Synchronous alternator based gridcode test system

Abstract

The present invention pertains to grid code test systems to determine compatibility of a generator set with grid code requirements, in particular to determine compatibility with predefined grid failure scenarios. Accordingly, a test system (10) for determining a grid code compatibility of a generator set (12) is suggested, comprising an alternator (14) driven by an actuator (16) and a circuit downstream of the alternator (14). The circuit comprises an output terminal (18), an adjustable impedance (20) serially connectable between the alternator (14) and the output terminal (18), and an adjustable load (22) serially connectable between the adjustable impedance (20) and the output terminal (18). The test system furthermore comprises a control unit (32), configured to provide a predefined voltage adjustment at the output terminal (18) by adjusting a function of the alternator (14), the impedance (20) level, and / or the load (22), wherein the predefined voltage adjustment corresponds to a predefined simulated grid failure.

Description

DescriptionSynchronous Alternator Based Gridcode Test SystemTechnical Field

[0001] The present invention pertains to grid code test systems to determine compatibility of a generator set with a grid protocol, in particular to determine compatibility with predefined grid code requirements.Technological Background

[0002] Connecting large power generating units such as generator sets to the public grid requires compliance with / the fulfillment of the local grid code requirements. Part of these requirements, especially for large plants, is a Fault Ride Through (FRT) capability, which requires that the generator set remains fully connected to the grid in case of a temporary voltage dip or increase at the point of connection. This enables that load is still available after the fault is cleared, which is a very important requirement for the grid operator to re-balance the grid network. In the absence of such availability of the load, the grid operator would struggle to balance the power input and output after fault clearance. Such grid fault may e.g. be caused by a trip of a large power generation plant trip due to short time disturbances within the grid, e.g. typically a branch dropped into a power line and causing a short-circuit for a short time. In such case, the power plants producing the power cannot be adjusted quickly enough, such that only a certain power is allowed to trip. Accordingly, it is essential to remain connected in case of a short-term voltage disturbance.

[0003] In order to test for grid compliance, specific test systems are available. However, the availability of such test systems in the market is very limited.Furthermore, these test systems do not have a standardized configuration, which is problematic, since a provider of a generator set, also known as “gensef ’, or other device under testing (DUT) is required to organize the different componentsof the test system from different external companies. The organization and the assembly of these components is accordingly not only tedious and time consuming. Moreover, use of such test systems is typically also very cost intensive.

[0004] In addition, local grid operators typically restrict the possible testing period to assess grid code compliance. This hence further increases the time pressure on a provider given the already problematic organization of the test system components.

[0005] Accordingly, a need exists to facilitate the assessment of grid code compatibility, in particular to determine a fault ride through capability, in a reliable and cost-efficient manner that is independent from currently available test systems.Summary of the invention

[0006] Starting from the prior art, it is an objective to provide a new and inventive test system to determine grid code compatibility. In particular, it may be an objective to provide a test system that is flexible to assess compatibility with different types of grid failure.

[0007] This objective is solved by means of the test system and a method for determining a grid code compatibility with the features of the independent claims. Preferred embodiments are set forth in the present specification, the Figures as well as the dependent claims.

[0008] Accordingly, a test system for determining a grid code compatibility of a generator set, is suggested, which comprises an alternator driven by an actuator, and a circuit downstream of the alternator. The circuit comprises an output terminal, an adjustable impedance serially connectable between the alternator and the output terminal, and an adjustable load serially connectable between the adjustable impedance and the output terminal. The test system furthermore comprises a control unit, which is configured to provide a predefined voltage adjustment at the output terminal by adjusting a function of the alternator,the impedance level, and / or the load, wherein the predefined voltage adjustment corresponds to a predefined simulated grid failure.

