Abstract:
A power converter includes a first electric power conversion unit having an inverter for converting a first DC electric power to an AC electric power, an AC circuit connected to the first electric power conversion means; 
     a second electric power conversion unit for receiving the first DC electric power and converting the same to a second DC electric power having a voltage level that differs from the voltage level of the first DC electric power, a power storage unit for storing the second DC electric power of the second electric power conversion unit; and a ripple suppressor having a first inductance for guiding the second DC electric power of the second electric power conversion unit to the power storage means and a second inductance for suppressing the ripple component included in the second DC electric power arranged between the second electric power conversion unit and the power storage unit.

Description:
[0001]    The present application is based on and claims priority of Japanese patent application No. 2011-049140 filed on Mar. 7, 2011, the entire contents of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The present invention relates to a power converter preferably applied to a controller for controlling an electric motor which is used as a drive source of a rolling stock, for example, and more specifically, relates to a power converter comprising an inverter, an AC load receiving electric power from the inverter, and a battery connected in parallel with the inverter. 
       Description of the Related Art 
       [0003]    Inverters widely used in the industrial world mainly adopt a system for converting DC electric power to AC electric power via variable voltage variable frequency (VVVF) control using a pulse width modulation (PWM) system. 
         [0004]    For example, in the field of rolling stocks, a variable voltage variable frequency (hereinafter abbreviated as VVVF) inverter is used as a system for driving the AC motor of the rolling stock. The rolling stock is accelerated by driving the electric motor via the VVVF inverter, and a regeneration brake control is performed widely in which the electric motor is operated as a generator during braking operation so as to convert kinetic energy into electric energy and to return the same to an overhead trolley (hereinafter referred to as overhead cable). 
         [0005]    Recently, an art of applying the battery to effectively utilize the regeneration electric power obtained via regeneration braking and to realize further energy saving has been studied and put to practical use. 
         [0006]    For example, patent document 1 teaches an art of driving the rolling stock highly efficiently by connecting a battery in parallel with an input side of an inverter in a power converter, so as to store the regeneration energy and effectively utilize the same. 
         [0007]    Further, patent document 2 discloses an art in which a battery is connected in series to a ground side of the input of the inverter so as to elevate the input voltage of the inverter, according to which the characteristic area of the high speed side of the electric motor is expanded and the performance of regeneration braking acquiring braking force by consuming the rotational energy of the electric motor or of power running for driving the rolling stock is enhanced. 
         [0008]    The VVVF inverter is also used in inverter air-conditioners and the like in the field of home electrical appliances. 
         [0009]    Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2009-89503 
         [0010]    Patent Document 2: Japanese Patent Application Laid-Open Publication No. 2008-278615 
         [0011]    Non-Patent Document 1: Technical Data on Lithium-Ion Battery, Sanyo Electric Co., Ltd (2002) (URL: http://www.orient-technology.com/Sanyo/technot/lion_J.pdf) 
         [0012]    Non-Patent Document 2: Power Electronics, Takao Hirasa, (p. 83-85), Kyoritsu Shuppan Co., Ltd (1992) 
         [0013]    According to a controller of a rolling stock equipped with a battery, during reduction of regeneration load, the regeneration electric power can be absorbed and stored in the battery, so that meaningless consumption of kinetic energy of the rolling stock can be prevented, and simultaneously, the consumption of air brake and the like due to reduction of regeneration brake force can be cut down. 
         [0014]    On the other hand, if a power storage battery is used as the battery, the power storage battery has a drawback in that generally, repeated discharge and charge thereof causes resolution of the electrolytic solution, which leads to characteristic degradation of the power storage such as the increase of internal resistance or the deterioration of battery capacity. Further, it is known that the speed of degradation is accelerated by over-charge and over-discharge of the battery or by the increase of temperature accompanying the same (refer to non-patent document 1). 
         [0015]    The discharge and charge of power of the battery is controlled via a power converter such as a DC-DC converter. Such a power converter is generally composed of a power semiconductor device, wherein the power semiconductor device is subjected to switching control so as to control the electric power being discharged from or charged to the battery, so that harmonic distortion is contained therein, similar to the aforementioned VVVF inverter. The ripples contained in the discharge and charge currents or the repeated precipitous change of currents lead to accelerated degradation of the battery, so that suppression thereof is desired. 
