Patent Publication Number: US-2013242628-A1

Title: Solar power conditioner

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on Japanese Patent Application No 2012-57232 filed on Mar. 14, 2012, the disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a solar power conditioner for converting a direct current electric power to an alternating current electric power in a solar 
     BACKGROUND 
     A solar power conditioner has been developed by various companies. In order to obtain a generated electric power in a solar cell effectively, a MPPT (maximum power point tracking) control is executed. In the MPPT control, normally, the electric power is maximized by changing an operational voltage since the operational voltage for obtaining the maximum electric power in a solar cell panel is successively varied. The MPPT control is described in JP-A-H11-103538 and JP-B-4527767. 
     In JP-A-H11-103538, in a solar cell module, each electric power converter executes the MPPT control so that an output current and an output voltage are controlled so as to always maximize the power generation efficiency. A common output current flows through an output terminal of each electric power converter. An output voltage of each electric power converter is automatically adjusted so as to set a ratio of the output voltage of each electric power converter to be equal to a ratio of the maximum electric power of each solar cell module. 
     In JP-B-4527767, multiple single-phase inverters include a first inverter, in which a first direct current power source having the maximum voltage among direct current power sources inputs an electric power, at least one second converter, connected to a first terminal of the first converter on an alternating current side, and at least one third inverter connected to a second terminal of the first, terminal on the alternating current side. 
     JP-A-2008-178158 and JP-B2-4527767 (U.S. 2009/0015071) teach that a voltage generated in the solar cell panel is input into a step up and down converter, and the, voltage is charged in a capacitor. Further, a direct current electric power in the capacitor is input into each of the first to third converters so that a voltage of a total of output voltages of these converters is output from an inverter unit. Further, JP-A-2007-58843 teaches that an electric charge accumulated in a capacitor is switched and output in an alternating current form. 
     In JP-A-H11-103538, the module merely performs the DC-DC conversion. Accordingly, it is necessary to add an electric power converter for performing the DC-AC conversion. Thus, a switching loss increases. In JP-A-2008-178158, and JP-B2-4527767, the voltage converter is arranged to correspond to each solar cell panel, and therefore, the maximum electric power of the solar cell panel is not effectively output. Further, in JP-A-2007-58843, a switching operation of the charge and discharge of the electric charge accumulation capacitor is controller at a frequency higher, by several hundred times to several tens of thousand times than a system frequency. Thus, a switching loss increases. 
     SUMMARY 
     It is an object of the present disclosure to provide a solar conditioner in order to reduce a switching loss and to improve an electric power conversion efficiency of solar cell panels. 
     According to an aspect of the present disclosure, a solar power conditioner includes: a synchronous controller; and a plurality of electric power converters connected in series with each other, the electric power converter being arranged at a plurality of panel groups, each of which includes one or more solar cell panels, respectively. Each electric power converter executes a maximum power point tracking control for tracking a maximum power point of an output electric power of the panel group. Each electric power converter converts a voltage and a current of the output electric power of the panel group. The synchronous controller synchronously controls the plurality of electric power converters to superimpose converted voltages in series, the converted voltages outputting from the electric power converters, so that the plurality of electric power converters output a predetermined pseudo sine wave voltage or a predetermined alternating current voltage. 
     In the above conditioner, since the electric power converter is arranged at each panel group having at least one solar cell panel, the converter can maximize the electric power conversion efficiency of the panel group. Further, each electric power converter executes the MPPT control of the output electric power of the panel group, and further, converts the voltage and the current of the output electric power of the panel group. Accordingly, when the synchronous controller superimposes the converted voltages of the electric power converters in series, and synchronously controls the converted voltages so as to output the predetermined pseudo sine wave voltage or the predetermined alternating current voltage, the direct current voltage output from the panel group is directly converted to the output electric power. Thus, the predetermined pseudo sine wave voltage or the predetermined alternating current voltage is effectively output. Therefore, the electric power conversion efficiency of the panel group is much improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
         FIG. 1  is a diagram showing a solar power conditioner according to a first embodiment; 
         FIG. 2  is a diagram showing a solar cell panel; 
         FIG. 3  is a diagram showing another solar cell panel; 
         FIG. 4  is a circuit diagram showing an electric power converter; 
         FIG. 5  is a graph showing a voltage dependency of an output electric power of the solar cell panel; 
         FIG. 6  is a graph showing a PWM signal; 
         FIG. 7  is a graph showing a PFM signal; 
         FIG. 8  is a diagram showing a waveform of a pseudo sine wave output from each electric power converter; 
         FIG. 9  is a diagram showing an on/off timing of each transistor; 
         FIGS. 10A and 10B  are diagrams showing control manners; 
         FIG. 11  is a diagram showing another control manner; 
         FIG. 12  is a diagram showing further another control manner; 
         FIG. 13  is a diagram showing another control manner; 
         FIG. 14  is a circuit diagram showing another electric power converter; 
         FIG. 15  is a circuit diagram showing further another electric power converter; 
         FIGS. 16A and 16B  are diagrams showing waveforms of output voltages; 
         FIG. 17  is a diagram showing a solar power conditioner according to a second embodiment; 
         FIG. 18  is a diagram showing an output waveform in main parts; 
         FIG. 19  is a diagram showing a solar power conditioner according to a third embodiment; 
         FIG. 20  is a diagram showing an output waveform in main parts according to the third embodiment; 
         FIG. 21  is a diagram showing a shaping way of a waveform; 
         FIG. 22  is a diagram showing a solar power conditioner according to a fourth embodiment; 
         FIG. 23  is a diagram showing an output waveform in main parts according to the fourth embodiment; 
         FIGS. 24A and 24B  are diagrams showing a control method of a normal waveform when an output electric power in a panel group is changed temporally; 
         FIG. 25  is a diagram showing a solar power conditioner according to a fifth embodiment; 
         FIG. 26  is a diagram showing a solar power conditioner according to a modification of the fifth embodiment; and 
         FIG. 27  is a diagram showing a solar power conditioner according to a sixth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
     A first embodiment will be explained with reference to  FIGS. 1 to 16 . A solar power conditioner  1  in  FIG. 1  includes an electric power converter  3   a - 3   d  for converting a direct current electric power output from one of solar cell panels  2   a - 2   d  to an alternating current electric power household use and for sending a system. Each electric power converter  3   a - 3   d  is arranged in one of the solar cell panels  2   a - 2   d,  and disposed on a backside of the panel  2   a - 2   d.    
