Patent Publication Number: US-2003223179-A1

Title: Capacitor for low voltage

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates to an electric device that requires high power consumption with a comparatively low voltage, such as a battery driven motor. The invention allows to suppress the surge voltage during switching by lowering the wiring inductance in the connection device of a capacitor, enabling to use low-loss high-efficient semiconductor devices with low-withstand voltage to thereby achieve a small-sized low-cost and high-performance electric device.  
       [0002] A method of improving the frequency response of an electrolytic capacitor connected to an electric device and suppressing the surge voltage has been discussed, for example, in Japanese Patent Laid-open No. Hei 6-275476. The method takes on the following construction illustrated in FIGS. 1A and 1B of the specification. In the method, tabs for taking out an anode lead and a cathode lead, which are installed on the upper part of a capacitor element made up with laminated plates, are separately tied up in a bundle and attached each to integrated leads. The integrated leads are coupled to external connection terminals through anode and cathode connection terminals for connecting to a sealing plate to seal the case. In this case, to form the integrated leads and the anode and cathode connection terminals into parallel broad plates will achieve a sufficient lowering of the internal inductance inside the case of the electrolytic capacitor.  
       [0003] As the second example, a method is discussed in the document “New Aluminum Electrolytic Capacitors With Low Inductance Allow Advanced Frequency Converter Design” Jurgen Roumen PCIM 2000 (2000). As illustrated in FIG. 4 in the above document, the method attaches multiple folder tabs to each of the anode foil and the cathode foil, thereafter houses the winding made by lap winding in the case, and connects the folder tabs to the electrode terminals mounted on the sealing plate. In this case, a sufficient spacing is required between the anode and cathode of the electrode terminals to secure insulation against a high voltage. As the conventional one illustrated on the left in FIG. 4, the spacing between the parts attached to the anode foil and cathode foil of the folder tabs is widely set, and the length of the connection devices extended to the upper electrode terminals is also set long. As the improved one illustrated on the right in FIG. 4 in the document, the spacing between the parts attached to the anode foil and cathode foil of the folder tabs is narrowed, and the length of the connection devices extended to the upper electrode terminals is shortened, thus achieving remarkably reduced inductance.  
       [0004] The total inductance that dominates generation of a surge voltage and a frequency response is the sum of the three components as follows.  
       [0005] Total inductance  
       [0006] =Inductance inside a capacitor  
       [0007] +Inductance of the power wiring for connecting the capacitor to an electric device  
       [0008] +Inductance inside the electric device  
       [0009] The above examples 1 and 2 introduced in the related art are the invention relating to the lowering of the inductance inside the capacitor in the first term on the right side of the above expression. For the reduction of the inductance inside the electric device in the third term there have been various inventions related to individual electric devices. However, these conventional techniques cannot lower the inductance of the power wiring for connecting the capacitor to the electric device in the second term of the above expression, which is a limit in regard to improving the frequency response and suppressing the surge voltage.  
       SUMMARY OF THE INVENTION  
       [0010] The present invention has been made in view of the above circumstances, and the invention intends to realize the reduction of the total inductance for the use of a low-voltage device by greatly reducing the inductance of the power wiring parts that connect an electrolytic capacitor to an electric device in order to improve the frequency response and suppress the surge voltage of the electric device. Further it is an object of the invention to allow the use of low-loss high-efficient semiconductor devices with a low-withstand voltage, thereby providing a small-sized low-cost and high-performance electric device.  
