Patent Publication Number: US-2023163677-A1

Title: Inrush current limiting and surge protection circuit and system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of and priority to U.S. application Ser. No. 17/076,045 filed Oct. 21, 2020, and issued as U.S. Pat. No. 11,489,438, the entire disclosure of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     Aspects of the disclosure are related to electronic components and in particular to surge protection and inrush current limiting for electronic components. 
     TECHNICAL BACKGROUND 
     Power converters are commonly used in a variety of systems including telecom systems, fast chargers for electric vehicles, and other applications requiring high power density and high efficiency. 
     Common power converter designs include a variety of protection devices designed to limit voltage spikes and current surges occurring at their input ports. Often a metal oxide varistor is placed between the input ports to reduce voltage spikes occurring at the inputs. However, this alone is not sufficient to protect power switching transistors within the converter from lightning induced surges, particularly when input power to the converter is disabled. 
     Overview 
     In an embodiment, a power conversion device is provided. The power conversion device includes a bulk capacitor, a current limiting resistor in series with the bulk capacitor, and an inrush current control device configured to bypass the current limiting resistor when activated. 
     The power conversion device also includes a bypass device in parallel with the current limiting resistor, configured to provide a low-resistance path to the bulk capacitor during a power surge. 
     In another embodiment, an inrush current limiting and surge protection circuit is provided. The inrush current limiting and surge protection circuit includes a bulk capacitor, a current limiting resistor in series with the bulk capacitor, and an inrush current control device configured to bypass the current limiting resistor when activated. 
     The inrush current limiting and surge protection circuit also includes a bypass device in parallel with the current limiting resistor, configured to provide a low-resistance path to the bulk capacitor during a power surge. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the disclosure can be better understood with reference to the following drawings. While several implementations are described in connection with these drawings, the disclosure is not limited to the implementations disclosed herein. On the contrary, the intent is to cover all alternatives, modifications, and equivalents. 
         FIG.  1    illustrates an exemplary prior art power converter circuit. 
         FIG.  2    illustrates an exemplary power converter circuit with a bridge rectifier including inrush current limiting and surge protection. 
         FIG.  3    illustrates an exemplary power converter circuit with bridgeless power factor correction including inrush current limiting and surge protection. 
         FIGS.  4 A- 4 F  illustrate exemplary bypass devices to limit inrush current and provide surge protection for power converter devices. 
         FIG.  5    illustrates an exemplary power converter circuit with bridgeless power factor correction including inrush current limiting and surge protection. 
         FIG.  6    illustrates an exemplary power converter circuit with bridge rectification and active power factor correction including inrush current limiting and surge protection. 
         FIG.  7    illustrates an exemplary power converter circuit with bridge rectification and active power factor correction including inrush current limiting and surge protection. 
     
    
    
     DETAILED DESCRIPTION 
     The example embodiments described herein illustrate different methods for limiting inrush current and providing surge protection for power converter devices. These embodiments limit inrush current at power on and provide power surge protection to power conversion devices when they are connected to the AC grid but the AC power is off. 
       FIG.  1    illustrates an exemplary prior art AC/DC power converter circuit  100  with bridge rectification and active power factor correction. This circuit includes inputs line  102 , neutral  104 , and protective earth  106 . Here the active power factor correction circuit includes inductor L 1   131 , diode D 6   126 , and power switching transistor Q 1   141 . Power switching transistor Q 1   141  is susceptible to large voltage spikes and current surges and must be protected to prevent damage. 
     In this prior art example, inrush current limiting components current limiting resistor R 1   151  and relay K 1   161  are placed in series with bulk capacitor C 5   115 . In this example relay K 1   161  acts as an inrush current control device. However, other examples may use metal-oxide-semiconductor field-effect transistors (MOSFETs), insulated-gate bipolar transistors (IGBTs), and the like, alone or in combination, as inrush current control devices. Initially the voltage across bulk capacitor C 5   115  is zero. When input power is applied to the power conversion device, inrush current charges bulk capacitor C 5   115  until the voltage of bulk capacitor C 5   115  reaches the peak of the rectified input voltage. 
     During the positive half cycle, inrush current passes through diode D 1   121 , diode D 5   125 , and current limiting resistor R 1   151  to charge bulk capacitor C 5   115  and returns through diode D 3   123 . During the negative half cycle, inrush current passes through diode D 2   122 , diode D 5   125 , and current limiting resistor R 1   151  to charge bulk capacitor C 5   115  and returns through diode D 4   124 . 
     Current limiting resistor R 1   151  limits the inrush current. Once bulk capacitor C 5   115  is fully charged, and the internal circuit starts to operate, relay K 1   161  is activated to short current limiting resistor R 1   151  to reduce power loss. 
     Other components of this exemplary circuit include metal oxide varistor MOV 1   107  connected between the line  102  and neutral  104  inputs to clamp voltage spikes across the inputs. Additionally, metal oxide varistors MOV 2   108  and MOV 3   109 , along with gas discharge tube GDT 1   105  are connected across the inputs in a configuration designed to clamp common mode power surges at the input lines. Typically, the metal oxide varistors (MOVs) or voltage dependent resistors (VDRs) used in power conversion devices are selected to comply with the Annex G8.2 requirements of IEC Standard IEC62368-1 or the Annex Q requirements of ITE Standard IEC61050-1, which states that the rated maximum continuous voltage of the MOV/VDR should be at least 125% of the upper rated voltage of the power conversion device. 
     For example, if the power conversion device is rated for 100-240V AC, the MOV/VDR rating should be at least 300V AC. If the power conversion device is rated for 100-250V AC, the MOV/VDR rating should be at least 312.5V AC. To meet the ITE Standard requirement, the clamping voltage of the appropriate MOV/VDR is greater than 700V as illustrated below in Table 1. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Varistor 
                 Maximum 
                   
