Control method, system and equipment of three-phase grid-connected inverter and storage medium

Abstract

The embodiment of the invention discloses a control method, system and equipment of a three-phase grid-connected inverter and a storage medium. The control method comprises the following steps: performing modulation and decoupling through a first dq-axis current, a dq-axis voltage, a second dq-axis current and a preset grid-connected current reference value to obtain a reference value of an inverter side output voltage; performing dq-abc coordinate conversion and PWM (Pulse Width Modulation) on the reference value of the output voltage at the inverter side to obtain a driving signal of the inverter; the driving signal is used for controlling the inverter. The modulated and decoupled reference value of the inverter side output voltage removes the influence of the dq-axis current coupling of the first filter capacitor, and also removes the influence of the dq-axis voltage coupling of the filter capacitor and the second dq-axis current coupling of the second filter inductor, and a driving signal is obtained according to the reference value of the inverter side output voltage. And the inverter is controlled by using the driving signal, so that the inverter realizes accurate control on the grid-connected current.

Description

[Technical Field]

[0001] This invention relates to the field of inverter control technology, and in particular to control methods, systems, devices and storage media for three-phase grid-connected inverters. [Background Technology]

[0002] Traditional LCL inverter control only models the inverter-side inductor, and its control target is the inverter-side inductor current. Essentially, it simplifies the LCL filter to an L-type filter and equates the inverter-side inductor current to the grid current. However, it ignores the influence of the filter capacitor and the grid-side inductor, making it impossible for the inverter to achieve precise control of the grid current. [Summary of the Invention]

[0003] In view of this, the present invention provides a control method, system, device and storage medium for a three-phase grid-connected inverter, so as to realize precise control of the grid-connected current by the inverter.

[0004] The specific technical solution of the first embodiment of the present invention is as follows: a control method for a three-phase grid-connected inverter, applied to a grid-connected control system, wherein the grid-connected control system includes at least an inverter, a first filter inductor, a filter capacitor, and a second filter inductor; the output terminal of the inverter is connected to one end of the first filter inductor, the other end of the first filter inductor is connected to one end of the filter capacitor and one end of the second filter inductor, the other end of the filter capacitor is grounded, and the other end of the second filter inductor is connected to the power grid; the method includes: obtaining the first three-phase current of the first filter inductor, the first three-phase voltage of the filter capacitor, the second three-phase current of the second filter inductor, and the second three-phase voltage of the power grid; constructing a coordinate transformation model based on the second three-phase voltage and preset coefficients; performing abc-dq coordinate transformation on the first three-phase current, the first three-phase voltage, and the second three-phase current respectively according to the coordinate transformation model to obtain the first dq axis current of the first three-phase current, the first three-phase voltage, and the second three-phase current, the first dq axis current of the first three-phase current, and the second three-phase voltage of the power grid; constructing a coordinate transformation model based on the second three-phase voltage and preset coefficients; and performing abc-dq coordinate transformation on the first three-phase current, the first three-phase voltage, and the second three-phase current respectively according to the coordinate transformation model to obtain the first dq axis current of the first three-phase current, the first three-phase voltage, and the second three-phase current. The first dq-axis voltage of the first three-phase voltage and the second dq-axis current of the second three-phase current are used to obtain a first error signal by subtracting the second dq-axis current from a preset grid-connected current reference value. A preset first PI regulator is used to modulate and decouple the first error signal to obtain a voltage reference value for the filter capacitor. The second error signal is obtained by subtracting the voltage reference value of the filter capacitor from the dq-axis voltage. A preset second PI regulator is used to modulate and decouple the second error signal to obtain a current reference value for the first filter inductor. A third error signal is obtained by subtracting the current reference value of the first filter inductor from the first dq-axis current. A preset third PI regulator is used to modulate and decouple the third error signal to obtain a reference value for the inverter-side output voltage. The reference value for the inverter-side output voltage is then subjected to dq-abc coordinate transformation and PWM modulation to obtain a drive signal for the inverter. The drive signal is used to control the inverter.

[0005] Preferably, the step of constructing the coordinate transformation model based on the second and third phase voltages and preset coefficients includes: obtaining the phase of the power grid using a preset phase-locked loop and the second and third phase potentials; and constructing the coordinate transformation model using the phase of the power grid and preset coefficients.

[0006] Preferably, the step of modulating and decoupling the first error signal to obtain the voltage reference value of the filter capacitor includes: modulating the first error signal using a preset first PI regulator to obtain the voltage reference value of the second filter inductor; and decoupling the voltage reference value of the second filter inductor to obtain the voltage reference value of the filter capacitor.

[0007] Preferably, the voltage reference value of the filter capacitor is obtained using the following formula:

[0008]

[0009] Among them, v dref The reference value for the d-axis voltage of the filter capacitor is v. qref The q-axis voltage reference value of the filter capacitor is defined by the d-axis voltage reference value and the q-axis voltage reference value of the filter capacitor. d2ref The d-axis current, i, is the preset grid-connected current reference value. q2ref The q-axis current is the preset grid-connected current reference value, i d2 Let i be the d-axis current of the second dq-axis current. q2 Let k be the q-axis current of the second dq-axis current. pd3 and k id3 k is the preset d-axis control parameter in the preset first PI controller. pq3 and k iq3 Here, s represents the preset q-axis control parameter in the first PI controller, and e represents the sign after the Laplace transform. d Let e ​​be the d-axis voltage of the power grid. q L1 is the q-axis voltage of the power grid, ω is the angular frequency of the power grid, and L2 is the inductance value of the second filter inductor.

