Robust active damping control method and system of grid-connected converter

Abstract

The invention relates to the technical field of power electronics, in particular to a robust active damping control method and system for a grid-connected converter. According to the robust active damping control method of the grid-connected converter, a current parameter and an extended state observer are combined to predict a predicted value of a capacitor current at a next moment, so that delay compensation in a system is realized based on the predicted value of the capacitor current at the next moment, and corresponding virtual impedance presents a positive real part in a wider range; the resonance problem caused by underdamping is reduced, and the stability of the system is improved.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a robust active damping control method and system for a grid-connected converter. Background Art

[0002] Grid-connected converters are widely used in new energy scenarios, and L or LCL filters are usually used to suppress high-frequency harmonics. Among them, LCL filters have better high-frequency harmonic attenuation performance than L filters and are smaller in size. However, time delays in digital control (such as algorithm execution and zero-order hold effects) will cause the active damping of capacitor currents to be equivalent to virtual impedance, changing the resonant frequency. When the grid impedance increases and the resonant frequency exceeds one-sixth of the sampling frequency, the virtual impedance exhibits negative resistance, which may cause the system to resonate due to underdamping, leading to system instability.

[0003] In order to reduce the impact of time delay on active damping performance, related technologies attempt to move the capacitor current sampling point to the moment of PWM reference update. However, due to the time limit of analog-to-digital conversion and algorithm execution, the delay compensation effect of this method is limited. In addition, this method may introduce high-frequency harmonics, reduce the power quality of the grid-side current, and due to the instantaneous changes in power device switching, it is difficult to completely avoid switching interference at the sampling moment.

[0004] In view of the above problems, it is urgent to propose a new time delay compensation strategy to improve the robustness and stability of the system while ensuring the power quality and avoiding the risk of resonance and system instability. Summary of the invention

[0005] The embodiments of the present application provide a robust active damping control method and system for a grid-connected converter, which realizes delay compensation in the system, reduces the problem of virtual impedance presenting negative resistance and causing system resonance, and improves the stability of the system.

[0006] In some embodiments, a robust active damping control method for a grid-connected converter is provided. The robust active damping control method for a grid-connected converter is applied to a robust active damping control system for a grid-connected converter. The robust active damping control system for a grid-connected converter includes a grid-connected converter, and the grid-connected converter includes a power converter. The robust active damping control method for a grid-connected converter includes: obtaining a current value i of an inverter side at a current moment in an α-β coordinate system in the grid-connected converter; 1,αβ , the current voltage value v of the common coupling point on the grid side pcc,αβ , the current value i of the grid side at the current moment 2,αβ , and the active current component reference value on the grid side in the dq coordinate system and reactive current component reference value and the phase angle θ of the power grid; based on the current value i of the inverter side at the current moment1,αβ , the current voltage value v of the common coupling point on the grid side pcc,αβ , the current value i of the grid side at the current moment 2,αβ , the extended state observer is used to determine the predicted value of the capacitor current at the next moment; based on the predicted value of the capacitor current at the next moment and the active damping coefficient k ad , determine the capacitor current active damping feedback corresponding to the predicted value of the capacitor current at the next moment; based on the active current component reference value Reactive current component reference value and a proportional resonant controller, determining a control signal P output by the proportional resonant controller; based on the control signal P and the voltage value v at the common coupling point on the grid side at the current moment pcc,αβ The pulse width modulation signal M is determined by the active damping feedback of the capacitor current; and the power converter is controlled based on the pulse width modulation signal M.

[0007] The robust active damping control method for the grid-connected converter provided in the embodiment of the present application is adopted. By combining the current parameters with the extended state observer, the predicted value of the capacitor current at the next moment is predicted, so that the delay compensation in the system is realized based on the predicted value of the capacitor current at the next moment, the problem of the virtual impedance presenting negative resistance and causing system resonance is reduced, and the stability of the system is improved.

[0008] Optionally, obtain the current value i of the inverter side at the current moment in the α-β coordinate system 1,αβ , the current voltage value v of the common coupling point on the grid side pcc,αβ , the current value i of the grid side at the current moment 2,αβ , including: obtaining the current value i of the inverter side at the current moment in the abc coordinate system 1,abc , the current voltage value v of the common coupling point on the grid side pcc,abc and the current value i of the grid side at the current moment 2,abc ; Set the current value i of the inverter side at the current moment 1,abc , the current voltage value v of the common coupling point on the grid side pcc,abc and the current value i of the grid side at the current moment 2,abc The coordinates are converted into the α-β coordinate system.

[0009] Optionally, based on the current value i of the inverter side at the current moment 1,αβ , the current voltage value v of the common coupling point on the grid side pcc,αβ , the current value i of the grid side at the current moment 2,αβ , using the extended state observer to determine the predicted value of the capacitor current at the next moment, including: 1,αβ , the current voltage value v of the common coupling point on the grid side pcc,αβ and the current value i of the grid side at the current moment 2,αβThe extended state observer is input to determine the inverter-side current prediction value and the grid-side current prediction value; the difference between the inverter-side current prediction value and the grid-side current prediction value is calculated to determine the capacitor current prediction value at the next moment.

