Current Commutation Process Research Articles

A fuse‐based DC circuit breaker with vacuum interrupter enhanced by an external transverse magnetic field

AbstractDue to the increasing power system capacity, the interruption of large fault currents has gradually become a major challenge in power systems. At the moment, such currents are interrupted mainly via circuit breakers based on the method of active current commutation. However, these types of circuit breakers tend to be costly and oversized. One possible alternative—a fuse‐based circuit breaker with current commutation process enhanced by an external transverse magnetic field (ETMF)—is proposed by the authors. Its main advantage lies in the fast current commutation achieved by an ETMF‐enhanced three‐stage increase of the vacuum arc voltage. The study of the current commutation process is mainly represented by the authors, and the influencing factors of the current commutation—contact opening speed and ETMF current—are discussed. At last, the proposed circuit breaker is verified by an experiment, whose results show that a short‐circuit current of 42 kA can be interrupted within just 2 ms.

Development of a Hybrid Fault Current Limiter Using Liquid Metal for Large Capacity MVdc Power Systems

A hybrid fault current limiter (FCL) for medium voltage direct current (MVDC) power systems is introduced in this paper. It achieves low operation loss and high current limiting resistance through the combination of a fast mechanical switch, a magnetic induction module and a number of liquid metal units (LMUs). Firstly, the parameters of the magnetic induction module are designed to achieve a desired fault current commutation process. Then, the working principle of LMU is introduced, and its resistance properties corresponding to the liquid metal arc are studied in detail. Equations are deduced to model the V-I characteristic of LMU. Thus the current limiting performance of the topology can be simulated. To verify the feasibility of the FCL, a 5-kV/5-kA prototype is developed and laboratory tests are implemented. Comparisons with other FCLs are also conducted to demonstrate the advantages of the proposed one. It is concluded that the prototype provides the basis for further commercial product development.

Technical Assessment on Self-Charging Mechanical HVDC Circuit Breaker

High-voltage DC (HVDC) circuit breaker is the necessary equipment for multiterminal HVDC grids, which is a prospective power transmission method in the future. Therefore, the research about HVDC interruption ushered in an explosive development in recent years. The mechanical DC circuit breaker based on the precharged capacitor for current commutation and interruption is considered to be one of the most promising HVDC interruption solution. However, the commutation capacitor requires a complicated precharging circuit, especially in high-voltage applications, which brings a great challenge to the promotion of mechanical interruption solution. In this article, a novel self-charging mechanical HVDC circuit breaker is proposed. It utilizes the induced voltage generated by part of current limiting reactor to adaptively charge the commutation capacitor under different fault current conditions without extra auxiliary charging circuit. By investigating the influence of capacitance and inductance on the charging time and current commutation process, the optimized parameters are determined. Then, the breaking performance of proposed HVDC breaker under different rising rates of fault current is evaluated in a two-terminal HVDC system. Finally, a low-power prototype is developed to verify the feasibility of the proposed topology and an improved scheme for rated current breaking is discussed.

Arc Characteristics of Ultra-Fast Opening Switching Contacts in Hybrid Breakers

A mechanical switch can be used instead of a power electronic load commutation switch in orderto reduce the losses during normal power flow in standard hybrid DC circuit breakers. The success of current commutation in such hybrid breakers depends on the arc voltage formed across the contacts in the mechanical switch. The behaviour of rapidly elongated, wall constricted arcsgenerated during the opening of an ultra-fast mechanical switch in the air is studied here. The voltage-current characteristics of the generated arcs are obtained for steady state contact opening velocities of 6, 11 and 21 m/s. It is found that the arc voltage at a given current and contact separation increases with the contact opening velocity. It is shown that stationary,zero-contact-velocity characteristics can not be used to accurately quantify the voltage build-up in fast elongating arcs in hybrid breakers. A best-fitting black-box equation for the dynamic arc characteristics is presented for the tested velocities. The obtained voltage-current characteristics are used as input to simulate the current commutation process in a 12 kV hybridDC circuit breaker case-study. Different scenarios of current commutation failure related to the arc voltage build up are identified. It is shown that these failures scenarios can be avoided by increasing the contact opening velocity.

