Multi-fan converter cluster LCL filter global broadband resonance suppression method and system

Abstract

The invention discloses a multi-fan converter cluster LCL filter global broadband resonance suppression method and system, and the method comprises the steps: collecting a multi-fan converter cluster scene system parameter, and calculating a resonant frequency range; determining the center frequency and bandwidth of the parallel double-second-order band-pass filter, and constructing broadband virtual damping; extracting a voltage harmonic component of a common connection point of the multi-fan converter cluster, and obtaining a broadband harmonic current control instruction of the fan converters; constructing a broadband harmonic composite controller of the fan converter, generating a driving signal, and realizing a damping multiplexing function; the resonant frequency range is expanded, the total harmonic distortion rate of the voltage of the multi-fan converter is calculated, and the broadband virtual damping gain iteration step length is determined; and the gain of the broadband virtual damping is iteratively updated successively according to the step length until the real-time detection value of the total harmonic distortion rate of the voltage is not higher than the target value. According to the invention, broadband variable virtual damping is constructed, multiplexing of an active damping control function is realized, and a global and broadband resonance suppression effect is achieved on the basis of not increasing equipment.

Description

Technical Field

[0001] This invention belongs to the field of resonance suppression technology, and more specifically, relates to a global broadband resonance suppression method and system for LCL filters in multi-wind turbine converter clusters. Background Technology

[0002] Wind power generation is a crucial component of new energy development and continues to grow rapidly. Its core component, the wind power converter, serves as the energy conversion interface connecting the generator and the power grid. Traditional wind power converters driven by PWM modulation technology generate abundant high-frequency harmonics due to frequent operation of power electronic switches, resulting in grid-connected harmonic distortion rates that do not meet grid connection requirements. Currently, more efficient LCL filters are widely used to meet the current national standards for wind power grid-connected harmonic distortion rates.

[0003] However, LCL filters have inherent resonance, and their resonant frequency and amplification are easily affected by changes in grid impedance and the interaction between other LCL wind turbine converter clusters, leading to complex and variable broadband resonance risks. This results in a surge in voltage and current distortion at the grid connection point, affecting grid stability and power quality.

[0004] In existing technologies, LCL filter resonance suppression often employs passive damping methods by increasing resistance and active damping methods by adding control algorithms. By increasing the damping at the LCL filter resonance point, the resonance peak is suppressed, thereby improving system stability and reducing harmonic levels.

[0005] However, passive damping methods suffer from numerous problems, including increased additional losses and reduced high-frequency suppression efficiency. Active damping methods increase the complexity of the control system and the number of sensors required for feedback. Especially in wind turbine converter cluster scenarios, the resonant frequency caused by the LCL filter is affected by the number of clusters, the unit's parameters, and the grid impedance, varying over a wide frequency range. Damping needs to be added to each wind turbine converter in the cluster to achieve the desired mitigation effect, further increasing implementation costs and control complexity.

[0006] Additionally, global resonance suppression in wind turbine converter cluster scenarios can be achieved by installing a control device employing active damping control technology. However, breakthroughs are still needed in real-time, accurate resonance frequency detection and identification technology under high interference conditions to adapt to the current situation of uncertain wideband resonance frequency distribution. Furthermore, due to the special characteristics of wind farm sites (such as mountainous and offshore areas), the availability of such devices is uncontrollable. Therefore, in multi-wind turbine converter cluster scenarios, a more efficient, low-cost, and feasible LCL filter resonance suppression method is required.

[0007] Prior art document 1 (CN119134412A) discloses a broadband oscillation suppression method for doubly-fed induction generator (DFIG) wind turbines based on adaptive impedance reshaping. However, prior art document 1, in order to solve the subsynchronous / supersynchronous frequency band resonance caused by the interaction of DFIG wind turbines in line series compensation capacitors or weak power grid scenarios, is applicable within the range of 5Hz to 100Hz. The shortcomings of prior art document 1 are: 1. Unable to resolve high-frequency (above 1kHz) resonance caused by LCL filters; 2. Low- and mid-frequency damping control is achieved by adding filters. However, high-order filters with many parameters and types can affect the response time and stability of the control system. 3. Structural changes and parameter linear adaptations are made to the original control loop, but the adaptive capability is limited. Moreover, it is a single-unit resonant problem in the secondary / supersynchronous frequency band of the doubly fed wind turbine converter, and it does not have the ability to improve the overall performance. 4. The active damping control on the GSC side is achieved through a second-order differential element. Its gain can only increase adaptively with the increase of frequency, and the gain cannot change at a fixed frequency. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a global broadband resonance suppression method and system for LCL filters in multi-wind turbine converter clusters.

[0009] The present invention adopts the following technical solution.

[0010] The first aspect of the present invention provides a global broadband resonance suppression method for LCL filters in multi-wind turbine converter clusters, comprising the following steps: Step 1: Collect system parameters for the multi-wind turbine converter cluster scenario. Calculate the upper and lower limits of the resonance induced by the LCL filter in this scenario based on the system parameters to obtain the resonant frequency range of the LCL filter. Step 2: Determine the center frequency and bandwidth of the parallel double second-order bandpass filter based on the upper and lower resonant frequencies, and construct a wideband virtual damping in the control loop of the wind turbine converter using the double second-order bandpass filter. Step 3: Extract the voltage harmonic components of the common connection point of the multi-wind turbine converter cluster and multiply them with the broadband virtual damping to obtain the broadband harmonic current control command of the wind turbine converter. Step 4: Construct a wideband harmonic composite controller for the wind turbine converter. Input the wideband harmonic current control command into the composite controller to generate a drive signal, thereby realizing the wideband active damping multiplexing function of the wind turbine converter. Step 5: When the multiplexing function is not enabled, expand the resonant frequency range of the LCL filter and calculate the total harmonic distortion of the voltage at the common connection point of the multi-wind turbine converter cluster within the expanded resonant frequency range. Based on the difference between the total harmonic distortion of the voltage and the set target value, determine the iteration step size of the broadband virtual damping gain. Step 6: Set the initial gain value and enable the multiplexing function. Iterate and update the gain of the broadband virtual damping step by step until the real-time detection value of the total harmonic distortion of the voltage is not higher than the target value, thus completing the global broadband resonance adaptive suppression of the multi-wind turbine converter cluster.