[0010] Optionally, the extended state observer includes an inverter-side extended state observer and a grid-side extended state observer;

[0011] The inverter side extended state observer is shown in the first formula group below:

[0012]

[0013] The grid-side extended state observer is shown in the second formula group below:

[0014]

[0015] Wherein, “(k)” indicates the discretization of parameters, the superscript “eso” indicates the extended state observer, the subscript “1” indicates the inverter side, the subscript “2” indicates the grid side, the subscript “α” indicates the α-axis component in the α-β coordinate system, and the subscript “β” indicates the β-axis component in the α-β coordinate system. is the estimated value of the generalized disturbance, L1 is the inductance on the inverter side, L2 is the inductance on the grid side, and L 1,c is the nominal value of L1, L ′,0 is the nominal value of L2, β1 is the first parameter of the extended state observer, and β2 is the second parameter of the extended state observer.

[0016] Optionally, based on the predicted value of the capacitor current at the next moment and the active damping coefficient k ad , determine the capacitor current active damping feedback corresponding to the capacitor current prediction value at the next moment, including: calculating the capacitor current prediction value at the next moment and the active damping coefficient k ad The product of determines the capacitor current active damping feedback.

[0017] Optionally, based on the active current component reference value Reactive current component reference value and a proportional resonant controller, determining a control signal P output by the proportional resonant controller, including: based on an active current component reference value Reactive current component reference value and phase angle θ to determine the grid-side current reference value in the α-β coordinate system Calculate the grid-side current reference value β The current value i of the grid side at the current moment 2,αβ The difference between the values ​​of the control signal and the error signal is used to determine the error signal. The error signal is input into the proportional resonant controller, and the proportional resonant controller outputs a control signal.

[0018] Optionally, based on the control signal P and the current voltage value v of the common coupling point on the grid side pcc,αβ and capacitor current active damping feedback, determining the pulse width modulation signal M, including: based on the control signal The current voltage value v at the common coupling point on the grid side pcc,αβ and capacitor current active damping feedback Calculate the modulation voltage signal v inv,αβ ; Based on the SVPWM algorithm, a pulse width modulation signal M corresponding to the modulation voltage signal is generated.

[0019] Optionally, the formula for calculating the modulation voltage signal is:

[0020]

[0021] Among them, G PR (s) is the transfer function of the proportional resonant controller.

[0022] Optionally, based on the SVPWM algorithm, a pulse width modulation signal M corresponding to the modulation voltage signal is generated, including: calculating the modulation voltage signal v inv，αβ The amplitude and phase of the modulated voltage signal v is determined based on the phase inv，αβ The sector where the pulse width modulation signal is located; determine the linear combination of two basic vectors and the zero vector adjacent to the sector; based on the linear combination, determine the action time of each basic vector and the zero vector to determine the duty cycle of each phase; compare the duty cycle of each phase with the triangular carrier signal, and output the pulse width modulation signal M.

[0023] In some embodiments, a robust active damping control system for a grid-connected converter is provided, comprising: a grid-connected converter and a controller connected to each other in communication; the grid-connected converter comprises a power converter; the controller is configured to obtain a current value i of the inverter side at a current moment in the α-β coordinate system in the grid-connected converter. 1,αβ , the current voltage value v of the common coupling point on the grid side pcc,αβ , the current value i of the grid side at the current moment 2,αβ , and the active current component reference value on the grid side in the dq coordinate system and reactive current component reference value and the phase angle θ of the power grid; based on the current value i of the inverter side at the current moment 1,αβ , the current voltage value v of the common coupling point on the grid side pcc,αβ , the current value i of the grid side at the current moment 2,αβ , the extended state observer is used to determine the predicted value of the capacitor current at the next moment; based on the predicted value of the capacitor current at the next moment and the active damping coefficient k ad , determine the capacitor current active damping feedback corresponding to the predicted value of the capacitor current at the next moment; based on the active current component reference value Reactive current component reference value and a proportional resonant controller, determining a control signal P output by the proportional resonant controller; based on the control signal P and the voltage value v at the common coupling point on the grid side at the current moment pcc,αβ The pulse width modulation signal M is determined by the active damping feedback of the capacitor current; and the power converter is controlled based on the pulse width modulation signal M.

[0024] It can be understood that the beneficial effects that can be achieved by the technical solution provided by the robust active damping control system of the grid-connected converter provided above can be referred to the beneficial effects of the robust active damping control method of the grid-connected converter and any of its optional implementations, and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solution of the present application, the drawings required for use in the embodiments are briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0026] Figure 1 It is the circuit topology diagram of LCL type grid-connected converter;

[0027] Figure 2 It is the grid-side current loop control block diagram of LCL type grid-connected converter;

[0028] Figure 3 is the equivalent circuit diagram of the LCL filter;

[0029] Figure 4 It is a simplified block diagram of LCL type grid-connected converter;

[0030] Figure 5 A structural block diagram of a robust active damping control system for a grid-connected converter provided in an embodiment of the present application;

[0031] Figure 6 A control strategy block diagram of a robust active damping control method for a grid-connected converter provided in an embodiment of the present application;

[0032] Figure 7 A flowchart of a robust active damping control method for a grid-connected converter provided in an embodiment of the present application;

[0033] Figure 8 A simplified block diagram of an LCL-type grid-connected converter based on an extended state observer provided in an embodiment of the present application. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be described clearly below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments of the present application, other embodiments obtained by ordinary technicians in this field without making creative work all belong to the protection scope of the present application.

