Abstract:
A power conversion apparatus is disclosed. In the case where a coil is arranged in a power module, the circuit system between the ends of the coil in the power module, regardless of where the coil is located, is structurally isolated and insulated from each other. This isolation and insulation prevents the capacitance from being created across the coil, and the coil can exhibits the effect as a filter, thereby improving the characteristics of a noise filter.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates a technique for providing a power conversion apparatus. 
         [0002]    In the power conversion apparatus such as an AC motor driven with variable speeds, electric and magnetic noises (hereinafter referred to as the “electro-magnetic interference” (EMi)) are known to be generated by the operation thereof. 
         [0003]    In the related art, a filter called the noise filter is known to be mounted as an electric circuit element for reducing the EMi as described in JP-A-08-308250 (pp. 5-6, and FIG. 1, for example), corresponding to U.S. Pat. No. 5,752,838 and DE19618736). 
       SUMMARY OF THE INVENTION 
       [0004]    In some recent cases, the rectifier portion and the inverter portion of a small-capacity inverter apparatus has been mounted on the same metal substrate within a single power module as a structure (hereinafter referred to as the module) for supporting the rectifier portion and the inverter portion integrally. 
         [0005]    The metal substrate is a collective name of the base substrate of aluminum, the insulating layer thereon and the circuit pattern arranged thereon. 
         [0006]    In this case, a capacitive coupling may be generated through metal plates including a substrate, an underlying aluminum base (hereinafter referred to as the aluminum base) and a conductor between the ends (input and output units) of the coil arranged in the power module as a circuit element to reduce EMi. Due to the effect of this capacitance, the problem of a reduced effect of the filter may be posed even in the case where the coil is arranged. 
         [0007]    In order to solve this problem, it is an object of this invention to provide a power conversion apparatus wherein the deterioration of the noise reducing effect is prevented as far as possible in the case where the coil is arranged in the power module having the rectifier portion and the inverter portion. 
         [0008]    Another object of the invention is to solve the aforementioned problem by providing a power conversion apparatus having a structure with a reduced capacitance generated by capacitive coupling, etc. 
         [0009]    The insulating layer and the aluminum base of the power module where the capacitance is generated are divided into two electrically isolated parts including a semiconductor chip making up the rectifier portion and a semiconductor chip making up the inverter portion. 
         [0010]    The cut section of division is covered with plastic to maintain insulation. As an alternative, an insulating material may be coated on the plastic formed up to about the height of the insulating layer. 
         [0011]    According to this invention, there is provided a power conversion apparatus having a higher reliability than in the prior art. 
         [0012]    Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a diagram showing a configuration of the power conversion apparatus according to an embodiment of the invention. 
           [0014]      FIG. 2  is a diagram for explaining the power module. 
           [0015]      FIG. 3  is a diagram for explaining another embodiment. 
           [0016]      FIG. 4  is a diagram for explaining still another embodiment. 
           [0017]      FIG. 5  is a diagram for explaining yet another embodiment. 
           [0018]      FIG. 6  is a diagram for explaining a further embodiment. 
           [0019]      FIG. 7  is a diagram showing an equivalent circuit of  FIG. 6 . 
           [0020]      FIG. 8  is a diagram for explaining the structure of the power module according to the invention. 
           [0021]      FIGS. 9A and 9B  show the result of a noise test conducted according to the prior art. 
           [0022]      FIGS. 10A and 10B  show the result of a noise test conducted by a method according to the invention. 
           [0023]      FIG. 11  is a diagram for explaining a case in which a coil is arranged in the power module. 
           [0024]      FIG. 12  is a diagram for explaining the structure of the power module according to another embodiment. 
           [0025]      FIG. 13  is a diagram for explaining the insulation in the case where a coil is arranged between the power input unit and the rectifier portion. 
           [0026]      FIG. 14  is a diagram for explaining the insulation in the case where a coil is arranged between the rectifier portion and the inverter portion. 
