TECHNICAL FIELD

The present disclosure relates to power systems and power generation systems based on photovoltaics. The disclosure presents a power system with two photovoltaic-based power generation systems combined together. The two power generation systems of the power system can be split and recombined.

BACKGROUND

A first exemplary power system uses a single photovoltaic-based power generation system, which is limited to 1500 V DC and 1000 V AC.

A second exemplary power system uses two photovoltaic-based power generation systems combined together. Compared to a comparable solution of two first exemplary power systems, which are independent, the second exemplary power system has a higher overall efficiency, and a lower part count, and thus lower CAPEX and OPEX.

However, the second exemplary power system may not comply with the European Low Voltage Directive (EU LVD), since the two combined power generation systems are quasi floating systems. A similar compliance issue may arise in regard to IEC LV standards.

SUMMARY

In view of the above, this disclosure aims to provide a different power system. An objective is to obtain the advantages of the second exemplary power system, while complying with the EU LVD and with IEC LV standards. Another objective is to avoid the need of any extra power conversion components (e.g., for voltage inversion), in order to not reduce the efficiency and to not add costs.

These and other objectives are achieved by this disclosure as described in the independent claims. Advantageous implementations are further described in the dependent claims.

A first aspect of this disclosure provides a power system comprising: a first power generation system comprising one or more first photovoltaic (PV) strings, and comprising a first power conversion system connected to the one or more first PV strings; a second power generation system comprising one or more second PV strings, and comprising a second power conversion system connected to the one or more second PV strings; one or more switches configured to selectively connect and disconnect the first power conversion system to and from the second power conversion system, and to selectively connect and disconnect the first power conversion system and the second power conversion system to and from earth.

The power system of the first aspect combines two power generation systems, and thus enjoys similar advantages as described above for the second exemplary power system, namely a higher overall efficiency, lower part count, and lower CAPEX and OPEX compared to the first exemplary power system. Moreover, since the one or more switches may be operated to connect the first power conversion system and the second power conversion system (and thus the two power generation systems) to and from earth, the power system of the first aspect may comply with EU LVD and IEC LV standards in use. Another advantage is that the one or more switches can be operated to disconnect the two power conversion systems (and thus the two power generation systems) from each other and from earth. This enables performing measurements at the power generation systems, like earth leakage detection measurements.

In an implementation form of the first aspect, the first power conversion system comprises a first DC/DC converter connected to the one or more first PV strings and comprises a first DC/ AC converter, wherein a first output of the first DC/DC converter is connected to a first input of the first DC/ AC converter, and a second output of the first DC/DC converter is connected to a second input of the first DC/ AC converter via the one or more switches; the second power conversion system comprises a second DC/DC converter connected to the one or more second PV strings and comprises a second DC/ AC converter, wherein a first output of the second DC/DC converter is connected to a first input of the second DC/AC converter via the one or more switches, and a second output of the second DC/DC converter is connected to a second input of the second DC/AC converter; and the one or more switches are configured to selectively connect and disconnect the second output of the first DC/DC converter to and from the first output of the second DC/DC converter, and to selectively connect and disconnect the second input of the first DC/AC converter to and from the first input of the second DC/AC converter and to and from earth. In an implementation form of the first aspect, the power system comprises two or more switches, wherein: a first switch of the two or more switches is configured to selectively connect and disconnect the first power conversion system to or from the second power conversion system; and a second switch of the two or more switches is configured to selectively connect and disconnect the first power conversion system and the second power conversion system to or from earth.

In an implementation form of the first aspect, the first switch is configured to selectively connect and disconnect the second output of the first DC/DC converter to and from the first output of the second DC/DC converter and to or from a common potential; and the second switch is configured to selectively connect and disconnect the second input of the first DC/AC converter and the first input of the second DC/AC converter to and from the common potential and to earth.

The two switches provide improved control over the connecting and disconnecting of the two power conversion systems.

In an implementation form of the first aspect, the first DC/DC converter is configured for a positive voltage between the first output and the second output of the first DC/DC converter; and the second DC/DC converter is configured for a positive voltage between the first output and the second output of the second DC/DC converter.

