A method and device for coordinated control of a doubly-fed wind turbine during low voltage ride through

Abstract

The application discloses a kind of low voltage ride through during the cooperative control method and device of double-fed fan. Among them, method includes: during low voltage ride through, set system damping ratio as 0.8, natural frequency is 10Hz, determine the PI controller parameter of RSC current inner loop;According to the pre-set GSC coefficient value range and the constraint that GSC ratio stator reaches output power limit first, determine GSC coefficient;According to the GSC output reactive power of set GSC coefficient output and the stator output reactive power of set PI controller parameter, determine the reactive power of double-fed fan.

Description

Technical Field

[0001] This invention relates to the field of doubly-fed induction generator (DFIG) technology, and more specifically, to a method and apparatus for coordinated control of DFIGs during low-voltage ride-through. Background Technology

[0002] Currently, the use of crowbar and other measures to suppress rotor overcurrent is a common strategy for low voltage ride-through (LVRT) control of DFIGs. While active crowbars can theoretically shorten the activation time under existing strategies, in practice, repeated crowbar activation can lead to a longer actual activation time. This phenomenon stems from factors such as the low damping of the existing RSC system and the lack of optimization of the natural frequency. When the crowbar is disconnected, the rotor will again experience overcurrent, and the overshoot cannot be ignored. Therefore, it is necessary to improve the current controller parameters to optimize system characteristics. During the crowbar activation period, the RSC is out of operation, the rotor cannot be controlled, and the doubly-fed induction generator (DFIG) cannot output reactive power to the grid; instead, it absorbs some reactive power (at this time, the DFIG is equivalent to an asynchronous motor with a large slip). This is detrimental to grid voltage recovery. When the crowbar is disconnected and the RSC is reactivated, the DFIG can still only output reactive power through the stator. Therefore, it is evident that the reactive power output strategy should be improved to enhance the reactive power output capability of the DFIG during LVRT. The main challenges of low voltage ride-through for existing doubly fed wind turbines are as follows: first, the crowbar may be repeatedly switched on and off; second, under LVRT conditions, the wind turbine cannot output sufficient reactive power. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a collaborative control method and apparatus for doubly fed wind turbines during low voltage ride-through.

[0004] According to one aspect of the present invention, a method for coordinated control of a doubly-fed induction generator (DFIG) during low-voltage ride-through is provided, comprising:

[0005] During low voltage ride-through, the system damping ratio is set to 0.8 and the natural frequency is 10Hz. The PI controller parameters for the inner loop of the RSC current are then determined.

[0006] The GSC coefficient is determined based on the pre-set range of GSC coefficient values ​​and the constraint that GSC reaches the output power limit before the stator.

[0007] The reactive power of the doubly-fed induction generator (DFIG) is determined based on the GSC output reactive power with set GSC coefficients and the stator output reactive power with set PI controller parameters.

[0008] Optionally, the system damping ratio is set to 0.8, the natural frequency is 10Hz, and the PI controller parameters for the RSC current inner loop are determined, including:

[0009] Determine the stator inductance, rotor inductance, and magnetizing inductance based on the damping ratio and natural frequency.

[0010] Determine the PI controller parameters based on the stator inductance, rotor inductance, and magnetizing inductance.

[0011] Alternatively, the formulas for determining the stator inductance, rotor inductance, and magnetizing inductance based on the damping ratio and natural frequency are as follows:

[0012]

[0013]

[0014] Wherein, the natural frequency ω n =10, damping ratio ξ=0.8, L r For rotor inductance, L s For stator inductance, L m For the magnetizing inductance, k p k i For the PI controller parameters of the RSC current loop, k p k is the proportional coefficient. i The coefficients of the integral element.

[0015] Optionally, the formula for determining the PI controller parameters based on the stator inductance, rotor inductance, and magnetizing inductance is as follows:

[0016]

[0017]

[0018] Among them, L r For rotor inductance, L s For stator inductance, L m For the magnetizing inductance, k p k i For the PI controller parameters of the RSC current loop, k p k is the proportional coefficient. i The coefficients of the integral element.

[0019] Optionally, the GSC coefficient can take the following values:

[0020]

[0021] Among them, R s ω represents the stator resistance. s For synchronous speed, k gsc ks These are the coefficients for reactive power droop control on the GSC side and stator side, respectively. The larger the coefficient, the more reactive power is allocated. s For stator inductance, L m It is the magnetizing inductor.

[0022] Optionally, the constraint that the GSC reaches the output power limit before the stator is as follows:

[0023]

[0024] Among them, i glim i rlim These represent the allowable current limits on the rotor of the GSC, which are determined by the capacity of the equipment used. gsc k s These are the coefficients for reactive power droop control on the GSC side and the stator side, respectively. The larger the coefficient, the more reactive power is allocated.

[0025] According to another aspect of the present invention, a cooperative control device for a doubly-fed wind turbine during low-voltage ride-through is provided, comprising:

[0026] The first determining module is used to set the system damping ratio to 0.8 and the natural frequency to 10Hz during low voltage ride-through, and to determine the PI controller parameters of the RSC current inner loop.

[0027] The second determining module is used to determine the GSC coefficient based on the pre-set range of GSC coefficient values ​​and the constraint that the GSC reaches the output power limit before the stator.

[0028] The third determining module is used to determine the reactive power of the doubly-fed wind turbine based on the GSC output reactive power output by the set GSC coefficient and the stator output reactive power output by the set PI controller parameters.

