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CN-122003791-A - PV energy generation facility with central inverter

CN122003791ACN 122003791 ACN122003791 ACN 122003791ACN-122003791-A

Abstract

The application describes a PV energy generation installation with a central inverter unit (20) for attachment to a PV generator, wherein the PV generator comprises a plurality of parallel-connected PV main strings (PVn) which are each connected to the central inverter unit 20 on the input side by a DC link. Each pair of DC lines associated with a PV main string (PVn) is associated with a monitoring unit (21. N), which comprises a differential current measuring device (8. N), a disconnection switch (9. N) and a monitoring control device (17. N), which is designed to switch the disconnection switch (9. N) and disconnect the PV main string (PV. N) after a differential current threshold I S,Diff has been exceeded. Additionally, a ground monitoring device (GFDI) (22) is arranged between one pole of the intermediate circuit (7) and the ground connection (13), comprising a ground current measuring device (10), a circuit breaking element (11) and a control device (12), wherein the control device (12) is designed to trigger the circuit breaking element (11) after a defined delay time T if the ground fault is still present after the delay time T after a ground fault has been detected by exceeding a ground current threshold I S . Furthermore, the application describes a method for fault current monitoring of a plant of this type.

Inventors

  • A. Falk

Assignees

  • 艾思玛太阳能技术股份公司

Dates

Publication Date
20260508
Application Date
20240924
Priority Date
20230926

Claims (15)

  1. A PV energy generation installation having a PV generator and a central inverter unit (20), wherein the PV generator comprises a plurality of PV main strings (PVn) connected in parallel, each of which is connected to the central inverter unit (20) on the input side by a DC link, and wherein the PV main strings are connected to an AC power grid (1) on the output side by a DC intermediate circuit (7), a DC/AC converter (5), an AC disconnection switch (4), a transformer (3) and a grid access device (2) of the central inverter unit (20), wherein each pair of DC links associated with a PV main string (PVn) is assigned a monitoring unit (21. N) comprising differential current measuring means (8. N), a disconnection switch (9. N) and a monitoring control means (17. N), wherein the monitoring control means (17. N) are designed to open the disconnection switch (9. N) for a reaction time T R after exceeding a current threshold I S,Diff , in order to disconnect the differential disconnection switch (7), and wherein a monitoring element (22) is connected between the PV main strings (7) and a ground connection (12), wherein the monitoring element (22) is connected to the ground (12), the control device (12) of the ground monitoring device (22) is designed to trigger the circuit breaking element (11) after a defined delay time T after the ground fault has been detected by exceeding a ground current threshold I S , if the detected ground fault is still present after the end of the delay time T, wherein the delay time T is selected to be greater than the reaction time T R .
  2. 2. The PV energy-generating facility of claim 1, wherein the delay time T is 50ms to 500ms.
  3. 3. The PV energy-generating installation according to claim 1 or 2, wherein the duration of the delay time T is related to the ground current measured by the ground current measuring device (10).
  4. 4. A PV energy-generating facility according to claim 3, wherein a plurality of ground current thresholds I S are defined, the ground current thresholds being associated with different delay times T.
  5. 5. A PV energy-generating facility according to claim 3, wherein the delay time T is set to zero in case a defined maximum ground current threshold I S,MAX is exceeded.
  6. 6. The PV energy production facility according to any one of the preceding claims, wherein a unique ground current threshold I S , or a minimum ground current threshold I S,MIN of the ground monitoring device (22) in case of multiple ground current thresholds, is greater than or equal to 1A.
  7. 7. The PV energy production facility according to any one of the preceding claims, wherein the differential current threshold I S,Diff of the monitoring unit (21. N) is less than or equal to 300mA.
  8. 8. The PV energy production facility according to any one of the preceding claims, wherein the differential current measurement device (8. N) is designed for detecting a change in the differential current according to IEC 62109-2 or IEC 63112 standard.
  9. 9. The PV energy generation facility according to any one of the preceding claims, wherein the ground monitoring device (22) has an over-current protection means.
  10. 10. The PV energy production facility of claim 9, wherein the over-current protection device comprises a damping resistor.
  11. 11. A PV energy production facility according to claim 10, wherein the damping resistance is less than the total resistance of the PV generator, preferably less than 10%, particularly preferably less than 1%.
  12. 12. The PV energy production facility of claim 1 wherein the central inverter unit is set up to be operated with a modulation that does not apply a common mode voltage to ground of a clock frequency to an AC voltage.
  13. 13. The PV energy production facility according to claim 1, wherein the monitoring unit (21 n) is arranged on a DC input line of the PV main string (PVn), which is arranged within a housing of the central inverter unit (20) and is thus part of the central inverter unit (20).
  14. 14. The PV energy production facility according to claim 1, wherein the monitoring unit (21 n) is part of a connection device which is assigned to each PV main string (PVn) and which connects a plurality of PV strings into one PV main string (PVn), wherein the connection device is arranged outside the housing of the central inverter unit (20).
  15. 15. Method for fault current monitoring of a PV energy generating installation according to any one of claims 1 to 15, wherein the monitoring unit (21. N) comprises a differential current measuring device (8. N), a circuit breaker (9. N) and a control device (17. N), wherein the control device (17. N) monitors a differential current fault by measuring a differential current I Diff by means of the differential current measuring device (8. N), wherein a differential current fault is identified by exceeding a differential current threshold I S,Diff , wherein the ground monitoring device (22) comprises a ground current measuring device (10), a circuit breaking element (11) and a control device (12), wherein the control device (12) monitors a ground fault by measuring a ground current I E by means of the ground current measuring device (10), wherein a ground fault is identified by exceeding a ground current threshold I S , Delaying the triggering of the circuit-breaking element (11) by a defined delay time T after the ground fault has been identified by the ground monitoring device (22), -After identification of a differential current fault, the monitoring control means (17. N) of the monitoring unit (21. N) opens the break switch (9. N) within a reaction time T R , and -The ground monitoring device (22) triggering the circuit breaking element (11) only if the ground fault remains after the defined delay time T, wherein the delay time T is selected to be greater than the reaction time T R of the monitoring unit (21. N).

