Multi-level circuit, three-phase multi-level circuit, and control method

Abstract

A multi-level circuit, a three-phase multi-level circuit, and a control method are provided. The multi-level circuit includes two groups of bus capacitors that are connected in series. The circuit further includes a plurality of switching transistor branches that are connected in parallel to the capacitors, where each switching transistor branch includes a first half bridge and a second half bridge, and a common terminal of the two half bridges is grounded. Furthermore, the circuit includes two coupled inductors, where each input terminal of each coupled inductor is connected to a common terminal of two switching transistors in the first half bridge in the switching transistor branches. In this circuit, a quantity of groups of bus capacitors is decreased and circuit design complexity is reduced. Further, a dropout voltage of the switching transistors is reduced.

What is claimed is: 
     
         1 . A multi-level circuit, comprising:
 a capacitance branch comprising a first capacitor and a second capacitor that are connected in series, wherein a common terminal of the first capacitor and the second capacitor is grounded;   at least two switching transistor branches that are connected in parallel to the capacitance branch, wherein each switching transistor branch comprises a first half bridge and a second half bridge, and a common terminal of the first half bridge and the second half bridge of each switching transistor branch is grounded; and   a first coupled inductor and a second coupled inductor, wherein an input terminal of the first coupled inductor is connected to a common terminal of two switching transistors in the first half bridge in the switching transistor branches; and an input terminal of the second coupled inductor is connected to a common terminal of two switching transistors in the second half bridge of the switching transistor branches.   
     
     
         2 . The multi-level circuit according to  claim 1 , wherein a third half bridge and a fourth half bridge are separately connected between an output terminal of the first coupled inductor and an output terminal of the second coupled inductor. 
     
     
         3 . The multi-level circuit according to  claim 2 , wherein two switching transistors in the first half bridge in each switching transistor branch and two switching transistors in the second half bridge in each switching transistor branch, and switching transistors forming the third half bridge and the fourth half bridge in each switching transistor branch are insulated-gate bipolar transistors (IGBTs) that have a diode inside or are metal-oxide-semiconductor field-effector transistors (MOSFETs). 
     
     
         4 . The multi-level circuit according to  claim 1 , wherein a first clamping diode is further connected between the output terminal of the first coupled inductor and a terminal, not connected to the second capacitor, of the first capacitor; and a second clamping diode is further connected between the output terminal of the second coupled inductor and a terminal, not connected to the first capacitor, of the second capacitor. 
     
     
         5 . A three-phase multi-level circuit, comprising:
 a capacitance branch comprising a first capacitor and a second capacitor that are connected in series, wherein a common terminal of the first capacitor and the second capacitor is grounded;   a first multi-level generation unit and a second multi-level generation unit, wherein the first multi-level generation unit and the second multi-level generation unit each comprise: at least two switching transistor branches that are connected in parallel to the capacitance branch, a first coupled inductor, and a second coupled inductor, wherein each switching transistor branch comprises a first half bridge and a second half bridge, and a common terminal of the first half bridge and the second half bridge of each switching transistor branch is grounded; an input terminal of the first coupled inductor is connected to a common terminal of two switching transistors in the first half bridge of the switching transistor branches; and an input terminal of the second coupled inductor is connected to a common terminal of two switching transistors in the second half bridge of the switching transistor branches;   a first inverter unit and a second inverter unit, wherein the first inverter unit comprises: a third half bridge and a fourth half bridge that are separately connected between the first coupled inductor and the second coupled inductor in the first multi-level generation unit; and the second inverter unit comprises: a third half bridge and a fourth half bridge that are separately connected between the first coupled inductor and the second coupled inductor in the second multi-level generation unit; and   a first power inductor, a second power inductor, and a third power inductor, wherein the first power inductor is connected to a common terminal of two switching transistors in the fourth half bridge in the first inverter unit; the second power inductor is separately connected to a common terminal of two switching transistors in the third half bridge in the first inverter unit, and a common terminal of the fourth half bridge in the second inverter unit; and the third power inductor is connected to a common terminal of the third half bridge in the second inverter unit.   
     
     
         6 . The three-phase multi-level circuit according to  claim 5 , wherein two switching transistors in the first half bridge and two switching transistors in the second half bridge in each switching transistor branch of the first multi-level generation unit and the second multi-level generation unit, and the switching transistors in the third half bridges and the fourth half bridges of the first inverter unit and the second inverter unit are insulated-gate bipolar transistors (IGBTs) that have a diode inside or are metal-oxide-semiconductor field-effector transistors (MOSFETs). 
     
