Method for commissioning an electrical power conversion system and electrical power conversion system

Abstract

The invention relates to a system (10) for electrical power conversion and a method for commissioning the system (10) for electrical power conversion. The system (10) comprises at least one power converter (16) with an intermediate circuit and a bridge circuit, wherein the system (10) is connected on a DC side (32) to at least one DC unit, in particular to a DC generator (12), and on an AC side (34) to an AC network (14), wherein the at least one power converter (16) can be connected on the DC side to the DC side (32) by means of at least one DC switch (18) and on the AC side to the AC side (34) by means of at least one AC switch (20). The method comprises: a first phase (A) involving the formation of an auxiliary network (36) for supplying power to components of the system (10); a second phase (B) with a temporarily connected AC network (14) without connection to the at least one DC unit; and a third phase (C) with a connected AC network (14) and at least one connected DC unit. The system is designed to carry out the method.

Description

[0001] METHOD FOR COMMISSIONING AN ELECTRICAL POWER CONVERSION SYSTEM AND ELECTRICAL POWER CONVERSION SYSTEM

[0002] TECHNICAL FIELD

[0003] The application relates to a method for commissioning a system for electrical power conversion, in particular a large-scale electrical system, e.g., from approximately 1 MW. The application further relates to a system for electrical power conversion, in particular a large-scale electrical system, e.g., from approximately 1 MW.

[0004] STATE OF THE ART

[0005] Commissioning a system for electrical power conversion with a power converter that includes at least one power electronic bridge circuit can, for example, involve switching the system on in normal mode. Switching on in normal mode can, in particular, result in the system operating at its rated power, if available. In the case of a photovoltaic generator (PV generator) as the system's energy source, the system can be configured in normal mode to maximize the output of the PV generator. In the case of a load, for example an electrolyzer as a DC unit on the power converter, the system can be configured in normal mode to supply the electrolyzer with a rated power.

[0006] During operation of the plant's power converter, errors can occur that cause the power converter to fail and / or destroy individual components. For power converters in plants of approximately 1 MW or larger, the failure of power converters and / or power converter components can result in costs of, for example, several tens of thousands of euros per fault.

[0007] Fault analyses of failed components reveal that there are faults in power converter components that arose during commissioning or shortly thereafter. Power converters can generally be repaired, but a serious fault, such as in a power electronic bridge circuit of the power converter, may not be possible at the power converter's installation site. This results in higher costs and effort for transporting the power converter and / or other parts of the system. Especially in large systems, the corresponding repair effort is particularly high due to the physical size of the power converter. TASK

[0008] The application is based on the object of providing a method and a system with improved commissioning so that damage to a power converter of the system is prevented during subsequent normal operation.

[0009] SOLUTION

[0010] The object is achieved by a method having the features of claim 1 and a system having the features of claim 16. Embodiments are specified in the dependent claims.

[0011] DESCRIPTION

[0012] A system for electrical power conversion has at least one power converter with an intermediate circuit and a bridge circuit. The power converter can in particular be an inverter that can convert electrical power from AC (alternating current) to DC (direct current) and / or vice versa. The system is connected on a DC side to at least one DC unit, in particular to a DC generator, and on an AC side to an AC grid, wherein the at least one power converter can be connected on the DC side by means of at least one DC switch to the DC side and on the AC side by means of at least one AC switch to the AC side.

[0013] A procedure for commissioning such a system comprises:

[0014] A) a first phase, which includes the creation of an auxiliary network for supplying power to components of the installation,

[0015] B) a second phase with temporarily connected AC network without connection to the at least one DC unit,

[0016] C) a third phase with connected AC grid and at least one connected DC unit.

[0017] Phase A) of the process can, for example, also involve the receipt of an input from a system operator. Such an input can, for example, trigger the start of the process. Alternatively, the process can also start automatically. The operator's input can, for example, also confirm the end of phase A) and thus trigger the start of phase B).

[0018] The DC units can include, for example, photovoltaic generators, batteries, and / or electrolyzers, and the like. The auxiliary network can, in particular, be a DC auxiliary network with a voltage of, for example, 12 volts, 15 volts, or 24 volts. The DC auxiliary network can, for example, be supplied from the AC grid via a system rectifier. The DC auxiliary network can alternatively or additionally be supplied with electrical power from an external source.

[0019] Phases A), B), and C) of the process can also be referred to as commissioning phases or test phases, in which various system states are specifically created to prepare and / or test the functioning of system components separately as part of the commissioning process. This can ensure the functioning of the system in the normal mode following commissioning or support troubleshooting.