[0029] According to another aspect of the present invention, a computer-readable storage medium is provided, the storage medium storing a computer program for performing the methods described in any of the above aspects of the present invention.

[0030] According to another aspect of the present invention, an electronic device is provided, the electronic device comprising: a processor; a memory for storing executable instructions of the processor; the processor being configured to read the executable instructions from the memory and execute the instructions to implement the method described in any of the preceding aspects of the present invention.

[0031] Therefore, this invention improves the RSC current loop PI controller parameters to enhance the system damping ratio and natural frequency, reducing rotor current overshoot after crowbar removal and preventing rotor current exceeding limits, thus solving the problem of repeated crowbar activation. Simultaneously, this invention employs a GSC-dominant reactive power output method, using stator-assisted reactive power output to improve the wind turbine's reactive power output capability in LVRT mode, thereby solving the problem of insufficient reactive power output. Attached Figure Description

[0032] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures:

[0033] Figure 1 This is a flowchart illustrating a cooperative control method for a doubly-fed wind turbine during low-voltage ride-through, provided by an exemplary embodiment of the present invention.

[0034] Figure 2 This is a schematic diagram of the DFIG topology provided in an exemplary embodiment of the present invention;

[0035] Figure 3 This is a schematic diagram of the equivalent model of DFIG after the crowbar is inserted, provided by an exemplary embodiment of the present invention;

[0036] Figure 4 This is a schematic diagram of the equivalent model of DFIG in the synchronous speed rotation dq coordinate system provided by an exemplary embodiment of the present invention;

[0037] Figure 5 This is a schematic diagram of a cooperative control strategy for a doubly-fed wind turbine during low-voltage ride-through provided by an exemplary embodiment of the present invention;

[0038] Figure 6 This is a schematic diagram of a cooperative control strategy for a doubly-fed wind turbine during low-voltage ride-through provided by an exemplary embodiment of the present invention, compared with the conventional approach;

[0039] Figure 7 This is a schematic diagram of an external DFIG system provided in an exemplary embodiment of the present invention;

[0040] Figure 8 This is a schematic diagram of the reactive power curve under a conventional strategy provided by an exemplary embodiment of the present invention;

[0041] Figure 9 This is a schematic diagram of the three-phase voltage curve under a conventional strategy provided by an exemplary embodiment of the present invention;

[0042] Figure 10 This is a schematic diagram of the reactive power curve output using an improved strategy provided in an exemplary embodiment of the present invention;

[0043] Figure 11 This is a schematic diagram of the terminal voltage of a doubly fed wind turbine employing an improved strategy, provided by an exemplary embodiment of the present invention;

[0044] Figure 12 This is a schematic diagram of the structure of a cooperative control device for a doubly fed wind turbine during low voltage ride-through provided in an exemplary embodiment of the present invention;

[0045] Figure 13 This is the structure of an electronic device provided in an exemplary embodiment of the present invention. Detailed Implementation

[0046] Hereinafter, exemplary embodiments according to the present invention will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments of the present invention. It should be understood that the present invention is not limited to the exemplary embodiments described herein.

[0047] It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention.

[0048] Those skilled in the art will understand that the terms "first," "second," etc., in the embodiments of the present invention are only used to distinguish different steps, devices, or modules, and do not represent any specific technical meaning, nor do they indicate a necessary logical order between them.

[0049] It should also be understood that in the embodiments of the present invention, "multiple" can refer to two or more, and "at least one" can refer to one, two or more.

[0050] It should also be understood that any component, data or structure mentioned in the embodiments of the present invention can generally be understood as one or more unless explicitly defined or given contrary instructions in the context.

[0051] Furthermore, the term "and / or" in this invention is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this invention generally indicates that the preceding and following related objects have an "or" relationship.

[0052] It should also be understood that the description of the various embodiments in this invention emphasizes the differences between the various embodiments, and the similarities or similarities can be referred to each other. For the sake of brevity, they will not be described in detail.

[0053] At the same time, it should be understood that, for ease of description, the dimensions of the various parts shown in the accompanying drawings are not drawn according to actual scale.

[0054] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use.

[0055] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, they should be considered part of the specification.

[0056] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures.

[0057] The embodiments of this invention can be applied to electronic devices such as terminal devices, computer systems, and servers, and can operate together with a wide range of other general-purpose or special-purpose computing system environments or configurations. Well-known examples of terminal devices, computing systems, environments, and / or configurations suitable for use with terminal devices, computer systems, servers, and other electronic devices include, but are not limited to: personal computer systems, server computer systems, thin clients, thick clients, handheld or laptop devices, microprocessor-based systems, set-top boxes, programmable consumer electronics, network PCs, minicomputer systems, mainframe computer systems, and distributed cloud computing environments including any of the above systems, etc.

[0058] Electronic devices such as terminal devices, computer systems, and servers can be described in the general context of computer system executable instructions (such as program modules) executed by a computer system. Typically, program modules can include routines, programs, object programs, components, logic, data structures, etc., which perform specific tasks or implement specific abstract data types. Computer systems / servers can be implemented in distributed cloud computing environments, where tasks are performed by remote processing devices linked through communication networks. In distributed cloud computing environments, program modules can reside on local or remote computing system storage media, including storage devices.

[0059] Exemplary methods

[0060] Figure 1 This is a schematic flowchart illustrating a cooperative control method for a doubly-fed induction generator (DFIG) during low-voltage ride-through, provided by an exemplary embodiment of the present invention. This embodiment can be applied to electronic devices, such as… Figure 1 As shown, the coordinated control method 100 for doubly-fed wind turbines during low-voltage ride-through includes the following steps:

[0061] Step 101: During the low voltage ride-through, set the system damping ratio to 0.8 and the natural frequency to 10Hz, and determine the PI controller parameters for the RSC current inner loop.

