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.

/pdf/dc-microgrid-protection-a-comprehensive-review-38dp561hfd.pdf

DC Microgrid Protection: A Comprehensive Review

This paper proposes a new $\boldsymbol {n}$ -port hybrid dc circuit breaker for offshore multiterminal HVDC grid application. The $\boldsymbol {n}$ -port dc circuit breaker can substitute $\boldsymbol {n-1}$ hybrid dc circuit breakers at a dc bus with $\boldsymbol {n-1}$ adjacent dc transmission lines. The system-level behavior of the proposed multiport hybrid dc circuit breaker is similar to other hybrid dc circuit breakers. The operation principles of the proposed multiport dc circuit breaker are introduced, analyzed, and compared to the existing solution in this work. The components ratings are compared to the existing solution, and the functionality of the proposed device is verified by simulation.

/pdf/multiport-hybrid-hvdc-circuit-breaker-1ejpcyyjxv.pdf

Multiport Hybrid HVDC Circuit Breaker

WWW: http://www.esat.kuleuven.be/electa Abstract --Theapplication oflocal generators in distribution gridshasconsequences fortheprotection system.In thispaper,protection issuesconcerning distributed generation arediscussed, followed by a discussion oftheresults ofsimulations. Thesesimulations concerntheeffect of localinduction generators on protection selectivity inasystem withparallel distribution feeders andtheeffect onfault detection. Itisfoundthatlocal induction generator canposea selectivity problem inasystem withparallel feeders whena line-to-line fault ora doubleline-to-ground fault occurs. Regarding thefault current detected atthebeginning ofa feeder, detected current islowest whenaline-to-line fault or a line-to-ground faultoccurs. Depending on therelay settings, this canresult inadetection problem. IndexTerms--Distributed generation, powersystem protection, selectivity, induction generator, powersystem simulation, short-circuit current.

Protection IssuesinMicrogridswithMultiple Distributed Generation Units

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.

/pdf/hvdc-circuit-breakers-a-comprehensive-review-41s3apcrt9.pdf

HVDC Circuit Breakers: A Comprehensive Review

Protection techniques for DC microgrid- A review

DC microgrids have some attractive characteristics, which have being investigated to utilize in future electrical power systems. However, they have several essential challenges, such as limiting and interrupting fault current, which should be rectified to have high-performance dc microgrids. In this paper, an efficient dc bidirectional fault current limiter and interrupter (FCLI) based on Z-source topology is proposed to overcome some of the challenges in dc microgrids. The FCLI is a multifunction device, by which power flow direction control, circuit breaking, fault current limiting, and interrupting in a dc system can be handled. Analytical analysis of the FCLI is discussed in detail for different operation modes. Performance of the proposed FCLI in the different operation modes is evaluated using some simulations and experiments. The results confirm high capability of the device to realize appropriate operation in dc systems. Fast response time of fault current limitation and interruption, simple and reliable structure, and negligible conduction loss are the main features of the proposed FCLI.

A Z-Source-Based Bidirectional DC Circuit Breaker With Fault Current Limitation and Interruption Capabilities

Since most of renewable energy resources are dc type, dc microgrids find more attention in deregulated power systems for improvement of reliability and efficiency of the system. In dc microgrids, there is no zero-crossing in current and voltage; so the circuit breaking and fault current limiting are serious concerns. Conventional thyristor-based dc fault current limiters are attractive solutions for tackling this problem. However, they impose permanent interruption on the system in case of temporary fault. In this paper, a novel hybrid circuit breaker (HCB) is proposed to improve power quality of the system by adopting different limiting behaviors for permanent and temporary faults. The proposed HCB transfers load power through a mechanical circuit breaker (MCB) under normal condition. Upon fault occurrence in both sides of the HCB, the fault current is transferred from the MCB to a current limiting path incorporating a zero voltage switching (ZVS) transition mechanism. The HCB limits the fault current for a predefined duration and then interrupts the faulty feeder. In case of temporary fault, the current is returned to the MCB in ZVS. The HCB operation principle is discussed in different operation modes. Capabilities of the proposed HCB are tested and verified by different experiments carried out on a prototype.