[0020] The phases of the commissioning process are at least partially automated and serve to slowly start up the system in order to avoid or limit serious and / or costly damage to the system, in particular to the system's power converter. The phases of the process are selected so that in the event of a fault, only the damage caused is as minimal as possible. This has the particular advantage that bridge circuits of the power converter, which include, for example, power modules with semiconductor power switches, in particular IGBT modules, are started up slowly by the process so that early failures in the bridge circuit can be avoided or detected immediately. If faults occur in the system's power path, the slow start-up minimizes or, if possible, avoids costly secondary damage.

[0021] Furthermore, the step-by-step commissioning procedure makes it possible to more accurately localize any faults in time and / or space, as the activities and resulting effects of the individual steps performed during commissioning are known. This makes it possible to understand what was tested and what happened.

[0022] The electrical power conversion system comprises a control unit designed and configured to execute the steps of the individual phases of the described method. The control unit can, for example, be located in the system's power converter and simultaneously assume the task of controlling the power switches in the power converter's bridge circuit.

[0023] In one embodiment of the method, the power converter of the system can be put into commissioning mode at the end of production, so that the power converter starts directly and exclusively in commissioning mode upon initial power-up. This can mean, for example, that the power converter's control unit automatically executes the described commissioning procedure upon initial power-up of the power converter.

[0024] The step-by-step commissioning described above can also reduce secondary damage to the system. The controlled, step-by-step start-up of at least one power converter allows early detection of any damage to a power component, such as a power semiconductor switch in the bridge circuit. This can prevent any resulting short-circuit currents, for example on the DC side of the power converter with connected DC units such as batteries, from subsequently triggering DC fuses, which would then have to be replaced, for example. Furthermore, it can prevent a fault in, for example, one of several bridges in the bridge circuit connected in parallel from spreading to neighboring bridges and causing consequential damage there, for example through unwanted circulating currents.

[0025] The commissioning procedure can therefore protect, in particular, the hardware components of at least one power converter in the system and reduce or prevent secondary faults. This could reduce the costs associated with secondary faults. The procedure can be automatic or at least partially automatic. A person responsible for commissioning, e.g., a system operator, can be assisted by the automatic or semi-automatic commissioning process. Aborting the procedure in the event of a fault can enable guided troubleshooting for the operator.

[0026] In one embodiment of the process, phase A comprises:

[0027] - Establishment of the auxiliary network for supplying power to components of the system from the AC network via a rectifier of the system, in particular for supplying the operation of the AC switch, the DC switches and a sine filter capacitor contactor,

[0028] - Closing the AC switch,

[0029] - Connecting a capacitor of an AC-side sine-wave filter to the AC network, in particular via the sine-wave filter capacitor contactor,

[0030] - Check the voltage supply from the auxiliary network and then open the AC switch, and

[0031] - Continuation of the procedure if the voltage supply from the auxiliary network is within predefined limits, or termination of the procedure if the voltage supply from the auxiliary network is outside the predefined limits.

[0032] In addition, individual or all steps of phase A) can optionally be acknowledged by the system operator through an input. The specified limits of the voltage supply via the auxiliary network can, for example, be permissible limits within which the system can be operated safely. The limits can be specified, for example, via the system control unit by the system operator.

[0033] By establishing the auxiliary network, in Phase A) the components that are supplied with electrical power by the auxiliary network, such as the system's switching devices, can be tested step by step. Furthermore, the stability of the auxiliary network during pre-charging processes, such as pre-charging a sine-wave filter capacitor, can be tested.

[0034] In one embodiment of the process, phase B comprises:

[0035] - Pre-charging of the DC link via a pre-charging circuit,

[0036] - Performing a self-test of the bridge circuit of the power converter,

[0037] - if the self-test is successful: connect the AC network by closing at least one AC switch.

[0038] This allows faults in the bridge circuit's power electronics to be detected early and subsequent failures to be prevented. In particular, the bridge circuit's switches can be tested for their basic switching function and dielectric strength essentially in a current-free environment. Only then is the AC grid connected. The AC grid is therefore only temporarily connected to the bridge circuit during phase B).

[0039] In one embodiment of the method, phase B): when the AC network is connected, comprises: clocking the bridge circuit of the at least one power converter for exchanging electrical reactive power, in particular inductive reactive power, between the intermediate circuit and the AC network.

[0040] By exchanging reactive power, the temperature of at least one power converter can be adjusted. During this phase, the system, and in particular the at least one power converter, can be brought into the temperature range for which it is designed for subsequent operation. This allows, in particular, semiconductor components of the at least one power converter to be brought into a temperature range that corresponds to an operating temperature during normal operation of the power converter, and in which the semiconductor switches operate efficiently and with a long service life.

