The phase-to-ground admittance in distribution networks is asymmetric. This asymmetry is aggravated by the arc suppression coil, resulting in zero-sequence overvoltage. The magnitude of zero-sequence ...overvoltage can exceed the line-to-ground voltage, endangering the operation of electrical equipment. Moreover, after the occurrence of a single-line-to-ground fault, the change law of the three-phase voltage is affected by the zero-sequence overvoltage, leading to misjudgment of the fault phase. Accordingly, this paper proposes a fault phase selection method based on active current injection that can adapt to asymmetric distribution networks. The fault phase is selected by injecting current and calculating the equivalent power supply voltage of the faulty line without increasing the ground-fault current. The high sensitivity of the proposed fault phase selection method was verified for high impedance faults through software simulations and prototype experiments. Moreover, the zero-sequence overvoltage can be suppressed by a single-phase flexible arc suppression device during the normal operation of distribution networks. The ground-fault current can be quickly suppressed at different ground-fault locations and resistance values, ensuring the extinguishment of the ground-fault arc.
As an essential apparatus in resonance grounding systems, the arc suppression coil is widely used in rejecting the single‐line‐to‐ground (SLG) fault of distribution networks. However, the resistive ...ground‐fault current cannot be compensated by an arc suppression coil (ASC). As a novel active arc suppression device, the hybrid flexible arc suppression device (HFASD) composed of ASC and flexible arc suppression device (FASD) can eliminate the capacitive component of ground‐fault current and the resistive component of ground‐fault current. After the SLG fault occurs, the FASD from stand‐alone mode to grid‐connected mode may lead to switching transients, affecting the stability of distribution networks. The soft grid connection (SGC) strategy can achieve low or without transient response during the grid synchronization of FASD to the grid. Thus, the HFASD based on SGC strategy and segmented proportional‐integral‐differential (SPID) and second‐order generalized integrator phase‐locked loop (SOGI‐PLL) control method is proposed for rejecting the current and voltage overshoot responses during the process of grid synchronization of FASD in this paper. Simulation and experimental results verify the effectiveness of the proposed method, and the benefit of the proposed method is indicated in comparison with the non‐SGC (NSGC) strategy.
•Single-phase flexible arc suppression device (SFASD) based on cascaded H-bridge topology.•Backstepping control and second-order generalized integrator phase-locked loop (BSC-SOGI-PLL) method is ...proposed.•BSC-SOGI-PLL and BSC method applied to SFASD are compared, respectively.•Decentralized control is applied to SFASD.•SFASD based on BSC-SOGI-PLL method rejects the ground-fault current in experiment testing.
The single line-to-ground (SLG) fault is a research focus, considering it is amongst the top frequent occurrences of faults in distribution systems. The neutral point treatment is crucial for continuous safe operation of distribution systems. However, the traditional arc suppression coil cannot compensate for the active component in ground current. Therefore, we present a single-phase flexible arc suppression device (SFASD) based on backstepping control and second-order generalized integrator phase-locked loop (BSC-SOGI-PLL) method. The SFASD with a cascaded H-bridge (CHB) topology is connected to the neutral point of distribution systems for eliminating the ground current. The comparisons between the BSC-SOGI-PLL and the BSC method concerning the effect of arc suppression are discussed. The effectiveness of the proposed SFASD based on the BSC-SOGI-PLL components for arc suppression is verified on the scale-down experimental platform.
The active distribution networks have a tendency to develop towards hybrid AC-DC systems constructed by power electronics, the magnitude and direction of power may change randomly at any time, making ...the usual protection potentially insensitive, raising the negative impacts of single-phase ground (SPG) fault which accounts for the majority of all faults that occurred in medium-voltage (MV) distribution networks in the past. The zero-sequence current in the impedance induced between the lines and ground will pass through the SPG fault branch as fault current. This study transfers the flow path of the zero-sequence current from the SPG fault branch to the power electronic branch connected between the faulty phase and ground involved in the construction of hybrid AC-DC system, thereby limiting SPG fault branch current and reducing fault node potential. This helps to suppress fault arc and provides engineers with safe conditions to clear faulty elements from the SPG fault branch. The power electronic carries this zero-sequence current instead of SPG fault branch and therefore absorb energy from the distribution networks in the same way as SPG fault, but the energy is not lost but routed back to the hybrid AC-DC system for reuse. Simulations and experiments validate the proposal.
•Flexible arc suppression device (FASD) based on cascaded H-bridge topology.•Improved distributed commutations modulation (IDCM) is proposed.•IDCM and PSCPWM applied to FASD are compared, ...respectively.•Decentralized control is applied to FASD.•FASD based on IDCM mitigates the fault current in experiment testing.
Because of the hazard of single-phase-to-ground faults on distribution networks for human security and device insulation, it is important for the ground-fault current to be eliminated by an arc-suppression device. However, owing to their shortcomings, passive arc-suppression devices cannot compensate the ground-fault current fully. Therefore, active arc-suppression devices have been studied. The flexible arc-suppression device (FASD) with a cascaded H-bridge (HB) topology is one type of active arc-suppression device. An FASD connected to a bus bar of distribution networks is applied to mitigate the ground-fault current. Owing to the high voltage and large current during the ground fault, a large number of HBs are required for the FASD. To modulate the HBs, an improved distributed commutations modulation method, which is combined with the flexible arc-suppression method, is proposed. The proposed modulation strategy aims to minimise the error between the reference signal and the tracking signal during each sampling period. Finally, the proposed strategy is validated via simulations and experiments to confirm its effectiveness for the FASD.