[0010] Preferably, the current reference value of the first filter inductor is obtained using the following formula:

[0011]

[0012] Among them, i d1ref i is the reference value for the d-axis current of the first filter inductor. q1ref The q-axis current reference value of the first filter inductor is given by v. The d-axis current reference value and the q-axis current reference value of the first filter inductor together constitute the current reference value of the first filter inductor. dref The reference value for the d-axis voltage of the filter capacitor is v. qref The reference value for the q-axis voltage of the filter capacitor is v. d The d-axis voltage of the first dq-axis voltage of the filter capacitor, v q k is the q-axis voltage of the first dq-axis voltage of the filter capacitor. pd2 and k id2 k is the preset d-axis control parameter in the preset second PI regulator. pq2 and k iq2 i is the preset q-axis parameter in the preset second PI regulator. d2 Let i be the d-axis current of the second dq-axis current. q2ω is the q-axis current of the second dq-axis current, C is the capacitance value of the filter capacitor, s is the sign after the Laplace transform, and ω is the angular frequency of the power grid.

[0013] Preferably, the reference value of the inverter-side output voltage is obtained using the following formula:

[0014]

[0015] Among them, u dref u is the d-axis reference value for the inverter-side output voltage. qref The q-axis reference value of the inverter-side output voltage, together with the d-axis reference value and the q-axis reference value, constitutes the reference value of the inverter-side output voltage. d1ref i is the reference value for the d-axis current of the first filter inductor. q1ref i is the reference value for the q-axis current of the first filter inductor. d1 Let i be the d-axis current of the first dq-axis current. q1 Let k be the q-axis current of the first dq-axis current. pd3 and k id3 k is the preset d-axis control parameter in the preset third PI regulator. pq3 k iq3 The preset q-axis control parameters in the preset third PI regulator, where s is the sign after Laplace transform, ω is the angular frequency of the power grid, and v d The d-axis voltage of the first dq-axis voltage of the filter capacitor, v q L1 is the q-axis voltage of the first dq-axis voltage of the filter capacitor, and L1 is the inductance value of the first filter inductor.

[0016] Preferably, the step of performing dq-abc coordinate transformation and PWM modulation on the reference value of the inverter-side output voltage to obtain the inverter drive signal involves: performing dq-abc coordinate transformation on the reference value of the inverter-side output voltage to obtain the three-phase output voltage of the inverter; and performing PWM modulation on the three-phase output voltage of the inverter to obtain the inverter drive signal.

[0017] The specific technical solution of the second embodiment of the present invention is as follows: a control system for a three-phase grid-connected inverter, the system including at least an inverter, a first filter inductor, a filter capacitor, and a second filter inductor; the output terminal of the inverter is connected to one end of the first filter inductor, the other end of the first filter inductor is connected to one end of the filter capacitor and one end of the second filter inductor, the other end of the filter capacitor is grounded, and the other end of the second filter inductor is connected to the power grid; the system further includes: a data acquisition module, a coordinate transformation model construction module, a first coordinate transformation module, a second filter inductor current control module, a filter capacitor voltage control module, a first filter inductor current control module, and a second coordinate transformation module; the data acquisition module is used to acquire the first three-phase current of the first filter inductor, the first three-phase voltage of the filter capacitor, the second three-phase current of the second filter inductor, and the second three-phase voltage of the power grid; the coordinate transformation model construction module is used to construct a coordinate transformation model based on the second three-phase voltage and preset coefficients; the first coordinate transformation module is used to perform abc-dq coordinate transformation on the first three-phase current, the first three-phase voltage, and the second three-phase current according to the coordinate transformation model to obtain the coordinate transformation model. The first three-phase current has a first dq-axis current, the first three-phase voltage has a first dq-axis voltage, and the second three-phase current has a second dq-axis current; the second filter inductor current control module is used to obtain a first error signal by subtracting the second dq-axis current from a preset grid-connected current reference value, and to obtain a voltage reference value of the filter capacitor by modulating and decoupling the first error signal using a preset first PI regulator; the filter capacitor voltage control module is used to obtain a second error signal by subtracting the voltage reference value of the filter capacitor from the first dq-axis voltage, and to obtain a current reference value of the first filter inductor by modulating and decoupling the second error signal using a preset second PI regulator; the first filter inductor current control module is used to obtain a third error signal by subtracting the current reference value of the first filter inductor from the first dq-axis current, and to obtain a reference value of the inverter-side output voltage by modulating and decoupling the third error signal using a preset third PI regulator; the second coordinate transformation module is used to perform dq-abc coordinate transformation and PWM modulation on the reference value of the inverter-side output voltage to obtain a drive signal for the inverter; the drive signal is used to control the inverter.

[0018] The specific technical solution of the third embodiment of the present invention is as follows: a control device for a three-phase grid-connected inverter, comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor performs the steps of the method as described in any one of the first embodiments of this application.

[0019] The specific technical solution of the fourth embodiment of the present invention is as follows: a computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, the processor performs the steps of the method as described in any one of the first embodiments of this application.

[0020] Implementing the embodiments of the present invention will have the following beneficial effects:

[0021] This invention obtains the first three-phase current of the first filter inductor, the first three-phase voltage of the filter capacitor, the second three-phase current of the second filter inductor, and the second three-phase voltage of the power grid; constructs a coordinate transformation model based on the second three-phase voltage and preset coefficients; performs abc-dq coordinate transformation on the first three-phase current, the first three-phase voltage, and the second three-phase current according to the coordinate transformation model to obtain the first dq-axis current, the first dq-axis voltage, and the second dq-axis current; obtains a reference value for the inverter-side output voltage by modulating and decoupling the first dq-axis current, the first dq-axis voltage, the second dq-axis current, and a preset grid-connected current reference value; and obtains the inverter-side drive signal by performing dq-abc coordinate transformation and PWM modulation on the reference value of the inverter-side output voltage; the drive signal is used to control the inverter.

