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CN-122026481-A - Control method of low-loss photovoltaic inverter

CN122026481ACN 122026481 ACN122026481 ACN 122026481ACN-122026481-A

Abstract

The invention relates to the technical field of photovoltaic inverters, in particular to a control method of a low-loss photovoltaic inverter, which comprises the steps of obtaining the logarithmic decrement corresponding to the DC bus voltage oscillation waveform of a power switch device in the turn-off time period in the grid-connected operation process of the photovoltaic inverter; the method comprises the steps of determining an inclination angle of a photovoltaic panel according to a logarithmic attenuation rate, obtaining common mode current of an alternating current output side three-phase cable of a photovoltaic inverter in a unit fundamental wave period, determining redundant vector distribution proportion in space vector pulse width modulation, obtaining current effective values corresponding to frequency spectrum components of alternating current output phase current of the alternating current output side three-phase cable in the unit fundamental wave period, calculating loss ratio of a preset frequency band, determining harmonic current injected into the alternating current output side according to the loss ratio, and controlling the photovoltaic inverter to complete grid-connected operation according to the redundant vector distribution proportion and the harmonic current injected into the alternating current output side. The invention realizes the improvement of the transmission efficiency of the photovoltaic inverter.

Inventors

  • ZHONG WENHAO
  • ZENG GUIHONG

Assignees

  • 广州伟洪成太阳能科技有限公司

Dates

Publication Date
20260512
Application Date
20260413

Claims (10)

  1. 1. A control method of a low-loss photovoltaic inverter, comprising: acquiring a direct current bus voltage oscillation waveform of a power switching device of the photovoltaic inverter in a grid-connected operation process in a turn-off time period when a temperature difference value at a photovoltaic panel of the photovoltaic inverter is larger than or equal to a preset temperature difference value; adjusting the inclination angle of the photovoltaic panel according to the logarithmic decrement corresponding to the DC bus voltage oscillation waveform; acquiring common mode current of the three-phase cable on the alternating current output side of the photovoltaic inverter in a unit fundamental wave period after the inclination angle is adjusted; determining a redundant vector allocation proportion in space vector pulse width modulation based on the effective value of the common mode current; Acquiring frequency spectrum components of alternating current output phase currents of the alternating current output side three-phase cable in a unit fundamental wave period; Calculating the loss duty ratio of a preset frequency band based on the corresponding harmonic current effective value of the frequency spectrum component in the unit fundamental wave period and the total current effective value of the alternating current output phase current; determining harmonic current injected into an alternating current output side according to the loss duty ratio; Controlling the photovoltaic inverter to complete a grid-connected operation process according to the redundant vector distribution proportion and the harmonic current injected into the alternating current output side, wherein, The photovoltaic inverter is a three-level photovoltaic inverter.
  2. 2. The method for controlling a low-loss photovoltaic inverter according to claim 1, wherein the adjusting the inclination angle of the photovoltaic panel according to the logarithmic decrement corresponding to the dc bus voltage oscillation waveform comprises: Comparing the logarithmic decrement with a preset decrement; if the logarithmic decrement is larger than the preset decrement, it is determined that the influence of water molecules accumulated on the back of the photovoltaic panel and the connection position of the cable on the transmission efficiency of the photovoltaic panel and the photovoltaic inverter is not satisfactory due to the condensation phenomenon at the photovoltaic panel, and the inclination angle of the photovoltaic panel is reduced.
  3. 3. The method of claim 2, wherein the inclination angle of the photovoltaic panel is inversely related to the logarithmic decrement, wherein, The inclination angle of the photovoltaic panel is an acute included angle between the plane where the photovoltaic panel is located and the horizontal plane.
  4. 4. The method of claim 3, wherein determining the redundancy vector allocation ratio in space vector pulse width modulation based on the effective value of the common mode current comprises: Comparing the effective value with a preset effective value; If the effective value is larger than the preset effective value, judging that the influence of accumulated heat generated by an oxide layer on the back of the photovoltaic panel and the back of the photovoltaic panel induced by water molecules at the connection position of the cable on the dielectric property of the cable insulating layer does not meet the requirement, and increasing the redundant vector distribution proportion in space vector pulse width modulation.
  5. 5. The method of claim 4, wherein the redundancy vector distribution ratio is in positive correlation with the effective value, wherein, The effective value is the root mean square value of the common mode current in a unit fundamental wave period; the redundant vector allocation proportion is the ratio of the acting time of the positive small vector in the space vector pulse width modulation in a single switching period to the acting time of the negative small vector in the single switching period.
  6. 6. The method according to claim 5, wherein the loss ratio is a ratio of a square of an effective value of harmonic current corresponding to the spectral component to a square of a total current effective value of the ac output phase within a preset frequency band.
  7. 7. The method according to claim 6, wherein the predetermined frequency band is a frequency band having a frequency greater than a first predetermined frequency and less than a second predetermined frequency in the spectral components.
  8. 8. The method for controlling a low-loss photovoltaic inverter according to claim 7, The effective value of the harmonic current is the root mean square value of a current component with the frequency within a preset frequency band in the AC output phase current; the total current effective value is the root mean square value of the alternating current output phase current in a unit fundamental wave period.
  9. 9. The method of claim 8, wherein determining the harmonic current injected into the ac output side based on the loss ratio comprises: Comparing the loss duty cycle with a preset loss duty cycle; If the loss duty ratio is larger than the preset loss duty ratio, the fact that the influence of the reduction of the skin depth of the conductor of the alternating current output cable on the charge distribution in the conductor is not satisfied is judged, and the harmonic current injected into the alternating current output side is increased.
  10. 10. The method of claim 9, wherein the harmonic current is positively correlated with the loss ratio, wherein, The phase of the harmonic current is 180 degrees out of phase with the harmonic component of the same frequency in the ac output phase current.

