EP3741040A1

EP3741040A1 - Smart cell-level power managed pv module

Info

Publication number: EP3741040A1
Application number: EP19715263.0A
Authority: EP
Inventors: Olindo ISABELLA; Hesan ZIAR; Miroslav Zeman
Original assignee: Technische Universiteit Delft
Current assignee: Technische Universiteit Delft
Priority date: 2018-01-18
Filing date: 2019-01-17
Publication date: 2020-11-25
Also published as: WO2019143242A4; TW201937746A; WO2019143242A1; NL2020289B1

Abstract

The present invention is in the field of a cell-level power managed PV-module, and a method of operating said module, such as operating a large number of PV-modules, such as in a solar farm. Typically a multitude of individual PV-cells is present at a front side of the module that need to be operated and controlled.

Description

Smart Cell-level Power Managed PV Module

FIELD OF THE INVENTION

The present invention is in the field of a cell-level power managed PV-module, and a method of operating said module, such as operating a large number of PV-modules, such as in a solar farm. Typically a multitude of individual PV-cells is present at a front side of the module that need to be operated and controlled .

BACKGROUND OF THE INVENTION

In the field of energy conversion PV-systems are known. These systems generally use at least one PN-junction to convert solar energy to electricity.

A disadvantage of such a system is that the conversion per se is not very efficient, typically, for Si-solar cells, lim ited to some 23%. Even using very advanced PV-cells, such as GaAs cells, the conversion is only about 30%. Inherently these systems are limited in their conversion.

Further these systems are still relative expensive to manu facture .

Systems are typically not optimized in terms of energy production, use of energy, availability of energy, etc., espe cially in view of consumption patterns of a building. Integration with for instance other household applications is other wise typically not provided.

Integration of systems is typically also in its initial stage. Not many applications are available yet.

So existing PV systems show huge power output losses, and significant quantities of generated power are not usable be cause of e.g. too low power at low light conditions, due to dirty cells, sub-optimal performance of certain cells, and shading, effecting the total output of a PV-module. Using a micro inverter or the like does not solve this problem.

Especially shading causes a huge power loss in a PV system and it is typically not proportional to the shaded area. Be sides, it also causes hot-spots on PV cells and ages the PV module faster.

Bypass diodes may be used in commercial PV modules to re duce effects of hot spots or shading on a PV module. Recently, the active bypass technology has been developed to reduce hotspot even more and provide higher efficiency. However, for these techniques still a considerable amount of PV module power is lost when a small area of shade is present (1/3 of the PV module

power or even more) .

Some prior art documents recite smart photovoltaic cells and modules, such as US 2011/073150 Al, WO 2017/048597 Al, and WO 2014/169295 Al . US 2011/073150 Al recites diodeless terres trial photovoltaic solar power arrays, i.e. without blocking diodes and/or without bypass diodes. The arrays may comprise a solar array tracker, a controller, and an inverter. When the controller senses that the solar module power is below a threshold level, the controller commands the solar tracker to vary the solar module's pointing until the solar module is op erating at its maximum power point for the solar module's level of illumination. In some embodiments, when the control ler senses that the solar module power is less than a minimum bypass threshold level, the controller commands a bi-position switch to bypass current around the solar module. WO

2017/048597 Al recites de-energizing a photovoltaic (PV) sys tem, which may include detecting a resistance between a first photovoltaic unit and ground, wherein the first photovoltaic unit is connected to at least one additional photovoltaic unit. If the resistance is less than a threshold, the first photovoltaic unit is shorted by connecting a positive conductor of the first photovoltaic unit with a negative conductor of the first photovoltaic unit. Shorting the first photovol taic unit causes the at least one additional photovoltaic unit to detect the resistance that is less than the threshold, thereby shorting the at least one additional photovoltaic unit by connecting a positive conductor of the at least one additional photovoltaic unit with a negative conductor of the at least one additional photovoltaic unit. WO 2014/169295 Al re cites a solar photovoltaic module laminate for electric power generation. A plurality of solar cells are embedded within module laminate and arranged to form at least one string of electrically interconnected solar cells within said module laminate. A plurality of power optimizers are embedded within the module laminate and electrically interconnected to and powered with the plurality of solar cells. Each of the dis tributed power optimizers capable of operating in either passthrough mode without local maximum- power-point tracking

(MPPT) or switching mode with local maximum-power- point tracking (MPPT) and having at least one associated bypass switch for distributed shade management.

