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This work addresses the fundamental concepts in the design of a voice communications system that uses the operating principles of direct current power line communications (DC-PLC: Direct Current - Power Line Communications) based on BFSK modulation. The system is composed of a transmission subsystem and a voice signal reception subsystem, these elements are interconnected through a DC-PLC channel referenced to a twisted copper pair. The transmission subsystem performs the functions associated with the conditioning, digitization and processing of the signal for its digital transfer with a BFSK modulation in the communication channel. The receiving subsystem performs the BFSK demodulation, processing and recovery of the voice signal for monitoring. For both subsystems a design based on the use of Silicon Laboratories 8051 core microcontrollers is proposed. The UART peripheral available in the 8051 microcontrollers is used for digital data transfer and is applicable as a transmission method in the DC-PLC channel type. In addition, the design criteria of the internal circuits are presented and exposed through their electrical schematics. [ABSTRACT FROM AUTHOR]

Stress evolution in a metal line embedded in a rigid confinement caused by the arbitrary wave-form time-dependent current loads is resolved by a direct analytic solution of the one-dimensional (1-D) Korhonen's equation. Electromigration induced stress buildup and relaxation kinetics resulted by time-dependent current density are obtained as functions of the relevant physical parameters. A novel methodology for physics based conversion between the time-dependent and effective DC current densities is developed based on a condition of equal void nucleation times resulted by these currents. It is shown that in the case of high frequency currents, with periods much smaller than the characteristic time of stress evolution, the stress buildup is proportional to the pulse duty factor. It is demonstrated that very short metal lines with preexisted thermal voids loaded with symmetrical bi-directional currents can demonstrate a notable resistance increase when a specific temperature oscillation is generated in the line by active devices of the integrated circuit. [ABSTRACT FROM AUTHOR]

The design of a cascade controller is demonstrated for a buck–boost converter that is combined with two control loops consisting of inner and outer controllers. The outer loop is implemented by a fractional‐order proportional‐integrated‐derivative (FO‐PID) controller that works as a voltage controller and generates a reference current for the inner control loop. To provide faster dynamic performance for inner loop, a self‐tuning regulator adaptive controller, which tries to regulates the current with the help of a novel improved exponential regressive least square identification in an online technique, is designed. Moreover, in the outer loop, to tune the gains of the FO‐PID controller, a novel algorithm of antlion optimizer algorithm is used that offers many benefits in comparison with other algorithms. The system provided by the boost mode is a non‐minimum phase system, which creates challenges for designing a stable controller. In addition, a single loop controller is proposed based on a PID controller tuned by a particle swarm optimization algorithm to be compared with the cascade controller. Cascade loop can present significant benefits to the controller such as better disturbance rejection. Finally, the strength of the presented cascade control scheme is verified in different performing situations by real‐time experiments. [ABSTRACT FROM AUTHOR]

Here, a novel photovoltaic power integration system based on LLC resonant converters is proposed for medium-voltage DC distribution network, which exhibits a feasible and efficient solution for large-scale solar energy integrating into DC grids. A control system with the voltage signal generation part and the frequency control part is designed to realise the current and voltage sharing of the sub-module, while achieving the maximum power point tracking (MPPT) of the PV arrays. To verify the practicability of the system with many switching devices, this paper proposes an optimisation model to accelerate the simulation speed of this system without losing accuracy. Finally, the feasibility of the proposed system is validated by the simulation based on PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]

A design procedure for the dual active bridge (DAB) converter is presented, which aims to optimised power density and computational effort. When designing a DAB, the selection of circuit design parameters such as switching frequency, leakage inductance and semiconductor technologies is a complex question when targeting losses and weight minimisation of the final design. In this study, analytical models of the operating waveforms, the losses and the weight of all DAB components are developed. The proposed design algorithm is used for designing a 3 kW high-frequency DAB for an aircraft DC power system. [ABSTRACT FROM AUTHOR]

Highlights • Feature extract method : Used CEEMDAN algorithm to extract the CFC of transient zero mode current. • Detection criterion : Constructed the starting criterion and discrimination criterion respectively, and realized the HIF accurate detection. • Solved the HIF detection difficulty in DC distribution network, and the needed data window of the criteria is only 2 ms, and criteria is accurate, the calculation speed is faster. Abstract Aiming at DC distribution network, we proposed a novel high impedance fault detection method in the paper, it main procedures are as follows: Firstly, used the algorithm of complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) to extract the first intrinsic mode function (IMF) of the characteristic mode. Secondly, calculated the singular point of mutation and the cumulative slope by the acquisition of the first order difference operation, and then, achieved to distinguish the fault state and the normal state by the comparison between the slope and the starting threshold. Thirdly, identified the first IMF with Prony algorithm to obtain the parameters of characteristic frequency components (CFC) and direct current components (DC), and calculated the energy ratio between them, and then, distinguished small impedance fault (SIF), medium impedance fault (MIF), high impedance fault (HIF) and load switching (LS) by different values of energy ratio. A large number of experiments show that the proposed method is accurate and effective. Compared with other methods, this method shows its merits in feature extraction accuracy, detection accuracy and calculation speed. [ABSTRACT FROM AUTHOR]