[0011] Preferably, in step 1, the resonant frequency induced by the LCL filter when the grid connection impedance is ignored and only one wind turbine converter cluster is connected to the grid is taken as the upper limit resonant frequency, expressed by the following formula:

[0012] In the formula: L H1 To account for the machine-side inductance of the LCL filter referred to the high-voltage side of the transformer, L H2 To account for the LCL filter network inductance referred to the high-voltage side of the transformer, C H This refers to the LCL filter capacitor referred to the high-voltage side of the transformer.

[0013] Preferably, in step 1, the resonant frequency induced by the LCL filter when the grid-connected impedance is maximum and all wind turbine converter clusters are connected to the grid is taken as the lower limit resonant frequency, expressed by the following formula:

[0014] In the formula: L H1 To account for the machine-side inductance of the LCL filter referred to the high-voltage side of the transformer, L H2 To account for the LCL filter network inductance referred to the high-voltage side of the transformer, C H The LCL filter capacitor is calculated and referred to the high-voltage side of the transformer. n The number of wind turbine converters, L g_max The inductance is the inductance corresponding to the maximum grid-connected impedance at the point of common coupling.

[0015] Preferably, the inductance of the LCL filter network referred to the high-voltage side of the transformer is... L H2 The following announcement indicates:

[0016] In the formula: k TThis refers to the rated turns ratio of the step-up transformer. L 2 is the grid-side inductor; Among them, the grid-side inductor L 2 is calculated in two cases: No LCL filter network-side inductor L 2_or In this case, the grid-side inductance on the low-voltage side of the transformer is calculated according to the following formula. L 2:

[0017] In the formula: U d This is the short-circuit impedance of the step-up transformer. U r The rated voltage of the wind turbine converter. S T This refers to the rated capacity of the step-up transformer. f 0 represents the fundamental frequency; LCL filter network-side inductor L 2_or In this case, the equivalent grid-side inductance on the low-voltage side of the transformer is calculated according to the following formula. Replace the grid-side inductor L 2: .

[0018] Preferably, step 2 includes: selecting two second-order bandpass filters of the same gain in parallel, using the upper and lower resonant frequencies as the center frequencies of the parallel two second-order bandpass filters, and using the difference between the upper and lower resonant frequencies as the bandwidth of the two second-order bandpass filters, and constructing a wideband virtual damping in the control loop of the wind turbine converter, the transfer function of which is expressed by the following formula:

[0019] In the formula: k z For the gain of the parallel double second-order bandpass filter, The upper limit resonant frequency, This is the lower limit resonant frequency.

[0020] Preferably, in step 3, a cascaded generalized integrator is used to extract the fundamental component of the point of common coupling voltage, and the point of common coupling voltage is subtracted from the fundamental component to obtain the harmonic component; the center frequency of the cascaded generalized integrator is set as the fundamental angular frequency.

[0021] Preferably, in step 3, the broadband harmonic current control command of the wind turbine converter is expressed by the following formula:

[0022] In the formula: ih_ref (αβ) represents the broadband harmonic current control command for the wind turbine converter in the αβ coordinate system. For broadband virtual damping, the transfer function is... u h (αβ) represents the harmonic components of the voltage at the common connection point in the αβ coordinate system.

[0023] Preferably, step 4 includes: A wideband harmonic composite controller for a wind turbine converter is constructed by combining a proportional controller and a repetitive controller in an embedded manner. The wideband harmonic current control command is compared with the harmonic components of the output current of the wind turbine converter, and input into the composite controller to generate a modulation wave. The drive signal is generated by PWM modulation to realize the wideband active damping multiplexing function of the wind turbine converter.

[0024] Preferably, in step 5, expanding the resonant frequency range of the LCL filter includes: Using half the difference between the lower and upper resonant frequencies, the resonant frequency range is extended both upwards and downwards to determine the upper harmonic order for calculating the total harmonic distortion of the voltage. h u and lower limit harmonic order h d It can be expressed by the following formula:

[0025] In the formula: For floor operations, For floor operations, The upper limit resonant frequency, The lower limit resonant frequency, f 0 represents the fundamental frequency.

[0026] Preferably, in step 5, the principle for setting the target value is as follows: The target value for the total harmonic distortion rate (THD) of the global voltage is set using the standard-specified limit for total harmonic distortion (THD) or based on empirical values.

[0027] Preferably, in step 6, the gain of the broadband virtual damping is iteratively updated step by step until the real-time detected value of the total harmonic distortion of the voltage is not higher than the target value, including: The total harmonic distortion (THD) of the voltage at the common connection point is detected in real time within the extended resonant frequency range. When the THD is in a relatively stable state, it is compared with the target value of the global harmonic voltage THD. Based on the comparison result, it is determined whether to proceed to the next iteration based on the gain. When the detected value is greater than the target value, the broadband virtual damping gain is updated by the iteration step size, and the new stable detected value after the gain iteration is compared with the target value. When the detected value is equal to or less than the target value, the corresponding broadband virtual damping gain is the final required value.

