DC microgrids have attracted significant attention over the last decade in both academia and industry. DC microgrids have demonstrated superiority over AC microgrids with respect to reliability, efficiency, control simplicity, integration of renewable energy sources, and connection of dc loads. Despite these numerous advantages, designing and implementing an appropriate protection system for dc microgrids remains a significant challenge. The challenge stems from the rapid rise of dc fault current which must be extinguished in the absence of naturally occurring zero crossings, potentially leading to sustained arcs. In this paper, the challenges of DC microgrid protection are investigated from various aspects including, dc fault current characteristics, ground systems, fault detection methods, protective devices, and fault location methods. In each part, a comprehensive review has been carried out. Finally, future trends in the protection of DC microgrids are briefly discussed.

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DC Microgrid Protection: A Comprehensive Review

This study presents a comprehensive review of high-power dc-dc converters for high-voltage direct current (HVDC) transmission systems, with emphasis on the most promising topologies from established and emerging dc-dc converters. In addition, it highlights the key challenges of dc-dc converter scalability to HVDC applications, and narrows down the desired features for high-voltage dc-dc converters, considering both device and system perspectives. Attributes and limitations of each dc-dc converter considered in this study are explained in detail and supported by time-domain simulations. It is found that the front-to-front quasi-two-level operated modular multilevel converter, transition arm modular converter and controlled transition bridge converter offer the best solutions for high-voltage dc-dc converters that do not compromise galvanic isolation and prevention of dc fault propagation within the dc network. Apart from dc fault response, the MMC dc auto transformer and the transformerless hybrid cascaded two-level converter offer the most efficient solutions for tapping and dc voltage matching of multi-terminal HVDC networks.

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Review of dc-dc converters for multi-terminal HVDC transmission networks

High voltage direct current (HVDC) transmission is an economical option for transmitting a large amount of power over long distances. Initially, HVDC was developed using thyristor-based current source converters (CSC). With the development of semiconductor devices, a voltage source converter (VSC)-based HVDC system was introduced, and has been widely applied to integrate large-scale renewables and network interconnection. However, the VSC-based HVDC system is vulnerable to DC faults and its protection becomes ever more important with the fast growth in number of installations. In this paper, detailed characteristics of DC faults in the VSC-HVDC system are presented. The DC fault current has a large peak and steady values within a few milliseconds and thus high-speed fault detection and isolation methods are required in an HVDC grid. Therefore, development of the protection scheme for a multi-terminal VSC-based HVDC system is challenging. Various methods have been developed and this paper presents a comprehensive review of the different techniques for DC fault detection, location and isolation in both CSC and VSC-based HVDC transmission systems in two-terminal and multi-terminal network configurations.

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A comprehensive review of DC fault protection methods in HVDC transmission systems

High voltage direct current (HVDC) systems are now well integrated into AC systems in many jurisdictions. The integration of renewable energy sources (RESs) is a major focus and the role of HVDC systems is expanding. However, the protection of HVDC systems against DC faults is a challenging issue that can have negative impacts on the reliable and safe operation of power systems. Practical solutions to protect HVDC grids against DC faults without a widespread power outage include: 1) using DC circuit breakers (CBs) to isolate the faulty DC-link, 2) using a proper converter topology to interrupt the DC fault current, and/or 3) using high-power DC transformers and DC hubs at strategic points within DC grids. The application of HVDC CBs is identified as the best approach that satisfies both DC grids and connected AC grids’ requirements. This article reports a comprehensive review of HVDC CBs technologies, including recent significant attempts in the development of modern HVDC CBs. The functional analysis of each technology is presented. Additionally, different technologies based on information obtained from literature are compared. Finally, recommendations for the improvement of CBs are presented.

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HVDC Circuit Breakers: A Comprehensive Review

A fault diagnosis technique for photovoltaic (PV) panels is presented. While a PV system is sampling the terminal voltage and current of its connected panel for tracking the maximum power point of the panels, the proposed technique utilizes the sampled data to estimate the intrinsic parameters of the panel simultaneously. Compared with the prior-art approach of using the static current–voltage characteristics, the proposed technique utilizes the dynamic current–voltage characteristics to determine the parameters. Apart from the fast parameter estimation, it also provides an in-depth understanding of the panel condition with the drift of the parameters. Several prototype devices with the proposed algorithm have been built. They are evaluated on a test bed with four 80-W panels, with two of them being healthy and the other two having different degrees of damage on the surfaces. Results reveal that the parameters of the cracked panels deviate significantly from their nominal values, giving a sign of panel failure. Furthermore, the device can communicate with and send the estimated parameters to the central control center over the panel cable via power line communication. The merits of this concept lie in its modularity, scalability, and remote fault diagnosis capability.

