Method for operating an electronic circuit breaker of a converter

Abstract

Method for operating at least one electronic circuit breaker (4, 5) and at least one power module (3) of an inverter (1) in a device for feeding electrical power into an electrical network (N), wherein the at least one circuit breaker (4, 5) is controlled via control means (9) and the at least one power module (3) of the inverter (1) is used for feeding electrical power into the electrical network, characterized in that external operating faults of the device for feeding electrical power into a network (N) are determined using fault detection means (2, 2') and a specific maximum tripping current for the at least one circuit breaker (4, 5) is specified depending on the determined external operating faults.

Description

[0001] The invention relates to a method for operating at least one electronic circuit breaker of a power module of an inverter in a device for feeding electrical power into an electrical network, wherein the at least one circuit breaker is controlled by control means and the at least one power module of the inverter is used for feeding electrical power into the electrical network. Furthermore, the invention relates to a device for feeding electrical power into an electrical network, in particular a wind turbine with at least one inverter having power modules, wherein the power modules have electronic circuit breakers and the device has control means for controlling the circuit breakers of the power modules of the inverter for feeding electrical power into the electrical network.

[0002] Devices for feeding electrical power into an electrical grid, which use converters for this purpose, are primarily used in the field of renewable energy generation. They are particularly common in wind turbines. Wind turbines with permanent magnet synchronous generators feed the entire mechanical wind power into the electrical grid via a converter. Wind turbines equipped with a doubly fed asynchronous machine feed a large portion of the mechanical energy from the wind rotors directly into the grid via the stator of the asynchronous machine. The remaining portion of the wind rotor drive power is fed into the electrical grid via the converter connected to the rotor of the asynchronous machine. For this purpose, the converter transforms the grid voltage into rotor voltages or currents of the asynchronous machine.Inverters used in devices for feeding electrical power into an electrical grid employ electronic power switches, such as insulated-gate bipolar transistors (IGBTs), for voltage conversion. These IGBTs are controlled, for example, by pulse-width modulation. IGBTs are capable of switching very high currents in a very short time. The power switches are typically arranged in power modules, each dedicated to a specific phase of a three-phase current. Due to the very high currents flowing through these electronic power switches, it is common practice to monitor them and disconnect them in case of overload, such as when switching excessively high currents.

[0003] The "Application Handbook for Power Semiconductors," Semikron International GmbH, 2nd revised edition, describes intelligent power modules that incorporate various sensors for monitoring the circuit breakers. These power modules feature current sensors at the AC output of the IGBT, which trip the circuit breaker if a maximum current is exceeded. This current is referred to as the maximum tripping current. Further monitoring of the circuit breakers for operational faults is provided via temperature sensors, sensors for measuring the collector-emitter voltage at the circuit breaker, and sensors for the supply voltage of the driver circuit. This protects the electronic circuit breakers of the power module from damage and allows for tripping or disabling them as needed. Overcurrent protection, as previously mentioned, is provided by current sensors at the AC output of the IGBTs.When the IGBT's maximum tripping current, as specified by the power module, is exceeded, the control signals for the circuit breaker are suppressed, and the circuit breaker or the entire bridge circuit is disabled. The tripping of individual electronic circuit breakers leads to so-called "tripping" and typically disconnects the entire power supply system from the grid.

[0004] The maximum tripping currents specified by the power modules for the circuit breakers are designed to prevent thermal damage to the electronic circuit breakers during continuous operation. This means that these currents may only be present at the circuit breaker during pulsed operation without causing damage. Therefore, these maximum tripping currents are generally set relatively low. This ensures that the circuit breaker does not suffer damage during normal pulsed operation and has a long service life. The magnitude of the maximum tripping current depends on the power rating of the circuit breakers and is specific to the design of the circuit breakers or the power module. This relatively low maximum tripping current is typically fixed by the power modules. As previously mentioned, exceeding this tripping current results in the locking or disconnection of at least one circuit breaker.

[0005] Current connection rules for devices that feed electrical power into an electrical grid require that these devices also contribute to maintaining the grid voltage. In the event of grid voltage deviations, such as those caused by short circuits, these deviations must be counteracted quickly. The connection rules stipulate, for example, that the device must be able to respond to the voltage drop with a step response of the reactive current. The device that feeds electrical power into an electrical grid should actively participate in maintaining the grid voltage for as long as possible and enable fault ride-through (FRT) operation. FRT operation is possible when the device does not have to disconnect from the grid during a sudden voltage change and can "ride through" the external fault.