[0041] In one embodiment of the method, a temperature in the power converter, in particular in a bridge circuit of the power converter, is detected and increased by adjusting the reactive power exchange and / or controlling a fan of the system until the temperature in the power converter exceeds a predeterminable lower threshold and / or reaches a predeterminable upper threshold. In particular, the temperature increase is carried out until the temperature in the power converter is within a predeterminable range, which can, for example, be between the lower threshold and the upper threshold.

[0042] In one embodiment of the method, the lower and upper thresholds have a temperature difference of at least 40 Kelvin, preferably at least 60 Kelvin. The temperature in the power converter, in particular in a bridge circuit of the power converter, is changed by controlling the reactive power exchange and / or by controlling the fan such that the lower and upper thresholds are reached alternately several times in succession.

[0043] Through these planned temperature increases, temperature effects of repeated warming up and cooling down can be used to prepare for later operation.

[0044] In one embodiment of the method, phase C): with a connected AC grid and with at least one connected DC unit comprises:

[0045] Exchange of power between the AC side and the DC side, recording the exchanged AC power and the exchanged DC power of the at least one power converter, and checking the plausibility of the recorded power. The power exchange can occur particularly at low power, especially at a power between 5% and 20% of the rated power of the at least one power converter.

[0046] In one embodiment of the method, phase C): with a connected AC grid and with several DC units connected in parallel on the DC side comprises:

[0047] Recording the currents of the DC units in the parallel circuit and checking the symmetry of the recorded currents. In particular, the individual currents of the individual DC units in the parallel circuit can be recorded and the symmetry of the recorded currents can be checked.

[0048] Optionally, voltages can also be recorded. Using the recorded voltages and currents, it can be determined by comparing them with predefined reference values ​​whether the DC units connected to the system, e.g. photovoltaic generators, batteries or loads such as electrolyzers, are functioning as intended. The predefined reference values ​​can, for example, be stored in a control unit of the system and / or entered by an operator via an interface. The recording of the individual currents can be carried out particularly when the DC units have a low power, e.g. when an electrolyzer is at a minimum power. Even or especially when the power is low, it is possible to detect a malfunction in the system by recording the currents and / or voltages.

[0049] In one embodiment of the process, phase C) further comprises:

[0050] Check the fan and / or other sensors in the system.

[0051] In one embodiment of the method, phase C) further comprises: with a connected AC grid and with at least one connected DC unit:

[0052] Exchange of power between the AC side and the DC side, with the power exchange being increased in several stages.

[0053] This allows at least one power converter to be gradually ramped up and subjected to a higher load. If an error occurs, the process can be aborted, and the level of load at which the error occurred may provide an indication of the cause of the error.

[0054] The power exchange between the AC and DC sides can be increased in several stages, ranging from approximately 10% of the system's rated power to approximately 60% of the system's rated power. The system's rated power can correspond to the rated power of the power converter—if there is exactly one power converter in the system. If the system includes multiple power converters, the system's rated power can correspond to the sum of the rated powers of the multiple power converters.

[0055] In one embodiment of the process, phase C) further comprises:

[0056] When at least one predeterminable temperature of the at least one power converter is reached for a predeterminable period of time: Termination of the commissioning procedure and start of normal operation of the system.

[0057] In one embodiment, the system includes the sine-wave filter capacitor contactor for connecting or switching on the sine-wave filter capacitor to the AC grid. The sine-wave filter capacitor contactor, for example, has an electrical control system that is powered by the auxiliary grid. This allows the contactor's functionality to be tested and assessed in phase A) of the process.

[0058] In one embodiment, the system comprises the auxiliary network with an auxiliary network disconnector for connecting the auxiliary network to the AC network, wherein the sine-wave filter capacitor contactor can be functionally coupled to the auxiliary network disconnector. This can serve, in particular, to reduce any interference with the auxiliary network when connecting the sine-wave filter capacitor to the AC network and, in particular, to prevent overvoltages in the auxiliary network. This enables a reliable power supply to the system components via the auxiliary network, even if large currents temporarily flow between the sine-wave filter capacitor and the AC network.

[0059] In one embodiment of the system, the auxiliary network has a rectifier that provides a DC auxiliary voltage. The functional coupling between the sine-wave filter capacitor contactor and the auxiliary network disconnector is configured to maintain the DC auxiliary voltage at a predefined quality when the sine-wave filter capacitor contactor is actuated. This can mean, for example, maintaining the auxiliary network voltage within a tolerance range around a nominal voltage of, for example, 24 V. This allows the components supplied with electrical power by the auxiliary network to be protected from voltage fluctuations in the auxiliary network.

