Method for operating an inverter assembly and inverter assembly for performing the method

Abstract

The invention relates to a method for operating an inverter assembly (1) and an inverter assembly (2) for carrying out the method. In order to reduce the risk of triggering a ground fault circuit breaker, when feeding in an AC voltage (U AC ), determine the leakage capacitance (C iso ), and determine which AC output terminal (10, 11) is connected to which line (L, N) of the power supply network (12), and, taking into account the leakage capacitance (C iso ) and the specified maximum leakage current (I A,max ) and the connection status of the AC output terminals (10, 11), asymmetrically modulate the power units (7, 8) so that the voltage (U 10 , U 11 ) have different amplitudes, wherein the AC output end (10) of the power unit (7) connected to the phase connection (L) generates a voltage (U 10 ), while the AC output terminal (11) of the power unit (8) connected to the neutral conductor (N) generates a voltage (U 11 ).

Description

Technical Field

[0001] The present invention relates to a method for operating an inverter assembly, which has at least one inverter, each of which converts a DC voltage into an AC voltage with a mains frequency, wherein in each inverter, a DC voltage of a DC power supply connected to a DC input terminal is converted into an intermediate circuit voltage by a DC / DC converter, and the intermediate circuit voltage is converted into an AC voltage in a DC / AC converter having two power units and output at an AC output terminal, each of the power units is connected to an AC output terminal and modulated with each other by a control device, and the AC voltage is fed into a power supply network connected to the AC output terminal.

[0002] In addition, the present invention relates to an inverter component, which has at least one inverter for converting a DC voltage into an AC voltage with a mains frequency, wherein each inverter has a DC / DC converter and a DC / AC converter, wherein the DC / DC converter converts the DC voltage of a DC power supply connected to a DC input terminal into an intermediate circuit voltage, and the DC / AC converter has two power units for converting the intermediate circuit voltage into an AC voltage, wherein a control device is provided for modulating the power unit of each inverter.

[0003] The term "inverter assembly" includes an assembly consisting of one or more inverters, each of which has an input connected to a respective DC power source, in particular a photovoltaic module or a string of photovoltaic modules, and an output connected to a power supply network. In the case of an inverter assembly having a plurality of inverters, all inverters may be controlled independently of one another, or they may be connected to one another via communication lines so that their functions can be coordinated.

[0004] In particular, the present invention relates to an advanced single-phase inverter without a transformer (transformerless inverter), which converts the DC voltage of a DC voltage source (e.g. a photovoltaic module) into an intermediate circuit voltage by means of a DC / DC converter, and converts the intermediate circuit voltage into the required AC voltage in a DC / AC converter, thereby converting the DC voltage into an AC voltage with a mains frequency, which is used to operate a load or feed into a power supply network. The DC / AC converter has two power units with semiconductor switches, which are modulated accordingly by a control device. Compared with an inverter with a transformer, the efficiency of a transformerless inverter is much higher. Background Art

[0005] Inverters without transformers and electrical insulation generate grid-related potential changes due to the modulation (pulse width modulation PWM) of the DC power supply (especially photovoltaic generators). Due to the unavoidable parasitic capacitances and insulation resistances between the components of the inverter assembly (especially the photovoltaic modules) and the ground, this potential change generates leakage currents to the ground. When the inverter is connected to the supply network, inadmissibly high leakage currents can lead to the mandatory residual current circuit breaker (ground fault circuit breaker) being triggered. The triggering of the ground fault circuit breaker can also inadvertently disconnect other equipment from the supply network. The switching on of the ground fault circuit breaker requires manual operation and therefore requires the presence of a person. Therefore, it is usually necessary to determine the leakage current or the leakage capacitance causing the leakage current and, if necessary, the insulation resistance, and if the maximum permissible leakage current is exceeded, to prevent the inverter from being connected to the supply network. Only after the cause of the high leakage current has been eliminated and the ground fault circuit breaker has been closed again, can the AC voltage generated in the inverter be used again to supply energy to the load or for feeding into the supply network. Before this, the converted energy cannot be used, which leads to a deterioration of the energy balance. As a result, the operator of the inverter assembly loses valuable feed-in time, feed-in power and feed-in energy, and thus loses money. The losses in feed-in time, feed-in power and feed-in energy increase in proportion to the size of the inverter assembly. In high-performance systems, very high revenue losses can occur.

[0006] EP 3 465 897 B1 describes a method for operating a single transformerless inverter, wherein when a limit value of the leakage current is exceeded, the inverter is controlled accordingly or the inverter is operated using a special clock method, whereby the leakage current can be reduced. Although this makes it possible to connect an inverter (which would otherwise not be allowed), the final energy balance is still reduced and the operator has to accept a corresponding loss of revenue. In addition, the determination of the leakage current also requires a certain amount of work.

[0007] CN 110323959 A describes a method for operating an inverter and such an inverter, wherein harmonics of the mains frequency are reduced by a filter circuit at the inverter output and leakage currents are reduced by additional capacitors and additional compensation circuits.