The positive voltage for the first DC/DC converter may be provided by a positive potential at the first output of the first DC/DC converter and zero potential, or at least a lower potential than the positive potential, at the second output of the first DC/DC converter. The positive voltage for the second DC/DC converter may be provided by a negative potential at the second output of the second DC/DC converter and zero potential, or at least a higher potential than the negative potential, at the first output of the second DC/DC converter.

In an implementation form of the first aspect, the first DC/AC converter is configured for a positive voltage between the first input and the second input of the first DC/AC converter; and the second DC/AC converter is configured for a positive voltage between the first input and the second input of the second DC/AC converter. The positive voltage for the first DC/ AC converter may be provided by a positive potential at the first input of the first DC/ AC converter and zero potential, or at least a lower potential than the positive potential, at the second input of the first DC/ AC converter. The positive voltage for the second DC/ AC converter may be provided by a negative potential at the second input of the second DC/ AC converter and zero potential, or at least a higher potential than the negative potential, at the first input of the second DC/AC converter.

In an implementation form of the first aspect, the one or more first PV strings comprise a plurality of positive PV fields, wherein each positive PV field has a positive potential to earth; and the one or more second PV strings comprise a plurality of negative PV fields, wherein each negative PV field has a negative potential to earth.

In an implementation form of the first aspect, the power system further comprises a voltage generator for providing a positive voltage; and one or more further switches configured to selectively connect and disconnect the voltage generator to and from the one or more second PV strings.

This enables countering potential induced degradation (PID) of the second PV strings, for instance, when the second PV strings are inactive.

In an implementation form of the first aspect, the power system comprises two or more further switches, wherein: a first further switch of the two or more further switches is configured to selectively connect and disconnect the first input of the second DC/AC converter, which comprises the voltage generator, to and from the second output of the second DC/DC converter; and a second further switch of the two or more further switches is configured to selectively connect and disconnect the second input of the second DC/AC converter to and from earth.

In an implementation form of the first aspect, the first output of the first DC/DC converter is connected to the first input of the first DC/AC converter via a first diode; and/or the second output of the second DC/DC converter is connected to the second input of the second DC/AC converter via a second diode.

In an implementation form of the first aspect, the first DC/AC converter comprises a three- phase AC output connectable to a winding of a first transformer station; and/or the second DC/ AC converter comprises a three-phase AC output connectable to a second winding of the first transformer station or to a winding of a second transformer station.

A second aspect of this disclosure provides a method of operating the power system according to the first aspect or any of its implementation forms, wherein the method comprises: operating the one or more switches to connect the first power conversion system to the second power conversion system, and to connect the first power conversion system and the second power conversion system to earth, if a first condition is fulfilled; and operating the one or more switches to disconnect the first power conversion system from the second power conversion system, and to disconnect the first power conversion system and the second power conversion system from earth, if a second condition is fulfilled.

In an implementation form of the second aspect, the first condition comprises that a power generated by the first and/or the second power generation system is above a threshold power; and/or the second condition comprises that the power generated by the first and/or the second power generation system is below the threshold power.

In an implementation form of the second aspect, the first condition comprises that it is day time or is an active time of the first and/or the second power generation system; and/or the second condition comprises that it is night time or is an inactive time of the first and/or the second power generation system.

In an implementation form of the second aspect, if the one or more switches are operated according to the first condition being fulfilled, the first output of the first DC/DC converter is at a positive potential, the second output of the first DC/DC converter and the first output of the second DC/DC converter are at earth, and the second output of the second DC/DC converter is at a negative potential.

In an implementation form of the second aspect, if the one or more switches are operated according the second condition being fulfilled, the first output of the first DC/DC converter is at a first positive potential to earth, the second output of the first DC/DC converter is at a first negative potential to earth or at a floating potential, the first output of the second DC/DC converter is at a second positive potential to earth or at a floating potential, and the second output of the second DC/DC converter is at a second negative potential to earth. In an implementation form of the second aspect, the method further comprises operating the one or more further switches to connect the voltage generator to the one or more second PV strings, when the one or more switches are operated according to the second condition being fulfilled; and operating the one or more further switches to disconnect the voltage generator from the one or more second PV strings, when the one or more switches are operated according to the first condition being fulfilled.

