A network-constructing type converter adaptive control method based on bus voltage synchronization

Abstract

The application discloses a kind of network type converter adaptive control method based on bus voltage synchronization, including based on bus voltage synchronization link, band pass filter adaptive parameter adjustment link and initial phase generation link.First, based on system closed-loop transfer function calculation closed-loop pole determines low-frequency oscillation frequency, and accordingly designs band pass filter;DC bus voltage deviation is handled in parallel by proportion controller and adaptive band pass filter, constitutes based on bus voltage synchronization link.Second, in the process of operation, real-time monitoring grid impedance variation and bus voltage low-frequency oscillation frequency deviation, by online parameter identification and spectrum analysis dynamically updates band pass filter parameter, realizes the adaptive adjustment of additional damping.In addition, introduce initial phase generation link to give converter initial phase, to realize the active output of system initial time, ensure fast grid connection.The method of the application can inhibit new energy grid-connected system low-frequency oscillation, improve system stability.

Description

Technical Field

[0001] This invention belongs to the field of power electronics and new energy grid-connected control technology, specifically relating to an adaptive control method for grid-connected converters based on bus voltage synchronization. Background Technology

[0002] With the rapid growth of installed capacity of new energy sources such as wind power and photovoltaics, the power system is exhibiting a high proportion of power electronics. Grid-based control technology, by simulating the external characteristics of synchronous generators, enables converters to possess voltage source characteristics, actively establishing voltage and frequency references, and providing inertial support and damping torque for the system. The grid-based control method based on bus voltage synchronization directly generates the phase angle of the grid-connected converter through DC bus voltage disturbances, which can effectively improve the dynamic response capability of the system and has become one of the key technologies for grid-friendly integration of new energy sources.

[0003] However, existing grid-based control methods based on bus voltage synchronization have the following problems:

[0004] (1) Low-frequency oscillations exist in grid-based control systems based on bus voltage synchronization. The closed-loop model of the grid-based control system based on bus voltage synchronization has two integrators. The first integrator is used to generate the phase angle from the frequency, and the second integrator is included in the transfer function between the DC side voltage and the active power. These two integrators produce a 180° phase lag, which deteriorates the phase margin of the closed-loop control and leads to low-frequency oscillations.

[0005] (2) Existing control strategies are too simplistic and difficult to adapt to grid transient disturbances and generator-side output power fluctuations. Current methods mainly rely on proportional-integral controllers to directly generate the grid-connected phase angle based on DC bus voltage disturbances, lacking adaptive adjustment for complex operating conditions. When the grid experiences sudden voltage changes, faults, or generator-side power changes, the system cannot quickly and flexibly adjust the phase angle and power output, leading to increased power imbalance and bus voltage fluctuations, which restricts the reliability and transient stability of new energy grid connection.

[0006] (3) The bus voltage fluctuates violently during the system startup phase, posing a risk of equipment damage and grid disconnection. During startup, the generator power cannot be delivered in time, and the DC bus voltage is prone to large fluctuations, which may exceed the withstand voltage limits of the bus capacitor and converter, leading to breakdown damage. At the same time, the violent disturbance of the bus voltage will cause instantaneous low voltage, the output voltage amplitude will drop, triggering the low voltage ride-through protection mechanism, and ultimately causing the system to disconnect from the grid.

[0007] To address the aforementioned issues, an adaptive control method for grid-type converters based on bus voltage synchronization is proposed. Summary of the Invention

[0008] The problem to be solved by this invention is to provide an adaptive control method for grid-connected converters based on bus voltage synchronization, which is applicable to grid-connected new energy grid-connected converters, energy storage converters and microgrid converters, etc., and can suppress low-frequency oscillations in new energy grid-connected systems and improve system stability.

[0009] This invention adopts the following technical solution: an adaptive control method for a grid-type converter based on bus voltage synchronization, wherein the input side of the grid-type converter is connected to a DC bus capacitor, and the output side is connected to the power grid via an LC filter. Grid control based on bus voltage synchronization is employed, specifically including:

[0010] Synchronization based on bus voltage: The closed-loop poles are calculated based on the system closed-loop transfer function and the low-frequency oscillation frequency is determined; an adaptive bandpass filter is constructed based on the low-frequency oscillation frequency; the DC bus voltage deviation is input by a synchronization link consisting of a proportional controller and an adaptive bandpass filter connected in parallel; the output is added to the rated angular frequency and integrated to obtain the phase angle deviation.