         [0016]    Known methods for suppressing the ripples superposed via the power converter generally relate to increasing the capacity of the reactor arranged within the power converter and increasing the switching frequency of the power semiconductor device (refer to non-patent document 2). 
         [0017]    On the other hand, the power storage capacity of the battery disposed in the rolling stock is set so as to absorb all the regeneration electric power generated via regeneration braking, but since the mounting area under the floor of the vehicle is limited, it is preferable that a battery with a minimum battery capacity is mounted on the vehicle. 
         [0018]    However, the reactor within the power converter has a high capacity and weight, and the increase in the size thereof is not desirable since the area under the floor of the vehicle is limited. It is also not desirable to increase the switching frequency of the power semiconductor device since the switching loss causes heat generation. 
       SUMMARY OF THE INVENTION 
       [0019]    The present invention aims at solving the prior art problems mentioned above by providing a power converter and a power converter of a rolling stock capable of absorbing ripples superposed via the power converter and suppressing characteristic degradation caused by over-charge and over-discharge of the battery. 
         [0020]    In order to achieve the above object, the present invention provides a power converter comprising an electric motor for driving a rolling stock, an inverter for controlling the electric motor, a battery for absorbing regeneration electric power of the electric motor, and a DC-DC converter for controlling the electric power absorbed via the battery, wherein a ripple suppression means for absorbing the current ripple superposed via the DC-DC converter is connected in parallel with respect to the battery, wherein the connection is performed so that the inductance of the electric wiring connected between the capacitor and the DC-DC converter becomes smaller than the inductance of the electric wiring connected between the battery and the DC-DC converter. 
         [0021]    According to the present invention, the current ripple superposed via the DC-DC converter can be absorbed by the capacitor, so that the characteristic degradation caused by over-charge and over-discharge of the battery can be suppressed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a configuration diagram of a power converter according to the (first embodiment of the) present invention applied to a rolling stock. 
           [0023]      FIG. 2  is a perspective view illustrating the configuration of components of a semiconductor power converter as represented by the inverter and the DC - DC converter of  FIG. 1 . 
           [0024]      FIG. 3  is a configuration diagram of a power converter according to the (second embodiment of the) present invention. 
           [0025]      FIG. 4  is a configuration diagram of a power converter according to the (third embodiment of the) present invention. 
           [0026]      FIG. 5  is a configuration diagram of a power converter according to the (fourth embodiment of the) present invention. 
           [0027]      FIG. 6  is a configuration diagram of a power converter having a battery according to the prior art. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    The present invention is preferably applied to a power converter of rolling stocks, and in the following description of the background art and preferred embodiments, the present invention is applied to a controller or a power converter of a rolling stock as an example, but the present invention can be applied to power converters other than for rolling stocks, and the applicable range of the present invention is not restricted to those illustrated in the present description. 
         [0029]      FIG. 6  illustrates one example of a power converter having a battery mounted thereon, and the configuration of the power converter will be described with reference to  FIG. 6 . 
         [0030]    In  FIG. 6 , reference number  1  denotes an overhead trolley,  2  denotes a current collector,  3  denotes a contactor,  4  denotes a reactor,  5  and  8  denote a capacitor,  6  denotes a DC-AC converter constituting an inverter (hereinafter referred to as an inverter),  7  denotes an electric motor,  9  denotes a DC-DC converter constituting a chopper, and  10  denotes a battery. 
         [0031]    Now, the inverter  6  and the DC-DC converter  9  are generally composed of a power semiconductor device. According to electric power conversion via a PWM system, DC electric power is converted to AC electric power via switching of the power semiconductor device, but during this electric power conversion, harmonic distortion is known to occur. Therefore, the harmonic distortion caused by the inverter  6  is designed to be absorbed via a filter circuit composed of a reactor  4  and a capacitor  5 , and the harmonic distortion caused by the DC-DC converter  9  is designed to be absorbed via a filter circuit composed of a reactor  4  and a capacitor  8 . According to this arrangement, harmonic distortion can be prevented from flowing into the overhead trolley  1 . 
         [0032]    During power running of the rolling stock, DC electric power is allowed by the power converter to enter from an overhead trolley  1  via a current collector  2  and through a line breaker  3 , a reactor  4  and a capacitor  5  to be fed to the inverter  6 , and thereafter, by having the DC electric power converted to three-phase AC electric power in the inverter  6 , the electric power drives the electric motor  7  to accelerate the vehicle. 
