In accordance with at least one aspect of this disclosure, a bi-directional DC to DC converter includes a DC to DC conversion circuit, and a controller operatively connected to the conversion circuit to control a current output of the conversion circuit, wherein the controller includes an observer based estimated current sensor module which is configured to simulate a physical current sensor and to input an estimated output current feedback inner state signal ∧ėo into a voltage output command feedback loop of the controller. The current sensor module can include an estimated sensor feedback loop.