Adaptive Reference Power Based Voltage Droop Control for VSC-MTDC Systems

Featuring low communication requirements and high reliability,the voltage droop control method is widely adopted in the voltage source converter based multi-terminal direct current(VSC-MTDC)system for autonomous DC voltage regulation and power-sharing.However,the traditional voltage droop control method with fixed droop gain is criticized for over-limit DC voltage deviation in case of large power disturbances,which can threaten stable operation of the entire VSCMTDC system.To tackle this problem,this paper proposes an adaptive reference power based voltage droop control method,which changes the reference power to compensate the power deviation for droop-controlled voltage source converters(VSCs).Besides retaining the merits of the traditional voltage droop control method,both DC voltage deviation reduction and power distribution improvement can be achieved by utilizing local information and a specific control factor in the proposed method.Basic principles and key features of the proposed method are described.Detailed analyses on the effects of the control factor on DC voltage deviation and imbalanced power-sharing are discussed,and the selection principle of the control factor is proposed.Finally,the effectiveness of the proposed method is validated by the simulations on a five-terminal VSC based high-voltage direct current(VSC-HVDC)system.

Enhancing Energy Utilization Efficiency of Pakistani System Considering FACTS Devices and Distributed Generation:Feasibility Study

In recent years,voltage stability issues have become a serious concern with regard to the safety of electrical systems,these issues are more evident and have wider consequences in vertical networks with an insufficient reactive power reserve.Pakistan is currently suffering from the worst energy crisis in its history.Owing to an increase in energy demand,the current transmission system is becoming increasingly inadequate.It has thus become necessary to reduce losses and enhance the system voltage profile for more efficient energy utilization.In this study,the main emphasis is on assessing the feasibility of using flexible AC transmission system devices and distributed generation to compensate power failures on the power lines of the Pakistani power transmission system.The load flow and contingency analyses are performed on a 132 kV transmission system that feeds power to the Quetta electric supply company.The region of Baluchistan is studied to evaluate the effectiveness of the proposed method.The system is simulated using NEPLAN,which accurately models the details of all system elements and the optimal power flow.The simulation results indicate that the proposed method helps reduce system losses,voltage deviation,and power flow congestion,with all system constraints within permissible limits.

A novel control strategy based on a look-up table for optimal operation of MTDC systems in post-contingency conditions

Multi terminal VSC-HVDC systems are a promising solution to the problem of connecting offshore wind farms to AC grids.Optimal power sharing and appropriate control of DC-link voltages are essential and must be maintained dur-ing the operation of VSC-MTDC systems,particularly in post-contingency conditions.The traditional droop control methods cannot satisfy these requirements,and accordingly,this paper proposes a novel centralized control strategy based on a look-up table to ensure optimal power sharing and minimum DC voltage deviation immediately during post-contingency conditions by considering converter limits.It also reduces destructive effects(e.g.,frequency devia-tion)on onshore AC grids and guarantees the stable operation of the entire MTDC system.The proposed look-up table is an array of data that relates operating conditions to optimal droop coefficients and is determined according to N-1 contingency analysis and a linearized system model.Stability constraints and contingencies such as wind power changes,converter outage,and DC line disconnection are considered in its formation procedure.Simulations performed on a 4-terminal VSC-MTDC system in the MATLAB-Simulink environment validate the effectiveness and superiority of the proposed control strategy.