Patent ID: 12218628

DETAILED DESCRIPTION

Reference will now be made in detail to features of various embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The features are described below to explain various embodiments by referring to the figures.

Before explaining various aspects in detail, it is to be understood that embodiments are not limited in their application to the details of design and the arrangement of the components set forth in the following description or illustrated in the drawings. Embodiments are capable of other features or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

It should be noted, that although the discussion herein relates primarily to photovoltaic systems, various embodiments may, by non-limiting example, alternatively be configured using other distributed power systems including (but not limited to) wind turbines, hydro turbines, fuel cells, storage systems such as battery, super-conducting flywheel, and capacitors, and mechanical devices including conventional and variable speed diesel engines, Stirling engines, gas turbines, and micro-turbines.

By way of introduction, various aspects are directed to circuitry integrated or integrable with a photovoltaic panel to form a photovoltaic module. The circuitry allows for galvanic isolation between the photovoltaic panel and the output of the circuitry.

According to an illustrative feature of various embodiments, the circuit is connected or connectible at the input terminals to a photovoltaic panel. The output terminals may be connected to form a string of photovoltaic modules. Multiple photovoltaic modules may be parallel connected to form the photovoltaic solar power harvesting system

The term “switch” as used herein may refer in various embodiments to an active semiconductor switch, e.g. a field effect transistor (FET), in which a controllable and/or variable voltage or current is applied to a control terminal, e.g. gate, of the switch which determines the amount current flowing between the poles of the switch, e.g. source and drain of the FET.

The term “activate” a switch as used herein may refer to opening, closing and/or toggling i.e. alternatively opening and closing the switch.

The term “galvanic isolation” as used herein is a way of isolating functional sections of electrical circuits and/or systems from the movement of charge-carrying particles from one section of an electrical circuit and/or a system to another. That is, there is no direct current between the functional sections of electrical circuits and/or systems. Energy or information, however, can still be exchanged between the sections of electrical circuits and/or systems by other means, e.g. capacitance, mutual inductance or electromagnetic waves, or by optical, acoustic or mechanical means.

The term “dual DC” input or output may refer in various embodiments to positive and negative terminals referenced to each other and referenced to a third terminal, such as ground potential, electrical ground or a neutral of an alternating current (AC) supply which may be connected to electrical ground at some point.

The term “single DC” input or output refers to positive and negative terminals referenced to each other, but not referenced or connected to a ground potential, electrical ground or a neutral of an alternating current (AC) supply, unless one of the terminals is coupled to a reference.

The term “two-level inverter” as used herein, refers to and inverter having an AC phase output having two voltage levels with respect to a negative terminal. The negative terminal is common to the AC phase output and the direct current (DC) input of the two-level inverter. The alternating current (AC) phase output of the two-level inverter may be a single phase output a two phase output or a three phase output. Therefore, the single phase output has two voltage levels with respect to the negative terminal. The two phase output has two voltage levels with respect to the negative terminal for each of two phases. The three phase output has two voltage levels with respect to the negative terminal for each of three phases.

Similarly, the term “three-level inverter” as used herein refers to and inverter having an alternating current (AC) phase output having three voltage levels. The AC phase output has three voltage levels with respect to a negative terminal. The negative terminal may be common to the AC phase output and the direct current (DC) input of the three-level inverter. The alternating current (AC) phase output of the three-level inverter may be a single phase output, a two phase output, or a three phase output. Therefore, the single phase output has three voltage levels with respect to the negative terminal. The two phase output has three voltage levels with respect to the negative terminal for each of the two phases. The three phase output has three voltage levels with respect to the negative terminal for each of the three phases.

The three-level inverter compared with the two-level inverter may have a cleaner AC output waveform, may use smaller size magnetic components and may have lower losses in power switches, since more efficient lower voltage devices may be used. Three-level inverter circuits may have dual (positive and negative) direct current (DC) inputs.

Reference is now made toFIG.1of a photovoltaic solar power harvesting system10, illustrating various aspects. Power harvesting system10includes multiple photovoltaic panels101connected respectively to multiple junction boxes103to form multiple photovoltaic modules. Junction box103may provide electrical input terminals and mechanical support for bus-bars a, b and c (not shown), which may be used as an input to junction box103from panel101. Junction box103may be attachable and/or re-attachable to panel101or may be permanently attachable to panel101using for example a thermoset adhesive, e.g. an epoxy adhesive, screws, or other mechanical attachment. The electrical voltage outputs (Vi) at output terminals of junction boxes103may be connected in series to form a series photovoltaic serial string107through which a string current (Istring) may flow. Multiple strings107may be connected in parallel and across an input of a load105. Viand Istringmay be different for every photovoltaic module and string107, respectively. Load105may be a direct current (DC) load such as a DC motor, a battery, an input to a DC to DC converter, or a DC input to a DC to AC inverter.