[0011] Adaptive parameter tuning of bandpass filter: During system operation, the changes in grid impedance and the deviation of low-frequency oscillation frequency of bus voltage are monitored in real time. The bus voltage spectrum analysis is used first to obtain the real-time oscillation frequency. When the oscillation frequency deviation is lower than the threshold or cannot be reliably extracted, the method of online grid impedance identification is switched. The center angular frequency and upper and lower cutoff frequencies of the bandpass filter are dynamically updated according to the real-time oscillation frequency or impedance changes.

[0012] Initial phase generation of grid-side converter: An initial phase generation algorithm is constructed based on line parameters and power flow equations to generate the initial phase of the grid-side converter.

[0013] Furthermore, the grid-type converter includes: a bus voltage synchronization loop, an initial phase generation loop, a reactive power control loop, and a voltage and current loop.

[0014] The bus voltage synchronization loop specifically includes: a proportional controller, an adaptive bandpass filter, and a phase angle calculation stage. The deviation between the actual and reference values ​​of the DC bus voltage is input to the proportional controller and the adaptive bandpass filter, respectively. The outputs of the proportional controller and the adaptive bandpass filter are added to obtain the angular velocity deviation Δω. The angular velocity deviation Δω is then compared with the rated angular frequency ω. g The summation yields the network control angular velocity ω; the network control angular velocity ω is integrated by an integrator to obtain the phase angle deviation Δθ.

[0015] The initial phase generation loop specifically includes: an initial phase calculation stage and an adder; the phase angle deviation Δθ is combined with the initial phase θ obtained by the initial phase calculation stage. init Summing these values ​​yields the network control phase angle θ.

[0016] The reactive power control loop specifically includes: a proportional controller, an integrator, and a droop circuit. The reactive power deviation ΔQ is obtained by subtracting the reference reactive power value from the actual reactive power value. The reactive power deviation ΔQ is then processed by the proportional controller and integrator to obtain the voltage amplitude deviation ΔU. The voltage amplitude deviation ΔU is then used by the droop circuit to control the reactive power deviation ΔQ. The voltage amplitude deviation ΔU is compared with the rated phase voltage amplitude U of the power grid. gm Summing yields the grid control voltage amplitude U;

[0017] The voltage-current loop specifically includes: a coordinate transformation stage and a PI controller; the three-phase reference voltage for grid control is obtained through the grid control voltage amplitude U and phase angle θ, and the dq-axis voltage reference value u is obtained through Park transformation. dg * u qg * The deviation between the dq-axis reference voltage and the actual dq-axis voltage at the grid connection point is used by a PI controller to obtain the dq-axis current reference value i. dg * i qg * ;dq axis current reference value i dg * i qg * The deviation from the actual output dq-axis current is used to obtain the dq-axis modulation voltage via a PI controller, and then the three-phase modulation voltage signal is obtained through inverse Park transformation, which is used to drive the grid-side converter.

[0018] Furthermore, the adaptive bandpass filter is constructed using the following steps:

[0019] S1. Based on the grid-type converter, obtain the small-signal model of the DC bus capacitor voltage, and obtain the closed-loop transfer function of the system active power based on the small-signal model.

[0020] S2. Calculate the closed-loop poles of the system based on the closed-loop transfer function obtained in S1, and determine the low-frequency oscillation frequency of the system based on the real and imaginary parts of the closed-loop poles.

[0021] S3. Based on the low-frequency oscillation frequency of the system in S2, design the cutoff frequency of the bandpass filter, and inject the output of the adaptive bandpass filter in parallel with the output of the bus voltage synchronization loop proportional controller to form an additional damping control loop.

[0022] As a preferred embodiment, the bandpass filter is constructed as follows:

[0023] S3.1 Setting the center angular frequency of the bandpass filter This aligns the filter's passband center with the dominant low-frequency oscillation frequency; among which, It is the dominant frequency of low-frequency oscillation;

[0024] S3.2 Design the bandpass filter as a second-order filter;

[0025] S3.3 Determine the lower cutoff angular frequency of the high-pass filter. With the upper cutoff angular frequency of the low-pass filter This allows the passband range to cover the expected drift range of the low-frequency oscillation frequency. , ],in, , ;

[0026] S3.4, according to , Determine the passband width B of the bandpass filter such that Based on the bus voltage synchronization loop gain Adjust the gain of the bandpass filter to make .