     The electric power converter  3   a  is connected to an input terminal of the solar cell panel  2   a.  Similarly, the electric power converter  3   b  is connected to an input terminal of the solar cell panel  2   b,  and the electric power converter  3   c  is connected to an input terminal of the solar cell panel  2   c.  The electric power converter  3   d  is connected to an input terminal of the solar cell panel  2   d.  The output sides of the electric power converters  3   a - 3   d  are connected in series with each other. 
       FIG. 1  shows the output sides of four electric power converters  3   a - 3   d  are connected in series with each other so that four step converters are connected. Alternatively, multiple step converters such as two step, three step or five step converters may be connected in series with each other. The number of steps is determined based on the output direct current voltage of each solar cell panel  2   a - 2   d  and an amplitude of a pseudo sine wave or an alternating current. A specific example of the determination of the number of steps will be explained later. 
     Each electric power converter  3   a - 3   d  is connected to one of the control circuits (i.e., synchronous controllers)  4   a - 4   d,  respectively. The control circuits  4   a - 4   d  are connected to each other via a communication line  5 . These control circuits  4   a - 4   d  synchronously control the electric power converters  3   a - 3   d  in a coordinated manner, respectively, so that each electric power converter  3   a - 3   d  outputs the electric power. In this case, since the electric power converters  3   a - 3   d  are connected in series with each other, the output voltage is output between the output terminals O 1 , O 2  under a condition that outputs from the converters  3   a - 3   d  are overlapped with each other. 
     The communication line  5  provides, for example, a network such as a CAN (controller area network) and a RS485 network. The solar power conditioner  1  may include the communication line  5  as necessary. For example, when the network is provided by a PLC (power line communication), the communication line  5  is not necessary in the conditioner  1 . 
     The output of the electric power converter  3   a  is connected to the output terminal O 1  of the conditioner  1 . The output of the electric power converter  3   d  is connected to the output terminal O 2  of the conditioner  1 . Thus, a total voltage of “VA+VB+VC+VD” of the electric power converters  3   a - 3   d  is output between the output terminals O 1 , O 2 . 
     In the present embodiment each output terminal O 1 , O 2  is connected to a reactor  6 ,  7  and a capacitor C as an AC filter so as to cut a high frequency component and to shape the waveform. The alternating current voltage output between the output terminals O 1 , O 2  via the AC filter  6 ,  7 , C. 
     The solar cell panels  2   a - 2   d  in  FIG. 1  include a crystal-type solar cell panel  8  shown in  FIG. 2 , a thin-film type solar cell panel  9  shown in  FIG. 3 , and the like. The crystal-type solar cell panel  8  in  FIG. 2  includes a solar cell element  10  having a side of several centimeters to several tens centimeters, which is mounted on a panel  11  having a side of one meter to several meters. On the other hand, the solar cell panel  9  in  FIG. 3  includes multiple thin-film type solar cell elements  13  mounted on a glass substrate  12 . 
     Each of the solar cell elements  10 ,  13  are always used as a combination of multiple elements  10 ,  13 , which are connected to each other. Thus, the solar cell element  10 ,  13  is rarely used alone. Since the element alone outputs a voltage about several hundreds millivolts at maximum, it is not suitable for large electric power supply. Thus, the elements  10 ,  13  are connected in series with each other so that the output voltage increases. Thus, the solar cell panel  8 ,  9  outputs the voltage about several volts to several tens volts. In the present embodiment, the solar cell panel  8 ,  9  is applied to the solar cell panels  2   a - 2   d.    
     The electric power converters  3   a - 3   d  may have the same circuit construction or different circuit constructions respectively. In the present embodiment the electric power converters  3   a - 3   d  have the same circuit construction. The circuit construction of the electric power converter  3   a  will be explained. Other circuit constructions of the electric power converters  3   b - 3   d  are the same. 
     As shown in  FIG. 4  of the circuit construction of the electric power converter  3   a,  the converter  3   a  includes a voltage conversion element  14  connected to the solar cell panel  2   a,  and a polarity conversion element  15  arranged on a later step from the voltage conversion element  14 . The voltage conversion element  14  includes a step up circuit having a reactor L 1 , a transistor M 1  and a diode D 1 . The transistor M 1  is a N channel type power MOSFET. The voltage conversion element  14  converts an output direct current voltage according to a pulse signal when the pulse signal is applied to a control terminal of the transistor M 1  from a control circuit  4   a.    
     The resistor R 1  shown in  FIG. 4  provides a current detector for measuring an output current of the solar cell panel  2   a.  The resistor R 2  provides a voltage detector for measuring an output voltage of the solar cell panel  2   a.  According to detection signals from the voltage detector and the current detector, the control circuit  4   a  executes the MPPT control. For example, the control circuit  4   a  controls the duty ratio and/or the cycle of the pulse signal to be applied to the control terminal of the transistor M 1 . 
       FIG. 5  shows a characteristic of a general solar cell panel between an electric power P and a voltage V. When the output operation voltage increases, the output electric power also increases. After the output operation voltage reaches a predetermined voltage, the current supply amount is reduced and therefore, the output electric power is also reduced. Accordingly, as shown in  FIG. 5 , the electric power P reaches the maximum electric power Pz at the maximum output operation voltage Vz. 