[0006] A sudden change in grid voltage is counteracted by a step response from the inverter, for example, a setpoint step of the reactive current. This setpoint step must be regulated with a short settling time, which can lead to overshoot. Therefore, if the reactive current is changed to the rated reactive current with a setpoint step, the maximum tripping currents of the power module can be exceeded. The circuit breaker trips, resulting in so-called "tripping." In this case, the device must be disconnected from the grid. However, if the device is to ensure FRT operation, for example, with rated reactive current, the electronic circuit breakers must be rated for higher power to guarantee the step response without disconnecting the device from the grid. This increases the cost of the circuit breakers.However, there is a constant need in the generation of renewable electricity to further reduce the costs of devices for feeding electrical power into an electrical grid with converters, such as wind turbines.

[0007] International patent application WO 2014 / 154 221 A2 discloses, for example, an intelligent driver circuit for power modules that performs real-time measurement of, for instance, the collector current of the IGBT in order to fully utilize the capacity of the power modules. If the maximum tripping current is exceeded, the circuit breaker trips immediately. Therefore, the circuit breaker also trips immediately in the event of an overshoot and exceedance of the maximum tripping current as a result of the step response control. Even with this driver circuit, the circuit breakers must be dimensioned with higher power ratings.

[0008] US patent 7,274,223 B2 discloses a power module with a plurality of predefinable maximum tripping currents, referred to here as "trip levels," which can be specified, for example, by determining the temperature of the circuit breaker. The fact that a high circuit breaker temperature can further reduce the maximum permissible tripping currents is possibly a consequence of an internal operating fault, such as the failure of a cooling element in the power module. External operating faults, such as a mains voltage drop, are not taken into account.

[0009] US patent application US 2011 / 0103110A1 also discloses the ability to detect external operating faults and, if a maximum tripping current is exceeded, to modify the control method of the circuit breakers to prevent this maximum tripping current from being exceeded. While the US patent application discloses the ability to calculate maximum tripping currents for each phase, it does not address the determination of external operating faults or the determination of specific tripping currents based on these faults.

[0010] External operating faults are defined as all conceivable disturbances in the electrical network to which the device is connected. Specifically, at least the following deviations from the target value of the network voltage are considered external operating faults: deviations in voltage level (i.e., undervoltage or overvoltage), deviations in frequency, and / or phase shifts of the network voltage. With external operating faults, the converters and power modules of the device for feeding electrical power into the network are not themselves affected. However, external operating faults can cause unexpectedly high currents in the circuit breakers, for example, due to overshoot during fault correction.

[0011] The present invention is therefore based on the objective of providing a method for operating at least one circuit breaker of a power module of an inverter of a device for feeding electrical power into an electrical network, which, while providing particularly fast control behavior, simultaneously makes better use of the power capacity of the electronic circuit breakers while fulfilling the connection rules. In addition, the invention is based on the objective of providing a corresponding device for carrying out the method according to the invention.

[0012] According to a first teaching of the present invention, the aforementioned problem is solved for a generic method by determining external operating faults of the device for feeding electrical power into a network using fault detection means and by specifying a specific maximum tripping current for the at least one circuit breaker depending on the determined external operating fault.

[0013] By adjusting the specific maximum tripping currents for the at least one circuit breaker to the occurrence of an external operating fault, in particular an unintended deviation in the mains voltage, it is possible to adapt the control behavior of the inverter's power modules in a device for feeding electrical power into an electrical grid to the required control behavior of modern connection rules, without using power modules with a higher power rating. This allows the power reserves of the power modules to be utilized even more effectively and costs to be reduced.

[0014] Previously, it was known that the maximum tripping currents of circuit breakers could only be determined with regard to internal operating faults, i.e., faults in the power module or the inverter itself. Internal operating faults include internal short circuits and voltage deviations. CEThe inventive method takes into account the DC link voltage, the supply voltage of the driver circuit, or an overtemperature of the circuit breakers. With this method, it is now possible to selectively adjust the power output capacity of the circuit breakers even during the occurrence of external operating faults. For example, when adjusting the maximum tripping currents, it can be taken into account that higher currents during external operating faults only occur for very short periods and can therefore exceed the maximum tripping currents intended for continuous operation.

[0015] According to a first embodiment of the inventive method, if the maximum tripping current specified for an external operating fault for the at least one circuit breaker is greater than the tripping current for an internal operating fault, the circuit breaker of the inverter can be adapted to an increased power output in the event of an external operating fault.

[0016] In a preferred embodiment of the method, the maximum tripping current for external operating faults is specified only for a predetermined period, so that after this period, for example, the maximum tripping current for internal operating faults can be reused. This ensures that after the external operating fault has subsided or resolved, the circuit breakers can be readjusted to "normal" continuous operation with respect to their maximum tripping currents.