[0027] As a preferred option, the bandpass filter adaptive parameter tuning preferentially adopts an adaptive parameter tuning method based on the bus voltage oscillation frequency. When the signal-to-noise ratio of the low-frequency oscillation component of the bus voltage is lower than a preset threshold or the dominant frequency cannot be reliably extracted by spectrum analysis, the adaptive parameter tuning method based on line impedance is switched.

[0028] The adaptive parameter tuning of the bandpass filter based on line impedance is as follows:

[0029] During system operation, the magnitude of the equivalent impedance of the power grid is obtained in real time through an online parameter identification algorithm. With phase angle Substituting the values ​​into the obtained real-time estimate of low-frequency oscillations Calculate the low-frequency oscillation frequency deviation and the relative change in the modulus of the power grid impedance ;when At that time, the parameters of the bandpass filter are dynamically updated; among them, This is a preset threshold.

[0030] The bandpass filter adaptive parameter tuning based on the bus voltage oscillation frequency is performed as follows:

[0031] During system operation, the DC bus voltage is sampled in real time, and its spectrum is analyzed using Fast Fourier Transform or Discrete Fourier Transform to extract the dominant frequency of the low-frequency oscillation component in the DC bus voltage, which is then used as the real-time low-frequency oscillation frequency. Calculate the low-frequency oscillation frequency deviation ;when The parameters of the bandpass filter are dynamically updated at that time.

[0032] As a preferred embodiment, the initial phase of the grid-side converter is generated based on the generator-side input power, line parameters, and power flow equations. The initial phase generation algorithm is expressed as follows:

[0033] ;

[0034] in, For machine-side input power, For grid reactance, This is the grid voltage.

[0035] Compared with the prior art, the present invention, employing the above technical solution, has the following technical effects:

[0036] 1. This invention first calculates the closed-loop poles based on the system's closed-loop transfer function to determine the low-frequency oscillation frequency, and designs a bandpass filter accordingly. The DC bus voltage deviation is processed in parallel with the adaptive bandpass filter via a proportional controller, forming a bus voltage synchronization link. Then, during operation, the changes in grid impedance and the low-frequency oscillation frequency deviation of the bus voltage are monitored in real time. The bandpass filter parameters are dynamically updated through online parameter identification and spectrum analysis to achieve adaptive adjustment of the additional damping. In addition, an initial phase generation link is introduced to give the converter an initial phase, so as to achieve active power output at the initial moment of the system and ensure rapid grid connection.

[0037] 2. The method described in this invention can significantly reduce output power fluctuations and low-frequency oscillations, suppress low-frequency oscillations in new energy grid-connected systems, and improve system stability while reducing system recovery time. Attached Figure Description

[0038] Figure 1 This is a block diagram of the grid-type converter system structure and control based on bus voltage synchronization according to the present invention.

[0039] Figure 2 This is a flowchart illustrating the design steps of the bandpass filter of this invention.

[0040] Figure 3 This is a flowchart of the adaptive parameter tuning method for the bandpass filter of the present invention;

[0041] Figure 4 This is a simulation waveform diagram of the initial moment of a grid-type converter based on bus voltage synchronization according to an embodiment of the present invention.

[0042] Figure 5 This is a simulation waveform diagram of the grid impedance change of a grid-type converter based on bus voltage synchronization, according to an embodiment of the present invention.

[0043] Figure 6 The above is a simulation waveform diagram of the input power fluctuation of a grid-type converter based on bus voltage synchronization, according to an embodiment of the present invention. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the application will be further described in detail below with reference to the accompanying drawings. The described embodiments are only a part of the embodiments involved in this invention. All non-innovative embodiments based on these embodiments by other researchers in the art are within the protection scope of this invention. Furthermore, the step numbers in the embodiments of this invention are only set for ease of explanation and do not limit the order of the steps. The execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0045] In one embodiment of the present invention, for a new energy grid-connected system with a constant power output of 4.5MW at the generator side, an adaptive control method for a grid-connected converter based on bus voltage synchronization is provided. The system structure is as follows: Figure 1 As shown, it includes a converter, DC bus capacitor, LC filter, and grid equivalent inductance.

