WO2021082481A1

WO2021082481A1 - Current sharing control method and inverter

Info

Publication number: WO2021082481A1
Application number: PCT/CN2020/098003
Authority: WO
Inventors: 金哲铭; 刘方诚; 王雄飞; 石荣亮
Original assignee: 华为技术有限公司
Priority date: 2019-10-30
Filing date: 2020-06-24
Publication date: 2021-05-06
Also published as: CN112751356A; CN112751356B

Abstract

Disclosed are a current sharing control method and an inverter. The method comprises: an inverter acquiring a voltage signal and a current signal output by itself; determining the active power according to the voltage signal and the current signal, and determining, on the basis of an active-frequency droop control policy, a reference phase corresponding to the active power; determining an alternating-current voltage drop according to the current signal and a preset virtual impedance; according to the reference phase, transforming the alternating-current voltage drop into a synchronous rotating coordinate system to obtain a direct-current voltage drop; regulating the direct-current voltage drop, and determining, according to the regulated direct-current voltage drop, a voltage vector amplitude value and a voltage vector phase angle; determining a voltage phase reference value according to the reference phase and the voltage vector phase angle, and transforming, according to the voltage vector amplitude value and the voltage phase reference value, into a static coordinate system to obtain a target alternating-current voltage; and regulating its own output voltage according to the target alternating-current voltage. Therefore, the current sharing control over each distributed power source in a distributed power generation system is realized.

Description

Current sharing control method and inverter

This application claims the priority of a Chinese patent application filed with the Chinese Patent Office on October 30, 2019, the application number is 201911046886.2, and the application name is "a current sharing control method and inverter", the entire content of which is incorporated by reference In this application.

Technical field

This application relates to the field of distributed power generation technology, and in particular to a current sharing control method and an inverter.

Background technique

Distributed power generation system refers to a power system in which multiple small power generation equipment is jointly networked to supply power to the load. Small power generation equipment includes but is not limited to photovoltaic power generation equipment, electric energy storage equipment, fuel cell equipment, and micro cogeneration equipment These small power generation equipment can be deployed in a flexible manner and do not need to be centrally arranged. They are also called distributed power sources. Figure 1 is a schematic structural diagram of an exemplary distributed power generation system. As shown in Figure 1, each distributed power source is connected to a common connection point (point of common coupling, PCC) through an independent transmission and distribution line to supply power to the system load. The system load can be a centralized load or a distributed load.

In a distributed power generation system, the distributed power sources jointly maintain the stable operation of the system, that is, the total active power and total reactive power input by each distributed power source are respectively equal to the total active power and total reactive power consumed by the transmission and distribution lines and system loads , Thereby avoiding system instability due to deviation between input power and output power. On this basis, in order to further improve the overall performance of the distributed power generation system, it is also necessary to perform current sharing control on each distributed power source, that is, to ensure the equal distribution of active power and reactive power among the distributed power sources.

At present, related technologies mainly implement current sharing control for each distributed power source in the following ways: a current sharing controller is provided for each distributed power source in the distributed power generation system, and the current sharing controller collects the inverse of the series connection with the distributed power source. The active power and reactive power output by the converter are determined based on the active-frequency droop control to determine the desired frequency ω, based on the reactive-voltage droop control to determine the desired voltage amplitude E, and then through the voltage control unit and the pulse width modulation unit to control the inverter The generator generates an AC voltage with a frequency of ω and an amplitude of E. However, this implementation method is usually difficult to achieve a good current sharing control for reactive power. The reason is that the reactive power of distributed power sources is related to the voltage of the access point, and is affected by actual environmental conditions in practical applications. There are usually large differences in the impedance of the transmission and distribution lines between the access points of the distributed power sources and the PCC, which will result in large differences in the voltages of the access points of the distributed power sources, so it is impossible to achieve a better response to the reactive power. Power current sharing control.

In summary, how to effectively realize the current sharing control of the distributed power sources in the distributed power generation system has become an urgent problem to be solved at present.

Summary of the invention

The embodiments of the present application provide a current sharing control method and an inverter, which can effectively perform current sharing control on each distributed power source in a distributed power generation system.

In view of this, the first aspect of the present application provides a current sharing control method, which is applied to a distributed power generation system. The distributed power generation system includes a distributed power supply and an inverter supporting the distributed power supply. The generator is connected to the public connection point through its corresponding transmission and distribution line to supply power to the load in the distributed power generation system. In practical applications, the inverter in the distributed power generation system adjusts its own output voltage through the current sharing control method provided in the embodiments of the present application, so as to realize current sharing control for the distributed power supply.

Specifically, the current sharing control method includes: the inverter obtains the voltage signal and current signal output by itself; determines the active power according to the obtained voltage signal and current signal, and determines the corresponding active power based on the active-frequency droop control strategy Determine the AC voltage drop according to the current signal and the preset virtual impedance; then, according to the reference phase, transform the AC voltage drop to the synchronous rotating coordinate system to obtain the DC voltage drop, adjust the DC voltage drop, and adjust according to The subsequent DC voltage drop determines the voltage vector amplitude and voltage vector phase angle; furthermore, determines the voltage phase reference value according to the reference phase and voltage vector phase angle; transforms the voltage vector amplitude and voltage phase reference value to the stationary coordinate system to obtain the target AC Voltage; Finally, adjust its output voltage according to the target AC voltage.

