A method for improving the transient characteristics of wind turbines based on wind-storage integration

Abstract

This invention discloses a method for improving the transient characteristics of wind turbines based on wind-storage integration. Aiming to improve the grid adaptability and power quality of wind turbines, this invention adopts the following scheme: when the grid connection point voltage of the wind turbine is detected to be in a low-voltage ride-through state, the wind-storage integration system switches to low-voltage ride-through mode; when the grid connection point voltage of the wind turbine is detected to be in a high-voltage ride-through state, the wind-storage integration system switches to high-voltage ride-through mode; when there is no trigger signal, the wind-storage integration system is in power quality mode. The advantage is that it integrates the fault ride-through control algorithms and power quality control algorithms of energy storage and wind turbines based on the wind-storage integration hardware topology, achieving unified coordination of the wind-storage integration control system and improving the transient characteristics of the wind turbine.

Description

Technical Field

[0001] This invention relates to the field of power system security analysis technology, and in particular to a method for improving the transient characteristics of wind turbine units based on wind-storage integration. Background Technology

[0002] Changing the energy structure and increasing the proportion of clean energy sources such as wind power in the energy mix are important strategic measures to achieve "carbon peaking and carbon neutrality." With the increase in grid-connected wind power capacity, the power system is shifting from a strong grid to a weak grid, and its power quality problems are becoming increasingly prominent, mainly in the following three aspects: The randomness and intermittency of wind resources cause significant fluctuations in grid-connected wind power, forming harmonic sources; wind turbines control grid-connected power through power electronic components, and the nonlinear volt-ampere characteristics of these components inject a large number of high-order harmonics into the power system; the non-sinusoidal distribution of the magnetomotive force of doubly-fed generators causes them to generate harmonic electromotive forces while emitting fundamental electromotive force. On the other hand, changes in the traditional power system grid structure will also place higher demands on the transient characteristics of wind turbines, such as fault ride-through.

[0003] Currently, there has been considerable research on improving the power quality of wind power grid connection, which can be mainly summarized into the following two categories: installing a Unified Power Quality Conditioner (UPQC) or utilizing energy storage technology.

[0004] To address the transient issues that arise after wind turbines are connected to the grid, some researchers have added centralized energy storage devices to the power supply side. These devices are used to smooth out power output and compensate for harmonics and imbalances using energy storage converters, thereby improving power quality during wind power grid connection. Furthermore, centralized energy storage serves as an important means of power system frequency regulation to enhance system frequency stability. Other researchers have integrated energy storage systems into wind turbines, developing a unified coordination controller for frequency regulation and fault ride-through. This controller utilizes energy storage to address low-voltage and high-voltage ride-through requirements as well as power system frequency regulation needs, coordinating active power balance and reactive power support.

[0005] For example, a Chinese patent document, "Electromagnetic Transient Characteristic Simulation System and Method for High Voltage Ride-Through Characteristics of Direct-Drive Wind Fans," with publication number CN112186815A and publication date January 5, 2021, provides an electromagnetic transient characteristic simulation system and method for high voltage ride-through characteristics of direct-drive wind fans. The system includes a high voltage ride-through determination module for determining whether the direct-drive wind fan has entered a high voltage ride-through state and generating a high voltage ride-through trigger signal; a high voltage ride-through moment current locking module for determining whether the direct-drive wind fan has entered a high voltage ride-through state, and if so, processing the active current reference signal to obtain an active current high voltage ride-through moment locking value; a high voltage ride-through stage reactive current control module for outputting the reactive current command value of the high voltage ride-through state or the reactive current reference value of the normal state as the reactive current command value based on the high voltage ride-through trigger signal; and a high voltage ride-through stage active current control module for outputting the normal current reference value or the active current high voltage ride-through moment locking value as the active current command value based on the high voltage ride-through trigger signal. This system can accurately reproduce the high voltage ride-through characteristics of actual direct-drive wind fans. This invention only takes into account high voltage ride-through, but does not take into account low voltage and power system frequency regulation needs, nor does it coordinate active power balance and reactive power support, nor does it consider power quality issues. Summary of the Invention

[0006] This invention, based on integrated wind and energy storage equipment, aims to improve the grid adaptability and power quality of wind turbines. It proposes a method for enhancing the transient characteristics of wind turbines based on this integrated system. This method solves the problem of integrating control strategies for energy storage and wind turbines, avoids overcurrent in the grid-side converter and overcharging / over-discharging of the energy storage battery during low-voltage ride-through, simplifies the original high-voltage ride-through algorithm for wind turbines, smooths power fluctuations while meeting reactive current requirements, and can autonomously select compensation current in specific frequency bands based on the energy storage battery's state of charge, actual unbalanced current, and harmonic current content.

[0007] The above-mentioned technical problems of the present invention are mainly solved by the following technical solutions:

[0008] When the grid connection point voltage of the wind turbine is detected to be in low voltage ride-through mode, the wind-storage integrated system switches to low voltage ride-through mode, the grid-side converter injects reactive current into the power system, and the energy storage converter connects to the DC side of the unit.

[0009] When the grid connection point voltage of the wind turbine is detected to be in high voltage ride-through mode, the wind-storage integrated system switches to high voltage ride-through mode. The grid-side converter executes the pre-fault dispatch command or outputs the active power corresponding to the actual wind conditions, and the energy storage converter is connected to the AC side of the unit. When there is no trigger signal, the wind-storage integrated system is in power quality mode. The grid-side converter operates normally, and the energy storage converter is connected to the AC side of the unit to compensate for the harmonic components and unbalanced components output during normal operation of the unit.

[0010] This algorithm solves the problem of integrating control strategies for energy storage and wind turbines. It can avoid overcurrent in the grid-side converter of the wind turbine and overcharging / over-discharging of the energy storage battery during low-voltage ride-through. It can also autonomously select the compensation current in a specific frequency band based on the state of charge of the energy storage battery, the actual unbalanced current, and the harmonic current content.

