The delta-connected high-voltage transformer-less battery energy storage system (D-HVTL-BESS) has a series of advantages such as large unit capacity

high operating efficiency

and fast response speed

which makes it an ideal solution for constructing large-scale energy storage power stations. However

low-frequency pulsating currents

mainly second harmonic currents (SHC)

flow in the battery of the D-HVTL-BESS

resulting in a large demands for DC filtering networks

which significantly increases the cost and size of the system and reduces the system response speed. Therefore

there is an urgent need to propose an SHC suppression strategy to reduce the demand of passive filters. To this end

this paper proposes an SHC suppression strategy for D-HVTL-BESS based on the third harmonic current injection. Firstly

the exact expressions of SHC at different power factor angles and different power levels are derived; then

the amplitudes and phases of the third harmonic currents under different operating conditions are designed to adaptively eliminate this SHC; moreover

the suppression effects of the injected third harmonic currents on the battery currents and capacitor voltage ripples are quantitatively evaluated; finally

a PSCAD/EMTDC simulation model of the D-HVTL-BESS is constructed for validation. The results show that

after adopting the proposed strategy

the ripple rates of the battery current and capacitor voltage are reduced by about 70% and 50%

respectively

with negligibly affecting the conversion efficiency of the system.