Grid-connected converter control method based on hybrid control of network following and network construction

Abstract

The invention relates to the technical field of new energy grid-connected converter control, in particular to a grid-connected converter control method based on grid-following and grid-construction hybrid control, which flexibly adjusts the characteristic proportion of grid-following and grid-construction by constructing a self-adaptive hybrid synchronous control model, ensures the smooth and efficient grid-connected process, and improves the grid-connected efficiency. A voltage and current double-loop control model is constructed to accurately regulate and control output voltage and current, the high-standard electric energy quality requirement of a power grid for new energy power generation is met, meanwhile, power grid impedance estimation is introduced for virtual impedance control, and the anti-interference capability and the response speed of the system are further enhanced. In conclusion, according to the grid-connected converter control method based on grid following and grid construction hybrid control, the adaptability and stability of the system to the complex power grid environment are remarkably improved, and the overall operation efficiency and reliability of the system are improved.

Description

Technical Field

[0001] The present application relates to the technical field of new energy grid-connected converter control, and in particular to a grid-connected converter control method based on hybrid control of grid following and grid building. Background Art

[0002] As the global demand for renewable energy continues to grow, new energy power generation technologies, especially grid-connected power generation systems based on converters, have been widely used. These systems convert direct current generated by new energy (such as solar energy, wind energy, etc.) into alternating current through converters, and connect them to the power grid safely and efficiently. As a key device connecting new energy power generation equipment to the power grid, the control strategy of the grid-connected converter is crucial to the stability and reliability of the system.

[0003] At present, the current closed-loop vector control method based on rotating coordinate transformation and phase locked loop (PLL) is widely used in wind power and photovoltaic grid-connected systems. The converter using this control method is often called grid-following (GFL) converter. For example, the patent with publication number CN115483843A provides an open-loop synchronization method that can improve the global stability of the grid-connected converter. By providing a grid synchronization current reference for the grid-connected converter's grid-following control, the nonlinear structure of the grid-connected inverter is greatly simplified, and the robustness of the grid-connected inverter system is significantly improved. The grid-following control has good stability under a strong power grid and fast power response speed. It can not only maximize the utilization rate of new energy through maximum power point tracking, but also has good economic efficiency and relatively mature technology. It is the mainstream control technology for new energy grid-connected converters at this stage.

[0004] However, when a large number of new energy sources are connected to the power grid, the proportion of synchronous generators is relatively reduced, the strength of the power grid decreases, and the power grid presents the characteristics of a "weak power grid". The system exhibits the characteristics of low inertia and weak damping. In the case of a weak power grid, the input of the phase-locked loop is usually the point of common coupling (PCC) voltage or the filter capacitor voltage, which causes the mutual coupling between the inverter, the phase-locked loop and the power grid, which easily leads to system instability and limits the power transmission capacity. Therefore, the concept of grid forming (GFM) converter control is proposed. Because it has the external characteristics of a voltage source, it can provide voltage and frequency support for weak power systems, and is widely used in new power systems with a high proportion of new energy and high power electronics. For example, the patent with publication number CN115513995A discloses a grid forming converter control method and system based on PQ compensation for weak power grids, which reduces the active power output of the converter during the fault period to achieve the purpose of reducing the current on the converter side, thereby suppressing the overcurrent of the system during the fault period, achieving low voltage ride-through, and improving the stability of the weak power system.

[0005] However, grid-type control has problems such as slow power regulation, strong multi-machine coupling, poor grid stability and economy. In actual power systems, changes in power generation equipment will lead to significant changes in grid strength, and the short-circuit ratio (SCR) of the common coupling point is usually used to measure changes in grid strength. New energy grid-connected converters with single grid-type or grid-type control modes are difficult to meet the stability requirements under large SCR fluctuations in actual power systems. Summary of the invention

[0006] Based on this, it is necessary to provide a grid-connected converter control method based on hybrid control of grid-following and grid-building to address the problem that new energy grid-connected converters with a single grid-following or grid-building control mode are difficult to meet the stability requirements under large SCR fluctuations in actual power systems.

[0007] The present application provides a grid-connected converter control method based on grid-following and grid-building hybrid control, the method comprising:

[0008] Step S1, establishing an adaptive hybrid synchronous control model, a voltage and current dual-loop control model and a virtual impedance control model; the adaptive hybrid synchronous control model includes a phase-locked loop control model, a power synchronous control model and a ratio adaptive adjustment model;

[0009] Step S2, obtaining the voltage and current of the AC bus;

[0010] Step S3, obtaining the phase-locked loop output angular velocity according to the phase-locked loop control model and the voltage of the AC bus, obtaining the grid synchronization angular velocity and the excitation electromotive force according to the power synchronization control model and the voltage and current of the AC bus, and obtaining the grid-following characteristic ratio and the grid-forming characteristic ratio according to the ratio adaptive regulation model and the voltage and current of the AC bus;

[0011] Step S4, obtaining the converter synchronization angle according to the grid-following characteristic ratio, the grid-forming characteristic ratio, the phase-locked loop output angular velocity and the grid synchronization angular velocity;

[0012] Step S5, obtaining voltage outer loop control parameters according to the converter synchronization angle, the excitation electromotive force and the virtual impedance control model;

[0013] Step S6, generating working control parameters of the grid-connected converter according to the voltage outer loop control parameters and the voltage and current dual loop control model.