[0008] EP 1 229 629 A2 describes an inverter which can detect leakage currents. Summary of the invention

[0009] The object of the present invention is to provide a method for operating an inverter assembly as mentioned above and an inverter assembly for carrying out the method, which is intended to ensure that the inverter assembly can be connected to the power supply network even in the case of expected higher leakage currents and also ensure that the converted energy can be utilized to achieve a better energy balance. The implementation of the method and the inverter assembly should be as simple and cost-effective as possible and should not involve any significant additional costs for the operator. The disadvantages of previous methods or devices should be avoided or at least reduced.

[0010] With regard to the method, the object according to the invention is achieved by determining the leakage capacitance to ground of the DC input of each inverter before feeding the AC voltage into the power supply network, determining which AC output is connected to which line of the power supply network, and taking into account the leakage capacitance and the specified maximum leakage current and the connection of the determined AC output, asymmetrically modulating the power cells of each inverter so that the voltage amplitudes of the AC outputs of the power cells are different, i.e., by modulating the power cells of the DC / AC converter connected to the phase connection of the power supply network, a voltage with a larger amplitude is generated at the AC output of the power cell, and by modulating the power cells of the DC / AC converter connected to the neutral conductor of the power supply network, a voltage with a smaller amplitude is generated at the AC output of the power cell. The method according to the invention provides for determining the leakage capacitance of the DC input of each inverter without measuring the actual leakage current, and thereby adjusting the modulation of the power cells of each inverter accordingly when the maximum leakage current and the connection of the inverter to the power supply network line are known, and correspondingly changing the voltage amplitudes of the power cell outputs, which are usually equal, or arranging them asymmetrically. Whereas, hitherto, the two power units of each inverter were modulated in such a way that opposite AC voltages of the same amplitude were generated, they are now controlled in an asymmetrical manner, generating voltages of different amplitudes at the AC outputs of the power units. As a result, the leakage current is minimized or optimized, so that the inverter can also be connected without the risk of exceeding the maximum leakage current and triggering the ground fault circuit breaker. As a result, the individual inverters can also make a positive contribution to the resulting energy balance, whereas according to the prior art the inverters must remain deactivated. Since the capacitive leakage current is usually significantly greater than the ohmic leakage current, it is the leakage capacitance, i.e. the capacitance ratio of the composite insulation resistance, rather than the ohmic component, i.e. the insulation resistance, that is, that is, the insulation resistance, that is primarily determined and taken into account. The leakage capacitance or system capacitance can be determined, for example, according to the method described in EP 3 879 283 A1.

[0011] The corresponding connection of the inverter to the power supply network line (i.e., which AC output terminal of the inverter is connected to the neutral conductor and which AC connection terminal of the inverter is connected to the phase connection of the power supply network) can be set by manual input on the inverter, or in some cases can also be determined automatically. For example, the connection situation can be determined during the installation of the inverter and archived or stored in an appropriate manner. Then, the method of the present invention accesses these archived or stored data to understand the connection situation. One way to automatically determine the connection situation is, for example, to measure the voltage in any available measuring unit to determine the insulation resistance, then only one power unit is connected to the power supply network, and the voltage in the measuring unit is measured a second time. If the AC voltage component in the second measurement has increased compared to the first measurement, it can be concluded that the power unit connected to the power supply network is connected to the phase connection (L) of the power supply network, and the other power unit is therefore connected to the neutral conductor (N). Subsequently, a control experiment can be carried out using another power unit, that is, only another power unit can be connected to the power supply network. Then, the AC voltage ratio of the voltages in the two measurements is compared again.

[0012] The method according to the invention can be applied in particular to inverter assemblies having a plurality of inverters, ie more powerful systems.

[0013] Typically, the power cells of each inverter are pulse-width modulated alternately at a predetermined switching frequency. Other modulation methods are also conceivable, which control the two power cells accordingly to generate a desired output AC voltage.

[0014] If, in the event of a maximum leakage current being reached, a predetermined time period is waited for and before feeding the AC voltage into the supply network the leakage capacitance of the DC input of each inverter to ground is determined again and a check is made again whether a prescribed maximum leakage current is exceeded, it is possible to check again after this predetermined time period whether the individual inverters of the inverter assembly can be connected without the risk of triggering the ground fault circuit breaker. For example, the predetermined time period may be in the range of a few minutes, for example 5 minutes. During this period, changes in the leakage capacitance may occur, which require a new check. As a function of the measured leakage capacitance, the modulation of the power cell of each inverter preferably varies linearly within predetermined limits. For example, the limits are determined by extreme values ​​of the leakage capacitance, which may indicate an incorrect determination of the inverter assembly or defective hardware.

[0015] If the reserve is taken into account within predetermined limits, then in addition to the leakage current of the inverter assembly, the leakage current of other equipment, such as a washing machine connected to the power supply network as a load, can also be taken into account.

[0016] When a predetermined upper limit value of the measured leakage capacitance of each inverter is reached, preferably each inverter remains deactivated, or each inverter is deactivated. The limit value of the leakage capacitance is selected and set based on experience.

