1500 V photovoltaic (PV) DC electric spring DC microgrid DC–AC converters DC–DC converter ESS sizing Electric spring History of engineering & technology NPC topology PFC PV applications PV generators PV inverters PV microinverters PV systems Renewable energy T-type converters ZCS ZVS active power active power up-regulation adaptive droop control bidirectional switch bridge-linked (BL) buck-boost burst control capability curves cascade multilevel converters cascaded H-bridge center-cross-tied (CCT)