Abstract:
Provided is a new control method that causes no time lag or hunting when a power conversion direction is reversed. The power conversion apparatus includes switching elements (S 1  and S 2 ) that alternately perform switching and are capable of reversing the power conversion direction without suspension, and an up/down counter register (RT) that has two different thresholds and selects counting up at a smaller threshold, counting down at a larger threshold, and holding of the value between the two thresholds. According to the value of the up/down counter register (RT), a gate pulse is generated to control the switching of the switching elements (S 1  and S 2 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a technical field of a power conversion apparatus. More specifically, it relates to a technical field of a nondirectional power conversion apparatus. 
       BACKGROUND ART 
       [0002]    As a prior art, there is a so-called bidirectional converter; however, performing a feedback control by connecting a plurality of converters with each other and by using a common DC bus voltage means that a plurality of voltage feedbacks operate in parallel within a single control system. This causes interference between mutual controls, whereby the control has not been successful. 
         [0003]    For example, a bidirectional converter A and a bidirectional converter B are connected in parallel, and a connected part thereof is referred to as a common DC bus. Here, in a case where the bidirectional converter A is regarded as an input side and the bidirectional converter B is regarded as an output side (called a mode A to B), electricity is supplied from an input side of the bidirectional converter A, then the electricity is output to the common DC bus, then the electricity is supplied to an input side of the bidirectional converter B, and finally, the electricity is output to an output side of the bidirectional converter B. 
         [0004]    Furthermore, in a case where an output from the bidirectional converter B, which occurs first, is regarded as an input and an input into the bidirectional converter A is regarded as an output (called a mode B to A) in an operating mode, electricity is supplied from the input side of the bidirectional converter B, then the electricity is output to the common DC bus, then the electricity is supplied to the input side of the bidirectional converter A, and finally, the electricity is output to an output side of the bidirectional converter A. 
         [0005]    A concept of a main circuit in this manner has been in existence, and operation by switching input and output feedbacks between the mode A to B and the mode B to A has been possible. Note that as a literature related to such background art, Non Patent Literature 1 below, for example, may be listed. 
       CITATION LIST 
     Non Patent Literature 
       [0006]    Non Patent Literature 1: “Efficiency Improvement of AC/DC Power Station,” Panasonic Electric Works Technical Report, 2011, Vol. 59, No. 3, pp. 4-11 (URL: “HYPERLINK “http://panasonic.co.jp/ptj/pew/593j/pdfs/593#01.pdf” http://panasonic.co.jp/ptj/pew/593j/pdfs/593#01.pdf”) 
       SUMMARY OF THE INVENTION 
     Technical Problem to be Solved 
       [0007]    In the above-described bidirectional converter, however, operating the feedbacks of the mode A to B and the mode B to A at the same time makes a voltage feedback and a proportional-integral-derivative (PID) control impossible, whereby it is not possible to control the converter. That is, in a case where a power conversion direction is reversed, it is not possible to control the converter by a normal voltage feedback, whereby it has not been possible to operate it as a reversible converter or a nondirectional converter. 
         [0008]    Furthermore, in view of a high-reliability demand and high power control in recent years, a digital control using a micro processing unit (MPU) is inevitable; however, in the digital control, a calculation result changes in steps. The number of steps is about one thousand from a practicality viewpoint, whereby an amount of change per step becomes large to some extent. At this time, when impedance is low such as in a case where a power source is constituted of a capacitor, it has not been possible to achieve stable control due to a drastic current change or a so-called hunting phenomenon in which electricity is reversed by ups and downs of one step. 
         [0009]    Accordingly, the present invention has been devised in view of each of the above-described problems, and an exemplary objective thereof is to provide a reversible or nondirectional power conversion apparatus of practical use and a new method for controlling the same. 
       Means for Solving the Problem 
       [0010]    To solve the above-described problems, in the present invention, a converter having a switching element, which alternately performs switching, is controlled by an up/down counter register, which has two thresholds different from each other, by generating a gate pulse. 
         [0011]    Furthermore, the present invention is a two-stage converting converter including a first converter having two thresholds different from each other, and a second converter having two thresholds that are different from each other and outside of the thresholds of the first converter. The first and second converters are connected in parallel by a common DC bus, and input and output thereof are separately controlled. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a circuit diagram illustrating an example of a basic principle circuit according to a first embodiment. 
           [0013]      FIG. 2  is a flowchart illustrating software control of a converter CB in the basic principle circuit according to the first embodiment. 
