CN-121813826-B - Energy-saving photovoltaic inverter control system and control method

CN121813826BCN 121813826 BCN121813826 BCN 121813826BCN-121813826-B

Abstract

The invention discloses an energy-saving photovoltaic inverter control system and a control method, in particular relates to the technical field of power electronic conversion control, and aims to solve the problem that the existing periodic MPPT disturbance is easy to generate interference coupling with external fluctuation under the fluctuation illumination condition, so that dynamic tracking energy is lost; the method comprises the steps of monitoring output power of a photovoltaic array and voltage ripple of a direct current bus, analyzing cooperative variation characteristics of the output power of the photovoltaic array and the voltage ripple of the direct current bus to identify interference phenomena, extracting external fluctuation main frequency, tracking phase relation between the external fluctuation main frequency and control disturbance, further evaluating interference coupling risk level, dynamically adjusting disturbance period according to the interference coupling risk level, enabling a control beat to actively avoid the external fluctuation main frequency, accurately identifying and effectively inhibiting harmful interference between control and external environment fluctuation, and accordingly improving energy capturing efficiency of a photovoltaic system under a fluctuation illumination condition.

Inventors

WANG JUN
DAI YUXING
ZHENG ZIJIE
Ke Zipeng

Assignees

湖南大学

Dates

Publication Date: 20260508
Application Date: 20260310

Claims (8)

