Abstract:
An enclosure design is disclosed to accommodate and support the unique features and capabilities of the Smart and Scalable Power Inverters or Mini-Inverters that have multiple input channels to easily connect to multiple solar PV panels, invert the DC power to AC power, and daisy chain together to generate AC power to feed the power grid or supply power to electrical devices. Further disclosed is a message system using LEDs (light-emitting diodes) mounted on the enclosure to indicate the system status and the status of each input channel of the Smart and Scalable Mini-Inverters.

Description:
This application claims priority to U.S. Provisional Application No. 61/503,400 filed on Jun. 30, 2011, which is herein incorporated by reference. 
    
    
     The subject of this patent relates to an enclosure and a message system for the Smart and Scalable Power Inverters or Mini-Inverters that invert DC (direct current) power from single or multiple DC power sources to single-phase or three-phase AC (alternating current) power, where the DC power sources include but are not limited to photovoltaic (PV) solar modules, fuel cells, batteries, and other DC power generators; and the generated AC power can be sent to an electrical power grid or to an AC load that is not connected to the power grid. 
     In the U.S. patent application Ser. No. 12/837,162, the entirety of which is hereby incorporated by reference, we described the novel Smart and Scalable Power Inverters and the unique scalable design so that the DC to AC power inversion system can include as few as one inverter and one DC source, up to a selected number of inverters and multiple DC sources. A number of smart single-input, dual-input, triple-input, quad-input, and multiple-input power inverters in a mixed variety can easily connect to single, dual, triple, quad, and multiple DC power sources, invert the DC power to AC power, and daisy chain together to generate a total power, which is equal to the summation of the AC power supplied by each smart and scalable power inverter. 
     In the U.S. patent application No. 61/442,991, the entirety of which is hereby incorporated by reference, we described the Scalable and Redundant Mini-Inverters that have double, triple, or quadruple redundant capabilities so that the Mini-Inverters can work in a harsh environment for a prolonged period of time. A number of regular, redundant, triple redundant, or quadruple redundant Mini-Inverters with one, two, three, or multiple input channels in a mixed variety can easily connect to one, two, three, or multiple DC power sources such as solar PV modules, invert the DC power to AC power, and daisy chain together to generate AC power to feed the power grid. 
     In the U.S. patent application No. 61/495,540, the entirety of which is hereby incorporated by reference, we described the Smart and Scalable Off-Grid Mini-Inverters that not only have the key scalable and redundant features as described in U.S. patent applications Ser. No. 12/837,162 and Ser. No. 61/442,991, but can also supply power to electrical devices that are not connected to the power grid including motors, pumps, fans, lights, appliances, and homes. 
     In this patent, we disclose the design of an enclosure that can accommodate and support the unique features and capabilities of the Smart and Scalable Power Inverters or Mini-Inverters. Further disclosed is a message system using LEDs (light-emitting diodes) mounted on the enclosure to indicate the system status and the status of each input channel of the Smart and Scalable Mini-Inverters. 
    
    
     
       In the accompanying drawing: 
         FIG. 1  is a drawing showing a perspective view of a 4-channel scalable Mini-Inverter enclosure according to an embodiment of this invention. 
         FIG. 2  is a drawing showing the front view, top view, and side view of a 4-channel scalable Mini-Inverter enclosure according to an embodiment of this invention. 
         FIG. 3  is a drawing showing a perspective view of a 12-channel scalable Mini-Inverter enclosure according to an embodiment of this invention. 
         FIG. 4  is a block diagram illustrating an m-channel smart and scalable Mini-Inverter that inverts the DC power from m solar panels to single-phase AC power, in which a message system with multiple LEDs (light-emitting diodes) is controlled by a digital microcontroller to indicate the system status and the status of each input channel of the Mini-Inverter according to an embodiment of this invention. 
         FIG. 5  is a block diagram illustrating an m-channel smart and scalable off-grid AC Master Mini-Inverter that inverts the DC power from m solar panels to three-phase AC power, in which a message system with multiple LEDs is controlled by a digital microcontroller to indicate the system status and the status of each input channel of the Mini-Inverter according to an embodiment of this invention. 
         FIG. 6  is a flow chart describing the main software program running in the digital microcontroller of a smart and scalable Mini-Inverter, which includes Control &amp; Management tasks, Redundancy tasks, and Communication tasks. 
         FIG. 7  is a flow chart describing the LED Status Subroutine, which is invoked by the Diagnosis Mechanism of  FIG. 6 , running in the digital microcontroller of an m-channel smart and scalable Mini-Inverter, which sends signals to the LEDs on the Mini-Inverter enclosure to indicate the inverter status according to an embodiment of this invention. 
         FIG. 8  is a flow chart describing the LED Status Subroutine, which is invoked by the Diagnosis Mechanism of  FIG. 6 , running in the digital microcontroller of an m-channel smart and scalable off-grid AC Master Mini-Inverter, which sends signals to the LEDs on the Mini-Inverter enclosure to indicate the inverter status according to an embodiment of this invention. 
     
