CN-119965956-B - Method for improving stability of frequency-coupled grid-connected inverter

Abstract

The invention discloses a method for improving stability of a frequency-coupled grid-connected inverter, which is characterized in that q-axis voltage and q-axis current are introduced into q-axis control in a positive feedback mode through a direct-current voltage ring q-axis compensation mode to serve as reference values of the q-axis current after a suppression link. The strategy can skillfully utilize the symbol difference of the frequency domain convolution per se on the positive sequence and the negative sequence, greatly reduce the amplitude of the coupling subsystem while increasing the amplitude of the main diagonal subsystem in the admittance matrix of the grid-connected inverter, ensure that the coupling subsystem has negligible compared with the main diagonal subsystem, essentially inhibit frequency coupling oscillation and improve the stability of the system.

Inventors

• ZHU DIFAN
• YANG LIAN
• HE QIJUN
• LIAN CHENXI
• LIAO JUNHAO
• LI YIBO

Assignees

• 广东工业大学

Dates

Publication Date

20260512

Application Date

20250114

Claims (2)

1. 1. The method for improving the stability of the frequency-coupled grid-connected inverter is characterized by comprising the following steps of: 1) Sampling abc three-phase voltage v abc and three-phase current i abc at a grid-connected point at a public coupling point, and performing park transformation on abc three-phase voltage v abc and three-phase current i abc to obtain d-axis voltage v d , q-axis voltage v q , d-axis current i d and q-axis current i q ; 2) On the Q axis, the Q-axis current i q is multiplied by a filter voltage coefficient X to obtain a filter voltage component suppression power P f for suppressing a coupling component related to a filter voltage, the Q-axis current i q is multiplied by a fundamental frequency voltage coefficient Q to obtain a fundamental frequency voltage component suppression power P V1 for suppressing a coupling component related to a fundamental frequency voltage, the Q-axis voltage v q is multiplied by a fundamental frequency current coefficient Z to obtain a fundamental frequency current component suppression power P I1 for suppressing a coupling component related to a fundamental frequency current, and the filter voltage coefficient X, the fundamental frequency voltage coefficient Q and the fundamental frequency current coefficient Z are expressed as follows: In the formula (1), s is a Laplacian operator, L f is a filter inductance value, and V 1 、I 1 is the amplitude of the fundamental frequency component of the grid-connected voltage and the grid-connected current respectively; Is the initial phase angle of the grid-connected current; 3) The total suppression power P A is subjected to direct current voltage ring PI controller G dc (s) to obtain q-axis control current I tq , and q-axis control current I tq is multiplied by direct current voltage ring coefficient D to obtain q-axis current reference value I qr , wherein the expression is as follows: In the formula (2), the expression of the direct-current voltage ring coefficient D is: In the formula (3), I pv is direct-current side current, C dc is direct-current bus capacitor, and V dc0 is direct-current voltage given value; 4) The q-axis current reference value I qr and the q-axis current I q are subjected to a comparison link to obtain a q-axis component difference value delta I q , then the q-axis component difference value delta I q is subjected to a current loop q-axis PI controller H qi (s) to obtain a q-axis control voltage V tq , and the q-axis control voltage V tq and a d-axis current coupling term K d i d are added to obtain a q-axis modulation signal m q , wherein K d is a decoupling coefficient; 5) On the d-axis, a direct-current voltage V dc and a direct-current voltage given value V dc0 are subjected to a comparison link to obtain a direct-current voltage difference value DeltaV dc , a direct-current voltage difference value DeltaV dc is subjected to a direct-current voltage ring PI controller G dc (s) to obtain a d-axis current reference value I dr , the d-axis current reference value I dr and a d-axis current I d are subjected to a comparison link to obtain a d-axis component difference value DeltaI d , then the d-axis component difference value DeltaI d is subjected to a current ring d-axis PI controller H di (s) to obtain a d-axis control voltage V td , and then the d-axis control voltage V td is subtracted by a q-axis current coupling term K d i q to obtain a d-axis modulation signal m d ; 6) And performing inverse park transformation on the d-axis modulation signal m d and the q-axis modulation signal m q to obtain an a-phase modulation signal m a , a b-phase modulation signal m b and a c-phase modulation signal m c under a static coordinate system.
2. 2. The method for improving the stability of the frequency-coupled grid-connected inverter according to claim 1, which is characterized by establishing a multi-harmonic linearization model of the grid-connected inverter and comprising the following steps: 1) Only considering the DC voltage disturbance quantity and the disturbance quantity derived by the control link, and establishing the positive sequence and negative sequence harmonic disturbance quantity of the grid-connected inverter port output voltage V iap 、V ian relative to the grid-connected voltage Positive sequence and negative sequence harmonic disturbance quantity of grid-connected current Is represented by the expression: In the formula (4), the [ Y v ] 2×2 ] is a voltage coefficient matrix before grid-connected voltage positive and negative sequence harmonic disturbance quantity, the [ Y i ] 2×2 ] is a current coefficient matrix before grid-connected current positive and negative sequence harmonic disturbance quantity, and the two are matrices related to a direct-current voltage ring in a grid-connected inverter model; In the voltage coefficient matrix [ Y v ] 2×2 , Y vpp is reflective Expression affecting V iap , Y vpn is a reflection Expression affecting V iap , Y vnp is a reflection Expression affecting V ian , Y vnn is a reflection The expression affecting V ian is specifically expressed as follows: In the formula (5), k m is a modulation factor; For modulating the fundamental frequency component of the signal, Is that Conjugate value of (2); for the fundamental frequency component of the grid-tie current, Is that J is an imaginary number, K(s) is a controller element, and the expression is: K(s)=k m V dc0 H di (s)G dc (s) (6) in the current coefficient matrix [ Y i ] 2×2 , Y ipp is reflective Expression affecting V iap , Y ipn is a reflection Expression affecting V iap , Y inp is a reflection Expression affecting V ian , Y inn is a reflection The specific expression affecting V ian is: in the formula (7), the amino acid sequence of the compound, Is the fundamental frequency component of the grid-connected voltage; 2) According to the formula (4), a grid-connected inverter multi-harmonic linearization model after the frequency coupling grid-connected inverter stability improving method is applied is established by combining the phase-locked loop disturbance quantity correlation matrix, the current loop disturbance quantity correlation matrix and the main circuit relation.

