Abstract:
The present disclosure relates to a photovoltaic power installation configured to deliver power to a power distribution grid at a point of common coupling, the photovoltaic power installation including a determination unit configured to determine an amount of self-consumed power of the photovoltaic power installation, and a first power inverter configured to generate power in accordance with 1) the determined amount of self-consumed power, and 2) a power level to be delivered at the point of common coupling. The disclosure further relates to an associated method.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Continuation of International Application number PCT/DK2013/050427 filed on Dec. 12, 2013, which claims priority to Danish Application number PA 2012 00824, and European Application number EP13000226.4, filed on Jan. 17, 2013, the contents of which are incorporated by reference in their entirety. 
       FIELD 
       [0002]    The present disclosure relates to a photovoltaic power distribution system. In particular, the present disclosure relates to a dynamic photovoltaic power distribution system taking into account the power consumption of the power distribution system itself. 
       BACKGROUND 
       [0003]    Photovoltaic (PV) power installations are becoming more and more popular both in relation to domestic installations and industrial installations. However, PV power installations of today are not used in an efficient manner due to a lack of control of the installation&#39;s own power consumption. 
       SUMMARY 
       [0004]    Some embodiments of the present disclosure provide a PV power distribution system that constantly delivers a predetermined amount of power at a point of common coupling. 
         [0005]    Some embodiments of the present disclosure provide a PV power distribution system that takes into account or compensates for the system&#39;s own consumption of power. 
         [0006]    In a first embodiment, a photovoltaic power installation configured to deliver power to a power distribution grid at a point of common coupling is disclosed. The photovoltaic power installation comprises 
         [0007]    a determination component or unit configured to determine an amount of self-consumed power of the photovoltaic power installation, and a first power inverter configured to generate power in accordance with the determined amount of self-consumed power, and a predetermined power level to be delivered at the point of common coupling in accordance with a power reference. 
         [0008]    It is an advantage of the photovoltaic (PV) power installation of one embodiment of the present disclosure that it may ensure that a predetermined power level delivered at the point of common coupling (PCC) complies with a power reference. Thus, the PV power installation of the present disclosure may compensate for fluctuations, intended or unintended, in the amount of self-consumed power. 
         [0009]    The power reference may be provided to the installation in various ways, such as by wireless or wired communication from the operator of the power grid or by the provision of one or more relays by the operator of the power grid. 
         [0010]    As an example the power reference may set a curtailment to a level of 70% of the nominal power level of the installation. This may imply that a power level of 70% of the nominal capacity of the installation is to be delivered at the PCC. For a 10 kW installation this corresponds to a maximum of 7 kW that is fed into the power grid until the power reference is changed. Alternatively, the power reference may be provided as an absolute value, such as for example a fixed value of 7 kW, or a value based on the installation&#39;s nominal power, name-plate power, acquired measured power, or on STC (Standard Test Conditions) of PV modules. Other alternatives for the power reference value may be dynamic values, such as those based on the time of day or year (schedule-based), or input obtained through an MMI (Man-Machine Interface) such as a display, personal computer, tablet computer or smartphone. 
         [0011]    The PV power installation of the present disclosure may be a domestic installation, i.e. an installation typically having a capacity below 10 kW. Alternatively, the power installation may form part of a larger industrial installation. 
         [0012]    The amount of self-consumed power may be determined in different ways. Firstly, the amount of self-consumed power may be measured directly within the installation by appropriate measuring means. Secondly, the amount of self-consumed power may be calculated from other power measurements within the installation. In this scenario the determining means may comprise the following measuring means; means for measuring a power level produced by the photovoltaic power installation and means for measuring a power level delivered at the PCC. 
         [0013]    The photovoltaic power installation may further comprise a second power inverter interconnected to the first power inverter via a data network, such as an Ethernet-based or wireless network. In this scenario the first power inverter may be configured as a master power inverter, and the second power inverter is configured as a slave power inverter. Obviously, additional slave power inverters being controllable by the master power inverter may be provided as well. The master inverter may be configured to provide output power references to the slave inverter in accordance with the determined amount of self-consumed power and the power reference. 
         [0014]    The master power inverter may be configured to receive and process information about the determined amount of self-consumed power. This information may originate from a direct measurement of self-consumed power, or it may originate from indirect measurements upon which the self-consumed power is calculated. Moreover, the master inverter may be configured to receive and process the power reference. The power reference may be received via a wireless receiver means, such as a radio receiver. As an example, a distribution network operator may provide a fixed or a dynamic power reference to the installation via the wireless receiver means, or alternatively via a wired connection. Alternatively, the power reference may be provided locally by the user or owner of the installation in agreement with the relevant authorities. 
         [0015]    The means for measuring a power level produced by the photovoltaic power installation may form an integral part of the first power inverter. 
         [0016]    In a second embodiment, the present disclosure relates to a method for operating a photovoltaic power installation configured to deliver power to a power distribution grid at a point of common coupling. The method comprises 
         [0017]    determining an amount of self-consumed power of the photovoltaic installation, and 
         [0018]    operating one or more power inverters of the photovoltaic power installation in accordance with: 
         [0019]    the determined amount of self-consumed power, and a power level to be delivered at the point of common coupling in accordance with power reference. 
         [0020]    Thus, the method of the second embodiment is concerned with the use of the photovoltaic power installation of the first embodiment. For that reason the configuration and implementation of the installation may be similar to what has been disclosed in connection with the first aspect. 
         [0021]    Generally, information about the determined amount of self-consumed power and the power reference may be provided to a master power inverter among the one or more power inverters. The master power inverter may provide output power references to one or more slave power inverters among the one or more power inverters in accordance with the determined amount of self-consumed power and in accordance with the power reference. The power reference of the master inverter may be provided to the one or more slave inverters via a data network, such as an Ethernet-based or wireless network. 
         [0022]    The properties of the power reference may be as disclosed in connection with the first embodiment. Thus, the power reference may be a fixed or a dynamic power reference provided by an operator of the power distribution grid or a local user of the installation. As mentioned earlier the power reference may reflect a percentage of a nominal power capacity of the photovoltaic power installation or it may be provided as an absolute value. In both cases the power reference may be a fixed or a dynamic value. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The present disclosure will now be described in further details with reference to the accompanying figures, where 
           [0024]      FIG. 1  shows a schematic of a simple power installation, and 
           [0025]      FIG. 2  shows a schematic of a master/slave power installation. 
       