    
    
     The term “mechanism” is used herein to represent hardware, software, or any combination thereof. The term “solar module” or “solar panel” refers to photovoltaic (PV) solar modules. The term “AC load” is used herein to represent one or more single-phase or three-phase electrical devices including but not limited to motors, pumps, fans, lights, appliances, and homes. The term “AC Master” is used herein to represent a special off-grid Mini-Inverter in a solar power generation system to generate AC power for off-grid applications as described in U.S. patent application No. 61/495,540. 
     Throughout this document, m=1, 2, 3, . . . , as an integer, which is used to indicate the number of the DC input ports of a Mini-Inverter. The term “input channel” refers to the DC input port of the Mini-Inverter. Then, an m-channel Mini-Inverter means that the Mini-Inverter has m input channels or m DC input ports. 
     Throughout this document, if a power inversion system or a power inverter is used to generate single-phase AC, it can also be applied to three-phase AC without departing from the spirit or scope of our invention. If a power inversion system or a power inverter is used to generate three-phase AC, it can also be applied to single-phase AC without departing from the spirit or scope of our invention. 
     Without losing generality, all numerical values given in this patent are examples. Other values can be used without departing from the spirit or scope of our invention. The description of specific embodiments herein is for demonstration purposes and in no way limits the scope this disclosure to exclude other not specially described embodiments of this invention. 
     DESCRIPTION 
       FIG. 1  is a drawing showing a perspective view of a 4-channel scalable Mini-Inverter enclosure according to an embodiment of this invention. The enclosure is comprised of a metal case  2 ; an AC input port grommet  4 , an AC input port cable  6 , an AC input port connector  8 , an AC output port grommet  10 , an AC output port cable  12 , an AC output port connector  14 , a system status LED  26 , a mounting bracket  30 , and three mounting slots  32 . For each input channel, the enclosure is also comprised of a DC female connector  16 , a DC male connector  18 , a pair of DC cables  20  and  22 , a DC grommet  24 , and a channel status LED  28 . In  FIG. 1 , a 4-channel Mini-Inverter enclosure is shown. That means, there are 4 pairs of DC cables and connectors and 4 channel status LEDs. Without losing generality, similar design can be made to include 1, 2, 3, . . . , m channels, where m is an integer to indicate the number of the DC input channels of a Mini-Inverter. 
     The metal case can be made of aluminum. A layer of conductive and non-corrosive layer such as alodine can be applied to the metal case surface for corrosion protection. In the solar power industry, most solar panels are shipped with a pair of standard MC4 DC connectors with DC cables. Therefore, the Mini-Inverter enclosure is designed to include a pair of standard MC4 DC connectors for each input channel to connect to the DC connectors of its corresponding solar panel. 
     There are no standards for the AC cables and connectors in the solar power industry. Since a Mini-Inverter will daisy chain with the next Mini-Inverter, the Mini-Inverter enclosure is designed to include a mare AC connector for the AC output port, and a female AC connector for the AC input port. Although we say the power inverters daisy chain, where the output port of each Mini-Inverter is connected to the input port of the next Mini-Inverter, the actual connection of the inverters is pass-through. That means, the generated AC power from each Mini-Inverter is added in parallel onto the AC powerline. For the same reason, the AC input port with a female AC connector can also be viewed as an AC output port, and the AC output port with a male AC connector can also be viewed as an AC input port. For a single-phase or split-phase Mini-Inverter, the AC cable can be designed to include 3-wires for L1, L2, and Neutral. The user is required to install the earth ground for the solar power system including any metal structure, solar panels and inverters. For a three-phase Mini-Inverter, the AC cable should include 4-wires for phase 1, 2, 3, and Neutral. Again, the user is required to ground any metal structure of the system including PV panels and inverters. 
     The mounting bracket  30  is used to mount the Mini-Inverter onto the solar panel metal frame at the back side of a solar panel. Three mounting slots  32  are designed to allow secured mounting. 
       FIG. 2  is a drawing showing the front view, top view, and side view of a 4-channel scalable Mini-Inverter enclosure according to an embodiment of this invention. The front view drawing shows the top part  34  of the metal case  2 , a mounting bracket  30 , three mounting slots  32 , two grounding screw holes  40 , and five LED holes  42 . The top view drawing shows the top part  34  of the metal case  2 , the bottom part  46  of the metal case  2 , metal case attachment rivet holes  48  and  50 , mounting bracket  30 , and six mounting bracket welding points  54 . The right side view drawing shows the top part  34  of the metal case  2 , AC cable cutout  58 , DC cable cutouts  60 , metal case attachment rivet holes  61  and  68 , bottom part  46  of the metal case  2 , AC cable cutout  64 , DC cable cutouts  66 , mounting bracket  30 , and grounding screw holes  40 . 
       FIG. 3  is a drawing showing a perspective view of a 12-channel scalable Mini-Inverter enclosure according to an embodiment of this invention. As an example, a Mini-Inverter that has 12 input channels can connect to 12 thin-film solar panels with power ratings of 75-88 Watts to produce a maximum AC power of 1,000 Watts. As another example, a larger size Mini-Inverter that has 12 input channels can connect to 12 crystalline silicon based solar panels with power ratings of 200-260 Watts to produce a maximum AC power of 3,000 Watts. 
