System and method for detecting a stator distortion filter in an electrical power system

Abstract

A method of detecting whether a stator distortion filter is connected to a generator of an electrical power system includes temporarily interrupting magnetic flux excitation of the generator of the power system. The method also includes observing a sinusoidal waveform of one or more electrical feedback of the generator. Further, when the sine wave is longer than the predetermined duration, the method includes determining that the passive load is connected to a generator of the electrical power system. When the sinusoidal waveform suddenly decays below a threshold for a period of time less than the predetermined duration, the method includes determining that the passive load is not connected to a generator of the electrical power system. Further, the method includes implementing a control action based on whether the passive load is connected to a generator of the electrical power system.

Description

Technical Field

[0001] The present disclosure generally relates to renewable energy power systems such as wind turbines, and more particularly to systems and methods for detecting stator distortion filters in renewable energy power systems. Background Art

[0002] Wind turbines, as a form of renewable energy, have received increasing attention. Wind turbines utilize wind to generate electricity. The wind turns a plurality of rotor blades connected to a rotor. The spin of the rotor blades caused by the wind causes the shaft of the rotor to spin, and the shaft is connected to a generator that generates electricity. Some wind turbines include a doubly-fed induction generator (DFIG) for converting wind energy into electrical power suitable for output to the power grid. A DFIG is typically connected to a power converter that regulates the electrical power flow between the DFIG and the power grid. More particularly, the power converter allows the wind turbine to output electrical power at the grid frequency, regardless of the rotational speed of the rotor blades.

[0003] A typical DFIG system includes a wind-driven DFIG having a rotor and a stator. The stator of the DFIG is coupled to the power grid via stator buses. A power converter is used to couple the rotor of the DFIG to the power grid. The power converter can be a two-stage power converter including a rotor-side converter and a line-side converter. The rotor-side converter can receive alternating current (AC) power from the rotor via a rotor-side bus and can convert the AC power into DC power. Then, the line-side converter can convert the DC power into AC power having a suitable output frequency (such as the grid frequency). The AC power is provided to the power grid via a line-side bus.

[0004] The DFIG wind turbine output current contains switching frequency harmonics contributed by the line-side converter and the rotor-side converter via the stator path. Since the rotor-side converter switching frequency varies with turbine operation, there are harmonics in the stator current path. Passive solutions such as using a stator distortion filter have been implemented in the past to reduce the harmonic level.

[0005] Accordingly, the present disclosure is directed to systems and methods for detecting stator distortion filters in electrical power systems. Summary of the Invention

[0006] Aspects and advantages of embodiments of the present disclosure will be set forth in part in the following description, or may be learned from the description, or may be learned by practice of the embodiments.

[0007] In one aspect, the present disclosure is directed to a method of detecting whether a passive load is connected to a generator of an electric power system. The generator has a rotor and a stator. The method includes temporarily interrupting the magnetic flux excitation of the generator via a controller. The method also includes observing, via the controller, a sine wave form of one or more electrical feedbacks of the generator. When the sine wave form persists for longer than a predetermined duration, the method includes determining, via the controller, that a passive load is connected to the generator of the electric power system. When the sine wave form suddenly decays below a threshold within a time period less than the predetermined duration, the method includes determining, via the controller, that a passive load is not connected to the generator of the electric power system. Additionally, the method includes implementing a control action via the controller based on whether a passive load is connected to the generator of the electric power system.

[0008] In another aspect, the present disclosure is directed to an electric power system connected to a power grid. The electric power system includes a generator having a stator and a rotor. The stator is connected to the power grid via a stator power path. The electric power system also includes a passive load and a power converter connected to the generator, the power converter having a line side converter coupled to the power grid via a converter power path and a rotor side converter coupled to the rotor bus and the line side converter via a DC link. Additionally, the electric power system includes a controller having at least one processor configured to perform a plurality of operations including, but not limited to, temporarily interrupting the magnetic flux excitation of the generator; observing a sine wave form of one or more electrical feedbacks of the generator; determining that a passive load is connected to the generator of the electric power system when the sine wave form persists for longer than a predetermined duration; determining that a passive load is not connected to the generator of the electric power system when the sine wave form suddenly decays below a threshold within a time period less than the predetermined duration; and implementing a control action based on whether a passive load is connected to the generator of the electric power system.

