High Voltage DC Power Research Articles

A multiport superconducting fault‐current‐limiting circuit breaker for a flexible DC power grid

The fault current of the high-voltage and large-capacity flexible DC power grid has the characteristics of a fast rising rate, high peak value, and large influence area; therefore, fault current suppression equipment suitable for the flexible DC power grid has become a research hotspot. First, the fault mechanism and fault current calculation associated with the DC converter are analysed in this study; subsequently, a multiport superconducting fault-current-limiting circuit breaker (SFCLCB) suitable for a flexible DC power grid is designed. The circuit breaker adopts ground drainage to transfer the fault current. It only needs to be equipped with a single-way conduction power electronic switch group and the number of switches is not affected by the number of DC lines, considerably improving the cost effectiveness of the equipment. In addition, the workflow and current-limiting principle of SFCLCB are analysed, and the optimal matching method is determined with respect to the resistance of the superconducting current limiter and the power electronic devices of the main circuit breaker. Afterwards, the four-terminal flexible DC transmission simulation system is observed to exhibit high efficiency in suppressing the fault current and high cost effectiveness based on comparative simulations. Finally, its engineering applicability is verified by the digital physical and hybrid simulation platform.

Analysis of conductivity of ZnO/LDPE Composites

The composites prepared by adding zinc oxide into polymer have been widely studied and applied because of their special properties of self homogenizing electric field distribution in non-uniform electric field, inhibiting space charge and electrical tree growth. In this paper, the effects of inorganic filler concentration and particle size on the conductivity of ZnO/LDPE Composites were studied by voltammetry combined with high voltage DC power supply and picoammeter to measure applied voltage and through current.

Contact pressure of high-voltage DC power relay change and life prediction and structure optimization

To effectively predict the life of high voltage dc power relay, the authors design the structure of the relay to extending its life. The contact failure mechanism of relay products is analyzed by observing the appearance of several contact failures. The electromagnetic-thermal field coupling model is established and the state of heat flow and distribution of temperature increase between electrical and thermal coupling contacts are analyzed through simulations and experiments. An adaptive neural network control system is established to conduct sample training, obtain the best stiffness coefficient of the main spring, and optimize the design of the main spring structure composed of composite springs. The action voltage, release voltage, contact resistance, contact pressure, action time, and release time as characteristic parameters, and the relative error, correlation degree, variance ratio, and small error probability of each characteristic parameter, are calculated. The precision grade index of contact resistance and action time is defined as level 1. The two characteristic parameters are selected as the prediction variables to establish the life-prediction model based on gray theory. The relative error between the predicted and test life is 5.31%–5.6%, indicating that the life-prediction model has high accuracy. The test results show that the combined main spring structure can extend the life of a relay by 18.15%.

Comparison of short-circuit ratios of converter control for high-voltage DC power transmission systems

Comparison of short-circuit ratios of converter control for high-voltage DC power transmission systems

–1 MV DC Filter and High-Voltage DC Measurement System for ITER Neutral Beam Injector System

This article proposes the one-package structure of –1 MV direct current (dc) filter circuit and dc measurement system composed of dc voltage dividers and dc current transducers (DCCTs). These apparatuses are becoming more important for the expansion of high-voltage dc (HVDC) power grids. However, at present, they are separately installed keeping a huge distance for air insulation, and an increase in equipment size and footprint has become a major issue. We succeeded in reducing the footprint to 1/100 by storing the aforementioned HVDC vital parts in one package of a pressure vessel. Our developed configuration uses sulfur hexafluoride (SF6) gas not only for insulation purpose but also as a refrigerant to forcibly ventilate vertically in order to allow the dc filter circuit, which is heat generation source, and the dc measuring instruments, which need to minimize the effect of temperature drift, to coexist. We also addressed another issue caused by the limited space in the one-package structure, where the stray capacitance of the dc voltage divider tends to become large and then lowers the measurement accuracy for transient voltage variation. As a countermeasure, the dc voltage divider is composed of much larger capacitance than the stray capacitance and additional damping resistance to avoid LC resonance with wiring inductance. The actual-product tests demonstrated the followings; the dc measurement system has satisfied high measurement accuracy of 0.5% and fast responsivity of 3.3 μ s retaining decay rate within −3 dB; the temperature rise of the dc voltage dividers and the DCCTs is reasonably suppressed; the dc measurement system and the dc filter circuit withstood DC −1.2 MV.