[0011] Preferably, the hardware device of the improvement method includes a power grid, a transformer, a wind-storage converter, a wind turbine, and a battery. The power grid is connected to the high-voltage side of the transformer, the low-voltage side of the transformer is connected to the output terminal of the wind-storage converter, the energy input terminal of the wind-storage converter is connected to the wind turbine, and the energy storage input terminal of the wind-storage converter is connected to the battery. The wind-storage converter includes an AC / DC converter, a No. 1 DC / AC converter, a No. 2 DC / AC converter, a DC / DC converter, switch K2, and switch K3. The output terminal of the No. 1 DC / AC converter is connected to the low-voltage side of the transformer. The output of AC / DC converter 1 is connected to the input of DC / AC converter 1, which in turn is connected to the wind turbine. The output of DC / AC converter 2 is connected to the second terminal of switch K3, which is connected to the low-voltage side of the transformer. The input of DC / AC converter 2 is connected to the output of DC / DC converter 1, which is connected to the battery. The first terminal of switch K2 is connected to the output of AC / DC converter 2, and the second terminal of switch K2 is connected to the output of DC / DC converter 2. This hardware topology, combined with the algorithm of this invention, can significantly improve the grid adaptability and power quality of wind turbines.

[0012] Preferably, when the grid connection point voltage of the wind turbine is between 0.2 pu and 0.85 pu, the wind turbine is in low-voltage ride-through mode, and the control strategy switches to low-voltage ride-through mode. At this time, the reactive current command of the grid-side converter of the wind turbine is...

[0013]

[0014] In the formula, U represents the reference value of the dynamic reactive current injected into the system by the wind turbine in the low-voltage control mode of the integrated wind and energy storage system. t U is the grid connection point voltage. t It can also be represented as a per-unit value, I N K1 is the rated current of the wind turbine generator set, and K1 is the reactive current proportional coefficient of the wind turbine generator set. According to the standard, the value range of K1 is 1.5≤K1≤3.0.

[0015] The energy storage converter is connected to the DC side of the generator unit, and the control command for energy storage is:

[0016]

[0017] In the formula, K represents the active power injected into the DC bus by energy storage in controlled low-power mode. P1 and K i1 These are the PI parameters of the outer loop controller for the energy storage voltage. V dc These are the given and actual measured values ​​of the DC bus voltage, respectively. This algorithm can avoid overcharging / over-discharging of the wind turbine's energy storage battery during low-voltage breakdown.

[0018] Preferably, the K-based fuzzy controller... P1 Selection rules:

[0019] WhenU t When the value is NB: When the SOC value is NB, NS, O, PS, or PB, K P1 All values ​​are NB;

[0020] WhenU t When the value is NS: If the value of SOC is NB, then K P1 The value is NB; if the SOC value is NS, O, PS, or PB, then K P1 The value is NS;

[0021] WhenU t When the value is 0: If the value of SOC is NB, then K P1 The value is NB; if the SOC value is NS, then K P1 The value is NS; if SOC is 0, PS, or PB, then K P1 The value is 0;

[0022] WhenU t When the value is PS: If the value of SOC is NB, then K P1 The value is NB; if the SOC value is NS, then K P1 The value is NS; if SOC is 0, then K P1 The value is 0; if SOC is PS or PB, then K P1 The value is PS; when U t When the value is PB: If the value of SOC is NB, then K P1 The value is NB; if the SOC value is NS, then K P1 The value is NS; if SOC is 0, then K P1 The value is 0; if SOC is PS, then K P1 The value is PS; if the value of SOC is PB, then K P1 The value is PB;

[0023] Among them, U tThe voltage range of NB in ​​the fuzzy set is [0.2, 0.3), the voltage range of NS is [0.3, 0.4), the voltage range of O is [0.4, 0.6), the voltage range of PS is [0.6, 0.7), and the voltage range of PB is [0.7, 0.8]. The SOC range of NB in ​​the fuzzy set is [0.1, 0.3), the SOC range of NS is [0.3, 0.4), the SOC range of O is [0.4, 0.6), the SOC range of PS is [0.6, 0.7), and the SOC range of PB is [0.7, 0.9]. K is given in per-unit values. P1 The fuzzy set NB ranges from [0, 0.1), NS from [0.2, 0.3), O from [0.3, 0.4), PS from [0.4, 0.5), and PB from [0.5, 0.7]; the reference value for the active current of the grid-side converter is obtained.

[0024]

[0025] In the formula, This refers to the reference value of the active current of the wind turbine in the low-voltage control mode of the integrated wind and energy storage system; I max This refers to the maximum current limit for the grid-side converter; I gq For the reactive current on the grid side of the generating unit; I s1 It is the output current for energy storage.

[0026] The proportional coefficient of the outer loop controller for energy storage voltage using this algorithm is adaptively adjusted based on a fuzzy controller. This can prevent overcurrent in the grid-side converter of the wind turbine during low voltage run-through. Optimizing parameters through fuzzy control can also extend the service life of the integrated wind and energy storage system.

[0027] Preferably, when the grid connection point voltage of the wind turbine is 1.13 pu-1.3 pu, the wind turbine is in high voltage ride-through mode, the control strategy switches to high voltage ride-through mode, and the active and reactive current commands of the grid-side converter of the wind turbine maintain the reactive current command at the moment before the fault. Functional instructions The reactive current command of the energy storage system remains unchanged.

[0028]

[0029] In the formula, K2 is the reference value of the dynamic reactive current absorbed by the energy storage device in the wind-storage integrated system under the control high-penetration mode. K2 is the reactive current proportional coefficient of the wind turbine. According to the standard, the value range of K2 is K2≥1.5.

[0030] During high-voltage ride-through, the reference power for charging and discharging of the energy storage device during high-voltage ride-through, based on the aforementioned first-order low-pass filter, can be specifically expressed as follows:

[0031]

[0032] In the formula, P is the active power injected into the system by energy storage in controlled high-voltage mode. e To consider the wind turbine output power under the constraints of wind resource characteristics and rotor speed, T s This is a time constant related to the control delay of the wind turbine converter.

