A Flexible Voltage Control Strategy Based on Stage-division for Microgrids

The occurrence of power flow reversal and off-limit of the voltage on common bus becomes more frequent because of the increasing penetration of renewable energy sources(RES)in microgrids.To guarantee the safe and stable operation,adjusting the power output of RES-based inverters to avoid the off-limit voltage is necessary.Considering the apparent power characteristics of inverters,as well as the minimum participation of active power,a voltage control strategy based on stage division to be within the voltage limit is investigated in this paper.In the case of unknown demand and distribution of loads,the proposed control strategy is able to make full use of the apparent power to regulate voltage using simple calculations,while the performance in economical operation is satisfactory.Simulation results prove the effectiveness of the proposed method on the common bus off-limit voltage adjustment.

An Approach for Establishing a Common Grid Model for Flow-based Market Mechanism Simulations

The discussions on the development of an electricity market model for accommodating cross-border cooperation remains active in Europe.The main interest is the establishment of market couplings without curtailing the fair use of the scarce transmission capacity.However,it is difficult to gain mutual consensus on this subject because of the absence of convincing simulation results for the entire region.To achieve that,researchers need a common grid model(CGM)which is a simplified representation of the detailed transmission model which comprises aggregated buses and transmission lines.A CGM should sufficiently represent the inter-area power flow characteristics.Generally,it is difficult to establish a standard CGM that represents the actual transmission network with a suf-ficient degree of exactness because it requires knowledge on the details of the transmission network,which are undisclosed.This paper addresses the issue and reviews the existing approaches in transmission network approximation,and their shortcomings.Then,it proposes a new approach called the adaptive CGM approximation(ACA)for serving the purpose.The ACA is a datadriven approach,developed based on the direct current power flow theory.It is able to construct a CGM based on the published power flow data between the inter-connected market areas.This is done by solving the issue as a non-linear model fitting problem.The method is validated using three case studies.