[0014] In one embodiment, the expression of the phase-locked loop control model is:

[0015]

[0016] Where U o is the AC bus voltage amplitude, u oq is the q-axis component of the AC bus voltage, k pllp is the proportional coefficient of the phase-locked loop PI controller, k plli is the integral coefficient of the phase-locked loop PI controller, ω pll is the phase-locked loop output angular velocity, θ pll The phase-locked loop output angular velocity ω pll The corresponding output phase angle, θ pllref is the output phase angle reference value.

[0017] In one embodiment, the expression of the power synchronization control model is:

[0018]

[0019] Where ω is the mechanical angular velocity, ω PBS represents the grid synchronization angular velocity, ω0 represents the grid reference angular velocity, θ PBS Represents the grid synchronization angular velocity ω PBS The corresponding virtual rotor position angle, J is the moment of inertia, D is the damping torque, T m is the torque reference value of the virtual synchronous generator, T e is the actual output value of the virtual synchronous generator torque, P m is the mechanical power, P e is the active power, T d is the damping torque, K Qis the PI adjustment coefficient, U ref is the reference voltage, Q ref is the reference reactive power, Q e is the reactive power, Q d is the reactive power with primary voltage regulation function, E is the excitation electromotive force, U n is the amplitude of the terminal voltage, U0 is the amplitude of the AC bus voltage, P ref is the reference active power, K p is the active power-frequency regulation coefficient, K q is the reactive power-voltage regulation coefficient; where the expressions of the AC bus voltage amplitude U0 and the grid reference angular velocity ω0 are:

[0020] ω o ≈ω pll =k pllp u oq +k plli ∫u oq dt

[0021]

[0022] In the formula, ω pll is the phase-locked loop output angular velocity, u od is the d-axis component of the AC bus voltage, u oq is the q-axis component of the AC bus voltage, k pllp is the proportional coefficient of the phase-locked loop PI controller, k plli is the integral coefficient of the phase-locked loop PI controller.

[0023] In one embodiment, the ratio adaptive adjustment model includes an SCR identification unit and a ratio adjustment unit. The expression of the SCR identification unit is:

[0024]

[0025] Where SCR is the short circuit ratio, S sc is the short-circuit capacity, S N is the rated capacity of the generator, Z * is the per unit value of the equivalent impedance of the power grid;

[0026] The expression of the ratio adjustment unit is:

[0027]

[0028] In the formula, SCR high Indicates the short-circuit ratio when the power grid is strong, SCR low Indicates the short-circuit ratio when the power grid is weak. PLL is the ratio of the network type characteristics, α is a real parameter, 0≤α≤2π.

[0029] In one embodiment, the expression of the grid equivalent impedance is:

[0030]

[0031] In the formula, R g Indicates the grid resistance, L g Represents the grid inductance, R gs Represents the total impedance, X gs Indicates total inductive reactance, L gg represents the grid-side inductance of the LCL filter; where the expressions of total impedance and total inductive reactance are:

[0032]

[0033] Where P e is the active power transmitted from the grid-connected converter to the grid, Q e is the reactive power transmitted from the grid-connected converter to the grid, v gf_ref The reference voltage of the converter output voltage, Δv gf_ref Represents voltage amplitude disturbance.

[0034] In one embodiment, the ratio adjustment unit includes a grid-type characteristic ratio lookup table, and the steps of calculating the grid-type characteristic ratio include:

[0035] Step S31, obtaining the grid-following characteristic ratio by looking up a table according to the short-circuit ratio of the common coupling point and the grid-following characteristic ratio.

[0036] In one embodiment, the calculation formula of the converter synchronization angle is:

[0037]

[0038] Where θ is the converter synchronization angle, ω0 is the grid reference angular velocity, θ0 is the integral of the grid reference angular velocity, and ω PLL is the phase-locked loop output angular velocity, θ PLL is the integral of the phase-locked loop output angular velocity, ω PBS is the grid synchronous angular velocity, θ PBS is the integral of the grid synchronization angular velocity, r PLL is the ratio of the network type characteristics, r PBS is the networking type characteristic ratio, and the sum of the networking type characteristic ratio and the networking type characteristic ratio is 1, and S is the Laplace operator.

