In　order　to　meet　the　increasingly　demands　and　complex　scenarios　under　the　power　supply　needs,we　developed　a　multi-mode　online　power-saving　mobile　energy　storage　device.　The　divice　can　provide　series,　parallel,　and　dual-loop　power　supply　modes　according　to　the　actual　situation.　Aiming　at　the　three　kinds　of　power　supply　modes,　we　introduced　the　access　method,　and　put　forward　the　power　supply　method　and　control　program　of　the　energy　storage　system.　The　control　strategy　of　energy　storage　device　and　the　seamless　switching　technology　were　analyzed.　The　combined　control　method　of　energy　storage　converter　with　repetitive　control　and　PID　control　was　proposed,　which　could　effectively　improve　the　power　quality　of　the　power　supply　system　when　nonlinear　load　was　connected.　The　experimental　platform　was　set　up　separately,　and　the　multi-mode　protection　power　supply　experiments　were　carried　out　for　the　load　of　the　three　types　of　resistance,　resistance-inductance,　and　resistance-capacity.　The　experiments　show　that　the　series　mode　of　the　device　has　the　best　power　supply　performances,　the　parallel　mode　realizes　seamless　switching,　and　the　double　loop　mode　realizes　the　multi-loop　power　supply.　In　general,　the　three　models　have　their　own　advantages　and　disadvantages.　The　device　can　provide　multi-mode　power　supply　plan　according　to　different　scenarios,　and　it　can　better　achieve　online　power　supply　and　other　targets.　©　2018,　High　Voltage　Engineering　Editorial　Department　of　CEPRI.　All　right　reserved.