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Aiming at the problems of large workload, low efficiency and incomplete function coverage in the maintenance process of VSC-HVDC project, this paper studies the SM detection technology of MMC. Firstly, it analyzes the background and significance of this research, then based on the elaboration of the working principle of SM, a SM function detection method is proposed. This method can not only realize the automatic detection of multiple mmc-sms, but also cover all the power components except the thyristor of SM, which greatly simplifies and improves the detection steps and efficiency. The feasibility and effectiveness of the method are verified by simulation analysis.

Nowadays, with the development of electric engineering, the majority of current civilian sources are portable, such as the battery. However, most of them are only able to output DC without a power inverter, so a power inverter must be applied. To realize the reduction of the volume of the inverter, this solution is based on the combination of MCU (microprogrammed Control Unit) and traditional inverter circuit, because of the limitations of the breadboard. The rationale is that by changing the state of thyristors with a certain frequency by input pulses from an MCU, the current direction flow is changed through the inductor. In this way, alternating currents are created. This design is first verified in SIMULINK, where the chosen MCU for physical construction is the Arduino series.

The change of operation mode of the HVDC project causes a change of the external characteristic of the converter valve, and the reverse recovery characteristic of the thyristor inside the converter valve changes accordingly. Therefore, the reverse recovery charge measurement values of thyristors under different operating conditions cannot be directly compared, and the status of thyristors cannot be evaluated online. Therefore, a method of measuring the reverse recovery charge of series thyristor based on the turn-off voltage is presented in this paper. Then, the operation mode of the HVDC project is analyzed, and the external characteristics of the converter valve under different operation modes are discussed. Secondly, the external factors that affect the reverse recovery characteristics of thyristors are analyzed essentially, and the relationship between the external factors and the external characteristics of the converter valve is discussed. A reverse recovery charge model considering external factors is established, and a method to reduce the error is proposed. Finally, the reverse-recovery charge normalization coefficient is derived for the normalization of the measured values in different working conditions. Based on the charge online measurement method and the normalization method proposed in this paper, the reverse-recovery characteristic evaluation method of the thyristor is proposed, and the evaluation steps are introduced.

The thyristor-assisted arc-quenching hybrid on-load tap changer (OLTC) integrates the benefits of both mechanical and power electronic OLTCs, utilizing anti-parallel thyristors to aid in mechanical contact switching. However, this hybrid OLTC faces challenges such as high di/dt during thyristor conduction and significant peak voltages and du/dt at thyristor turn-off. This paper presents a simulation study on the transient current and voltage characteristics during thyristor conduction and natural turn-off. It also determines key technical parameters like the critical du/dt and di/dt for the thyristor in a 35 kV hybrid OLTC.

In this article, a false trigger pulse elimination circuit is proposed to be used for a low-frequency energy harvesting active rectifier. It is divided into two-stage circuits, each stage almost including a switching signal generation circuit, a switching inverter, and an inverter to eliminate false triggering pulses on the rising edge and falling edge respectively. There is an edge detection circuit in each switching signal generation circuit, generating a switching signal that controls the switching inverter’s on-off behavior. This allows the inverter to achieve inverter output voltage clamping by turning off its inverter function and turning it into a switch that is only turned on at the high or low level. At the same time, a thyristor delay element is used to determine and adjust the effective level time of the switching signal, which can reach over 150 μs, completely covering the rising or falling edge false trigger pulse so that no GΩ-level resistors are needed in the low-frequency field. The results show that the low-frequency false trigger pulse elimination circuit proposed in this article can better eliminate false trigger pulses on both rising and falling edges. It can also achieve on-chip integration, reduce the power consumption of the self-adaptive delay compensation loop, and enhance the stability of the circuit.