Reference is now made toFIG.2b, which shows a plan view photovoltaic panel101. The plan view shows casing220and photovoltaic cells252with tracks250showing through transparent glass228and sheet224b.

Reference is now made toFIG.2awhich shows a partial cross section290of section YY shown inFIG.2bfor a photovoltaic panel101. The partial cross section is located near a side220aof casing220. Side220ais located at the perimeter of casing220as illustrated inFIG.2b. Casing220includes a back220band four sides220a. Casing220may be fabricated using a metal alloy, aluminum, stainless steel, plastic or other material having sufficient strength to house the panel components. Casing220may hold together a sandwich of various sheets. Nearest to back220bis an insulating sheet222. Next to insulating sheet222is a reactive encapsulant sheet224a. Encapsulant sheet224amay be made from a polymer, e.g., ethylene vinyl acetate (EVA) polymer, polyvinyl-butyral (PVB), etc. Next to reactive encapsulant sheet224ais a photovoltaic substrate226followed by another reactive encapsulant sheet224b, that may be transparent. Encapsulant sheet224bmay be made out of the same or similar material as224a. Finally after reactive encapsulant sheet224bis a sheet of low iron flat glass228. The side (i.e., surface) of photovoltaic substrate226adjacent to reactive encapsulant sheet224bis where the metal tracks250(not shown) may be located. Metal tracks250connect electrically the photovoltaic cells252(not shown) of photovoltaic substrate226. Junction box103may be mounted on back220band bus-bars a, b and c (not shown) may terminate inside junction box103and connect to tracks250. In other embodiments, junction box103is mounted separate from panel101.

Reference is now made toFIG.3awhich shows more details of junction box103and photovoltaic panel101shown inFIG.1, according to an illustrative feature. According to the example, photovoltaic panel101includes two sub-strings11of serially connected photovoltaic cells which output to bus-bars a, b and c which are the input terminals to junction box103. Sub-strings11may include one or more cells. The input of junction box103may include two bypass diodes120aand120bwith anodes connected respectively to bus-bars c and b and cathodes connected respectively to bus-bars a and b. Connected across bus-bars a and c is the input to a direct current (DC) to DC converter322. When sub-strings11are illuminated, the current into converter322is substantially that of current IPVflowing from strings11and the voltage VPinput to converter322is the voltage across bus-bars a and c. The output of converter322is Viand the output of a converter322may be placed in series with other panels101and/or junction boxes103to form a string107as shown inFIG.1.

Reference is now made toFIGS.3band3cwhich show implementations of converter322shown inFIG.3a, according to various embodiments. BothFIGS.3band3care isolating DC to DC converters shown by converter circuits322aand322brespectively. Converters322aand322bhave primary inputs (VP) which may be connected across a panel101as shown inFIG.3aand secondary outputs (Vi) which may be connected in series to form a serial string107as shown inFIG.1.

Converter322ahas a single switch S1wired in series with a primary side of a mutual inductor L. The secondary side of inductor L is wired in series with a diode D. The anode of diode D may be connected to one end of inductor L and the cathode of diode D may be connected to the positive voltage terminal of secondary output Vi. The other end of inductor L not connected to diode D may be connected to the negative terminal of secondary output Vi. A resistor R and capacitor C may be wired in parallel across the secondary output Vi. In an alternate version, the cathode of diode D may be connected to one end of inductor L, the anode of diode D may be connected to the negative terminal of secondary output Vi, and the other end of inductor L not connected to diode D may be connected the positive terminal of secondary output Vi. A resistor R and capacitor C may be wired in parallel across secondary output Viin the alternate version.

Converter322amay be an -isolating buck-boost converter with the inductor (L) split to form a transformer, so that voltage ratios of V1and V2are multiplied as well as having galvanic isolation between primary input VPand secondary output Vi.