Research on Influence Factors and Acceleration Methods of Current Commutation

The vacuum interrupter is widely used due to the advantages of no arc-extinguishing medium and high insulation strength. However, the arc voltage generated by the commonly used CuCr contacts is low. In hybrid DC circuit breakers (DCCB), hybrid automatic transfer switches (ATS), medium voltage compound switches and other fields, it is difficult to rely on vacuum arc to complete natural commutation, which restricts the development of hybrid switches. In order to understand the current commutation process deeply, the influence of internal and external factors on the current commutation is analyzed by experiments. The coupling mathematical model of arc-commutated branch is established. The criterion for the success of current commutation is summarized. The parameters of the arc model are reconstructed through repeated breaking experiments to explore the influence of internal factors on the arc characteristics. Based on this, the influence law of arc current, contacts gap and transverse magnetic field (TMF) is analyzed. An acceleration method of current commutation is proposed. A prototype for accelerating experiments with an electromagnetic repulsion mechanism and TMF is developed. The commutated branch equivalent to practical applications is built. The experimental results show that the commutation time is effectively shortened and meets the requirements of practical applications through the acceleration method, which provides new thought for the development of hybrid switches.

Simulation Analysis of Main and Arcing Contact Current Commutation Process in SF6 Circuit Breaker

In order to study the current variation characteristic and its influencing factors of the main and arcing contact during switching and opening process of high voltage circuit breaker, it is necessary to calculate the current commutation process. Firstly, the current formula in the commutation process was obtained based on the circuit model of current commutation. Secondly,based on the theoretical model of switching arc, the MODELS module and language were used to simulate the resistance variation characteristics of piecewise time-varying arc model. Finally, a simplified model of the SF6 circuit breaker arc quenching chamber was established in ATP-EMTP, and each calculation parameter was selected. The current commutation process was calculated by comparing the effect of main contact resistance and arcing contact resistance on current commutation time. It was found that the effect of the contact resistance on the current commutation time was consistent with the contact variation trend. But the effect of main contact resistance on current commutation time was small, while that of arcing contact was large.

Influence of Paralleling Dies and Paralleling Half-Bridges on Transient Current Distribution in Multichip Power Modules

This letter addresses the transient current distribution in the multichip half-bridge power modules, where two types of paralleling connections with different current commutation mechanisms are considered: paralleling dies and paralleling half-bridges. It reveals that with paralleling dies, both the high-side and low-side paralleled devices experience a similar transient current imbalance due to the mismatched stray inductance. However, with paralleling half-bridges and with the same mismatched stray inductances, the high-side paralleled devices have much smaller transient current imbalance, the cause of which is found be to the current commutation process. Theoretical analysis based on the circuit modeling and current commutation process elaborates the findings, which are then confirmed by experimental results.

An Overlap-Time Compensation Method for Current-Source Space-Vector PWM Inverters

In voltage-source inverters, it is necessary to add the dead time between gating signals of the upper and lower switches to prevent short circuit in a phase leg. But in current-source inverters (CSI), due to the large series inductor in dc link, it is necessary to add the overlap time in gating signals of switches during the commutation process for avoiding voltage spikes generated by the intermittent dc current. However, the overlap time will cause negative influence in the output current waveform. In this paper, the current commutation process of CSI within a carrier period is investigated, which shows that the overlap time can cause output-current-vector errors. The output-current-vector errors are then analyzed, which are equivalent to a superposition and introducing additional low-order harmonics in the output current waveform. The relationship between harmonic distortion and the overlap time is derived. An overlap-time compensation method is then proposed, which compensates the dwell time of vectors according to the relations of voltages at the ac side of the inverter. The proposed overlap-time compensation method can effectively decrease the current harmonics introduced by the overlap time and improve the output current of the inverter. Simulation and experimental results are finally provided to verify the feasibility and validity of the proposed method.

