Abstract:
A control method of a solar inverter system includes calculating total output power outputted by a first inverter and a second inverter; determining whether the total output power is less than a threshold value; and executing a corresponding operation according to a determination result.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a solar inverter system and a control method, and particularly to a solar inverter system and a control method that can utilize a controller to control output power of inverters included in the solar inverter system to increase efficiency of the solar inverter system and decrease harmonic distortion of the solar inverter system. 
         [0003]    2. Description of the Prior Art 
         [0004]    Generally speaking, when output power of an inverter is lower (e.g. the output power of the inverter is lower than 30% maximum output power of the inverter), efficiency and harmonic distortion of the solar inverter system including the inverter are worse. In a solar inverter system with multi-inverters, because total output power of the solar inverter system is evenly distributed to each inverter (that is, output power of each inverter is the same), output power of each inverter is much lower, resulting in efficiency and harmonic distortion of the solar inverter system with multi-inverters being much worse. Those skilled in the art can refer to U.S. Pat. No. 7,893,346 and U.S. Pat. No. 8,013,472. 
         [0005]    Therefore, in the solar inverter system with multi-inverters, the efficiency and the harmonic distortion of the solar inverter system with multi-inverters are usually worse than a solar inverter system with an inverter because each inverter of the solar inverter system with multi-inverters outputs the same power. 
       SUMMARY OF THE INVENTION 
       [0006]    An embodiment provides a control method of a solar inverter system. The solar inverter system includes a first inverter, a second inverter, and a controller. The first inverter and the second inverter are connected in parallel with an alternating current (AC) line network. The controller optionally controls the first inverter to output total output power alone, or controlling the first inverter and the second inverter to simultaneously output the total output power. The control method includes calculating the total output power outputted by the first inverter and the second inverter; determining whether the total output power is less than a threshold value; and executing a corresponding operation according to a determination result. 
         [0007]    Another embodiment provides a solar inverter system. The solar inverter system includes a first inverter, a second inverter, and a controller. The first inverter has a first input terminal and a first output terminal, where the first input terminal is coupled to a solar panel. The second inverter has a second input terminal and a second output terminal, where the second input terminal is coupled to the solar panel, and the first output terminal and the second output terminal are connected in parallel with an AC line network. The controller is coupled to the first inverter and the second inverter, where the controller is used for optionally controlling the first inverter to output total output power alone, or controlling the first inverter and the second inverter to simultaneously output the total output power. 
         [0008]    The present invention provides a solar inverter system and a control method thereof. The solar inverter system and the control method utilize a controller to calculate total output power of the solar inverter system, and determine whether the total output power of the solar inverter system is less than a threshold value. Then, when the total output power of the solar inverter system is less than the threshold value, the controller controls a first inverter to output the total output power of the solar inverter system alone; when the total output power of the solar inverter system is greater than the threshold value, the controller controls the first inverter and a second inverter to simultaneously output the total output power of the solar inverter system. Compared to the prior art, because efficiency and harmonic distortion of the solar inverter system is determined by an inverter (included in the solar inverter system) with greater output power, the solar inverter system provided by the present invention has better efficiency and lower harmonic distortion. 
         [0009]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a diagram illustrating a solar inverter system according to an embodiment. 
           [0011]      FIG. 2  is a diagram illustrating a solar inverter system according to another embodiment. 