Highlights: • Fault transient voltage is analyzed under condition of distributed-parameter dc line. • Fault transient voltage is used to discriminate between internal and external faults. • Faulty pole selection is based on the change rate of positive- and negative-pole currents. Abstract Multi-terminal flexible HVDC grids are required due to the high penetration of renewable energy. However, they are vulnerable to dc faults. To ensure their high reliability and continuous operation, fast and selective protection schemes are indispensable. This paper analyses the transient voltages in the case of dc line faults in modular multilevel converter (MMC)-based HVDC grid. Then, making use of the boundary effect of current-limiting reactors, a fast non-unit dc line protection scheme based on fault transient voltage is proposed. In addition, the faulty pole identification criterion is constructed based on fault currents. A MMC-based four-terminal HVDC grid is modelled using PSCAD/EMTDC, and extensive simulations are conducted to validate the effectiveness of the proposed scheme. Simulation results show that the proposed protection method not only can detect faults rapidly and accurately, but is also effective in detecting large-resistance faults. [ABSTRACT FROM AUTHOR]

Highlights • Introducing a stochastic multi-objective planning model for AC-DC hybrid smart DSs. • Determining the optimal AC-DC network that optimizes both the DS costs and reliability. • The trade-off between the cost and reliability is evaluated using the Pareto optimality concept. • The benefits were verified through a comparison of the AC and hybrid Pareto fronts. • The AC-DC hybrid system achieved improvements in both the DS costs and reliability. Abstract This paper introduces a stochastic multi-objective optimization model for the planning of AC-DC hybrid smart distribution systems (DSs). The proposed model determines the optimal AC-DC network configuration that achieves two main objectives: (1) minimizing system costs, and (2) maximizing system reliability. The second objective is achieved through the minimization of the expected energy not supplied. Network buses and lines can become either AC or DC in order to achieve the planning objectives. The model features a Monte-Carlo simulation (MCS) for addressing stochastic variations related to load demands and renewable distributed generators (DGs). The hybrid planning problem has been solved by means of a multi-objective genetic algorithm, and the trade-off between the DS costs and reliability has been evaluated using the Pareto optimality concept. The proposed model has been tested using a case study involving a hybrid DS that included a variety of types of loads and DGs. Solving the same case study using a traditional AC planning technique provided verification of the benefits offered by the proposed model, whose efficacy was confirmed through a comparison of the AC and hybrid Pareto fronts. [ABSTRACT FROM AUTHOR]

Highlights • Basic principles of graph theory yield an optimal communication network topology. • A combination of "centralized plus distributed" strategies is adopted for coordinated control. • The second-level power optimization controller determines the voltage and frequency reference values of distributed micro generators. Abstract Due to the increasing coupling degree of the power network, natural gas network, and thermal network, this paper discusses a flexible DC power distribution network based on the consistency algorithm theory regarding the advantages and disadvantages of centralized control and distributed control. A layered network control architecture is presented. Considering the multi-time-scale control characteristics of the system, the control architecture is divided into three layers: energy management layer, bus control layer, and converter control layer. In the energy management layer, the dispatch optimization center optimizes the system operating cost through the multi-objective energy optimization management of the integrated energy system consisting of the DC distribution network, natural gas network, and heating network. In the bus control layer, the DC bus voltage is taken into account. The control characteristics are divided into three categories corresponding to three working modes according to the range of the DC bus voltage, which is used to realize the conversion mode control of every distributed device in the distribution network. In the converter control layer, based on the original droop control, the voltage and frequency deviations of every distributed device are compensated twice, and every distributed device controller communicates only with the adjacent controller to achieve the voltage and frequency consistency control with the "virtual leader" node. Finally, using the typical eight-terminal VSC flexible DC distribution network control architecture, the proposed control strategy is verified by the PSCAD/EMTDC simulation software. [ABSTRACT FROM AUTHOR]

Highlights • Real-power economic dispatch of AC/DC systems formed by VSC-HVDC equipment. • It uses the Lagrange multipliers method. • The different control strategies of the VSCs are considered. • Its results are compared against those obtained by the SQP method. • Its practicality is also demonstrated with an AC/DC grid comprising seven VSC units. Abstract This paper presents a practical approach for the real-power economic dispatch of AC/DC power transmission systems formed by VSC-HVDC equipment. It uses the Lagrange multipliers method combined with a comprehensive representation of the AC/DC power system. The power losses of the AC systems, DC grid and power converters are considered in this novel formulation by using incremental transmission loss factors. For realistic solutions, the different control strategies of the power converters forming any VSC-based power grid are considered. Interestingly, this approach permits to conclude that the AC grids coupled to converters charged with DC voltage control define the nodal marginal prices in the DC network, and in turn, the energy prices in the VSC-connected passive grids are inherited from the DC network. Overall, this modelling approach yields great flexibility to model any arbitrary VSC-based HVDC power grid interconnecting various AC systems. The developed method has been validated using a two-terminal VSC-HVDC network interconnecting two otherwise independent AC grids. Its results are compared against those obtained by the sequential quadratic programming method available in the optimisation toolbox of Matlab©, with both solutions exhibiting differences inferior to 0.30% in the total generation costs, therefore concurring very well between each other. The practicality of this approach is also demonstrated by carrying out the real-power economic dispatch of an AC/DC transmission system comprising seven VSC units which give rise to a thirteen-node DC grid. [ABSTRACT FROM AUTHOR]

