Offshore wind plant centralized active harmonic suppression method and device and storage medium

Abstract

The invention discloses an offshore wind power plant centralized active harmonic suppression method and device and a storage medium, and the method comprises the following steps: building a grid-connected system overall impedance model based on an offshore wind power plant grid-connected system according to the transmission relation between an AC harmonic voltage vector and an AC harmonic current vector, adding a control model to the frequency domain impedance model of the single SVG, obtaining the optimal parameters of the control model based on the control model and the overall impedance model of the grid-connected system, and obtaining a control signal according to the control model and the optimal parameters; and adding a control signal in a control loop of a corresponding single SVG in the offshore wind plant grid-connected system so as to suppress harmonic waves in the offshore wind plant grid-connected system. According to the centralized active harmonic suppression method for the offshore wind plant, additional sampling equipment does not need to be added, the economical efficiency is good, the robustness is high, the operation stability of a grid-connected system of the offshore wind plant is improved, and the electric energy quality is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a centralized active harmonic suppression method, device and storage medium for an offshore wind farm. Background Art

[0002] The large-scale access of new energy equipment to the power grid has made the harmonic problem of the power system increasingly serious. In addition, due to the geographical distribution characteristics of my country's load and energy, there are many scenarios in which electricity is transmitted through long-distance AC transmission lines. The capacitance effect of long-distance transmission lines can easily raise the resonance peak of the system's grid connection point, amplifying the background harmonics. The harmonic level at the grid connection point exceeds the standard, causing equipment damage, wind turbine disconnection and other accidents, seriously affecting the stable operation of the power system and the safe absorption of electricity.

[0003] The above-mentioned problems are particularly serious in offshore wind farm grid-connected systems. my country's offshore wind power is often transmitted using high-voltage AC submarine cables. Multiple submarine cables are connected in parallel, which makes the resonance point frequency between the offshore wind farm and the onshore AC power grid lower. The resonance frequency is close to the specific harmonic frequency. Coupled with the low inertia and weak damping characteristics of the offshore wind farm grid-connected system, the harmonic problem is significant. Existing research solutions are not targeted enough to this problem, and can often only suppress single-frequency harmonics, which is not enough to solve the problem of background harmonic resonance and cannot centrally suppress background harmonics at different frequencies from the system level. Summary of the invention

[0004] In order to solve the above-mentioned problems in the prior art, the present invention provides a centralized active harmonic suppression method for offshore wind farms, which aims to suppress harmonics of various frequencies under different operating conditions of offshore wind farms connected to the grid via cables or overhead lines, so as to ensure the safe and stable operation of offshore wind farms.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides a centralized active harmonic suppression method for an offshore wind farm, comprising the following steps:

[0006] Construct the grid-connected system topology based on the offshore wind farm grid-connected system;

[0007] Based on the offshore wind farm grid-connected system, main circuit parameters and control parameters are obtained;

[0008] Based on the transmission relationship between the AC harmonic voltage vector and the AC harmonic current vector and the topological structure of the grid-connected system, a frequency domain impedance model of a single direct-drive wind turbine and a frequency domain impedance model of a single SVG are respectively constructed according to the main circuit parameters and the control parameters;

[0009] Based on the grid-connected system topology, a frequency domain impedance model of a submarine cable and a frequency domain impedance model of an AC power grid are respectively constructed according to the main circuit parameters and the control parameters;

[0010] Based on the grid-connected system topology, an overall impedance model of the grid-connected system is obtained according to the frequency domain impedance model of the single SVG, the frequency domain impedance model of the AC power grid, the frequency domain impedance model of a single direct-drive wind turbine, and the frequency domain impedance model of the submarine cable;

[0011] Based on the overall impedance model of the grid-connected system, a control model is added to the frequency domain impedance model of the single SVG to obtain the overall impedance model of the grid-connected system after the control model is added;

[0012] Obtaining optimal parameters of the control model according to the overall impedance model of the grid-connected system and the overall impedance model of the grid-connected system after the control model is added;

[0013] Obtaining a control signal based on the optimal parameters of the control model and the control model; adding the control signal to a control loop of a single SVG corresponding to the frequency domain impedance model of the single SVG in the offshore wind farm grid-connected system based on the grid-connected system topology;

[0014] The single SVG based on the additional control signal in the control loop suppresses harmonics in the offshore wind farm grid-connected system.

[0015] Furthermore, the steps of constructing the frequency domain impedance model of the single direct-drive wind turbine are:

[0016] Based on the steady-state operation state, the transfer relationship between the AC harmonic voltage vector and the AC harmonic current vector of a single direct-drive wind turbine is calculated to obtain a frequency domain impedance model of the single direct-drive wind turbine;

[0017] The frequency domain impedance model of the single direct-drive fan is:

[0018]

[0019] In the formula, Z VSC (s) is the frequency domain impedance of the direct-drive fan, G mod2val is the small signal transfer function from the modulation signal to the valve side voltage, G i2mod is the small signal transfer function from AC current to modulated signal, G v2mod is the small signal transfer function from AC voltage to modulated signal, L fVSC is the filter inductor of the direct-drive fan, R VSC is the resistance of the direct-drive wind turbine, and s is the Laplace operator.

[0020] Furthermore, the steps of constructing the frequency domain impedance model of the SVG are:

[0021] Based on the steady-state operation state, the transfer relationship between the AC harmonic voltage vector and the AC harmonic current vector of a single SVG is calculated to obtain a frequency domain impedance model of the SVG;

[0022] The frequency domain impedance model of the SVG is:

[0023]

[0024] In the formula, Z SVG (s) is the frequency domain impedance of SVG, G mod2val is the small signal transfer function from the modulation signal to the valve side voltage, G i2mod is the small signal transfer function from AC current to modulated signal, G v2mod is the small signal transfer function from AC voltage to modulated signal, G dc2val is the small signal transfer function from capacitor voltage to valve side voltage, G i2dc is the small signal transfer function from AC current to capacitor voltage, G v2dc is the small signal transfer function from AC voltage to capacitor voltage, G dc2mod is the small signal transfer function from capacitor voltage to modulation signal, L fSVG is the filter inductance of SVG, R SVG is the resistance of SVG, and s is the Laplace operator.