[0033] In this algorithm, the energy storage device needs to absorb dynamic reactive current and smooth active power fluctuations. The output power of the wind turbine controlled by the converter can be regarded as a delay element, which simplifies the high-throughput control strategy of the wind turbine itself and avoids overcurrent of the grid-side converter while meeting the reactive current requirements.

[0034] Preferably, when the grid voltage vector is oriented along the d-axis, the reference value of the active current of the energy storage converter is expressed as follows:

[0035]

[0036] In the formula, E represents the reference value of the active current injected into the system by the energy storage device in the high-voltage control mode of the wind-storage integrated system. gd The three-phase voltage at the wind turbine terminals is the d-axis voltage after Park transformation.

[0037] This algorithm, to a certain extent, mitigates power fluctuations and emphasizes the flow characteristics of active power during faults.

[0038] Preferably, when the per-unit value of the wind turbine is 0.85 pu-1.13 pu, the wind turbine is in power quality mode. When the three-phase current of the grid contains harmonic components and asymmetrical components, the expression in the three-phase stationary coordinate system is:

[0039]

[0040]

[0041]

[0042] In the formula, These are the effective values ​​of the positive and negative sequence components of the grid current at different frequency harmonics. Let ω0 be the initial phase of the grid current at different harmonics; n be the fundamental frequency of the system; C be the harmonic order; ω0 be the initial phase of the grid current at different harmonics; ω0 be the fundamental frequency of the system; n be the harmonic order; C ... abc-αβ The Clark transformation matrix representing constant power is specifically expressed as follows:

[0043]

[0044] In this algorithm, the Clark transformation converts vectors in the stationary coordinate system into vectors in the equivalent stationary two-phase coordinate system, which can ensure that the magnetic field potential is the same before and after.

[0045] Preferably, the expression for the grid current containing harmonic and asymmetric components in the two-phase stationary coordinate system is:

[0046]

[0047] Preferably, when the output capacity of the energy storage system is less than the calculated capacity, the energy storage system performs limited output compensation based on the actual unbalanced current and harmonic current content. The system SOC calculation method can be expressed as follows:

[0048]

[0049] In the formula, SOC ini t represents the system's current state of charge; t represents the discharge time; and C represents the battery capacity.

[0050] This algorithm is designed to calculate the state of charge of energy storage batteries, providing parameter support for power quality mode control strategies.

[0051] Preferably, the device includes a proportional resonant controller, and the algorithm of the proportional resonant controller is as follows:

[0052]

[0053] In the formula, V PR The output of the proportional resonant controller, when modulated with a triangular wave, generates the trigger pulse for the switching device; I err (s) represents the difference between the reference current and the actual current in the complex domain; nω0 represents the unbalanced current and harmonic current components to be compensated; ω c k is the frequency response width. rn The integral parameters are for the nth harmonic; the principle for determining the current compensation component based on the energy storage SOC is as follows:

[0054] When the SOC value range is (0, 20], the current compensation component is not taken;

[0055] When the SOC value ranges from (20, 30], the current compensation component is Max1;

[0056] When the SOC value ranges from (30, 40], the current compensation components are Max1 and Max2.

[0057] When the SOC value ranges from (40, 50], the current compensation components are Max1, Max2, and Max3.

[0058] When the SOC value range is (50, 60], the current compensation components are Max1, Max2, Max3 and Max4.

[0059] When the SOC value range is (60, 70], the current compensation components are Max1, Max2, Max3, Max4, and Max5.

[0060] When the SOC value range is (70, 80], the current compensation components are Max1, Max2, Max3, Max4, Max5, and Max6.

[0061] When the SOC value range is (80, 100), the current compensation component takes all values;

[0062] Among them, Max1 is the current component with the highest content in the harmonics; Max2 is the current component with the highest content in the harmonics after removing Max1; Max3 is the current component with the highest content in the harmonics after removing Max1 and Max2; Max4 is the current component with the highest content in the harmonics after removing Max1, Max2 and Max3; Max5 is the current component with the highest content in the harmonics after removing Max1, Max2, Max3 and Max4; and Max6 is the current component with the highest content in the harmonics after removing Max1, Max2, Max3, Max4 and Max5.

[0063] This algorithm autonomously selects the compensation current in a specific frequency band based on the energy storage battery's state of charge, actual unbalanced current, and harmonic current content. This improves the unit's transient characteristics while extending the service life of the integrated wind and energy storage system.

[0064] The beneficial effects of this invention are:

[0065] 1. Based on the integrated wind and energy storage hardware topology, the fault ride-through control algorithm and power quality control algorithm of energy storage and wind turbine are integrated to realize the unified coordination of the integrated wind and energy storage control system and improve the transient characteristics of wind turbine.

[0066] 2. During the low-voltage ride-through process, an adaptive fuzzy controller is established based on the capacity of the grid-side converter of the wind turbine and the state of charge of the energy storage battery to avoid overcurrent of the grid-side converter of the wind turbine and overcharging / over-discharging of the energy storage battery during the low-voltage ride-through process, thereby extending the service life of the wind-storage integrated system.

[0067] 3. The high-voltage ride-through control strategy using energy storage devices simplifies the high-voltage ride-through control strategy of the wind turbine itself. While meeting the reactive current requirements, it avoids overcurrent in the grid-side converter. Furthermore, the algorithm mitigates power fluctuations to a certain extent and emphasizes the flow characteristics of active power during faults.

[0068] 4. When suppressing harmonic current and unbalanced current (power quality mode), the control strategy automatically selects the compensation current in a specific frequency band based on the state of charge of the energy storage battery, the actual unbalanced current, and the content of harmonic current. This improves the transient characteristics of the unit and extends the service life of the integrated wind and energy storage system. Attached Figure Description

[0069] Figure 1 This is a hardware topology diagram of the wind-storage integration method for improving the transient characteristics of wind turbine units based on the wind-storage integration of the present invention.