[0060] The effect on the auxiliary grid of a connection involving power exchange between the sine-wave filter capacitor and the AC grid can also be tested and assessed in phase A) of the procedure. In this case, the functioning of the functional coupling between the sine-wave filter capacitor contactor and the auxiliary grid disconnector can be verified in phase A). This is particularly relevant when electrically precharging the sine-wave filter capacitor via the AC grid.

[0061] BRIEF DESCRIPTION OF THE CHARACTERS

[0062] In the following, the application is further explained and described using exemplary embodiments shown in the figures.

[0063] Fig. 1 shows a schematic flow of the process.

[0064] Fig. 2 shows a schematic diagram of a system for electrical power conversion.

[0065] Fig. 3 shows a schematic diagram of the influence of temperature in an electrical power conversion system.

[0066] FIGURE DESCRIPTION

[0067] Fig. 1 shows a schematic flow of the method with phases A), B), and C). In phases A), B), and C), also called stages, specific states of a system 10 are created through which the functioning of individual components of the system can be checked and / or prepared. The sequence of the states and the components involved are selected such that any error that occurs has the least possible consequences and, in particular, results in the least possible or no subsequent errors.

[0068] In the first phase A), an auxiliary network 36, in particular a DC auxiliary network, is established to supply voltage to components of the system 10. Further steps of phase A) are carried out with the auxiliary network 36 established.

[0069] Electrically controlled switching devices, such as switches and contactors, can be supplied with power via the auxiliary network 36. In phase A), the functionality of the switches, in particular an AC switch 20, DC switches 18, and a sine-wave filter capacitor contactor 30, can thus be tested.

[0070] The steps of the second phase B) are carried out by temporarily connecting the system 10 to an AC grid 14. During the steps of phase B), the connection to DC units of the system 10 is disconnected.

[0071] In phase B), the DC intermediate circuits of the power converters 16 of the system 10 can first be precharged via a precharging circuit 22. This can be followed by a self-test of the power converters 16 with the AC grid 14 disconnected. Following this, after a successful self-test, semiconductor switches of the respective bridge circuits of the power converters 16 can be preheated by exchanging reactive power with the AC grid, i.e., their temperature can be brought to a predeterminable range, wherein the range is preferably a temperature range that corresponds to typical operating temperatures during normal operation and / or in which the semiconductor switches demonstrate good efficiency and / or long service life.

[0072] The steps of phase C) are carried out with the AC grid 14 connected and at least one DC unit connected, e.g. with a DC generator 12 connected.

[0073] In phase C), the system 10, and in particular the power converters 16, can be tested during a power exchange between their respective AC and DC sides. In particular, currents and / or voltages can be recorded and checked for plausibility by comparing them with predefined values.

[0074] Phase D) is used to commission plant 10 with AC and DC power, during which the power is gradually ramped up. Cycles and power boosts are planned for this purpose.

[0075] Fig. 2 shows an embodiment of the system 10 for electrical power conversion. The system 10 comprises the power converters 16, which are connected to a DC bus via the DC switch 18. The DC bus provides a DC-side connection between the power converters 16 and the DC side 32 of the system 10. DC units, e.g. DC generators 12 as an energy source and / or batteries (not shown) as energy storage devices and / or loads (not shown) such as electrolyzers, can be connected to the DC side 32 of the system 10. On the AC side, the power converters 16 are connected to the AC side 34 of the system 10 via the AC switch 20. On an AC side 34, the system 10 can be connected to the AC grid 14 via a first transformer T1.

[0076] The auxiliary network 36 can be connected to the AC side of the system 10 via an auxiliary network disconnect switch 38 and a second transformer T2, thus drawing electrical power from the AC network 14. Components of the system 10, e.g., the fan 24, the heater, and / or switching elements of the system 10, can be supplied with electrical energy via the auxiliary network 36.

[0077] A possible sequence of the procedure for commissioning system 10 is explained in more detail in Fig. 2.

[0078] Phase A) serves in particular to commission and test the self-supply of system 10 with electrical energy via the auxiliary network 36. The auxiliary network 36 can also be referred to as the on-board network and includes in particular a DC network, e.g., a 24V DC network.

[0079] The auxiliary network 36 of the system 10 can be supplied from the AC network 14, to which the power section of the respective power converter 16 is connected on the AC side. Alternatively or additionally, the auxiliary network 36 can be supplied by an external electrical source that is independent of this AC network 14, for example, from a separate low-voltage network that is independent of the AC network 14. In both cases, an AC voltage is converted into a DC voltage by means of a rectifier 40 to supply the auxiliary network 36.

