WO2018006681A1

WO2018006681A1 - Reactive power compensation method and apparatus, photovoltaic grid-connected inverter, and computer storage medium

Info

Publication number: WO2018006681A1
Application number: PCT/CN2017/087529
Authority: WO
Inventors: 戴志威; 魏学海; 唐弘扬; 陈景熙
Original assignee: 中兴通讯股份有限公司
Priority date: 2016-07-07
Filing date: 2017-06-08
Publication date: 2018-01-11
Also published as: CN107591816A

Abstract

A reactive power compensation method and apparatus, a photovoltaic grid-connected inverter, and a computer storage medium. The method comprises: when the photovoltaic grid-connected inverter is in an active power output mode, acquiring first output state information of a photovoltaic cell (101); determining whether the first output state information satisfies a first switching condition (102); when the first output state information satisfies the first switching condition, switching the photovoltaic grid-connected inverter from the active power output mode to a reactive power compensation mode (103); when the photovoltaic grid-connected inverter is in the reactive power compensation mode, acquiring second output state information of the photovoltaic cell (104); determining whether the second output state information satisfies a second switching condition (105); and when the second output state information satisfies the second switching condition, switching the photovoltaic grid-connected inverter from the reactive power compensation mode to the active power output mode (106).

Description

Reactive power compensation method, device, photovoltaic grid-connected inverter and computer storage medium

Cross-reference to related applications

The present application is filed on the basis of the Chinese Patent Application No. PCT Application No.

Technical field

The invention relates to the field of new energy power electronic control technology, in particular to a reactive power compensation method and device, a photovoltaic grid-connected inverter and a computer storage medium.

Background technique

The load of photovoltaic power plant project operation is mostly inductive load. A large number of inductive loads not only cause the system power factor to be too low, the production efficiency is reduced, the enterprise's electric energy expenses increase, but also cause grid voltage fluctuations, which seriously affects the safe operation of the loaded equipment and brings unnecessary economic losses to the enterprise. . According to the "State Grid Corporation photovoltaic power plant access grid technical regulations", the power factor of large and medium-sized photovoltaic power plants should be continuously adjustable from 0.98 (leading) to 0.98 (lag). Therefore, large-scale centralized and distributed photovoltaic power plants need to improve the power factor through reactive power compensation to ensure power quality and grid security.

The reactive demand equipment operating in the photovoltaic power station is mainly the inductive component - the step-up transformer. In order to improve the power factor, reduce the loss, and ensure the stability of the power grid system, according to the national standard "GB/T29321-2012 photovoltaic power station reactive power compensation technical specifications": photovoltaic power station should make full use of the reactive power capacity of the grid-connected inverter and Adjusting ability, when the reactive capacity of the grid-connected inverter can not meet the system voltage and reactive power regulation needs, the centralized reactive power compensation device should be configured in the photovoltaic power station, and comprehensively consider the various output levels and access systems of the photovoltaic power station. After various operating conditions Transient, dynamic process, configuration of dynamic reactive power compensation device with sufficient capacity.

Among them, the reactive power compensation of the current photovoltaic power plant project, especially the method of adding reactive power compensator (SVG), which is mainly used for nighttime reactive power compensation, has the following problems:

1. The reactive power compensation capability of the photovoltaic grid-connected inverter has not been fully tapped, resulting in waste of power compensation device and increased configuration cost;

2. The introduction of reactive power compensation device improves the operation and maintenance cost of the power station and reduces the system reliability.

3. Compared with photovoltaic grid-connected inverters that do not stop working at night, the current method reduces the life of AC inverters of photovoltaic inverters.

Summary of the invention

Embodiments of the present invention are expected to provide a reactive power compensation method, device, photovoltaic grid-connected inverter, and computer storage medium, which can realize automatic switching between active power output mode and reactive power compensation mode, and effectively solve photovoltaic power station reactive power compensation device. Introduced capacity waste and cost increases issues and deficiencies.

In order to solve the above technical problem, the embodiment of the present invention adopts the following technical solutions:

According to a first aspect of the embodiments of the present invention, a reactive power compensation method is provided, including:

Obtaining first output state information of the photovoltaic cell when the photovoltaic grid-connected inverter is in an active power output mode;

Determining whether the first output state information satisfies a first switching condition;

Switching the photovoltaic grid-connected inverter from the active power output mode to a reactive power compensation mode when the first output state information satisfies the first switching condition;

Obtaining second output state information of the photovoltaic cell when the photovoltaic grid-connected inverter is in the reactive power compensation mode;

Determining whether the second output state information satisfies a second switching condition;

When the second output state information satisfies the second switching condition, the photovoltaic is connected to the network The inverter switches from the reactive power compensation mode to the active power output mode.

In an embodiment, the first output state information includes an output power or an output voltage of the photovoltaic cell, and the step of determining whether the first output state information satisfies a first switching condition comprises:

When the output power of the photovoltaic cell is less than the first power threshold, determining whether the output power of the photovoltaic cell is less than the first time duration that the first power threshold continues to reach the first time threshold, if the first duration reaches The first time threshold, the first output state information satisfies the first switching condition; or

When the output voltage of the photovoltaic cell is less than the first voltage threshold, determining whether the output voltage of the photovoltaic cell is less than a second duration that the first voltage threshold continues to reach the first time threshold, if the second When the duration reaches the first time threshold, the first output state information satisfies the first switching condition.

In an embodiment, the switching the photovoltaic grid-connected inverter from the active power output mode to the reactive power compensation mode comprises:

Turning off the maximum power tracking function of the photovoltaic grid-connected inverter;

Stepping up the output voltage of the photovoltaic cell according to the first preset step, until the output current of the photovoltaic cell reaches the first current threshold, stopping increasing the output voltage of the photovoltaic cell, and The current output voltage of the battery is recorded as the first bus voltage regulation value;

Adjusting a bus voltage of the photovoltaic grid-connected inverter to stabilize the bus voltage at the first bus voltage regulation value;

Disconnecting the connection between the photovoltaic cell and the photovoltaic grid-connected inverter when the voltage value of the bus voltage is stable when the duration of the first bus voltage regulation reaches a second time threshold;

Adjusting a bus voltage of the photovoltaic grid-connected inverter to stabilize the bus voltage to a second bus voltage regulation value, and the photovoltaic grid-connected inverter enters the reactive power compensation mode;

The second bus voltage regulation value is greater than the AC line voltage peak of the photovoltaic inverter.