       [0011] In order to solve the problem, in regard to the low-voltage device, by utilizing the property that to shorten a distance between the anode and cathode of the external terminals placed on the outside of an electrolytic capacitor will not generate the dielectric breakdown, the terminals are placed close to the external terminals of the case. And, for the power wirings that connect an electric device to the electrolytic capacitor is used a laminated wiring in which two broad flat plates with an insulating layer sandwiched in-between are overlapped. Being placed in proximity to the external terminals of the case, the laminated wiring increases the suppression effect of inductance to a great extent, thus achieving the reduction of inductance of the power wiring parts. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0012] Other objects and advantages of the invention will become apparent from the following description of embodiments with reference to the accompanying drawings in which:  
     [0013]FIGS. 1A and 1B illustrate an overlapping effect of to-and-fro currents in the power wiring parts, which is the effect of the present invention;  
     [0014]FIGS. 2A and 2B illustrate a state that a difference of the distance between the terminals creates a difference in the overlapping effect of to-and-fro currents in the power wiring parts, as the effect of the invention;  
     [0015]FIG. 3 illustrates the overlapping effect of a current by two capacitors arranged in parallel in reverse polarity, as the effect of the invention;  
     [0016]FIGS. 4A and 4B illustrate a second embodiment of the invention;  
     [0017]FIGS. 5A to  5 C illustrate a third embodiment of the invention;  
     [0018]FIG. 6 illustrates a fourth embodiment of the invention;  
     [0019]FIGS. 7A and 7B illustrate a fifth embodiment of the invention;  
     [0020]FIGS. 8A to  8 C illustrate a sixth embodiment of the invention;  
     [0021]FIG. 9 illustrates a seventh embodiment of the invention;  
     [0022]FIG. 10 illustrates an eighth embodiment of the invention; and  
     [0023]FIG. 11 illustrates a ninth embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0024] First Embodiment  
     [0025] The basic construction common to a first embodiment of this invention will be described with the accompanying drawings. FIG. 1A and FIG. 1B comparably illustrate two types of power wirings that connect electrolytic capacitors to electric devices. In FIG. 1A, an anode electrode terminal  2   a  and a cathode electrode terminal  2   b  that are attached to a case  1  of an electrolytic capacitor are connected to an electric device  3  by means of a power wiring  4   a  on the anode side and a power wiring  4   b  on the cathode side. The power wirings  4   a  and  4   b  are made of narrow conductive plates, and are arranged in parallel with a spacing substantially equal to the distance between the electrode terminals  2   a  and  2   b . Because of this construction, a charge/discharge current  5   a  of the capacitor that flows through the power wiring  4   a  on the anode side and a charge/discharge current  5   b  of the capacitor that flows through the power wiring  4   b  on the cathode side do not have an overlapped area. Accordingly, the to-and fro currents ( 5   a ,  5   b ) induces a strong magnetic field in the surrounding space, whereby the power wirings  4   a ,  4   b  will possess large wiring inductances. In contrast to this, this embodiment adopts a method as illustrated in FIG. 1B as a measure to reduce the inductance. Both the power wiring  4   a  on the anode side and the power wiring  4   b  on the cathode side employ wide conductive plates, and both plates are arranged in parallel to overlap each other. Because of this construction, the currents  5   a  and  5   b  flowing through the power wirings come close and overlap each other in a middle area  6  between the electric device  3  and the case  1  of the electrolytic capacitor, which suppresses the magnetic field induced on the surrounding space almost to zero, thus reducing the inductance.  
     [0026] In order to further reduce the inductance, an area  7  near the electrolytic capacitor of the power wirings  4   a ,  4   b  needs to be small. For this purpose, the electrode terminals  2   a  and  2   b  are arranged to come close as illustrated in FIG. 2A. Thus, the area  7  where the currents does not overlap is made small in comparison to the case in FIG. 2A, which will reduce the inductance of the power wirings to a great extent. Alternatively, as shown in FIG. 3, a first capacitor  8  and a second capacitor  9  of a small capacitance are arranged adjacently with the anode electrode terminal  2   a  and the cathode electrode terminal  2   b  put in reverse polarity. Here, the capacitances of the two capacitors  8 ,  9  are set equal. Then, currents  10   a ,  10   b  flowing through the first capacitor  8  and currents  11   a ,  11   b  flowing through the second capacitor  9  overlap each other, and the magnitudes of the currents become equal with reverse directions each other, so that the inductance can be reduced. Generally, in case of two or more capacitors but even number thereof, to arrange two capacitors of an equal capacitance in a pair of reverse polarity will attain the above effect.  