[0039] In one embodiment, the voltage-current dual-loop control model includes a voltage outer loop control loop and a current inner loop control loop, and the expression of the voltage outer loop control loop is:

[0040]

[0041] In the formula, i dref represents the d-axis component of the reference current, i qref represents the q-axis component of the reference current, u dref represents the d-axis component of the reference voltage, u qref Represents the q-axis component of the reference voltage, K PU1 and K PU2 are the proportional coefficients of the voltage loop PI controller, K IU1 and K IU are the integral coefficients of the voltage loop PI controller, ω g is the angular frequency of the power grid at the sending end, C f is the filter capacitor, S is the Laplace operator, i od is the d-axis component of the AC bus current, i oq is the q-axis component of the AC bus current;

[0042] The expression of the current inner loop control loop is:

[0043]

[0044] In the formula, i Ld is the d-axis component of the grid-connected converter output current, i Lq is the q-axis component of the grid-connected converter output current, L f is the filter inductance, K PI1 and K PI2 are the proportional coefficients of the current loop PI controller, K II1 and K II2 They are the integral coefficients of the current loop PI controller.

[0045] In one embodiment, the expression of the virtual impedance control model is:

[0046] u dref =-R s i Ld +e d +wLi Lq

[0047] u qref =-R s i Ld +e q -wLi Lq

[0048] In the formula, e d 、e q is the dq axis component of the excitation electromotive force, R s is the virtual resistance value, and wL is the virtual reactance value.

[0049] The above-mentioned grid-connected converter control method based on hybrid control of following the grid and building the grid, by constructing an adaptive hybrid synchronous control model to flexibly adjust the proportion of the characteristics of following the grid and building the grid, ensures that the grid connection process is smooth and efficient, and constructs a voltage and current dual-loop control model to accurately regulate the output voltage and current, meeting the high-standard power quality requirements of the power grid for renewable energy power generation. At the same time, the introduction of grid impedance estimation for virtual impedance control further enhances the system's anti-interference ability and response speed. In summary, the grid-connected converter control method based on hybrid control of following the grid and building the grid provided in this application significantly improves the system's adaptability and stability to complex power grid environments, and improves the overall operating efficiency and reliability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 A schematic diagram of the structure of a new energy grid-connected power generation system in one embodiment;

[0051] Figure 2 It is a flowchart of a grid-connected converter control method based on hybrid control of grid following and grid building in one embodiment;

[0052] Figure 3 A schematic diagram of the structure of an adaptive hybrid synchronization control model in an embodiment;

[0053] Figure 4 (a) is a schematic diagram of equivalent impedance estimation of a new energy grid-connected power generation system in one embodiment;

[0054] Figure 4 (b) is a phasor diagram of equivalent impedance estimation of a new energy grid-connected power generation system in one embodiment;

[0055] Figure 5 A schematic diagram of the relationship between the network type characteristic ratio and the short circuit ratio in one embodiment;

[0056] Figure 6 A schematic diagram of the structure of a voltage-current dual-loop control model in one embodiment;

[0057] Figure 7 A schematic diagram of the structure of a virtual impedance control model in one embodiment;

[0058] Figure 8 FIG. 4 is a schematic diagram showing the relationship between the network type characteristic ratio and the short circuit ratio in another embodiment. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0060] The embodiment of the present application provides a grid-connected converter control method based on grid-following and grid-building hybrid control, which can be applied to Figure 1 The control device in the renewable energy grid-connected power generation system shown in the figure comprises a renewable energy grid-connected converter (hereinafter referred to as grid-connected converter 101), a power grid 102 and a control device 103. The grid-connected converter 101 is connected to the power grid 102 via an AC bus. Figure 1 Where Lf is the inductance on the converter side of the LCL filter, Rf is the filter resistor, Cf is the filter capacitor, Lgg is the inductance on the grid side of the LCL filter, Rg is the grid resistor, Lg is the grid inductance, and Vg represents the grid voltage source. The first end of the control device 103 is connected to the grid 102, and the second end is connected to the grid-connected converter 101.

[0061] The control device 103 includes an abc-dq coordinate conversion module, a power calculation module, a hybrid control module 113, a dq-abc coordinate conversion module and a PWM modulator. The abc-dq coordinate conversion module is used to convert the AC bus voltage U o(abc) Converted to the voltage component U in the dq coordinate system od and U oq , the AC bus current I o(abc) Converted to the current component I in the dq coordinate system od and I oq , the output current i of the grid-connected converter L (abc) is converted into the current component i in the dq coordinate system Ld and i Lq The power calculation module is used to calculate the power of od , U oq ,I od and I oq Calculate the active power P transmitted to the grid by the grid-connected converter 101 e and reactive power Q e .

[0062] The hybrid control module 113 first establishes an adaptive hybrid synchronous control model, a virtual impedance control model and a voltage-current dual-loop control model, and the adaptive hybrid synchronous control model includes a phase-locked loop control model, a power synchronous control model and a ratio adaptive adjustment model; then the phase-locked loop output angular velocity is obtained according to the phase-locked loop control model and the voltage of the AC bus, the grid synchronous angular velocity and the excitation electromotive force are obtained according to the power synchronous control model and the voltage and current of the AC bus, and the grid-following characteristic ratio and the grid-forming characteristic ratio are obtained according to the ratio adaptive adjustment model and the voltage and current of the AC bus; then the converter synchronization angle is obtained according to the grid-following characteristic ratio, the grid-forming characteristic ratio, the phase-locked loop output angular velocity and the grid synchronous angular velocity, and the voltage outer loop control parameters are obtained according to the converter synchronization angle, the excitation electromotive force and the virtual impedance control model; finally, the working control parameters of the grid-connected converter are generated according to the voltage outer loop control parameters and the voltage-current dual-loop control model, and the working control parameters are used to control the grid-connected converter to perform adaptive grid connection.