Optimal power flow (OPF) is one of the challenging optimization problems in power domain. The complexity of the problem escalates with incorporation of uncertain and intermittent renewable sources into the electrical network. Flexible AC transmission system (FACTS) devices are also becoming more commonplace in modern power system to mitigate growing demand and to relieve congestion from the network. This paper aims to solve the OPF where the generation cost is optimized with incorporation of stochastic wind power and several types of FACTS devices such as static VAR compensator, thyristor-controlled series compensator and thyristor-controlled phase shifter. Case studies with both fixed and uncertain load demands are performed. The stochastic wind energy and load demand are modeled using suitable probability density functions. Optimization objective considers cost of thermal generation, direct cost of scheduled wind power, penalty cost for underestimation and reserve cost for overestimation of the wind power. In addition, both locations and ratings of the FACTS devices are optimized to minimize total generation cost of the system. Success history-based adaptive differential evolution (SHADE), a powerful evolutionary algorithm, is adopted to perform the optimization task. The constraints of OPF problem are handled using superiority of feasible solutions (SF) method. The integration approach of SF method with several popular metaheuristic algorithms has been proposed in this work, and a detailed comparative analysis among various algorithms establishes SHADE algorithm to be the best performer.

High voltage direct current (HVDC) transmission is an economical option for transmitting a large amount of power over long distances. Initially, HVDC was developed using thyristor-based current source converters (CSC). With the development of semiconductor devices, a voltage source converter (VSC)-based HVDC system was introduced, and has been widely applied to integrate large-scale renewables and network interconnection. However, the VSC-based HVDC system is vulnerable to DC faults and its protection becomes ever more important with the fast growth in number of installations. In this paper, detailed characteristics of DC faults in the VSC-HVDC system are presented. The DC fault current has a large peak and steady values within a few milliseconds and thus high-speed fault detection and isolation methods are required in an HVDC grid. Therefore, development of the protection scheme for a multi-terminal VSC-based HVDC system is challenging. Various methods have been developed and this paper presents a comprehensive review of the different techniques for DC fault detection, location and isolation in both CSC and VSC-based HVDC transmission systems in two-terminal and multi-terminal network configurations.

A system is considered, in the control loop of which there are thyristor converters or a special type of indirect control system. An example of constructing self-oscillations in a system describing the behavior of electrical devices using such elements in the control loop is given. Solutions for self-oscillations of a given period are constructed. Conditions for the existence of orbital asymptotic stability and Lyapunov stability for periodic solutions with a given period are presented, and a control loop is synthesized that ensures the existence of such solutions.

With the widespread use of underground cables, a large amount of distributed capacitance is added to the urban power grid circuit, which brings great challenges to the transmission capacity and stability of the system. The mainstream suppression control method of distributed capacitance of power grid cable mostly depends on the characteristics of power grid cable material itself. In practical engineering applications, the characteristics of cable material itself are easily affected by environmental factors, which affects the suppression and compensation effect. In view of the above problems, this paper proposes a multi-winding transformer-type graded continuously adjustable reactor for distributed capacitance compensation of urbanized cables. The distributed capacitance of urbanized cables is compensated through practical application requirements. The thyristor and voltage-type full-bridge PWM inverter are used as the load on the secondary side of the transformer, and the switching control of multiple thyristors realizes the coarse adjustment of the adjustable reactance. The output current of the inverter is controlled to achieve fine adjustment of the reactance value. The device can improve the compensation accuracy and improve the power quality of the power grid. The validity and correctness of the proposed method are preliminarily verified by MatLab software.

An investigation into the increased leakage currents and reduced blocking voltages associated with 1450°C lifetime enhancement oxidation for the 4H-SiC p-GTOs is presented. Roughening of the 4H-SiC surface due to localized crystallization of SiO2, or crystobalite formation, during the high temperature oxidation was identified as one of the main causes of this issue. A factor of 30 difference in permeability to O2 between amorphous SiO2 and crystobalite caused uneven oxidation, which resulted in significant roughness. This roughness, placed at the metallurgical junction between the gate and the drift layer, where the E-field is greatest, is believed to be responsible for the premature breakdown characteristics. A 2-step lifetime enhancement process, which moves this roughness to the lower E-field region of the device was introduced to alleviate this issue. A 15 kV 4H-SiC p-GTO with the 2-step lifetime enhancement process demonstrated a significant reduction in VF over the 1300°C oxidized devices, without any impact on blocking characteristics.