     
         7 . The three-phase multi-level circuit according to  claim 5 , wherein a first clamping diode is further connected between an output terminal of the first coupled inductor in each of the first multi-level generation unit and the second multi-level generation unit and a terminal, not connected to the second capacitor, of the first capacitor; and a second clamping diode is further connected between an output terminal of the second coupled inductor in each of the first multi-level generation unit and the second multi-level generation unit and a terminal, not connected to the first capacitor, of the second capacitor. 
     
     
         8 . The three-phase multi-level circuit according to  claim 5 , wherein a ground terminal of the three-phase multi-level circuit is further configured to connect to a common terminal of an external three-phase power source, to act as a ground cable of the three-phase power source. 
     
     
         9 . A three-phase multi-level circuit control method, applied to the three-phase multi-level circuit according to  claim 5 , wherein the control method comprises:
 controlling, in each switching transistor branch of the first multi-level generation unit, two switching transistors in the first half bridge to emit pulses complementarily, and two switching transistors in the second half bridge to emit pulses complementarily; and controlling, in two adjacent switching transistor branches, first switching transistors in first half bridges to emit pulses alternately with a phase difference of N degrees, and second switching transistors in second half bridges to emit pulses alternately with a phase difference of N degrees, wherein N is a result of dividing 360 by a quantity of switching transistor branches;   controlling, in each switching transistor branch of the second multi-level generation unit, two switching transistors in the first half bridge to emit pulses complementarily, and two switching transistors in the second half bridge to emit pulses complementarily; and controlling, in two adjacent switching transistor branches, first switching transistors in first half bridges to emit pulses alternately with the phase difference of N degrees, and second switching transistors in second half bridges to emit pulses alternately with a phase difference of N degrees, wherein N is a result of dividing 360 by a quantity of switching transistor branches;   controlling, in the first inverter unit, two switching transistors in the third half bridge to emit pulses complementarily, and two switching transistors in the fourth half bridge to emit pulses complementarily; and   controlling, in the second inverter unit, two switching transistors in the third half bridge to emit pulses complementarily, and two switching transistors in the fourth half bridge to emit pulses complementarily.   
     
     
         10 . The control method according to  claim 9 , further comprising:
 for a phase of the voltage of the output terminal in a range of 0-60 degrees, controlling a first switching transistor in the fourth half bridge in the first inverter unit, a second switching transistor in the third half bridge in the second inverter unit, and a first switching transistor in the fourth half bridge in the second inverter unit to be turned on;   for a phase of the voltage of the output terminal, in a range of 60-120 degrees, controlling a second switching transistor in the third half bridge in the first inverter unit, the first switching transistor in the fourth half bridge in the first inverter unit, and the second switching transistor in the third half bridge in the second inverter unit to be turned on;   for a phase of the voltage of the output terminal, in a range of 120-180 degrees, controlling the second switching transistor in the third half bridge in the first inverter unit, the first switching transistor in the fourth half bridge in the first inverter unit, and a first switching transistor in the third half bridge in the second inverter unit to be turned on; or controlling the first switching transistor in the fourth half bridge in the first inverter unit, a first switching transistor in the third half bridge in the second inverter unit, and a second switching transistor in the fourth half bridge in the second inverter unit to be turned on;   for a phase of the voltage of the output terminal, in a range of 180-240 degrees, controlling a second switching transistor in the fourth half bridge in the first inverter unit, the first switching transistor in the third half bridge in the second inverter unit, and the second switching transistor in the fourth half bridge in the second inverter unit to be turned on;   for a phase of the voltage of the output terminal, in a range of 240-300 degrees, controlling the second switching transistor in the fourth half bridge in the first inverter unit, a first switching transistor in the third half bridge in the first inverter unit, and the first switching transistor in the third half bridge in the second inverter unit to be turned on; or   for a phase of the voltage of the output terminal, in a range of 300-360 degrees, controlling the second switching transistor in the fourth half bridge in the first inverter unit, the first switching transistor in the third half bridge in the first inverter unit, and the second switching transistor in the third half bridge in the second inverter unit to be turned on; or controlling the second switching transistor in the fourth half bridge in the first inverter unit, the first switching transistor in the third half bridge in the second inverter unit, and the second switching transistor in the third half bridge in the second inverter unit to be turned on.