CN-114567008-B - Method and system for controlling stable output of inverter

CN114567008BCN 114567008 BCN114567008 BCN 114567008BCN-114567008-B

Abstract

The invention discloses a method and a system for controlling stable output of an inverter, which are used for acquiring power grid voltage, inputting the power grid voltage into a pre-constructed inverter main circuit control model comprising improved feedforward decoupling and PI links, and outputting stable voltage; the construction of the inverter main circuit control model comprising the improved feedforward decoupling and PI links comprises the steps of obtaining a main circuit topology of an LC-type inverter to be processed, analyzing the main circuit topology to determine a mathematical model under a two-phase rotation dq coordinate system of the main circuit topology, performing current inner loop decoupling on the mathematical model by adopting an improved feedforward decoupling mode to obtain a voltage ring considering a dynamic link of the current ring, setting PI parameters of the current inner loop and the voltage outer loop according to the voltage ring considering the dynamic link of the current ring, and obtaining the inverter main circuit control model of the improved feedforward decoupling and PI links according to the PI parameters of the current inner loop and the voltage outer loop. The method has the advantages that the fluctuation of the output voltage of the inverter under large disturbance can be effectively restrained, and the dynamic response speed of the system is improved.

Inventors

SHI JIANQIANG
ZHAO NINGNING
LI SHUANG
Niu Qiushi
XU MENGXI
TIAN FENGMIN

Assignees

南京工程学院
南京工程学院

Dates

Publication Date: 20260421
Application Date: 20220303
Priority Date: 20220303

Claims (5)