In an embodiment, the second output state information includes an open circuit voltage of the photovoltaic cell;

The step of determining whether the second output state information meets the second switching condition comprises:

When the open circuit voltage is greater than or equal to the second voltage threshold, determining whether the third time duration that the open circuit voltage is greater than or equal to the second voltage threshold reaches a third time threshold, if the third duration reaches the The third time threshold, the second output state information satisfies the second switching condition.

In an embodiment, the switching the photovoltaic grid-connected inverter from the reactive power compensation mode to the active power output mode comprises:

Using the open circuit voltage as a third bus voltage regulation value, and adjusting a bus voltage of the photovoltaic grid-connected inverter to stabilize the third bus voltage regulation value;

Recovering a connection between the photovoltaic cell and the photovoltaic grid-connected inverter;

Obtaining a current output power and a current output voltage of the photovoltaic cell and a current output power of the photovoltaic grid-connected inverter;

When the current output power of the photovoltaic cell is greater than or equal to the first power threshold, and the current output voltage of the photovoltaic cell is greater than or equal to the first voltage threshold, and the current output of the photovoltaic grid-connected inverter When the power is less than or equal to the second power threshold, the photovoltaic grid-connected inverter starts the maximum power tracking function and enters the active power output mode.

In an embodiment, the method further includes:

When the photovoltaic grid-connected inverter is in the reactive power compensation mode, a power scheduling instruction is acquired, and reactive power is output according to the power scheduling instruction.

According to a second aspect of the embodiments of the present invention, a reactive power compensation apparatus is provided, including:

a first acquiring module configured to acquire first output state information of the photovoltaic cell when the photovoltaic grid-connected inverter is in an active power output mode;

The first determining module is configured to determine whether the first output state information acquired by the first acquiring module meets the first switching condition;

a first switching module, configured to: when the first determining module determines that the first output state information meets the first switching condition, switch the photovoltaic grid-connected inverter from the active power output mode to none Power compensation mode;

a second acquiring module, configured to acquire second output state information of the photovoltaic cell when the first switching module switches the photovoltaic grid-connected inverter in a reactive power compensation mode;

a second determining module, configured to determine whether the second output state information acquired by the second acquiring module meets a second switching condition;

a second switching module, configured to switch the photovoltaic grid-connected inverter from the reactive power compensation mode to when the second determining module determines that the second output state information meets the second switching condition The active power output mode.

In an embodiment, the first output state information includes an output power or an output voltage of the photovoltaic cell, and the first determining module includes:

a first determining unit, configured to determine, when the output power of the photovoltaic cell is less than the first power threshold, whether the first time duration that the output power of the photovoltaic cell is less than the first power threshold reaches a first time threshold, If the first duration reaches the first time threshold, the first output state information satisfies the first switching condition; or

a second determining unit, configured to determine, when the output voltage of the photovoltaic cell is less than the first voltage threshold, determining whether the output voltage of the photovoltaic cell is less than the second duration that the first voltage threshold continues to reach the first time a threshold, if the second duration reaches the first time threshold, the first output state information satisfies the first switching condition.

In an embodiment, the first switching module includes:

a shutdown unit configured to turn off a maximum power tracking function of the photovoltaic grid-connected inverter;

a first adjusting unit, configured to: after the closing unit turns off the maximum power tracking function of the photovoltaic grid-connected inverter, gradually increase the output voltage of the photovoltaic cell according to the first preset step, until the photovoltaic Stop increasing the photovoltaic power when the output current of the battery reaches the first current threshold The output voltage of the pool, and recording the current output voltage of the photovoltaic cell as the first bus voltage regulation value;

a second adjusting unit, configured to adjust a bus voltage of the photovoltaic grid-connected inverter, so that the bus voltage is stabilized at the first bus voltage regulation value;

a first control unit configured to disconnect the photovoltaic cell and the photovoltaic grid-connected inverter when a voltage value of the bus voltage is stable for a duration of the first bus voltage regulation value to reach a second time threshold the connection between;

a third adjusting unit configured to adjust a bus voltage of the photovoltaic grid-connected inverter to stabilize the bus voltage to a second bus voltage regulation value, and the photovoltaic grid-connected inverter enters the reactive power compensation mode ;

In an embodiment, the second output state information includes an open circuit voltage of the photovoltaic cell, and the second determining module includes:

a third determining unit, configured to determine, when the open circuit voltage is greater than or equal to the second voltage threshold, whether the third time duration that the open circuit voltage is greater than or equal to the second voltage threshold reaches a third time threshold, if The third time period reaches the third time threshold, and the second output state information satisfies the second switching condition.

In an embodiment, the second switching module includes:

a fourth adjusting unit configured to use the open circuit voltage as a third bus voltage regulation value, and adjust a bus voltage of the photovoltaic grid-connected inverter to stabilize the third bus voltage regulation value;

a second control unit configured to restore a connection between the photovoltaic cell and the photovoltaic grid-connected inverter;

a third acquiring unit, configured to acquire a current output power and a current output voltage of the photovoltaic cell and a current output power of the photovoltaic grid-connected inverter;

Activating unit configured to: when a current output power of the photovoltaic cell is greater than or equal to the first power threshold, and a current output voltage of the photovoltaic cell is greater than or equal to the first voltage threshold And when the current output power of the photovoltaic grid-connected inverter is less than or equal to the second power threshold, the photovoltaic grid-connected inverter starts a maximum power tracking function and enters the active power output mode.

In an embodiment, the apparatus further includes:

The scheduling module is configured to: when the photovoltaic grid-connected inverter is in the reactive power compensation mode, acquire a power scheduling instruction, and output reactive power according to the power scheduling instruction.

According to a third aspect of the embodiments of the present invention, there is also provided a photovoltaic grid-connected inverter comprising the reactive power compensation device described above.

According to a fourth aspect of the present invention, a computer storage medium is provided, wherein the computer storage medium stores computer executable instructions, and the computer executable instructions are configured to perform reactive power according to an embodiment of the present invention. Compensation method.

