Abstract:
A zero sequence current control apparatus and a zero sequence current control method for parallel power converters are disclosed to overcome the issue of having uniform output power for the parallel operation of a plurality of single module voltage control power converters, and an eCAN BUS acts as a communication interface for transmitting instructions, so that when each of the single module voltage control power converters is operated in the parallel operation, the effect of outputting uniform voltage, current and power can be achieved.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    The present invention relates to a zero sequence current control apparatus and method for parallel power converters, in particular to the zero sequence current control apparatus and method capable of modulating and uniformly allocating an output power of a plurality of single module voltage control power converters in a parallel operation and outputting uniform voltage, current and power from each of the single module voltage control power converters during the parallel operation. 
         [0003]    2. Description of Related Art 
         [0004]    As the capacity of power conversion (DC-to-AC conversion) becomes increasingly larger, and power switch components of a power converter are limited by the resistance of voltage and current, the output capacity of a single power converter is unable to meet the requirements. In recent years, several power converters are generally connected in parallel to one another to increase the capacity of the power conversion, but the parallel operation may have the issues of output voltage phase, current phase and frequency synchronization control, which are the synchronous signal control issues. If current is not controlled properly, then the circulation problem must result, and thus controlling synchronous signals and overcoming the circulation problem are the problems of the power converter that require solutions in a parallel operation. In general, the manufacture of the power converters is mainly divided into two types, respectively a power converter with an independent power supply and a power converter with a utility power network, and their rated power is the capacity for single converters. If a load side requires high power and large capacity, the parallel operation of the power converters will be adopted. Regardless of the power converters with independent power supply or utility power network, both require a special control mechanism. When the power converters in parallel with each other are operated, the most commonly used method involves the synchronous signal control method and a host/slave hardware detection control method. In these methods, the standalone operation and the parallel operation have different control mechanism, and thus it is an additional burden to manufacturers to produce two different models. 
         [0005]    Therefore, it is a main subject for related manufacturers to develop and provide a control mechanism for standalone power converters or parallelly operated power converters. 
       SUMMARY OF THE INVENTION 
       [0006]    Therefore, it is a primary objective of the present invention to provide a zero sequence current control apparatus and method for parallel power converters, in particular to the zero sequence current control apparatus and method capable of modulating and uniformly allocating an output power of a plurality of single module voltage control power converters in a parallel operation and outputting uniform voltage, current and power from each of the single module voltage control power converters during the parallel operation. 
         [0007]    To achieve the aforementioned and other objectives, the present invention provides a zero sequence current control apparatus of parallel power converters, comprising: a control and management system, including an automatic allocation device and a control device; a plurality of modules; 
         [0008]    a local area network, having an input terminal electrically coupled to the automatic allocation device and the control device, and an output terminal communicated with the modules; wherein, the automatic allocation device locates a host module according to a boot registration sequence of each module, and converts other modules into slave modules, and the automatic allocation device allocates an output voltage, an output current and an output power of the host module and the slave modules. 
         [0009]    To achieve the aforementioned and other objectives, the present invention further provides a zero sequence current control method for parallel power converters, comprising the steps of: initializing a control and management system; combining a first-group single module voltage control power converter into the system; registering the first-group single module voltage control power converter; operating the first-group single module voltage control power converter independently; writing numeric values of the voltage, current and power of the first-group single module voltage control power converter into the eCAN BUS; and determining whether the writing of numeric values into the eCAN BUS is completed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The technical characteristics and objectives of the present invention can be further understood by the following detailed description of preferred embodiments and related drawings in which: 
           [0011]      FIG. 1  is a schematic view of a zero sequence current control apparatus for parallel power converters of the present invention; 
           [0012]      FIG. 2  is a schematic view of a parallel single module voltage control power converter installed in an automatic allocation device of the present invention; 
           [0013]      FIGS. 3A and 3B  are flowchart ( 1 ) and flowchart ( 2 ) of a zero sequence current control method for parallel power converters of the present invention respectively; and 
           [0014]      FIG. 4  is a schematic view of a mailbox of a zero sequence current control apparatus for parallel power converters of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    With reference to  FIG. 1  for a zero sequence current control apparatus for parallel power converters in accordance with the present invention, the zero sequence current control apparatus comprises a control and management system  11 , and the control and management system  11  is comprised of an automatic allocation device  111 , a control device  112 , a local area network  113  and a plurality of modules  114 . 
         [0016]    The local area network  113  has an input terminal electrically coupled to the automatic allocation device  111  and the control device  112 , such that an output terminal of the control and management system  11  can communicate with the modules  114 . Wherein, the automatic allocation device  111  locates a host module  114   a  according to a boot registration sequence of each module  114  and converts other modules into slave module (such as  114   b ,  114   c , and  114   d ), and the automatic allocation device  111  allocates an output voltage, an output current and an output power to the host module  114   a  and the slave modules  114   b ,  114   c ,  114   d.    
         [0017]    In addition, the control device  112  sends out a control instruction to write numeric values of the output voltage, output current and output power of the host module  114   a  and the slave modules  114   b ,  114   c ,  114   d  into the local area network  113 , and the local area network  113  is an enhanced controller local area network (eCAN BUS). 