Description

Method for improving stability of frequency-coupled grid-connected inverter Technical Field The invention relates to the field of grid-connected stability of novel power systems, in particular to a method for improving the stability of a frequency-coupled grid-connected inverter. Background In the new power system construction process, renewable energy duty ratio is continuously rising. Grid-connected inverters are increasingly favored as key ties for accessing distributed power sources such as photovoltaic, wind power, energy storage systems and the like into a power grid. However, due to the interaction between the grid-tied inverter and the grid, the system will oscillate in a wide frequency range of a few hertz to kilohertz, severely threatening the stability of the system. Among them, the problem of frequency-coupled oscillation occurring near the sidebands of the fundamental frequency has been attracting attention in recent years. Due to the influence of the frequency coupling effect, a coupling subsystem in an output admittance model of the grid-connected inverter cannot be ignored, so that system mechanism analysis and stability analysis are complicated. If the frequency coupling effect is ignored, the actual stable state of the power system cannot be accurately judged, misjudgment risks exist, the frequency coupling effect also causes subsynchronous oscillation, the stability of the system is threatened, the generator is disconnected when serious, and the frequency coupling oscillation is inhibited. However, in view of the frequency coupling problem, most of the existing methods are proposed for phase-locked loops, and most of the existing methods are proposed from the aspects of system damping and stability, and the frequency coupling effect is only reflected in the modeling process. Therefore, there is a lack of a suppression method proposed for dc voltage rings, which is based on the nature of suppressing frequency coupling. Disclosure of Invention In order to solve the technical problems, the invention provides a method for improving the stability of a frequency-coupled grid-connected inverter. In order to achieve the above purpose, the invention is implemented according to the following technical scheme: The method for improving the stability of the frequency-coupled grid-connected inverter comprises the following steps of: 1) Sampling abc three-phase voltage v abc and three-phase current i abc at a grid-connected point at a public coupling point, and performing park transformation on abc three-phase voltage v abc and three-phase current i abc to obtain d-axis voltage v d, q-axis voltage v q, d-axis current i d and q-axis current i q; 2) On the Q axis, the Q-axis current i q is multiplied by a filter voltage coefficient X to obtain a filter voltage component suppression power P f for suppressing a coupling component related to a filter voltage, the Q-axis current i q is multiplied by a fundamental frequency voltage coefficient Q to obtain a fundamental frequency voltage component suppression power P V1 for suppressing a coupling component related to a fundamental frequency voltage, the Q-axis voltage v q is multiplied by a fundamental frequency current coefficient Z to obtain a fundamental frequency current component suppression power P I1 for suppressing a coupling component related to a fundamental frequency current, and the filter voltage coefficient X, the fundamental frequency voltage coefficient Q and the fundamental frequency current coefficient Z are expressed as follows: In the formula (1), s is a Laplacian operator, L f is a filter inductance value, V 1、I1 is the amplitude of the fundamental frequency component of the grid-connected voltage and the grid-connected current respectively, and phi i1 is the initial phase angle of the grid-connected current; 3) The total suppression power P A is subjected to direct current voltage ring PI controller G dc(s) to obtain q-axis control current I tq, and q-axis control current I tq is multiplied by direct current voltage ring coefficient D to obtain q-axis current reference value I qr, wherein the expression is as follows: In the formula (2), the expression of the direct-current voltage ring coefficient D is: In the formula (3), I pv is direct-current side current, C dc is direct-current bus capacitor, and V dc0 is direct-current voltage given value; 4) The q-axis current reference value I qr and the q-axis current I q are subjected to a comparison link to obtain a q-axis component difference value delta I q, then the q-axis component difference value delta I q is subjected to a current loop q-axis PI controller H qi(s) to obtain a q-axis control voltage V tq, and the q-axis control voltage V tq and a d-axis current coupling term K did are added to obtain a q-axis modulation signal m q, wherein K d is a decoupling coefficient; 5) On the d-axis, a direct-current voltage V dc and a direct-current voltage given value V dc0 are subjected to a compa