System and method for operating inverter-based resources in a grid forming mode (GFM) for enhanced stability during transient grid power events

Abstract

A method for operating a renewable energy source having an inverter-based resource (IBR) system connected to a power grid, the method comprising: operating the IBR system as a virtual synchronous machine (VSM) under grid formation mode (GFM) control; deriving a power error signal (Perr) between a real power output (Pfbk) and a power reference (Pref) from the IBR system; generating an internal frequency signal ([omega] 1) using the power error signal (Perr) using an inertial power regulator having an integral characteristic, the internal frequency signal being used to generate a phase shifted signal ([delta] IT) applied to a power angle command signal used by an inverter controller in the IBR system; and generating a compensation signal for modifying the internal frequency signal ([omega] 1) or the phase shift signal ([delta] IT) based on the power error signal (Perr) via a control function having at least one of proportional, differential or washout characteristics.

Description

Technical Field

[0001] The present disclosure generally relates to the operation of inverter-based resources such as wind turbine generators, and more particularly, to systems and methods for operating a wind turbine generator as a virtual synchronous machine (VSM) in a grid-forming mode (GFM). Background Art

[0002] Wind power is considered to be one of the cleanest and most environmentally friendly energy sources currently available, and wind turbines have received increasing attention in this regard. Modern wind turbines typically include a tower, a generator, a gearbox, a nacelle, and one or more rotor blades. The rotor blades capture the kinetic energy of the wind using known airfoil principles. For example, the rotor blades typically have a cross-sectional profile of an airfoil such that during operation, air flows over the blade, thereby creating a pressure difference between the two sides. Thus, a lift force acting from the pressure side towards the suction side acts on the blade. The lift force generates a torque on the main rotor shaft, which is typically meshed with a generator for generating electricity.

[0003] Wind turbines can be classified into two types: fixed-speed turbines and variable-speed turbines. Traditionally, variable-speed wind turbines have been controlled as current sources connected to the power grid. In other words, variable-speed wind turbines rely on the grid frequency detected by a phase-locked loop (PLL) as a reference and inject a specified amount of current into the grid. The traditional current source control of wind turbines is based on the assumption that the grid voltage waveform is a fundamental voltage waveform with a fixed frequency and amplitude, and the penetration of wind power into the grid is low enough so as not to cause interference to the grid voltage amplitude and frequency. Therefore, the wind turbine simply injects a specified current into the grid based on the fundamental voltage waveform. However, with the rapid growth of wind power systems, the penetration into some grids has increased to a level where wind turbine generators have a significant impact on the grid voltage and frequency. When a wind turbine is located in a weak grid, wind turbine power fluctuations may cause an increase in the amplitude and frequency variations of the grid voltage. These fluctuations may adversely affect the performance and stability of the PLL and wind turbine current control.

[0004] In addition, a decrease in the ratio of synchronous machines to asynchronous machines that determine the grid-defined parameters voltage and frequency has contributed to a reduction in the stability margin. When subjected to voltage and frequency disturbances in the grid, the direct consequence of the reduced stability margin is a grid collapse. To address this issue, many renewable resource machines such as inverter-based resources (IBR) configured as doubly-fed induction generators in wind turbine power systems operate in a "grid-forming mode".

[0005] In the "Grid Forming Mode" (GFM), the converter provides a voltage source characteristic where the angle and magnitude of the voltage are controlled to achieve the regulation functions required by the grid. In GFM operation, renewable resources are controlled to operate as a Virtual Synchronous Machine (VSM), which has an inertial power regulator that replicates the behavior of a synchronous machine. Similar to an actual synchronous machine, this control exhibits an inertial response. Additionally, in GFM mode control, the main system variables of frequency and terminal voltage magnitude are regulated. With this configuration, the current will flow according to the grid's demand, and the converter helps to establish voltage and frequency for the grid. This characteristic can be comparable to that of a traditional generator based on a turbine-driven synchronous machine.

[0006] The basic control structure used to achieve the above grid-forming objectives was developed and field-proven for battery systems in the early 1990s (see, for example, U.S. Patent No. 5,798,633 titled "Battery Energy Storage Power Conditioning System"). The application to full-converter wind turbines and solar generators is disclosed in U.S. Patent No. 7,804,184 (titled "System and Method for Control of a Grid Connected Power Generating System") and U.S. Patent No. 9,270,194 (titled "Controller for controlling a power converter"). The application of grid-forming control to a doubly-fed wind turbine generator is disclosed in PCT / US2020 / 013787 (titled "System and Method for Providing Grid-Forming Control for a Doubly-Feb Wind Turbine Generator").

[0007] For effectiveness, grid-forming based inverter resources (IBR) must be able to maintain the internal voltage phasor such that when there are changes in grid conditions, such as sudden load addition / removal, opening or closing of a grid connection that result in phase jumps and / or rapid frequency changes, the phasor does not move rapidly. Such events include, for example, low voltage ride through (LVRT), high voltage ride through (HVRT), multiple fault ride through (MFRT), and phase jump events. In other words, the power from the grid-forming resources must be able to change suddenly to stabilize the grid, whereupon it is then slowly reset to power from a higher level control function command. Additionally, the grid-forming resources must be able to quickly implement power limitations that exist due to constraints on the power handling section of the device. Such a response is required for severe disturbances on the grid, such as faults, where the power limitations will be dynamically adjusted to coordinate with the grid conditions for a safe recovery from the fault. Further, the grid-forming resources should be able to quickly track changes in commands from higher level controls, for example, for damping mechanical vibrations in a wind turbine. However, such requirements may be difficult to achieve.

