Harmonics Suppression for Critical Loads Using Electric Springs With Current-Source Inverters

A novel control strategy of direct current control and harmonic suppression function, similar to the control of active power filter (APF), is proposed using a new type of electric spring (ES) with current-source inverters (CSIs) to improve the performances of ESs. Compared with the existing control methods, total harmonic distortion can be greatly reduced by changing voltage-source inverters to CSIs and also by replacing voltage control with direct current control. System performance can also be improved further by an additional harmonic suppression function, of which the control is similar to APF where the input current is separated into fundamental part and other components with the help of the single-phase dq0 transformation. The concept of ESs can also be interpreted more clearly by the proposed direct current control. Operating principles of the proposed ES and control are well illustrated. The effectiveness of the control strategy has been validated by the simulation results.