[0017] Advantageously, before the feed-in operation of at least one inverter, the ohmic insulation resistance to ground of the DC input of each inverter can also be measured and taken into account in addition to the leakage capacitance when modulating the power unit. As described above, the influence of the ohmic insulation resistance is usually very small or even negligible compared to the influence of the leakage capacitance. However, if the ohmic component of the composite insulation resistance is also taken into account, a more efficient operation of the inverter assembly can be achieved. The ohmic insulation resistance can be determined, for example, according to the method described in EP 3 879 277 A1.

[0018] According to another feature of the invention, the location at which the DC power source is connected to the ground can be determined, and the determined location can also be taken into account when modulating the power unit of the inverter. For example, whether the ground leakage occurs in the positive connection or negative connection area of ​​the DC input terminal of the inverter, or between individual DC power sources (especially photovoltaic modules, etc.), may be relevant to the modulation. Determining the location at which the ohmic insulation resistance is connected to the DC power source can, for example, be carried out together with determining the ohmic insulation resistance.

[0019] Advantageously, the inverter is deactivated when the intermediate circuit voltage reaches a predetermined upper limit value. In the method according to the invention, a higher intermediate circuit voltage may be required, as a result of which the overall efficiency of the inverter assembly is reduced. When a certain intermediate circuit voltage (e.g. 500 V) is exceeded, it is useful to deactivate the inverter for safety reasons and for reasons of reduced efficiency.

[0020] Before and / or during the feed-in operation of at least one inverter, harmonics of the AC voltage at the AC output can also be determined and taken into account when modulating the power cells of the inverter. Since harmonics occur in practice and affect the grid conditions and cause leakage currents, when harmonics are taken into account, the inverters of the inverter assembly can be better utilized, thereby improving the overall energy balance. Harmonics in the output AC voltage can be determined, for example, by selective filtering or Fourier transformation.

[0021] For example, the determined harmonics can be attenuated by modulating the power cells of each inverter connected to an AC output connected to a neutral conductor of the supply network, and the attenuation can be corrected accordingly by modulating the power cells of each inverter connected to an AC output connected to a phase connection of the supply network. This represents a method of taking harmonics into account.

[0022] According to another feature of the invention, the DC voltage at the DC input of each inverter can be measured and taken into account when modulating the power cells of each inverter. Taking into account the DC voltage of the DC source (in particular the DC voltage of the photovoltaic module) can bring further advantages, in particular in inverter assemblies with multiple inverters, because the control of the individual inverters can also be configured as a function of the individual input voltages. However, even if there is only one inverter, taking into account the DC voltage at the DC input of the inverter during modulation is advantageous and helps to further improve efficiency.

[0023] If the amplitude of the AC voltage is also determined during the feed-in operation of at least one inverter and taken into account when modulating the power cells of each inverter, then for example harmonics can be taken into account during operation of the inverter assembly and the modulation can be adapted in an optimal manner to any changing circumstances.

[0024] In the case of multiple inverters, the power unit of each inverter is preferably modulated as a function of the measured system capacitance of each inverter. In this case, the control or modulation of each inverter is independent of the other inverters, so that each inverter does not experience a proportionally determined maximum leakage current and thus each inverter can contribute to the energy balance.

[0025] In the simplest case, in an inverter assembly having a plurality of inverters, the determined maximum leakage current may be divided by the number of all inverters in the inverter assembly.

[0026] Preferably, the number of inverters in the inverter assembly can be determined automatically via the communication lines between the inverters.A particularly yield-optimizing variant of the invention can be achieved if, in addition to the number of inverters, the DC voltage at the input of each inverter is also measured and taken into account.

[0027] The object of the present invention is also achieved by the above inverter assembly, which is configured to perform the above method. The functions of the inverter assembly can be easily implemented in the control device of the inverter by software. For the advantages that can be achieved, please refer to the above method description. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention is further explained with reference to the accompanying drawings, in which:

[0029] Figure 1 A block diagram of an inverter assembly having an inverter is shown;

[0030] Figure 2 The figure shows the time curves of the voltage at the AC output terminal of the power unit, the AC voltage generated by the inverter, and the leakage current generated according to the prior art;

[0031] Figure 3 A flow chart is shown, illustrating a first embodiment of a method according to the invention for operating an inverter assembly;

[0032] Figure 4 The method according to the present invention shows the time curves of the AC output terminal voltage of the power unit, the AC voltage generated by the inverter, and the leakage current generated in an ideal power supply network;

[0033] Figure 5 The figure shows the time curves of the AC output terminal voltage of the power unit and the generated AC voltage of the inverter and the generated leakage current in a power supply network with harmonics according to the prior art;

[0034] Figure 6 Shows when the application is based on Figure 3 When the method of the present invention is used, in a faulty power supply network with unprocessed harmonics, the time curves of the AC output terminal voltage of the power unit and the generated AC voltage of the inverter and the generated leakage current;