[0035] In the following, the terms "first", "second", etc. are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0036] In addition, in the present application, directional terms such as "upper", "lower", "inner" and "outer" are defined relative to the orientation of the components schematically placed in the drawings. It should be understood that these directional terms are relative concepts. They are used for relative description and clarification, and they can change accordingly according to the changes in the orientation of the components placed in the drawings.

[0037] In order to facilitate the understanding of the technical solution of the application, the relevant technologies involved in this application are first explained below.

[0038] Figure 1 This is the circuit topology diagram of the LCL type grid-connected converter.

[0039] Combination Figure 1 As shown, the grid-connected converter includes a power converter, an LCL filter and a grid-connected interface that are electrically connected to each other. The connection side of the LCL filter and the power converter is the inverter side, and the connection side of the LCL filter and the grid-connected interface is the grid side. The grid-connected converter mainly realizes the power conversion function from DC to AC, and can also realize the power conversion from AC to DC, and has the ability of bidirectional power flow. dc is a DC power supply, and the DC bus capacitor is C dc , the DC side voltage is V dc .

[0040] The power converter part adopts a three-phase bridge topology. The three-phase full-bridge power switch includes a first bridge arm, a second bridge arm and a third bridge arm. The first bridge arm includes a first switch S a and the second switch The second bridge arm includes a third switch S b And the fourth switch The third bridge arm includes a fifth switch S c and the sixth switch Among them, the aforementioned switches are all IGBT switch devices, and the upper and lower switches in each bridge arm operate in a complementary mode.

[0041] The LCL filter includes an inverter-side inductor L1, a grid-side inductor L2, and a filter capacitor C f , the LCL filter is configured to filter out the higher harmonics of the current in the grid-connected converter. Figure 1 i1, v c and i2 represent the inverter side current, filter capacitor voltage and grid side current respectively.

[0042] The grid-connected interface is connected through the grid impedance L g With the grid v g The voltage at the common coupling point on the grid side is v pcc .

[0043] Figure 2 It is the grid-side current loop control block diagram of LCL type grid-connected converter; Figure 3 This is the equivalent circuit diagram of the LCL filter.

[0044] according to Figure 1 Defined current direction, we get Figure 2 The grid-side current loop control block diagram of the LCL grid-connected converter is shown in Figure 1. In this system, the grid-side current reference value The error signal is obtained by subtracting the grid-side current sampling value i2, and the error signal is sent to the proportional resonant controller, and further through the digital control delay link, the inverter output voltage v is obtained. inv By moving the feedback node, the equivalent block diagram of capacitor current active damping feedback can be obtained, as shown in Figure 2 as shown (highlighted by dot-dashed lines).

[0045] In the control strategy provided in the embodiment of the present application, the controller of the grid-side current loop uses a proportional resonant controller in the αβ coordinate system, and the transfer function G of the proportional resonant controller is c (s) is as follows (1):

[0046]

[0047] Among them, k p is the proportional gain, k r is the resonant gain, ω i is the resonant cutoff frequency, ω0 is the grid angular frequency; s is the complex frequency variable in the Laplace transform, which represents the frequency response characteristics of the system.

[0048] In digital control systems, time delay is caused by the analog-to-digital conversion time, algorithm execution process, and the zero-order hold effect of PWM. If at the kth beat, the actual values ​​of the voltage and current are sampled and used to calculate the modulation signal v inv (k). Since a certain amount of analog-to-digital conversion and algorithm execution time is required, vinv (k) cannot be loaded at the kth beat, but only at the k+1th beat to avoid multiple intersections of the modulation wave and the carrier. Therefore, there is a one-beat lag in the modulation signal loading time relative to the current signal sampling time. This one-beat lag is the calculation delay, which exists in both the grid-side current loop and the capacitor current feedback active damping. Introducing the pure delay transfer function in the s domain (T s For the sampling period, this effect is explained. Within a sampling period after loading, under the action of the zero-order hold, the modulated signal remains unchanged and is compared with the triangular carrier to obtain the duty cycle. The time delay caused by the zero-order hold effect of PWM is 0.5 beats. The pure delay transfer function in the s domain is approximately:

[0049] Therefore, the total time delay caused by digital control can be expressed as follows (2):

[0050]

[0051] Due to the time delay, the capacitor current active damping feedback gain k ad Becomes a virtual impedance Z eq , connected in parallel with the filter capacitor, such as Figure 3 As shown. Virtual impedance Z eq The expression of (s) is as follows:

[0052]

[0053] Among them, G d (s) is the digital control delay, is the equivalent virtual resistance without time delay, T s is the sampling period, k ad is the active damping coefficient. Substituting s=j×ω (i.e. the complex frequency part, which is related to the oscillation frequency or natural frequency of the system) into equation (3), the frequency characteristic expression of the virtual impedance can be obtained as shown in equation (4):

[0054]

[0055] Among them, jX eq Represents the imaginary part of virtual impedance.

