Dc Distribution Applications Research Articles

A Novel Flexible Fault Current Limiter for DC Distribution Applications

As an effective carrier of new energy collection, DC power grid has characteristics of low inertia and weak damping, which makes DC fault propagate extremely fast. However, the existing protection and DC circuit breaker (DCCB) technique still could not match its fault propagation speed. Therefore, to solve this problem, a novel of flexible fault current limiter (NFFCL) is presented in this paper. Under normal operation condition, NFFCL is connected to DC line in series without negative influence. When a fault occurs to DC line, NFFCL’s rectifier circuit, according to the protection criterion, provides cascade inductor, which is connected to DC line in series, with a set-slope linear current. In this case, the voltage drop between both ends of inductor can be clamped flexibly, which can even completely isolate the fault area. A controlled voltage source (CCVS) is applied to generate inverse flux to prevent the cascading inductor from magnetic saturation. When the fault disappears, the energy of current-limit inductor can be released and transferred to AC power grid through NFFCL’s converter. Finally, simulation cases are carried out to verify the working principles and practicability of proposed NFFCL.

High‐frequency‐link DC solid state transformer based on voltage self‐balancing control for MVDC power distribution application

This paper presents a novel voltage self-balancing converter (VBC) applied to DC solid-state transformer (DCSST), analyzes the operating principle of the proposed VBC, and proves the voltage balance performance. Based on this converter, a novel DCSST topology is proposed, which can be used in medium and low voltage DC distribution application, microgrid and medium and low voltage energy storage system. Compared with the previous work, under the same voltage level, it can effectively reduce the number of transformers and switches, reduce the voltage level of switches, and realize the soft switching of the VBC switches, so as to improve the system efficiency and power density, and then improve the system reliability. Meanwhile, the fault handling ability and fault tolerance ability of DCSST are improved, which makes DCSST more reliable when multiple isolated bi-directional DC/DC Converters (IBDC) are connected in series. In addition, with this topology, the input voltage self-balancing control strategy of the IBDC is not needed because of the voltage self-balancing characteristic of VBC, which simplifies the control complexity and greatly improves the control accuracy of the control system. Experimental results agree well with the accuracy and correctness of the proposed topology.

Soft-Switching Full-Bridge Converter with Multiple-Input Sources for DC Distribution Applications

Due to the advantages of power supply systems using the DC distribution method, such as a conversion efficiency increase of about 5–10%, a cost reduction of about 15–20%, etc., AC power distribution systems will be replaced by DC power distribution systems in the future. This paper adopts different converters to generate DC distribution system: DC/DC converter with PV arrays, power factor correction with utility line and full-bridge converter with multiple input sources. With this approach, the proposed full-bridge converter with soft-switching features for generating a desired voltage level in order to transfer energy to the proposed DC distribution system. In addition, the proposed soft-switching full-bridge converter is used to generate the DC voltage and is applied to balance power between the PV arrays and the utility line. Due to soft-switching features, the proposed full-bridge converter can be operated with zero-voltage switching (ZVS) at the turn-on transition to increase conversion efficiency. Finally, a prototype of the proposed full-bridge converter under an input voltage of DC 48 V, an output voltage of 24 V, a maximum output current of 21 A and a maximum output power of 500 W was implemented to prove its feasibility. From experimental results, it can be found that its maximum conversion efficiency is 92% under 50% of full-load conditions. It was shown to be suitable for DC distribution applications.

Hybrid‐wave modulation for modular multilevel high‐frequency DC converter in DC distribution application

Compared with AC distribution networks, DC distribution networks reduce the utilisation of power converters, power loss, and construction cost. In DC distribution network, the high-frequency modular multilevel DC converter (MDCC), which connects the low-voltage DC link with medium- or high-voltage DC links, becomes a practical equipment to realise the bus connection, voltage conversion, and electrical isolation. Especially, high-frequency link (HFL) modulation plays an important role in converter performance. The square-wave (SW) modulation obtains better power transfer capability and higher DC voltage utilisation. However, the SW modulation leads to a large dv/dt stress upon HFL transformer. The sinusoidal, triangle and quasi-square-wave (QSW) modulations reduce dv/dt and harmonics significantly. However, the power transfer capability and DC voltage utilisation are also reduced. To address dv/dt stress problem, ensure high DC-voltage utilisation and maintain a strong power transfer capability simultaneously, a hybrid-wave modulation strategy, which composed of QSW and SW modulation, is proposed for MDCC. The experimental results verify the analysis and proposed scheme.