The present invention therefore relates to an improved cell-level power managed PV-module, and a method of operating such a module, which solve one or more of the above problems and drawbacks of the prior art, providing reliable results, without jeopardizing functionality and advantages.

SUMMARY OF THE INVENTION

The present invention relates to a cell-level power managed PV-module according to claim 1. In a generic perspective the power (circuit) part of the module comprises PV-cells, intelligent bypasses and drivers, and a supply voltage unit for addressing drivers. The control part comprises at least one (micro- ) processor and an interface circuit and optionally a communication circuit. The module comprises a multitude of PV- cells (i,j), typically a physical array of n*m cells, ie [l;n] , and je[l;m], wherein n may be from 2-2¹⁰, preferably 3-2⁸, more preferably 4-2⁶, even more preferably 5-2⁵, such as 6-2⁴, and wherein m may be from 2-2¹⁰, preferably 3-2⁸, more preferably 4-2⁶, even more preferably 5-2⁵, such as 6-2⁴. The PV-cells are located at a front side of the module, typically facing the sun. Contrary to prior art PV-modules the present cells may be operated individually, and combinations of electrically connected cells, in parallel, in series, or a combination

thereof, are established based on operational characteristics of individual cells. The electrical operation topology is most likely very different from a physical topology with the array of n*m cells. For instance an arbitrary example cell n=l m=l may be connected to a further arbitrary cell n=21 m=8; such a connection is without the present invention at least physically complex or impossible. Thereto, in the present module each individual cell is individually connected by electrical connections to a junction box and controlled by a switching network. The switching network is aimed at providing an elec trically based order. The junction box comprises the switching network, the switching network comprises a plurality of switchable bypass elements, a processor for actively control ling the bypass elements, such as by opening and closing these, a current or voltage sensor per cell, the switching network forming at least one string of PV-cells by electri cally connecting k PV-cells, a current and voltage sensor per string of k cells, a memory, and a plurality of switches and may comprise a wireless transceiver. Therein each bypass ele ment comprises a NPN or PNP bipolar junction transistor. Based on operational characteristics of individual cells these cells are mutually connected in parallel, in series, or a combina tion thereof, or are left out, such that an optimal power output is achieved. Typically the connections are continuously re-evaluated in terms of power output, and an electrical con figuration of PV-cells and the junction box is provided when in operation; this configuration therefore comprises active and contributing PV-cells, electrical connections from the cells to the junction box, the switched network in the junc tion box, and leaves out underperforming or inactive PV-cells. Connection may be established or switched off at a frequency of O.lHz-1 MHz, and typically at a rate above 40 kHz.

The present switch is controlled by a bipolar transistor, which may be of NPN or PNP type. The switching network provides a response based on input provided by the current sen sors, the voltage sensors, and optionally by temperature sen sors. At a sensing step recorded data from the memory may be compared with a previous set of data, such as for establishing a working conditions (e.g. in terms of voltage and current) of all individual cells. The (micro- ) processor can than switch the network such that a maximum output is obtained. In addi tion the processor can evaluate safety issues, such as by identifying to hot cells, and shorts.

Various possible scenarios of operation may occur. In a first scenario no or virtually no current passes through a current sensor. In such as case all cells are in operation un der uniform irradiation and the cells have compared to an av erage c.q. to one and another a minor mismatch. Any electrical configuration is now possible and typically strings of cells are formed such that a maximum voltage and/or power is obtained. In a second scenario a small amount of leakage current passes through at least one current sensor. There seems to be no need for immediate action and therefore no bypass is acti vated yet. It may be assumed that to the leakage current corresponding cells are sub-optimally functioning, such as caused by dust, cracking, ageing, an inherent mismatch, or a combina tion thereof. The cause may be determined based on a time duration of the situation. At regular intervals the control circuit (or controller, or processor) decides whether it is bet ter to turn a corresponding bypass on or leave it off, or turn it off. Eventually an alarm may be generated and sent to an operator, such that a visual inspection of the module may be performed. In a third scenario a considerable amount of current, such as 1mA-10A, passes through at least one current sensor. The to the leakage current corresponding cells may be shaded significantly or damaged seriously, which now forces the bypass system to be activated for such cells. Based on a measured output power, and optionally a temperature, the control circuit may decide whether to keep the corresponding by pass activated or to force the current to pass through such cells, which may be determined on a maximum power or on safety requirements .