In an implementation form of the second aspect, the method further comprises performing one or more measurements at the first power generation system and/or at the second power generation system, when the one or more switches are operated according to the second condition being fulfilled.

In an implementation form of the second aspect, the one or more measurements comprise an earth leakage detection measurement.

The method of the second aspect and its implementation forms achieve similar advantages as described above for the power system of the first aspect.

A third aspect of this disclosure provides a computer program comprising instructions which, when the program is executed by a computer, cause the computer to control the one or more switches, and optionally the one or more further switches of the power system according to the first aspect or any implementation form thereof, so as to perform the method according to the second aspect or any implementation form thereof.

A concept of this disclosure is the interconnection of two power generation systems - which may be two low voltage systems, each of them up to 1500 V DC and 1000 V AC - which is done by the one or more switches that can also connect the systems to earth at the interface between the two power generation systems. The power system thus has the same benefits as two hard connected and earthed systems, for example, which may make the total installation 100% LVD compliant. The solution of this disclosure has the one or more switches in the earth connection, which can connect (combine) the two power generation systems, and can connect them to earth at the same spot, to hold on to earth and avoid any possible potential shift that may cause higher voltages than 1500 V DC to earth. The two power generation systems may further be connected only when needed, by operating the one or more switches, which may be during the phase of power generation from the PV strings. For instance, when there is power generation at daylight time.

The first one of the two power generation systems may operate with a positive voltage versus earth, and the second one of the two power generation systems may operate with the same absolute voltage, but negative voltage to earth. The first one may not have any problems related to the PV cell physics, however, the second one may experience PID on the PV fields. PID is a slow process that weakens the power generation over time. This disclosure envisions reversing such PID by using the voltage generator to apply a reversed (positive) voltage of the same amplitude for the same time to the PV fields of the second PV strings. In this disclosure, the two power generation systems may be split by opening the one or more first switches, for instance, during the night, and applying a positive voltage to the negative voltage cable ends of the second PV strings in the second power generation system.

It has to be noted that all devices, elements, units and means described in the present application could be implemented in the software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

BRIEF DESCRIPTION OF DRAWINGS

The above described aspects and implementation forms will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which FIG. 1 shows a power system according to this disclosure.

FIG. 2 shows a first exemplary power system according to this disclosure.

FIG. 3 shows a second exemplary power system according to this disclosure.

FIG. 4 shows a method for operating a power system, according to this disclosure. DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows a power system 100 according to this disclosure. The power system is PV-based, may be a low voltage power system, and may comply with EU LVD and IEC LV standards.

The power system 100 comprises a first power generation system 110 and a second power generation system 120. The first power generation system 110 comprises one or more first PV strings 111 and a first power conversion system 112, which is connected to the one or more first PV strings 111. Each first PV string 111 may comprise one or more PV panels and/or one or more PV fields that are able to generate power based on received light. The second power generation system 120 comprises one or more second PV strings 121 and a second power conversion system 122, which is connected to the one or more second first PV strings 121. Each second PV string 121 may comprise one or more PV panels and/or one or more PV fields that are able to generate power based on received light.

Further, the power system 100 may comprise one or more switches, wherein an example with one switch 101 is illustrated in FIG. 1. The switch 101 is configured to selectively connect and disconnect the first power conversion system 112 to and from the second power conversion system 122, and to selectively connect and disconnect the first power conversion system 112 and the second power conversion system 122 to and from earth 102 (may also be ground). For example, the switch 101 may be operated to either connect (e.g., closed switch 101) the first power conversion system 112 to the second power conversion system 122, or to disconnect (e.g., opened switch 101) the first power conversion system 112 from the second power conversion system 122. For example, the switch 101 may be operated to either connect (e.g., closed switch 101) the first power conversion system 112 and the second power conversion system 122 to earth 102, or to disconnect (e.g., opened switch 101) the first power conversion system 112 and the second power conversion system 122 from earth 102.