Highlights • A virtual capacitor droop control (CDC) using fuzzy logic algorithm in multiple HESSs can adaptively adjust the droop coefficient, so as to eliminate the impact of the line impedance on the power splitting and improve the power sharing accuracy. This study has not been reported in previous work. • Both the small-signal model and eigenvalue analysis are presented to study the stability of the HESS system using CDC, investigate the impact of the droop coefficient variation on the system dynamics and determine an optimal range of the modified droop coefficient. This work has not been involved in the previous studies. Abstract In a DC microgrid, virtual capacitor droop control (CDC) can achieve power allocation according to different frequency characteristics of a hybrid energy storage system (HESS). However, the control performance may be easily affected by the line impedance. In this paper, an adaptive droop controller based on a fuzzy logic algorithm is proposed. By detecting the unbalanced power and the voltage deviation, the droop coefficient can be adaptively adjusted to mitigate the influence of the line impedance and achieve desirable power splitting in the HESS. Furthermore, the small-signal model of the HESS is established and the impact of the droop coefficient variation on the stability of the DC microgrid is exploited. The simulation results in PSCAD/EMTDC verify the effectiveness of the proposed adaptive droop controller. It has been proved that desirable power splitting can be obtained among multiple HESSs under different scenarios. [ABSTRACT FROM AUTHOR]

Presents a study that measured the optical absorption spectra, direct current conductivity, thermal activation energy, photoluminiscence and the infrared spectra of silicon-carbon-germanium-hydrogen (SiCGeH) films. Use of radio frequency sputtering; Importance of hydrogenated amorphous silicon carbide films; Electrical and optical properties of sputtered SiCGeH films.

In smart grid power system operation, frequency regulation is one of the most critical tasks towards power balance in the grid. This paper presents the schemes for improvement in operation of secondary loop of turbine-generator unit for frequency regulation in non-synchronous AC areas connected via multi-terminal direct current (MTDC) network. Two schemes have been discussed; (i) voltage droop based lead/lag compensator and (ii) DC power modulation at converter terminal depending upon frequency deviation from each AC area. In the first scheme, droop design based on lead/lag compensator using DC voltage deviation is introduced as supplementary signal at turbine-generator unit in each AC area, to balance the active power, following the load disturbance on AC side and DC power flow conditions. On other hand, in second scheme, frequency regulation is addressed, adopting DC power modulation at MTDC converter, defined in terms of cumulative frequency deviation of AC areas connected to droop controlled terminals. Both the schemes, utilizing converter signals, thus being fast in action compensates the inherently slow response of secondary loop control of turbine-generator unit. Further, effectiveness of derivative based virtual inertia (VI) is also demonstrated to fully compensate the initial frequency response. It is shown that variation of turbine power, i.e. its contribution towards power balance remains minimum with inclusion of voltage droop based lead/lag compensator or/and DC power modulation technique(s). Finally, the comparison between the above control schemes is also discussed. It is indicated that the frequency deviation remains minimum using combined control scheme. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of regulating the output voltage of a DC‐DC buck‐boost converter feeding a constant power load, which is a problem of current practical interest. Designing a stabilising controller is theoretically challenging because its average model is a bilinear second order system that, due to the presence of the constant power load, is non‐minimum phase with respect to both states. Moreover, to design a high‐performance controller, the knowledge of the extracted load power, which is difficult to measure in industrial applications, is required. In this paper, an adaptive interconnection and damping assignment passivity‐based control—that incorporates the immersion and invariance parameter estimator for the load power—is proposed to solve the problem. Some detailed simulations are provided to validate the transient behaviour of the proposed controller and compare it with the performance of a classical PD scheme. [ABSTRACT FROM AUTHOR]

DC distribution networks and micro grids are gaining importance enabling the integration of hybrid distributed generation, energy storage units, modern loads including electric vehicles and different micro grid topologies, thus permitting the consequent development of DC Distribution Systems (DCDS). For maximum utilization of distribution network without compromising the security and reliability of the supply system, determination of critical loading is crucial. With this objective, this paper proposes a modified DC continuation power flow based approach for determining the loadability limit of the active DCDS. DC-DC converters play an important role in bus voltage regulation and system loadability. Impact of these converters must be accounted in any analysis and planning of active DCDS. In this paper, two different mathematical models of lossless DC-DC converters are developed to account them in power flow model of the system. The proposed approach can be applied to both radial and meshed DCDS. Impacts of integration of converters in the system are illustrated by results of two realistic DCDS and results are compared with the corresponding AC Distribution Systems (ACDS). [ABSTRACT FROM AUTHOR]

This paper presents the development of methods and mathematical models to determine the DC/AC average efficiency of inverters that allow to optimize estimates of electricity generation of photovoltaic systems. The adaptive hybrid mathematical model of DC/AC average efficiency of inverters of photovoltaic systems proposed in this paper may be composed of three function settings–Linear, Lognormal, and Polynomial–considering the influence of the relative power, which varies with the sizing factor inverter and the DC input voltage. Determining of the average efficiency with a high degree of accuracy guarantees greater reliability in estimating electricity generation of photovoltaic systems. Depending on the specific behavior of each model and topology of inverter, the adaptive hybrid mathematical model determines the fit functions with highest coefficient R 2 , and estimates with accuracy the DC/AC average efficiency that represents the operation and dynamic behavior of the inverters. [ABSTRACT FROM AUTHOR]

Peak fault current and energy dissipation in high-voltage direct current (HVdc) circuit breakers (CBs) are very important parameters that impact dc grid protection development. This paper analyzes a hybrid DCCB (HCB) control that reduces peak current and energy dissipation by regulating the voltage across contacts of the ultrafast disconnector (UFD). This is achieved by manipulating the number of inserted surge arresters while contacts of the UFD are moving apart. The controller is seamlessly integrated with the current controller of HCBs. An analytical model for current and energy calculation is presented, verified, and employed for parametric studies. A PSCAD simulation with 320-kV, 16-kA test circuit confirms that the proposed voltage control reduces the peak current and energy dissipation by around 20%–30%. A 900-V, 500-A HCB laboratory hardware is described and the experimental results are shown to corroborate simulation conclusions. [ABSTRACT FROM PUBLISHER]