The embodiment of the invention further provides a computer storage medium, wherein the computer storage medium stores computer executable instructions, and the computer executable instructions are configured to execute the reactive power compensation method according to the embodiment of the invention.

The reactive power compensation method according to the embodiment of the present invention determines whether the photovoltaic grid-connected inverter meets the switching condition of the working mode according to the output state information of the photovoltaic cell, that is, when the photovoltaic grid-connected inverter is in the active power output mode, Whether the output state information of the photovoltaic cell satisfies the first switching condition, and when satisfied, the photovoltaic grid-connected inverter is switched from the active power output mode to the reactive power compensation mode; when the photovoltaic grid-connected inverter is in the reactive power compensation mode When it is determined whether the output state information of the photovoltaic cell satisfies the second switching condition, and when satisfied, the photovoltaic grid-connected inverter is switched from the reactive power compensation mode to the active power output mode.

It can be seen that the embodiment of the present invention can utilize the photovoltaic grid-connected inverter to provide the required reactive power for the power grid at night, and can automatically switch between the active power output mode and the reactive power compensation mode, effectively solving the problem. The capacity waste and cost increase problems and defects introduced by photovoltaic power plant reactive power compensation devices.

DRAWINGS

1 is a flow chart showing a reactive power compensation method according to a first embodiment of the present invention;

2 is a flow chart showing the working cycle process of the photovoltaic grid-connected inverter in the first embodiment of the present invention;

Figure 3 is a graph showing the current-voltage and power-voltage curves of the photovoltaic cell at the first irradiance and the first temperature in the evening of the first embodiment of the present invention;

4 is a schematic diagram showing a specific implementation process of switching a photovoltaic grid-connected inverter from an active power output mode to a reactive power compensation mode in the first embodiment of the present invention;

Figure 5 is a graph showing current-voltage and power-voltage curves of a photovoltaic cell at a second irradiance and a second temperature in the morning of the first embodiment of the present invention;

6 is a schematic diagram showing a specific implementation process of switching a photovoltaic grid-connected inverter from a reactive power compensation mode to an active power output mode in the first embodiment of the present invention;

7 is a schematic diagram showing an active power and reactive power output control strategy of a photovoltaic grid-connected inverter in a first embodiment of the present invention;

Figure 8 is a block diagram showing the structure of a reactive power compensation device according to a second embodiment of the present invention;

Fig. 9 is a block diagram showing the second embodiment of the reactive power compensation apparatus according to the second embodiment of the present invention.

detailed description

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While the embodiments of the present invention have been shown in the drawings, the embodiments Rather, these embodiments are provided so that this disclosure will be more fully understood and the scope of the disclosure will be fully disclosed.

First embodiment

An embodiment of the present invention provides a reactive power compensation method. As shown in FIG. 1, the method includes:

Step 101: Acquire a photovoltaic cell when the photovoltaic grid-connected inverter is in an active power output mode The first output status information.

The reactive power compensation method of the embodiment of the invention is applied to a photovoltaic grid-connected inverter. The photovoltaic grid-connected inverter is in an active power output mode during the day, converting the photovoltaic cell power into a sinusoidal current in phase with the same frequency of the grid; at night, it is in a reactive power compensation mode, providing the grid with no need at night. Power.

Wherein, when the photovoltaic grid-connected inverter is in the active power output mode, if the output power of the photovoltaic cell is greater than or equal to the first power threshold, and the output power of the photovoltaic grid-connected inverter is less than or equal to the second power threshold S _max , When the output voltage of the photovoltaic cell is greater than or equal to the first voltage threshold, the photovoltaic grid-connected inverter turns on the maximum power point tracking function to detect the maximum output power of the photovoltaic cell. The second power threshold S _{max is} less than the rated power of the photovoltaic grid-connected inverter and is a predetermined threshold.

At this point, according to the formula

Calculating the maximum value Q _{max of the} reactive power that the photovoltaic grid-connected inverter can provide when the current output power of the photovoltaic grid-connected inverter is P. Among them, by

The first formula is available:

And the second formula:

That is, the maximum reactive power generated by the photovoltaic grid-connected inverter is Q _max2 , and the maximum reactive power absorbed is Q _max1 .

Therefore, when the PV grid-connected inverter is in the active power output mode during the daytime, when receiving the upper layer scheduling command, the reactive power of the corresponding value may be emitted or absorbed according to the demand value Q _{ord of the} reactive power carried in the scheduling instruction. . That is, when the absolute value of Q _ord is less than the absolute value of Q _max , the photovoltaic grid-connected inverter absorbs or emits corresponding reactive power, and when Q _ord <Q _max1 , the inverter can only absorb reactive power-Q _Max1 ; When Q _ord >Q _max2 , the inverter can only output the reactive power Q _max2 . It can be seen that when the photovoltaic grid-connected inverter is in the active power output mode, the photovoltaic grid-connected inverter can be used to provide the required reactive power to the grid through the upper layer scheduling command.

In addition, in the embodiment of the present invention, when the photovoltaic grid-connected inverter is in the active power output mode, it is required to obtain the output state information of the photovoltaic cell, such as the output voltage and the output power, in real time. Whether to switch the working mode is required.

Step 102: Determine whether the first output state information satisfies a first switching condition.

With the arrival of the evening, the output voltage and output power of the photovoltaic cell will gradually decrease until the threshold value is reached, and the photovoltaic cell's power generation capacity is reduced, which is insufficient to support the bus voltage of the photovoltaic grid-connected inverter. Therefore, whether the photovoltaic inverter needs to be switched from the active power output mode to the reactive power compensation mode can be determined by the output voltage or output power of the photovoltaic cell.

Specifically, step 102 includes:

When the output power of the photovoltaic cell is less than the first power threshold, determining whether the output power of the photovoltaic cell is less than the first time duration that the first power threshold continues to reach the first time threshold, if the first duration reaches The first time threshold, the first output state information satisfies the first switching condition; or when the output voltage of the photovoltaic cell is less than the first voltage threshold, determining that the output voltage of the photovoltaic cell is less than the Whether the second duration that the first voltage threshold continues to reach the first time threshold, and if the second duration reaches the first time threshold, the first output state information satisfies the first switching condition.