[0009] These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] A detailed discussion of embodiments for those of ordinary skill in the art is set forth in the specification with reference to the drawings, in which:

[0011] Figure 1 A perspective view of a wind turbine is illustrated in accordance with an example embodiment of the present disclosure;

[0012] Figure 2 An electric power system is illustrated in accordance with an example embodiment of the present disclosure;

[0013] Figure 3A schematic diagram illustrating suitable components that may be included within a controller of a wind turbine and / or an electric power system and / or a controller of a power converter according to an example embodiment of the present disclosure;

[0014] Figure 4 A schematic diagram illustrating an example power converter suitable for use in a wind turbine system according to an example embodiment of the present disclosure;

[0015] Figure 5 Illustrated according to an aspect of the present disclosure Figure 2 A simplified schematic circuit of a part of a wind turbine system;

[0016] Figure 6 A flowchart illustrating an embodiment of a method for detecting whether a passive load such as a stator distortion filter is connected to a generator of an electric power system according to an aspect of the present disclosure;

[0017] Figure 7 A flowchart illustrating an embodiment of an algorithm for detecting whether a stator distortion filter is connected to a generator of a wind turbine electric power system according to an aspect of the present disclosure;

[0018] Figures 8A - 8D Various graphs of a sinusoidal voltage waveform of stator voltage feedback according to the present disclosure, where a stator distortion filter is connected to the generator; and

[0019] Figures 9A - 9D Various graphs of a sinusoidal voltage waveform of stator voltage feedback according to the present disclosure, where a stator distortion filter is not connected to the generator. Detailed Description

[0020] Reference will now be made in detail to the embodiments, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the embodiments and not limitation of the present disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments without departing from the scope or spirit of the present disclosure. For example, features illustrated or described as part of one embodiment can be used with another embodiment to yield yet another embodiment. Accordingly, it is intended that aspects of the present disclosure cover such modifications and variations.

[0021] Now referring to the drawings, Figure 1FIG. illustrates a perspective view of one embodiment of a wind turbine 10 in accordance with the present disclosure. In particular, as shown, the wind turbine 10 includes a tower 12 extending from a support surface 14, a nacelle 16 mounted on the tower 12, and a rotor 18 coupled to the nacelle 16. The rotor 18 includes a rotatable hub 20 and at least one rotor blade 22 coupled to and extending outwardly from the hub 20. For example, in the illustrated embodiment, the rotor 18 includes three rotor blades 22. However, in alternative embodiments, the rotor 18 may include more or less than three rotor blades 22. Each rotor blade 22 may be spaced about the hub 20 to facilitate rotation of the rotor 18 such that kinetic energy can be converted from the wind into useful mechanical energy and subsequently into electrical energy. For example, the hub 20 may be rotatably coupled to a Figure 2 generator 120 located within the nacelle 16 to permit the generation of electrical energy. The wind turbine 10 may also include a turbine controller 26 for controlling yaw regulation of the wind turbine 10, pitch regulation of the rotor blades 22 about respective pitch axes 34, and / or Figure 2 torque regulation of the generator 120. Additionally, in an embodiment, the turbine controller 26 may interface with components within the wind turbine 10 such as Figure 2 a converter controller 140.

[0022] Now referring Figure 2 , FIG. illustrates a schematic view of an embodiment of a DFIG wind turbine system 100 in accordance with aspects of the present disclosure. It should be appreciated that the present disclosure will generally be described with reference to the wind turbine system 100 shown in Figure 2 . However, those of ordinary skill in the art using the disclosure provided herein should understand that aspects of the present disclosure may also be applicable to other power generation systems.

[0023] As shown, the wind turbine system 100 may define a stator power path 148 and a converter power path 150. Additionally, as shown, the generator 120 (e.g., DFIG) may be coupled to the stator bus 122 and the power converter 130 via the rotor side bus 124. The stator bus 122 may provide output polyphase power (e.g., three-phase power) from the stator of the generator 120, and the rotor side bus 124 may provide output polyphase power (e.g., three-phase power) of the rotor of the generator 120. The power converter 130 may have a rotor side converter 132 and a line side converter 134. The generator 120 may be coupled to the rotor side converter 132 via the rotor side bus 124. The rotor side converter 132 may be coupled to the line side converter 134, which in turn may be coupled to the line side bus 138. The rotor side converter 132 and the line side converter 134 may be coupled via DC links 135, 137, across which are DC link capacitors 136.