[0035] Figure 7 A flow chart is shown illustrating another embodiment of a method according to the invention for operating an inverter assembly;

[0036] Figure 8 Shown in accordance with Figure 6 In the method of the present invention, in a fault power supply network with attenuated harmonics, the time curves of the AC output terminal voltage of the power unit and the generated AC voltage of the inverter and the generated leakage current; and

[0037] Fig. 9 A block diagram of an inverter assembly with multiple inverters and batteries is shown. DETAILED DESCRIPTION

[0038] Figure 1 The block diagram of the inverter assembly with a single-phase transformerless inverter 2 is shown. The inverter 2 is used to convert a DC voltage U provided by a DC power source 3 (particularly a photovoltaic module 3' or a string of a plurality of photovoltaic modules 3') into a DC voltage U DC The output of the inverter 2 is converted into a mains frequency f AC The AC voltage U AC The inverter 2 includes a DC / DC converter 5 for converting a DC voltage U DC Converted into an intermediate circuit capacitor C ZK Intermediate circuit voltage U ZK The DC / DC converter 5 is preferably formed by a boost converter. The intermediate circuit voltage U ZK The DC / AC converter 6 converts the voltage into an AC voltage U ACTo this end, the DC / AC converter 6 has two power units 7, 8, usually with corresponding semiconductor switches in a bridge circuit (not shown), which are alternately controlled so that an AC voltage U is generated at the output of the DC / AC converter 6. AC A corresponding control device 9 is provided for modulating the power units 7, 8. Pulse width modulation is usually performed at a predetermined switching frequency. The voltage U 10 Applied to the AC output terminal 10 of the power unit 7, and the lower input terminal of the power unit 7 (or the intermediate circuit voltage U ZK The negative pole) voltage is opposite, and the voltage U 11 Applied to the AC output terminal 11 of the power unit 8, and the lower input terminal (or intermediate circuit voltage U ZK The two AC output terminals 10 and 11 of the power units 7 and 8 of the DC / AC converter 6 jointly form the output terminal of the inverter 2, to which an AC voltage U is applied. AC , and is connected to a single-phase power supply network 12. In the example shown, the AC output terminal 10 of the power unit 7 is connected to the phase connection L, and the AC output terminal 11 of the power unit 8 is connected to the neutral conductor N of the power supply network 12. The output choke 13 can be arranged in the line at the output of the inverter 2. In addition, an AC isolator 17 is located at the output of the inverter 2, and the inverter 2 can be isolated from the power supply network 12 by means of the AC isolator 17. A ground fault circuit breaker 14 is arranged between the inverter 2 and the power supply network 12 for measuring the total current and interrupting the circuit breaker when the specified maximum leakage current I to ground PE is exceeded. A,max The leakage current I A It is caused by insulation failure, caused by the leakage capacitance C between the DC power supply 3 and the ground PE iso And insulation resistance R iso The composite insulation resistance Z in parallel iso Indicates the location of the insulation fault (i.e. the ohmic insulation resistance R iso The point at which the DC power source 3 is connected to the DC power source 3 will also affect the leakage current I A The ideal situation is that the insulation fault is symmetrically arranged between the two connections of the DC input terminal 4 of the inverter 2, because this causes the leakage current I A The DC component of is the lowest because when the inverter 2 is in the feeding mode, the voltage to the ground PE is the lowest in absolute value at the center. Therefore, in some cases, it is advantageous to determine the connection position of the DC power source 3 to the ground PE. For example, this determination can be the ohmic insulation resistance R iso If the location is known, the measured voltage of the insulation fault to earth PE can be divided by the ohmic insulation resistance R iso , apply Ohm's law to determine the leakage current I AThe DC component of the leakage current I A The DC component of the leakage current I A The allowable capacitance ratio needs to be taken into account in the modulation of power units 7 and 8.

[0039] In order to prevent the ground fault circuit breaker 14 from being triggered, the leakage current I is measured before the inverter 2 is connected to the power supply network 12 via the AC isolator 17. A , or determine the leakage capacitance C iso , and if necessary, determine the ohmic insulation resistance R iso , and only if the maximum leakage current I A,max Otherwise, the inverter 2 cannot be connected to the power supply network 12, and the DC voltage U DC Converted AC voltage U AC It cannot be fed into the power supply network 12 and therefore cannot contribute to the energy balance. Of course, this will result in a loss of revenue for the operator of the inverter assembly 1, which is particularly significant in the case of large and high-performance systems.

[0040] According to the invention, taking into account the determined leakage capacitance C iso and the specified maximum leakage current I A,max and the determined connection conditions, the modulation of the power cells 7, 8 of each inverter 2 is adjusted so that the voltage U at the output terminals 10, 11 of the power cells 7, 8 is 10 , U 11 The magnitudes of are different or asymmetrical. Therefore, the leakage current I A Minimized or optimized (I A,opt ), so that the maximum leakage current I A,max The inverter 2 can be connected without the risk of triggering the ground fault circuit breaker 14. The corresponding inverter 2 can thus also make a positive contribution to the resulting energy balance, whereas according to the prior art the inverter would have to remain deactivated.

