Abstract:
Solar energy is definitely the future trend of energy because it is a free, clean and environmentally friendly energy source that doesn&#39;t contribute to climate change. But due to current solar systems&#39; low efficiency, high cost, long battery charging time, and inadequate energy management, they are hardly popularized in the market. A solar energy system utilizing a Multi-Function Power Converter System (MFPCS) which can be operated as both solar energy converter system and high power battery charger/discharger system with a unique solar energy extension control method is remedy for these problems. This advanced solar energy generation system performs energy conversion and battery charging/discharging operations, such as interleaved multi-phase DC/DC converter operation, direct battery charging with solar power operation, and PWM rectifier battery charger operation. By utilizing high power super charger and single stage conversion techniques, it eliminates the major deficiencies of current solar energy generation systems in the prior art and features high battery charging efficiency, i.e. much shorter battery charging time comparing to current one (in minutes rather than hours), and intelligent solar energy management. As a result, it can maximize solar energy potential and minimize grid power usage effectively.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application 62/350,829 and hereby incorporates the application by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to solar energy systems utilizing battery super charger system, capable of maximizing solar energy usage by extending sun peak hour, such as but not limited to solar energy systems with built-in battery super charger and it&#39;s method. 
       BACKGROUND 
       [0003]    As the world&#39;s population increases, the demand for electric power usage also increases proportionally. Fossil fuels based electric power generation causes environmental pollution and degradation to global warming and the attendant climate change. Therefore it is necessary for humanity to resort the use of energy that is non-polluting, renewable and sustainable. Solar energy is one of the desirable types of renewable energy because it is a free, clean and environmentally friendly energy source that doesn&#39;t contribute to climate change. For years it has been touted as the most promising energy source for our increasingly industrialized society. 
         [0004]    The most popular application of solar energy is grid-connected solar system. It connects to the electric power grid. The two main components of such system are the solar modules and the solar power converter. A grid-connected solar power system, also called grid-tied system, has the main objective of extracting as much energy as possible from the solar modules when sunlight impinges on them while maintaining acceptable power quality, reliability and cost-competitiveness. However, achieving this objective is fraught with many challenges such as low conversion efficiency of the system, intermittency and variability nature of solar energy, Load variations and high cost of system. In order to mitigate the aforementioned problems, attempts have been made to produce an improved solar energy system. For example, adding an energy storage battery in such system mitigates some of these challenges, as it provides stored energy during nights, resulting in minimizing solar energy intermittency and variability effects and reducing customers&#39; utility bills. However, such systems still have general shortcomings and do not adequately address the aforementioned problems. 
         [0005]    The techniques disclosed in U.S. Pat. Application US 2011/0210694 A1 and U.S. Pat. No. 5,522,944 represent the prior art of solar energy system with storage battery technology. These systems suffer three major deficiencies: (1) low battery charging efficiency because it requires two stages of power conversions (DC-AC and AC-DC); (2) long battery charging time because its battery charger is limited to low power charger due to cost; the typical battery recharging time is in several hours compared to in several minutes by a high power charger; thus, it cannot charge or discharge storage battery several times during the day to maximize the solar energy use; even if a separate high power battery charger is installed with a high cost, it still has very low battery charging efficiency as indicated in (1) above; (3) lack of optimal energy management control method for varying load power because it cannot quickly charge/discharge storage battery several times during the day. Therefore, a solar energy system with a high power single stage battery super charger system along with optimal energy management control method is best solution for the future solar energy system. 
         [0006]    The object of this invention is to provide a solar energy conversion system with a built-in high power storage battery super charger/discharger system and an optimal energy management control method to maximize solar energy usage by extend sun peak hour resulting in consuming less grid power. 