    
    
       [0026]    While the disclosure is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of examples in the drawings and will be described in detail herein. It should be understood, however, that the disclosure is not intended to be limited to the particular forms disclosed. Rather, the disclosure is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0027]    In its most general aspect the present disclosure relates to a PV power installation that is capable of maintaining a predetermined power level at a PCC independent of an actual level of self-consumed power. 
         [0028]    Referring now to  FIG. 1  a schematic of a PV power installation  100  according to the present disclosure is depicted. As depicted in  FIG. 1  the installation  100  comprises a PV array  101  which is connected to a power inverter  102 . The power inverter  102  is configured to convert DC power from the PV array  101 , or any other DC energy sources, to AC power, such as single or multiphase AC power. The installation is adapted to feed power, such as three-phase AC power, into a power grid (not shown) via PCC  107 . The power may optionally be fed into the power grid via a grid transformer (not shown). 
         [0029]    The PV power installation  100  has a self-consumption of power indicated by bulb  103 . The term self-consumption should here be understood as in principle any kind of drawing of power from between the power inverter  102  and the PCC  107 . The power may be drawn from a single phase or from a plurality of phases. 
         [0030]    According to the present disclosure, the amount of self-consumed power must be determined. Still referring to  FIG. 1 , this determination can be performed in various ways. Firstly, the amount of self-consumed power may be measured directly by power meter  105 . Alternatively, the amount of self-consumed power may be determined by subtracting the power level measured by meter  106  from the power level measured by meter  104  while noting that meter  104  may optionally be integrated in the power inverter  102 . In any case the following expression applies: 
         [0000]    
       
      
       P 
       INVERTER 
       =P 
       self 
       +P 
       PCC  
      
     
         [0000]    where P INVERTER  is the inverter generated power, P self  is the self-consumed power and P PCC  is the amount of power delivered at the PCC. 
         [0031]    Information relating to the amount of self-consumed power is provided to or calculated by the power inverter  102  or to a controller (not shown) for further data processing. The power inverter  102  or the controller may use this information for controlling the power output of the power inverter  102  or for controlling a total amount of self-consumed power. The latter may involve activation or deactivation of for example home or industrial appliances in order to increase or decrease the consumed amount of power, respectively. 
         [0032]    Referring now to  FIG. 2 , a PV power installation  200  comprising a master inverter  201  and a slave inverter  202  is depicted. Additional slave power inverters may optionally be provided. The master and slave power inverters communicate via an Ethernet, or similar communication network  208 , such as RS485, Bluetooth, ZigBee, Zeeware etc. The AC power generated by inverters  201 ,  202  is fed to the PCC via the internal power grid  210 . The power inverters  201 , 202  are fed from respective PV modules/arrays  212 ,  213 . A wireless receiver  208 , such as a radio receiver, which is adapted to receive a power reference, is connected to the master power inverter  201  via communication link  211 . The power reference may alternatively be provided via a wired connection. 
         [0033]    The power reference may be provided by the operator of the power distribution grid. Alternatively, the power reference may be provided by a local user of the installation in agreement with the relevant authorities. The local user may enter the power reference into the installation by using a keyboard or touchscreen of the installation. As previously discussed this power reference may be a fixed reference or a dynamic reference. The power reference itself may reflect various parameters, such as an amount of power (fixed or variable) to be delivered at the PCC, a percentage of the nominal capacity of the installation (i.e. power a curtailment level) etc. 
         [0034]    Results of various power measurements within the installation are provided from measuring devices  203 ,  204 ,  205  to the master power inverter  201  via a common communication link  209 . Only two of the measuring devices are needed in order to gain the required power information. The installation&#39;s self-consumption is illustrated by bulb  207 . 
         [0035]    The master power inverter  201  is capable of controlling the slave power inverter  202  via communication link  208 . Thus, the master power inverter  201  controls its own power production as well as the power production of the slave power inverter  202  (and additional slave inverters as well) using at least one of the following control parameters:
   1. The available amount of power from the PV module/array   2. The power reference   3. The amount of self-consumed power   
 