[0022] In this invention, the reference value of the inverter-side output voltage after modulation and decoupling removes the influence of the dq-axis current coupling of the first filter capacitor, as well as the influence of the first dq-axis voltage coupling of the filter capacitor and the second dq-axis current coupling of the second filter inductor. Based on the drive signal obtained from the reference value of the inverter-side output voltage, the inverter is controlled by the drive signal, enabling the inverter to achieve precise control of the grid-connected current. [Attached Image Description]

[0023] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of an LCL-type grid-connected inverter and its control system.

[0025] Figure 2 A flowchart illustrating the steps of the control method for a three-phase grid-connected inverter;

[0026] Figure 3 A flowchart outlining the steps involved in constructing a coordinate transformation model;

[0027] Figure 4 A flowchart outlining the steps to obtain the voltage reference value for the filter capacitor.

[0028] Figure 5 Flowchart of steps to obtain the inverter's drive signal;

[0029] Figure 6 This is a schematic diagram of the control system of a three-phase grid-connected inverter.

[0030] Figure 7 A schematic diagram of the control model of a three-phase grid-connected inverter in the dq coordinate system;

[0031] Figure 8 This is a control structure framework diagram of this application;

[0032] Figure 9a This is a control-side framework diagram in this application;

[0033] Figure 9b This is a system-side framework diagram in this application;

[0034] Figure 10 The simulation results are shown in the simulation diagrams used in this application.

[0035] Figure 11 The waveform diagram shows the deformation caused by a sudden change in DC side voltage.

[0036] Figure 12 The grid-connected current waveform is shown under the condition of a sudden change in DC side voltage.

[0037] Figure 13 Waveforms of different parameters when the grid-connected current amplitude is 10A;

[0038] Among them, 601 is the data acquisition module; 602 is the coordinate transformation model construction module; 603 is the first coordinate transformation module; 604 is the second filter inductor current control module; 605 is the filter capacitor voltage control module; 606 is the first filter inductor current control module; and 607 is the second coordinate transformation module.

Detailed Implementation Methods

[0039] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0040] Please see Figure 1A grid-connected control system refers to a system that regulates and manages the power grid in a distributed energy system. A grid-connected control system includes at least an inverter, a first filter inductor L1, a filter capacitor C, and a second filter inductor L2. The output terminal of the inverter is connected to one end of the first filter inductor L1, the other end of the first filter inductor L1 is connected to one end of the filter capacitor C and one end of the second filter inductor L2, the other end of the filter capacitor C is grounded, and the other end of the second filter inductor L2 is connected to the power grid PCC.

[0041] Please see Figure 2 This is a flowchart illustrating the steps of a control method for a three-phase grid-connected inverter according to the first embodiment of this application. Applied to a grid-connected control system, it enables the inverter to achieve precise control of the grid-connected current. The method includes:

[0042] Step 101: Obtain the first three-phase current of the first filter inductor, the first three-phase voltage of the filter capacitor, the second three-phase current of the second filter inductor, and the second three-phase voltage of the power grid;

[0043] Specifically, the a-phase, b-phase, and c-phase currents of the first inductor L1 are detected respectively to obtain the first three-phase current i. a1 i b1 and i c1 The voltages of phases a, b, and c of the filter capacitor C are measured respectively to obtain the first three-phase voltage v. a v b and v c The a-phase, b-phase, and c-phase currents of the second inductor L2 are measured respectively to obtain the second three-phase currents ia2, ib2, and ic2; the a-phase, b-phase, and c-phase voltages of the power grid are measured respectively to obtain the second three-phase voltage e. a e b and e c ;

[0044] Step 102: Construct a coordinate transformation model based on the second and third phase voltages and preset coefficients;

[0045] Specifically, based on the second and third phase voltages e a e b and e c And construct the coordinate transformation model T using preset coefficients. abc-dq ;

[0046] Step 103: Perform abc-dq coordinate transformation on the first three-phase current, the first three-phase voltage, and the second three-phase current according to the coordinate transformation model to obtain the first dq axis current of the first three-phase current, the first dq axis voltage of the first three-phase voltage, and the second dq axis current of the second three-phase current.

[0047] Specifically, using coordinate transformation model T abc-dqFor the first three-phase current i a1 i b1 i c1 The first three-phase voltage V a v b v c Second and third current i a2 i b2 i c2 Perform abc-dq coordinate transformations to obtain the first dq-axis current i of the first three-phase current. d1 i q1 The first dq axis voltage v of the first three-phase voltage d v q and the second dq axis current i of the second and third phase currents d2 i q2 ;

[0048] Step 104: Obtain a first error signal by subtracting the preset grid-connected current reference value from the second dq-axis current, and use a preset first PI regulator G1 to modulate and decouple the first error signal to obtain the voltage reference value of the filter capacitor.

[0049] Specifically, based on the preset grid-connected current reference value of the dq axis and the second dq axis current i d2 i q2 The first error signal is obtained by subtraction, and the first error signal is modulated and decoupled using a preset first PI regulator to obtain the voltage reference value v of the filter capacitor on the dq axis. dref v qref ;

[0050] Step 105: Obtain a second error signal by subtracting the voltage reference value of the first dq axis voltage from the voltage reference value of the filter capacitor, and use a preset second PI regulator G2 to modulate and decouple the second error signal to obtain the current reference value of the first filter inductor;

[0051] Specifically, based on the first dq axis voltage v d v q The voltage reference value v along the dq axis of the filter capacitor dref v qref The second error signal is obtained by subtracting the first error signal. The first error signal is then modulated and decoupled using a preset second PI regulator to obtain the current reference value i of the dq axis of the first filter inductor. d1ref i q1ref ;

[0052] Step 106: Obtain a third error signal by subtracting the reference value of the first dq axis current from the current reference value of the first filter inductor, and use a preset third PI regulator G3 to modulate and decouple the third error signal to obtain a reference value of the inverter side output voltage.