       SUMMARY 
       [0007]    One non-limiting aspect of the present invention contemplates a solar energy converter with built-in high power storage battery charger/discharger to produce electricity, quickly charge/discharge storage battery, and maximize solar power usage comprising a solar power system architecture with a Multi-Function Power Conversion System (MFPCS), several operation switches, LCL filters plus a transformer, multiple DC inductors, a solar power source, a storage battery power source, an AC grid power source and numerous operation modes including an interleaved multi-phase super charger mode (Mode  1 ), a solar power generation plus direct battery charging mode (Mode  2 ), a solar power generation mode (Mode  3 ), a solar/storage battery discharger mode (Mode  4 ), and a PWM rectifier battery charger mode (Mode  5 ). 
         [0008]    One non-limiting aspect of the present invention contemplates a MFPCS to provide DC/AC, AC/DC, DC/DC power conversion hardware functions comprising a three phase IGBT module, a liquid cooled heatsink, a DC-link capacitor, a IGBT drive circuit card, a DSP interface circuit card, and a Texas Instrument (TI) DSP control Card. 
         [0009]    One non-limiting aspect of the present invention contemplates a TI DSP control Card to be responsible for power conversion and battery charging software control functions comprising a Mode  1  control library comprising interleaved multi-phase battery charging control algorithms, a Mode  2  control library comprising optimized solar power generation plus direct battery charging control algorithms, a Mode  3  control library comprising a three-phase solar power grid-tied inverter control algorithms, a Mode  4  control library comprising a three-phase solar/battery power grid-tied inverter control algorithms, and a Mode  5  control library comprising PWM rectifier battery charging control algorithms. 
         [0010]    One non-limiting aspect of the present invention contemplates a Mode  1  control library comprising an optimal solar power tracking means for regulating charging current of storage battery in constant current mode, a battery voltage control means for regulating charging voltage of storage battery in constant voltage mode, a multi-phase DC current control means for regulating DC currents of DC inductors, and an interleaved multi-phase PWM means for controlling three-phase IGBT module to convert solar power to storage battery power. 
         [0011]    One non-limiting aspect of the present invention contemplates a Mode  2  control library comprising a Maximum Power Point Tracking (MPPT) means to extract the maximum solar power, a DC voltage control means to regulate the output voltage of solar power, a battery charging power calculation means, a inverter power command generation means, a AC current reference generation means, a AC current control means, and a Space Vector Modulation (SVM) means to produce AC grid power plus directly charge storage battery. 
         [0012]    One non-limiting aspect of the present invention contemplates Mode  3  control library comprising a MPPT means, a DC voltage control means, a AC current reference generation means, a AC current control means, and a SVM means to convert solar power to AC grid power. 
         [0013]    One non-limiting aspect of the present invention contemplates Mode  4  control library comprising an active power control means, a AC current reference generation means, a AC current control means, and a SVM means to convert both solar power and storage battery power to AC grid power. 
         [0014]    One non-limiting aspect of the present invention contemplates Mode  5  control library comprising a battery voltage control means and a battery current control means to control charging voltage and current of storage battery power source, a AC current reference generation means, a AC current control means, and a SVM means to convert AC grid power to storage battery power. 
         [0015]    One non-limiting aspect of the present invention contemplates an interleaved multi-phase battery charging control algorithms in Mode  1  control library comprising a single layer current (Imp) control loop for Constant Current (CC) mode with the current reference Impr generated by optimal solar power tracking function to ensure the maximum battery charging current and optimal solar power extraction, a two layers cascade control loop structure for Constant Voltage (CV) mode with a battery voltage loop as the outer loop and a current loop as the inner loop. 
         [0016]    One non-limiting aspect of the present invention contemplates a three-phase grid-tied inverter control algorithms in Mode  3  control library and an optimized solar power generation plus direct battery charging control algorithms in Mode  2  control library comprising two layers cascade control loop structure with a DC voltage control loop as the outer loop and an AC current loop as the inner loop. 
         [0017]    One non-limiting aspect of the present invention contemplates operation mode switches which are operable to select configurations of operation mode being controlled by a controller based on an operation mode control table. 