     [0027] In case of a high-voltage electric device, there is a restriction to reducing the spacing between the anode electrode terminal  2   a  and the cathode electrode terminal  2   b  in order to secure insulation. However, since a corona discharge does not occur in case of a low-voltage electric device for use in 390 volts or more, only securing the creeping distance will make it possible to bring the anode terminal and the cathode terminal close, thereby reducing the inductance.  
     [0028] Second Embodiment  
     [0029] A second embodiment of this invention will be described with FIGS. 4A and 4B. Referring to FIG. 4A, on the upper surface of a sealing plate  12  of an electrolytic capacitor are mounted an anode electrode terminal  2   a  and a cathode electrode terminal  2   b  of L-letter shaped plate. In the connection with an electric device  3 , a broad plate-formed anode power wiring  4   a  and a cathode power wiring  4   b  are used so as to sandwich an insulating sheet  13  in-between. The power wirings  4   a ,  4   b  are fastened to the electrode terminals  2   a ,  2   b  with screws  14 . Accordingly, as shown in FIG. 4B, screw-fitting holes  15  are pierced in the electrode terminals  2   a ,  2   b , and window holes  16  are bored so as to prevent the screws  14  used for mounting the power wiring  4   b  of one pole from contacting with the power wiring  4   a  of the other pole. Owing to such a construction, the anode electrode terminal  2   a  is connected only to the anode power wiring  4   a , and the cathode electrode terminal  2   b  is connected only to the cathode power wiring  4   b ; since the running currents overlap in all the areas on the power wirings, a remarkable reduction of the inductance of the power wiring  4  is possible. In this embodiment, it is possible to expand the degree of bringing the electrode terminals  2  close, in comparison with the case of the long cylindrical electrode terminals as illustrated in FIG. 2B. In case of FIG. 2B, a high current has to be flown through the long cylindrical electrode terminals, and the diameter of the electrode was needed to be sufficiently large to prevent increase of the current density. This gave a limit to placing the electrode terminals  2  adjacently. However, since the first embodiment employs broad conductive plates for the electrode terminals, it is possible to prevent increase of the current density in the electrode terminals, and to decrease the thickness of the conductive plates. Therefore, it is possible to place the electrode terminals sufficiently close.  
     [0030] Third Embodiment  
     [0031] A third embodiment of this invention will be described with FIGS. 5A to  5 C. Referring to FIGS. 5A and 5B, an anode tab connection plate  17   a  and a cathode tab connection plate  17   b  each have two electrode terminals  2   a  and  2   b  mounted thereon. As shown in FIG. 5C, the tab connection plates  17   a ,  17   b  are integrally molded using resin into a sealing plate  12 . On the upper surface of the sealing plate  12 , the anode electrode terminals  2   a  and the cathode electrode terminals  2   b  are alternately projected in a slightly dislocated manner.  
     [0032] On the lower surface of the sealing plate  12 , the anode tab connection plate  17   a  and the cathode tab connection plate  17   b  are exposed with a partition plate  18  put in-between. In the connection with an electric device  3 , in the same manner as the first embodiment, a broad plate-formed anode power wiring  4   a  and a cathode power wiring  4   b  are used so as to sandwich the insulating sheet  13  in-between. According to this embodiment, since the currents flowing through almost all the areas on the power wirings overlap except for a limited area between the electrode terminal  2   b  and the cathode power wiring  4   b  near the capacitor connection area, a significant reduction of the inductance of the power wiring  4  can be realized. In this embodiment, in the same manner as in the first embodiment, it is possible to expand the degree of bringing the electrode terminals  2  close in comparison with the case in FIG. 2B. In other words, in the second embodiment, it is possible to prevent increase of the current density in the electrode terminals because plural electrode terminals are used, and the diameter of the electrode terminals can be thinned. Accordingly, the electrode terminals can be placed sufficiently adjacently.  