[0070] Figure 2 This is a flowchart of the joint control strategy for a wind turbine transient characteristic improvement method based on wind-storage integration, according to the present invention.

[0071] Figure 3 This is a control strategy diagram for an integrated wind and energy storage system based on a method for improving the transient characteristics of wind turbine units according to the present invention.

[0072] Figure 4 This is a schematic diagram of the unbalanced current and harmonic current detection principle of a wind turbine transient characteristic improvement method based on wind-storage integration according to the present invention.

[0073] In the diagram: 1. Power grid, 2. Transformer, 3. Wind-storage converter, 4. Wind turbine, 5. Battery. Detailed Implementation

[0074] The technical solution of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings.

[0075] Example:

[0076] This embodiment presents a method for improving the transient characteristics of wind turbine generators based on wind-storage integration, such as... Figure 1 As shown, including

[0077] When the wind turbine is detected to be in low voltage ride-through mode, the wind-storage integrated system switches to low voltage ride-through mode. The grid-side converter injects reactive current into the power system to support voltage recovery, and the energy storage converter is connected to the DC side of the unit to stabilize the DC bus voltage.

[0078] When a wind turbine is detected to be in high voltage ride-through mode, the wind-storage integrated system switches to high voltage ride-through mode. The grid-side converter executes the pre-fault scheduling command or outputs the active power corresponding to the actual wind conditions. The energy storage converter is connected to the AC side of the unit to absorb dynamic reactive current and smooth out active power fluctuations.

[0079] When there is no trigger signal, i.e., the wind turbine is not in fault ride-through mode, the integrated wind and energy storage system operates in power quality mode. The grid-side converter operates normally, and the energy storage converter is connected to the AC side of the turbine to compensate for the harmonic and unbalanced components output during normal turbine operation. Among them, the low-level ride-through mode is mode 1, the high-level ride-through mode is mode 2, and the power quality mode is mode 3.

[0080] In the three modes, the control strategies for grid-side converters and energy storage converters need to be selected based on the actual grid conditions, while the control strategy for generator-side converters can be any one of the current source or voltage source control strategies.

[0081] Hardware topology diagram of integrated wind and energy storage, such as Figure 1 As shown, wind turbine 4 is connected to wind-storage converter 3 as the energy input terminal, and battery 5 is connected to wind-storage converter 3 as the energy storage input terminal. The wind-storage converter 3 outputs 690V voltage and is connected to the low-voltage side of transformer 2. The high-voltage side of transformer 2 is connected to grid 1 through a 35kV (or 10kV) collector line. Wind-storage converter 3 includes an AC / DC converter, a No. 1 DC / AC converter, a No. 2 DC / AC converter, a DC / DC converter, switch K2, and switch K3. The output terminal of the No. 1 DC / AC converter is connected to the low-voltage side of transformer 2, and the output terminal of the AC / DC converter is connected to the input terminal of the No. 1 DC / AC converter. The input terminal of the AC / DC converter is connected to the wind turbine 4. The output terminal of the second DC / AC converter is connected to the second terminal of switch K3. The first terminal of switch K3 is connected to the low-voltage side of transformer 2. The input terminal of the second DC / AC converter is connected to the output terminal of the DC / DC converter. The input terminal of the DC / DC converter is connected to battery 5. The first terminal of switch K2 is connected to the output terminal of the DC / AC converter. The second terminal of switch K2 is connected to the output terminal of the DC / DC converter. When the system switches to mode 1, switch K2 is closed and switch K3 is open. When the system switches to mode 2 or mode 3, switch K3 is closed and switch K2 is open.

[0082] The flowchart of the joint control strategy is as follows: Figure 2 As shown, the process begins with the startup of the integrated wind and energy storage equipment. After the system starts, the voltage U at the wind turbine's grid connection point is monitored. t If there is no high-low voltage connection to the grid or a generator failure, the system will operate stably in mode 3. If a generator failure occurs, the integrated wind and energy storage system will shut down, and the process will end. If a high-low voltage connection to the grid occurs, the voltage U at the wind turbine's grid connection point needs to be determined. t If 0.85 < U t If U < 1.13, switch back to mode 3; if U t The condition 0.85 < U is not satisfied. t <1.13 but satisfies U t ≤0.85, while satisfying Ut If the value is less than 0.2, the integrated wind and storage equipment will shut down directly, and the system will terminate. However, if the value of U is met... t It satisfies ≤0.85 and 0.2≤U t The system will then switch to mode 1, and after implementing the algorithm strategy of mode 1, if U t If the value is greater than 0.9, the system will switch to mode 3. If U t If U ≤ 0.9, the system will switch back to the algorithm strategy of mode 1, and repeat this process; if U t The condition 0.85 < U is not satisfied. t <1.13 also does not satisfy U t ≤0.85 but satisfy U t If the value is greater than 1.3, the integrated wind and storage equipment will shut down directly, and the system will terminate. If the value is 1.13 ≤ U, the system will terminate. t If U is ≤1.3, the system will switch to mode 2. After the algorithm strategy of mode 2, if U t If the value is less than 1.08, the system will switch to mode 3; otherwise, it will switch to mode 2.

[0083] Wind energy storage integrated system control strategy, such as Figure 3 As shown in the figure, M1 represents mode 1, M2 represents mode 2, M3 represents mode 3, and the three-phase voltage E on the low-voltage side of transformer 3 is... gabc and the three-phase current I of the power grid gabc After Park transformation, it is converted into a two-phase voltage E. gdq and two-phase current I gdq Two-phase voltage E gdq and current I gdq Enter the PI parameters of the current inner loop controller. When the system mode is switched to mode 1, switch K2 is closed, switch K3 is open, and all switches in the diagram are switched to M1. The per-unit value in the upper right corner of the diagram is 0.8-U. t Then through the algorithm The reactive current command of the grid-side converter can be obtained. After algorithm Active current command can be obtained Reactive current command and active current command After passing through the inner current loop controller, the output two-phase voltage is... After Park transformation, it becomes a three-phase voltage. Three-phase voltage After PWM modulation, it serves as the switching signal for the DC / AC converter. When switch K2 is closed, the DC / AC converter and the DC / DC converter are connected, and the DC bus voltage setpoint is... Subtract the actual measured value of DC bus voltage V dcAfter passing through the adaptive PI controller, it is transformed into active power injected into the DC bus. After passing through the PI controller, it becomes After being modulated by PWM by a PI controller, it becomes the switching signal for the DC / DC converter. A capacitor is connected in parallel with the DC / AC converter, and the voltage across the capacitor is V. dc .