In the above current sharing control method, in the process of current sharing control, the influence caused by the impedance of the transmission and distribution line is suppressed by means of equivalent series virtual impedance, so as to improve the current sharing control accuracy of reactive power. In addition, in order to ensure the accuracy of current-sharing control while ensuring that the voltage does not drop significantly, the current-sharing control method provided in this application further transforms the voltage control component generated by the series virtual impedance to a synchronous rotating coordinate system to realize active and reactive power components. Component decoupling, after adjusting the DC voltage drop obtained by decoupling, the target AC voltage used to adjust the inverter output voltage is obtained through the synthesis of the voltage vector, thereby realizing the effect of the equivalent series virtual impedance. The pressure drop compensation ensures the power supply reliability of the distributed power generation system while ensuring the current sharing control accuracy of the distributed power generation system.

In addition, compared to the implementation of current sharing control of the inverter by using an independent host computer, the current sharing control method provided in this application directly uses the inverter itself to achieve current sharing control, without the need for an additional inverter and host computer. Therefore, it can avoid the influence of the communication system failure or delay on the current sharing control performance. In addition, when the distributed power generation system is expanded, the "plug and play" of distributed power can be realized, that is, the distributed power and inverter can be directly connected to the distributed power generation system to achieve capacity expansion without adding a host computer. There is no need to arrange the communication line between the host computer and the inverter; accordingly, when the distributed power source is cut out from the distributed power generation system, there is no need to change the communication line, which is the access and cut out of the distributed power source. Brought great convenience.

In the first implementation manner of the first aspect of the embodiments of the present application, the DC voltage drop obtained by the inverter transforming the AC voltage drop to the synchronous rotating coordinate system includes a d-axis component and a q-axis component. Accordingly, the inverter may Adjust the d-axis component and the q-axis component separately; furthermore, determine the voltage vector amplitude according to the preset reference voltage vector, the adjusted d-axis component and the adjusted q-axis component; according to the reactive component in the reference voltage vector , The adjusted d-axis component and the adjusted q-axis component determine the phase angle of the voltage vector.

In this way, by separately adjusting the d-axis component and the q-axis component, the decoupling of the active and reactive components can be adjusted; based on the preset reference voltage vector, the adjusted d-axis component and the adjusted q-axis The components respectively determine the voltage vector amplitude and the voltage vector phase angle required for the subsequent synthesis of the target AC voltage, thereby effectively preventing the voltage drop caused by the equivalent series virtual impedance and ensuring the stability of the distributed power generation system.

In the second implementation manner of the first aspect of the embodiments of the present application, when the distributed power generation system applied to the current sharing control method provided in the embodiments of the present application is a three-phase AC distributed power generation system, the voltage output by the inverter is The signal is a three-phase AC voltage signal, and the current signal output by the inverter is a three-phase AC current signal. At this time, the inverter can be equivalently connected in series with the virtual impedance in the following way: that is, the product of the current signal and the preset virtual impedance matrix is calculated to obtain the three-phase AC voltage drop as the above-mentioned AC voltage drop, where the preset virtual impedance matrix is 3 *3 Matrix; further, according to the reference phase, the three-phase AC voltage drop is transformed to the synchronous rotating coordinate system to obtain the corresponding DC voltage drop.

In this way, by calculating the product of the three-phase AC current signal and the preset virtual impedance matrix with a size of 3*3, the equivalent series of virtual impedances are realized, thereby suppressing the reactive power adjustment caused by the impedance of the transmission and distribution lines in the distributed power generation system. Impact, improve the current-sharing control accuracy of reactive power in the three-phase AC distributed power generation system.

In the third implementation manner of the first aspect of the embodiments of the present application, when the distributed power generation system applied to the current sharing control method provided in the embodiments of the present application is a three-phase AC distributed power generation system, the voltage output by the inverter is The signal is a three-phase AC voltage signal, and the current signal output by the inverter is a three-phase AC current signal. At this time, the inverter can connect the virtual impedance in series in the following way: first transform the current signal to a two-phase stationary coordinate system to obtain a two-phase AC current signal, and then calculate the product of the two-phase AC signal and the preset virtual impedance matrix to obtain two The phase AC voltage drop is used as the aforementioned AC voltage drop, and the preset virtual impedance matrix here is a 2*2 matrix; further, the two-phase AC voltage drop is transformed into a synchronous rotating coordinate system according to the reference phase to obtain the corresponding DC voltage drop.

In this way, the two-phase AC current signal is obtained by transforming the three-phase AC current signal to the two-phase static coordinate system, and then the product of the two-phase AC current signal and the large-scale 2*2 preset virtual impedance matrix is calculated to realize the virtual impedance. Effective series connection, thereby suppressing the influence of the impedance of the transmission and distribution lines in the distributed power generation system on the reactive power adjustment, and improving the current-sharing control accuracy of the reactive power in the three-phase AC distributed power generation system.

In the fourth implementation manner of the first aspect of the embodiments of the present application, the preset virtual impedance matrix mentioned in the foregoing second implementation manner and the third implementation manner may be a diagonal matrix. The diagonal element is determined according to the preset virtual impedance, and the preset virtual impedance is greater than the impedance of the transmission and distribution line between the access point of any inverter in the distributed power generation system and the PCC.