[0008] One result of the GFM operation of traditional IBRs is that rapid changes in grid voltage magnitude, frequency, or angle can lead to large deviations of the active power from the expected operating point, potentially resulting in power overloads and / or oscillations. For this reason, an improved grid-forming power regulation would be beneficial, which is capable of achieving faster control of power under certain conditions to avoid these overloads. Summary of the Invention

[0009] Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned by practice of the invention.

[0010] The present disclosure relates to a method and system for operating a renewable energy source having an inverter-based resource (IBR) system connected to a power grid, wherein the method allows for regulating the relationship between active power, frequency, and power angle. The method includes: operating the IBR system as a virtual synchronous machine (VSM) under grid-forming mode (GFM) control; deriving a power error signal (Perr) between the real power output (Pfbk) from the IBR system and a power reference (Pref) representative of the desired power output of the IBR system; using an inertial power regulator having an integral characteristic to generate an internal frequency signal (ω1) using the power error signal (Perr), and generating a phase shift signal (δIT) using the internal frequency signal (ω1), the phase shift signal being applied to a power angle command signal used by an inverter controller in the IBR system; and generating a compensation signal based on the power error signal (Perr) via a control function having at least one of proportional, derivative, or washout characteristics, and applying the compensation signal to modify the internal frequency signal (ω1) or the phase shift signal (δIT), thereby providing an additional mechanism for regulating the relationship between active power, frequency, and power angle.

[0011] In a particular embodiment, the renewable energy source is a wind turbine power system, which may include a doubly-fed induction generator (DFIG).

[0012] In an alternative embodiment, the renewable energy source may be a battery energy storage system (BESS), a solar power generation system, or a hydroelectric power system.

[0013] The method and system will be described herein with reference to a wind turbine power system, but it should be appreciated that this is for illustrative purposes only and the method and system are not limited to a wind turbine power system.

[0014] The method and associated system can be implemented in response to different transient power events on the power grid, which may include: low voltage events, high voltage events, multi-fault events, phase jump events, or frequency offset events, and are determined based on detected grid characteristics exceeding a predetermined value.

[0015] In a particular embodiment, the compensation signal includes a frequency compensation signal (ωPerr_cmp), which is applied to a phase-locked loop frequency (ωPLL) to generate a phase-locked frequency signal (ωPLL-Perr) adjusted by the power error received by the inertial power regulator. The frequency compensation signal (ωPerr_cmp) can be derived as a function of the power error signal (Perr) input to the inertial power regulator.

[0016] In another embodiment, the compensation signal includes a power angle compensation signal (δPerr_cmp), which is applied to a phase shift signal (δIT) to generate a phase shift signal adjusted for power error (δIT-Perr) received by an inverter controller in the IBR system. The power angle compensation signal (δPerr_cmp) can be derived as a function of a power error signal (Perr) input to an inertial power regulator.

[0017] The present disclosure also includes a renewable energy source connected to a power grid, where the renewable energy source includes: an inverter-based resource (IBR) system; a controller for controlling the IBR system, the controller including a processor configured to perform a plurality of operations. The plurality of operations include: operating the IBR system as a virtual synchronous machine (VSM) under grid-forming mode (GFM) control; deriving a power error signal (Perr) between an actual power output (Pfbk) from the IBR system and a power reference (Pref) representative of a desired power output of the IBR system; using an inertial power regulator having an integral characteristic, using the power error signal (Perr) to generate an internal frequency signal (ω1), using the internal frequency signal (ω1) to generate a phase shift signal (δIT), the phase shift signal being applied to a power angle command signal used by an inverter controller in the IBR system; and generating a compensation signal based on the power error signal (Perr) via a control function having at least one of proportional, derivative, or washout characteristics, and applying the compensation signal to modify the internal frequency signal (ω1) or the phase shift signal (δIT), thereby providing an additional mechanism for regulating the relationship between active power, frequency, and power angle.

[0018] The controller can be configured to perform or implement any combination of the control functionality discussed above and described in more detail herein.

[0019] These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and the 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

[0020] A complete and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth in the specification, which makes reference to the accompanying drawings, in which:

[0021] FIG. 1 illustrates a perspective view of an embodiment of a conventional wind turbine;

[0022] FIG. 2 illustrates a schematic diagram of an embodiment of a wind turbine electrical power system suitable for use with the wind turbine shown in FIG. 1;

[0023] FIG. 3 illustrates a block diagram of an embodiment of a controller according to the present disclosure;

[0024] FIG. 4 illustrates a schematic diagram of an embodiment of a main circuit of grid-forming control of an asynchronous machine system according to a conventional configuration;

[0025] Figure 5 is a control diagram of the operation of an inverter-based resource in grid-forming mode according to the present disclosure;

[0026] Figure 6 is a control diagram of the operation of an inverter-based resource in grid-forming mode according to the present disclosure; and

[0027] Figure 7 is a control diagram of the operation of an inverter-based resource in grid-forming mode according to the present disclosure. DETAILED DESCRIPTION

[0028] Reference will now be made in detail to embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the invention and not limitation of the invention. Indeed, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For example, features illustrated or described as part of one embodiment can be used with another embodiment to yield yet a further embodiment. Accordingly, it is intended that the present invention cover such modifications and variations as fall within the scope of the appended claims and their equivalents.

