Aiming at the different response characteristics of multi-terminal HVDC transmission system in the case of AC system faults, this paper introduces the electromechanical transient modeling method of the primary system and control system of multi-terminal HVDC transmission system. A three-terminal DC transmission system with one sending end and two receiving ends is constructed, considering the combination of LCC-LCC-LCC, LCC-VSC-LCC and LCC-VSC-VSC, the corresponding simulation models are established. This paper compares the response characteristics of different multi-terminal DC transmission system in the case of AC system faults with different voltage drops. The comparison results show that the VSC converter on the inverter side can effectively reduce the probability that the DC system cannot perform effective power transmission due to the commutation failure of inverter. The use of VSC converters in both inverters can give full play to the advantages of VSC converters without commutation failure, and maximize the transmission of DC power. At the same time, the full play of the VSC converter requires the close cooperation of the multi-terminal DC transmission control system.

Aiming at the limitation that the traditional Z-source inverter has large starting impulse current insufficient boosting ability, and large capacitance voltage stress, a quasi-Z source neutral point clamped (NPC) three-level inverse topology is proposed. Firstly, the working principle of the proposed structure and the design of the quasi-Z source parameters are analyzed, the inverter can achieve higher voltage output at low shoot-through duty ratio, which optimizes the power quality and reduces quasi-Z source network capacitor voltage. Secondly, simplified PQ control strategy is introduced to achieve unit power factor grid connection, and current harmonic distortion rate is reduced. Finally, through the simulink software and experimental hardware research, the superiority of the new quasi-Z source three-level inverter and the effectiveness of the grid-connected control strategy are verified.

In order to improve the control performance and drive capacity of brushless DC motor, diode clamped three-level inverter instructures are often adopted, but there are such problems as bridge arm inner power switch device switching overvoltage and neutral point potential imbalance. In this paper, a novel topology instructure driven by three-level inverter is proposed and studied. Firstly, the six power switching devices clamping mechanism of this topology inside the clamped three-phase bridge arm is analyzed, and the four switching state automatic voltage equalization principles are studied, the influence characteristics of 64 voltage space vectors on the neutral point potential are also analyzed. Secondly, the clamped capacitor voltage balance control strategy is proposed, and then the space vector pulse width modulation (SVPWM) strategy is given,and the double closed-loop pulse width modulation (PWM) control strategy of brushless DC motor based on a novel three-level inverter instucture is presented. Finally, an experiment is carried out based on the prototype platform, and the results confirm the correctness and effectiveness of the research content.

Grounding electrode is an important part of the DC transmission project. Traditional grounding electrode occupies a large area, causing us extremely difficult to select the site and perform requisition of lands. China Southern Power Grid proposes a technical route to solve the problem by constructing a deep-well grounding electrode, and carries out a demonstration project construction of deep-well grounding electrode. Based on the practice of the demonstration project, this paper studies the influence on the grounding temperature rise of the deep well by the length of the single electrode of the grounding electrode, the total number of parallel electrodes, the buried depth of the grounding electrode, the spacing of the electrodes, and the diameter of the filled coke. The results show that the above-mentioned five factors can cause changes in the grounding overflow density, which affects the overall temperature rise of the grounding electrode and the maximum temperature rise. The temperature rise shows a trend of decreases with the increase of the length of a single electrode, or the total number of parallel electrodes, or the cross-sectional area of coke, but the trend of decrease tends to be gradual. The buried depth of the grounding electrode needs to be selected according to the stratification of the soil at the electrode site. Choosing a suitable buried depth where the soil layer has low and relatively even resistivity, is beneficial to reduce the temperature rise of the grounding electrode. the spacing of the electrodes is related to the land occupied by the electrode site, but due to the limitation of the construction technique of deep well drilling, the electrode spacing cannot be too small.

Electromagnetic transient calculation method based on time domain transformation takes advantage of the special characteristics of voltage and current in power systems, whose waveforms are close to be sinusoidal. It can use a larger time step and improve the efficiency of simulation without accuracy loss. To accurately and efficiently simulate the dynamics of power systems related to generators, a synchronous generator model based on the time domain transformation method is developed in this paper. Diverse test cases are used to verify the validation of the presented model. Test results show that the accuracy of the presented model keeps good even with time steps of milliseconds.