[0041] Figure 2 According to the prior art, the voltage U at the AC output terminals 10 and 11 of the power units 7 and 8 is shown. 10 , U 11 and the AC voltage U generated by the inverter 2 AC And the time curve of the leakage current generated. Figure 1 Block diagram of an inverter assembly 1, wherein the AC output 10 of the power unit 7 of the inverter 2 is connected to the phase connection L, and the AC output 11 of the power unit 8 of the inverter 2 is connected to the neutral conductor N of the supply network 12. The modulation of the power units 7, 8 of the DCTAC converter 6 of the inverter 2 is carried out in such a way that the two voltages U 10 and U11 The output is in the opposite direction with the same amplitude. 10 and U 11 The maximum possible amplitude is the maximum intermediate circuit voltage U ZK , here is 500V. As shown in the figure, the selected amplitude is 325V. AC The amplitude of is also 325V, that is, the voltage of the power supply network 12. As a result, a leakage current I A (For example, in this case, the amplitude is 50mA and the RMS value is 35mA).

[0042] Figure 3 A flow chart is shown illustrating a first embodiment of a method of operating an inverter assembly 1 according to the present invention. According to step 101, the leakage capacitance C is determined using known methods. iso , and possibly also determine the ohmic insulation resistance R iso , and according to step 102, the leakage capacitor C iso and mains frequency f AC Calculate the capacitance ratio X of the insulation resistance iso , the calculation formula is:

[0043]

[0044] Then, according to step 103 of the method, the prescribed maximum leakage current I A,max In the case of the inverter 2 and the ground fault circuit breaker 14, the maximum leakage current I A,max is determined by the ground fault circuit breaker 14 because it is for a specific maximum leakage current I A,max In the case where there are multiple inverters 2 in the inverter assembly 1 (see Fig. 9 ), the specified maximum leakage current I A,max For example, the maximum leakage current of each inverter 2 is determined by dividing by the number i of the inverters 2. However, the maximum leakage current I specified by the ground fault circuit breaker 14 is A,max This also applies here.

[0045] According to step 104, the voltage U is calculated 10 or U 11 This is achieved by setting the maximum leakage current I A,max Multiply the capacitance ratio X by the insulation resistance iso For example, the leakage capacitor C iso =1μF, at the grid frequency f AC =50Hz, produces X iso =3.18kOhm, and at the intermediate circuit voltage U ZK=500V, the voltage U 10 , U 11 The lower amplitude is about 75 V. Subtracting the lower amplitude from the 325 V AC voltage of the power supply network 12 (which is the product of the square root of 2 and the 230 V voltage) yields the voltage U 10 and U 11 The maximum amplitude of U is about 250 V. However, since a certain tolerance (e.g. + / - 10%) is also realistic in the power supply network 12, the voltage of the power supply network 12 can also be measured continuously to obtain the current value. AC The amplitude must also be 325V or correspond to the current measured value. AC The voltage U corresponding to the AC output terminals 10 and 11 of the two power units 7 and 8 of the inverter 2 10 and U 11 The sum of .

[0046] At this point, the connection situation has not yet been determined, ie, it is not yet known which AC output terminal 10, 11 is connected to the phase conductor L or the neutral conductor N of the power supply network 12. However, this is also irrelevant to the current basic determination.

[0047] According to query 105, the determined voltage U is checked 10 , U 11 Is the maximum value of the intermediate circuit voltage U ZK / 2. If yes, it can be fed in. If no, it cannot be fed in. ZK When the voltage U is 500V (amplitude), 10 or U 11 The maximum amplitude can reach 250V.

[0048] If this condition is met, the voltage U 10 or U 11 The maximum value does not exceed half of the intermediate circuit voltage U ZK / 2, firstly determine the connection status according to step 106, that is, determine which AC output terminal 10, 11 of the inverter 2 is connected to which line L, N of the power supply network 12.

[0049] The AC isolator 17 is arranged at the output of the inverter 2, each conductor comprising at least one relay. These relays can be controlled accordingly, for example by the control device 9 and / or by the power units 7, 8. As soon as the relay in the phase conductor L is closed, a sufficiently large AC voltage component relative to the ground PE can be measured, for example, by the control device 9 at a frequency of 50 Hz. This is not the case when the relay in the neutral conductor N is closed. For example, the connection condition can be automatically determined in this way. Usually, the contacts of the relays of the AC isolator 17 are checked regularly to see if they are in poor contact. The automatic determination of the connection condition can also be carried out during this test.

[0050] According to step 107, the power cells 7, 8 of each inverter 2 are modulated accordingly. The power cell 7 at the neutral conductor N is modulated in such a way that a voltage U having a lower amplitude is generated at the output 10. 10 The power unit 8 at the phase conductor L is modulated in such a way that a voltage U having a relatively high amplitude is generated at the output 11. 11 . So the leakage current I A will not exceed the maximum leakage current I A,max , and accordingly, the ground fault circuit breaker 14 will not be triggered. Assuming that the leakage current I A Within a certain range, the leakage current can be reduced to the maximum leakage current I by modulating the power units 7 and 8. A,max the following.