Power Factor Corrector with Bridgeless Flyback Converter for DC Loads Applications

Since power systems with a DC distribution method has many advantages, such as conversion efficiency increase of about 5–10%, cost reducing by about 15–20% and so on, the AC distribution power system will be replaced by a DC distribution one. This paper presents a DC load power system for a DC distribution application. The proposed power system includes two converters: DC/DC converter with battery source and power factor corrector (PFC) with a line source to increase the reliability of the power system when renewable energy or energy storage equipment are adopted. The proposed PFC adopts a bridgeless flyback converter to achieve power factor correction for supplying power to DC loads. When the bridgeless flyback converter is used to achieve PFC, it needs two transformers to process positive and negative half periods, respectively. In order to increase conversion efficiency, the flyback one can add two sets of the active clamp circuit to recover energies stored in leakage inductances of transformers in the converter. Therefore, the proposed bridgeless flyback converter can not only integrate two transformers into a single transformer, but also share a clamp capacitor to achieve energy recovery of leakage inductances and to operate switches with zero-voltage switching (ZVS) at the turn-on transition. With this approach, the proposed converter can increase conversion efficiency and decrease component counts, where it results in a higher conversion efficiency, lower cost, easier design and so on. Finally, a prototype with a universal input voltage source (AC 90–265 V) under output voltage of 48 V and maximum output power of 300 W has been implemented to verify the feasibility of the proposed bridgeless flyback converter. Furthermore, the proposed power system can be operated at different cases among load power PL, output power PDC1 of DC/DC converter and output power PDC2 of the proposed PFC for supplying power to DC loads.

Smart Internet of Things (IOT) System for Performance Improvement of Dual Bridge LLC Resonant Converter by Using Sophisticated Distribution Control Method (SDC)

A resonant converter is a kind of electric power converter that contains a system of inductors and capacitors called a resonant tank, tuned to resonate at a particular frequency in this work recommends a better-quality dual bridge LLC resonant converter with a novel controller technique. The resonant converters include the serial or parallel connections of inductors and capacitors to activate the switch to realize the Zero Current Switching (ZCS) and Zero Volt Switching (ZVS) under resonance conditions. The resonant effects are switching sufferers, turning strain and electromagnetic interference problems the switching resonant converter controls the output voltage through changing frequency and generally can be sub classified in ZCS converter and ZVS converter. This scheme had combined wireless monitoring for dual bridge LLC resonant converter for dc distribution applications based on sophisticated distribution controller (SDC) through the internet of things and embedded structure access and other mechanisms. The consequence of our exhibition demonstrates that the framework can monitor and store the manipulate data from the converter. Thus, the wireless monitoring functions are realized in real-time. This converter permits both forward and reverses power exchange between the source and the load, to keep up the output voltage consistent, regardless of load and line unsettling influences, it is important to work the converter as a closed loop system. The proposed SDC based dual bridge resonant converter has validated through simulation in Matlab Simulink environment. A hardware setup is also developed to validate the simulation. General 97% effectiveness accomplished at full load condition in light of the dual bridge resonant converter.

An Input-Series-Output-Series Modular Multilevel DC Transformer With Inter-Module Arithmetic Phase Interleaving Control to Reduce DC Ripples

This paper presents an input-series-output-series modular multilevel dc transformer (ISOS-M2DCT) with an inter-module arithmetic phase interleaving control (IAPIC) for high-voltage dc transmission and medium-voltage dc distribution application. The presented ISOS-M2DCT has several advantages over conventional dual active bridge (DAB)-based dc transformer (DAB-DCT) and M2DCTs. It possesses a higher power capacity, a dc fault tolerant superiority, and a higher power factor in heavy load than DAB-DCT; it simplifies the manufacturing of ac link transformers and averts the problem of circulating currents among different modules compared with M2DCTs. The introduced IAPIC is able to cut down the dc ripples without any rise in volume of passive elements, thereby making it easier to realize the compact design of ISOS-M2DCT. In this paper, the topology, operation principle, modulation strategy, basic control scheme, power characterization, the generating mechanism of dc ripples, and the IAPIC scheme are proposed and analyzed successively. Finally, an ISOS-M2DCT prototype is built, and the proposed method is verified by simulation and experimental results.