         [0033]    During regeneration, the vehicle is decelerated via regeneration brake power, and at the same time, the regeneration electric power generated by the electric motor  7  is returned to the overhead trolley through the same path used during power running, according to which the regeneration electric power can be used as electric power for enabling power running to be performed in other vehicles on the same track. 
         [0034]    On the other hand, according to the present device configuration, even if there is not enough rolling stock performing power running on the same track during the above-described regeneration control, by absorbing the regeneration electric power generated via the electric motor  7  in a battery  10 , it becomes possible to efficiently utilize electric power by reducing the number of times of ineffective regeneration caused by continuous operation of the regeneration brake during which regeneration electric power cannot be fully returned. 
         [0035]    In this example, the regeneration electric power generated from the electric motor  7  is charged via an inverter  6 , a capacitor  5 , a capacitor  8  and a DC-DC converter  9  to a battery  10 . Now, the electric power charged to the battery  10  is controlled via the DC-DC converter  9 . 
         [0036]    Further, the electric power charged in the battery  10  is discharged through the same path used for charging of the battery  10  to be utilized as auxiliary power for controlling power running of the vehicle, and also as electric power for emergency running of the vehicle to a station when supply of electric power cannot be received such as when power failure occurs to the overhead trolley  1 . 
         [0037]    However, the illustrated example lacks to consider the above-mentioned problems of the prior art. The present invention aims at solving the above-mentioned problems by providing a power converter described below. 
         [0038]    Now, the preferred embodiments of the present invention will be described with reference to the drawings. 
       [Embodiment 1] 
       [0039]      FIG. 1  is a view illustrating a first embodiment of a power converter of a rolling stock according to the present invention. The same sections as  FIG. 6  are denoted with the same reference numbers. 
         [0040]    According to the power converter illustrated in  FIG. 1 , reference number  1  denotes an overhead trolley (overhead cable),  2  denotes a current collector for collecting the DC electric power of the overhead trolley  1 ,  3  denotes a contactor (high-speed breaker, line breaker),  4  denotes a reactor,  5  denotes a capacitor,  6  denotes an inverter constituting a DC-AC converter (first conversion control means), wherein these components constitute a first electric power conversion means. The reactor  4  and the capacitor  5  constitute a filter circuit for smoothing the DC electric power. Reference number  7  denotes an electric motor driven by the AC electric power supplied from the inverter  6 , which constitute an AC circuit. 
         [0041]    Reference number  9  denotes a DC-DC converter (second conversion control means) connected in parallel with the inverter  6 , wherein the conversion equipment is composed of a switching section composed of two switching devices  9 - 1  adopting a series configuration connected to the electric wiring and a ground wire disposed on the current collector side, and a reactor  9 - 2  connected to a connection section of the switching device. A capacitor  8  is connected on a front side of the DC-DC converter  9 , constituting a second electric power conversion means. The DC-DC converter  9  is connected in parallel with the inverter  6  and functions to absorb the DC electric power generated from the inverter. 
         [0042]    Reference number  10  denotes a battery (first power storage means) for storing DC electric power from the DC-DC converter, which is composed for example of a battery. 
         [0043]    Reference numbers  12  and  13  denote electric wiring for connecting the reactor  9 - 2  of the DC-DC converter  9  and one of the electrodes of the battery  10 , wherein the electric wiring has a desired inductance. Reference number  11  denotes a capacitor connected between the electric wiring  12  and  13  and the other electrode (ground wire) of the battery  10 , which has a power storage function. These components constitute a ripple suppression means for suppressing ripple components and preventing the same from being supplied from the DC-DC converter to the battery  10 . Ripple suppression refers to a technique of reducing ripple components moderately so as not to affect the battery  10 . 
         [0044]    Now, the inductance contained in the electric wiring  12  is referred to as Lc, and the total inductance contained in the electric wiring  12  and the electric wiring  13  is referred to as Lb. 
         [0045]    Further, the battery  10  has a property in which the battery capacity is greater than the capacitor  11 , and the capacitor  11  has a property of enabling a greater current to be flown than the battery  10 . 