[0053] Specifically, based on the first dq axis current i d1 i q1 The reference value of the current i along the dq axis of the first filter inductor d1ref i q1ref The third error signal is obtained by subtraction. The third error signal is then modulated and decoupled using a preset third PI regulator to obtain the reference value u of the dq axis of the inverter-side output voltage. abcref ;

[0054] Step 107: Perform dq-abc coordinate transformation and PWM modulation on the reference value of the inverter output voltage to obtain the inverter drive signal; the drive signal is used to control the inverter.

[0055] Specifically, the reference value u of the dq axis of the inverter-side output voltage is... abcref Using coordinate transformation model T abc-dq The inverter's drive signal is obtained by performing inverse coordinate transformation and PWM modulation.

[0056] In this embodiment, the reference value of the inverter-side output voltage after modulation and decoupling removes the influence of the dq-axis current coupling of the first filter capacitor, as well as the influence of the first dq-axis voltage coupling of the filter capacitor and the second dq-axis current coupling of the second filter inductor. Based on the drive signal obtained from the reference value of the inverter-side output voltage, the inverter is controlled by the drive signal, enabling the inverter to achieve precise control of the grid-connected current.

[0057] For specific implementation details, please refer to [link / reference]. Figure 3 Step 102 involves constructing a coordinate transformation model based on the second and third phase voltages and preset coefficients, including:

[0058] Step 201: Obtain the phase of the power grid using a preset phase-locked loop and the second and third phase potentials;

[0059] Step 202: Construct the coordinate transformation model using the phase of the power grid and preset coefficients.

[0060] Specifically, through the preset phase-locked loop (PLL) and the second and third phase potentials e a e a and e c The angular frequency ω of the power grid is obtained, and the coordinate transformation model is constructed using the angular frequency ω and preset coefficients. The coordinate transformation model is obtained using the following formula:

[0061]

[0062] Among them, T abc-dq This is a coordinate transformation model, where ω is the angular frequency of the power grid and t is time. The phase of the power grid can accurately reflect the vector phase angle of voltage and current. By using the phase of the power grid to construct a coordinate transformation model, the three-phase voltage or current can be accurately converted into voltage or current on the dq axis.

[0063] In a specific embodiment, the first three-phase current is obtained by performing an abc-dq coordinate transformation based on the coordinate transformation model to obtain the first dq-axis current of the first three-phase current, including:

[0064] The state equation of the first filter inductor is established based on the first three-phase current. The state equation of the first filter inductor is:

[0065]

[0066] Among them, u a u b u c Let r1 be the internal resistance of the first filter inductor, L1 be the inductance of the first filter inductor, and i be the voltages of phases a, b, and c at the inverter output. a1 i b1 i c1 Let v be the a, b, and c phase currents of the first three-phase current. a v b v c These are the a, b, and c phase voltages of the first three-phase voltage;

[0067] Using coordinate transformation model T abc-dq By performing coordinate transformation on the state equation of the first filter inductor, the first dq-axis current of the first three-phase current is obtained, and the specific formula is as follows:

[0068]

[0069] Among them, u d u q These are the voltages at the output of the d-axis and q-axis inverters, respectively, i d1 i q1 The first dq-axis currents, v and v', are respectively the d-axis and q-axis currents. d v q R1 represents the voltage across the d-axis and q-axis of the filter capacitor, respectively; R1 represents the internal resistance of the first filter inductor; L1 represents the inductance of the first filter inductor; and ω represents the angular frequency of the power grid.

[0070] In a specific embodiment, performing an abc-dq coordinate transformation on the first three-phase voltage according to the coordinate transformation model to obtain the first dq-axis voltage of the first three-phase voltage includes:

[0071] Based on the first three-phase voltage, the state equation of the filter capacitor is established as follows:

[0072]

[0073] Among them, v a v b v c These are the capacitor voltages of phases a, b, and c of the first three-phase voltage, respectively, where C is the capacitance value of the filter capacitor, and i a1 i b1 i c1 These are the a, b, and c phase currents of the first filter inductor, respectively, i a2 i b2 i c2 These are the a-phase, b-phase, and c-phase currents of the second filter inductor, respectively.

[0074] Using coordinate transformation model T abc-dq By performing coordinate transformation on the state equation of the filter capacitor, the first dq-axis voltage of the first three-phase voltage is obtained, and the specific formula is as follows:

[0075]

[0076] Among them, v d v q These are the d-axis voltage and q-axis voltage of the first dq-axis voltage of the first three-phase voltage, respectively. a v b v c These are the capacitor voltages of phases a, b, and c of the first three-phase voltage, respectively, i a1 i b1 i c1 These are the a, b, and c phase currents of the first filter inductor, i. a2 i b2 i c2 These are the a, b, and c phase currents of the second filter inductor, respectively.

[0077] In a specific embodiment, the second three-phase current is obtained by performing an abc-dq coordinate transformation based on the coordinate transformation model to obtain the second dq-axis current of the second three-phase current, including:

[0078] The state equation of the second filter inductor is established based on the second and third phase currents. The state equation of the second filter inductor is as follows:

[0079]

[0080] Among them, v a v b v cLet r1 be the phase voltage of the filter capacitor (a, b, c), r2 be the internal resistance of the second filter inductor, and L2 be the inductance of the second filter inductor. a2 i b2 i c2 These are the a, b, and c phase currents of the second and third phases, respectively, e a e b e c These are the voltages of phases a, b, and c of the power grid, respectively.