         [0018]    One non-limiting aspect of the present invention contemplates an interleaved multi-phase super charger mode (Mode  1 ) comprising a configuration of a MFPCS connecting to solar power source with intermedium of three DC inductors and storage battery power source through operation switches and Mode  1  control library, when solar power voltage is less than battery voltage (Vmp&lt;Vb). 
         [0019]    One non-limiting aspect of the present invention contemplates a solar power generation plus direct battery charging mode (Mode  2 ) comprising a configuration of a MFPCS connecting to solar power source, storage battery power source and LCL filters plus a transformer which also connecting to AC grid power source through operation switches and Mode  2  control library, when solar power voltage is greater than battery voltage (Vmp&gt;Vb). 
         [0020]    One non-limiting aspect of the present invention contemplates a solar power generation mode (Mode  3 ) comprising a configuration of a MFPCS connecting to solar power source and LCL filters plus a transformer which also connecting to AC grid power source through operation switches and Mode  3  control library. 
         [0021]    One non-limiting aspect of the present invention contemplates a solar/storage battery discharger mode (Mode  4 ) comprising a configuration of a MFPCS connecting to solar power source, storage battery power source and LCL filters plus a transformer which also connecting to AC grid power source through operation switches and Mode  4  control library. 
         [0022]    One non-limiting aspect of the present invention contemplates a PWM rectifier battery charger mode (Mode  5 ) comprising a configuration of a MFPCS connecting to storage battery power source and LCL filters plus a transformer which also connecting to AC grid power source through operation switches and Mode  5  control library. 
         [0023]    One non-limiting aspect of the present invention contemplates a solar power extension method to expand solar power usage, i.e. to maximize peak sun hour comprising a minimum grid power import means with charge/discharge of storage batteries to make the most of solar power and minimize grid power usage. 
         [0024]    One non-limiting aspect of the present invention contemplates a minimum grid power import means comprising the steps of: calculating a output power P S  of solar power source, a load power P L , a State of Charge (SOC) of battery power source; sensing a output voltage V MP  of solar power source, a terminal voltage V B  of battery power source; determining on peak-hour/off peak-hour periods in accordance with time of the day; performing comparison logic operations of SOC, P S  and P L , V MP  and V B . 
         [0025]    One non-limiting aspect of the present invention contemplates a minimum grid power import means comprising the steps of: setting Mode=1 when V MP  is less than V B , battery is within normal range and P S  is greater than P L , or when V MP  is less than V B  and battery is fully discharged; setting Mode=2 when V MP  is greater than V B  battery is within normal range and P S  is greater than P L , or when V MP  is greater than V B  and battery is fully discharged; setting Mode=3 when Ps is greater than P L , battery is within normal range and during off peak-hour period, or when Ps is greater than P L  and battery is fully charged; setting Mode=4 when in on peak-hour period, battery is within normal range and P S  is greater than P L , or when in off peak-hour period, battery is fully charged; setting Mode=5 when P S =0, during off peak-hour period and battery needs charge. 
         [0026]    One non-limiting aspect of the present invention contemplates a solar power conversion system with built-in high power storage battery charger/discharger and a method to maximize solar power use and minimize grid power expenditure comprising a MFPCS to convert solar power to AC grid power and charge/discharge storage battery in high power, set battery charging power reference and inverter power reference based on logic comparison operations and execute control functions through selected operation mode, such as operation mode  1  of interleaved multi-phase battery charger; or operation mode  2  of solar power converter plus direct battery charger; or operation mode  3  of solar power converter; or operation mode  4  of solar power converter plus battery discharger; or operation mode  5  of AC PWM rectifier battery charger. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    The present invention is pointed out with particularity in the appended claims. However, other features of the present invention will become more apparent and present invention will be best understood by referring to the following detailed description in conjunction with the accompany drawings in which: 
           [0028]      FIG. 1  illustrates the functional block diagram of prior art solar power system with storage battery and its low power charger. 