[0080] During phase A), it should be ensured that both the external DC units and the external AC grid 14 are disconnected from the power converters 16. This can be done, for example, by a qualified person, such as an operator of the system 10 or a service technician.

[0081] In the next steps of phase A), the switching elements of the system 10, e.g. the DC switch 18, the AC switch 20 and / or the sine-wave filter capacitor contactor 30, can be gradually put into operation and tested.

[0082] To do this, the DC switches 18 are first switched on and off several times. Each DC switch 18 is switched individually. After all DC switches 18 have been switched once, the switching process for each DC switch 18 is repeated two more times. A wait of approximately 2 minutes should be made between each switching process. These switching processes can be performed automatically by the process or manually.

[0083] Since the DC switches 18 are switched individually, it can be detected, e.g., by an operator, if certain switches are not switching. Alternatively or additionally, at least one DC switch 18 can include self-diagnosis and automatically issue a corresponding message. If an error is detected during this phase, the process is aborted to prevent subsequent damage to the system 10.

[0084] In the next step of phase A), AC switch 20 is turned on and off twice. A wait of approximately 2 minutes should be made between each switching operation. These switching operations can be performed automatically by the process or manually.

[0085] In the next step of phase A), the sine-wave filter capacitor contactor 30 is switched on and off twice. These switching operations can be performed automatically by the process or manually. Optionally, the sine-wave filter capacitor 26 can be precharged beforehand using a suitable precharging circuit.

[0086] If the sine-wave filter capacitor contactor 30 is switched on with the AC switch 20 closed, i.e., with an existing connection to the AC grid 14, significant compensating currents can arise due to any voltage differences between the sine-wave filter capacitor 26 and the grid voltage to equalize the voltage between the sine-wave filter capacitor 26 and the AC grid 14. This can lead to a significant fluctuation in the input voltage of the auxiliary grid 36, which can lead to a failure of the auxiliary grid 36, in particular to a shutdown of the rectifier 40. Therefore, the sine-wave filter capacitor contactor 30 and the auxiliary grid disconnector 38 are coupled in such a way that switching on the voltage of the sine-wave filter capacitor contactor 30 leads to a brief shutdown of the auxiliary grid disconnector 38.This means that when the sine-wave filter capacitor contactor 30 is actuated, the auxiliary network 36 is briefly disconnected from the AC side 34 of the system 10 by opening the auxiliary network isolating switch 38. This keeps any potential voltage fluctuation due to the compensating currents to the sine-wave filter capacitor 26 away from the auxiliary network 36. The auxiliary network 36 itself can bridge such an interruption for a short period of time, approximately a few seconds, in particular approximately one second, wherein in particular a 24 V DC network can be maintained by means of a buffer capacitor. The 24 V DC network can be used in particular to control the switching elements of the system 10, such as e.g. DC switches 18, AC switch 20 and / or sine-wave filter capacitor contactor 30. In this respect, by test switching the sine-wave filter capacitor contactor 30, it can be checked whether the voltage supply of the auxiliary network, e.g. B. its 24 V DC power supply, is safely guaranteed, ieremains unaffected by the switching operations. Maintaining a target voltage, e.g., 24 V, can be used as an acceptance criterion.

[0087] After this check of the self-supply, system 10 can automatically switch to phase B) or - in the event of a fault - switch off and go into a safe state.

[0088] During phase A), it is possible for a person, e.g., a service technician, to be on-site. This person can provide support during phase A) and / or some of the switching devices can be switched manually. Phase A) can be acknowledged, for example, by an input from the person. If the test aborts, it can be made clear at which point the abort occurred. After appropriate repairs have been made, the process can then be restarted with phase A).

[0089] Phase B) serves to commission plant 10 with at least partial supply of AC power from the AC grid 14.

[0090] First, in phase B), a self-test of the respective bridge circuit, the so-called stack, of the power converters 16 is performed. The AC pre-charging circuit 22 pre-charges the respective DC intermediate circuit of the power converters 16. After the pre-charging is complete, a self-test of the respective bridge circuit of the power converters 16 can be performed without the AC network 14 and without the DC unit.

[0091] The self-test can be performed once, for example. If the self-test is passed, the AC grid 14 can be connected by closing the AC switch 20.

[0092] In the next step of phase B), the power converters 16 of the system can be operated in the so-called Q@night mode, in which a reactive power exchange, in particular a pure reactive power exchange, takes place with the AC grid 14 with open DC switches 18.