In this way, by setting the preset virtual impedance to be greater than the impedance of the transmission and distribution line between the access point of any inverter in the distributed power generation system and the PCC, the method of ensuring the equivalent series virtual impedance can more effectively suppress the distributed power generation The influence of the impedance of the transmission and distribution line in the system on the reactive power adjustment, that is, when the preset virtual impedance is set large enough, the influence of the impedance of the transmission and distribution line in the distributed power generation system is almost negligible, thereby improving the distribution Control precision of reactive power current sharing in power generation system.

In the fifth implementation manner of the first aspect of the embodiments of the present application, the inverter may determine the reference phase for adjusting the active power in the following manner: determine the reference frequency corresponding to the active power according to the preset active-frequency droop curve ; And then integrate the reference frequency to obtain the corresponding reference phase. That is, the inverter will bring the active power calculated according to its own output voltage signal and current signal into the preset active-frequency droop control curve to determine the corresponding frequency of the active power on the active-frequency droop control curve as Reference frequency, and then integrate the reference frequency to obtain the corresponding reference phase.

Since the frequencies of different nodes in the same distributed power generation system are basically the same, determining the reference phase for generating the target AC voltage through the above method can effectively ensure the current sharing control accuracy for the active power.

In the sixth implementation manner of the first aspect of the embodiments of the present application, the inverter can adjust its output voltage according to the target AC voltage in the following manner: generate the target control according to the deviation between the target AC voltage and the AC signal output by itself. Signal, and further generate a drive signal according to the target control signal, and use the drive signal to control the turning on and off of the semiconductor in the inverter, thereby adjusting the output target AC voltage of the inverter.

In the seventh implementation manner of the first aspect of the embodiments of the present application, the inverter can adopt a single closed-loop control method to generate the target control signal, that is, the inverter can directly generate the target control signal according to the difference between the target AC voltage and the voltage signal output by itself. Deviation, based on the voltage proportional resonance (proportion resonant, PR) control strategy to generate the target control signal.

In the eighth implementation manner of the first aspect of the embodiments of the present application, in order to further improve the control efficiency, the inverter can adopt a double closed-loop control method to generate the target control signal, that is, the inverter can firstly generate the target control signal according to the target AC voltage and its own output Based on the deviation between the voltage signals of the voltage PR control strategy, a basic control signal is generated, and then based on the deviation between the basic control signal and the current signal output by the inverter, the target control signal is generated based on the current PR control strategy.

The second aspect of the present application provides an inverter, the input end of the inverter is connected to the distributed power source in the distributed power generation system, and the output end of the inverter is connected to the corresponding transmission and distribution line Common connection point; the inverter includes:

A sampling unit for acquiring the voltage signal and current signal output by the inverter;

An active current sharing control unit, configured to determine active power according to the voltage signal and the current signal, and determine a reference phase according to the active power based on an active-frequency droop control strategy;

A virtual impedance compensation unit, configured to determine an AC voltage drop according to the current signal and a preset virtual impedance;

The voltage vector adjustment unit is configured to transform the AC voltage drop to a synchronous rotating coordinate system according to the reference phase to obtain a DC voltage drop; adjust the DC voltage drop, and determine the voltage vector amplitude according to the adjusted DC voltage drop Value and voltage vector phase angle;

A voltage vector synthesis unit, configured to determine a voltage phase reference value according to the reference phase and the voltage vector phase angle; transform to a stationary coordinate system according to the voltage vector amplitude and the voltage phase reference value to obtain a target AC voltage;

The adjusting unit is configured to adjust the output voltage of the inverter according to the target AC voltage.

In the first implementation manner of the second aspect of the embodiments of the present application, the DC voltage drop includes: a d-axis component and a q-axis component; then the voltage vector adjustment unit is specifically configured to:

The d-axis component and the q-axis component are adjusted separately, and the voltage vector amplitude is determined according to the preset reference voltage vector, the adjusted d-axis component, and the adjusted q-axis component; and according to the reference voltage The reactive component in the vector, the adjusted d-axis component, and the adjusted q-axis component determine the voltage vector phase angle.

In the second implementation manner of the second aspect of the embodiments of the present application, when the distributed power generation system is a three-phase AC distributed power generation system, the voltage signal is a three-phase AC voltage signal, and the current signal is a three-phase AC voltage signal. Phase alternating current signal; the virtual impedance compensation unit is specifically used for:

Calculating the product of the current signal and a preset virtual impedance matrix to obtain a three-phase AC voltage drop as the AC voltage drop; the preset virtual impedance matrix is a 3*3 matrix;

Then the voltage vector adjustment unit is specifically used for:

The three-phase AC voltage drop is transformed into a synchronous rotating coordinate system according to the reference phase to obtain the DC voltage drop.

In the third implementation manner of the second aspect of the embodiments of the present application, when the distributed power generation system is a three-phase AC distributed power generation system, the voltage signal is a three-phase AC voltage signal, and the current signal is a three-phase AC voltage signal. Phase alternating current signal; the virtual impedance compensation unit is specifically used for:

Transforming the current signal to a two-phase stationary coordinate system to obtain a two-phase alternating current signal;

Calculating the product of the two-phase AC current signal and a preset virtual impedance matrix to obtain a two-phase AC voltage drop as the AC voltage drop; the preset virtual impedance matrix is a 2*2 matrix;

Then the voltage vector adjustment unit is specifically used for:

The two-phase AC voltage drop is transformed into a synchronous rotating coordinate system according to the reference phase to obtain the DC voltage drop.

