HVDC Commutation Failure Research Articles

The HVDC commutation failure mechanism impacted by harmonics and its suppression method

Harmonics are an important cause of voltage distortion, and voltage reduction and voltage distortion are the main causes of commutation failure. But most of the current research studies on commutation failure are based on the drop in fundamental voltage after a fault, and there are few reports on the impact of voltage distortion on commutation failure. Aiming to solve the above problem, this article first analyzes the generation and transmission characteristics of harmonics in AC and DC systems, as well as the coupling degree of harmonics in DC systems. Then, starting from the mechanism of the commutation process, a commutation failure analysis method based on the harmonic voltage time area is proposed. This method can quantitatively analyze the impact of different harmonics on commutation failure. On this basis, the harmonic criteria for causing commutation failure are established, and the harmonic characteristics of AC voltage when harmonics cause subsequent commutation failure are quantitatively analyzed. Finally, a preventive controller is proposed to suppress commutation failure caused by different harmonics, where the above analysis is verified by the simulations.

Comprehensive Physical Commutation Characteristic Analysis and Test of Hybrid Line Commutated Converter Based on Physics Compact Model of IGCT

In order to mitigate commutation failure of high voltage direct current (HVdc) system, a novel hybrid line commutated converter (H-LCC) based on integrated gate commutated thyristor (IGCT) and thyristor has been proposed. To verify the proposed scheme's effectiveness and correctness, the physics-based compact model of reverse blocking IGCT (RB-IGCT) and physics-based model of thyristor are established in this article. By comparing the features of physics-based model with other simulation methods, it can be observed that the former has obvious advantages. On the basis, a simulation study of proposed H-LCC based on physics compact model of RB-IGCT and physics-based model of thyristor is conducted to analyze the physical commutation characteristics comprehensively, which is verified by equivalent commutation tests. The H-LCC can mitigate commutation failure of HVdc effectively and physics-based model of H-LCC is expected to be applied in the simulation of dc grid equipment and provide reference for commutation characteristics analysis and snubber parameter optimization that need rapid and multiple simulations.

Coordinated optimization method for suppressing transient overvoltage caused by HVDC commutation failure considering large wind power integration

In order to suppress the sending end transient overvoltage caused by HVDC commutation failure considering large wind power integration, this paper proposes a coordinated optimization method for the control parameters of DC and wind power, which can suppress the sending end transient overvoltage and ensure the performance of the DC control system. By analyzing the mechanism of DC and wind power control parameters affecting the sending end transient overvoltage, and studying the influence of control parameters on the performance of the DC control system, a multi-objective and multi-equipment coordination optimization model of the HVDC transmission system considering large wind power integration is constructed. The multi-objective adaptive differential evolution algorithm is used to realize the coordinated optimization of DC and wind power control parameters based on PSCAD simulation joint invocation. Finally, through simulation and optimization in different cases, it is found that the multi-objective parameter optimization has more obvious advantages than single-objective optimization in the case of weak receiving end power grid. In addition, it is concluded that the same control parameters can be used in different wind power penetration scenarios to achieve the purpose of suppressing transient overvoltage, which verifies the effectiveness and accuracy of the method proposed in this paper.

A detection method for HVDC commutation failure based on the variation rate of commutation inductance energy

Concerning the insufficient accuracy of the criterion for identifying commutation failure in HVDC transmission systems, a new detection method for commutation failure based on the variation rate of commutation inductance energy is proposed. First, the conducting states of the converter valves in both normal commutation and commutation failure conditions are analysed, and the correlation between the differential of valve-side line current and the conducting state of the converter in different commutation scenarios is established. On this basis, combining the topologies of D/Y-bridge converters, a model to calculate the variation rate of commutation inductance energy is built. Then, considering the fault characteristics of DC current, DC voltage and valve currents, it is found that the calculated value of the variation rate of commutation inductance energy is consistent with the actual value under normal commutation conditions but inconsistent under commutation failure conditions. This allows for the construction of a criterion for identifying the commutation failure. Finally, the simulation results obtained with the RT-LAB platform verify that, the proposed method can detect the occurrence of commutation failure quickly without measuring the valve currents, and it remains accurate when dealing with commutation failure near the threshold.

