Abstract:
There is provided an inverter test apparatus for testing an inverter interconnected with an alternating-current power system, the apparatus including an alternating-current power output unit configured to output alternating-current power, and an alternating-current power controller configured to control the alternating-current power output from the alternating-current power output unit to simulate an alternating-current load of the inverter.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2012-056351, filed Mar. 13, 2012, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to an apparatus for use in testing an inverter. 
         [0004]    2. Description of the Related Art 
         [0005]    In general, in a dispersed power supply system such as a photovoltaic power system, an inverter is used to establish interconnection with an alternating current (AC) power system. In such an inverter, a function for avoiding islanding may be demanded in some cases (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 2008-104262). 
         [0006]    For example, in the Institute of Electrical and Electronics Engineers (IEEE) 1547 standard, conducting the following islanding test is demanded. 
         [0007]    First, to conduct the anti-islanding test, a circuit is configured to interconnect an AC power system with an inverter. An AC load is connected to this circuit so that AC power can be supplied from the AC power system and the inverter. This AC load is set such that inductance and capacitance thereof have the same value. Then, electric power is supplied to the AC load by parallel operations of the AC power system and the inverter, whereby the AC load is caused to resonate. In this resonating state, the AC power system is disconnected from the circuit, and islanding of the inverter is allowed. At this time, the inverter solely supplies electric power to the AC load. In this anti-islanding test, it is confirmed that the inverter is automatically stopped in such an islanding state. 
         [0008]    However, a capacity of the AC load provided to conduct the above-described test must be increased as a capacity of the inverter as a test target is raised. Therefore, when the inverter is large, the AC load is also large. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    It is an object of the invention to provide an inverter test apparatus capable of simulating an AC load which is used for testing an inverter. 
         [0010]    In accordance with an aspect of embodiments of the invention, there is provided an inverter test apparatus for use in testing an inverter interconnected with an alternating-current power system, the apparatus comprising an alternating-current power output unit configured to output alternating-current power; and an alternating-current power controller configured to control the alternating-current power output from the alternating-current power output unit to simulate an alternating-current load of the inverter. 
         [0011]    Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0012]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
           [0013]      FIG. 1  is a block diagram showing a test circuit to which an AC load simulator according to a first embodiment of the invention is applied; 
           [0014]      FIG. 2  is a block diagram showing a test circuit to which an AC load simulator according to a second embodiment of the invention is applied; 
           [0015]      FIG. 3  is a block diagram showing a test circuit to which an AC load simulator according to a third embodiment of the invention is applied; and 
           [0016]      FIG. 4  is a block diagram showing a test circuit to which an AC load simulator according to a fourth embodiment of the invention is applied. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    Embodiments according to the invention will now be described hereinafter with reference to the accompanying drawings. 
       First Embodiment 
       [0018]      FIG. 1  is a block diagram showing a test circuit  10  to which an AC load simulator  1  according to a first embodiment of the invention is applied. It is to be noted that like reference numbers denote like parts in subsequent drawings to omit a detailed description thereof, and different parts will be mainly described. In regard to subsequent embodiments, an overlapping description will be likewise omitted. 
         [0019]    The test circuit  10  is configured to include the AC load simulator  1 , three AC load resistors  2 , three AC load capacitors  3 , an inverter  21 , a power system simulation power supply  22 , an inverter-side circuit breaker  23 , and a system-side circuit breaker  24 . 
         [0020]    The inverter  21  is connected to the power system simulation power supply  22  via the inverter-side circuit breaker  23  and the system-side circuit breaker  24  in the mentioned order. The inverter  21  is an apparatus which is a test target. To achieve interconnection with the power system simulation power supply  22 , the inverter  21  controls three-phase AC power to output. The inverter  21  is interconnected with the power system simulation power supply  22  and supplies AC power to AC loads  1 ,  2 , and  3 . 
         [0021]    The power system simulation power supply  22  is a power supply configured to simulate a grid. The power system simulation power supply  22  generates the three-phase AC power. The power system simulation power supply  22  is interconnected with the inverter  21  and supplies the AC power to the AC loads  1 ,  2 , and  3 . 
         [0022]    The inverter-side circuit breaker  23  is a switch configured to disconnect the inverter  21  from the test circuit  10 . 
         [0023]    The system-side circuit breaker  24  is a switch configured to disconnect the power system simulation power supply  22  from the test circuit  10 . 
         [0024]    The AC load simulator  1  is connected between the inverter-side circuit breaker  23  and the system-side circuit breaker  24 . The AC load simulator  1  is a test apparatus that simulates inductance of a passive load in order to conduct an anti-islanding test of the inverter  21 . 
         [0025]    Each of the three AC load resistors  2  is provided between respective lines of a circuit provided between the inverter-side circuit breaker  23  and the system-side circuit breaker  24 . The AC load resistor  2  is a passive element configured to simulate resistance of the passive load. 