[0081] Using coordinate transformation model T abc-dq By performing coordinate transformation on the state equation of the second filter inductor, the second dq-axis current of the second three-phase current is obtained, and the specific formula is as follows:

[0082]

[0083] Among them, v d v q These are the d-axis and q-axis voltages of the filter capacitor, respectively, i d2 i q2 These are the d-axis and q-axis currents of the second dq-axis current, respectively, e d e q ω represents the d-axis and q-axis voltages of the power grid, respectively, and ω is the angular frequency of the power grid.

[0084] Based on the formulas for obtaining the first dq current, dq voltage, and second dq current, it can be seen that due to the presence of inductors and capacitors, the dq-axis quantities will influence and couple with each other during the abc-dq transformation. The d and q-axis currents, besides being affected by u... d u q In addition to the influence, it is also affected by the coupling amount ωL1i q1 ,ωCv q , -ωCv d ,ωL2i q2 , -ωL2i d2 Due to the influence of current, if the d-axis and q-axis are not decoupled for control, the current command tracking performance of the d-axis and q-axis will be unsatisfactory when using current closed-loop control of the grid. Therefore, based on the grid-connected inverter in the dq coordinate system, a first PI regulator, a second PI regulator, and a third PI regulator are designed for decoupling. Specifically, the grid-connected inverter is of type LCL.

[0085] In a specific embodiment, please refer to Figure 4 Step 104, which modulates and decouples the first error signal to obtain the voltage reference value of the filter capacitor, includes:

[0086] Step 301: Modulate the first error signal using a preset first PI regulator to obtain the voltage reference value of the second filter inductor;

[0087] Step 302: Decouple the voltage reference value of the second filter inductor to obtain the voltage reference value of the filter capacitor.

[0088] Specifically, the first PI regulator modulates the first error signal to obtain the target voltage reference value of the second filter inductor, i.e., the voltage reference value of the second filter inductor. The voltage reference value of the second filter inductor is decoupled to remove the coupling amount in the voltage reference value of the second filter inductor, so as to obtain the voltage reference value of the filter capacitor, thereby improving the current command tracking effect in the power grid.

[0089] In a specific embodiment, the voltage reference value of the filter capacitor is obtained using the following formula:

[0090]

[0091] Among them, v dref The reference value for the d-axis voltage of the filter capacitor is v. qref The q-axis voltage reference value of the filter capacitor is defined by the d-axis voltage reference value and the q-axis voltage reference value of the filter capacitor. d2ref The d-axis current, i, is the preset grid-connected current reference value. q2ref The q-axis current is the preset grid-connected current reference value, i d2 Let i be the d-axis current of the second dq-axis current. q2 Let k be the q-axis current of the second dq-axis current. pd3 and k id3 k is the preset d-axis control parameter in the preset first PI controller. pq3 and k iq3 Here, s represents the preset q-axis control parameter in the first PI controller, and e represents the sign after the Laplace transform. d Let e ​​be the d-axis voltage of the power grid. q Let ω be the q-axis voltage of the power grid, ω be the angular frequency of the power grid, L2 be the inductance value of the second filter inductor, and i be the q-axis voltage of the power grid. q2 This is the q-axis current of the second dq-axis current. By modulating the first error signal using the preset d-axis and q-axis control parameters in the first PI regulator, and by decoupling the inductance value of the second filter inductor from the angular frequency of the power grid, a precise voltage reference value for the filter capacitor is obtained.

[0092] In a specific embodiment, the current reference value of the first filter inductor is obtained by modulating and decoupling the second error signal using a preset second PI regulator, including: modulating the second error signal using a preset second PI regulator to obtain the current reference value of the filter capacitor, and decoupling the current reference value of the filter capacitor to obtain the current reference value of the first filter inductor.

[0093] In a specific embodiment, the current reference value of the first filter inductor is obtained using the following formula:

[0094]

[0095] Among them, i d1ref i is the reference value for the d-axis current of the first filter inductor. q1ref The q-axis current reference value of the first filter inductor is given by v. The d-axis current reference value and the q-axis current reference value of the first filter inductor together constitute the current reference value of the first filter inductor. dref The reference value for the d-axis voltage of the filter capacitor is v. qref The reference value for the q-axis voltage of the filter capacitor is v. d v is the d-axis voltage of the first dq-axis voltage. q k is the q-axis voltage of the first dq-axis voltage. pd2 and k id2 k is the preset d-axis control parameter in the preset second PI regulator. pq2 and k iq2 i is the preset q-axis parameter in the preset second PI regulator. d2 Let i be the d-axis current of the second dq-axis current. q2 Here, q is the q-axis current of the second dq-axis current, C is the capacitance value of the filter capacitor, s is the sign after Laplace transform, and ω is the angular frequency of the power grid. By modulating the second error signal using the preset d-axis and q-axis control parameters in the second PI regulator, and by decoupling the filter capacitor value and the angular frequency of the power grid, a precise current reference value for the first filter inductor is obtained.

[0096] In a specific embodiment, the reference value of the dq axis of the inverter-side output voltage is obtained by modulating and decoupling the third error signal using a preset third PI regulator, including: modulating the third error signal using a preset third PI regulator to obtain a voltage reference value of the first filter inductor, and decoupling the voltage reference value of the first filter inductor to obtain a reference value of the dq axis of the inverter-side output voltage.