A New Reclosing and Re-breaking DC Thyristor Circuit Breaker for DC Distribution Applications

The DC circuit breaker is essential for supplying stable DC power with the advent of DC transmission/distribution and sensitive loads. Compared with mechanical circuit breakers, which must interrupt a very large fault current due to their slow breaking capability, a solid-state circuit breaker (SSCB) can quickly break a fault current almost within 1 [ms]. Thus, it can reduce the damage of an accident a lot more than mechanical circuit breakers. However, previous DC SSCBs cannot perform the operating duty, and are not economical because many SCR are required. Therefore, this paper proposes a new DC SSCB suitable for DC grids. It has a low semiconductor conduction loss, quick reclosing and rebreaking capabilities. As a result, it can perform the operating duties of reclosing and rebreaking. The proposed DC SSCB is designed and implemented so that it is suitable for home dc distribution at a rated power of 5 [kW] and a voltage of 380 [V]. The operating characteristics are confirmed by simulation and experimental results. In addition, this paper suggests design guidelines so that it can be applied to other DC grids. It is anticipated that the proposed DC SSCB may be utilized to design and realize many DC grid systems.

A Cascaded Hybrid Multilevel Inverter Incorporating a Reconfiguration Technique for Low Voltage DC Distribution Applications

A cascaded hybrid multilevel inverter including a reconfiguration technique for low voltage dc distribution applications is proposed in this paper. A PWM generation fault detection and reconfiguration paradigm after an inverter cell fault are developed by using only a single-chip controller. The proposed PWM technique is also modified to reduce switching losses. In addition, the proposed topology can reduce the number of required power switches compared to the conventional cascaded multilevel inverter. The proposed technique is validated by using a 3-kVA prototype. The switching losses of the proposed multilevel inverter are also investigated. The experimental results show that the proposed hybrid inverter can improve system efficiency, reliability and cost effectiveness. The efficiency of proposed system is 97.45% under the tested conditions. The proposed hybrid inverter topology is a promising method for low voltage dc distribution and can be applied for the multiple loads which are required in a data center or telecommunication building.

DC Microgrids—Part II: A Review of Power Architectures, Applications, and Standardization Issues

DC microgrids (MGs) have been gaining a continually increasing interest over the past couple of years both in academia and industry. The advantages of dc distribution when compared to its ac counterpart are well known. The most important ones include higher reliability and efficiency, simpler control and natural interface with renewable energy sources, and electronic loads and energy storage systems. With rapid emergence of these components in modern power systems, the importance of dc in today's society is gradually being brought to a whole new level. A broad class of traditional dc distribution applications, such as traction, telecom, vehicular, and distributed power systems can be classified under dc MG framework and ongoing development, and expansion of the field is largely influenced by concepts used over there. This paper aims first to shed light on the practical design aspects of dc MG technology concerning typical power hardware topologies and their suitability for different emerging smart grid applications. Then, an overview of the state of the art in dc MG protection and grounding is provided. Owing to the fact that there is no zero-current crossing, an arc that appears upon breaking dc current cannot be extinguished naturally, making the protection of dc MGs a challenging problem. In relation with this, a comprehensive overview of protection schemes, which discusses both design of practical protective devices and their integration into overall protection systems, is provided. Closely coupled with protection, conflicting grounding objectives, e.g., minimization of stray current and common-mode voltage, are explained and several practical solutions are presented. Also, standardization efforts for dc systems are addressed. Finally, concluding remarks and important future research directions are pointed out.

Design and Implementation of a Power Converter to Process Renewable Energy for Step-down Voltage Applications

In this study a power converter to process renewable energy is proposed, which can not only process solar energy but deal with wind power. The proposed converter is derived from two series modified forwards to step down voltage for charger system or dc distribution application, so as called Modified-Forward Dual-Input Converter (MFDIC). The MFDIC mainly contains an upper Modified Forward (MF), a lower MF, a common output inductor and a DSP-based system controller. The upper and lower MFs can operate individually or simultaneously to accommodate the variation of atmospheric conditions. Since the MFDIC can process renewable power with interleaved operation, the ripple of output current is suppressed significantly and thus better performance is achieved. In the MFDIC only a common output inductor is needed, instead of two separated inductors, so that the volume of the converter is reduced significantly. To draw maximum power from PV panel and wind turbine, perturb-and-observe method is adopted to achieve the feature of Maximum Power Point Tracking (MPPT). The MFDIC is constructed, designed, analyzed, simulated and tested. Simulations and practical measurements have demonstrated the validity and the feasibility of the proposed dual-input converter.