     The 12-channel Mini-Inverter enclosure is comprised of a metal case  74 , an AC input port cable and connector  76 , an AC output port cable and connector  78 , 12 pairs of DC cables and connectors  80 , a mounting bracket  82 , a system status LED  84 , and 12 input-channel status LEDs  86 . Similar designs can accommodate a smaller or larger number of input channels for the smart and scalable Mini-Inverters. 
       FIG. 4  is a block diagram illustrating an m-channel smart and scalable Mini-Inverter that inverts the DC power from m solar panels to single-phase AC power, in which a message system with multiple LEDs (light-emitting diodes) is controlled by a digital microcontroller to indicate the system status and the status of each input channel of the Mini-Inverter according to an embodiment of this invention. The Mini-Inverter comprises m DC-DC boost converters  92 ,  93 , . . . ,  94 , a DC power combiner  96 , a DC-AC inverter  98 , a load interface circuit  100 , an internal AC powerline  102 , a solid-state switch  104 , a digital microcontroller  106 , a line sensing circuit  108 , an interface circuit for powerline communications  110 , a powerline communications Modem  112 , a DC power supply  114 , an external AC powerline  116 , an LED driver circuit  118 , m channel status LEDs  120 , and a system status LED  122 . 
     The power from DC sources  88 ,  89 , . . . ,  90  is delivered to the corresponding DC-DC boost converters  92 ,  93 , . . . ,  94 , respectively. The DC power is then combined in the DC power combiner  96 . The total combined DC power is inverted to AC power with voltage larger than 240VAC by the DC-AC inverter  98 . The generated AC power goes through the load interface circuit  100  to be combined with the AC power in the internal AC powerline  102 . A solid-state switch  104  controlled by the digital microcontroller  106  is used to isolate the internal AC powerline  102  from the external AC powerline  116  when solar power is not being generated. A line sensing circuit  108  connected to the AC powerline  102  is used to detect the phase and zero-crossing point of the incoming AC power from the power grid. The phase and zero-crossing point signals are sent to the digital microcontroller  106  for AC power synchronization to assure that the Mini-Inverter provides high quality synchronized power to the grid. A powerline communications Modem  112 , which is isolated by an interface circuit  110 , is used to establish a 2-way digital signal communication between the digital microcontroller  106  and the outside world through the AC powerline. The DC power combiner  96  provides adequate power to the DC power supply  114 , which supplies DC power to the electronic components of the Mini-Inverter. 
     The DC-DC boost converters that can be used in this embodiment are any of a number of well known converters described in the “Power Electronics Handbook” edited by Muhammad H. Rashid, published by Academic Press in 2007, including Buck Converter, Boost Converter, Buck-Boost Converter, Super-Lift Luo Converter, and Cascade Boost Converter. The DC-AC inverters that can be used in this embodiment are any of a number of well known DC-AC inverters described in the same book including Half-Bridge Inverter, Full-Bridge Inverter, Bipolar PWM Inverter, Unipolar PWM Inverter, and Sinusoidal PWM Inverter. The DC combiners used in this embodiment can be designed with a circuit that allow the output from all DC-DC boost converters to connect in parallel so that all DC currents will be added together. The Powerline Modem that can be used in this embodiment can be any of a number of commercially available integrated circuits capable of providing 2-way digital communications through a powerline. Other modules discussed in this embodiment including load interface, solid state switch, line sensing circuit, powerline interface circuit, and DC power supply can be implemented using one or more known combinations of conventional electronic components such as resisters, capacitors, inductors, solid-state switches, transformers, diodes, transistors, operational amplifiers, and ceramic filters, etc. 
     An LED driver circuit  118  controlled by the digital microcontroller  106  is used to turn a specific LED to certain color and pattern to indicate the system status and the status of each input channel of the Mini-Inverter. The LED driver circuit that can be used in this embodiment is any of a number of well known current drivers such as an emitter follower transistor driver. 
     The digital microcontroller  106  is used to perform a number of tasks including (i) monitoring the DC boost voltage from each DC-DC boost converter, (ii) controlling the DC-DC boost converters, (iii) performing maximum power point tracking (MPPT) for each input channel, (iv) performing DC-AC inversion and AC power synchronization, (v) monitoring AC current and voltage for generated power amount and status, (vi) performing powerline communications, (vii) performing logic controls such as AC powerline switching and isolation, (viii) performing diagnosis functions, (ix) driving LED driver circuits, and (x) performing the functions of the message system. 
     For an m-channel smart and scalable Mini-Inverter, a message system is designed to include one 2-color LED to show the system status of the Mini-Inverter. The Case number, LED color (green or red), pattern (solid or flashing), and corresponding indicated messages for the system status is listed in Table 1. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                 Solar Power 
                   