In a fourth implementation manner of the second aspect of the embodiments of the present application, the preset virtual impedance matrix is a diagonal matrix, and diagonal elements of the preset virtual impedance matrix are determined according to the preset virtual impedance The preset virtual impedance is greater than the impedance of the transmission and distribution line between the access point of the inverter and the public access point in the distributed power generation system.

In the fifth implementation manner of the second aspect of the embodiments of the present application, the active power current sharing control unit is specifically configured to:

The reference frequency corresponding to the active power is determined according to a preset active power-frequency droop curve; and the reference phase is obtained by integrating the reference frequency.

In a sixth implementation manner of the second aspect of the embodiments of the present application, the adjustment unit includes:

A control signal generating subunit, configured to generate a target control signal according to the deviation between the target AC voltage and the AC signal output by the inverter;

The modulation subunit is configured to generate a drive signal according to the target control signal, and use the drive signal to control the on and off of the semiconductor switch in the inverter, so that the inverter outputs the target AC voltage.

In a seventh implementation manner of the second aspect of the embodiments of the present application, the control signal generation subunit includes:

The first voltage adjustment module is configured to generate the target control signal based on a voltage proportional resonance control strategy according to the deviation between the target AC voltage and the voltage signal output by the inverter.

In an eighth implementation manner of the second aspect of the embodiments of the present application, the control signal generation subunit includes:

The second voltage adjustment module is configured to generate a basic control signal based on a voltage proportional resonance control strategy according to the deviation between the target AC voltage and the voltage signal output by the inverter;

The current adjustment module is configured to generate the target control signal based on a current proportional resonance control strategy according to the deviation between the basic control signal and the current signal output by the inverter.

Description of the drawings

Figure 1 is a schematic structural diagram of an exemplary distributed power generation system;

Figure 2 is a schematic diagram of another exemplary distributed power generation system;

Fig. 3 is a schematic diagram of the structure of the power supply side of an exemplary three-phase AC distributed power generation system;

Figure 4 is a schematic diagram of the implementation architecture of the current sharing control method in related technologies;

Figure 5 is a schematic diagram of the active power-frequency droop control curve and the reactive power-voltage droop control curve;

Figure 6 is a schematic diagram of the reactive power-voltage droop control curve;

FIG. 7 is a schematic flowchart of a current sharing control method provided by an embodiment of the application;

FIG. 8 is a schematic diagram of an implementation architecture of a current sharing control method provided by an embodiment of the application;

FIG. 9 is a schematic diagram of another implementation architecture of the current sharing control method provided by an embodiment of the application;

Fig. 10 is a schematic structural diagram of yet another exemplary distributed power generation system;

Figure 11 is a graph of power changes obtained through experiments;

Figure 12 is a graph of voltage changes obtained through experiments;

FIG. 13 is a schematic structural diagram of an inverter provided by an embodiment of the application.

Detailed ways

In order to enable those skilled in the art to better understand the solution of the application, the technical solutions in the embodiments of the application will be clearly and completely described below in conjunction with the drawings in the embodiments of the application. Obviously, the described embodiments are only It is a part of the embodiments of the present application, but not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of this application.

The terms "first", "second", "third", "fourth", etc. (if any) in the description and claims of this application and the above-mentioned drawings are used to distinguish similar objects, without having to use To describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in a sequence other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations of them are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those clearly listed. Those steps or units may include other steps or units that are not clearly listed or are inherent to these processes, methods, products, or equipment.

In order to facilitate the understanding of the technical solutions provided by the embodiments of the present application, the distributed power generation system is first introduced below. The distributed power generation system includes a distributed power supply and an inverter supporting the distributed power supply. The inverter is connected to the PCC through its corresponding transmission and distribution line to supply power to the system load in the distributed power generation system. Normally, a distributed power generation system includes: at least two distributed power sources and respective inverters for each distributed power source. Each inverter is connected to the PCC through its corresponding transmission and distribution line; of course, in practical applications, The distributed power generation system may also include only one distributed power source and the inverter supporting the distributed power source. This application does not account for the number of distributed power sources included in the distributed power generation system and the matching of the distributed power source. There is no limit to the number of inverters.

Refer to FIG. 2, which is a schematic structural diagram of an exemplary distributed power generation system. As shown in Figure 2, the distributed power generation system includes: a distributed power source 210, a distributed power source 220, a distributed power source 2n0, an inverter 211 matching the distributed power source 210, and an inverter matching the distributed power source 220 221 and the inverter 2n1 matched with the distributed power source 2n0. The inverter 211 is used to invert the electric energy generated by the distributed power source 210 into an AC signal, the inverter 221 is used to invert the electric energy generated by the distributed power source 220 into an AC signal, and the inverter 2n1 is used to convert the distributed power source The electric energy transmitted by 2n0 is inverted into an AC signal. The inverter 211, the inverter 221, and the inverter 2n1 transmit the inverted AC signals to the PCC through their corresponding transmission and distribution lines, so as to provide electrical energy for the system load 230.

