Continuous Commutation Failure Research Articles

Asymmetrical Advancing Angle Difference and its Application in Predicting Continuous Commutation Failure for LCC-HVDC Systems Under Asymmetrical Faults

Asymmetrical Advancing Angle Difference and its Application in Predicting Continuous Commutation Failure for LCC-HVDC Systems Under Asymmetrical Faults

The Strategy of Continuous Commutation Failure Suppression by Combining Turn-off Angle Compensation and Dynamic Nonlinear VDCOL

In recent years, with the continuous growth in China’s economy, the continuous advancement of urbanization and industrialization, the contradiction between rapid economic development and the continuous reduction in traditional fossil energy reserves such as coal, oil, and natural gas, the continuous aggravation of environmental pollution has become increasingly prominent. In this era, clean energy power generation technologies such as hydropower, wind power, and solar power generation, which have the advantages of renewability, environmental protection, and economy, have developed rapidly. However, wind and photovoltaic power plants are often located in remote areas, which means significant losses in the transmission process. High-voltage direct current (HVDC) transmission technology becomes the best choice to solve this problem. The HVDC transmission system based on a grid commutator is widely used in China’s AC-DC hybrid power grid. When an AC fault occurs on the inverter side, the line-commutated converter high-voltage direct current (LCC-HVDC) system is more prone to continuous commutation failure, which brings serious harm to system operation. To better suppress the problem of continuous commutation failure on the contravariant side, this paper analyzes the mechanism of continuous commutation failure from multiple angles. The DC current command sensitivity of a voltage-dependent current order limiter (VDCOL) in the LCC-HVDC system is low, which will lead to different degrees of continuous commutation failure. In addition, the rapid rise in DC current and the drop in commutation voltage during the fault will cause the turn-off angle to drop, and the probability of continuous commutation failure of the system will increase significantly. Based on the above theoretical analysis, a new control strategy combining the dynamic compensation of the turn-off angle of a virtual inductor and the suppression of continuous commutation failure by dynamic nonlinear VDCOL is proposed. A dynamic nonlinear VDCOL control strategy is proposed for the low sensitivity of current command adjustment under conventional VDCOL control. Secondly, two concepts of virtual inductance and DC current change rate are introduced, and a control strategy based on virtual inductance is proposed to comprehensively ensure that the switching angle has sufficient commutation margin during fault recovery. Finally, based on the CIGRE standard test model in PSCAD/EMTDC, the accuracy of the correlation mechanism analysis and the effectiveness of the suppression method are verified.

Continuous commutation failure suppression method based on dynamic compensation of firing angle deviation

In the line commutated converter based high voltage direct current(LCC-HVDC) transmission system, it has important meaning to suppress continuous commutation failure(CCF) for the safe and stable operation of the system. Aiming at CCF caused by poor dynamic performance of DC control system, this paper first analyzes that firing angle deviation is an important cause of CCF in the dynamic process of recovery after first commutation failure(FCF). Then, the reasons for firing angle deviation caused by the underlying firing control at this stage are analyzed: One is the phase deviation caused by the inherent response of the phase locked loop(PLL), which is a second-order system; the other is the phase deviation of the asymmetric commutation voltage. On this basis, a CCF suppression method based on dynamic compensation of firing angle deviation is proposed. The method dynamically and adaptively compensates firing angle deviation through the actual measurement value, which improves the controllability of actual firing angle in the dynamic process, thereby suppressing CCF. Finally, it is verified that the improved method has good suppression effects on CCF in the CIGRE HVDC benchmark model.