Analysis and Simulation Research of Cascading Faults in AC/DC Hybrid Grid

In the development of power systems, the traditional AC power grids are gradually evolving into AC/DC hybrid grids. However, the safety of hybrid grids is threatened by cascading faults, which is a set of chain events caused by a single fault and will eventually lead to a blackout. Based on the blackout accident that happened in Brazil on March 21st, 2018, this paper analyzes the cause, mechanism, and development of cascading faults in AC/DC hybrid grids. Simulations based on PSCAD/EMTDC software have been carried out to illustrate the typical cascading fault scenario including HVDC commutation failure, DC blocking, power flow transferring, incorrect relay protection and the outage of the network. Both analysis and simulation results shows that the “strong DC weak AC” structure and unreasonable cooperation of relay protections and stability control devices are important factors of cascading faults. Finally, this paper prospects a series of protection and control technologies that are expected to solve the problem.

Optimization of dynamic reactive power devices’ coordinate operation for minimizing HVDC’s successive commutation failure based on PSO

More and more dynamic reactive power devices (DRPDs) have been put into operation to improve voltage stability in AC/DC hybrid power system. In order to make full use of these devices, this paper presented an optimization technology for multiple DRPDs’ coordinate operation in receiving-end of AC/DC hybrid power system. DRPDs’ steady-state reactive instructions are treated as optimization variables in the proposed model, while the objective is minimizing the successive times of HVDC’s commutation failure under a number of grounding faults. Power flow constraints and electro-mechanical transient process are considered simultaneously. Based on the characteristics of the model, commutation failure of HVDC under each grounding fault could be obtained by employing time-domain simulation method. Furthermore, particle swarm optimization (PSO) is used to get DRPDs’ optimal reactive instruction in steady-state. The simulation is done by considering Jiangsu power grid in eastern china, including synchronous condenser, STATCOM and UPFC. The results show that the proposed model and algorithm are corrective and effective.

Modeling and Analysis of Transient Reactive Power Characteristics of DFIG Considering Crowbar Circuit under Ultra HVDC Commutation Failure

Ultra high voltage direct current (UHVDC) transmission is an effective means of long-distance transmission of renewable power generation, which has obtained a lot of research and practical applications. The commutation failure is a common DC transmission fault, which will cause the voltage amplitude of the sending ac grid in UHVDC system to first decrease then increase. The existing transient mathematical models of the wind power generation system (WPGS) are difficult to apply to scenarios where the grid voltage changes continuously. A mathematical model suitable for commutation failure is established to analyze the transient reactive power characteristics of the doubly fed induction generator (DFIG)-based WPGS with the consideration of the crowbar circuit trigger. The correctness of the mathematical model is validated by an experiment based on the control hardware-in-loop (CHIL) platform. Based on the proposed mathematical model, the influence of the crowbar parameters on the reactive power output of the DFIG is analyzed, and the selection of crowbar parameters to suppress the overvoltage of the sending ac grid is investigated. A simulation model is built based on Matlab/Simulink to verify the overvoltage suppression effect of the proposed selection scheme.

Multi-feed System Partitioning Method Based on N-1 Preconceived Fault Set and Local Expansion Theory

In view of the fact that the AC system with multiple LCC-HVDC feeds is prone to simultaneous commutation failure, this paper proposes the scheme of grid division for the multiple feed system to isolate the coupling between multiple HVDC and reduce the risk of occurring simultaneous commutation failure. First, N-1 scan is performed on the multi-feed system to find the set of lines that can cause simultaneous commutation failure of multiple HVDC. The line with high line load rate is removed from the line set. Then, on the basis of local expansion theory, the nodes in the system are aggregated to form the initial partition. In this process, the calculation method of voltage/reactive sensitivity matrix considering PV node and LCC-HVDC is firstly given; moreover, the corresponding indexes were calculated by the node aggregation function and the partition fitness function. Finally, the results of the partition are modified by considering the circuit set and the partition short circuit ratio, and the flow chart of the partition scheme is given. The partitioning process is validated with an IEEE 39-node system as an example. The results show that the partitioning method is reasonable and solves the problem of the failure of commutation effectively.