           [0029]      FIG. 2  illustrates the functional block diagram of a solar power system architecture incorporating built-in battery super charger as contemplated by one non-limiting aspect of the present invention. 
           [0030]      FIG. 3  schematically illustrates a MFPCS as contemplated by one non-limiting aspect of the present invention. 
           [0031]      FIGS. 4 a  and 4 b    graphically illustrates the waveforms of battery current and voltage during the charging process in time domain and current-voltage (IV) domain respectively;  FIG. 4 c    illustrates the IV curves of solar panel with Maximum Power Point (MPP) indicated under different operating temperatures;  FIG. 4 d    illustrates the IV curves of solar panel and battery in battery charging process under different operating temperatures as contemplated by one non-limiting aspect of the present invention. 
           [0032]      FIG. 5  illustrates an operation mode switch control table as contemplated by one non-limiting aspect of the present invention. 
           [0033]      FIG. 6  illustrates the detailed schematic circuit diagram of a solar power system with built-in super charger as contemplated by one non-limiting aspect of the present invention. 
           [0034]      FIG. 7  illustrates the functional block diagram of three phase grid-tied inverter control algorithms as contemplated by one non-limiting aspect of the present invention. 
           [0035]      FIG. 8  illustrates the functional block diagram and detailed control diagram of optimized solar power generation plus direct battery charging control algorithms as contemplated by one non-limiting aspect of the present invention. 
           [0036]      FIG. 9  illustrates the functional block diagram and detailed control loop diagram of interleaved multi-phase battery charging control algorithms as contemplated by one non-limiting aspect of the present invention. 
           [0037]      FIG. 10  illustrates the functional block diagram of three-phase PWM rectifier battery charging control algorithms as contemplated by one non-limiting aspect of the present invention. 
           [0038]      FIG. 11  illustrates the solar power extension software environment as contemplated by one non-limiting aspect of the present invention. 
           [0039]      FIG. 12  illustrates solar power extension method flowchart as contemplated by one non-limiting aspect of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0040]    As required, detailed embodiments of the present invention are disclosed herein; However, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some figures may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
         [0041]      FIG. 1  illustrates a functional block diagram of a prior art solar power system  10  incorporating storage batteries and its low power charger. In system  10 , solar power source  12  is converted to AC grid power  14  by solar Power Conversion System (PCS)  16  and LCL filter plus isolation transformer  18 . The storage battery  22  with the same nominal operating voltage of solar power source  12  is used to store the extra solar power during the sunny day and to be discharged by same solar PCS  16  when solar power  12  is not present. A separate low power battery charger  20  is used to charge the battery  22  by converting already inverted AC power back to DC. The battery charging is limiting to low power due to the high cost of high power battery charger. The switch  24  is only closed during the battery discharging period. 
         [0042]    In a solar power system with built-in super charger  26  as disclosed in this invention and illustrated in  FIG. 2 , a MFPCS  30  connecting to storage battery power source  42  and DC inductors  40  which further connecting to solar power source  36  through operation switches SW 2   48 , SW 3   50  operates in Mode 1  to convert solar power to storage battery power when solar power voltage is less than battery voltage (Vmp&lt;Vb); through operation switches SW 1   46 , SW 2   48 , and SW 4   44 , the MFPCS  30  connecting to solar power source  36 , storage battery power source  42  and LCL filters plus transformer  32  which also connecting to AC grid power source  34  operates in Mode  2  to convert solar power to AC grid power and directly charge battery when solar power voltage is greater than battery voltage (Vmp&gt;Vb); through operation switches SW 1   46  and SW 4   44 , the MFPCS  30  connecting to solar power source  36  and LCL filters plus transformer  32  which also connecting to AC grid power source  34  operates in Mode  3  to convert solar power to AC grid power; through operation switches SW 1   46 , SW 2   48 , and SW 4   44 , MFPCS  30  connecting to solar power source  36 , storage battery power source  42  and LCL filters plus transformer  32  which also connecting to AC grid power source  34  operates in Mode  4  to convert both solar power and storage battery power to AC grid power; through operation switches SW 2   48  and SW 4   44 , MFPCS  30  connecting to storage battery power source  42  and LCL filters plus transformer  32  which also connecting to AC grid power source  34  operates in Mode  5  to charge storage battery power with AC grid power. Sub-section  38  illustrates the DC/DC power conversion system configuration in Mode  1 . Sub-section  28  illustrates the DC/AC or AC/DC power conversion configurations in Modes  2 ,  3 ,  4 ,  5 . 