[0029] Generally, the present disclosure is directed to systems and methods for controlling inverter-based resources (IBR) connected to a power grid, where the IBR operates as a virtual synchronous machine (VSM) in grid-forming mode (GFM). As used herein, inverter-based resources generally refer to electrical devices that can generate or absorb electrical power through the switching of power electronic devices. Thus, inverter-based resources can include wind turbine generators, solar inverters, battery energy storage systems, or hydroelectric power systems. For example, in one embodiment, the inverter-based resource can be a wind turbine power system having a rotor-side converter, a line-side converter, and a doubly-fed induction generator (DFIG) connected to a power grid.

[0030] Referring now to the drawings, FIG. 1 illustrates a perspective view of one embodiment of a wind turbine 10 in accordance with the present disclosure. As shown, the wind turbine 10 generally 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. 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 wind to useful mechanical energy and subsequently to electrical energy. For example, the hub 20 may be rotatably coupled to an electric generator 102 (FIG. 4) positioned within the nacelle 16 to permit electrical energy to be generated.

[0031] The wind turbine 10 may also include a wind turbine controller 26 centralized within the nacelle 16. However, in other embodiments, the controller 26 may be located within any other component of the wind turbine 10 or at a location external to the wind turbine 10. Additionally, the controller 26 may be communicatively coupled to any number of components of the wind turbine 10 in order to control the operation of such components and / or to effect corrective or control actions. Accordingly, the controller 26 may include a computer or other suitable processing unit. Thus, in several embodiments, the controller 26 may include suitable computer-readable instructions that, when implemented, configure the controller 26 to perform a variety of different functions, such as receiving, transmitting, and / or executing wind turbine control signals. Accordingly, the controller 26 may generally be configured to control various operating modes (e.g., startup or shutdown sequences), reduce or increase the ratings of the wind turbine and / or individual components of the wind turbine 10.

[0032] Referring to the wind turbine power system 100 of FIG. 2, the rotor 18 of the wind turbine 10 can be coupled to the gearbox 38 via a high-speed shaft (HSS), where the gearbox 38 is in turn coupled to the generator 102 via a low-speed shaft (LSS). The generator 102 can be a doubly-fed induction generator (DFIG). As shown, the DFIG 102 can be connected to the stator bus 104. In addition, the power converter 106 can be connected to the DFIG 102 via the rotor bus 108 and to the stator bus 104 via the line-side bus 110. Thus, the stator bus 104 can provide output polyphase power (e.g., three-phase power) from the stator of the DFIG 102, and the rotor bus 108 can provide output polyphase power (e.g., three-phase power) from the rotor of the DFIG 102. The power converter 106 can also include a rotor-side converter (RSC) 112 and a line-side converter (LSC) 114. The DFIG 102 is coupled to the rotor-side converter 112 via the rotor bus 108. In addition, the RSC 112 is coupled to the LSC 114 via a DC link 116, across which is a DC link capacitor 118. The LSC 114 is in turn coupled to the line-side bus 110.

[0033] The RSC 112 and the LSC 114 can be configured for normal operating modes in a three-phase pulse-width modulation (PWM) arrangement using one or more switching devices (such as insulated gate bipolar transistor (IGBT) switching elements). In addition, the power converter 106 can be coupled to a converter controller 120 to control the operation of the rotor-side converter 112 and / or the line-side converter 114, as described herein. It should be noted that the converter controller 120 can be configured as an interface between the power converter 106 and the turbine controller 26 and can include any number of control devices.

[0034] In a typical configuration, various line contactors and circuit breakers (including, for example, a grid circuit breaker 122) can also be included to isolate the various components necessary for the normal operation of the DFIG 102 during connection to and disconnection from a load (such as a power grid 124). For example, a system circuit breaker 126 can couple the system bus 128 to a transformer 130, which can be coupled to the power grid 124 via the grid circuit breaker 122. In an alternative embodiment, fuses can replace some or all of the circuit breakers.

[0035] In operation, the alternating current (AC) power generated at the DFIG 102 by rotating the rotor 18 is supplied to the power grid 124 via a two-path defined by the stator bus 104 and the rotor bus 108. On the rotor bus side 108, sinusoidal polyphase (e.g., three-phase) AC power is supplied to the power converter 106. The rotor-side converter 112 converts the AC power supplied from the rotor bus 108 into direct current (DC) power and supplies the DC power to the DC link 116. As is generally understood, the switching elements (e.g., IGBTs) used in the bridge circuit of the rotor-side converter 112 can be modulated to convert the AC power supplied from the rotor bus 108 into DC power suitable for the DC link 116.