         [0046]    By connecting the battery  10  and the capacitor  11  via the arrangement illustrated in  FIG. 1 , the relationship shown in the following expression (1) is realized regarding the inductance Lc contained in the electric wiring  12  and the total inductance Lb contained in the electric wiring  12  and electric wiring  13 . 
         [0000]      Lc&lt;Lb  Expression (1)
 
         [0047]    Now, an example of decelerating a vehicle via regeneration braking will be described as an operation example of  FIG. 1 . 
         [0048]    The regeneration electric power generated from the electric motor  7  via regeneration braking is output through the inverter  6 , the capacitor  5 , the reactor  4  and the contactor  3  and via the current collector  2  to the overhead trolley  1 , but if the regeneration electric power cannot be absorbed by an electric power substation or if no vehicle performing power running exists on the same track, the power can be charged via the inverter  6 , the capacitor  5 , the capacitor  8  and the DC-DC converter  9  to the battery  10 . 
         [0049]    The charging electric power to the battery  10  is controlled by operating the switching device  9 - 1  of the DC-DC converter  9 , but at this time, when the electric power is converted, ripples are superposed to the voltage and the current within the DC-DC converter  9 . Furthermore, it is known that characteristic degradation of power storage properties of the battery  10  is hastened by overcurrents, so it is desirable to suppress ripples and the extreme changes of the discharge and charge currents. 
         [0050]    Now, the current flowing through the reactor  9 - 2  is flown through the electric wiring  12  to the capacitor  11  and also through the electric wiring  12  and electric wiring  13  to the battery  10 , but since the relationship of above-described expression (1) is satisfied of the inductance Lc contained in the electric wiring  12  and the inductance Lb contained in the electric wiring  12  and the electric wiring  13 , so that the DC components of the regeneration electric power flows to the battery  10  having a large inductance while ripples being AC components flow to the capacitor  11  having a small inductance, so that the present arrangement enables to suppress current ripples. 
         [0051]      FIG. 2  illustrates a configuration example of components of a semiconductor power converter as represented by the DC-DC converter  9  or the inverter  6 . Reference number  101  denotes a filter capacitor of the power converter, and  102  denotes a semiconductor electric power conversion device. The filter capacitor  101  of  FIG. 2  corresponds to capacitor  5 ,  8  and  11  of  FIG. 1 , and the semiconductor electric power conversion device  102  of  FIG. 2  corresponds to the switching device  9 - 1  of  FIG. 1 . 
         [0052]    According to the arrangement illustrated in  FIG. 2 , the filter capacitors  101  and the semiconductor electric power conversion devices  102  are arranged approximate one another while a battery not shown is arranged in a separate location, so that the inductance Lc in the electric wiring  12  in  FIG. 1  will be smaller than the total inductance Lb of in the electric wiring  12  and  13 , so that the current ripples overlapped via the semiconductor electric power conversion device  102  can be absorbed via the filter capacitor  101 . 
         [0053]    On the other hand, if it is not possible according to the arrangement of the device to integrate the filter capacitor  101  and the semiconductor electric power conversion device  102  as shown in  FIG. 2  and if the relationship of inductance Lc of the electric wiring  12  and the total inductance Lb of the electric wiring  12  and  13  does not satisfy the above expression (1), similar effects can be achieved by inserting a reactor to the electric wiring of the battery  10 . 
       [Embodiment 2] 
       [0054]      FIG. 3  illustrates a second embodiment of a power converter of a rolling stock according to the present invention. The same components as those included in  FIGS. 1 and 6  are denoted with the same reference numbers. 
         [0055]    In the power converter of  FIG. 3 , reference number  1  denotes an overhead trolley,  2  denotes a current collector,  3  denotes a contactor,  4  denotes a reactor,  5  and  15  denote a capacitor,  6  denotes an inverter,  7  denotes an electric motor,  14  denotes a battery,  16  denotes a DC-DC converter,  17  denotes an electric wiring connecting the capacitor  15  and the DC-DC converter  16 , and  18  denotes an electric wiring connecting the battery  14  and the DC-DC converter  16 . According to the present embodiment, the battery  14  (first power storage means), the DC-DC converter  16 , the electric wiring  17  and  18  connecting the above components and the capacitor  15  are arranged between one end of the capacitor  5  and the ground, and connected as illustrated. 