[0062] Step 102: Determine the GSC coefficient based on the pre-set range of GSC coefficient values ​​and the constraint that GSC reaches the output power limit before the stator.

[0063] Step 103: Determine the reactive power of the doubly-fed induction generator (DFIG) based on the GSC output reactive power of the set GSC coefficient and the stator output reactive power of the set PI controller parameters.

[0064] Optionally, the system damping ratio is set to 0.8, the natural frequency is 10Hz, and the PI controller parameters for the RSC current inner loop are determined, including:

[0065] Determine the stator inductance, rotor inductance, and magnetizing inductance based on the damping ratio and natural frequency.

[0066] Determine the PI controller parameters based on the stator inductance, rotor inductance, and magnetizing inductance.

[0067] Alternatively, the formulas for determining the stator inductance, rotor inductance, and magnetizing inductance based on the damping ratio and natural frequency are as follows:

[0068]

[0069]

[0070] Wherein, the natural frequency ω n =10, damping ratio ξ=0.8, L r For rotor inductance, L s For stator inductance, L m For the magnetizing inductance, k p k i For the PI controller parameters of the RSC current loop, k p k is the proportional coefficient. i The coefficients of the integral element.

[0071] The damping ratio of a second-order system is a parameter describing the damping effect during the vibration of a physical system. In a second-order system, vibration occurs at a certain frequency and amplitude, and the damping ratio describes the degree of energy loss during vibration. When the damping ratio is 0, the system vibration is not affected by damping, and energy is continuously recycled; when the damping ratio is greater than 0, the vibration gradually decreases, and energy is converted into other forms until it eventually disappears; when the damping ratio is greater than 1, the vibration gradually becomes smaller and smaller until it eventually stops; if the damping ratio is less than 0, the system will continuously absorb energy, causing instability.

[0072] The natural frequency of a second-order system refers to the frequency of the system's inherent vibrations when no external force is applied. The natural frequency is likened to the system's "natural frequency".

[0073] The typical transfer function of a second-order system is shown below:

[0074]

[0075] Optionally, the formula for determining the PI controller parameters based on the stator inductance, rotor inductance, and magnetizing inductance is as follows:

[0076]

[0077]

[0078] Among them, L r For rotor inductance, L s For stator inductance, L m For the magnetizing inductance, k p k i For the PI controller parameters of the RSC current loop, k p k is the proportional coefficient. i The coefficients of the integral element.

[0079] If the control system performs well, the PI controller can make the rotor current approach its command value.

[0080] Optionally, the GSC coefficient can take the following values:

[0081]

[0082] Among them, R s ω represents the stator resistance. s For synchronous speed, k gsc k s These are the coefficients for reactive power droop control on the GSC side and stator side, respectively. The larger the coefficient, the more reactive power is allocated. s For stator inductance, L m It is the magnetizing inductor.

[0083] Optionally, the constraint that the GSC reaches the output power limit before the stator is as follows:

[0084]

[0085] Among them, i gli m、i rlim These represent the allowable current limits on the rotor of the GSC, which are determined by the capacity of the equipment used. gsc k s These are the coefficients for reactive power droop control on the GSC side and the stator side, respectively. The larger the coefficient, the more reactive power is allocated.

[0086] Specifically, the topology and modeling of a doubly-fed wind turbine:

[0087] The stator of a doubly-fed induction generator (DFIG) wind turbine is directly connected to the power grid, while the rotor side is connected via a back-to-back converter, thus achieving decoupled control of active and reactive power. This electrical topology allows for more stable output power and a wider speed range and higher power density. Direct grid connection via a transformer allows for convenient and quick grid connection by boosting the grid voltage to a level suitable for the DFIG stator. On the rotor side, the back-to-back converter controls the rotor current and voltage, keeping reactive power within the required range. This method enables reactive power control, resulting in more stable output power and meeting the power system's reactive power requirements. Its topology is as follows: Figure 2 As shown: Since the crowbar resistance used in this paper is not very large, it will not generate DC capacitor overvoltage. Therefore, this paper does not consider the crowbar on the DC capacitor side, but only the crowbar on the rotor side to prevent RSC overcurrent. When the AC grid experiences a voltage drop, the rotor current of the doubly-fed induction generator (DFIG) may become too large, thereby damaging the electrical equipment on the rotor side. To avoid this, a crowbar device is usually connected. Once the crowbar device is triggered, it will disconnect the rotor-side converter from the grid, preventing it from continuing to operate and suffering further damage. At the same time, to protect the rotor-side converter, it is usually also locked. In this way, although the output power of the DFIG will decrease, its electrical equipment can be effectively protected from damage caused by overcurrent and other factors. After the crowbar is put into operation, the equivalent model of the DFIG in the synchronously rotating dq axis coordinate system is as follows: Figure 3 As shown. When the crowbar device is triggered, the rotor excitation voltage stops and the rotor current begins to decay because the rotor-side converter is disconnected from the grid. As the crowbar resistance increases, the decay rate of the rotor current also increases. When the rotor current drops to a certain level, the crowbar device can be deactivated, the rotor-side converter can be reconnected to the grid, and then the RSC (rotor-side PWM converter) can be used to control the rotor current. During this process, a certain overshoot will occur due to current redirection, but this overshoot can usually be adjusted by controlling the rotor-side PWM. Through precise control methods, the overshoot amplitude can be minimized, ensuring the stable operation of the doubly-fed wind turbine. After the crowbar is deactivated, the equivalent model of the doubly-fed wind turbine rotating at synchronous speed on the dq-axis is as follows. Figure 4 As shown.