[0024] Additionally, the power converter 130 may be coupled to a converter controller 140 to control the operation of the rotor side converter 132 and the line side converter 134. For example, the converter controller 140 may be configured to operate the rotor side converter 132 in an overmodulation regime or near an overmodulation regime. The converter controller 140 may include any number of control devices. In one embodiment, the control device may include a processing device (e.g., a microprocessor, a microcontroller, etc.) that executes computer-readable instructions stored in a computer-readable medium. The instructions, when executed by the processing device, may cause the processing device to perform operations including providing control commands (e.g., switching frequency commands) to the switching elements 142 ( Figure 4 ) of the power converter 130.

[0025] Still referring to Figure 2 , the wind turbine system 100 may include a transformer 160 that couples the wind turbine system 100 to the power grid 168. In an embodiment, the transformer 160 may be a three-winding transformer, which may include, for example, a high-voltage (e.g., greater than 12 kVAC) primary winding 162 coupled to the power grid, a medium-voltage (e.g., 6 kVAC) secondary winding 164 coupled to the stator bus 122, and / or a low-voltage (e.g., 575 VAC, 690 VAC, etc.) auxiliary winding 166 coupled to the line side bus 138. It should be understood that the transformer 160 may be a three-winding transformer as shown, or alternatively may be a two-winding transformer having only a primary winding 162 and a secondary winding 164; may be a four-winding transformer having a primary winding 162, a secondary winding 164, an auxiliary winding 166, and an additional auxiliary winding; or may have any other suitable number of windings.

[0026] On the stator bus 122, sinusoidal polyphase (e.g., three-phase) alternating current (AC) power can be provided from the stator of the generator 120 to the stator bus 122 and from the stator bus 122 to the transformer 160, e.g., to its secondary winding 164. Various circuit breakers, fuses, contactors, and other devices (such as the grid circuit breaker 158, the stator bus circuit breaker 156, the switch 154, and the line-side bus circuit breaker 152) can be included in the wind turbine system 100 to connect or disconnect the corresponding buses, e.g., when the current flow is excessive and can damage components of the wind turbine system 100, or for other operational considerations. Additional protection components can also be included in the wind turbine system 100.

[0027] Now referring to Figure 3 , a block diagram of an embodiment of suitable components (e.g., one or more control devices) that can be included within the turbine controller 26 and / or the converter controller 140 in accordance with the present disclosure is illustrated. As shown, the controllers 26, 140 can include one or more processors 60 and associated (one or more) memory devices 62, which are configured to perform various computer-implemented functions (e.g., execute the methods, steps, calculations, etc. disclosed herein). Additionally, the controllers 26, 140 can also include a communication module 64, which is used to facilitate communication between the controllers 26, 140 and various components of the wind turbine 10. For example, the communication module 64 can be used as an interface to allow the turbine controller 26 to transmit control signals to one or more pitch adjustment mechanisms to, e.g., control the pitch of the rotor blades 22. The communication module 64 can additionally and / or alternatively be used as an interface to allow the turbine controller 26 to transmit signals (e.g., control signals or status signals) to the converter controller 140. The communication module 64 can additionally and / or alternatively be used to allow the converter controller 140 to provide control signals to the power converter 130. Further, the communication module 64 can include a sensor interface 66 (e.g., one or more analog-to-digital converters), which is used to allow input signals transmitted from various sensors (such as voltage sensors and current sensors) to be converted into signals that can be understood and processed by the (one or more) processors 60.

[0028] Now referring to Figure 4 , an example embodiment of the power converter 130 illustrated in accordance with aspects of the present disclosure is Figure 2 shown in a schematic diagram. As shown, the rotor-side converter 132 includes a parallel bridge having a plurality of bridge circuits, where each phase of the rotor-side bus 124 input to the rotor-side converter 132 is coupled to a single bridge circuit. Additionally, the line-side converter 134 can also include a parallel bridge having a plurality of bridge circuits. Similar to the rotor-side converter 132, the line-side converter 134 also includes a single bridge circuit for each output phase of the line-side converter 134.

