JP2016010314A - Method and device for detecting island network condition in energy supply network - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide method and device for detecting an island network condition in an energy supply network.SOLUTION: A method for detecting an island network condition in an energy supply network 5 comprises: a step of determining, during a first period having a predetermined duration, whether a frequency variation is larger than a first threshold value or not; a step of determining whether the frequency variation is larger than a predetermined second threshold value under the condition that the first threshold value is not equal to the second threshold value and the first period is not a second period; and a step of detecting the island network condition in the energy supply network 5 when the frequency variation is higher than the predetermined first threshold value of at least the first period and higher than the predetermined second threshold value of at least the second period, and the first period is within the second period.

Description

  The present invention relates to a method for detecting an island network condition in an energy supply network when an inverter is connected to the energy supply network for the purpose of supplying energy. In this case, the method includes a step of determining a frequency of the energy supply network, a step of determining a frequency change rate that is an absolute value of the change rate of the frequency, and a period having a predetermined duration by analyzing the frequency change rate. And determining whether the frequency change rate is larger than a predetermined first threshold value. The invention also relates to an apparatus suitable for carrying out the method.

  The frequency of, for example, AC voltage or alternating current in the energy supply network is strictly defined within a narrow range in the energy supply network and is kept constant, for example by a generator supplying the network. In this case, nominal values of 50 hertz (Hz) or 60 hertz (Hz) are common in many countries. For example, an inverter that is part of an energy generation system is connected to an energy supply network to supply energy to the energy supply network, and assumes a frequency within the energy supply network during supply.

  During operation of such an inverter, an operating situation may occur in which part of the energy supply network supplied by the inverter is disconnected from other parts of the network. In this case, the inverter can also be completely disconnected from the energy supply network and connected only to the local network where the inverter is located. This results in a so-called island network situation in which the inverter must be switched off after a predetermined period of time normally defined by the operator for the energy supply network.

  In order to detect such an island network situation, the method mentioned at the beginning is often used in which frequency variations in the energy supply network or possibly in the cut-off part of the energy supply network are analyzed. This method is also known as the ROCOF (rate of change of frequency) method. The magnitude of the frequency change rate is taken into account. If the rate of change exceeds a predetermined magnitude, eg, 0.2 Hz / s, for a period longer than a predetermined period, eg, 200 milliseconds (ms), this is interpreted as an island network situation. For example, depending on the regulations applied to the energy supply network, the inverter can then be switched off or must be switched off.

  However, within an energy supply network, there is also often a requirement on the inverter to break through a specific failure situation of the energy supply network without disconnecting the inverter from the network (FRT (Fault Ride Through)). This requirement consideration can contradict known island network detection by the ROCOF method.

  US 2010/0286838 A1 discloses an extended version of the ROCOF method in which the absolute value of the frequency variation is also determined in addition to the rate of change of the frequency. The island network situation is estimated only if both determined parameters (frequency change rate and frequency variation) meet specific conditions. However, the combination of these criteria also does not allow an island network situation to be clearly detected in all cases where the FRT criteria applicable in the energy supply network are met simultaneously.

  The island network situation is also detected by utilizing the ROCOF method of WO2013 / 144304A2. If another network failure is additionally evaluated and the period when another network failure occurs overlaps with the period when the island network condition is detected, this is considered a network failure and is considered an island network condition. Not considered.

  In the method known from U.S. Pat. No. 6,850,074 B2, for the purpose of passively detecting island networks, the rate of change of frequency is greater than the first period assigned to the respective assigned threshold or It is determined whether each exceeds for a longer period of time than the second period, thereby allowing various forms of island network conditions to occur to be detected. This corresponds to the logical sum (OR) of the two ROCOF methods performed independently of each other. This does not provide improved identification of island network detection and FRT situation detection.

  Accordingly, one object of the present invention is a method for detecting an island network, which is used to reliably detect an existing island network situation without causing an undue disconnection in a situation that must be overcome by a supply inverter. Is to provide a method. Another object is to describe a suitable apparatus for performing the above method.

  This object is achieved by a method and device having the features of the independent claims. The dependent claims relate to advantageous refinements and developments.