[0009] According to a further aspect of the invention, a method for determining a grid code compatibility of a generator set, comprising the steps of providing an alternator driven by an actuator and a circuit downstream of the alternator; and adjusting, using a control unit, a function of the alternator, an impedance level of the circuit, and / or a load within the circuit to adjust a voltage at an output terminal of the circuit, wherein the voltage adjustment corresponds to a predefined simulated grid failure, wherein the output terminal is connected to the generator set.Brief description of the drawings

[0010] The present disclosure will be more readily appreciated by reference to the following detailed description when being considered in connection with the accompanying drawings in which:

[0011] Figure 1 shows a schematic depiction of a test system according to the invention in a preferred embodiment and connected to a power source and a generator set.Detailed description of preferred embodiments

[0012] In the following, the invention will be explained in more detail with reference to the accompanying figures. In the Figures, like elements are denoted by identical reference numerals and repeated description thereof may be omitted in order to avoid redundancies.

[0013] In Figure 1 a test system 10 is schematically depicted according to a preferred embodiment. However, it will be understood that some features of this embodiment may be optional depending on the types of tests to be performed, e.g. according to the respective grid code.

[0014] The test system comprises an alternator 14, which in the present example is a synchronous alternator 14. The alternator 14 is coupled to anactuator 16, such that the alternator 14 may be driven by the actuator to generate a corresponding voltage. The actuator 16 according to the present example is an electric motor, however, it will be understood that other actuators 16 may be implemented, e.g. a fuel-based combustion engine. The voltage that is generated by the alternator 14 is provided at a voltage output terminal 18, which is part of a circuit arranged downstream of the alternator 14 and which may be formed as a switch, as depicted in Figure 1.

[0015] In order to modify the voltage, the test system 10 furthermore comprises an adjustable (serial) impedance, which is serially connected between the alternator 14 and the output terminal 18, as well as a load 22, which may be present as an electrical component configured to consume and balance the reactive and active power of the test system and the device under test, and preferably serves as a shunt for the test system 10. The impedance 20 and the load 22 may be connected via a respective first switch 24 and a second switch 26. Accordingly, the impedance 20 may be bypassed and the load 22 may be optionally disconnected from the circuit.

[0016] The voltage adjustment may furthermore be facilitated by adjustment of a function of the alternator 14. Such adjustment may be enabled by a control 28 of the actuator 16 or electric motor, which may accordingly adjust a speed or frequency of the actuator 16. Accordingly, the function of the alternator 14 may be indirectly adjusted by adjustment of the actuator 16. Moreover, the excitation level and / or the tap changer position at the winding or at the auxiliary winding of the alternator 14 may be adjusted by means of a controller 30. Thereby, a direct adjustment at the level of the alternator 14 is enabled.

[0017] The adjustment of the impedance 20, the load 22, the alternator 14, and the actuator 16 are controlled and monitored by a control unit 32, which is depicted as a separate component of the test system 10, but may alternatively be integrated into one of the other components of the test system 10. As indicated with the dashed lines, the control unit 32 is communicatively coupled to each of the components and may hence output a corresponding control signal to adjustthe corresponding operating parameter of the respective component. By the same token, the control unit 32 may be configured to receive a feedback signal from one or more components, e.g. via a respective sensor and / or communication interface, such that the required adjustment may be monitored and adapted.

[0018] Accordingly, as an example, should the test system 10 be configured to simulate a low voltage ride through as a grid failure, the control unit 32 may maintain the first switch 24 in the open position, such that no bypass of the impedance 20 is provided. The control unit 32 may furthermore actuate the second switch 26 to ensure that the load 22 is connected within the circuit. In order to provide the required voltage adjustment, the control unit 32 furthermore outputs a control signal to the control 30 to adjust the excitation level at the alternator 14 while a further control signal is output to the control 28 to maintain the actuator 16 at nominal operation. By means of the adjustment of the excitation level, a voltage adjustment, e.g. a voltage dip, is provided at or close to a predefined voltage change rate corresponding with a simulated low voltage ride through event.