Taking the distributed power supply as photovoltaic cells and the distributed power generation system as a three-phase AC power generation system as an example, as shown in Figure 3, the photovoltaic cells 301 are connected in series with a three-phase inverter 302, and the three-phase inverter 302 includes energy storage. Capacitor Vdc, semiconductor switch Sa, semiconductor switch Sb, semiconductor switch Sc and three filters L; under the control of the controller, the three-phase inverter 302 inverts the DC signal generated by the photovoltaic cell 301 into a three-phase AC signal, The three-phase AC signal is then input into the three-phase AC system 303 to provide electrical energy to the system load through the transmission and distribution line.

It should be understood that, in practical applications, the distributed power source can be a power source such as a fuel cell, an energy storage battery, etc., in addition to photovoltaic cells, and this application does not specifically limit the type of distributed power source in the distributed power generation system.

In the related art, a current-sharing controller is provided for each inverter supporting the distributed power in the above-mentioned distributed power generation system, and the current-sharing controller realizes the current sharing of the distributed power based on the control process shown in FIG. 4 control. Specifically, the current sharing controller collects the voltage signal Vout and the current signal Iout output by the inverter supporting the distributed power supply, and the power measurement unit calculates the active power Pout and the reactive power Qout according to the voltage signal Vout and the current signal Iout; further, Determine the desired frequency ω based on the active-frequency droop control curve (P Droop) and the active power Pout shown in Figure 5 (a), and integrate the desired frequency ω to obtain the desired phase θ_m; based on Figure 5 (b) The shown reactive power-voltage droop control curve (Q Droop) and reactive power Qout determine the voltage amplitude E; finally, the pulse width modulation (PWM) unit is used to control the inverter to generate phase θ_m and amplitude AC voltage with value E.

According to the inventor's research, since the frequencies of different nodes in the same distributed power generation system are basically the same, the current sharing control process shown in FIG. 4 can better realize the current sharing control of the active power of each distributed power source. The reactive power of distributed power is related to the voltage of the inverter access point. In practical applications, it is affected by the actual environmental conditions. The length of the transmission and distribution line between each inverter access point and the PCC is usually large. This will lead to large differences in the impedance of the transmission and distribution lines between the access points of each inverter and the PCC. When the voltage at the PCC is constant, the voltage at the access points of the inverters will have a large difference. As a result, the reactive power generated by the distributed power sources will be quite different, that is, it cannot be guaranteed that the reactive power generated by the distributed power sources meets the current sharing characteristics.

In order to facilitate a further understanding of the reason why the related technology cannot achieve better current sharing control for reactive power, the following is an explanation in conjunction with the reactive power-voltage droop control curve shown in FIG. 6. Assuming that the distributed power generation system includes two distributed power sources, which correspond to the droop control curves DG1 and DG2, for ease of description, the droop control curve shown in Figure 6 is calculated after converting the respective transmission and distribution line impedances of the two inverters. The droop control curve obtained. As shown in Figure 6, when the voltage at the PCC is E, the two distributed power sources work at point A and point C, respectively. The reactive power generated by the distributed power source at point A is Q1', and it works at point C. The reactive power generated by the distributed power source is Q2', and the reactive power difference between the two is ΔQ. Obviously, there is a big difference between the reactive power generated by the two distributed power sources.

In order to enable the current-sharing control process shown in Figure 4 to control the reactive power to meet the current-sharing characteristics, it can be achieved by increasing the droop coefficient of the reactive power-voltage droop control curve. However, the increase of the droop coefficient will cause the system to supply power. Reliability suffers. As shown in Figure 6, after increasing the droop coefficient, the two DGs correspond to the droop control curves DG3 and DG4, respectively. The two droop control curves are the same after converting the corresponding transmission and distribution line impedances of the two inverters. The droop control curve. As shown in Figure 6, after increasing the droop coefficient, the two distributed power sources work at point B and point D respectively. The reactive power generated by the distributed power source working at point B is Q1", and the distributed power source working at point D The reactive power generated by the power supply is Q2", and the difference in reactive power between the two is ΔQ'. Obviously, ΔQ' is less than ΔQ. It can be seen that increasing the droop coefficient improves the current sharing characteristics of reactive power. However, when the droop coefficient is not increased, the voltage drop between the voltage E* generated by the distributed power source (E* is the average value of the voltage E1* and E2* generated by the two distributed power sources) and the voltage E at the PCC Is ΔE, and after increasing the droop coefficient, the voltage drop between the voltage E* generated by the distributed power source and the voltage E'at the PCC becomes ΔE’, which is obviously greater than ΔE, that is to say, although the droop coefficient is increased, It can improve the current-sharing characteristics of reactive power, but it will cause a large drop in the system voltage, which will have a greater impact on the reliability of the system's power supply.

It can be seen that the current related technology cannot achieve better current sharing control of the distributed power in the distributed power generation system while ensuring the reliability of the power supply of the system.

In order to solve the above technical problems, embodiments of the present application provide a current sharing control method that can be applied to a distributed power generation system. When the distributed power generation system only includes one distributed power source and an inverter supporting the distributed power source, The inverter adjusts its own output voltage through the current sharing control method provided in this application; when the distributed power generation system includes at least two distributed power sources and the inverters associated with each distributed power source, each inverter The output voltage is adjusted respectively through the current sharing control method provided in this application. In the process of current sharing control, the current sharing control method suppresses the influence of transmission and distribution line impedance by means of equivalent series virtual impedance, thereby improving the current sharing control accuracy of reactive power. In addition, in order to ensure the accuracy of current-sharing control while ensuring that the voltage does not drop significantly, the current-sharing control method provided in this application further transforms the voltage control component generated by the series virtual impedance to a synchronous rotating coordinate system to realize active and reactive power components. Component decoupling, after adjusting the DC voltage drop obtained by decoupling, the target AC voltage used to adjust the inverter output voltage is obtained through the synthesis of the voltage vector, thereby realizing the effect of the equivalent series virtual impedance. The pressure drop compensation ensures the power supply reliability of the distributed power generation system while ensuring the current sharing control accuracy of the distributed power generation system.