     [0033] Fourth Embodiment  
     [0034] A fourth embodiment of this invention will be described with FIG. 6. An anode foil  19   a  and a cathode foil  19   b  each have conductive foil folder tabs  20  stuck thereon in a manner that the upper parts of the tabs  20  protrude, and then electrolyte layers are put in-between and wound in a roll to form a winding  21 . The upper parts of the folder tabs  20  that protrude from the anode foil  19   a  and the cathode foil  19   b  are separately bundled. As described in the third embodiment, the non-molded exposed portions of anode and cathode tab connection plates  17   a  and  17   b  are provided on the lower surface of a sealing plate  12 , and on both sides of the partition plate  18 . The bundled folder tabs  20  are connected to these exposed portions, and are fastened by tightening stops  22  with bolts  23  and nuts  24 . The winding  21  is housed in the case  1 , which is sealed by the sealing plate  12 , and the electrolytic capacitor is completed. According to this embodiment, even if the electrode terminals  2  are placed adjacently on the upper surface of the sealing plate  12 , the folder tabs  20  can easily be mounted, and the manufacturing process becomes simple, which makes it possible to provide a low-cost and high-performance electrolytic capacitor.  
     [0035] Fifth Embodiment  
     [0036] A fifth embodiment of this invention will be described with FIGS. 7A and 7B. When the folder tabs  20  are connected to the tab connection plates  17  on the lower surface of the sealing plate  12  in the fourth embodiment, tightening the stops  22  with the bolts  23  and the nuts  24  fastens the folder tabs  20 . In this embodiment, the folder tabs  20  are pressed to the tab connection plates  17  on both sides of the partition plate  18  by the stops  22 , and then fixed under pressure by spring clips  25 , thereby eliminating the thread fastening work and still more improving the workability.  
     [0037] Sixth Embodiment  
     [0038] A sixth embodiment of this invention will be described with FIGS. 8A to  8 C. A chip capacitor  26  has anode electrode pads  27  and cathode electrode pads  28  arranged along the facing sides on the upper surface thereof. A printed board has an anode side  29  and a cathode side  30  that are composed of a conductive plate, which are bonded as a solid plane. The anode side  29  and cathode side  30  each have the same number of via holes  31  as that of the anode electrode pads  27  and cathode electrode pads  28  on the upper side of the chip capacitor  26 . The via holes are adjacently provided and connected to the opposite side. A first chip capacitor  26   a  and a second chip capacitor  26   b  are pasted each at the same positions on the anode side  29  and the cathode side  30  of the printed board. The first chip capacitor  26   a  is connected directly to the anode side  29 , but through the via holes  31  to the cathode side  30  of the printed board. In the same manner, the second chip capacitor  26   b  is connected directly to the cathode side  30 , but through the via holes  31  to the anode side  29  of the printed board. A first current running through the first chip capacitor  26   a  flows through a wire lead  32   b , the first chip capacitor  26   a , a wire lead  32   a , and the cathode side  30  of the printed board in this order. A second current running through the second chip capacitor  26   b  flows through the anode side  29  of the printed board, a wire lead  32   c , the second chip capacitor  26   b , and a wire lead  32   d  in this order. Owing to this method, the first current running through the first chip capacitor  26   a  and the second current running through the second chip capacitor  26   b  run in the opposite direction and overlap in the vertical direction to the printed board; therefore, a sharp reduction of the inductance becomes possible.  