[0063] The grid-connected converter control method based on hybrid control of following the grid and building the grid of the present application is described in detail below in conjunction with some specific embodiments.

[0064] Embodiment 1

[0065] An embodiment of the present disclosure provides a grid-connected converter control method based on hybrid control of grid following and grid building, such as Figure 2 As shown, the specific steps include:

[0066] Step S1, establishing an adaptive hybrid synchronous control model, a voltage and current dual-loop control model and a grid impedance estimation model. The adaptive hybrid synchronous control model includes a phase-locked loop control model, a power synchronous control model and a ratio adaptive regulation model.

[0067] The adaptive hybrid synchronization control model realizes grid synchronization through the phase-locked loop control model, the power synchronization control model simulates the characteristics of the virtual synchronous generator (VSG), and the ratio adaptive regulation model dynamically adjusts the ratio of the grid-following and grid-building characteristics according to the changes in the grid strength. Among them, the specific structure of the adaptive hybrid synchronization control model is as follows: Figure 3 As shown, the phase-locked loop control model includes a voltage coordinate transformation unit and a PI controller, which is used to track the voltage phase of the AC bus and output the corresponding angular velocity. Its mathematical expression is shown in formula (1):

[0068]

[0069] Where U o is the AC bus voltage amplitude, u oq is the q-axis component of the AC bus voltage, k pllp is the proportional coefficient of the phase-locked loop PI controller, k plliis the integral coefficient of the phase-locked loop PI controller, ω pll is the phase-locked loop output angular velocity, θ pll The phase-locked loop output angular velocity ω pll The corresponding output phase angle, θ pllref It is the preset output phase angle reference value.

[0070] The power synchronization control model includes an active power control loop and a reactive power control loop. The active power control loop is used to control the active power P transmitted to the grid by the grid-connected converter. e Output grid synchronous angular velocity ω PBS The reactive power control loop is used to control the reactive power Q transmitted to the grid by the grid-connected converter. e Output excitation electromotive force E. Among them, active power P e and reactive power Q e All can be based on the AC bus voltage U o(abc) The dq component (u od 、u oq ) and AC bus current I o(abc) The dq component (i od 、i oq ) is calculated. Specifically, this embodiment adds a primary frequency modulation function to the active power control loop and a primary voltage regulation function to the reactive power control loop to effectively support the terminal voltage frequency and amplitude. The expression of the power synchronization control model with the primary frequency modulation function and the primary voltage regulation function is shown in equations (2)-(3):

[0071]

[0072] Where ω is the mechanical angular velocity, ω PBS represents the grid synchronous angular velocity, ω0 represents the grid reference angular velocity, and the grid reference angular velocity in this embodiment is the AC bus voltage frequency, θ PBS Represents the grid synchronization angular velocity ω PBS The corresponding virtual rotor position angle, J is the moment of inertia, D is the damping torque, T m is the torque reference value of the virtual synchronous generator, T e is the actual output value of the virtual synchronous generator torque, which can be obtained by P m is the mechanical power, P e is the electromagnetic power, that is, the active power, T d is the damping torque, K Q is the PI adjustment coefficient, U ref is the reference voltage, specifically the reference voltage of the excitation electromotive force, Q ref is the reference reactive power, Q e is the reactive power, Q dis the reactive power with primary voltage regulation function, E is the excitation electromotive force, U n is the amplitude of the terminal voltage, U0 is the amplitude of the AC bus voltage, P ref is the reference active power, K p is the active power-frequency regulation coefficient, K q is the reactive power-voltage regulation coefficient. Among them, the AC bus voltage amplitude U0 and the AC bus voltage frequency ω0 are obtained through the phase-locked loop control model, and the specific expressions are shown in equations (4) and (5) respectively:

[0073] ω o ≈ω pll =k pllp u oq +k plli ∫u oq dt (4)

[0074]

[0075] In the formula, ω pll is the phase-locked loop output angular velocity, u od is the d-axis component of the AC bus voltage, u oq is the q-axis component of the AC bus voltage, k pllp is the proportional coefficient of the phase-locked loop PI controller, k plli is the integral coefficient of the phase-locked loop PI controller.