In addition, compared to the implementation of current-sharing control of the inverter by using an independent current-sharing controller, the current-sharing control method provided in this application directly uses the inverter itself to realize the current-sharing control without the need for an additional inverter and The communication system between the current-sharing controllers can avoid the influence of the communication system failure or delay on the current-sharing control performance. In addition, when the distributed power generation system is expanded, the "plug and play" of distributed power can be realized, that is, the capacity can be expanded by directly connecting the distributed power and inverter to the distributed power generation system, without the need for additional current sharing control. There is no need to arrange the communication line between the current sharing controller and the inverter; accordingly, when the distributed power source is cut out from the distributed power generation system, there is no need to change the communication line, which is the connection of the distributed power source. In and out brings great convenience.

Method embodiment one

Refer to FIG. 7, which is a schematic flowchart of a current sharing control method provided by an embodiment of the application. The execution body of the current sharing control method is the inverter matched with the distributed power supply in the distributed power generation system. The inverter runs the current sharing control method provided in this application through its own internal integrated control system to control its own output The voltage is adjusted to realize the current sharing control of the distributed power supply. In practical applications, when multiple distributed power sources are included in the distributed power generation system, a control system with the same hardware configuration is integrated in the inverters of each distributed power source. As shown in Figure 7, the method includes the following steps:

Step 701: the inverter obtains the voltage signal and current signal output by itself.

When the inverter performs current sharing control on the distributed power in the distributed power generation system, it needs to obtain the voltage signal and current signal output by itself. Specifically, the output terminal of the inverter is usually provided with a voltage sampling unit and a current sampling unit. The voltage sampling unit can collect the voltage signal output by the inverter, and convert the voltage signal into the inverter for internal control. After the voltage signal processed by the system, the converted voltage signal is transmitted to the internal control system of the inverter; similarly, the current sampling unit can collect the current signal output by the inverter, and convert the current signal into a corresponding After the current signal processed by the internal control system of the inverter, the converted current signal is transmitted to the internal control system of the inverter; in this way, the inverter can obtain the voltage signal and current signal output by itself.

It should be understood that in practical applications, the above-mentioned voltage sampling unit and current sampling unit can realize electrical isolation between the high-voltage power transmission system and the low-voltage control system in the inverter.

It should be noted that the above method of obtaining the voltage signal and current signal output by the inverter is only an example. In practical applications, the control system in the inverter can also directly collect the voltage signal and current signal output by the inverter. And the collected voltage signals and current signals are converted into processable voltage signals and current signals accordingly, without the need to pass through the voltage sampling unit and the current sampling unit; this application does not deal with the implementation of the inverter collecting voltage signals and current signals. Make any restrictions.

It should be understood that when the current sharing control method provided by the embodiment of the present application is applied to a three-phase AC distributed power generation system, the voltage signal obtained by the inverter is a three-phase AC voltage correspondingly, and the current signal obtained is a three-phase AC voltage correspondingly. Phase AC current; when the current sharing control method provided by the embodiments of this application is applied to a single-phase AC distributed power generation system, the voltage signal obtained by the inverter is correspondingly a single-phase AC voltage, and the obtained current signal is correspondingly Single-phase alternating current.

Step 702: The inverter determines active power according to the voltage signal and the current signal, and determines a reference phase according to the active power based on the active frequency droop control strategy.

After the inverter obtains the voltage signal and current signal output by itself, it calculates the active power according to the obtained voltage signal and current signal, and executes the active-frequency droop control strategy for the active power to determine the reference phase corresponding to the active power .

In specific implementation, the inverter can determine the reference frequency corresponding to the active power calculated based on the obtained voltage signal and current signal according to the preset active-frequency droop control curve; further, the reference frequency is integrated to obtain the reference Phase. That is, after the inverter calculates the active power according to the obtained voltage signal and current signal, it brings the active power into the preset active-frequency droop control curve, thereby determining that the active power corresponds to the active-frequency droop control curve , And then integrate the reference frequency to obtain the corresponding reference phase.

Specifically, it is assumed that the active power calculated by the inverter according to the voltage signal and current signal obtained by it is

Then the active power can be calculated by formula (1)

Corresponding reference frequency ω:

Among them, D _P is the droop coefficient corresponding to the active power-frequency droop control curve, P _set is the preset active power reference value, and ω ₀ is the preset frequency reference value.

Furthermore, the reference phase θ corresponding to the reference frequency ω can be calculated by formula (2):

Among them, s is the integral operation symbol in the s domain.

Step 703: The inverter determines the AC voltage drop according to the current signal and the preset virtual impedance.

After the inverter obtains the current signal output by itself, it can calculate the product of the current signal and the preset virtual impedance as the AC voltage drop.

