Simultaneous AC-DC Transmission Research Articles

Optimal power flow and computer‐based analysis of a simultaneous AC–DC power transmission system

AbstractElectricity demand is constantly increasing with the growing population, and the process of establishing new transmission lines has become complicated due to the rise in industrialization and urbanization. One solution to meeting this increased demand is to improve the power transfer capability by increasing the transmission voltage. However, the existing transmission lines may not be able to handle the increased load if they are pushed to their thermal limit. This paper presents a mathematical analysis of a simultaneous AC–DC transmission system transmitting power at different values of parameters. The computational analysis is carried out using MATLAB, and the circuit model simulation is validated by using power systems computer aided design (PSCAD/EMTDC). The transmitted power is evaluated by varying the transmission angle and transmission length for a fixed voltage, and then by varying the transmission angle and voltage for a fixed transmission length. Both these cases are analyzed using approximate and actual formulas. The results of the computation and simulation show close conformity.

Techno-Economic Comparisons of HVAC and Simultaneous AC-DC Transmission

Electric power consumption has been increasing rapidly across the globe; this increase specially accelerated in the last decade. Consequently, existing transmission lines are becoming overloaded beyond their power transfer capability. The inadequacy of the transmission lines has contributed to power interruptions and instability of the power system. Construction of new transmission lines can be a solution to mitigate these problems. However, to build the whole structure of a new transmission line, a huge investment is required. Besides this, environmental concerns would create further barriers that delay the accomplishment of the project. Therefore, the effective and quickest solution to tackle this problem is enhancing the power transfer capability and stability margin of existing transmission lines. This paper studied the techno-economic feasibility of converting an existing HVAC line into a simultaneous AC-DC power transmission system to enhance power transfer capability as well as to improve power system stability. Using the proposed method, the loadability of Tana Beles to Addis Ababa 400 kV, 476.2 km AC line has increased to more than double which is from 1091.66 MW to 2196.85 MW. The active power loss and corona loss evaluation of the two systems ensured that simultaneous AC-DC system is more efficient than HVAC system. It is also shown that the instability can be effectively improved by simultaneous AC-DC power transmission with fast DC power modulation. From the economic point of view, rather than constructing new HVAC line, converting existing HVAC line into simultaneous AC-DC transmission system has a price reduction of about 107,984,968.56 USD or 32.46% of the new HVAC line cost. Considering a 35-year project life cost analysis, it is observed that the life cycle cost of the simultaneous AC-DC transmission system is about 29.2% lower than the life cycle cost of a new 400 kV HVAC line. Thus, the designed simultaneous AC-DC power transmission system has better technical performance and also is less costly than constructing a new HVAC line.

Research on Hybrid Microgrid Based on Simultaneous AC and DC Distribution Network and Its Power Router

Under the dual pressure of environmental pollution and energy crisis, the global energy consumption structure reform deepens unceasingly and the concept of energy internet has developed rapidly. The widespread volatility, randomness, and uncertainty of distributed new energy generation impose new requirements on distribution systems. The zigzag transformer is used as the coupling and isolating device for simultaneous AC–DC transmission. The basic principle and structure of simultaneous AC–DC power distribution network is analyzed. The topology structure of the simultaneous AC–DC hybrid microgrid and basic operating principle of the microgrid under different operating modes are proposed for the distributed power grid technology. Combined with power electronic technology, a modular multi-interface structure of power routers applied to AC–DC hybrid microgrid and its control strategy are proposed to realize the power routing control of microgrid and ensure reliable operation control of the microgrid. By building the model of simultaneous AC–DC hybrid microgrid and its power router, the rationality and effectiveness of the power router for microgrid routing control are verified.

A Mathematical Model for the Transient Stability Analysis of a Simultaneous AC–DC Power Transmission System

The outcome of recent numerical simulation shows that the conversion of an AC transmission line to a simultaneous AC–DC line improves the system stability. This paper presents a mathematical model, suitable for the stability analysis of a simultaneous AC–DC transmission system, transmitting both AC and DC powers simultaneously through an existing AC line. The model is based on the principle of equal area criterion. The salient feature of this model is the introduction of a solution technique of an integral component of the model, which avoids the trial and error approach for the analysis. The model development process considers a single machine-infinite bus system with a transmission line connecting the machine and the infinite bus. The process also considers the severe most fault at the sending end bus. The validation of the model is executed through two different approaches; comparison of the results obtained applying the proposed model to the power system with the published ones in the literature and with the results obtained using standard software, MATLAB–Simulink, based circuit simulations. The model is also applied to a realistic system and IEEE benchmark systems to verify its capability of evaluating the benefits of a simultaneous AC–DC transmission system.

A mathematical model for the loadability analysis of a simultaneous AC–DC power transmission system

Simultaneous AC–DC power transmission system can, generally, increase the load carrying capability of an existing long AC transmission line. A mathematical model of a simultaneous AC–DC transmission system, transmitting power through an existing AC transmission line, is proposed in this paper. The model is based on the development of expression for AC and DC power flow of simultaneous AC–DC system in terms of the power flow of original AC system. It incorporates the thermal constraint of the line, the allowable maximum percentage of DC voltage mix in an already installed AC line and the operating practice of a long transmission line. The validation of the model is executed through two different approaches; comparison of the results obtained applying the proposed model to the power system with the published ones in the literature and with the results obtained using two different standard software packages, PSpice and MATLAB simulink, based circuit simulations. The model is also applied to a realistic system to verify its capability of evaluating the benefits of a simultaneous AC–DC transmission system. The model is an analytical tool for transmission planners to take the decision whether an existing AC transmission system would increase the power transfer capability if it were converted into a simultaneous AC–DC system.