1. A method of controlling a stable output of an inverter, comprising: acquiring power grid voltage, inputting the power grid voltage into a pre-constructed inverter main circuit control model comprising improved feedforward decoupling and PI links, and outputting stable voltage; the construction of the inverter main circuit control model comprising the improved feedforward decoupling and PI links comprises the following steps: Acquiring a main circuit topology of an LC-type inverter to be processed, and analyzing the main circuit topology to determine a mathematical model of the main circuit topology under a two-phase rotation dq coordinate system; performing current inner loop decoupling on the mathematical model by adopting an improved feedforward decoupling mode to obtain a voltage loop considering a dynamic link of the current loop; Setting PI parameters of a current inner ring and a voltage outer ring according to a voltage ring considering a dynamic link of the current ring, and obtaining an inverter main circuit control model of the improved feedforward decoupling and PI link according to the PI parameters of the current inner ring and the voltage outer ring; The method for performing current inner loop decoupling on the mathematical model by adopting an improved feedforward decoupling mode to obtain a voltage loop considering a dynamic link of the current loop comprises the following steps: the closed loop transfer function of the current loop is equivalent to a first-order inertia link, namely: (6); in the formula (6), the amino acid sequence of the compound, For the first-order inertia link, τ i is the time constant of the current loop, τ i = , Is the proportionality coefficient of the inner loop of the current, For the integral coefficient of the inner loop of the current, voltage control decoupling is realized by adopting the idea of feedforward decoupling control, and the following steps: (7); In the formula (7), the amino acid sequence of the compound, Is the reference current for the d-axis, For q-axis reference current, i od 、i oq 、u od 、u oq is the inverter output current, d-axis and q-axis components of the inverter output voltage, ω is angular frequency, C is filter capacitance, i ud 、i uq is the output of the voltage loop PI controller, namely: (8); In the formula (8), k up and k ui are respectively a proportional coefficient and an integral coefficient of the voltage ring PI controller, and u odref 、u oqref is d and q axis reference voltages; After the Laplace transformation is carried out on the formula (7), the formula (6) is substituted into the formula to obtain a voltage ring considering the dynamic link of the current ring, as shown in the formula (10), (10)。
2. The method of controlling the stable output of an inverter according to claim 1, wherein the obtaining the main circuit topology of the LC-type inverter to be processed, analyzing the main circuit topology to determine a mathematical model of the main circuit topology in a two-phase rotation dq coordinate system, comprises: The LC-type inverter main circuit adopts a three-phase full-bridge topology, the midpoints of three bridge arms of the inverter are connected with an LC filter, and the output voltage is the terminal voltage of a filter capacitor; Selecting filter capacitor voltage, namely output voltage and filter inductance current, as control objects, meeting the condition that parameters of a three-phase system are consistent, neglecting parasitic resistance of a filter capacitor, and obtaining a circuit equation according to kirchhoff voltage and current law: (1); In the formula (1), L is a filter inductor, R is a parasitic resistance of the filter inductor L, i a 、i b 、i c is a three-phase current of the filter inductor, i oa 、i ob 、i oc is an inverter output current, u a 、u b 、u c is an inverter bridge arm midpoint voltage, u oa 、u ob 、u oc is an inverter output voltage, and t is time; The mathematical model in which the expression (1) is transformed from a three-phase static abc coordinate system to a two-phase rotating dq coordinate system by using constant amplitude Park transformation can be obtained (2); (3); In the formulas (2) and (3), i d ,i q 、i od ,i oq ,u d ,u q 、u od 、u oq is the filter inductance current, the inverter output current, the inverter bridge arm midpoint voltage, and the d-axis and q-axis components of the inverter output voltage, respectively, and are angular frequencies.
3. The method for controlling stable output of an inverter according to claim 2, wherein the setting PI parameters of the current inner loop and the voltage outer loop according to the voltage loop considering the dynamic link of the current loop, and obtaining the improved feedforward decoupling and PI link inverter main circuit control model according to the PI parameters of the current inner loop and the voltage outer loop, comprises: The open loop transfer function of the current inner loop is: (11); In the formula, As an open loop transfer function of the inner loop of the current, Is the proportionality coefficient of the inner loop of the current, The integral coefficient of the inner loop of the current; ; expression τ i : (13); Wherein f s is the switching frequency of the inverter; the open loop transfer function of the voltage loop obtained from equation (6) is: (14); In the formula (14), the amino acid sequence of the compound, As an open loop transfer function of the voltage loop, Is the ratio coefficient of the voltage loop, Is an integration time constant; the closed loop transfer function of the voltage ring from equation (14) is: ; In the formula, As a closed loop transfer function of the voltage ring, Is a constant value, and is used for the treatment of the skin, Is an integration time constant; (15); (16); In the formula (16), k is a symmetry coefficient, and is obtained by the formulas (15) (16): (17); Substituting the formula (17) into the formula (14) to obtain a simplified voltage loop open-loop transfer function as follows: (18); The open loop shear frequency ω x of the voltage ring satisfies: (19); In the formula, As an open loop transfer function of the voltage loop, An impedance angle of 90 degrees in the complex frequency domain; The formula (19) is obtained after simplification: (20); the phase angle margin gamma of the voltage ring is: (21); Obtained from the formulas (18), (20) and (21): (22); In the formula, Is a phase angle margin; Phase angle margin 30-60 Degrees should be taken to obtain: (23); the cut-off frequency ω b of the voltage ring is: (24); (25); let h=τ i ω b , and after reduction by substituting h into equation (25), h and k satisfy the following relationship: (26); the inner ring bandwidth is at least 2 times of the outer ring bandwidth, and then: (27); as can be seen from equation (27), to satisfy bandwidth constraints, there are: (28); and (3) combining the formula (23) again to obtain the k value range meeting the bandwidth and phase angle margin constraint, wherein the k value range is as follows: (29); The second-order filtering link and the differential link are connected in series to obtain an expression of a transfer function G l(s) of the differential link: (30); In the formula (30), the transfer function G l(s) of the differential link is equivalent to a band-pass filter, omega 0 is the cut-off frequency of the band-pass filter, and omega 0 is 3-5 times of the outer ring bandwidth omega b ; And determining the inverter main circuit control model comprising the improved feedforward decoupling and PI links according to the open-loop transfer function of the current inner loop, the open-loop transfer function of the voltage loop and the transfer function of the differential link.
4. A method of controlling a stable output of an inverter according to claim 3, wherein the control process of the inverter main circuit control model including improved feedforward decoupling and PI links comprises: u od 、u oq 、i od 、i oq is calculated according to the input power grid voltage and a mathematical model under a two-phase rotation dq coordinate system of the main circuit topology; Calculating according to u od 、u oq 、i od 、i oq and the obtained d and q-axis reference voltages of the mathematical model under the two-phase rotation dq coordinate system of the main circuit topology to obtain the d-axis reference current and the q-axis reference current of the mathematical model under the two-phase rotation dq coordinate system of the main circuit topology; D-axis and q-axis components of the filter inductance current are obtained through calculation of a current inner loop transfer function G oi (s) and a voltage outer loop transfer function G ou (s); And suppressing the noise of d-axis and q-axis components of the filter inductance current through a differential link transfer function G l (s), obtaining components under the stabilized dq coordinates, and then converting to obtain the output stabilized voltage.
5. A system for controlling a stable output of an inverter, comprising: The acquisition module is used for acquiring the power grid voltage; The processing module is used for inputting the power grid voltage into a pre-constructed inverter main circuit control model comprising improved feedforward decoupling and PI links and outputting stable voltage; the construction of the inverter main circuit control model comprising the improved feedforward decoupling and PI links comprises the following steps: Acquiring a main circuit topology of an LC-type inverter to be processed, and analyzing the main circuit topology to determine a mathematical model of the main circuit topology under a two-phase rotation dq coordinate system; performing current inner loop decoupling on the mathematical model by adopting an improved feedforward decoupling mode to obtain a voltage loop considering a dynamic link of the current loop; Setting PI parameters of a current inner ring and a voltage outer ring according to a voltage ring considering a dynamic link of the current ring, and obtaining an inverter main circuit control model of the improved feedforward decoupling and PI link according to the PI parameters of the current inner ring and the voltage outer ring; The method for performing current inner loop decoupling on the mathematical model by adopting an improved feedforward decoupling mode to obtain a voltage loop considering a dynamic link of the current loop comprises the following steps: the closed loop transfer function of the current loop is equivalent to a first-order inertia link, namely: (6); in the formula (6), the amino acid sequence of the compound, For the first-order inertia link, τ i is the time constant of the current loop, τ i = , Is the proportionality coefficient of the inner loop of the current, For the integral coefficient of the inner loop of the current, voltage control decoupling is realized by adopting the idea of feedforward decoupling control, and the following steps: (7); In the formula (7), the amino acid sequence of the compound, Is the reference current for the d-axis, For q-axis reference current, i od 、i oq 、u od 、u oq is the inverter output current, d-axis and q-axis components of the inverter output voltage, ω is angular frequency, C is filter capacitance, i ud 、i uq is the output of the voltage loop PI controller, namely: (8); In the formula (8), k up and k ui are respectively a proportional coefficient and an integral coefficient of the voltage ring PI controller, and u odref 、u oqref is d and q axis reference voltages; After the Laplace transformation is carried out on the formula (7), the formula (6) is substituted into the formula to obtain a voltage ring considering the dynamic link of the current ring, as shown in the formula (10), (10)。