     In the present embodiment, the control circuit  4   a  varies temporally the duty ratio and/or the period of the pulse signal to be applied to the control terminal of the transistor M 1  so that the control circuit  4   a  executes a MPPT (maximum power point tracking) control in order to set the output voltage of each solar cell panel  2   a - 2   d  to be the maximum output operation voltage Vz or a near value thereof. Thus, the generated electric power of the solar cell panel  2   a  is effectively obtained. 
       FIGS. 6 and 7  show examples of a pulse signal for executing the control to be applied to the control terminal of the transistor M 1 .  FIG. 6  shows an example of the pulse width modulation (PWM) signal having a constant cycle T and various pulse widths tw 1 , tw 2 , tw 3  and so on.  FIG. 7  shows a pulse frequency modulation (PFM) signal having a constant pulse width tw and various frequencies T 1 , T 2 , T 3  and so on. 
     In general, when the rising edge waveform and the falling edge waveform are smoothed with using the soft switching technique, the constant pulse width tw or the varied pulse widths wt 1 , tw 2 , tw 3  are set to be equal to or larger than a predetermined value. Thus, in this case, the pulse frequency modulation signal having the constant pulse width tw may be used. Here, when the load is small, it is necessary to control=the frequency lower than a predetermined value. In this case, the pulse width modulation signal may be used and the signal has the constant frequency in a non audible frequency range, not in an audible range. For example, the constant frequency is set to be slightly higher than 20 kHz. Here, the audible range represents the frequency smaller than 20 kHz. 
     The maximum output electric power of the solar cell panel  2   a  is varied according to the influence of solar radiation intensity, which depends on weather, solar altitude, shadow and the like. Accordingly, the control circuit  4   a  detects the voltage and the current with using the resistors R 1 , R 2  so that the electric power is monitored. Thus, the control circuit  4   a  controls the panel  2   a  to obtain the maximum electric power. Here, a capacitor (not shown) may be arranged between the output nodes N 1 , N 2 . Alternatively, the capacitor may not be arranged between the output nodes N 1 , N 2 . 
     The polarity conversion element  15  includes transistors M 2  to M 5 . These transistors M 2 -M 5  provide a full bridge connection having four N channel power MOSFETs. In  FIG. 4 , when the control circuit  4   a  controls the transistor M 2  to turn off, the transistor M 3  to turn on, the transistor M 4  to turn on and the transistor M 5  to turn off, the positive polarity voltage is output between the output terminals O 1   a,  O 2   a.  Further, when the control circuit  4   a  controls the transistor M 2  to turn on, the transistor M 3  to turn off, the transistor M 4  to turn off and the transistor M 5  to turn on the negative polarity voltage is output between the output terminals O 1   a,  O 2   a.  Although the output terminals O 1   a,  O 2   a  are not shown in  FIG. 1 , the electric power converters  3   a - 3   d  outputs the voltages VA-VD between output terminals O 1   a,  O 2   a,  respectively. 
     When the control circuits  4   a  controls the transistors M 3 , M 5  to turn on and the transistors M 2 , M 4  to turn off, the electric power converters  3   a - 3   d  outputs almost zero volt between output terminals O 1   a,  O 2   a,  respectively. Accordingly, the converter  3   a  can output the pulse voltage having the positive polarity or the pulse voltage having the negative polarity between the output terminals O 1   a,  O 2   a.    
     When the control circuits  4   a - 4   d  control the transistors M 1 -M 5  to turn on and off, each electric power converter  3   a - 3   d  outputs a voltage shown in  FIG. 8 . Here, in a time domain defined by a cross-out box (i.e., in a time domain defined as ( 1 ), ( 2 ), ( 3 ), ( 5 ), ( 6 ) and ( 8 )), at least one of the transistors M 2 -M 5  is controlled to switch on and of so that a part of the voltage having a pseudo sine waveform is output. 
     In a time domain sandwiched between the cross-out boxes (i.e., in a time domain defined as ( 4 ) and ( 7 )), the pulse voltage having the positive or negative polarity and a constant voltage in a predetermined time interval is output. 
     For example, the output voltage VA of the electric power converter  3   a  is switched between zero volt and the positive amplitude voltage of +VA 1  at high speed in the time domain defined as ( 1 ). Then, the output voltage VA is set to be zero. After that, the output voltage VA is switched between zero volt and the negative amplitude voltage of −VA 2  at high speed in the time domain defined as ( 2 ). Thus, in the time domains defined as ( 1 ) and ( 2 ), the electric power converter  3   a  outputs the pulse voltage having the cycle shorter than the pulse voltage in the time domain defined as ( 4 ) or ( 7 ). 
     The output voltage VB of the electric power converter  3   b  is switched between zero volt and the positive amplitude voltage of +VB 1  at high speed in the time domain defined as ( 3 ) so that the converter  3   b  outputs the short pulse voltage. Just after that, the converter  3   b  outputs the pulse voltage having the constant voltage of the positive amplitude voltage of +VB 1  for a predetermine time interval, which is defined as the time domain of ( 4 ). Specifically, the predetermined time interval is equal to the short pulse voltage output period of the converter  3   a,  i.e., the time domain defined as ( 1 ). Just after that, the output voltage VB of the electric power converter  3   b  is switched between zero volt and the positive amplitude voltage of +VB 1  at high speed in the time domain defined as ( 5 ) so that the converter  3   b  outputs the short pulse voltage. Then, the output voltage VB is set to be zero. 