[0051] Therefore, according to step 108, the inverter assembly 1 is operated in such a way that the power units 7, 8 output different voltages U at the AC output terminals 10, 11. 10 , U 11 , so as not to exceed the maximum leakage current I A,max , and inverter 2 optimizes the leakage current I A,opt operate.

[0052] If the above-mentioned condition of query 105 is not met, then according to step 109 no feed into the power supply network 12 takes place by not connecting the respective inverter 2 to the power supply network 12 .

[0053] In this case, according to step 110, it is preferred to wait for a predetermined period of time Δt, for example 5 minutes, and then start again to determine the leakage capacitance C according to step 101. iso During the time period Δt, it is also possible to try to increase the intermediate circuit voltage U ZK For example, a 500 to 550 V booster is used (depending on the intermediate circuit capacitor used and the inverter topology).

[0054] Figure 4 The method according to the present invention shows that, under the condition of an ideal power supply network 12 without harmonics, the voltage U at the AC output terminals 10 and 11 of the power units 7 and 8 is 10 , U 11 And the resulting AC voltage U of inverter 2 AC and the resulting leakage current I A According to the present invention, when the AC voltage U AC Before feeding into the power supply network 12, the leakage capacitance C between the DC input terminal 4 of each inverter 2 and the ground PE is determined. iso , and according to Figure 3 The flow chart in determines the voltage U of the power units 7 and 8 10 , U 11 , and modulate the power units 7 and 8 accordingly, thereby generating voltages U having corresponding different amplitudes 10 , U 11 .

[0055] In accordance with Figure 1 In the exemplary embodiment shown, the AC output 10 of the power unit 7 of the inverter 2 is connected to the phase connection L, and the AC output 11 of the power unit 8 of the inverter 2 is connected to the neutral conductor N of the power supply network 12. Therefore, the voltage U 11 Outputted by power unit 8, with a relatively large voltage U 10 Output by power unit 7. As shown in the figure, voltage U 10 The amplitude is about 250V, the voltage U 11 The amplitude is about 75V. Correspondingly, for the AC voltage U AC For example, its amplitude is 325V (230V multiplied by the square root of 2), which corresponds to the amplitude of the power supply voltage 12.

[0056] As mentioned before, the lower voltage fluctuation on the neutral conductor N has a significant effect on the leakage current I A level has a positive impact.

[0057] The asymmetrical modulation of the power cells 7 and 8 results in an optimized leakage current I A,opt , and the leakage current I A Compared to the Figure 2 ). In the example shown, the optimized leakage current I A,opt The magnitude is about 23 mA, or corresponds to a root mean square value of about 16 mA. A conventional ground fault circuit breaker 14, for example, A,max Therefore, before and during the operation of the inverter 2, the method according to the present invention can optimize the leakage current I A,optKeep it at a low level so that as long as the conditions (low insulation resistance, high leakage capacitance, little mains interference, almost no harmonics, etc.) allow, it remains at the maximum leakage current I A,max As a result, the inverter 2 can feed power to the power supply network 12 for a longer period of time (connect earlier, disconnect later), thereby making a greater contribution to the energy balance.

[0058] Figure 5 The diagram shows the voltage U at the AC output terminals 10 and 11 of the power units 7 and 8 in a power supply network 12 with harmonics according to the prior art. 10 , U 11 and the AC voltage U generated by the inverter 2 AC and the time curve of the resulting leakage current. Harmonics arise from faults in the supply network 12 which are superimposed on the voltage U 10 , U 11 Correspondingly, these high-frequency faults will also be superimposed on the leakage current I A This increases the leakage current I A The amplitude of - as shown in the figure, reaches a root mean square value of about 80mA or about 43mA, because the voltage U of the AC output terminal 11 of the power unit 8 11 The voltage fluctuations will be amplified accordingly.

[0059] Figure 6 Shows when the application is based on Figure 3 In the method of the present invention, the voltage U with harmonics in the faulty power supply network 12 with harmonics 10 , U 11 and the resulting optimized leakage current I A,opt The voltage amplitude shown corresponds to Figure 4 The amplitude in, that is, U 10 For 250V, U 11 is 75V, U AC is 325V. The time curve is different from Figure 4 time curve, since high-frequency harmonics are superimposed on the supply network 12 and are accordingly transferred to the voltage U 10 and U 11 For example, here the harmonic frequency is f OW =350 Hz. This superposition leads in particular to a more volatile voltage U on the neutral conductor N. 11 , which causes the leakage current I A The amplitude fluctuation is larger. As shown in the figure, the amplitude is about 60mA or the root mean square value is about 33mA. In this case, it will exceed the maximum leakage current I specified to trigger the ground fault circuit breaker 14. A,max However, the method according to the present invention still shows its effect, because Figure 5Compared with the existing technology, the leakage current I A The amplitude fluctuation will be larger.

[0060] Figure 7 A flow chart is shown for illustrating another embodiment of a method for operating an inverter assembly 1 according to the present invention. Figure 3 Compared with the flowchart of FIG. 1 , step 111 is added here, that is, before and / or during the feeding operation of at least one inverter 2, the AC voltage U of the AC output terminal 10, 11 is determined. AC The harmonics of f and are taken into account when modulating the power units 7, 8 of the inverter 2. The network analysis according to step 111 can be performed by determining the specific frequency f in step 112 OW By taking into account such harmonics that often occur in reality, the method of the present invention can be further improved, such as Figure 8 As shown, this ultimately leads to a better energy balance.

[0061] Figure 8 It is shown that in the method according to claim 9, with attenuated harmonics and optimized leakage current I A In the fault power supply network 12, the voltage U 10 , U 11 and the AC voltage U generated by inverter 2 AC And the leakage current I A In this case, as shown in the time curve of the voltage U 11 As can be seen from the time curve of , the determined harmonics are correspondingly attenuated by modulating the power unit 7 of the inverter 2, which is connected to the neutral conductor N of the power supply network 12. The attenuation is correspondingly corrected by modulating the power unit 8 of the inverter 2, which is connected to the AC output terminal 10, which is connected to the phase connection L of the power supply network 12. The correction or attenuation is carried out in such a way that the voltage U 11 The high frequency ratio is transmitted to the voltage U through the corresponding filters in the power units 7 and 8. 10 This can be seen from the voltage U 10 The superimposed oscillation amplitude on Figure 7 The voltage U 10 Therefore, the voltage U 11 No longer has any high frequency ratio.

[0062] The result is an optimized leakage current I with lower harmonic superposition A Therefore, as long as the environmental conditions (low insulation resistance, high leakage capacitance, small network interference, almost no harmonics, etc.) allow, the leakage current I A Keep below the maximum leakage current IAmax As shown in the figure, the amplitude is about 40mA or the RMS value is about 23mA. Therefore, a longer energy feeding is achieved.

[0063] Fig. 9 The block diagram of an inverter assembly 1 is shown, which has two inverters 2 and a battery 16 for buffering the obtained energy. It is also possible to arrange more than two inverters 2 in parallel in the inverter assembly 1, which are connected together to the power supply network 12. The control devices 9 can be connected to each other via a communication line 15. In the simplest case, the specified maximum leakage current I when the common ground fault circuit breaker 14 of the inverter assembly 1 is triggered A,max It can be divided by the number of inverters 2 i (here two), and half of the specified maximum leakage current I A,max / 2 for each inverter as the basis or new maximum leakage current I A,max ', and for the maximum leakage current I A,max '=I A,max Each inverter 2 of / 2 performs the method according to the present invention (according to Figure 3 or Figure 7 ).

[0064] In addition, another possibility is to allocate the maximum leakage current I of each inverter 2 according to its rated power. A,max Compared with the inverter 2 with a lower rated power, the inverter 2 with a higher rated power in the inverter assembly 1 will be assigned a total maximum leakage current I A,max A larger proportion of .

[0065] In a yield-optimized variant of an inverter assembly 1 having a plurality of inverters 2 , it is also possible to calculate for each inverter 2 the leakage current I per mA. A How much rated power can be converted. Due to different leakage capacitance C iso , the situation of each inverter 2 is also different. Unit rated power leakage capacitance C iso The smallest inverter 2 is assigned the total maximum leakage current I A,max If the total quota has not been used up, the next available inverter 2 is supplied, and so on. In this way, the total maximum leakage current I A,max to achieve maximum profit.

[0066] Finally, when applying the method according to the invention (according to Figure 3 or Figure 7 ), in an inverter assembly 1 having multiple inverters 2, other aspects of the individual inverters 2 (such as service life, operating hours, etc.) will also come into play and be taken into account.

[0067] A method according to the invention for operating an inverter assembly 1 having at least one (preferably a plurality of) inverters 2 (according to Figure 3 or Figure 7 ), by considering the leakage capacitance C iso and connection conditions, the power units 7 and 8 of the inverter 2 are specially modulated so that the leakage current I A minimizes the leakage current in excess of the specified maximum I A,max Since this can increase the feed-in time and feed-in power, a better energy balance is achieved, which brings higher profits to the operator of the inverter assembly 1.