[0017] According to a further embodiment of the inventive method, if a driver circuit specifies a maximum tripping current for internal operating faults for the at least one circuit breaker, the tripping current for internal operating faults can be specified at the level of the power modules, and the tripping currents for external operating faults can then be specified via the control means of the device for feeding electrical power into an electrical network. The measurement signals or data necessary for determining external operating faults are generally already available here.

[0018] According to a further embodiment of the method according to the invention, in the event of an internal operating fault, the at least one circuit breaker is not tripped if, in the case of an external operating fault and a specified maximum tripping current, only the exceedance of the maximum tripping current provided for internal operating faults is detected as the internal operating fault. This prevents the destruction of a circuit breaker even if the specified maximum tripping current of the circuit breaker has not yet been reached in the case of a simultaneous external operating fault, but an internal operating fault has occurred.

[0019] According to a further embodiment of the method according to the invention, the fault detection means evaluate at least mains voltage measurements, preferably measured at the mains connection point of the device for feeding electrical power into an electrical network, for fault detection. This ensures that the device for feeding electrical power into an electrical network can be operated in compliance with mains connection rules that require rapid countermeasurement against mains voltage fluctuations directly at the mains connection point.

[0020] Furthermore, according to a further embodiment of the inventive method, it is advantageous that the fault detection means evaluate additional operating parameters of the device for feeding electrical power into an electrical network for fault detection, wherein at least the network currents at the network connection point are evaluated as additional operating parameters. This makes it possible to consider the power output when specifying the maximum tripping currents via the fault detection means. The fault detection means can also consider other operating parameters, such as the operating temperature of the circuit breaker, for specifying the maximum tripping current in the event of an external operating fault. If, in addition to the network voltage measurements, the network currents at the network connection point are also considered by the fault detection means, a distinction can also be made between an internal and an external operating fault based on the current direction.This allows the fault detection tools to also identify internal operational errors.

[0021] According to a further embodiment of the method according to the invention, a mains overvoltage, a mains undervoltage, or a phase angle change of the mains voltage is detected during operation by the fault detection means as external operating faults, and a maximum tripping current is specified for each specific operating fault for the at least one circuit breaker. Due to the control behavior of the converter, which is known for the various specific external operating faults and is also specified in connection rules such as VDE-AR-N 4110, it is possible to provide a higher level of operational reliability for the circuit breaker for the various specific external operating faults by adapting the maximum tripping currents to the specific external operating fault and thus avoiding unnecessarily high maximum tripping currents of the circuit breakers.

[0022] To counteract external operating faults as quickly as possible, a further embodiment of the method specifies that the time interval for setting the maximum tripping current and the magnitude of the maximum tripping current of at least one circuit breaker in the event of an external operating fault are determined by the fault detection means in such a way that the inverter can react to the external operating fault with a setpoint step in a reactive or active current component of the supplied electrical power. Transient processes occur during a setpoint step in a reactive or active current component of the electrical power, which the time interval and the specified maximum tripping current account for, so that despite any overshoots that may occur, the circuit breaker does not trip.For example, the maximum tripping current of the circuit breaker specified during a setpoint step can account for the overshoot if the inverter's control behavior is known. The duration of the maximum tripping current setting should then cover the potential overshoot period.

[0023] According to a further embodiment of the method, it is therefore advantageous that the time span for specifying the maximum switching current is at most the settling time T. ein_Δx This corresponds to the step response of the inverter in a reactive or active current component. After the settling time T ein_Δx The controlled variable, for example the reactive current, lies within a tolerance band with a width Δx around the controlled variable. Preferably, the time interval of the setpoint is a maximum of 60 ms.

[0024] According to a further embodiment of the method according to the invention, in the event of an external operating fault, a fault ride-through (FRT) operation of the device for feeding electrical power into an electrical network is carried out, wherein, at least temporarily during FRT operation, specific tripping currents are specified to the circuit breakers via fault detection means. During FRT operation, the device for feeding electrical power into an electrical network continues to be operated on the network despite the existing external operating fault, for example, in the case of a network undervoltage, in order to counteract the undervoltage, for example. This is achieved, for example, by a setpoint step in the reactive power feed-in.Here, the specific maximum tripping currents designed for external operating faults come into play, preventing circuit breakers from tripping and simultaneously avoiding damage to the circuit breaker. This design of the method allows the device to operate in FRT mode for feeding electrical power into an electrical network without having to design the power modules for higher output powers, such as those that only occur briefly during FRT operation. The power capacity of the circuit breakers, and thus of the power modules, can therefore be better utilized.