[0028] A second aspect of the present invention provides a global broadband resonance suppression system for LCL filters in a multi-wind turbine converter cluster, comprising a method for global broadband resonance suppression of LCL filters in the multi-wind turbine converter cluster, including: The resonant frequency calculation module is used to collect system parameters in multi-wind turbine converter cluster scenarios and calculate the resonant frequency range of LCL filters. The virtual damping construction module is used to determine the center frequency and bandwidth of the parallel double second-order bandpass filters and construct broadband virtual damping in the control loop of the wind turbine converter. The control command generation module is used to extract the voltage harmonic components of the common connection point of the multi-wind turbine converter cluster and generate broadband harmonic current control commands for the wind turbine converter. The multiplexing function building module is used to build a wideband harmonic composite controller for wind turbine converters, generate drive signals, and realize the wideband active damping multiplexing function of wind turbine converters. The iteration step size calculation module is used to expand the resonant frequency range of LCL filters, calculate the total harmonic distortion rate of the voltage at the common connection point of a multi-wind turbine converter cluster within the expanded resonant frequency range, and determine the iteration step size of the broadband virtual damping gain. The damping gain update module is used to set the initial gain value and iteratively update the gain of the broadband virtual damping in step increments.

[0029] Compared with the prior art, the beneficial effects of the present invention include at least the following: This invention proposes a global broadband resonance suppression method and system for LCL filters in multi-wind turbine converter clusters. Considering the complex interactive resonant frequency range of LCL filters, a broadband variable virtual damping is constructed using a parallel configuration of dual bandpass filters. Active damping control is reused within the wind turbine converter cluster. Without adding equipment, a global and broadband resonance suppression effect is achieved, providing an important foundation for high-quality grid connection of high-proportion, large-scale wind power generation. Specifically, it includes: 1. This invention fully considers the resonance variation range of LCL filter in wind turbine converter clusters under complex interactive conditions, determines the frequency boundary of parallel second-order bandpass filter, and flexibly adjusts the filter gain according to the real-time detected high-frequency harmonic voltage of the power grid and the requirements of the governance target, so as to ensure the frequency applicability of broadband active damping in different scenarios and the adaptive damping value. 2. The parallel dual bandpass filter method used in this invention has a simple structure, has little impact on the response time of the control system, and has higher stability; 3. This invention avoids the problem of unsatisfactory mitigation effect caused by the detection and identification of changing resonant frequencies in complex scenarios through a wide-band damping design, and has global improvement capability; 4. This invention can solve the LCL filter resonance problem of the wind turbine converter cluster globally by multiplexing the broadband active damping function of a single or several wind turbine converters without the need for additional mitigation devices. Attached Figure Description

[0030] Figure 1 This is a flowchart of a global broadband suppression method for LCL filter resonance in a multi-wind turbine converter cluster according to an embodiment of the present invention; Figure 2 This is a schematic diagram of a wind turbine converter control system with wideband active damping multiplexing function provided according to an embodiment of the present invention; Figure 3 This is a broadband virtual damping frequency response characteristic diagram constructed from a parallel double second-order bandpass filter according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the broadband virtual damping gain iteration process provided in accordance with an embodiment of the present invention; Figure 5 This is a graph showing the total harmonic distortion rate of the voltage at the common connection point within the extended resonant frequency range after enabling the multiplexing function, according to an embodiment of the present invention. Figure 6 This is a schematic diagram comparing the voltage waveform and harmonic content of the common connection point before and after resonance suppression according to an embodiment of the present invention; Figure 7 This is a schematic diagram comparing the current waveforms and harmonic content of the common connection point before and after resonance suppression according to an embodiment of the present invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0032] like Figure 1 As shown, Embodiment 1 of the present invention provides a global broadband resonance suppression method for LCL filters in multi-wind turbine converter clusters, comprising the following steps: Step 1: Collect system parameters for a multi-wind turbine converter cluster scenario. Based on the system parameters, calculate the upper and lower limits of the resonance frequencies that can be induced by the LCL filter in this scenario, and obtain the resonant frequency range of the LCL filter.

[0033] In a preferred but non-limiting embodiment of the present invention, step 1 specifically includes: Step 1.1: Collect system parameters for a multi-wind turbine converter cluster scenario, specifically including the number of wind turbine converters. n Rated voltage of wind turbine converter U r (kV), LCL filter machine-side inductance L 1(H), LCL filter network-side inductor L 2_or (H), LCL filter capacitor C (F), Rated capacity of the step-up transformer S T (MVA), the rated turns ratio of a step-up transformer. k T The short-circuit impedance of the step-up transformer U d (%), Nominal voltage at point of common coupling U N (kV) and minimum short-circuit capacity S min (MVA).

[0034] Step 1.2: Calculate the network-side inductance of the LCL filter and transfer the LCL filter parameters to the high-voltage side.

[0035] In practice, wind turbine converters all need to be connected to the grid via step-up transformers. To control costs, manufacturers often use the short-circuit impedance of the step-up transformer windings as the grid-side inductance. L 2. Combined with an LC filter to form an LCL filter. Therefore, in a further preferred but non-limiting embodiment of the present invention, the calculation of the grid-side inductance should be divided into the grid-side inductance with and without an LCL filter. L 2_or Two scenarios.