[0036] Additionally, the line-side converter 114 converts the DC power on the DC link 116 into AC output power suitable for the power grid 124. In particular, the switching elements (e.g., IGBTs) used in the bridge circuit of the line-side power converter 114 can be modulated to convert the DC power on the DC link 116 into AC power on the line-side bus 110. The AC power from the power converter 106 can be combined with the power from the stator of the DFIG 102 to provide polyphase power (e.g., three-phase power) having a frequency that is substantially maintained at the frequency of the power grid 124 (e.g., 50 Hz or 60 Hz).

[0037] Additionally, various circuit breakers and switches (such as the grid breaker 122, the system breaker 126, the stator synchronous switch 132, the converter breaker 134, and the line contactor 136) can be included in the wind turbine power system 100 to connect or disconnect the corresponding buses, for example, when the current flow is excessive and can damage the components of the wind turbine power system 100 or for other operating considerations. Additional protection components can also be included in the wind turbine power system 100.

[0038] Furthermore, the power converter 106 can receive control signals from the converter controller 120 via the wind turbine controller 26. The control signals can be based on the sensed state or operating characteristics of the wind turbine power system 100, etc. Generally, the control signals provide control over the operation of the power converter 106. For example, feedback in the form of the sensed speed of the DFIG 102 can be used to control the conversion of the output power from the rotor bus 108 to maintain a correct and balanced polyphase (e.g., three-phase) power supply. Other feedback from other sensors can also be used by the controller(s) 120, 26 to control the power converter 106, including, for example, stator and rotor bus voltage and current feedback. Using various forms of feedback information, switching control signals (e.g., gate timing commands for IGBTs), stator synchronous control signals, and circuit breaker signals can be generated.

[0039] The power converter 106 also compensates for or adjusts the frequency of the three-phase power from the rotor for changes in the wind speed, for example, at the hub 20 and the rotor blades 22. Thus, the mechanical and electrical rotor frequencies are decoupled and are substantially independent of the mechanical rotor speed to facilitate matching of the electrical stator and rotor frequencies.

[0040] In some states, the bi-directional nature of the power converter 106 and specifically the bi-directional nature of the LSC 114 and the RSC 112 facilitate feeding back at least some of the generated electrical power into the generator rotor. More specifically, electrical power can be transferred from the stator bus 104 to the line-side bus 110 and then through the line contactor 136 and into the power converter 106, specifically into the LSC 114, which acts as a rectifier and rectifies the sinusoidal three-phase AC power into DC power. The DC power is transferred into the DC link 116. The capacitor 118 facilitates reducing the DC link voltage amplitude variations by facilitating the mitigation of the DC ripple sometimes associated with three-phase AC rectification.

[0041] The DC power is then transferred to the RSC 112, which converts the DC electrical power into three-phase sinusoidal AC electrical power by adjusting the voltage, current, and frequency. This conversion is monitored and controlled via the converter controller 120. The converted AC power is transferred from the RSC 112 to the generator rotor via the rotor bus 108. In this way, the generator reactive power control is facilitated by controlling the rotor current and voltage.

[0042] Now referring to FIG. 3, a block diagram of an embodiment of suitable components that may be included within a controller (such as any one of the converter controller 120, the turbine controller 26, and / or the field-level controller) in accordance with example aspects of the present disclosure is illustrated. As shown, the controller may include one or more processors 58, a computer, or other suitable processing unit and associated memory device(s) 60, the memory device(s) 60 may include suitable computer-readable instructions that, when implemented, configure the controller to perform various different functions, such as receiving, transmitting, and / or executing wind turbine control signals (e.g., performing the methods, steps, calculations, and the like disclosed herein).

[0043] As used herein, the term "processor" refers not only to integrated circuits known in the art as being included in a computer, but also to controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application specific integrated circuits, and other programmable circuits. Additionally, the memory device(s) 60 generally may include memory element(s), including but not limited to computer-readable media (such as random access memory (RAM)), computer-readable non-volatile media (such as flash memory), floppy disks, compact disc read-only memory (CD-ROM), magneto-optical discs (MOD), digital versatile discs (DVD), and / or other suitable memory elements.

[0044] One or more such memory devices 60 generally may be configured to store suitable computer-readable instructions that, when implemented by the processor(s) 58, configure the controller to perform the various functions described herein. Additionally, the controller may further include a communication interface 62 for facilitating communication between the controller and the various components of the wind turbine 10. The interface may include one or more circuits, terminals, pins, contacts, conductors, or other components for transmitting and receiving control signals. Further, the controller may include a sensor interface 64 (such as one or more analog-to-digital converters) for permitting signals transmitted from the sensors 66, 68 to be converted into signals that may be understood and processed by the processor(s) 58.

[0045] Referring now to FIG. 4, a control diagram for providing grid-forming mode (GFM) control to a renewable energy source operating as a virtual synchronous machine (VSM) according to a conventional configuration is illustrated. As shown, the converter controller 1 receives references (e.g., V ref and P ref ) and limits (e.g., V cmdLimits and P cmdLimits ) from a higher-level controller 2. These high-level limits are physical quantities regarding voltage, current, and power. The main regulators include a fast voltage regulator 3 and a slow power regulator 4, where the slow power regulator includes an inertial power regulator that provides the VSM control of the machine. These regulators 3, 4 have ultimate limits for the converter control commands applied to the voltage magnitude (e.g., V cnvCmd ) and angle (e.g., θ Pang and θ PLL ) to respectively implement the constraints on the reactive and real components of the current. Additionally, such limits are based on predetermined fixed values as default values, where if the current exceeds the limit, the closed-loop control reduces the limit.