[0025] Preferably, according to a further embodiment of the method, each exceedance of the maximum tripping current of the circuit breakers intended for internal operating faults, for example during an FRT event due to an external operating fault, is counted. The number of FRT events with exceedances of the maximum tripping currents intended for internal operating faults can then be evaluated, for example, for preventive maintenance of the power modules.

[0026] According to a further teaching of the present invention, the problem for a device for feeding electrical power into an electrical network, in particular for a wind turbine with at least one converter with power modules, wherein the power modules have electronic circuit breakers and the device has control means for controlling the circuit breakers of the power modules of the converter for feeding electrical power into the electrical network, is solved by providing fault detection means which detect external operating faults of the device for feeding electrical power into a network and which, depending on the detected external operating fault, can specify a specific maximum tripping current for the at least one circuit breaker.

[0027] As previously explained, external operating faults can be used via the fault detection means to specify maximum tripping currents for the at least one circuit breaker. The device according to the invention can provide the short-term higher tripping currents required for at least one circuit breaker in the event of external operating faults without having to design the circuit breakers or the power modules to handle the power peaks during external operating faults. Specifically, the device according to the invention can provide short-term power peaks, such as those required for the rapid compensation of a setpoint step, by increasing the maximum tripping currents, without having to design the circuit breakers for a higher power rating.The control behavior of the device for feeding electrical power into an electrical network can be adapted to the network connection rules without having to change the circuit breakers with regard to their continuous power output.

[0028] According to a further embodiment of the device according to the invention, the fault detection means are provided by at least one separately provided electronic circuit or, in a software-based manner, by the control means of the device for feeding electrical power into an electrical network. A separate electronic circuit, for example an ASIC, makes it possible to integrate the fault detection means into the power modules. Alternatively, the existing control means of the device for feeding electrical power into an electrical network can be used for the fault detection means by means of a software-based provision.

[0029] Preferably, according to a further embodiment of the device according to the invention, means for determining operating parameters of the device for feeding electrical power into an electrical network are provided. These means can determine at least the network voltage as an operating parameter, so that the determined operating parameters can be evaluated by the fault detection means. This provides the fault detection means with the fundamental operating parameters to detect external operating faults and to specify corresponding tripping currents for the circuit breakers of the power modules in the inverters. Optionally, the alternating currents supplied by the at least one inverter can also be determined as operating parameters, so that it is also possible, in principle, to distinguish between internal and external operating faults.

[0030] The invention will now be explained in more detail using exemplary embodiments in conjunction with the drawing. The drawing shows: Fig. 1 and Fig. 2 Two typical embodiments of devices according to the invention for feeding electrical power into an electrical network in the form of wind turbines, Fig. 3 a circuit diagram of an exemplary power module for one phase of the mains voltage, Fig. 4 a schematic block diagram of a power module of an embodiment of a device according to the invention for feeding electrical power into an electrical network, Fig. 5 and Fig. 6 two flowcharts of an embodiment of a method according to the invention for operating circuit breakers, Fig. 7 examples of undervoltage and overvoltage profiles depending on the time for FRT operation and Fig. 8 A typical transient response of a fast controller during a setpoint step.

[0031] In the Fig. 1 and Fig. Figure 2 shows two typical designs of devices for feeding electrical power into an electrical network N, in which the rotor hub M mechanically drives a generator in the form of a synchronous generator SG or a doubly fed asynchronous machine G. The in Fig. The synchronous generator shown in Figure 1 is permanently excited and, through its rotation, generates a three-phase alternating voltage in the stator. This voltage is first converted into a direct current and then into an alternating current in the inverter 1 with a DC link. For this purpose, the inverter contains... Fig. One circuit breaker (not shown in detail) is provided. Fault detection means 2 according to the invention determine whether an external operating fault is present at the grid-side inverter of the converter 1. According to the invention, all deviations of the grid voltage from the target state are considered external operating faults. This includes, in particular, grid undervoltages, grid overvoltages, deviations from the grid frequency, and phase angle jumps of the grid voltage. The fault detection means 2 have in Fig. 1. Means (not shown) for determining operating parameters, which can determine the mains voltage of the electrical network applied to the inverter 1. Preferably, the means for determining the operating parameters of the device determine the mains voltage at the mains connection point of the device.

[0032] If the fault detection devices 2 detect an external operating fault, they specify a maximum tripping current for at least one circuit breaker of the inverter 1 in order to optimize the inverter's control behavior in the event of an external operating fault. This is achieved, for example, by briefly specifying an increased maximum tripping current for at least one circuit breaker. The circuit breaker can then be operated briefly with this increased maximum tripping current without having to be switched off. External operating faults can thus be particularly well controlled.