[0097] Specifically, the reference value of the inverter-side output voltage is obtained using the following formula:

[0098]

[0099] Among them, u dref u is the d-axis reference value for the inverter-side output voltage. qref The q-axis reference value of the inverter-side output voltage is given by the d-axis reference value and the q-axis reference value of the inverter-side output voltage, which together constitute the reference value u of the inverter-side output voltage. abcref i d1ref i is the reference value for the d-axis current of the first filter inductor. q1ref i is the reference value for the q-axis current of the first filter inductor. d1 Let i be the d-axis current of the first dq-axis current. q1 Let k be the q-axis current of the first dq-axis current. pd3 and k id3 k is the preset d-axis control parameter in the preset third PI regulator. pq3 k iq3 The preset q-axis control parameters in the preset third PI regulator, where s is the sign after Laplace transform, ω is the angular frequency of the power grid, and v d v is the d-axis voltage of the first dq-axis voltage. q L1 is the q-axis voltage of the first dq-axis voltage, and L1 is the inductance value of the first filter inductor. By modulating the third error signal using the preset d-axis and q-axis control parameters in the third PI regulator, and by decoupling the inductance value of the first filter inductor from the angular frequency of the power grid, a precise reference value for the inverter-side output voltage is obtained.

[0100] In a specific embodiment, please refer to Figure 5 In step 107, the reference value of the inverter-side output voltage is subjected to dq-abc coordinate transformation and PWM modulation to obtain the inverter's drive signal:

[0101] Step 401: Perform dq-abc coordinate transformation on the reference value of the inverter-side output voltage to obtain the three-phase output voltage of the inverter;

[0102] Step 402: PWM modulate the three-phase output voltage of the inverter to obtain the drive signal of the inverter.

[0103] Specifically, the reference value of the inverter output voltage is transformed into dq-abc coordinates to obtain the three-phase output voltage u of the inverter. a u b u c And the three-phase output voltage u of the inverter a u b u cPWM modulation is performed to obtain the inverter's drive signal, so that the drive signal controls the inverter.

[0104] In a specific embodiment, please refer to Figure 6 This is a control system for a three-phase grid-connected inverter according to a second embodiment of the present application. The system includes at least an inverter, a first filter inductor, a filter capacitor, and a second filter inductor. The output terminal of the inverter is connected to one end of the first filter inductor, the other end of the first filter inductor is connected to one end of the filter capacitor and one end of the second filter inductor, the other end of the filter capacitor is grounded, and the other end of the second filter inductor is connected to the power grid.

[0105] The system further includes: a data acquisition module 601, a coordinate transformation model construction module 602, a first coordinate transformation module 603, a second filter inductor current control module 604, a filter capacitor voltage control module 605, a first filter inductor current control module 606, and a second coordinate transformation module 607; the data acquisition module 601 is used to acquire the first three-phase current of the first filter inductor, the first three-phase voltage of the filter capacitor, the second three-phase current of the second filter inductor, and the second three-phase voltage of the power grid; the coordinate transformation model construction module 602 is used to construct a coordinate transformation model based on the second three-phase voltage and preset coefficients; the first coordinate transformation module 603 is used to perform abc-dq coordinate transformation on the first three-phase current, the first three-phase voltage, and the second three-phase current according to the coordinate transformation model to obtain the first dq axis current of the first three-phase current, the first dq axis voltage of the first three-phase voltage, and the second dq axis current of the second three-phase current; the second filter inductor current control module 604 is used to acquire the first three-phase current of the first filter inductor, the first three-phase voltage of the first filter capacitor, and the second three-phase current of the second filter capacitor ... A first error signal is obtained by subtracting the second dq-axis current from a preset grid-connected current reference value. A preset first PI regulator is used to modulate and decouple the first error signal to obtain a voltage reference value for the filter capacitor. The filter capacitor voltage control module 605 is used to obtain a second error signal by subtracting the voltage reference value for the first dq-axis voltage from the voltage reference value for the filter capacitor. A preset second PI regulator is used to modulate and decouple the second error signal to obtain a current reference value for the first filter inductor. The first filter inductor current control module 606 is used to obtain a third error signal by subtracting the current reference value for the first dq-axis current from the current reference value for the first filter inductor. A preset third PI regulator is used to modulate and decouple the third error signal to obtain a reference value for the inverter-side output voltage. The second coordinate transformation module 607 is used to perform dq-abc coordinate transformation and PWM modulation on the reference value for the inverter-side output voltage to obtain a drive signal for the inverter. The drive signal is used to control the inverter.

[0106] In a specific embodiment, please refer to the model of the control system of the three-phase grid-connected inverter in the dq coordinate system. Figure 7 For the control framework diagram of the three-phase grid-connected inverter control system, please refer to [link / reference]. Figure 8 Please refer to the control flow diagram of the three-phase grid-connected inverter control system. Figure 9a and Figure 9b By using the control system in this embodiment, a reference value of the inverter-side output voltage after modulation and decoupling is obtained. This not only removes the coupling effect of the dq-axis current of the first filter capacitor, but also removes the effects of the first dq-axis voltage coupling of the filter capacitor and the second dq-axis current coupling of the second filter inductor. Based on the drive signal obtained from the reference value of the inverter-side output voltage, the inverter is controlled by the drive signal, enabling the inverter to achieve precise control of the grid-connected current.

[0107] In a specific embodiment, the inverter operates at unit power, with the current (grid-connected current amplitude) of the second filter inductor set to 1.67kA, and a model is built in MATLAB / Simulink software for simulation. The parameters used in the simulation are shown in Table 1.

[0108]

[0109]

[0110] Table 1 Parameters of LCL-type Grid-connected Inverter

[0111] Simulation results are as follows Figure 10 As shown, the control system (hereinafter referred to as the system) of the three-phase grid-connected inverter has a smooth output, I a2 I b2 I c2 These represent the currents of the second filter inductors for phases a, b, and c, respectively, i.e., the grid-connected currents. The system reaches steady state within 0.01s with no overshoot. The grid-connected current amplitude is 1670A, and its phase is consistent with the grid phase. Steady state is reached within 0.02s.