[0029] Each bridge circuit may generally include a plurality of switching elements (eg, IGBTs) 142 coupled in series with one another. Figure 4 As shown in , each bridge circuit includes an upper switch element 144 and a lower switch element 146. In addition, a diode can be coupled in parallel with each of the switch elements 142. In an alternative embodiment, the parallel switch elements 142 and the diode can be used to increase the current rating of the converter. As generally understood, the line side converter 134 and the rotor side converter 132 can be controlled, for example, by providing a control command to the gate of the switch element 142 using a suitable driver circuit. For example, the converter controller 140 can provide a suitable gate timing command to the gate of the switch element 142 of the bridge circuit. The control command can control the switching frequency of the switch element 142 to provide a desired output. It should be appreciated by those of ordinary skill in the art that the power converter 130 may include any suitable switch element 142, such as an insulated gate bipolar transistor (IGBT), an insulated gate commutated thyristor, a MOSFET (e.g., a MOSFET based on silicon or silicon carbide), a bipolar transistor, a silicon controlled rectifier or other suitable switch element.

[0030] Reference now Figure 5 , according to aspects of the present disclosure, illustrates Figure 2 1 is a simplified schematic circuit diagram of a portion of a wind turbine system 100. In particular, as shown, the wind turbine system 100 includes a passive load 170 coupled to a stator power path 148 that connects a stator of the generator 120 to a power grid 168. In particular, as shown and previously described, the passive load 170 may be a stator distortion filter 172 coupled in parallel with the stator power path 148. Thus, as described herein, a stator distortion filter 172 may be provided to mitigate the output current (i WT ) in the high frequency harmonics. In particular, as shown, the output current (i WT ) usually includes the stator current (i S ) and the converter current (i Y ). For example, Figure 5 As shown in , the stator distortion filter 172 may be coupled to the stator bus 122 , ie, between the generator stator and the transformer 160 .

[0031] Reference now Figure 6 , a flow chart of an embodiment of a method 200 of detecting whether a passive load is connected to a generator of an electric power system is illustrated according to aspects of the present disclosure. For example, in an embodiment, the passive load includes a stator distortion filter in a stator power path connecting a stator of the generator to the power grid.

[0032] As used herein, an electric power system may include a wind turbine power system 100, a solar power system, an energy storage power system, or a hybrid power system including a combination thereof. Generally, method 200 will be described herein as being implemented using a controller of a wind turbine system (such as turbine controller 26 or converter controller 140 of the DFIG wind turbine system 100 described above with reference to Figures 1 - 4 However, it should be appreciated that the disclosed method 200 may be implemented using any other suitable power generation system configured to supply power for an application to a load. Additionally, although Figure 6 steps are depicted for purposes of illustration and discussion as being performed in a particular order, the methods described herein are not limited to any particular order or arrangement. Using the disclosure provided herein, one of ordinary skill in the art will appreciate that the various steps of the method may be omitted, rearranged, performed simultaneously, combined, and / or adapted in various ways. Additional steps not disclosed herein may be performed without departing from the scope or spirit of the disclosure.

[0033] As shown at (202), method 200 includes temporarily interrupting magnetic flux excitation of a generator via a controller. For example, in an embodiment, temporarily interrupting magnetic flux excitation of generator 120 may include using a grid / stator synchronization sequence to temporarily interrupt magnetic flux excitation of generator 120. More specifically, in an embodiment, the grid / stator synchronization sequence may include setting zero current excitation in the rotor circuit of generator 120.

[0034] Returning to reference Figure 6 As shown at (204), method 200 includes observing a sine wave form of one or more electrical feedbacks of a generator via a controller. For example, in an embodiment, the (one or more) electrical feedbacks of generator 120 may be stator voltage feedback, stator current feedback, or both, or any other suitable electrical feedback of generator 120.

[0035] As shown at (206), when the sine wave form persists for longer than a predetermined duration, method 200 includes determining via a controller that a passive load is connected to the generator of the electric power system. In an embodiment, the predetermined duration may be equal to or less than approximately 10 milliseconds. As shown at (208), when the sine wave form suddenly decays below a threshold within a period of time less than the predetermined duration, method 200 includes determining via a controller that a passive load is not connected to the generator of the electric power system.

[0036] As shown at (210), method 200 includes implementing control actions via a controller based on whether a passive load is connected to a generator of an electric power system. For example, in an embodiment, implementing control actions based on whether a passive load is connected to generator 120 can include connecting the passive load to generator 120 after the controller determines that the passive load is not connected to generator 120. Additionally, in an embodiment, implementing control actions based on whether a passive load is connected to generator 120 can include determining whether power converter 130 is configured to operate with a passive load connected to generator 120. If power converter 130 is configured to operate with a passive load connected to generator 120, operate power converter 130 to account for the passive load being connected to generator 120.