[0088] Strategy 1: Controlling the number of times crowbar inputs are used during LVRT

[0089] During low-voltage ride-through, after the crowbar is disconnected, an overshoot phenomenon occurs because the RSC current loop has just started, causing the rotor to experience overcurrent again. If traditional RSC current loop PI controller parameters are used, the lack of optimization for parameters such as damping ratio can result in a large overshoot. If this overshoot exceeds the crowbar trigger current, the crowbar will be reactivated, leading to prolonged rotor uncontrollability. Therefore, the first part of this paper will optimize the RSC current loop PI controller parameters. Figure 3 The rotor voltage and flux linkage equations for a doubly-fed wind turbine can be listed below:

[0090] U r =R r i r +j(ω s -ω r )ψ r +pψ r (1)

[0091] ψ r =L r i r +L m i s (2)

[0092] In the formula, U r Indicates rotor voltage, i r Represents the rotor current, ω s Indicates synchronous speed, ω r ψ represents the rotor speed. r This indicates rotor flux linkage.

[0093] The commanded value for the rotor voltage is designed as follows:

[0094] U rref =R r i rref +jω r (L r i rref +L m i s_estim )

[0095] +k p (i rre fi r )+k i ∫(i rre fi r )dt (3)

[0096] Among them, U rref Indicates the rotor voltage command value; i rref This is the rotor current command, calculated from the inner current loop of the RSC; is_estim This is the formula for estimating the stator current.

[0097] The output voltage of the PWM rectifier is obtained by rectifying the PWM output signal generated in the frequency converter. When the rotor voltage command value of the doubly-fed wind turbine is U... rre When f is reached, the PWM controller generates a corresponding PWM output signal, which is converted into a corresponding high-frequency pulse voltage by inverting the AC power supply in the inverter. After rectification and filtering, the final voltage signal will approximate the rotor voltage command value. In a doubly fed wind turbine, if the influence of higher harmonic components is ignored, the output voltage of the PWM rectifier is basically approximate to the rotor voltage command value. This command value can be controlled by the controller, thereby effectively controlling the output voltage and current of the doubly fed wind turbine. Combining equation (1) and equation (3), and approximately eliminating R r i r 、(ω s -ω r )ψ r From these two terms, the voltage equation on the rotor side can be derived as follows:

[0098] p(L r i r +L m i s )=k p (i rref -i r )+k i ∫(i rref -i r )dt (4)

[0099] Applying the Laplace transform to the above equation and ignoring the initial components, we obtain:

[0100]

[0101] The above equation is the frequency domain rotor voltage equation for a doubly-fed induction generator (DFIG). Meanwhile, under all operating conditions, the stator equation for the DFIG can be expressed as:

[0102] U s =R s i s +jω s ψ s +pψ s (6)

[0103] ψ s =L ss i s +L m i r (7)

[0104] In the formula, U s Indicates the stator voltage, is ψ represents the stator current. s Let represent the stator flux linkage. The above stator equations can be written in frequency domain form as follows:

[0105] U s (s)=(R s +jω s L s +sL s )I s (s)+(jω s L m +s)I r (s) (8)

[0106] By simultaneously solving the rotor and stator equations and eliminating the stator current component, the transfer function of the rotor current can be obtained as follows:

[0107] I r (s)=G1(s)I rref (s)+G2(s)U s (s)

[0108]

[0109]

[0110] As can be seen from the above equation, the poles of the system can be written in the following form:

[0111]

[0112]

[0113]

[0114] Therefore, the damping ratio of the system can be written as:

[0115]

[0116] Its natural frequency can be written as:

[0117]

[0118] When the damping of a doubly-fed induction generator (DFIG) is relatively small, it can easily lead to a large overshoot in the system. If the overshoot exceeds the starting current, it will trigger the crowbar protection again, resulting in repeated switching on and off and prolonged switching time, which will adversely affect the recovery of the grid voltage.

[0119] Generally, the following measures can be taken to reduce overshoot:

[0120] 1. Optimize the control strategy to minimize the starting current and increase the crowbar resistance to reduce the impact of the actual current on the overshoot.

[0121] 2. Thoroughly debug and test the system to ensure a smooth transition between the rotor-side PWM converter and the power grid.

[0122] 3. High-performance controllers and regulating devices are used to improve the system's response speed and accuracy, and enhance the system's anti-interference and control capabilities.

[0123] Since the upper limit of the crowbar resistance is affected by the capacitor voltage, this paper adopts the scheme of increasing the system damping ratio to control the overshoot. To improve the system response speed, the system is usually designed as underdamped with a relatively large natural frequency. Underdamped systems can improve response speed. However, if the damping ratio is set too low, the system response near the natural frequency becomes very sensitive, easily leading to instability. Therefore, the damping ratio needs to be reasonably selected and controlled. In parameter design, a PI controller can effectively solve the system control problem. It is important to note that when designing the PI controller parameters, the stability and robustness of the controller must be ensured. Therefore, parameter design needs to be combined with the specific characteristics of the system to achieve better control performance. In practical engineering, the damping ratio is usually set between 0.4 and 0.8. Since the system response near the natural frequency becomes particularly sensitive, it is necessary to avoid operating the system near this frequency. Since power systems are typically 50Hz or 60Hz, this paper selects a natural frequency of 10Hz and a damping ratio of 0.8, i.e., ω... n =10, ξ=0.8. Combining equations (11) and (12), the PI controller parameters of the RSC current inner loop are obtained.