  The method according to the present invention for detecting the island network status in the energy supply network when the inverter is connected to the energy supply network for the purpose of supplying energy has the following additional steps in addition to the steps described at the beginning: . An analysis is performed to determine whether the frequency change rate is greater than a predetermined second threshold for a second period having a predetermined duration, the first threshold being set to the second threshold The step of not equaling the first period is not equal to the second period. The island network condition in the energy supply network is such that the rate of frequency change is higher than a predetermined first threshold for at least a first period and higher than a predetermined second threshold for at least a second period, and the first Is detected when the period is within the second period. That is, the first period begins simultaneously with or later than the second period and ends simultaneously with or earlier than the second period.

  According to the present invention, for the purpose of reliably detecting the island network situation and distinguishing this situation from the FRT case, the frequency change rate has different evaluation parameters (in each case, a threshold and a period) 2. Analyzed by two ROCOF methods, the island network situation is detected only when the condition is satisfied in any case. Criteria based on which periods must exist within other periods ensure that the frequency change rate in either case can be attributed to the same situation. The combination of two ROCOF methods with different evaluation parameters makes it possible to evaluate the situation in the energy supply network in a differential manner. Nevertheless, techniques that have established basic suitability for detecting island network conditions are used.

  In one advantageous refinement of the method, the first threshold is greater than the second threshold and the first period is shorter than the second period. Applicant's studies have shown that for island network situations, a high frequency change rate typically occurs at least for a short period of time and a lower frequency change rate occurs for a longer period of time. This feature is exploited in this refinement by selecting an evaluation parameter.

  In another advantageous refinement of the method, an island network situation is detected when the first period is completely within the second period. That is, the start of the first period is after the start of the second period, and the end of the first period is before the end of the second period.

  In another advantageous refinement of the method, the first threshold is at least twice, preferably at least 10 times the second threshold.

  The second threshold is preferably in the range of 0.1 to 0.5 Hz / s (Hertz / second). Furthermore, the duration of the second period is preferably at least 5 times, more preferably at least 20 times the duration of the first period. The duration of the second period is preferably in the range of 100 to 500 ms (milliseconds). The range of the evaluation parameter values was particularly suitable for reliably detecting the island network situation.

  In a further advantageous refinement of the method, after determining that the first threshold has been exceeded for at least the first period, the RS flip-flop is set or a D-type flip-flop or monoflop is triggered, Or an auxiliary variable is set. In this case, the output of the RS flip-flop, D-type flip-flop, or monoflop, or the state of the auxiliary variable is the result of a check that determines whether the frequency change rate has exceeded the second threshold for at least the second period. It is preferable to combine with. This combination is particularly preferably an AND combination. The modification is an improved form in which the two determination criteria can be skillfully combined with each other in consideration of time series.

  An apparatus according to the present invention for detecting an island network condition in an energy supply network when an inverter is connected to the energy supply network for the purpose of supplying energy includes a frequency determiner for determining a frequency of the energy supply network, and a frequency It has a discriminator for judging the change rate and an analysis unit for evaluating the frequency change rate. The apparatus is characterized in that it is configured to perform the above method or one of its improvements. The advantages associated with the method are obtained.

  In one advantageous refinement of the device, the analysis unit has two threshold switches that monitor when the first and second thresholds are exceeded. The threshold switch is used to record when the first and second thresholds are exceeded.

  In another advantageous refinement, the device is fully or partially integrated in the inverter. Inverters connected to an energy supply network for the purpose of supplying electrical energy often already have components that detect the frequency in the energy supply network and / or its rate of change. At this time, these components can be used within the scope of the method described herein, which makes the method easier to implement and more cost effective.

  The invention is explained in more detail below with the aid of exemplary embodiments with the help of the accompanying drawings.

FIG. 1 shows a schematic view of a PV installation. FIG. 2 shows an exemplary embodiment of an analysis unit of an apparatus for detecting an island network. FIG. 3 shows a timing diagram illustrating various signal profiles in an apparatus for detecting an island network in one operating situation of an energy supply network. FIG. 4 shows a timing diagram illustrating the profile of various signals in an apparatus for detecting an island network in another operating situation of the energy supply network. FIG. 5 shows another exemplary embodiment of an analysis unit of an apparatus for detecting an island network. FIG. 6 shows a flowchart of a method for detecting an island network in an energy supply network. FIG. 7 shows a flowchart of a method for detecting an island network in an energy supply network.

  FIG. 1 shows a schematic view of a photovoltaic installation (PV installation) configured to perform a method for detecting an island network.

  The PV facility has a PV generator 1 connected to a DC input of an inverter 3 via a direct current (DC) line 2.