[0076] The ratio adaptive regulation model includes an SCR identification unit and a ratio adjustment unit. The SCR identification unit is used to calculate the short-circuit ratio SCR of the common coupling point. Its mathematical expression is shown in formula (6):

[0077]

[0078] Where SCR is the short circuit ratio, S sc is the short-circuit capacity, which can be calculated from the voltage and current of the AC bus. The specific calculation formula is: In this formula, U PCC and I PCC They represent the voltage and current of the common coupling point, respectively. The voltage and current of the common coupling point in this embodiment are the voltage U0 and current I0 of the AC bus. N is the rated capacity of the generator, Z * is the per unit value of the grid equivalent impedance.

[0079] Furthermore, this embodiment also provides an impedance estimation method for calculating the equivalent impedance of a power grid. Specifically, Figure 4 (a) is a simplified schematic diagram of grid impedance estimation, in which the grid-connected converter is modeled as a controllable AC voltage source V gf ∠0°, and select the converter output voltage Vgf The phase of ∠0° is used as the reference angle. is the grid current phasor, V s ∠-δ is the grid voltage phasor, Z gs ∠θ is the impedance connected between the two voltage sources. This impedance is the inductance L of the grid side of the LCL filter. gg , Grid resistance R g and grid inductance L g Therefore, the impedance Z gs ∠θ can be expressed by formula (7):

[0080] Z gs ∠θ=R gs +jX gs =R g +jω0(L gg +L g ) (7)

[0081] In the formula, R gs is the total impedance, R gs =R g , X gs is the total inductive reactance, X gs =L gg +L g .

[0082] based on Figure 4 (a), the impedance of the grid resistance and grid inductance is estimated below. In order to more intuitively reflect the relationship between the various phase quantities, Figure 4 (b) shows the phasor diagram including each phasor. Figure 4 (b) The expression of the grid current phasor can be derived, as shown in formula (8):

[0083]

[0084] In addition, the active power Pe and reactive power Qe transmitted by the grid-connected converter to the grid are obtained by the complex product of the converter output voltage and the conjugate current phasor, as shown in equations (9)-(10):

[0085]

[0086] Generally speaking, grid-connected converters can operate under voltage or power control. In the case of voltage control, the power control part should be ignored, and the voltage amplitude V of the grid-connected converter can be directly adjusted. gf and phase angle θ. When the control device is working normally, the voltage amplitude of its output voltage is V gf and the phase angle δ are shown in equations (11)-(12):

[0087] Vgf =v gf_ref =V gf_ref +Δv gf_ref (11)

[0088] δ=θ PBS (12)

[0089] Among them, v gf_ref Represents the reference voltage of the converter output voltage, that is, the reference value of the output voltage after the converter is equivalent to a controllable AC voltage source, V gf_ref is the reference voltage amplitude, which is equal to the grid voltage amplitude, that is, V gf_ref =V s , V s is obtained before grid connection to avoid inrush current, Δv _gf_ref Represents the voltage amplitude disturbance, and its value is equal to Figure 3 The output value of the PI controller in the reactive power control loop, Δv gf_ref =Δv ref According to equations (11) and (12), and assuming δ≈0°, equations (9) and (10) can be simplified to equations (13) and (14):

[0090]

[0091] Furthermore, according to equations (13) and (14), the total impedance R can be derived gs And the total impedance X gs The mathematical expression of is as shown in formula (15)-(16):

[0092]

[0093] Finally, the grid equivalent impedance is obtained as shown in equations (17)-(18), including the grid resistance as shown in equation (17) and the grid inductance as shown in equation (18):

[0094] R g =R gs (17)

[0095]

[0096] In the formula, R g Indicates the grid resistance, L g Represents the grid inductance, L gg Represents the grid-side inductance of the LCL filter.

[0097] The ratio adjustment unit simulates the hysteresis loop of the magnetic material and obtains the following Figure 5 The approximate relationship between the SCR and the grid-following characteristic ratio is shown in equation (19):

[0098]

[0099] Where α is a real parameter (0≤α≤2π), SCR high Indicates the short-circuit ratio when the power grid presents "strong power grid" characteristics, SCR low Indicates the short-circuit ratio when the grid is "weak grid" characteristic. The hysteresis loop characteristic helps to reduce the sensitivity to small fluctuations of the SCR, thereby preventing rapid changes in the characteristics of the grid or grid formation.

[0100] The voltage-current dual-loop control model includes an outer voltage control loop and an inner current control loop. It ensures that the renewable energy power generation system can supply power to the grid according to the preset power and power quality requirements by precisely controlling the output voltage and current of the grid-connected converter. Figure 6 The specific structure of the voltage and current dual-loop control model is shown. Figure 6 It can be seen that the expression of the voltage outer loop control loop is shown in equations (20)-(21), and the expression of the current inner loop control loop is shown in equations (22)-(23):

[0101]

[0102] In the formula, i dref represents the d-axis component of the reference current, i qref represents the q-axis component of the reference current, u dref represents the d-axis component of the reference voltage, u qref Represents the q-axis component of the reference voltage, K PU1 and K PU2 are the proportional coefficients of the voltage loop PI controller, K IU1 and K IU are the integral coefficients of the voltage loop PI controller, ω g is the angular frequency of the power grid at the sending end, C f is the filter capacitor, S is the Laplace operator, i od is the d-axis component of the AC bus current, i oq is the q-axis component of the AC bus current.