Active current injection circuit breakers (ACICBs), which utilize the mechanical switch and a parallel-connected precharged capacitor, have broad application prospects in future multiterminal dc grids. However, with the increase of system voltage, the precharged capacitor leads to the great cost and size being spent on the charging circuit and auxiliary commutating appliances. To address this shortcoming, an innovative dc circuit breaker (DCCB) based on a magnetic induction current commutation module (MICCM) is proposed. The influence of the main component parameters on the commutation performance is investigated by calculation, in which the self-, mutual, and stray inductances are involved. Besides, the validity of calculation is experimentally proved. Then, by applying the MICCM to the ACICB, the breaking characteristics of the ACICB are analyzed in detail. Finally, a 10-kV DCCB prototype is developed, verifying the feasibility of current commutation concept and the validity of simulated interruption results. Our studies show that a 10-kA bidirectional fault current can be interrupted successfully with a commutation duration less than 250 μs. [ABSTRACT FROM PUBLISHER]

A new control method for a line-commutated converter-based (LCC) high-voltage direct-current (HVdc) system is presented and compared to a conventional strategy. In the proposed method, both the dc voltage and current of an LCC HVdc system are regulated to increase the short-term operating margin of dc power transfer and improve transient responses to dc power references. In particular, an increased operating margin of dc power transfer is achieved via the dc voltage regulation method. To verify the effectiveness of the proposed method, a state space model of an LCC HVdc system is developed considering dc voltage and current references as input variables and analyzed for various values of the dc line inductance and converter controller gains. The state space model can be used for time-efficient analyses of the dynamic characteristics of an LCC HVdc system. Simulation case studies are performed using MATLAB, where the state space model of the Jeju–Haenam HVdc system is implemented as a test case and compared to its comprehensive PSCAD model. The case study results suggest that the proposed method increases the short-term operating margin and speeds up the transient response of the HVdc system. Therefore, it will effectively improve real-time grid frequency regulation. [ABSTRACT FROM PUBLISHER]

This paper presents a novel approach to damp interarea oscillations by designing a robust multi-input multioutput supplementary controller for multiterminal dc (MTDC) systems embedded in ac grids. The key idea to achieve robustness lies in explicitly modeling the MTDC current injection as disturbances using an \mathcal H\infty mixed-sensitivity formulation in the linear matrix inequality framework. Control directions are established by selecting wide-area feedback signals and the relative gain array computation. Robustness is assessed through dynamic simulations for scenarios including: first, disturbances on the ac side, second, disturbances on the dc-side such as loss of a converter pole including actuator, third, partial loss of feedback signal, and fourth, communication latencies. The performance of the proposed controller is compared against the conventional \mathcal H\infty based design, using a four-terminal dc grid embedded within the New England–New York test system. The results suggest that the proposed approach demonstrates superior performance following dc-side disturbances, actuator outages, and latency. [ABSTRACT FROM PUBLISHER]

This paper studies protection and control methods for a large dc grid based solely on full-bridge modular multilevel converters (MMCs). An initial theoretical study concludes that dc circuit breakers (CB) energy dissipation will depend on inductance and square of fault current, but not on protection operating time. Using differential protection is proposed because of robust selectivity and since it operates well with small series inductors. The analysis of dc CB dissipated energy leads to new protection logic design that delays tripping signals until local current reduces to low values. Low-speed dc CB with very small inductors are adequate. The design of controllers for MMC converters should be coordinated with dc grid protection and the study derives values for current controller references. The fault recovery time is found to depend on current reference settings at MMC terminals, and optimal values are derived. The conclusions are confirmed using Electromagnetic Transients Program (EMTP) simulation on a 400-kV, 4-MMC dc grid considering two topologies: with five overhead lines and with five dc cables. [ABSTRACT FROM PUBLISHER]

For lack of the appropriate global distribution of dc currents, the conventional suppression method to suppress dc bias based on capacitive dc blocking device (BD) redirects current to the ground as much as possible, which predisposes to the exceeding neutral current of other transformers in the regional power grid and leads to the contradiction between the power grid corporation and other public enterprises. Therefore, this paper presents a flexible suppression method for dc bias based on a novel dc-bias suppression device. First, a current balancing device (CBD) based on adjustable parallel resistances is designed. The mathematical model for global optimal switching of CBDs is established by a field-circuit coupling method with the equivalent resistance network of an ac system along with the location of substations and ground electrodes. The optimal switching scheme to minimize the global maximum dc current is obtained by gravitational search algorithm. Based on the aforementioned work, we propose a suppression strategy considering electro-corrosion of metal pipelines. The effectiveness and superiority of suppression methods are verified by comparative case studies of the Yichang power grid. [ABSTRACT FROM PUBLISHER]

Fault current limitation is an urgent but challenging technology for medium-voltage dc (MVDC) power systems. For a liquid metal current limiter (LMCL), the arc discharge characteristics often determine its current-limiting properties. The evolving arc in liquid metal is measured by contacting voltage probes, and the properties of the formed dumbbell-like arc column are studied and discussed in detail. It indicates that the total arc voltage almost behaves as a linear function of arc current for an LMCL. Besides, a simplified numerical arc model based on magnetohydrodynamics theory is built and solved by the software FLUENT. It is concluded that the temperature rather than the slightly fluctuant pressure dominates the arc properties, which coincides well with test results to some extent. Finally, a fault current limiter topology including serial LMCLs and parallel resistors is put forward, whose feasibility for MVDC application is discussed on the basis of its current-limiting behaviors. [ABSTRACT FROM AUTHOR]