               
               
                 Case 
                 Green 
                 Red 
                 System Status 
                 Possible Issues 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 Solid 
                 — 
                 Mini-Inverter is 
                   
               
               
                   
                   
                   
                 Working. 
               
               
                 2 
                 Flash- 
                 — 
                 Mini-Inverter is 
                 a. Communication error. 
               
               
                   
                 ing 
                   
                 Working but 
                 b. Inverter output AC 
               
               
                   
                   
                   
                 Has Warnings. 
                 voltage approaching limits. 
               
               
                   
                   
                   
                   
                 c. Inverter output AC 
               
               
                   
                   
                   
                   
                 current approaching limits. 
               
               
                 3 
                 — 
                 Solid 
                 Mini-Inverter 
                 a. Inverter output AC 
               
               
                   
                   
                   
                 Error. 
                 voltage out of limits. 
               
               
                   
                   
                   
                   
                 b. Inverter output AC 
               
               
                   
                   
                   
                   
                 current out of limits. 
               
               
                 4 
                 — 
                 Flash- 
                 Power Grid 
                 a. Grid AC frequency out of 
               
               
                   
                   
                 ing 
                 Error. 
                 limits. 
               
               
                   
                   
                   
                   
                 b. Grid AC voltage out of 
               
               
                   
                   
                   
                   
                 limits. 
               
               
                 5 
                 — 
                 — 
                 LED is OFF. 
                 a. Not enough PV power. 
               
               
                   
                   
                   
                   
                 Mini-Inverter is off. 
               
               
                   
                   
                   
                   
                 b. Not enough PV power to 
               
               
                   
                   
                   
                   
                 generate AC, but the digital 
               
               
                   
                   
                   
                   
                 microcontroller is running. 
               
               
                   
                   
                   
                   
                 c. There is enough PV 
               
               
                   
                   
                   
                   
                 power and the Mini-Inverter 
               
               
                   
                   
                   
                   
                 is waking up. 
               
               
                   
                   
                   
                   
                 d. LED error, if there is 
               
               
                   
                   
                   
                   
                 power in the system. 
               
               
                   
               
             
          
         
       
     
     The message system for the m-channel smart and scalable Mini-Inverter also includes m 2-color LEDs to show the status for each input channel of the Mini-Inverter. The Case number, LED color (green or red), pattern (solid or flashing), and corresponding indicated messages for the input channel status is listed in Table 2. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                 DC Input 
                   
               
               
                 Case 
                 Green 
                 Red 
                 Channel Status 
                 Possible Issues 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 6 
                 Solid 
                 — 
                 Input Channel 
                   
               
               
                   
                   
                   
                 is Working. 
               
               
                 7 
                 Flash- 
                 — 
                 Low Input DC 
                 Channel temperature 
               
               
                   
                 ing 
                   
                 Voltage from 
                 approaching limits. 
               
               
                   
                   
                   
                 Solar Panel. 
               
               
                 8 
                 — 
                 Solid 
                 Input Channel 
                 Defective Channel. 
               
               
                   
                   
                   
                 Error 
               
               
                 9 
                 — 
                 Flash- 
                 Input Channel 
                 a. Channel out of 
               
               
                   
                   
                 ing 
                 Warning. 
                 temperature limits. 
               
               
                   
                   
                   
                   
                 b. Channel out of voltage 
               
               
                   
                   
                   
                   
                 limits. 
               
               
                   
                   
                   
                   
                 c. Channel out of current 
               
               
                   
                   
                   
                   
                 limits. 
               
               
                 10 
                 — 
                 — 
                 LED is OFF. 
                 a. Not enough PV power. 
               
               
                   
                   
                   
                   
                 Mini-Inverter is off. 
               