                 Maximum 
                   
               
               
                 Voltage 
                 Continuous 
                   
                 Clamping Voltage 
               
               
                 (@ 1 mA DC) 
                 Voltage 
                   
                 (8/20 μs) 
               
            
           
           
               
               
               
               
               
            
               
                 V 1 mA   
                 V AC(rms)   
                 V DC   
                 V P   
                 I P   
               
               
                 (V) 
                 (V) 
                 (V) 
                 (V) 
                 (A) 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 470 (423~517) 
                 300 
                 385 
                 775 
                 50 
               
               
                 510 (459~561) 
                 320 
                 410 
                 845 
                 50 
               
               
                   
               
            
           
         
       
     
     This exemplary circuit also includes an electromagnetic interference (EMI) filter comprising capacitors C 1   111 , C 2   112 , C 3   113 , and C 4   114 , along with inductor L 2   132 . Capacitors C 1   111  and C 4   114  are X capacitors configured to reduce differential mode noise, while capacitors C 2   112  and C 3   112  are Y capacitors configured to reduce common mode noise. 
     If power conversion device  100  is connected to the AC grid, but the AC is off or disabled, then the internal circuit is not able to operate and relay K 1   161  remains open. If a lightning surge couples to the AC lines when power conversion device  100  is in that state, the power surge (due to the lightning) is only clamped by the MOVs/VDRs and GDT at the input interface, and power switching transistor Q 1   141  is at risk of damage. 
     In this scenario the clamping voltage is high and the residual power surge energy is not absorbed by bulk capacitor C 5   115  since relay K 1   161  is open. Power switching transistor Q 1   141  is exposed to that residual power surge voltage, resulting in electrical over stress failure of power switching transistor Q 1   141 . 
       FIG.  2    illustrates an exemplary power converter circuit  200  with bridge rectification and active power factor correction including inrush current limiting and surge protection. This exemplary power converter circuit  200  is identical to power converter circuit  100  from  FIG.  1    with the addition of bypass device BD 1   210  which is added in parallel to current limiting resistor R 1   151 . 
     During normal power up, power converter circuit  200  operates very similar to power converter circuit  100  from  FIG.  1   . When input power is applied to the power conversion device, inrush current charges bulk capacitor C 5   115  until the voltage of bulk capacitor C 5   115  reaches the peak of the rectified input voltage. 
     During the positive half cycle, inrush current passes through diode D 1   121 , diode D 5   125 , and current limiting resistor R 1   151  to charge bulk capacitor C 5   115  and returns through diode D 3   123 . During the negative half cycle, inrush current passes through diode D 2   122 , diode D 5   125 , and current limiting resistor R 1   151  to charge bulk capacitor C 5   115  and returns through diode D 4   124 . 
     Current limiting resistor R 1   151  limits the inrush current. Once bulk capacitor C 5   115  is fully charged, and the internal circuit starts to operate, relay K 1   161  is activated to short current limiting resistor R 1   151  to reduce power loss. In this example relay K 1   161  acts as an inrush current control device. However, other examples may use MOSFETs, insulated-gate bipolar transistors (IGBTs), and the like, alone or in combination as inrush current control devices. 
     If power conversion device  200  is connected to the AC grid, but the AC is off or disabled, then the internal circuit is not able to operate and relay K 1   161  remains open. If a lightning surge couples to the AC lines when power conversion device  200  is in that state, the power surge (due to the lightning) is first clamped by the MOVs/VDRs and GDT at the input interface. The residual power surge then activates bypass device BD 1   210 , which then provides a low-resistance path to bulk capacitor C 5   115 . The residual power surge energy passes through bypass device BD 1   210  and is absorbed by bulk capacitor C 5   115  even though relay K 1   161  is open. Thus, power switching transistor Q 1   141  is protected from the power surge energy. 
     Examples of bypass device BD 1   210  are illustrated in  FIGS.  4 A- 4 D  and discussed in detail below. 
       FIG.  3    illustrates an exemplary power converter circuit  300  with bridgeless power factor correction including inrush current limiting and surge protection. This example power converter circuit  300  is similar to power converter circuit  200  from  FIG.  2   , but in a H-bridge bridgeless power factor correction configuration. 