           [0012]      FIG. 3  is a flowchart illustrating a control method of a solar inverter system according to another embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Please refer to  FIG. 1 .  FIG. 1  is a diagram illustrating a solar inverter system  100  according to an embodiment. The solar inverter system  100  includes a first inverter  102 , a second inverter  104 , and a controller  106 , where the first inverter  102  and the second inverter  104  are the same, but the first inverter  102  can be also different from the second inverter  104 . But, the present invention is not limited to the solar inverter system  100  only including the first inverter  102  and the second inverter  104 . That is to say, the solar inverter system  100  can include at least two inverters. The first inverter  102  has a first input terminal and a first output terminal, where the first input terminal is coupled to a solar panel  108 . The second inverter  104  has a second input terminal and a second output terminal, where the second input terminal is coupled to the solar panel  108 . As shown in  FIG. 1 , the first output terminal of the first inverter  102  and the second output terminal of the second inverter  104  are connected in parallel with an alternating current (AC) line network  112  through a sensor  110 , where the sensor  110  is used for sensing an AC current IAC and an AC voltage VAC generated by the first inverter  102  and the second inverter  104  converting a direct current voltage VDC of the solar panel  108 . In addition, the AC line network  112  has an AC frequency (e.g. 50 Hz or 60 Hz) and an AC voltage (e.g. 110V or 220V). The controller  106  is coupled to the first inverter  102 , the second inverter  104 , and the sensor  110 , where the controller  106  is used for calculating total output power of the solar inverter system  100  according to the AC current IAC and the AC voltage VAC. 
         [0014]    When the total output power of the solar inverter system  100  is less than a threshold value (that is, maximum output power of the first inverter  102 ), the controller  106  controls the first inverter  102  to output the total output power of the solar inverter system  100  alone; when the total output power of the solar inverter system  100  is greater than the threshold value, the controller  106  controls the first inverter  102  and the second inverter  104  to simultaneously output the total output power of the solar inverter system  100 , where output power of the first inverter  102  is equal to the maximum output power of the first inverter  102 , and output power of the second inverter  104  is equal to the total output power of the solar inverter system  100  minus the maximum output power of the first inverter. 
         [0015]    For example, the maximum output power of the first inverter is equal to 120 W. When the total output power of the solar inverter system  100  is 110 W, because the total output power (110 W) of the solar inverter system  100  is less than the threshold value (120 W), the controller  106  controls the first inverter  102  to output the total output power (110 W) of the solar inverter system  100  alone; when the total output power of the solar inverter system  100  is 130 W, because the total output power (130 W) of the solar inverter system  100  is greater than the threshold value (120 W), the controller  106  controls the first inverter  102  and the second inverter  104  to simultaneously output the total output power (130 W) of the solar inverter system  100 . Meanwhile, the output power of the first inverter  102  is equal to the maximum output power (120 W) of the first inverter  102 , and the output power of the second inverter  104  is equal to the total output power (130 W) of the solar inverter system  100  minus the maximum output power (120 W) of the first inverter  102 . That is to say, the output power of the second inverter  104  is equal to 10 W. 
         [0016]    In addition, in another embodiment of the present invention, the solar inverter system  100  further includes the sensor  110 . 
         [0017]    Please refer to  FIG. 2 .  FIG. 2  is a diagram illustrating a solar inverter system  200  according to another embodiment. A difference between the solar inverter system  200  and the solar inverter system  100  is that the controller  106  includes a counter  1062 , where the counter  1062  is used for counting a number of total output power of the solar inverter system  200  being greater than the threshold value (120 W) within a predetermined period. When the number is not greater than N (N is a positive integer), the controller  106  controls the first inverter  102  to output the total output power of the solar inverter system  200  alone; when the number is greater than N, the controller  106  controls the first inverter  102  and the second inverter  104  to simultaneously output the total output power of the solar inverter system  200 , where the output power of the first inverter  102  is equal to the maximum output power (120 W) of the first inverter  102 , and the output power of the second inverter  104  is equal to the total output power of the solar inverter system  200  minus the maximum output power (120 W) of the first inverter  102 . In addition, in another embodiment of the present invention, the solar inverter system  200  further includes the sensor  110 . In addition, subsequent operational principles of the solar inverter system  200  are the same as those of the solar inverter system  100 , so further description thereof is omitted for simplicity. 
         [0018]    Please refer to  FIG. 1 ,  FIG. 2 , and  FIG. 3 .  FIG. 3  is a flowchart illustrating a control method of a solar inverter system according to another embodiment. The method in  FIG. 3  is illustrated using the solar inverter system  100  in  FIG. 1 . Detailed steps are as follows: 
         [0019]    Step  300 : Start. 