               
                   
                   
                   
                   
                 b. Not enough PV power to 
               
               
                   
                   
                   
                   
                 generate AC in this channel, 
               
               
                   
                   
                   
                   
                 but the digital 
               
               
                   
                   
                   
                   
                 microcontroller is running. 
               
               
                   
                   
                   
                   
                 c. There is enough PV 
               
               
                   
                   
                   
                   
                 power in this channel and 
               
               
                   
                   
                   
                   
                 the Mini-Inverter is waking 
               
               
                   
                   
                   
                   
                 up. 
               
               
                   
                   
                   
                   
                 d. LED error, if there is 
               
               
                   
                   
                   
                   
                 power in the system. 
               
               
                   
               
             
          
         
       
     
       FIG. 5  is a block diagram illustrating an m-channel smart and scalable off-grid AC Master Mini-Inverter that inverts the DC power from m solar panels to three-phase AC power, in which a message system with multiple LEDs is controlled by a digital microcontroller to indicate the system status and the status of each input channel of the Mini-Inverter according to an embodiment of this invention. The Mini-Inverter comprises m DC-DC boost converters  132 ,  133 , . . . ,  134 , a DC power combiner  136 , a DC-AC inverter  138 , a load interface circuit  140 , an internal AC powerline  142 , a load detector  144 , a digital microcontroller  146 , a line sensing circuit  148 , an interface circuit for powerline communications  150 , a powerline communications Modem  152 , a DC power supply  154 , an external AC powerline  156 , an LED driver circuit  158 , m channel status LEDs  160 , and a system status LED  162 . 
     The power from DC sources  128 ,  129 , . . . ,  130  is delivered to the corresponding DC-DC boost converters  132 ,  133 , . . . ,  134 , respectively. The DC power is then combined in the DC power combiner  136 . The total combined DC power is inverted to AC power within a user specified voltage range such as 120VAC+/−10% or 240VAC+/−10% by the DC-AC inverter  138 . The generated AC power goes through the load interface circuit  140  to be combined with the AC power in the internal AC powerline  142 . A line sensing circuit  148  connected to the AC powerline  142  is used to detect if there is AC power on the powerline prior to the startup of the AC Master Mini-Inverter. The line sensing circuit  148  is also used for monitoring the load on the AC powerline for over voltage, under voltage, over current, or under current conditions so that the total AC output voltage can be regulated to protect the Mini-Inverters in the power generation system and the AC load. A powerline communications Modem  152 , which is isolated by an interface circuit  150 , is used to establish a 2-way digital signal communication between the digital microcontroller  146  and the outside world through the AC powerline. The DC power combiner  136  provides adequate power to the DC power supply  154 , which supplies DC power to the electronic components of the Mini-Inverter. 
     The load detector  144  is an electronic circuit that can detect the impedance of the connected AC load. If no AC power is detected on the powerline, the load detector  144  checks the impedance of the AC powerline to determine if the connected AC load is within certain specifications. The load detector in this embodiment can be designed using standard. LRC meter impedance measurement circuits and mechanism such as those described in the book, “The measurement of Lumped Parameter Impedance: A Metrology Guide” published by University of Michigan Library in January 1974. 
     An LED driver circuit  158  controlled by the digital microcontroller  146  is used to turn a specific LED to certain color and pattern to indicate the system status and the status of each input channel of the off-grid AC Master Mini-Inverter. The LED driver circuit that can be used in this embodiment is any of a number of well known current drivers such as an emitter follower transistor driver. 
     For an m-channel smart and scalable off-grid AC Master Mini-Inverter, the digital microcontroller  146  performs the tasks including (i) monitoring the DC boost voltage from each DC-DC boost converter, (ii) controlling the DC-DC boost converters, (iii) performing maximum power point tracking (MDPT) for each input channel, (iv) performing DC-AC inversion, (v) monitoring AC current and voltage for generated power amount and status, (vi) performing powerline communications, (vii) checking the impedance of the AC powerline to determine if the connected AC load is within certain specifications, (viii) initially energizing the AC powerline that has no power running to it, (ix) continually delivering AC power to the AC powerline to allow the other off-grid Mini-Inverters also connected on the same powerline to synchronize the AC power being produced, (x) continually checking and determining whether the AC load is too large or too small for the power generation system to handle, (xi) turning the power off and triggering an error signal if the load is too large or too small, (xii) performing diagnosis functions, (xiii) driving LED driver circuits, and (xiv) performing the functions of the message system. 
     For an m-channel off-grid AC Master Mini-Inverter, a message system is designed to include one 2-color LED to show the system status of the Mini-Inverter. The Case number, LED color (green or red), pattern (solid or flashing), and corresponding indicated messages for the system status is listed in Table 3. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                   
                 Solar Power 
                   
               
               
                 Case 
                 Green 
                 Red 
                 System Status 
                 Possible Issues 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 11 
                 Solid 
                 — 
                 Mini-Inverter is 
                   
               
               
                   
                   
                   
                 Working. 
               