A novel low-voltage current-limiting control strategy with improved voltage compensation

By optimizing the design of the conventional low-voltage current limiting controller (VDCOL), the continuous commutation failure on the receiving end of the traditional LCC-HVDC transmission system is effectively suppressed. In order to overcome low insensitivity of conventional VDCOL under mild and moderate faults, the dc current deviation value is superimposed into the starting voltage of the VDCOL in the form of a compensation voltage to enhance sensitivity of the VDCOL to the dynamic changes of the dc current during mild and moderate faults. In the face of severe faults, the conventional VDCOL adopts a linear adjustment method with a fixed slope, which is bad for suppressing continuous commutation failure. Aiming at this problem, a nonlinear VDCOL strategy is adopted, which the dc current command and the dc voltage are a nonlinear function relationship with a variable slope with the increasing or decreasing of the dc voltage. In the PSCAD/EMTDC simulation platform, the proposed control strategy is verified using the International Council on Large Electric Systems (CIGRE) standard model. Simulation results reveal that the proposed nonlinear VDCOL strategy with improved voltage compensation method can well suppress continuous commutation failures in the case of single-phase and three-phase short-circuit faults, and it is beneficial to restore dc voltage and transmission power and ensure the normal operation of the HVDC transmission system.

Continuous commutation failure suppression strategy in hybrid multi-infeed HVDC transmission system

Continuous commutation failure suppression strategy in hybrid multi-infeed HVDC transmission system

Continuous Commutation Failure Suppression Method Based on Dynamic Compensation of Trigger Angle Deviation

Continuous Commutation Failure Suppression Method Based on Dynamic Compensation of Trigger Angle Deviation

A coordination control strategy to suppress commutation failure based on LCC-VSC

The receiving end hybrid LCC-VSC system is a new type of hybrid DC transmission system. In order to suppress continuous commutation failure, this paper optimizes and improves the firing angle control strategy of LCC with AC fault voltage and the DC power recovery to predict the commutation failure. And the reactive power compensation value is determined according to the degree of voltage drop and attached to the reactive power outer loop control link of multiple VSCs. By increasing the VSC output The reactive power plays a role in restraining the commutation failure. Based on the receiver-end hybrid LCC-VSC model in PSCAD/EMTDC, the proposed LCC-VSC control strategy is simulated and verified. The simulation results show that when the AC voltage drops, the proposed control strategy can effectively suppress the drop of the turn-off angle and avoid the occurrence of continuous commutation failure.

Rapid Recovery Control Method Based on Improved VDCOLs for Hybrid Multi-Infeed DC Transmission System After AC Failure

Continuous commutation failure is very likely to occur in the hybrid Multi-infeed high-voltage direct current (HMIDC) after AC failure. In order to improve the recovery quality after HMIDC failure, an AC-DC voltage-dependent current order limiter (VDCOL) based on system strength index is proposed in this article. Firstly, the control mode transition process and system recovery process after DC failure are analyzed based on the hybrid multi-infeed DC transmission port model. Then, considering the impact of AC voltage and DC voltage input signals of VDCOL on AC voltage recovery and DC power recovery, respectively, the interaction factor and strength index of the hybrid multi-infeed system are constructed. Moreover, the weight coefficient of AC and DC voltage is calculated according to the strength of the multi-infeed system. Finally, a three-infeed hybrid DC transmission simulation model is built in the MATLAB/Simulink digital simulation platform. The simulation results demonstrate that the rapid recovery strategy proposed in this article can effectively suppress continuous commutation failure and improve the recovery speed of AC voltage and DC power.

Switching System's MLE Based Transient Stability Assessment of AC/DC Hybrid System Considering Continuous Commutation Failure

The commutation failure of Line Commutated Converter-High Voltage Direct Current (LCC-HVDC) cannot be avoided. This paper presents a novel transient stability assessment approach for AC/DC hybrid system considering continuous commutation failure. First, the conception and mathematical background of Maximum Lyapunov Exponent (MLE) of switching system is introduced, and the switching compensation matrix is derived. Next, the switching system model of AC/DC hybrid system considering continuous commutation failure caused by AC faults is established. On the basis of switching compensation, the MLE of switching system is calculated accurately, and the MLE based criteria are proposed to assess the transient stability of the switching system. Finally, the modified 39-bus system with LCC-HVDC added and the real power system are used as test systems to investigate the validity and effectiveness of the proposed transient stability assessment approach.