  The PV generator 1 is symbolically represented in FIG. 1 by the circuit symbol of only one PV cell. In one embodiment of the PV installation shown, for example, the PV generator 1 has a plurality of PV modules formed by interconnecting a plurality of PV cells and connected in series to form a row. obtain. If appropriate, a plurality of these rows can also be connected in parallel and / or in series. The PV generator 1 is likewise composed of a plurality of PV partial generators connected to the inverter 3 in an electrically interconnected form or in any case connected to the inverter 3 via a separate DC line 2. Can be done. The inverter 3 is in the form of a so-called multi-string inverter and has, for example, a plurality of DC inputs that can be controlled independently of each other.

  The inverter 3 is connected to an energy supply network 5 via an AC line 4 connected to an alternating current (AC) output. As an example, both the inverter 3 and the connection terminal to the energy supply network 5 have a single-phase design here. However, the energy supply network 5 can be multi-phase, in particular three-phase, like the inverter 3.

  In addition, FIG. 1 does not show elements of PV equipment that are not essential within the scope of the present description. For example, a switching element (eg, a cutting element, a contactor), a filter (eg, a sine wave filter), a network monitoring device, and / or a transformer (not shown herein) may be connected to the inverter 3 DC and / or AC. Can be provided on the side.

  An apparatus 10 for detecting an island network is provided in the PV facility of FIG. In the exemplary embodiment shown, this device 10 is arranged outside the inverter 3. However, it is conceivable to incorporate the device 10 completely or partially in the inverter 3.

  The device 10 has an input 11 to which the voltage of the energy supply network 5 at the output of the inverter 3 is supplied. For this purpose, the input 11 of the device 10 is connected to the AC line 4 via a tap 6. The device 10 includes a frequency determiner 12 that determines the frequency f of the energy supply network 5 from the signal supplied to the input 11. The value of the frequency f is output to the output of the frequency determiner 12. Within the scope of the present application, the frequency f of the energy supply network 5 may be understood to mean the frequency of the electrical parameters of the energy supply network 5, for example the frequency of the voltage with respect to one of the phases of the energy supply network 5. Thus, it is also possible to use energy supply network variables other than the voltage used as an example in FIG. 1, eg current, to determine the frequency. It should be noted that when determining the frequency f, filtering (eg, low-pass filtering) can be performed and / or a moving average can be created.

  A direct connection of the frequency determiner 12 to the energy supply network 5 is shown as in the exemplary embodiment of FIG. Or, for example, a voltage signal proportional to the voltage profile in the energy supply network 5, such as a low voltage signal, can be taken from means arranged in the AC line 4 (eg network monitoring means) and supplied to the device 10. obtain.

  It is also conceivable that means operating in the same manner as the frequency determiner 12 already exists in the inverter 3. An output signal indicative of the frequency f of the energy supply network 5 is made available to the device 10 for detecting the island network by means of an inverter 3 via an information line 7, such as an optional element shown using dashed lines in FIG. obtain. In this case, it is possible to dispense with the frequency determiner 12.

  A signal indicating the frequency f is supplied to the discriminator 13 in the device 10 for detecting the island network. The discriminator 13 first generates a first time derivative df / dt of a signal indicating the frequency f. The first-order time differential df / dt is also called the rate of change of the frequency f. An absolute value of the rate of change df / dt (the mathematical sign is removed from the negative rate of change) is also generated. Regardless of whether the frequency f increases or decreases with time, the absolute value of the rate of change df / dt is positive. The absolute value of the rate of change df / dt is expressed by the expression | df / dt | and is called the frequency rate of change.

  This frequency change rate | df / dt | is supplied to the analysis unit 14, and a signal indicating the presence of an island network condition is output to the output unit 15. In the exemplary embodiment shown in FIG. 1, this output signal is transmitted to the inverter 3 via the signaling line 8. After receiving such a signal, the inverter 3 adjusts its supply mode, for example according to the regulations of the energy supply network operator, and is disconnected from the energy supply network 5 as the case may be.

  FIG. 2 shows a block diagram of one possible first refinement of an analysis unit 14 (eg, the analysis unit shown in FIG. 1) used in the apparatus 10 for detecting an island network.