[0046] Figure 5Illustrated is the basic control of an IBR energy system connected to a utility system (e.g., a power grid), where the inverter is controlled via gate pulses from the PWM gating logic 142. The basic control provides a synchronization function to synchronize the inverter output waveform with the power utility waveform in both phase and frequency. The synchronization function is provided by detecting the phase of the measured voltage output from the power inverter in the phase detector 156. The output signal θ from the phase detector 156 T represents the phase of the voltage VT, which is the voltage supplied by the utility. The phase signal is supplied to a phase-locked loop (PLL) regulator 158 of a type well known in the art, and the phase-locked loop regulator 158 generates a phase-locked loop frequency output signal ω PLL . The signal ω PLL is supplied to an angle ramp generator 150, and the angle ramp generator 150 generates a phase-locked loop feedback signal θ PLL , and the phase-locked loop feedback signal θ PLL is supplied as a feedback signal to the PLL regulator 158. The phase-locked loop circuit including the PLL regulator and the angle ramp generator 150 is a conventional type of phase regulator well known in the art and provides a synchronization function to control the phase of the inverter terminal voltage E1. The signal θ from the phase detector 156 T is the angle between the reference and the terminal bus voltage V T . As long as the system operates in a steady state, the angle θ T and the angle θ PLL will be the same angle. Since Figure 5 the control is intended to operate in conjunction with the utility power, no separate independent frequency reference signal is supplied to the phase-locked loop.

[0047] The phase angle (“power angle”) signal provides a means for controlling the amount of real power supplied by the power inverter. More specifically, the amount of reactive power and the amount of real power coupled to the power grid through the transformer can be adjusted by controlling the phase angle θ1. The phase shift signal (δ IT ) generated by the inertia power regulator 168 is used to adjust the value of θ1 to change this angle and thereby control the amount of real power flowing through the transformer. The inertia power regulator 168 operates as an integrator on the power error signal P ERR and is also affected by the signal ω PLL supplied to the angle ramp generator 150. The phase shift signal (δ IT ) is added to the θ PLL signal at the adder 165 to produce θ1. The power error signal P ERR is the actual measured real power component Pfbk is generated by the difference between and the power reference P generated at the summing node 166, where the power reference signal P ref represents the desired power output of the inverter. The δ ref signal supplied to the inertial power regulator 168 controls the limit by which the value of (δ LIMIT ) can be varied to control the angle between V IT and E1. T

[0048] Still referring Figure 5 to, the frequency reference signal ω REF is supplied to the inertial power regulator 168 in combination with the coupling of the signal ω PLL from the phase-locked loop. The signal ω REF represents the desired frequency of the output voltage generated by the inverter and will typically represent a frequency of 60 Hz for use in the United States. During stable operation, the signal ω PLL represents the actual output voltage frequency.

[0049] Figure 6 depicts an embodiment in accordance with aspects of the present method and system, where the IBR system operates as a virtual synchronous machine (VSM) under grid-forming mode (GFM) control, where a compensation signal based on the power error signal (P err ) is generated and applied to modify a phase shift signal (v err ) that is a function of the change in the power error signal (P IT ).

[0050] Still referring Figure 6 to, the inertial power regulator ( Figure 5 168 in) includes an inertia regulator 184 that modifies the power error signal P err to simulate the inertia of a synchronous machine, thereby providing VSM control functionality. More particularly, the inertia regulator 184 prevents sudden frequency changes or power changes that could result in transient torques generated by motors coupled to the inverter output if a sudden change in the inverter output is experienced. The inertia regulator 184 includes a conventional electronic circuit having the characteristics of an integrator 185 in that its output signal increases gradually in response to an increase in the input signal.

[0051] The power reference signal P ω can be modified by a frequency bias circuit with a power offset signal (Δp REF ). The purpose of such modification is to adjust the power reference signal P REF as a function of frequency shift. More particularly, the system attempts to keep the system output frequency constant such that if there is an error between the output frequency and the reference frequency, the power reference signal P REF is adjusted to compensate for the frequency error. Further, the power system to which the inverter is coupled may include reactive loads such as AC induction and synchronous motors, the speed of which is directly related to the frequency of the inverter output signal. If additional power is supplied from the inverter, the machines will tend to accelerate, while a reduction in power will cause the frequency to drop, due to their inductive reaction as the machines start to decelerate. Thus, the frequency bias circuit provides an important function in achieving control of the torque output of machines coupled to the inverter output.

