Load balancing

Abstract

A load balancing apparatus for balancing the current supplied on each phase of a multiple phase supply, Each supply phase feeds an AC load, as well as an AC-DC converter. The apparatus measures the current supplied from each phase of the supply as well as the power consumed by each of the AC loads. The power consumed by each of the AC-DC converters is adjusted so that the sum of the current drawn by any one of the AC loads, plus the current drawn by the AC-DC converter on the same supply phase, is substantially balanced between the supply phases. Typically, the AC-DC converters supply a common DC bus, such as a battery. In some examples each AC load includes a DC-AC converter configured to supply power from the common DC battery to one or more of the AC loads.

We claim: 
     
         1 . A load balancing apparatus for providing a substantially balanced load on a 3-phase power supply, the apparatus including:
 a first AC input having an associated first input load sensing circuit, the first AC input having a current path to a first AC output and a first AC-DC converter feeding a first DC output;   a second AC input having an associated second input load sensing circuit, the second AC input having a current path to a second AC output and a second AC- DC converter feeding a second DC output;   a third AC input having an associated third input load sensing circuit, the third AC input having a current path to a third AC output and a third AC-DC converter feeding a third DC output; and   a control circuit, wherein the control circuit is configured to dynamically adjust the power output from one or more of the first AC-DC converter, the second AC-DC converter or the third AC-DC converter to provide a balanced load on each of the first AC input, the second AC input and the third AC input,   wherein at least two of the first AC-DC converter, the second AC-DC converter, or the third AC-DC converter feed a common DC bus, and   wherein the control circuit dynamically varies the DC output voltage of one or more of the first AC-DC converter, the second AC-DC converter, or the third AC-DC converter to vary the distribution of the load current supplied by one or more of the AC-DC converters through the common DC bus.   
     
     
         2 . The load balancing apparatus as claimed in  claim 1  wherein the first AC input is configured to electrically couple to a first phase of the 3-phase power supply, the second AC input is configured to electrically couple to a second phase of the 3-phase power supply and the third AC input is configured to electrically couple to a third phase of the 3-phase power supply. 
     
     
         3 . The load balancing apparatus as claimed in  claim 1  wherein the apparatus is configured to be electrically connected between a 3-phase utility feed to a premises and at least a portion of the electrical load presented by that premises. 
     
     
         4 . The load balancing apparatus as claimed in  claim 1  wherein the apparatus is configured to be electrically connected between a 3-phase feed and a load comprising at least one of an AC component or a DC component. 
     
     
         5 . The load balancing apparatus as claimed in  claim 1 , wherein at least one of the first input load sensing circuit, the second input load sensing circuit, or the third input load sensing circuit includes current transformers coupled to the first AC input current path, the second AC input current path, or the third AC input current path, respectively. 
     
     
         6 . The load balancing apparatus as claimed in  claim 1 , wherein at least one of the first AC-DC converter, the second AC-DC converter, or the third AC-DC converter is configured to provide a variable DC output voltage. 
     
     
         7 . The load balancing apparatus as claimed in  claim 1 , wherein the common DC bus supplies a battery bank.