Wherein, in order to prevent the output voltage of the photovoltaic cell from accidentally decreasing to the first voltage threshold, and the output power accidentally decreases to the first power threshold, causing the false switching of the photovoltaic grid-connected inverter operating mode, the output of the photovoltaic cell needs to be detected. When the voltage is less than the first voltage threshold or the output power is less than the first power threshold, further determining whether the duration of the state in which the output voltage of the photovoltaic cell is less than the first voltage threshold or the output power is less than the first power threshold reaches a predetermined first time a threshold value, when the duration of the state in which the output voltage of the photovoltaic cell is less than the first voltage threshold or the output power is less than the first power threshold reaches a predetermined first time threshold, determining that the first output state information of the photovoltaic cell satisfies the first The switching condition, that is, the photovoltaic grid-connected inverter can be switched from the active power output mode to the reactive power compensation mode.

In addition, the first power threshold, the first voltage threshold, and the first time threshold are previously passed through a plurality of tests and determined based on relevant test data.

Step 103: Switch the photovoltaic grid-connected inverter from the active power output mode to the reactive power compensation mode when the first output state information satisfies the first switching condition.

Specifically, step 103 includes:

Wherein, when the photovoltaic grid-connected inverter is switched from the active power output mode to the reactive power compensation mode, the connection between the photovoltaic cell and the photovoltaic grid-connected inverter needs to be disconnected. In addition, the photovoltaic grid-connected inverter has the maximum power tracking function in the active power output mode, and does not turn off the photovoltaic grid-connected inverter before disconnecting the photovoltaic cell from the photovoltaic grid-connected inverter. The maximum power tracking power will cause the PV grid-connected inverter to stop due to low power failure, disconnected from the grid, and cannot switch to the reactive power compensation mode. Therefore, when switching the working mode at this time, it is first necessary to turn off the maximum power tracking function of the photovoltaic grid-connected inverter.

In addition, although the second output state information of the photovoltaic cell satisfies the second switching condition, the photovoltaic cell is still connected to the photovoltaic grid-connected inverter at this time, that is, the photovoltaic cell still has a current output, but the current value is small. Therefore, if the maximum power tracking function of the photovoltaic grid-connected inverter is turned off, it is very unsafe to directly disconnect the connection between the photovoltaic cell and the photovoltaic grid-connected inverter. Therefore, it is necessary Find a working point that can be safely disconnected and disconnect the PV cell from the PV grid-connected inverter.

Wherein, according to the first preset step size, the output voltage of the photovoltaic cell is increased at this time, so that the output current of the photovoltaic cell is reduced until the first current threshold is reached, that is, the output current of the photovoltaic cell is sufficiently small, which can be safely Disconnect the connection between the photovoltaic cell and the photovoltaic grid-connected inverter. In addition, in order to prevent current surge when disconnecting the photovoltaic cell from the photovoltaic grid-connected inverter, it is necessary to make the bus voltage of the photovoltaic grid-connected inverter equal to the output voltage of the photovoltaic cell. Therefore, after finding a safe disconnection point, the output voltage of the photovoltaic cell at this time is used as the first bus voltage regulation value, and the bus voltage of the photovoltaic grid-connected inverter is stabilized at the first bus voltage regulation value.

In addition, after disconnecting the photovoltaic cell from the photovoltaic inverter, in order to facilitate the subsequent switching of the photovoltaic grid-connected inverter from the reactive power compensation mode to the active power output mode, the output voltage of the photovoltaic grid-connected inverter is required. Further adjusted to the second bus voltage regulation value. The second bus voltage regulation value is greater than the AC line voltage peak of the photovoltaic inverter. In addition, it can be known from experience that the first bus voltage regulation value is smaller than the open circuit voltage of the photovoltaic cell when the photovoltaic grid-connected inverter turns off the maximum power tracking function, and the second bus voltage regulation value is greater than the open circuit voltage.

The first preset step size, the first current threshold value, the second time threshold value, and the second bus voltage regulation value are all determined by a plurality of tests according to relevant test data.

As shown in FIG. 3, when the irradiance is the first irradiance and the temperature is the first temperature, the current-voltage characteristic curve of the photovoltaic cell is curve 1 (Curve1), and the power-voltage characteristic curve is curve 2 (Curve2). Point A is the maximum power point or the maximum power point voltage tracking lower limit value, point B current is equal to the first current threshold Ipv_min, and point C voltage is the open circuit voltage of the photovoltaic cell when the irradiance is E1 and the temperature is T1. When the power at point A is less than the first power threshold, or the voltage at point A is less than the first voltage threshold, if the duration of the state reaches the first time threshold, it is determined that the active power at point A is too low, and the photovoltaic grid-connected inverter is turned off. The maximum power tracking function adjusts the working state of the photovoltaic cell from point A to point B, and stabilizes the bus voltage of the photovoltaic inverter at the voltage of point B, and disconnects when the stable duration reaches the second time threshold. Photovoltaic cell output and bus The voltage regulation value is adjusted to the second bus voltage regulation value.

In order to explain the magnitude relationship between the first bus voltage regulation value, the open circuit voltage, and the second bus voltage, the second bus voltage regulation value is indicated by D point in FIG. That is, as shown in FIG. 3, the first bus voltage regulation value is less than the C point voltage value, and the second bus voltage regulation value is greater than the C point voltage value.

In another aspect of the embodiment of the present invention, the switching process of the photovoltaic grid-connected inverter from the active power output mode to the reactive power compensation mode may be performed by a control loop of the bus voltage outer loop inductor current inner loop as shown in FIG. 4 . achieve. That is, the output state information (such as voltage and current) of the DC input side photovoltaic cell is sampled and analyzed, and sent to the maximum power tracking controller (MPPT controller), and the bus voltage regulation reference Vref is obtained according to the first switching condition. The difference between the bus voltage regulation reference Vref and the feedback voltage Udc collected from the bus model passes through the first regulator to obtain an output inductor current reference Iref. The difference between the inductor current reference Iref and the feedback current I collected from the inverter model passes through the second regulator, and a pulse width modulation (PWM) wave is output and sent to the inverter model.