         [0043]      FIG. 3  schematically illustrates a MFPCS  30  having an IGBT module  54  mounted on a liquid cooled heatsink  56  and connected to DC-link capacitor  58  as contemplated by one non-limiting aspect of the present invention. The MFPCS  30  is shown for exemplary and non-limiting purpose being as a power electronic converter utilized in a solar power system with built-in super charger  26  (in  FIG. 2 ) for performing DC/AC, AC/DC, and DC/DC power conversion functions. 
         [0044]    In  FIG. 3  AC current sensing system  60  and a DC current sensing system  62  may be included which provide sensed currents of LCL filter plus isolation transformer  32  in solar power generation/battery discharger system  28  (in  FIG. 2 ), or of DC inductors  40  in interleaved multi-phase battery charger system  38  (in  FIG. 2 ), and of DC-link capacitor  58 , so as to control of DC/AC, AC/DC, DC/DC power conversions. The DSP interface card  66  may condition and filter feedback signals from current sensors  60 ,  62  and other sensing devices within the system, and provide them to TI DSP control card  68  for further processes. The TI DSP control card  68  being loaded with Mode  1  control library  70 , Mode  2  control library  72 , Mode  3  control library  74 , Mode  4  control library  88 , and Mode  5  control library  90  may cooperate with DSP interface card  66  and IGBT gate drive card  64  to control IGBT module  54  such as the opening and closing of switches  76 ,  78 ,  80 ,  82 ,  84 ,  86  to produce the desired voltage/current waveform patterns for DC/AC, AC/DC and DC/DC power conversions. 
         [0045]      FIG. 4 a    illustrates time domain waveforms of battery current I B    300  and battery voltage V B    294  during the charging period. In constant current mode period I  296 , the battery charging current I B    300  is regulated to its reference value I BR    302  and the voltage V B    294  increases from starting voltage V BMIN    304  to its float voltage V BF    298 . Then the charging process switches to a constant voltage mode period II  306  where the voltage V B    294  is regulated to its reference value V BR    292 , meanwhile the current I B    300  starts to fall until reaching zero to complete the charging process.  FIG. 4 b    illustrates an example of battery charging curve in IV plane. In this graph, when V B =300 v, the charger starts to charge battery with a constant current I BR    264  until the battery voltage V B =450 v. Then V B  is regulated at  450   v  until battery current I B  falls to zero. 
         [0046]      FIG. 4 c    illustrates an example IV curve of solar panels under different operating temperatures. When temperature is 25° C., the Maximum Power Point (MPP) occurs at V MP =375 v; When temperature is −10° C., the MPP occurs at V MP =415 v; When temperature is 68° C., the MPP occurs at V MP =300 v. 
         [0047]      FIG. 4 d    maps the IV curves of battery charging process into solar power IV plane. When solar power MPP voltage V MP  is less than battery voltage V B  (V MP &lt;V B ), an interleaved multi-phase DC/DC converter topology (Mode  1 ) is used to charge battery from solar power with maximum charging current over entire battery voltage range (300 v-450 v). When solar power MPP voltage V MP  is greater than battery voltage V B  (V MP &gt;V B ), a grid-tied inverter is used to directly charge battery with part of solar power and convert the rest of solar power to AC grid power (Mode  2 ). 