[0084] When the system mode switches to mode 2, switch K2 is open and switch K3 is closed. The active and reactive current commands of the grid-side converter maintain the reactive current command from the moment before the fault. Active current command Reactive current command and active current command After passing through the inner current loop controller, the output two-phase voltage is... After Park transformation, it becomes a three-phase voltage. Three-phase voltage After PWM modulation, it is used as the switching signal for the DC / AC converter. Reactive current command algorithm for energy storage system. Active current command algorithm for energy storage converter After passing through the inner current loop controller and undergoing PWM modulation, the signal is used as the switching signal for the DC / AC converter. A capacitor is connected in parallel with the DC / AC converter, and the voltage across the capacitor is V. dcs The current is I dcs Reference voltage value Subtract the actual voltage value V dcs After passing through the PI controller, it becomes After passing through a PI controller and being modulated by PWM, it becomes the switching signal for the DC / DC converter.

[0085] When the system mode switches to mode 3, switch K2 is open and switch K3 is closed. The reactive current command per unit value in mode 3 is 0, and the DC bus voltage setpoint is... Subtract the actual measured value of DC bus voltage V dc After passing through the PI controller, and then through the inner current loop controller, the two-phase voltage is output. After Park transformation, it becomes a three-phase voltage. Three-phase voltage After PWM modulation, it is used as a switching signal for the DC / AC converter. Reference voltage value. Subtract the actual voltage value V dcs After passing through the PI controller, it becomes After passing through a PI controller and being modulated by PWM, it serves as the switching signal for the DC / DC converter. The reference value i of the harmonic, reactive, and unbalanced negative sequence component compensation current in the wind-storage integrated system in the αβ coordinate system. αβh Subtract the actual value i αβs Generate I err (s), through the algorithm V PR V is the output of the proportional resonant controller. PR After being modulated by PMW, it serves as a DC / AC switching signal. A capacitor is connected in parallel with the DC / AC converter, and the voltage across the capacitor is V. dcs The current is I dcs .

[0086] 1. Low-profile penetration mode control strategy (Mode 1)

[0087] When a low-voltage ride-through is detected in the wind turbine, the control strategy switches to mode 1. At this time, the reactive current command for the wind turbine's grid-side converter is...

[0088]

[0089] In the formula, This refers to the reference value of the dynamic reactive current injected into the system by the wind turbine in the integrated wind and energy storage system under control mode 1; U t This refers to the grid connection point voltage or per-unit value; I N K1 is the rated current of the wind turbine generator set; K1 is the reactive current proportional coefficient of the wind turbine generator set. According to the standard, the value range of K1 is 1.5≤K1≤3.0.

[0090] The energy storage converter is connected to the DC side of the unit, and K2 is closed to stabilize the bus voltage. At this time, the control command for the energy storage is:

[0091]

[0092] In the formula, The active power injected into the DC bus by energy storage in controlled low-drive mode; K P1 and K i1 These are the PI parameters of the outer loop controller for the energy storage voltage; V dc These are the given value and the actual measured value of the DC bus voltage, respectively.

[0093] The lower the system voltage, the greater the reactive current that the wind turbine needs to inject into the system. If the energy storage discharges excessively, it will cause overcurrent in the grid-side converter, which is not conducive to the wind turbine completing low-voltage ride-through. When the supercapacitor state of charge (SOC) of the energy storage is too low, if the control coefficient remains unchanged, it is easy to cause over-discharge of the energy storage, which is not conducive to the safe and stable operation of the wind-storage integrated system. Therefore, the capacity of the wind turbine grid-side converter and the SOC of the energy storage battery (energy storage batteries are not limited to electrochemical energy storage, but also include mechanical and electromagnetic energy storage) should be considered simultaneously. The proportional coefficient of the outer loop controller of the energy storage voltage should be adaptively adjusted based on the fuzzy controller. The control rules are as follows:

[0094] Table 1. KP1 Selection Rules Based on Fuzzy Controller

[0095]

[0096] Among them, U t The voltage range of NB in ​​the fuzzy set is [0.2, 0.3), the voltage range of NS is [0.3, 0.4), the voltage range of O is [0.4, 0.6), the voltage range of PS is [0.6, 0.7), and the voltage range of PB is [0.7, 0.8]. The SOC range of NB in ​​the fuzzy set is [0.1, 0.3), the SOC range of NS is [0.3, 0.4), the SOC range of O is [0.4, 0.6), the SOC range of PS is [0.6, 0.7), and the SOC range of PB is [0.7, 0.9] (the SOC range should refer to the upper and lower limits of SOC specified by the battery manufacturer; this is just an example). K is given in per-unit value. P1 The fuzzy set has the following values: NB ([0, 0.1)), NS ([0.2, 0.3)), O ([0.3, 0.4)), PS ([0.4, 0.5)), and PB ([0.5, 0.7]). If the controller input is a named value, the rated voltage at the output of the energy storage DC / DC converter is used as the voltage reference value U. base The energy storage output power is the power reference value P. base Perform per-unit conversion of the baseline value to the parameter: such as K P1 When given a per-unit value of 0.1, it indicates that the output voltage of the DC / DC converter has increased by 0.2U. base At that time, the power reference value changed by 0.02P. base .

[0097] Finally, the reference value for the active current of the grid-side converter can be obtained.

