Abstract:
Usability is improved and noise and fuel consumption are lowered by preventing stopping of a generator output. A hybrid power generator  1  includes a battery  4,  an alternator  3,  a rectifier unit  51,  a DC-DC converter  9  stepping up an output of the battery  4,  and an inverter unit  53  converting outputs of the rectifier unit  51  and the DC-DC converter  9  to AC and outputting the AC as a generator output. At a time when a load output reaches an upper limit of an allowable power range of the DC-DC converter  9,  the engine  2  is started and power supplying from the battery  4  is switched to power generation by the alternator  3.  A generated power restricting unit  27  suppresses the output of the inverter unit  53  during the starting of the engine so that the generator outputs allowable power range of the DC-DC converter  9.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a power supply source switching apparatus for a hybrid engine generator and particularly relates to a power supply source switching apparatus for a hybrid engine generator capable of switching between a battery output and an output of an alternator driven by an engine without stopping the generator. 
       BACKGROUND ART 
       [0002]    A hybrid engine generator that includes a generator, which is driven by an engine, and a battery is known. A hybrid engine generator having a controller that enables selection between a generator and a storage battery as a power supply source by enabling supply of power from both the generator and the storage battery when a power assist mode switch is on, switching from the generator to the storage battery when the power assist mode switch is off and a power supply source changeover switch is on, and switching from the storage battery to the generator when both the power assist mode switch and the power supply source changeover switch are off is proposed in Patent Document 1. 
       CITATION LIST 
     Patent Document 
     Patent Document 1 “Japanese Patent Publication No. 3941927” 
     SUMMARY OF INVENTION 
     Technical Problem 
       [0003]    With a conventional hybrid engine generator, although the power supply source is selected by the changeover switch, each time the power supply source is to be switched, the changeover switch must be operated upon stopping the generator output. Operation is thus complicated and there is an issue of poor usability. 
         [0004]    An object of the present invention is to provide, in response to the above issue, a power supply source switching apparatus for a hybrid engine generator that enables switching between power supply sources to be performed without using a changeover switch and while maintaining an output of the generator. 
       Solution to Problem 
       [0005]    A first feature of the present invention is a power supply source switching apparatus for a hybrid power generator, which includes a battery, an alternator driven by an engine, a rectifier unit rectifying an output of the alternator, a DC-DC converter stepping up an output voltage of the battery, and an inverter unit converting outputs of the rectifier unit and the DC-DC converter to AC and outputting the AC as a generator output, the power supply source switching apparatus for a hybrid power generator comprising: a load output detecting unit detecting a load output of the generator; an engine starting unit starting the engine by the output of the battery; and a generated power restricting unit starting the engine and switching from power supplying from the battery to power generation by the alternator at a point in time at which the load output reaches an upper limit of an allowable power of the DC-DC converter, and suppressing the output of the inverter unit during the starting of the engine for the switching so that the generator output does not exceed an allowable power range of the DC-DC converter. 
         [0006]    A second feature of the present invention is that the rectifier unit is used in common as a drive inverter for starting the engine by the output of the DC-DC converter, and the generated power restricting unit is arranged to perform output restriction of the battery by subtracting power, corresponding to power consumed for engine starting, from the battery output. 
         [0007]    A third feature of the present invention is that the engine is stopped and switching to the output from the battery is performed when the load output falls below the allowable output range of the DC-DC converter. 
       Advantageous Effects of Invention 
       [0008]    According to the first to third aspects of the present invention, when the load output exceeds the power capacity (allowable power) of the DC-DC converter, the generator output is lowered just temporarily during engine startup in consideration of the power capacity and an engine starting power to enable the output power of the battery to be supplied in a well-balanced manner to the load and the alternator that serves as an engine starter. Also, usability is improved because the switching between power supply means can be performed while maintaining the generator output. Further, power supplying can be maintained within the power capacity of the DC-DC converter so that use of large-sized DC-DC converter can be avoided and low noise and low fuel consumption can be achieved by continuous, smooth operation without interruption of the generator output. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]      FIG. 1  is a block diagram of a system arrangement of a hybrid engine generator that includes a power supply source switching apparatus according to an embodiment of the present invention. 
           [0010]      FIG. 2  is a circuit diagram of an output control apparatus of the hybrid engine generator shown in  FIG. 1 . 
           [0011]      FIG. 3  is a circuit diagram of an isolation-type DC-DC converter. 
           [0012]      FIG. 4  is a flowchart of an operation of the power supply source switching apparatus. 
           [0013]      FIG. 5  is a flowchart of an operation of a generator output suppression control apparatus. 