[0124]

[0125]

[0126] By optimizing the parameters, the damping ratio and natural frequency of the system can be effectively improved. Furthermore, while keeping the system insensitive to stator voltage fluctuations, the overshoot of the rotor current can be minimized, thereby avoiding repeated crowbar input and achieving the requirements of objective one.

[0127] Strategy 2: Scheme to output reactive power during LVRT

[0128] When the flux linkage reaches steady state during the low-voltage ride-through, the rate of change is 0. If stator voltage orientation is used, the stator voltage equation of the DFIG can be written in the following form:

[0129] U sd =R s isd -ω s ψ sq

[0130] 0 = R s i sq +ω s ψ sd (15)

[0131] Among them, U sd i represents the d-axis component of the grid voltage. sd and i sq ψ represents the stator current. sd and ψ sq Let represent the stator flux linkage, which satisfies equation (7). The d-axis and q-axis components of the stator current can be obtained from the above equation:

[0132]

[0133] In the above formula, since R s Much smaller than ω s L s Therefore, the presence of i can be approximately ignored. rd One approach considers the stator current q-axis component to be dominated by the rotor current q-axis component. In steady state, it can be assumed that the rotor current is equal to its commanded value, and its q-axis component can be written in the following form:

[0134] i rqref =k s (1-U sd (17)

[0135] During low voltage ride-through, the rotor current q-axis will have a large component because the stator voltage is much lower than its rated value. Since the stator current q-axis component is strongly correlated with reactive power, the stator will interact with the grid during RSC activation, which can be approximated as follows:

[0136]

[0137] Since this paper adopts the convention of electric motors, that is, the stator current inflow is positive, the above formula represents the stator absorbing negative reactive power, and the stator voltage U sd The lower the value, the higher the q-axis component of the current i sq The larger the value, the greater the value. However, the upper limit of the commanded value of the rotor current q-axis component determines the maximum value of the stator current q-axis component. The rotor q-axis current command limit can be expressed as:

[0138]

[0139] In the above formula, i rlim This indicates the maximum value of the rotor current. Due to the d-axis component of the rotor current, the command i... rdrefThe q-axis component is typically large, therefore its q-axis component is small, usually not exceeding 0.45 pu. Thus, it is evident that the stator's ability to output reactive power is relatively weak.

[0140] Since the GSC remains operational throughout the low-voltage ride-through process, it can also be used to output reactive power. The q-axis current command is set as follows:

[0141] i gqref =k gsc ·(1-U sd (20)

[0142] It is evident that when the voltage is 1, the GSC operates under a constant power factor. When the voltage drops, the GSC generates a q-axis current, which will produce reactive power. The q-axis current command of the GSC should satisfy the following relationship:

[0143]

[0144] Due to the d-axis current command i of GSC gdref Typically small, therefore its q-axis current command is large, usually approximately equal to the current limit i of the GSC. glim Therefore, GSC has a strong reactive power output capability, and its reactive power output can be calculated as follows:

[0145]

[0146] In the above formula, i gq The output from the GSC to the grid is considered positive. Therefore, during the crowbar operation period, the total reactive power output of the doubly-fed induction generator (DFIG) is Q. gsc The total reactive power output of the doubly-fed induction generator (DFIG) after the crowbar is removed and the RSC is activated, along with the reactive power loss caused by the crowbar, is Q. gsc +Q s Considering that the GSC has a strong reactive power output capability, and that only the GSC can control reactive power when the crowbar is engaged, the coefficient allocation objective of this paper is to make the GSC output the main reactive power, while the stator outputs a small amount of reactive power in coordination.

[0147] After the crowbar is removed, the total power output of the DFIG can be expressed as:

[0148]

[0149] The low voltage ride-through criterion stipulates that the reactive power generated by a doubly-fed induction generator (DFIG) should satisfy the following relationship:

[0150] i q ≥1.5·(0.9-U sd ) (twenty four)

[0151] The range of values ​​for the stator voltage is shown below:

[0152] 0.2≤U sd ≤0.9 (25)

[0153] Therefore, the range of values ​​for the coefficients should satisfy the following conditions:

[0154]

[0155] Meanwhile, since this paper chooses the GSC to dominate the output reactive power, it is desirable that the GSC reaches the output power limit before the stator when the voltage drops, that is:

[0156]

[0157] The above equation satisfies the priority of GSC reactive power output, enabling DFIG to output a large amount of reactive power even during RSC blocking. Furthermore, the reactive power output delay of GSC is extremely short, meeting the requirement of reactive power output within 75ms in the low-voltage ride-through criterion. In summary, the reactive power output scheme proposed in this paper satisfies the requirements of small delay and large reactive power output, thus fulfilling objective two.

[0158] In summary, the following cooperative control strategies can be used: Figure 5 and Figure 6 This paper proposes two control strategies, namely Strategy 1 and Strategy 2. During LVRT, doubly-fed induction generators (DFIGs) typically use a crowbar to suppress rotor overcurrent. However, after the crowbar is disconnected, the rotor may experience overcurrent again, causing the crowbar to be triggered multiple times, thus prolonging its activation time. To address this issue, an improved RSC current loop with optimized PI controller parameters is first proposed. This control strategy optimizes the system's damping ratio and natural frequency, significantly reducing overshoot, thereby suppressing repeated crowbar triggering and reducing its activation time.

