CN113572383A - Photovoltaic power generation inversion system and photovoltaic power generation inversion control method - Google Patents

Abstract

The invention relates to a photovoltaic power generation inversion system and a photovoltaic power generation inversion control method. The photovoltaic power generation inversion system comprises a direct current bus, two low-voltage inversion modules and a three-phase three-winding transformer, wherein the direct current bus consists of a positive half bus and a negative half bus, the input sides of the two low-voltage inversion modules are respectively connected with the positive/negative half bus, the output sides of the two low-voltage inversion modules are respectively connected with two windings on the low-voltage side of the three-phase three-winding transformer, and the high-voltage side of the three-phase three-winding transformer is connected with a power grid. The photovoltaic power generation inversion control method comprises a synchronous work control method and a filtering control method; the synchronous working control method comprises the following steps: controlling the output current of one low-voltage inversion module based on the output current of the other low-voltage inversion module; the filtering control method comprises the following steps: when the harmonic of the output current of one low-voltage inversion module is detected to exceed the standard, the other low-voltage inversion module is controlled to output harmonic with reversed phase and equal amplitude. The invention can reduce the development cost and the control difficulty, realize the induction filtering and improve the grid-connected current quality.

Description

Photovoltaic power generation inversion system and photovoltaic power generation inversion control method

Technical Field

The invention belongs to the technical field of power conversion, and particularly relates to a photovoltaic power generation inversion system and a photovoltaic power generation inversion control method applied by the same.

Background

The maximum voltage of a direct-current system of the photovoltaic grid-connected inverter is determined, and various inverter topologies can be applied. As the dc system voltage rises further, the inversion topology selection may be difficult. Two-level and three-level inversion topology control is simple, technology application is mature, but in order to adapt to high voltage, a plurality of tubes are required to be connected in series for voltage division, and the problems of large number of tubes and uneven voltage exist. The five-level inversion topological structure is complex, the control is difficult, and the application is less at present.

Therefore, for a direct current system with higher voltage, the selection and application of an inverter topology become difficult, the inversion is directly carried out on the higher direct current voltage, and both hardware topology and software control are complex.

Disclosure of Invention

The invention aims to provide a photovoltaic power generation inverter system which can realize the inverter output of a higher-voltage direct current system, reduce the development cost and the control difficulty and improve the quality of grid-connected current.

In order to achieve the purpose, the invention adopts the technical scheme that:

the photovoltaic power generation inversion system comprises a direct-current bus formed by a positive half bus and a negative half bus, and further comprises two low-voltage inversion modules and a three-phase three-winding transformer which work synchronously, wherein the input sides of the two low-voltage inversion modules are respectively connected with the positive half bus and the negative half bus, the output sides of the two low-voltage inversion modules are respectively directly connected with two windings on the low-voltage side of the three-phase three-winding transformer, and the high-voltage side of the three-phase three-winding transformer is connected with a power grid.

The three-phase three-winding transformer is a Y/D/D transformer or a Y/Y/D transformer.

The low-voltage inversion module is a three-phase low-voltage inversion module.

The highest voltage of the positive half bus and the highest voltage of the negative half bus are equal.

The invention also provides a photovoltaic power generation inversion control method applicable to the photovoltaic power generation inversion system, which has the scheme that:

a photovoltaic power generation inversion control method is applied to the photovoltaic power generation inversion system and comprises a synchronous work control method for controlling two low-voltage inversion modules to work synchronously and a filtering control method for realizing inductive filtering;

the synchronous working control method comprises the following steps: the output current of one low-voltage inversion module is used as a target, the output current of the other low-voltage inversion module is used as a controlled object, and therefore the controlled object is controlled based on the target, the output currents and the phases of the two low-voltage inversion modules are kept consistent, and synchronous work of the two low-voltage inversion modules is achieved;

the filtering control method comprises the following steps: when the harmonic waves of the output current of one low-voltage inversion module are detected to exceed the standard, the other low-voltage inversion module is controlled to output harmonic waves with opposite phases and equal amplitudes with the harmonic waves exceeding the standard, and the harmonic waves output by the two low-voltage inversion modules are mutually offset in the magnetic core of the three-phase three-winding transformer.

Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages: the invention realizes the inversion output of a better voltage direct current system by using the low-voltage inversion module, does not need to develop the high-voltage inversion module, can reduce the development cost and the control difficulty, can realize the induction filtering and improves the grid-connected current quality.

Drawings

Fig. 1 is a circuit diagram of a photovoltaic power generation inverter system of the present invention.

Detailed Description

The invention will be further described with reference to examples of embodiments shown in the drawings to which the invention is attached.

The first embodiment is as follows: as shown in fig. 1, a photovoltaic power generation inverter system includes a dc bus, two low-voltage inverter modules, and a three-phase three-winding transformer.

The direct current bus comprises a positive half bus and a negative half bus, and the highest voltage of the positive half bus is equal to that of the negative half bus. The low-voltage inversion module is a three-phase low-voltage inversion module of a low-voltage direct current system. The two low-voltage inversion modules are respectively a low-voltage inversion module 1 and a low-voltage inversion module 2. The input sides of the two low-voltage inversion modules are respectively connected with the positive half bus and the negative half bus, namely the input side of the low-voltage inversion module 1 is connected with the positive half bus, and the input side of the low-voltage inversion module 2 is connected with the negative half bus. The output sides of the two low-voltage inversion modules are respectively and directly connected with two windings on the low-voltage side of the three-phase three-winding transformer, namely the output side of the low-voltage inversion module 1 is connected to an S-side winding of the three-phase three-winding transformer, and the output side of the low-voltage inversion module 2 is connected to a T-side winding of the three-phase three-winding transformer. The high-voltage side of the three-phase three-winding transformer, i.e. its P-side winding, is connected to the grid. The three-phase three-winding transformer is a Y/D/D transformer or a Y/Y/D transformer or other three-phase three-winding transformers.

