VSG-based Adaptive Droop Control for Frequency and Active Power Regulation in the MTDC System

In this paper,a VSG(virtual synchronous generator)-based method with adaptive active power and DC voltage droop is proposed for the control of VSC stations in the multi-terminal DC(MTDC)system.This control strategy can improve the inertial level of the AC networks and attenuate the rate of change of frequency when a disturbance occurs.In addition,the droop control of the active power and DC voltage is implemented to make the AC networks share the unbalanced power in the MTDC.The droop coefficients are adaptively adjusted depending on the frequency margin of every AC network,which makes the allocation of unbalanced power among AC networks more reasonable from the frequency variation perspective.The control strategy is evaluated in the scenarios of sudden load change and wind turbine tripping,and the results are presented to demonstrate its effectiveness.

Adaptive Bidirectional Droop Control for Electric Vehicles Parking with Vehicle-to-grid Service in Microgrid

With the popularity of electric vehicles(EVs),a large number of EVs will become a burden to the future grid with arbitrary charging management.It is of vital significance to the control of the EVs charging and discharging state appropriately to enable the EVs to become friendly to the grid.Therefore,considering the potential for EVs seen as energy storage devices,this paper proposes a multiport DC-DC solid state transformer topology for bidirectional photovoltaic/battery-assisted EV parking lot with vehicle-to-grid service(V2G-PVBP).Relying on the energy storage function of EVs,V2G-PVBP is able to not only satisfy the normal requirements of EVs’owner,but also provide the function of load shifting and load regulation to the microgrid.In this paper,EVs are categorized into limited EV and freedom EV.Limited EVs are always kept in charging state and freedom EVs can take part in the load regulation of the microgrid.The proposed adaptive bidirectional droop control is designed for freedom EVs to make them autonomously charge or discharge with certain power which according to each EV’s state of charge,battery capacity,leaving time,and other factors to maintain the stability of the future microgrid.Eventually,the simulation and experiment of the adaptive bidirectional droop control based V2G-PVBP are provided to prove the availability of V2G-PVBP.

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.