Research on Transient Overvoltage Suppression Measures for Photovoltaics Connected to the DC Sending End in the Smart Power System for Industry 4.0

The development of smart power systems in Industry 4.0 will bring people better quality electrical energy. The photovoltaic power generation system in the smart grid for Industry 4.0 is also the focus of development. The rapid development of photovoltaic power generation systems will bring people cleaner and greener energy. However, it will cause the transient overvoltage phenomenon near the DC sending terminal when the large-scale photovoltaic plant is connected to the power grid, further bringing about a profound impact on the power grid and its security and stability. In this paper, it is proposed that the rise of transient overvoltage at the photovoltaic terminal is caused by three main factors including the reactive power surplus of DC commutation failure, the weak power grid at the sending terminal, and the control characteristics of the photovoltaic plant. Then, the coordinated control strategy of transient overvoltage is proposed, and the overvoltage control strategy of the DC transmission terminal and the photovoltaic power plant control strategy are, respectively, optimized. Finally, the influence parameters of overvoltage are analysed and the corresponding photovoltaic strategy is presented. The optimization results of photovoltaic parameters and the proposed strategies of photovoltaic power generation can effectively restrain the voltage or frequency fluctuation and power oscillation caused by HVDC commutation failure. This study promotes the development of the photovoltaic power generation system in the intelligent power system of industry 4.0.

Research on Emergency Control Strategy of Synchronous Condenser for Inhibiting HVDC Commutation Failure

As multi-infeed HVDC systems are integrated into power grid, the operation characteristics of power grid have changed significantly. The problems of the shortage of dynamic reactive power reserve and voltage support need the allocation of dynamic reactive compensation device such as synchronous condenser urgently. This paper researches the influence of installing synchronous condenser on system performance in multi-infeed HVDC power grid. Based on the analysis of the defects of synchronous condenser on HVDC commutation failure under existing conventional control mode, this paper presents the emergency control strategy and system architecture with synchronous condenser. In the end, the effectiveness of the proposed control strategy is verified based on the actual grid simulation.

Simulation of large-scale energy storage to improve high-voltage DC stability

Study on large-scale electrochemical energy storage simulation is carried out in this paper to discuss its feasibility in enhancing the stability of HVDC power transmission, thus providing a reference for large-scale energy storage planning and design in the background of global energy internet. The paper introduces the development status quo of the large-scale energy storage technology, and provides an analysis of the active and inactive power features after HVDC commutation failure by establishing a large-scale energy storage model and a HVDC power transmission system commutation failure model, thereby exploring the configuration feasibility of the large-scale energy storage technology; Then, a simulation analysis is given on the effect of large-scale energy storage on HVDC power transmission fault features; Finally, a prospect was expected towards the application tendency of large-scale energy storage in global energy internet.

Three-stage Evolution Mechanism of Multiple Stability Problems and Control Strategies of AC/DC Power System with Large-scale Wind Turbine Generators

There exists interactive evolution process of multiple stability problems of AC/DC power system with large-scale HVDC and wind power, such as voltage or frequency fluctuation and power oscillation, which can be caused by HVDC commutation failure. Further research is required on the evolution mechanism and control strategies of this kind of power system. In this paper, firstly three-stage evolution mechanism is proposed, including large-scale wind turbine generators tripping off caused by transient overvoltage, transient angle instability caused by power flow transferring in weak transmission section, and out-of-step separation caused by cross-regional power oscillation. Secondly, evolution processes and typical models of different stability problems are studied deeply. The prevention and control strategies are proposed. Finally, simulation results and analysis based on real-sized power grid in China prove the rationality and effectiveness of the proposed three-stage evolution mechanism and control strategies.