[0033] In Fig. 2. On the machine side, converter 1' is connected to the rotor of the doubly fed asynchronous machine G. The stator of the doubly fed asynchronous machine is directly connected to the electrical grid N. Converter 1' converts the grid voltage into a rotor voltage via a DC link, thereby determining the rotor currents. These currents ensure that the stator is in a fixed phase relationship with the grid voltage and that the mechanical power of the rotor hub M is converted into electrical power with precise phase angle accuracy. In the event of an external operating fault, such as a grid undervoltage, increased currents can occur in the circuit breakers on both the rotor and grid sides of converter 1' to counteract the external operating fault, for example, by means of a setpoint step.In order to provide for specific, especially higher maximum tripping currents for short periods, which cause the circuit breaker to trip, for at least one circuit breaker, the following are required in . Fig. 2 fault detection means 2' are provided for both the rotor-side circuit breakers and the grid-side circuit breakers.

[0034] According to a preferred embodiment, the tripping currents specified by the fault detection means 2, 2' in the event of an external operating fault are higher than in the event of an internal operating fault of the inverter 1, 1'. Internal operating faults are defined as all disturbances caused by the inverter itself. These include, for example, a voltage deviation in the collector-emitter voltage at the IGBT-implemented circuit breaker, an excessively high temperature of the circuit breaker, a deviation in the voltage supply to the circuit breaker's driver circuit, etc. The maximum tripping current, which takes an internal operating fault into account, ensures that the at least one circuit breaker can be loaded up to the maximum tripping current during normal operation without sustaining damage. This maximum tripping current is therefore relatively low and does not correspond to the current that the circuit breaker can handle for short periods.For external operating faults, which are generally singular events and only require a very brief exceedance of the maximum tripping currents for internal operating faults, the maximum tripping current can therefore be briefly increased by the fault detection means 2, 2', for example, without damaging the circuit breakers. The power reserves of the power modules can therefore be better utilized with the method according to the invention.

[0035] A typical power module 3 for one phase is shown in a circuit diagram. Fig. 3. The power module 3 has two power switches 4, 5, which are implemented here as IGBTs. Freewheeling diodes 6, 7 are provided in parallel with the power switches 4, 5. An alternating current I can be applied to the AC output. outThe current is measured, which is generated by switching the power switches 4 and 5. For this purpose, the power switches 4 and 5 are controlled using pulse width modulation to generate a predefined current or voltage waveform at the AC output 8 of the power module.

[0036] Fig. Figure 4 shows a schematic block diagram of a power module 3 of an embodiment of a device according to the invention for feeding electrical power into an electrical network. The power module 3 has a PWM control unit 9, which controls both power switches 4 and 5. Sensors of the power module transmit error signals to the PWM control unit 9 concerning measured values ​​of internal operating faults. For this purpose, the power module 3 has temperature sensors of the power switches 10 and 11, and the intermediate switches 12 and 13 for measuring the collector-emitter voltage V. CECircuit breakers 4 and 5, medium 14 for measuring the DC voltage of the intermediate circuit, and medium 15 for monitoring the voltage supply of the driver circuit of circuit breakers 4 and 5. The current sensor 16a determines the current at the AC output and transmits its measured value to the overcurrent protection device 16. The overcurrent protection device 16 checks whether the measured current exceeds a predefined maximum tripping current. If the measured current is greater than the predefined maximum tripping current, the overcurrent protection device 16 transmits an error signal to the PWM control 9, which causes the respective circuit breaker 4 or 5 to be blocked. This results in the power module 3 tripping.

[0037] According to the invention, fault detection means 2 are provided which, for example, by measuring and evaluating the mains voltage, preferably at the mains connection point, can detect an external operating fault and, via the overcurrent protection means 16 provided here, can specify a higher maximum tripping current for the at least one circuit breaker 4, 5. The circuit breaker 4, 5 or the power module 3 can then switch an increased current without the circuit breaker 4, 5 being switched off.

[0038] Preferably, the increased maximum tripping current is specified by the fault detection means 2 only for a predetermined period of time, for example a period of time in which the specified maximum tripping current is expected during the specific external operating fault.

[0039] How Fig. Figure 4 shows that the driver circuit of at least one circuit breaker 4, 5 specifies a maximum tripping current for at least one circuit breaker 4, 5 in the event of an internal operating fault, which is intended to ensure the normal operation of the circuit breakers. The maximum tripping current for normal operation is set low to protect the circuit breakers 4, 5 from damage in the event of internal operating faults and to ensure the continuous operation (normal operation) of the circuit breakers up to the maximum tripping current.