[0093] The power converters 16 start up in what is known as Q@night mode. In this mode, the respective power converter 16 exchanges reactive power between the AC grid 14 and its intermediate circuit capacitance by appropriately timing its bridge circuit in order to heat the semiconductor power switches, which are designed, for example, as IGBT modules. The DC voltage can be kept low, in particular to safely remove any residual moisture from the IGBT modules. For example, the DC voltage can be set slightly above the rectified value of the AC voltage so that the IGBT modules are subjected to minimal stress in terms of any fault currents during the drying process. Furthermore, the heating, in particular cyclic heating, can trigger settlement mechanisms and reduce mechanical stresses that may have arisen during storage and transport of the system 10.

[0094] In addition, phase B) can support the process of thermal paste distribution within the power converters 16, particularly between the IGBT modules in the bridge circuit and a respective associated heat sink. The thermal paste distribution may not yet be complete during commissioning. If this is the case, the IGBT modules are not yet fully operational. For example, IGBT modules may have undefined cavities on the base plate that should be filled with thermal paste. Thermal strokes are beneficial for this, setting the respective IGBT module in motion, like a pumping process, so that the thermal paste reaches the right places.Since the power converters 16 are thermally designed for a nominal power and the dissipation of the resulting maximum power loss, assuming a defined heat dissipation during operation, this process is advantageous in order to enable optimal distribution of the thermal paste and thus the expected heat dissipation.

[0095] It is advantageous to run at least five cycles with temperature gradients to optimally distribute the paste on the heat sinks, e.g., of the IGBT modules. After this process, a better thermal transition is achieved. This improvement in the thermal transition can be achieved by thermally ramping up the power converters 16 in stages.

[0096] Fig. 3 shows an example of the curve for the reactive power Q exchanged via the bridge circuit of the respective power converter 16. In the upper diagram, the reactive power Q is shown as a fraction of the nominal apparent power S_nominal of the respective power converter 16. The lower diagram shows the curve for the resulting temperatures, measured at the bridge circuit in the IGBT module, temperature TM (larger value) and at the base plate, temperature TB (smaller value). The energy supply and the thermal cycles increase continuously, with several temperature cycles with temperature differences ranging from approximately 30 Kelvin at the beginning to over 60 Kelvin in the last cycle being achieved. Temperature cycles with temperature differences of approximately 60-70 Kelvin are particularly advantageous and can be achieved by extending the individual cycles accordingly and / or by increasing the reactive power in the heating-up phase and / or the cooling power, e.g.by the fan 14, in the cooling phase.

[0097] The reactive power setting and the control of the fan 24 can thus be controlled "temperature-controlled." It may be advantageous to favor inductive reactive power Q if the respective power converter is connected to an AC grid 14 via appropriate medium-voltage cables, which is designed as a medium-voltage grid. Phase B) can last longer than phase A). It can, for example, run automatically at night. It is possible for phase B) to run without personnel on-site at the system 10. Once phase B) is completed, the process can automatically transition to phase C).

[0098] If the test is aborted, it can be identified, for example, at which point the abort occurred. After any necessary repairs, the process can then be restarted from the beginning with phase A) or phase B). Preferably, the process is run again from the beginning, starting with phase A).

[0099] Phase C) is used to commission the system 10 with AC and DC power, ie with the AC network 14 connected and the DC units connected.

[0100] In the first step of Phase C), plausibility checks are performed with regard to various aspects of System 10. These plausibility checks can be performed, in particular, by determining measured values, e.g., currents and voltages, and comparing them with specified test values. The test values ​​can be stored in the control unit of System 10 and / or entered by the operator.

[0101] First, the efficiency of the respective power converters 16 is checked for plausibility. At low power levels, the ratio of measured AC power to measured DC power is determined and checked. The test involves a comparison with a predefined test value within a tolerance range. If the measured ratio of AC power to DC power lies outside the tolerance range, then an error has occurred. Parameters of the respective power converter may be incorrectly set, or the measuring equipment, e.g., measuring sensors, may be defective. The objective of this test can be, in particular, to check whether the parameters are correctly set and / or whether the measuring equipment is functioning. The efficiency check itself does not need to be performed in this step.

[0102] In a next step of phase C), the DC current symmetry between several parallel DC inputs to which the DC units, in particular the DC generators, are connected can be checked.