FIG. 2 shows a first exemplary power system 100 of this disclosure, which further develops the power system 100 shown in FIG. 1. The power system 100 of FIG. 2 has some additional, optional features. These optional features are described in the following, and can either be added individually to the power system 100 of FIG. 1, or in any possible feature combination. Like the power system 100 of FIG. 1, the power system 100 of FIG. 2 also comprises the first power generation system 110 and the second power generation system 120. Thus, it also comprises the first power conversion system 112 and the second power conversion system 122. It also comprises the one or more switches, as an example, the power system 100 of FIG. 2 comprises two switches 101a and 101b.

The first power conversion system 112 comprises a first DC/DC converter 211, which is connected to the one or more first PV strings 111. The first DC/DC converter 211 may be a unipolar smart string controller DC/DC. Further, the first power conversion system 112 comprises a first DC/AC converter 212, which may be a smart PV controller DC/ AC. A first output of the first DC/DC converter 211 is connected to a first input of the first DC/AC converter 212, for example, via an optional first diode 218. A second output of the first DC/DC converter 211 is connected to a second input of the first DC/AC converter 212 via the switches 101a and 101b. The first DC/DC converter 211 is configured for a positive voltage between the first output and the second output of the first DC/DC converter, and accordingly the first DC/AC converter 212 is configured for the positive voltage between the first input and the second input of the first DC/AC converter 212. The first DC/DC converter 211 may comprise a power electronic switch 221 for switching on and off the positive voltage.

Likewise, the second power conversion system 122 comprises a second DC/DC converter 213, which is connected to the one or more second PV strings 121. The second DC/DC converter 213 may be a unipolar smart string controller DC/DC. Further, the second power conversion system 122 comprises a second DC/AC converter 214, which may be a smart PV controller DC/AC. A first output of the second DC/DC converter 213 is connected to a first input of the second DC/AC converter 214 via the switches 101a and 101b. A second output of the second DC/DC converter 213 is connected to a second input of the second DC/AC converter 214, for example, via an optional second diode 219. The second DC/DC converter 213 is configured for a positive voltage between the first output and the second output of the second DC/DC converter 213, and accordingly the second DC/AC converter 214 is configured for the positive voltage between the first input and the second input of the second DC/AC converter 214. The second DC/DC converter 213 may comprise a power electronic switch 221 for switching off the positive voltage. As can also be seen, a first switch 101a of the two switches 101a and 101b is configured, in this example, to selectively connect and disconnect the second output of the first DC/DC converter 211 to and from the first output of the second DC/DC converter 213, and to or from a common potential 215. A second switch 101b of the two switches 101a and 101b is configured to selectively connect and disconnect the second input of the first DC/ AC 212 converter and the first input of the second DC/ AC converter 214 to and from the common potential 215 and to earth 102. In this way, the first switch 101a is configured to selectively connect and disconnect the first power conversion system 112 to or from the second power conversion system 122, and the second switch 101b is configured to selectively connect and disconnect the first power conversion system 112 and the second power conversion system 122 to or from earth 102 via the common potential 215.

If the first switch 101a is closed in FIG. 2, the first power generation system 110 is connected to the second power generation system 120, and when the first switch 101a is opened, these power generation systems 110, 120 are split. If the second switch 101b is closed in FIG. 2, the first power generation system 110 and the second power generation system 120 are connected to earth 102, and when the second switch 101b is opened, these power generation systems 110, 120 are disconnected from earth 101.

Optionally, the power system 100 may comprises two identical power generation systems 110 and 120. The first power generation system 110 may be configured to operate with a positive potential towards earth, and the second power generation system may be configured to operate with a negative voltage towards earth 102. That is, the one or more first PV strings 111 may comprise a plurality of positive PV fields, as shown in FIG. 2, wherein each positive PV field has a positive potential to earth 102, for instance, a positive DC voltage up to +1500 V. The one or more second PV strings 121 may comprise a plurality of negative PV fields, wherein each negative PV field has a negative potential to earth 102, for instance, a negative DC voltage up to -1500 V.

The switches 101a and 101b may be operated to be closed only during an active period of the power system 100, which may be when there is power generated in the PV fields 111 and 121 of the multiple PV strings (for instance, PV fields of multiple PV panels). The active period may be the time with daylight. During an inactive period of the power system 100, for instance when there is no daylight, like during night, the two switches 101a and 101b may be operated to be open, and thus the two power generation systems 110 and 120 are disconnected from each other. Since there is no power generated by the PV fields in the inactive period, there is also no voltage on the line(s) (e.g., +1500 V line) of the first PV strings 111 and on the line(s) (e.g., - 1500 V line) of the second PV strings 121.