A Petersen coil was used as a passive arc-suppression device (ASD) to mitigate ground-fault current when a single-phase-to-ground fault occurred in distribution networks. However, passive ASDs cannot ...compensate for the active and harmonic components of ground-fault current. Furthermore, a massive residual ground-fault current would endanger human life and the reliable operation of distribution networks. To overcome the shortcomings of passive ASDs, a three-phase flexible ASD (FASD) with a three-phase cascaded H-bridge topology was presented. A three-phase FASD connected to a bus bar of distribution networks was employed to compensate for the ground-fault current. In this study, the FASD with the backstepping control (BSC) based on current-compensation principle was proposed to completely eliminate the ground-fault current. The effectiveness of the proposed FASD with the BSC method was verified using the simulation and experimental results.
•Hybrid flexible arc suppression device (HFASD) consists of Petersen coil and FASD.•Twice injection current method is proposed for insulation parameters measurement.•SOGI-PLL algorithm and twice ...injection current method is applied on HFASD.•Proposed method is verified on MATLAB/SIMULINK software and physical systems.
As one kind of active arc suppression devices, the hybrid flexible arc suppression device (HFASD) with current-based arc suppression method can eliminate the ground-fault current during the single-line-to-ground (SLG) fault. One of the most important aspects for current-based arc suppression method is the insulation parameters measurement. The reference current of current-based arc suppression method is calculated by the insulation parameters, including the ground capacitance and ground leakage conductance. For the sake of obtaining high-precision reference current of current-based arc suppression method, the insulation parameters should be measured accurately. However, the most of existing methods of insulation parameters measurement should increase the additional device cost and measure inaccurately. In this paper, HFASD based on second-order generalized integrator phase-locked loop (SOGI-PLL) algorithm and twice injection current method is proposed to measure the insulation parameters under the normal condition of distribution networks. The simulation and experimental results verify the effectiveness of the proposed method under different influence factors.
•The flexible compensation device is based on the cascaded H-bridge topology and applied to suppress the ground fault .•A double-loop passivity-based control method is proposed. Simulation and ...experiment verify the effectiveness of the method.•The current and voltage arc suppression method work in parallel, which enhances the compensation effect of the device.
Aiming at the problem that the existing single-phase-to-ground fault flexible compensation device has low compensation accuracy, long response time, and needs DC side power supply, a flexible compensation device based on double-loop passivity-based control is proposed. Firstly, the topology and working principle of the device are analyzed. And a compensation current distribution method of the bridge arm is proposed. Secondly, a double-loop passivity-based controller is designed. Finally, the proposed method is verified by MATLAB/Simulink software and 10 kV physical simulation system of distribution network. The comparisons between double-loop passivity-based control, passivity-based control, and proportional integration control is discussed. The result shows that the proposed method can accurately and rapidly compensate the fault current.
Traditional arc-suppression devices have a weak effect on the arc-extinguishing result of earth fault because of increased active and harmonic components of fault current. To solve the problem, in ...this paper, a flexible arc-suppression device based on a three-phase cascaded H-bridge (CHB) converter with auxiliary sources is further developed; on this basis, an arc-suppression method based on the improved finite control set model predictive control is proposed. The proposed approach, which uses a combination of two voltage levels in a sampling period to reduce the steady-state current error, controls the CHB converter to inject compensation current into the distribution network. Taking into account the reduction of switching losses and balancing heat in each H-bridge cell, a novel method that causes the switching transitions to be distributed evenly among the H-bridge cells is proposed to select the optimal switching combination. The tracking capability of the improved control method is analyzed, and the parameters affecting the arc-suppression performance are obtained. The simulation and experimental results show that the proposed method achieves an excellent performance of suppressing fault current and extinguishing arc. Moreover, the balance of switching transitions is also achieved.
•Flexible fault eliminator (FFE) is based on the cascaded H-bridge topology.•FFE is applied to suppress the ground fault current.•CHB inverter is based on the active disturbance rejection control ...(ADRC) method.•Current-based on the ADRC method is proposed to limit the ground fault current.•ADRC, BSC, and PID control methods applied to FFE are compared, respectively.
Among the possible fault types in the distribution networks, single-line-to-ground (SLG) fault has the highest probability. The SLG fault current and arc can easily cause personal injury and death. This study proposed a flexible fault eliminator (FFE) based on a cascaded H-bridge topology to limit the SLG fault current and extinguish fault arc in the medium voltage distribution networks. An active disturbance rejection controller for the FFE was designed to improve the current limiting performance of FFE in the presence of insulation parameter measurement errors and sampling errors from potential/current transformers. The controller with good robustness adapts to different ground fault resistances. In addition, a soft grid-connection control scheme based on bistable smooth switching was proposed to avoid the injected current impulse of FFE at the moment of grid connection. Simulation and experimental results showed that the fault current was limited to a small enough value and the fault arc was extinguished effectively. The output current and voltage of FFE at the time of grid connection were in a smooth transition, avoiding the impulse on the power grid system. The FFE can eliminate the SLG fault flexibly and stably.
PDF