     Here, the power factor correction circuit includes power switching transistors Q 1   341  and Q 2   342 , along with inductor L 1   331 , and diodes D 5   325  and D 6   326 . 
     During normal power up, power converter circuit  300  operates very similar to power converter circuit  200  from  FIG.  2   . When input power is applied to the power conversion device, inrush current charges bulk capacitor C 5   115  until the voltage of bulk capacitor C 5   115  reaches the peak of the rectified input voltage. 
     During the positive half cycle, inrush current passes through diode D 1   121  and current limiting resistor R 1   151  to charge bulk capacitor C 5   115  and returns through diode D 3   123 . During the negative half cycle, inrush current passes through diode D 2   122  and current limiting resistor R 1   151  to charge bulk capacitor C 5   115  and returns through diode D 4   124 . 
     Current limiting resistor R 1   151  limits the inrush current. Once bulk capacitor C 5   115  is fully charged, and the internal circuit starts to operate, relay K 1   161  is activated to short current limiting resistor R 1   151  to reduce power loss. In this example relay K 1   161  acts as an inrush current control device. However, other examples may use MOSFETs, insulated-gate bipolar transistors (IGBTs), and the like, alone or in combination as inrush current control devices. 
     If power conversion device  300  is connected to the AC grid, but the AC is off or disabled, then the internal circuit is not able to operate and relay K 1   161  remains open. If a lightning surge couples to the AC lines when power conversion device  300  is in that state, the power surge (due to the lightning) is first clamped by the MOVs/VDRs and GDT at the input interface. The residual lightning surge then activates bypass device BD 1   310 , which then provides a low-resistance path to bulk capacitor C 5   115 . The residual lightning surge energy passes through bypass device BD 1   310  and is absorbed by bulk capacitor C 5   115  even though relay K 1   161  is open. Thus, power switching transistors Q 1   341  and Q 2   134  are protected from the lightning surge energy. 
     Examples of bypass device BD 1   310  are illustrated in  FIGS.  4 A- 4 D  and discussed in detail below. 
     While the examples illustrated in  FIGS.  2  and  3    show current limiting resistor R 1   151 , relay K 1   161 , and bypass devices BD 1   210  and  310 , adjacent to bulk capacitor C 5   115 , other embodiments may place these elements on the line input  102  at some location between MOV 1   107  and C 4   114 . However, when placed in this location, relay K 1   161  would need to be sized to handle more current than when adjacent to bulk capacitor C 5   115 , which increases the size and cost of relay K 1   161 . 
     Also, while the examples illustrated in  FIGS.  2  and  3    show AC/DC power converters, various embodiments of the present invention may also be used in various other circuits including, but not limited to, DC/DC converters, high voltage DC converters, and the like. 
       FIGS.  4 A- 4 D  illustrate exemplary bypass devices to limit inrush current and provide surge protection for power converter devices. In these example embodiments, a portion of a power converter device (such as power converter devices  200  and  300  from  FIGS.  2  and  3    respectively) is illustrated. These circuits all include current limiting resistor R 1   402 , relay K 1   404 , and bulk capacitor C 5   406 . In these examples relay K 1   404  acts as an inrush current control device. However, other examples may use MOSFETs, insulated-gate bipolar transistors (IGBTs), and the like, alone or in combination, as inrush current control devices. 
       FIG.  4 A  illustrates an example circuit where the bypass device is a gas discharge tube GDT 1   400 . In this example, gas discharge tube GDT 1   400  is selected such that its DC breakdown voltage is higher than the maximum rectified input voltage, but lower than the rated voltage of power switching transistor Q 1   141  of  FIG.  2    or power switching transistors Q 1   341  and Q 2   342  of  FIG.  3   . 
       FIG.  4 B  illustrates an example circuit where the bypass device is a spark gap SG 1   410 .  FIG.  4 C  illustrates an example circuit where the bypass device is a transient voltage suppressor TVS 1   420 .  FIG.  4 D  illustrates an example circuit where the bypass device is a MOV/VDR MOV 2   430 .  FIGS.  4 E,  4 F  illustrate example circuits where the bypass device includes multiple bypass devices such as bypass devices  440 ,  450  ( FIG.  4 E ) or bypass devices  460 ,  470 , and  480  ( FIG.  4 F ). Each bypass device  440 ,  450 ,  460 ,  470 , and  480  may be one of the bypass devices shown in  FIGS.  4 A- 4 D . While two and three bypass devices are illustrated in  FIGS.  4 E and  4 F , embodiments may include more than three bypass devices. All of these various bypass devices are ideally selected to meet both inrush current limits and lightning surge requirements. 