During the inactive period, when there is no power generated by the first PV strings 111 and the second PV strings 121, a positive voltage with respect to earth may be fed back into the (negative) second PV strings 121. Thus, an opposite electric field compared to the active (daylight) period may be generated, which can reverse a PID in the PV fields of the second PV strings 121. To this end, the power system 100 may further comprise a voltage generator 217, which is configured to provide this positive voltage.

In FIG. 2, the voltage generator 217 may be included in the second DC/ AC converter 214. The power system 100 may comprise one or more further switches configured to selectively connect and disconnect the voltage generator 217 to and from the one or more second PV strings 121. As an example, the power system 100 of FIG. 2 is shown to have a first further switch 216a, which is configured to selectively connect and disconnect the first input of the second DC/ AC converter 214 (which comprises the voltage generator 217) to and from the second output of the second DC/DC converter 213. The power system 100 is also shown to have a second further switch 216b, which is configured to selectively connect and disconnect the second input of the second DC/AC converter 214 to and from earth 102. In this way, the positive voltage can be provided to the second PV strings 112.

FIG. 3 shows another power system 100 of this disclosure, which is similar to the power system 100 of FIG. 2. However, the voltage generator 217 is an additional voltage source, and the positive voltage is taken from this additional, independent voltage source. In this case, one further switch 216 is provided and configured to selectively connect and disconnect the voltage generator 217 to and from the second output of the second DC/DC converter 213.

In FIG. 3 and FIG. 4 is further shown that the first DC/AC converter 212 comprises a three- phase AC output connectable to winding of first transformer station 220. Further, the second DC/AC converter 214 comprises a three-phase AC output connectable to a second winding of the first transformer station 220. Alternatively, the three-phase AC output of the second DC/AC converter 214 may be connectable to a winding of a second transformer station. The power system 100 may comprise a processor or processing circuitry (not shown) configured to perform, conduct or initiate the various operations of the power system 100 herein, in particular, to control the one or more switches 101, 101a, 101b, and optionally the one or more further switches 216a, 216b of the power system 100. The processing circuitry may comprise hardware and/or the processing circuitry may be controlled by software. The hardware may comprise analog circuitry or digital circuitry, or both analog and digital circuitry. The digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable arrays (FPGAs), digital signal processors (DSPs), or multipurpose processors. The power system 100 may further comprise memory circuitry, which stores one or more instruction(s) that can be executed by the processor or by the processing circuitry, in particular under control of the software. For instance, the memory circuitry may comprise a non-transitory storage medium storing executable software code which, when executed by the processor or the processing circuitry, causes the various operations of the switches of the power system 100. In one embodiment, the processing circuitry comprises one or more processors and a non-transitory memory connected to the one or more processors. The non-transitory memory may carry executable program code which, when executed by the one or more processors, causes the power system 100 to perform, conduct or initiate the operations or methods described herein.

FIG. 4 shows a method 400 for operating the power system 100 of FIG. 1, FIG. 2, or FIG. 3. The method 400 may comprise a step 401 of operating the one or more switches 101, 101a, 101b to connect the first power conversion system 110 to the second power conversion system 120, and to connect the first power conversion system 110 and the second power conversion system 120 to earth 102, if a first condition is fulfilled. The method 400 may further comprise a step 402 of operating the one or more switches 101, 101a, 101b to disconnect the first power conversion system 110 from the second power conversion system 120, and to disconnect the first power conversion system 110 and the second power conversion system 120 from earth 102, if a second condition is fulfilled.

The first condition may comprise at least one of the following: a power generated by the first and/or the second power generation system 110, 120 is above a threshold power; it is day time; it is an active time of the first and/or the second power generation system 110, 120. The second condition may comprise at least one of the following: a power generated by the first and/or the second power generation system 110, 120 is below a threshold power; it is night time; it is an inactive time of the first and/or the second power generation system 110, 120. The present disclosure has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed matter, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.