[0036] For using the short-circuit impedance of the step-up transformer winding as the grid-side inductance L 2, i.e., no LCL filter network-side inductor L 2_or In this case, the grid-side inductance on the low-voltage side of the transformer can be calculated according to equation (1). L 2: (1) In the formula: f 0 is the fundamental frequency. f 0 = 50Hz.

[0037] If the wind turbine converter uses a standard LCL filter, then there is an LCL filter grid-side inductance. L 2_or In the case of the step-up transformer winding short-circuit impedance, the equivalent grid-side inductance is calculated according to equation (2). Replace the grid-side inductorL 2. Perform subsequent calculations.

[0038] (2) It is worth noting that, due to the transformer, the LCL filter parameters need to be converted from the low-voltage side of the step-up transformer to the high-voltage side for subsequent resonant frequency calculation. Specifically, this can be calculated according to the turns ratio using equation (3): (3) In the formula: L H1 To account for the machine-side inductance of the LCL filter referred to the high-voltage side of the transformer, L H2 To account for the LCL filter network inductance referred to the high-voltage side of the transformer, C H This refers to the LCL filter capacitor referred to the high-voltage side of the transformer.

[0039] Step 1.3: Calculate the upper and lower limits of resonance that the LCL filter may induce in the multi-wind turbine converter cluster scenario based on the LCL filter parameters calculated in Step 1.2.

[0040] In a further preferred but non-limiting embodiment of the present invention, step 1.3 specifically includes: Step 1.2.1: When the grid connection impedance is not considered and only one wind turbine converter cluster is connected to the grid, the resonant frequency induced by the LCL filter is the highest. The corresponding frequency is taken as the upper limit resonant frequency that appears in this scenario and can be calculated according to formula (4).

[0041] (4) Step 1.2.2, considering the maximum grid connection impedance and all n When the typhoon generator converter cluster is connected to the grid, the resonant frequency induced by the LCL filter is the lowest. The corresponding frequency is taken as the lower limit resonant frequency in this scenario and can be calculated according to formula (5).

[0042] (5) In the formula: L g_max The inductance corresponding to the maximum grid-connected impedance at the point of common connection is, more preferably, calculated according to equation (6).

[0043] (6) Step 1.2.3, set the resonant frequency range in the multi-wind turbine converter cluster scenario caused by the inherent characteristics of the LCL filter body of the wind turbine converter and the interactive coupling between the filter and the power grid and other LCL-type wind turbine converters to []. ω rd , ωru ].

[0044] Step 2: Determine the center frequency and bandwidth of the parallel double second-order bandpass filter based on the upper and lower resonant frequencies, and use this filter to construct a wideband virtual damping in the control loop of the wind turbine converter.

[0045] In a preferred but non-limiting embodiment of the present invention, step 2 specifically includes: Step 2.1: Select two second-order bandpass filters with the same gain connected in parallel to construct a basic form of broadband virtual damping in the control loop of the wind turbine converter. The corresponding transfer function is shown in equation (7): (7) In the formula: ω 1 and ω 2 represents the center frequencies of the parallel dual second-order bandpass filters; ω c1 and ω c2 These are the bandwidths of the parallel dual second-order bandpass filters; k z This represents the gain of the parallel double second-order bandpass filter.

[0046] Step 2.2, the upper and lower resonant frequencies are taken as the center frequencies of the above-mentioned dual second-order bandpass filter, respectively, and expressed by the following formula (8): (8) Step 2.3, the difference between the upper and lower resonant frequencies is taken as the bandwidth of the above-mentioned dual second-order bandpass filter, as expressed by the following formula (9): (9) Step 2.4: Based on the upper and lower limit frequencies of the resonance that the LCL filter may induce in the multi-wind turbine converter cluster scenario calculated in Step 1.3, substitute Equations (8) and (9) into Equation (7) to obtain the broadband virtual damping constructed in the control loop of the wind turbine converter, as shown in Equation (10).

[0047] (10) Step 3: Extract the voltage harmonic components of the common connection point of the multi-wind turbine converter cluster and multiply them with the broadband virtual damping to obtain the broadband harmonic current control command of the wind turbine converter.

[0048] In a preferred but non-limiting embodiment of the present invention, step 3 specifically includes: Step 3.1: In order to reduce the influence of broadband virtual damping on the fundamental component of the wind power converter, a cascaded generalized integrator (CGI) with a transfer function as shown in Equation (11) is selected to extract the fundamental component of the point of common coupling voltage. The point of common coupling voltage is subtracted from the fundamental component according to Equation (12) to obtain the harmonic components.

[0049] (11) In the formula: ω 0 represents the center frequency of the cascaded generalized integrator; k c For the gain of the cascaded generalized integrator. In a further preferred but non-limiting embodiment, for extracting the fundamental component of the point of common coupling voltage, ω 0 is taken as the fundamental angular frequency, i.e. ω 0 = 2π f 0; To balance dynamic performance, k c The value is 1.

[0050] (12) In the formula: u PCC (αβ) represents the voltage at the common connection point in the αβ coordinate system; u h (αβ) represents the harmonic components of the voltage at the common connection point in the αβ coordinate system.

[0051] Step 3.2: The harmonic components of the point of common coupling voltage are processed by a wideband virtual damper constructed using parallel double second-order bandpass filters to obtain the wideband harmonic current control command of the wind turbine converter in the αβ coordinate system. i h_ref (αβ), expressed by the following formula: (13) Step 4: Construct a wideband harmonic composite controller for the wind turbine converter. Input the wideband harmonic current control command into the composite controller to generate a drive signal, thereby realizing the wideband harmonic active damping multiplexing function of the wind turbine converter.