         [0039]    The nominal power capacity of each power inverter may vary from a few kW to, in principle, any capacity. Also, the nominal power capacity of the installation as a whole may be tuned to specific purposes by selecting an appropriate number of power inverters. 
         [0040]    The applicability of the PV power installation according to the disclosure is huge, and it may thus cover the following approaches in which the availability of measurements of two of: 1) the available amount of power from the PV module/array, 2) the power supplied at the point of common coupling and 3) the amount of self-consumed power together with the power reference, enable the PV power installation to control the self-consumed power so that some optimum state is achieved. 
         [0041]    This optimum state may be, for example, that as much power is generated by the PV module/array whilst complying the curtailment level in force. As an example the power reference may set a curtailment to a level of 70% of the nominal power level of the installation. This may imply that a power level of 70% of the nominal capacity of the installation is to be delivered at the PCC. For a 10 kW installation this corresponds to a maximum of 7 kW which is fed into the power grid until the power reference is changed. 
         [0042]    In the case that the installation is capable of generating, for example, 9 kW at a particular point in time, selected consumer devices, such as home or industrial appliances, may be activated automatically by the installation. In this example the total power consumption of the selected consumer devices must be kept above 2 kW in order to comply with the curtailment level of 70% while simultaneously allowing the PV module/array to generate as much of the 9 kW available at the time as possible. 
         [0043]    Approaches suitable for realizing this method include the following: 
       Active Timing of Home Appliances  
       [0044]    This approach is considered the easiest way to increase the self-consumption of the installation. It only requires a small change in consumer&#39;s behavior, namely that the consumer delays the start of a certain appliance, i.e. the consumer does not start a certain appliance immediately when the appliance is ready. Instead the consumer programs a starting time of the appliance depending on the PV power installation and season. This approach may be relevant for washing of clothes loaded into the washing machines. 
       Use of Signaling Output of Power Inverter Based on Available PV Power  
       [0045]    Home appliance devices of today, such as washing machines and clothes dryers, have built-in delay functions. It is expected that these home appliance devices will be prepared for external triggering in the future. Thus, in case a master power inverter is capable of generating triggering signals for external use the PV power installation may trigger, and thereby start, home appliance devices, such as washing machines, clothes dryers etc., at appropriate time periods, such as during periods with high power production. 
       Utilization of Signaling By PV Inverter Based on PV Production and on Power Flow at PCC 
       [0046]    This control scheme involves external information from power meters, power production, the existence of a power curtailment (remote or local, temporary or constant) requirement, as well as information, such as the time of day, season, load profile, consumption of home appliances and specific/historical data (i.e. production and load profiles) if available. The available information is applied in order to decide which home appliance it would be optimal to use, and subsequently signal (by visualization, SMS, relay or direct control) that a particular home appliance or appliances, or a sequence of home appliances, should be turned on or off. The described approach could also be used when power curtailment is applied at the PCC to evaluate the true generation plant maximum output power. 
         [0047]    Another way of signaling is visualization to the end user. This could be done in a variety of ways, such as a warning light (light bulb, LED etc.), push notification, Twitter, sending an SMS etc. This method of signaling overcomes the problem that home appliances are not currently remotely controllable, i.e. directly triggerable using a trigger signal. Instead this method makes use of the fact that the end user, or someone in the end user&#39;s family, might be at home, and thereby able to turn on the relevant home appliances. 
         [0048]    Many variations and modifications may be made to the preferred embodiments of the disclosure without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of the present disclosure, as defined by the following claims.