An apparatus comprising: a DC-link; a load (28,30) coupled to the DC-link; and an energy conversion system comprising: a first energy storage device; a first voltage converter coupled to the first energy storage device and to the DC-link, the first voltage converter configured to: convert a first DC voltage from the first energy storage device into a second DC voltage based on a command signal and based on a first adjustment signal; and supply the second DC voltage to the DC-link; a first bus voltage controller coupled to the DC-link and to the first voltage converter, the first bus voltage controller configured to: iterate calculation of the first adjustment signal based on the command signal and based on a measured voltage of the DC-link; and communicate each iterated calculation of the first adjustment signal to the first voltage converter; a supervisory controller coupled to the first voltage converter and to the first bus voltage controller, the supervisory controller configured to: iterate calculation of the command signal based on the load (28,30) and based on a desired DC-link voltage for the load (28,30); and communicate each iterated calculation of the command signal to the first voltage converter and to the first bus voltage controller; and wherein a frequency of the first bus voltage controller to iteratively update each calculation of the first adjustment signal and to communicate each iterated calculation of the first adjustment signal is higher than a frequency of the supervisory controller to iteratively update each calculation of the command signal and to communicate each iterated calculation of the command signal. a DC-link; a load (28,30) coupled to the DC-link; and an energy conversion system comprising: a first energy storage device; a first voltage converter coupled to the first energy storage device and to the DC-link, the first voltage converter configured to: convert a first DC voltage from the first energy storage device into a second DC voltage based on a command signal and based on a first adjustment signal; and supply the second DC voltage to the DC-link; a first bus voltage controller coupled to the DC-link and to the first voltage converter, the first bus voltage controller configured to: iterate calculation of the first adjustment signal based on the command signal and based on a measured voltage of the DC-link; and communicate each iterated calculation of the first adjustment signal to the first voltage converter; a supervisory controller coupled to the first voltage converter and to the first bus voltage controller, the supervisory controller configured to: iterate calculation of the command signal based on the load (28,30) and based on a desired DC-link voltage for the load (28,30); and communicate each iterated calculation of the command signal to the first voltage converter and to the first bus voltage controller; and wherein a frequency of the first bus voltage controller to iteratively update each calculation of the first adjustment signal and to communicate each iterated calculation of the first adjustment signal is higher than a frequency of the supervisory controller to iteratively update each calculation of the command signal and to communicate each iterated calculation of the command signal. a first energy storage device; a first voltage converter coupled to the first energy storage device and to the DC-link, the first voltage converter configured to: convert a first DC voltage from the first energy storage device into a second DC voltage based on a command signal and based on a first adjustment signal; and supply the second DC voltage to the DC-link; convert a first DC voltage from the first energy storage device into a second DC voltage based on a command signal and based on a first adjustment signal; and supply the second DC voltage to the DC-link; a first bus voltage controller coupled to the DC-link and to the first voltage converter, the first bus voltage controller configured to: iterate calculation of the first adjustment signal based on the command signal and based on a measured voltage of the DC-link; and communicate each iterated calculation of the first adjustment signal to the first voltage converter; iterate calculation of the first adjustment signal based on the command signal and based on a measured voltage of the DC-link; and communicate each iterated calculation of the first adjustment signal to the first voltage converter; a supervisory controller coupled to the first voltage converter and to the first bus voltage controller, the supervisory controller configured to: iterate calculation of the command signal based on the load (28,30) and based on a desired DC-link voltage for the load (28,30); and communicate each iterated calculation of the command signal to the first voltage converter and to the first bus voltage controller; and iterate calculation of the command signal based on the load (28,30) and based on a desired DC-link voltage for the load (28,30); and communicate each iterated calculation of the command signal to the first voltage converter and to the first bus voltage controller; and wherein a frequency of the first bus voltage controller to iteratively update each calculation of the first adjustment signal and to communicate each iterated calculation of the first adjustment signal is higher than a frequency of the supervisory controller to iteratively update each calculation of the command signal and to communicate each iterated calculation of the command signal.