Patent Publication Number: US-9847707-B2

Title: Converter

Description:
RELATED APPLICATIONS 
     This application claims priority to China Application Serial Number, 201510514914.4, filed Aug. 20, 2015, which is herein incorporated by reference. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a converter. More particularly, the present disclosure relates to a converter having a voltage clamping protection. 
     Description of Related Art 
     Recently, converters have been widely applied in various fields, which include, for example, solar inverters, uninterruptible power supply (UPS), power conditioning system (PCS), etc. 
     The converter generally includes switching units. In the operations of the converter, the voltage spikes are generated, during the switching units are turned off, to have an impact on elements of the converter. In some approaches, a voltage clamping protection is applied to the converter, in order to prevent the switching units from being damaged by the voltage spikes. 
     In current approaches, the voltage clamping protection is only able to absorb the voltage spikes having a single frequency. However, with the different parasitic inductances or capacitances, the voltage spikes, generated during the switching units are turned off, may have multiple frequencies. Thus, the operations of the current voltage clamping protection cannot provide a complete protection for the switching units. 
     SUMMARY 
     An aspect of the present disclosure is to provide a converter. The converter includes a first bridge arm and a voltage clamping unit. The first bridge arm includes a first switching unit. The voltage clamping unit is coupled to the first bridge arm, and includes a first charging branch and a second charging branch. The first charging branch is configured to have a first resonant frequency, to absorb a first spike of the first switching unit. The second charging branch is configured to have a second resonant frequency to absorb a second spike of the first switching unit. 
     Yet another aspect of the present disclosure is to provide a voltage clamping unit. The voltage clamping unit includes a first charging branch, a second charging branch, a first discharging branch, and a second discharging branch. The first charging branch is coupled in parallel with a switching unit, and is configured to have a first resonant frequency, to absorb a first spike of the switching unit. The second charging branch is coupled in parallel with the switching unit, and is configured to have a second resonant frequency, to absorb a second spike of the switching unit. The first discharging branch is coupled between an input power source and the first charging branch, to discharge the first charging branch. The second discharging branch is coupled between the input power source and the second charging branch, to discharge the second charging branch. 
     It is to be understood that both the foregoing general description and the following detailed description are by examples, and are intended to provide further explanation of the disclosure as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows: 
         FIG. 1A  is a schematic diagram of a converter, in accordance with some embodiments of the present disclosure; 
         FIG. 1B  is a schematic diagram illustrating a spike generated during the switch S 2  in  FIG. 1A  is turned off, in accordance with some embodiments of the present disclosure; 
         FIG. 1C  is a schematic diagram illustrating a spike generated during reverse recovery of the diode D 2  in  FIG. 1A , in accordance with some embodiments of the present disclosure; 
         FIG. 2  is a schematic diagram of a converter, in accordance with some embodiments of the present disclosure; 
         FIG. 3  is a schematic diagram of a converter, in accordance with some embodiments of the present disclosure; 
         FIG. 4  is a schematic diagram of a converter, in accordance with some embodiments of the present disclosure; 
         FIG. 5  is a schematic diagram of a converter, in accordance with some embodiments of the present disclosure; and 
         FIG. 6  is a schematic diagram of a converter, in accordance with some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     Although the terms “first,” “second,” etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used to distinguish one element from another. 
     In this document, the term “coupled” may also be termed as “electrically coupled”, and the term “connected” may be termed as “electrically connected”. “Coupled” and “connected” may also be used to indicate that two or more elements cooperate or interact with each other. 
     As used herein, “around”, “about” or “approximately” shall generally mean within 20 percent, preferably within 10 percent, and more preferably within 5 percent of a given value or range. Numerical quantities given herein are approximate, meaning that the term “around”, “about” or “approximately” can be inferred if not expressly stated. 
     Reference is now made to  FIG. 1A .  FIG. 1A  is a schematic diagram of a converter  100 , in accordance with some embodiments of the present disclosure. As shown in  FIG. 1A , the converter  100  includes a bridge arm  120  and a voltage clamping unit  140 . The bridge arm  120  includes a switching unit  122  and a switching unit  124 . A first terminal of the switching unit  122  is coupled to an input power source VBUS, a second terminal of the switching unit  122  is coupled to a first terminal of the switching unit  124 , and a second terminal of the switching unit  124  is coupled to the input power source VBUS. 