  The analysis unit 14 includes two threshold switches, that is, a first threshold switch 141 and a second threshold switch 142 to which a frequency change rate | df / dt | is supplied. Each of the threshold switches 141, 142 is characterized by two predefinable evaluation parameters, in particular a frequency change rate threshold dF and a duration period T. These evaluation parameters such as outputs of threshold switches 141 and 142 described later are distinguished from each other by an index as follows. In this case, the index “1” indicates the parameter and output of the first threshold switch 141, and the index “2” indicates the parameter and output of the second threshold switch 142.

Each of the threshold switches 141, 142 has two outputs, namely the first output RAT ₁ or RAT ₂ , and the first output RAT ₁ or RAT ₂ has a frequency change rate | df / dt | Whether the corresponding threshold value dF ₁ or dF _{2 is} greater is signaled. In each second output ID ₁ or ID ₂ , it is signaled whether the threshold value dF ₁ or dF ₂ has been permanently exceeded for a period longer than the first period T ₁ or the second period T ₂ .

  In this case, the functions of threshold switches 141, 142 each essentially correspond to implementing a known ROCOF method. Also in this case, it is signaled whether a predetermined threshold value of the frequency change rate has been exceeded for a period longer than a predetermined period.

  As an alternative to providing a frequency change rate, it is also possible to supply either the value of the frequency f or a variable (eg voltage) from the energy supply network 5 to each of the threshold switches 141, 142, respectively. Note that there is. In this case, at this time, a frequency discriminator similar to the frequency discriminator 12 in FIG. 1 and an identifier similar to the discriminator 13 in FIG. 1 must be incorporated in the threshold switches 141 and 142, respectively.

  3 and 4 show the signal profiles at various inputs or outputs and nodes of the analysis unit 14 of FIG. 2 for two exemplary operating situations of the energy supply network 5. The upper part of each of FIGS. 3 and 4 shows a graph of an exemplary profile of the rate of change df / dt of frequency f. Beginning with this profile of the rate of change df / dt of the frequency f, the lower regions of FIGS. 3 and 4 represent the signals at various points in the analysis unit 14. The signal profile shown is a digital signal profile having only two levels. The level on the ordinate shown is considered a logic “0”, and higher levels are considered a logic “1”. In this case, the assignment relating to which voltage level the corresponding logic level corresponds to may be selected in any desired manner. The signal profile having the designation “MFO” relates to the exemplary embodiment described in connection with FIG.

From the signal profiles at the outputs RAT ₁ , RAT ₂ , ID ₁ , ID ₂ of FIG. 3, the initial rapidly rising signal profile of the indicated rate of change df / dt of the frequency f first exceeds the threshold dF ₂ , then it recognized that exceeds the threshold value dF _1. After exceeding the maximum value, the rate of change df / dt of the frequency f is initially below the first threshold value dF ₁ and then below the second threshold value dF ₂ . Both thresholds dF ₁ and dF ₂ were exceeded for a period longer than their assigned times T ₁ and T ₂ . For this reason, both the signal ID ₁ and the signal ID ₂ are at least temporarily activated.

Thus, the profile of the rate of change df / dt of the frequency f shown has exceeded the _second smaller threshold dF ₂ during the second longer period T ₂ and is relatively short but the first period T _1. Both the longer period first higher threshold has been exceeded.

  The situation shown in FIG. 3 is a feature of the island network situation. The frequency profile in an island network situation, when an island network situation exists, a large and sudden variation in frequency first occurs, the variation has a frequency variation superimposed on the frequency, and the frequency variation lasts for a relatively long period of time Are identified according to analysis and investigation based on having a low rate of frequency change. According to this exemplary embodiment of the method according to the invention, the signal at the output of the threshold switches 141, 142 thus exceeds a predetermined threshold of both frequency change rates during the respective assigned period, and the first Are combined in such a way that island network conditions are detected when the period of time exceeding the higher threshold of is within the period of exceeding the second lower threshold.

In the exemplary embodiment of FIG. 2, the output signal is logically connected by RS flip-flop 143 and AND gate 144. The S input (set) of the RS flip-flop 143 is connected to the output ID ₁ of the first threshold switch 141. Thus, once the output ID ₁ becomes logic “1”, the RS flip-flop is set and outputs a signal having a logic “1” level to its output Q. The output Q, ie the signal at this output, will be referred to below and in FIGS. 3 and 4 as RFO. With respect to the temporal profile according to the operating situation of FIG. 3, the signal at the output RFO is set to logic “1” as soon as the signal at the output ID ₁ of the first threshold switch 141 changes to logic “1”. The inverted R input (reset) of the RS flip-flop 143 is connected to the output RAT ₂ of the second threshold switch. Thus, a logic “0” level at the output RAT ₂ of the second threshold switch 142 will reset the RS flip-flop 143 and set the output RFO to logic “0” again.