[0103]

[0104] In the formula, i Ld is the d-axis component of the grid-connected converter output current, i Lq is the q-axis component of the grid-connected converter output current, L f is the filter inductance, K PI1 and K PI2 are the proportional coefficients of the current loop PI controller, K II1 and K II2 They are the integral coefficients of the current loop PI controller.

[0105] Figure 7 The specific structure of the virtual impedance control model is shown, and its mathematical expression is:

[0106]

[0107] In the formula, e d 、e q is the dq axis component of the excitation electromotive force, R s is the virtual resistance value, corresponding to Figure 1 R f , wL is the virtual reactance value, corresponding to Figure 1 L f .

[0108] Step S2, obtaining the voltage and current of the AC bus.

[0109] Among them, the voltage of the AC bus is the three-phase voltage U o(abc) , the current of the AC bus is the three-phase current I o(abc) .

[0110] Step S3, obtain the phase-locked loop output angular velocity according to the phase-locked loop control model and the voltage of the AC bus, obtain the grid synchronization angular velocity and excitation electromotive force according to the power synchronization control model and the voltage and current of the AC bus, and obtain the grid-following characteristic ratio and the grid-forming characteristic ratio according to the ratio adaptive adjustment model and the voltage and current of the AC bus.

[0111] Specifically, first, the phase-locked loop output angular velocity ω is obtained according to the phase-locked loop control model shown in formula (1) according to the AC bus voltage Uo. pll . Then according to the active power P e and reactive power Q e The excitation electromotive force E and the grid synchronization angular velocity ω are calculated by the power synchronization control model shown in equations (2)-(3): PBS Then, according to the voltage and current of the AC bus and the ratio adaptive regulation model shown in equations (6) and (19), the grid-following characteristic ratio r is obtained. PLL , with the network type characteristic ratio r PLL The value is usually less than 1, and finally 1 is subtracted from the network characteristic ratio r PLL The result is taken as the network characteristic ratio r PBS The value of .

[0112] Step S4, obtaining the converter synchronization angle according to the grid-following characteristic ratio, the grid-forming characteristic ratio, the phase-locked loop output angular velocity and the grid synchronization angular velocity.

[0113] Specifically, the calculation formula of the converter synchronization angle is shown in formula (25):

[0114]

[0115] Where θ is the converter synchronization angle, ω0 is the grid reference angular velocity, θ0 is the integral of the grid reference angular velocity, and ω PLL is the phase-locked loop output angular velocity, r PLL is the ratio of the network type characteristics, θ PLL is the phase-locked loop output phase angle, ω PBS is the grid synchronous angular velocity, θ PBS Represents the virtual rotor position angle, ω PBS The integral of PBS is the network-type characteristic ratio, and S is the Laplace operator.

[0116] Step S5, obtaining voltage outer loop control parameters according to the converter synchronization angle, the excitation electromotive force and the virtual impedance control model.

[0117] The voltage outer loop control parameters include the dq axis component u of the reference voltage of the voltage outer loop control loop. dref and u qref . Specifically, Figure 7 As shown in the figure, the virtual impedance control model first transforms the converter synchronization angle θ and the excitation electromotive force E to obtain the d-axis component u d and the q-axis component u q , and then transmitted to the filter inductor L f The d-axis component of the current i Ld and the q-axis component i Lq , and the dq-axis component of the excitation electromotive force e d and e q Calculate u dref and u qref .

[0118] Step S6, generating working control parameters of the grid-connected converter according to the voltage outer loop control parameters and the voltage and current dual loop control model, wherein the working control parameters are used to control the grid-connected converter to perform adaptive grid connection.

[0119] The working control parameters of the grid-connected converter include the component u of the target working voltage of the grid-connected converter in the dq rotating coordinate system: d and u q , which is the output value of the inner current control loop.

[0120] Specifically, first, according to the u obtained in step S5 dref and u qref And the voltage and current dual-loop control model shown in equations (20)-(23) obtains u d and u q , and then to u d and uq Perform coordinate transformation to convert the target working voltage from the dq rotating coordinate system to the abc three-phase stationary coordinate system, so as to obtain the control voltage component u in the abc three-phase stationary coordinate system abc , and then based on this control voltage component u abc Further generate the driving signals of each switching tube in the grid-connected converter. These driving signals regulate the voltage amplitude and phase angle of the grid-connected converter output by controlling the on-off of the switching tubes, so as to achieve precise tracking of the power grid and adaptive grid connection.