In the control loop, when the difference between the bus voltage regulation reference Vref and the feedback voltage Udc changes, the duty ratio of the obtained PWM wave changes, and when the duty ratio of the PWM wave is stable, Stabilize the bus voltage near the bus regulation reference Vref. Therefore, the control loop enables static-free control of the bus voltage and the inductor current.

Wherein, when the bus voltage needs to be stabilized to the first bus voltage regulation value, the bus voltage regulation reference Vref is equal to the first bus voltage regulation value; when the bus voltage needs to be stabilized to the second bus voltage regulation value, the bus voltage regulation reference Vref is equal to the second bus regulation value.

Step 104: Acquire second output state information of the photovoltaic cell when the photovoltaic grid-connected inverter is in the reactive power compensation mode.

After the photovoltaic grid-connected inverter passes the switching process of step 103, the photovoltaic grid-connected inverter enters the reactive power compensation mode after the connection between the photovoltaic cell and the photovoltaic grid-connected inverter is disconnected. In this mode, the photovoltaic grid-connected inverter can be used to provide the required reactive power to the grid through the upper-level scheduling commands. That is, the photovoltaic grid-connected inverter can obtain a power scheduling instruction and adjust according to the power The degree command outputs reactive power.

In addition, in the embodiment of the present invention, when the photovoltaic grid-connected inverter is in the reactive power compensation mode, the output state information of the photovoltaic cell, such as an open circuit voltage, needs to be acquired in real time to determine whether the operation mode switching is needed.

Step 105: Determine whether the second output state information satisfies a second switching condition.

Among them, since the photovoltaic grid-connected inverter is in the reactive power compensation mode, the connection with the photovoltaic cell has been disconnected, and the open circuit voltage can be measured. Therefore, the second output state information may include an open circuit voltage of the photovoltaic cell.

Specifically, step 105 includes:

When the photovoltaic grid-connected inverter is in the reactive power compensation mode, as the external irradiance and temperature gradually increase, the open circuit voltage of the photovoltaic cell gradually increases, and when it increases to the second voltage threshold, the photovoltaic cell The power generation capability can meet the power generation capacity of the power grid, and the photovoltaic grid-connected inverter needs to be switched from the reactive power compensation mode to the active power output mode.

Step 106: When the second output state information meets the second switching condition, the photovoltaic grid-connected inverter is switched from the reactive power compensation mode to the active power output mode.

Specifically, step 106 includes:

Wherein, switching the photovoltaic grid-connected inverter from the reactive power compensation mode to the active power output mode requires restoring a connection between the photovoltaic cell and the photovoltaic grid-connected inverter. However, when the photovoltaic grid-connected inverter is in the reactive power compensation mode, the bus voltage is stabilized at the second bus voltage regulation value, and the voltage of the photovoltaic cell at this time is the open circuit voltage, and the second bus voltage regulation value is not Equal to the open circuit voltage of the photovoltaic cell at this time. Therefore, the voltage on both sides of the photovoltaic grid-connected inverter is not equal. If the connection between the photovoltaic cell and the photovoltaic grid-connected inverter is directly restored at this time, a current surge will occur. Therefore, before restoring the connection between the photovoltaic cell and the photovoltaic grid-connected inverter, it is necessary to stabilize the bus voltage at the open circuit voltage of the photovoltaic cell at this time.

In addition, in order to enable the photovoltaic grid-connected inverter to work normally after connecting the photovoltaic cells, it is also required to turn on when the output voltage and output power of the photovoltaic cells and the output power of the photovoltaic grid-connected inverter reach a preset threshold. The maximum power tracking function of the PV grid-connected inverter smoothly enters the active power output mode.

Wherein, the third time threshold is also determined in advance according to relevant test data after multiple tests.

As shown in FIG. 5, when the irradiance is the second irradiance and the temperature is the second temperature, the current-voltage characteristic curve of the photovoltaic cell is curve 3 (Curve3), and the power-voltage characteristic curve is curve 4 (Curve4). , point F is the open circuit voltage point at the current irradiation and battery temperature. Wherein, in order to conveniently explain the relationship between the second bus voltage regulation value and the open circuit voltage of the photovoltaic cell at this time, the second bus voltage regulation value is indicated by G point in FIG. 5.

When the voltage at point F is not less than the second voltage threshold, and the duration of the state reaches the third time threshold, it is determined that the photovoltaic power generation capacity satisfies the grid-connected power generation capability, and the bus voltage voltage is regulated from G. Adjust the point to point F, then restore the connection between the photovoltaic cell and the photovoltaic grid-connected inverter, and then turn on the maximum power tracking function of the photovoltaic grid-connected inverter, so that the working point of the photovoltaic cell is adjusted from point F to point E. .

In another aspect of the embodiment of the present invention, the switching process of the photovoltaic grid-connected inverter from the reactive power compensation mode to the active power output mode may be performed by a control loop of the bus voltage outer loop inductor current inner loop as shown in FIG. 6 . achieve. That is, the DC input side photovoltaic cell voltage and current information (for example, open circuit voltage) is sampled and analyzed, and the bus regulation reference Vref is given according to the second switching condition. The difference between the bus voltage regulation reference Vref and the feedback voltage Udc collected from the bus model passes through the first regulator to obtain an output inductor current reference Iref. The difference between the inductor current reference Iref and the feedback current I collected from the inverter model passes through the second regulator, and a pulse width modulation (PWM) wave is output and sent to the inverter model.

In the control loop, when the difference between the bus voltage regulation reference Vref and the feedback voltage Udc changes, the duty ratio of the obtained PWM wave changes, and when the duty ratio of the PWM wave is stable, Stabilize the bus voltage near the bus regulation reference Vref. When the duty cycle of the PWM wave is stable, after the connection between the photovoltaic cell and the photovoltaic and the inverter is restored, the voltage and current of the photovoltaic cell are sent to the MPPT.

Wherein, in the process of switching from the reactive power compensation mode to the active power output mode, the bus voltage needs to be stabilized at the third bus voltage regulation value, where the bus voltage regulation reference Vref is equal to the third bus voltage regulation value.