A Fast Vacuum Arc Detection Method Based on the Neural Network Data Fusion Algorithm for the High-Voltage DC Power Supply of Vacuum Tubes

Vacuum arc is one of the most important failure factors of the vacuum tubes. The amount of delivered energy from the high-voltage dc power supply to the vacuum tube is an important issue during the vacuum arc in the tube. Vacuum arc acts as a short-circuit fault (SCF) at the power supply output. The majority of converters use a single current sensor to measure only the converter output current for detecting the SCF. However, the sensor may provide unreliable data because of the noise effect. Application of a low-pass filter reduces the noise effect. Regarding the delay of the low-pass filter, the interval of arc detection increases and more energy is delivered to the tube. In this article, a fast vacuum arc diagnosis system is proposed based on the neural network data fusion algorithm. The proposed scheme consists of two sensors: the conventional current sensor and the existing voltage sensor used for controlling and monitoring. The data of these two sensors are combined by neural networks to diagnose the vacuum arc and to reject false alarms in noisy environments. The proposed method has a fast response time to the real SCFs while it remains inactive against the false data which are generated by noise. Simulations and experimental tests are carried out to evaluate the proposed scheme.

On-line fault diagnosis and fault-tolerant operation of modular multilevel converters — A comprehensive review

Modular multilevel converters (MMCs) have been one of the most broadly used multilevel converter topologies in industrial applications, particularly in medium-voltage motor drives and high-voltage dc power conversion systems. However, due to the utilization of large amount of semiconductor devices, the reliability of MMCs becomes one of the severe challenges constraining their further development and applications. In this paper, common electrical faults of the MMC have been summarized and analyzed, including open-circuit switching faults, short-circuit switching faults, dc-bus short-circuit faults, and single line-to-ground faults on the ac side. A thorough and comprehensive review of the existing online fault diagnostic methods has been conducted. In addition, fault-tolerant operation strategies for such various fault scenarios in MMCs have been presented. All the fault diagnosis and fault-tolerant operation strategies are comparatively evaluated, which aims to provide a state-of-the-art reference on the MMC reliability for future research and industrial applications.

Controlled islanding algorithm for AC/DC hybrid power systems utilising DC modulation

The controlled islanding problem is typically considered only for pure ac power systems, with the ultimate objective of either minimising power imbalance or power-flow among islands. However, as ac/dc hybrid power systems are becoming popular worldwide, current controlled islanding schemes should be redesigned to take into account the presence of high-voltage dc (HVDC) links, possibly connecting different islands. Accordingly, in this study, the authors solve the classic islanding problem combining HVDC power modulation with the conventional ac cutset search. The flexibility of the HVDC allows the authors' strategy to jointly capture the previously mentioned objectives, and provides even lower power imbalances than the minimum imbalance strategy, at a relatively small cost of increasing power-flow impact. Then, the optimisation problem is formulated as a mixed-integer linear programming problem, which can be conveniently solved with existing commercial solvers. Finally, they validate their proposed strategy in two case studies, corresponding to a modified IEEE-118 system and to the China Southern Power Grid system. In both cases, dynamic simulations show that their proposed approach outperforms classic algorithms where the presence of HVDC power modulation is not explicitly taken into account.