           [0027]      FIG. 15  is a diagram for explaining the insulation in the case where a coil is arranged between the inverter portion and the output unit of an induction motor. 
           [0028]      FIG. 16  is a diagram for explaining the case in which a coil is arranged between the power input unit and the rectifier portion. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    Embodiments of the invention are explained below sequentially with reference to the accompanying drawings. 
         [0030]    In the drawings, reference characters R(L 1 ), S, T(N) designate a three- or single-phase AC power input, and U(T 1 ), V(T 2 ), W(T 3 ) a three-phase AC output. 
         [0031]      FIG. 1  is a diagram for explaining an embodiment. In the configuration shown in  FIG. 1 , a power conversion apparatus  1  and an induction motor  5  driven are connected to each other. 
         [0032]    In  FIG. 1 , the three- or single-phase AC power is input from the commercial power supply through the terminals R(L 1 ), S, T(N) of the power conversion apparatus  1 , and converted into the DC power by a rectifier portion  3 . The output of the rectifier portion  3 , after being smoothed by a smoothing portion  18 , is input to an inverter portion  4 . In the inverter portion  4 , the power from the smoothing portion  18  is converted into the AC power again and supplied to an induction motor  5  through the terminals U(T 1 ), V(T 2 ), (T 3 ). 
         [0033]    In the process, the inverter portion  4  is controlled by a control portion  19  according to the pulse width modulation scheme. In  FIG. 1 , the control portion  19 , receiving a current signal from the power module  2 , etc., performs the arithmetic operation and outputs the PWM control signal, etc. to the inverter portion  4  thereby to carry out the control operation. 
         [0034]    Also, the rectifier portion  3  and the inverter portion  4  are arranged within the power module  2 . 
         [0035]    In the embodiment shown in  FIG. 1 , a coil  6  providing a component part of a noise filter to prevent the EMi is connected to the output of the rectifier portion  3 , and the output of the coil  6  is connected to the smoothing portion  18 . 
         [0036]      FIG. 2  is a diagram for explaining the configuration of the power module  2 . 
         [0037]    The power module  2  having mounted thereon a power semiconductor element for driving the induction motor  5  is built in the power conversion apparatus  1 . The power module  2  contains therein at least the rectifier portion  3  for rectifying the three- or single-phase power input and the inverter portion  4  for converting the rectified power into the AC power again and supplying the induction motor  5 . 
         [0038]    As shown in  FIG. 1 , the coil  6  providing a component part of the noise filter aimed at prevention of EMi, if connected to the power conversion apparatus, is normally inserted between the power input unit and the rectifier portion  3 , between the rectifier portion  3  and the inverter portion  4  or between the inverter portion  4  and the output unit of the induction motor  5 . Taking this connection into consideration, the parts described above are isolated electrically from each other in the power module. 
         [0039]      FIG. 2  shows an example of the rectifier portion  3  and the inverter portion  4  isolated from each other in the case where the coil is arranged between the rectifier portion  3  and the inverter portion  4 , in which case the output of the rectifier portion  3  is designated as P 1 , N 1  and the input to the inverter portion  4  as P 2 , N 2 . 
         [0040]    A lead pin is arranged taking into consideration the fact that the substrate mounted on the power module  2  is soldered or in view of the fact that in the case where the filter part such as the coil  6  is mounted in the power module, the mounting pad is arranged. Therefore, the shape of the input and output P 1 , N 1 , P 2 , N 2  is determined case by case. 
         [0041]    In the case where the coil explained in the embodiment is arranged as a circuit part in the power module, the noise filter effect is improved by employing an appropriate internal structure of the power module regardless of whether the actual position of the coil is inside or outside of the power module. 
         [0042]      FIG. 3  shows an example of a circuit with the coil  6  inserted between the rectifier portion  3  and the inverter portion  4 . 
         [0043]      FIG. 4  shows an example of a case in which the coil  6  is mounted on a separate substrate connected by soldering to the power module  2  in actual mounting work. The explanation below refers to this case, in which the power conversion apparatus is called the inverter apparatus. 