     In some embodiments, any one of the switching unit  122  and the switching unit  124  includes a power semiconductor switch and a diode that are coupled in parallel with each other. For illustration, as shown in  FIG. 1A , the switching unit  122  includes a power semiconductor switch S 1  and a diode D 1  that are coupled in parallel with each other. Similarly, the switching unit  124  includes a switch S 2  and a diode D 2  that are coupled in parallel with each other. In various embodiments, the switch S 1  and the switch S 2  are implemented with various types of transistors, including, for example, insulated gate bipolar transistors (IGBT), metal-oxide-semiconductor field effect transistors (MOSFET), etc. 
       FIG. 1B  is a schematic diagram illustrating a spike generated during the switch S 2  in  FIG. 1A  is turned off, in accordance with some embodiments of the present disclosure.  FIG. 1C  is a schematic diagram illustrating a spike generated during reverse recovery of the diode D 2  in  FIG. 1A , in accordance with some embodiments of the present disclosure. 
     As described above, in some embodiments, any one of the switching unit  122  and the switching unit  124  generally includes a power semiconductor switch and a diode that are coupled in parallel with each other. For simplicity, the following embodiments and the related drawings are described with IGBT, but the present disclosure is not limited thereto. 
     The operating characteristics of the IGBT and that of the diodes are different from each other. For example, when the switching unit  124  is turned off, the voltage peak value and the oscillating frequency 1/T2 of the spike on the diode D 2  are different from the voltage peak value and the oscillating frequency 1/T1 of the spike between two terminals of the switch S 2 . As shown in  FIG. 1B  and  FIG. 1C , compared with the spike of the switch S 2 , a much higher voltage peak value and higher oscillating frequency are presented in the spike of the diode D 2 . Therefore, based on the differences of the oscillating frequency and the voltage peak value of these spikes, in different embodiments, the spikes generated by the switch S 2  and the diode D 2 , respectively, are able to be absorbed by the voltage clamping unit  140  having multiple branches. As a result, a better protection can be achieved. 
     The voltage clamping unit  140  includes a charging branch  142 _ 1  and a charging branch  142 _ 2 . The charging branch  142 _ 1  is configured to have a first resonant frequency FS 1 , to absorb the spike of the switching unit  124 . The charging branch  142 _ 2  is configured to have a second resonant frequency FS 2 , to absorb the spike of the switching unit  124 . As a result, when the switching unit  124  is turned off, the spikes having the different frequencies, generated from the switching unit  124 , are able to be absorbed by the charging branch  142 _ 1  and the charging branch  142 _ 2 . Effectively, the charging branch  142 _ 1  and the charging branch  142 _ 2  are able to provide a voltage clamping protection to improve a reliability of the switching unit  124 . 
     As shown in  FIG. 1A , the charging branch  142 _ 1  includes a diode DC 1 , an inductor LC 1 , and a capacitor CC 1 , and the charging branch  142 _ 2  includes a diode DC 2 , an inductor LC 2 , and a capacitor CC 2 . An anode of the diode DC 1  and an anode of the diode DC 2  are coupled to the first terminal of the switching unit  124 . The inductor LC 1  is coupled between a cathode of the diode DC 1  and the capacitor CC 1 , and the inductor LC 2  is coupled between a cathode of the diode DC 2  and the capacitor CC 2 . The capacitor CC 1  and the capacitor CC 2  are further coupled to another terminal of the switching unit  124 . With such arrangement, when the switching unit  124  is turned off, if the peak values of the spikes are higher than the bus voltage, the capacitor CC 1  and the capacitor CC 2  will be charged by absorbing the corresponding spikes. As a result, the spike voltage between two terminals of the switching unit  124  can be reduced. 
     In various embodiments, the first resonant frequency FS 1  of the charging branch  142 _ 1  is configured to correspond to the oscillating frequency of the spike generated during the switch S 2  is turned off, and the second resonant frequency FS 2  of the charging branch  142 _ 2  is configured to correspond to the oscillating frequency of the spike during the diode D 2  is in a transition of reverse recovery. In some embodiments, the first resonant frequency FS 1  of the charging branch  142 _ 1  is about the same as the oscillating frequency of the spike generated during the switch S 2  is turned off, and the second resonant frequency FS 2  of the charging branch  142 _ 2  is about the same as the oscillating frequency of the spike during the diode D 2  is in the transition of reverse recovery. In yet some embodiments, the first resonant frequency FS 1  of the charging branch  142 _ 1  is equal to the oscillating frequency of the spike generated during the switch S 2  is turned off, and the second resonant frequency FS 2  of the charging branch  142 _ 2  is equal to the oscillating frequency of the spike during the diode D 2  is in the transition of reverse recovery. 
