Abstract:
An apparatus for the conversion and optimized management of power produced from renewable sources, and in particular from solar sources, in the household environment and not only, adapted to control the use of power in order to maximize the management cost-effectiveness whilst ensuring the optimization of the energy collection by the photovoltaic generator.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to systems for the conversion of power, in particular, but not exclusively, the present invention relates to systems for converting power produced by photovoltaic panel systems and adapted to be connected directly to the power grid. 
       BACKGROUND ART 
       [0002]    In the technical field of power conversion and, in particular, in the technical field of systems for the conversion of power produced by photovoltaic panel and wind systems, adapted to be connected directly to the power grid, managing the power consumption, in the household environment and not only, in the presence of power generation systems from renewable sources, is increasingly important. 
         [0003]    Systems of this type comprise a generator of power from alternative sources, such as photovoltaic panels, associated with an inverter apparatus in turn connected to the alternating voltage power grid and possibly to a group of storage batteries, adapted to operate, also in the presence of said grid AC voltage, to optimize the transfer of power to and from the grid. 
         [0004]    Said inverter apparatus, for example comprising a double conversion stage consisting of a first DC-DC converter and a second DC-AC converter, is adapted to convert the power from the alternative source (the photovoltaic panel, the wind turbine etc.) into alternating power for the supply to the primary power grid (e.g. ENEL grid). 
         [0005]    In the case of renewable sources including, in particular, photovoltaic generators, the power conversion systems of the type described have to manage the production of power by the photovoltaic generator and the supply of said power to the primary power grid. 
         [0006]    In addition to this, systems of this type must manage the rules that the power distribution provider normally imposes on the supply of power produced locally in the grid, rules which are becoming increasingly stringent and burdensome for the users. These rules ensure that the ideal situation for a household installation is the one in which said household installation is as independent from the power grid as possible, both as regards the use of energy—self-produced energy is obviously more convenient than that taken from the power grid—and as regards the supply of self-produced power to the grid, which is subject to increasingly stringent constraints and is increasingly less convenient, when not already burdensome, for individual users. 
         [0007]    Therefore, an object of the present invention is the provision of an apparatus for the conversion and optimized management of power produced from renewable sources, and in particular from solar sources, for household use and not only, adapted to control the use of power in order to maximize the management cost-effectiveness whilst ensuring the MPPT (Maximum Power Point Tracking), i.e. maximizing the energy power collection by the photovoltaic generator. 
         [0008]    Another object of the present invention is the provision of a photovoltaic system for the production of power comprising an apparatus for the conversion and optimized management of the use of power in the household environment and not only, adapted to control the use of the power produced so as to maximize the management cost-effectiveness. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Further objects, features and advantages of the present invention will become more apparent from the following detailed description, given by way of a non-limiting example and shown in the accompanying figures, in which: 
           [0010]      FIG. 1  shows a schematic block diagram of a preferred embodiment of the apparatus for the conversion and management of the power produced from renewable sources and adapted to be connected directly to the power grid, according to the present invention; 
           [0011]      FIG. 2  shows the pattern of the typical power production of a photovoltaic generator during a day; 
           [0012]      FIG. 3  shows the pattern of the typical power production of a photovoltaic generator during a day in relation to the limit imposed by some power grid providers, on the amount of self-produced power that can be supplied to the power grid; and 
           [0013]      FIG. 4  shows one of the preferred operating modes of the power conversion and management apparatus according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    With reference to the accompanying  FIG. 1 , the apparatus according to the present invention comprises: 
         [0015]    input terminals  20  coupled to a DC voltage preferably coming from a generator of renewable power, for example based on photovoltaic or wind sources; 
         [0016]    an inverter module  10  in turn comprising
       a first DC-DC conversion stage  11 , connected in input to said input terminals  20 ,   a second DC-AC conversion stage  12 , having the input coupled to the output of said first DC-DC conversion stage  11  and the output connected to the power grid  21 ,   a battery-charger module  19  associated in input to the output of said first DC-DC conversion stage  11  and to the input of said second DC-AC conversion stage  12 ,   a control module  17  adapted to adjust the operation of said inverter module  10 ;       
 
         [0021]    a battery module  13  associated, through said battery-charger module  19 , to the output of said first DC-DC conversion stage  11  and to the input of said second DC-AC conversion stage  12  according to a configuration commonly called “DC link system”, said battery module  13  being adapted to store power from said first stage  11 , during recharge, and to supply energy to said second stage  12  during discharge; 
         [0022]    at least one house load  14  associated to the output of said second stage  12  and to the power grid  21 ; 
         [0000]    power measurement means adapted to measure the power in input and output to/from said inverter module  10  and the power absorbed by or supplied to grid  21 ; 
         [0023]    a switching module  16  adapted to control the switching on or off of said at least one house load  14 . 
         [0024]    Said control module  17  is further associated to said power measurement means and to said switching module  16  and to a user interface, preferably comprising at least a display and a keyboard. 
         [0025]    Said power measurement means preferably comprises a bidirectional meter device  15  of the AC power consumption connected between the output of said second stage  12  and the power grid  21 , downstream of said at least one house load  14 . 
