Soft-switching techniques for power inverter legs

Abstract

This invention relates to new soft-switching techniques for minimizing switching losses and stress in power electronic circuits using inverter legs. By choosing the switching frequency with specific relationships with the resonant frequency of the power electronic circuits, the proposed switching technique enables the power electronic circuits to achieve soft switching under full load and short-circuit conditions at the defined frequencies for both capacitive and inductive loads. This technique can be applied to an electronic circuit with two switches connected in totem pole configuration between two dc voltage rails or commonly known as a power inverter leg or inverter arm. Examples of these circuits are class-D power converter, half-bridge power converters and full-bridge power converters or inverters. The proposed techniques allow inverter circuits with resistive, capacitive and inductive loads to achieve soft switching.

1 . A method of operating a power electronics circuit comprising an inverter and a load including a resonant tank, wherein said inverter is switched at a frequency f s  and said resonant tank has a resonant frequency f r , wherein K<f r /f s <K+1 where K is an even-numbered integer.  
     
     
         2 . A method of operating a power electronics circuit comprising an inverter and a load, wherein said load as first and second operating conditions associated with respective first (f r1 ) and second (f r2 ) resonant frequencies, f r2  being greater than f r1 , and wherein said inverter is switched at first (f s1 ) and second (f s2 ) switching frequencies corresponding to said first and second operating conditions, f s2  being greater than f s1 , and wherein K<f r2 /f s1 <K+1 where K is an even-numbered integer.  
     
     
         3 . A method as claimed in  claim 2  wherein an auxiliary resonant tank is provided between said inverter and said load and having a resonant frequency (f a ), and wherein K−f s f s1 <K+1 where K is an even-numbered integer.  
     
     
         4 . A method as claimed in  claim 3  wherein f s2 >f a .  
     
     
         5 . A method as claimed in  claim 2  wherein f s2 >f r2 .  
     
     
         6 . A method as claimed in  claim 2  wherein said power electronics circuit is an electronic ballast for driving a high intensity discharge lamp.  
     
     
         7 . A method of operating a power electronics circuit comprising an inverter and a load, wherein said load as first and second operating conditions associated with respective first (f r1 ) and second (f r2 ) resonant frequencies, f r2  being greater than f r1 , and wherein said inverter is switched at first (f s1 ) and second (f s2 ) switching frequencies corresponding to said first and second operating conditions, f s2  being greater than f s1 , wherein an auxiliary resonant tank is provided between said inverter and said load and having a resonant frequency (f a ), and wherein K<f a /f s1 <K+1 where K is an even-numbered integer, and wherein K<f r2 /f s1 <K+1, and f s2 >f r2  and f s2 >f a .  
     
     
         8 . A method as claimed in  claim 7  wherein f a  is close to f r2 .  
     
     
         9 . A method of operating a power electronics circuit comprising an inverter and a load, wherein said load as first and second operating conditions associated with respective first (f r1 ) and second (f r2 ) resonant frequencies, f r2  being greater than f r1 , and wherein said inverter is switched at first (f s1 ) and second (f s2 ) switching frequencies corresponding to said first and second operating conditions, f s2  being greater than f s1 , wherein an auxiliary resonant tank is provided between said inverter and said load and having a resonant frequency (f a ), wherein K<f r2 /f s1 <K+1 and f s1 >f a .  
     
     
         10 . A method of operating a power electronics circuit comprising an inverter and a load including a resonant tank, wherein an auxiliary resonant tank is provided between said inverter and said load whereby in the event of the load acting as a short-circuit during operation, current provided by said auxiliary resonant tank enables soft-switching of said inverter.  
     
     
         11 . A power electronics circuit comprising an inverter, a load including a resonant tank, and an auxiliary resonant load provided between said inverter and said load.