The output RFO of the RS flip-flop 143 is then combined with the output ID _{2 of} the second threshold switch 142 via the AND gate 144. The output of the AND gate 144 is also the output of the analysis unit 14 and thus the output 15 of the device 10. Make. The signal at the output is called the IDO (Island Detection Out) signal and is shown in the temporal profiles of FIGS.

In the temporal profile of the rate of change df / dt of the frequency f, as shown in FIG. 3, the frequency first exceeds the first threshold dF ₁ for a period longer than the period T ₁ , and as a result, the first threshold switch 141 The output ID ₁ becomes active, and therefore the output RFO of the RS flip-flop 143 becomes active. Since the rate of change df / dt of the frequency f is also longer than the second threshold value dF _{2 for} a period longer than the second period T ₂ , the RS flip-flop 143 is not reset. On the other hand, RAT ₂ is a logic “1” during this period, and on the other hand, output ID ₂ is similarly activated after the second period T ₂ has ended. Thus, both inputs of AND gate 144 are a logic “1”, so the output IDO is also a logic “1”. Thus, the graph of FIG. 3 represents a temporal profile of the rate of change df / dt of the frequency f indicating that the device 10 according to the invention for detecting an island network indicates the presence of an island network situation.

In contrast, FIG. 4 shows a profile of the rate of change df / dt of frequency f where the presence of an island network situation is not detected. The first threshold dF ₁ is exceeded for a period longer than the first period T ₁ , so both the signal ID ₁ from the first threshold switch 141 and the output RFO of the RS flip-flop 143 are set, but the signal ID _{The second} threshold dF ₂ is not exceeded for a period long enough for _{2 to} be set. At the end of the first period when signal RAT ₂ is logic “1”, RS flip-flop 143 is reset as a result of the absence of this signal, so that output RFO also changes to logic “0” again. I understand that. As a result, even if the second threshold value dF ₂ is exceeded for a period longer than the second time period T ₂ , the island network situation exceeds the first threshold value dF ₁ , and the second threshold value dF ₂ is compared. It was not detected because it was not observed in connection with exceeding the target period.

It is further noted that instead of the RS flip-flop 143, it is also possible to use a D-type flip-flop with an inverting asynchronous input (reset). Here, a logic “1” is permanently applied to the D input, the clock input is connected to the output ID ₁ of the first threshold switch 141, and the inverting asynchronous R input (reset) is the output RAT of the second threshold switch. ₂ is connected. For RS flip-flops, an undefined state can occur when the set and reset inputs are at opposite signal levels. Since the D-type flip-flop is edge-controlled, such an undefined state that can occur in the RS flip-flop is avoided.

  FIG. 5 illustrates another exemplary embodiment of a possible refinement of the analysis unit 14 used, for example, in the exemplary embodiment of FIG. The same reference numbers indicate the same elements or groups of elements herein that operate in the same manner as the exemplary embodiment of FIG.

Threshold switches 141 and 142, which are known from FIG. 2 and have the parameters dF ₁ , T ₁ , dF ₂ , T ₂ respectively, are used again. Only the output ID ₁ and ID _{2 of} these threshold switches 141 and 142 are required here. Instead of an RS flip-flop 143, a monoflop 145 is used, whose input is connected to the output ID ₁ of the first threshold switch. A signal applied to output ID ₁ and indicating that the first threshold value dF ₁ has been exceeded for a period longer than period T ₁ is extended by monoflop 145 by a predetermined duration τ. Thus, a signal is applied to the output MFO of monoflop 145 indicating that output ID ₁ was at a logic “1” at least once in the previous duration τ. The temporal profile of the signal at the output MFO is shown in FIGS. 3 and 4 for the situation described in connection with FIGS.

Monoflop 145 is preferably retriggerable, i.e. restarted by the edge of signal ID ₁ rising from logic "0" to logic "1". The output MFO of the monoflop 145 is supplied to the AND gate 144 similarly to the output ID _{2 of} the second threshold switch 142. Again, at this time, the IDO of the signal at the output of the AND gate 144 exceeds the _second threshold dF ₂ for a period longer than the second period T _{2 and} is longer than the first period T _1. It indicates that the first threshold value dF ₁ has been exceeded at least once in a period. The time parameter τ of the monoflop 145 is preferably selected such that τ = T ₂ −T ₁ . The signal profile of the signal IDO is therefore shorter when combined with the signal at the output MFO of FIG. 5 than when combined with the signal at the output RFO. This is indicated using a dashed line in the signal IDO of FIG.