[0046] Specifically, the grid-side converter's input side is connected to a DC bus capacitor, and its output side is connected to a three-phase equivalent grid via an LC filter. The grid-side converter employs grid control based on bus voltage synchronization, which includes: a bus voltage synchronization loop, an initial phase generation loop, a reactive power control loop, and a voltage-current loop.

[0047] Furthermore, the adaptive synchronization loop based on bus voltage specifically includes a proportional controller, an adaptive bandpass filter, and a phase angle calculation stage.

[0048] The deviation between the actual and reference values ​​of the DC bus voltage is input to a proportional controller and an adaptive bandpass filter, respectively, with the adaptive bandpass filter connected in parallel with the proportional controller. The outputs of the proportional controller and the adaptive bandpass filter are added together to obtain the angular velocity deviation Δω. The angular velocity deviation Δω is then compared with the rated angular frequency ω. g The sums are used to obtain the netting control angular velocity ω; the netting control angular velocity ω is integrated by an integrator to obtain the phase angle deviation Δθ.

[0049] Furthermore, the proportional gain of the bus voltage synchronization proportional controller is: It can be calculated using the following formula:

[0050] ;

[0051] Where k1 is the bus voltage synchronization coefficient. This is the steady-state value of the DC bus voltage. This is the rated angular frequency. In this embodiment... , , rad / s.

[0052] The initial phase generation loop specifically includes an initial phase calculation stage and an adder. The phase angle deviation Δθ generated by the bus voltage adaptive synchronization loop and the initial phase θ obtained by the initial phase calculation stage are... init The summation yields the phase angle θ for network control.

[0053] The reactive power control loop includes a proportional controller, an integrator, and a droop circuit. The reactive power deviation ΔQ is obtained by subtracting the reactive power reference value from the actual reactive power value. The reactive power deviation ΔQ is then processed by the proportional controller and integrator to obtain the voltage amplitude deviation ΔU. The voltage amplitude deviation ΔU is then used by the droop circuit to control the reactive power deviation ΔQ. The voltage amplitude deviation ΔU is compared with the rated phase voltage amplitude U of the power grid. gm The summation yields the grid control voltage amplitude U.

[0054] Furthermore, the proportional gain of the reactive power control loop proportional controller is K. q , reactive power droop coefficient D q It can be calculated using the following formula:

[0055] ;

[0056] Among them, P rated Where B is the system rated power, T is the voltage deviation to reactive power transfer coefficient, and L is the reactive power response time constant. g Grid inductance, U gm This is the rated phase voltage amplitude. In this embodiment, P... rated =4.5MW, U gm =563.3V, L g =0.1mH, T=0.05s.

[0057] The voltage-current loop includes a coordinate transformation stage and a PI controller. It obtains the three-phase reference voltage for grid control by controlling the voltage amplitude U and phase angle θ, and then obtains the dq-axis voltage reference value u through Park transformation. dg * u qg * The deviation between the dq-axis reference voltage and the actual dq-axis voltage at the grid connection point is used by a PI controller to obtain the dq-axis current reference value i. dg * i qg * ;dq axis current reference value i dg * i qg * The deviation from the actual output dq-axis current is used to obtain the dq-axis modulation voltage via a PI controller, and then the three-phase modulation voltage signal is obtained through inverse Park transformation, which is used to drive the grid-side converter.

[0058] In this embodiment, the voltage outer loop controller parameter is selected as: K pu =8,K iu =30; The parameters for the inner current loop controller are selected as: K pi =0.3, K ii =10.

[0059] In this embodiment, the bandpass filter is designed as follows: Figure 2 As shown, the specific steps are as follows:

[0060] S1. Based on the grid-type converter system, a small-signal model of the DC bus capacitor voltage is obtained, and based on the small-signal model, the closed-loop transfer function of the system active power is obtained.

[0061] In this embodiment, the small-signal model of the DC bus capacitor voltage is represented as follows:

[0062] ;

[0063] in, This represents the DC bus voltage disturbance. This refers to the power disturbance input from the generator side. C represents the DC-side output power disturbance. dc V is the capacitance of the DC bus. dc0 This represents the steady-state value of the DC bus voltage. For the Laplace operator; in this embodiment, C dc =0.05F.