[0052] In a preferred but non-limiting embodiment of the present invention, step 4 specifically includes: Step 4.1, to achieve zero steady-state error control for each harmonic over a wide frequency range and ensure response performance, an embedded proportional controller and a repetitive controller are combined to form a composite controller. In a further preferred but non-limiting embodiment of the present invention, step 4.1 specifically includes: Step 4.1.1, set the proportional controller according to formula (14): (14) In the formula: kp The proportional gain is for proportional control, and its specific value range is determined by the performance and stability of the wind turbine converter.

[0053] Step 4.1.2, set the repeat controller according to formula (15): (15) In the formula: Q The cumulative error control coefficient for repetitive control is recommended to be 0.95; T 0 represents the fundamental period of the system. T 0 = 0.02s.

[0054] Step 4.1.3: Connect the proportional controller and the repetitive controller in series to realize the composite controller of the wideband active damping control loop of the wind turbine converter in an embedded manner. The transfer function of the composite controller is shown in equation (16): (16) Step 4.2: Using the same cascaded generalized integrator (CGI) with the same parameters as in Step 3.1, extract the harmonic components of the output current of the wind turbine converter in the same way as the voltage harmonic components in Step 3.1, as shown in Equation (17): (17) In the formula: i R (αβ) represents the output current of the wind turbine converter in the αβ coordinate system; i h (αβ) represents the harmonic components of the output current of the wind turbine converter in the αβ coordinate system.

[0055] Step 4.3, transmit the broadband harmonic current control command. i h_ref (αβ) and harmonic components of the output current of the wind turbine converter i h (αβ) Comparison, input composite controller generates modulation wave, and then generates drive signal through PWM modulation to realize the wideband active damping multiplexing function of wind turbine converter.

[0056] Step 5: When the multiplexing function is not enabled, expand the resonant frequency range of the LCL filter and calculate the total harmonic distortion (THD) of the voltage at the common connection point of the multi-wind turbine converter cluster within the expanded resonant frequency range. Based on the difference between the THD and the set target value, determine the iteration step size of the broadband virtual damping gain.

[0057] The control system diagram of the wind turbine converter with wideband active damping multiplexing function is shown below. Figure 2 As shown, in a preferred but non-limiting embodiment of the present invention, step 5 specifically includes: Step 5.1: When the multiplexing function is not enabled, the voltage at the common coupling point of the multi-wind turbine converter cluster is analyzed using FFT at a single-cycle time interval to obtain the fundamental and harmonic voltage amplitudes, which are respectively... and The highest harmonic order required for FFT analysis. h max The corresponding frequency must be higher than the sum of the differences between the upper and lower resonant frequencies, i.e.: (18) Step 5.2, considering the resonance amplification effect caused by the cluster of multiple LCL wind turbine converters, the upper and lower resonance frequency ranges are extended by half the difference between the lower and upper resonance frequencies, and the total harmonic distortion rate of the calculated voltage after the extension is determined according to formula (19). THDu r Upper limit of harmonic order (%) h u and lower limit harmonic order h d It can be expressed by the following formula: (19) In the formula: This is for rounding up; This is for floor function.

[0058] Step 5.3: According to equation (20), perform the square root operation on the harmonic voltages within the upper and lower harmonic orders, and then calculate the percentage relative to the fundamental voltage to obtain the total harmonic distortion rate of the harmonic voltages within the extended resonant frequency range. THDu r (%), expressed by the following formula: (20) Step 5.4: Set the target value for the total harmonic distortion of the global voltage to be suppressed to be [value missing]. THDu g (%).

[0059] In a preferred but non-limiting embodiment of the present invention, the total harmonic distortion rate (THD) limit specified in standard GB / T 14549 is used as the target value for the global THD; or, based on system stability or other safe operating procedures, an empirical value not exceeding the national standard limit is set for the global THD. In an exemplary but non-limiting embodiment of the present invention... THDu g The value is set at 0.5%.

[0060] Step 5.5: The difference (percentage) between the total harmonic distortion rate of the voltage within the extended resonant frequency range when the multiplexing function is not enabled is used as the gain iteration step size for the wideband virtual damping constructed by the parallel dual second-order bandpass filters, expressed by the following formula: (twenty one) Step 6: Set the initial gain value and enable the multiplexing function. Iterate and update the gain of the broadband virtual damping step by step until the total harmonic distortion rate of the voltage at the real-time detected common connection point in the extended resonant frequency range is not higher than the target value. Complete the adaptive determination of the final broadband virtual damping gain value according to the set target value, and realize the global broadband resonance adaptive suppression of the multi-wind turbine converter cluster.

[0061] In a preferred but non-limiting embodiment of the invention, k z =0 is used as the initial value for the broadband virtual damping gain.

[0062] In a preferred but non-limiting embodiment of the present invention, the total harmonic distortion (THD) of the voltage within the resonant frequency range of the LCL filter after the common connection point is expanded in step 5.2 is detected in real time. When the THD (detected value) is in a relatively stable state, it is compared with the target value of the global harmonic voltage THD. Based on the comparison result, it is determined whether to proceed to the next iteration for gain. Specifically, this includes: When the detected value is greater than the target value, that is At that time, the broadband virtual damping gain is updated according to Equation (22) with an iteration step size, and the new stable detection value after gain iteration is compared with the target value.

[0063] (twenty two) When the detected value is equal to or less than the target value, that is At this time, the corresponding broadband virtual damping gain is the final required value, thereby realizing the global broadband resonance adaptive suppression of the multi-wind turbine converter cluster as expected.