               
                 12 
                 Flash- 
                 — 
                 Mini-Inverter is 
                 a. Communication error. 
               
               
                   
                 ing 
                   
                 Working but 
                 b. Inverter output AC 
               
               
                   
                   
                   
                 Has Warnings. 
                 voltage approaching limits. 
               
               
                   
                   
                   
                   
                 c. Inverter output AC 
               
               
                   
                   
                   
                   
                 current approaching limits. 
               
               
                 13 
                 — 
                 Solid 
                 Mini-Inverter 
                 a. Inverter output AC 
               
               
                   
                   
                   
                 Error. 
                 voltage out of limits. 
               
               
                   
                   
                   
                   
                 b. Inverter output AC 
               
               
                   
                   
                   
                   
                 current out of limits. 
               
               
                   
                   
                   
                   
                 c. AC is present. 
               
               
                   
                   
                   
                   
                 d. Failed impedance test. 
               
               
                 14 
                 — 
                 Flash- 
                 AC Load Error. 
                 a. Load AC frequency out of 
               
               
                   
                   
                 ing 
                   
                 limits. 
               
               
                   
                   
                   
                   
                 b. Load AC voltage out of 
               
               
                   
                   
                   
                   
                 limits. 
               
               
                   
                   
                   
                   
                 c. Load AC current out of 
               
               
                   
                   
                   
                   
                 limits. 
               
               
                 15 
                 — 
                 — 
                 LED is OFF. 
                 a. Not enough PV power. 
               
               
                   
                   
                   
                   
                 Mini-Inverter is off. 
               
               
                   
                   
                   
                   
                 b. Not enough PV power to 
               
               
                   
                   
                   
                   
                 generate AC, but the digital 
               
               
                   
                   
                   
                   
                 microcontroller is running. 
               
               
                   
                   
                   
                   
                 c. There is enough PV power 
               
               
                   
                   
                   
                   
                 and the Mini-Inverter is 
               
               
                   
                   
                   
                   
                 waking up. 
               
               
                   
                   
                   
                   
                 d. LED error, if there is 
               
               
                   
                   
                   
                   
                 power in the system. 
               
               
                   
               
             
          
         
       
     
     The message system for the m-channel off-grid AC Master Mini-Inverter also includes m 2-color LEDs to show the status for each input channel of the Mini-Inverter. The Case number, LED color (green or red), pattern (solid or flashing), and corresponding indicated messages for the input channel status is listed in Table 4. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                   
                   
                   
                 Solar Power 
                   
               
               
                 Case 
                 Green 
                 Red 
                 System Status 
                 Possible Issues 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 16 
                 Solid 
                 — 
                 Mini-Inverter is 
                   
               
               
                   
                   
                   
                 Working. 
               
               
                 17 
                 Flash- 
                 — 
                 Mini-Inverter is 
                 a. Communication error. 
               
               
                   
                 ing 
                   
                 Working but 
                 b. Inverter output AC 
               
               
                   
                   
                   
                 Has Warnings. 
                 voltage approaching limits. 
               
               
                   
                   
                   
                   
                 c. Inverter output AC 
               
               
                   
                   
                   
                   
                 current approaching limits. 
               
               
                 18 
                 — 
                 Solid 
                 Mini-Inverter 
                 a. Inverter output AC 
               
               
                   
                   
                   
                 Error. 
                 voltage out of limits. 
               
               
                   
                   
                   
                   
                 b. Inverter output AC 
               
               
                   
                   
                   
                   
                 current out of limits. 
               
               
                 19 
                 — 
                 Flash- 
                 AC Load Error. 
                 a. Load AC frequency out of 
               
               
                   
                   
                 ing 
                   
                 limits. 
               
               
                   
                   
                   
                   
                 b. Load AC voltage out of 
               
               
                   
                   
                   
                   
                 limits. 
               
               
                   
                   
                   
                   
                 c. Load AC current out of 
               
               
                   
                   
                   
                   
                 limits. 
               
               
                 20 
                 — 
                 — 
                 LED is OFF. 
                 a. Not enough PV power. 
               
               
                   
                   
                   
                   
                 Mini-Inverter is off. 
               
               
                   
                   
                   
                   
                 b. Not enough PV power to 
               
               
                   
                   
                   
                   
                 generate AC in this channel, 
               
               
                   
                   
                   
                   
                 but the digital 
               
               
                   
                   
                   
                   
                 microcontroller is running. 
               