[0064] Furthermore, based on the small-signal model of the system, the closed-loop transfer function of the system is expressed as:

[0065] ;

[0066] Among them, G Pdc The transfer function from phase angle deviation to DC bus power deviation can be specifically expressed as:

[0067] ;

[0068] Among them, K p K is the active power transfer coefficient, which is related to the grid parameters. q k is the reactive power droop coefficient. c ω is the active and reactive power coupling coefficient; v ω is the closed-loop bandwidth of the voltage outer loop; i This represents the closed-loop bandwidth of the inner current loop.

[0069] S2. Calculate the closed-loop poles of the system based on the closed-loop transfer function obtained in S1, and determine the low-frequency oscillation frequency of the system based on the real and imaginary parts of the closed-loop poles.

[0070] Based on the system's closed-loop transfer function, the poles of the system's closed-loop transfer function are solved, and the results are calculated by substituting the specific parameters of this embodiment. , ;

[0071] in, , The real part of the pole is represented. , Represents the imaginary part of the pole. Indicates the imaginary part; λ 1，2 The real part being less than zero determines the synchronous oscillation frequency; λ 3，4 A real part greater than zero determines the low-frequency oscillation frequency. The dominant low-frequency oscillation frequency can be expressed as: .

[0072] S3. Design the cutoff frequency of the bandpass filter based on the low-frequency oscillation frequency of the system in S2. The output of the bandpass filter is injected in parallel with the output of the bus voltage synchronization loop proportional controller to form an additional damping control loop.

[0073] Furthermore, a bandpass filter is designed based on the system's low-frequency oscillation frequency. The specific steps are as follows:

[0074] S3.1 Setting the center angular frequency of the bandpass filter This aligns the filter passband center with the dominant low-frequency oscillation frequency.

[0075] S3.2 The bandpass filter is a second-order filter, as shown in the following formula:

[0076] ;

[0077] Among them, K neg For the gain coefficient, ω0 = 2πf lfo Here, B is the center angular frequency, and B is the bandwidth parameter.

[0078] S3.3 Determine the lower cutoff angular frequency ω of the high-pass filter. low With the upper cutoff angular frequency ω of the low-pass filter high This allows the passband range to cover the expected drift range of the low-frequency oscillation frequency [f] LFO,min f LFO,max ], where ω low =2πf LFO,min ω high =2πf LFO,max In this embodiment, considering the range of low-frequency oscillations in the bus voltage and the impact of the bandpass filter on dynamic control performance, f LFO,min =0.1Hz, f LFO,max =0.3Hz.

[0079] S3.4, according to ω lowω high Determine the passband width B of the bandpass filter such that B = ω low -ω high =1.256; based on the bus voltage synchronization loop gain K dc Adjust the gain of the bandpass filter so that K neg =-K dc =0.0131.

[0080] Furthermore, to avoid the bandpass filter's damping effect decreasing due to changes in the system's low-frequency oscillation frequency caused by system operating conditions and grid transients, the changes in grid impedance and the deviation of the low-frequency oscillation frequency of the bus voltage are monitored in real time during system operation. The bandpass filter parameters are then dynamically updated through online parameter identification and spectrum analysis.

[0081] An adaptive method based on line impedance is activated during power grid transients and changes in power grid parameters. The modulus |Z| of the equivalent power grid impedance is obtained in real time using an online parameter identification algorithm. g | and phase angle ∠Z g Substituting into step S2 above, we obtain the real-time estimate of the low-frequency oscillation, f. LFO,real Calculate the low-frequency oscillation frequency deviation. ; where f LFO,nom The nominal low-frequency oscillation frequency. Calculate the relative change in the modulus of the grid impedance. Among them, |Z g,nom | represents the nominal value of the power grid impedance modulus.

[0082] In this embodiment, it is assumed that |Z is acquired in real time. g |=0.2Ω,|Z g,nom If |=0.1Ω, then Δ|Z g |=0.05. Substitute into the small-signal model to calculate f. LFO,real =0.745Hz, f LFO,nom =0.211Hz, then Δf LFO =0.534Hz. When |Δf LFO |>f th (f) th When the frequency is 0.1Hz, the parameters of the bandpass filter are dynamically updated according to the following rules:

[0083] The center angular frequency is updated to:

[0084] ;

[0085] The lower cutoff angular frequency has been updated to:

[0086] ;

[0087] The upper limit cutoff angular frequency has been updated to:

[0088] ;

[0089] Where, k f k Z k low,f k low,Z k high,f k high,Z All are positive adaptive adjustment coefficients. In this embodiment, k f =0.5, k Z =0.2、k low,f =0.4、k low,Z =0.3、k high,f =0.4、k high,Z =0.3.