           [0014]      FIG. 3  is a graph illustrating control thresholds of the converter CB according to the first embodiment. 
           [0015]      FIG. 4  is a graph illustrating transition of current and voltage of the converter CB according to the first embodiment in a case where a load/power source P 1  is a capacitor. 
           [0016]      FIG. 5  is a circuit diagram illustrating an example of a basic principle circuit according to a second embodiment. 
           [0017]      FIG. 6  is a flowchart illustrating software control of a converter CB 1  and a converter CB 2  in the basic principle circuit according to the second embodiment. 
           [0018]      FIG. 7  is a graph illustrating a relationship of control thresholds of the converter CB 1  and the converter CB 2  according to the second embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0019]    A method for controlling according to the present invention is described herein. 
       (I) First Embodiment 
       [0020]    First, an example of a basic principle circuit according to a first embodiment is described with reference to  FIGS. 1 to 4 . 
         [0021]    A converter CB according to the first embodiment illustrated in  FIG. 1  is a converter included in a power conversion apparatus SS 1  according to the first embodiment. The converter CB comprises a power conversion unit in which a switching element  51  and a switching element S 2  alternately perform switching. For a voltage V 2  of a load/power source P 2  (hereinafter, simply referred to as a “voltage V 2 ” in the first embodiment) detected by a detection unit DT, the converter CB generates a gate pulse by an up/down counter register RT, which has a threshold (A+) and a threshold (A−) exemplified in  FIG. 3  and is provided to a micro processing unit (MPU)  10 , so as to control the voltage V 2  to be approximately within a range of the threshold (A+) and the threshold (A−). The power conversion unit also includes a reactor L 1  as well as a capacitor C 1  and a capacitor C 2  illustrated in  FIG. 1  in addition to the above-described switching element S 1  and the switching element S 2 . 
         [0022]    Next, in  FIG. 2 , a flowchart of software control of the converter CB illustrated in  FIG. 1  is illustrated. 
         [0023]    A basic method for controlling the converter CB illustrated in  FIG. 1  is as described below using  FIGS. 3 and 4 . 
         [0024]    First, in a case where electricity is supplied from a load/power source P 1  and where the load/power source P 2  consumes the electricity as a load, the voltage V 2  is decreased by increasing the load. When reaching threshold (A−)&gt;voltage V 2 , counting up of the up/down counter register RT is performed as illustrated in  FIG. 2 . When a count value of the up/down counter register RT becomes large, an output from a gate driver GD is output so as to increase an ON time on a switching element S 2  side and to decrease an ON time on a switching element S 1  side. 
         [0025]    As a result, a step-up ratio is increased so as to suppress a voltage decrease of the voltage V 2 . 
         [0026]    Here, in a case where the load/power source P 1  is a capacitor, although a terminal voltage V 1  thereof gradually decreases accompanying discharge of electricity, the step-up ratio increases for a while, whereby the voltage V 2  is kept near the threshold (A−). 
         [0027]    Next, in a case where consumption of electricity by the load/power source P 2  ends, the voltage V 2  immediately exceeds the threshold (A−) and enters a control dead zone, and the count value of the up/down counter register RT is held. Accordingly, the step-up ratio is fixed, and the voltage V 2  keeps a fixed voltage with no fluctuation. 
         [0028]    Next, a case where the electricity is supplied from the load/power source P 2  is described. The voltage V 2  is increased as the electricity is supplied from the load/power source P 2 ; however, since the step-up ratio is fixed since the count value of the up/down counter register RT is held due to entering the above-described control dead zone, a direction of current is reversed. Thus, operation transits into that of a step-down converter, but power conversion is performed using the same step-up/down ratio. 
         [0029]    In the case where the load/power source P 1  is a capacitor, the terminal voltage V 1  thereof gradually increases by receiving stepped down electricity supplied from the load/power source P 2 . Accordingly, since the step-down ratio is fixed, the voltage V 2  gradually increases as well accompanying a voltage increase of the load/power source P 1 . 
         [0030]    When the voltage V 2  increases and reaches threshold (A+)&lt;voltage V 2 , now the up/down counter register RT performs counting down as illustrated in  FIG. 2 . When a count value of the up/down counter register RT becomes small, an output from the gate driver GD is output so as to decrease the ON time on the switching element S 2  side and to increase the ON time on the switching element S 1  side. 
         [0031]    As a result, the step-down ratio is decreased so as to suppress a voltage increase of the voltage V 2 . 