[0052] The synthesized signal identified as P ORD is generated at the output terminal of the summing circuit 180 and is applied to the summing circuit 182, in which the commanded power or set power is compared with the measured output power P B (true power generated at the inverter output). The output signal from the summing circuit 182 represents the power error signal applied to the inertia regulator 184. As described above, the signal generated by the inertia regulator represents the desired frequency ω1 of the internal voltage E1, and if the frequency is correctly tracked, this signal will be the same as the frequency ωPLL. In this regard, the signal ω1 generated at the output of the inertia regulator 184 is summed with ω PLL signal at the summing node 186. Any difference between the phase-locked loop frequency and the signal ω1 results in an error signal that is applied to the integrator 188 to generate the phase shift signal (δIT) described above with reference to Figure 5 .

[0053] The integrator 188 is an integrator of the conventional type, the output signal of which (δ IT ) is an angular offset which, according to aspects of the present invention, is summed with a compensation signal based on the power error signal (Perr) to modify the phase shift signal (δIT) as a function of the variation of the power error signal (Perr).

[0054] In the Figure 6 depicted embodiment, the compensation signal includes a power angle compensation signal (δPerr cmp) which is applied to the phase shift signal (δIT) to generate a phase shift signal (δIT-Perr) adjusted for the power error received by the inverter controller in the IBR system. The power angle compensation signal (δPerr_cmp) can be derived as a function of the power error signal (Perr) input to the inertia power regulator at 190 according to the following formula: (δPerr_cmp) = Perr2δ()*Perr =(kp * Perr) / (1 + s * T) kp = Tunable gain parameter (constant or dynamically adjusted) T = Filter time constant Perr = Power error signal.

[0055] Figure 7 An embodiment is depicted in which the compensation signal includes a frequency compensation signal (ωPerr_cmp), and the frequency compensation signal (ωPerr_cmp) is applied to the phase - locked loop frequency (ωPLL) (as discussed regarding Figure 5 to generate a phase - locked loop frequency signal (ωPLL - Perr) adjusted by the power error received by the inertial power regulator. The frequency compensation signal (ωPerr_cmp) can be derived as a function of the power error signal (Perr) input to the inertial power regulator at 190 according to the following formula: (ωPerr_cmp)=Perr2ω()*Perr =(kp * s * Perr) / (1 + s * T) kp = Tunable gain parameter (constant or dynamically adjusted) T = Filter time constant Perr = Power error signal.

[0056] This written description uses examples to disclose the invention (including the best mode), 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 non - material differences from the literal language of the claims, then it is intended that such other examples be within the scope of the claims.

[0057] Additional aspects of the invention are provided by the subject matter of the following clauses:

[0058] Clause 1: A method for continuously operating renewable energy, the renewable energy having an inverter-based resource (IBR) system connected to a power grid, wherein the method minimizes the impact of transient power events from the power grid. The method includes: operating the IBR system as a virtual synchronous machine (VSM) under grid-forming mode (GFM) control; deriving a power error signal (Perr) between the real power output (Pfbk) from the IBR system and a power reference (Pref) representing the desired power output of the IBR system; using an inertial power regulator with integral characteristics to generate an internal frequency signal (ω1) using the power error signal (Perr), and generating a phase shift signal (δIT) using the internal frequency signal (ω1), the phase shift signal (δIT) being applied to a power angle command signal used by an inverter controller in the IBR system; and generating a compensation signal based on the power error signal (Perr) via a control function having at least one of proportional, derivative, or washout characteristics, and applying the compensation signal to modify the internal frequency signal (ω1) or the phase shift signal (δIT), thereby providing an additional mechanism for regulating the relationship between active power, frequency, and power angle.

[0059] Clause 2: The method according to Clause 1, wherein the renewable energy is a wind turbine power system.

[0060] Clause 3: The method according to any one of Clauses 1-2, wherein the IBR system includes a doubly-fed induction generator (DFIG).

[0061] Clause 4: The method according to any one of Clauses 1-3, wherein the renewable energy is a battery energy storage system (BESS).

[0062] Clause 5: The method according to any one of Clauses 1-4, wherein the renewable energy is a solar power generation system or a hydroelectric power generation system.

[0063] Clause 6: The method according to any one of Clauses 1-5, wherein the method minimizes the impact of transient power events from the power grid, and the transient power events include any one or combination of the following: low voltage event, high voltage event, multi-fault event, phase jump event, or frequency offset event.

[0064] Clause 7: The method according to any one of Clauses 1-6, wherein the compensation signal includes a frequency compensation signal (ωPerr_cmp), and the frequency compensation signal (ωPerr_cmp) is applied to a phase-locked loop frequency (ωPLL) to generate a phase-locked frequency signal (ωPLL-Perr) adjusted by the power error received by the inertial power regulator.

[0065] Clause 8: The method according to any one of Clauses 1-7, wherein the frequency compensation signal (ωPerr_cmp) is derived as a function of the power error signal (Perr) input to the inertial power regulator according to the following formula: (ωPerr_cmp) = Perr2ω() * Perr = (kp * s * Perr) / (1 + s * T) kp = adjustable gain parameter (constant or dynamically adjusted) T = filter time constant Perr = power error signal.

[0066] Clause 9: The method according to any one of Clauses 1-8, wherein the compensation signal includes a power angle compensation signal (δPerr_cmp), and the power angle compensation signal is applied to the phase shift signal (δIT) to generate a phase shift signal (δIT-Perr) adjusted by the power error received by the inverter controller in the IBR system.