[0090] An adaptive method based on the bus voltage oscillation frequency is activated when the input power fluctuates. The DC bus voltage is sampled in real time, and its spectrum is analyzed using Fast Fourier Transform (FFT) to extract the dominant frequency of the low-frequency oscillation component as the real-time fo. LFO,real Based on the real-time low-frequency oscillation, and following the adaptive bandpass filter parameter design and update method described in step S3, the updated center angular frequency ω0 and lower cutoff angular frequency ω are calculated and applied. low Upper limit cutoff angular frequency ω high .

[0091] In this embodiment, it is assumed that the dominant frequency f of the low-frequency component of the bus voltage is obtained by sampling. LFO,real =0.418Hz, then Δf LFO =0.207Hz>f th (f) th =0.1Hz), dynamically update the parameters of the bandpass filter, and the update rule is:

[0092] The center angular frequency is updated to:

[0093] ;

[0094] The lower cutoff angular frequency has been updated to:

[0095] ;

[0096] The upper limit cutoff angular frequency has been updated to:

[0097] .

[0098] like Figure 3As shown, the adaptive parameter tuning stage of the bandpass filter preferentially adopts the adaptive parameter tuning method based on the bus voltage oscillation frequency. When the signal-to-noise ratio of the low-frequency oscillation component of the bus voltage is lower than the preset threshold or the spectrum analysis cannot reliably extract the dominant frequency, it switches to the adaptive parameter tuning method based on the line impedance.

[0099] To avoid significant fluctuations in the system bus voltage due to input-output power mismatch at the initial stage, this embodiment introduces an initial phase generation loop to give the grid-side converter an initial phase, thereby achieving active power output at the initial stage of the system.

[0100] The initial phase generation loop calculates the converter active power reference using the input power reference and grid parameters, and generates the initial phase reference θ. init The initial phase calculation formula is:

[0101] ;

[0102] Among them, P g X is the machine-side input power. g For the power grid reactance, U g This is the mains voltage. In this embodiment, P g =4.5MW, X g =0.1mH, U g =563.3V, then θ init ≈0.14 rad. The initial phase θ init The phase angle θ of the network control is obtained by summing the phase angle deviation Δθ.

[0103] Table 1 shows the key system parameters of the grid-type converter based on bus voltage synchronization.

[0104] Table 1

[0105]

[0106] A system simulation model was built according to the parameters in Table 1, and the system was verified. The results are as follows. Figure 4 As shown. Figure 4 (a) in the text represents the traditional bus voltage synchronization control method. Figure 4 (b) shows the bus voltage synchronization control method with bandpass filter proposed in this invention. The simulation shows the initial stage and steady state. It can be seen that the method of this invention can significantly reduce output power fluctuation and low frequency oscillation.

[0107] like Figure 5 As shown, Figure 5 (a) in the text indicates that no adaptive parameter tuning step was introduced. Figure 5(b) in the figure represents the introduction of an adaptive parameter tuning stage for the bandpass filter. When the grid impedance changes by 0.1 pu, the low-frequency oscillation amplitude is significantly reduced after the bandpass filter parameters are adjusted through impedance-based adaptive updates.

[0108] like Figure 6 As shown, Figure 6 (a) in the text indicates that no adaptive parameter tuning step was introduced. Figure 6 (b) in the figure represents the introduction of an adaptive parameter tuning stage for the bandpass filter. When the input power fluctuates by 0.3 pu, the FFT-based adaptive parameter tuning mechanism for the bandpass filter can significantly reduce the system recovery time.