In order to ensure the balance of the positive half bus voltage and the negative half bus voltage and the normal operation of the three-phase three-winding transformer, the two low-voltage inverter modules need to keep synchronous operation, namely, the input voltage and the current keep basically consistent (the difference value is within a set range), and the output current and the phase keep basically consistent (the difference value is within the set range). Therefore, for the control of the photovoltaic power generation inverter system, the following synchronous working control method is adopted to control the two low-voltage inverter modules to work synchronously: the output current of one low-voltage inverter module is taken as a target, the output current of the other low-voltage inverter module is taken as a controlled object, for example, the output current of the low-voltage inverter module 1 is taken as a target, and the output current of the low-voltage inverter module 2 is taken as a controlled object, or vice versa. And controlling the controlled object based on the target, so that the output currents and the phases of the two low-voltage inversion modules are kept consistent (the difference value is within a set allowable range), and the synchronous work of the two low-voltage inversion modules is realized.

The photovoltaic power generation inverter system not only utilizes the low-voltage inverter module to realize the inverter output of higher direct current system voltage, but also can utilize two secondary windings of the three-phase three-winding transformer to realize induction filtering. The filtering control method for realizing the inductive filtering comprises the following steps: when the harmonic waves of the output current of one low-voltage inversion module are detected to exceed the standard, the other low-voltage inversion module is controlled to output harmonic waves with opposite phases and equal amplitudes with the harmonic waves exceeding the standard, and the harmonic waves output by the two low-voltage inversion modules are mutually offset in the magnetic core of the three-phase three-winding transformer. For example, when the harmonic output by the low-voltage inverter module 1 exceeds the standard, the low-voltage inverter module 2 can be controlled to output an anti-phase harmonic with the same amplitude, the two harmonics are mutually offset in the magnetic fields of the three-phase three-winding transformer magnetic cores, the subharmonic can be eliminated for the current waveform output by the primary side of the three-phase three-winding transformer, and the electric energy quality of grid-connected current is improved. If the carrier phases modulated by the two low-voltage inversion modules have wrong phases, the ripple of the primary side grid-connected current of the three-phase three-winding transformer can be reduced by utilizing the characteristic, so that the capacity of the transformer is reduced.

The photovoltaic power generation inversion system utilizes the existing low-voltage inversion module to realize inversion output of higher direct current system voltage by means of the three-phase three-winding transformer, and utilizes the characteristics of the three-phase three-winding transformer that the common magnetic core and the inversion output are controllable to realize induction filtering, eliminate redundant higher harmonics and reduce grid-connected current ripples. Therefore, the beneficial effects are as follows: the high-voltage inverter module is not required to be developed, development cost and control difficulty are reduced, induction filtering is realized without additionally adding a hardware circuit by means of the three-phase three-winding transformer, and grid-connected current quality is improved.

The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims (5)

1. The utility model provides a photovoltaic power generation inverter system, includes the direct current bus that constitutes by positive half generating line and negative half generating line, its characterized in that: the photovoltaic power generation system further comprises two low-voltage inversion modules and a three-phase three-winding transformer, wherein the two low-voltage inversion modules work synchronously, the input sides of the two low-voltage inversion modules are respectively connected with the positive half bus and the negative half bus, the output sides of the two low-voltage inversion modules are respectively directly connected with two windings on the low-voltage side of the three-phase three-winding transformer, and the high-voltage side of the three-phase three-winding transformer is connected with a power grid.

2. The photovoltaic power generation inversion system according to claim 1, wherein: the three-phase three-winding transformer is a Y/D/D transformer or a Y/Y/D transformer.

3. The photovoltaic power generation inversion system according to claim 1, wherein: the low-voltage inversion module is a three-phase low-voltage inversion module.

4. The photovoltaic power generation inversion system according to claim 1, wherein: the highest voltage of the positive half bus and the highest voltage of the negative half bus are equal.

5. A photovoltaic power generation inversion control method applied to the photovoltaic power generation inversion system according to any one of claims 1 to 4, characterized in that: the photovoltaic power generation inversion control method comprises a synchronous work control method for controlling two low-voltage inversion modules to work synchronously and a filtering control method for realizing induction filtering;

the synchronous working control method comprises the following steps: the output current of one low-voltage inversion module is used as a target, the output current of the other low-voltage inversion module is used as a controlled object, and therefore the controlled object is controlled based on the target, the output currents and the phases of the two low-voltage inversion modules are kept consistent, and synchronous work of the two low-voltage inversion modules is achieved;

the filtering control method comprises the following steps: when the harmonic waves of the output current of one low-voltage inversion module are detected to exceed the standard, the other low-voltage inversion module is controlled to output harmonic waves with opposite phases and equal amplitudes with the harmonic waves exceeding the standard, and the harmonic waves output by the two low-voltage inversion modules are mutually offset in the magnetic core of the three-phase three-winding transformer.

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