A The DC distribution technology brings challenges and opportunities to the penetration of large-scale distributed renewable energy sources. In a medium-voltage DC (MVDC) distribution network, operation mode switch occurs owing to some large disturbances. To manage these disturbances and achieve seamless switch of the operation mode, a hierarchical control strategy with two layers, namely local and global layers, is proposed in this work. The novel local layer controller called P--U--I controller is designed to enhance the voltage stability, improve system controllability and suppress overcurrent under large disturbances. This controller only needs local information and does not rely on fast communication. Furthermore, as the scale of the DC distribution network expands continuously, the number of system operation mode increases in geometric progression. Therefore, a global layer controller based on breadth-first search algorithm is proposed. This controller can automatically identify the system topology and adjust the control mode of converters to optimise the system operating characteristics. Thus, this hierarchical control strategy can accurately control the system power in steady state, suppress overcurrent under large disturbances and suit large-scale DC distribution networks. Finally, a three-terminal MVDC distribution network simulation model established on power systems computer-aided design and RT-LAB validates the proposed strategy. [ABSTRACT FROM AUTHOR]

Surface charge accumulation on spacer is an important factor to cause surface flashover. An experimental set-up is established to measure surface potential over a truncated cone-type spacer under DC voltage in SF6 gas at atmospheric pressure using a Kelvin vibrating electrostatic probe. The surface charge density is calibrated based on multipoint measurement technique, which takes the influence of electrostatic probe into account. The experimental results show that surface charge distribution patterns can be divided into three classes including centrosymmetric distribution, spot-like distribution, and cloud-like distribution. The symmetrically distributed charges are injected by electrode, which migrate along spacer surface through the surface conductivity. While the charges showing spot-like and cloud-like distribution are generated by the ionisation of SF6 due to local electrical field concentrated. Besides, the hetero-charges are more easily to be saturated with different charging durations and the polarity of the net charge is the same as that of applied voltage. [ABSTRACT FROM AUTHOR]

In medium voltage direct current (MVDC)-based power distribution scheme DC faults can cause instant disruption in service continuity to various connected loads. Many integrated power systems (IPS) found MVDC as a better replacement of MVAC for detection, isolation as well as protection against DC faults. DC fault protection strategy for developed MVDC-IPS system (which is accompanied by LVDC subsystem), is proposed here by introducing a modified series Z-source breaker circuitry which minimize fault or transient current that reflects back at the DC source by keeping its common ground return path and to re-energize the DC load after fault clearance. The versatility of the proposed idea also include to energize the loads after the fault clearance. The main problem is that a large value of fault/transient current 0 that reflects back at the source and SCR (when it stops commutation). This large reflective current value is much greater than the value of the SCR peak cycle surge value and can damage the SCR permanently. To overcome this problem in the developed technique, an addition of series resistance is made with capacitors which minimize the effect of transient level on SCR and source. Furthermore, due to this resistance the other component size or value is decreased which helps in minimizing the effect of transient current at SCR and source. Another aim is to build the breaker structure in such an optimize way so that to minimize dissipation and weight as compared to its classic structure along with enhancement of efficiency. The proposed strategy of DC fault for IPS is validated through two case studies done in PSCAD simulations. [ABSTRACT FROM AUTHOR]

Different from the synchronisation stability for alternating current (AC) systems, the potential risk caused by the interaction between different terminals in voltage source converter-based multi-terminal direct current (VSC-MTDC) grids is emerging, which may impose negative influences on system operation and control. Focusing on this topic, a comprehensive modal analysis is presented to analyse and characterise the dynamic behaviours and interactions of VSC-MTDC grids. The state-space model of VSC-MTDC grids associated with AC systems is developed and participation factor analysis is utilised to identify the physical source of the oscillation modes. This study investigates the voltage fluctuations in VSC-MTDC grids induced by the oscillation modes with the application of extended participation factors. A Monte Carlo-based statistic method has been adopted for the calculations. The interactions between different terminals are identified using mode shape analysis, and quantitative calculation of eigenvalue sensitivities is presented to assess the effect of parameter variation on modal shift. Furthermore, an approach based on the singular value decomposition is proposed for the quantitative analysis of the interaction strength among different control loops. Simulations on a multi-terminal test system are carried out to verify the analytical results. [ABSTRACT FROM AUTHOR]

The international thermonuclear experimental reactor poloidal field converter unit is comprised of four converter bridges, dc reactors, dc switches, etc., and most are nonstandard. To evaluate the performance of these equipments, a high-power dc test platform has been built to carry out the steady-state current test and impulse current test. The latter is significant to verify the fault suppression capability of products. The dc test platform can output the rated 400-kA impulse current. The principle design and structure of the dc test platform is introduced in this paper. The transient large current in impulse current test could cause huge impact reactive power and grid voltage sag. The impact is analyzed by theoretical calculation and simulation. A static var compensator system is added to suppress the transient effects of the reactive power. A predictive reactive power control strategy is proposed to improve the dynamic response. The comparisons with the traditional control demonstrate that the proposed control is effective in compensating impact reactive power and it also performs well on inhibiting the grid voltage sag. [ABSTRACT FROM AUTHOR]