     After that, the output voltage VB is switched between zero volt and the negative amplitude voltage of −VB 2  at high speed in the time domain defined as ( 6 ) so that the converter  3   b  outputs the short pulse voltage for the pseudo sine wave. Just after that, the converter  3   b  outputs the pulse voltage having the constant voltage of the negative amplitude voltage of −VB 2  for a predetermine time interval, which is defined as the time domain of ( 7 ). Specifically, the predetermined time interval is equal to the short pulse voltage output period of the converter  3   a,  i.e., the time domain defined as ( 2 ). Just after that, the output voltage VB of the electric power converter  3   b  is switched between zero volt and the negative amplitude voltage of −VB 2  at high speed in the time domain defined as ( 8 ) so that the converter  3   b  outputs the short pulse voltage for the pseudo sine wave. Thus, the converter  3   b  outputs the pulse voltage and the short pulse voltage. Further, as shown in  FIG. 8 , the converters  3   c,    3   d  also output the pulse voltage and the short pulse voltage as the output voltages VC, VD, respectively. 
     The power conditioner  1  superimposes in series and synchronizes the output voltages VA-VD between the output terminals O 1   a,  O 2   a  of the electric power converters  3   a - 3   d  so that the conditioner  1  outputs the pseudo sine wave. Thus the conditioner  1  outputs the alternating current voltage having almost the sine waveform between the output terminals O 1 , O 2  via the AC filter, provided by the reactors  6 ,  7  and the capacitor C. 
       FIG. 9  shows an on/off control method of the transistor in the electric power converter. When the electric power converter  3   n  outputs the pulse voltage and the short pulse voltage having the amplitude of the positive amplitude voltage of +VN 1  as the output voltage VN, as shown on a left side of  FIG. 9 , the transistors M 2 , M 5  turn off, the transistor M 4  turns on, and the transistor M 3  switches between the on state and the off state so that the converter  3   n  executes the switching control. Here, the suffix “n” represents one of “a,”“b,”“c,” and “d,” and the suffix “N” represents one of “A,”“B,”“C,” and 
     For example, in the time domain of ( 3 ) and ( 5 ), the converter  3   n  outputs the short pulse voltage having the output voltage VN between zero volt and the positive amplitude voltage of +VN 1 . Under a condition that the transistors M 2 , M 5  are in the off state, and the transistor M 4  is in the on state, the transistor M 3  switches between the on state and the off state at high speed. 
     In the time domain of ( 4 ), when the converter  3   n  outputs the short pulse voltage between zero volt and the positive amplitude voltage of +VN 1  as the output voltage VN, the transistors M 1 , M 5  turn off, the transistor M 4  turns on, and the transistor M 3  turns on and off at high speed. In this case, the output voltage of the transistor M 3  provides a part of the pseudo sine wave in the time domains of ( 3 ) and ( 5 ). Accordingly, in the time domain of ( 3 ), as time elapses from the starting time to the ending time of the time domain of ( 3 ), the on time width is gradually enlarged. In the time domain of ( 5 ), as time elapses from the starting time to the ending time of the time domain of ( 5 ), the on time width is gradually reduced. 
     When the electric power converter  3   n  outputs the pulse voltage and the short pulse voltage having the amplitude of the negative amplitude voltage of −VN 2  as the output voltage VN, as shown on a right side of  FIG. 9 , the transistors M 3 , M 4  turn off, the transistor M 2  turns on, and the transistor M 5  switches between the on state and the off state at high speed. 
     In this case, the output voltage of the transistor M 5  provides a part of the pseudo sine wave in the time domains of ( 6 ) and ( 8 ). Accordingly, in the time domain of ( 6 ), as time elapses from the starting time to the ending time of the time domain of ( 6 ), the on time width is gradually enlarged. In the time domain of ( 8 ), as time elapses from the starting time to the ending time of the time domain of ( 8 ), the on time width is gradually reduced. 
     For example, when the control circuits  4   a - 4   d  execute the synchronization control with using the converters  3   a - 3   d,  so that the pseudo sine wave is generated to provide the alternating current voltage having the frequency of 50 Hz as a target signal, the one cycle of the pseudo sine wave is 20 micro seconds. Accordingly, each converter  3   a - 3   d  outputs the pulse positive voltage or the pulse negative voltage having one cycle of a few micro seconds, which is shorter than 20 micro seconds. The pulse positive voltages or the pulse negative voltages from the converters  3   a - 3   d  are superimposed in series and synchronized according to the control manner of the control circuits  4   a - 4   d.    
     Each control circuit  4   a - 4   d  as a controller controls one of the electric power converters  3   a - 3   d,  respectively. In this case, one control circuit  4   a - 4   d  communicates with another control circuit  4   a - 4   d,  which is connected to the one control circuit  4   a - 4   d  via the communication line  5  so that the one control circuit  4   a - 4   d  controls the conversion electric power of one electric power converter  3   a - 3   d.  Accordingly, the one control circuit  4   a - 4   d  can conform the electric power conversion condition of other control circuits  4   a - 4   d,  and the one control circuit  4   a - 4   d  adjusts the electric power conversion condition of the electric power converter  3   a - 3   d  in the one control circuit  4   a - 4   d.  Thus the electric power conversion efficiency is improved. 
     (First Control Method) 
     As shown in  FIG. 10A , the electric power converter  3   n  may change the positive amplitude voltage +VN 1  as the output voltage VN. Alternatively, the electric power converter  3   n  may change the negative amplitude voltage −VN 2  as the output voltage VN so that the converter  3   n  converts the electric power. As shown in  FIG. 10B , the electric power converter  3   n  may change the time width Twa, in which the converter  3   n  executes high speed switching control when the converter  3   n  outputs the short pulse voltage. Alternatively, the converter  3   n  may change a total time width Twb of outputting the pulse voltage and the short pulse voltage. 