In summary, the embodiment of the present invention increases the nighttime reactive power compensation mode and can realize the working mode of the photovoltaic grid-connected inverter on the basis of the active power output mode in the daytime compared with the prior art. Seamless and smooth switching between these two modes of operation. That is, as shown in Figure 2, during the day, it is in the active power output mode. In the evening, it is judged whether the first switching condition is satisfied. If it is satisfied, it switches to the reactive power compensation mode; at night, it enters the reactive power compensation mode, and in the morning, it determines whether it is Satisfying the second switching condition, if it is satisfied, switching to the active power output mode to achieve photovoltaic The network inverter does not stop working for 24 hours a day.

In addition, the photovoltaic grid-connected inverter outputs active power and reactive power according to the control strategy as shown in FIG. 7 during the above work. That is, during the active power output mode during the day, the active power corresponds to the d-axis inductor current reference Idref, and the reactive power corresponds to the q-axis inductor current reference Iqref. In this mode, the bus voltage regulation reference Vref is the maximum power tracking controller output of the photovoltaic cell, the photovoltaic cell generates electricity, the energy flows to the grid, and the grid active current feedback Id>0. Wherein, the difference between the Vref and the feedback voltage Udc passes through the first regulator, and the output inductor current refers to the Idref, and the difference between the Idref and the grid active current feedback Id is passed through the second regulator. Iqref is determined by the upper layer scheduling. If Iqref>0, the inverter outputs reactive power, Iqref<0, the inverter absorbs reactive power, and Iqref and grid reactive current feedback Iq pass through the second regulator. The second regulator output is modulated by a PWM to generate a PWM wave.

In the night reactive power compensation mode, the d-axis inductor current reference Idref is 0, and the reactive power corresponds to the q-axis inductor current reference Iqref. Vref is determined by the second switching condition, the grid energy rectification maintains the bus voltage, and the grid active current feedback Id<0; the difference between Id and Idref is passed through the second regulator; Iqref is determined by the upper layer scheduling, if Iqref>0, the inverter output Reactive power, Iqref<0, the inverter absorbs reactive power, and the difference between Iqref and grid reactive current feedback Iq is passed through the second regulator. The second regulator output is modulated by a PWM to generate a PWM wave. Since most of the photovoltaic power plants require reactive power for inductive loads, the inverter is capacitive and outputs reactive power when nighttime reactive power compensation.

Second embodiment

Embodiments of the present invention provide a reactive power compensation device for a photovoltaic grid-connected inverter. As shown in FIG. 8, the device 800 includes:

The first obtaining module 801 is configured to acquire first output state information of the photovoltaic cell when the photovoltaic grid-connected inverter is in the active power output mode;

The first determining module 802 is configured to determine whether the first output state information acquired by the first acquiring module 801 meets the first switching condition;

The first switching module 803 is configured to: when the first determining module 802 determines the first output When the status information satisfies the first switching condition, the photovoltaic grid-connected inverter is switched from the active power output mode to the reactive power compensation mode;

The second obtaining module 804 is configured to acquire second output state information of the photovoltaic cell when the first switching module 803 switches the photovoltaic grid-connected inverter to be in a reactive power compensation mode;

The second determining module 805 is configured to determine whether the second output state information acquired by the second acquiring module 804 meets the second switching condition;

The second switching module 806 is configured to: when the second determining module 805 determines that the second output state information meets the second switching condition, the photovoltaic grid-connected inverter is removed from the reactive power compensation mode Switch to the active power output mode.

As an embodiment, the first output state information includes an output power or an output voltage of the photovoltaic cell. As shown in FIG. 9, the first determining module 802 includes:

The first determining unit 8021 is configured to determine, when the output power of the photovoltaic cell is less than the first power threshold, whether the first time duration that the output power of the photovoltaic cell is less than the first power threshold reaches a first time threshold. And if the first duration reaches the first time threshold, the first output state information satisfies the first switching condition; or

The second determining unit 8022 is configured to determine, when the output voltage of the photovoltaic cell is less than the first voltage threshold, whether the output voltage of the photovoltaic cell is less than the second duration of the first voltage threshold a time threshold, wherein the first output state information satisfies the first switching condition if the second duration reaches the first time threshold.

As an implementation manner, as shown in FIG. 9, the first switching module 803 includes:

The closing unit 8031 is configured to turn off a maximum power tracking function of the photovoltaic grid-connected inverter;

The first adjusting unit 8032 is configured to: after the closing unit 8031 turns off the maximum power tracking function of the photovoltaic grid-connected inverter, gradually increase the output voltage of the photovoltaic cell according to the first preset step size until the When the output current of the photovoltaic cell reaches the first current threshold, stopping increasing the output voltage of the photovoltaic cell and recording the current output voltage of the photovoltaic cell as the first Bus voltage regulation value;

The second adjusting unit 8033 is configured to adjust a bus voltage of the photovoltaic grid-connected inverter to stabilize the bus voltage to the first bus voltage regulation value;

The first control unit 8034 is configured to disconnect the photovoltaic cell and the photovoltaic grid-connected inverter when the voltage value of the bus voltage is stable for a duration of the first bus voltage regulation value to reach a second time threshold Connection between devices;

The third adjusting unit 8035 is configured to adjust a bus voltage of the photovoltaic grid-connected inverter to stabilize the bus voltage to a second bus voltage regulation value, and the photovoltaic grid-connected inverter enters the reactive power compensation mode;

As an embodiment, the second output state information includes an open circuit voltage of the photovoltaic cell. As shown in FIG. 9, the second determining module 805 includes:

The third determining unit 8051 is configured to determine, when the open circuit voltage is greater than or equal to the second voltage threshold, whether the third time duration that the open circuit voltage is greater than or equal to the second voltage threshold reaches a third time threshold, if And the third time duration reaches the third time threshold, and the second output state information satisfies the second switching condition.