[0040] In the illustrated embodiment in Fig. 4 The overcurrent protection already known from the power modules 3 is combined with the inventive specification of maximum tripping currents in the event of external operating faults. The fault detection means 2 are in Fig. 4 For example, the control elements of the device for feeding electrical power into an electrical network are implemented in a software-based manner and specify the maximum disconnect currents in the event of external operating faults via the overcurrent protection devices 16 of the power module 3. However, the fault detection devices 2 can also be implemented by a separate electronic circuit, for example in the form of an ASIC in the power module.

[0041] At the in Fig. In the embodiment shown in Figure 4, if an internal operating fault occurs, for example, if the maximum temperature of the circuit breaker is exceeded, at least the relevant circuit breaker 4, 5 is always switched off by a corresponding signal to the PWM control 9. This also occurs if a higher maximum tripping current is specified due to an external operating fault, so that damage to the circuit breakers is prevented in any case.

[0042] Fig. Figure 5 shows a flowchart of an embodiment of a method according to the invention for operating at least one circuit breaker 4, 5 of a power module of a converter in a device for feeding electrical power into a network, in which a first maximum tripping current, designated as "OCP Level 1", is specified in normal operation 17. This maximum tripping current for normal operation "OCP Level 1" is dimensioned low and is intended to specify the maximum current that can be continuously switched by the at least one circuit breaker in normal operation without causing damage to the circuit breaker or a significant reduction in its service life. In the Fig. In the embodiment of the method according to the invention shown in Figure 5, the maximum shutdown current “OCP Level 1” is designed as the lowest maximum shutdown current.

[0043] During normal operation, fault detection device 2 monitors for external operating faults. If, for example, a mains undervoltage is detected by fault detection device 2 (step 18), a specific maximum tripping current, referred to here as "OCP Level 4", is specified for at least one circuit breaker according to step 18a. The specification of the maximum tripping current in the event of an external operating fault can be adjusted according to the [reference to relevant section / document]. Fig. 4. This is achieved via overcurrent protection device 16 as shown in the illustrated embodiment.

[0044] As in Fig. As shown in Figure 5, in the event of a grid undervoltage, the highest maximum tripping current for at least one circuit breaker is specified. This particularly high maximum tripping current is advantageous in the event of undervoltage to achieve maximum voltage support against the voltage drop by means of a setpoint step to maximum reactive power injection. The duration of the specified maximum tripping current "OCP Level 4" can be selected to be particularly short in this case, for example, a maximum of 60 ms, in order to increase the maximum tripping current for at least one circuit breaker to "OCP Level 4" only during the settling time for the setpoint step. This ensures, for example, low-voltage ride-through (LVRT) operation of the inverter.

[0045] If no LVRT event is detected as an external operating fault, but rather a phase shift in the mains voltage (step 19) or a mains overvoltage (step 20), the maximum tripping current "OCP Level 3" or "OCP Level 2" of the at least one circuit breaker is specified depending on the detected external operating fault according to steps 19a and 20a, respectively. Preferably, the maximum tripping current "OCP Level 3" for a mains phase shift is greater than the maximum tripping current "OCP Level 2" for a mains overvoltage. Both specified maximum tripping currents allow fault ride-through (FRT) operation, for example, high-voltage ride-through (HVRT) operation, to be carried out and to counteract the fault by the device for feeding electrical power into a grid.

[0046] If the maximum tripping currents increased compared to "OCP Level 1" are specified for "OCP Level 2", "OCP Level 3", "OCP Level" 4 according to step 18a, 19a or 20a, the following applies according to the Fig. In the embodiment shown in section 5, an FRT timer is used to set a specific value t. s , which corresponds, for example, to the calculation cycle time for determining the existing error, is increased in step 21 and then in step 22 with the maximum time span t max for the specification of increased maximum disconnect currents compared. Is the time interval t max If the limit for FRT operation is exceeded, "OCP Level 1" is reset and normal operation resumes. If the then-predefined maximum tripping current is exceeded again, the circuit breaker is switched off (see Fig. 6) If the time period, which in principle can also be specifically defined for each individual maximum tripping current “OCP Level 2”, “OCP Level 3”, “OCP Level 4”, has not yet been exceeded, a specific maximum tripping current “OCP Level 2”, “OCP Level 3”, “OCP Level 4” is specified for at least one circuit breaker in the event of a corresponding external operating fault, and the FRT timer is extended by the time t. s increased. As soon as the time interval t max If the limit is exceeded, the FRT timer will also be reset to zero when regular operation resumes according to step 17.