[0064] More preferably, the steady state is measured by the relative rate of change between the current total harmonic distortion rate of the voltage and the previous adjacent total harmonic distortion rate. When the rate of change does not exceed 5%, it is considered to have reached a relatively stable state.

[0065] To better understand this invention, the above process is described in detail below with specific examples. The values ​​used in this example are merely illustrative, and users can make corresponding changes according to their actual needs. Taking a multi-wind turbine converter cluster in a wind farm as an example, each converter in this wind farm uses a step-up transformer as the grid-side inductor to form an LCL filter. The specific parameters of the converter, step-up transformer, and grid in this scenario are as follows: Table 1. Collected System Parameters

[0066] Based on the collected parameters of the multi-wind turbine converter cluster, the grid-side inductance formed by the short-circuit impedance of the step-up transformer is calculated according to equation (1). L 2 = 2.35 × 10 -5 H, then according to equation (3), all LCL filter parameters are converted to the high-voltage side of the step-up transformer, where the machine-side inductance L H1 =514.59×10 -3 H, Network-side inductor L H2 =60.46×10 -3 H, Filter capacitor C H =0.175×10 - 6 F; In addition, the inductance corresponding to the maximum grid impedance at the point of common coupling is calculated according to equation (6). L g_max =10×10 -3 H. Finally, substituting the calculation results of the above variables into equations (4) and (5) respectively, we obtain the upper limit resonant frequency induced by the LCL filter. ω ru =10277.05 rad / s and lower limit resonant frequency ω rd =6834.93rad / s, then the resonant frequency range of the LCL filter body of the wind turbine converter and the interaction coupling between it and the power grid and other LCL wind turbine converters is [6834.93, 10277.05].

[0067] A wideband virtual damping is constructed in the control loop of the wind turbine converter using two parallel second-order bandpass filters of the same gain. The upper and lower resonant frequencies are used as the center frequencies of the parallel two second-order bandpass filters, respectively. ω 1= ω ru =10277.05 rad / s, ω 2= ω rd =6834.93 rad / s; the difference between the upper and lower resonant frequencies is taken as the bandwidth of the above-mentioned parallel dual second-order bandpass filter, i.e. ω c1 = ω c2 = ω ru - ω rd=3442.12 rad / s. Under different gain conditions, the broadband virtual damping frequency response characteristics constructed by the above-mentioned parallel double second-order bandpass filters are as follows: Figure 3 As shown in the Bode Diagram, the horizontal axis represents frequency in radians per second (rad / s), and the vertical axis represents magnitude in decibels (dB).

[0068] The cascaded generalized integrator of Equation (11) is used to extract the fundamental component of the common coupling point voltage of the multi-wind turbine converter cluster. The common coupling point voltage is subtracted from the fundamental component according to Equation (12) to obtain the harmonic components. Then, the harmonic components are multiplied by the broadband virtual damping to obtain the broadband harmonic current control command of the wind turbine converter. i h_ref (αβ), and harmonic components of the output current of the wind turbine converter. i h (αβ) Comparison: The input is a composite controller consisting of a proportional control and a repetitive control in an embedded manner. This patent sets the proportional gain of the proportional control. k p The value is 400, which generates a modulation wave, and then generates a drive signal through PWM modulation to realize the wideband active damping multiplexing function of the wind turbine converter.

[0069] When the wind farm has 8 wind turbine converters connected to the grid at the same time, the LCL filter resonates at 7196.32 rad / s (corresponding to 1145 Hz), which amplifies the 19th to 26th harmonics in the wind farm, causing a surge in the voltage and current distortion rate at the point of common coupling, which endangers the stability and safety of the system.

[0070] When the multiplexing function is not enabled, the voltage at the common connection point of the multi-wind turbine converter cluster is detected by FFT analysis at a single cycle time interval to obtain the amplitude of the fundamental and 2nd to 50th harmonic voltages. Then, the total harmonic distortion rate of the voltage after expansion is determined according to Equation (19). THDu r Upper limit of harmonic order (%) h u =39 and lower limit harmonic order h d =16, and then calculate the total harmonic distortion of the voltage of the harmonics of concern within the extended resonant frequency range according to equation (20). THDu r =3.19%. This invention selects a target value for the global total harmonic distortion (THD). THDu g =0.5%, and finally the gain iteration step size of the wideband virtual damping composed of parallel double second-order bandpass filters is determined according to equation (21). k =2.69.

[0071] by k z =0 is used as the initial value of the broadband virtual damping gain. The multiplexing function is enabled, and the broadband virtual damping gain is iteratively updated step-by-step until the total harmonic distortion of the voltage within the resonant frequency range of the extended LCL filter is not higher than the target value. The iteration process of the gain is as follows: Figure 4 As shown, the corresponding change in total harmonic distortion (THD) of the voltage is as follows: Figure 5 As shown. The final gain value of the broadband virtual damping is adaptively determined according to the set target value. The voltage and current waveforms before and after suppression are compared, as shown below. Figure 6 and Figure 7 As shown, by developing the wideband active damping control multiplexing function of the wind turbine converter, global wideband resonance adaptive suppression of multi-wind turbine converter clusters is achieved.