This paper presents a new rapid and reliable directional protection scheme for Multi-Terminal DC (MTDC) grid with an inductive DC terminal. The proposed method determines an internal or external fault easily by comparing the transient energy polarities of traveling waves measured at both ends of each line section. Compared with the conventional direction principle based on traveling waves, the proposed method performs more reliably in the case of an inductive terminal. Moreover, the double-end fault location method based on traveling waves is integrated into the protection scheme to predict the accurate fault location. The effectiveness of the proposed method is verified by a meshed DC grid modeled in PSCAD/EMTDC software. Extensive simulation results show the proposed method is able to determine internal or external faults correctly under conditions of different fault types, fault distances and fault resistances. Furthermore, the proposed method is also insensitive to the sampling frequency and noises. [ABSTRACT FROM AUTHOR]

As the capacity of all-electric ships (AESs) increases dramatically, the sudden changes in the system load may lead to serious problems, such as voltage fluctuations of the ship power grid, increased fuel consumption, and environmental emissions. In order to reduce the effects of system load fluctuations on system efficiency, and to maintain the bus voltage, we propose a hybrid energy storage system (HESS) for use in AESs. The HESS consists of two elements: a battery for high energy density storage and a superconducting magnetic energy storage (SMES) for high power density storage. A dynamic droop control is used to control charge/discharge prioritization. Maneuvering and pulse loads are the main sources of the sudden changes in AESs. There are several types of pulse loads, including electric weapons. These types of loads need large amounts of energy and high electrical power, which makes the HESS a promising power source. Using Simulink/MATLAB, we built a model of the AES power grid integrated with an SMES/battery to showits effectiveness in improving the quality of the power grid. [ABSTRACT FROM AUTHOR]

DC power flow analysis is based on a linear approximation model for AC power flow equations, and represents an efficient approach for acquiring the bus angles and active transmission power of a power grid. However, the input data and network parameters of the power grid are uncertain due to numerous internal and external factors. Therefore, the DC power flow model should be considered as an uncertain problem, which makes deterministic DC power flow analysis methods unworkable. The present work overcomes this problem by regarding uncertain input data and network parameters as interval values, respectively, and establishes the interval DC power flow (IDCPF) models considering interval input data only (denoted as IDCPF01), and IDCPF model including both interval input data and network parameters (denoted as IDCPF02). Analyses based on the IDCPF models seek to obtain conservative ranges of bus angles and active transmission power flow, which can be employed by dispatchers to develop strategies for ensuring the operational security of the power system. The optimizing-scenarios method (OSM) is employed here to solve the IDCPF models. In addition, it is proven that the lower (or upper) bounds of the bus angles of the IDCPF01 model are simultaneously obtained when the injected power is set as its lower (or upper) interval bounds. This fact greatly improves the efficiency of the OSM for solving the IDCPF models. The results obtained by the proposed method are compared with those obtained by Monte Carlo simulation, the AA-based method, and the interval AC power flow method. The overall simulation results demonstrate the effectiveness and robustness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper analyses the impacts of the growth of renewable energy production and German nuclear phase-out on the electricity transmission systems in Central Europe. The principal concern is the significant disparity between the growth of renewable production and the pace at which new transmission lines for the transport of electricity have been built, especially in Germany. This imbalance profoundly endangers the system stability and reliability in the whole region. The assessment of these impacts on the transmission grid is analysed by the direct current load flow model ELMOD. Two development scenarios for the year 2025 are evaluated by 3 representative weeks. The results illustrate the issue from three different perspectives. First, the distribution of loads in the grids is shown. Second, hourly patterns during particular weeks are analysed. Third, a geographical decomposition is made, and problematic regions are identified. The high solar or wind power generation decrease the periods of very low transmission load and increase the mid- and high load on the transmission lines. High solar feed-in has less detrimental impacts on the transmission grid than high wind feed-in. High wind feed-in burdens the transmission lines in the northsouth direction in Germany and water-pump-storage areas in Austria. [ABSTRACT FROM AUTHOR]

Compared to AC microgrids, DC microgrids have the advantage of higher reliability and efficiency and are convenient to connect with various distribution energy resources (DERs). Concentrated in different time-scale control objectives, a multi-level control structure can guarantee that none of the control objectives affect each other. Considering this, an extensive review on the hierarchical structure of the DC microgrid is applied, and two typical control structures are presented in detail: two-level control architecture and three-level control architecture. Furthermore, the primary, secondary, and tertiary control levels are systematically analyzed and classified according to different control objectives. In order to improve the control capability of the primary control level, an energy efficiency improved DC bus voltage control strategy is proposed to increase the energy efficiency and system reliability. Finally, a distributed DC microgrid model is established and simulated in the RT-LAB to verify the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

Three pulse-width-modulation (PWM) digital control approaches are evaluated to provide the current sharing between phases in high-power dual-interleaved DC–DC converters. The implementation of a digital peak current, multi-sample averaged current and an enhanced single-sample averaged current control in a TMS320F28377D is described. A summary of stability requirements is provided for designing the controllers and experimental results from a 60 kW, 75 kHz silicon carbide DC–DC converter are used to evaluate the steady-state and dynamic performance of the three control methods. Overall the best performance in terms of tracking and speed of response was achieved by the enhanced single-sample method. The multisampled technique provided the highest tracking accuracy, but at the expense of the slowest dynamic response. The fastest dynamic response was achieved by the digital peak current control, but this method is limited by poor noise immunity and instability for duty ratios in the region of 0.5. [ABSTRACT FROM AUTHOR]