[0019] In order to further modify the voltage adjustment, the control unit 32 may furthermore actuate the first switch 24 and the second switch 26 in an alternating manner, such that the impedance 20 is set a predefined ratio relative to the load 22. Such predefined ratio is preferably defined as the ratio of the impedance, preferably of a serial impedance, to the equivalent load impedance, which may be a shunt. When the same current flows through both the serial impedance and the load (or shunt), the voltage across each element is proportional to its equivalent impedance. By adjusting the values of the serial impedance and the load or shunt, the voltage applied to the test device can be varied from 0% to 100% of the rated voltage. It has been found that, in particular, voltage adjustment between 5% and 90% of the rated voltage are sufficient for testing purposes.

[0020] The test system 10 furthermore comprises a third switch 34, which enables a selective connection of the grid with the terminal of the alternator 14.The third switch 34 may e.g. be initially provided in the open state, e.g. upon start-up of the test system 10 prior to connecting the test system 10 with the generator set 12. Furthermore, the third switch 34 enables that e.g. grid support tests or power quality tests may be performed in a selective manner.

[0021] In the present example the test system 10 furthermore comprises a fourth switch 38, which functions as an input terminal of the test system 10 and may be selectively coupled to a power source 36. In the actuated state of the fourth switch 38, the power source 36 hence powers the actuator 16 and the alternator 14. The power source 36 may be provided as a grid, e.g. a local grid or an external grid. Thereby, the test system 10 may be efficiently use existing power systems present in proximity of the generator set. Alternatively, the fourth switch 38 may also be connected to an internal power supply or an energy feedback loop from the test system 10. In such configuration, the test system 10 may be provided essentially as a stand-alone test system 10 that may be operated independently of any available infrastructure.

[0022] It will be obvious for a person skilled in the art that these embodiments and items only depict examples of a plurality of possibilities. Hence, the embodiments shown here should not be understood to form a limitation of these features and configurations. Any possible combination and configuration of the described features can be chosen according to the scope of the invention.

[0023] This is in particular the case with respect to the following optional features which may be combined with some or all embodiments, items and / or features mentioned before in any technically feasible combination.

[0024] A test system for determining a grid code compatibility of a generator set, is provided.

[0025] The test system comprises an alternator driven by an actuator, and a circuit downstream of the alternator. The circuit comprises an output terminal, an adjustable impedance serially connectable between the alternator and the output terminal, and an adjustable load serially connectable between the adjustableimpedance and the output terminal. The test system furthermore comprises a control unit, which is configured to provide a predefined voltage adjustment at the output terminal by adjusting a function of the alternator, the impedance level, and / or the load, wherein the predefined voltage adjustment corresponds to a predefined simulated grid failure.

[0026] By means of the configuration according to the invention, a test system is provided, which may be adapted to one or more predefined grid failure scenarios. In particular, the alternator, which is preferably a synchronous alternator, and the actuator may be adjusted to achieve a predefined voltage adjustment at a terminal of the alternator. The adjustable impedance and the adjustable load in this regard enable a preferred further fine tuning of the voltage adjustment to achieve output variations corresponding to the predefined grid failure test. Since the test system requires only few components that are furthermore comparatively cheap, the test system enables advantageous flexibility for the testing scenarios required according to a grid code in a cost- efficient manner.

[0027] The control unit of the test system may be communicatively coupled to each of the components of the test system to facilitate adjustment of the respective component. The control unit may also be present within or integrated in a control unit of one of the components and / or may communicate with one or more components via another control unit. The control unit may also receive measurements from one or more of the components, preferably from each of the components, to facilitate the adjustment of the respective component, e.g. via one or more sensors and a corresponding communication interface. For example, the control unit may receive an output voltage of the alternator, an actuating speed or frequency of the actuator, an impedance value, and / or a load value.

[0028] The output terminal of the circuit may be formed as a connecting interface to a device under testing (DUT), preferably a generator set. By the same token, the test system preferably comprises an input terminal enabling a power input from a power source to the actuator and the alternator. Preferably, thepower source of the testing system is a local or external grid, but may alternatively be provided as an internal power supply or, at least partly, as an energy feedback loop of the test system.

[0029] The adjustable impedance is preferably configured as a serial impedance. This allows a step-wise adjustment of the impedance. The adjustable load, which may be connected or disconnected within the circuit may enable that the active power and the reactive power of the test system are properly balanced. The load may be present as an electrical component configured to consume and balance the reactive and active power of the test system and the device under test. In particular, the load may be a shunt.