As an implementation manner, as shown in FIG. 9, the second switching module 806 includes:

The fourth adjusting unit 8061 is configured to use the open circuit voltage as a third bus voltage regulation value, and adjust a bus voltage of the photovoltaic grid-connected inverter to stabilize the third bus voltage regulation value;

a second control unit 8062, configured to restore a connection between the photovoltaic cell and the photovoltaic grid-connected inverter;

The third obtaining unit 8063 is configured to acquire a current output power and a current output voltage of the photovoltaic cell and a current output power of the photovoltaic grid-connected inverter;

The starting unit 8064 is configured to: when the current output power of the photovoltaic cell is greater than or equal to the first power threshold, and the current output voltage of the photovoltaic cell is greater than or equal to the first power When the threshold value is pressed, and the current output power of the photovoltaic grid-connected inverter is less than or equal to the second power threshold, the photovoltaic grid-connected inverter starts the maximum power tracking function and enters the active power output mode.

As an embodiment, as shown in FIG. 9, the device further includes:

The scheduling module 807 is configured to: when the photovoltaic grid-connected inverter is in the reactive power compensation mode, acquire a power scheduling instruction, and output reactive power according to the power scheduling instruction.

The reactive power compensation device of the embodiment of the invention can use the photovoltaic grid-connected inverter to provide the required reactive power for the power grid at night, and can automatically switch between the active power output mode and the reactive power compensation mode, effectively solving the problem. The capacity waste and cost increase problems and defects introduced by photovoltaic power plant reactive power compensation devices.

Third embodiment

Embodiments of the present invention provide a photovoltaic grid-connected inverter comprising the reactive power compensation device of the photovoltaic grid-connected inverter described above.

In the several embodiments provided by the present invention, it should be understood that the disclosed method and apparatus may be implemented in other manners. The device embodiments described above are merely illustrative. For example, the division of the modules is only a logical function division. In actual implementation, there may be another division manner, for example, multiple modules or components may be combined, or Can be integrated into another system, or some features can be ignored or not executed. In addition, the communication connections between the various components shown or discussed may be indirect coupling or communication connections through some interfaces, devices or modules, and may be electrical, mechanical or otherwise.

The modules described above as separate components may or may not be physically separated. The components displayed as modules may or may not be physical modules, that is, may be located in one place or distributed to multiple network modules; Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the embodiment.

In addition, each functional module in each embodiment of the present invention may be integrated into one processing module. In the block, each module may be separately used as one module, or two or more modules may be integrated into one module; the integrated module may be implemented in the form of hardware or a hardware plus software function module. Formal realization.

It will be understood by those skilled in the art that all or part of the steps of implementing the foregoing method embodiments may be performed by hardware related to program instructions. The foregoing program may be stored in a computer readable storage medium, and when executed, the program includes The foregoing steps of the method embodiment; and the foregoing storage medium includes: a removable storage device, a read-only memory (ROM), a magnetic disk or an optical disk, and the like, which can store program codes.

Alternatively, the above-described integrated module of the embodiment of the present invention may be stored in a computer readable storage medium if it is implemented in the form of a software function module and sold or used as a stand-alone product. Based on such understanding, the technical solution of the embodiments of the present invention may be embodied in the form of a software product in essence or in the form of a software product stored in a storage medium, including a plurality of instructions. A computer device (which may be a personal computer, server, or network device, etc.) is caused to perform all or part of the methods described in various embodiments of the present invention. The foregoing storage medium includes various media that can store program codes, such as a mobile storage device, a ROM, a magnetic disk, or an optical disk.

The memory switching method and apparatus described in the embodiments of the present invention are only exemplified by the foregoing embodiments, but are not limited thereto, and those skilled in the art should understand that the technical solutions described in the foregoing embodiments may still be modified. Equivalent replacement of some or all of the technical features may be made without departing from the scope of the technical solutions of the embodiments of the present invention.

The above is only the preferred embodiment of the present invention and is not intended to limit the scope of the present invention.

Industrial applicability

The technical solution of the embodiment of the invention can utilize the photovoltaic grid-connected inverter to provide the grid at night The required reactive power can be automatically switched between the active power output mode and the reactive power compensation mode, which effectively solves the problem of capacity waste and cost increase introduced by the photovoltaic power plant reactive power compensation device.

Claims

A reactive power compensation method includes:

Obtaining first output state information of the photovoltaic cell when the photovoltaic grid-connected inverter is in an active power output mode;

Determining whether the first output state information satisfies a first switching condition;

Switching the photovoltaic grid-connected inverter from the active power output mode to a reactive power compensation mode when the first output state information satisfies the first switching condition;

Obtaining second output state information of the photovoltaic cell when the photovoltaic grid-connected inverter is in the reactive power compensation mode;

Determining whether the second output state information satisfies a second switching condition;

When the second output state information satisfies the second switching condition, the photovoltaic grid-connected inverter is switched from the reactive power compensation mode to the active power output mode.
The method of claim 1, wherein the first output state information comprises an output power or an output voltage of the photovoltaic cell, and the step of determining whether the first output state information satisfies a first switching condition comprises :

When the output power of the photovoltaic cell is less than the first power threshold, determining whether the output power of the photovoltaic cell is less than the first time duration that the first power threshold continues to reach the first time threshold, if the first duration reaches The first time threshold, the first output state information satisfies the first switching condition; or

When the output voltage of the photovoltaic cell is less than the first voltage threshold, determining whether the output voltage of the photovoltaic cell is less than a second duration that the first voltage threshold continues to reach the first time threshold, if the second When the duration reaches the first time threshold, the first output state information satisfies the first switching condition.
The method of claim 2, wherein the switching the photovoltaic grid-connected inverter from the active power output mode to the reactive power compensation mode comprises:

Turning off the maximum power tracking function of the photovoltaic grid-connected inverter;

Stepping up the output voltage of the photovoltaic cell according to the first preset step, until the output current of the photovoltaic cell reaches the first current threshold, stopping increasing the output voltage of the photovoltaic cell, and The current output voltage of the battery is recorded as the first bus voltage regulation value;

Adjusting a bus voltage of the photovoltaic grid-connected inverter to stabilize the bus voltage at the first bus voltage regulation value;

Disconnecting the connection between the photovoltaic cell and the photovoltaic grid-connected inverter when the voltage value of the bus voltage is stable when the duration of the first bus voltage regulation reaches a second time threshold;

Adjusting a bus voltage of the photovoltaic grid-connected inverter to stabilize the bus voltage to a second bus voltage regulation value, and the photovoltaic grid-connected inverter enters the reactive power compensation mode;