[0103] In the case of parallel-connected and essentially similar DC generators 12, e.g., photovoltaic generators (PV generators), the DC currents at the parallel DC inputs can be determined automatically using the measuring equipment if the DC generators 12 are producing DC power. If, for example, in a power converter 16, which is a PV inverter with several parallel-connected DC generators 12 designed as PV strings, there is an asymmetry of the input currents, e.g., the string currents, of more than 4%, then there may be a defect in the connection distribution, e.g., in the structure of the PV strings. This defect can then be corrected. This step of the method can, for example, be carried out with a minimum power of between 10% and 30% of the nominal power of the respective power converter 16, e.g., approximately 20%. In areas of lower power, measurement inaccuracies can distort the comparison of the measured values.

[0104] In a further step, the thermal management of system 10 can be checked for plausibility. This can include checking whether the fans are running according to the setpoint specifications and / or whether all temperature and humidity sensors are displaying a plausible value.

[0105] This can optionally be followed by a self-test of the respective DC units, e.g., PV, battery, electrolyzer.

[0106] Phase C), for example, can be completed automatically. It is possible for phase C) to be completed without personnel on-site at system 10. Once phase C) is completed, the process can proceed automatically to phase D).

[0107] If the test is aborted, it can be identified, for example, at which point the abort occurred. After any necessary repairs, the process can then be restarted from the beginning with phase A), phase B, or phase C. Preferably, the process is run through again from the beginning, starting with phase A).

[0108] Phase D) is used to commission plant 10 with AC and DC power, during which the power is gradually ramped up. Cycles and power boosts are planned for this purpose.

[0109] In the first step of phase D), power converter 16 is started with power limitation and its power is gradually increased. Alternatively or in addition to heating with reactive power in phase B), phase D can be used to heat power converter 16 with exchanged active power.

[0110] In the case of PV generators as DC units, for example, the power is naturally limited by the irradiation and therefore there is no guarantee that sufficiently high power is available for heating in this phase D); therefore, in this case, heating using reactive power as in phase B) may be preferred.

[0111] In the case of, for example, batteries or electrolyzers as DC units, however, it is fundamentally possible to effect the heating in a targeted manner by means of adjustable active power between 0 and the nominal power of the respective power converter 16 in this phase D), so that heating by means of reactive power as in phase B) could be dispensed with.

[0112] Specifically, the following times can be used for heating in phase D), especially for batteries as DC units: The first 8 hours: 10 - 60% of the rated power of the respective power converter 16.

[0113] The second 8 hours: 10 - 80% of the rated power of the respective power converter 16, whereby a stop can be forced after approximately 4 hours in this process in order to obtain an additional heat-cold cycle.

[0114] After 16 hours, the test can be completed; if necessary, the times can be reduced, e.g., to complete in one day / within one daylight period.

[0115] Phase D) can, for example, be completed automatically. It is possible for phase D) to be completed without personnel on-site at system 10. Once phase D) is completed, the process can be terminated and system 10 can, for example, automatically return to normal operation.

[0116] If the test is aborted, it can be identified, for example, at which point the abort occurred. After any necessary repairs, the process can then be restarted from the beginning with phase A), phase B), phase C), or phase D. Preferably, the process is run from the beginning again, starting with phase A).

[0117] In this step, additional parameters for the operating management are set in such a way that the system will operate in normal mode when it is subsequently restarted.

[0118] All four phases of the process can be documented in one or more log files and identified as individual phases. As soon as the process terminates, the point at which the termination occurs can be identified. This can also be indicated in the log file.

[0119] LIST OF REFERENCE SYMBOLS

[0120] 10 Appendix

[0121] 12 DC generator

[0122] 14 AC network

[0123] 16 power converters

[0124] 18 DC switches

[0125] 20 AC switches

[0126] 22 Precharge circuit

[0127] 24 fans

[0128] 26 Sine filter capacitor

[0129] 30 sine filter capacitor contactor

[0130] 32 DC page

[0131] 34 AC side

[0132] 36 AC auxiliary network

[0133] 38 Auxiliary network disconnector

[0134] 40 rectifiers

[0135] A), B), C) Phases of the procedure

[0136] T1, T2 transformer

Claims

PATENT CLAIMS 1. A method for commissioning a system (10) for electrical power conversion, which has at least one power converter (16) with an intermediate circuit and a bridge circuit, wherein the system (10) is connected on a DC side (32) to at least one DC unit, in particular to a DC generator (12), and on an AC side (34) to an AC network (14), wherein the at least one power converter (16) is connectable on the DC side by means of at least one DC switch (18) to the DC side (32) and on the AC side by means of at least one AC switch (20) to the AC side (34), wherein the method comprises: a first phase (A), which comprises establishing an auxiliary network (36) for supplying voltage to components of the system (10), a second phase (B) with a temporarily connected AC network (14) without connection to the at least one DC unit, a third phase (C) with a connected AC network (14) and at least one connected DC unit.