     When the converter  3   n  actually controls the output voltage, the converter  3   n  may set the time width Twa and/or the-total time width Twb to be constant, and the converter  3   n  may change the amplitude voltage of +VN 1  and −VN 2 , so that the converter  3   n  converts and outputs the output voltage. Alternatively, the converter  3   n  may set the amplitude voltage of +VN 1  and −VN 2  to be constant, and the converter  3   n  may change the time width Twa and/or the total time width Twb, so that the converter  3   n  converts and outputs the output voltage. Thus, since the number of parameters to be adjusted is reduced control circuit  4   n  easily controls the converter  3   n.    
     (Second Control Method) 
       FIG. 11  shows a second control method of the converter  3   n  when the sun light shines on only the solar cell panels  2   c,    2   d,  and does not shine on the solar cell panels  2   a,    2   b.  In this case, the converters  3   a,    3   b  does not substantially output the generated electric power, but the converters  3   c,    3   d  output the generated electric power. Thus, even if the generated electricity by the converters  3   a,    3   b  is reduced, the converters  3   c,    3   d  generate the electricity. Thus, the generated electric power by the converters  3   c,    3   d  is shaped to be a part of the pseudo sine wave voltage, and then, the shaped electric power of each converter  3   c    3   d  is superimposed in series so that the voltage is output. 
     In the above case, the voltage between ends of the resistor R 1 , R 2  is measured so that the voltage and the current in the solar cell panel  2   a - 2   d  are detected. Thus, based on the voltage and the current in the panel  2   a - 2   d,  it is determined whether the sun light is blocked, i.e., whether the panel is in the light interception state. When a light interception detection circuit detects the light interception, only the panel, in which the circuit does not detect the light interception, may convert the output voltage. In this case, the voltage conversion element  14  and the polarity conversion element  15  corresponding to the solar cell panel, in which the circuit detects the light interception, may not be operated, and only the electric power conversion portion corresponding to the solar cell panel, in which the circuit does not detect the light interception, may be operated. In this case, the switching loss of the transistors M 1 -M 5  for providing the voltage conversion element  14  and the polarity conversion element  15  is reduced, so that the electric power conversion efficiency is improved. Thus, the alternating current voltage between the output terminals O 1 , O 2  having a sine waveform is output. 
     (Third Control Method) 
       FIG. 12  shows a third control method of the converter  3   n.  In  FIG. 12 , only the electric power converter  3   a  among the converters  3   a - 3   d  outputs the short pulse voltage. Accordingly, in the other converters  3   b - 3   d,  each transistor M 2 -M 5  is switched so that the transistor M 2 -M 5  outputs the pulse voltage as a constant voltage in predetermined time interval. Thus, the functions of the converters  3   a - 3   d  are preliminary determined such that the converter  3   a  outputs the short pulse voltage, and the converters  3   b - 3   d  output the pulse voltage. Thus, when the transistors in only a part of the converters  3   a - 3   d  execute the high speed switching operation, it is not necessary to prepare a complicated control method. The alternating current voltage between the output terminals O 1 , O 2  having a sine waveform is output. 
     (Fourth Control Method) 
       FIG. 13  shows a fourth control method of the converter  3   n.  The pulse voltage output time width twa 1  of the positive amplitude voltage of +VA 1  may be different from the pulse voltage output time width twa 2  of the negative amplitude voltage of −VA 2 . 
     The relationship between the pulse voltage output time widths twb 1 , twb 2  in the converter  3   b,  the relationship between the pulse voltage output time widths twc 1 , twc 2  in the converter  3   c  and the relationship between the pulse voltage output time widths twd 1 , twd 2  in the converter  3   d  are also the same as the above relationship between the pulse voltage output time widths twa 1 , twa 2  in the converter  3   a.  Specifically, based on the control of the control circuits  4   a - 4   d,  all of the output voltages VA-VD of the converters  3   a - 3   d  are superimposed so that the pseudo sine wave is obtained. Thus, the alternating current voltage between the output terminals O 1 , O 2  having a sine waveform is output. 
     (First Modification) 
       FIG. 14  shows an electric power converter  23   a  instead of the converter  3   a  as a modification of the electric power converter. The converter  23   a  includes a voltage conversion element  24  and the polarity conversion element  15 . 
     The voltage conversion element  24  includes a capacitor C 1 , a transformer L 2  and a transistor M 1  into which the solar cell panel  2   a  outputs an electric power. The capacitor C 1  is connected to an output side of the panel  2   a.  A primary side of the transformer L 2  and a series circuit of the transistor M 1  are connected between both ends of the capacitor C 1 . A secondary side of the transformer L 2  is connected to a diode D 1  for rectification, and further connected to the polarity conversion element  15  after the diode D 1 . Accordingly, the voltage conversion element  24  is provided by an input/output isolation type circuit. When the transistor M 1  is operated to execute an on/off control, the maximum electric power point is searched, and the output of the element  24  is controlled. The polarity conversion element  15  on a latter step of the voltage conversion element  24  converts the polarity of the output voltage, so that the converter  23   a  outputs a part of the pseudo sine wave between the output terminals O 1   a,  O 2   a.    
     (Second Modification) 
       FIG. 15  shows an electric power converter  33   a  instead of the converter  3   a  as a modification of the electric power converter. The converter  33   a  includes a voltage conversion element  34  and the polarity conversion element  15 . The capacitor C 1  is connected between terminals of the solar cell panel  2   a.  Further, the transistors M 2 , M 3  of the polarity conversion element  15  are connected in parallel to the capacitor C 2 . 
     The voltage conversion element  34  includes transistors M 6 , M 7  connected in series between both ends of the capacitor C 1 , transistors M 8 , M 9  connected in series with the capacitor C 2 , and a reactor L 3  between a first common connection point and a second common connection point. The first common connection point is disposed between the transistors M 6 , M 7 , and the second common connection point is disposed between the transistors M 8 , M 9 . 