Converter322bmay have a single switch S1wired in series with a primary side of a transformer Tr. Again transformer Tr provides galvanic isolation between primary input VPand secondary output Vi. One end of the secondary winding of transformer Tr may connect to the anode of a diode D1and the cathode of D1may connect to one end of an inductor L. The other end of inductor L may be connected to the positive voltage terminal of secondary output Vi. The other end of the secondary winding may be connected to the negative voltage terminal of secondary output Vi. The other end of the secondary winding may connect to the anode of diode D2and the cathode of D2may connect to the cathode of diode D1. A capacitor C may be connected across secondary output Vi. Other variation of converter322bmay be used with D1, D2, L and C used in various other arrangements to provide the same output Vi Converter322bmay be a forward converter and performs the same function of converter322aand may be more energy efficient than converter322a. Numerous other isolated DC to DC converter topologies may be used with respect to converter322, for example, ringing choke converter, resonant forward, half-bridge and full-bridge converters. A feature of DC to DC converters may be an adjustable duty cycle for conversion of DC power. Converters322aand322b, therefore, may be adjusted to give an adjustable desired open circuit voltage across secondary output Viprior to connection in a string107.

Reference is now made toFIG.3dwhich shows an isolating DC to alternating current (AC) isolating inverter322c, according to an illustrative feature. A switch S1may be wired in series with the primary side of a transformer T. In some variations, switch S1may be a metal oxide semi-conductor field effect transistor (MOSFET). A DC voltage (VP) may be applied across the source of switch S1and one side of primary coil T. The other side of primary coil T may be connected to the drain of switch S1. In some variations the source and drain of S1may reversed. A diode D may be connected in series with the secondary coil with of transformer T with the cathode of D connected to one end of the coil. Connected across the series connection of the secondary coil of transformer T and diode D may be capacitor C1. One end of capacitor C1may be connected to the anode of diode D and the other end of capacitor C1may be connected to the end of the secondary coil not connected to the diode D. The end of the secondary coil not connected to diode D may also be connected to one end of an inductor L and the other end of inductor L connected to anodes of switch control rectifiers SAC1, SAC2and one end of capacitor C2. The other end of capacitor C2may connect to the anode of diode D and the cathodes of switch control rectifiers SAC3and SAC4. The cathode of switch control rectifier SAC1may connect to the anode of switch control rectifier SAC3to form a first terminal of secondary AC output VGrid. The cathode of switch control rectifier SAC2may connect to the anode of switch control rectifier SAC4to form a second terminal of secondary AC output VGrid. Multiple secondary AC outputs (VGrid) from multiple inverters322cmay be connected in either series to give a series AC string or in parallel to give a parallel AC string.

Converter circuits322a,322band322cmay having one terminal of respective primary sides (VP) connected to a ground and/or casings220of panels101which may also be connected to the ground. The ground may be electrical earth and/or a local earth provided in the immediate vicinity of panels101. Further connections to electrical earth may be made by bonding to casings220of panels101and framework used to mount panels101.

Reference is now made toFIG.3ewhich shows a photovoltaic module30, according to an illustrative feature. Photovoltaic module30includes one or more panels101series connected with sub-strings11which are in series and connected across the primary input (VP) of an isolating converter322. Converter322provides a secondary output (VS) which may be galvanically isolated from the primary input (VP). The secondary output (VS) may be DC and/or AC. Circuitry of converter322may be integrated or integrable with a photovoltaic panel101and/or housed in a junction box103.

Reference is now made toFIG.5which shows a method501which may be applied to system10/10aand junction boxes103, according to an illustrative feature as shown inFIGS.1and4. With reference toFIG.3a, in step503, a single primary DC input (VP) of converter322is connected to bus-bars a and c via terminations, which may be located in in junction box103. Where converter103has a dual DC input, connection may be made to bus bar b. In the case of dual DC input into converter322bus bar b may be additionally connected to a local ground or electrical earth. Similar connections may be made in multiple converters322(which may be in respective multiple junction boxes103) integrated with panels101. In step505, the outputs (Vi) of converters322may be wired in series to form a string107illustrated inFIG.4. During the irradiation of strings107if an isolating converter322is used, in step507, DC power on the primary input (VP) may be converted with galvanic isolation to the secondary output (Vi). The galvanic isolation between primary input (VP) and secondary output (Vi), may additionally allow for different ground potentials on either side of the primary input (VP) and the secondary output (Vi). The galvanic isolation of different ground potentials, on either side of322, may allow for use of various configurations of single or dual DC input and/or outputs on the primary inputs (VP) and the secondary outputs (Vi) within string107, since each VPmay be isolated from every other VP.