[0047] In the Fig. In the embodiment shown in Figure 5, the maximum disconnect currents “OCP Level 2”, “OCP Level 3”, and “OCP Level 4” are dimensioned such that a setpoint change in a reactive or active current component of the supplied electrical power can react to the corresponding external operating fault. The time interval t maxThe specification of maximum shutdown currents "OCP Level 2", "OCP Level 3", and "OCP Level 4" preferably takes into account the transient response of the inverter's control system and is, for example, a maximum of 60 ms. The magnitude of the maximum shutdown currents "OCP Level 2", "OCP Level 3", and "OCP Level 4" is preferably adapted to the current overshoot during the transient response process for compensating the setpoint step against external operating errors, in order to avoid "tripping" and simultaneously prevent excessively high maximum shutdown currents.

[0048] Fig. Figure 6 now shows the interaction of the control of the maximum disconnect currents according to Fig. 5 with internal operating errors, such as an excessively high driver voltage V driver or an excessively high IGBT temperature T IGBTIf, during normal operation, 17 exceedances of the intended maximum tripping current for normal operation 17 “OCP Level 1” are detected (step 23), the counter for an “OCP event” in step 24 is incremented by 1. Subsequently, according to step 25, it is checked whether an FRT timer in step 18, 19, or 20 ( Fig. 5) was started. If this is not the case, an internal operating fault exists and at least one circuit breaker 4, 5, and thus the inverter, are switched off (step 26). If an FRT timer is started in steps 18, 19, or 20 and an external operating fault is detected, step 27 checks whether the maximum number of "OCP events" has been exceeded. If the maximum number of OCP events is exceeded, at least one circuit breaker, and thus the inverter, can also be switched off. An excessive number of OCP events can reduce the service life of the circuit breakers, so the circuit breakers are switched off preventively during these events. If no exceedance of OCP level 1 is detected in step 23, normal operation 17 continues.

[0049] This also applies if, as shown in steps 28 and 29, an internal operating parameter exhibits an impermissible deviation. For example, if the driver voltage V driver (Step 28) is undershot or the temperature of the IGBT T IGBT (Step 29) is exceeded, in these cases at least one circuit breaker and thus the inverter is switched off according to step 26. In this embodiment, therefore, the inverter is switched off in any case if an internal operating fault is present, even if the specified maximum tripping current has not yet been reached, but an internal operating fault exists.

[0050] In Fig. Figure 7 is the time course of the ratio of the mains voltage U measured at the mains connection point. NAP to the specified target mains voltage U NThe process is illustrated for a two-phase voltage dip 32 or a three-phase voltage dip 31, as well as for a network overvoltage 30. In the method according to the invention, the fault detection means 2 react to the three-phase voltage dip 31 by setting the maximum disconnecting current "OCP Level 4". The two-phase voltage dip 32 results, on the one hand, in a network phase shift and, on the other hand, also in a network undervoltage, which, in the present embodiment, causes the fault detection means to set the maximum disconnecting current "OCP Level 3". The aforementioned maximum disconnecting currents allow the inverter to counteract the respective external operating fault by means of a setpoint step of a reactive or active current component and to permit FRT operation, i.e., passing through the fault, for example, according to the intended network connection rules.The device according to the invention for supplying electrical power therefore remains connected to the mains during the passage of the external operating fault. At the respective jumps in the mains voltage U. NAP 30a, 30b, 30c, 31a, 31b, 32a, 32b: A setpoint step is implemented in a reactive or active current component of the supplied electrical power, resulting in a specific transient response of the circuit breaker regulation and thus of the required currents in the circuit breaker. An example of a transient response of a controlled variable during the regulation of a setpoint step is shown in Fig. 8 shown.

[0051] In Fig.Figure 8 represents the controlled variable, for example, the reactive current x(t), as a function of time. The setpoint, for example, the reactive current output of the device, is shown with dashed lines. At time t0, in response to, for example, a sudden voltage drop, the setpoint of the reactive current jumps from 0% to 100%. To counteract the voltage drop as quickly as possible, the reactive current x(t) is allowed to be regulated with an overshoot, as otherwise the voltage drop could not be counteracted quickly enough. The overshoot Δx max In previously known methods for operating circuit breakers, the step response x(t) of the reactive current leads to a “tripping” of the circuit breaker, since the maximum tripping currents “OCP Level 1” are exceeded during overshoot.