[0056] Combination Figure 3 As shown in the above formula (4), the introduced jX eq This changes the resonant frequency and impairs the damping performance, since only the real part will damp the resonant energy. In the low frequency range, the equivalent virtual resistance R eq Equal to R ad The resonant frequency exceeds the sampling frequency f sWhen f=f, the virtual impedance will show negative resistance and lose the effective suppression effect on the resonance peak. In the case of underdamping, it may cause system resonance and lead to system instability. s / 6, equivalent virtual resistance R eq As f>f s / 6, the real part of the virtual impedance R eq It presents a negative value and cannot damp the resonance peak, which may cause system resonance and endanger the stability of the system.

[0057] Figure 4 It is a simplified block diagram of LCL type grid-connected converter.

[0058] See also Figure 4 As shown, and Defined as the inverter output voltage v inv The transfer functions from the power supply to the grid side are shown in equations (5) and (6) respectively:

[0059]

[0060] Among them, ω a is the anti-resonance frequency, ω r is the resonant angular frequency of the LCL filter. In the embodiment of the present application, the time delay compensation of the active damping loop is mainly considered.

[0061] The dynamic characteristics of the inverter side current are expressed as follows:

[0062]

[0063] Among them, i1 is the inverter side current, v inv is the inverter side voltage, v c is the filter capacitor voltage.

[0064] The dynamic characteristics of the grid-side current are expressed as follows:

[0065]

[0066] Among them, i2 is the grid side current.

[0067] In summary, a mathematical model of the grid-connected converter in the α-β coordinate system is constructed, wherein the mathematical model of the inverter side is shown in the following equation (9), and the mathematical model of the grid side is shown in the following equation (10):

[0068]

[0069] The subscript “α” represents the component of the parameter on the α-axis in the α-β coordinate system, and the subscript “β” represents the component of the parameter on the β-axis in the α-β coordinate system.

[0070] Figure 5 A structural block diagram of a robust active damping control system for a grid-connected converter provided in an embodiment of the present application.

[0071] Combined with the above description, if Figure 5 As shown, an embodiment of the present application provides a robust active damping control system for a grid-connected converter, comprising: a grid-connected converter 1 and a controller 2 that are communicatively connected to each other. The controller 2 is configured to obtain information at the current moment in the grid-connected converter 1, predict the capacitor current value at the next moment based on the information at the current moment, and compensate for the delay in the control system based on the predicted capacitor current value at the next moment.

[0072] The robust active damping control system of the grid-connected converter provided in the embodiment of the present application is used to implement delay compensation in the system, reduce the problem of virtual impedance presenting negative resistance and causing system resonance, and improve the stability of the system.

[0073] Figure 6 A control strategy block diagram of a robust active damping control method for a grid-connected converter provided in an embodiment of the present application.

[0074] Combination Figure 6 As shown in the figure, the overall control strategy is mainly composed of LCL filter, phase lock loop (PLL), extended state observer (ESO), proportional resonant controller and space vector pulse width modulation (SVPWM) module. Among them, the LCL filter is used to filter the harmonic components in the grid-connected current to ensure the smoothness of the current waveform. The phase-locked loop is used to synchronize the phase and frequency of the grid to obtain the phase angle θ. Based on the prediction module of the extended state observer, the measured value of the input at the current moment (i.e., moment (k)) is predicted by forward Euler discretization, and the predicted value of the next moment (i.e., moment (k+1)) is output. The proportional resonant controller is located in the grid-side current control loop and is used to adjust the grid-side current. The SVPWM module is used to generate a PWM signal to control the switching device of the grid-connected converter.

[0075] Figure 7 A flowchart of a robust active damping control method for a grid-connected converter provided in an embodiment of the present application.

[0076] Figure 8A simplified block diagram of an LCL-type grid-connected converter based on an extended state observer provided in an embodiment of the present application. Specifically, time delay compensation of an LCL-type grid-connected converter is implemented based on an extended state observer.

[0077] Combination Figure 5 The robust active damping control system of the grid-connected converter shown in FIG. Figure 6 The control strategy shown, and Figure 8 The simplified block diagram of the LCL type grid-connected converter shown in FIG. 1 is a simplified block diagram of the LCL type grid-connected converter shown in FIG. 1 . The present application also provides a robust active damping control method for a grid-connected converter. The method is applied to a robust active damping control system of a grid-connected converter. Figure 7 As shown, the method includes steps S1 to S6, which are specifically as follows:

[0078] Step S1, obtaining the current value i of the inverter side in the α-β coordinate system in the grid-connected converter 1,αβ , the current voltage value v of the common coupling point on the grid side pcc,αβ , the current value i of the grid side at the current moment 2,αβ , and the active current component reference value on the grid side in the dq coordinate system and reactive current component reference value and the phase angle θ of the grid.