     For example, the first resonant frequency FS 1  is able to be set by adjusting the capacitance value of the capacitor CC 1  and the inductance value of the inductor LC 1 , and the second resonant frequency FS 2  is able to be set by adjusting the capacitance value of the capacitor CC 2  and the inductance value of the inductor LC 2 . The capacitor CC 1  and the capacitor CC 2  are satisfied with the following equations: 
     
       
         
           
             
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               1 
               
                 
                   
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                       1 
                     
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                       2 
                     
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     Where C 1  is the capacitance value of the capacitor CC 1 , C 2  is the capacitance value of the capacitor CC 2 , L 1  is the inductance value of the inductor LC 1 , and L 2  is the inductance value of the inductor LC 2 . 
     Since the characteristics of the switch S 2  is different from the characteristics of the diode D 2 , the oscillating frequency of the spike generated during the diode D 2  is in the transition of reverse recovery is generally higher than the oscillating frequency of the spike generated during the switch S 2  is turned off. In this embodiment, the charging branch  142 _ 1  is configured to absorb the spike, generated during the switch S 2  is turned off, of the switching unit  124 . The charging branch  142 _ 2  is configured to absorb the spike, generated during the diode D 2  is in the transition of reverse recovery, of the switching unit  124 . Accordingly, the impacts of the spikes having different frequencies generated from the switching unit  124  are able to be reduced by the voltage clamping unit  140 . 
     In some embodiments, the inductor LC 1  and the capacitor CC 1  are configured to operate as a series-resonant circuit of the voltage clamping unit  140 . When the switch S 2  is turned off, a resonance is correspondingly occurred in the inductor LC 1  and the capacitor CC 1 . At the series-resonant point, the impedance of the charging branch  142 _ 1  of the voltage clamping unit  140  is lowest. As a result, the spike generated from the switch S 2  can be fully absorbed by the charging branch  142 _ 1 . Effectively, the spike, generated during the switch S 2  is turned off, is able to be fully limited by the inductor LC 1  and the capacitor CC 1 . 
     Similarly, when the diode D 2  is in the transition of reverse recovery, a resonance is correspondingly occurred in the inductor LC 2  and the capacitor CC 2 . At the series-resonant point, the impedance of the charging branch  142 _ 2  of the voltage clamping unit  140  is lowest. As a result, the spike generated from the diode D 2  can be fully absorbed by the charging branch  142 _ 2 . Effectively, the spike, generated during the diode D 2  is in the transition of reverse recovery, is able to be fully limited by the inductor LC 2  and the capacitor CC 2 . 
     In some other embodiments, the resonant frequency of the aforementioned series-resonant circuit is set to be close to the oscillating frequency of the corresponding spike. Accordingly, the function of absorbing the corresponding spike can be achieved as well. 
     In some embodiments, the inductor LC 1  and the inductor LC 2  are parasitic inductances on the transmission lines. For example, by utilizing a simulation or a network analyzer to test the charging branch  141 _ 1  and the charging branch  141 _ 2 , the inductance values of the inductor LC 1  and the inductor LC 2  are obtained. Accordingly, the capacitance values of the capacitor CC 1  and capacitor C 2  are then set. Alternatively, in some other embodiments, the inductor LC 1  and the inductor LC 2  implemented by directly using inductive elements. The arrangements of the inductor LC 1  and the inductor LC 2  are given for illustrative purposes only, and the present disclosure is not limited thereto. Person skilled in the art is able to adjust the arrangements of the inductor LC 1  and the inductor LC 2  according to practical applications. 
     Furthermore, with continued reference to  FIG. 1A , the voltage clamping unit  140  further includes a discharging branch  144 _ 1  and a discharging branch  144 _ 2 . The discharging branch  144 _ 1  is coupled between the charging branch  142 _ 1  and a positive terminal of the input power source VBUS, and the discharging branch  144 _ 2  is coupled between the charging branch  142 _ 2  and a positive terminal of the input power source VBUS. In some embodiments, the discharging branch  144 _ 1  includes a resistor RC 1 , and the discharging branch  144 _ 2  includes a resistor RC 2 . The electrical energy absorbed by the capacitor CC 1  is able to be released via the resistor RC 1 , and the electrical energy absorbed by the capacitor CC 2  is able to be released via the resistor RC 2 . As a result, the operations of the voltage clamping, corresponding to the switch S 2  and the diode D 2 , can be constantly performed, in order to prevent the impacts of the spikes from happening to the switch D 2  and the diode D 2 . 