         [0032]    Here, in a case where the load/power source P 1  is a capacitor, although the terminal voltage V 1  thereof gradually increases while the electricity is supplied, the step-down ratio decreases for a while, whereby the voltage V 2  is kept near the threshold (A+). 
         [0033]    In a case where the electricity that has been supplied from the load/power source P 2  ends, the voltage V 2  immediately falls below the threshold (A+) and enters the control dead zone, whereby ups and downs are not caused, and the count value of the up/down counter register RT is held. Accordingly, the step-down ratio is fixed, and the voltage V 2  keeps a fixed voltage with no fluctuation. 
         [0034]    Here, setting of the threshold (A+) itself and the threshold (A−) itself is described. As described above, in the converter CB according to the first embodiment, a power conversion direction is reversed between the load/power source P 1  and the load/power source P 2 , and the voltage V 2  fluctuates within the range of the threshold (A+) and the threshold (A−). Then, in general, it is suitable to set the threshold (A+) and the threshold (A−) described above such that a difference therebetween is a value from 3% to 5% of an absolute value of the voltage V 2  as a range in which the voltage V 2  can be regarded as being substantially constant or requiring only a small correction. 
         [0035]    In addition, reversal of the power conversion direction between the load/power source P 1  and the load/power source P 2  is switched by any external factor. 
         [0036]    In this way, since the counting up and the counting down by the up/down counter register RT are performed interposing the control dead zone between the threshold (A+) and the threshold (A−), the up/down counter register RT does not transit into the counting down in a routine following the counting up. Thus, as in  FIG. 4 , a hunting phenomenon, which occurs when the power conversion direction is reversed, can be completely prevented, and it is possible to reverse the conversion direction without any time lag. 
       (II) Second Embodiment 
       [0037]    Next, an example of a basic principle circuit according to a second embodiment is described with reference to  FIGS. 5 to 7 . 
         [0038]    In a power conversion apparatus SS 2  according to the second embodiment illustrated in  FIG. 5 , a converter CB 1 , which is constituted of a switching element S 1 , a switching element S 2 , a reactor L 1 , and a capacitor C 1  and which has the same configuration as the configuration of the converter CB illustrated in  FIG. 1 , and a converter CB 2 , which is constituted of a switching element S 3 , a switching element S 4 , a reactor L 2 , and a capacitor C 3 , are connected in parallel by a capacitor C 2 , which is a common DC bus capacitor. The converter CB 1  generates a gate pulse by an up/down counter register RT 1 , which has thresholds of a threshold (A+) and a threshold (A−) and is provided to a MPU  20 , and outputs the gate pulse to a gate driver GD 1  to drive the switching element S 1  and the switching element S 2 . Furthermore, the converter CB 2  generates a gate pulse by an up/down counter register RT 2 , which has thresholds of a threshold (B+) and a threshold (B−) and is provided to the MPU  20 , and outputs the gate pulse to a gate driver GD 2  to drive the switching element S 3  and the switching element S 4 . 
         [0039]    In control of the converters illustrated in  FIG. 5 , the converter CB 1  having the thresholds of the threshold (A+) and the threshold (A−) controls a voltage V 2  of a common DC bus detected by a detection unit DT so that the voltage V 2  is suppressed to be within a range of the threshold (A+) and the threshold (A−). Hereinafter, in the second embodiment, the voltage V 2  of the common DC bus is referred to as a “voltage V 2 ” as necessary. On the other hand, since the converter CB 2  has the thresholds within which the up/down counter register RT 2  operates of the threshold (B+) and the threshold (B−), which are outside of the threshold (A+) and the threshold (A−), fluctuation of the voltage V 2  of the common DC bus normally does not reach the threshold (B+) and the threshold (B−), whereby operation of the up/down counter register RT 2  is not performed. 
         [0040]    Control of the up/down counter register RT 2  of the converter CB 2  of  FIG. 5  changes so as to make a voltage setting of a voltage V 3  on a load/power source P 2  side from a demand as a power conversion system. 
         [0041]    That is, in the converter CB 2 , in a case where electricity is extracted from the load/power source P 2  and is supplied to the common DC bus, a count value of the up/down counter register RT 2  is counted up in a direction of either increasing the voltage V 3 , which is a voltage source of the load/power source P 2 , or increasing the voltage V 2 . 
