Abstract:
The present invention concerns a device that combines the functionality of an inverter and a bi-directional converter. The device provides, on a number of identical channels, transformation of a DC voltage source of a given level to a filtered DC voltage of another level. The inverter and bi-directional converter of the present invention also has the capability to invert a DC power input to thereby supply, on an AC output, AC power to an AC load, such a fluorescent light. The DC voltage sources at the inputs of inverter and bi-directional converter may act as sources of DC power or sinks of DC power depending on the voltage level of each input and a winding ratio between the channels. Passing from being a source to a sink of DC power is performed smoothly and without interference with the operation of the AC load.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This is the first application filed for the present invention.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to the field of electrical inverters and converters. More particularly, the invention deals with inverters and converters having DC power sources and/or loads.  
       BACKGROUND OF THE INVENTION  
       [0003]     In order to achieve DC bi-directional conversion many electrical components must be used. These electrical components are complex, require a large number of parts and hence are costly.  
       SUMMARY OF THE INVENTION  
       [0004]     The present invention concerns a device that combines the functionality of an inverter and a bi-directional converter. The device provides, on a number of identical channels, transformation of a DC voltage source of a given level to a filtered DC voltage of another level. The inverter and bi-directional converter of the present invention also has the capability to invert a DC power input to thereby supply, to an AC output, AC power to an AC load, such as a fluorescent light. The DC voltage sources at the inputs of inverter and bi-directional converter may act as sources of DC power or sinks of DC power (e.g., for recharging) depending on the voltage level of each input and a winding ratio between the channels. The change of the source of DC power from a DC voltage source on one channel to a DC voltage on another channel is performed smoothly and without interference with the operation of the AC load.  
         [0005]     In an embodiment, the present invention provides a converter for transforming a DC voltage source into a filtered DC voltage, said converter comprising: a first channel including an input for receiving said DC voltage source, and a first inductor connected to said input for converting said DC voltage source into a DC current source thereby producing AC energy; a second channel including a second inductor; transfer means for transferring said AC energy between said first inductor and said second inductor; and a switching and inverting circuit receiving said DC current source and producing unfiltered DC energy; wherein said second inductor sums said unfiltered DC energy and said transferred AC energy to provide said filtered DC voltage on said second channel.  
         [0006]     In another embodiment, the invention provides an inverter and bi-directional converter comprising: at least two converter channels, each of said converter channels comprises an input/output; an inductor; an alternating switch; and a parallel LC circuit; a common inductor core for transferring AC energy, produced by said inductor, to and from each inductor; and a common transformer core for transferring a magnetic field, produced by said LC circuit, to and from each LC circuit; wherein while in an input operation mode: said input/output receives a DC voltage source; said inductor converts said DC voltage source into a DC current source, said inductor produces AC energy that is induced in a common inductor core, said induced AC energy being transferred through said common inductor core to an inductor on another channel, each said inductors being wound on said common inductor core; said alternating switch in combination with said parallel LC circuit produce an AC signal from said DC current source thereby producing said magnetic field; wherein while in an output operation mode: said magnetic field is induced in said parallel LC circuit which produces another AC signal; said alternating switch, acting as a synchronized rectifier, receives said another AC signal to produce unfiltered DC energy; and said unfiltered DC energy is summed with said transferred AC energy to provide a filtered DC voltage source.  
         [0007]     In yet another embodiment, the invention provides a multi-source uninterruptible power supply (UPS) for providing power to an AC load, said UPS receiving power from a primary power source and a secondary power source, said primary power source having, in normal operating conditions, a higher voltage value than said secondary power source, said UPS comprising: a DC converter for transitioning from said primary to said secondary power sources when said primary power source decreases below a selected voltage level; and an AC output for producing, from one of said primary and secondary power sources, an output AC signal adapted to drive said AC load.  
         [0008]     Still in another embodiment, the invention provides a method for converting a DC voltage source into a filtered DC voltage, said method comprising: receiving and converting said DC voltage source into a DC current, thereby producing AC energy; producing, from said DC current, unfiltered DC energy; and summing said unfiltered DC energy and said AC energy to provide said filtered DC voltage. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0009]     Further features and advantages of the present invention will become apparent from the following detailed description, taken in combination with the appended drawings, in which:  
         [0010]      FIG. 1  is a block diagram showing an inverter and bi-directional converter according to an embodiment of the invention; and  
         [0011]      FIG. 2  is a block diagram showing the inverter and bi-directional converter that may be used in a ballast application. 
     