         [0018]    With reference to  FIG. 2  for the parallel single module voltage control power converters installed in the automatic allocation device  111  of the present invention, the automatic allocation device  111  comprises a plurality of single module voltage control power converters  111   a   1 ,  111   a   2 ,  111   a   3  . . .  111   an  and a plurality of isolation transformers  111   t   1 ,  111   t   2 ,  111   t   3  . . .  111   tn , and the single module voltage control power converters  111   a   1 ,  111   a   2 ,  111   a   3  . . .  111   an  have an input terminal electrically coupled to a first power supply  2 , and an output terminal electrically coupled to an input terminal of the isolation transformers  111   t   1 ,  111   t   2 ,  111   t   3  . . .  111   tn , and the output terminal of the isolation transformers  111   t   1 ,  111   t   2 ,  111   t   3  . . .  111   tn  is electrically coupled to a second power supply  3 . The first power supply  2  is a DC power supply network, and the second power supply  3  is an AC power supply network. 
         [0019]    Since the present invention transmits an instruction from the eCAN BUS to allocate the power and suppresses the use of the zero sequence circulation, each system registration sequence is provided for determining the host module and slave modules. Each single module voltage control power converter  111   a   1 ,  111   a   2 ,  111   a   3  . . .  111   an  has the eCAN BUS installed therein and provided for communication through the eCAN BUS to confirm the relation between the host module and the slave modules of each system, so as to allocate the power and suppress the zero sequence circulation. 
         [0020]    With reference to  FIGS. 3A and 3B  for a zero sequence current control method for parallel power converters of the present invention, the method comprises the following steps: 
         [0021]    S 10 : Initialize the control and management system  11 . 
         [0022]    S 11 : Combine a first-group single module voltage control power converter  111   a   1  into the system. 
         [0023]    S 12 : Register the first-group single module voltage control power converter  111   a   1 . 
         [0024]    S 13 : Operate the first-group single module voltage control power converter  111   a   1  independently. 
         [0025]    S 14 : Write numeric values of the voltage, current and power of the first-group single module voltage control power converter  111   a   1  into the eCAN BUS. 
         [0026]    S 15 : Determine whether the writing into the eCAN BUS is completed. If yes, then go to S 16 , or else return to S 14 . 
         [0027]    S 16 : Combine a second-group single module voltage control power converter  111   a   2  into the system. 
         [0028]    S 17 : Register the second-group single module voltage control power converter  111   a   2 . 
         [0029]    S 18 : Read a mailbox of the eCAN BUS. 
         [0030]    S 19 : Detect and determine whether a zero sequence current of the first-group single module voltage control power converter  111   a   1  is zero. If yes, then go to S 20 , or else go to S 21 . 
         [0031]    S 20 : Operate the second-group single module voltage control power converter  111   a   2  independently, and then return to S 19 . 
         [0032]    S 21 : Perform a compensation control of the second-group single module voltage control power converter  111   a   2 , and then return to Step S 20 . 
         [0033]    With reference to  FIG. 4  for a mailbox of a zero sequence current control apparatus for parallel power converters of the present invention, the functions of the mailbox are defined according to the functional requirements of the instructions, and the mailbox is defined as follows: 
         [0034]    (1) Mailbox  1  relates to a host/slave system registration sequence. Wherein, the host has the station number  1 , and the slaves have the station number starting from  2 . The initial station number  0  may be provided for defining the control device  112 , if needed. 
         [0035]    (2) Mailbox  2  relates to the status of a host/slave.  0  refers to an interrupt, and  1  refers to an operation. 
         [0036]    (3) Mailbox  3  shows the power of a single module voltage control power converter. 
         [0037]    (4) Mailbox  4  shows the voltage of a single module voltage control power converter. 
         [0038]    (5) Mailbox  5  shows the current of a single module voltage control power converter. 
         [0039]    The zero sequence current control apparatus for parallel power converters of the present invention may set the communication structure and instruction mode of a plurality of single module voltage control power converters  111   a   1 ,  111   a   2 ,  111   a   3  . . .  111   an  primarily for setting the zero sequence circulation of the total output to zero, and suppressing the circulation, so that the current allocated for the host and slaves can be uniform to prevent losses due to any overload of the single module voltage control power converters  111   a   1  ,  111   a   2 ,  111   a   3  . . .  111   an  and accomplish the power modulation among the single module voltage control power converters  111   a   1 ,  111   a   2 ,  111   a   3  . . .  111   an  to facilitate the control side to adjust the total output power successfully and adjust the total output power according to the variable loads. 
         [0040]    The automatic allocation device  111  of the present invention uses the eCAN BUS as a communication interface to execute the parallel instruction of dividing the single module voltage control power converters  111   a   1 ,  111   a   2 ,  111   a   3  . . .  111   an  into the host and slaves according to the boot registration sequence, and an instruction is transmitted from the host to the slaves through the eCAN BUS, so that the host and slaves can perform power modulation simultaneously, and the power can be controlled and modulated according to the quantity of registered slaves. 
         [0041]    In summation, the zero sequence current control apparatus and method for parallel power converters of the present invention can overcome the problem of modulating and allocating output power to each of the single module voltage control power converter  111   a   1 ,  111   a   2 ,  111   a   3  . . .  111   an  in a parallel operation and adopt the eCAN BUS as a communication interface for transmitting instruction, so that the uniform output voltage, current and power of each single module voltage control power converter  111   a   1 ,  111   a   2 ,  111   a   3  . . .  111  can be achieved in the parallel operation. 
         [0042]    In summation of the description above, the present invention improves over the prior art and complies with the patent application requirements, and thus is duly filed for patent application.