           [0014]      FIG. 6  is an operation timing chart of the power supply source switching apparatus. 
           [0015]      FIG. 7  is a block diagram of principal functions of the power supply source switching apparatus. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0016]    An embodiment of the present invention shall now be described with reference to the drawings.  FIG. 1  is a system arrangement diagram of a hybrid engine generator that includes an output control apparatus according to an embodiment of the present invention. In  FIG. 1 , the hybrid engine generator  1  includes an alternator  3  coupled to an engine  2  that is a first power source, and a battery  4  that is a second power source. The alternator  3  is a motor-generator that is driven by the engine  2  to generate power and can also be operated as a starting motor for the engine  2  and is arranged, for example, from a three-phase multipolar magnetic generator. 
         [0017]    Output sides of the alternator  3  and the battery  4  are connected to a power conversion unit  5 , and an output side of the power conversion unit  5  is connected to an output terminal (for example, an outlet)  6 . A load  7  is connected to the outlet  6 . 
         [0018]    A controller  8  includes a microcomputer, detects a load output and battery information, such as a remaining capacity of the battery  4 , etc., and instructs output allocation between the battery  4  and the alternator  3  to the power conversion unit  5  and a rotation speed to the engine  2 . 
         [0019]      FIG. 2  is a specific circuit diagram of the hybrid engine generator  1 . The power conversion unit  5  includes a rectifier unit  51 , a DC unit  52 , an inverter unit  53 , and a waveform shaping circuit  54 . The rectifier unit  51  is a hybrid bridge rectifier circuit that includes diodes D 1 , D 2 , and D 3  and switching elements (hereinafter explained as “FETs”) Q 1 , Q 2 , and Q 3  that are bridge-connected. A winding  3 U of the alternator  3  is connected to a junction of the diode D 1  and the FET Q 1 , a winding  3 V is connected to a junction of the diode D 2  and the FET Q 2 , and a winding  3 W is connected to a junction of the diode D 3  and the FET Q 3 , respectively. 
         [0020]    The rectifier unit  51  that is thus arranged rectifies and supplies the output of the alternator  3  to the DC unit  52  and also functions as a drive inverter that converts a DC output voltage of the battery  4  to a three-phase AC voltage by on/off control of the FETs Q 1  to Q 3  and applies the AC voltage to the alternator  3 . 
         [0021]    The battery  4  is connected between the rectifier unit  51  and DC unit  52  via an isolation-type DC-DC converter  9 . The isolation-type DC-DC converter  9  is a bidirectional DC-DC converter between the battery  4  and the rectifier unit  51  and provides power to the battery  4  and the rectifier unit  51  bidirectionally and, as shall be described below, is arranged from a primary side and a secondary side that are connected via an isolation unit (transformer). 
         [0022]    The DC unit  52  is a switching converter (a step-down type in the present embodiment) and includes an FET Q 4 , a choke coil L 3 , capacitors C 1  and C 2 , a diode D 4 , etc. The inverter unit  53  is arranged by bridge connection of four FETs Q 5 , Q 6 , Q 7 , and Q 8 . An output of the inverter unit  53  is connected to the waveform shaping circuit  54 , which is arranged from coils L 1  and L 2  and a capacitor C 3 . The FETs Q 1  to Q 3 , Q 4 , and Q 5  to Q 8  is controlled by instructions from the controller  8 . 
         [0023]      FIG. 3  is a circuit diagram of an arrangement example of the isolation-type DC-DC converter  9 . The isolation-type DC-DC converter  9  includes a transformer  10  having a primary low voltage side winding  10 - 1  and a secondary high voltage side winding  10 - 2 . A step-up ratio of the isolation-type DC-DC converter  9  is determined by a winding ratio of the low voltage side winding  10 - 1  to the high voltage side winding  10 - 2 . 
         [0024]    A low voltage side switching unit  11  is inserted at the low voltage side winding  10 - 1  side and a high voltage side switching unit  12  is inserted at the high voltage side winding  10 - 2  side. The low voltage side switching unit  11  is arranged, for example, by bridge connection of four FETs Q 9 , Q 10 , Q 11 , and Q 12 , and the high voltage side switching unit  12  is likewise arranged by bridge connection of four FETs Q 13 , Q 14 , Q 15 , and Q 16 . 
         [0025]    Diodes D 7 , D 8 , D 9 , and D 10  and diodes D 11 , D 12 , D 13 , and D 14  are respectively connected in parallel to the FETs Q 9  to Q 16  of the low voltage side switching unit  11  and the high voltage side switching unit  12 . These diodes may be parasitic diodes of the FETs, or may be independently connected diodes parallel to the FETs. Together with the rectifier elements D 7  to D 14  that are connected in parallel, the low voltage side switching unit  11  and the high voltage side switching unit  12  may be considered as being switching/rectifier units, respectively. 