A Predictive Method of LCC-HVDC Continuous Commutation Failure Based on Threshold Commutation Voltage Under Grid Fault

Line-commutated converter based high-voltage direct-current (LCC-HVDC) has been extensively applied in power system. LCC-HVDC is prone to continuous commutation failure (CCF), which consequently causes numerous active and reactive impacts, thereby resulting in various power system security and stability issues. Given that there is no CCF predictive method at present, the effect of CCF suppression measure is still limited, and the control margin of DC commutation station and power grid cannot be fully applied, so that the negative impact of CCF is difficult to reduce through advance control. In view of this situation, this paper aims at proposing a predictive method of LCC-HVDC CCF, which occurs again during the first CF recovery process. First, the predictability of CCF is demonstrated, and the idea for predicting CCF by comparing commutation voltage is proposed; Second, the calculation equation of CCF threshold voltage is derived by analyzing the CF process; Third, a predictive method of CCF based on threshold commutation voltage is proposed; Finally, the correctness of the theoretical analysis and predictive method is verified through the CIGRE HVDC standard system. Simulation results show that the proposed method has high accuracy and can provide sufficient time margin for emergency control to suppress the LCC-HVDC CCF.

Continuous Commutation Failure Suppression Method Based on Self-adaptive Auto-disturbance Rejection Proportional-integral Controller for HVDC Transmission System

Once an asymmetrical fault occurs on the AC side of the receiving-end of a high-voltage direct current (HVDC) transmission system, the current reference will be affected by the control regulation on the DC inverter side and the commutation voltage asymmetry. In this case, the advance firing angle will fluctuate periodically, causing security threats to the system. If the fault cannot be cleared in time, the effect may be even more serious. However, the traditional proportional-integral (PI) controller cannot effectively suppress the periodic components in the input error signal, which is an important cause of continuous commutation failure. Thus, the system requires more time to recover from the fault. Motivated by this, a self-adaptive auto-disturbance rejection PI controller is proposed in this study. The controller has the advantages of fast response speed and strong anti-interference ability of the auto-disturbance rejection controller. On one hand, it can automatically adjust PI, and the parameters can maintain the system's adaptive ability. On the other hand, the discretization process satisfies the computer simulation requirements. By applying the proposed controller to a system under constant current control and extinction angle control, the dynamic response speed can be improved and the robust performance of the system can be ensured when dealing with a wide range of perturbations. Finally, simulation results show that the proposed algorithm can effectively suppress the continuous commutation failure of DC transmission systems.

Simulation study on commutation failure control and recovery of UHVDC with hierarchical connection mode

UHVDC transmission projects with hierarchical receivers are connected in series on the DC side. When a single voltage level of AC system fails, commutation failure may occur in both hierarchies of DC system, and the impact will be more serious when the electrical connection is strong. In the process of fault recovery, inappropriate control strategy will also lead to successive commutation failures. In this paper, a commutation failure control and recovery strategy based on real-time fault detection and determination is proposed. In view of the instantaneous faults of AC system, the starting time is determined according to the predicted results of commutation failure, so as to reduce the starting times and prevent the continuous commutation failure in the recovery process. When the single-hierarchy AC system is permanently severely faulted, the fault hierarchy is isolated and the non-fault layer operates normally. The PSCAD/EMTDC simulation model of an UHVDC transmission project is built. Instantaneous and permanent faults are set up to simulate. It is verified that the proposed strategy can effectively reduce the number of successive commutation failures and improve transmission reliability.