[0067] Clause 10: The method according to any one of Clauses 1-9, wherein the power angle compensation signal (δPerr_cmp) is derived as a function of the power error signal (Perr) input to the inertial power regulator according to the following formula: (δPerr_cmp) = Perr2δ() * Perr = (kp * Perr) / (1 + s * T) kp = adjustable gain parameter (constant or dynamically adjusted) T = filter time constant Perr = power error signal.

[0068] Clause 11: The method according to any one of Clauses 1-10 further includes setting limits and gains for the compensation signal and dynamically adjusting the limits and the gains or maintaining the limits and the gains constant based on the type of event detected on the power grid.

[0069] Clause 12: A renewable energy source connected to a power grid, comprising: an inverter-based resource (IBR) system; a controller for controlling the IBR system, the controller including a processor configured to perform a plurality of operations, the plurality of operations including: operating the IBR system as a virtual synchronous machine (VSM) under grid-forming mode (GFM) control; deriving a power error signal (Perr) between an actual power output (Pfbk) from the IBR system and a power reference (Pref) representative of a desired power output of the IBR system; using an inertial power regulator having an integral characteristic to generate an internal frequency signal (ω1) using the power error signal (Perr), generating a phase shift signal (δIT) using the internal frequency signal (ω1), the phase shift signal (δIT) being applied to a power angle command signal used by an inverter controller in the IBR system; and generating a compensation signal based on the power error signal (Perr) via a control function having at least one of proportional, derivative, or washout characteristics, and applying the compensation signal to modify the internal frequency signal (ω1) or the phase shift signal (δIT) to provide an additional mechanism for regulating the relationship between active power, frequency, and power angle.

[0070] Clause 13: The renewable energy source according to Clause 12, wherein the renewable energy source includes a wind turbine power system, and wherein the IBR system includes a doubly-fed induction generator (DFIG).

[0071] Clause 14: The renewable energy source according to any one of Clauses 12 - 13, wherein the renewable energy source includes a battery energy storage system (BESS).

[0072] Clause 15: The renewable energy source according to any one of Clauses 12 - 14, wherein the renewable energy source includes a solar power generation system or a hydroelectric power generation system.

[0073] Clause 16: The renewable energy source according to any one of Clauses 12 - 15, wherein the plurality of operations includes deriving the compensation signal as a frequency compensation signal (ωPerr_cmp), the frequency compensation signal (ωPerr_cmp) being applied to a phase-locked loop frequency (ωPLL) to generate a phase-locked frequency signal (ωPLL-Perr) adjusted by the power error received by the inertial power regulator.

[0074] Clause 17: The renewable energy source according to any one of Clauses 12 - 16, wherein the frequency compensation signal (ωPerr_cmp) is derived as a function of the power error signal (Perr) input to the inertial power regulator according to the following formula: (ωPerr_cmp) = Perr2ω()*Perr =(kp * s * Perr) / (1 + s * T) kp = adjustable gain parameter (constant or dynamically adjusted) T = filter time constant Perr = power error signal.

[0075] Clause 18: The renewable energy according to any one of Clauses 12 - 17, wherein the plurality of operations includes deriving the compensation signal as a power angle compensation signal (δPerr_cmp), and the power angle compensation signal (δPerr_cmp) is applied to the phase shift signal (δIT) to generate a phase shift signal (δIT - Perr) adjusted by the power error received by the inverter controller in the IBR system.

[0076] Clause 19: The renewable energy according to any one of Clauses 12 - 18, wherein the power angle compensation signal (δPerr_cmp) is derived as a function of the power error signal (Perr) input to the inertial power regulator according to the following formula: (δPerr_cmp)=Perr2δ()*Perr =(kp * Perr) / (1 + s * T) kp = adjustable gain parameter (constant or dynamically adjusted) T = filter time constant Perr = power error signal.

[0077] Clause 20: The renewable energy according to any one of Clauses 12 - 19, wherein the plurality of operations further includes setting limits and gains for the compensation signal, and dynamically adjusting the limits and the gains or maintaining the limits and the gains constant based on the type of event detected on the power grid.

Claims

1. A method for operating a renewable energy source having an inverter-based resource (IBR) system connected to a power grid, wherein the method allows for regulating the relationship between active power, frequency, and power angle, the method comprising: Operating the IBR system as a virtual synchronous machine (VSM) under grid-forming mode (GFM) control; Deriving a power error signal (Perr) between the real power output (Pfbk) from the IBR system and a power reference (Pref) representative of the desired power output of the IBR system; Using an inertial power regulator having an integral characteristic to generate an internal frequency signal (ω1) using the power error signal (Perr), and generating a phase shift signal (δIT) using the internal frequency signal (ω1), the phase shift signal (δIT) being applied to a power angle command signal used by an inverter controller in the IBR system; And Generating a compensation signal based on the power error signal (Perr) via a control function having at least one of proportional, derivative, or washout characteristics, and applying the compensation signal to modify the internal frequency signal (ω1) or the phase shift signal (δIT), thereby providing an additional mechanism for regulating the relationship between active power, frequency, and power angle.