[0121] The grid-connected converter control method based on the hybrid control of grid following and grid forming disclosed in this embodiment flexibly adjusts the ratio of grid following and grid forming characteristics by constructing an adaptive hybrid synchronization control model, ensuring a smooth and efficient grid connection process. A voltage-current double-loop control model is constructed to precisely regulate the output voltage and current, meeting the high-standard power quality requirements of the power grid for new energy power generation. At the same time, grid impedance estimation is introduced for virtual impedance control, further enhancing the anti-interference ability and response speed of the system. In summary, the grid-connected converter control method using the hybrid control of grid following and grid forming in this embodiment significantly improves the adaptability and stability of the system to complex grid environments, and improves the overall operation efficiency and reliability of the system.

[0122] Embodiment 2

[0123] The difference from Embodiment 1 is that the ratio adjustment unit of this embodiment includes a grid-following characteristic ratio look-up table, and step S3 includes:[[]]

[0124] Step S31, obtain the grid-following characteristic ratio according to the short-circuit ratio of the point of common coupling and the grid-following characteristic ratio look-up table.

[0125] Among them, the grid-following characteristic ratio look-up table includes the grid-following characteristic ratios corresponding to the short-circuit ratios of different points of common coupling. Table 1 shows a preferred implementation of the grid-following characteristic ratio look-up table. When SCR ≤ 2, r PLL = 0. When 2 < SCR ≤ 5, r PLL = 10%. When 5 < SCR ≤ 10, r PLL = 20%. When 10 < SCR ≤ 15, r PLL = 90%. When SCR > 15, r PLL = 100%. It can be understood that those skilled in the art can adjust the relationship between the short-circuit ratio and the characteristic ratio in the table according to actual needs to apply to different application scenarios.

[0126] Table 1

[0127] SCR≤2 2<SCR≤5 5<SCR≤10 10<SCR≤15 SCR>15 <![CDATA[r PLL =0]]> <![CDATA[r PLL =10%]]> <![CDATA[r PLL =20%]]> <![CDATA[r PLL =90%]]> <![CDATA[r PLL =100%]]>

[0128] Specifically, after completing the impedance estimation, the short-circuit ratio SCR of the common coupling point is calculated according to formula (5), and then the corresponding grid-type characteristic ratio is found from the grid-type characteristic ratio lookup table according to the value of SCR, and then the grid-type characteristic ratio is obtained according to the grid-type characteristic ratio. Figure 8 The short-circuit ratio of SCR and the grid-following characteristic ratio r is shown. PLL As can be seen from the figure, SCR and r PLL The relationship satisfies the network characteristic ratio lookup table shown in Table 1.

[0129] This embodiment obtains the corresponding grid-following type characteristic ratio from the grid-following type characteristic ratio lookup table according to the value of SCR, which greatly reduces the amount of calculation, thereby further improving the control efficiency of the hybrid control of grid-following and grid-building.

[0130] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0131] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A grid-connected converter control method based on hybrid control of grid following and grid building, characterized in that: The method comprises: Step S1, establishing an adaptive hybrid synchronous control model, a voltage and current dual-loop control model and a virtual impedance control model; the adaptive hybrid synchronous control model includes a phase-locked loop control model, a power synchronous control model and a ratio adaptive adjustment model; Step S2, obtaining the voltage and current of the AC bus; Step S3, obtaining a phase-locked loop output angular velocity according to the phase-locked loop control model and the voltage of the AC bus, obtaining a power grid synchronization angular velocity and an excitation electromotive force according to the power synchronization control model and the voltage and current of the AC bus, and obtaining a grid-following characteristic ratio and a grid-forming characteristic ratio according to the ratio adaptive adjustment model and the voltage and current of the AC bus; Step S4, obtaining a converter synchronization angle according to the grid-following characteristic ratio, the grid-forming characteristic ratio, the phase-locked loop output angular velocity, and the grid synchronization angular velocity; Step S5, obtaining voltage outer loop control parameters according to the converter synchronization angle, the excitation electromotive force and the virtual impedance control model; Step S6, generating working control parameters of the grid-connected converter according to the voltage outer loop control parameters and the voltage-current dual loop control model.

2. The grid-connected converter control method based on hybrid control of grid following and grid building according to claim 1 is characterized in that: The expression of the phase-locked loop control model is: Where U o is the AC bus voltage amplitude, u oq is the q-axis component of the AC bus voltage, k pllp is the proportional coefficient of the phase-locked loop PI controller, k plli is the integral coefficient of the phase-locked loop PI controller, ω pll is the phase-locked loop output angular velocity, θ pll The phase-locked loop outputs an angular velocity ω pll The corresponding output phase angle, θ pllref is the output phase angle reference value.

