A power electronic drive circuit on-board of a vehicle comprising: a dc bus ; a first energy storage device coupled to the dc bus , the first energy storage device configured to output a dc voltage; a first bi-directional dc-to-ac voltage inverter coupled to the first energy storage device and to the dc bus ; a first electromechanical device coupled to the first bi-directional dc-to-ac voltage inverter ; a charging system coupled to the dc bus via a charge bus , the charging system comprising: a receptacle configured to mate with a connector coupled to a voltage source external to the power electronic drive circuit ; and an isolation transformer configured to electrically isolate the charge bus from the receptacle ; and a controller configured to cause the charging system to supply a charging voltage to the dc bus based on a voltage received from the voltage source external to the power electronic drive circuit ; the charging system further comprising a pair of transistors ; characterized in that the charging system further comprises: a resonance capacitor ; and wherein the isolation transformer , the pair of transistors , and the resonance capacitor form an isolation ac-to-dc inverter ; and the controller is configured to independently control the transistors in a series resonance mode such that the resonance capacitor and a transformer leakage inductance (LR) of the transformer operate substantially at or slightly above resonance in open loop, wherein the controller is further configured to cause the isolation ac-to-dc inverter to operate in a series resonance mode. a dc bus ; a first energy storage device coupled to the dc bus , the first energy storage device configured to output a dc voltage; a first bi-directional dc-to-ac voltage inverter coupled to the first energy storage device and to the dc bus ; a first electromechanical device coupled to the first bi-directional dc-to-ac voltage inverter ; a charging system coupled to the dc bus via a charge bus , the charging system comprising: a receptacle configured to mate with a connector coupled to a voltage source external to the power electronic drive circuit ; and an isolation transformer configured to electrically isolate the charge bus from the receptacle ; and a receptacle configured to mate with a connector coupled to a voltage source external to the power electronic drive circuit ; and an isolation transformer configured to electrically isolate the charge bus from the receptacle ; and a controller configured to cause the charging system to supply a charging voltage to the dc bus based on a voltage received from the voltage source external to the power electronic drive circuit ; the charging system further comprising a pair of transistors ; characterized in that the charging system further comprises: a resonance capacitor ; and wherein the isolation transformer , the pair of transistors , and the resonance capacitor form an isolation ac-to-dc inverter ; and the controller is configured to independently control the transistors in a series resonance mode such that the resonance capacitor and a transformer leakage inductance (LR) of the transformer operate substantially at or slightly above resonance in open loop, wherein the controller is further configured to cause the isolation ac-to-dc inverter to operate in a series resonance mode. a resonance capacitor ; and wherein the isolation transformer , the pair of transistors , and the resonance capacitor form an isolation ac-to-dc inverter ; and the controller is configured to independently control the transistors in a series resonance mode such that the resonance capacitor and a transformer leakage inductance (LR) of the transformer operate substantially at or slightly above resonance in open loop, wherein the controller is further configured to cause the isolation ac-to-dc inverter to operate in a series resonance mode. <EOS>