         [0044]    In the conventional power module, the capacitance  7  is generated by coupling between the ends of the coil  6 , resulting in a worse effect as a filter. 
         [0045]      FIG. 5  shows an example of the sectional structure of an ordinary power module according to the prior art. In  FIG. 5 , the coil  6  is designated by a circuit symbol.  FIG. 5  represents, as in  FIG. 3 , a case in which the coil  6  is arranged between the rectifier portion  3  and the inverter portion  4  in the power module  2 . 
         [0046]    The power module  2  is covered by a plastic mold  8  or the like and contains therein semiconductor chips  9  making up the rectifier portion  3  and semiconductor chips  10  making up the inverter portion  4 . The semiconductor chips  9 ,  10  are mounted by soldering on copper foils  11  constituting the circuit. 
         [0047]    An insulating layer  12  is formed under the copper foils  11 . An aluminum base  13  is formed under the insulating layer  12  and fixed by the plastic mold  8  as a body case. Actually, though not shown, a heat spreader may be further arranged. 
         [0048]    The coil  6  is mounted on the substrate  15  by leads  14   a ,  14   b  from the power module  2 . The lead  14   a  corresponds to the P 1  or N 1  portion, and the lead  14   b  corresponds to the P 2  or N 2  portion shown in  FIG. 2  or  4 . Specifically, the coil  6  is arranged, though physically outside the power module  2 , inside the power module as a circuit element. 
         [0049]    In the process, it is desirable that no capacitance is generated across the coil  6  in order to increase the filter effect. Specifically, it is desired to secure the electrical insulation positively between the P 1  and P 2  portions and between the N 1  and N 2  portions. This structure, however, generates the capacitance  7  between the lead  14   a  and the lead  14   b  through the copper foils  11 , the insulating layer  12  and the aluminum base  13  making up a conductor. 
         [0050]    Also, in the case where the P 1  copper foil and the P 2  copper foil in the power module are arranged in proximity to each other, the capacitance is generated even in the presence of the copper foils and the insulating layer  12  as an intermediary.  FIG. 6  shows the route and place of capacitance generation with the insulating layer  12  and the aluminum base  13  in enlarged form. The capacitance  7  is generated in an equivalent circuit as shown in  FIG. 7 . 
         [0051]    The reason why the filter effect is deteriorated by the generation of the capacitance  7  is explained with reference to  FIG. 7 . Once the induction motor is driven by the inverter, the high-frequency switching noises are generated by the inverter portion  4 . The switching noises provisionally flow into the ground through the grounding capacitance of the noise filter arranged separately, and then return to the point Q in  FIG. 7 . At the same time, all the noise components ideally return to the inverter portion (induction motor) through the route  17   a . Then, the noise flow toward the power supply would be suppressed thereby to reduce the noise level. 
         [0052]    As described above, however, upon generation of the capacitance  7  across the coil, the noises which normally should be suppressed by the coil undesirably flow toward the power supply through the route  17   b  or  17   c  by way of the capacitance low in impedance, resulting in a lower noise reduction effect. 
         [0053]    An embodiment of this invention realizes a configuration of an inverter apparatus in which the noise reduction effect is not deteriorated in the case where the coil is arranged as a circuit component in a single power module having both the rectifier portion and the inverter portion. 
         [0054]    The problem described above is solved by a structure for reducing the capacitance  7  thus generated.  FIG. 8  shows a structure for minimizing the capacitance  7  generated. This example also represents a case in which the coil is arranged between the rectifier portion and the inverter portion. 
         [0055]    The insulating layer  12  and the aluminum base  13  where the capacitance  7  is generated are isolated from each other into the semiconductor chip  9  side making up the rectifier portion and the semiconductor chip  10  side making up the inverter portion. In other words, the insulating layer  12  and the aluminum base  13  conventionally integrated with each other are separated from each other. 