[0030] Preferably, the actuator of the test system comprises an electric motor with an electric motor control, wherein the control unit is configured to adjust the function of the alternator by outputting a signal to the electric motor control to adjust the motor speed.

[0031] By means of an adjustment of the electric motor speed, a change in frequency may be effected. Although other actuators such as fuel-operated engine may be used, the implementation of an electric motor has the advantage that it may be powered with locally available power sources, such as a grid, reducing the overall complexity of the test system. Furthermore, the use of an electric motor and motor control allows for instant and rapid adjustments, preferably in a stepless manner, which is particularly advantageous to provide rapid voltage and / or frequency adjustments at the output terminal.

[0032] The alternator may comprises an excitation control, wherein the control unit is preferably configured to adjust the function of the alternator by outputting a signal to the excitation control to adjust the excitation level and / or by adjusting a tap changer position of the alternator winding or its auxiliary winding.

[0033] The present inventors have found that since the alternator terminal voltage is directly proportional to the excitation current present in the windings of the alternator, modifications of the excitation current and / or the tap changer position may be used to adjust the voltage at the output terminal. To this end, theexcitation pulse width modulation voltage, which is proportional to the excitation current, may have a frequency of about 10 kHz, which corresponds to about 10 ms.

[0034] For most types of grid failure tests, it was found that an adjustment of the output voltage based on the modification of the alternator is hence sufficient, since e.g. fault-ride-through profiles typically require a longer time to achieve a corresponding voltage dip or voltage swell, e.g. between 150 ms and 60 seconds. Hence, by means of the adjustment of the function of the alternator, a voltage changing rate may be achieved that corresponds to a predefined grid failure and which may be provided to test compliance of a device under testing with a corresponding grid code.

[0035] The test system preferably comprises a first switch to selectively bypass the adjustable impedance and / or a second switch to selectively connect the adjustable load, preferably both. Thereby, the circuit may be readily adapted to different grid code test scenarios, as explained further below. By the same token, the circuit may comprise a third switch, which enables that the circuit may be selectively connected and disconnected with the alternator, e.g. via a corresponding terminal.

[0036] One requirement of the grid code may be the compliance with a fault- ride-through scenario, e.g. the requirement that a device under testing remains connected, when a sudden voltage change occurs, e.g. a voltage drop or a voltage swell. The grid code typically includes a characteristic curve, which defines for which voltage changes over a predefined time a consumer or connected device needs to maintain its connected state to the grid. In order to test for such scenario, the control unit is preferably configured to maintain the actuator at nominal operation, to adjust the terminal voltage within a predefined time by controlling the function of the alternator, and to adjust the impedance to maintain a predefined ratio between the impedance and the load. Such predefined ratio is preferably defined as the ratio of the impedance, preferably of a serial impedance, to the equivalent load impedance, which may be a shunt. When the same currentflows through both the serial impedance and the load (or shunt), the voltage across each element is proportional to its equivalent impedance. By adjusting the values of the serial impedance and the load or shunt, the voltage applied to the test device can be varied from 0% to 100% of the rated voltage. It has been found that, in particular, voltage adjustment between 5% and 90% of the rated voltage are sufficient for testing purposes.

[0037] The voltage adjustment at the terminal may correspond to a voltage dip to establish a low voltage ride through test (LVRT) or a voltage swell to establish a high voltage ride through test (HVRT). As described above, the function of the alternator may be particularly adjusted by adjusting an excitation current, such that very rapid voltage adjustments may be caused and a voltage changing rate corresponding with a fault-ride-through scenario may be simulated by the test system.

[0038] Preferably, the test system furthermore comprises a first switch to selectively bypass the adjustable impedance and a second switch to selectively connect the adjustable load, wherein the control unit is configured to alternate operation of the first switch and the second switch between a closed position and an open position. Thereby, the test system may be further adapted to simulate a grid failure corresponding to a low voltage ride through or a high voltage ride through. By means of the alternating operation of the first switch and the second switch, a further fine-tuning of the ratio between the impedance and the load may be facilitated.