     The control circuit  4   a  controls the transistors M 6 -M 9  to turn on and off, so that the output electric power of the solar cell panel  2   a  is accumulated in the reactor L 3  temporally. The voltage and the current of the accumulated electric power in the reactor L 3  is converted, and then, the converted power is input into the polarity conversion element  15 . The polarity conversion element  15  converts the positive polarity and the negative polarity, and then, the element  15  outputs a part of the pseudo sine wave between the output terminals O 1   a,  O 2   a.  In this case, the output voltage of the solar cell panel  2   a  can be controlled to increase and to decrease. Thus, the voltage is much stabilized. 
       FIG. 16  shows a waveform of the output voltage. The time interval t 1 , t 2 , during which the electric power converter  3   n  does not output the voltage, exists between the switching operations of each transistor M 6 -M 9 . Since the capacitors C 1 , C 2  are attached to the electric power converter  33   a  in  FIG. 15 , the converter  33   a  can output the pulse voltage and the short pulse voltage just after the time interval t 1 , t 2 . Alternatively, the converter  33   a  may not include the capacitors C 1 , C 2 . Alternatively, the converter  33   a  may include only one of the capacitors C 1 , C 2 . Alternatively, the converter  3   a  shown in  FIG. 4  and the converter  23   a  shown in  FIG. 14  may include the capacitors C 1 , C 2 , which are arranged at the same position as in  FIG. 15 . 
     In the above embodiment, each solar cell panel  2   a - 2   d  includes one electric power converter  3   a - 3   d.  The converter  3   a - 3   d  follows the maximum electric power point of the output voltage from the panel  2   a - 2   d.  Therefore, the electric power conversion efficiency is much improved. Further, the dimensions of the AC filter  6 ,  7  connected between the output terminals O 1 , O 2  is minimized. 
     Since each converter  3   a - 3   d  includes one polarity conversion element  15 , each converter  3   a - 3   d  can convert the positive polarity and the negative polarity of the pulse voltage. Thus, the control circuit  4   a - 4   d  can execute the waveform shaping process with high degree of freedom. 
     Second Embodiment 
       FIG. 17  shows a solar power conditioner according to a second embodiment. The differences between the second embodiment and the above first embodiment are such that only one polarity conversion element is arranged in the conditioner, the polarity conversion element corresponding to all of the voltage conversion elements, and being arranged on the latter step of the voltage conversion element. The conditioner according to the present embodiment will be explained with using the construction of the conditioner according to the second modification of the first embodiment. Specifically, the conditioner according to the present embodiment includes the voltage conversion element  34  and the polarity conversion element  15 . In the following explanation, the suffix “a” to “d” is added to the voltage conversion element  34 , the transistor M 6 -M 9  and the capacitor C 1 . 
     As shown in  FIG. 17 , a secondary side of each voltage conversion element  34   a - 34   d  is connected in series with each other. A voltage obtained by a series connection of the voltage conversion elements  34   a - 34   d  is totally input into the polarity conversion element  15 . The polarity conversion element  15  is connected to the control circuit  4   e.  The control circuit  4   e  sets the control signal to be applied to the transistors M 2 -M 5  in the polarity conversion element  15  in accordance with the detection voltage between the series output terminals O 3 , O 4 . The polarity conversion element  15  converts polarity of the input voltage (i.e., the conversion voltage obtained by the series connection of the voltage conversion elements  34   a - 34   d ) and outputs the converted voltage. 
     When each control circuit  4   a - 4   d  controls the output voltage of the voltage conversion element  34   a - 34   d,  the voltage output shown in (a) of  FIG. 18  is obtained. Since each voltage conversion element  34   a - 34   d  outputs a part of the pseudo sine wave voltage having the positive polarity, when these output voltages are superimposed in series with each other, the voltage waveform (i.e., the positive polarity waveform of the pseudo sine wave) shown in (a) of  FIG. 18  is input into the polarity conversion element  15 . 
     The control circuit  4   a  reverses the polarity of the pseudo sine wave of the input voltage into the polarity conversion element  15  every half cycle. In this case, the control circuit  4   e  outputs the voltage with the positive polarity in a time domain of ( 9 ) in (a) and (b) of  FIG. 18 . In a time domain of ( 10 ), the control circuit  4   e  converts the voltage to the negative polarity. Further, in a time domain of ( 11 ), the control circuit  4   e  maintains the positive polarity, and outputs the positive polarity, voltage. The time domains of ( 9 ) to ( 11 ) are set according to the detection voltage between the output terminals O 3 , O 4 . Under this control, the polarity conversion element  15  outputs the pseudo sine wave. When the polarity conversion element  15  outputs the pseudo sine wave, the element  15  outputs the alternating current voltage between the output terminals O 3 , O 4  through the AC filter  6 ,  7 , C 3 . Alternatively, the voltage conversion element  14 ,  24  may be used as the voltage conversion element  34 . 
     Third Embodiment 
       FIG. 19  shows a solar power conditioner according to a third embodiment. The differences between the third embodiment and the above embodiments are such that a polarity conversion element is arranged on a latter step of each voltage conversion element. Further, one waveform shaping element is arranged on a latter step of all of the polarity conversion elements. 
     In the present embodiment, the voltage conversion element  14 , and the polarity conversion element  15  are used. In the following explanation, the suffix “a” to “d” is added to the voltage conversion element  14 , the polarity conversion element  15 , the transistor M 6 -M 9 , the reactor L 1 , the capacitor C 2 , the diode D 1  and the node B 1 , which are provided in each solar cell panel  2   a - 2   d    
     The voltage conversion element  14   a - 14   d  and the polarity conversion element  15   a - 15   d  according to the present embodiment are the same as the first embodiment. A voltage obtained by the series connection of the output of the polarity conversion elements  15   a - 15   d  is totally input into one waveform shaping element  40 . 