By way of numerical example, a comparison may be made between ten panels101having converters322in a string107and ten panels without converters322connected in a serial string. In the serial string the first panel101has the negative terminal connected to a ground and the chassis of the first panel101connected to the ground as well. The remaining nine panels101only have their respective chassis connected to the ground. If the output of each panel is 40 Volts, then the top tenth panel101has a voltage of 10 times 40V=400 Volts at its positive output terminal and the ninth panel has voltage of 9 times 40=360 Volts at its positive output terminal. By comparison in a string107using isolating converters, the primary side of the respective converters322have a ground connection as shown inFIG.3eas well as the chassis of each respective panel101being connected to the ground as well. In such a string107with isolating converters322, the primary side and hence the output of each panel101is at 40 Volts by virtue of the galvanic isolation between the primary side and the secondary side of each respective converter322. The secondary sides of converters322in series string107still give 10 times 40V=400 Volts but each panel101in string107only operates at 40 Volts with respect to the ground. Therefore, the voltage rating of each panel101in a string107is only 40 Volts compared to the panels101in the serial string of panels101. Panels101in the serial string may have to have a voltage rating of at least 400 Volts if the first panel101has the negative terminals connected to the ground and possibly a much greater rating of 400 Volts if the first panel101has the negative terminal not connected to the ground. The negative terminal not connected to the ground may allow the voltage of the serial string to float, so that the tenth panel101in the serial string may have a voltage greater than 400 Volts.

Further, as shown inFIG.4, the series string of secondary outputs of converters322may be referenced to ground at various points to provide a reduced maximum voltage with respect to the ground reference of the primary side. For example, a secondary output of an intermediate converter in each string may be grounded, such that converters connected in the string on one side (e.g., the positive side) of the ground point may have a positive voltage with respect to ground, and converters connected in the string on the other side (e.g., the negative side) of the ground point have a negative voltage. In the example above, the 400V across the secondary output string can be referenced to a range of −200V to +200V with respect to the ground reference. Thus, the maximum primary to secondary side voltage difference can be reduced from 400V to 200V. Reference is now made toFIG.6which shows a method601which may be applied to system10/10aand a junction box103, according to an illustrative feature. Method601may be applied to junction box and/or panel101, prior to making a series connection of the outputs (Vi) of converters322to form a string107. In step603, a single primary DC input (VP) of converter322is connected to bus-bars a and c via terminations, which may be located in junction box103. Where converter103has a dual DC input, connection may be made to bus bar b. In step605a panel101may be then irradiated to provide a voltage on the primary input (VP) of converter322. Alternatively, another DC voltage source may be connected to the primary input (VP) of converter322. With a panel101connected (step603) to the primary input (VP) and the panel101irradiated (step605) or DC voltage applied to the primary input (VP), DC power on the primary input (VP) may be converted with galvanic isolation to the secondary output (Vi). During the conversion of power by converter322, the duty cycle of converter322may be adjusted to vary and set the open circuit voltage on the secondary output (Vi) of converter322(step609). Alternatively, the duty cycle of converter may be adjusted to vary and set the operating voltage on the secondary output (Vi) of converter322when the secondary output (Vi) is connected to a load and/or within a string107.

The indefinite articles “a”, “an” is used herein, such as “a photovoltaic panel”, “a junction box” have the meaning of “one or more” that is “one or more photovoltaic panels” or “one or more junction boxes”.

Aspects of the disclosure have been described in terms of illustrative embodiments thereof. While illustrative systems and methods as described herein embodying various aspects of the present disclosure are shown, it will be understood by those skilled in the art, that the disclosure is not limited to these embodiments. Modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. For example, each of the features of the aforementioned illustrative examples may be utilized alone or in combination or sub combination with elements of the other examples. For example, any of the above described systems and methods or parts thereof may be combined with the other methods and systems or parts thereof described above. For example, one of ordinary skill in the art will appreciate that the steps illustrated in the illustrative figures may be performed in other than the recited order, and that one or more steps illustrated may be optional in accordance with aspects of the disclosure. It will also be appreciated and understood that modifications may be made without departing from the true spirit and scope of the present disclosure. The description is thus to be regarded as illustrative instead of restrictive on the present disclosure.