[0039] Alternatively, the control unit may be configured to maintain the first switch in an open position and to maintain the second switch in a closed position. Thereby, a voltage dependent test may be provided as a simulated grid failure.

[0040] In order to adjust the excitation level of the alternator, the alternator preferably comprises an excitation control. Furthermore, in addition to the adjustment of the excitation level to cause a corresponding voltage change, the control unit may be configured to control the function of the alternator by additionally adjusting a tap changer position of the alternator winding or itsauxiliary winding such that these are provided at a predefined ratio to each other. By establishing such ratio, a predefined voltage changing rate may be achieved required for the respective test scenario.

[0041] For certain grid codes, the established voltage change is required to be provided in a step-wise manner. To support such test functionality, the control unit may be configured to adjust the function of the alternator at predefined steps for predefined periods of time. In other words, the voltage may be changed with predefined, discrete voltage levels, wherein each increase or decrease in voltage is maintained for a predefined time period to ensure that the device under testing is capable of staying connected.

[0042] According to an alternative embodiment, the test system may also comprise a first switch to selectively bypass the adjustable impedance. However, the control unit according to this embodiment is configured to maintain the alternator at nominal operation and is furthermore configured to maintain the first switch in a closed position. Furthermore, the control unit is configured to adjust the actuating speed and / or frequency of the actuator, such that a simulated grid failure is achieved corresponding to a rate of change of frequency test.

[0043] In other words, contrary to a configuration adapted to simulate e.g. a low voltage ride through, the function of the alternator is not adjusted. Instead, while the alternator may be operated at a nominal voltage, an adjustment of the speed of e.g. an electrical motor may be provided to achieve a corresponding change in frequency. Since the first switch is in a closed position, the adjustable impedance is bypassed in such configuration.

[0044] The test system according to the present invention hence has the advantage that e.g. both a low voltage ride through (LVRT) test and a rate of change of frequency (Rocof) test may be successively enabled by the same test system, wherein between said tests only the control of the alternator, the control of the actuator, and the control of the switch(es) is accordingly adapted by the control unit. Hence, no complex structural requirements are required, such that the tests may be performed with a high level of flexibility and at low costs.

[0045] While the above tests may be of considerable importance to determine grid code compatibility, the test system may also be configured for various other tests, either additionally or alternatively. Accordingly, the test system may also comprise a first switch to selectively bypass the adjustable impedance and a third switch to selectively connect the circuit to the alternator. The control unit is preferably configured to maintain the alternator at nominal operation, to maintain the actuator at nominal operation, to maintain the first switch in a closed position, and to maintain the third switch in a closed position or to alternate the third switch between a closed position and an open position.

[0046] Accordingly, no adjustments may be performed at the alternator and the actuator, i.e. the alternator may be operated at nominal voltage and the actuator, e.g. an electric motor, may be operated at nominal speed and frequency. Furthermore, the adjustable impedance is bypassed based on the closed position of the first switch.

[0047] The difference according to this embodiment, compared with the previous embodiments, is hence that the third switch may either be in a closed position. In such configuration the circuit of the test system is fully connected to the alternator, which enables that a power quality or electrical characteristic test may be simulated by the test system.

[0048] Alternatively, the third switch may be alternated between a closed position and an open position, such that the circuit may be connected and disconnected in an alternating manner. Such configuration enables that a grid support test or a test according to redated standards may be simulated to determine compliance of the device under testing.

[0049] Accordingly, a variety of tests may be simulated to assess compatibility of e.g. a generator set with a grid code, wherein the tests may be successively performed by means of the corresponding control output of the control unit, e.g. at the level of the actuator, the alternator, the adjustable impedance, and / or one or more switches.