[0072] Embodiment 2 of the present invention provides a global broadband suppression system for LCL filter resonance in a multi-wind turbine converter cluster, which operates the global broadband suppression method for LCL filter resonance in a multi-wind turbine converter cluster as described in Embodiment 1, including: The resonant frequency calculation module is used to collect system parameters in multi-wind turbine converter cluster scenarios and calculate the resonant frequency range of LCL filters. The virtual damping construction module is used to determine the center frequency and bandwidth of the parallel double second-order bandpass filters and construct broadband virtual damping in the control loop of the wind turbine converter. The control command generation module is used to extract the voltage harmonic components of the common connection point of the multi-wind turbine converter cluster and generate broadband harmonic current control commands for the wind turbine converter. The multiplexing function building module is used to build a wideband harmonic composite controller for wind turbine converters, generate drive signals, and realize the wideband active damping multiplexing function of wind turbine converters. The iteration step size calculation module is used to expand the resonant frequency range of LCL filters, calculate the total harmonic distortion rate of the voltage at the common connection point of a multi-wind turbine converter cluster within the expanded resonant frequency range, and determine the iteration step size of the broadband virtual damping gain. The damping gain update module is used to set the initial gain value and iteratively update the gain of the broadband virtual damping in step increments.

[0073] Compared with the prior art, the beneficial effects of the present invention include at least the following: This invention proposes a global broadband resonance suppression method and system for LCL filters in multi-wind turbine converter clusters. Considering the complex interactive resonant frequency range of LCL filters, a broadband variable virtual damping is constructed using a parallel configuration of dual bandpass filters. Active damping control is reused within the wind turbine converter cluster. Without adding equipment, a global and broadband resonance suppression effect is achieved, providing an important foundation for high-quality grid connection of high-proportion, large-scale wind power generation. Specifically, it includes: 1. This invention fully considers the resonance variation range of LCL filter in wind turbine converter clusters under complex interactive conditions, determines the frequency boundary of parallel second-order bandpass filter, and flexibly adjusts the filter gain according to the real-time detected high-frequency harmonic voltage of the power grid and the requirements of the governance target, so as to ensure the frequency applicability of broadband active damping in different scenarios and the adaptive damping value. 2. The parallel dual bandpass filter method used in this invention has a simple structure, has little impact on the response time of the control system, and has higher stability; 3. This invention avoids the problem of unsatisfactory mitigation effect caused by the detection and identification of changing resonant frequencies in complex scenarios through a wide-band damping design, and has global improvement capability; 4. This invention can solve the LCL filter resonance problem of the wind turbine converter cluster globally by multiplexing the broadband active damping function of a single or several wind turbine converters without the need for additional mitigation devices.

[0074] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for global broadband resonance suppression of LCL filters in multi-wind turbine converter clusters, characterized in that, Includes the following steps: Step 1: Collect system parameters for the multi-wind turbine converter cluster scenario. Calculate the upper and lower limits of the resonance induced by the LCL filter in this scenario based on the system parameters to obtain the resonant frequency range of the LCL filter. Step 2: Determine the center frequency and bandwidth of the parallel double second-order bandpass filter based on the upper and lower resonant frequencies, and construct a wideband virtual damping in the control loop of the wind turbine converter using the double second-order bandpass filter. Step 3: Extract the voltage harmonic components of the common connection point of the multi-wind turbine converter cluster and multiply them with the broadband virtual damping to obtain the broadband harmonic current control command of the wind turbine converter. Step 4: Construct a wideband harmonic composite controller for the wind turbine converter. Input the wideband harmonic current control command into the composite controller to generate a drive signal, thereby realizing the wideband active damping multiplexing function of the wind turbine converter. Step 5: When the multiplexing function is not enabled, expand the resonant frequency range of the LCL filter and calculate the total harmonic distortion of the voltage at the common connection point of the multi-wind turbine converter cluster within the expanded resonant frequency range. Based on the difference between the total harmonic distortion of the voltage and the set target value, determine the iteration step size of the broadband virtual damping gain. Step 6: Set the initial gain value and enable the multiplexing function. Iterate and update the gain of the broadband virtual damping step by step until the real-time detection value of the total harmonic distortion of the voltage is not higher than the target value, thus completing the global broadband resonance adaptive suppression of the multi-wind turbine converter cluster.

2. The global broadband resonance suppression method for LCL filters in multi-wind turbine converter clusters according to claim 1, characterized in that: In step 1, the resonant frequency induced by the LCL filter when the grid connection impedance is ignored and only one wind turbine converter cluster is connected to the grid is taken as the upper limit resonant frequency, expressed by the following formula: In the formula: L H1 To account for the machine-side inductance of the LCL filter referred to the high-voltage side of the transformer, L H2 To account for the LCL filter network inductance referred to the high-voltage side of the transformer, C H This refers to the LCL filter capacitor referred to the high-voltage side of the transformer.

3. The global broadband resonance suppression method for LCL filters in multi-wind turbine converter clusters according to claim 1, characterized in that: In step 1, the resonant frequency induced by the LCL filter when the grid-connected impedance is at its maximum and all wind turbine converter clusters are connected to the grid is taken as the lower limit resonant frequency, expressed by the following formula: In the formula: L H1 To account for the machine-side inductance of the LCL filter referred to the high-voltage side of the transformer, L H2 To account for the LCL filter network inductance referred to the high-voltage side of the transformer, C H The LCL filter capacitor is calculated and referred to the high-voltage side of the transformer. n The number of wind turbine converters, L g_max The inductance corresponding to the maximum grid-connected impedance at the point of common coupling.