         [0056]    Although aluminum is taken up by way of explanation above, a metal plate or a conductor high in heat conductivity may alternatively be used to release outside, by heat conduction, the heat generated in the rectifier portion and the inverter portion. Copper, silver or gold, for example, may be used instead of aluminum. 
         [0057]    The section by which the insulating layer  12  and the aluminum base  13  are separated from each other is covered with a plastic mold  8  to secure insulation. As an alternative, the plastic mold is covered up to about the height of the insulating layer and coated with an insulating material. 
         [0058]    As shown in  FIG. 8 , a test has been conducted to make sure that EMi is reduced after division of the power module and the divisive effect has been confirmed. 
         [0059]      FIGS. 9A ,  9 B show the result of measuring the noise level before dividing the power module.  FIGS. 10A ,  10 B, on the other hand, show the result of measuring the noise level after dividing the power module. The noise terminal voltage has been measured in accordance with European Norm EN61800-3 on an inverter apparatus of 400 V class, 3.7 kW in output, with a general-purpose three-phase induction motor of 3.7 kW, 400 V class. 
         [0060]    As shown in  FIG. 8 , by dividing the power module interior completely, the EMi level improvement of 15 dB or more in terms of quasi-peak (QP) value has been confirmed. 
         [0061]    This embodiment represents a case in which the coil for the filter is mounted on the substrate outside the power module. In view of the fact that the coil generates heat, however, a high cooling effect is obtained by arranging the coil in the power module and radiating the heat from the heat sink in contact with the power module. This indicates that this embodiment is effective also in the case where the coil is arranged in the power module, as explained below with reference to  FIG. 11 . 
         [0062]      FIG. 11  is a case in which the filter coil is mounted directly on the metal substrate in the power module instead of erecting the pins  14   a ,  14   b  to mount an external substrate in  FIG. 8 . Also in this case, the power module is separated, and therefore the effect of the coil is not deteriorated as the capacitance  7  is not generated across the coil as in the aforementioned case. 
         [0063]    As another embodiment, as shown in  FIG. 12 , only the insulating layer  12  may be electrically isolated in the power module  2 . By eliminating the capacitance  7   a  in  FIGS. 6 ,  7 , therefore, the total capacitance value can be reduced. Although the effect of the filter is reduced as compared with the case of complete separation shown in  FIG. 8 , the effect is greater than in the presence of the insulating layer. This configuration is effective in the case where the separation of the aluminum base poses the problem of the mounting flatness of the power module. 
         [0064]    Apart from the aforementioned cases in which the coil is arranged between the rectifier portion and the inverter portion as a circuit element, a similar effect can be obtained by arranging the coil between the power input unit and the rectifier portion or between the inverter portion and the output unit of the induction motor. In other words, a power module structure is effective as long as the circuit portions at the ends of the coil are isolated and insulated from each other. 
         [0065]      FIG. 13  shows a case in which the coil  6  is inserted between the power input unit and the rectifier portion,  FIG. 14  a case in which the coil  6  is arranged between the rectifier portion and the inverter portion, and  FIG. 15  a case in which the coil  6  is arranged between the inverter portion and the output unit of the induction motor. In all of these cases, the effect of the coil as a filter can be improved by employing the aforementioned isolating/insulating structure between the portions A and B in the drawings. 
         [0066]      FIG. 16  shows a circuit example in which the coil  6  is arranged between the power input unit and the rectifier portion  3  as a circuit element. 
         [0067]    According to the embodiments of the invention, as explained above, the effect of the noise filter can be improved by changing the structure of the power module. 
         [0068]    Also, the structures according to the embodiments described above makes it possible to maintain the filter effect even in the case where the coil is mounted in the power module as a circuit element. The term “across the coil” or “between the ends of the coil” is defined as “between the ends of the coil winding” regardless of the number of phases. 
         [0069]    Also, the wording “in the power module as a circuit element” means that a given part, even if arranged physically outside the power module, is connected to the interior of the power module as a circuit element, and subject to the effect of the capacitance generated by the structure of the power module. 
         [0070]    It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.