Hybrid DC Circuit Breaker and Fault Current Limiter With Optional Interruption Capability

Modular battery-integrated converters or so-called dynamically reconfigurable battery packs are expanding into emerging applications. Although they offer many degrees of freedom (DoF), the state of the art focuses on single-output systems and neglects the potential of such systems to generate multiple outputs with minimum added components. This paper investigates the feasibility of a multiport system for various independent loads. The proposed techniques can achieve higher functionality and reduce power conversion stages. Interleaved ports with shared modules can also increase modules’ utilization, avoid redundant power electronics, and reach a better cost-weight trade-off. However, using conventional modulation techniques in particular phase-shifted carrier modulation can be challenging with shared modules among multiple ports, and different control objectives can adversely impact the overall performance. Therefore, this paper analyzes the inherent dynamics of modular batteries and proposes a strategy to decouple the control of multiple ports to simplify power electronics’ complexity and size while improving performance. In addition to the distinct advantages of modular reconfigurable batteries, the proposed concept would not require additional active switches, can operate with a wide range of output voltages, can reduce the size of the filters and transformers, and is extendable to larger setups. Simulation and experiments verify the developed concept. 

Topology, Analysis, and Modulation Strategy of a Fully Controlled Modular Reconfigurable DC Battery Pack with Interconnected Output Ports for Electric Vehicles

In this paper, a hybrid DC circuit breaker based on natural Zero Current Switching for DC microgrid is proposed. In the DC networks, arc quenching is a dramatic challenge due to lack of zero crossing of current, which results in corrosion and reduction of circuit breaker lifetime. The hybrid circuit breaker conducts the current using a mechanical switch in normal condition. In fault condition, counter current of a discharging capacitor makes mechanical switch to experience zero crossing condition. Therefore, the arc can be quenched safely. Also, the fault current with relatively higher impedance can be interrupted using zero voltage switching. The proposed breaker structure is described and its performance is evaluated using different simulations.

A hybrid DC circuit breaker for DC microgrid based on zero current switching

The modular multilevel converter (MMC) is a popular solution in high-voltage applications with significant potential in others. However, its stable operation is at the expense of numerous sensors, high communication burden, and complicated balancing strategies, which reduce its cost-effectiveness. Hence, the introduction of a sensorless voltage-balancing strategy with a simple controller is an attractive objective. The diode-clamped MMC offers the simplest and yet a highly effective solution for creating a balancing path between two modules through a diode with a fraction of the rated current. To compensate the lack of bidirectional energy transfer, a modified modulation technique is necessary. Level-adjusted phase-shifted-carrier (LA-PSC) modulation introduces a small circulating current that ensures the correct balancing direction. Although the open-loop operation is possible, monitoring and protection functions may still necessitate the independent tracking of the modules’ voltages. This article proposes a simple voltage-estimation method based on back-propagation without additional measurement. The algorithm further considers the balancing effect of the diode-clamped and the introduced circulating currents that reduces steady-state errors as well as fluctuations. Simulations and experiments verify the provided analysis and confirm that the proposed estimator can track the modules’ voltages with <1% and <3% errors in balanced and imbalanced conditions, respectively.

Voltage Estimation in Combination With Level-Adjusted Phase-Shifted-Carrier Modulation (LA-PSC) for Sensorless Balancing of Diode-Clamped Modular Multilevel Converters (MMCs)

Davood Keshavarzi

Papers

A Z-Source-Based Bidirectional DC Circuit Breaker With Fault Current Limitation and Interruption Capabilities

Hybrid DC Circuit Breaker and Fault Current Limiter With Optional Interruption Capability

Topology, Analysis, and Modulation Strategy of a Fully Controlled Modular Reconfigurable DC Battery Pack with Interconnected Output Ports for Electric Vehicles

A hybrid DC circuit breaker for DC microgrid based on zero current switching

Voltage Estimation in Combination With Level-Adjusted Phase-Shifted-Carrier Modulation (LA-PSC) for Sensorless Balancing of Diode-Clamped Modular Multilevel Converters (MMCs)