         [0042]    In contrast, in a case where supply of the electricity to the load/power source P 2  is demanded, the count value of the up/down counter register RT 2  is counted down in a direction of simply increasing a size of the load of the load/power source P 2  or of decreasing the voltage V 2  while increasing the voltage V 3  on the load/power source P 2  side. 
         [0043]    The threshold (B+) and the threshold (B−) of the converter CB 2  has a function as protection against deviation from the threshold (A+) and the threshold (A−), or a normal operation range. 
         [0044]    A description is given on control of  FIGS. 5 and 6 . 
         [0045]    To the converter CB 1  of  FIG. 5 , the method of controlling described with reference to  FIG. 1  is directly applied. Thus, a description is given on the converter CB 2 . 
         [0046]    The thresholds of the converter CB 2  is the threshold (B+) and the threshold (B−), and as illustrated in  FIG. 7 , values thereof are set to be outside of the threshold (A+) and the threshold (A−) of the converter CB 1 . Normally, the voltage V 2  of the common DC bus is controlled to be within the range of the threshold (A+) and the threshold (A−) and does not reach the threshold (B+) and the threshold (B−), whereby the up/down counter register RT 2  of the converter CB 2  stays within a control dead zone and does not make ups and downs. 
         [0047]    More specifically, when the up/down counter register RT 2  counts the voltage V 2  that is equal to or smaller than the smallest threshold (B−), the gate pulse, which is an output from the gate driver GD 2 , is output so as to increase an ON time of the switching element S 4  and to decrease an ON time of the switching element S 3 . On the other hand, when it counts the voltage V 2  equal to or greater than the largest threshold (B+), the gate pulse, which is an output from the gate driver GD 2 , is output so as to decrease the ON time of the switching element S 4  and to increase the ON time of the switching element S 3 . Furthermore, when the voltage V 2  is between the threshold (B−) and the threshold (B+), the up/down count register RT 2  selects to hold the count value. 
         [0048]    Here, setting of the threshold (B+) itself and the threshold (B−) itself is described. As described above, in a circuit according to the second embodiment, in the same way as that in the first embodiment, a power conversion direction is reversed between a load/power source P 1  and the load/power source P 2 , and the voltage V 2  fluctuates within the range of the threshold (A+) and the threshold (A−). Then, it is suitable to set the threshold (A+) and the threshold (A−) described above as a range in which the voltage V 2  can be regarded as being substantially constant or requiring only a small correction. In addition, in general, it is suitable to set the threshold (B+) and the threshold (B−) such that a difference therebetween is a value from 5% to 10% of an absolute value of the voltage V 2 . Note that a relationship of threshold (B−)&lt;threshold (A−)&lt;threshold (A+)&lt;threshold (B+) is maintained at this time. 
         [0049]    Control of the converter CB 2  is control for converting the voltage V 2  of the common DC bus into the voltage V 3  demanded by the load/power source P 2  in accordance with a demand of the system. 
         [0050]    Since the converter CB 2  is a converter for adapting the voltage to a form demanded by the load/power source P 2 , the basic method for controlling does not change even with an alternating current power source. 
         [0051]    Reversal of the power conversion direction between the load/power source P 1  and the load/power source P 2  according to the second embodiment relates to a setting of the voltage V 3  on the load/power source P 2  side, and in a case where the circuit according to the second embodiment is applied to control of a vehicle, for example, the setting of the voltage V 3  changes between a case where the vehicle is accelerated as an accelerator thereof is pressed upon driver&#39;s will and a case where the vehicle is decelerated as the accelerator is released. Here, in a case where the load/power source P 2  is a so-called motor generator, an alternating current is used, and for the voltage V 3 , a voltage, a frequency, and a phase need to be set. 
       INDUSTRIAL APPLICABILITY 
       [0052]    As described above, the present invention can be used in a field of a power conversion apparatus, and more specifically, it is particularly effective when used in a field of a power conversion apparatus connected between load/power sources capable of mutually giving and receiving electricity. 
       REFERENCE SIGNS LIST 
       [0053]      10 ,  20  MPU 
         [0054]    CB, CB 1 , CB 2  converter 
         [0055]    SS 1 , SS 2  power conversion apparatus 
         [0056]    S 1 , S 2 , S 3 , S 4  switching element 
         [0057]    DT detection unit 
         [0058]    P 1 , P 2  load/power source 
         [0059]    RT, RT 1 , RT 2  up/down counter register 
         [0060]    GD, GD 1 , GD 2  gate driver 
         [0061]    L 1 , L 2  reactor 
         [0062]    C 1 , C 2 , C 3  capacitor