1. An energy-saving photovoltaic inverter control method is characterized by comprising the following steps: S1, monitoring and obtaining output power of a photovoltaic array and direct current bus voltage of a photovoltaic inverter to form an output power fluctuation sequence and a direct current bus voltage ripple sequence; s2, carrying out correlation analysis on the output power fluctuation sequence and the direct current bus voltage ripple sequence, and judging whether a cooperative variation characteristic representing periodic disturbance input exists or not; S3, when the cooperative variation characteristics exist, analyzing the frequency distribution of the output power fluctuation sequence and extracting the dominant wave frequency, wherein the method comprises the following steps: determining a time period corresponding to the cooperative variation characteristic in the output power fluctuation sequence; Performing frequency spectrum estimation on the output power fluctuation sequence in the time period to obtain power spectrum density; identifying local peaks in the power spectrum density, and determining the frequency and amplitude corresponding to each local peak; determining the frequency corresponding to the highest peak with the amplitude exceeding the preset amplitude threshold as the main wave frequency; s4, analyzing a real-time phase difference between a fluctuation period corresponding to the main wave frequency and a disturbance period of the maximum power point tracking control, and tracking a change track of the real-time phase difference in a continuous disturbance period; S5, evaluating the risk level of interference coupling between the main fluctuation frequency and the disturbance period according to the energy aggregation characteristics of the output power fluctuation sequence in the frequency sideband range of the disturbance period and combining the change track, wherein the method comprises the following steps: the disturbance frequency of the maximum power point tracking control is taken as a central frequency, the main wave frequency is taken as a sideband offset, and a frequency sideband range is determined; calculating the ratio of a power spectrum integral value of the output power fluctuation sequence in a frequency sideband range to a total power spectrum integral value in the whole effective analysis frequency band to obtain a sideband energy amplification coefficient representing the energy aggregation characteristic; Analyzing the change track, and judging whether the real-time phase difference presents a quasi-steady state characteristic of limited fluctuation around a certain fixed value; If the real-time phase difference presents a quasi-steady state characteristic, judging that the system enters a stable phase-locked state, and evaluating the risk level of interference coupling represented by energy aggregation in the stable phase-locked state based on the magnitude of a sideband energy amplification coefficient; if the real-time phase difference does not show the quasi-steady state characteristic, evaluating the risk level of dynamic interference coupling based on the magnitude of the sideband energy amplification coefficient and the change trend of the real-time phase difference; s6, adjusting the disturbance period of the maximum power point tracking control according to the risk level so that the adjusted disturbance period and the main wave frequency are staggered.
2. The energy-saving type photovoltaic inverter control method according to claim 1, wherein S1 comprises: synchronously collecting output current and output voltage of the photovoltaic array and synchronously collecting direct current bus voltage according to a preset synchronous sampling period; calculating to obtain an instantaneous power value according to the synchronously acquired output current and output voltage; filtering the instantaneous power values to form an output power fluctuation sequence; And carrying out alternating current component extraction processing on the synchronously collected direct current bus voltage to form a direct current bus voltage ripple sequence.
3. The energy-saving type photovoltaic inverter control method according to claim 1, wherein S2 comprises: Time alignment is carried out on the output power fluctuation sequence and the direct current bus voltage ripple sequence; respectively calculating cross correlation coefficients between the output power fluctuation sequences after time alignment and the direct current bus voltage ripple sequences in a plurality of continuous sliding time windows; judging whether the calculated cross correlation coefficient continuously exceeds a preset association threshold value in a continuous sliding time window; and when the cross-correlation coefficient continuously exceeds a preset association threshold value in a continuous sliding time window, judging that cooperative variation characteristics representing periodic disturbance input exist.
4. The method for controlling an energy-efficient photovoltaic inverter according to claim 1, characterized in that S4 comprises: Calculating a corresponding fluctuation period according to the main wave frequency; In the disturbance period of each maximum power point tracking control, calculating the real-time phase offset of the fluctuation period relative to the starting moment of the current disturbance period by taking the zero crossing point or a specific phase point of the output power fluctuation sequence as a reference; Recording real-time phase offset calculated in a plurality of continuous disturbance periods; And connecting the real-time phase offsets recorded in the continuous disturbance periods in time sequence to form a change track of the real-time phase difference in the continuous disturbance periods.
5. The method for controlling an energy-efficient photovoltaic inverter according to claim 1, the sideband energy amplification factor characterizing the energy concentration is obtained by: the disturbance frequency of the maximum power point tracking control is taken as a central frequency, the main wave frequency is taken as a sideband offset, and the upper boundary frequency and the lower boundary frequency of the frequency sidebands are determined; calculating a power spectrum integral value of the output power fluctuation sequence in a frequency range between a lower boundary frequency and an upper boundary frequency as sideband energy; Calculating the total power spectrum integral value of the output power fluctuation sequence in the whole effective analysis frequency band; the ratio of the sideband energy to the total power spectrum integration value is taken as the sideband energy amplification factor.
6. The method according to claim 1, wherein analyzing the change track to determine whether the real-time phase difference exhibits a quasi-steady state characteristic that fluctuates around a fixed value includes: calculating standard deviation of a change track formed by the real-time phase difference in a plurality of continuous disturbance periods; calculating an average value of absolute values of differences between adjacent real-time phase differences in the change track as an average change rate; when the standard deviation is smaller than a preset first threshold value and the average change rate is smaller than a preset second threshold value, the real-time phase difference is judged to present a quasi-steady state characteristic.
7. The method for controlling an energy-efficient photovoltaic inverter according to claim 1, characterized in that S6 comprises: selecting a disturbance period candidate value different from the current disturbance period from a plurality of preset disturbance period candidate values as a target disturbance period based on the level of the risk level; calculating the absolute value of the difference between the frequency corresponding to the target disturbance period and the main oscillation frequency; When the absolute value of the difference value is smaller than a preset safety frequency interval, adjusting the step length according to a preset disturbance period, and recalculating a target disturbance period by taking the absolute value of the difference value as a target direction; And updating the disturbance period of the maximum power point tracking control to the finally determined target disturbance period.
8. An energy-saving photovoltaic inverter control system for implementing the energy-saving photovoltaic inverter control method according to any one of claims 1 to 7, comprising: The sequence forming module is used for monitoring and acquiring the output power of the photovoltaic array and the direct current bus voltage of the photovoltaic inverter to form an output power fluctuation sequence and a direct current bus voltage ripple sequence; The characteristic judging module is used for carrying out correlation analysis on the output power fluctuation sequence and the direct current bus voltage ripple sequence and judging whether cooperative variation characteristics representing periodic disturbance input exist or not; The frequency extraction module is used for analyzing the frequency distribution of the output power fluctuation sequence and extracting the main wave frequency when the cooperative variation characteristics exist; the track tracking module is used for analyzing the real-time phase difference between the fluctuation period corresponding to the main wave frequency and the disturbance period of the maximum power point tracking control and tracking the change track of the real-time phase difference in the continuous disturbance period; the grade evaluation module is used for evaluating the risk grade of interference coupling between the main fluctuation frequency and the disturbance period according to the energy aggregation characteristics of the output power fluctuation sequence in the frequency sideband range of the disturbance period and combining the change track; And the level adjustment module is used for adjusting the disturbance period of the maximum power point tracking control according to the risk level so as to enable the adjusted disturbance period and the main wave frequency to be staggered.