               
                   
                   
                   
                   
                 c. There is enough PV power 
               
               
                   
                   
                   
                   
                 in this channel and the Mini- 
               
               
                   
                   
                   
                   
                 Inverter is waking up. 
               
               
                   
                   
                   
                   
                 d. LED error, if there is 
               
               
                   
                   
                   
                   
                 power in the system. 
               
               
                   
               
             
          
         
       
     
       FIG. 6  is a flow chart describing the main software program running in the digital microcontroller of a smart and scalable Mini-Inverter, which includes Control &amp; Management tasks, Redundancy tasks, and Communication tasks. At Block  300 , initialization is taking place in the microcontroller device level, peripheral level, system level, and for the interrupt service routine and analog and digital control routines. More specifically, initialization will include but is not limited to setting up registers, I/Os, and timers and enabling interrupts for the interrupt service routine. At the end, it will set Task=1. In the main program, there are three major tasks. Task  1  is related to the control and management of the Mini-Inverter. Task  2  is related to the redundancy of the Mini-Inverter. Task  3  is related to the communications of the Mini-Inverter to the outside world through the powerline Modem. After initialization, the main program enters the main loop entry point  302  and then goes to Block  304 . 
     At Block  304 , the program checks to see if Task  1  is scheduled to run. If the answer is Yes, the program will execute the functions in Block  306  to (i) turn on/off the power generation mechanism based on the conditions of the DC power source(s), the Mini-Inverter, and the AC powerline, (ii) calculate power statistics such as the amount of power generated during a certain period of time, and (iii) perform system diagnosis. Then, it sets Task=2 and returns to Block  302 , which is the entry of the main loop. 
     When the program continues, it will go through Block  304 , and reach Block  308 . At Block  308 , the program checks to see if Task  2  is scheduled to run. If the answer is Yes, the program will execute the functions in Block  310  to run the redundancy routine for each input channel that the Mini-Inverter has. Then, it sets Task=3 and returns to Block  302 . 
     When the program further continues, it will go through Block  304  and  308 , and reach Block  312 . At Block  312 , the program checks to see if Task  3  is scheduled to run. If the answer is Yes, the program will execute the functions in Block  314  to (i) set the unit address for the Mini-Inverter, and (ii) respond to queries from data gathering or acquisition devices to report the power statistics. Then, it sets Task=1 and returns to Block  302 . The main program runs continuously based on a preset loop rate to execute the scheduled tasks. At any time an interrupt is triggered, the digital microcontroller immediately processes the pending interrupt service routine. 
     The key components, functions, and steps in the interrupt service routine embedded in the digital microcontroller are described in the U.S. patent application Ser. No. 12/837,162. 
       FIG. 7  is a flow chart describing the LED Status Subroutine, which is invoked by the Diagnosis Mechanism at Block  306  of  FIG. 6 , running in the digital microcontroller of an m-channel smart and scalable Mini-Inverter, which sends signals to the LEDs on the Mini-Inverter enclosure to indicate the inverter status according to an embodiment of this invention. The Diagnosis Mechanism comprises hardware and software to watch the status of the Mini-Inverter in real-time based on case statement tables as illustrated in Tables 1 and 2. As listed in these tables, Case  1  to Case  5  indicate the system status and Case  6  to Case  10  indicate the channel status for each input channel. The LED status subroutine can simply turn the corresponding LED to the color and pattern based on the Case number. 
     At Block  320 , the subroutine checks if Case=1, if it is, the subroutine will go to Block  322  and turn the system LED to solid green, and then go to Block  339 . If the answer is No, the subroutine will go to Block  324  to check if Case=2. If it is, the subroutine will go to Block  326  and turn the system LED to flashing green, and then go to Block  339 . If the answer is No, the subroutine will go to Block  328  to check if Case=3. If it is, the subroutine will go to Block  330  and turn the system LED to solid red, and then go to Block  339 . If the answer is No, the subroutine will go to Block  332  to check if Case=4. If it is, the subroutine will go to Block  334  and turn the system LED to flashing red, and then go to Block  339 . If the answer is No, the subroutine will go to Block  336  to check if Case=5. If it is, the subroutine will go to Block  338  and turn the system LED off, and then go to Block  339 . If the answer is No, the subroutine will proceed to Block  339 . 