     Reference is now made to  FIG. 2 .  FIG. 2  is a schematic diagram of a converter  200 , in accordance with some embodiments of the present disclosure. Compared with  FIG. 1A , the voltage clamping unit  140  of the converter  200  in  FIG. 2  only employs a single diode DC 3  and a single resistor RC 3 . In other words, in this embodiment, additional diodes, i.e., the diode DC 1  and the diode DC 2  in  FIG. 1A , are not utilized in the charging branch  142 _ 1  and the charging branch  142 _ 2 . Instead, the charging branch  142 _ 1  and the charging branch  142 _ 2  are coupled to the switching unit  124  via a diode DC 3 . Effectively speaking, the diode DC 1  and the diode DC 2  in  FIG. 1A , is implemented with a single diode DC 3 . 
     In greater details, as shown in  FIG. 2 , the charging branch  142 _ 1  only includes a capacitor CC 1  and an inductor LC 1 , and the charging branch  142 _ 2  only includes a capacitor CC 2  and an inductor LC 2 . The capacitor CC 1  and the capacitor CC 2  are coupled to the switching unit  124  via the same diode DC 3 , to absorb the corresponding spikes. 
     Similarly, in this embodiment, the voltage clamping unit  140  only includes a single discharging branch  144 _ 3 , which can be implemented with the aforementioned resistor RC 3 . In other words, in this embodiment, the capacitor CC 1  and the capacitor CC 2  are discharged via the same resistor RC 3 . Effectively speaking, the discharging branch  144 _ 1  and the discharging branch  144 _ 2  in  FIG. 1A  are implemented with the single discharging branch  144 _ 3 . 
     The numbers of the diodes and the discharging branches of the voltage clamping unit  140 , as illustrated in the previous embodiments, are given for illustrative purposes only, and the present disclosure is not limited thereto. Various numbers of the diodes and the discharging branches or any combination of each embodiment are within the contemplated scope of the present disclosure. For example, in some other embodiments, the voltage clamping unit  140  utilizes two diodes DC 1  and DC 2 , but only utilizes a single discharging branch  144 _ 3 , i.e., a single resistor RC 3 . Alternatively, in some embodiments, the voltage clamping unit  140  utilizes a single diodes DC 3 , and also utilizes two discharging branches  144 _ 1  and  144 _ 2 . 
     Reference is now made to  FIG. 3 .  FIG. 3  is a schematic diagram of a converter  300 , in accordance with some embodiments of the present disclosure. Compared with  FIG. 1A , the voltage clamping unit  140  of the converter  300  further includes charging branches  142 _ 1 - 142 _N and discharging branches  144 _ 1 - 144 _N. The arrangements of the charging branches  142 _ 1 - 142 _N and discharging branch  144 _ 1 - 144 _N are similar with the aforementioned charging branches  142 _ 1  and  142 _ 2 , and the discharging branches  144 _ 1  and  144 _ 2 . Thus, the repetitious descriptions are not given here. 
     In various embodiments, as described in  FIG. 2  above, at least two of the charging branches  142 _ 1 - 142 _N are able to be implemented with the same diode. In some further embodiments, all of the diodes DC 1 -DCN are able be implemented with the same diode. Similarly, in various embodiments, as described in  FIG. 2  above, at least two of the discharging branches  144 _ 1 - 144 _N are implemented with the same discharging branch. In some further embodiments, all of the discharging branches  144 _ 1 - 144 _N are implemented with the same discharging branch. 
     In this embodiment, the respective frequencies of the charging branches  142 _ 1 - 142 _N are configured to be different from each other. For example, the charging branches  142 _ 1  have a first resonant frequency, the charging branches  142 _ 2  have a second resonant frequency, and the charging branches  142 _N have an N-th resonant frequency, in which the first resonant frequency, the second resonant frequency, and the N-th resonant frequency are different from each other, and N is a positive integer greater than 2. As a result, the charging branches  142 _ 1 - 142 _N are able to absorb the spikes, having different oscillating frequencies, generated during the switching unit  124  is turned off. In other words, in some embodiments, considering the impacts caused from parasitic inductances and parasitic capacitances in the circuit or other variations, the spikes, having various oscillating frequencies, possibly generated by the switching unit  124  are able to be absorbed by using the charging branches  142 _ 1 - 142 _N, which have different resonant frequencies. Accordingly, the reliability of the switching unit  124  is able to be further improved. 