Description

Energy-saving photovoltaic inverter control system and control method Technical Field The invention relates to the technical field of power electronic conversion control, in particular to an energy-saving photovoltaic inverter control system and method. Background The photovoltaic inverter is used as core electric energy conversion equipment of a photovoltaic power generation system, and has the core functions of adjusting working points in real time through tracking control of maximum power points so as to extract as much electric energy as possible from a photovoltaic array and convert the electric energy into alternating current meeting grid-connected requirements. In an actual running environment, due to factors such as cloud drift, building or vegetation shielding and the like, the illumination intensity received by the photovoltaic array is not constant, but shows dynamic fluctuation characteristics. In order to ensure that the maximum power point can still be effectively tracked under the fluctuation condition, the inverter generally adopts a periodic MPPT algorithm, such as a disturbance observation method or a conductivity increment method, and periodically applies small disturbance to the output voltage or current of the photovoltaic array in a fixed sampling and control period, and decides the subsequent disturbance direction according to the power change trend so as to gradually approach the maximum power point. However, the conventional periodic MPPT control method has the defects that when the fluctuation frequency of external illumination changes is close to or in a specific relation with the inherent disturbance period of the MPPT algorithm, mutual coupling and interference can be generated between the fluctuation frequency of external illumination changes and the inherent disturbance period of the MPPT algorithm, so that a power change signal detected by the MPPT algorithm is a superposition result of the combined action of natural illumination fluctuation and active control disturbance, and a systematic deviation appears in the judgment of the power change trend of the algorithm, and as a result, the MPPT algorithm can continuously track a target with a phase lag behind a real maximum power point and cannot be stably locked near an optimal working point, and unnecessary and low-efficiency reciprocating search is performed around the MPPT algorithm, so that continuous dynamic tracking energy loss is caused, and the overall energy capturing efficiency of the photovoltaic system under the condition of fluctuating illumination is reduced. Disclosure of Invention The invention provides an energy-saving photovoltaic inverter control system and a control method aiming at the technical problems in the prior art. The technical scheme for solving the technical problems is as follows: An energy-saving photovoltaic inverter control method, comprising: S1, monitoring and obtaining output power of a photovoltaic array and direct current bus voltage of a photovoltaic inverter to form an output power fluctuation sequence and a direct current bus voltage ripple sequence; s2, carrying out correlation analysis on the output power fluctuation sequence and the direct current bus voltage ripple sequence, and judging whether a cooperative variation characteristic representing periodic disturbance input exists or not; s3, when the cooperative variation characteristics exist, analyzing the frequency distribution of the output power fluctuation sequence and extracting the main wave frequency; s4, analyzing a real-time phase difference between a fluctuation period corresponding to the main wave frequency and a disturbance period of the maximum power point tracking control, and tracking a change track of the real-time phase difference in a continuous disturbance period; s5, evaluating the risk level of interference coupling between the main fluctuation frequency and the disturbance period according to the energy aggregation characteristics of the output power fluctuation sequence in the frequency sideband range of the disturbance period and combining the change track; s6, adjusting the disturbance period of the maximum power point tracking control according to the risk level so that the adjusted disturbance period and the main wave frequency are staggered. Further, S1 includes: synchronously collecting output current and output voltage of the photovoltaic array and synchronously collecting direct current bus voltage according to a preset synchronous sampling period; calculating to obtain an instantaneous power value according to the synchronously acquired output current and output voltage; filtering the instantaneous power values to form an output power fluctuation sequence; And carrying out alternating current component extraction processing on the synchronously collected direct current bus voltage to form a direct current bus voltage ripple sequence. Further, S2 includes: Time alignment is carried out on the output