         [0048]      FIG. 5  illustrates a operation mode switch control table  92  used by a controller to select operation mode of solar power system with built-in super charger based on the IV curves of solar power generation and battery charging processes. When V MP &lt;V B , an interleaved multi-phase super charger mode (Mode  1 ) is selected with SW 1 =0, SW 2 =1, SW 3 =1, SW 4 =0. When V MP &gt;V B , an optimized solar power generation plus direct battery charger mode (Mode  2 ) is selected with SW 1 =1, SW 2 =1, Sw 3 =0, Sw 4 =1. When battery voltage V B =450 v (float voltage) indicating the battery is fully charged, a solar power generation mode (Mode  3 ) is selected with SW 1 =1, SW 2 =0, Sw 3 =0, Sw 4 =1. When battery voltage is between 300V and 450V and solar power is less than load power, a solar/battery discharger mode (Mode  4 ) is selected with SW 1 =1, SW 2 =1, SW 3 =0 SW 4 =1. When V MP =0V indicating the solar power is not present, a PWM rectifier battery charger mode (Mode  5 ) is selected with SW 1 =0, SW 2 =1, SW 3 =0 SW 4 =1. 
         [0049]      FIG. 6  illustrates the detailed electrical schematic diagram of a solar power system with built-in super charger  26 , that may be configured with multiple operation modes providing solar power generation and storage battery charging/discharging functions. In Mode  1  where V MP &lt;V B , MFPCS  30  is operated as an interleaved multi-phase DC/DC converter with DC inductors  40  and operation switches set as SW 1 ( 46 )=0, SW 2 ( 48 )=1, SW 3 ( 50 )=1, SW 4 ( 44 )=0, to charge the storage battery  42  with solar power source  36 . The solar power source  36  provides the maximum charging current over entire battery voltage range (300 v-450 v) in this mode. In mode  2  where V MP &gt;V B , MFPCS  30  is operated as a three-phase grid-tied inverter connecting to both solar power  36  and storage battery  42  with operation switches set as SW 1 ( 46 )=1, SW 2 ( 48 )=1, SW 3 ( 50 )=0, SW 4 ( 44 )=1, to extract maximum solar power with MPPT and directly charge battery  42  with part of solar power  36  and also convert the rest of solar power to AC grid power  34 . In Mode  3  where V B =V BR  (450 v) and battery charging process is ended, MFPCS  30  is operated as a three-phase grid-tied inverter connecting only to solar power  36  with operation switches set as SW 1 ( 46 )=1, SW 2 ( 48 )=0, SW 3 ( 50 )=0, SW 4 ( 44 )=1, to convert all solar power  36  to AC grid power  34 . In Mode  4  where battery voltage is between 300V and 450V and solar power is less than load power, MFPCS  30  is operated as a three-phase grid-tied inverter connecting to solar power  36  and battery  42  with operation switches set as SW 1 ( 46 )=1, SW 2 ( 48 )=1, SW 3 ( 50 )=0 SW 4 ( 44 )=1, to convert solar power  36  and battery power  42  to AC grid power  34 . When V MP =0V indicating the solar power is not present, MFPCS  30  is operated as a three-phase PWM rectifier battery charger connecting to battery  42  with operation switches set as SW 1 ( 46 )=0, SW 2 ( 48 )=1, SW 3 ( 50 )=0 SW 4 ( 44 )=1, to convert AC grid power  34  to battery power  42 . 
         [0050]      FIG. 7  illustrates the functional block diagram of three-phase grid-tied inverter control  114 . In this control algorithm, the MPPT  116  extracts the maximum solar power by producing a dynamic voltage reference to DC voltage control  118 . The DC voltage control  118  regulates the DC voltage by generating a power command for AC current reference generation  120 . The reference generation  120  produces the current reference for AC current control  122  which regulates AC current by commanding Space Vector Modulation (SVM)  124  to generate PWM signals controlling IGBT  126  to convert solar power to AC grid power. 