[0159] However, even with Strategy 1, the DFIG still absorbs reactive power when the crowbar is engaged. Therefore, this paper proposes Strategy 2, which uses the GSC to primarily output reactive power while the stator assists in outputting reactive power. This control strategy allows the DFIG to output sufficient reactive power even when the crowbar is engaged, and it can output a large amount of reactive power after the crowbar is disconnected, thus compensating for the shortcomings of Strategy 1. Furthermore, Strategy 2 is also applicable to normal operating conditions, thereby avoiding the switching from reactive power output commands under normal operating conditions to fault conditions and reducing delays.

[0160] Furthermore, among the many wind turbines, they are divided into two types according to their rated terminal voltage: 575V (suitable for regions such as the United States and Canada) and 690V (suitable for regions such as Europe and Asia). The model selected in this paper is a GE wind turbine, whose parameters are relatively publicly available, with a rated terminal voltage of 575V. For simulation, we built a 9MW doubly-fed wind farm in Matlab / Simulink, consisting of six 1.5MW GE doubly-fed wind turbines. Through simplification of the system topology, we obtain... Figure 7 The structure shown is as follows:

[0161] Table 1 Parameters of a single 1.5MW doubly-fed wind turbine

[0162]

[0163] In this paper, the starting current is selected as 1.5 pu, and the crowbar turn-off delay is set to 0.1 s. Simultaneously, with a wind speed of 15 m / s, it is assumed that the 120 kV grid voltage drops to 0 p.u. at 1 s. For comparison, this paper first uses the conventional PI controller parameters from a traditional GE 1.5MW wind turbine, as shown in Table 2:

[0164] Table 2 Parameters of a Traditional RSC Current Loop PI Controller

[0165]

[0166] Simulations show that when a voltage drop occurs at 1 second, the rotor current experiences overcurrent, triggering the crowbar. After a delay, the crowbar is deactivated when the rotor current decays to a certain level. However, this results in overshoot, and under traditional RSC PI controller parameters, the crowbar will reactivate, leading to repeated cycles that could ultimately cause the doubly-fed induction generator (DFIG) to become uncontrollable for extended periods.

[0167] In contrast, strategy one is adopted for improvement. From equations (13) and (14), the parameters of the improved PI controller for the RSC current loop can be calculated as follows:

[0168] Table 3. Parameters of the improved RSC current loop PI controller

[0169]

[0170] Simulations show that the rotor current amplitude is related to time. It is found that when the improved RSC PI controller parameters are used, the rotor current will have a very small overshoot when the crowbar is cut off, and the crowbar will only be engaged once. This greatly reduces the time when the rotor current is uncontrollable, which is beneficial to the recovery of the grid voltage.

[0171] Based on the preceding text, if the traditional method of rotor output reactive power is adopted, and the PI controller parameters of the improved RSC proposed earlier are used, then the reactive power output and terminal voltage of the DFIG during a fault can be obtained as follows: Figure 8 and Figure 9 As shown, it can be seen that simply improving the PI controller parameters of RSC can reduce the uncontrollable time, but the reactive power output of the doubly-fed induction generator (DFIG) is still very low, and its terminal voltage is also relatively low. Therefore, it is clear that proposing a coordinated control strategy is crucial.

[0172] In contrast, an improved reactive power output strategy is presented below. This involves using a gas-controlled generator (GSC) to output a certain amount of reactive power, while simultaneously providing auxiliary reactive power output at the stator. Simulations show that the reactive power output and terminal voltage of the doubly-fed induction generator (DFIG) are as follows: Figure 10 and Figure 11 As shown, by adopting the strategy of GSC reactive power output and supplementing it with reactive power output on the stator, the doubly-fed induction generator (DFIG) can output a large amount of reactive power, sufficient to support the terminal voltage of the DFIG. Furthermore, it can still output a large amount of reactive power when the crowbar is engaged, thus facilitating voltage recovery. Therefore, it can be seen that using the improved RSC PI controller parameters, combined with the GSC reactive power output strategy, can effectively improve the low-voltage ride-through performance of the DFIG.

[0173] This application presents an improved PI controller parameter that reduces rotor current overshoot by increasing the damping ratio, thereby minimizing the number of times the crowbar is engaged and ensuring stable operation of the doubly-fed induction generator (DFIG). This improved control measure can significantly reduce the rotor-side transient overcurrent problem of the DFIG during grid voltage dips and recovery, demonstrating significant innovation and applicability.

[0174] This application presents a complementary strategy that employs a gas-cooled steam turbine (GSC) to output primary reactive power while simultaneously providing auxiliary reactive power output on the stator. By using a command expression for the reactive power output from the GSC, it addresses the low-level reactive power (LVRT) problem even under normal operating conditions, avoiding delays in control measure switching. This strategy improves the reactive power output of the doubly-fed induction generator (DFIG) during LVRT, maximizing its ability to provide stable reactive power to the grid. Furthermore, it continues to output reactive power even when the crowbar is engaged, contributing to grid recovery and demonstrating high practical value and economic benefits.

[0175] Therefore, this invention improves the RSC current loop PI controller parameters to enhance the system damping ratio and natural frequency, reducing rotor current overshoot after crowbar removal and preventing rotor current exceeding limits, thus solving the problem of repeated crowbar activation. Simultaneously, this invention employs a GSC-dominant reactive power output method, using stator-assisted reactive power output to improve the wind turbine's reactive power output capability in LVRT mode, thereby solving the problem of insufficient reactive power output.