[0112] Specifically, taking phase a as an example, the I of the second dq current (hereinafter referred to as the grid-connected current) a2 The fundamental amplitude is 1671A, and the THD is 0.03%. The grid-connected current has a small error compared to the reference value, the total harmonic distortion is small, and the phase is consistent with the grid phase.

[0113] To verify the system's anti-interference performance, a DC-side voltage fluctuation was simulated. At 0.06 seconds, the DC-side voltage decreased from 1500V to 1400V. The waveform of the sudden DC-side voltage change is shown below. Figure 11 As shown. The grid-connected current waveform under the condition of a sudden change in DC side voltage is as follows. Figure 12As shown, there is no significant change; the phase and amplitude are consistent with those before the fluctuation, demonstrating good tracking performance of the target value and strong anti-interference capability of the controller.

[0114] When the inverter output power is low, the grid-connected current is small. At this time, the difference between the inverter-side inductor current and the grid-connected current is large. Traditional control methods treat the inverter-side inductor current as equivalent to the grid-connected current, resulting in a large error and failing to guarantee accurate control of the grid-connected current. The method designed in this paper can maintain accurate control precision even under conditions of small grid-connected current.

[0115] Using a grid-connected current amplitude of 10A as the target value, the following is obtained: Figure 13 The output waveforms shown, from top to bottom, are the grid-connected voltage, inverter-side inductor current, and grid-connected current.

[0116] The system reached steady state within 0.01s with no overshoot. The grid-connected current amplitude was 10A, and its phase was consistent with the grid phase.

[0117] Taking phase a as an example, the fundamental amplitude of the inverter-side output current Ia1 is 14.85A, which differs from the actual grid-connected current by 48%. The THD is 3.69%, and the phase deviates from the grid phase. These results indicate that the traditional control method using the inverter-side inductor current as the control target will have significant errors. Because the filter capacitor and grid-side inductance are not considered, the amplitude, phase, and total harmonic distortion all differ significantly from the reference values. (Grid-connected current Ia1) a2 The fundamental amplitude is 9.922A, and the THD is 1.41%. The grid-connected current has a small error compared to the reference value, the total harmonic distortion is small, and the phase of the grid-connected current is consistent with the phase of the power grid. Even with a small grid-connected current, it still maintains precise control over the grid-connected current.

[0118] In a specific embodiment, the third embodiment of this application provides a control device for a three-phase grid-connected inverter, including a memory and a processor. The memory stores a computer program, and when the computer program is executed by the processor, the processor performs the steps of the method as described in any one of the first embodiments of this application.

[0119] In a specific embodiment, the fourth embodiment of this application provides a computer-readable storage medium storing a computer program, which, when executed by a processor, causes the processor to perform the steps of the method as described in any one of the first embodiments of this application.

[0120] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments described above. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), RAMbus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and RAMbus dynamic RAM (RDRAM), etc.

[0121] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above 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.

[0122] The above embodiments merely illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A control method for a three-phase grid-connected inverter, applied to a grid-connected control system, wherein the grid-connected control system includes at least an inverter, a first filter inductor, a filter capacitor, and a second filter inductor; the output terminal of the inverter is connected to one end of the first filter inductor, the other end of the first filter inductor is connected to one end of the filter capacitor and one end of the second filter inductor, the other end of the filter capacitor is grounded, and the other end of the second filter inductor is connected to the power grid, characterized in that... The method includes: The first three-phase current of the first filter inductor, the first three-phase voltage of the filter capacitor, the second three-phase current of the second filter inductor, and the second three-phase voltage of the power grid are obtained. A coordinate transformation model is constructed based on the second and third phase voltages and preset coefficients; Based on the coordinate transformation model, the first three-phase current, the first three-phase voltage, and the second three-phase current are respectively subjected to abc-dq coordinate transformation to obtain the first dq axis current of the first three-phase current, the first dq axis voltage of the first three-phase voltage, and the second dq axis current of the second three-phase current. The first error signal is obtained by subtracting the preset grid-connected current reference value from the second dq axis current. The first error signal is then modulated and decoupled using a preset first PI regulator to obtain the voltage reference value of the filter capacitor. The second error signal is obtained by subtracting the voltage reference value of the filter capacitor from the voltage of the first dq axis. The second error signal is then modulated and decoupled using a preset second PI regulator to obtain the current reference value of the first filter inductor. The third error signal is obtained by subtracting the current reference value of the first filter inductor from the first dq axis current. The third error signal is then modulated and decoupled using a preset third PI regulator to obtain the reference value of the inverter-side output voltage. The reference value of the inverter output voltage is transformed into dq-abc coordinates and modulated with PWM to obtain the drive signal of the inverter; the drive signal is used to control the inverter.

2. The control method for a three-phase grid-connected inverter as described in claim 1, characterized in that, The step of constructing a coordinate transformation model based on the second and third phase voltages and preset coefficients includes: The phase of the power grid is obtained using a preset phase-locked loop and the second and third phase potentials; The coordinate transformation model is constructed using the phase of the power grid and preset coefficients.

3. The control method for a three-phase grid-connected inverter as described in claim 1, characterized in that, The step of modulating and decoupling the first error signal to obtain the voltage reference value of the filter capacitor includes: The voltage reference value of the second filter inductor is obtained by modulating the first error signal using a preset first PI regulator. The voltage reference value of the filter capacitor is obtained by decoupling the voltage reference value of the second filter inductor.

