Search

• The faulty operation of MMC with hot-reserved SMs is analyzed. • NLM corrector based fault-tolerant strategy for high-voltage MMC is proposed. • The strategy features simplicity, low voltage stress and little influence scope. The reliable and consistent operations of modular multilevel converters (MMCs) under fault conditions are crucial for high-voltage and high-power applications. To strengthen the performances of MMCs under submodule (SM) faults, a fault- tolerant strategy based on the nearest level modulation (NLM) is proposed in this paper. According to the changed AC component in the faulty arm voltage, this method adds a corrector in NLM, which remedies the faulty arm voltage by adjusting the number of inserted SMs for the faulty arm. Then, the faulty operation can be recovered to the normal. The corrector is simple to realize and can effectively suppress the odd-order circulating currents. Under the proposed method, only the ripples of the capacitor voltages in the faulty arm rise. The average voltage stress on each capacitor is the same as that in normal operation since the rated capacitor voltage in the faulty arm has no rise. No measure and influence impose on healthy arms. With features of simplicity, low voltage stress and little influence scope, the proposed strategy is fit for high-voltage MMCs. The feasibility of the proposed strategy is verified by the simulation results with the professional tool Matlab/Simulink. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an extensive analysis of the influence of the DC voltage on the compensation performance of Static Var Generator (SVG). A method to design the DC voltage rated value is proposed according to the compensation performance. First, a required lowest value of the DC voltage for full compensation (a unity total power factor) is obtained by using the analysis of the equivalent circuit. For the situation where the DC voltage is smaller than the above-obtained lowest value, two basic options which are the sinusoidal modulation and the over modulation for the PWM control of SVG are considered. Then, the quantitative relationship between the DC voltage rated value and the compensation performance is detailed. In addition, the lowest value of the DC voltage in the SVG with a battery energy storage device is also obtained for the reactive and active output current. Based on the above analysis, the design of the DC voltage rated value for SVG is quite straight forward. Both simulation results and the hardware experimental results are finally presented to verify the validity of the analysis results and the proposed design method. [Copyright &y& Elsevier]

• The study of the combined operation of RSFCLs and DCCBs has shown effective protecting results. • Detailed models of the RSFCL and DCCB are built in this paper. • The influence of four kinds of different parameters on the fault clearing process are investigated. • Converters in the system remain unblocked, making the fast recovery of the system possible through DCCBs' reclosing. The high rate of rise and large amplitude of a dc fault current in MMC-MTDC system make its interruption difficult for DC Circuit Breakers (DCCBs). In order to tackle this issue, this paper proposes a combined operation of a Resistive-type Superconducting Fault Current Limiter (RSFCL) and a DCCB. By analyzing the fault current in a symmetrical monopole MMC-MTDC system, the effectiveness and necessity of adding a resistive type fault current limiting device into the system after fault is established. With detailed modeling of the RSFCL and DCCB including the quench and recovery processes of the RSFCL, their combined operation is investigated. The influence of different parameters, such as the maximum quench resistance of the RSFCL, the insertion time of the energy absorption branch in the DCCB, and the quench and recovery process of RSFCL, on the fault clearing process are investigated in detail. The effectiveness of the combined operation is verified by extensive simulations in PSCAD/EMTDC. The results indicate that the combination of RSFCLs and DCCBs can obtain a suppression rate of at least 25% on the peak value of the fault current. Besides, the energy that DCCBs need to absorb in their arresters has been reduced by more than 60%, and the total fault clearing time is also reduced. Furthermore, all the converters remain unblocked, making the fast recovery of MMC-MTDC system possible through DCCBs reclosing. It is concluded that the combination of RSFCLs and DCCBs provides an effective solution to handle short circuit faults in MMC-MTDC systems. [ABSTRACT FROM AUTHOR]