3. The grid-connected converter control method based on hybrid control of grid following and grid building according to claim 1 is characterized in that: The expression of the power synchronization control model is: Where ω is the mechanical angular velocity, ω PBS represents the grid synchronization angular velocity, ω0 represents the grid reference angular velocity, θ PBS represents the grid synchronous angular velocity ω PBS The corresponding virtual rotor position angle, J is the moment of inertia, D is the damping torque, T m is the torque given value of the virtual synchronous generator, T e is the actual output value of the virtual synchronous generator torque, P m is the mechanical power, P e is the active power, T d is the damping torque, K Q is the PI adjustment coefficient, U ref is the reference voltage, Q ref is the reference reactive power, Q e is the reactive power, Q d is the reactive power with primary voltage regulation function, E is the excitation electromotive force, U n is the amplitude of the terminal voltage, U0 is the amplitude of the AC bus voltage, P ref is the reference active power, K p is the active power-frequency regulation coefficient, K q is the reactive power-voltage regulation coefficient; wherein the expressions of the AC bus voltage amplitude U0 and the grid reference angular velocity ω0 are respectively: ω o ≈ω pll =k pllp u oq +k plli ∫u oq dt In the formula, ω pll is the phase-locked loop output angular velocity, u od is the d-axis component of the AC bus voltage, u oq is the q-axis component of the AC bus voltage, k pllp is the proportional coefficient of the phase-locked loop PI controller, k plli is the integral coefficient of the phase-locked loop PI controller.

4. The grid-connected converter control method based on hybrid control of grid following and grid building according to claim 1 is characterized in that: The ratio adaptive adjustment model includes an SCR identification unit and a ratio adjustment unit. The expression of the SCR identification unit is: Where SCR is the short circuit ratio, S sc is the short-circuit capacity, S N is the rated capacity of the generator, Z * is the per unit value of the equivalent impedance of the power grid; The expression of the ratio adjustment unit is: In the formula, SCR high Indicates the short-circuit ratio when the power grid is strong, SCR low Indicates the short-circuit ratio when the power grid is weak. PLL is the following network type characteristic ratio, α is a real parameter, 0≤α≤2π.

5. The grid-connected converter control method based on hybrid control of grid following and grid building according to claim 4 is characterized in that: The expression of the equivalent impedance of the power grid is: In the formula, R g Indicates the grid resistance, L g Represents the grid inductance, R gs Represents the total impedance, X gs Indicates total inductive reactance, L gg represents the grid-side inductance of the LCL filter; wherein the expressions of the total impedance and the total inductive reactance are respectively: Where P e is the active power transmitted from the grid-connected converter to the grid, Q e is the reactive power transmitted from the grid-connected converter to the grid, v gf_ref The reference voltage of the converter output voltage, Δv gf_ref Represents voltage amplitude disturbance.

6. The grid-connected converter control method based on hybrid control of grid following and grid building according to claim 4 is characterized in that: The ratio adjustment unit includes a network-type characteristic ratio lookup table, and the calculation step of the network-type characteristic ratio includes: Step S31, obtaining the grid-following type characteristic ratio by looking up a table according to the short-circuit ratio of the common coupling point and the grid-following type characteristic ratio.

7. The grid-connected converter control method based on hybrid control of grid following and grid building according to claim 1 is characterized in that: The calculation formula of the converter synchronization angle is: Where θ is the converter synchronization angle, ω0 is the grid reference angular velocity, θ0 is the integral of the grid reference angular velocity, ω PLL is the phase-locked loop output angular velocity, θ PLL is the integral of the phase-locked loop output angular velocity, ω PBS is the grid synchronous angular velocity, θ PBS is the integral of the grid synchronization angular velocity, r PLL is the following network characteristic ratio, r PBS is the networking type characteristic ratio, and the sum of the following networking type characteristic ratio and the networking type characteristic ratio is 1, and S is the Laplace operator.

8. The grid-connected converter control method based on hybrid control of grid following and grid building according to claim 1 is characterized in that: The voltage-current dual-loop control model includes a voltage outer loop control loop and a current inner loop control loop. The expression of the voltage outer loop control loop is: In the formula, i dref represents the d-axis component of the reference current, i qref represents the q-axis component of the reference current, u dref represents the d-axis component of the reference voltage, u qref Represents the q-axis component of the reference voltage, K PU1 and K PU2 are the proportional coefficients of the voltage loop PI controller, K IU1 and K IU are the integral coefficients of the voltage loop PI controller, ω g is the angular frequency of the power grid at the sending end, C f is the filter capacitor, S is the Laplace operator, i od is the d-axis component of the AC bus current, i oq is the q-axis component of the AC bus current; The expression of the current inner loop control loop is: In the formula, u d is the d-axis component of the target operating voltage of the grid-connected converter, u q is the q-axis component of the target operating voltage of the grid-connected converter, i Ld is the d-axis component of the grid-connected converter output current, i Lq is the q-axis component of the grid-connected converter output current, L f is the filter inductance, K PI1 and K PI2 are the proportional coefficients of the current loop PI controller, K II1 and K II2 They are all integral coefficients of the current loop PI controller.

9. The grid-connected converter control method based on hybrid control of following the grid and building the grid according to claim 8 is characterized in that: The expression of the virtual impedance control model is: u dref -R s i Ld +e d +wLi Lq u qref -R s i Ld +e q -wLi Lq In the formula, e d 、e q is the dq axis component of the excitation electromotive force, R s is the virtual resistance value, and wL is the virtual reactance value.

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