Effects of leakage inductance on the input current of double star diode rectifier with active inter-phase reactor

An active inter-phase reactor（AIPR）is often employed to inject triangle current to improve the input current quality of double star diode rectifier. Due to the existed leakage inductance of transformer, the input current harmonics suppression ability of the injected triangle current would be weaken. In this paper, the current commutation process of the double star diode rectifier with AIPR is analyzed initially. Then, according to the relation between the input current and output current of the double star transformer, the relation between the leakage inductance and the input line current of double star diode rectifier with AIPR is established. Such factors like the input current THD, the input current lag angle and power factor of the double star diode rectifier with AIPR, their relations with the leakage inductance are also obtained. The theoretical analysis demonstrate that the leakage inductance increase the input current THD and lag angle. It indicates that the leakage inductance decrease the displacement factor and power factor. To ensure the input current THD is less than 5% and the power factor is more than 0.998, the leakage inductance factor KLs should be less than 0.22. Simulation results verify the theoretical analysis.

An Integrated Multiport Power Converter With Small Capacitance Requirement for Switched Reluctance Motor Drive

This paper presents an integrated multiport converter with capacitance reduction for a switched reluctance machine (SRM). The conventional drive for the SRM is based on an asymmetrical H-bridge which needs large capacitor on the dc bus to absorb the transient energy caused by current commutation. The proposed topology consists of a multiport converter which introduces the dc bus capacitor as an extra port in addition to the input port and is integrated based on the switch multiplexing technique. With such a converter, the required capacitance can be reduced significantly by allowing an increase of the voltage ripple on the dc bus. In addition, the current commutation process can be accelerated with the high-voltage dc bus because the dc bus voltage is adjustable. The requirement of capacitance in an asymmetrical H-bridge and the proposed topology is analyzed in detail. The corresponding control method for the presented converter is introduced briefly as well. Simulation results in MATLAB/Simulink and experimental waveforms verified the feasibility of the proposed topology and its superior performance as compared with the asymmetrical H-bridge converter.

Discharge Process of the Multiphase Air-Core Compulsator-Based Railgun Systems

Along with the ever-increasing requirement of power and energy density in the electromagnetic launch field, the air-core compulsator has been the research focus for the last two decades. However, when considering the multiphase air-core compulsators designed for railguns, no existing published papers have investigated the different discharge processes and different performances caused by different phase numbers. This paper has investigated the different performances influenced by the phase number of the air-core compulsator. The current commutation is of great importance especially in the fast electromechanical energy conversion. The current commutation and pulse regulation in the discharge process of the multiphase air-core compulsator have been studied in detail. Three different railgun systems have been discussed in which a three-phase, a four-phase, and a novel five-phase compulsator are adopted. Besides, three sets of corresponding parameters have been designed and proposed for simulation under the premise that all compulsators have the same volume and weight. Different from the traditional applications in which the current commutation is always avoided, the key point in this paper is the utilization of the current commutation process. A new idea for the design of the phase number of the air-core compulsator is presented. The conclusion is pioneering and instructive to the design of the multiphase compulsator for railgun systems.

Investigation of DC hybrid circuit breaker based on high-speed switch and arc generator.

A new design of DC hybrid circuit breaker based on high-speed switch (HSS) and arc generator (AG), which can drastically profit from low heat loss in normal state and fast current breaking under fault state, is presented and analyzed in this paper. AG is designed according to the magnetic pinch effect of liquid metal. By utilizing the arc voltage generated across AG, the fault current is rapidly commutated from HSS into parallel connected branch. As a consequence, the arcless open of HSS is achieved. The post-arc conducting resume time (Δ tc) of AG and the commutation original voltage (Uc), two key factors in the commutation process, are investigated experimentally. Particularly, influences of the liquid metal channel diameter (Φ) of AG, fault current rate of rise (di/dt) and Uc on Δ tc are focused on. Furthermore, a suitable Uc is determined during the current commutation process, aiming at the reliable arcless open of HSS and short breaking time. Finally, the fault current breaking test is carried out for the current peak value of 11.8 kA, and the validity of the design is confirmed by the experimental results.