     [0039] Seventh Embodiment  
     [0040] A seventh embodiment in which this invention is applied to a dc/ac inverter will be described. FIG. 9 illustrates three-phase two-level IGBT inverter. The alternate power supplied from a commercial ac power source  33 , after passing through a diode rectifier  35  using a rectifying diode  34 , is stored in an electrolytic capacitor  36  as a dc power. And, the dc power is again inverted into an ac power of a variable frequency by means of a dc/ac inverter  39  using an IGBT  37  and a freewheeling diode  38 , thus driving an ac motor  40 . If the inductance of a power wiring  4  that connects the electrolytic capacitor  36  to the dc/ac inverter  39  is large, a high surge voltage is applied to the IGBT  37  during the off operation of the IGBT  37 , which possibly gives a risk that destroys the IGBT  37 . The use of the electrolytic capacitor  36  of the present invention will suppress the surge voltage to prevent destruction of the device.  
     [0041] Eighth Embodiment  
     [0042] An eighth embodiment in which this invention is applied to a switching power supply will be described. FIG. 10 illustrates a switching power supply using one-transistor forward converter. A high-voltage dc power stored in the electrolytic capacitor  36  is converted into a pulse current by turning on and off a MOSFET  41  on the primary side, which is supplied to the primary side of a high frequency transformer  42 . Then, a low-voltage pulse is generated on the secondary side of the high frequency transformer  42 . The high-voltage dc power is converted into a low-voltage dc power by rectifying a current flowing through the secondary side by the pulse voltage generated by means of a MOSFET  43  on the secondary side and a reactor  44 . In this time, if the inductance of the power wiring  4  that connects the electrolytic capacitor  36  to the switching power supply  45  is high, the high frequency characteristics are deteriorated. The use of the electrolytic capacitor  36  of this invention will improve the frequency characteristic.  
     [0043] Ninth Embodiment  
     [0044] A ninth embodiment in which this invention is applied to a vehicle will be described. FIG. 11 illustrates a construction of a drive system in a vehicle. In FIG. 11, reference numeral  46  denotes a motor,  47  a power conversion device;  48  a dc power supply;  36  the electrolytic capacitor;  49  an output wiring;  50  the vehicle;  51  a control device;  52  a transmission gear;  53  an engine;  54   a ,  54   b ,  54   c ,  54   d  a wheel; and  55  a signal terminal. The signal terminal  55  receives signals relating to the driving state of the vehicle, and the commands from the driver, such as start, acceleration, deceleration, stop, etc. The control device  51  transmits a control signal to the power conversion device  47  on the basis of information received from the signal terminal  55 , and drives the motor  46  by the power from the dc power supply  48 . The motor  46  transfers the torque to the engine shaft, and is able to drive the wheels through the transmission gear  52 . That is, the drive system in FIG. 11 allows the motor  46  to drive the wheels  54   a  through  54   d  when the engine  53  is in stop, and also to assist a torque when the engine  53  is operative. It is also possible to make the engine  53  drive the motor  46 , and to convert an ac power generated by the motor  46  into a dc power by means of the power conversion device  47  to thereby charge the dc power into the dc power supply  48 . The electrolytic capacitor  36  is disposed between the dc power supply  48  and the power conversion device  47 , whereby the power is stored temporarily to increase the capacity of the dc power supply  48  apparently and to improve the transient response of the dc power supply  48 .  
     [0045] In the drive system in FIG. 11, since a high torque is required during driving the wheels only by the motor  46  or assisting the torque, and the dc power supply is a low-voltage power supply such as a storage battery, the motor  46  has to be driven by a low-voltage high-current power. Accordingly, it is essential that the power conversion device  47  adopts a semiconductor device of a low resistance that dissipates little power in a high current. However, the semiconductor device of a low resistance is vulnerable to a surge excessive voltage, and an efficient power conversion device has to provide a surge voltage suppression mechanism. The adoption of the electrolytic capacitor  36  of this invention will suppress the surge voltage, which makes it possible to provide a vehicle having a high-efficient drive system.  
     [0046] The invention achieves an electrolytic capacitor having an excellent frequency response, which enables to suppress a surge voltage.  
     [0047] While the invention has been described in its embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention its broader aspects.