[0079] Specifically, the active current component reference value on the grid side in the dq coordinate system is and reactive current component reference value It is calculated based on the active power and reactive power requirements of the grid-connected converter and the grid voltage, and is a set reference value.

[0080] Specifically, obtaining the phase angle θ of the power grid includes: using a PLL to phase-lock the power grid to obtain the phase angle θ.

[0081] Optionally, obtain the current value i of the inverter side at the current moment in the α-β coordinate system 1,αβ , the current voltage value v of the common coupling point on the grid side pcc,αβ , the current value i of the grid side at the current moment 2,αβ , including step S11 and step S12, which are specifically as follows:

[0082] Step S11, obtaining the current value i of the inverter side at the current moment in the abc coordinate system 1,abc , the current voltage value v of the common coupling point on the grid side pcc,abc and the current value i of the grid side at the current moment 2,abc .

[0083] Step S12: The current value i of the inverter side at the current moment is 1,abc , the current voltage value v of the common coupling point on the grid sidepcc,abc and the current value i of the grid side at the current moment 2,abc The coordinates are converted into the α-β coordinate system.

[0084] In this embodiment, by converting i 1,abc 、v pcc,abc and i 2,abc The coordinates of i in the α-β coordinate system are obtained. 1,αβ 、v pcc,αβ and i 2,αβ .

[0085] Specifically, the conversion formula from the abc coordinate system to the α-β coordinate system is shown in the following formula (11):

[0086]

[0087] Among them, x∈(i1,i2,v pcc ).

[0088] Step S2: based on the current value i of the inverter side at the current moment 1,αβ , the current voltage value v of the common coupling point on the grid side pcc,αβ , the current value i of the grid side at the current moment 2,αβ , the extended state observer is used to determine the predicted value of the capacitor current at the next moment.

[0089] Optionally, step S2 includes step S21 and step S22, which are specifically as follows:

[0090] Step S21: The current value i of the inverter side at the current moment is 1,αβ , the current voltage value v of the common coupling point on the grid side pcc,αβ and the current value i of the grid side at the current moment 2,αβ The extended state observer is input to determine the inverter side current prediction value and the grid side current prediction value.

[0091] Step S22, calculating the difference between the inverter side current prediction value and the grid side current prediction value, and determining the capacitor current prediction value at the next moment.

[0092] In this embodiment, the prediction of the capacitor current at the next moment is realized by an extended state observer, so as to realize the delay compensation in the system according to the predicted value of the capacitor current at the next moment.

[0093] Optionally, the extended state observer includes an inverter-side extended state observer and a grid-side extended state observer.

[0094] The inverter side extended state observer is shown in the first formula group below:

[0095]

[0096] The first formula group; specifically, the first formula group includes formula (12) to formula (15).

[0097] The grid-side extended state observer is shown in the second formula group below:

[0098]

[0099] The second formula group; specifically, the second formula group includes formula (16) to formula (19).

[0100] Wherein, “(k)” indicates the discretization of parameters, the superscript “eso” indicates the extended state observer, the subscript “1” indicates the inverter side, the subscript “2” indicates the grid side, the subscript “α” indicates the α-axis component in the α-β coordinate system, and the subscript “β” indicates the β-axis component in the α-β coordinate system. is the estimated value of the generalized disturbance, L1 is the inductance on the inverter side, L2 is the inductance on the grid side, and L 1,0 is the nominal value of L1, L 2,0 is the nominal value of L2, β1 is the first parameter of the extended state observer, and β2 is the second parameter of the extended state observer.

[0101] Specifically, let z1 = i1, z2 = f, where f represents the extended state variable including model uncertainty and external disturbance. From the above equation (7), we get z2 = -b × v c +(b-b0)×u, where u=v inv , b=1 / L1,b0=1 / L 1,0 The state space expression is as follows (20):

[0102]

[0103] in, represents a restricted and locally Lipschitz continuous dynamic function of f, the dynamic function The rate of change of will not increase infinitely within a specific interval. In the embodiment of the present application, by reasonably designing the observer gain, the following extended state observer (the following formula (21)) can achieve the error asymptotically convergence to zero:

[0104]

[0105] Among them, β1 and β2 are the parameters of the extended state observer, and β1>0, β2>0. By studying the estimation error, that is, The dynamic characteristic expression can be obtained as follows (22):

[0106]

[0107] Among them, Aeso and B eso are the state matrix and input matrix of the error dynamics, respectively. In equation (22), since A eso is a Hurwitz matrix, so the system is stable. In addition, In the absence of converges to zero. arrive The transfer function is as follows (23):

[0108]

[0109] make Where a1 and a2 are positive constants, and ε<<1, equation (23) can be written as equation (24):

[0110]

[0111] If ε is small enough, then:

[0112]

[0113] From formula (25), we can see that Eventually it decays to zero, and the estimated value converges to the actual value z.

