Method and apparatus for bypassing cascaded h-bridge (chb) power cells and power sub cell for multilevel inverter

Abstract

Multilevel power converters, power cells and methods are presented for selectively bypassing a power stage of a multilevel inverter circuit, in which a single relay or contactor includes first and second normally closed output control contacts coupled between a given power cell switching circuit and the given power cell output, along with a normally open bypass contact coupled across the power stage output, with a local or central controller energizing the coil of the relay or contactor of a given cell to bypass that cell.

The following is claimed: 
     
         1 . A power conversion system, comprising:
 a plurality of power stages connected in series to form a multilevel inverter circuit for connection to a load, the power stages individually comprising:
 a DC link capacitor coupled between first and second DC link nodes of a DC link circuit, 
 an output coupled with at least one other power stage in the multilevel inverter circuit, 
 a switching circuit including a plurality of switching devices to provide an output voltage signal having an amplitude of one of at least two discrete levels, and 
 a single relay or contactor including:
 a coil, 
 a plurality of normally closed contacts operative in a first state to allow current to flow between the switching circuit and the output when the coil is deenergized, and operative in a second state to electrically isolate the switching circuit from the output when the coil is energized, and 
 a normally open contact coupled across the output to allow normal operation of the output in a first state when the coil is deenergized, and to bypass the output in a second state when the coil is energized. 
 
   
     
     
         2 . The power conversion system of  claim 1 , wherein the plurality of normally closed contacts of the single relay or contactor of the individual power stages includes:
 a first normally closed contact coupled between a first internal node of the switching circuit and a first output terminal of the output, the first normally closed contact operative in a first state to electrically connect the first internal node to the first output terminal when the coil is deenergized, and operative in a second state to electrically disconnect the first internal node from the first output terminal when the coil is energized; and   a second normally closed contact coupled between a second internal node of the switching circuit and a second output terminal of the output, the second normally closed contact operative in a first state to electrically connect the second internal node to the second output terminal when the coil is deenergized, and operative in a second state to electrically disconnect the second internal node from the second output terminal when the coil is energized.   
     
     
         3 . The power conversion system of  claim 2 , further comprising a controller to provide switching control signals to operate the plurality of switching devices of the switching circuit of the at least one power stage. 
     
     
         4 . The power conversion system of  claim 3 , wherein the controller is a local controller, further comprising a second controller to selectively energize the coil of at least one power stage to bypass the at least one power stage. 
     
     
         5 . The power conversion system of  claim 1 , further comprising a controller to selectively energize the coil of at least one power stage to bypass the at least one power stage. 
     
     
         6 . The power conversion system of  claim 5 , wherein the controller is a local controller to provide switching control signals to operate the plurality of switching devices of the switching circuit of the at least one power stage. 
     
     
         7 . The power conversion system of  claim 5 , comprising a plurality of multilevel inverter circuits individually including a plurality of the power stages connected in series to form a corresponding single phase of a multi-phase output of the power conversion system. 
     
     
         8 . The power conversion system of  claim 1 , comprising a plurality of multilevel inverter circuits individually including a plurality of the power stages connected in series to form a corresponding single phase of a multi-phase output of the power conversion system. 
     
     
         9 . A power cell for use as a power stage in a multilevel inverter circuit, the power cell comprising:
 a DC link capacitor coupled between first and second DC link nodes of a DC link circuit;   an output to be coupled with at least one other power stage in the multilevel inverter circuit;   a switching circuit including a plurality of switching devices to provide an output voltage signal having an amplitude of one of at least two discrete levels; and   a single relay or contactor including:
 a coil, 
 a plurality of normally closed contacts operative in a first state to allow current to flow between the switching circuit and the output when the coil is deenergized, and operative in a second state to electrically isolate the switching circuit from the output when the coil is energized, and 
 a normally open contact coupled across the output to allow normal operation of the output in a first state when the coil is deenergized, and to bypass the output in a second state when the coil is energized. 
   
     
     
         10 . The power cell of  claim 9 , wherein the plurality of normally closed contacts of the single relay or contactor includes:
 a first normally closed contact coupled between a first internal node of the switching circuit and a first output terminal of the output, the first normally closed contact operative in a first state to electrically connect the first internal node to the first output terminal when the coil is deenergized, and operative in a second state to electrically disconnect the first internal node from the first output terminal when the coil is energized; and   a second normally closed contact coupled between a second internal node of the switching circuit and a second output terminal of the output, the second normally closed contact operative in a first state to electrically connect the second internal node to the second output terminal when the coil is deenergized, and operative in a second state to electrically disconnect the second internal node from the second output terminal when the coil is energized.   
     
     
         11 . The power cell of  claim 9 , further comprising a controller to provide switching control signals to operate the plurality of switching devices of the switching circuit. 
     
     
         12 . The power cell of  claim 11 , wherein the controller is configured to selectively energize the coil. 
     
     
         13 . A method for bypassing a power stage of a multilevel inverter circuit, the method comprising:
 energizing a coil of a single relay or contactor to electrically isolate a switching circuit of the power stage from an output of the power stage, and to bypass the output of the power stage.   
     
     
         14 . The method of  claim 13 , wherein energizing the coil of the single relay or contactor opens a plurality of normally closed contacts of the single relay or contactor to electrically isolate the switching circuit of the power stage from the output of the power stage. 
     
     
         15 . The method of  claim 14 , wherein energizing the coil of the single relay or contactor closes a normally open contact of the single relay or contactor to bypass the output of the power stage. 
     
     
         16 . The method of  claim 14 , wherein:
 energizing the coil of the single relay or contactor opens a first normally closed contact coupled between a first internal node of the switching circuit and a first output terminal of the output to electrically disconnect the first internal node from the first output terminal; and   energizing the coil of the single relay or contactor opens a second normally closed contact coupled between a second internal node of the switching circuit and a second output terminal of the output to electrically disconnect the second internal node from the second output terminal.   
     
     
         17 . The method of  claim 16 , wherein energizing the coil of the single relay or contactor closes a normally open contact of the single relay or contactor to electrically connect the first output terminal to the second output terminal. 
     
     
         18 . The method of  claim 13 , wherein energizing the coil of the single relay or contactor closes a normally open contact of the single relay or contactor to bypass the output of the power stage. 
     
     
         19 . The method of  claim 18 , wherein energizing the coil of the single relay or contactor closes the normally open contact to electrically connect a first output terminal of the output to a second output terminal of the output. 
     
     
         20 . The method of  claim 13 , wherein energizing the coil of the single relay or contactor closes a normally open contact to short a first output terminal of the output to a second output terminal of the output.