     Reference is now made to  FIG. 4 .  FIG. 4  is a schematic diagram of a converter  400 , in accordance with some embodiments of the present disclosure. Compared with  FIG. 3 , as shown in  FIG. 4 , the charging branches  142 _ 1 - 142 _N of the converter  400  are coupled in parallel with the bridge arm  120 . In greater detail, the diode DC 1  and the diode DC 2  are coupled to a first terminal of the switching unit  122 , and the first terminal of the switching unit  122  is coupled to a positive terminal of the input power source VBUS. The capacitor CC 1  and the capacitor CC 2  are coupled to a second terminal of the switching unit  124 , and the second terminal of the switching unit  124  is coupled to an negative terminal of the input power source VBUS. 
     Compared with the embodiments above, in this embodiment, the spiked, generated during the switching unit  124  is turned off, are transmitted to the charging branches  142 _ 1 - 142 _N via the switching unit  122 , in order to charge the capacitors CC 1 -CCN in the charging branches  142 _ 1 - 142 _N. Effectively, the corresponding spikes are absorbed by the charging branches  142 _ 1 - 142 _N. Accordingly, the spikes are thus limited. Moreover, in this embodiments, the charging branches  142 _ 1 - 142 _N are able to simultaneously absorb at least one spike, having a corresponding oscillating frequency, generated during the switching unit  122  is turned off. For example, the charging branch  142 _ 1  and the charging branch  142 _ 2  are configured to absorb the spikes from the switching unit  124 , and the switching unit  142 _N− 1  (not shown) and the switching unit  142 _N are configured to absorb the spikes from the switch S 1  and the diode D 1  of the switching unit  122 . In other words, the charging branches  142 _ 1 - 142 _N are able to absorb the spikes, having different frequencies, generated from the bridge arm  120 . The arrangements described above are given for illustrative purposes only, and other types of the arrangements are also within the contemplated scope of the present disclosure. 
     As shown in  FIG. 4 , the voltage clamping unit  140  further includes discharging branches  144 _ 1 - 144 -N. The discharging branches  144 _ 1 - 144 -N correspond to the charging branches  142 _ 1 - 142 _N, respectively. The capacitors CC 1 -CCN of the charging branches  142 _ 1 - 142 _N are able to be discharged via the corresponding one of the discharging branches  144 _ 1 - 144 -N. As described above, in some embodiments, at least two of the diodes DC 1 -DCN of the charging branches  142 _ 1 - 142 -N are able to be implemented with the same diode. In further embodiments, all of the diodes DC 1 -DCN are able to be implemented with the same diode. As described above, in some embodiments, at least two of the discharging branches  144 _ 1 - 144 _N are able to be implemented with the same discharging branch. In further embodiments, all of the discharging branches  144 _ 1 - 144 _N are able to be implemented with the same discharging branch. 
     Reference is now made to  FIG. 5 .  FIG. 5  is a schematic diagram of a converter  500 , in accordance with some embodiments of the present disclosure. As shown in  FIG. 5 , the converter  500  includes a bridge arm  520 , a bridge arm  540 , and the voltage clamping unit  140 . In this embodiment, the converter  500  is a T-type neutral point clamped (TNPC) circuit. An input power source VBUS+ and an input power source VBUS− are coupled to a neural point N. The bridge arm  520  includes a switching unit  522  and a switching unit  524 . A first terminal of the switching unit  522  is coupled to the voltage clamping unit  140 , a second terminal of the switching unit  522  is coupled to a first terminal (which is referred to as a connection point N 1 ) of the switching unit  524 , and a second terminal of the switching unit  524  is coupled to an negative terminal of the input power source VBUS−. The bridge arm  540  is coupled between the neural point N and the connection point N 1 . The bridge arm  540  includes a switching unit  542  and a switching unit  544 . The switching unit  542  and the switching unit  544  are coupled in series. In greater detail, the emitting terminal of the switch S 4  of the switching unit  542  is connected to the emitting terminal of the switch S 3  of the switching unit  542 . The arrangements of the switching units  522 ,  524 ,  542 , and  544  are similar with the switching units  122  and  122  described in the previous embodiments, and thus the repetitious descriptions are not given here. 