  It goes without saying that an improvement of the device 10 for detecting island networks as shown in FIGS. 1, 2 and 5 can be implemented both in hardware and software or partly in hardware and partly in software. . The flowcharts described below in FIGS. 6 and 7 describe a rather software-oriented embodiment of a method for detecting island network conditions in an energy supply network. Both methods can be used in the exemplary embodiment of FIG. 1, for example, if the device 10 for detecting an island network has a flow controller (eg, a microcontroller).

In the exemplary embodiment of FIG. 6, the variables t ₁ , t ₂ , IDO are set to the value 0 in the first step S101.

  In the second step S102, the rate of change df / dt of the frequency f of the energy supply network is determined. If the method is performed inside an inverter (eg inverter 3 according to FIG. 1), it is possible to rely on the information already present if necessary.

The next step S103, the Shosa whether the absolute value is larger than the first threshold value dF ₁ rate of change df / dt of the frequency f. Otherwise, the method branches to step S101 where the variable is reset.

When the frequency change rate | df / dt |, which is the absolute value of the change rate df / dt of the frequency f, exceeds the threshold value in step S103, both variables t ₁ and t ₂ are incremented in the next step S104, that is, Each is increased by one.

The next step S105 is the value of the variable t ₁ is Shosa whether greater than a predetermined value T _1. Otherwise, the method branches to step S102 and steps S102 to S105 are executed again. In this case, it is assumed that the loop created by the steps S102 to S105 is executed within a predetermined time, and as a result, the variable t ₁ has a frequency change rate | df / dt | larger than the first threshold value dF _1. Used as a timer for a period of time. Thus, the constant T ₁ represents the period T ₁ described in connection with FIGS.

If the determination criterion in step S105 is satisfied, the method branches to the next step S106, and the variation df / dt of the frequency f is determined in the same manner as in step S102. The next step S107 associated frequency change rate | df / dt | is Shosa whether the second threshold value dF ₂ or greater. Otherwise, the method starts again from step S101. If so, the counting variable _{t 2} is incremented in the next step S108.

The next step S109, the count variable t ₂ is Shosa whether it has a value greater than a predetermined value T _2. Otherwise, the method branches to step S106. In a similar manner to Step S102 to S105, steps S106~S109 therefore, the frequency change rate | constituting a loop is used to determine the second threshold value dF ₂ greater than the duration | df / dt. Since exceeding the first threshold dF ₁ in step S103 also means exceeding the _second smaller threshold dF ₂ , these times have already been taken into account in step S104.

Longer periods allotted period T _2, the fact that the second threshold value dF ₂ also exceeded if it is determined in step S109, the variable IDO is set in step S110 to the value 1, thus the presence of the island network conditions indicated It is. The method is then terminated.

In the flowchart of FIG. 7 showing the alternative method of FIG. 6, the counting variables t ₁ and t ₂ and the output variable IDO are similarly set to 0 in the first step S201.

The next steps S202 to S204 are the same as steps S106 to S108. That is, the time exceeding the second threshold value dF ₂ is recorded with the variable t ₂ . Within the loop, then, whether it exceeds a first threshold value dF ₁ there is queried at the next step S205. Otherwise, the corresponding count variable t ₁ is reset to 0, the process jumps to step S202, if so, the counting variable t ₁ is incremented in step S207.

The next step S208 checks whether or not the first threshold value dF ₁ has been exceeded for a period longer than the first period T ₁ . Inside the loop, step S209~S212 then detects whether the remaining exceeds the second threshold value dF ₂ remains. Otherwise, the method is reset and starts the process and S201 again.

If it is determined in the period T ₂ is longer than the period second of step S212 that exceeds the threshold value dF _2, the variable IDO is set in step S213 to 1. Therefore, in the signal that island network condition exists Reportedly. The method is then terminated.

Note that instead of multiple queries, the next queried auxiliary variable (flag) may be set to determine whether the first or second threshold dF ₁ or dF ₂ has been exceeded.