[0025] Furthermore, the π-type equivalent is adopted to construct the submarine cable frequency domain impedance model according to Formula 1, which is:

[0026]

[0027]

[0028]

[0029]

[0030] In the formula, Z l is the equivalent impedance of the series branch of the line, Z c is the wave impedance, γ is the propagation constant, is the length of the submarine cable, Y p is the equivalent impedance of the parallel branch of the line, L0 is the equivalent inductance per unit length of the submarine cable, C0 is the equivalent capacitance per unit length of the submarine cable, R0 is the equivalent resistance per unit length of the submarine cable, ω is the angular frequency, and j is the imaginary unit.

[0031] Further, the control model includes a single-channel control module or a plurality of single-channel control modules connected in parallel, and the single-channel control module includes a proportional link, a band-pass filter link and a second-order low-pass filter link cascaded in sequence;

[0032] The transfer function of the single-channel control module is:

[0033] G sc (s) = Kv G BPF (s)G LPF (s),

[0034]

[0035]

[0036] In the formula, G sc is the transfer function of the single-channel control module, K v is the magnification factor of the proportional link, G BPF is the transfer function of the bandpass filter, G LPF is the transfer function of the second-order low-pass filter, s is the Laplace operator, Q is the quality factor, ω c is the characteristic angular frequency.

[0037] Furthermore, the steps of obtaining the optimal parameters of the control model are:

[0038] Obtaining an objective function of the single-channel control module according to the transfer function of the single-channel control module and the overall impedance model of the grid-connected system;

[0039] Obtain the parameters to be optimized according to the objective function; construct constraints according to the objective function, and the constraints are:

[0040] F(f)<F set ;

[0041] In the formula, F set is the boundary constraint value;

[0042] Obtaining the feasible region boundary of the parameter to be optimized according to the constraint condition;

[0043] Obtaining optimal parameters of a single-channel control module according to the objective function and the feasible region boundary of the parameters to be optimized;

[0044] Based on the control model, optimal parameters of the control model are obtained according to optimal parameters of the single-channel control module.

[0045] Further, the parameters to be optimized include the amplification factor of the proportional link and the characteristic frequency; the overall impedance model of the grid-connected system after the additional control model includes the overall impedance model of the grid-connected system after the additional single-channel control;

[0046] The steps of obtaining the objective function of the single-channel control module are:

[0047] Let the bandpass center frequency of the transfer function of the bandpass filter link and the cutoff frequency of the transfer function of the second-order low-pass filter link be equal to the characteristic frequency respectively;

[0048] Obtaining the harmonic frequency of the offshore wind farm grid-connected system;

[0049] Based on the harmonic frequency and the overall impedance model of the grid-connected system, calculating the overall impedance of the grid-connected system before additional single-channel control and the average phase margin before additional single-channel control;

[0050] Obtaining the overall impedance model of the grid-connected system after the additional single-channel control based on the transfer function of the single-channel control module and the overall impedance model of the grid-connected system;

[0051] Based on the harmonic frequency and the overall impedance model of the grid-connected system after the additional single-channel control, calculating the overall impedance of the grid-connected system after the additional single-channel control and the average phase margin after the additional single-channel control;

[0052] Based on the harmonic frequency, the objective function of the single-channel control module is constructed according to the amplification factor of the proportional link, the characteristic frequency, the overall impedance of the grid-connected system before the additional single-channel control, the overall impedance of the grid-connected system after the additional single-channel control, the average phase margin before the additional single-channel control, and the average phase margin after the additional single-channel control; the objective function is:

[0053]

[0054] In the formula, F is the objective function, Z sc is the overall impedance of the grid-connected system after adding single-channel control, K v is the magnification factor of the proportional link, f c is the characteristic frequency, f is the harmonic frequency, Z0 is the overall impedance of the grid-connected system before adding single-channel control, P sc P0 is the average phase margin before adding single-channel control, and P1 is the average phase margin after adding single-channel control.

[0055] Further, the average phase margin before the additional single-channel control and the average phase margin after the additional single-channel control are calculated according to Formula 2, and the Formula 2 is:

[0056]

[0057] Where P is the average phase margin, L is the length of the frequency band considered, Z is the overall impedance of the grid-connected system, and ∠Z(f) is the phase angle of Z at f.

[0058] A device for implementing the offshore wind farm centralized active harmonic suppression method, comprising a modeling unit, a calculation unit and a control application unit;

[0059] The modeling unit:

[0060] Used to construct the grid-connected topology structure according to the offshore wind farm grid-connected system;

[0061] Used to construct a frequency domain impedance model of a single direct-drive wind turbine and a frequency domain impedance model of a single SVG respectively based on the transmission relationship between the AC harmonic voltage vector and the AC harmonic current vector and the topological structure of the grid-connected system, according to the main circuit parameters and the control parameters;

[0062] Used to construct a frequency domain impedance model of a submarine cable and a frequency domain impedance model of an AC power grid respectively based on the grid-connected system topology structure and according to the main circuit parameters and the control parameters;

[0063] Used to obtain the overall impedance model of the grid-connected system based on the topological structure of the grid-connected system, according to the frequency domain impedance model of the single SVG, the frequency domain impedance model of the AC power grid, the frequency domain impedance model of a single direct-drive wind turbine and the frequency domain impedance model of the submarine cable;

[0064] Used to add a control model to the frequency domain impedance model of the single SVG based on the overall impedance model of the grid-connected system and obtain the overall impedance model of the grid-connected system after adding the control model;

[0065] The calculation unit is used to obtain the optimal parameters of the control model according to the overall impedance model of the grid-connected system and the overall impedance model of the grid-connected system after the control model is added;

[0066] The control application unit is used to obtain a control signal based on the optimal parameters of the control model and the control model, to add a control signal in a control loop of a single SVG corresponding to the frequency domain impedance model of the single SVG in the offshore wind farm grid-connected system based on the grid-connected system topology, and to suppress harmonics in the offshore wind farm grid-connected system based on the single SVG to which the control signal is actually added in the control loop.