    
     DETAILED DESCRIPTION  
       [0012]     Referring to  FIG. 1 , an Inverter and Bi-directional Converter (henceforth referred to as Converter  10 ) will now be described. Generally, a purpose of Converter  10  is to provide, among other things, a simple device for transforming a DC voltage source  12  at a given input level into a filtered DC voltage  14  of another selected level. At all times, at least one of DC Sources  12 ,  14 , and  16  is a source of DC power while the others may be DC loads. A DC load could be, for example, a rechargeable DC battery. Converter  10  also has the capability to invert a DC input to produce an AC output  36  to thereby supply AC power to a load  38 .  
         [0013]     Converter  10  is shown having three (3) channels  7 ,  8  and  9 . It is understood that the number of channels could be greater than three. As understood from this description, the minimum number of channels is two, where at least one is acting as a source of power. The number of channels is dictated by the selected application. Each channel (e.g., Channels  7 ,  8  and  9 ), comprises an input/output at which is provided a DC source or Load  12 ,  14  and  16 . Each channel further includes an inductor (e.g., Inductors  18 ,  20  and  22 ) that converts DC voltage source  12  into a DC current source. In the conversion from a DC voltage to a DC current source, Inductor  18  also produces AC energy.  
         [0014]     Converter  10  comprises a transfer means for transferring the AC energy to and from each Inductor  18 ,  20 ,  22 . In an embodiment of the invention, the transfer means includes Common Inductor Core  23  that is common to all channels and that performs the transfer of AC energy from Inductor  18  to Inductors  20  and  22 . The use of AC energy will be further discussed below.  
         [0015]     Converter  10  includes a switching and inverting circuit that receives said DC current source and that produces unfiltered DC energy. In an embodiment, switching and inverting circuit comprises at least two alternating switches (e.g., two of Alternating Switches  24 ,  26 , and  28 ), at least two parallel LC circuits (e.g., two of Parallel LC Circuits  30 ,  32 , and  34 ) and a Common Transformer Core  35 .  
         [0016]     In the presently described embodiment, Alternating Switch  24  in combination with Parallel LC Circuit  30  produce, from the DC current source, an AC signal and thereby producing a magnetic field. Common Transformer Core  35  transfers the magnetic field to and from each Parallel LC Circuit  30 ,  32 , and  34 .  
         [0017]     In this embodiment, the magnetic field is therefore induced from Channel  7  to Channel  8  through Common Transformer Core  35 . From the magnetic field, Parallel LC Circuit  32  produces another AC signal. Persons skilled in the art will recognize that the L&#39;s (inductors) in LC Circuits  30 ,  32 , and  34  and Common Transformer Core form a transformer. Alternating Switch  26 , acting as a synchronized rectifier, receives the other AC signal and produces unfiltered DC energy. The unfiltered DC energy is summed with the previously mentioned transferred AC energy to provide the filtered DC voltage source at the output of Channel  8 .  
         [0018]     A person skilled in the art will understand that, in the previously described embodiment, Channel  7  is in input operation mode while Channel  8  is in output operation mode.  
         [0019]     Also shown on  FIG. 1  are: a converter AC Output  36  comprising a coil and an AC Load  38 . In an exemplary embodiment, AC load  38  could be one or more fluorescent lights, an AC electric motor, another transformer, or any other AC device.  