[0114] The parameters of the extended state observer are adjusted by analyzing its characteristic polynomial and eigenvalue. Its characteristic polynomial is shown in equation (26):

[0115] |λI-A eso |=λ 2 +β1λ+β2=0 (26);

[0116] To establish the standard form of the second-order system, the conditions that must be met are shown in equations (27) and (28):

[0117] 2×ξ eso ×ω n,eso =β1 (27);

[0118]

[0119] Among them, ξ eso and ω n,eso They represent the damping coefficient and natural frequency of the extended state observer respectively. eso =1,ω n,eso =ω s / 6=10472rad / s. Among them, ω s =2πf s / 6. Through forward Euler discretization, the prediction of the inverter side current at the next sampling point (k+1) is achieved as shown in the following equation (29):

[0120]

[0121] Similarly, by defining z1=i2, And u=v pcc To predict the grid side current. Among them, the lumped disturbance f includes the filter capacitor voltage v c Therefore, in the extended state observer proposed in the embodiment of the present application, it is not necessary to measure v c . And then through (ie step S22) obtaining the filter capacitor current of the active damping loop (ie the predicted value of the capacitor current at the next moment).

[0122] Specifically, Figure 8 G shown in eso (s) is the distance from z1 to The expression of the transfer function is:

[0123]

[0124] Step S3, based on the predicted value of the capacitor current at the next moment and the active damping coefficient k ad , determine the capacitor current active damping feedback corresponding to the predicted value of the capacitor current at the next moment.

[0125] Optionally, step S3 includes step S31, which is specifically as follows:

[0126] Step S31, calculating the predicted value of the capacitor current at the next moment and the active damping coefficient k ad The product of determines the capacitor current active damping feedback.

[0127] In this embodiment, the capacitor current active damping feedback is determined based on the predicted value of the capacitor current at the next moment, so as to compensate for the time delay by using the capacitor current active damping feedback.

[0128] Step S4, based on the active current component reference value Reactive current component reference value and a proportional resonant controller to determine a control signal P output by the proportional resonant controller.

[0129] Optionally, step S4 includes steps S41 to S43, which are specifically as follows:

[0130] Step S41, based on the active current component reference value Reactive current component reference value and phase angle θ, determine the grid-side current reference value in the α-β coordinate system

[0131] In this step, the dq coordinate system is transformed into the α-β coordinate system by the following equation (31):

[0132]

[0133] in,

[0134] Step S42, calculating the grid-side current reference value The current value i of the grid side at the current moment 2,αβ The difference between the two determines the error signal.

[0135] Step S43, inputting the error signal into the proportional resonant controller, and the proportional resonant controller outputs a control signal.

[0136] In this embodiment, the proportional resonant controller adjusts the control signal according to the amplitude and frequency characteristics of the current error. The control signal is applied to the power converter as a control input to adjust the output current and gradually reduce the error until the system is stable.

[0137] Step S5: based on the control signal P and the voltage value v of the common coupling point at the grid side at the current moment pcc,αβ And the capacitor current active damping feedback determines the pulse width modulation signal M.

[0138] Optionally, step S5 includes step S51 and step S52, which are specifically as follows:

[0139] Step S51, based on the control signal The current voltage value v at the common coupling point on the grid side pcc,αβ and capacitor current active damping feedback Calculate the modulation voltage signal v inv,αβ .

[0140] Optionally, the formula for calculating the modulation voltage signal is:

[0141]

[0142] Among them, G PP (s) is the transfer function of the proportional resonant controller.

[0143] Step S52: Generate a pulse width modulation signal M corresponding to the modulation voltage signal based on the SVPWM algorithm.

[0144] Optionally, step S52 includes steps S521 to S525, which are specifically as follows:

[0145] Step S521, calculate the modulation voltage signal v inv，αβ amplitude and phase.

[0146] Step S522, determining the modulation voltage signal v based on the phase inv，αβ The sector where it is located.

[0147] Step S523, determining a linear combination of two adjacent basic vectors and a zero vector of the sector.

[0148] Step S524: Based on the linear combination, determine the action time of each basic vector and the zero vector to determine the duty cycle of each phase.

[0149] Step S525, compare the duty cycle of each phase with the triangular carrier signal, and output a pulse width modulation signal M.

[0150] In this embodiment, the generated pulse width modulation signal can control the output voltage and frequency of the grid-connected converter and can ensure that harmonics and errors are minimized as much as possible when operating in a specific sector.

[0151] In this embodiment, a pulse width modulation signal corresponding to the modulation voltage signal is generated so as to control the power converter according to the pulse width modulation signal, thereby achieving compensation for the time delay.

[0152] Step S6, based on the pulse width modulation signal M, controlling the power converter.

[0153] The robust active damping control method for the grid-connected converter provided in the embodiment of the present application is adopted. By combining the current parameters with the extended state observer, the predicted value of the capacitor current at the next moment is predicted, so that the delay compensation in the system is realized based on the predicted value of the capacitor current at the next moment, the problem of the virtual impedance presenting negative resistance and causing system resonance is reduced, and the stability of the system is improved.