         [0051]      FIG. 8  illustrates the functional block diagram  130  and detailed control loop diagram  156  of optimized solar power generation plus direct battery charging control  128 . In functional diagram  130 , MPPT  116  extracts the maximum solar power by producing a dynamic voltage reference to DC voltage control  118 . The DC voltage control  118  regulates the DC voltage by generating a solar power command  136 . It is then subtracted from required battery power  138  calculated by block  140  based on battery charging current reference Ibr  142  and battery voltage Vb  144 , to get inverter power command  146 . The inverter power command  146  is fed to AC current reference generation  120  to produce current reference for AC current control  122  which regulates AC currents by commanding SVM  124  to generate PWM signals controlling IGBT  126  to directly charge the battery with part of solar power and to convert rest of solar power to AC grid power. 
         [0052]    The detailed control loop diagram  156  illustrates two layers control loop used in control algorithms  128 . This cascade control structure is based on the balance of solar power command P R    158 , battery charging power command P batr    160 , inverter power command P INVR    162  (P INVR =P R −P batr ) and relationships of solar voltage V MP    176 , solar current I mp    164 , battery charging current I br    166 , inverter current √{square root over (2)} Ia sin (wt)  182 , and DC current Idc  170  where 
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         [0000]    Imp=f(Vmp). In control loop diagram  156 , MPPT  116  determines solar voltage reference V MPR    174 . V MPR    174  is subtracted from measured DC voltage V MP    176 , the error is fed into DC voltage control  178  which produces solar power command P R    158 . Under constant current mode, the battery charging current is controlled by its reference Ibr  166  while the battery voltage V B    262  increases, resulting in an increased battery charging power command P batr  ( 160 )=Ibr×V B . The solar power command P R    158  is subtracted from P batr    160  to obtain inverter power command P INVR    162 . P INVR  is fed to an AC current reference generation circuit to create an AC current command I R =√{square root over (2)} Iar sin(ωt)  180 . Then it is compared with measured current √{square root over (2)}Ia sin(ωt)  182 . The error is fed to current control  184  which generate a PWM command. The PWM command is amplified by PWM inverter  186  as an input voltage  188  (V) of LCL filter  190 . The sum of three phase output power of inverter Sa  192 , Sb  194 , Sc  196  is equal to DC power Pdc  198  at inverter DC-link. The DC power Pdc  198  is divided by measured DC voltage Vdc  200  to obtain DC current Idc  170  which is changed to DC voltage V MP    176  with the block  202 . 
         [0053]      FIG. 9  illustrates the functional block diagrams  204  and control loop diagrams  208 ,  210  of interleaved multi-phase battery charging control algorithms  212 . In functional block diagram  204  while battery voltage is regulated by battery voltage control  214 , battery current is regulated by optimal solar power tracking  216 . Fed by Impr  218  that is the output of either voltage control  214  or optimal solar power tracking  216 , a multi-phase current control  220  regulates DC current of each DC inductor by commanding interleaved multi-phase PWM  222  to generate PWM signals controlling IGBT  126  to charge storage batteries. 
         [0054]    In constant current control loop diagram  208 , the battery voltage Vb  226  and solar voltage Vmp  228  are used by function block  230  to derive the inverse duty cycle 
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         [0000]    The solar current reference Impr  234  is related to battery charging current reference Ibr  236  with 
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         [0000]    The current reference Impr  234  is compared with the measured current Imp  238  and the error is fed into current control  240  which generates a PWM command. This command is amplified by interleaved multi-phase DC/DC converter  242  as input voltage  244  (V) of plant block  246  to force solar current Imp  238  to follow its reference Impr  234 . 
         [0055]    In constant voltage control loop diagram  210 , battery voltage reference Vbr  248  is compared with measured battery voltage Vb  250  and the error is fed into battery voltage control  252  which produces a solar current reference Impr  254 . The solar current Imp  256  is controlled to follow the current reference Impr  254  with the current loop. The current Imp  256  is transformed to battery voltage Vb  250  by the Interleaved Multi-Phase Power Converter transfer function  258  and the battery voltage Vb  250  is regulated to match its reference Vbr  248 . 