Various circuit topologies may be envisaged. A first cir cuit topology optimises efficiency and has a low chance of hot spots, a second circuit topology slightly optimises efficiency and has a low chance of hot spots, a third circuit topology optimises efficiency and has a high chance of hot spots, and a fourth circuit topology slightly optimises efficiency and has a high chance of hot spots. As such the invention provides for a variety in possible circuits.

To minimize shading losses and to reduce their negative ef fects, the present cell-level power management system is de veloped to control each cells performance at shading condition which may also to communicate with an operator. A smart cell- level power managed PV module may contain a printed circuit board inside its junction box while all PV cells of the mod ules are typically connected to this box through a back sheet routing system. This smart PV module can understand the work ing condition of its cells and manage them to obtain a highest available power. It may also provide communication signals containing information about working condition PV cells for the user. Therefore, more energy will be saved during shading and a PV system user may also be notified about the working condition of every individual cell within the PV system. The ability to decide when and which bypass elements should be turned on or off to obtain a maximum possible power is novel.

So obtained results are a higher efficiency, a longer life time, improved grid stability, and more reliability for Smart cell-level power managed PV module in comparison with current commercially available PV modules, and therefore a lower costs of ownership.

The present switching network with many bypass elements is controlled by a (micro- ) processor to make the module intelligent and robust against non-uniform irradiation conditions.

The processor is adapted, such as by programming, to give the module the ability to detect its own working condition, select the best circuit topology for that specific working condition, and also providing information for a PV system user through a communication circuit and monitoring system.

In a second aspect the present invention relates to a method of operating a PV-module comprising n*m cells, and a switching network comprising a plurality of switchable bypass elements, a processor for controlling the bypass elements, a current or voltage sensor per cell, wherein each PV-cell is individually connected by electrical connections to and con trolled by the switching network, comprising receiving for at least two cells a cell current, and a cell voltage, and con necting or disconnecting a switchable bypass element.

As identified throughout the description the present module and likewise the present method may comprises further elements or details, as provided throughout the description, and in particular in the claims.

Thereby the present invention provides a solution to one or more of the above mentioned problems and drawbacks.

Advantages of the present description are detailed through out the description. DETAILED DESCRIPTION OF THE INVENTION

The present invention relates in a first aspect to a module according to claim 1.

In an exemplary embodiment of the present module the PV- cells may be back contacted PV-cells. The back contacted PV- cells have a relatively larger surface area available for con verting light into electricity. In addition it is easier to contact each individual cell to the present junction box.

In an exemplary embodiment of the present module the junc tion box may be located at a back side of the module and is centrally placed, preferably at an intersect of two diagonals of the module. As such power losses are minimized, switching times are minimal, and a minimum amount of material is neces sary for connecting the individual cells. It is noted that prior art modules typically have a junction box, without any further components other than junctions and bypass diodes, lo cated at a top side of a module.

In an exemplary embodiment of the present module the junc tion box may comprise a printed circuit board provided with a power circuit.

In an exemplary embodiment of the present module the bypass element may comprise in electrical connection a MOSFET driver, a charge pump and an N-channel MOSFET. Typically the charge pump, MOSFET driver, and MOSFET are in parallel connected. In addition a bipolar junction may be provided in parallel for switching .

In an exemplary embodiment of the present module the bypass element may comprise in electrical connection a Schottky diode and a NPN or PNP bipolar junction transistor.

In an exemplary embodiment of the present module the switch may comprise in electrical connection a DC/DC isolator, a

MOSFET driver, and an N-channel MOSFET. Typically these elements are connected in series, and further the MOSFET driver is connected to the microprocessor, and the MOSFET is at one end connected to a currents sensor, and at another end to a string of PV-cells.

In an exemplary embodiment of the present module the switch may comprise in electrical connection a transistor and a diode as a bidirectional half control switch. The diode and transistor are typically connected in parallel, the diode connected to the collector and emitter of the transistor, the base of the transistor being in connection with the microprocessor, and the emitter may further be in connection to a string of PV-cells and the collector may further be in connection to a current sensor.