         [0020]     Finally, Converter  10  may further include synchronizing means (not shown) for synchronizing Alternating Switches  24 ,  26 , and  28  with the resonance frequency of the switching and inverting circuit. The AC signals on each of the channels may thereby be in phase with each other. In an embodiment of the invention, each Alternating Switch  24 ,  26 , and  28  may include a transistor arrangement that provides the necessary synchronized switching function. This type of synchronized switching arrangement is well known to those skilled in the art and will not be further described herein.  
         [0021]     Converter  10  automatically and smoothly transitions between DC power sources  12 ,  14 , and  16 . This is possible by selecting the appropriate turn ratios for Inductors  18 ,  20 , and  22 . Transformer Coil Ratios are conversely selected and calculated. Turn ratios can be calculated according to the selected “Turn On” and “Turn Off” DC voltage levels. The Turn On and Turn Off voltages are used to determine which of the DC voltage sources  12 ,  14 , or  18  will provide the DC power to feed the others and AC output  38 . It is understood that the Turn On and Turn Off voltage levels can be a range of values and not necessarily a discrete value thereby ensuring the transition from one channel to another within a window of voltage levels in a gradual manner. Converter  10  differentially transfers the load thereby balancing the energy it requires, within the window of voltage levels, from its respective DC voltage sources. The window is therefore centered on the Turn On and Turn Off voltages.  
         [0022]     In Table 1, DC Voltage Source  12  on Channel  1  will act as the source of DC power (first priority) until its voltage level reaches the window centered on 85.0 VDC. At this point, Converter  10  decreases its energy consumption from DC Voltage Source  12  to increase proportionally the energy consumption from DC Voltage Source  14  thereby maintaining constant the energy at AC Output  36  and/or at other outputs of Converter  10 . This ensures the smooth transition between sources discussed earlier.  
         [0023]     DC Voltage Source  14  on Channel  8  should be at 74.0 VDC and it will takeover as the DC power source until either DC Voltage Source  12  on Channel  7  reaches the bottom of the window centered on 85 VDC or more again, or DC Voltage Source  14  itself drops below the top of the window centered on 50.0 VDC. At that point, DC Voltage Source  16  on Channel  9  will takeover, in the same manner as DC Voltage Source  14  took over above, and act as the source of DC power for AC load  38  until either DC Voltage Source  14  reaches the bottom of the window centered on 50.0 VDC or more again, or DC Voltage Source  16  on itself drops below 6.0 VDC. At this point, if there is not another available channel, the last channel&#39;s DC power source will simply completely discharges itself.  
         [0024]     Two examples for calculating Transformer and Inductor Coil Ratios are given in Tables 1 and 2 below.  
                                                     TABLE 1                                       Transformer       Channel       Turn On   Turn Off   and Inductor       Priority   Channel no.   Voltage (V)   Voltage (V)   Coil Ratio (%)                                First   7   120.0   85.0   100.0       Second   8   74.0   50.0   87.1       Third   9   7.2   6.0   8.5                  
 
