Query: Commutation Failure

title: A Predictive Control Strategy for Mitigation of Commutation Failure in LCC Based HVDC Systems
abstract: High voltage direct current (HVDC) systems are being widely employed in various applications because of their numerous advantages such as bulk power transmission, efficient long distance transmission, and flexible power flow control. However, line commutated converter based HVDC systems suffer from commutation failure, which is a major drawback, leading to increased device stress and interruptions in transmitted power. This paper proposes a predictive control strategy, deploying a commutation failure prevention module to mitigate the commutation failures during ac system faults. The salient feature of the proposed strategy is that it has the ability to temporarily decrease the firing angle of thyristor valves depending on the fault intensity to ensure a sufficient commutation margin. In order to validate the performance of the proposed strategy, several simulations have been conducted on the CIGRE Benchmark HVDC model using PSCAD/EMTDC software. Additionally, practical performance and feasibility of the proposed strategy are evaluated through laboratory testing, using the real time Opal RT hardware prototyping platform. Simulation and experimental results demonstrate that the proposed strategy can effectively inhibit the commutation failure or repetitive commutation failures under different fault types, fault impedances, and fault initiation times.

title: Commutation Failure Prediction Method Considering Commutation Voltage Distortion and DC Current Variation
abstract: Commutation failure (CF) at the inverter side is one of the most common failures in the line commutated converter based high voltage direct current (LCC HVDC) system. Effective prediction of CF helps to formulate and implement protection measures timely. Since abnormal commutation voltage and DC current are the main reasons causing CF, these two factors should be fully considered in CF prediction. In this paper, to consider the effect of commutation voltage distortion, the time domain response of the commutation voltage Fourier coefficient is deduced based on the first order circuit response. To consider the effect of DC current variation, the time domain response of the DC current is derived by superimposing its steady state component and transient component, respectively. Based on these two predictive value, the extinction angle (EA) during the commutation is calculated according to the commutation voltage time area, and the criterion based on EA is proposed to predict the occurrence of CF. The simulation results of the test system built in the PSCAD/EMTDC demonstrate the effectiveness and validity of this method.

title: A Calculation Method of Pseudo Extinction Angle for Commutation Failure Mitigation in HVDC
abstract: This letter presents a novel pseudo extinction angle (PEA) for the HVDC inverter, as well as its calculation method. The proposed PEA extends the measured extinction angle (EA) into a real time calculated value. As a result, the non measurability of the EA between two adjacent EA updating times, which is likely to cause commutation failures (CFs) can be avoided effectively. Simulation results verify the validity of the proposed PEA calculation method and prove the capability of the PEA to mitigate the CFs.

title: Dynamic Phasor Modeling of LCC HVDC Systems: Unbalanced Operation and Commutation Failure
abstract: This paper develops a dynamic phasor model of a line commutated converter high voltage direct current (LCC HVDC) system that includes unbalanced operation and commutation failure. This model is beneficial in studying the behavior of the HVDC systems under asymmetrical faults, and it complements the conventional transient simulation based methods. Equally, importantly, the model includes the representation of commutation failure that may arise as a result of severe faults. Due to its selectivity of the considered harmonics, the developed model has markedly less computational intensity than an electromagnetic transient (EMT) simulation model. This gives the model a distinct advantage in the study of large signal transients of the LCC HVDC systems, particularly where repetitive simulations are required. Validation of the proposed model is done using a detailed EMT model of the CIGRE monopolar LCC HVDC benchmark.

title: Characteristics of commutation failure based on fault recording
abstract: Commutation failure of the high voltage direct current (HVDC) transmission system is common fault in a converter station. The fault recording in one converter station when commutation failure caused by the disturbance of the AC system was collected, and the turn off angle of valves, zero crossing offset, and landing amplitude of bus voltage were calculated and statistically analysed. The results suggested that, in the case of commutation failure, the turn off angle of the 82% of cases was 90% cases, and the average was ~4.6% The number of cases, whose zero sequence voltage peaks was <50 kV, accounted for 97% of the total. The results will provide basic data for analysing the main influencing factors of commutation failure and setting up countermeasures for the HVDC system.

