Switching sequence controlled current steering for stacked half bridge converters

Abstract

A stacked half bridge converter may be configured to provide an AC output voltage from either a DC or an AC input voltage. The switching devices of the converter may be operated according to a plurality of switching sequences, each switching sequence including one or more switching patterns, each switching pattern including one or more switching states of the switching devices. The switching sequences, patterns, and states may be selected to improve operation of the converter, by regulating the voltage at a neutral point of the converter to reduce ripple, increase switching efficiency, protect the switching devices from overvoltages, and the like.

1 . A stacked half bridge converter configured to provide an AC output voltage, the stacked half bridge converter comprising:
 four switching devices configured in an upper half bridge and a lower half bridge and at least two capacitors, wherein:
 an input of the stacked half bridge converter is provided across a first terminal of a first switching device and a second terminal of a fourth switching device and an output of the stacked half bridge converter is provided between a junction of a second terminal of the first switching device and a first terminal of a second switching device and a junction of a second terminal of a third switching device and a first terminal of the fourth switching device; 
 the at least two capacitors include a first capacitor coupled between the first terminal of the first switching device and a neutral point corresponding to a junction of a second terminal of the second switching device and a first terminal of the third switching device and a second capacitor coupled between the second terminal of the fourth switching device and the neutral point; and 
   a control circuit configured to operate the switching devices according to a plurality of pulse width modulated switching sequences, each switching sequence including one or more switching patterns, each switching pattern including one or more switching states of the switching devices;   wherein the input of the stacked half bridge converter is configured to receive a DC voltage greater than a voltage rating of the switching devices, and the control circuit is configured balance the voltage appearing across the first and second capacitors to prevent exceeding the voltage rating of the switching devices.   
     
     
         2 . A stacked half-bridge DC-AC converter comprising:
 a first half bridge including a first switching device and a second switching device, wherein a junction point of the first and second switching devices is coupled to a first AC output terminal of the stacked half-bridge DC-AC converter;   a second half bridge including a third switching device and a fourth switching device, wherein a junction point of the third and fourth switching devices is coupled to a second AC output terminal of the stacked half-bridge DC-AC converter and wherein the first and second half bridges are connected in a ladder configuration across a DC input of the stacked half-bridge DC-AC converter;   first and second input capacitors connected in a ladder configuration across the DC input of the stacked half-bridge DC-AC converter, wherein a junction point of the first and second input capacitors is connected to a junction point of the first and second half bridges forming a neutral point of the stacked half-bridge DC-AC converter; and   a controller configured to operate the switching devices according to a plurality of switching sequences, each switching sequence including one or more switching patterns, and each switching pattern including a plurality of switching states, each switching state including pulse width modulated operation of at least one switching device from each of the first and second half bridges, wherein:
 at least one of the plurality of switching sequences includes one or more patterns of switching states selected to inject current into the neutral point to regulate a voltage of the neutral point, reduce a ripple voltage of the neutral point, or equalize losses among the switching devices. 
   
     
     
         3 . The stacked half-bridge DC-AC converter of  claim 2  wherein:
 at least one of the plurality of switching sequences injects positive current into the neutral point to increase the voltage of the neutral point; and 
 at least one switching sequence is selected to inject negative current into the neutral point to decrease the voltage of the neutral point. 
 
     
     
         4 . The stacked half-bridge DC-AC converter of  claim 2  wherein the plurality of switching states are selected from the group consisting of:
 a first switching state in which the first and fourth switching devices are operated; 
 a second switching state in which the second and third switching devices are operated; 
 a third switching state in which the first and third switching devices are operated; and 
 a fourth switching state in which the second and fourth switching devices are operated. 
 
     
     
         5 . The stacked half-bridge DC-AC converter of  claim 4  wherein the one or more switching patterns are selected from the group consisting of:
 a first switching pattern consisting of the third switching state, followed by the first switching state, followed by the third switching state, followed by the second switching state; 
 a second switching pattern consisting of the fourth switching state, followed by the first switching state, followed by the fourth switching state, followed by the second switching state; 
 a third switching pattern consisting of the third switching state, followed by the first switching state, followed by the fourth switching state, followed by the second switching state; and 
 a fourth switching pattern consisting of the fourth switching state, followed by the first switching state, followed by the third switching state, followed by the second switching state. 
 
     
     
         6 . The stacked half-bridge DC-AC converter of  claim 5  wherein the one or more switching sequences are selected from the group consisting of:
 a first switching sequence consisting of a number of repetitions of the first switching pattern followed by an equal number of repetitions of the second switching pattern; 
 a second switching sequence consisting of a number of repetitions of the first switching pattern followed by an equal number of repetitions of the second switching pattern, wherein a first occurrence of the second switching pattern is replaced with the third switching pattern; and 
 a third switching sequence consisting of a number of repetitions of the first switching pattern followed by an equal number of repetitions of the second switching pattern, wherein a first occurrence of the first switching pattern is replaced with the fourth switching pattern. 
 