[0067] Further, the modeling unit includes a topology building module, an impedance model building module and a control model building module;

[0068] The topology building module is used to build the grid-connected system topology structure according to the offshore wind farm grid-connected system;

[0069] The impedance model construction module is used to construct the frequency domain impedance model of the single direct-drive wind turbine, the frequency domain impedance model of the single SVG, the frequency domain impedance model of the AC power grid and the frequency domain impedance model of the submarine cable according to the offshore wind farm grid-connected system and the grid-connected system topology structure, and is used to construct the overall impedance model of the grid-connected system according to the grid-connected system topology structure, the frequency domain impedance model of the single direct-drive wind turbine, the frequency domain impedance model of the single SVG, the frequency domain impedance model of the AC power grid and the frequency domain impedance model of the submarine cable;

[0070] The control model building module is used to add a control model to the frequency domain impedance model of a single SVG of the overall impedance model of the grid-connected system and obtain the overall impedance model of the grid-connected system after the additional single-channel control.

[0071] Furthermore, a storage medium includes a stored program, and when the program is run, the device where the storage medium is located is controlled to execute the centralized active harmonic suppression method for offshore wind farms.

[0072] The beneficial effects of the present invention are as follows: the present invention does not require the addition of additional devices to the offshore wind farm grid-connected system, does not require the provision of additional sampling equipment for the SVG, has good economy, can adapt to different operating conditions of the system, has certain robustness, enhances the operating stability of the offshore wind farm grid-connected system, and improves the quality of electric energy.

[0073] The present invention can centrally suppress background harmonics at different frequencies at the system level, thereby ensuring the stable operation of the power system and the safe consumption of electric energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 It is a flow chart of the centralized active harmonic suppression method for offshore wind farms of the present invention;

[0075] Figure 2 A schematic diagram of a topological structure of a grid-connected system constructed based on an offshore wind farm grid-connected system in an embodiment of the present invention;

[0076] Figure 3 Schematic diagram of a small signal transmission path of a direct-drive fan and SVG in an embodiment of the present invention;

[0077] Figure 4 It is a schematic diagram of the submarine cable frequency domain impedance model of a 220kV high voltage AC submarine cable and a 35kV collector submarine cable in an embodiment of the present invention;

[0078] Figure 5 It is a schematic diagram of an SVG control loop after adding a control signal in an embodiment of the present invention;

[0079] Figure 6 A schematic diagram of frequency conversion after considering specific subharmonics in an embodiment of the present invention;

[0080] Figure 7 for Figure 5 The feasible domain boundaries of the parameters to be optimized in the objective function corresponding to the additional control signal shown in FIG: (a) is channel 1, and (b) is channel 2. DETAILED DESCRIPTION

[0081] In order to clearly illustrate the technical features of this solution, this solution is described below through a specific implementation method.

[0082] See also Figure 1 The embodiment of the present invention provides a centralized active harmonic suppression method for an offshore wind farm, comprising the following steps:

[0083] Construct the grid-connected system topology based on the offshore wind farm grid-connected system;

[0084] Based on the offshore wind farm grid-connected system, obtain the main circuit parameters and control parameters;

[0085] Based on the transmission relationship between the AC harmonic voltage vector and the AC harmonic current vector and the topological structure of the grid-connected system, the frequency domain impedance model of a single direct-drive wind turbine and the frequency domain impedance model of a single SVG are constructed according to the main circuit parameters and control parameters. Specifically:

[0086] The steps of constructing the frequency domain impedance model of a single direct-drive wind turbine are as follows: adopting the harmonic linearization method, specifically: assuming that the single direct-drive wind turbine is in a steady-state operation state, at this time, a harmonic voltage signal is injected into the port of the single direct-drive wind turbine, and the transfer relationship between the AC harmonic voltage vector and the AC harmonic current vector of the single direct-drive wind turbine is calculated, and the frequency domain linearization expression of the single direct-drive wind turbine is established, that is, based on the steady-state operation state, the transfer relationship between the AC harmonic voltage vector and the AC harmonic current vector of the single direct-drive wind turbine is calculated, and the control parameters and the main circuit parameters of the direct-drive wind turbine are substituted into the calculation process to obtain the frequency domain impedance model of the single direct-drive wind turbine. The main circuit parameters of the direct-drive wind turbine include the filter inductance of the direct-drive wind turbine and the resistance of the direct-drive wind turbine. The control parameters participate in the calculation of each transfer function. This is the prior art and will not be repeated here. Since the harmonic frequency studied in the present invention is relatively high, the impedance model of a single direct-drive wind turbine in the present invention only considers the dynamic characteristics of the grid-side converter of the direct-drive wind turbine. The frequency domain impedance model of a single direct-drive wind turbine is:

[0087]

[0088] In the formula, Z VSC (s) is the frequency domain impedance of the direct-drive fan, G mod2val is the small signal transfer function from the modulation signal to the valve side voltage, G i2mod is the small signal transfer function from AC current to modulated signal, G v2modis the small signal transfer function from AC voltage to modulated signal, L fVSC is the filter inductor of the direct-drive fan, R VSC is the resistance of the direct-drive wind turbine, s is the Laplace operator; G mod2val , G i2mod , G v2mod All are functions of s, and s is omitted for simplicity. The frequency domain impedance model of a single direct-drive fan established based on the above transfer function clearly shows the position of different control loops in the frequency domain impedance model of a single direct-drive fan. If the control logic of the direct-drive fan is changed, only the corresponding transfer function needs to be changed. Based on this, the frequency domain impedance characteristics of a single direct-drive fan can be easily calculated, which has the characteristics of easy expansion.