     Since there are multiple input channels in a scalable Mini-Inverter, the subroutine is designed to have a loop to go through each of the input channels. Let us use i as the software loop number and assume the total number of input channel is m. At Block  339 , we will first set the channel number to 1 by letting i=1. At Block  340 , the subroutine checks if Case=6, if it is, the subroutine will go to Block  342  and turn the corresponding channel LED to solid green, and then go to Block  360 . If the answer is No, the subroutine will go to Block  344  to check if Case=7. If it is, the subroutine will go to Block  346  and turn the corresponding channel LED to flashing green, and then go to Block  360 . If the answer is No, the subroutine will go to Block  348  to check if Case=8. If it is, the subroutine will go to Block  350  and turn the corresponding channel LED to solid red, and then go to Block  360 . If the answer is No, the subroutine will go to Block  352  to check if Case=9. If it is, the subroutine will go to Block  354  and turn the corresponding channel LED to flashing red, and then go to Block  360 . If the answer is No, the subroutine will go to Block  356  to check if Case=10. If it is, the subroutine will go to Block  358  and turn the corresponding channel LED off, and then go to Block  360 . If the answer is No, the subroutine will proceed to Block  360 . At Block  360 , the subroutine checks if i=m. That means, it checks if the loop has gone through all the input channels. If the answer is No, it will add the channel number by 1 at Block  362  and then starts to check the new channel at Block  340 . If the answer is Yes, the subroutine will exit. 
       FIG. 8  is a flow chart describing the LED Status Subroutine, which is invoked by the Diagnosis Mechanism at Block  306  of  FIG. 6 , running in the digital microcontroller of an m-channel smart and scalable off-grid AC Master Mini-Inverter, which sends signals to the LEDs on the Mini-Inverter enclosure to indicate the inverter status according to an embodiment of this invention. The Diagnosis Mechanism comprises hardware and software to watch the status of the off-grid AC Master Mini-Inverter in real-time based on case statement tables as illustrated in Tables 3 and 4. As listed in these tables, Case  11  to Case  15  indicate the system status and Case  16  to Case  20  indicate the channel status for each input channel of an off-grid AC Master Mini-Inverter. The LED status subroutine can simply turn the corresponding LED to the color and pattern based on the Case number. 
     At Block  370 , the subroutine checks if Case=11, if it is, the subroutine will go to Block  372  and turn the system LED to solid green, and then go to Block  389 . If the answer is No, the subroutine will go to Block  374  to check if Case=12. If it is, the subroutine will go to Block  376  and turn the system LED to flashing green, and then go to Block  389 . If the answer is No, the subroutine will go to Block  378  to check if Case=13. If it is, the subroutine will go to Block  380  and turn the system LED to solid red, and then go to Block  389 . If the answer is No, the subroutine will go to Block  382  to check if Case=14. If it is, the subroutine will go to Block  384  and turn the system LED to flashing red, and then go to Block  389 . If the answer is No, the subroutine will go to Block  386  to check if Case=15. If it is, the subroutine will go to Block  388  and turn the system LED off, and then go to Block  389 . If the answer is No, the subroutine will proceed to Block  389 . 
     Since there are multiple input channels in a scalable Mini-Inverter, the subroutine is designed to have a loop to go through each of the input channels. Let us use i as the software loop number and assume the total number of input channel is m. At Block  389 , we will first set the channel number to 1 by letting i=1. At Block  390 , the subroutine checks if Case=16, if it is, the subroutine will go to Block  392  and turn the corresponding channel LED to solid green, and then go to Block  410 . If the answer is No, the subroutine will go to Block  394  to check if Case=17. If it is, the subroutine will go to Block  396  and turn the corresponding channel LED to flashing green, and then go to Block  410 . If the answer is No, the subroutine will go to Block  398  to check if Case=18. If it is, the subroutine will go to Block  400  and turn the corresponding channel LED to solid red, and then go to Block  410 . If the answer is No, the subroutine will go to Block  402  to check if Case=19. If it is, the subroutine will go to Block  404  and turn the corresponding channel LED to flashing red, and then go to Block  410 . If the answer is No, the subroutine will go to Block  406  to check if Case=20. If it is, the subroutine will go to Block  408  and turn the corresponding channel LED off, and then go to Block  410 . If the answer is No, the subroutine will proceed to Block  410 . At Block  410 , the subroutine checks if i=m. That means, it checks if the loop has gone through all the input channels. If the answer is No, it will add the channel number by 1 at Block  412  and then starts to check the new channel at Block  390 . If the answer is Yes, the subroutine will exit. 
     To summarize, since the innovative Smart and Scalable Power Inverters or Mini-Inverters can have multiple input channels to connect to multiple solar panels, the enclosure design has to be unique and practically useful. In addition, the Mini-Inverters have to work in a harsh environment for a prolonged period of time, an LED based message system is an effective and user-friendly way of communicating with the solar system installers. This is especially true when the number of input channels is large. The design of having an LED for each input channel along with the indicated messages can help the installers troubleshoot potential mistakes or problems during the installation process. The inventive enclosure and message system for the Smart and Scalable Mini-Inverters can help the solar power industry reduce the installation cost, which accounts for a big percentage of the total cost for a solar power system.