This study proposes an input-voltage-sharing control scheme for use in input-series-output-series (ISOS) systems. An ISOS system consists of a set of closed-loop DC/DC converters. Each converter has a metal–oxide–semiconductor field-effect transistor (MOSFET) connected in parallel on the input side that is controlled by an input-voltage-sharing loop. The MOSFET works in the linear region to adjust the input power equilibrium. The proposed control scheme makes the closed-loop converters function as power devices that can be combined quickly and flexibly according to the specific voltage conversion requirements, which greatly shortens the time required to develop an ISOS system. The design principle of the input-voltage-sharing loop and the time and frequency domain simulation results are also provided in this study. A 600 W prototype composed of two DC/DC converters was built and employed to verify the steady state and dynamic characteristics of the proposed control scheme. [ABSTRACT FROM AUTHOR]

This study introduces a new active-clamped current-fed push-pull dc-dc converter for renewable energy conversion applications. The proposed converter conserves small input current pulsation, high-voltage conversion ratio, zero-voltage switching (ZVS) and zero-current-switching operation for primary switches and rectifier diodes, respectively, over a large load range. Also, the additional active clamping circuit serves to suppress the voltage spike across all primary switches, as well as assists in achieving ZVS operation. So, the low-voltage switches with low on-state resistance can be adopted. These features can reduce switching loss, voltage stress, transformer turns ratio and diode reverse-recovery effect. More importantly, similar characteristics can be obtained with minimised switches compared with the reported converters that enable to reduce the cost and improve the reliability. Detailed steady-state operation, analysis, performance comparison, experimental results and loss breakdown of the proposed converter are fully discussed in this study. Finally, a 520 W prototype verifies the theoretical analysis. [ABSTRACT FROM AUTHOR]

This study proposes a technique that is able to improve the speed response of a four-phase DC-DC converter switching. The basic concept of the proposed technique is the inclusion of two shunt-connected voltage sources in series to the converter system. Using a higher input voltage to drive the load, a higher current per microsecond output system will be obtained and reverts to its nominal input upon obtaining desired references. Thus, the transient response observed when using this proposed technique is found to be much faster when compared to the conventional converter. Moreover, this technique is easily implemented as it requires only an additional voltage source, power switch, and power diode. The integrated model of the two shunt voltage-source in a four-phase DC-DC converter was simulated in MATLAB/Simulink and validated against the experimental results of a laboratory prototype, 600 W four-phase DC-DC converter. The novelty of this proposed technique is its ability to provide faster operations for critical loads applications, lower output capacitor and lower operating frequency. [ABSTRACT FROM AUTHOR]

An improved high efficiency wide zero-voltage-switching (ZVS) range push–pull converter for low-voltage to highvoltage power conversion is proposed in this study. For this improved converter, all of primary switches are turned on with ZVS operation from full load to light load by using the energy stored in the leakage inductance aided by the magnetising inductance. The resonance between the leakage inductor and the voltage-doubler-rectifier capacitors reduces not only the voltage and current stresses of rectifier diodes but also the turns ratio of high-frequency transformer and conduction loss. In addition, the circulating energy is decreased dramatically compared with the similar converter resulting in lower conduction loss. This topology features simpler structure and higher efficiency. Detailed operational principle, design, comparative study and experimental results are fully discussed in the text. Finally, a 200 W experimental prototype has been built to verify the effectiveness of the proposed concept. [ABSTRACT FROM AUTHOR]

Modern DC–DC resonant converters are normally built around a voltage-source series-resonant converter. This study aims to facilitate the practical use of current-source parallel-resonant converters due to their outstanding properties. To this end, this study presents a sliding-mode control scheme, which provides the following features to the closed-loop system: (i) high robustness to external disturbances and parameter variations and (ii) fast transient response during large and abrupt load changes. In addition, a design procedure for determining the values of the control parameters is presented. The theoretical contributions of this study are experimentally validated by selected tests on a laboratory prototype. [ABSTRACT FROM AUTHOR]

DC/DC converters are crucial in DC distribution networks for converting voltage and interconnecting different voltage links. The modular multilevel high-frequency-link DC transformer (MDCT), which employs multiplex conversion principle and provides many advantages, realises voltage conversion, power transfer and electrical isolation between links in medium-voltage DC distribution networks. To improve the performance of MDCT, this study investigates the modulation with the phase-shift strategy and its influence on current stress, power characteristic and efficiency characteristic of MDCT. Besides, to simultaneously achieve an optimal solution for both current stress and efficiency characteristics of MDCT, an optimal modulation strategy based on dual-phase-shift is proposed. Finally, an MDCT prototype is constructed and experimental results verify the correctness and effectiveness of the analysis and proposed scheme. [ABSTRACT FROM AUTHOR]

During the operation of dc rapid transit systems, the rail passenger vehicles are subjected to surge transient events that can damage the on-board equipment and cause service interruption. During the testing phase, vehicle manufacturers must demonstrate the performance of the vehicles under the specified transients. However, system testing is generally not available during design. Engineering analysis must be performed to ensure that the design will meet the transient requirements, and that the overvoltage and overcurrent protective devices are coordinated on a system level. In response to these design challenges, detailed time-domain simulation models of a switching surge transient generator and the vehicle equipment have been developed and validated experimentally. These models are used to evaluate vehicle system parameters sensitivity, as well as to provide design guidelines for increased vehicle power system safety, reliability, and availability. [ABSTRACT FROM AUTHOR]

DC microgrid is one of the feasible and effective solutions to supply reliable electricity as well as to integrate renewable energy resources. The control objectives of the DC microgrid are equal current sharing in per unit and the bus voltage regulation within permissible limits. The droop control is a reliable method adopted to implement the control of the distributed power system with multiple energy units. However, in the application of the distributed power system, the nominal voltage reference mismatch and unequal cable line parameters require a trade-off between bus voltage regulation and current sharing error. In this paper, a simplified compensation structure is proposed to minimize trade-off between proportional equal current sharing and the bus voltage regulation within permissible limits for unequal cable resistances. The proposed control scheme is improved transient performance of output current sharing and the bus voltage by using a voltage droop control and hysteretic current control. The global stability is also insured for the communication time delay. The performance of the proposed model is verified in the MATLAB/Simulink environment. [ABSTRACT FROM AUTHOR]