[0089] The steps of constructing the frequency domain impedance model of SVG are as follows: Similar to the steps of constructing the frequency domain impedance model of a single direct-drive wind turbine, a harmonic linearization method is used, assuming that a single SVG is in a steady-state operation state, a harmonic voltage signal is injected into the port of the single SVG at this time, and the transfer relationship between the AC harmonic voltage vector and the AC harmonic current vector of the single SVG is calculated, and a frequency domain linearization expression of a single SVG is established, that is, based on the steady-state operation state, the transfer relationship between the AC harmonic voltage vector and the AC harmonic current vector of the single SVG is calculated, and the control parameters and the main circuit parameters of SVG are substituted into the calculation process to obtain the frequency domain impedance model of SVG. The main circuit parameters of SVG include the filter inductance of SVG and the resistance of SVG, and the control parameters participate in the calculation of each transfer function. This is a prior art and will not be repeated here; the small signal transmission path of the direct-drive wind turbine (PMSG) and SVG is as follows Figure 3 As shown;

[0090] The frequency domain impedance model of a single SVG in the present invention is obtained by considering the transmission relationship between DC capacitance and AC voltage and AC current on the basis of the frequency domain impedance model of a single direct-drive wind turbine. The frequency domain impedance model of a single SVG is:

[0091]

[0092] In the formula, Z SVG (s) is the frequency domain impedance of SVG, G mod2val is the small signal transfer function from the modulation signal to the valve side voltage, G i2mod is the small signal transfer function from AC current to modulated signal, G v2mod is the small signal transfer function from AC voltage to modulated signal, G dc2val is the small signal transfer function from capacitor voltage to valve side voltage, G i2dc is the small signal transfer function from AC current to capacitor voltage, G v2dc is the small signal transfer function from AC voltage to capacitor voltage, G dc2modis the small signal transfer function from capacitor voltage to modulation signal, L fSVG is the filter inductance of SVG, R SVG is the resistance of SVG, s is the Laplace operator, and similarly, G mod2val , G i2mod , G v2mod , G dc2val , G i2dc , G v2dc , G dc2mod All are functions of s, and s is omitted for simplicity. It should be clarified that all transfer functions in the frequency domain impedance model of a single SVG in the present invention are related to the control structure and control parameters of the actual single SVG. When the control structure changes, it is only necessary to modify the transfer function of the corresponding position. For example, the transfer function of the single-channel control module proposed in the present invention is G sc (s), the additional position is between the inner loop output end and the PWM input end, and the single-pass control module is added in parallel. Therefore, the control signal added by the present invention directly acts on the PWM input end without passing through the inner loop and the outer loop. The single-pass control module added in parallel does not change the transfer function of the original control. It only needs to add G to the numerator and denominator in the above formula. sc The frequency domain impedance model of a single SVG proposed in the present invention has the characteristic of being easily expandable and can clearly demonstrate the effect of the small signal transmission path on the impedance.

[0093] Based on the topological structure of the grid-connected system, a frequency domain impedance model of the submarine cable and a frequency domain impedance model of the AC power grid are respectively constructed according to the main circuit parameters and the control parameters; specifically: constructing the frequency domain impedance model of the AC power grid is an existing technology and will not be described in detail here;

[0094] When constructing the submarine cable frequency domain impedance model, obtain the submarine cable length, equivalent inductance per unit length of the submarine cable, equivalent capacitance per unit length of the submarine cable, and equivalent resistance per unit length of the submarine cable, see Figure 2 The grid-connected system topology in the offshore wind farm includes a 220kV high-voltage AC submarine cable ( Figure 2 Medium and high voltage AC submarine cable) and 35kV collector submarine cable ( Figure 2 CIMC submarine cable) adopts π-type equivalent, considers the distributed parameter characteristics of the line, modifies the impedance model parameters in the frequency domain according to the length, and constructs the submarine cable frequency domain impedance model according to formula 1, which is:

[0095]

[0096]

[0097]

[0098]

[0099] In the formula, Z l is the equivalent impedance of the series branch of the line, Z c is the wave impedance, γ is the propagation constant, is the length of the submarine cable, Y p is the equivalent impedance of the parallel branch of the line, L0 is the equivalent inductance per unit length of the submarine cable, C0 is the equivalent capacitance per unit length of the submarine cable, R0 is the equivalent resistance per unit length of the submarine cable, ω is the angular frequency, and j is the imaginary unit.

[0100] The submarine cable frequency domain impedance model includes a transmission submarine cable impedance model and a collection submarine cable impedance model: based on the grid-connected system topology, a transmission submarine cable impedance model is constructed for a pair of 220kV high-voltage AC submarine cables according to the formula, and a collection submarine cable impedance model is constructed for a pair of 35kV collection submarine cables according to the formula.

[0101] Based on the topological structure of the grid-connected system, the overall impedance model of the grid-connected system is obtained according to the frequency domain impedance model of a single SVG, the frequency domain impedance model of the AC power grid, the frequency domain impedance model of a single direct-drive wind turbine, and the frequency domain impedance model of the submarine cable.