Novel pilot protection for AC transmission line connected to LCC-HVDC inverter station

As known, after AC transmission line fault occurs, LCC-HVDC inverter station has three different statuses: no commutation failure, single commutation failure and continuous commutation failure. And the different statuses of inverter station could lead to wrong operation of traditional protection principles (such as current differential protection and directional pilot protection). Firstly, the paper establishes inverter station’s equivalent model under different statuses and analyzes relationship between voltage and current vectors. Secondly, the paper analyzes the adaptability of conventional protection principles including current differential protection and directional pilot protection. Thirdly, using empirical mode decomposition algorithm, novel pilot protection principle suitable for AC transmission line which is connected to inverter station is proposed. The novel protection principle is only based on power frequency current signal of two ends, and it requires no time synchronization system. Eventually, a PSCAD/EMTDC simulation model of ±800 kV LCC-HVDC and 500 kV AC transmission system is established. And the simulation results prove that the novel protection principle is immune to inverter station working status, fault resistance and fault type.

Study on the method of fault set for AC/DC system operation considering wind power

With the rapid development of power system, wind power becomes an important generating way in AC/DC hybrid power grid. Due to the interference between the wind power and the AC network, the risk of DC system continuous commutation failure will be affected. In order to evaluate this effect reasonably, a method for running out of the fault set is presented in this study. Firstly, a distribution factor is proposed to determine the power line transfer after wind power or power line fault, the line with maximum load rate is chosen as the candidate failure lines; Secondly, the η short-circuit ratio and η effective short-circuit ratio indexes of the DC system is evaluated after every fault; they are used to judge whether the cascading fault of AC system induces the transient overvoltage of the converter bus to lead to wind turbines to take off the power grid net. Thus, a cascading fault sequence of the AC system is formed, and a cascading fault set that causes the transient overvoltage of the converter bus is completed. Finally, the simulation results calculated by power system department-bonneville power administration show that when the commutation failure occurs in the DC system, the system runs out immediately, and the validity of the method is verified.

A Commutation Failure Suppression Control Method Based on the Controllable Operation Region of Hybrid Dual-Infeed HVDC System

With the increased use of high voltage direct current (HVDC) systems, line commutated converters (LCC-HVDC) and voltage source converters (VSC-HVDC) tend to feed into AC systems over short electrical distances. The flexible power control of VSC-HVDC systems provides an effective approach to suppress the commutation failure of LCC-HVDC systems. A suppression method, based on a controllable operation region, is proposed in this study to reduce the probability of commutation failure in a hybrid dual-infeed HVDC system. First, the quantitative transient reactive power control requirement of VSC-HVDC inverter that could fulfill the suppression control boundary condition of commutation failure was analyzed. Given the maximum current constraint of the VSC-HVDC inverter and the primary frequency modulation constraint of the sending-end grid, a controllable operation region of the hybrid dual-infeed HVDC system was proposed. Furthermore, a commutation failure suppression control method, based on the controllable operation region, was proposed to mitigate continuous commutation failure. Finally, the validity and accuracy of the proposed method was verified by the simulation of PSCAD/EMTDC. The proposed control method can realize reasonable use of the reactive power control capability of the VSC-HVDC system, which effectively improves immunity to commutation failure of the LCC-HVDC system under grid fault.

Superposition feature of the switching functions for the dynamic phasor model of the converters under commutation failure

Switching function is very important for the dynamic phasor model of converters. It is used to represent the relationship between the AC side voltage/current and the DC side voltage/current in the dynamic phasor models of converters. The existing switching functions consider no effect of the commutation failure (CF), which restricts the development of the dynamic phasor model of converters. A method to obtain the switching functions considering the effects of the CF is proposed in this study. First, following a detailed analysis, the two phenomenon are found that: (1) if there is only a single CF, then the corresponding switching functions can be calculated through the normal three phase switching functions; and (2) if there is an occurrence of continuous CFs, the switching functions in the dynamic phasor model can be obtained through the normal switching functions and the corresponding single CFs, which consists of the continuous CFs. Second, the details of the method to obtain the switching functions considering various operation conditions are presented. Finally, numerical tests show that the proposed method and the modified switching functions are valid and effective.

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.