[0098]

[0099] In the formula, This refers to the reference value of the active current of the wind turbine in the integrated wind and energy storage system under control mode 1; I max This refers to the maximum current limit for the grid-side converter; I gd For the reactive current on the grid side of the generating unit; I s1 It is the output current for energy storage.

[0100] 2. High Penetration Mode Control Strategy (Mode 2)

[0101] When a high-voltage ride-through is detected in the wind turbine, the control strategy switches to mode 2. At this time, the reactive and active current commands of the grid-side converter of the wind turbine maintain the reactive and active current commands from the moment before the fault. The reactive current command of the energy storage system remains unchanged.

[0102]

[0103] In the formula, K1 is the reference value of the dynamic reactive current absorbed by the energy storage device in the wind-storage integrated system under control mode 2; K2 is the reactive current proportional coefficient of the wind turbine, and according to the standard, the value range of K2 is K2≥1.5.

[0104] During high-voltage ride-through, energy storage devices need to absorb dynamic reactive current while also smoothing active power fluctuations. The output power of the wind turbine controlled by the converter can be considered as a delay element. Therefore, the charging and discharging reference power of the energy storage device during high-voltage ride-through can be designed based on a first-order low-pass filter, which can be specifically expressed as follows:

[0105]

[0106] In the formula, P represents the active power injected into the system by energy storage under control mode 2. e To consider the wind resource characteristics and rotor speed constraints of the wind turbine output power; T s This is a time constant related to the control delay of the wind turbine converter.

[0107] When the grid voltage vector is oriented along the d-axis, the reference value of the active current of the energy storage converter can be expressed as:

[0108]

[0109] In the formula, E represents the reference value of the active current injected into the system by the energy storage device in the integrated wind and energy storage system under control mode 2. gd The three-phase voltage at the wind turbine terminals is the d-axis voltage after Park transformation.

[0110] 3. Power Quality Mode Control Strategy (Mode 3)

[0111] First, the synchronization rotation angle is determined based on the positive sequence voltage. Then, Park transformation is performed on the rotation angle to obtain the compensation current containing harmonics, reactive power, and unbalanced fundamental negative sequence components. Figure 4 As shown, the frequency division control of each harmonic and fundamental component is finally performed according to the capacity of the energy storage converter itself, so as to compensate for the finite number of current harmonics and current imbalance, and improve the power quality of the unit.

[0112] exist Figure 4 In Chinese, dq -1 Represents the inverse dq transform; i dq This represents active and reactive current in DC form, and the current contains harmonics (the harmonics originate from i). αβ (Harmonics, reactive power, and unbalanced negative sequence components); LPF (Low Pass Filter) is a low-pass filter; i dq-dc The active and reactive currents are DC currents without harmonics; i αβh This is the reference value of the compensation current for harmonics, reactive power, and unbalanced negative sequence components in the wind-storage integrated system in the αβ coordinate system.

[0113] The method for extracting positive-sequence voltage after filtering out AC components is not limited, but the extraction of positive-sequence voltage should consider the phase-locking deviation caused by three-phase voltage imbalance, voltage harmonics, voltage amplitude and frequency abrupt changes in phase angle; when the three-phase current of the power grid contains harmonic and asymmetrical components, the expression in the three-phase stationary coordinate system is:

[0114]

[0115]

[0116]

[0117] In the formula, These are the effective values ​​of the positive and negative sequence components of the grid current at different frequency harmonics. Let ω0 be the initial phase of the grid current at different harmonics; n be the fundamental frequency of the system; C be the harmonic order; ω0 be the initial phase of the grid current at different harmonics; ω0 be the fundamental frequency of the system; n be the harmonic order; C ... abc-αβ The Clark transformation matrix representing constant power is specifically expressed as follows:

[0118]

[0119] Therefore, the expression for the grid current containing harmonic and asymmetric components in the two-phase stationary coordinate system is:

[0120]

[0121] Since PI controllers can only track DC components by reducing errors and cannot track AC components, proportional resonant controllers can be used to track the aforementioned AC quantities.

[0122] In this control mode, the SOC of the energy storage system also needs to be considered: when the output capacity of the energy storage system is greater than the calculated capacity to be compensated, the energy storage system directly follows the reference value of the compensation current; when the output capacity of the energy storage system is less than the calculated capacity, the energy storage system performs limited output compensation based on the actual unbalanced current and harmonic current content. The system SOC calculation method can be expressed as follows:

[0123]

[0124] In the formula, SOC ini The system's current state of charge is t; the discharge time is t, which is set to 2s according to the standard GB / T 14549-1993 Power Quality Public Power Grid Harmonics. (This time can be reselected depending on different reference criteria.) The battery capacity is C.

[0125] The proportional resonant controller algorithm can be expressed as:

[0126]

[0127] In the formula, V PR The output of the proportional resonant controller, when modulated with a triangular wave, generates the trigger pulse for the switching device; I err (s) represents the difference between the reference current and the actual current in the complex domain; nω0 represents the unbalanced current and harmonic current components to be compensated; ω c To increase the frequency response width, the original gain range can be expanded; k rn Let be the integral parameter of the nth harmonic.

[0128] The control law between SOC and compensation current is shown in the table below. When SOC is below 20%, no current compensation is performed. When SOC is above 80%, all unbalanced currents and harmonic currents are compensated. That is, the energy storage system directly follows the reference value of the compensation current.

[0129] Table 2. Principles for Determining Current Compensation Components Based on Energy Storage SOC

[0130]

[0131] In the table, Max1 is the highest current component in the harmonics; Max2 is the highest current component in the harmonics after removing Max1; Max3 is the highest current component in the harmonics after removing Max1 and Max2; Max4 is the highest current component in the harmonics after removing Max1, Max2, and Max3; Max5 is the highest current component in the harmonics after removing Max1, Max2, Max3, and Max4; and Max6 is the highest current component in the harmonics after removing Max1, Max2, Max3, Max4, and Max5.

