Variable Extinction Angle Control Strategy Based on Virtual Resistance to Mitigate Commutation Failures in HVDC System

Abstract

To mitigate commutation failures (CFs) and minimize the instability of HVDC systems due to AC faults or control mode ambiguity, a constant extinction voltage-time area based control strategy with virtual resistance is proposed. In this strategy, using sine-cosine components detector and considering zerocrossing phase shift of commutation voltage, the extinction angle setting value can be adjusted dynamically. Meanwhile, to reflect the characteristics of DC current during the fault and recovery process, a virtual resistance is introduced into the control system and DC voltage considering the voltage drop of the virtual resistance is taken as the input of voltage-dependent current order limiter (VDCOL). Through theoretical analysis, the proposed strategy not only reduces the firing angle dynamically, but also reduces DC current by lowering the current order on the rectifier side immediately when the AC voltage disturbance is detected, thereby further reducing the occurrence of CFs. Therefore, the control strategy can effectively suppress successive and intermittent CFs. The effectiveness of the proposed control strategy is verified by simulation of the single HVDC and multi-infeed HVDC model based on the CIGRE HVDC benchmark system, in which AC-DC current criterion of identifying CF and suppression ratio index are adopted. The simulation results show that the proposed control strategy can effectively mitigate CFs under single-phase and three-phase faults to a certain extent. Comparing with the existing control strategies based on controller modification, i.e. commutation failure prevention, DC current predictive control, smooth logic switching control and DC current limitation control strategy based on virtual resistance, the proposed control strategy is superior in mitigation effects. The average suppression rates of these strategies are 1.66%, 3.21%, 6.11%, 3.35%, and 8.33% under single-phase fault, respectively; with the rates of 1.4%, 2.72%, 4.97%, 0%, and 6.8% under three-phase fault, respectively.

Protection of an HVDC Link Towards Modeling and Simulation Based DC Connection Defects

“…The system depicted in Fig. 1 is a monopolar HVDClink system (500 kV/2kA) with 12-pulse thyristor converters on both the rectifier and inverter sides in this analysis, which is focused on the first CIGRÉ HVDC benchmark system [12] [13]. As seen in Table 1, the model was applied in the simulator, with the rectifier connected to the first AC system (315 kV, SCR=5) and the inverter connected to the second AC system (230 kV, SCR=3).…”

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

“…The HMIDC system refers to the network formed when VSC-HVDC and LCC-HVDC are connected with the same or similar electrical distance to the converter bus (Wei et al, 2020). For any hybrid multi-infeed DC transmission system, it is assumed that a total of N inverter stations are connected to the receiving AC grid, which contains k LCC inverter stations and N-k VSC inverter stations.…”

Impact of Commutation Failure Preventions on HVDC System Based on a Multi-Index Value Set Approach

“…Load bus The nominal solution of the system is as follows: P2 (0) + jQ2 (0) = 0.5 + j0. 3 and Vx (0) + jVy (0) = 1.051 − j0.014. Considering P2 and Q2 as uncertain parameters, we have: 22 j ( j )(1.06 j ) ( j0.03)…”

“…It is well-known, however, that a HVDC system is inherently vulnerable to voltage drops caused by AC network faults. This is because inverters may experience commutation failures if the AC voltage is below certain threshold [2], [3]. Since most of the HVDC links deliver a very large amount of power, the commutation failure of one single link often induces a severe disturbance to the AC grid, further increasing the risk of cascading faults [4], [5].…”