         [0026]    Each of the three AC load capacitors  3  is provided between the respective lines of the circuit provided between the inverter-side circuit breaker  23  and the system-side circuit breaker  24 . Each AC load capacitor  3  is connected in parallel with each AC load resistor  2 . The AC load capacitor  3  is a passive element configured to simulate capacitance of the passive load. 
         [0027]    The AC load simulator  1  comprises a load simulation inverter  11 , a controller  12 , and a capacitor  13 . 
         [0028]    An AC side of the load simulation inverter  11  is connected to each phase between the inverter-side circuit breaker  23  and the system-side circuit breaker  24 . The capacitor  13  is connected to a direct-current side of the load simulation inverter  11 . It is to be noted that the capacitor  13  may be a capacitor that is built in the load simulation inverter  11 . Therefore, the capacitor does not necessarily have to be connected to direct-current terminals of the load simulation inverter  11 . 
         [0029]    The controller  12  controls an AC output from the load simulation inverter  11  to simulate the inductance of the AC load. For example, if load power of the AC load resistors  2  is 500 kW and load power of the AC load capacitors  3  is 500 kvar, the controller  12  controls the load simulation inverter  11  to simulate load power of 500 kvar of the reactance having a sign opposite to that of the AC load capacitors  3 . As a result, the AC capacitors  3  are caused to resonate. 
         [0030]    In the anti-islanding test, resonance is effected by control of the controller  12 , and then the system-side circuit breaker  24  is opened. As a result, the inverter  21  becomes in a state of solely supplying electric power to the AC load. As test conditions, for example, in a state that the interconnection is achieved, a power supply ratio of the inverter  21  with respect to the AC load is set to, for example, 98%. When the system-side circuit breaker  24  is opened, the power supply ratio of the inverter  21  with respect to the AC load becomes 100% (an islanding state). In the anti-islanding test, it is confirmed that the inverter  21  is automatically stopped in this islanding state. 
         [0031]    According to this embodiment, when the AC load simulator  1  is controlled to simulate the inductance, the anti-islanding test can be conducted without providing reactors (inductors) as the AC load for the test. 
         [0032]    As a result, even if the inverter  21  as the test target has a large capacity, a large-capacity reactor does, not have to be provided for the anti-islanding test. Therefore, when the capacity of the inverter  21  is increased, it is possible to suppress a cost and a circuit scale required for the circuit used for the conducting the anti-islanding test. 
       Second Embodiment 
       [0033]      FIG. 2  is a block diagram showing a test circuit  10 A to which an AC load simulator  1 A according to a second embodiment of the invention is applied. 
         [0034]    The test circuit  10 A has the AC load simulator  1 A that substitutes for the AC load simulator  1  and three AC reactors  4  that substitute for the three AC load capacitors  3  in the test circuit  10  according to the first embodiment shown in  FIG. 1 . Other structures are the same as those in the test circuit  10  according to the first embodiment. 
         [0035]    Each of the three AC load reactors  4  is provided between respective lines of a circuit provided between the inverter-side circuit breaker  23  and the system-side circuit breaker  24 . Each AC load reactor  4  is connected in parallel with each AC load reactor  2 . Each AC reactor  4  is a passive element configured to simulate inductance of a passive load. 
         [0036]    The AC load simulator  1 A has a controller  12 A that substitutes for the controller  12  in the AC load simulator  1  according to the first embodiment. Other structures are the same as those in the AC load simulator  1  according to the first embodiment. 
         [0037]    The controller  12 A controls an AC output from the load simulation inverter  11  to simulate capacitance of the AC load. For example, if load power of the AC load resistors  2  is 500 kW and load power of the AC load reactors  4  is 500 kvar, the controller  12 A controls the load simulation inverter  11  to simulate load power of 500 kvar of reactance having a sign opposite to that of the AC load reactors  4 . As a result, the AC load reactors  4  are caused to resonate. 
         [0038]    A method of conducting an anti-islanding test is the same as that of the first embodiment. 
         [0039]    According to this embodiment, when the AC load simulator  1 A is controlled to simulate the capacitance, the anti-islanding test can be conducted without providing capacitors as the AC load for the test. 
         [0040]    As a result, even if the inverter  21  as the test target has a large capacity, a large-capacity reactor does not have to be provided for the anti-islanding test. Therefore, when the capacity of the inverter  21  is increased, it is possible to suppress a cost and a circuit scale required for the circuit used for the conducting the anti-islanding test. 
       Third Embodiment 
       [0041]      FIG. 3  is a block diagram showing a test circuit  10 B to which an AC load simulator  1 B according to a third embodiment of the invention is applied. 
         [0042]    The test circuit  10 B has the AC load simulator  1 B that substitutes for the AC load simulator  1 , three AC load reactors  4  that substitute for the three AC load resistors  2 , and an additionally provided AC power supply  25  in the test circuit  10  according to the first embodiment shown in  FIG. 1 . Other structures are the same as those in the test circuit  10  according to the first embodiment. 
