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Similar to other major electrical apparatuses, the reliability and stability of the dc network is becoming the most important issue when using the voltage-source-converter-based multiterminal dc (VSC-MTDC) system for offshore wind power integration. A coordinated control strategy of VSC-MTDC named master–auxiliary is proposed by combining the advantages of the voltage margin and voltage droop control. This strategy has three advantages. First, the master converter station with the constant dc voltage control can provide reference to the system dc voltage and is helpful for the stabilization of dc voltage. Second, the integrated control of the dc voltage in both master and auxiliary converter stations are helpful for providing adequate active power control (APC) and restraining large power variation. Third, the APC converter station can serve as a backup for the dc voltage control in abnormal conditions. In order to guarantee the reliability and stability of the system under various operating conditions, this paper introduces the priority of dc voltage control to the coordination control strategy. Moreover, a parameter optimizing method of controllers for this strategy is also proposed. Finally, the effectiveness of the master–auxiliary control is verified by simulations under normal and abnormal conditions.

In this paper, new formulations of the power flow and continuation power flow that allow for electro-thermal coupling in transmission lines have been proposed. The new formulations capture the overhead lines' electro-thermal coupling effects by treating their series resistances as temperature dependent variables. They generate results that can differ from the results of conventional formulations markedly, particularly for problems centring on line impedances. The paper demonstrates this by applying the new formulations to the power transfer limit calculation. Generally, power transfer limits are defined either by encountering a line's thermal limit or detecting the onset of voltage collapse in the system. Studies based on 2-bus and 14-bus test systems are used to demonstrate the efficacy of the new formulations for both situations. For these studies, specific point-to-point power transfer limits are calculated with and without the lines' electro-thermal coupling effects and the results are compared.

This paper proposes a three-level transformer condition assessment model based on matter-element cloud theory and evidential reasoning decision-making theory. Both quantitative and qualitative factors are considered in the model. Matter-element cloud model is utilized to integrate the quantitative indices with their optimal weights to assess the condition of items, including Dissolved Gas Analysis(DGA), electrical testing and oil testing in the first level in the form of association degrees with state grades to generate the original basic probability assignments for the second-level model. D-S evidential reasoning decision-making model is utilized in the second level to assess the condition of systems including quantitative system and qualitative system and in the third level to assess condition of the overall transformer. Both fuzziness and randomness are taken into consideration in this model. Experimental cases confirm that the assessing model is capable of offering an overall assessment of the observed transformer condition and assisting the maintenance strategy development.

This paper proposes a multi-point DC voltage control strategy of voltage source converter based multi-terminal DC (VSC-MTDC) transmission system for integrating large-scale offshore wind power. Taking a typical four-terminal DC transmission system for example, DC power flow distribution is analyzed, DC flow calculation model is derived and active power control of auxiliary converter station with DC voltage-active power characteristic is proposed. Finally, simulations in PSCAD/EMTDC are conducted to verify the validity of multi-point DC voltage control method under various operating state and MATLAB programming are undertaken to verify the accuracy of DC power flow model. Results show that this method can guarantee the active power allocation of VSC-MTDC transmission system and good control effects are obtained.

Since the crisis of energy and climate intensifies, wind power, one of the most perspective renewable energy, develops rapidly around the worldwide. After the publication and implement of Renewable Energy Law, China wind generation is growing dramatically and Shandong province will be the eighth ten-gigawatt-level wind power base by 2020. In this paper, some characteristics of power grid and wind power development of Shandong province are given, such as features in power grid and power sources, installed capacity of wind power, geographical distribution of wind generation, wind farms and wind turbine generators and off-shore wind power. Next, the problems of wind power operation in this area are proposed in the following aspects: peak regulation and frequency regulation, wind power penetration in regional grid, voltage control in regional network, the stability of power grid and the effect of HVDC system on wind power integration. Then, the reasons for the above problems are analyzed, which can be attributed to several respects: imperfection of technical rules and policies, uncoordinated development with power sources and grid, lack of technical tools for wind power dispatching, poor performance of supervisory control and data acquisition system (SCADA) system in wind farms, poor performance of wind turbine generators. Finally, some suggestions and measures are put forward, which will be a guiding reference for the wind power integrating and operating.

The desired impedance of Thyristor Controlled Series Capacitor (TCSC) is usually obtained by adjusting the firing angle and it is of great importance to make clear the relationship between the two quantities. The relationship between firing angle and conduction angle is proposed in this paper considering the influence of the thyristor conduction characteristics and the equivalent resistance in the reactor branch. In the derivation of the fundamental-frequency impedance, it is found out that there are dual solutions corresponding to the same firing angle in most steady operation area of TCSC. One is inductive and the other is capacitive. This phenomenon is demonstrated by both digital simulation and dynamic emulation experiment. Some conclusions and experiment results can provide reference to engineering exploitation and bottom control design of TCSC.