[0154] Specifically, the embodiments of the present application observe and estimate the unmodeled dynamics and external disturbances of the system as expanded states in real time, and can adaptively adjust the compensation strategy when facing circuit parameter changes and external interference, thereby significantly improving the robustness of the system.

[0155] Corresponding to the embodiment of the robust active damping control method of the aforementioned grid-connected converter, the present application also provides an embodiment of the robust active damping control system of the grid-connected converter. The robust active damping control system of the grid-connected converter includes: a grid-connected converter and a controller that are connected to each other in communication; the grid-connected converter includes a power converter; the controller is configured to obtain the current value i of the inverter side in the α-β coordinate system at the current moment in the grid-connected converter 1,αβ , the current voltage value v of the common coupling point on the grid side Pcc,αβ , the current value i of the grid side at the current moment 2,αβ , and the active current component reference value on the grid side in the dq coordinate system and reactive current component reference value and the phase angle θ of the power grid; based on the current value i of the inverter side at the current moment 1,αβ , the current voltage value v of the common coupling point on the grid side pcc,αβ , the current value i of the grid side at the current moment 2,αβ , the extended state observer is used to determine the predicted value of the capacitor current at the next moment; based on the predicted value of the capacitor current at the next moment and the active damping coefficient k ad , determine the capacitor current active damping feedback corresponding to the predicted value of the capacitor current at the next moment; based on the active current component reference value Reactive current component reference value and a proportional resonant controller, determining a control signal P output by the proportional resonant controller; based on the control signal P and the voltage value v at the common coupling point on the grid side at the current moment pcc,αβ The pulse width modulation signal M is determined by the active damping feedback of the capacitor current; and the power converter is controlled based on the pulse width modulation signal M.

[0156] The robust active damping control method for the grid-connected converter provided in the embodiment of the present application is adopted. By combining the current parameters with the extended state observer, the predicted value of the capacitor current at the next moment is predicted, so that the delay compensation in the system is realized based on the predicted value of the capacitor current at the next moment, the problem of the virtual impedance presenting negative resistance and causing system resonance is reduced, and the stability of the system is improved.

[0157] It should be noted that those skilled in the art will easily think of other embodiments of the present application after considering the specification and practicing the application disclosed herein. The present application is intended to cover any modification, use or adaptation of the present application, which follows the general principles of the present application and includes common knowledge or customary technical means in the art that are not disclosed in the present application. The specification and examples are only regarded as exemplary, and the true scope of the present application is indicated by the claims.

[0158] It should be understood that the present application is not limited to the precise structures that have been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. A robust active damping control method for a grid-connected converter, characterized in that: The robust active damping control method of the grid-connected converter is applied to a robust active damping control system of the grid-connected converter, the robust active damping control system of the grid-connected converter comprises a grid-connected converter, and the grid-connected converter comprises a power converter; The robust active damping control method of the grid-connected converter comprises: Obtain the current value i of the inverter side at the current moment in the α-β coordinate system in the grid-connected converter 1,αβ , the current voltage value v at the common coupling point on the grid side pcc,αβ , the current value i of the grid side at the current moment 2,αβ , and the active current component reference value on the grid side in the dq coordinate system and reactive current component reference value and the phase angle θ of the grid; Based on the current value i of the inverter side at the current moment 1,αβ , the voltage value v at the grid side common coupling point at the current moment pcc,αβ , the current value i of the grid side at the current moment 2,αβ , using the extended state observer to determine the predicted value of the capacitor current at the next moment; Based on the predicted value of the capacitor current at the next moment and the active damping coefficient k ad , determining the capacitor current active damping feedback corresponding to the predicted value of the capacitor current at the next moment; Based on the active current component reference value The reactive current component reference value and a proportional resonant controller, determining a control signal P output by the proportional resonant controller; Based on the control signal P, the voltage value v of the common coupling point on the grid side at the current moment pcc,αβ and the capacitor current active damping feedback to determine the pulse width modulation signal M; Based on the pulse width modulation signal M, the power converter is controlled.

2. The robust active damping control method for a grid-connected converter according to claim 1, characterized in that: Get the current value i of the inverter side at the current moment in the α-β coordinate system 1,αβ , the current voltage value v at the common coupling point on the grid side pcc,αβ , the current value i of the grid side at the current moment 2,αβ ,include: Get the current value i of the inverter side at the current moment in the abc coordinate system 1,abc , the current voltage value v at the common coupling point on the grid side pcc,abc and the current value i of the grid side at the current moment 2,abc ; The current value i of the inverter side at the current moment 1,abc , the voltage value v at the grid side common coupling point at the current moment pcc,abc and the current value i of the grid side at the current moment 2,abc The coordinates are converted into the α-β coordinate system.

