has been proposed for contingency analysis of line outage in DC distribution networks. This method incorporates the uncertainties in source/load which become considerable in the system with increasing renewable generations and time‐varying loads. Two‐stage contingency analysis approach is adopted in this method. For the first stage of contingency screening, a contingency filter has been developed based on interval matrix norm to quickly estimate the bounds of operating state in the post‐outage period. For the second stage of detailed analysis to the selected contingencies, the interval analytical model is first transformed into a non‐linear programming‐based equivalent model. To solve this model accurately and efficiently, successive linear programming and reformulation‐linearisation techniques are employed. The proposed method is benchmarked against Monte Carlo simulations and line outage distribution factor‐based method. [ABSTRACT FROM AUTHOR]

In dc distribution networks, the parallel H-bridge dc/dc converters (HBDCs) are widely adopted to convert voltage levels with the higher power rating and reliability, in which the parallel HBDCs are naturally connected in input-parallel output-parallel (IPOP) form. However among IPOP HBDCs, there are complicated circulating currents that will influence the safe and steady operation of dc distribution networks. This paper focuses on the suppression of these circulating currents. First, the detailed mathematic models of circulating currents among IPOP HBDCs are derived. Through the model, it is found that various types of circulating currents exist in the system, including the circulating currents within the single HBDC and the circulating currents among the multiple HBDCs. Hence, the suppression of circulating currents among IPOP HBDCs is a multiobjective control problem. In this paper, it is proven that the conventional one degree of freedom control based on the bipolar modulation cannot eliminate all the circulating currents. Second, a novel two degrees of freedom control method is proposed to suppress all kinds of circulating currents based on the improved modulation way of HBDCs, which consists of two parts. The droop based control is used to suppress the circulating currents among the multiple HBDCs, whereas the common mode control is used to control the circulating currents within the single HBDC. All the theoretical analyses are verified by the real-time hardware-in-loop tests. [ABSTRACT FROM AUTHOR]

Several methods have been published aiming to detect islanding in ac distribution networks. On the other hand, islanding detection in dc networks appears more challenging, as many electric parameters, such as frequency and reactive power, are absent and thus, several methods used in ac networks are nonapplicable. This paper proposes a novel islanding detection method (IDM) that is effective in dc networks and at the same time provides an index to evaluate the effectiveness of the various IDMs. The proposed IDM is evaluated by simulation and experimental testing according to Standards IEEE 1547 and UL1741 proving its satisfactory performance. [ABSTRACT FROM PUBLISHER]

Direct current (DC) power systems have recently been proposed as a promising technology for distribution networks and microgrids. By eliminating unnecessary conversion stages, DC distribution systems can enable seamless integration of natively DC devices such as photovoltaic cells and batteries. Moreover, DC technologies can overcome several disadvantages of alternating current (AC) distribution systems, such as synchronization requirements and reactive power compensation. Therefore, in this paper, the first steps are taken towards designing demand response programs for DC distribution networks. The idea is to adjust the internal parameters of power electronics loads to ensure reliable and efficient operation of the DC distribution system. In this regard, first, an optimization-based foundation is proposed for demand response in DC distribution networks in presence of distributed generators. Then, the formulated problem is solved using both centralized and decentralized approaches, where the latter requires devising a pricing mechanism. Finally, simulation results are presented to assess the performance and to gain insights into the proposed demand-response paradigm. [ABSTRACT FROM PUBLISHER]

The advantages arising from dc distribution networks are related to the possibilities of achieving higher quality supply and easier reconfigurability of the system. This paper presents the concept of introducing some dc islands interconnected with the ac distribution network. This will make it easier to connect storage systems, electrical drives, power converters, and renewable sources (i.e., photovoltaic panels). In order to realize the aforementioned goals, a methodology for designing the control strategy of different power converters connected to a dc bus without a centralized system management control unit is proposed. In this way, a plug-and-play functionality for connecting new power converter interfaced elements in the dc network able to stabilize the voltage under different working conditions is realized. In order to prove the advantages obtainable with such a network, a 100-kW dc test facility has been realized at the laboratories of RSE. Different working conditions were tested by means both of numerical and experimental results, proving the effectiveness of the proposed strategy for voltage regulation, continuity of service, and the smart use of storage devices. [ABSTRACT FROM AUTHOR]

The concept of DC power distribution has gained interest within the research community in the past years, especially due to the rapid prevalence of solar PVs as a tool for distributed generation in DC microgrids. Various efficiency analyses have been presented for the DC distribution paradigm, in comparison to the AC counterpart, considering a variety of scenarios. However, even after a number of such comparative efficiency studies, there seems to be a disparity in the results of research efforts, wherein a definite verdict is still unavailable. Is DC distribution a more efficient choice as compared to the conventional AC system? A final verdict is absent primarily due to conflicting results. In this regard, system modeling and the assumptions made in different studies play a significant role in affecting the results of the study. The current paper is an attempt to critically observe the modeling and assumptions used in the efficiency studies related to the DC distribution system. Several research efforts are analyzed for their approach toward the system upon which they have performed efficiency studies. Subsequently, the paper proposes a model that may alleviate the shortcomings in earlier research efforts and be able to give a definite verdict regarding the comparative efficiency of DC and AC networks for residential power distribution. [ABSTRACT FROM AUTHOR]