A Very Low-Ripple High-Voltage High-Power DC Power Supply Using an Interleaved Converter and a Linear Ripple Elimination Unit

High-voltage dc power supplies (HVDCPSs) have been widely adopted for the vacuum tubes. In this application field, the low ripple voltage cannot be easily achieved by increasing the size of the output capacitance of the HVDCPS due to the limited permissible level of the stored energy. To obtain a low level of the output ripple as well as the limited value of the stored energy, the previously published literature proposed switching frequency increment. This approach has several shortcomings such as switching power loss increment, a limited level of the achievable ripple, and low value of the insulators’ lifetime. To improve the mentioned deficiencies, this article hybridizes the series linear regulator and a high-frequency high-power dc interleaved converter. Using the proposed method, at the first stage, the level of the ripple decreases to a rational margin with increasing the ripple frequency. At the second stage, the level of the ripple reduces using the linear regulator to reach the expected precision. In order to validate the performance of the proposed structure, simulation and experimental results are provided for a 15-kV and 22.5-kW converter with the output voltage precision of 0.02%.

Controlled Rectifier for Improved Harmonic Performance of a Pulse Step Modulated High Voltage Power Supply

Research in ITER grade magnetic confinement fusion uses high power radio frequency sources and accelerated neutral particles to heat the plasma to fusion temperature. These devices require high voltage DC power supplies in the range of several tens of kilovolts at a power level of few megawatts. Pulse step modulation technique is widely used to generate high voltage by cascading bulk numbers of low voltage switched power modules, offers a minimum ripple with microsecond order transient response and low let-through energy in case of load fault. However, the power quality and reliability of these systems still need enhancement for compatibility with an industrial environment. In a conventional diode rectifier-based switched power module, current drawn from the multisecondary transformer is highly distorted affecting transformer performance, leading to deploy higher capacity with enhanced thermal management. A novel concept of pulsewidth modulated (PWM) rectifiers in pulse step modulated power supplies is attempted for the first time with comparative analysis over conventional diode rectifiers, quoting an example of dual output high voltage power supply. Articles also discuss the development of a laboratory-scale prototype of the switched power supply module utilizing a PWM rectifier.

Dielectric elastomer generator with piezoelectric offset

In the past studies, dielectric elastomer generators (DEGs) need a high voltage DC power supply to provide an offset voltage, which restricts the application of DEG technology in practical projects. To solve this problem, this study adopts piezoelectric materials to provide an offset voltage for DEGs and a self-priming circuit to recycle the energy generated by DEGs. A new DEG with piezoelectric offset is designed to solve the problem of self-supply in the DEG power generation process. Before the experiment, the mathematical model is established by analyzing the dielectric elastomer generator and piezoelectric offset circuit and self-priming circuit, and the above models are simulated through the MATLAB/Simulink software. The simulation results demonstrate that the elastic restoring force of dielectric elastomers overcomes the electric field force and converts mechanical energy into electrical energy, and piezoelectric materials can provide an offset voltage for DEGs. The experimental results are in good agreement with the simulation analysis, and the calculated power of DEG-SPC is 673 mW, which lay a foundation for further research on dielectric elastomer power generation technology.

Performance of Flywheel Energy Storage System for Fault Ride through Support of Grid Connected Vsc-Hvdc Based Offshore Wind Farms

For the sake of uninterrupted power supply to the loads we are using renewable energy sources. Among them wind energy and the solar energy is the most familiar renewable energy sources we are using now-a-days. Voltage source converter based high voltage DC transmission is considered as future of offshore power transmission. This paper proposes the high voltage DC power transmission system and maintains system balance during each faults. This results in the voltage and current losses on the switching devices. This strategy implements the flywheel energy storage system based on a squirrel cage induction machine connected in parallel to the grid side converter. It is connected in shunt which present on the grid side circuit of VSC-HVDC based squirrel cage induction motor. Due to this the FESS stores the trapped energy in the DC link during AC side faults for long transmission system using a voltage source converter. When there is insufficient of fault meet the grid at load demand. The series of simulation results we carried out the main part of theFESS system under fault conditions achieved using the software Matlab/Simulink. This project possesses the dynamic performance during ‘steady state’ during normal and fault operating conditions.

High voltage DC power supply with power factor correction based on LLC resonant converter.