[0037] Reference Figures 7 - 9D can be better understood Figure 6 of method 200. In particular, Figure 7 FIG. illustrates a flowchart of a particular embodiment of algorithm 300 for detecting whether stator distortion filter 172 is connected to generator 120 of wind turbine power system 100 in accordance with aspects of the present disclosure; Figures 8A - 8D FIGS. illustrate various graphs of sine waveforms of stator voltage feedback in accordance with the present disclosure, where the stator distortion filter is connected to generator 120; and Figures 9A - 9D FIGS. illustrate various graphs of sine waveforms of stator voltage feedback in accordance with the present disclosure, where the stator distortion filter is not connected to generator 120.

[0038] In particular reference to Figure 7 , as shown at (302), algorithm 300 includes exciting the rotor circuit of generator 120 with a non - zero current. As shown at (304), algorithm 300 includes monitoring the stator voltage feedback of generator 120. As shown at (306), algorithm 300 includes determining whether a sinusoidal voltage waveform is detected in the stator voltage feedback and has a high enough amplitude. If the sinusoidal voltage waveform is not detected and / or does not have a high enough amplitude, as shown at (318), algorithm 300 includes generating a diagnostic signal indicating an error associated with generator 120.

[0039] However, when a sinusoidal voltage waveform is detected and has a high enough amplitude, as shown at (308), algorithm 300 includes setting a zero current excitation in the rotor circuit of generator 120. Additionally, and continuing to (310), algorithm 300 includes determining the time it takes for the amplitude of the sinusoidal voltage waveform to decay below a predetermined threshold. Algorithm 300 also includes comparing the time it takes for the amplitude of the sinusoidal voltage waveform to decay below a predetermined threshold with a predetermined duration. Thus, as shown at (312), algorithm 300 determines whether the decay time is longer than the predetermined duration. If so, as shown at (318), algorithm 300 includes generating a diagnostic signal indicative of an error associated with generator 120. Conversely, as shown at (314), if the decay time is less than the predetermined duration, algorithm 300 proceeds to (316) and (320). More specifically, as shown at (316), if the decay time is not less than the predetermined duration, algorithm 300 determines that a filter or passive load (e.g., stator distortion filter 172) is connected to the generator stator. If the decay time is less than the predetermined duration, as shown at (320), algorithm 300 includes determining that a filter or passive load (e.g., stator distortion filter 172) is not connected to the generator stator.

[0040] Now referring to Figures 8A - 9D , as mentioned, various graphs 400, 500, 600, 700, 800, 900, 1000, 1100 illustrate sinusoidal waveforms of stator voltage feedback in accordance with the present disclosure, where a stator distortion filter is connected to generator 120 ( Figures 8A - 8D ), and where a stator distortion filter is not connected to generator 120 ( Figures 9A - 9D ). More specifically, as shown, Figures 8A - 9D illustrates a comparison between stator voltage feedback captured in a wind turbine power system with a connected stator distortion filter ( Figures 8A - 8D ) and without such a stator distortion filter ( Figures 9A - 9D ). In particular, Figure 8A and 9A illustrate the stator voltage rotation vector magnitude, while Figures 8B - 8D and 9B - 9D illustrate the stator line - to - neutral phase voltage. All graphs are in volts. Additionally, as shown, Figures 8A - 9D the decay envelopes 402, 502, 602, 702, 802, 902, 1002, 1102 in each of Figures 8A - 8D are significantly different between systems with a connected stator distortion filter ( Figures 9A - 9D ) and those without such a stator distortion filter. Thus, the differences can be robustly detected by the algorithm(s) described herein. Additionally, as shown, when there is no connected distortion filter (Figures 9A - 9D ) The increment between the cursor positions is the time it takes for the phase voltage to reach near zero level. Additionally, as Figures 8A - 8D shown, when the connected stator distortion filter and the generator continue to exchange energy after the rotor excitation is removed, a voltage with a significant amplitude and still oscillating is sensed.