In the distributed power generation system, the impedance of the transmission and distribution line between each inverter access point and the PCC usually has a large difference. This difference in the impedance of the transmission and distribution line will cause a large voltage value at each inverter access point. Differences, which in turn lead to the fact that the reactive power generated by the distributed power sources in the distributed power generation system is difficult to meet the current sharing characteristics. In order to solve the technical problem of the distributed power generation system in the related technology that it is difficult to ensure that the reactive power meets the current sharing characteristics, the method provided by the embodiment of the present application suppresses the influence caused by the impedance of the transmission and distribution line by way of series virtual impedance, and in order to ensure that it is more effective The ground has a restraining effect on the impedance of the transmission and distribution line. Usually, the preset virtual impedance is set to be greater than the impedance of the transmission and distribution line between any inverter and the PCC in the distributed power generation system, that is, by setting the preset virtual impedance to A larger impedance value can neglect the influence of the impedance of the transmission and distribution line as much as possible, so as to realize the current-sharing control of the reactive power.

It should be noted that in actual applications, step 702 can be performed first, and then step 703, or step 703 can be performed first, and then step 702 can be performed, or step 702 and step 703 can be performed at the same time; the steps are not correct in this application. The execution order of 702 and step 703 is subject to any limitation.

Step 704: The inverter transforms the AC voltage drop to a synchronous rotating coordinate system according to the reference phase to obtain a DC voltage drop; adjusts the DC voltage drop, and determines the voltage vector amplitude according to the adjusted DC voltage drop And the voltage vector phase angle.

The inverter determines the reference phase corresponding to the active power based on the active-frequency droop control strategy, and calculates the AC voltage drop according to the current signal and the preset virtual impedance, and then transforms the AC voltage to the synchronous rotating coordinate system according to the reference phase , The corresponding DC voltage drop is obtained; further, the DC voltage drop is adjusted, and the voltage vector amplitude and the voltage vector phase angle are determined according to the adjusted DC voltage drop.

In step 703, the equivalent series virtual impedance of the inverter usually causes a large drop in voltage. In order to prevent a large drop in voltage from affecting the stability of the system, the method provided in this embodiment of the present application will further cause the equivalent series virtual impedance to generate The AC voltage drop is transformed to the synchronous rotating coordinate system to realize the decoupling of the active and reactive components, and then adjust the decoupling active and reactive components separately, and then based on the adjusted active and reactive components Determine the target AC voltage used to adjust the output voltage of the inverter, so as to realize the compensation for the voltage drop caused by the equivalent series virtual impedance, and ensure the stability of the distributed power generation system while ensuring that the reactive power meets the current sharing characteristics .

In specific implementation, after the inverter transforms the AC voltage drop to the synchronous rotating coordinate system according to the reference phase, the DC voltage drop including the d-axis component and the q-axis component will be obtained; The component and the q-axis component are respectively adjusted for gain, and then the voltage vector amplitude is calculated according to the preset reference voltage vector, the adjusted d-axis component and the adjusted q-axis component; according to the reactive power in the preset reference voltage vector Component, adjusted d-axis component and q-axis component to calculate the voltage vector phase angle.

Specifically, assuming that the inverter converts the AC voltage drop to the synchronous rotating coordinate system, the DC voltage drop obtained includes the d-axis component ΔV ^d and the q-axis component ΔV ^q , then the d-axis component ΔV ^d and The q-axis component ΔV ^q is adjusted separately for gain:

Among them, K _d is the gain adjustment coefficient of the d-axis component, and K _q is the gain adjustment coefficient of the q-axis component;

Is the adjusted d-axis component,

Is the adjusted q-axis component.

Furthermore, suppose the preset reference voltage vector is

(j is an imaginary unit), the voltage vector amplitude and voltage vector phase angle can be determined by formula (4) and formula (5):

Among them, |V ^ref | is the magnitude of the voltage vector, and γ is the phase angle of the voltage vector.

It should be noted that, under normal circumstances, the coefficient a in the reference voltage vector can be set to zero.

Step 705: The inverter determines a voltage phase reference value according to the reference phase and the voltage vector phase angle; transforms to a stationary coordinate system according to the voltage vector amplitude and the voltage phase reference value to obtain a target AC voltage.

After the inverter determines the voltage vector amplitude and the voltage vector phase angle, it completes the synthesis of the voltage vector based on the voltage vector amplitude and the voltage vector phase angle; specifically, the inverter can compare the reference phase determined in step 702 with The voltage vector amplitude is added to obtain the voltage phase reference value; further, the voltage vector amplitude and the voltage phase reference value are transformed to the stationary coordinate system to obtain the target AC voltage.

Specifically, assuming that the reference phase is θ, the voltage vector phase angle is γ, and the voltage vector amplitude is |V ^ref |, the target AC voltage can be determined by formula (6)

Step 706: The inverter adjusts its output voltage according to the target AC voltage.

After the inverter obtains the target AC voltage, it can adjust its output voltage according to the target AC voltage, so that its output voltage reaches the target AC voltage.

In specific implementation, the inverter can generate a target control signal according to the deviation between the target AC voltage and the AC signal output by itself; further, generate a drive signal according to the target control signal, and use the drive signal to control each half of the inverter circuit The conduction switch is turned on and off, thereby adjusting the output voltage of the inverter to the target AC voltage.

In a possible implementation manner, the inverter can control based on the voltage proportional resonance (PR) based on the deviation between the target AC voltage and the voltage signal output by itself (that is, the voltage signal collected in step 701) The strategy generates the above-mentioned target control signal.