This paper presents analysis, design and experimentation of a high voltage DC power supply (HVDCPS) with power factor correction based on LLC resonant converter. For power factor correction improvement, the proposed topology has an input rectifier with two filter capacitors, two inductors with a bus capacitor (Cbus) and a resonant tank. To prevent the reverse current flow towards the source diodes (D9 & D10) are employed. A couple of power switches are inserted in a single leg that makes a half-bridge network. To form an LLC resonance circuit, a capacitor and two inductors are connected to the primary winding of the high voltage transformer (HVT). To rectify the high frequency and high voltage, a full-bridge rectifier is inserted to secondary side of high voltage transformer (HVT). The secondary diodes always get on and off under zero current switching (ZCS) due to discontinuous conduction mode of proposed topology. It is found that due to power factor correction, less cost, lower losses and smaller size, the proposed topology achieves several major improvements over the conventional high voltage power supply. To obtain zero voltage switching (ZVS) the converter operate in a narrow frequency range. The output voltage can be varied or regulate through pulse width modulation of power switches. Due to ZVS and ZCS, the proposed topology has minimum switching losses and therefore higher efficiency. To verify the feasibility of the proposed topology a prototype is being implemented and verified by simulation & experimental results for 1.5KV prototype of the proposed topology. The results make sure the achievement, good efficiency and successful operation of the proposed topology.

An Innovation in Corona Charging of Electrets

An innovation in corona charging of electrets of polymer films has been adopted in locally designed and fabricated corona charging set up by replacing the regular high voltage DC power supply with a light, portable handy 3V-6V DC to DC 400kV boost step-up power module high voltage generator. Polymer film electrets of polyethylene transparency film have been corona charged using this innovative setup. The measurements were done and the results have been analyzed in the light of cited literature to show the effectiveness and advantage of the innovation.

A Voltage Balancing Method for Series-Connected IGBTs Operating as a Fault Current Limiter in High-Voltage DC Power Supplies

This article proposes a high-voltage fault current limiter (HVFCL) for high-voltage dc power supplies (HVdcPSs) which limits the current of the power supply automatically in the short-circuit fault (SCF). The proposed HVFCL is based on the series-connected insulated gate bipolar transistors (IGBTs). The main achievements of this article are the balanced voltage sharing and a very low value of the short-circuit current near to the load nominal current for the series-connected IGBTs during the SCF. These achievements result in a longer maximum permissible short-circuit time. These achievements are obtained by a control strategy that puts the series-connected IGBTs in a specific operating point in the active region during the SCF. Based on the proposed master-slave control strategy, one of the IGBTs is current controlled and rolls as the master. The other IGBTs are voltage controlled and imitate the master IGBT voltage. Consequently, a balanced voltage sharing is guaranteed for the series-connected IGBTs in the SCF. PSPICE simulations and experimental results are provided to verify the proper performance of the proposed HVFCL.

Bridge‐type fault current limiter and hybrid breaker for HVDC grids applications

The fast raising nature of DC fault currents and sensitivity of high-voltage DC (HVDC) power converters to DC faults is critical protection issues. On the other hand, DC fault current does not meet zero; which causes DC to fault current breaking process become more challenging. Specifically, to protect HVDC grids against DC fault currents, the development of very fast breakers is crucial. This study proposes a DC fault current limiter and breaker, which is able to protect the HVDC system/grid in a very fast and safe manner. The main goal of this study is to enhance the performance of already in the market hybrid DC circuit breakersincluding the magnitude of fault current and breaker operation speed. In the proposed HVDC fault current limiter and breaker, the fault current is limited in two stages by an inductive and resistive current limiter, which drastically decreases the main breaker dissipated energy. The functionality of the proposed HVDC fault current limiter and breaker is mathematically analysed, and then verified by PSCAD and Matlab/Simulink. Finally, simulation results are validated by scaled-down laboratory examinations.