[0132] This invention uses grid connection point voltage as the switching condition between the fault ride-through control algorithm and the power quality control algorithm, and proposes three control strategies: low-voltage ride-through mode control strategy, high-voltage ride-through mode control strategy, and power quality mode control strategy. The low-voltage ride-through mode control strategy avoids overcurrent in the wind turbine grid-side converter and overcharging / over-discharging of the energy storage battery during low-voltage ride-through. The high-voltage ride-through mode control strategy simplifies the original high-voltage ride-through algorithm for wind turbines, smoothing power fluctuations while satisfying reactive current requirements. The power quality mode control strategy autonomously selects compensation current in a specific frequency band based on the energy storage battery's state of charge, actual unbalanced current, and harmonic current content.

[0133] It should be understood that the embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for improving the transient characteristics of wind turbine generators based on wind-storage integration, characterized in that, When the grid connection point voltage of the wind turbine is detected to be in low voltage ride-through mode, that is, when the per-unit value of the grid connection point voltage of the wind turbine is 0.2pu-0.85pu, the wind-storage integrated system switches to low voltage ride-through mode, the grid-side converter injects reactive current into the power system, and the energy storage converter is connected to the DC side of the unit. In the wind-storage integrated system, the reference value of the dynamic reactive current injected into the system by the wind turbine in the low-voltage ride-through mode is obtained by multiplying the wind turbine's reactive current proportional coefficient K1 (0.8) by the difference between the per-unit value of the grid connection voltage and the rated current of the wind turbine, where 1.5 ≤ K1 ≤ 3.

0. The active power injected into the DC bus by the energy storage in the low-voltage ride-through mode is obtained by multiplying the difference between the DC bus voltage setpoint and the actual measured value by the transfer function of the energy storage voltage outer loop controller. When the grid connection voltage of the wind turbine is detected to be in a high-voltage ride-through state, i.e., when the per-unit value of the grid connection voltage of the wind turbine is 1.13pu-1.3pu, the wind-storage integrated system switches to the high-voltage ride-through mode. The grid-side converter executes the pre-fault scheduling command or outputs the active power corresponding to the actual wind conditions. The energy storage converter connects to the AC side of the unit, and the active and reactive current commands of the wind turbine's grid-side converter maintain the reactive power command at the moment before the fault. Functional instructions constant; When there is no trigger signal, the wind-storage integrated system is in power quality mode. The grid-side converter operates normally, and the energy storage converter is connected to the AC side of the unit to compensate for the harmonic and unbalanced components output during normal unit operation.

2. The method for improving the transient characteristics of wind turbine units based on wind-storage integration according to claim 1, characterized in that, The hardware device for the aforementioned boosting method includes a power grid, a transformer, a wind-storage converter, a wind turbine, and a battery. The power grid is connected to the high-voltage side of the transformer, the low-voltage side of the transformer is connected to the output terminal of the wind-storage converter, the energy input terminal of the wind-storage converter is connected to the wind turbine, and the energy storage input terminal of the wind-storage converter is connected to the battery. The wind-storage converter includes an AC / DC converter, a No. 1 DC / AC converter, a No. 2 DC / AC converter, a DC / DC converter, a switch K2, and a switch K3. The output terminal of the No. 1 DC / AC converter is connected to the low-voltage side of the transformer, the output terminal of the AC / DC converter is connected to the input terminal of the No. 1 DC / AC converter, the input terminal of the AC / DC converter is connected to the wind turbine, the output terminal of the No. 2 DC / AC converter is connected to the second terminal of switch K3, the first terminal of switch K3 is connected to the low-voltage side of the transformer, the input terminal of the No. 2 DC / AC converter is connected to the output terminal of the DC / DC converter, the input terminal of the DC / DC converter is connected to the battery, the first terminal of switch K2 is connected to the output terminal of the AC / DC converter, and the second terminal of switch K2 is connected to the output terminal of the DC / DC converter.

3. The method for improving the transient characteristics of wind turbine units based on wind-storage integration according to claim 1, characterized in that, When the grid connection voltage per unit value of the wind turbine is 0.2 pu-0.85 pu, the wind turbine is in low voltage ride-through mode, and the control strategy switches to low-voltage ride-through mode. At this time, the reactive current command of the grid-side converter of the wind turbine is... In the formula, U represents the reference value of the dynamic reactive current injected into the system by the wind turbine in the low-voltage control mode of the integrated wind and energy storage system. i I is the per-unit value of the grid connection point voltage. N K1 is the rated current of the wind turbine generator set, and K1 is the reactive current proportional coefficient of the wind turbine generator set. According to the standard, the value range of K1 is 1.5≤K1≤3.

0. The energy storage converter is connected to the DC side of the generator unit, and the control command for energy storage is: In the formula, K represents the active power injected into the DC bus by energy storage in controlled low-power mode. P1 and K i1 These are the PI parameters of the outer loop controller for the energy storage voltage. V dc These are the given value and the actual measured value of the DC bus voltage, respectively.

