Method and apparatus for achieving current balance in parallel connected switching devices

For transferring electrical power between two electrical power sources, a switching arrangement comprising:

• a) at least one plurality of series connections each comprising a switching device and an inductor, the series connections being connected in parallel with the parallel combination being connected between said two power sources;
• b) means to control the conductive state of said switching devices to effect periods of simultaneous current within each of the series connections alternating with periods of no current within said connections;
• c) means to provide individual current signals representing the respective currents in each of the simultaneously conducting devices of said plurality;
• d) means to provide an average current signal representing the average value of said individual current signals;
• e) means to develop a difference signal, with respect to each of said individual current signals, as a function of the difference between the respective individual current signal and the average current signal;
• f) means to generate control signals operative to render conductive associated ones of said switching devices;
• and
• g) means responsive to the difference signal to vary the time, with respect to a predetermined norm of associated devices, of application of said control signal to the associated ones of said devices whereby differences in current value within said devices are reduced.

In a power switching system of the type having at least one leg connected between two power sources, each leg comprising a plurality of respective series connections being connected in parallel with each other, each of the series connections comprising a switching device and a respective inductor, each switching device being operable in successive control cycles so that the switching device is in a conductive state for a first time period of each control cycle and in a nonconductive state for a second time period of each control cycle to cause current to flow in the series connection during the first time period and to prevent current from flowing during the second time period, a method of controlling the switching devices in a respective leg to enhance current balance within the plurality of series connections and comprising the steps of:

• a) selectively controlling the conductive state of each of the switching devices during each control cycle by applying respective control signals to each of the switching devices to effect substantially coincident respective first time periods of simultaneously current flow in all of the series connections alternating with respective second time periods of no current flow;
• b) generating a respective individual current signal representative of current flow within each of the series connections during respective first time periods of simultaneous current flow;
• c) generating an average current signal representative of the average current flow within the series connections based upon the individual current signals;
• d) generating a respective difference signal as a function of the difference between each of the individual current signals and the average current signal;
• and
• e) selectively adjusting relative timing of the application of respective control signals to respective switching devices during respective first time periods of current flow during a control cycle responsive to respective difference signals from a prior control cycle to thereby enhance current balance within the plurality of series connections of the respective leg of the power switching system.

For transferring electrical power between two electrical power sources, a switching arrangement comprising:

• a) at least one plurality of series connections being connected in parallel with each other and with the parallel combination being connected between the two power sources, each switching device being operable in a conductive state, during which current flows in the series connection, and a nonconductive state, during which no current flows in the series connection;
• b) means for controlling the conductive state of said switching devices in successive control cycles by application of respective control signals to said switching devices to effect substantially coincident first time periods of simultaneous current flow within all of the series connections alternating with second time periods of no current flow;
• c) means for providing individual current signals representing the respective currents in each of the switching devices during respective first time periods of simultaneous current flow;
• d) means for providing an average current signal representative of the average current flow within the series connections based upon said individual current signals;
• e) means for providing a difference signal, as a function of the difference between an individual current signal and the average current signal;
• and
• f) means cooperating with said control means for selectively adjusting relative timing of the application of respective control signals to respective switching devices during respective first time periods of current flow in a control cycle responsive to respective difference signals from a prior control cycle to thereby enhance current balance within said plurality of series connections.