2. The method according to claim 1, wherein the first phase (A) comprises: - establishing an auxiliary network (36) for supplying voltage to components of the system (10) from the AC network (14) via a rectifier (40) of the system (10), in particular for supplying the actuation of the AC switch (20), the at least one DC switch (18) and a sine-wave filter capacitor contactor (30), - Closing the AC switch (20), - connecting a capacitor (26) of an AC-side sine filter to the AC network (14), - Check the voltage supply from the auxiliary network (36) and then open the AC switch (20), and - Continuation of the process if the voltage supply by the auxiliary network (36) is within predeterminable limits, or termination of the process if the voltage supply by the auxiliary network (36) is outside the predeterminable limits.

3. A process according to claim 1 or 2, wherein the second phase (B) comprises: - Pre-charging of the DC link via a pre-charging circuit (22), - performing a self-test of the bridge circuit of the at least one power converter (16), - if the self-test is successful: connecting the AC network (14) by closing at least one AC switch (20).

4. Method according to one of claims 1 to 3, wherein the second phase (B) comprises: with the AC network (14) connected: clocking the bridge circuit of the at least one Power converter (16) for exchanging electrical reactive power, in particular inductive reactive power between the intermediate circuit and the AC network (14).

5. The method according to claim 4, wherein a temperature in the power converter (16), in particular in a bridge circuit of the power converter (16) is detected and is increased by adjusting the reactive power exchange and / or controlling a fan (24) of the system (10) until the temperature in the power converter exceeds a predeterminable lower threshold and / or reaches a predeterminable upper threshold.

6. The method according to claim 5, wherein the lower and upper thresholds have a temperature difference of at least 40 Kelvin, preferably at least 60 Kelvin, and are reached alternately several times in succession by means of a control of the reactive power exchange.

7. Method according to one of the preceding claims, wherein the third phase (C) comprises: with a connected AC network (14) and with at least one connected DC unit: exchanging power between the AC side (34) and the DC side (32), detecting an exchanged AC power and an exchanged DC power of the at least one power converter (16) and checking the plausibility of the detected powers.

8. The method according to claim 7, wherein the power exchange takes place at low power, in particular at between 5% and 20% of the rated power of the at least one power converter (16).

9. Method according to one of the preceding claims, wherein the third phase (C) comprises: with a connected AC network (14) and with several DC units connected in parallel on the DC side (32): Recording currents of the DC units of the parallel circuit and checking the symmetry of the recorded currents.

10. The method according to claim 9, wherein the detection of the currents is carried out at a low power, in particular at a minimum power, of the DC units. 11 . Method according to one of the preceding claims, wherein the third phase (C) comprises: checking the fan (24) and / or other sensors of the system (10).

12. Method according to one of the preceding claims, wherein the third phase (C) comprises: with a connected AC network (14) and with at least one connected DC unit: Exchange of power between the AC side (32) and the DC side (34), whereby the power exchange is increased in several stages.

13. The method of claim 12, wherein the power exchange is increased in several stages between approximately 10% of the rated power and approximately 60% of the rated power.

14. The method according to claim 12 or 13, wherein the power exchange is increased in several stages between approximately 10% of the rated power and approximately 80% of the rated power.

15. A method according to any one of claims 12 to 14, comprising: When at least one predeterminable temperature of the at least one power converter (16) is reached for a predeterminable period of time: terminating the commissioning process and starting normal operation of the system (10).

16. A system (10) for electrical power conversion, which system has at least one power converter (16) with an intermediate circuit and a bridge circuit, wherein the system (10) can be connected on a DC side (32) to at least one DC generator (12) and on an AC side (34) to an AC network (14), wherein the at least one power converter (16) can be connected on the DC side by means of the at least one DC switch (18) to the DC side (32) and on the AC side by means of at least one AC switch (20) to the AC side (34), wherein the system (10) has a control unit which is designed and configured to carry out the method according to one of the preceding claims.

17. System (10) according to claim 16, wherein the system (10) comprises a sine filter capacitor contactor (30) and an auxiliary network with an auxiliary network disconnect switch (38) for connecting the auxiliary network (36) to the AC network (14), wherein the sine filter capacitor contactor (30) is functionally coupled to the auxiliary network disconnect switch (38).

18. System (10) according to claim 16 or 17, wherein the auxiliary network (36) has a rectifier (40) which provides a DC auxiliary voltage, wherein the functional coupling between the sine-wave filter capacitor contactor (30) and the auxiliary network isolating switch (38) is designed to maintain the DC auxiliary voltage in a predeterminable quality when the sine-wave filter capacitor contactor (30) is actuated.

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