A New Testing Method for the Diagnosis of Winding Faults in Transformer

In this article, a new testing method for the diagnosis of winding faults based on the resonant frequency of the transformer is proposed. The system that consists of the high-voltage dc power and high-voltage insulated gate bipolar transistor (IGBT) could charge the transformer periodically. The response measured from the bushing of the winding is the oscillating wave that can be used for evaluating the status. Carrying out the new test on a 220-kV three-winding, three-phase transformer in the field, the tests of insulation and the winding have been completed in one test. The calculated frequency verifies the feasibility and applicability of the method in theory and the voltage does not affect the resonant frequency in the test. The three-winding, three-phase model transformer was built to simulate the various parameters of the power supply, which proves that the features of the oscillating waves are brought about by the properties of the transformer. Also, the new testing method provides a new opportunity to do parameter identification of axial displacement and short-circuit (SC) fault. The abovementioned research shows that the proposed method can conduct the test of winding and insulation in one test for a short time, which proves a reference in the field.

High voltage DC power distribution: a panoramic view

"High voltage DC power systems (HVDC) provide essential technical advantages in relation with the AC classical distribution networks: increasing the capacity and the stability in a natural and efficient way, simultaneously with the decoupling of some local disturbances that may occur in their subsystems and the easy interconnection of power AC grids with different parameters. In addition, the increased share of renewable energy sources and the fact that their production takes place in concentrated areas, often away from the consumption areas, require the existence of distribution facilities in the field of GW power levels, with flexible connectivity possibilities. The paper presents general aspects regarding the configuration and the main components of a HVDC power system, implementation in several representative applications. "

A Comprehensive Design of the Thyristor-Based Crowbar for Vacuum Tube High-Voltage DC Power Supplies

High-voltage power supplies (HVPSs) are widely used to drive vacuum tubes, inherently susceptible to vacuum arc faults. Owing to the considerable cost of vacuum tubes, the HVPS should enjoy a reliable, fast protection mechanism. A common protection mechanism against vacuum arc faults is the shunt crowbar. The crowbar diverts the energy stored in the elements of the HVPS through itself as a parallel path, thereby protecting vacuum tubes from irrecoverable damages. Among all types of the shunt crowbar, the thyristor-based crowbar along with the fault current limiter (FCL) resistors attracts more attention because of its more reliable operation. The absence of the comprehensive design procedure providing an insight into selecting the key components of the crowbar is strongly felt. This article presents a comprehensive design procedure for selecting these components. All constraints which should be satisfied by the protection mechanism and key components are elaborated. By doing so, the upper and lower limits of the FCL resistors, the thyristor specifications, and their series inductance are specified. It is shown that thyristors with high nominal peak current cannot contribute to the operation of the crowbar. The intersection area of the constraints and optimum values are determined for one case study. The simulations and experimental tests are exploited to evaluate the effectiveness of the presented design procedure.

A Novel High-Frequency Bipolar Pulsed Power Generator for Biological Applications

High-frequency bipolar high-voltage pulsed electric field can be used in tumor ablation to uniform the electric field distribution in the ablated region and inhibit muscle contraction effectively. Developing a high-frequency bipolar pulsed power generator (HBPPG) with wide range of specifications, such as voltage magnitude, waveform, repetition rate, and pulsewidth, is of great significance for promoting the clinical application of irreversible electroporation. Hence, in this article, a novel modular high-voltage HBPPG circuit topology is proposed for such application. Each module consists of an H-bridge and an isolated inductor. Theoretical analysis, simulation, and experimental results show that this generator perfectly combines the advantages of solid-state Marx and bridge circuit, with high stability and redundancy. The pulse frequency, pulse duration, and waveform can be flexibly adjusted by a controller software algorithm according to load parameters. The viability of the proposed HBPPG is demonstrated by PSpice simulation and equal-scale prototype. The key parameters of the developed HBPPG are as follows: voltage amplitude up to ±10 kV with 500 ns-5 μs pulsewidths, 500 kHz within the burst, and 10 kHz within the continuation limited by the input high-voltage dc power supply. All the pulse parameters can be programmed arbitrarily.