Study on the stability mechanism of the sending‐side three‐machine‐group system after multiple HVDC commutation failure

Study on the stability mechanism of the sending‐side three‐machine‐group system after multiple HVDC commutation failure

Improvement of HVDC commutation failure response based on compound phase‐shifting control

Improvement of HVDC commutation failure response based on compound phase‐shifting control

Analysis of the sending-side system instability caused by multiple HVDC commutation failure

Analysis of the sending-side system instability caused by multiple HVDC commutation failure

Fast Calculation of Power Oscillation Peak Value on AC Tie-Line After HVDC Commutation Failure

This letter proposes a fast approach to calculate the power oscillation peak value on AC tie-line after HVDC commutation failure. The proposed approach does not require modeling power system components in detail for dynamic simulation and is especially suitable for practical bulk power systems. It is useful to help operators rapidly assess the system stability margin after commutation failures. The proposed approach has been implemented on a practical system in China.

Study on the Application of a Flux-Coupling-Type Superconducting Fault Current Limiter for Decreasing HVdc Commutation Failure

Commutation failure is a serious malfunction in high-voltage direct current (HVdc) converters and is mainly caused by ac side faults, where the change of dc current during fault conditions should be given adequate attention. Employing superconducting fault current limiters (SFCLs) for an HVdc system can suppress its dc fault current’s amplitude and maintain a small rate of the dc current change, which is helpful to inhibit the commutation voltage reduction. Accordingly, introducing SFCLs may act as one possible solution to decreasing HVdc commutation failure. In this paper, a flux-coupling-type SFCL is adopted to play this role. The SFCL’s topology structure and working principle are presented first, and then its influence mechanism to HVdc commutation failure is systematically investigated. Further, considering several different fault conditions, the transient performance of a 500-kV HVdc system equipped with the SFCLs is evaluated in MATLAB. From the results, installing the SFCLs can effectively decrease the duration of the commutation failure and facilitate the fault recovery process, and sometimes a possible successive commutation failure is avoided, as a result of improving the power transmission characteristics. Finally, in view of ac loss and equipment selection, the application feasibility of the SFCL for a high-voltage/large-scale system is preliminarily discussed, and some valuable conclusions are obtained.

The Summary of HVDC Commutation Failure and Example Analysis

Commutation Failure is the common fault of HVDC, continuous commutation failure may lead to HVDC block and affect the stability of the power system. Especially in southern power grid, china, its special that the end of four HVDC system are all in Guangzhou. If the AC system occurs serious fault, all of the HVDC system may occur commutation Failure, HVDC block, even occurs large area blackout. So how to avoid continuous commutation failure and restore the stability of HVDC is important for AC and DC parallel power system. This paper based on the mechanism of commutation failure, analyze the reason of commutation failure and identification method, preventive measures. At last, this paper uses actual recorded wave to analyze the diversification of system after commutation failure.

Research on Commutation Failure of HVDC

The waveforms of the RTDS(Real Time Digital Simulator) commutation failure and ABB MACH2 system commutation failure protection have been combined to analyze the mechanism of HVDC commutation failure. Several reasons for inverter commutation failure have been found, and a detailed analysis is also been given for the missing pulse and commutation which are caused by the AC system fault. This is practical for HVDC transmission project.

Design a Fuzzy Controller to Minimize the Effect of HVDC Commutation Failure on Power System

Commutation failure, which is a very frequent dynamic event in HVDC inverters, can deteriorate the availability 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, efforts are made to lower the effect of commutation failure on the power system, and the remedy is implemented in a fuzzy controller. In order to achieve control flexibility, the output of the fuzzy controller is made appropriate by setting a self-adjusting proportional factor. The validity and effectiveness of the fuzzy controller is verified by simulation which shows that the fuzzy controller can decrease commutation failure frequency induced by ac system faults.