[0050] According to a further aspect of the invention, a method for determining a grid code compatibility of a generator set is provided. The method comprises the steps of:providing an alternator driven by an actuator and a circuit downstream of the alternator; andadjusting, using a control unit, a function of the alternator, an impedance level of the circuit, and / or a load within the circuit to adjust a voltage at an output terminal of the circuit, wherein the voltage adjustment corresponds to a predefined simulated grid failure, wherein the output terminal is connected to the generator set.

[0051] Preferably, the method is performed using a test system as described above. The adjustable impedance is preferably serially connected between the alternator and the output terminal and the adjustable load is preferably serially connectable between the adjustable impedance and the output terminal. By means of the control output, a predefined voltage adjustment may be provided, which corresponds to a predefined simulated grid failure to assess compatibility of the generator set or other device under testing connected at the output terminal of the circuit.

[0052] According to one embodiment, the actuator is preferably maintained at normal operation, wherein the terminal voltage is adjusted within a predefined time by controlling the function of the alternator, and wherein the impedance is adjusted to maintain a predefined ratio between the impedance and the load. The voltage is preferably adjusted to simulate a low voltage ride through or a high voltage ride through as a predefined grid failure. In particular, while the actuator, preferably an electric motor, is operated at nominal speed and / or frequency, an excitation level of the alternator may be adjusted while simultaneously a ratio between the impedance and the load is established to provide a voltage change range at the output terminal as required for the simulation of a fault-ride-through test.

[0053] The alternator may also be maintained at nominal operation, e.g. at a nominal voltage, wherein the adjustable impedance is bypassed using a first switch, and wherein the actuating speed and / or frequency of the actuator is adjusted to simulate a rate of change of frequency test as a grid failure. Although such test may be performed as an alternative to a fault-ride-through test, these methods are preferably performed successively to determine grid code compatibility. Since the methods may be performed by the same test system, this only requires that the control of the components is accordingly adapted.

[0054] Preferably, the actuator and the alternator are powered by a local grid, an external grid, an internal power supply, or an energy feedback loop from the test system. Accordingly, the method and test system considerably differ from solutions that are based on a modification within a local grid, e.g. by modifying characteristics of one or more wind turbines within a wind turbine plant. The test system and corresponding method are operated and performed independent from the any locally present power plant characteristics. Instead, the test system may be flexibly applied to any device under testing, preferably a generator set, and may only comprise an input terminal to couple the test system to a power source, e.g. a grid. The grid failure simulation, however, is fully based on the configuration and control of the test system itself, not on the characteristics of the power source.Industrial Applicability

[0055] With reference to the Figures, a test system for determining a grid code compatibility of a generator set is suggested. The suggested test system enables that a device under testing (DUT) such as a generator set may be tested for compatibility with a local grid code. The suggested test system functions independently from the characteristics of a grid or local power plant and enables that various grid code compliance tests may be performed in a successive manner without requiring adaptations on the hardware level. The test system may be formed as test bench, which obviates the need to organize separate test systemcomponents for different tests and enables grid failure simulations at significantly lower cost and with a reduced complexity.List of reference numerals 10 Test system12 Generator set14 Alternator16 Actuator18 Output terminal 20 Impedance22 Load24 First switch26 Second switch 28 Control30 Control32 Control unit34 Third switch36 Power source 38 Fourth switch

Claims

ClaimsWhat is claimed is:

1. A test system (10) for determining a grid code compatibility of a generator set (12), comprising:an alternator (14) driven by an actuator (16);a circuit downstream of the alternator (14), the circuit comprisingan output terminal (18);an adjustable impedance (20) serially connectable between the alternator (14) and the output terminal (18); andan adjustable load (22) serially connectable between the adjustable impedance (20) and the output terminal (18);a control unit (32), configured to provide a predefined voltage adjustment at the output terminal (18) by adjusting a function of the alternator (14), the impedance (20) level, and / or the load (22), wherein the predefined voltage adjustment corresponds to a predefined simulated grid failure.

2. The test system (10) according to claim 1, wherein the actuator (16) comprises an electric motor with an electric motor control (28) and wherein the control unit (32) is configured to adjust the function of the alternator (14) by outputting a signal to the electric motor control (28) to adjust the motor speed.