In an exemplary embodiment of the present module the switch of each cell ie[l,n] may be driven by a current C(i) from the processor. Cells may still be coupled in rows or likewise columns, and combinations thereof, wherein a switch of each cell is driven by the processor, such as to optimize a power out put .

In an exemplary embodiment of the present module the NPN or PNP bipolar junction transistor of each cell ie[l,n] may be driven by a current B(i) from the processor.

In an exemplary embodiment of the present module the first bypass i=l may comprise a NPN or PNP bipolar junction transis tor and wherein the i=n+l^th bypass may comprise a NPN or PNP bipolar junction transistor, and bypasses ie[2,n] may comprise a NPN bipolar junction transistor and an anti-parallel diode to work as bidirectional half control switch

In an exemplary embodiment of the present module the pro cessor may be a microprocessor.

In an exemplary embodiment of the present module the pro cessor may be integrated in the module, such as a PCB.

In an exemplary embodiment of the present module the pro cessor may comprise at least one of a clock, a ground, a Vcc, an AD current, an AD-voltage, and a temperature sensor.

In an exemplary embodiment the present module may comprise a communication circuit.

In an exemplary embodiment of the present module electrical connections of each individual cell (i,j) may have a thickness of <0.1 mm, a width of < 10 , and a length of < 200 cm, and optionally a doping of 1 * 10¹⁷ /cm³-5 * 10¹⁹/cm³, preferably such that power losses are minimal.

In an exemplary embodiment the present module may comprise embedded software for operating the module.

In an exemplary embodiment the present module may comprise at least one power provider selected from a battery, a battery charger, and a voltage regulator.

In an exemplary embodiment the present module may comprise an alarm.

The one or more of the above examples and embodiments may be combined, falling within the scope of the invention.

EXAMPLES

The below relates to examples, which are not limiting in nature .

The invention is further detailed by the accompanying fig ures, which are exemplary and explanatory of nature and are not limiting the scope of the invention. To the person skilled in the art it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protec tion, defined by the present claims.

FIGURES

The invention although described in detailed explanatory context may be best understood in conjunction with the accompanying figures.

Figs la-e show schematics of a first topology of the pre sent module.

Figs. 2a-e show schematics of a second topology of the present module.

Figs. 3a-e show schematics of a third topology of the pre sent module.

Figs. 4a-e show schematics of a fourth topology of the pre sent module.

Fig. 5 shows a work flow.

Figs. 6a-c show schematics of a solar panel.

DETAILED DESCRIPTION OF THE FIGURES

Figures la-4a, as part of power circuit, schematically show PV cells within the PV module. P(l) to P(n+1) nodes connect the bypass circuits to the PV cells (interacting figures la-4a and lb-4b) .

Figures lb-4b, as part of power circuit, show bypasses, switches, and current and voltage sensors. Ports AD(1) to AD(ntl), AD(current) and AD (voltage) provide feedbacks from power circuit to the control circuit while ports C(l) to

C{ntl) and B(l) to B(n+1) are command signals from control circuit to power circuit (interacting figures lb-4b and ld- 4d) . Figures lb-4b contain different types of elements for by passes and switches but the circuit' s functionality is the s me .

Figures lc-4c, as part of power circuit, show power supply units to provide stable voltage for the microprocessor, driv ers, and other internal consumers.

Figures ld-4d, as part of control circuit, show microprocessor with required ports for controlling the PV cells.

Figures le-4e show a communication circuit and its required ports .

Figure 5 shows a working algorithm of the microprocessor. The flowchart demonstrates all the actions that the micropro cessor may perform step-by-step to make sure that PV module will provide the highest possible power in a safe working condition .

Figs. 6a-c show schematics of a solar panel. In fig. 6a a module is shown with a glass plate 61 provided on an array of back contacted solar cells. Further electrical connections 63 are shown, which individually connect each solar cell to a junction box, and a back plate 64, which are located at a back side of the module. Further a frame 65, typically of alumin ium, is present. Fig. 6b shows a view from the back side of the module, wherein the junction box is located at a back side of the module. The central part of the figure shows the junc tion box, and the right part functionality of the junction box. The switching network addresses the (individual) bypass elements. The status and control of the switching network and bypass elements may be wireless communicated. In. fig 6c electrical connection to junction box 66 are shown, in this case for a limited number of cells.