Influence of interphase transformers and ac line reactances on the thyristor bridges' current sharing in 18-pulse rectifiers

In this paper, computer simulation models of two different topologies of 18-pulse rectifiers are presented. Each rectifier topology consists of three parallel, three-phase six-pulse full-bridge thyristor converters connected via interphase transformers. The influence of the interphase transformer's layout and AC line reactances variations on the particular thyristor converter current sharing is analysed. Various configurations of 18-pulse rectifiers are examined by simulating operation with symmetric input voltage supply, as well as in the cases of different levels of voltage supply asymmetry, at unequal input conductors impedance, and at different thyristor voltage drops. According to computer simulation results, an optimal 18-pulse rectifier circuit topology is recommended. The optimal topology has three AC line reactances with two input current-balancing interphase transformers. These added AC reactances are also involved with the current commutation process between thyristors. Application of the recommended optimal topology of an 18-pulse rectifier could enable the reduction of the AC line reactances number from nine to three, while the dissipated power of the AC/DC converter's most loaded thyristor could be reduced by approximately 11 %. During the simulation of the nominally loaded 18-pulse rectifier, in all considered cases the effective value of the output signal ripple below one promil of total current and voltage values has been achieved.

An All-SiC Three-Phase Buck Rectifier for High-Efficiency Data Center Power Supplies

The low power losses of silicon carbide (SiC) devices provide new opportunities to implement an ultra high-efficiency front-end rectifier for data center power supplies based on a 400- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX"> ${\rm V}_{\rm dc}$</tex></formula> power distribution architecture, which requires high conversion efficiency in each power conversion stage. This paper presents a 7.5-kW high-efficiency three-phase buck rectifier with 480- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{V}_{{\rm ac}, {\rm rms}}$</tex></formula> input line-to-line voltage and 400- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm V}_{\rm dc}$</tex></formula> output voltage using SiC MOSFETs and Schottky diodes. To estimate power devices' losses, which are the dominant portion of total loss, the method of device evaluation and loss calculation is proposed based on a current source topology. This method simulates the current commutation process and estimates devices' losses during switching transients considering devices with and without switching actions in buck rectifier operation. Moreover, the power losses of buck rectifiers based on different combinations of 1200-V power devices are compared. The investigation and comparison demonstrate the benefits of each combination, and the lowest total loss in the all-SiC rectifier is clearly shown. A 7.5-kW prototype of the all-SiC three-phase buck rectifier using liquid cooling is fabricated and tested, with filter design and switching frequency chosen based on loss minimization. A full-load efficiency value greater than 98.5% is achieved.

Influence of the Current-Limiting Resistance on the Arc Commutation Process Across the Gap of a Separated Arc Runner

With measuring the arc current, arc voltage and arc images, the high-current air arc commutation process across the separated electrodes was investigated. It shows that the existence of a short stable arc in the gap may increase the current commutation time. According to the energy balance of the arc column, the conditions to maintain the short stable arc were introduced and the effects of the current limiting resistance on the current commutation process were discussed.

Numerical simulation method for the slip power recovery system

A numerical simulation method for the slip power recovery system is presented. The dq induction-machine model, using flux linkages as state variables is used. This leads to a simple and efficient computer program. The diode bridge rectifier is modelled using three switching functions that are determined by the sign of the corresponding AC currents. The model obtained is very simple, and accurately represents the three-phase diode bridge rectifier including the current commutation process. To merge the models of the induction machine and the diode-bridge rectifier, no difficulties arise when a direct-voltage intermediate circuit is present. When a direct-current circuit is used in the intermediate circuit a model of the whole ‘induction machine and diode-bridge rectifier’ must be used. Park&apos;s variables can be used in this case, also. The operations performed to model the system are equivalent to assuming that the diode bridge rectifier and the DC circuits are transformed into a nonlinear circuit connected to the rotor terminals. MATLAB/simulink is used to integrate the equations. Experimental and simulated results are presented and compared showing good accuracy.