The second bus voltage regulation value is greater than the AC line voltage peak of the photovoltaic inverter.
The method of claim 3 wherein said second output state information comprises an open circuit voltage of said photovoltaic cell;

The step of determining whether the second output state information meets the second switching condition comprises:

When the open circuit voltage is greater than or equal to the second voltage threshold, determining whether the third time duration that the open circuit voltage is greater than or equal to the second voltage threshold reaches a third time threshold, if the third duration reaches the The third time threshold, the second output state information satisfies the second switching condition.
The method of claim 4, wherein the switching the photovoltaic grid-connected inverter from the reactive power compensation mode to the active power output mode comprises:

Using the open circuit voltage as a third bus voltage regulation value, and adjusting a bus voltage of the photovoltaic grid-connected inverter to stabilize the third bus voltage regulation value;

Recovering a connection between the photovoltaic cell and the photovoltaic grid-connected inverter;

Obtaining a current output power and a current output voltage of the photovoltaic cell and a current output power of the photovoltaic grid-connected inverter;

When the current output power of the photovoltaic cell is greater than or equal to the first power threshold, and the current output voltage of the photovoltaic cell is greater than or equal to the first voltage threshold, and the current output of the photovoltaic grid-connected inverter When the power is less than or equal to the second power threshold, the photovoltaic grid-connected inverter starts the maximum power tracking function and enters the active power output mode.
The method of claim 1 wherein the method further comprises:

When the photovoltaic grid-connected inverter is in the reactive power compensation mode, a power scheduling instruction is acquired, and reactive power is output according to the power scheduling instruction.
A reactive power compensation device includes:

a first acquiring module configured to acquire first output state information of the photovoltaic cell when the photovoltaic grid-connected inverter is in an active power output mode;

The first determining module is configured to determine whether the first output state information acquired by the first acquiring module meets the first switching condition;

a first switching module, configured to: when the first determining module determines that the first output state information meets the first switching condition, switch the photovoltaic grid-connected inverter from the active power output mode to none Power compensation mode;

a second acquiring module, configured to acquire second output state information of the photovoltaic cell when the first switching module switches the photovoltaic grid-connected inverter in a reactive power compensation mode;

a second determining module, configured to determine whether the second output state information acquired by the second acquiring module meets a second switching condition;

a second switching module, configured to switch the photovoltaic grid-connected inverter from the reactive power compensation mode to when the second determining module determines that the second output state information meets the second switching condition The active power output mode.
The apparatus according to claim 7, wherein the first output state information comprises an output power or an output voltage of the photovoltaic cell, and the first determining module comprises:

a first determining unit configured to: when an output power of the photovoltaic cell is less than a first power threshold And determining, by the first time threshold that the output power of the photovoltaic cell is less than the first power threshold, the first time threshold is reached, and if the first time duration reaches the first time threshold, the first output is The status information satisfies the first switching condition; or

a second determining unit, configured to determine, when the output voltage of the photovoltaic cell is less than the first voltage threshold, determining whether the output voltage of the photovoltaic cell is less than the second duration that the first voltage threshold continues to reach the first time a threshold, if the second duration reaches the first time threshold, the first output state information satisfies the first switching condition.
The apparatus of claim 8, wherein the first switching module comprises:

a shutdown unit configured to turn off a maximum power tracking function of the photovoltaic grid-connected inverter;

a first adjusting unit, configured to: after the closing unit turns off the maximum power tracking function of the photovoltaic grid-connected inverter, gradually increase the output voltage of the photovoltaic cell according to the first preset step, until the photovoltaic When the output current of the battery reaches the first current threshold, stopping increasing the output voltage of the photovoltaic cell, and recording the current output voltage of the photovoltaic cell as the first bus voltage regulation value;

a second adjusting unit, configured to adjust a bus voltage of the photovoltaic grid-connected inverter, so that the bus voltage is stabilized at the first bus voltage regulation value;

a first control unit configured to disconnect the photovoltaic cell and the photovoltaic grid-connected inverter when a voltage value of the bus voltage is stable for a duration of the first bus voltage regulation value to reach a second time threshold the connection between;

a third adjusting unit configured to adjust a bus voltage of the photovoltaic grid-connected inverter to stabilize the bus voltage to a second bus voltage regulation value, and the photovoltaic grid-connected inverter enters the reactive power compensation mode ;

The second bus voltage regulation value is greater than the AC line voltage peak of the photovoltaic inverter.
The apparatus of claim 9, wherein the second output state information comprises an open circuit voltage of the photovoltaic cell, and the second determining module comprises:

a third determining unit configured to: when the open circuit voltage is greater than or equal to a second voltage threshold, Determining whether the third duration that the open circuit voltage is greater than or equal to the second voltage threshold reaches a third time threshold, and if the third duration reaches the third time threshold, the second output state information is satisfied. The second switching condition.
The apparatus of claim 10, wherein the second switching module comprises:

a fourth adjusting unit configured to use the open circuit voltage as a third bus voltage regulation value, and adjust a bus voltage of the photovoltaic grid-connected inverter to stabilize the third bus voltage regulation value;

a second control unit configured to restore a connection between the photovoltaic cell and the photovoltaic grid-connected inverter;

a third acquiring unit, configured to acquire a current output power and a current output voltage of the photovoltaic cell and a current output power of the photovoltaic grid-connected inverter;

a startup unit configured to: when a current output power of the photovoltaic cell is greater than or equal to the first power threshold, and a current output voltage of the photovoltaic cell is greater than or equal to the first voltage threshold, and the photovoltaic grid-connected inverse When the current output power of the transformer is less than or equal to the second power threshold, the photovoltaic grid-connected inverter starts the maximum power tracking function and enters the active power output mode.
The apparatus of claim 7 wherein said apparatus further comprises:

The scheduling module is configured to: when the photovoltaic grid-connected inverter is in the reactive power compensation mode, acquire a power scheduling instruction, and output reactive power according to the power scheduling instruction.
A photovoltaic grid-connected inverter comprising the reactive power compensation device according to any one of claims 7 to 12.
A computer storage medium having computer executable instructions stored therein, the computer executable instructions being configured to perform the reactive power compensation method of any one of claims 1 to 6.