[0102] Based on the overall impedance model of the grid-connected system, a control model is added to the frequency domain impedance model of a single SVG to obtain the overall impedance model of the grid-connected system after adding the control model. Figure 1 , the frequency domain impedance model of the control model pointing to a single SVG represents the additional direction of the control model;

[0103] Obtaining optimal parameters of the control model according to the overall impedance model of the grid-connected system and the overall impedance model of the grid-connected system after adding the control model;

[0104] obtaining a control signal based on optimal parameters of the control model and the control model;

[0105] Based on the grid-connected system topology, a control signal is added to the control loop of a single SVG corresponding to the frequency domain impedance model of a single SVG in the offshore wind farm grid-connected system, see Figure 1 , the control signal is directed to a single SVG, indicating the additional direction of the control signal;

[0106] Single SVG suppresses harmonics in offshore wind farm grid-connected systems based on additional control signals in the control loop, see Figure 1 , a single SVG points to the offshore wind farm grid-connected system to indicate the control direction. The specific steps are:

[0107] Based on the offshore wind farm grid-connected system, the current inner loop control signal of a single SVG is obtained; the AC voltage dq axis component v d , v q As an additional control signal input to the SVG control loop;

[0108] The SVG current inner loop control signal and the additional control signal are inputted into the pulse width modulation module of the offshore wind farm grid connection system, and a modulation wave is generated in the pulse width modulation module;

[0109] Controlling harmonics in offshore wind farm grid-connected systems by modulating waves.

[0110] Furthermore, the control model includes a single-channel control module or a plurality of single-channel control modules connected in parallel, and the single-channel control module includes a proportional link, a bandpass filter link and a second-order low-pass filter link cascaded in sequence; see Figure 5 , Channel 1 and Channel 2 in the figure are two single-channel control modules connected in parallel;

[0111] The transfer function of the single-channel control module is:

[0112] G sc (s) = K v G BPF (s)G LPF (s),

[0113]

[0114]

[0115] In the formula, G sc is the transfer function of the single-channel control module, K v is the magnification factor of the proportional link, G BPF is the transfer function of the bandpass filter, G LPF is the transfer function of the second-order low-pass filter, s is the Laplace operator, Q is the quality factor, ω c is the characteristic angular frequency.

[0116] The quality factor Q of the bandpass filter link is set to be relatively high, so as to achieve a certain degree of decoupling between channels, i.e., between single-channel control modules, so that each single-channel control module can suppress harmonics of different frequencies respectively. Furthermore, a control signal is added to the control loop of the SVG of the offshore wind farm grid-connected system to achieve centralized resonance suppression. The specific method is: Since the control loop of the power electronic device is often set in the dq domain to achieve control decoupling, the positive-sequence impedance characteristics of the SVG at the harmonic frequency f depend on the characteristics of the controller at the frequency (f-f0), f0 is the fundamental frequency, and the negative-sequence impedance characteristics at the frequency f depend on the characteristics of the controller at the frequency (f-f0), so a controller with a bandpass frequency of 6n is designed in the dq rotating coordinate system, which can simultaneously control the negative-sequence harmonics with a frequency of 6n-1 and the positive-sequence harmonics with a frequency of 6n+1 in the stationary coordinate system. The schematic diagram of the frequency conversion process in this embodiment is shown as follows. Figure 6 As shown, Figure 6The frequency correspondence between negative-sequence harmonics and positive-sequence harmonics in the power system before and after frequency conversion in the converter is revealed, and the process is derived as follows:

[0117]

[0118]

[0119]

[0120]

[0121] Where T(ω0) is the Clark-Park coordinate transformation matrix, u abc_pos is the positive sequence component in the stationary coordinate system, u d_pos is the positive sequence component of the d-axis in the dq rotating coordinate system, u q_pos is the positive sequence component of the q axis in the dq rotating coordinate system, u abc_neg is the negative sequence component in the stationary coordinate system, u d_neg is the negative sequence component of the d-axis in the dq rotating coordinate system, u q_neg is the negative sequence component of the q axis in the dq rotating coordinate system, ω0 is the fundamental angular frequency, t is the time, U m is the steady-state quantity, ω p is the harmonic angular frequency.

[0122] Furthermore, the steps to obtain the optimal parameters of the control model are:

[0123] Obtaining the objective function of the single-channel control module according to the transfer function of the single-channel control module and the overall impedance model of the grid-connected system;

[0124] Obtain the parameters to be optimized according to the objective function; construct constraints according to the objective function, and the constraints are:

[0125] F(f)<F set ;

[0126] In the formula, F set is the boundary constraint value;

[0127] Obtain the feasible region boundary of the parameters to be optimized according to the constraint conditions;

[0128] Obtain the optimal parameters of the single-channel control module according to the feasible region boundary of the objective function and the parameters to be optimized;

[0129] Based on the control model, the optimal parameters of the control model are obtained according to the optimal parameters of the single-channel control module.

[0130] Furthermore, the parameters to be optimized include the amplification factor and characteristic frequency of the proportional link; the overall impedance model of the grid-connected system after the additional control model includes the overall impedance model of the grid-connected system after the additional single-channel control;

[0131] The steps to obtain the objective function of a single-channel control module are:

[0132] Let the bandpass center frequency of the transfer function of the bandpass filter link and the cutoff frequency of the transfer function of the second-order low-pass filter link be equal to the characteristic frequency respectively;

[0133] Obtain the harmonic frequency of the offshore wind farm grid-connected system;

[0134] Based on the harmonic frequency and the overall impedance model of the grid-connected system, the overall impedance of the grid-connected system before the additional single-channel control and the average phase margin before the additional single-channel control are calculated;

[0135] Based on the transfer function of the single-channel control module and the overall impedance model of the grid-connected system, the overall impedance model of the grid-connected system after the additional single-channel control is obtained;

[0136] Based on the harmonic frequency and the overall impedance model of the grid-connected system after the additional single-channel control, the overall impedance of the grid-connected system after the additional single-channel control and the average phase margin after the additional single-channel control are calculated;

[0137] Based on the harmonic frequency, the objective function of the single-channel control module is constructed according to the amplification factor of the proportional link, the characteristic frequency, the overall impedance of the grid-connected system before the additional single-channel control, the overall impedance of the grid-connected system after the additional single-channel control, the average phase margin before the additional single-channel control, and the average phase margin after the additional single-channel control; the objective function is:

[0138]

[0139] In the formula, F is the objective function, Z sc is the overall impedance of the grid-connected system after adding single-channel control, K v is the magnification factor of the proportional link, f c is the characteristic frequency, f is the harmonic frequency, Z0 is the overall impedance of the grid-connected system before adding single-channel control, P sc P0 is the average phase margin before adding single-channel control, and P1 is the average phase margin after adding single-channel control.