         [0026]    An LC oscillator circuit  13  is inserted at the high voltage side winding  10 - 2  side of the transformer  10 . The LC oscillator circuit  13  makes a current, which flows when at least one of either the low voltage side switching unit  11  or the high voltage side switching unit  12  is driven, have a sinusoidal form and thereby functions to reduce switching loss and prevent FET breakdown due to a large current. This is because the FETs can be switched on and off near zero cross points of the sinusoidal current. The LC oscillator circuit  13  may be provided at the primary side instead of at the secondary side. 
         [0027]    Switching control of the FETs Q 9  to Q 12  of the low voltage side switching unit  11  and the FETs Q 13  to Q 16  of the high voltage side switching unit  12  is performed by the controller  8 . The capacitors  14  and  15  that are connected to the primary side and the secondary side are output smoothing capacitors. 
         [0028]    During operation, the low voltage side switching unit  11  and the high voltage side switching unit  12  are driven by the same signal and synchronized completely so that the isolation-type DC-DC converter  9  performs bidirectional power conversion automatically. As is well-known, this drive is performed by alternately turning on and off the pair of FETs Q 9  and Q 12  and the pair of FETs Q 10  and Q 11  at the low voltage side switching unit  11  and alternately turning on and off the pair of FETs Q 13  and Q 16  and the pair of FETs Q 14  and Q 15  at the high voltage side switching unit  12 . 
         [0029]    In startup of the engine, power conversion from the primary side to the secondary side of the isolation-type DC-DC converter  9  is performed, and the DC voltage of the battery  4  that is thereby stepped up is provided to the rectifier unit  51  serving as the drive inverter. The rectifier unit  51  performs PWM drive of Q 1  to Q 6  in a well-known manner and thereby converts the input DC voltage to a three-phase AC voltage and applies the AC voltage to the alternator  3 . The engine  2  is thereby started. In this process, change of current distribution by a back voltage that arises in accordance with the operation of the alternator  3  can be used to judge the phase and perform synchronous drive by sensorless control. 
         [0030]    When the engine  2  is started, the alternator  3  is driven by the engine to generate an output. At this point, the FETs Q 1  to Q 3  of the rectifier unit  51  are not driven and, the output of the alternator  3  is rectified by the diodes D 1  to D 3  of the rectifier unit  51 . 
         [0031]    The output voltage of the rectifier unit  51  is smoothened and adjusted by the DC unit  52  and further converted to an AC power of a predetermined frequency (for example, the commercial power frequency) at the inverter unit  53 . At the DC unit  52 , PWM of the FET Q 4  is performed in accordance with an operation signal from the controller  8 . 
         [0032]    The isolation-type DC-DC converter  9  is a bidirectional DC-DC converter and thus if the remaining capacity of the battery  4  is less than a predetermined value and the output of the alternator  3  is adequate, the battery  4  is charged by the output voltage of the rectifier unit  51  being stepped down by the isolation-type DC-DC converter  9  and input into the battery  4 . Also, in a case where the remaining capacity of the battery  4  is high, power from the battery  4  is also supplied to the load through the isolation-type DC-DC converter  9  to compensate (assist) the output power of the alternator  3 . 
         [0033]    Power supply source switching control of the hybrid engine generator  1  shall now be described.  FIG. 4  is a flowchart of an output control operation. This operation can be realized by the microcomputer inside the controller  8 . In step S 1  of  FIG. 4 , the isolation-type DC-DC converter  9  is made to operate to output the power of the battery  4  to the DC unit  52 . This enables power to be supplied to the load, connected to the outlet  6 , by the voltage from the battery  4  (battery power generation). 
         [0034]    In step S 2 , it is judged whether or not a power demand from the load, that is, the load output exceeds an allowable power of the isolation-type DC-DC converter  9 . Output from the battery  4  is continued while the judgment result is negative. If an affirmative judgment is made at step S 2 , that is, if the load output reaches a value that is set close to an upper limit of the allowable power of the isolation-type DC-DC converter  9 , step S 3  is entered to start the engine  2  and drive the alternator  3 . After starting the engine  2 , generator output suppression control is performed in step S 4 . Details of the generator output suppression control shall be described below. 