     Note that further embodiments of the present invention may use any of these bypass devices, alone or in combination, within specific applications to provide inrush current limiting and lightning surge protection. 
       FIG.  5    illustrates an exemplary power converter circuit  500  with bridgeless power factor correction including inrush current limiting and surge protection. This example power converter circuit  500  is similar to power converter circuit  300  from  FIG.  3   , but in a totem-pole bridgeless power factor correction configuration. 
     Here, the power factor correction circuit includes power switching transistors Q 1   541  and Q 2   542 , along with inductor Ll  531 , and diodes D 3   523  and D 4   524 . 
     During normal power up, power converter circuit  500  operates very similar to power converter circuit  300  from  FIG.  3   . When input power is applied to the power conversion device, inrush current charges bulk capacitor C 5   115  until the voltage of bulk capacitor C 5   115  reaches the peak of the rectified input voltage. 
     During the positive half cycle, inrush current passes through diode D 1   121  and current limiting resistor R 1   151  to charge bulk capacitor C 5   115  and returns through diode D 4   524 . During the negative half cycle, inrush current passes through diode D 3   523  and current limiting resistor R 1   151  to charge bulk capacitor C 5   115  and returns through diode D 2   522 . 
     Current limiting resistor R 1   151  limits the inrush current. Once bulk capacitor C 5   115  is fully charged, and the internal circuit starts to operate, relay K 1   161  is activated to short current limiting resistor R 1   151  to reduce power loss. In this example relay K 1   161  acts as an inrush current control device. However, other examples may use MOSFETs, insulated-gate bipolar transistors (IGBTs), and the like, alone or in combination as inrush current control devices. 
     If power conversion device  500  is connected to the AC grid, but the AC is off or disabled, then the internal circuit is not able to operate and relay K 1   161  remains open. If a lightning surge couples to the AC lines when power conversion device  500  is in that state, the power surge (due to the lightning) is first clamped by the MOVs/VDRs and GDT at the input interface. The residual power surge then activates bypass device BD 1   510 , which then provides a low-resistance path to bulk capacitor C 5   115 . The residual power surge energy passes through bypass device BD 1   510  and is absorbed by bulk capacitor C 5   115  even though relay K 1   161  is open. Thus, power switching transistors Q 1   541  and Q 2   542  are protected from the power surge energy. 
     Examples of bypass device BD 1   510  are illustrated in  FIGS.  4 A- 4 D  and discussed in detail above. 
     While the examples illustrated in  FIGS.  2 ,  3 , and  5    show current limiting resistor R 1   151 , relay K 1   161 , and bypass devices BD 1   210 ,  310 , and  510 , adjacent to bulk capacitor C 5   115 , other embodiments may place these elements on the line input  102  at some location between MOV 1   107  and C 4   114 . However, when placed in this location, relay K 1   161  would need to be sized to handle more current than when adjacent to bulk capacitor C 5   115 , which increases the size and cost of relay K 1   161 . 
       FIG.  6    illustrates an exemplary power converter circuit  600  with bridge rectification and active power factor correction including inrush current limiting and surge protection. This example power converter circuit  600  is similar to power converter circuit  200  from  FIG.  2   , however this example circuit includes MOSFET Q 2   642  as an inrush current control device in place of relay K 1   161 . 
     MOSFET Q 2   642  is placed in parallel with bulk resistor R 1   151  and bypass device BD 1   610 , and operates similarly to relay K 1   161  of  FIG.  2   . 
       FIG.  7    illustrates an exemplary power converter circuit  700  with bridge rectification and active power factor correction including inrush current limiting and surge protection. This example power converter circuit  700  is similar to power converter circuit  200  from  FIG.  2   , however this example circuit includes MOSFET Q 2   742  as an inrush current control device in parallel with relay K 1   761 . 
     MOSFET Q 2   742  is placed in parallel with bulk resistor R 1   151 , bypass device BD 1   710 , and relay K 1   761 . Here both MOSFET Q 2   742  and relay K 1   761  operate together in parallel as an inrush current control device. 
     The included descriptions and figures depict specific embodiments to teach those skilled in the art how to make and use the best mode. For the purpose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these embodiments that fall within the scope of the invention. Those skilled in the art will also appreciate that the features described above may be combined in various ways to form multiple embodiments. As a result, the invention is not limited to the specific embodiments described above, but only by the claims and their equivalents.