4. The control method for a three-phase grid-connected inverter as described in claim 1, characterized in that, The voltage reference value of the filter capacitor is obtained using the following formula: Among them, v dref The reference value for the d-axis voltage of the filter capacitor is v. qref The q-axis voltage reference value of the filter capacitor is defined by the d-axis voltage reference value and the q-axis voltage reference value of the filter capacitor. d2ref The d-axis current, i, is the preset grid-connected current reference value. q2ref The q-axis current is the preset grid-connected current reference value, i d2 Let i be the d-axis current of the second dq-axis current. q2 Let k be the q-axis current of the second dq-axis current. pd3 and k id3 k is the preset d-axis control parameter in the preset first PI controller. pq3 and k iq3 Here, s represents the preset q-axis control parameter in the first PI controller, and e represents the sign after the Laplace transform. d Let e ​​be the d-axis voltage of the power grid. q L1 is the q-axis voltage of the power grid, ω is the angular frequency of the power grid, and L2 is the inductance value of the second filter inductor.

5. The control method for a three-phase grid-connected inverter as described in claim 4, characterized in that, The reference value of the current of the first filter inductor is obtained using the following formula: Among them, i d1ref i is the reference value for the d-axis current of the first filter inductor. q1ref The q-axis current reference value of the first filter inductor is given by v. The d-axis current reference value and the q-axis current reference value of the first filter inductor together constitute the current reference value of the first filter inductor. dref The reference value for the d-axis voltage of the filter capacitor is v. qref The reference value for the q-axis voltage of the filter capacitor is v. d The d-axis voltage of the first dq-axis voltage of the filter capacitor, v q k is the q-axis voltage of the first dq-axis voltage of the filter capacitor. pd2 and k id2 k is the preset d-axis control parameter in the preset second PI regulator. pq2 and k iq2 i is the preset q-axis parameter in the preset second PI regulator. d2 Let i be the d-axis current of the second dq-axis current. q2 ω is the q-axis current of the second dq-axis current, C is the capacitance value of the filter capacitor, s is the sign after the Laplace transform, and ω is the angular frequency of the power grid.

6. The control method for a three-phase grid-connected inverter as described in claim 5, characterized in that, The reference value of the inverter-side output voltage is obtained using the following formula: Among them, u dref u is the d-axis reference value for the inverter-side output voltage. qref The q-axis reference value of the inverter-side output voltage, together with the d-axis reference value and the q-axis reference value, constitutes the reference value of the inverter-side output voltage. d1ref i is the reference value for the d-axis current of the first filter inductor. q1ref i is the reference value for the q-axis current of the first filter inductor. d1 Let i be the d-axis current of the first dq-axis current. q1 Let k be the q-axis current of the first dq-axis current. pd3 and k id3 k is the preset d-axis control parameter in the preset third PI regulator. pq3 k iq3 The preset q-axis control parameters in the preset third PI regulator, where s is the sign after Laplace transform, ω is the angular frequency of the power grid, and v d The d-axis voltage of the first dq-axis voltage of the filter capacitor, v q L1 is the q-axis voltage of the first dq-axis voltage of the filter capacitor, and L1 is the inductance value of the first filter inductor.

7. The control method for a three-phase grid-connected inverter as described in claim 1, characterized in that, The inverter drive signal is obtained by performing dq-abc coordinate transformation and PWM modulation on the reference value of the inverter output voltage: The three-phase output voltage of the inverter is obtained by performing a dq-abc coordinate transformation on the reference value of the inverter side output voltage; The drive signal for the inverter is obtained by PWM modulation of the three-phase output voltage of the inverter.

8. A control system for a three-phase grid-connected inverter, the system comprising at least an inverter, a first filter inductor, a filter capacitor, and a second filter inductor; the output terminal of the inverter is connected to one end of the first filter inductor, the other end of the first filter inductor is connected to one end of the filter capacitor and one end of the second filter inductor, the other end of the filter capacitor is grounded, and the other end of the second filter inductor is connected to the power grid, characterized in that, The system further includes: a data acquisition module, a coordinate transformation model construction module, a first coordinate transformation module, a second filter inductor current control module, a filter capacitor voltage control module, a first filter inductor current control module, and a second coordinate transformation module; The data acquisition module is used to acquire the first three-phase current of the first filter inductor, the first three-phase voltage of the filter capacitor, the second three-phase current of the second filter inductor, and the second three-phase voltage of the power grid. The coordinate transformation model construction module is used to construct a coordinate transformation model based on the second and third phase voltages and preset coefficients; The first coordinate transformation module is used to perform abc-dq coordinate transformation on the first three-phase current, the first three-phase voltage and the second three-phase current respectively according to the coordinate transformation model, so as to obtain the first dq axis current of the first three-phase current, the first dq axis voltage of the first three-phase voltage and the second dq axis current of the second three-phase current; The second filter inductor current control module is used to obtain a first error signal by subtracting the second dq axis current from the preset grid-connected current reference value, and to obtain the voltage reference value of the filter capacitor by modulating and decoupling the first error signal using a preset first PI regulator. The filter capacitor voltage control module is used to obtain a second error signal by subtracting the voltage reference value of the filter capacitor from the first dq axis voltage, and to obtain the current reference value of the first filter inductor by modulating and decoupling the second error signal using a preset second PI regulator. The first filter inductor current control module is used to obtain a third error signal by subtracting the current reference value of the first filter inductor from the first dq axis current, and to use a preset third PI regulator to modulate and decouple the third error signal to obtain a reference value of the inverter side output voltage. The second coordinate transformation module is used to perform dq-abc coordinate transformation and PWM modulation on the reference value of the inverter output voltage to obtain the drive signal of the inverter; the drive signal is used to control the inverter.

9. A control device for a three-phase grid-connected inverter, comprising a memory and a processor, characterized in that, The memory stores a computer program that, when executed by the processor, causes the processor to perform the steps of the method as described in any one of claims 1 to 7.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it causes the processor to perform the steps of the method as described in any one of claims 1 to 7.

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