[0176] This invention aims to improve the low-voltage ride-through (LVRT) performance of doubly-fed induction generator (DFIG) wind turbines, involving technologies such as crowbar control strategies, RSC current loop design, and GSC command value design. This invention is applicable to scenarios where a three-phase short-circuit fault in the AC grid causes a sudden voltage drop at the DFIG terminal, leading the wind turbine into an LVRT state. By improving the RSC current loop and refining the GSC commands, this invention can enhance the LVRT performance of DFIG wind turbines. This technology can be widely applied in the wind power industry, significantly improving the stability and reliability of wind turbines and further promoting the development of the wind power industry.

[0177] Exemplary device

[0178] Figure 12 This is a schematic diagram of the structure of a cooperative control device for a doubly-fed wind turbine during low-voltage ride-through, provided in an exemplary embodiment of the present invention. Figure 12 As shown, the device 1200 includes:

[0179] The first determining module 1210 is used to set the system damping ratio to 0.8 and the natural frequency to 10Hz during low voltage ride-through, and to determine the PI controller parameters of the RSC current inner loop.

[0180] The second determining module 1220 is used to determine the GSC coefficient based on the preset range of GSC coefficient values ​​and the constraint that the GSC reaches the output power limit before the stator.

[0181] The third determining module 1230 is used to determine the reactive power of the doubly fed wind turbine based on the GSC output reactive power output by the set GSC coefficient and the stator output reactive power output by the set PI controller parameters.

[0182] Optionally, the first determining module 1210 sets the system damping ratio to 0.8 and the natural frequency to 10Hz, and determines the PI controller parameters of the RSC current inner loop, including:

[0183] The first determining submodule is used to determine the stator inductance, rotor inductance, and magnetizing inductance based on the damping ratio and natural frequency.

[0184] The second determining submodule is used to determine the PI controller parameters based on the stator inductance, rotor inductance, and magnetizing inductance.

[0185] Alternatively, the formulas for determining the stator inductance, rotor inductance, and magnetizing inductance based on the damping ratio and natural frequency are as follows:

[0186]

[0187]

[0188] Wherein, the natural frequency ω n =10, damping ratio ξ=0.8, L r For rotor inductance, L s For stator inductance, L m For the magnetizing inductance, k p k i For the PI controller parameters of the RSC current loop, k p k is the proportional coefficient. i The coefficients of the integral element.

[0189] Alternatively, the formula for determining the PI controller parameters based on the stator inductance, rotor inductance, and magnetizing inductance is as follows:

[0190]

[0191]

[0192] Among them, L r For rotor inductance, L s For stator inductance, L m For the magnetizing inductance, k p k i For the PI controller parameters of the RSC current loop, k p k is the proportional coefficient. i The coefficients of the integral element.

[0193] Optionally, the GSC coefficient can take the following values:

[0194]

[0195] Among them, R s ω represents the stator resistance. s For synchronous speed, k gsc k s These are the coefficients for reactive power droop control on the GSC side and stator side, respectively. The larger the coefficient, the more reactive power is allocated. s For stator inductance, L m It is the magnetizing inductor.

[0196] Optionally, the constraint that the GSC reaches the output power limit before the stator is as follows:

[0197]

[0198] Among them, i glim i rlim These represent the allowable current limits on the rotor of the GSC, which are determined by the capacity of the equipment used. gsc k s These are the coefficients for reactive power droop control on the GSC side and the stator side, respectively. The larger the coefficient, the more reactive power is allocated.

[0199] Exemplary electronic devices

[0200] Figure 13 This is the structure of an electronic device provided in an exemplary embodiment of the present invention. For example... Figure 13 As shown, the electronic device 130 includes one or more processors 131 and memory 132.

[0201] The processor 131 may be a central processing unit (CPU) or other form of processing unit with data processing capabilities and / or instruction execution capabilities, and may control other components in the electronic device to perform desired functions.

[0202] The memory 132 may include one or more computer program products, which may include various forms of computer-readable storage media, such as volatile memory and / or non-volatile memory. The volatile memory may include, for example, random access memory (RAM) and / or cache memory. The non-volatile memory may include, for example, read-only memory (ROM), hard disk, flash memory, etc. One or more computer program instructions may be stored on the computer-readable storage medium, and the processor 131 may execute the program instructions to implement the methods of the software programs of the various embodiments of the present invention described above, and / or other desired functions. In one example, the electronic device may also include an input device 133 and an output device 134, these components being interconnected via a bus system and / or other forms of connection mechanisms (not shown).

[0203] In addition, the input device 133 may also include, for example, a keyboard, a mouse, etc.

[0204] The output device 134 can output various information to the outside. The output device 134 may include, for example, a display, a speaker, a printer, and a communication network and its connected remote output devices, etc.

[0205] Of course, for the sake of simplicity, Figure 13Only some of the components of this electronic device relevant to the present invention are shown, omitting components such as buses, input / output interfaces, etc. In addition, the electronic device may include any other suitable components depending on the specific application.

[0206] Exemplary computer program products and computer-readable storage media

[0207] In addition to the methods and apparatus described above, embodiments of the present invention may also be computer program products, which include computer program instructions that, when executed by a processor, cause the processor to perform the steps in the methods according to various embodiments of the present invention described in the "Exemplary Methods" section above.