Description

Control method of low-loss photovoltaic inverter Technical Field The invention relates to the technical field of photovoltaic inverters, in particular to a control method of a low-loss photovoltaic inverter. Background With the rapid development of photovoltaic power generation technology in solar industry, the photovoltaic inverter is used as core equipment for connecting a photovoltaic array and a power grid, the operation efficiency and reliability of the photovoltaic inverter directly influence the benefits and safety of the whole power generation system, wherein the three-level topological structure has the advantages of low voltage stress, small output harmonic, high efficiency and the like of a switching device, the photovoltaic inverter is widely applied to a medium-high-power photovoltaic inverter, a distributed control architecture is generally adopted in a large-scale photovoltaic power station, the integral efficiency of the system is improved through the cooperative operation of a plurality of inverters, the higher requirement is provided for the long-term stability of a single inverter, however, the contact surface of a direct current busbar connector of the photovoltaic inverter in the prior art is easily corroded by oxidation in the long-term operation, the contact resistance is increased, the existing monitoring means are mainly dependent on the direct measurement of busbar temperature of a temperature sensor, the temperature detection has larger thermal inertia, the fault can be found when the temperature is abnormally increased, the oxidation is serious at the moment, potential safety hazards exist, the time of the power switching device of the existing inverter is usually fixed, the time is a fixed value, the contact resistance of the busbar is not changed, the contact resistance is adjusted, the dynamic change is reduced, the conduction time of the system is reduced, the total loss is not balanced, and the conduction loss of the system is reduced due to the dynamic change of the contact resistance is reduced. According to the technical scheme, the photovoltaic inverter topology circuit, the identification method, the control system and the control method are characterized in that input pins of each direct current conversion module are respectively connected with two ends of a photovoltaic string, output pins of each direct current conversion module are connected with input pins of the inversion module, output pins of the inversion module are connected with two ends of a load, when part of direct current conversion modules are connected with the photovoltaic string, and part of direct current conversion modules are not connected with the photovoltaic string, a change-over switch is connected in series between the direct current conversion modules connected with the photovoltaic string and the direct current conversion modules not connected with the photovoltaic string, and therefore, the photovoltaic inverter topology circuit, the identification method, the control system and the control method have the advantages that due to the fact that a photovoltaic board is prone to accumulating on the back of the photovoltaic board and at a cable connection under the action of temperature difference and condensation phenomena, electrochemical oxidation is induced under the action of electrostatic adsorption, the surface of a box terminal generates an oxide film, contact resistance is increased, the temperature of a junction cable is increased, the contact resistance is increased, the temperature of a three-phase alternating current transmission cable is increased, and the parasitic capacitance is lowered, and the parasitic capacitance is increased due to the fact that the temperature of a three-phase transmission cable is increased. Disclosure of Invention Therefore, the invention provides a control method of a low-loss photovoltaic inverter, which is used for solving the problems that in the prior art, water molecules are easy to accumulate on the back surface of a photovoltaic panel and at the junction of cables under the action of day and night temperature difference change and condensation phenomenon of the photovoltaic panel, electrochemical oxidation is induced under the action of electrostatic adsorption, so that an oxide film is generated on the surface of a terminal of a junction box, the contact resistance is increased, additional joule heat generated along with the increase of the contact resistance is conducted to an alternating current output side three-phase cable, the temperature of an insulating layer of the cable is increased, the dielectric constant drifts, parasitic capacitance to the ground fluctuates, the impedance of a leakage path is reduced, and the common-mode leakage current is increased, so that the transmission efficiency of grid-connected operation is reduced. In order to achieve the above object, the present invention provides a control method of a low-loss photovolta