         [0056]      FIG. 10  illustrates three-phase PWM rectifier battery charging control  308 . In this control algorithm, while battery is regulated by battery voltage control  310  in constant voltage mode, the battery current is regulated by battery current control  312  in constant current mode. Using the output of OR block  314  that is the output of either voltage control  310  or current control  312 , AC current reference generation  120  produces AC current reference for AC current control  122 . AC current control  122  regulates AC current by commanding SVM  124  to generate PWM signals controlling IGBT  126  to charge battery with AC grid power. 
         [0057]      FIG. 11  illustrates solar power extension software environment  260  used in solar power system with built-in super charger. In software environment  260 , solar power extension software  272  inside MFPCS  30  determines when and how to charge or discharge the storage batteries based on internal data from MFPCS, the weather condition information from internet weather channel  266 , and peak hour electricity rate from the data base  268 . 
         [0058]    Referring to the flow chart of  FIG. 12  for a more detailed description of minimum grid power import method, upon start  274 , function  276  calculates the solar power P S , load power P L , and battery SOC; senses the solar power output voltage V MP , battery voltage V B ; and determines on peak-hour/off peak-hour periods in accordance with time of the day. Functions  278 ,  280  examine if battery is within normal range (Min&lt;SOC&lt;Max), fully discharged (SOC&lt;Min), or fully charged (SOC&gt;=Max). Functions  282 ,  284 ,  286  check if solar power P S  is greater than load power P L . Functions  288 ,  290 ,  292  determine if solar power voltage V MP  is greater than battery voltage V B . If battery SOC is within normal range, mode is set to 1 (MODE=1) when solar power P S  is greater than load power P L  and solar power voltage V MP  is less than battery voltage V B ; mode is set to 2 (MODE=2) when solar power P S  is greater than load power P L  and solar power voltage V MP  is greater than battery voltage V B ; mode is set to 3 (MODE=3) when solar power P S  is less than load power P L , during off peak-hour period, and solar power P S  is greater than zero; mode is set to 4 (MODE=4) when solar power P S  is less than load power P L  and during on peak-hour period; mode is set to 5 (MODE=5) when solar power P S  is less than load power P L , during off peak-hour period, and solar power P S  is equal to zero. If battery is fully discharged (SOC&lt;Min), mode is set to 1 (MODE=1) when solar power P S  is greater than load power P L , and solar voltage V MP  is less than storage battery voltage V B ; mode is also set to 1 (MODE=1) when solar power Ps is less than load power P L  and solar voltage V MP  is less than battery voltage V B ; mode is set to 2 (MODE=2) when solar power P S  is greater than load power PL and solar voltage V MP  is greater than said battery voltage V B . If battery is fully charged (SOC&gt;=Max), mode is set to 3 (MODE=3) when solar power P S  is greater than load power P L  or solar power Ps is less load power P L  during off peak-hour period; mode is set to 4 (MODE=4) when solar power Ps is less than load power P L  during on peak-hour period. If battery is fully discharged (SOC&lt;Min), mode is set to 2 (MODE=2), battery charging power reference P BR =P S /4, and inverter power reference P INVR =P S ×¾ when solar power Ps is less than load power P L , solar voltage V MP  is greater than battery voltage V B , and during on peak-hour period; mode is also set to 2 (MODE=2), but battery charging power reference P BR =P S ×¾, inverter power reference P INVR =P S /4 when solar power P S  is less than load power P L , solar voltage V MP  is greater than battery voltage V B , and during off peak-hour period; mode is set to 5 (MODE=5) when solar power P S  is less than load power P L , solar voltage V MP  is greater than battery voltage V B , during off peak-hour period, and solar power P S  is equal to zero. 
         [0059]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention, rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without depart from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.