         [0056]    In the drawing,  16 - 1  denotes a switching device and  16 - 2  denotes a reactor formed within the DC-DC converter  16 . The inductances of electric wiring  17  and electric wiring  18  satisfy a similar relationship of inductances of electric wiring  12  and electric wiring  13  illustrated in  FIG. 1 , wherein the inductance contained in electric wiring  17  is denoted as Lc and the total inductance contained in electric wiring  17  and electric wiring  18  is denoted as Lb. Thus, the relationship of inductances of electric wiring  17  and electric wiring  18  satisfies the relationship shown in expression (1). 
         [0057]    Now, we will describe the operation of  FIG. 3 . In the present embodiment, the input voltage of the inverter  6  is increased via the battery  14  and the DC-DC converter  16  so as to expand the characteristic area of the electric motor  7  in a high-speed area, according to which the performances of power running and regeneration braking are enhanced (refer to the description related to patent document  2 ). The DC-DC converter  16  (second electric power conversion means) constitutes a DC-DC conversion control means for controlling the DC voltage of the first DC electric power of the inverter  6  (first electric power conversion means) by the second DC electric power according to the device. 
         [0058]    The elevation of input voltage of the inverter  6  is controlled via the switching device  16 - 1  of the DC-DC converter  16 , but also according to the present embodiment, current ripples occur by the operation of the switching device  16 - 1 . 
         [0059]    Now, since the inductance Lc of the electric wiring  17  and the total inductance Lb of the electric wiring  17  and  18  satisfy the above-described expression (1), the DC components of the discharge and charge current flow to the battery  14  having a large inductance and the ripples as AC components flow to the capacitor  15  having a smaller inductance. 
         [0060]    The present embodiment also adopts a structure in which the filter capacitor  101  and the semiconductor electric power conversion element  102  are integrated and a battery not shown is arranged in a separate location, as shown in  FIG. 2 , so that the inductance Lc contained in the electric wiring of the filter capacitor  101  becomes smaller than the inductance Lb included in the electric wiring of the battery not shown, according to which the present embodiment can suppress the current ripples of the battery  14 , similar to embodiment  1 . 
       [Embodiment 3] 
       [0061]      FIG. 4  illustrates a third embodiment of a power converter of a rolling stock according to the present invention. The same components as those shown in  FIGS. 1 ,  3  and  6  are denoted with the same reference numbers. 
         [0062]      FIG. 4  has replaced the capacitor  11  (a device having a power storage function) of  FIG. 1  with a battery  19  (second power storage means). Therefore, the battery  19  has a function to suppress ripple components and constitutes a ripple suppression means. Now, battery  10  (first power storage means) and battery  19  (second power storage means) have different power storage properties, wherein battery  10  has a greater battery capacity than battery  19  and the inner impedance of battery  10  is greater than the inner impedance of battery  19 . Further, the inductance Lc of the electric wiring  12  and the total inductance Lb of the electric wiring  12  and electric wiring  13  satisfy the relationship of expression (1), similar to the first embodiment of the present invention. 
         [0063]    According to the above arrangement, the DC components included the discharge and charge current flow to the battery  10  having a greater inductance, while the ripples as AC components flow to the battery  19  having a smaller inductance, so that the arrangement enables to suppress ripples in the current flowing to the battery  10 . 
       [Embodiment 4] 
       [0064]      FIG. 5  is a drawing illustrating a fourth embodiment of a power converter of a rolling stock according to the present invention. The same components as those shown in  FIGS. 1 ,  3 ,  4  and  6  are denoted with the same reference numbers. 
         [0065]      FIG. 5  has replaced the capacitor  15  of  FIG. 3  with a battery  20 . In the present embodiment, battery  14  and battery  20  have different power storage properties, wherein battery  14  has a greater battery capacity than battery  20  and the inner impedance of battery  14  is greater than the inner impedance of battery  20 . Further, the inductance Lc of the electric wiring  17  and the total inductance Lb of the electric wiring  17  and electric wiring  18  satisfy the relationship of expression (1), similar to the second embodiment of the present invention. According to the present arrangement, the DC components including the discharge and charge current flow to the battery  14  having a greater inductance, while the ripples as AC components flow to the battery  20  having a smaller inductance, so that the arrangement enables to suppress ripples in the current flowing to the battery  14 .