     The voltage clamping unit  140  includes charging branches  142 _ 1 - 142 _N and  142 _X, and discharging branches  144 _ 1 - 144 _N and  144 _X. The charging branches  142 _ 1 - 142 _N are coupled between the neural point N and the positive terminal of the input power source VBUS+. The charging branch  142 _ 1 - 142 _N are able to absorb the spikes generated from the switching units  522 ,  542 , and  544 , and are able to be discharged via the discharging branches  144 _ 1 - 144 _N. The charging branch  142 _X is disposed between the neutral point N and the negative terminal of the input power source VBUS, to absorb the spikes generated from the switching units  524 ,  522 , 542 , and  544 . Similarly, the charging branch  142 _X is able to be discharged via the discharging branch  144 _X. As a result, the voltage clamping operations for each switching units  522 ,  524 ,  542 , and  544  of the converter  500  can be performed. 
     The numbers of the charging branches and the numbers of the discharging branches described are given for illustrative purposes only, and the present disclosure is not limited thereto. For example, in some other embodiments, much more charging branches  142 _X can be employed, to absorb spikes having the different oscillating frequencies. 
     Reference is now made to  FIG. 6 .  FIG. 6  is a schematic diagram of a converter  600 , in accordance with some embodiments of the present disclosure. As shown in  FIG. 6 , the converter  600  includes a bridge arm  620 , a diode DB 1 , a diode DB 2 , and the voltage clamping unit  140 . In this embodiment, the converter  600  is a diode neutral-point-clamped (DNPC) circuit. 
     The input power source VBUS+ and the input power source VBUS− are coupled to the neutral point N. The bridge  620  includes a switching unit  622 , a switching unit  624 , a switching unit  626 , and a switching unit  628 . A first terminal of the switching unit  622  is coupled to the positive terminal of the input power source VBUS+, and a second terminal of the switching unit  622  is coupled to a first terminal (which is referred to as a connection point A hereinafter) of the switching unit  624  and a cathode of the diode DB 1 . A second terminal of the switching unit  624  is coupled to a first terminal (which is referred to as a connection point B hereinafter) of the switching unit  626 . A second terminal of the switching unit  626  is coupled to a first terminal (which is referred to as a connection point C hereinafter) of the switching unit  628  and an anode of the diode DB 2 . A second terminal of the switching unit  628  is coupled to the negative terminal of the input power source VBUS−. A cathode of the diode DB 2  and an anode of diode DB 1  are coupled to together and then coupled to the neutral point N, the anode of the diode DB 1  is coupled to the connection point A, and the cathode of the diode DB 2  is coupled to the connection point C. The arrangements of the switching units  622 ,  624 ,  626 , and  628  are similar with the switching units  122  and  124  in the previous embodiments, and thus the repetitious descriptions are not given here. 
     The voltage clamping unit  140  includes the charging branches  142 _ 1 - 142 _N and  142 _X and the discharging branches  144 _ 1 - 144 _N and  144 _X. The charging branches  142 _ 1 - 142 _N are coupled between the cathode of the diode DB 2 , i.e., the neutral point N, and the first terminal of the switching unit  622 . As a result, the charging branches  142 _ 1 - 142 _N are able to absorb the spikes generated from the switching unit  622  and the diode DB 1 , and the charging branches  142 _ 1 - 142 _N are discharged via the discharging branches  144 _ 1 - 144 _N. The charging branch  142 _X is disposed between the cathode of the diode DB 2 , i.e., the neutral point N, and the second terminal of the switching unit  628 , to absorb spikes generated from the switching unit  628  and the diode DB 2 . Similarly, the charging branch  142 _X is able to be discharged via the discharging branch  144 _X. Accordingly, the voltage clamping operations for the switching units  622  and  628 , and the diodes DB 1 -DB 2  of the converter can be performed. 
     The numbers of the charging branches and the numbers of the discharging branches described above are given for illustrative purposes only, and the present disclosure is not limited thereto. For example, in some other embodiments, much more charging branches  142 _X can be employed, to absorb spikes having the different oscillating frequencies. 
     The applications of the voltage clamping unit  140  are given for illustrative purposes only, and the present disclosure is not limited thereto. Various types of the converter, which are able to employ the voltage clamping unit  140 , are also within the contemplated scope of the present disclosure. 
     As described above, the converter and the voltage clamping unit thereof provided in the present disclosure are able to absorb the spikes, having different oscillating frequencies, generated from switching units. Effectively, the spikes, generated during the switching units are turned off, can be limited, to achieve a complete voltage clamping protection. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims.