Inverter assembly and method for operating an inverter assembly

Abstract

The invention relates to an inverter assembly comprising at least two inverters (7; 7') and a control unit (1) connected to the inverters (7; 7'), wherein the control unit (1) is designed to continuously or at discrete time intervals: transmit to the inverters (7; 7') their permissible electrical power range; in particular their minimum power value P min and / or their maximum power value P max ; determine or receive from the inverters the current power balance of the individual inverters (7; 7'); and change the permissible electrical power range of the inverters (7; 7') such that the power balance of the entire inverter assembly does not leave a predetermined range. The invention also relates to a method for operating such an inverter assembly.

Description

Technical Field

[0001] The present invention relates to an inverter assembly and a method for operating the inverter assembly. Background Technology

[0002] Inverter assemblies with multiple inverters are known for many applications in the field of electrical engineering. In particular, drive units for electric and hybrid vehicles are equipped with inverter assemblies with multiple inverters to provide drive power and control the motor to convert the DC voltage supplied by the battery into a suitable AC or DC voltage for the motor to be driven or other electrical appliances in the vehicle.

[0003] Electric vehicle test benches typically also include inverter assemblies with multiple inverters, whether currently used to test the powertrains, mechanical components such as gearboxes, or battery packs of electric vehicles, hybrid vehicles, and traditional internal combustion engine vehicles. Battery pack testing, in particular, is often conducted in parallel, where multiple battery cells, modules, or packs are tested simultaneously with inverters arranged in parallel.

[0004] Electronic control units for such inverter assemblies are disclosed in the prior art. Typically, they are designed to start these inverters in a specific order based on required target parameters; this can also include starting all inverters simultaneously. For example, in an electric vehicle, maximum acceleration (forced downshifting) or emergency braking may be required, resulting in the simultaneous activation of multiple inverters in the vehicle. In test benches for drivetrains with multiple motors or for multi-cell battery modules, the established test methods (so-called test runs) may also require the simultaneous activation of multiple inverters in the inverter assembly.

[0005] The problem here is that the power supply for such inverter components is typically limited, whether in the form of batteries installed in electric vehicles or in the form of a central grid typically available on test benches, either in the form of an AC grid or a DC voltage intermediate circuit. In particular, the DC voltage intermediate circuit should be field-formed using the most compact possible components (so-called grid rectifiers), which in turn limits the maximum energy flow handled during test runs. Simultaneous operation of multiple inverters can also lead to central grid overload, either by excessively consuming power from the power supply (e.g., during forced downscaling) or by outputting excessive power to the power supply (e.g., during emergency braking). Summary of the Invention

[0006] The object of the present invention is particularly to provide an inverter assembly and a method for controlling the inverter assembly, which avoids overloading of the power supply unit and allows for a fairly uniform distribution of inverter load so that the power supply load of the central grid is as low as possible or, in the best case, completely free of load.

[0007] These and other tasks are accomplished by the inverter assembly and the method for controlling the inverter assembly according to the invention.

[0008] The inverter assembly according to the invention includes at least two inverters and a control unit connected to the inverters. The control unit can be designed as an electronic data processing unit, particularly a computer, microcontroller, microprocessor, etc., and may include an electronic data processing unit and an electronic memory unit.

[0009] According to the present invention, the control unit is designed to continuously or at intermittent time intervals receive measurement data from the inverter, particularly current and voltage measurements or power data, and transmit control data to the inverter. For this purpose, the control unit can be connected to a data bus designed for bidirectional communication with the inverter via an interface unit such as a USB interface.

[0010] The control unit is also designed to transmit the allowable range of electrical power to the inverter components. Here, it can be specifically configured to be an inverter that can transmit a minimum power value P. min and / or maximum power value P max The power range is defined. During operation, the control unit thus receives measurement data from the inverter or other electrical components and provides each inverter in the inverter assembly with its permissible power range. Here, the invention is not limited to positive power (power consumption, motor mode), but also includes negative power (power output, generator mode).

[0011] Furthermore, this control unit can also be designed to transmit the current power target value to the inverter. For example, this could be the desired test bench state during test runs, or the requirements of the vehicle driver during operation. The control unit here ensures that the power target value remains within the power range allowed by the respective inverter.

[0012] This invention specifies that the control unit is designed to determine the current power balance of the inverter or receive it from the inverter via a data bus. The term "current power balance" here refers to the current power consumption or power output of the inverter. It should be noted that the inverter of this invention allows for bidirectional operation, meaning it can both consume power and output power. In particular, the inverter can be a so-called active front-end inverter. Relatedly, an active front-end inverter refers to a bidirectional inverter capable of transmitting electrical energy in both directions, such as an active switched bridge rectifier or a bridge inverter.

[0013] The control unit is also designed to calculate the power balance of the entire inverter assembly based on the power balance received from the individual inverters. Here, it is typically the sum of the power balances of the individual inverters. Alternatively, the control unit may be specified to be connected to upstream voltage and current sensors, which allow for the calculation of the power balance of the entire inverter assembly.

[0014] The control unit is also designed to change the allowable power range of the inverter so that the power balance of the entire inverter assembly does not deviate from a predetermined range. Here, the power ranges of the inverters operating in motor mode and generator mode can cancel each other out, so that the entire inverter assembly operates within a low power range, even though these inverters consume or output high power respectively.

[0015] To determine the current power balance of the inverter, the control unit can be connected to at least one voltage sensor for measuring the inverter input voltage and one current sensor for measuring the inverter input current.

[0016] Specifically, it can be specified that the inverter is fed by a DC voltage intermediate circuit, and the control unit is connected to a voltage sensor for measuring the voltage at the DC voltage intermediate circuit. This allows the control unit to easily calculate the corresponding current power consumption or power output of each inverter.

[0017] However, to determine the inverter's current power balance, the control unit can also be connected to a voltage sensor for measuring the inverter's output voltage and a current sensor for measuring the inverter's output current. This allows for the determination of the inverter's power balance on the output side. It can be an AC voltage sensor or an AC current sensor.

[0018] However, the inverter can also be connected to an internal or external voltage sensor for measuring its output voltage and an internal or external current sensor for measuring its output current, and is designed to transmit the measured values ​​to the control unit. In these cases, the inverter supplies its current power balance or its current current and voltage values ​​to the control unit itself.

[0019] The control unit can be designed to change the inverter's permissible power range when the input voltage of the inverter, particularly the voltage of the DC voltage intermediate circuit supplying the inverter, is below or above a predetermined threshold. Therefore, the control unit ensures that the DC voltage of the DC voltage intermediate circuit remains within a predetermined range. If the DC voltage is above this range, the permissible power range of one or all inverters is reduced; if the DC voltage is below this range, the permissible power consumption of one or all inverters is reduced. This prevents overload of the DC voltage intermediate circuit. If this requires changing the power value defined in the test run, the change is always more advantageous than an unexpected termination of the test run due to intermediate circuit overload.

[0020] It can also be specified that a discharge device connected to the control unit is provided to reduce the voltage at the DC voltage intermediate circuit, and the control unit is designed to activate the discharge device when the voltage at the DC voltage intermediate circuit is higher than a predetermined threshold.

[0021] The discharge device can be, for example, a heating resistor designed to reduce the voltage at the intermediate DC circuit. This allows for a particularly rapid reduction of the voltage at the intermediate DC circuit, for example, during sudden braking of a vehicle, or when all batteries are discharging simultaneously in a battery test bench.

[0022] Therefore, the device of the present invention achieves the goal of minimizing the load on the DC voltage intermediate circuit. In particular, the inverters can be configured in a "connected-to-each" arrangement, where the power output of the first inverter is directly used to power the second inverter, thus requiring only the energy needed to overcome losses. Specifically, the control unit can be designed to modify a predetermined test run so that the power balance of the inverter components does not deviate from a predetermined range at any time during the test run.

[0023] This inverter can be designed as an active front-end inverter with bidirectional power flow. In particular, it can be used as a machine inverter in drive test benches or as a DC-DC inverter in battery test benches.

[0024] Other inverter components according to the invention can be used for grid balancing in a hierarchical grid structure. Here, the invention specifies that at least two of the inverters are designed as grid inverters, particularly AC-DC inverters, which preferably feed power from the central grid to separate sub-grids via individual DC voltage intermediate circuits. Here, the control unit can be designed to change the permissible power range of the inverters so that the power balance of the central grid does not deviate from a predetermined range. In this case, the control unit thus controls the power distribution from the central grid to the respective sub-grids, so that the power balance of the central grid is maintained within a certain power range as much as possible.

[0025] According to the present invention, in such a power grid structure, at least two additional inverters can be arranged in at least one of the subgrids, wherein the control unit is designed to change the allowable power range of the inverters such that the power balance of each subgrid does not deviate from a predetermined range. This allows for hierarchical grid balancing, both at the subgrid level and at the central grid level.

[0026] The present invention also relates to a test bench for selecting multiple test specimens, such as components of a drive unit or energy storage devices such as batteries, comprising an inverter assembly according to the invention. Specifically, it may be specified that a DC voltage intermediate circuit for power supply is provided, and all inverters are connected to the control unit via a bidirectional data bus.

[0027] The present invention also relates to a method for operating an inverter assembly having at least two inverters and a control unit connected to the inverters, the method comprising the steps of: in a first step, transmitting a permissible power range, particularly a minimum power value P, to the inverters via the control unit. min and / or maximum power value P max In a further step, the control unit receives or calculates the current power balance of these inverters. In a further step, the control unit calculates the power balance of the entire inverter assembly. In a further step, the control unit adjusts the allowable power range of the inverters so that the power balance of the entire inverter assembly does not deviate from a predetermined range.

[0028] The control unit also continuously supplies the target electrical power value to the inverter. This can be, for example, a planned supply within the trial operation range, or an unplanned supply, such as in response to the vehicle driver's expectations.

[0029] To calculate the inverter's current power balance, the control unit can receive the inverter input voltage from at least one voltage sensor and the inverter input current from a current sensor. The control unit can also receive the voltage of the DC voltage intermediate circuit from the voltage sensor.

[0030] The control unit can receive the inverter output voltage from a voltage sensor and the inverter output current from a current sensor. If the inverter's input voltage, particularly the voltage of the DC voltage intermediate circuit that powers the inverter, is below or above a predetermined threshold, the control unit can change the inverter's allowable power range.

[0031] When the voltage at the intermediate DC voltage circuit exceeds a predetermined threshold, the control unit can activate the discharge device connected to the control unit to reduce the voltage at the intermediate DC voltage circuit.

[0032] The control unit can also change the allowable power range of the inverter in the central grid so that the power balance of the inverter in the central grid does not deviate from the predetermined range, and change the allowable power range of the inverter in at least one sub-grid so that the power balance of the inverter in each sub-grid does not deviate from the predetermined range.

[0033] The present invention also extends to a computer-readable storage medium comprising computer-readable instructions that cause an electronic control unit, such as a computer, microcontroller, or microprocessor, to perform the method of the present invention. Attached Figure Description

[0034] Other features of the invention are derived from the claims, figures, and the following description of the drawings. The invention will now be explained based on non-exclusive embodiments.

[0035] Figure 1 A schematic circuit block diagram showing the topology of the inverter assembly of the present invention in a test bench for a drive device;

[0036] Figure 2 A schematic circuit block diagram showing the topology of the inverter assembly of the present invention in a battery test bench (so-called battery cycler);

[0037] Figures 3a-3b A schematic circuit block diagram showing the topology of the inverter assembly of the present invention in a hierarchical grid structure with two sub-grids. Detailed Implementation

[0038] Figure 1 A schematic circuit block diagram illustrating the topology of an embodiment of the inverter assembly of the present invention in a test bench for a drive unit is shown. The test bench includes a grid inverter that converts the central grid 14 (multiphase AC grid voltage) available on the test bench into a DC voltage of approximately 820V. This DC voltage is referred to as the intermediate circuit voltage (DC link) and is used on the test bench to power the test specimen. The grid inverter is a DC voltage transformer (AC-DC inverter) in the form of a switched active front-end bridge rectifier.

[0039] In this embodiment, the test bench is designed to test the electrical and mechanical components of a drive unit test specimen 13 having a powertrain 11 (such as an electric motor) and a transmission 12. The drive unit to be tested can be a motor vehicle, especially an electric vehicle or hybrid vehicle. In this embodiment, two motors 16, 16' (load machines, so-called dynamometers) are provided, which are connected to the shaft of the drive unit test specimen 13. These motors 16, 16' are powered by two inverters 7, 7' (machine inverters), which convert the intermediate circuit DC voltage V DC Converted to AC voltage. Inverters 7 and 7' are designed as AC voltage inverters (DC-AC inverters), for example, in the form of switched active front-end bridge rectifiers.

[0040] In addition to the mechanical transmission system of the drive unit 13, the electric powertrain 11 of the drive unit prototype 13 is also tested in this embodiment.

[0041] For this purpose, the test bench includes another bidirectional inverter 7'', which is connected to the intermediate circuit 9 and provides a variable AC voltage to the powertrain 11. Depending on the operating state, the powertrain 11 consumes power or outputs power to the intermediate circuit.

[0042] Current sensors 6, 6', and 6'' are provided in the DC voltage input lines of inverters 7, 7', and 7'', and voltage sensor 5 is located in the DC voltage intermediate circuit 9. These sensors continuously transmit the voltage measurement values ​​at the intermediate circuit 9 and the input current measurement values ​​of inverters 7, 7', and 7'' to the control unit 1 via the data bus 10. In this embodiment, the inverter assembly includes three inverters 7, 7', and 7'', but it is not a grid inverter.

[0043] Control unit 1 is also connected to inverters 7, 7', 7'' and discharge device 8 via data bus 10. This connection is used to predefine the allowable power range of the inverters and possibly the power rating P. soll Or it can be used to start the discharge device 8 to reduce the voltage at the intermediate circuit 9.

[0044] In this embodiment, the control unit 1 is designed as an electronic microcontroller with a central data processing unit (CPU) 2, such as an ARM microprocessor or an ASIC. The data processing unit 2 is connected to the memory unit 3 and the interface unit 4 via a data bus. The memory unit 3 can be any machine-readable data memory, such as non-volatile or volatile semiconductor memory, ROM, EPROM, EEPROM, RAM, SRAM, flash memory, etc.

[0045] Interface unit 4 can be based on industry standards such as USB, FireWire, Ethernet, USART, and I2S. It can also specify wireless network protocols such as Wi-Fi and Bluetooth. The appropriate implementation of the control unit is well-known to those skilled in the art, therefore, it is unnecessary to describe each component of control unit 1 in detail.

[0046] During operation, the control unit 1 continuously measures the voltage at the intermediate circuit 9 and the current of inverters 7, 7', and 7'', and provides the inverters 7, 7', and 7'' with their respective power ratings and allowable power ranges. If the DC voltage measured by the DC voltage sensor 5 drops below a predetermined threshold or exceeds a predetermined threshold, the control unit 1 adjusts the allowable power range to compensate for the voltage drop or rise.

[0047] This ensures that the voltage at point 9 in the intermediate circuit always fluctuates within a certain bandwidth, so the grid inverter only bears a slight load.

[0048] Ideally, control unit 1 adjusts the power flow of inverters 7, 7', 7'' so that the grid inverter only needs to cover power losses. This can be achieved when at least one of inverters 7, 7', 7'' supplies power to intermediate circuit 9 and at least one of inverters 7, 7', 7'' draws power from intermediate circuit 9. Control unit 1 can be designed to actively generate this "continuous" operating state, even under possible changes in predetermined test modes. This allows for a very compact design of the grid inverter.

[0049] Figure 2 A schematic circuit block diagram of the topology of another embodiment of the battery test bench (so-called battery cycler) according to the present invention is shown. In this embodiment, four active front-end inverters 7, 7', 7'', and 7''', controlled by a control unit 1, are provided. These are all designed as switching DC / DC inverters and charge and discharge batteries 15, 15', 15'', and 15'''. In this embodiment, the inverter assembly includes four inverters 7, 7', 7'', and 7''', but does not include a grid inverter that generates an intermediate circuit voltage.

[0050] The working mode and basis of control unit 1 Figure 1 The implementation is similar. Control unit 1 adjusts the allowable power range of inverters 7, 7', 7'', 7''' in such a way that the total power of the inverters is below a predetermined threshold.

[0051] If the voltage at intermediate circuit 9 is higher than a predetermined threshold, control unit 1 activates discharge unit 8 (e.g., a heating resistor) to reduce the load on intermediate circuit. If the voltage at intermediate circuit 9 drops below another threshold, control unit 1 reduces the power range of individual or all inverters, causing the voltage at intermediate circuit 9 to recover.

[0052] Instead of individual batteries 15, 15', 15'', 15''', individual battery cells or battery modules (combinations of battery cells) can also be tested in embodiments not shown.

[0053] Figures 3a-3b A schematic circuit block diagram illustrating the topology of the inverter assembly of the present invention in a hierarchical grid structure with two sub-grids is shown. Figure 3aTwo sub-grids 17 and 17' are provided, which are fed from the central grid 14 (three-phase AC grid) through inverters 7 and 7'. In this embodiment, inverters 7 and 7' are grid inverters, i.e., rectifiers, which feed DC voltage intermediate circuits 9 and 9' respectively. Voltage sensors 5 and 5' are arranged in the DC voltage intermediate circuits 9 and 9', and they provide their measurements to the control unit 1 via data bus 10. In addition, current sensors 6 and 6' are arranged in the DC lines of inverters 7 and 7' and also provide their measurements to the control unit 1 via data bus 10. The DC voltage intermediate circuits 9 and 9' feed the two inverters in the first sub-grid 17 to test the battery 15, and feed the inverter for operating the motor 16 in the second sub-grid 17' to test the drive unit test piece 13. However, these inverters are not connected to the control unit 1.

[0054] Control unit 1 is used to continuously transmit the allowable power range to inverters 7, 7' via data bus 10 to achieve a reasonable balance between the two sub-grids 17, 17'. This control unit 1 may also activate one of the two discharge devices 8, 8' to reduce the voltage at intermediate circuits 9, 9'. However, in this embodiment, no active influence on the power of the inverters in the sub-grids is achieved.

[0055] Figure 3b Showing according to Figure 3a This is a direct improvement to the previous embodiment. In this embodiment, the two inverters 7'' and 7''' of the subgrid 17 used for testing the battery 15 are also connected to the control unit 1 via the data bus 10. Therefore, the control unit 1 can not only balance the power of the subgrids 17 and 17' relative to the central grid 14, but also apply allowable power ranges to both inverters 7'' and 7''' within the subgrid 17, so that the power balance within the subgrid 17 is maintained within a predetermined range. This implementation is particularly advantageous in practice because it allows different test systems to operate on the same central network 14.

[0056] In other embodiments not shown, as an alternative to the control unit, each inverter is itself connected to an internal or external voltage sensor for measuring its output voltage and to an internal or external current sensor for measuring its output current. The inverter transmits the current and voltage measurements to the control unit, or calculates its current power balance itself and transmits it to the control unit. It is also evident that in embodiments where some controlled inverters determine their own power balance, while for others, the control unit is responsible for determining the power balance of those inverters. Accordingly, the invention is not limited to the embodiments described above.

[0057] This invention is not limited to the embodiments described above, but includes all inverter components and methods for operating inverter components within the scope of the following claims.

[0058] The terms used herein, such as inverter, grid inverter, or machine inverter, should not be interpreted too narrowly. The inverters of this invention, namely both machine inverters and grid inverters, can be understood as any controlled electrical and / or electronic circuit that converts DC voltage to another DC voltage or AC voltage, or converts AC voltage to another AC voltage or DC voltage. Such circuits can be, for example, but not exclusively, direct inverters, matrix inverters, AC voltage inverters, DC voltage inverters, switched-bridge inverters, switched-bridge rectifiers, etc. The specific circuitry implementation of the inverter is not important. The inverters specified in this invention can also provide internal current isolation and can be configured for high power, such as power in the range of 100kW at 850V DC voltage or 300kVA AC power.

[0059] List of reference numerals

[0060] 1 Control Unit

[0061] 2 Data Processing Unit

[0062] 3 Memory Units

[0063] 4 Interface Unit

[0064] 5. 5' Voltage Sensor

[0065] 6, 6', 6'', 6''' Current Sensors

[0066] 7, 7', 7'', 7''' Inverters

[0067] 8.8' Discharge Device

[0068] 9.9' DC voltage intermediate circuit

[0069] 10 Data Bus

[0070] 11 Powertrain

[0071] 12. Transmission

[0072] 13 Drive unit test specimens

[0073] 14 Central Power Grid

[0074] 15, 15', 15'', 15''' batteries

[0075] 16' motor

[0076] 17' Sub-grid

Claims

1. An inverter assembly comprising at least two inverters (7; 7') and a control unit (1) connected to said inverters (7; 7'), Its features are, The control unit (1) is designed to operate continuously or at discontinuous time intervals. - The inverter (7;7') is supplied with its allowable power range, which is determined by its minimum power value P. min and / or its maximum power value P max The power range constituted - Determine or receive the current power balance of each inverter (7; 7') from these inverters. - Calculate the power balance of the entire inverter assembly, and - Change the allowable power range of the inverter (7;7') so that the power balance of the entire inverter assembly does not deviate from the predetermined range. The control unit (1) is designed such that when the input voltage of the inverter (7;7'), i.e. the voltage V of the DC voltage intermediate circuit (9) fed to the inverter (7;7'), is... DC When the power output is below or above a predetermined threshold, the allowable power range of the inverter (7;7') is changed.

2. The inverter assembly according to claim 1, characterized in that, In order to determine the current power balance of the inverter (7;7'), the control unit (1) is connected to at least one voltage sensor for measuring the input voltage of the inverter (7;7') and to a current sensor (6;6') for measuring the input current of the inverter (7;7').

3. The inverter assembly according to claim 1 or 2, characterized in that, The control unit is connected to the voltage V on the DC voltage intermediate circuit (9) for measuring the voltage. DC Voltage sensor (5).

4. The inverter assembly according to claim 1 or 2, characterized in that, In order to determine the current power balance of the inverter (7;7'), the control unit (1) is connected to a voltage sensor for measuring the output voltage of the inverter (7;7') and a current sensor for measuring the output current of the inverter (7;7').

5. The inverter assembly according to claim 1 or 2, characterized in that, The inverter (7;7') is connected to a voltage sensor for measuring its output voltage and a current sensor for measuring its output current, and is designed to transmit the measured values ​​to the control unit (1).