Description

PV energy generation facility with central inverter Technical Field The present invention relates to a PV energy production facility with a central inverter unit comprising a DC/AC converter that can both feed energy into and extract energy from an alternating current grid (AC grid). In particular, the PV energy generating installation can be monitored for possible ground faults, wherein the PV energy generating installation has a circuit breaker for the DC-side energy source, in particular a photovoltaic generator. The invention further relates to a method for fault current monitoring of a PV energy generation installation of this type and for switching off an energy source on the DC side. Background PV energy generation facilities open up an increasingly wide range of application possibilities in the framework of large facilities. In addition to private household energy production (i.e. converting the DC voltage provided by the PV generator into an AC grid voltage by means of an inverter and feeding it into the household grid or into the public supply grid), PV power plants in increasingly larger power classes play a significant role in public current supply as large power plants. The PV installation can here comprise a large number of electrical components, in particular a large number of PV modules, which are distributed over a large area in a decentralized manner. A group of PV modules grouped in strings, i.e. in series connection with each other, is also referred to as a PV string. The PV generator of the PV installation can have one or more PV sub-generators or main strings, which are composed of a plurality of PV strings, which are connected to one another in parallel by means of a connection device (also referred to as a combiner box), if appropriate in each case via a separate DC/DC converter with a common direct voltage intermediate circuit (DC intermediate circuit) of the PV inverter, or, depending on the application, with other power converter units (for example DC/DC converters). Each of the PV sub-generators may have one or more PV strings interconnected in parallel with each other. For structural reasons, the PV modules of the PV installation always have a capacitance with respect to their environment, in particular with respect to their usually grounded support. This capacitance is not mandatory for the function of the PV installation, but is inevitably generated by the mechanical structure of the PV module. Therefore, this capacitance is commonly referred to as "parasitic capacitance" or "derived capacitance". The parasitic capacitance of a PV installation generally increases with the size of the PV generator associated with the PV installation, and therefore, PV generators with a high power also have correspondingly large parasitic capacitances. Furthermore, the parasitic capacitance is dependent on the environmental conditions and increases further, for example in the event of rain, due to the moist surfaces of the PV modules associated therewith and/or the dielectric constant of the air which changes as a result of increased air humidity. Due to the parasitic capacitance of the PV module with respect to ground potential, there is always a more or less strong leakage current of the PV generator with respect to ground potential during normal operation of the PV installation. Now, if contact of the earthing person with a component of the PV generator that directs the voltage (e.g. a damaged line) occurs due to a fault (e.g. a damaged line insulation), additional fault current with respect to ground potential is usually produced in a leap-like manner due to this direct contact. Since fault currents can be dangerous to humans from values of about 30mA and fire-protection-related from about 300mA, reliable detection of fault currents of this type is required in a standard manner in freely accessible PV installations, but not in closed electrical operating sites, and further measures are introduced when fault currents of this type are detected, such as switching off and/or short-circuiting the PV generator, in particular the associated PV sub-generator. Here, two standards are generally required to be complied with. On the one hand, the fault current must not have a jump, i.e. a rapid rise above a relatively low limit value (for example 30 mA), in order to ensure maximum personal protection. On the other hand, for fire protection and protection reasons, the total differential current or capacitive leakage current, which is measured via the attachment lines of the PV generator, must not exceed a significantly higher limit value of several hundred mA. As the rated power of PV installations becomes greater and greater, the parasitic capacitance of the associated PV generator or PV sub-generator increases, and thus the capacitive leakage current that is always present during normal operation of the PV installation increases. However, the threshold value associated with the leakage current (e.g., 3