For grid-connected LCL-filtered inverters, the inverter-side current can be used as the control object with one current sensor for both LCL resonance damping and over-current protection, while the grid-voltage feedforward or harmonic resonant compensator is used for suppressing low-order grid current harmonics. However, it was found that the grid current harmonics were high and often beyond the standard limitations with this control. The limitations of the inverter-side current control in suppressing low-order grid current harmonics are analyzed through inverter output impedance modeling. No matter which compensator is used, the maximum magnitudes of the inverter output impedance at lower frequencies are closely related to the LCL parameters and are decreased by increasing the control delay. Then, to improve the grid current quality without complicating the control or design, this study proposes designing the filter capacitance considering the current harmonic constraint and using a PWM mode with a short control delay. Test results have confirmed the limitation and verified the performance of the improved approaches. [ABSTRACT FROM AUTHOR]

With the development of DC distribution system within the isolated power system of a ship or an aircraft, more constant frequency loads will be supplied by inverters connected to DC main bus. In the operating mode conversion process of an isolated power system, inverters will inevitably suffer from serious disturbance and affect the stability of the system. Therefore, it is important to establish a model of the inverter that reflects its dynamic characteristics and based on which to conduct the stability analysis. This paper proposes a 12-pulse inverter model based on the generalized state space averaging (GSSA) method. This model can overcome the limitations of 12-pulse inverter state space averaging (SSA) model in transient analysis with good accuracy and fast analysis ability effectively. Three kinds of models for a 12-pulse aircraft inverter are built in MATLAB, namely GSSA model, SSA model and detail device model. The simulation results show the high accuracy of GSSA model in stability analysis. This study provides an effective analytical tool for stability analysis of 12-pulse inverter and also provides a reference for inverter modeling research of isolated power system such as in aircraft or ship. [ABSTRACT FROM AUTHOR]

Various DC tests performed recently with full-size 60 kA HTS cable prototypes in the EDIPO test facility demonstrated that proposed design of HTS strand at Swiss Plasma Center (SPC) – stack of HTS tapes twisted and soldered between two copper profiles – is applicable for high-current fusion cables, but improvement of the strand mechanical properties against the cyclic loading is still needed. Based on experimentally obtained correlation between the performances of cable prototypes at different operating conditions, further investigation of cyclic transverse load on the strand performance was performed at 77 K. Aiming to obtain a strand design able to withstand a continuous cyclic load operation of some thousand cycles, influence of the strand geometry and tape's manufacturer has been studied. Cyclic load has been applied up to 1000 cycles for straight and bent samples at the load amplitudes up to 4 MPa. Based on the obtained data, next design of HTS cable prototype will be discussed. [ABSTRACT FROM AUTHOR]

In this paper, an on-line management system for the optimal efficiency operation of a multi-bus DC home distribution system is proposed. The operation of the system is discussed with reference to a distribution system with two conversion stages and three voltage levels. In each of the conversion stages, three paralleled DC/DC converters are implemented. A Genetic Algorithm performs the on-line optimization of the DC network’s global efficiency, generating the optimal current sharing ratios of the concurrent power converters. The overall DC/DC conversion system including the optimization section is modelled using MATLAB/Simulink. Thanks to the implemented online algorithm, considering the system modelling as dynamic master/slave configuration, reliability, robustness and flexibility of the whole conversion system is enhanced. Since an online algorithm is implemented, several variables are accounted for, such as: components loss parameters, components ageing, load currents, switching frequency and input voltage. Simulation results considering several case studies are presented and the benefits brought by the optimization algorithm in terms of power saving are widely discussed for each case study. [ABSTRACT FROM AUTHOR]

The proposed study is about the design and experimental results of a power supply for gate drivers that can sustain 40 kV of insulation voltage with a parasitic capacitance of 4 pF. The first section focuses on insulation materials suitable for medium voltage capabilities and therefore to justify the use of polyesterimide and Teflon polytetrafluoroethylene materials. In a second step, experimental results are provided to guaranty that with a thickness of 1 mm of the insulation material, an insulation voltage of 40 kV is provided. Then, a DC-DC converter based on a series-series topology is designed and lead to a physical prototype of 5 W. The measured parasitic capacitance is 4 pF between the primary and the secondary sides. [ABSTRACT FROM AUTHOR]

Based on the loss distribution and efficiency analysis, a comparative study between a series resonant three-port bidirectional DC-DC converter (SR-TBC) and a multi-resonant three-port bi-directional DC-DC converter (MR-TBC) is reported here. By using the Fourier equivalent analysis method in hand, the resonant current, switching current expressions, zero voltage soft switching (ZVS) conditions of MR-TBC and SR-TBC are deduced. Besides, in consideration of efficiency and soft switching aspects, the loss models of main power components and resonant elements are integrated and optimized for both topologies. Their loss distributions are established, and the different effects derived from the adoption of SiC MOSFET and Si MOSFET on the converter efficiency are discussed. Finally, to verify the theoretical analyses, comparative experiments under diverse load states are conducted based on the prototypes of the MR-TBC and SR-TBC. The obtained results demonstrate that the MR-TBC successfully broadens the ZVS range and thus achieves higher efficiency along the entire load range. [ABSTRACT FROM AUTHOR]