4. The global broadband resonance suppression method for LCL filters in multi-wind turbine converter clusters according to claim 2 or 3, characterized in that: LCL filter network inductance referred to the high-voltage side of the transformer L H2 The following announcement indicates: In the formula: k T This refers to the rated turns ratio of the step-up transformer. L 2 is the grid-side inductor; Among them, the grid-side inductor L 2 is calculated in two cases: No LCL filter network-side inductor L 2_or In this case, the grid-side inductance on the low-voltage side of the transformer is calculated according to the following formula. L 2: In the formula: U d This is the short-circuit impedance of the step-up transformer. U r The rated voltage of the wind turbine converter. S T This refers to the rated capacity of the step-up transformer. f 0 represents the fundamental frequency; LCL filter network-side inductor L 2_or In this case, the equivalent grid-side inductance on the low-voltage side of the transformer is calculated according to the following formula. Replace the grid-side inductor L 2: 。 5. The global broadband resonance suppression method for LCL filters in multi-wind turbine converter clusters according to claim 1, characterized in that: Step 2 includes: selecting two second-order bandpass filters of the same gain in parallel, using the upper and lower resonant frequencies as the center frequencies of the parallel two second-order bandpass filters, and using the difference between the upper and lower resonant frequencies as the bandwidth of the two second-order bandpass filters, and constructing a wideband virtual damping in the control loop of the wind turbine converter. Its transfer function is expressed by the following formula: In the formula: k z For the gain of the parallel double second-order bandpass filter, The upper limit resonant frequency, This is the lower limit resonant frequency.

6. The global broadband resonance suppression method for LCL filters in multi-wind turbine converter clusters according to claim 1, characterized in that: In step 3, a cascaded generalized integrator is selected to extract the fundamental component of the point of common coupling voltage. The point of common coupling voltage is subtracted from the fundamental component to obtain the harmonic component. The center frequency of the cascaded generalized integrator is set as the fundamental angular frequency.

7. The global broadband resonance suppression method for LCL filters in multi-wind turbine converter clusters according to claim 1, characterized in that: In step 3, the broadband harmonic current control command of the wind turbine converter is expressed by the following formula: In the formula: i h_ref (αβ) represents the broadband harmonic current control command for the wind turbine converter in the αβ coordinate system. For broadband virtual damping, the transfer function is... u h (αβ) represents the harmonic components of the voltage at the common connection point in the αβ coordinate system.

8. The global broadband resonance suppression method for LCL filters in multi-wind turbine converter clusters according to claim 1, characterized in that: Step 4 includes: A wideband harmonic composite controller for a wind turbine converter is constructed by combining a proportional controller and a repetitive controller in an embedded manner. The wideband harmonic current control command is compared with the harmonic components of the output current of the wind turbine converter, and input into the composite controller to generate a modulation wave. The drive signal is generated by PWM modulation to realize the wideband active damping multiplexing function of the wind turbine converter.

9. The global broadband resonance suppression method for LCL filters in multi-wind turbine converter clusters according to claim 1, characterized in that: In step 5, expanding the resonant frequency range of the LCL filter includes: Using half the difference between the lower and upper resonant frequencies, the resonant frequency range is extended both upwards and downwards to determine the upper harmonic order for calculating the total harmonic distortion of the voltage. h u and lower limit harmonic order h d It can be expressed by the following formula: In the formula: For floor operations, For floor operations, The upper limit resonant frequency, The lower limit resonant frequency, f 0 represents the fundamental frequency.

10. The global broadband resonance suppression method for LCL filters in multi-wind turbine converter clusters according to claim 1, characterized in that: In step 5, the principle for setting the target value is as follows: The target value for the total harmonic distortion rate (THD) of the global voltage is set using the standard-specified limit for total harmonic distortion (THD) or based on empirical values.

11. The global broadband resonance suppression method for LCL filters in multi-wind turbine converter clusters according to claim 1, characterized in that: In step 6, the gain of the broadband virtual damping is iteratively updated step by step until the real-time detected value of the total harmonic distortion of the voltage is not higher than the target value, including: The total harmonic distortion (THD) of the voltage at the common connection point is detected in real time within the extended resonant frequency range. When the THD is in a relatively stable state, it is compared with the target value of the global harmonic voltage THD. Based on the comparison result, it is determined whether to proceed to the next iteration based on the gain. When the detected value is greater than the target value, the broadband virtual damping gain is updated by the iteration step size, and the new stable detected value after the gain iteration is compared with the target value. When the detected value is equal to or less than the target value, the corresponding broadband virtual damping gain is the final required value.

12. A global broadband suppression system for LCL filter resonance in a multi-wind turbine converter cluster, implementing the global broadband suppression method for LCL filter resonance in a multi-wind turbine converter cluster as described in any one of claims 1-11, characterized in that, include: The resonant frequency calculation module is used to collect system parameters in multi-wind turbine converter cluster scenarios and calculate the resonant frequency range of LCL filters. The virtual damping construction module is used to determine the center frequency and bandwidth of the parallel double second-order bandpass filters and construct broadband virtual damping in the control loop of the wind turbine converter. The control command generation module is used to extract the voltage harmonic components of the common connection point of the multi-wind turbine converter cluster and generate broadband harmonic current control commands for the wind turbine converter. The multiplexing function building module is used to build a wideband harmonic composite controller for wind turbine converters, generate drive signals, and realize the wideband active damping multiplexing function of wind turbine converters. The iteration step size calculation module is used to expand the resonant frequency range of LCL filters, calculate the total harmonic distortion rate of the voltage at the common connection point of a multi-wind turbine converter cluster within the expanded resonant frequency range, and determine the iteration step size of the broadband virtual damping gain. The damping gain update module is used to set the initial gain value and iteratively update the gain of the broadband virtual damping in step increments.

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