         [0043]    The AC load simulator  1 B is connected between the inverter-side circuit breaker  23  and the system-side circuit breaker  24 . The AC simulator  1 B is a test apparatus that simulates resistance of a passive load in order to conduct an anti-islanding test of the inverter  21 . The AC simulator  1 B comprises a load simulation power converter  11 B and a controller  12 B. 
         [0044]    The load simulation power converter  11 B is configured of a back-to-back (BTB) converter. The load simulation power converter  11 B comprises an inverter  111  and a converter  112 . A direct-current side of the inverter  111  is connected to a direct-current side of the converter  112 . An AC side of the inverter  111  is connected to each phase of a circuit between the inverter-side circuit breaker  23  and the system-side circuit breaker  24 . An AC side of the converter  112  is connected to an AC power supply  25 . 
         [0045]    The load simulation power converter  11 B converts AC power supplied from the inverter  21  and a power system simulation power supply  22  into AC power that is synchronized with the AC power supply  25 . The load simulation power converter  11 B supplies the converted AC power to the AC power supply  25 . 
         [0046]    The controller  12 B controls the AC output from the load simulation power converter  11 B to simulate resistance of an AC load. For example, if both load power of the AC load capacitors  3  and load power of the AC load reactors  4  are 500 kvar, the controller  12 B controls the load simulation power converter  11 B to simulate load power of 500 kW. At this time, the AC load capacitors  3  and the AC reactors  4  are caused to resonate. 
         [0047]    A method of conducting the anti-islanding test is the same as that of the first embodiment. 
         [0048]    According to this embodiment, when the AC load simulator  1 B is controlled to simulate the resistance, the anti-islanding test can be conducted without providing resistors as the AC load for the test. 
         [0049]    As a result, even if the inverter  21  as the test target has a large capacity, a large-capacity resistor does not have to be provided for the anti-islanding test. Therefore, when the capacity of the inverter  21  is increased, it is possible to suppress a cost and a circuit scale required for the circuit used for the conducting the anti-islanding test. 
       Fourth Embodiment 
       [0050]      FIG. 4  is a block diagram showing a test circuit  100  to which an AC load simulator  10  according to a fourth embodiment of the invention is applied. 
         [0051]    The test circuit  10 C has the AC load simulator  1 C that substitutes for the AC load simulator  1  and eliminates the three AC load resistors  2  and the three AC load capacitors  3  in the test circuit  10  according to the first embodiment shown in  FIG. 1 . Other structures are the same as those in the test circuit  10  according to the first embodiment. 
         [0052]    The AC load simulator  1 C is connected between the inverter-side circuit breaker  23  and the system-side circuit breaker  24 . The AC load simulator  1 C is a test apparatus that simulates a passive load in order to conduct an anti-islanding test of the inverter  21 . 
         [0053]    The AC load simulator  1 C comprises an inductance simulation inverter  111 , a capacitance simulation inverter  11   c , two capacitors  13 , the resistance simulation power converter  11 B according to the third embodiment, and a controller  12 C. Here, the inductance simulation inverter  111  is the same as the load simulation inverter  11  according to the first embodiment. Further, the capacitance simulation inverter  11   c  is the same as the load simulation inverter  11  according to the second embodiment. Each capacitor  13  is connected to a direct-current side of each of the inductance simulation inverter  11   i  and the capacitance simulation inverter  11   c  like the first embodiment. 
         [0054]    The controller  12 C controls an AC output from the inductance simulation inverter  11   i  to simulate inductance of an AC load. The controller  12 C controls an AC output from the capacitance simulation inverter  11   c  to simulate capacitance of the AC load. The controller  12 C controls an AC output from the resistance simulation power converter  11 B to simulate resistance of the AC load. As a result, the controller  12 C controls the AC output to simulate impedance as a test condition. 
         [0055]    For example, the controller  12 C controls the AC outputs such that the resistance of load power becomes 500 kW, the inductance of the load power becomes 500 kvar, and the capacitance of the load power becomes 500 kvar. As a result, resonance occurs in the test circuit  10 . 
         [0056]    A method of conducting the anti-islanding test is the same as that in the first embodiment. 
         [0057]    According to this embodiment, when output of the AC power is controlled to simulate the impedance as the test condition, the anti-islanding test can be conducted without providing the AC load for the test. 
         [0058]    As a result, even if the inverter  21  as the test target has a large capacity, a large-capacity AC load does not have to be provided for the anti-islanding test. Therefore, when the capacity of the inverter  21  is increased, it is possible to suppress a cost and a circuit scale required for the circuit used for the conducting the anti-islanding test. 
         [0059]    It is to be noted that the description has been given as to each of the AC load simulator  1 ,  1 A,  1 B, and  1 C that simulate any one or all of the resistance, the inductance, and the capacitance in each of the foregoing embodiments, but an AC load formed of any other combination may be configured. That is, an AC load simulator that simulates an AC load which is a combination of arbitrary two selected from the resistance, the inductance, and the capacitance can be likewise configured. 
         [0060]    Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.