[0041] Another aspect of the present invention is provided by the subject matter of the following clauses:

[0042] A method for detecting whether a passive load is connected to a generator of an electric power system, the generator having a rotor and a stator, the method comprising: temporarily interrupting the magnetic flux excitation of the generator via a controller; observing, via the controller, a sine wave form of one or more electrical feedbacks of the generator; when the sine wave form persists for longer than a predetermined duration, determining, via the controller, that the passive load is connected to the generator of the electric power system; when the sine wave form suddenly decays below a threshold within a time period less than the predetermined duration, determining, via the controller, that the passive load is not connected to the generator of the electric power system; and implementing a control action via the controller based on whether the passive load is connected to the generator of the electric power system.

[0043] The method as described in any of the preceding clauses, wherein the passive load includes a stator distortion filter in a stator power path connecting the stator of the generator to an electrical grid.

[0044] The method as described in any of the preceding clauses, wherein temporarily interrupting the magnetic flux excitation of the generator further includes using a synchronization sequence to temporarily interrupt the magnetic flux excitation of the generator.

[0045] The method as described in any of the preceding clauses, wherein the synchronization sequence further includes setting a zero current excitation in a rotor circuit of the generator.

[0046] The method as described in any of the preceding clauses, wherein the one or more electrical feedbacks of the generator include one or more stator voltage feedbacks, one or more stator current feedbacks, or both.

[0047] The method as described in any of the preceding clauses, wherein the one or more electrical feedbacks of the generator include the stator voltage feedback.

[0048] The method as described in any of the preceding clauses, wherein implementing the control action based on whether the passive load is connected to the generator of the electric power system further includes connecting the passive load to the generator after the controller determines that the passive load is not connected to the generator.

[0049] A method as described in any of the preceding clauses, wherein implementing the control action based on whether the passive load is connected to the generator of the electric power system further includes: determining whether a power converter of the electric power system is configured to operate with the passive load connected to the generator; and when the power converter is configured to operate with the passive load connected to the generator, operating the power converter to account for the passive load being connected to the generator.

[0050] A method as described in any of the preceding clauses, further includes: exciting a rotor circuit of the generator with a non-zero current before temporarily interrupting the magnetic flux excitation of the generator; monitoring one or more electrical feedbacks of the generator before temporarily interrupting the magnetic flux excitation of the generator; and determining whether the sine waveform is detected and has an amplitude exceeding a pre-determined threshold before temporarily interrupting the magnetic flux excitation of the generator.

[0051] A method as described in any of the preceding clauses, further includes: determining the time taken for the amplitude of the sine waveform to decay below the threshold; and comparing the time taken for the amplitude of the sine waveform to decay below the threshold with the predetermined duration.

[0052] A method as described in any of the preceding clauses, wherein implementing the control action based on whether the passive load is connected to the generator of the electric power system further includes: generating a diagnostic signal indicating an error associated with the generator when the time taken for the amplitude of the sine waveform to decay below the threshold is longer than the predetermined duration.

[0053] A method as described in any of the preceding clauses, wherein the predetermined duration is equal to or less than about 10 milliseconds.

[0054] A method as described in any of the preceding clauses, wherein the electric power system includes at least one of a wind turbine electric power system, a solar electric power system, an energy storage electric power system, or a combination thereof.

[0055] A method as described in any of the preceding clauses, wherein the controller includes at least one of a turbine controller or a converter controller of the wind turbine power system.

[0056] An electric power system connected to a power grid, the electric power system comprising: a generator including a stator and a rotor, the stator being connected to the power grid via a stator power path; a passive load connected to the generator; a power converter including a line-side converter coupled to the power grid via a converter power path and a rotor-side converter coupled to a rotor bus of the rotor and the line-side converter via a DC link; a controller including at least one processor configured to perform a plurality of operations, the plurality of operations including: temporarily interrupting a magnetic flux excitation of the generator; observing a sine waveform of one or more electrical feedbacks of the generator; determining that the passive load is connected to the generator of the electric power system when the sine waveform persists for longer than a predetermined duration; determining that the passive load is not connected to the generator of the electric power system when the sine waveform suddenly decays below a threshold within a time period less than the predetermined duration; and implementing a control action based on whether the passive load is connected to the generator of the electric power system.

[0057] The electric power system according to any of the preceding clauses, wherein the passive load includes a stator distortion filter in the stator power path connecting the stator of the generator to the power grid.