6. The inverter assembly according to claim 1 or 2, characterized in that, A discharge device (8) is provided connected to the control unit (1) for reducing the voltage at the DC voltage intermediate circuit (9), and the control unit (1) is designed to activate the discharge device when the voltage at the DC voltage intermediate circuit (9) exceeds a predetermined threshold.

7. The inverter assembly according to claim 1 or 2, characterized in that, The inverter (7;7') is designed as an active front-end inverter with bidirectional power flow.

8. The inverter assembly according to claim 7, characterized in that, The inverter (7;7') is used as a machine inverter in a drive unit test bench or as a DC-DC converter in a battery test bench.

9. The inverter assembly according to claim 1 or 2, characterized in that, At least two of the inverters (7; 7') are designed as grid inverters, which are fed from the central grid (14) to separate sub-grids (17; 17') in the form of separate DC voltage intermediate circuits (9; 9'). The control unit (1) is designed to change the allowable power range of the inverters (7; 7') so that the power balance of the inverters (7; 7') of the central grid (14) does not deviate from a predetermined range.

10. The inverter assembly according to claim 9, characterized in that, At least two additional inverters (7''; 7''') are arranged in at least one of the subgrids (17; 17'), wherein the control unit (1) is designed to change the allowable power range of the inverters (7''; 7''') such that the power balance of the inverters (7''; 7''') in each subgrid (17; 17') does not deviate from a predetermined range.

11. A method for operating an inverter assembly having at least two inverters (7; 7') and a control unit (1) connected to the inverters (7; 7'), the method comprising the steps of: a. The control unit (1) transmits the allowable power range to the inverter (7; 7'), the allowable power range being determined by the minimum power value P. min and / or maximum power value P max The power range constituted b. The control unit (1) receives or calculates the current power balance of these inverters (7; 7'). c. The power balance of the entire inverter assembly is calculated by the control unit (1), and d. The allowable power range of the inverter (7; 7') is adjusted by the control unit (1) so that the power balance of the entire inverter assembly does not deviate from the predetermined range. Among them, when the input voltage of the inverter (7;7'), that is, the voltage V of the DC voltage intermediate circuit (9) that supplies power to the inverter (7;7'), DC When the power is below or above a predetermined threshold, the control unit (1) adjusts the allowable power range of the inverter (7; 7').

12. The method according to claim 11, characterized in that, In order to calculate the current power balance of the inverter (7;7'), the control unit (1) receives the input voltage of the inverter (7;7') from at least one voltage sensor and the input current of the inverter (7;7') from a current sensor (6;6').

13. The method according to claim 11 or 12, characterized in that, The control unit (1) receives the voltage V from the DC voltage intermediate circuit (9) from the voltage sensor (5). DC .

14. The method according to claim 11 or 12, characterized in that, The control unit (1) receives the output voltage of the inverter (7;7') from the voltage sensor and the output current of the inverter (7;7') from the current sensor.

15. The method according to claim 11 or 12, characterized in that, The inverter (7;7') is connected to a voltage sensor for measuring its output voltage and a current sensor for measuring its output current, and transmits the measured values ​​to the control unit (1).

16. The method according to claim 11 or 12, characterized in that, When the voltage at the DC voltage intermediate circuit (9) exceeds a predetermined threshold, the control unit (1) activates the discharge device (8) connected to the control unit (1) to reduce the voltage at the DC voltage intermediate circuit (9).

17. The method according to claim 11 or 12, characterized in that, The control unit (1) - Change the allowable power range of the inverters (7; 7') of the central power grid (14) so ​​that the power balance of the inverters (7; 7') of the central power grid (14) does not deviate from the predetermined range, and - Change the allowable power range of the inverters (7''; 7''') of at least one subgrid (17; 17') such that the power balance of the inverters (7''; 7''') of each subgrid (17; 17') does not deviate from the predetermined range.

18. A computer-readable storage medium comprising computer-readable instructions that cause a control unit (1) to perform the method according to any one of claims 11 to 17.

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