         [0026]    In further detail, said first DC-DC conversion stage  11  is adapted to convert the input direct voltage from a renewable source—such as a photovoltaic generator—in a direct voltage of different level and to adjust the load of the photovoltaic generator so as to optimize the operation thereof, for example, in the case of photovoltaic sources, by applying the known MPPT (Maximum Power Point Tracking) techniques. 
         [0027]    Said second DC-AC conversion stage  12  is adapted to convert the direct voltage in output from said first stage  11  into an alternating voltage adapted to be supplied to grid  21  and to supply electrical loads such as household appliances and the like; 
         [0028]    Said control module  17 , in particular, by suitably interacting with said power meter means and with said switching module  16 , is adapted to manage the use of the power produced from said renewable source so as to maximize the management cost-effectiveness, in particular by maximizing the so-called self-consumption, defined as the ratio between the amount of self-produced power or electrical energy that is consumed by the user in his home and the total amount of self-produced power or electrical energy, and the maximization of self-sufficiency, i.e. the ratio between the portion of power or electrical energy produced and used locally and the total amount of power or electrical energy consumed by the user in his home. 
         [0029]    More generally, the control module  17  of the apparatus according to the present invention allows adjusting the operation of said inverter module  10  and of said switching module  16 , so that the combination of the value of the input and output power to/from said inverter module  10  and of the value of the power absorbed by or supplied to grid  21 , is approximately equal to a required value. 
         [0030]    In this way, by acting on appropriate combinations of the various powers involved, each one optionally weighted by suitable and predefined multiplicative coefficients, for example having a value between 0 and 1, it is possible to adapt the operation of the apparatus according to the present invention to all the various conditions, optimizing the behavior thereof as a function of the result to be achieved such as cost-effectiveness, own consumption, energy self-sufficiency, etc. 
         [0031]    Considering, for example, a renewable energy source consisting of a photovoltaic generator, the graph shown in the accompanying  FIG. 2  represents the production of said photovoltaic generator in a typical day. The vertical line indicates approximately the energy production peak time. 
         [0032]    With reference to the inverter module  10  described, in one of the selectable operating modes we have that before the time in which there is the greatest power production it is preferable to fully utilize the power contained in said group of batteries  13  to meet the demand of said at least one house load  14 . In fact, in the next hours, a considerable amount of power produced by said photovoltaic generator will still be available to fully charge the battery so as to meet the evening consumption peak of said at least one house load  14 . 
         [0033]    The graph shown in the accompanying  FIG. 3  still represents the production of said photovoltaic generator in a typical day, in relation to the limit, often imposed by grid  21  providers and represented by the horizontal line, on the amount of self-produced power that can be supplied to the grid freely or at least without incurring reductions of the incentive rate or even sanctions. The leftmost vertical line indicates the time at which the above limit is exceeded. 
         [0034]    Before reaching the above limit time, therefore, it is preferable to fully use the energy contained in said group of batteries  13  to meet the demand of said at least one house load  14 . The objective therefore is to reach the time when the production limit is exceeded with the group of batteries  13  containing the minimum possible amount of power so as to be able to absorb the excess of self-produced power by recharging said group of batteries  13 . 
         [0035]    In the latter case, said group of batteries  13  is thus used as power buffer able to optimize the self-produced power management both for the loads to be supplied and for the provider&#39;s requirements governing and restricting the supply of self-produced power to the grid. 
         [0036]    To further optimize the management of self-produced power, said switching module  16  connects or disconnects the output of said second stage  12  with said at least one house load  14  so as to maximize the management cost-effectiveness, in particular by maximizing the so-called self-consumption, defined as the ratio between the amount of self-produced power that is consumed by the user in his home and the total amount of self-produced power, and the maximization of self-sufficiency, i.e. the ratio between the portion of power produced and used locally and the total amount of power consumed by the user in his home. 
         [0037]    In a preferred embodiment of the present invention, said switching module  16  includes at least one controlled switch  18  adapted to stop or enable the supply of power to said at least one house load  14 . 
         [0038]    In another preferred embodiment of the present invention, said switching module  16  may be implemented through any communication line, either wired or wireless, able to drive the switching on or off of house loads provided with a suitable communication interface (so-called smart appliances). 
         [0039]    With reference to the accompanying  FIG. 1 , we can see power P 1  produced by the photovoltaic generator, power P 2  in output from said second stage  12 , power P 3  which supplies said at least one house load  14 , the bidirectional power P 4  which flows from (in this case indicated as P 4 −) and to (in this case indicated as P 4 +) said bidirectional meter device  15  and power P 5 —bidirectional too—which flows from (in this case indicated as P 5 +) and to (in this case indicated as P 5 −) said group of batteries  13  during the discharge and recharge steps, respectively. 
         [0040]    Power P 2  generated by the inverter module  10  is a function of both the renewable power available P 1  (maximized, for example, through an MPPT algorithm implemented by said control module  17 ) and of power P 5  that can be supplied or absorbed by the battery. 