[0058] The electric power system according to any of the preceding clauses, wherein temporarily interrupting the magnetic flux excitation of the generator further includes using a synchronization sequence to temporarily interrupt the magnetic flux excitation of the generator, and the synchronization sequence further includes setting a zero current excitation in a rotor circuit of the rotor of the generator.

[0059] The electric power system according to any of the preceding clauses, wherein the one or more electrical feedbacks of the generator include one or more stator voltage feedbacks, one or more stator current feedbacks, or both.

[0060] The electric power system according to any of the preceding clauses, wherein implementing the control action based on whether the passive load is connected to the generator of the electric power system further includes: after the controller determines that the passive load is not connected to the generator, connecting the passive load to the generator; determining whether the power converter of the electric power system is configured to operate with the passive load connected to the generator; and when the power converter is configured to operate with the passive load connected to the generator, operating the power converter to account for the passive load being connected to the generator.

[0061] An electric power system as described in any of the foregoing clauses, wherein the plurality of operations further includes: determining the time taken for the amplitude of the sine wave form to decay below the threshold; and comparing the time taken for the amplitude of the sine wave form to decay below the threshold with the predetermined duration; and wherein implementing the control action based on whether the passive load is connected to the generator of the electric power system further includes: generating a diagnostic signal indicating an error associated with the generator when the time taken for the amplitude of the sine wave form to decay below the threshold is longer than the predetermined duration.

[0062] This written description uses examples, including the best mode, to disclose the invention and also enables any person skilled in the art to practice the invention, including making and using any device or system and performing any combined method. The patentable scope of the invention is defined by the claims and may include other examples that occur to those skilled in the art. If such other examples include structural elements that do not differ from the literal language of the claims, or if such other examples include equivalent structural elements that have insubstantial differences from the literal language of the claims, then such other examples are intended to be within the scope of the claims.

Claims

1. A method for detecting whether a passive load is connected to a generator of an electric power system, the generator having a rotor and a stator, the method comprising: temporarily interrupting, via a controller, magnetic flux excitation of the generator; observing, via the controller, a sinusoidal waveform of one or more electrical feedbacks of the generator; determining, via the controller, that the passive load is connected to the generator of the electric power system when the sinusoidal waveform continues longer than a predetermined duration; determining, via the controller, that the passive load is not connected to the generator of the electric power system when the sinusoidal waveform suddenly decays below a threshold value within a time period less than the predetermined duration; and A control action is implemented via the controller based on whether the passive load is connected to the generator of the electric power system.

2. The method according to claim 1, wherein: The passive load comprises a stator distortion filter connecting the stator of the generator in a stator power path to a power grid.

3. The method according to claim 1, wherein: Temporarily interrupting the flux excitation of the generator further comprises temporarily interrupting the flux excitation of the generator using a synchronization sequence.

4. The method according to claim 3, wherein: The synchronization sequence also includes setting zero current excitation in a rotor circuit of the generator.

5. The method according to claim 1, wherein: The one or more electrical feedbacks of the generator include one or more stator voltage feedbacks, one or more stator current feedbacks, or both.

6. The method according to claim 5, wherein: The one or more electrical feedbacks of the generator include the stator voltage feedback.

7. The method according to claim 1, wherein: Implementing the control action based on whether the passive load is connected to the generator of the electric power system further includes connecting the passive load to the generator after the controller determines that the passive load is not connected to the generator.

8. The method according to claim 6, wherein: Implementing the control action based on whether the passive load is connected to the generator of the electric power system further includes: determining whether a power converter of the electric power system is configured to operate with the passive load connected to the generator; and When the power converter is configured to operate with the passive load connected to the generator, the power converter is operated to account for the passive load being connected to the generator.

9. The method according to claim 1, further comprising: energizing a rotor circuit of the generator with a non-zero current before temporarily interrupting the magnetic flux energization of the generator; monitoring the one or more electrical feedbacks of the generator prior to temporarily interrupting the magnetic flux excitation of the generator; as well as Prior to temporarily interrupting the magnetic flux energization of the generator, a determination is made as to whether the sinusoidal waveform is detected and has an amplitude exceeding a predetermined threshold.

10. The method according to claim 1, further comprising: determining the time taken for the amplitude of the sinusoidal waveform to decay below the threshold; as well as The time taken by the amplitude of the sinusoidal waveform to decay below the threshold is compared to the predetermined duration.

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