3. The test system (10) according to claim 1 or 2, wherein the alternator (14) comprises an excitation control (30) and wherein the control unit (32) is configured to adjust the function of the alternator (14) by outputting asignal to the excitation control (30) to adjust the excitation level and / or by adjusting a tap changer position of the alternator winding or its auxiliary winding.

4. The test system (10) according to any of the preceding claims, comprising a first switch (24) to selectively bypass the adjustable impedance (20) and / or a second switch (26) to selectively connect the adjustable load (22).

5. The test system (10) according to any of the preceding claims, wherein the control unit (32) is configured to maintain the actuator (16) at nominal operation, to adjust the terminal voltage within a predefined time by controlling the function of the alternator (14), and to adjust the impedance (20) to maintain a predefined ratio between the impedance (20) and the load (22).

6. The test system (10) according to claim 5, comprising a first switch (24) to selectively bypass the adjustable impedance (20) and a second switch (26) to selectively connect the adjustable load (22), wherein the control unit (32) is configured to alternate operation of the first switch (24) and the second switch (26) between a closed position and an open position, wherein the simulated grid failure is a low voltage ride through or a high voltage ride through.

7. The test system (10) according to claim 5, comprising a first switch (24) to selectively bypass the adjustable impedance (20) and a second switch (26) to selectively connect the adjustable load (22), wherein the control unit (32) is configured to maintain the first switch (24) in an open position and to maintain the second switch (26) in a closed position, wherein the simulated grid failure is a voltage dependent test.

8. The test system (10) according to any of claims 5 to 7, wherein the alternator (14) comprises an excitation control (30) and wherein the control unit (32) is configured to control the function of the alternator (14) byadjusting a tap changer position of the alternator winding or its auxiliary winding and by adjusting the excitation level at a predefined ratio to each other.

9. The test system (10) according to any of claims 5 to 8, wherein the control unit (32) is configured to adjust the function of the alternator (14) at predefined steps for predefined periods of time.

10. The test system (10) according to any of claims 1 to 4, comprising a first switch (24) to selectively bypass the adjustable impedance (20), wherein the control unit (32) is configured to maintain the alternator (14) at nominal operation, to maintain the first switch (24) in a closed position, and to adjust the actuating speed and / or frequency of the actuator (16), wherein the simulated grid failure is a rate of change of frequency test.

11. The test system (10) according to any of claims 1 to 4, comprising a first switch (24) to selectively bypass the adjustable impedance (20) and a third switch (34) to selectively connect the circuit to the alternator (14), wherein the control unit (32) is configured to maintain the alternator (14) at nominal operation, to maintain the actuator (16) at nominal operation, to maintain the first switch (24) in a closed position, and to maintain the third switch (34) in a closed position or to alternate the third switch (34) between a closed position and an open position.

12. A method for determining a grid code compatibility of a generator set (12), comprising the steps of:providing an alternator (14) driven by an actuator (16) and a circuit downstream of the alternator (14);adjusting, using a control unit (32), a function of the alternator (14), an impedance (20) level of the circuit, and / or a load (22) within the circuit to adjust a voltage at an output terminal (18) of the circuit, wherein the voltageadjustment corresponds to a predefined simulated grid failure, wherein the output terminal (18) is connected to the generator set (12).

13. The method according to claim 12, wherein the actuator (16) is maintained at normal operation, wherein the terminal voltage is adjusted within a predefined time by controlling the function of the alternator (14), and wherein the impedance (20) is adjusted to maintain a predefined ratio between the impedance (20) and the load (22), wherein the simulated grid failure is a low voltage ride through or a high voltage ride through.

14. The method according to claim 12, wherein the alternator (14) is maintained at nominal operation, wherein the adjustable impedance (20) is bypassed using a first switch (24), and wherein the actuating speed and / or frequency of the actuator (16) is adjusted, wherein the simulated grid failure is a rate of change of frequency test.

15. The method according to any of claims 12 to 14, wherein the actuator (16) and the alternator (14) are powered by a local grid, an external grid, an internal power supply, or an energy feedback loop from the test system.

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