title: Research on commutation failure of Jinsu DC transmission project caused by a complex AC fault
abstract: Commutation failure is an important factor on safe and stable operation of the receiving end power grid for high voltage direct current (HVDC) project. A commutation failure event in Jinsu DC transmission project caused by a complex AC failure was taken as background, process of fault and action sequences of protection was introduced, and the reason of the commutation failure and protection action was analysed from principle. Real time digital simulation (RTDS) was connected to the true type device of ultra high voltage direct current (UHVDC) control and protection to form a closed loop simulation platform. The commutation failure event was inversed, and the simulation result was compared with the actual recorded wave. The results show that abnormal AC voltage leads to the commutation failure.

title: A Fault Current Limiting Approach for Commutation Failure Prevention in LCC HVDC Transmission Systems
abstract: Commutation failure is one of the most frequent failures in line commutated converter based high voltage direct current (LCC HVdc) systems which may lead to the outage of HVdc links, and thus affect the performance of the power system. Most commutation failures are caused by voltage reduction due to ac system faults. In this paper, a commutation failure prevention module (CFPM) is developed, which inserts the optimal value of resistance proportional to the reduced extinction angle in series with the fault current path using a simple switching method. When a fault occurs at the inverter ac side, a self turn off switch starts switching with a pre specified frequency and controlled modulation index, which limits the fault current to the desired value and inhibits commutation failure. The salient feature of the proposed CFPM is that it is fully controllable. In addition, despite the available controller modification methods which are not effective for low impedance faults, the proposed CFPM can prevent commutation failure regardless of the fault severity. The practical performance and feasibility of the developed CFPM is validated through laboratory testing, using the real time Opal RT hardware prototyping platform. The experimental results demonstrate that the proposed strategy can effectively eliminate the commutation failure or repetitive commutation failures under different fault types.

title: Fast Evaluation of Commutation Failure Risk in Multi Infeed HVDC Systems
abstract: This paper presents a fast and reliable method to evaluate risk of single or multiple commutation failures for multi infeed HVDC systems following faults occurring at the receiving end ac system. First, a fast calculation method of multi infeed interaction factor, describing the interactivity and mutual impact between two inverter AC buses on is proposed. It is then refined to being the AC DC system voltage interaction factor (ADVIF) to represent the relationship in bus voltages between inverter and AC buses at the re ceiving end systems. Then, a critical AC DC system voltage interaction factor (CADVIF) based on the minimum extinction angle criteria is proposed. By calculating and comparing ADVIFs and CADVIFs, which can be obtained quickly, it is possible to identify AC buses that, if a fault occurs, would cause commutation failures at one or more HVDC systems. The validity and accuracy of the proposed approach are demonstrated by comparing with simulations results using a two infeed HVDC test system and an actual large power grid.

title: Evaluation of Commutation failure Risk for HVDC Caused by Harmonic Voltage
abstract: The commutation failure is one of the most common faults in high voltage direct current transmission (HVDC) systems. The research on the HVDC commutation failure has made some achievements at home and abroad. However, the influence of harmonic on the commutation failure of HVDC has not been studied thoroughly. Based on the commutation process of HVDC and the commutation voltage time area analysis, a harmonic influence factor is derived, and the influence of harmonics on the commutation process in HVDC is quantitatively analyzed. The evaluation index of the risk of commutation failure due to harmonics, which is defined as the harmonic influence superposition Esup, is proposed, and a method using Esup to evaluate the risk of commutation failure caused by harmonic voltage is given consequently. Finally, based on the PSCAD/EMTDC electromagnetic transient simulation platform, the proposed evaluation indicators are simulated and verified.

title: A Control Strategy for Suppressing HVDC Continuous Commutation Failure Risk under Weak AC State
abstract: The HVDC receiving end system with inverter short line fault is in the weak AC state. At this time, the inverter is prone to continuous commutation failure. And the continuous commutation failure will cause the voltage and power angle fluctuations, which seriously threatens power system security. In this paper, the mechanism of HVDC continuous commutation failure is studied. The commutation failure is divided into the transient and steady process. Then, the effects of HVDC control strategy and receiving end system reactive power support capability to continuous commutation failure are analyzed. Based on the continuous commutation failure mechanism and the actual HVDC control system, a fast decrease strategy of DC power is proposed. Finally, it is validated by the actual HVDC transmission system that the proposed fast decrease strategy of DC power is effective to suppress the risk of continuous commutation failure.