The figures have been detailed throughout the description.

Claims

1. Cell-level power managed PV-module comprising

a multitude of individual PV-cells (i,j) located at a front side of the module, in an array of n*m cells, ie[2;n], and j e [2 ;m]

a junction box comprising a switching network, the switching network comprising a plurality of switchable bypass elements wherein each PV-cell comprises at least one bypass element, a processor for actively controlling cell connection with the bypass elements, a current or voltage sensor per cell, the switching network actively forming at least one string of PV-cells by electrically connecting k PV-cells, a current and voltage sensor per string of k cells, a memory, and a plurality of switches,

wherein each bypass element comprises a NPN or PNP bipolar junction transistor,

wherein each PV-cell is individually connected by electrical connections to the junction box and controlled by the switching network, such that an electrical configuration of PV-cells and the junction box is provided, wherein an electrical opera tion topology is adaptable by said switching network.

2. Module according to claim 1, wherein the PV-cells are back contacted PV-cells.

3. Module according to any of claims 1-2, wherein the junction box is located at a back side of the module and is centrally placed.

4. Module according to any of claims 1-3, wherein the junction box comprises a printed circuit board provided with a power circuit.

5. Module according to any of claims 1-4, wherein the by pass element comprises in electrical connection a MOSFET driver, a charge pump, and an N-channel MOSFET.

6. Module according to any of the claims 1-4, wherein the bypass element comprises in electrical connection a Schottky diode and a NPN or PNP bipolar junction transistor.

7. Module according to any of claims 1-6, wherein the switch comprises in electrical connection a DC/DC isolator, a MOSFET driver, and an N-channel MOSFET.

8. Module according to any of claims 1-7, wherein the switch comprises in electrical connection a transistor and a diode as a bidirectional half control switch.

9. Module according to any of claims 1-8, wherein the switch of each cell ie[l,n] is driven by a current C(i) from the processor.

10. Module according to any of claims 1-9, wherein the NPN or PNP bipolar junction transistor of each cell ie[l,n] is driven by a current B(i) from the processor.

11. Module according to any of claims 1-10, wherein the first bypass i=l comprises a NPN or PNP bipolar junction tran sistor and wherein the i=n+l^th bypass comprises a NPN or PNP bipolar junction transistor, and bypasses ie[2,n] comprise a NPN bipolar junction transistor and an anti-parallel diode to work as bidirectional half control switch.

12. Module according to any of claims 1-11, wherein the processor is a microprocessor.

13. Module according to any of claims 1-12, wherein the processor is integrated in the module.

14. Module according to any of claims 1-13, wherein the processor comprises at least one of a clock, a ground, a Vcc, an AD current, an AD-voltage, and a temperature sensor.

15. Module according to any of claims 1-14, comprising a communication circuit.

16. Module according to any of claims 1-15, wherein elec trical connections of each individual cell (i,j) have a thick ness of <0.1 mm, a width of < 10 mm, and a length of < 200 cm, and/or a doping of l*10¹⁷/cm³-5*10^l9/cm³.

17. Module according to any of claims 1-16, comprising embedded software for operating the module.

18. Module according to any of claims 1-17, comprising at least one power provider selected from a battery, a battery charger, and a voltage regulator.

19. Module according to any of claims 1-18, comprising an alarm.

20. Method of operating a cell-level power managed PV- odule according to any of claims 1-19, the PV-module comprising n*m cells, and a switching network comprising a plurality of switchable bypass elements, a processor for controlling the bypass elements, a current or voltage sensor per cell, wherein each PV-cell is individually connected by electrical connec tions to and controlled by the switching network, comprising receiving for at least two cells a cell current, and a cell voltage,

and connecting or disconnecting a switchable bypass ele ment .

21. Method according to claim 20, wherein the bypass ele ment is connected by activating B(i) or is disconnected by de- activating B(i).

22. Method according to claim 20 or 21, wherein a cell temperature is measured.

23. Method according to any of claims 20-22, wherein an output power of at least two cells is measured.

24. Method according to any of claims 20-23, wherein 2⁶- 2²⁰ PV modules are maintained and operated.