     The waveform shaping element  40  includes the transistors M 10 -M 13 , the capacitor C 4 , and the control circuit  4   f,  which is connected to the communication line  5 . The transistors M 10 -M 13  provide the full bridge connection. the capacitor C 4  is connected between a first common connection point and a second common connection point. The first common connection disposed between the transistors M 10 , M 12 , and the second common connection point is disposed between the transistors M 11 , M 13 . One terminal of a series connection circuit of the polarity conversion elements  15   a - 15   d  is connected to a common connection point between the transistors M 10 , M 11 . The other terminal of the series connection circuit is connected to an input node of the AC filter  6 ,  7 , C 3 . The voltage of the series connection circuit provides the input voltage of the waveform shaping element  40 . 
     The voltage conversion elements  14   a - 14   d  and the polarity conversion elements  15   a - 15   d  convert the voltage, so that the voltage waveform shown in (a) of  FIG. 20  is obtained. Here, the pulse voltage waveform in (a) of  FIG. 20  is the pulse voltage (i.e., the single pulse rectangular wave) having the constant voltage in a predetermined time interval. The input voltage of the waveform shaping element  40  provides a stepwise voltage, which is prepared by superimposing the pulse voltage having the single pulse rectangular wave. 
     As shown in  FIG. 21 , the waveform shaping element  40  accumulates the electricity in the capacitor C 4 , the electricity being prepared based on the rising edge rectangular voltage of the pulse voltage (i.e., the single pulse rectangular wave) in the stepwise voltage as the input voltage. Further, the element  40  adds the voltage just after the accumulation so that the element  40  shapes a voltage to be a target alternating current voltage waveform. When the waveform shaping element  40  detects the rising voltage of the pulse voltage as the single pulse rectangular wave, the transistors M 10 , M 13  turn on, and the transistors M 11 , M 12  turn off, so that the electricity is stored in the capacitor C 4 . then, when the element  40  detects reduction of the voltage waveform gradient, the transistors M 10 , M 13  turn off, and the transistors M 11 , M 12  turn on, so that the electricity is discharged to the output side, and the voltage is added to the latter voltage in order to approximate the alternating current voltage waveform as a target voltage waveform. Thus, as shown in (b) of  FIG. 20 , the alternating current voltage is obtained between the output terminals O 5 , O 6 . 
     Fourth Embodiment 
       FIGS. 22 to 24  show a solar power conditioner according to a fourth embodiment. The circuit construction according to the present embodiment is provided by a combination of the second and third embodiments. 
     As shown in  FIG. 22 , an output from a circuit, which is provided by the series connection of all of the voltage conversion elements  34   a - 34 , is inputted into the polarity conversion element  15 . As shown in (a) of  FIG. 23 , when the stepwise voltage having the positive polarity is input into the polarity conversion element  15 , the polarity conversion element  15  converts the polarity to the negative polarity every half cycle, as shown in (b) of  FIG. 23 . After the waveform shaping element  40  shapes the waveform, the polarity conversion element  15  outputs the voltage between the output terminals O 7 , O 8  via the AC filter  6 ,  7 , C 3 . Thus, the alternating current voltage shown in (c) of  FIG. 23  is obtained. 
       FIGS. 24A and 24B  show an example of a control method when the output electricity from the solar cell panel is changed temporally under a condition that the MPPT control is executed.  FIG. 24A  shows a waveform in a normal time, and  FIG. 24B  shows a waveform when the electricity generation of the solar cell panels  2   c,    2   d  is zero. In  FIGS. 24A and 24B , the pulse width of the pulse voltage as the single pulse rectangular wave is fixed, and the voltage amplitude of the single pulse rectangular wave is controlled to increase and decrease. 
     Specifically, in, the normal time, when the voltage conversion elements  34   a - 34   d  execute the MPPT control according to the control signals of the control circuits  4   a - 4   d,  respectively, the amplitude of the pulse voltage is controlled to increase and decrease under a condition that the pulse width of the pulse voltage as the single pulse rectangular wave is set to be a predetermined width. Thus, the maximum electricity of each solar cell panel  2   a - 2   d  is obtained according to the MPPT control. 
     For example, when the weather is suddenly changed, and only the light receiving regions of the solar cell panels  2   c,    2   d  are shadowed, the electricity generation of the solar cell panels  2   c,    2   d  is almost zero. In this case, since the electricity generation of the solar cell panels  2   a,    2   b  is not changed, the voltage conversion elements  34   a,    34   b  functions to maintain the maximum electricity point of the solar cell panels  2   a,    2   b.  In accordance with the operation of the MPPT control, the voltage conversion elements  34   a,    34   b  automatically increase the output. 
     The reason of the above operation is as follows. The voltage conversion elements  34   a,    34   b  accumulate the generated electricity of the solar cell panels  2   a,    2   b  temporarily in the reactor. L 3   a,  L 3   b,  respectively. Then, the elements  34   a,    34   b  discharges the electricity to the output side. Since the energy accumulated in the reactors L 3   a,  L 3   b  is controlled by the MPPT control method, the energy corresponding to the maximum electricity of the solar cell panels  2   a    2   b  is accumulated. When the MPPT control is executed, the voltage conversion elements  34   a,    34   b  maintain the maximum electricity point. Thus, accumulated energy in the reactor L 3   a,  L 3   b  is discharged. Since the voltage conversion elements  34   a,    34   b  discharges the accumulated electricity, the elements  34   a,    34   b  automatically increases the voltage and decrease the current at the output side. Thus, the electricity is output between the output terminals O 7 , O 8  through the polarity conversion element  15 , the waveform shaping element  40  and the AC filter  6 ,  7 , C 3 , and the pseudo sine wave is shaped based on only the generated electricity of the solar cell panels  2   a,    2   b,  as shown in (b) of  FIG. 24 . 