         [0025]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
               
               
                   
                   
                   
                   
                 Transformer 
               
               
                 Channel 
                   
                 Turn On 
                 Turn Off 
                 and Inductor 
               
               
                 Priority 
                 Channel no. 
                 Voltage (V) 
                 Voltage (V) 
                 Coil Ratio (%) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 First 
                 7 
                 74.0 
                 50.0 
                 100.0 
               
               
                 Second 
                 8 
                 120.0 
                 85.0 
                 240.0 
               
               
                 Third 
                 9 
                 7.2 
                 6.0 
                 14.4 
               
               
                   
               
             
          
         
       
     
         [0026]     As can be seen from the examples above, Transformer and Inductor Coil Ratio can be calculated by the following formulae: 
 
(Present Turn On Voltage/Precedent Turn Off Voltage)×100 
 
         [0027]     For example, in Table 1, if the number of turns in Inductor  18  is the reference (100%), the Inductor Coil Ratio to determine the number of turns in Inductor  20  would be calculated as follows: 
 
(74/85)×100=87.1 
 
         [0028]     Furthermore, it will be obvious to persons skilled in the art that DC Voltage Sources  12 ,  14 , or  18  may be selected as a function of the AC Load  38  and/or of the desired time of operation of the AC Load  38 .  
         [0029]     Now referring to  FIG. 2 , Converter  10  is shown in an emergency lighting ballast application. In this context, a multi-source uninterruptible power supply (UPS) designated by numeral  80  will now be described. In this particular embodiment, the purpose of UPS  80  is to receive electrical power inputs Primary Input  40 , Secondary Input  42 , and Local Input  44 , and to transition between the power sources available to them to eventually provide appropriate power to light a lamp or lamps (e.g., Lamps  64 ). Lamps  64  include any type of fluorescent lamps, High Intensity Discharge (HID) lamps, etc. UPS  10  also has the capability to recharge the power source at Secondary Input  42  from the power source Primary Input  40 , and to recharge the power source at Local Input  44  from the power sources at Secondary Input and/or Primary Input  40 . Secondary Input  8  and Local Input  44  can therefore accommodate sinks as well as sources of power. Furthermore, UPS  10  receives Test &amp; Control Signal  46  that is used to advise UPS  10  of a variation in a local condition, such the output of a local battery pack (not shown), or activating only the local battery pack. Operation of UPS  10  may therefore factor in Test &amp; Control Signal  4  into its decision making process.  
         [0030]     UPS  10  as shown in the embodiment of  FIG. 2  may be used in the context of providing different lighting levels such as would be required in “emergency” conditions. This context would be present, for example, in public transit vehicles (e.g., trains, metros, busses, ferries, aircraft, etc.), in office buildings, multi-family housing, homes, etc. “Emergency” lighting includes lighting provided at the same or lower level as in “normal” conditions, for a given or undetermined period of time (referred to as the emergency period), when a long term source of power is no longer available or intermittent, or when a decrease over time of a primary power source is detected. Details of the requirements for providing “emergency” lighting may be found in legislation and may vary according to each jurisdiction.  
         [0031]     Referring back to  FIG. 2 , UPS  10  as discussed above has three inputs, namely Primary Input  40 , Secondary Input  42  and Local Input  44  for electrical power. More specifically, in this embodiment, Primary Input  40  receives an AC power source while Secondary Input  42  and Local Input  44  receive DC power sources.  
         [0032]     In this example, Primary Input  40  is converted to a DC power source through Rectifier &amp; Filter Protection Circuit  48  and Power Factor Corrector (PFC) &amp; Voltage Regulator  49 . The AC voltage source at Primary Input could be, in this example, 120 VAC. The DC voltage level at the output of PFC &amp; Voltage Regulator  49  could be, for example, at a higher level (i.e., 200 VDC) than at Secondary Input  42  (i.e., 74.0 VDC) which itself is at a higher level (i.e., 7.2 VDC). Refer to Tables 1 and 2 above for other examples and further details. In an embodiment, Primary Input  40 , Secondary Input  42  and Local Input  44  are independent from one another.  
         [0033]     Primary Input  40  may be from a central AC power source while Secondary Input  42  may be from a DC battery (e.g., in the range 50 VDC to 90 VDC). Local Input  44  is normally from a smaller DC battery (e.g., in the range 5 VDC to 12 VDC).  
         [0034]     Controller  10  operates in the same manner as described above. Controller  10  will therefore contribute in determining from which source UPS  80  will drain power to drive lamps  64 . The output of Controller  10  will therefore reflect the highest power at its input.  
         [0035]     Lamp Level Control blocks  54 ,  56  receive the AC signal from Converter  10  and introduce an appropriate delay and adjustment in the AC signal under the control of Ballast Controller CPU  62 . Lamp Shutdown Switches  58 ,  60  simply provide the ability to control, from the Ballast Controller CPU  62 , the shutting down of a selection from lamps  64 .  
         [0036]     Finally, Ballast Controller CPU  62  receives inputs from components listed above and performs its functions as discussed earlier. Moreover, Ballast Controller CPU  30  may include a timer for monitoring the period after which Primary Input  40  is not in function.  
         [0037]     Persons skilled in the art will understand that when power on Primary Input  40  drops below a given level (refer to examples in Tables 1 and 2), UPS  80  simply draws power from a secondary battery (not shown) at Secondary Input  42 .  
         [0038]     The embodiment(s) of the invention described above is (are) intended to be exemplary only. The scope of the invention is therefore intended to be limited solely by the scope of the claims to be later appended to the corresponding non-provisional patent application.