[0140] Specifically, the bandpass filter transfer function G is set BPF The bandpass center frequency and the second-order low-pass filter transfer function G LPF The cut-off frequency is f c , to amplify link K v and f cThe objective function F is set for the parameter to be optimized, and the feasible domain boundary of the parameter to be optimized is set when the objective function F is less than 0.5. The feasible domain boundary of the parameter to be optimized in each single-channel control module is established, and the overlapping area of ​​the feasible domain of the parameter to be optimized under the two harmonic frequencies of 6n±1 is selected as the actual parameter feasible domain, and the parameter combination that minimizes the objective function F under the two harmonic frequencies of 6n±1 is set as the optimal parameter of the single-channel control module. The feasible domain results of the parameters to be optimized of the two single-channel control modules calculated in the embodiment of the present application are as follows: Figure 7 As shown in the figure, the solid line is the feasible domain of the parameters to be optimized under the negative-sequence harmonic suppression target, the dotted line is the feasible domain of the parameters to be optimized under the positive-sequence harmonic suppression target, and the overlapped part of the dotted line and the solid line is the feasible domain of the control parameters to be optimized that are actually obtained.

[0141] Furthermore, the average phase margin before the additional control and the average phase margin after the additional control are calculated according to Formula 2, which is:

[0142]

[0143] Where P is the average phase margin, L is the length of the frequency band considered, Z is the overall impedance of the grid-connected system, and ∠Z(f) is the phase angle of Z at f.

[0144] The meaning of average phase margin is the average distance between the impedance phase angle and ±90 at each harmonic frequency point in the frequency band. For the harmonic frequency points with impedance phase angles between -45° and 45°, it is considered that they have good resonant stability and are not considered. Therefore, L in the formula is the length of the frequency band after removing the harmonic frequency points with -45°<∠Z(f)<45° in Z(f).

[0145] Verification Example

[0146] In the control loop of a single SVG located at the onshore grid connection point in the offshore wind farm grid connection system, a control signal is added, and different working conditions are set as shown in Table 1 to verify the effect of the centralized active harmonic suppression method for offshore wind farms proposed in the present invention. Table 1 shows the resonance peak position of the offshore wind farm grid connection system without and with additional control signals under different working conditions. The working conditions in the table cover a total of 6 cases under different submarine cable investment times, different wind turbine access percentages, and different onshore AC grid equivalent inductances. When the resonance peak position is close to a specific subharmonic frequency, the harmonic problem of the offshore wind power grid connection system is more serious.

[0147] Table 1

[0148]

[0149] According to the different working condition settings in Table 1, the multi-channel centralized active harmonic controller proposed in the present invention is added to the control loop of a single SVG located at the onshore grid connection point in the offshore wind farm grid connection system, that is, the actual additional control signal. The control effect under the working condition in Table 1 is shown in Table 2. In Table 2, HD represents the harmonic distortion rate, THD represents the total harmonic distortion rate, and PCC represents the grid connection point. It can be seen that the power quality in different scenarios is well improved, and the additional control signal has a good suppression effect on harmonics of different frequencies.

[0150] Table 2

[0151]

[0152] The embodiment of the present invention also provides a device for implementing a centralized active harmonic suppression method for an offshore wind farm, comprising a modeling unit, a calculation unit, and a control application unit;

[0153] Modeling unit:

[0154] Used to construct a grid-connected topology structure according to the offshore wind farm grid-connected system;

[0155] It is used to construct the frequency domain impedance model of a single direct-drive wind turbine and the frequency domain impedance model of a single SVG respectively based on the transmission relationship between the AC harmonic voltage vector and the AC harmonic current vector and the topological structure of the grid-connected system according to the main circuit parameters and the control parameters;

[0156] It is used to construct the frequency domain impedance model of the submarine cable and the frequency domain impedance model of the AC power grid respectively based on the topology of the grid-connected system, main circuit parameters and control parameters;

[0157] Based on the topology of the grid-connected system, the overall impedance model of the grid-connected system is obtained according to the frequency domain impedance model of a single SVG, the frequency domain impedance model of the AC power grid, the frequency domain impedance model of a single direct-drive wind turbine, and the frequency domain impedance model of the submarine cable;

[0158] Based on the overall impedance model of the grid-connected system, a control model is added to the frequency domain impedance model of a single SVG to obtain the overall impedance model of the grid-connected system after the control model is added;

[0159] The calculation unit is used to obtain the optimal parameters of the control model according to the overall impedance model of the grid-connected system and the overall impedance model of the grid-connected system after the control model is added;

[0160] The control application unit is used for obtaining a control signal based on the optimal parameters of the control model and the control model, for adding a control signal in a control loop of a single SVG corresponding to a frequency domain impedance model of the single SVG in the offshore wind farm grid-connected system based on the grid-connected system topology, and for suppressing harmonics in the offshore wind farm grid-connected system based on the single SVG with the actual added control signal in the control loop.