2. The method according to claim 1, wherein, The renewable energy source is a wind turbine power system.

3. The method according to claim 2, wherein, The IBR system includes a doubly-fed induction generator (DFIG).

4. The method according to claim 1, wherein, The renewable energy source is a battery energy storage system (BESS).

5. The method according to claim 1, wherein The renewable energy source is a solar power generation system or a hydroelectric power generation system.

6. The method according to claim 1, wherein, The method minimizes the impact of transient power events from the power grid, the transient power events including any one or combination of the following: low voltage events, high voltage events, multi-fault events, phase jump events, or frequency offset events.

7. The method according to claim 1, wherein The compensation signal includes a frequency compensation signal (ωPerr_cmp), the frequency compensation signal (ωPerr_cmp) being applied to a phase-locked loop frequency (ωPLL) to generate a phase-locked frequency signal (ωPLL-Perr) adjusted by the power error received by the inertial power regulator.

8. The method according to claim 7, wherein The frequency compensation signal (ωPerr_cmp) is derived as a function of the power error signal (Perr) input to the inertial power regulator according to the following formula: (ωPerr_cmp) = Perr2ω()*Perr = (kp*s*Perr) / (1 + s*T) kp = adjustable gain parameter (constant or dynamically adjusted) T = filter time constant Perr = power error signal.

9. The method according to claim 1, wherein, The compensation signal includes a power angle compensation signal (δPerr_cmp), the power angle compensation signal being applied to the phase shift signal (δIT) to generate a phase shift signal (δIT-Perr) adjusted by the power error received by the inverter controller in the IBR system.

10. The method according to claim 9, wherein, The power angle compensation signal (δPerr_cmp) is derived as a function of the power error signal (Perr) input to the inertial power regulator according to the following formula: (δPerr_cmp) = Perr2δ() * Perr = (kp * Perr) / (1 + s * T) kp = adjustable gain parameter (constant or dynamically adjusted) T = filter time constant Perr = power error signal.

11. The method according to claim 1, further comprising setting limits and gains for the compensation signal and dynamically adjusting the limits and the gains or maintaining the limits and the gains constant based on the type of event detected on the power grid.

12. A renewable energy source connected to a power grid, comprising: An inverter-based resource (IBR) system; A controller for controlling the IBR system, the controller including a processor configured to perform a plurality of operations, the plurality of operations including: Operating the IBR system as a virtual synchronous machine (VSM) under grid formation mode (GFM) control; Deriving a power error signal (Perr) between the real power output (Pfbk) from the IBR system and a power reference (Pref) representative of the desired power output of the IBR system; Using an inertial power regulator having an integral characteristic, using the power error signal (Perr) to generate an internal frequency signal (ω1), using the internal frequency signal (ω1) to generate a phase shift signal (δIT), the phase shift signal (δIT) being applied to a power angle command signal used by an inverter controller in the IBR system; and Generating a compensation signal based on the power error signal (Perr) via a control function having at least one of proportional, derivative, or washout characteristics, and applying the compensation signal to modify the internal frequency signal (ω1) or the phase shift signal (δIT), thereby providing an additional mechanism for regulating the relationship between active power, frequency, and power angle.

13. The renewable energy according to claim 12, wherein, The renewable energy source includes a wind turbine power system, wherein the IBR system includes a doubly-fed induction generator (DFIG).

14. The renewable energy according to claim 12, wherein, The renewable energy source includes a battery energy storage system (BESS).

15. The renewable energy according to claim 12, wherein, The renewable energy source includes a solar power generation system or a hydroelectric power generation system.

16. The renewable energy according to claim 12, wherein, The plurality of operations includes deriving the compensation signal as a frequency compensation signal (ωPerr_cmp), the frequency compensation signal (ωPerr_cmp) being applied to a phase-locked loop frequency (ωPLL) to generate a phase-locked frequency signal (ωPLL-Perr) adjusted by the power error received by the inertial power regulator.

17. The renewable energy according to claim 16, wherein, The frequency compensation signal (ωPerr_cmp) is derived as a function of the power error signal (Perr) input to the inertial power regulator according to the following formula: (ωPerr_cmp) = Perr2ω() * Perr = (kp * s * Perr) / (1 + s * T) kp = adjustable gain parameter (constant or dynamically adjusted) T = filter time constant Perr = power error signal.

18. The renewable energy according to claim 12, wherein, The plurality of operations includes exporting the compensation signal as a power angle compensation signal (δPerr_cmp), and the power angle compensation signal (δPerr_cmp) is applied to the phase shift signal (δIT) to generate a phase shift signal (δIT-Perr) adjusted by power error received by the inverter controller in the IBR system.

19. The renewable energy according to claim 18, wherein, The power angle compensation signal (δPerr_cmp) is derived as a function of the power error signal (Perr) input to the inertial power regulator according to the following formula: (δPerr_cmp) = Perr2δ() * Perr = (kp * Perr) / (1 + s * T) kp = adjustable gain parameter (constant or dynamically adjusted) T = filter time constant Perr = power error signal.

20. The renewable energy according to claim 12, wherein, The plurality of operations further includes setting limits and gains for the compensation signal, and dynamically adjusting the limits and the gains or maintaining the limits and the gains constant based on the type of event detected on the power grid.

Images