         [0041]    In fact, said control module  17  reads the bidirectional meter device  15  and receives information about the amount of power P 4  exchanged with the grid. At this point, said control module  17  adjusts the operation of said inverter module  10  so as to keep power P 4 , exchanged with the grid, at a threshold set by the user by varying the contribution of power P 5  exchanged with said group of batteries  13 . In addition, said control module  17  controls said switching module  16  so as to switch on or off a house load (boiler, heater, etc.). The control module  17  therefore acts so as to also vary the household consumptions P 3  according to the needs, based on the user&#39;s settings and on the value of instant powers P 1 , P 2 , P 5  and P 4  measured. 
         [0042]    For example, said control module  17  can operate so as to maximize the self-consumption, as defined above, in addition to the renewable power available P 1 , through, for example, the use of a suitable MPPT algorithm. The amount of self-produced power that is consumed by the user within his home is therefore equal to the self-produced power (equal to the product of the self-produced power P 2  by time t) decreased of the power supplied to grid  21  (equal to the product of power P 4 + flowing to said bidirectional meter device  15  by time t). 
         [0043]    Therefore, in general terms, the aim is to maximize the following ratio: 
         [0000]      [(P2)*t−(P4+)*t]/P2*t.
 
         [0044]    To do so, said control module  17  can operate so as to drive said switching module  16  according to the following modes:
       a) The adjustment of said inverter module  10  and the switching on of said switching module  16 , and thus the closure of one or more switches  18  belonging to it, are dependent on the achievement, by the self-produced power P 4 + which is supplied to grid  21  and is detected by said bidirectional meter device  15 , of a threshold (P 4 +) th . In practice, when the amount of self-produced power which is supplied to the grid P 4 + becomes too large and is likely to become an undesired excess for the provider or the user, one or more of said at least one house load  14  is activated so as to use this excess for household appliances connected to said inverter module  10 . In this case, self-consumption is maximized by keeping the ratio [(P 2 )*t−(P 4 +)*t]/P 2 *t high and exceeding the limits imposed by the provider on the amount of self-produced power supplied to the grid is prevented as well. If the activation of one or more of said at least one house loads  14  is not sufficient to fall within the limits desired, in this operating mode it is possible to further limit the power generated by said inverter of said second stage  12 .   b) The adjustment of said inverter module  10  and the activation of said switching module  16 , and thus the closure of one or more of the switches belonging to it, are dependent on the achievement of a threshold for the level of self-produced power P 4 + that is supplied to grid  21 . In practice, when the amount of self-produced power that is supplied to grid P 4 + becomes too large and exceeds a certain activation threshold, the amount of power P 5 − which is used is increased to charge said group of batteries  13  and/or one or more of said at least one house loads  14  is activated. The goal, in this case, is both to prevent exceeding the limits set by the provider on the amount of self-produced power and supplied to the grid and to maximize self-consumption by assigning a priority to the house loads  14  in relation to the battery charge while always maximizing the available renewable power P 1  through, for example, the use of a suitable algorithm MPPT. Since loads  14  are priority, in order to meet the requirements of a load the battery charge may be interrupted and it may also be set to discharge. If the activation of one or more of said at least one house loads  14  is not sufficient to fall within the limits desired and the limit of self-produced power P 4 + that is supplied to the grid imposed by the grid provider is still exceeded, in this operating mode it is possible to limit power P 2  generated by said inverter of said second stage  12 .   c) The activation of said switching module  16 , and thus the closure of one or more of the switches belonging to it, are dependent on the achievement of a threshold for the level of power P 2  supplied by said second stage  12 . In practice, when the amount of power supplied by the inverter of said second stage  12  becomes too large and exceeds the activation threshold, one or more of said at least one house loads  14  is activated. In this case, it is not necessary to use said bidirectional meter device  15 , since power P 2  is read directly by the inverter of said second stage  12  and having to reduce power P 2  as in previous case b) is also prevented.   d) The adjustment of said inverter module  10  and the activation of said switching module  16 , and thus the closure of one or more of the switches belonging to it, take place in such a way as to give higher priority to the discharge of said battery module  13  (for example using the power contained therein for supplying said at least one house load  14  and/or to send it, converted into AC, to grid  21 ) in a first time window and then give, in a second time window, higher priority to the charging of said battery module  13 . In this way, it is ensured that said battery module  13  contains the least possible amount of power at the end of said first time window, making itself available to accumulate a possible excess of power provided in input to said inverter module  10  in successive time windows.   e) As shown in the accompanying  FIG. 4 , said switching module  16  is associated with a plurality of time windows within which a different activation threshold is evaluated, relative to a different control parameter. In this way, said activation threshold may be related to the self-produced power P 4 + that is supplied to grid  21 , to the sum of the self-produced power supplied to the grid and of the battery charge power (P 4 +)+(|P 5 −|), or to the photovoltaic power P 1  generated.       
 
         [0050]    Other operating modes may be programmed and selected by the user by acting on said control module  17  through the respective user interface, preferably comprising at least a display and a keyboard. 
         [0051]    It is also clear that the operating modes described, based on the reading, calculation and setting of power values, may of course be extended to similar operating modes not based on the power value but on the electrical energy power, simply by introducing a suitable reference time interval since energy, as known, is equal to power multiplied by time.