Claims

1. A method for operating an inverter assembly (1), the inverter assembly (1) having at least one inverter (2) for respectively converting a DC voltage (U DC ) is converted to the mains frequency (f AC ) of the AC voltage (U AC ),in, In each inverter (2), the DC voltage (U DC ) is converted into an intermediate circuit voltage (U ZK ), the intermediate circuit voltage (U ZK ) is converted into an AC voltage (U AC ), each of the power units (7, 8) is connected to an AC output terminal (10, 11) and is modulated with each other by a control device (9), the AC voltage (U AC ) corresponds to the voltage at the AC output terminal (10, 11) of the power unit (7, 8) relative to the intermediate circuit voltage (U ZK ) The opposite voltage of the negative electrode (U 10 , U 11 ), the AC voltage (U AC ) is fed into a power supply network (12) connected to the AC output terminals (10, 11), characterized in that, when the AC voltage (U AC ) is fed into the power supply network (12), the leakage capacitance (C iso ), and determine which AC output terminal (10, 11) is connected to which line (L, N) of the power supply network (12), and, taking into account the determined leakage capacitance (C iso ) and the specified maximum leakage current (I A,max ) and the determined connection status of the AC output terminals (10, 11), asymmetrically modulating the power units (7, 8) of each inverter (2) through a control device (9), so that the AC output terminals (10, 11) of the power units (7, 8) are connected to the AC voltage (U AC ) corresponds to the voltage (U 10 , U 11 ) of different amplitudes, in the manner of: modulating a power unit (7) of a DC / AC converter (6) connected to a phase connection (L) of a power supply network (12) so that an AC output end (10) of the power unit (7) generates a voltage (U 10 ), and by modulating a power unit (8) of a DC / AC converter (6) connected to a neutral conductor (N) of a power supply network (12), so that an AC output terminal (11) of the power unit (8) generates a voltage (U 11 ), thereby minimizing the leakage current (I A ) and can be used without exceeding the specified maximum leakage current (I A,max ) without the risk of connecting each inverter (2).

2. The method according to claim 1, characterized in that: When the maximum leakage current (I A,max ), wait for a predetermined period of time (Δt), and then increase the AC voltage (U AC ) is fed into the power supply network (12), the leakage capacitance (C iso ), and recheck whether the specified maximum leakage current (I Amax ).

3. The method according to claim 1 or 2, characterized in that: As the measured leakage capacitance (C iso ), the modulation of the power cells (7, 8) of each inverter (2) varies linearly within predetermined limits.

4. The method according to any one of claims 1 to 3, characterized in that When the leakage capacitance (C iso ) reaches the predetermined upper limit (C iso_max ), the corresponding inverter (2) remains disabled or is disabled.

5. The method according to any one of claims 1 to 4, characterized in that: Before the feeding operation of the at least one inverter (2), the ohmic insulation resistance (R iso ), and when modulating the power unit (7, 8), in addition to considering the leakage capacitance (C iso ) also considers the ohmic insulation resistance (R iso ).

6. The method according to claim 5, characterized in that The position of the connection of the DC power source (3) to ground (PE) is determined and the determined position is taken into account when modulating the power units (7, 8) of the inverter (2).

7. The method according to any one of claims 1 to 6, characterized in that: Before and / or during a feed-in operation of the at least one inverter (2), an AC voltage (U AC ) and take them into account when modulating the power cells (7, 8) of the inverter (2).

8. The method according to claim 7, characterized in that The determined harmonics are attenuated by modulating the power cell (7) of each inverter (2), the power cell (7) being connected to an AC output terminal (11) which is connected to a neutral conductor (N) of a power supply network (12), and the attenuation is correspondingly corrected by modulating the power cell (8) of each inverter (2), the power cell (8) being connected to an AC output terminal (10) which is connected to a phase connection (L) of the power supply network (12).

9. The method according to any one of claims 1 to 8, characterized in that During the feed-in operation of the at least one inverter (2), the AC voltage (U AC ) and takes it into account when modulating the power cells (7, 8) of each inverter (2).

10. The method according to any one of claims 1 to 9, characterized in that In the case of multiple inverters (2), the power cells (7, 8) of each inverter (2) serve as the measured system capacitance (C iso ) function for modulation.

11. The method according to claim 10, characterized in that The specified maximum leakage current (I A,max ) divided by the number (i) of all inverters (2) in the inverter assembly (1).

12. The method according to claim 10 or 11, characterized in that: Measure the DC voltage (U) at the DC input terminal (4) of each inverter (2) DC ) and takes it into account when modulating the power cells (7, 8) of each inverter (2).

13. The method according to any one of claims 10 to 12, characterized in that The number (i) of inverters (2) of the inverter assembly (1) is determined by a communication line (15) between the inverters (2).

14. An inverter assembly (1) comprising at least one inverter (2) for converting a DC voltage (U DC ) is converted to the mains frequency (f AC ) of the AC voltage (U AC ),in, Each inverter (2) has a DC / DC converter (5) and a DC / AC converter (6). The DC / DC converter (5) converts the DC voltage (U) of the DC power source (3) connected to the DC input terminal (4) into an AC voltage (U DC ) is converted into the intermediate circuit voltage (U ZK ), the DC / AC converter (6) having two power units (7, 8) for converting the intermediate circuit voltage (U ZK ) is converted into AC voltage (U AC ), wherein a control device (9) is provided for modulating the power cells (7, 8) of each inverter (2), characterized in that the control device (9) is configured to execute the method according to any one of claims 1 to 13.

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