[0109] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0110] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. An adaptive control method for a grid-type converter based on bus voltage synchronization, characterized in that, The grid-type converter is connected to the DC bus capacitor on its input side and connected to the power grid via an LC filter on its output side. It employs grid-type control based on bus voltage synchronization, specifically including: Synchronization based on bus voltage: The closed-loop poles are calculated based on the system closed-loop transfer function and the low-frequency oscillation frequency is determined; an adaptive bandpass filter is constructed based on the low-frequency oscillation frequency; the DC bus voltage deviation is input by a synchronization link consisting of a proportional controller and an adaptive bandpass filter connected in parallel; the output is added to the rated angular frequency and integrated to obtain the phase angle deviation. Adaptive parameter tuning of bandpass filter: During system operation, the changes in grid impedance and the deviation of low-frequency oscillation frequency of bus voltage are monitored in real time. The bus voltage spectrum analysis is used first to obtain the real-time oscillation frequency. When the oscillation frequency deviation is lower than the threshold or cannot be reliably extracted, the method of online grid impedance identification is switched. The center angular frequency and upper and lower cutoff frequencies of the bandpass filter are dynamically updated according to the real-time oscillation frequency or impedance changes. Initial phase generation of grid-side converter: An initial phase generation algorithm is constructed based on line parameters and power flow equations to generate the initial phase of the grid-side converter.

2. The adaptive control method for grid-type converters based on bus voltage synchronization according to claim 1, characterized in that, The grid-type converter includes: Based on the bus voltage synchronization loop: This specifically includes a proportional controller, an adaptive bandpass filter, and a phase angle calculation stage. The deviation between the actual and reference values ​​of the DC bus voltage is input to the proportional controller and the adaptive bandpass filter, respectively. The outputs of the proportional controller and the adaptive bandpass filter are added together to obtain the angular velocity deviation Δω. The angular velocity deviation Δω is then compared with the rated angular frequency ω. g The summation yields the network control angular velocity ω; the network control angular velocity ω is integrated by an integrator to obtain the phase angle deviation Δθ. Initial phase generation loop: specifically includes an initial phase calculation stage and an adder; the phase angle deviation Δθ is combined with the initial phase θ obtained from the initial phase calculation stage. init Summing these values ​​yields the network control phase angle θ. Reactive power control loop: includes a proportional controller, an integrator, and a droop circuit; the reactive power deviation ΔQ is obtained by subtracting the reactive power reference value from the actual reactive power value; the reactive power deviation ΔQ is processed by the proportional controller and integrator to obtain the voltage amplitude deviation ΔU; the voltage amplitude deviation ΔU is used by the droop circuit to control the reactive power deviation ΔQ; the voltage amplitude deviation ΔU is compared with the rated phase voltage amplitude U of the power grid. gm Summing yields the grid control voltage amplitude U; Voltage-current loop: includes coordinate transformation stage and PI controller; the three-phase reference voltage for grid control is obtained through the grid control voltage amplitude U and phase angle θ, and the dq-axis voltage reference value u is obtained through Park transformation. dg * u qg * The deviation between the dq-axis reference voltage and the actual dq-axis voltage at the grid connection point is used by a PI controller to obtain the dq-axis current reference value i. dg * i qg * ;dq axis current reference value i dg * i qg * The deviation from the actual output dq axis current is used to obtain the dq axis modulation voltage via a PI controller, and then the three-phase modulation voltage signal is obtained through inverse Park transformation, which is used to drive the grid-type converter.

3. The adaptive control method for grid-type converters based on bus voltage synchronization according to claim 1, characterized in that, The adaptive bandpass filter is constructed using the following steps: S1. Based on the grid-type converter, obtain the small-signal model of the DC bus capacitor voltage, and obtain the closed-loop transfer function of the system active power based on the small-signal model. S2. Calculate the closed-loop poles of the system based on the closed-loop transfer function obtained in S1, and determine the low-frequency oscillation frequency of the system based on the real and imaginary parts of the closed-loop poles. S3. Based on the low-frequency oscillation frequency of the system in S2, design the cutoff frequency of the bandpass filter, and inject the output of the adaptive bandpass filter in parallel with the output of the bus voltage synchronization loop proportional controller to form an additional damping control loop.

4. The adaptive control method for grid-type converters based on bus voltage synchronization according to claim 3, characterized in that, In step S1, the small-signal model of the DC bus capacitor voltage is expressed as: ； in, This represents the DC bus voltage disturbance. This refers to the power disturbance input from the generator side. This refers to the DC-side output power disturbance. This refers to the DC bus capacitor capacity. This represents the steady-state value of the DC bus voltage. For the Laplace operator; The closed-loop transfer function of the active power of the system is expressed as: ； in, To determine the gain of the proportional controller in the bus voltage synchronization loop. The transfer function from phase angle deviation to DC bus power deviation is expressed as: ； in, This is the active power transfer coefficient, which is related to the power grid parameters; This is the reactive power droop coefficient; The active and reactive power coupling coefficient; The closed-loop bandwidth of the voltage outer loop; This represents the closed-loop bandwidth of the inner current loop.