[0208] The computer program product can be written in any combination of one or more programming languages ​​to perform the operations of the embodiments of the present invention. The programming languages ​​include object-oriented programming languages ​​such as Java and C++, as well as conventional procedural programming languages ​​such as C or similar languages. The program code can be executed entirely on the user's computing device, partially on the user's computing device, as a standalone software package, partially on the user's computing device and partially on a remote computing device, or entirely on a remote computing device or server.

[0209] Furthermore, embodiments of the present invention may also be computer-readable storage media storing computer program instructions thereon, which, when executed by a processor, cause the processor to perform the steps of the methods according to various embodiments of the present invention described in the "Exemplary Methods" section above.

[0210] The computer-readable storage medium may be any combination of one or more readable media. A readable medium may be a readable signal medium or a readable storage medium. A readable storage medium may be, for example, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, device, or any combination thereof. More specific examples (a non-exhaustive list) of readable storage media include: an electrical connection having one or more wires, a portable disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof.

[0211] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0212] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For system embodiments, since they largely correspond to method embodiments, the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

[0213] The block diagrams of devices, systems, devices, and systems involved in this invention are merely illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As those skilled in the art will recognize, these devices, systems, devices, and systems can be connected, arranged, and configured in any manner. Words such as “comprising,” “including,” “having,” etc., are open-ended terms meaning “including but not limited to,” and are used interchangeably with them. The terms “or” and “and” as used herein refer to the terms “and / or,” and are used interchangeably with them unless the context clearly indicates otherwise. The term “such as” as used herein refers to the phrase “such as but not limited to,” and is used interchangeably with it.

[0214] The methods and systems of the present invention may be implemented in many ways. For example, they may be implemented by software, hardware, firmware, or any combination of software, hardware, and firmware. The above-described order of steps for the methods is for illustrative purposes only, and the steps of the methods of the present invention are not limited to the order specifically described above unless otherwise specifically stated. Furthermore, in some embodiments, the present invention may also be implemented as a program recorded on a recording medium, the program comprising machine-readable instructions for implementing the methods according to the present invention. Thus, the present invention also covers recording media storing programs for performing the methods according to the present invention.

[0215] It should also be noted that in the systems, apparatus, and methods of the present invention, the components or steps can be disassembled and / or recombined. These disassemblies and / or recombinations should be considered equivalents of the present invention. The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use the invention. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other aspects without departing from the scope of the invention. Therefore, the invention is not intended to be limited to the aspects shown herein, but rather to be carried out within the widest scope consistent with the principles and novel features disclosed herein.

[0216] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of the invention to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations therein.

Claims

1. A method for coordinated control of a doubly-fed induction generator (DFIG) during low-voltage ride-through, characterized in that, include: During low voltage ride-through, the system damping ratio is set to 0.8 and the natural frequency is 10Hz. The PI controller parameters for the inner loop of the RSC current are then determined. The GSC coefficient is determined based on the pre-set range of GSC coefficient values ​​and the constraint that GSC reaches the output power limit before the stator. The reactive power of the doubly fed wind turbine is determined based on the GSC output reactive power output by the set GSC coefficient and the stator output reactive power output by the set PI controller parameters. With the system damping ratio set to 0.8 and the natural frequency to 10Hz, determine the PI controller parameters for the RSC current inner loop, including: The stator inductance, rotor inductance, and magnetizing inductance are determined based on the damping ratio and the natural frequency. The parameters of the PI controller are determined based on the stator inductance, rotor inductance, and magnetizing inductance. Based on the damping ratio and the natural frequency, the formulas for determining the stator inductance, rotor inductance, and magnetizing inductance are as follows: Among them, natural frequency Damping ratio , For rotor inductance, For stator inductance, For magnetizing inductance, , These are the PI controller parameters for the current loop of the RSC. This is the coefficient for the proportional element. The coefficients of the integral element; Based on the stator inductance, rotor inductance, and magnetizing inductance, the formula for determining the PI controller parameters is as follows: in, For rotor inductance, For stator inductance, For magnetizing inductance, , These are the PI controller parameters for the current loop of the RSC. This is the coefficient for the proportional element. The coefficients of the integral element; The range of GSC coefficient values ​​is as follows: in, Indicates stator resistance. To achieve synchronous speed, , These are the coefficients for reactive power droop control on the GSC side and stator side, respectively. The larger the coefficient, the more reactive power is allocated. For stator inductance, For magnetizing inductance; The constraint that the GSC reaches the output power limit before the stator is as follows: in, , These represent the allowable current limits on the rotor of the GSC, which are determined by the capacity of the equipment used. , These are the coefficients for reactive power droop control on the GSC side and the stator side, respectively. The larger the coefficient, the more reactive power is allocated.

2. A cooperative control device for a doubly-fed induction generator (DFIG) during low-voltage ride-through, for implementing the method of claim 1, characterized in that, include: The first determining module is used to set the system damping ratio to 0.8 and the natural frequency to 10Hz during low voltage ride-through, and to determine the PI controller parameters of the RSC current inner loop. The second determining module is used to determine the GSC coefficient based on the pre-set range of GSC coefficient values ​​and the constraint that the GSC reaches the output power limit before the stator. The third determining module is used to determine the reactive power of the doubly-fed wind turbine based on the GSC output reactive power output by setting the GSC coefficient and the stator output reactive power of setting the PI controller parameters.

3. A computer-readable storage medium, characterized in that, The storage medium stores a computer program for executing the method described in claim 1.

4. An electronic device, characterized in that, The electronic device includes: processor; Memory used to store the processor's executable instructions; The processor is configured to read the executable instructions from the memory and execute the instructions to implement the method of claim 1.

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