[0161] Further, the modeling unit includes a topology building module, an impedance model building module and a control model building module;

[0162] The topology building module is used to build a grid-connected system topology structure according to the offshore wind farm grid-connected system;

[0163] The impedance model building module is used to build the frequency domain impedance model of a single direct-drive wind turbine, the frequency domain impedance model of a single SVG, the frequency domain impedance model of the AC power grid and the frequency domain impedance model of the submarine cable according to the offshore wind farm grid-connected system and the grid-connected system topology; and is used to build the overall impedance model of the grid-connected system according to the grid-connected system topology, the frequency domain impedance model of a single direct-drive wind turbine, the frequency domain impedance model of a single SVG, the frequency domain impedance model of the AC power grid and the frequency domain impedance model of the submarine cable;

[0164] The control model building module is used to add a control model to the frequency domain impedance model of a single SVG of the overall impedance model of the grid-connected system and obtain the overall impedance model of the grid-connected system after adding single-channel control.

[0165] An embodiment of the present invention further provides a storage medium, comprising a stored program, which controls a device where the storage medium is located to execute a centralized active harmonic suppression method for an offshore wind farm when the program is running.

[0166] The system embodiment described above is merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art may understand and implement it without creative work.

[0167] Through the description of the above implementation methods, those skilled in the art can clearly understand that each implementation method can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solution is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a disk, an optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0168] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A centralized active harmonic suppression method for an offshore wind farm, characterized in that: The following steps are involved: Construct the grid-connected system topology based on the offshore wind farm grid-connected system; Based on the offshore wind farm grid-connected system, main circuit parameters and control parameters are obtained; Based on the transmission relationship between the AC harmonic voltage vector and the AC harmonic current vector and the topological structure of the grid-connected system, a frequency domain impedance model of a single direct-drive wind turbine and a frequency domain impedance model of a single SVG are respectively constructed according to the main circuit parameters and the control parameters; Based on the grid-connected system topology, a frequency domain impedance model of a submarine cable and a frequency domain impedance model of an AC power grid are respectively constructed according to the main circuit parameters and the control parameters; Based on the grid-connected system topology, an overall impedance model of the grid-connected system is obtained according to the frequency domain impedance model of the single SVG, the frequency domain impedance model of the AC power grid, the frequency domain impedance model of a single direct-drive wind turbine, and the frequency domain impedance model of the submarine cable; Based on the overall impedance model of the grid-connected system, a control model is added to the frequency domain impedance model of the single SVG to obtain the overall impedance model of the grid-connected system after the control model is added; Obtaining optimal parameters of the control model according to the overall impedance model of the grid-connected system and the overall impedance model of the grid-connected system after the control model is added; Obtaining a control signal based on the optimal parameters of the control model and the control model; adding the control signal to a control loop of a single SVG corresponding to the frequency domain impedance model of the single SVG in the offshore wind farm grid-connected system based on the grid-connected system topology; The single SVG based on the additional control signal in the control loop suppresses harmonics in the offshore wind farm grid-connected system.

2. The centralized active harmonic suppression method for offshore wind farms according to claim 1, characterized in that: The steps of constructing the frequency domain impedance model of the single direct-drive wind turbine are: Based on the steady-state operation state, the transfer relationship between the AC harmonic voltage vector and the AC harmonic current vector of a single direct-drive wind turbine is calculated to obtain a frequency domain impedance model of the single direct-drive wind turbine; The frequency domain impedance model of the single direct-drive fan is: In the formula, Z VSC (s) is the frequency domain impedance of the direct-drive fan, G mod2val is the small signal transfer function from the modulation signal to the valve side voltage, G i2mod is the small signal transfer function from AC current to modulated signal, G v2mod is the small signal transfer function from AC voltage to modulated signal, L fVSC is the filter inductor of the direct-drive fan, R VSC is the resistance of the direct-drive wind turbine, and s is the Laplace operator.

3. The centralized active harmonic suppression method for offshore wind farms according to claim 1 is characterized in that: The steps of constructing the frequency domain impedance model of the SVG are: Based on the steady-state operation state, the transfer relationship between the AC harmonic voltage vector and the AC harmonic current vector of a single SVG is calculated to obtain a frequency domain impedance model of the SVG; The frequency domain impedance model of the SVG is: In the formula, Z SVG (s) is the frequency domain impedance of SVG, G mod2val is the small signal transfer function from the modulation signal to the valve side voltage, G i2mod is the small signal transfer function from AC current to modulated signal, G v2mod is the small signal transfer function from AC voltage to modulated signal, G dc2val is the small signal transfer function from capacitor voltage to valve side voltage, G i2dc is the small signal transfer function from AC current to capacitor voltage, G v2dc is the small signal transfer function from AC voltage to capacitor voltage, G dc2mod is the small signal transfer function from capacitor voltage to modulation signal, L fSVG is the filter inductance of SVG, R SVG is the resistance of SVG, and s is the Laplace operator.

4. The centralized active harmonic suppression method for offshore wind farms according to claim 1, characterized in that: The π-type equivalent is adopted to construct the submarine cable frequency domain impedance model according to Formula 1, which is: Z l =Z c born(γl), In the formula, Z l is the equivalent impedance of the series branch of the line, Z c is the wave impedance, γ is the propagation constant, l is the length of the submarine cable, Y p is the equivalent impedance of the parallel branch of the line, L0 is the equivalent inductance per unit length of the submarine cable, C0 is the equivalent capacitance per unit length of the submarine cable, R0 is the equivalent resistance per unit length of the submarine cable, ω is the angular frequency, and j is the imaginary unit.

5. The centralized active harmonic suppression method for offshore wind farms according to claim 1, characterized in that: The control model includes a single-channel control module or a plurality of single-channel control modules connected in parallel, wherein the single-channel control module includes a proportional link, a band-pass filter link and a second-order low-pass filter link cascaded in sequence; The transfer function of the single-channel control module is: G sc (s)=K v G BPF (s)G LPF (s), In the formula, G sc is the transfer function of the single-channel control module, K v is the magnification factor of the proportional link, G BPF is the transfer function of the bandpass filter, G LPF is the transfer function of the second-order low-pass filter, s is the Laplace operator, Q is the quality factor, ω c is the characteristic angular frequency.

