AC power converter

Abstract

The present invention relates to apparatus used in power control, such as apparatus for controlling the power level in an AC electrical circuit. Such an apparatus is referred to as an AC power converter. In one form, the present invention particularly relates to a power converter suitable for use in lighting dimmer control although other applications of the present invention are not to be excluded from the scope of the present application. A number of aspects of the power converter are disclosed. One aspect is directed to the problem of freewheeling in a power converter. In another aspect the linearity of the circuit transfer characteristic is improved when operating in response to small load outputs. A further aspect relates to surge detection by controlling the pulse width and accordingly, the amplitude of a spike. In a still further aspect, communication between a number of power converters uses a network such as ethernet, or preferably LON™.

The claims defining the invention are as follows:  
     
         1 . A power converter including: 
 input means for receiving supply power,    switch means responsive to control means for providing control of power delivered to an output load, and    detecting means to detect a difference in polarity or amplitude between selected waveforms or points in the converter, in which    the control means controls the operation of the switch means in a manner that enables the switch means to be ‘on’ when required for control purposes.    
     
     
         2 . A power converter as claimed in  claim 1 , wherein the switch means is enabled ‘on’ when there is a difference in polarity detected.  
     
     
         3 . A power converter as claimed in  claim 1  or  2 , in which the switch means is enabled ‘on’ when a difference in polarity between voltage and current waveforms is detected.  
     
     
         4 . A power converter as claimed in  claim 3 , in which the current waveform is input current and the voltage waveform is input voltage.  
     
     
         5 . A power converter as claimed in  claim 1 , in which the switch means is enabled ‘on’ when a difference in polarity between input voltage and voltage across the switch means is detected.  
     
     
         6 . A power converter as claimed in any one of  claims 1  to  5 , in which the power converter is a high frequency switch mode converter.  
     
     
         7 . A dimmer including the power converter of any one of  claims 1  to  6 .  
     
     
         8 . A method of reducing energy dissipation in a power converter, the method including the steps of: 
 detecting a polarity difference between selected waveforms or points in the converter,    enabling a switch ‘on’ in response to detecting opposing polarity.    
     
     
         9 . A method as claimed in  claim 8 , in which the switch is enabled ‘on’ when a difference in polarity between voltage and current waveforms is detected.  
     
     
         10 . A method as claimed in  claim 9 , in which the voltage waveform is input voltage and the current waveform is input current.  
     
     
         11 . A method as claimed in  claim 8 , in which the switch is enabled ‘on’ when a difference in polarity between input voltage and voltage across the switch is detected.  
     
     
         12 . A power converter incorporating the method of any one of  claims 8  to  11 .  
     
     
         13 . A method of controlling over-current conditions in a circuit, including the steps of: 
 providing PWM sampling of the input waveform,    sampling the input waveform,    measuring current as it passes through a mainswitch to detect an over-voltage or over-current condition,    turning the mainswitch off in response to the detection of the over-voltage or over-current condition, and    adjusting the PWM sampling in order to attenuate voltage or current through the converter.    
     
     
         14 . A method as claimed in  claim 13 , further including sensing output voltage and transient currents so as to discriminate between an overload and a short circuit output condition.  
     
     
         15 . A method as claimed in  claim 14 , in which: 
 if the output voltage is within a predetermined level while the over-current condition occurs, an overload condition is detected, whereas    if the output voltage is substantially zero volts while the over-current condition occurs, a short circuit condition is detected.    
     
     
         16 . A control unit adapted to control a power converter, the control unit being provided integrally with the power converter in which the control unit is attached to and communicates directly to the power converter, or remotely of the power converter in which the control unit is detached and communicates remotely via a suitable mode of communication to the power converter.  
     
     
         17 . A network of power converters being at least two power converters coupled via a communication network, and including the control unit of  claim 16 .  
     
     
         18 . A network as claimed in  claim 17 , in which the control unit is also operable to control at least any selected one of the power converters.  
     
     
         19 . A network as claimed in  claim 17  or  18 , in which messages and other required information is communicated between the power converters via a control unit.  
     
     
         20 . An LC filter including: 
 a capacitive element,    a first inductance having a relatively high impedance at switching frequency and a relatively low impedance at line frequency, the relative impedance of the first inductance being relative to the load impedance, the improvement including: 
 a second inductance having a relatively high impedance at switching frequency and at line frequency when current is relatively low, and the second inductance having a relatively low impedance at switching frequency and at line frequency when the current is relatively high.  
   
     
     
         21 . An LC filter in which the first and second inductances are provided in one inductive element.  
     
     
         22 . An AC power converter including the LC filter of claims  20  or  21 .  
     
     
         23 . A power converter as claimed in  claim 1 , including the adaptive inductance of claim  20 .