     
     
         7 . The stacked half-bridge DC-AC converter of  claim 6  wherein the number of repetitions is five. 
     
     
         8 . A stacked half bridge converter configured to provide an AC output voltage, the stacked half bridge converter comprising:
 four switching devices configured in an upper half bridge and a lower half bridge and at least two capacitors, wherein:
 an input of the stacked half bridge converter is provided across a first terminal of a first switching device and a second terminal of a fourth switching device and an output of the stacked half bridge converter is provided between a junction of a second terminal of the first switching device and a first terminal of a second switching device and a junction of a second terminal of a third switching device and a first terminal of the fourth switching device; 
 the at least two capacitors include a first capacitor coupled between the first terminal of the first switching device and a neutral point corresponding to a junction of a second terminal of the second switching device and a first terminal of the third switching device and a second capacitor coupled between the second terminal of the fourth switching device and the neutral point; and 
   a control circuit configured to operate the switching devices according to a plurality of switching sequences, each switching sequence including one or more switching patterns, each switching pattern including one or more switching states of the switching devices, wherein:
 at least one of the plurality of switching sequences injects positive current into the neutral point to increase the voltage of the neutral point; and 
 at least one switching sequence is selected to inject negative current into the neutral point to decrease the voltage of the neutral point; 
   wherein the input of the stacked half bridge converter is configured to receive a DC voltage greater than a voltage rating of the switching devices, and the control circuit is configured balance the voltage appearing across the first and second capacitors to prevent exceeding the voltage rating of the switching devices.   
     
     
         9 . A stacked half-bridge DC-AC converter comprising:
 a first half bridge including a first switching device and a second switching device, wherein a junction point of the first and second switching devices is coupled to a first AC output terminal of the stacked half-bridge DC-AC converter;   a second half bridge including a third switching device and a fourth switching device, wherein a junction point of the third and fourth switching devices is coupled to a second AC output terminal of the stacked half-bridge DC-AC converter and wherein the first and second half bridges are connected in a ladder configuration across a DC input of the stacked half-bridge DC-AC converter;   first and second input capacitors connected in a ladder configuration across the DC input of the stacked half-bridge DC-AC converter, wherein a junction point of the first and second input capacitors is connected to a junction point of the first and second half bridges forming a neutral point of the stacked half-bridge DC-AC converter; and   a controller configured to operate the switching devices according to a plurality of switching sequences, each switching sequence including one or more switching patterns, and each switching pattern including a plurality of switching states, each switching state including modulated operation of at least one switching device from each of the first and second half bridges, wherein:
 at least one of the plurality of switching sequences includes one or more patterns of switching states selected to inject current into the neutral point wherein:
 at least one of the plurality of switching sequences injects positive current into the neutral point to increase the voltage of the neutral point; and 
 at least one switching sequence is selected to inject negative current into the neutral point to decrease the voltage of the neutral point. 
 
   
     
     
         10 . The stacked half-bridge DC-AC converter of  claim 9  wherein the plurality of switching states are selected from the group consisting of:
 a first switching state in which the first and fourth switching devices are operated; 
 a second switching state in which the second and third switching devices are operated; 
 a third switching state in which the first and third switching devices are operated; and 
 a fourth switching state in which the second and fourth switching devices are operated. 
 
     
     
         11 . The stacked half-bridge DC-AC converter of  claim 10  wherein the one or more switching patterns are selected from the group consisting of:
 a first switching pattern consisting of the third switching state, followed by the first switching state, followed by the third switching state, followed by the second switching state; 
 a second switching pattern consisting of the fourth switching state, followed by the first switching state, followed by the fourth switching state, followed by the second switching state; 
 a third switching pattern consisting of the third switching state, followed by the first switching state, followed by the fourth switching state, followed by the second switching state; and 
 a fourth switching pattern consisting of the fourth switching state, followed by the first switching state, followed by the third switching state, followed by the second switching state. 
 
     
     
         12 . The stacked half-bridge DC-AC converter of  claim 11  wherein the one or more switching sequences are selected from the group consisting of:
 a first switching sequence consisting of a number of repetitions of the first switching pattern followed by an equal number of repetitions of the second switching pattern; 
 a second switching sequence consisting of a number of repetitions of the first switching pattern followed by an equal number of repetitions of the second switching pattern, wherein a first occurrence of the second switching pattern is replaced with the third switching pattern; and 
 a third switching sequence consisting of a number of repetitions of the first switching pattern followed by an equal number of repetitions of the second switching pattern, wherein a first occurrence of the first switching pattern is replaced with the fourth switching pattern. 
 
     
     
         13 . The stacked half-bridge DC-AC converter of  claim 12  wherein the number of repetitions is five.