6. The centralized active harmonic suppression method for offshore wind farms according to claim 5, characterized in that: The steps of obtaining the optimal parameters of the control model are: Obtaining an objective function of the single-channel control module according to the transfer function of the single-channel control module and the overall impedance model of the grid-connected system; Obtain the parameters to be optimized according to the objective function; construct constraints according to the objective function, and the constraints are: F(f)<F set ; In the formula, F set is the boundary constraint value; Obtaining the feasible region boundary of the parameter to be optimized according to the constraint condition; Obtaining optimal parameters of a single-channel control module according to the objective function and the feasible region boundary of the parameters to be optimized; Based on the control model, optimal parameters of the control model are obtained according to optimal parameters of the single-channel control module.

7. The centralized active harmonic suppression method for offshore wind farms according to claim 6, characterized in that: The parameters to be optimized include the amplification factor of the proportional link and the characteristic frequency; the overall impedance model of the grid-connected system after the additional control model includes the overall impedance model of the grid-connected system after the additional single-channel control; The steps of obtaining the objective function of the single-channel control module are: Let the bandpass center frequency of the transfer function of the bandpass filter link and the cutoff frequency of the transfer function of the second-order low-pass filter link be equal to the characteristic frequency respectively; Obtaining the harmonic frequency of the offshore wind farm grid-connected system; Based on the harmonic frequency and the overall impedance model of the grid-connected system, calculating the overall impedance of the grid-connected system before additional single-channel control and the average phase margin before additional single-channel control; Obtaining the overall impedance model of the grid-connected system after the additional single-channel control based on the transfer function of the single-channel control module and the overall impedance model of the grid-connected system; Based on the harmonic frequency and the overall impedance model of the grid-connected system after the additional single-channel control, calculating the overall impedance of the grid-connected system after the additional single-channel control and the average phase margin after the additional single-channel control; Based on the harmonic frequency, the objective function of the single-channel control module is constructed according to the amplification factor of the proportional link, the characteristic frequency, the overall impedance of the grid-connected system before the additional single-channel control, the overall impedance of the grid-connected system after the additional single-channel control, the average phase margin before the additional single-channel control, and the average phase margin after the additional single-channel control; the objective function is: In the formula, F is the objective function, Z sc is the overall impedance of the grid-connected system after adding single-channel control, K v is the magnification factor of the proportional link, f c is the characteristic frequency, f is the harmonic frequency, Z0 is the overall impedance of the grid-connected system before adding single-channel control, P sc P0 is the average phase margin before adding single-channel control, and P1 is the average phase margin after adding single-channel control.

8. The centralized active harmonic suppression method for offshore wind farms according to claim 7, characterized in that: The average phase margin before the additional single-channel control and the average phase margin after the additional single-channel control are calculated according to Formula 2, which is: Where P is the average phase margin, L is the length of the frequency band considered, Z is the overall impedance of the grid-connected system, and ∠Z(f) is the phase angle of Z at f.

9. A device for implementing the centralized active harmonic suppression method for offshore wind farms according to any one of claims 1 to 8, characterized in that: It includes a modeling unit, a calculation unit and a control application unit; The modeling unit: Used to construct the grid-connected topology structure according to the offshore wind farm grid-connected system; Used to construct a frequency domain impedance model of a single direct-drive wind turbine and a frequency domain impedance model of a single SVG respectively based on the transmission relationship between the AC harmonic voltage vector and the AC harmonic current vector and the topological structure of the grid-connected system, according to the main circuit parameters and the control parameters; Used to construct a frequency domain impedance model of a submarine cable and a frequency domain impedance model of an AC power grid respectively based on the grid-connected system topology structure and according to the main circuit parameters and the control parameters; Used to obtain the overall impedance model of the grid-connected system based on the topological structure of the grid-connected system, according to the frequency domain impedance model of the single SVG, the frequency domain impedance model of the AC power grid, the frequency domain impedance model of a single direct-drive wind turbine and the frequency domain impedance model of the submarine cable; Used to add a control model to the frequency domain impedance model of the single SVG based on the overall impedance model of the grid-connected system and obtain the overall impedance model of the grid-connected system after adding the control model; The calculation unit is used to obtain the optimal parameters of the control model according to the overall impedance model of the grid-connected system and the overall impedance model of the grid-connected system after the control model is added; The control application unit is used to obtain a control signal based on the optimal parameters of the control model and the control model, to add a control signal in a control loop of a single SVG corresponding to the frequency domain impedance model of the single SVG in the offshore wind farm grid-connected system based on the grid-connected system topology, and to suppress harmonics in the offshore wind farm grid-connected system based on the single SVG to which the control signal is actually added in the control loop.

10. The device according to claim 9, characterized in that The modeling unit includes a topology building module, an impedance model building module and a control model building module; The topology building module is used to build the grid-connected system topology structure according to the offshore wind farm grid-connected system; The impedance model construction module is used to construct the frequency domain impedance model of the single direct-drive wind turbine, the frequency domain impedance model of the single SVG, the frequency domain impedance model of the AC power grid and the frequency domain impedance model of the submarine cable according to the offshore wind farm grid-connected system and the grid-connected system topology structure, and is used to construct the overall impedance model of the grid-connected system according to the grid-connected system topology structure, the frequency domain impedance model of the single direct-drive wind turbine, the frequency domain impedance model of the single SVG, the frequency domain impedance model of the AC power grid and the frequency domain impedance model of the submarine cable; The control model building module is used to add a control model to the frequency domain impedance model of a single SVG of the overall impedance model of the grid-connected system and obtain the overall impedance model of the grid-connected system after the additional single-channel control.

11. A storage medium, characterized in that: It comprises a stored program, which, when running, controls the device where the storage medium is located to execute the centralized active harmonic suppression method for an offshore wind farm as described in any one of claims 1 to 8.

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