         [0035]    In step S 5 , power generation with the alternator  3  as the power supply source is started. In step S 6 , it is judged whether or not the load output is below the allowable power of the isolation-type DC-DC converter  9 . Power generation with the alternator  3  as the power supply source is continued while a negative judgment is made at step S 6 . If an affirmative judgment is made at step S 6 , step S 7  is entered and the engine  2  is stopped. When the engine  2  is stopped, a return to step S 1  is performed. 
         [0036]      FIG. 5  is a flowchart of the generator output suppression control. In step S 41 , an engine starting power is detected. The engine starting power is determined in advance by either or both of experiment and calculation. In step S 42 , the load output and the starting power of the engine  2  are added to compute a required power. In step S 43 , a difference (deficit power) between the required power and the allowable power of the isolation-type DC-DC converter  9  is computed. In step S 44 , PWM control of the inverter unit  53  is performed to reduce the generator output (output of the inverter unit  53 ) by just the deficit power. By this control, the generator output is maintained in a suppressed state while securing the starting power of the engine  2 . When the engine  2  starts in the state where the generator output is suppressed by the generator output suppression control and the engine rotation speed reaches a predetermined rotation speed (when the engine enters a started state), the output of the battery  4  is stopped and switching to power generation with the alternator  3  as the power supply source is performed. 
         [0037]      FIG. 6  is a timing chart of the power supply source switching control. From timing t 0  to t 1  in  FIG. 6 , power supply (battery power generation) by the battery  4  is performed. At the timing t 1 , a load output exceeding the power generation capability of the battery  4 , that is, the allowable power of the isolation-type DC-DC converter  9  arises, and the engine  2  is started by the output of the battery  4  at the timing t 1 . At the same time, the inverter unit  53  is controlled to reduce the output of the battery  4 , that is, the generator output at this point. At a timing t 2 , the engine  2  is in the started state and the power for engine starting begins to decrease, and the output unit  52  is thus controlled to increase the generator output. At a timing t 3 , the generator output increases to match the load output, the isolation-type DC-DC converter  9  is controlled so that the output of the battery  4  stops, and only the output of the alternator  3  driven by the engine  2  becomes the generator output. 
         [0038]      FIG. 7  is a block diagram of principal functions of the power supply source switching apparatus. In  FIG. 7 , a load output detecting unit  23  detects the load output based on the output current and the output voltage of the inverter unit  53 . An allowable power value setting unit  24  is a means that sets the allowable output power value of the isolation-type DC-DC converter  9  in advance. A comparing unit  25  compares the load output detected by the load output detecting unit  23  and the allowable power value and turns on a comparing unit output when the load output is greater than the allowable power value and turns off the comparing unit output when the load output is less than the allowable power value. 
         [0039]    An engine starting/stopping unit  26  performs, in response to the turning on of the comparing unit output, switching control of the rectifier unit  51  as the drive inverter so that the output of the isolation-type DC-DC converter  9  is supplied to the alternator  3 . The alternator  3  is driven by the voltage of the battery  4  that is applied through the rectifier unit  51  and thereby starts the engine  2 . With the starting of the engine  2 , a generated power restricting unit  27  is energized in response to the turning on of the comparing unit output, and PWM control of the inverter unit  53  is performed to restrict its output voltage. The restriction of the output voltage is performed in consideration of the starting power of the engine  2 . If the load output is less than the allowable power value, that is, if the comparing unit output is off, a battery power generation starting unit  28  is energized and a voltage is applied from the battery  4  to the inverter unit  53  via the isolation-type DC-DC converter  9  and the DC unit  52 . At the same time, an engine starting/stopping unit  26  stops the engine  2  (stops both or either of ignition and fuel supply). 
         [0040]    As described above, with the present embodiment, when the load increases and the capacity of the isolation-type DC-DC converter  9  is about to become deficient, switching from the battery-based power supplying system to the alternator-based power supplying system is performed. In the process of switching, the generator output, that is, the output of the inverter unit  53  is lowered temporarily in consideration of the starting power of the engine and, the alternator  3  is started by the output power from the battery  4  to start the engine. The output from the battery  4  is thereby balanced as the power for the load and the power for starting the engine. 
         [0041]    Although the present invention has been described in accordance with the embodiment, the present invention is not restricted to the embodiment and modifications are possible based on the matters described in the claims and the known art. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  . . . hybrid engine generator 
           2  . . . engine 
           3  . . . alternator 
           4  . . . battery 
           5  . . . power conversion unit 
           7  . . . load 
           8  . . . controller 
           9  . . . isolation-type DC-DC converter 
           23  . . . load output detecting unit 
           24  . . . allowable power setting unit 
           25  . . . comparing unit 
           26  . . . engine starting/stopping unit 
           27  . . . generated power restricting unit