5. The adaptive control method for grid-type converters based on bus voltage synchronization according to claim 3, characterized in that, In step S2, the method for determining the low-frequency oscillation frequency of the system is as follows: Solving for the poles of the closed-loop transfer function of the system based on the active power closed-loop transfer function of the system, we obtain: ； in, , The real part of the pole is represented. , Represents the imaginary part of the pole. Indicates the imaginary part; Less than zero, Determine the synchronous oscillation frequency; Greater than zero, Determines the low-frequency oscillation frequency; Obtain the dominant frequency of low-frequency oscillation. , is represented as: .

6. The adaptive control method for grid-type converters based on bus voltage synchronization according to claim 5, characterized in that, In step S3, the design of the bandpass filter includes the following sub-steps: S3.1 Setting the center angular frequency of the bandpass filter This aligns the filter passband center with the dominant low-frequency oscillation frequency. S3.2 The bandpass filter is a second-order filter, expressed as: ； in, This is the gain coefficient. B is the center angular frequency, and B is the bandwidth parameter. S3.3 Determine the lower cutoff angular frequency of the high-pass filter. With the upper cutoff angular frequency of the low-pass filter This allows the passband range to cover the expected drift range of the low-frequency oscillation frequency. , ],in, , ; S3.4, according to , Determine the passband width B of the bandpass filter such that Based on the gain of the proportional controller in the bus voltage synchronization loop Adjust the gain of the bandpass filter to make .

7. The adaptive control method for grid-type converters based on bus voltage synchronization according to claim 6, characterized in that, The method for adaptive parameter tuning of a bandpass filter based on line impedance is as follows: During system operation, the magnitude of the equivalent impedance of the power grid is obtained in real time through an online parameter identification algorithm. With phase angle Substituting the values ​​into the obtained real-time estimate of low-frequency oscillations Calculate the low-frequency oscillation frequency deviation: ； in, This is the nominal low-frequency oscillation frequency; Calculate the relative change in the magnitude of the power grid impedance: ； in, The nominal value of the power grid impedance modulus; when hour, This is a preset threshold used to dynamically update the parameters of the bandpass filter; The center angular frequency is updated to: ； The lower cutoff angular frequency has been updated to: ； The upper limit cutoff angular frequency has been updated to: ； Where, k f k Z k low,f k low,Z k high,f k high,Z All are positive adaptive adjustment coefficients.

8. The adaptive control method for grid-type converters based on bus voltage synchronization according to claim 7, characterized in that, The bandpass filter adaptive parameter tuning based on the bus voltage oscillation frequency is performed as follows: During system operation, the DC bus voltage is sampled in real time, and its spectrum is analyzed using Fast Fourier Transform or Discrete Fourier Transform to extract the dominant frequency of the low-frequency oscillation component in the DC bus voltage, which is then used as the real-time low-frequency oscillation frequency. Calculate the low-frequency oscillation frequency deviation: ； when The parameters of the bandpass filter are dynamically updated at that time. The center angular frequency is updated to: ； The lower cutoff angular frequency has been updated to: ； The upper limit cutoff angular frequency has been updated to: 。 9. The adaptive control method for a grid-type converter based on bus voltage synchronization according to claim 8, characterized in that, The adaptive parameter tuning of the bandpass filter preferentially adopts an adaptive parameter tuning method based on the bus voltage oscillation frequency. When the signal-to-noise ratio of the low-frequency oscillation component of the bus voltage is lower than a preset threshold or the dominant frequency cannot be reliably extracted by spectrum analysis, the adaptive parameter tuning method based on line impedance is switched.

10. The adaptive control method for a grid-type converter based on bus voltage synchronization according to claim 1, characterized in that, The initial phase of the grid-side converter is generated using the following method: The initial phase of the grid-type converter is generated based on the generator-side input power, line parameters, and power flow equations. The initial phase generation algorithm is as follows: ； in, For machine-side input power, For grid reactance, This is the grid voltage.

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