1 PV generator 2 DC line (DC line)
3 Inverter 4 AC line (AC line)
DESCRIPTION OF SYMBOLS 5 Energy supply network 6 Tap 7 Information line 8 Signaling line 10 Island network detection apparatus 11 Input 12 Frequency discriminator 13 Discriminator 14 Analysis unit 15 Output 141 Threshold switch 142 Threshold switch 143 RS flip-flop 144 AND gate 145 Monoflop f Frequency df / Dt Frequency change rate | df / dt | Frequency change rate (absolute value of frequency change rate)
dF ₁ first threshold dF ₂ second threshold T ₁ first period T ₂ second period t ₁ , t ₂ counting variable IDO output of the apparatus of the method, ie output variable RAT ₁ , RAT ₂ threshold switch output ID ₁ and ID ₂ threshold switch output RSO RS flip-flop output MFO mono-flop output

Claims (13)

In a method for detecting an island network condition in the energy supply network (5) when an inverter (3) is connected to the energy supply network (5) for the purpose of supplying energy,
-Determining the frequency (f) of the energy supply network (5);
-Determining a frequency change rate (| df / dt |) which is an absolute value of a change rate (df / dt) of the frequency (f);
The frequency change rate (| df / dt |) is analyzed, and during the first period (T ₁ ) having a predetermined duration, the frequency change rate (| df / dt |) is a predetermined first threshold value ( determining whether the frequency change rate (| df / dt |) is equal to or greater than dF ₁ ), and the frequency change rate (| df / dt |) is a second value having a predetermined duration. Determining whether it is greater than a predetermined second threshold (dF ₂ ) during a period (T ₂ ), wherein the first threshold (dF ₁ ) is equal to the _second threshold (dF ₂ ) The first period (T ₁ ) is not equal to the _second period (T ₂ ), and
The frequency change rate (| df / dt |) is higher than the predetermined first threshold (dF ₁ ) for at least the first period (T ₁ ) and at least the second period (T ₂ ); Within the energy supply network (5) if it is higher than the predetermined second threshold (dF ₂ ) for a period of time and the first period (T ₁ ) is within the second period (T ₂ ) Detecting an island network condition. The method of claim 1, wherein the first threshold (dF ₁ ) is greater than the second threshold (dF ₂ ), and the first period (T ₁ ) is the second period (T ₂ ). A method characterized by being shorter. The method according to claim 1 or 2, characterized in that the island network situation is detected when the first period (T ₁ ) is completely within the second period (T ₂ ). how to. 4. The method according to claim 1, wherein the first threshold value (dF ₁ ) is at least twice, preferably at least 10 times, the second threshold value (dF ₂ ). A method characterized by. 5. The method according to claim 1, wherein the second threshold value (dF ₂ ) is in the range of 0.1 to 0.5 Hz / s. 6. A method according to any one of claims 1 to 5, at least 5 times the duration of the duration of the first period of the second period _{(T 2) (T 1)} , preferably at least A method characterized in that it is 20 times. A method according to any one of claims 1 to 6, the duration of the second period (dF ₂₎ is in the range of 100～500Ms, wherein the. The method according to any one of claims 1 to 7, wherein after determining that the first threshold (dF ₁ ) has been exceeded for at least the first period (T ₁ ), an RS flip-flop (143 ) Is set, or a D-type flip-flop or monoflop (145) is triggered, or an auxiliary variable is set. 9. The method according to claim 8, wherein the output of the RS flip-flop (143), the D-type flip-flop or the mono-flop (145), or the state of the auxiliary variable is such that the frequency change rate is at least the second A method characterized in that it is combined with the result of a check to determine whether said second threshold (dF ₂ ) has been exceeded during a period (T ₂ ).   The method according to claim 9, wherein the combination is a combination of logical products. An apparatus (10) for detecting an island network situation in the energy supply network (5) when an inverter (3) is connected to the energy supply network (5) for the purpose of supplying energy,
A frequency determiner (12) for determining the frequency (f) of the energy supply network (5);
In an apparatus (10) having a discriminator (13) for determining a frequency change rate (| df / dt |) and an analysis unit (14) for evaluating the frequency change rate (| df / dt |).
Device (10), characterized in that the device is set to perform the method according to any one of claims 1 to 10. The apparatus (10) according to claim 11, wherein the analysis unit (14), when said first and second threshold value _(dF 1, dF ₂₎ monitors whether more than two threshold switches (141, 142 A device (10) characterized in that   Device (10) according to claim 11 or 12, characterized in that it is fully or partially integrated in the inverter (3).

Images