4. The method for improving the transient characteristics of wind turbine units based on wind-storage integration according to claim 3, characterized in that, K-based fuzzy controller P1 Selection rules: When U i When the value is NB: When the SOC value is NB, NS, O, PS, or PB, K P1 All values ​​are NB; WhenU i When the value is NS: If the value of SOC is NB, then K P1 The value is NB; if the SOC value is NS, O, PS, or PB, then K P1 The value is NS; When U i When the value is 0: If the value of SOC is NB, then K P1 The value is NB; if the SOC value is NS, then K P1 The value is NS; if SOC is 0, PS, or PB, then K P1 The value is 0; WhenU i When the value is PS: If the value of SOC is NB, then K P1 The value is NB; if the SOC value is NS, then K P1 The value is NS; if SOC is 0, then K P1 The value is 0; if SOC is PS or PB, then K P1 The value is PS; When U i When the value is PB: If the value of SOC is NB, then K P1 The value is NB; if the SOC value is NS, then K P1 The value is NS; if SOC is 0, then K P1 The value is 0; if SOC is PS, then K P1 The value is PS; if the value of SOC is PB, then K P1 The value is PB; Among them, U i The voltage range of NB in ​​the fuzzy set is [0.2, 0.3), the voltage range of NS is [0.3, 0.4), the voltage range of O is [0.4, 0.6), the voltage range of PS is [0.6, 0.7), and the voltage range of PB is [0.7, 0.8]. The SOC range of NB in ​​the fuzzy set is [0.1, 0.3), the SOC range of NS is [0.3, 0.4), the SOC range of O is [0.4, 0.6), the SOC range of PS is [0.6, 0.7), and the SOC range of PB is [0.7, 0.9]. K is given in per-unit values. P1 The fuzzy set NB ranges from [0, 0.1), NS from [0.2, 0.3), O from [0.3, 0.4), PS from [0.4, 0.5), and PB from [0.5, 0.7]; the reference value for the active current of the grid-side converter is obtained. In the formula, This refers to the reference value of the active current of the wind turbine in the low-voltage control mode of the integrated wind and energy storage system; I max This refers to the maximum current limit for the grid-side converter; I gq For the reactive current on the grid side of the generating unit; I s1 It is the output current for energy storage.

5. The method for improving the transient characteristics of wind turbine units based on wind-storage integration according to claim 1, characterized in that, When the grid connection voltage per unit value of the wind turbine is 1.13 pu-1.3 pu, the wind turbine is in high voltage ride-through mode, and the control strategy switches to high voltage ride-through mode. The active and reactive current commands of the grid-side converter of the wind turbine maintain the reactive current command at the moment before the fault. Functional instructions The reactive current command of the energy storage system remains unchanged. In the formula, K2 is the reference value for the dynamic reactive current absorbed by the energy storage device in the wind-storage integrated system under controlled high-voltage mode. K2 is the reactive current proportional coefficient of the wind turbine. According to the standard, the range of K2 is K2≥1.

5. i This is the per-unit value of the grid connection point voltage; During high-voltage ride-through, the reference power for charging and discharging of the energy storage device during high-voltage ride-through, based on the aforementioned first-order low-pass filter, can be specifically expressed as follows: In the formula, P is the active power injected into the system by energy storage in controlled high-voltage mode. g To consider the wind turbine output power under the constraints of wind resource characteristics and rotor speed, T s This is a time constant related to the control delay of the wind turbine converter.

6. The method for improving the transient characteristics of wind turbine units based on wind-storage integration according to claim 5, characterized in that, When the grid voltage vector is oriented along the d-axis, the reference value of the active current of the energy storage converter is expressed as follows: In the formula, E represents the reference value of the active current injected into the system by the energy storage device in the high-voltage control mode of the wind-storage integrated system. gd The three-phase voltage at the wind turbine terminals is the d-axis voltage after Park transformation.

7. The method for improving the transient characteristics of wind turbine units based on wind-storage integration according to claim 1, characterized in that, The grid connection voltage per unit value for wind turbine generators is 0.85 pu- At 1.13 pu, the wind turbine is in power quality mode. When the three-phase grid current contains harmonic and asymmetrical components, the expression in the three-phase stationary coordinate system is: In the formula, These are the effective values ​​of the positive and negative sequence components of the grid current at different frequency harmonics. Let ω0 be the initial phase of the grid current at different harmonics; n be the fundamental frequency of the system; C be the harmonic order; ω0 be the initial phase of the grid current at different harmonics; ω0 be the fundamental frequency of the system; n be the harmonic order; C ... abc-αβ The Clark transformation matrix representing constant power is specifically expressed as follows:

8. The method for improving the transient characteristics of wind turbine units based on wind-storage integration according to claim 7, characterized in that, The expression for the grid current containing harmonic and asymmetrical components in a two-phase stationary coordinate system is as follows:

9. The method for improving the transient characteristics of wind turbine units based on wind-storage integration according to claim 8, characterized in that, When the output capacity of the energy storage system is less than the calculated capacity, the energy storage system performs limited output compensation based on the actual unbalanced current and harmonic current content. The system's State of Charge (SOC) calculation method can be expressed as follows: In the formula, SOC ini t represents the system's current state of charge; t represents the discharge time; and C represents the battery capacity.

10. A method for improving the transient characteristics of wind turbine units based on wind-storage integration according to claim 7, characterized in that, The algorithm for the proportional resonant controller is as follows: In the formula, V PR V is the output of the proportional resonant controller. PR Modulation with a triangular wave can generate trigger pulses for switching devices; I err (s) represents the difference between the reference current and the actual current in the complex domain; nω0 represents the unbalanced current and harmonic current components to be compensated. ω2 is the frequency response width; k rn The integral parameters are for the nth harmonic; the principle for determining the current compensation component based on the energy storage SOC is as follows: When the SOC value range is (0, 20], the current compensation component is not taken; When the SOC value ranges from (20, 30], the current compensation component is Max1; When the SOC value ranges from (30, 40], the current compensation components are Max1 and Max2. When the SOC value ranges from (40, 50], the current compensation components are Max1, Max2, and Max3. When the SOC value range is (50, 60], the current compensation components are Max1, Max2, Max3 and Max4. When the SOC value range is (60, 70], the current compensation components are Max1, Max2, Max3, Max4, and Max5. When the SOC value range is (70, 80], the current compensation components are Max1, Max2, Max3, Max4, Max5, and Max6. When the SOC value range is (80, 100), the current compensation component takes all values; Among them, Max1 is the current component with the highest content in the harmonics; Max2 is the current component with the highest content in the harmonics after removing Max1; Max3 is the current component with the highest content in the harmonics after removing Max1 and Max2; Max4 is the current component with the highest content in the harmonics after removing Max1, Max2 and Max3; Max5 is the current component with the highest content in the harmonics after removing Max1, Max2, Max3 and Max4; and Max6 is the current component with the highest content in the harmonics after removing Max1, Max2, Max3, Max4 and Max5.

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