Fault Diagnosis of Photovoltaic Panels Using Dynamic Current–Voltage Characteristics

This paper presents a topology for dc grids which enables very robust dc fault protection with moderate costs, good operating flexibility, and simple controls. It is postulated that radial dc systems are best suited for limited-size local dc grids. Radial topology enables robust and fast protection selectivity using only local signals and exploiting the advantages of hybrid dc circuit breakers (CBs). To enable flexible expansion options to national/international systems, it is suggested to interconnect star points of radial systems using dc/dc converters. DC/dc converters enable inherent isolation of dc faults and provide firewall between radial dc grids. Each interconnecting cable is protected by a dc/dc at one end and a hybrid CB at the other end. The control options for dc/dc converter and the radial grids are analyzed. A detailed simulation model of six terminal dc grid with two-star points is presented. The power systems computer aided design (PSCAD) simulation results confirm dc fault isolation and good control performance of the proposed topology for a range of dc fault contingencies.

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Offshore DC Grids as an Interconnection of Radial Systems: Protection and Control Aspects

This article presents a topology for DC grids which enables very robust DC fault protection with moderate costs, good operating flexibility and simple controls. It is postulated that radial DC systems are best suited for limitedsize local DC grids. Radial topology enables robust and fast protection selectivity using only local signals and exploiting the advantages of hybrid DC circuit breakers. To enable flexible expansion options to national/international systems, it is suggested to interconnect star points of radial systems using DC/DC converters. DC/DC converters enable inherent isolation of DC faults and provide firewall between radial DC grids. Each interconnecting cable is protected by a DC/DC at one end and a hybrid Circuit Breaker at the other end. The control options for DC/DC converter and the radial grids are analysed. A detailed simulation model of 6 terminal DC grid with 2-star points is presented. The PSCAD simulation results confirm DC fault isolation and good control performance of the proposed topology for a range of DC fault contingencies.

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Offshore DC grids as an interconnection of radial systems: Protection and control aspects

This paper starts by describing a silicon solar panel model based on a comprehensive solar cell equivalent circuit. Then, as a case study, four similar modelled panels are considered in lateral sides of a satellite as its power source. Considering the panel model with different combinations of its equivalent circuit essential elements, the model operation is evaluated in a orbit attitude with some eclipse times. The variations in output characteristics of the panels due to changes in received solar irradiance and panels' temperature are calculated for each equivalent configuration. The values of maximum generated power and total generated energy during a satellite typical period are compared for different spin rates. Finally, the best topology for panel equivalent circuit is stated based on the compared results.

Modelling of Silicon Solar Panel by MATLAB/Simulink and Evaluating the Importance of Its Parameters in a Space Application

Solar panels are power sources in photovoltaic applications. Solar panels I-V curves depend on environmental conditions such as irradiance, temperature, load and degradation level. In this paper, design and implementation of simultaneous fuzzy-based maximum power point tracker (MPPT) and sun tracker are presented for deployable solar panels. A digital controller was implemented by an AVR microcontroller. Results showed that the proposed system ensure to have photovoltaic system with higher efficiency. Finally, we observed that, using the proposed fuzzy-based MPP tracking and sun tracking simultaneously, solar panel output power can be remarkably increased leading in turn to reduction of the size, weight and cost of solar panels in photovoltaic systems.

Combination of Fuzzy-Based Maximum Power Point Tracker and Sun Tracker for Deployable Solar Panels in Photovoltaic Systems

This paper describes the reliability comparison of different schemes connection for Electrical Power Subsystem (EPS) of satellite. EPS has to be able to provide sufficient power to the satellite subsystems under all possible satellite attitudes. There are eight schemes for EPS, which could be used for power supplying. In these schemes, two main system groups are Peak Power Tracking (PPT) and Direct Energy Transfer (DET) systems. Also in each system, we have four different connections which are Unregulated Bus Using Parallel Batteries, Unregulated Bus Using Linear Charge Current Control Recharge Control, Quasi-Regulated Bus with Constant Current Chargers and Systems Using a Fully Regulated Bus. In this paper we will compare the reliability of different schemes and will introduce the best reliable connection in these two systems for ESP.

Mohsen Taherbaneh

Papers

Offshore DC Grids as an Interconnection of Radial Systems: Protection and Control Aspects

Offshore DC grids as an interconnection of radial systems: Protection and control aspects

Modelling of Silicon Solar Panel by MATLAB/Simulink and Evaluating the Importance of Its Parameters in a Space Application

Combination of Fuzzy-Based Maximum Power Point Tracker and Sun Tracker for Deployable Solar Panels in Photovoltaic Systems

Extracting best reliable scheme for Electrical Power Subsystem (EPS) of satellite