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In this paper, a new HVDC shunt tap is proposed. The proposed configuration consists of a unidirectional hybrid modular DC–DC converter followed by a voltage source converter for DC–AC conversion to feed a local AC network connected to the tap output terminals. The proposed DC–DC converter consists of a high-voltage valve, and series-connected unidirectional half-bridge Sub-Modules (SMs). Unlike Marx generator circuit concept, the DC–DC conversion in the proposed configuration is achieved by enabling simultaneous charging of series-connected capacitors (i.e. SMs capacitors), and sequential discharging of capacitors. Compared to Marx-generator based switched capacitor DC–DC converters, the proposed configuration has a lower number of semiconductor devices, which affects positively the system cost, and reduces the control complexity. Detailed illustration, design, and control of the proposed approach are presented. Simulation results are presented to validate the proposed approach. [ABSTRACT FROM AUTHOR]

This paper proposes a new three-phase transformerless STATic synchronous COMpensator (STATCOM) for shunt reactive power compensation in medium/high-voltage applications. The proposed STATCOM is based on a hybrid Boost Modular Multilevel Converter (hybrid BMMC) with a reduced number of Full-Bridge SubModules (FB-SMs). Operating with almost zero displacement factor at the ac terminals of the converter guarantees sufficient charging and discharging time intervals for the Half-Bridge SMs (HB-SMs) which ensures well-balanced capacitor voltages. Conventionally, each arm in a hybrid BMMC contains FB-SMs and HB-SMs with a ratio of 2:1 respectively. In this work, a new hybrid BMMC with a ratio of 1:2 is employed, which enables operating with a reduced number of FB-SMs with the same boosting capability, therefore, enabling transformerless operation. Nonetheless, the tradeoff is the loss of the dc fault blocking capability compared to the 2:1 configuration. This may be acceptable in STATCOM applications, as the possibility of having a dc side fault in such application is limited, compared to, for instance, MMC in high voltage dc network applications. In this work, detailed illustration of the proposed STATCOM configuration along with its controllers are presented. Finally, simulation case studies are considered to demonstrate the effectiveness of the proposed approach. The simulation results show promising and satisfactory performance. [ABSTRACT FROM AUTHOR]

Highlights • A new switching pattern is proposed for zero voltage switching of hybrid modular dc-dc converter. • The switching losses is greatly reduced by enabling operation with ZVS of the involved HV valve. • The dynamic voltage sharing of series-connected IGBTs based HV valve is simplified as the switching occurs at zero voltage. Abstract In this paper, a bidirectional non-isolated hybrid modular DC–DC converter for high-voltage (HV) applications is investigated. In this configuration, conventional Half-Bridge Sub-Modules (HB-SMs) are employed. The proposed DC–DC converter is based on connecting the SMs capacitors in series across the high DC voltage level while connecting them sequentially across the low DC voltage level. On another frontier, an HV valve, based on series-connected Insulated-Gate Bipolar Transistors (IGBTs), is required at the HV side. The main confronted challenge of the series-connected IGBTs is the voltage sharing during turn-on and turn-off periods, which necessitates the engagement of an intricate voltage sharing technique. In this work, a switching pattern is proposed to ensure zero-voltage switching (ZVS) of the involved HV valve. In order to reduce the switching losses and avoid complex active gate control recruited for dynamic voltage sharing, the zero-voltage state is extended beyond the switching time. A detailed illustration of the hybrid modular DC–DC converter is presented, elucidating the proposed switching pattern. Simulation results, using Matlab/Simulink platform, are presented to validate the contribution of the paper. Finally, a scaled-down prototype is employed for experimental verification. [ABSTRACT FROM AUTHOR]

This paper introduces a non-communication based protection algorithm for Multi-Terminal High Voltage Direct Current (MTHVDC) transmission lines. The algorithm relies on using electrical current data at one end for identification of the fault zone without communication between relays. The concept is to use the fault generated transients to differentiate between internal and external faults. Shunt capacitors with predetermined values are installed at the boundary between each two HVDC line sections to assist, together with the busbar stray capacitance, in the classification of internal faults. The high frequency transients will reach the relaying point without any attenuation if the fault is internal; nevertheless, the high frequency transients will be highly attenuated if the fault is external due to the stray capacitance and the installed shunt capacitor at the connection busbar. Discrete Wavelet Transform (DWT) is used to analyze the fault current signals. MTHVDC system modeling and relay design are carried out in the MATLAB/SIMULINK environment. The results of the proposed algorithm were highly reliable regarding different types of faults with different fault resistances and at various locations. [ABSTRACT FROM AUTHOR]

This paper presents a technique for differential protection of Multi-terminal High Voltage Direct Current (MTHVDC) transmission lines. The proposed technique depends on the electrical current data at both ends of each line section. Discrete Wavelet Transform (DWT) is used to detect DC faults as well as filter out the high frequency transients superimposed on the current signals. An operating signal and a restraining signal are used in this technique to discriminate between internal faults and external faults through their ratio in each section of the MTHVDC. The operating and restraining signals depend on energy contents of the de-noised current signals at both ends of each line section. MTHVDC modeling and relay design are carried out in the MATLAB environment. The results demonstrate the high reliability of the proposed relay in the zonal protection of MTHVDC. [ABSTRACT FROM AUTHOR]