     Here, the control circuits  4   a,    4   b  may independently control the electricity generation of the solar cell panels  2   a - 2   b  with the MPPT control method. Alternatively, the control circuits  4   a,    4   b  may execute the MPPT control with receiving the information about the electricity generation amount successively from the control circuits  4   c,    4   d,  which are connected to the control circuits  4   a,    4   b  via the communication line  5 . Accordingly, even if only the light receiving regions of the solar cell panels  2   c,    2   d  is shadowed, the electricity generation performance of the solar cell panels  2   a,    2   b  is maintained, and the control circuits  4   a,    4   b  execute the MPPT control, so that the pseudo sine wave is shaped. 
     Fifth Embodiment 
       FIGS. 25 and 26  show a solar power conditioner according to a fifth embodiment. A difference between the present embodiment and the above embodiments is such that multiple solar cell panels are connected in series with each other, and the panel group is arranged in each electric power converter. Further, one polarity conversion element and one waveform shaping element are arranged at a whole of the series connection of multiple electric power converters. Furthermore, multiple electric power converters are integrated into one unit in accordance with multiple panel groups. 
     As shown in  FIG. 25 , the solar cell panels  2   a  provide the panel group  2 A, and panels  2   a  are connected in series with an input terminal of the voltage conversion element  34   a.  Similarly, each of the panels  2   b - 2   d  are connected in series with an input terminal of the voltage conversion element  34   b - 34   d,  so that the panels  2   b - 2   d  provide the panel group  2 B- 2 D. 
     As described in the above embodiments, the solar cell panel  2   a  generates the DC voltage of a few volts to a few tens volts. For example, four voltage conversion elements  34   a - 34   d  are connected in series with each other, so that a target alternating current voltage is set to be the output of the 200 VAC system. The maximum amplitude of the target alternating current voltage is calculated by multiplying 200 and a square root of 2, so that the maximum amplitude is 282.8 volts. Thus when one panel of the solar cell panel  2   a  outputs the direct current voltage of 15 volts, five panels of each solar cell panel  2   a - 2   d  are connected in series with each other, the solar cell panel  2   a - 2   d  connecting to the input terminal of the voltage conversion element  34   a - 34   d.    
     Specifically, one electric power converter  3   a  outputs the voltage of 75 volts which is calculated by multiplying 15 as the series voltage of one panel and 5 as the number of panels. When four electric power converters  3   a - 3   d  are connected in series with each other, the output voltage is calculated by multiplying 75 volts and four as the number of converters, so that the output voltage is 300 VDC. Thus, it is sufficient to secure the voltage larger than 282.8 volts. 
     In the present embodiment, the apparatus Pa includes the voltage conversion elements  34   a - 34   d,  the polarity conversion element  15 , the waveform shaping element  40  and the control circuits  4   a - 4   d,    4   g,  which are integrated into one unit. Thus, the apparatus Pa outputs the pseudo sine wave between the output terminals O 7 , O 8  when the panel groups  2 A- 2 D are connected. For example, as shown in  FIG. 8 , the voltage conversion elements  34   a - 34   d  cooperate with each other and output the pseudo sine wave so that the output voltages VA-VD of the electric power converters  34   a - 34   d  are obtained. 
     When the apparatus Pa has the electric construction in  FIG. 25 , the control circuits  4   a - 4   d,    4   g  cooperate with each other, and the voltage conversion elements  34   a - 34   d  output the voltage. When the circuits  4   a - 4   d,    4   g  execute the cooperation control, the circuits  4   a - 4   d,    4   g  can execute a parallel process. The control circuit for managing these controls is preliminary determined. The managing control circuit mainly executes a whole of the controls. When the apparatus Pa is the integrated one unit according to the present embodiment, the control circuit  4   g  for controlling the waveform shaping element  40  and the polarity conversion element  15  at the last step may be the managing control circuit. 
     The reason why the control circuit  4   g  is the managing control circuit is as follows. Since the control circuit  4   g  detects the voltage between the output terminals O 7 , O 8  so that the control circuit  4   g  executes the feedback control, the control circuit  4   g  can input the control instructions into the control circuits  4   a - 4   d,  respectively, and further, the control circuit  4   g  easily shapes the waveform of the output voltage of each voltage conversion element  34   a - 34   d.    
     Further, as shown in  FIG. 26 , alternatively, a monitor  41  may be arranged independently from the control circuit  4   g.  The monitor  41  is connected to the communication line  5 , so that the monitor  41  detects the voltage between the output terminals O 7 , O 8 . Further, the monitor  41  transmits the detection voltage information to each control circuit  4   a - 4   d,    4   g.  The monitor  41  may provide the function of the managing control circuit. In this case, the monitor  41  outputs the managing control information to each control circuit  4   a - 4   d,    4   g,  so that each control circuit  4   a - 4   d,    4   g  can execute the control according to the managing control information. In the present embodiment, since the control circuit  4   g  or the monitor  41  manages the conversion electricity of multiple electric power converters  3   a - 3   d,  the electric power conversion efficiency is improved. 
     Sixth Embodiment 
       FIG. 27  shows a solar power conditioner according to a sixth embodiment. In the first embodiment, two reactors  6 ,  7  are arranged for a whole output of the solar power conditioner  1 . In the solar power conditioner  1   a  in  FIG. 27 , each electric power converter  43   a - 43   d  provide the electric construction of the electric power converter  3   a - 3   d.  Each reactor La-Ld and each capacitor Ca-Cd may be arranged after the output of the electric power converter  3   a - 3   d.  In this case, the solar power conditioner is outputs the pseudo sine wave, and further outputs the target alternating current voltage between the output terminals O 1 , O 2 . 
     While the present disclosure has been described with reference to embodiments thereof, it is to be understood that the disclosure is not limited to the embodiments and constructions. The present disclosure is intended to cover various modification and equivalent arrangements. In addition, while the various combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the present disclosure.