         [0020]    Step  302 : The sensor  110  senses an AC current IAC and an AC voltage VAC outputted from the first output terminal of the first inverter  102  and the second output terminal of the second inverter  104 . 
         [0021]    Step  304 : The controller  106  calculates total output power of the solar inverter system  100  according to the AC current IAC and the AC voltage VAC. 
         [0022]    Step  306 : The controller  106  determines whether the total output power of the solar inverter system  100  is less than a threshold value; if yes, go to Step  308 ; if no, go to Step  310 . 
         [0023]    Step  308 : The controller  106  controls the first inverter  102  to output the total output power of the solar inverter system  100  alone; go to Step  306 . 
         [0024]    Step  310 : The controller  106  controls the first inverter  102  and the second inverter  104  to simultaneously output the total output power of the solar inverter system  100 ; go to Step  306 . 
         [0025]    In Step  306 , the threshold value is equal to the maximum output power of the first inverter  102 . In Step  308 , when the total output power of the solar inverter system  100  is less than the threshold value, the controller  106  controls the first inverter  102  to output the total output power of the solar inverter system  100  alone. For example, the maximum output power of the first inverter is equal to 120 W. when the total output power of the solar inverter system  100  is 110 W, because the total output power (110 W) of the solar inverter system  100  is less than the threshold value (120 W), the controller  106  controls the first inverter  102  to output the total output power (110 W) of the solar inverter system  100  alone. In Step  310 , when the total output power of the solar inverter system  100  is greater than the threshold value, the controller  106  controls the first inverter  102  and the second inverter  104  to simultaneously output the total output power of the solar inverter system  100 , where the output power of the first inverter  102  is equal to the maximum output power of the first inverter  102 , and the output power of the second inverter  104  is equal to the total output power of the solar inverter system  100  minus the maximum output power of the first inverter  102 . For example, when the total output power of the solar inverter system  100  is 130 W, because the total output power (130 W) of the solar inverter system  100  is greater than the threshold value (120 W), the controller  106  controls the first inverter  102  and the second inverter  104  to simultaneously output the total output power (130 W) of the solar inverter system  100 , where the output power of the first inverter  102  is equal to the maximum output power (120 W) of the first inverter  102 , and the output power of the second inverter  104  is equal to the total output power (130 W) of the solar inverter system  100  minus the maximum output power (120 W) of the first inverter  102 . That is to say, the output power of the second inverter  104  is equal to 10 W. 
         [0026]    In addition, in another embodiment of the present invention, in Step  306 , the controller  106  of the solar inverter system  200  determines whether a number (counted by the counter  1062 ) of total output power of the solar inverter system  200  being greater than the threshold value (120 W) within a predetermined period is greater than N (N is a positive integer). When the number is not greater than N, the controller  106  controls the first inverter  102  to output the total output power of the solar inverter system  200  alone; when the number is greater than N, the controller  106  controls the first inverter  102  and the second inverter  104  to simultaneously output the total output power of the solar inverter system  200 , where the output power of the first inverter  102  is equal to the maximum output power (120 W) of the first inverter  102 , and the output power of the second inverter  104  is equal to the total output power of the solar inverter system  200  minus the maximum output power (120 W) of the first inverter  102 . 
         [0027]    To sum up, the solar inverter system and the control method thereof utilize the controller to calculate total output power of the solar inverter system, and determine whether the total output power of the solar inverter system is less than a threshold value. Then, when the total output power of the solar inverter system is less than the threshold value, the controller controls the first inverter to output the total output power of the solar inverter system alone; when the total output power of the solar inverter system is greater than the threshold value, the controller controls the first inverter and the second inverter to simultaneously output the total output power of the solar inverter system. Compared to the prior art, because efficiency and harmonic distortion of the solar inverter system is determined by an inverter (included in the solar inverter system) with greater output power, the solar inverter system provided by the present invention has better efficiency and lower harmonic distortion. 
         [0028]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.