The line impedance between the DG units are always different in the islanded AC microgrid, which can result in circulating current and unreasonably sharing reactive power among inverters by using conventional droop control method. To solve this problem, an improved droop control strategy of adaptive virtual impedance based on fuzzy controller is proposed. The central controller calculates the reactive power difference between them and the variation of the reactive power difference. And then it sends the calculated results to each inverter. The fuzzy controller adaptively adjusts the virtual impedance by using the reactive power information of the inverter to compensate for the voltage drop difference caused by the inconsistent equivalent impedance, thereby achieving reactive power sharing. At the same time, in order to solve the problem of the voltage drop of inverter output voltage, a voltage compensation unit is introduced to restore the output voltage to the rated value. Finally, simulations are performed in MATLAB/Simulink to verify the validity of the proposed control strategy.

The subsynchronous oscillation of the power system can be effectively suppressed by the supplementary subsynchronous damping controller (SSDC). Parameter design processes of phase compensator and proportional gain are the key parts of the SSDC parameter design. Firstly, the design method of the parameters of the phase compensator is proposed in this paper. And based on the determination of the compensation phase of the SSDC, the design method of the paramenter of the proportional gain is proposed. Finally, the correctness of the proposed paramenter design method of SSDC is verified by case study.

The phenomenon of "secondary commutation failure" in the process of fault recovery for the HVDC system with STATCOM is described and reproduced. The relationship among STATCOM reactive power compensation, HVDC system control characteristics and fault degree is analyzed. The research shows that the existing STATCOM reactive power control strategy will deteriorate the system recovery characteristics when serious AC side faults occur. Furthermore, an improved STATCOM transient reactive power control strategy is proposed,which can allocate reactive power compensation mode of STATCOM differently according to the fault level. Finally, the proposed control strategy is simulated in PSCAD/EMTDC. The simulation results show that the proposed control strategy can effectively reduce the probability of secondary commutation failure and significantly improve the recovery characteristics of the system.

With the penetration of wind power in the power grid increasing, the impact of wind power on the system stability becomes more and more apparent. Constructing a double-fed induction generator (DFIG) model that is suitable for the power system simulation is the basis for the dynamic study of wind power embedded system. Detailed DFIG model often increases the dimensions of the system and needs relatively long simulation time. Therefore, a reduced order method based on selection modal analysis (SMA) is proposed in this paper. The configuration, control system and the modal analysis of DFIGs are firstly introduced, and then the steps and methods for reducing order based on SMA are introduced. The reduced-order analysis of the DFIGs is based on the detailed model and the reduced order method. This method retains the original physical meaning of the variables and has strong flexibility and applicability. The numerical simulation results show that the reduced model can well fit the original steady-state and transient behavior of the system, which significantly reduces the computational complexity and thus improves the computational efficiency.

Several serious accidents caused by subsynchronous oscillation (SSO) have occurred. In order to study the subsynchronous oscillation, the impedance matrix and the characteristic equation are analyzed. By means of equivalent circuit, the physical meanings of the characteristic equation and impedance are analyzed from the view of impedance. Then, the eigenvalues of the oscillation mode of the system are estimated according to the frequency impedance curve. A quantitative analysis method based on the impedance method is proposed, and the deficiency of existing stability analysis methods based on impedance model is resolved. Finally, the practicability and effectiveness of the impedance stability analysis method are verified through simulation case.

Developing wind power is becoming the national energy strategy and will play an important role in economic development. Since there are differences in economic development, power grid structure, power consumption cost and electricity price level in different regions, finding a way to quantitatively evaluate comprehensive economy after wind power integration is helpful to guide wind power planning and construction. This paper proposes a comprehensive economy evaluation method from six aspects, including system operation cost, coal consumption and emission, conventional unit utilization hours, wind power subside cost, operating benefit of power grid company and coal fire plant electricity price. Then, taking a provincial power grid as an example, the comprehensive economy with large-scale wind power integration is evaluated, and the effectiveness of this method is verified.

Currently, Bitcoin are most popular ways to implement electronic cash transactions. As Bitcoin is one of the proof-of-work (PoW) blockchain implementations. This transaction mode also explored and applied in the electric power trading. Although the security of blockchain has been thoroughly analyzed, the security of forked PoW blockchains has not been carefully investigated. This paper builds a novel and quantifiable model of power trading systems based on blockchain technology. According to the behavior of forked blockchain, the analysis and model are proposed by Markov decision process (MDP). An MDP-like security analytical model for PoW blockchain by adding sidechains is established. In addition, a blockchain-based power trading simulator is designed. Through the simulation experiment, the influence of block generation interval and block size on the blockchain in the electric power trading system is analyzed.