[0052] If an external operating fault, such as a sudden voltage drop, occurs, the inventive method detects an external operating fault via the fault detection means 2 and specifies the maximum tripping current, for example, in the case of a mains voltage dip, the tripping current “OCP Level 4”, which determines the overshoot Δx max permitted and preferred for the settling time T ein_ΔxFor which at least one circuit breaker is specified. Due to the short duration of the increased maximum tripping current, the circuit breaker can briefly switch an increased tripping current to regulate the settling time without sustaining damage. Therefore, the circuit breaker does not need to be adapted to the power peaks occurring during LVRT, HVRT, or phase-change events of the grid voltages and does not need to be switched off when the device is operating in FRT mode. The design of the circuit breakers of inverters in devices for feeding electrical power into a grid can thus be further optimized.

Claims

[1] Method for operating at least one electronic circuit breaker (4, 5) and at least one power module (3) of an inverter (1) in a device for feeding electrical power into an electrical network (N), wherein the at least one circuit breaker (4, 5) is controlled via control means (9) and the at least one power module (3) of the inverter (1) is used for feeding electrical power into the electrical network, characterized by , that external operating faults of the device for feeding electrical power into a network (N) are determined using fault detection means (2, 2') and depending on the determined external operating faults a specific maximum tripping current is specified for the at least one circuit breaker (4, 5). [2] Method according to claim 1, characterized by, that the maximum tripping current specified for an external operating fault for the at least one circuit breaker (4, 5) is greater than the tripping current for internal operating faults. [3] Method according to claim 1 or 2, characterized by , that the maximum shutdown current for external operating faults is only specified for a predetermined period of time. [4] Method according to any one of claims 1 to 3, characterized by , that a driver circuit for the at least one power switch (4, 5) specifies a maximum tripping current for internal operating faults. [5] Method according to any one of claims 1 to 4, characterized by, that in the event of an internal operating fault, at least one circuit breaker (4,5) will not be switched off only if, in the event of an external operating fault and the specification of an increased maximum tripping current, only the exceedance of the maximum tripping current provided for internal operating faults is determined as the internal operating fault. [6] Method according to any one of claims 1 to 5, characterized by , that the fault detection means (2, 2') evaluate at least mains voltage measurements, preferably measured at the mains connection point of the device for feeding electrical power into an electrical network (N) for fault detection. [7] Method according to any one of claims 1 to 6, characterized by, that the fault detection means (2, 2') evaluate further operating parameters of the device for feeding electrical power into an electrical network (N) for fault detection, wherein at least the alternating currents generated by the converter (1) are evaluated as further operating parameters. [8] Method according to any one of claims 1 to 7, characterized by , that a mains overvoltage, a mains undervoltage or a phase angle change of the mains voltage is detected during operation as an external operating fault by the fault detection means (2, 2') and for each specific operating fault a maximum tripping current is specified for the at least one circuit breaker (4, 5). [9] Method according to any one of claims 3 to 8, characterized by, that the specified time period and the magnitude of the maximum tripping current of the at least one circuit breaker (4, 5) in the event of an external operating fault are specified by the fault detection means (2, 2') in such a way that the converter (1) can react to the external operating fault with a setpoint step of a reactive current or active current component of the supplied electrical power. [10] Method according to any one of claims 3 to 9, characterized by , that the time span of the specification of the maximum switching current is at most the settling time T ein_Δx corresponds to a setpoint step of the converter (1) in a reactive or active current component. [11] Method according to any one of claims 1 to 10, characterized by, that in the event of an external operating fault, a Fault-Ride-Through(FRT) operation of the device for feeding electrical power into an electrical network (N) is carried out, wherein at least temporarily during the FRT operation fault-specific tripping currents are specified to the circuit breakers (4, 5) via fault detection means (2, 2'). [12] Method according to any one of claims 1 to 11, characterized by , that each exceedance of the maximum tripping current of the circuit breakers (4, 5) intended for internal operational faults is counted. [13] Device for feeding electrical power into an electrical network (N), in particular a wind turbine, with at least one converter (1) with power modules (3), wherein the power modules (3) have electronic circuit breakers (4, 5) and the device has control means (9) for controlling the circuit breakers (4, 5) of the power modules (3) of the converter (1) for feeding electrical power into the electrical network, characterized by , that fault detection means (2, 2') are provided which can detect external operating faults of the device for feeding electrical power into a network (N) and, depending on the detected external operating fault, can specify a specific maximum tripping current for the at least one circuit breaker (4, 5). [14] Device according to claim 13, characterized by, that the fault detection means (2, 2') are provided by at least one separately provided electronic circuit or software-based in the control means of the device for feeding electrical power into an electrical network (N). [15] Device according to claim 13 or 14, characterized by , that means for determining operating parameters of the device are provided which can determine at least the mains voltage of the electrical network (N) as operating parameters, so that the determined operating parameters can be evaluated by the fault detection means (2, 2').

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