3. The robust active damping control method for a grid-connected converter according to claim 1, characterized in that: The current value i of the inverter side at the current moment is based on 1,αβ , the voltage value v at the grid side common coupling point at the current moment pcc,αβ , the current value i of the grid side at the current moment 2,αβ , the extended state observer is used to determine the predicted value of the capacitor current at the next moment, including: The current value i of the inverter side at the current moment 1,αβ , the voltage value v at the grid side common coupling point at the current moment pcc,αβ and the current value i of the grid side at the current moment 2,αβ Input the extended state observer to determine the inverter side current prediction value and the grid side current prediction value; The difference between the inverter-side current prediction value and the grid-side current prediction value is calculated to determine the capacitor current prediction value at the next moment.

4. The robust active damping control method for a grid-connected converter according to claim 1, characterized in that: The extended state observer includes an inverter-side extended state observer and a grid-side extended state observer; The inverter side extended state observer is shown in the following first formula group: First Formula Group; The grid-side extended state observer is shown in the second formula group below: The second formula group; Wherein, "(k)" represents the discretization representation of the parameter, the superscript "eso" represents the extended state observer, the subscript "1" represents the inverter side, the subscript "2" represents the grid side, the subscript "α" represents the α-axis component in the α-β coordinate system, and the subscript "β" represents the β-axis component in the α-β coordinate system. is the estimated value of the generalized disturbance, L1 is the inductance on the inverter side, L2 is the inductance on the grid side, and L 1,0 is the nominal value of L1, L 2,0 is the nominal value of L2, β1 is the first parameter of the extended state observer, and β2 is the second parameter of the extended state observer.

5. The robust active damping control method for a grid-connected converter according to claim 1, characterized in that: The predicted value of the capacitor current at the next moment and the active damping coefficient k ad , determining the capacitor current active damping feedback corresponding to the predicted value of the capacitor current at the next moment, including: Calculate the predicted value of the capacitor current at the next moment and the active damping coefficient k ad The product of determines the capacitor current active damping feedback.

6. The robust active damping control method for a grid-connected converter according to claim 1, characterized in that: The active current component reference value The reactive current component reference value and a proportional resonant controller, determining a control signal P output by the proportional resonant controller, comprising: Based on the active current component reference value The reactive current component reference value and the phase angle θ, determine the grid-side current reference value in the α-β coordinate system Calculate the grid-side current reference value The current value i of the grid side at the current moment 2,αβ The difference between , determines the error signal; The error signal is input into the proportional resonant controller, and the proportional resonant controller outputs the control signal.

7. The robust active damping control method for a grid-connected converter according to claim 1, characterized in that: The control signal P and the voltage value v of the common coupling point at the grid side at the current moment are based on the control signal P and the voltage value v of the common coupling point at the grid side at the current moment. pcc,αβ and the capacitor current active damping feedback to determine the pulse width modulation signal M, including: Based on the control signal The current voltage value v of the common coupling point on the grid side pcc,αβ and the capacitor current active damping feedback Calculate the modulation voltage signal v inv,αβ ; Based on the SVPWM algorithm, a pulse width modulation signal M corresponding to the modulation voltage signal is generated.

8. The robust active damping control method for a grid-connected converter according to claim 7, characterized in that: The formula for calculating the modulation voltage signal is: Among them, G PR (s) is the transfer function of the proportional resonant controller.

9. The robust active damping control method for a grid-connected converter according to claim 7, characterized in that: Based on the SVPWM algorithm, a pulse width modulation signal M corresponding to the modulation voltage signal is generated, including: Calculate the modulation voltage signal v inv，αβ The amplitude and phase of Determine the modulation voltage signal v based on the phase inv，αβ The sector in which it is located; Determine a linear combination of two base vectors and a zero vector adjacent to the sector; Based on the linear combination, determining the action time of each of the basic vectors and the zero vector to determine the duty cycle of each phase; The duty cycle of each phase is compared with the triangular carrier signal, and the pulse width modulation signal M is output.

10. A robust active damping control system for a grid-connected converter, characterized in that: include: Grid-connected converters and controllers that are communicatively connected to each other; The grid-connected converter comprises a power converter; The controller is configured to obtain the current value i of the inverter side at the current moment in the α-β coordinate system in the grid-connected converter. 1,αβ , the current voltage value v at the common coupling point on the grid side pcc,αβ , the current value i of the grid side at the current moment 2,αβ , and the active current component reference value on the grid side in the dq coordinate system and reactive current component reference value and the phase angle θ of the power grid; based on the current value i of the inverter side at the current moment 1,αβ , the voltage value v at the grid side common coupling point at the current moment pcc,αβ , the current value i of the grid side at the current moment 2,αβ , using the extended state observer to determine the predicted value of the capacitor current at the next moment; Based on the predicted value of the capacitor current at the next moment and the active damping coefficient k ad , determining the capacitor current active damping feedback corresponding to the predicted value of the capacitor current at the next moment; Based on the active current component reference value The reactive current component reference value and a proportional resonant controller, determining a control signal P output by the proportional resonant controller; based on the control signal P and the voltage value v at the grid side common coupling point at the current moment pcc,αβ and the capacitor current active damping feedback to determine the pulse width modulation signal M; Based on the pulse width modulation signal M, the power converter is controlled.

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