Description

Method and system for controlling stable output of inverter Technical Field The invention relates to a method and a system for controlling stable output of an inverter, and belongs to the technical field of inverter parameter control. Background The renewable energy sources such as wind power, photovoltaic power generation and the like are used for replacing the thermal power mainly comprising coal, and the method is an important way for achieving the aims of carbon peak and carbon neutralization in the energy field of China. The three-phase LC type inverter generally adopts a current inner loop voltage outer loop double closed loop PI control mode to improve the control precision and dynamic response capability of a VSI system, wherein the control method can be divided into an inductance current inner loop and a capacitance current inner loop control according to different controlled amounts of the current inner loop. The voltage tracking effect of the inductive current inner loop and the voltage tracking effect of the capacitive current inner loop control mode are the same, but when the capacitive current is used as the inner loop control quantity, disturbance information of load current is not contained in the current inner loop, so that the load disturbance resistance of the capacitive current inner loop is superior to that of the inductive current inner loop, when the inductive current inner loop is adopted, the inductive current is the current flowing through a switching tube, the current limiting protection of the switching tube can be realized by limiting the inductive current, so that the current protection capacity of the inductive current inner loop is stronger than that of the capacitive current inner loop, and meanwhile, if load current feedforward is added into a control system, the load disturbance resistance of the inductive current inner loop can be improved. Therefore, the current inner loop is equivalent to a first-order inertia link in a pole-zero cancellation mode, PI parameter setting of the voltage outer loop is simplified to be symmetrical coefficient k setting by utilizing a symmetrical optimization method, a value range of k is given based on phase angle margin and controller bandwidth constraint, and fluctuation of VSI output voltage in large disturbance is restrained. Disclosure of Invention The invention aims to overcome the defects of the prior art and provide a method and a system for controlling stable output of an inverter. In order to solve the above technical problems, the present invention provides a method for controlling stable output of an inverter, including: acquiring power grid voltage, inputting the power grid voltage into a pre-constructed inverter main circuit control model comprising improved feedforward decoupling and PI links, and outputting stable voltage; the construction of the inverter main circuit control model comprising the improved feedforward decoupling and PI links comprises the following steps: Acquiring a main circuit topology of an LC-type inverter to be processed, and analyzing the main circuit topology to determine a mathematical model of the main circuit topology under a two-phase rotation dq coordinate system; performing current inner loop decoupling on the mathematical model by adopting an improved feedforward decoupling mode to obtain a voltage loop considering a dynamic link of the current loop; And setting PI parameters of the current inner ring and the voltage outer ring according to a voltage ring considering a dynamic link of the current ring, and obtaining the improved feedforward decoupling and PI-link inverter main circuit control model according to the PI parameters of the current inner ring and the voltage outer ring. Further, the obtaining the main circuit topology of the LC-type inverter to be processed, analyzing the main circuit topology to determine a mathematical model of the main circuit topology under a two-phase rotation dq coordinate system, includes: The LC-type inverter main circuit adopts a three-phase full-bridge topology, the midpoints of three bridge arms of the inverter are connected with an LC filter, and the output voltage is the terminal voltage of a filter capacitor; Selecting filter capacitor voltage, namely output voltage and filter inductance current, as control objects, meeting the condition that parameters of a three-phase system are consistent, neglecting parasitic resistance of a filter capacitor, and obtaining a circuit equation according to kirchhoff voltage and current law: In the formula (1), L is a filter inductor, R is a parasitic resistance of the filter inductor L, C is a filter capacitor, i a、ib、ic is a three-phase current of the filter inductor, i oa、iob、ioc is an inverter output current, u a、ub、uc is an inverter bridge arm midpoint voltage, u oa、uob、uoc is an inverter output voltage, and t is time; The mathematical model in which the expression (1) is transformed from a three-phase static abc