Active stabilization methods of electric power systems with constant power loads:a review

Modern electric power systems have increased the usage of switching power converters.These tightly regulated switching power converters behave as constant power loads(CPLs).They exhibit a negative incremental impedance in small signal analysis.This negative impedance degrades the stability margin of the interaction between CPLs and their feeders,which is known as the negative impedance instability problem.The feeder can be an LC input filter or an upstream switching converter.Active damping methods are preferred for the stabilization of the system.This is due to their higher power efficiency over passive damping methods.Based on different sources of damping effect,this paper summarizes and classifies existing active damping methods into three categories.The paper further analyzes and compares the advantages and disadvantages of each active damping method.

A 6n-Order Low-Frequency Mathematical Model of Multiple Inverters Based Microgrid

Microgrid stability analysis is a critical issue especially due to the inverters’low-inertia nature.The voltage and current control loops influences on stability are researched frequently most of which focus on medium and high-frequency characteristic.Although the complete state-space model aims at low-frequency characteristic,it is too complicated and the calculation amount is huge with the scale of the microgrid increasing.One available reduced-order model of an inverter is simple,but it is suitable for only single inverter without network dynamic in microgrid.To fill in these gaps,a novel modeling method is proposed in this paper to investigate the low-frequency instability phenomenon and describe the whole DG connected system including network.In consideration of the high penetration level of induction motor(IM)loads and constant power(CP)loads in practical applications,the low-frequency mathematical model of IM and CP loads on the basis of static load is also built in this paper.Simulation and experimental results verify the effectiveness of the proposed model.

Stability Analysis and Efficiency Improvement of a Multi-converter System Using Multi-objective Decision Making

Multi-converter system is mainly used in advanced automotive systems.Different converters and inverters are taking part in automotive systems to provide different voltage levels in a multi-converter system.It involves constant voltage load(CVL),constant power load(CPL)and other loads.The CPL in such systems offers negative impedance characteristic and it creates a destabilizing effect on the main converter.The effect of destabilization can be reduced by increasing the CVL or inserting parasitic components.Attempts have been made by authors to improve the stability by using parasitics of different components such as switch,diode and inductor.Influence of insertion of parasitics including the series equivalent resistance of the filter capacitor and variation in CVL on the performance of main converter is mathematically analyzed and conflicting behavior between system stability and efficiency is observed.The optimum solution between these two functions is obtained by using multi-objective decision making(MODM)by varying parasitics of different components and CVL.An attempt has been made to demonstrate the effect of CVL load and the parasitics on the stability and efficiency of the main converter,experimentally.

A review of stabilization methods for DCMG with CPL,the role of bandwidth limits and droop control

DC microgrids(DCMGs)integrate and coordinate various DC distribution generation units including various renew-able energy sources and battery storage systems,and have been used in satellites,the International Space Station,telecom power stations,computer power supplies,electric aircraft,and electric ships.However,the presence of constant power loads(CPLs)can cause instability in DCMGs.Thus,this paper reviews the stabilization techniques that can resolve instability caused by CPLs,as well as various parameters of CPLs,such as bandwidth,and the frequency of the CPLs that can stabilize the DCMGs.It also discusses recent trends and future work in finding stability limits using the parameters of CPLs.It should be useful for directing research towards appropriate mathematical and experimental approaches for the stability of DCMGs with CPLs.