Integration and Operation of a Single-Phase Bidirectional Inverter With Two Buck/Boost MPPTs for DC-Distribution Applications

This study is focused on integration and operation of a single-phase bidirectional inverter with two buck/boost maximum power point trackers (MPPTs) for dc-distribution applications. In a dc-distribution system, a bidirectional inverter is required to control the power flow between dc bus and ac grid, and to regulate the dc bus to a certain range of voltages. A droop regulation mechanism according to the inverter inductor current levels to reduce capacitor size, balance power flow, and accommodate load variation is proposed. Since the photovoltaic (PV) array voltage can vary from 0 to 600 V, especially with thin-film PV panels, the MPPT topology is formed with buck and boost converters to operate at the dc-bus voltage around 380 V, reducing the voltage stress of its followed inverter. Additionally, the controller can online check the input configuration of the two MPPTs, equally distribute the PV-array output current to the two MPPTs in parallel operation, and switch control laws to smooth out mode transition. A comparison between the conventional boost MPPT and the proposed buck/boost MPPT integrated with a PV inverter is also presented. Experimental results obtained from a 5-kW system have verified the discussion and feasibility.

Efficiency Characterization and Optimization of Isolated Bidirectional DC–DC Converter Based on Dual-Phase-Shift Control for DC Distribution Application

Compared to the traditional single-phase-shift control, dual-phase-shift (DPS) control can greatly improve the performance of the isolated bidirectional dc–dc converter (IBDC). This paper gives a detailed switching characteristic analysis of IBDC under DPS control, establishes a power loss model to predict the dissipated power for each power component, and analyzes the efficiency-optimized characteristic across the whole range. On this basis, an efficiency-optimized switching strategy is proposed and the corresponding control scheme is designed and implemented. At last, an experimental prototype was implemented to verify the feasibility of the proposed switching strategy and correctness of the theoretical analysis. The experimental results show that the proposed method can minimize the power loss and maximize the system efficiency, and these performances are particularly effective for operation conditions with high voltage conversion ratio.

Multi-Input Converter with MPPT Feature for Wind-PV Power Generation System

A multi-input converter (MIC) to process wind-PV power is proposed, designed, analyzed, simulated, and implemented. The MIC cannot only process solar energy but deal with wind power, of which structure is derived from forward-type DC/DC converter to step-down/up voltage for charger systems, DC distribution applications, or grid connection. The MIC comprises an upper modified double-ended forward, a lower modified double-ended forward, a common output inductor, and a DSP-based system controller. The two modified double-ended forwards can operate individually or simultaneously so as to accommodate the variation of the hybrid renewable energy under different atmospheric conditions. While the MIC operates at interleaving mode, better performance can be achieved and volume also is reduced. The proposed MIC is capable of recycling the energy stored in the leakage inductance and obtaining high step-up output voltage. In order to draw maximum power from wind turbine and PV panel, perturb-and-observe method is adopted to achieve maximum power point tracking (MPPT) feature. The MIC is constructed, analyzed, simulated, and tested. Simulations and hardware measurements have demonstrated the feasibility and functionality of the proposed multi-input converter.

Applications of High Temperature Superconductors to Direct Current Electric Power Transmission and Distribution

For several reasons, the application of superconductors to both the transmission and distribution of electric power is a desire that is best accomplished by using direct current. The inherent low loss, high current capability of dc superconducting cables allows the replacement of ultra-high voltage apparatus and the associated high cost and inversion-rectification difficulties with a compact potentially lower cost, low profile, high current, cable system. This paper discusses the history of dc transmission and distribution applications and the reasons that high temperature superconductors, modern cryogenic systems, and cryogenic power electronics are the potential enabling technologies. The economic and performance enhancements that follow from the integration of these high current, superconducting dc systems into the electric grid are presented together with the expected potential operational benefits. Possible cable and rectifier-inverter configurations are summarized along with the technical and economic challenges that must be overcome to achieve a significant penetration of dc cable technology on both the transmission and distribution grids. Finally, the steps needed to achieve large-scale applications of high-current dc transmission and dc distribution in the future electric grid are summarized.