Metaheuristic Based Solution For The Non-linear Controller Of The Multiterminal High-voltage Direct Current Networks

An increase in power demand has resulted in the production of more complex and large power systems.The classic structure of power flow based on top to down model is changing with an introduction of Energiewende.The main reason behind this change is the integration of more decentralized and intermittent renewable energy sources at all levels of the power system.Thus,a power system’s operation is facing new difficulties to guarantee the robustness and credibility of the system.Voltage source converter-based HVDC(VSC-HVDC)provides the answer to remove these difficulties and add flexibility that can upgrade the power system’s performance in the near future.Amid typical operation,additional control is added to the AC system while using VSC based HVDC systems.Further,VSC-HVDC set-points are optimized using transmission system,which in return optimizes the power flow of the AC system and can avoid congestion.But when the AC system is under the influence of some disturbance,VSC-HVDC links could help improve the stability of the power system.This can be done by modulating the system’s active and reactive power with controllers at a grid.This research aims to develop a constraint-free and reliable control structure for VSC stations in MTHVDC transmission systems.Proportional Integral(PI)controllers are emerging as an efficient and robust control structure for the VSC stations.But its control parameters add complexities and overrun the system like convergence problems and delayed responses.The conventional techniques used the approximated linear models to tune the control parameters that do not produce optimal results.Therefore,it is inevitable for the VSC-HVDC system’s dynamic and reliable operation that these parameters should be optimized.In this research,the issues as mentioned above are rectified by implementing a metaheuristic technique,i.e.,Artificial Bee Colony(ABC)optimization,on the PI parameters,improving the VSC station’s dynamic response in any disturbance.Thus,the multiobjective based ABC technique is employed to tune the control parameters of VSC stations optimally.The multiobjective function helps to tune inner current and outer current controllers simultaneously.This research work presents an optimized control structure that suggests the ABC algorithm and further investigated it.To validate the results of the proposed technique,the ABC algorithm has been developed in MATLAB and then optimized PI parameters will be implemented on a CIGRE four-terminal VSC-HVDC transmission system developed in PSCAD/EMTDC and will validate the expected outcome.CIGRE standard model is used as a reference and for comparison purposes.Further,two parallel sets of PI controller operating for inner and outer loop simultaneously optimized using multiobjective ABC technique to attain optimized control structure.During the simulation,both classically tuned and ABCbased tuned parameters are tested.Results show the steady-state and transient control performance of both for classically tuned and ABC-based tuned parameters,during i)unbalance wind power generation,ii)unbalance load demand at AC grids,and iii)eventual permanent VSC disconnection.