In another possible implementation manner, in order to improve the control efficiency, the inverter can be based on the voltage PR control strategy based on the deviation between the target AC voltage and the voltage signal output by itself (that is, the voltage signal collected in step 701) Generate a basic control signal; and then generate the above-mentioned target control signal based on the current PR control strategy according to the deviation between the basic control signal and the current signal output by itself (that is, the current signal collected in step 701).

It should be noted that in practical applications, the inverter can realize the above-mentioned current-sharing control process through one digital chip, or it can realize the above-mentioned current-sharing control process through multiple digital chips, for example, using digital signal processing (digital signal processing). The DSP) chip executes the target AC voltage generation process described in step 701 to step 705, and uses a complex programmable logic device (CPLD) to perform the driving process described in step 706. This application does not apply to inverters. There are any restrictions on the number of digital chips used to implement the current sharing control process.

In addition, compared to the implementation of current-sharing control of the inverter using an independent current-sharing controller, the above-mentioned current-sharing control method directly uses the inverter itself to realize the current-sharing control, without the need for additional inverters and current-sharing control. The communication system between the devices can avoid the influence of the communication system failure or delay on the current sharing control performance. In addition, when the distributed power generation system is expanded, the "plug and play" of distributed power can be realized, that is, the capacity can be expanded by directly connecting the distributed power and inverter to the distributed power generation system, without the need for additional current sharing control. There is no need to arrange the communication line between the current sharing controller and the inverter; accordingly, when the distributed power source is cut out from the distributed power generation system, there is no need to change the communication line, which is the connection of the distributed power source. In and out brings great convenience.

In order to facilitate a further understanding of the current sharing control method provided in the embodiments of the present application, the current sharing control method provided in the embodiments of the present application is applied to a three-phase AC distributed power generation system as an example, and the current sharing provided in the embodiments of the present application is combined with the accompanying drawings. Two possible implementations of the control method are introduced in detail.

Method embodiment two

Referring to FIG. 8, FIG. 8 is a schematic diagram of an implementation architecture of a current sharing control method applied to a three-phase AC distributed power generation system according to an embodiment of the application.

As shown in Figure 8, the control system inside the inverter obtains the three-phase AC voltage signal output by the inverter circuit

with

(Hereinafter referred to as

The superscript abc means a-phase, b-phase and c-phase), and three-phase AC current signal

with

(Hereinafter referred to as

The superscript abc represents phase a, phase b and phase c). After active power calculation, according to the obtained three-phase AC voltage signal

And three-phase AC current signal

Get the total active power

And the active power

Bring in the functional relationship corresponding to the preset active power-frequency droop control curve (denoted as DP in Figure 8), and determine the active power by formula (7)

Corresponding reference frequency ω:

Furthermore, the reference frequency ω is integrated by formula (8) to obtain the corresponding reference phase θ:

Among them, s is the integral operation symbol in the s domain.

At the same time, the inverter can calculate the three-phase AC current signal

Multiplying the product with the preset virtual impedance matrix to obtain the three-phase AC voltage drop ΔV ^abc , the three-phase AC voltage drop is the AC voltage drop described in method embodiment 1; the preset virtual impedance matrix is a 3*3 matrix. In specific implementation, the three-phase AC voltage drop ΔV ^abc can be calculated by formula (9):

Among them, _Kaa , _Kab , K _ac , K _ba , K _bb , K _bc , K _ca , K _cb and K _cc are all parameters in the preset virtual impedance matrix. In practical applications, these parameters can be preset according to The virtual impedance is determined.

In a typical implementation manner, the above-mentioned preset virtual impedance matrix is a diagonal matrix, and the diagonal elements of the diagonal matrix are all determined according to the preset virtual impedance _Lv . For example, the diagonal elements can be equalized. Set to sL _v (s is the Laplacian operator); the preset virtual impedance L _{v is} greater than the impedance of the transmission and distribution line between any inverter access point and the PCC in the distributed power generation system. When the preset virtual impedance matrix is a diagonal matrix and the diagonal elements are all sL _v , the three-phase AC voltage drop ΔV ^abc can be calculated by formula (10):

Then, according to the reference phase θ calculated by equation (8), the three-phase AC voltage drop ΔV ^{abc is} transformed to the synchronous rotating coordinate system (represented as abc/dq in Fig. 8), and the d-axis components ΔV ^d and q are obtained. The DC voltage drop ΔV ^{dq of the} axis component ΔV ^q ; specifically, the three-phase AC voltage drop ΔV ^{abc can be} transformed to the synchronous rotating coordinate system by formula (11):

Then, the voltage adjustment matrix is used to adjust the gain ^{of the d-axis component ΔV d} and the q-axis component ΔV ^{q respectively through equation (12):}

Among them, Kd is ^{the gain adjustment coefficient corresponding to the d-axis component ΔV d} in the voltage adjustment matrix, and Kq is the gain adjustment coefficient corresponding to the ^{q-axis component ΔV q in the voltage adjustment matrix.}

Furthermore, based on the adjusted DC voltage drop and the preset reference voltage vector

Voltage vector calculation to obtain a voltage vector magnitude | V ^ref | gamma] and the voltage vector phase angle; specific implementation, may each voltage vector magnitude is calculated by the formula (13) and (14) | V ^ref | voltage and Vector phase angle γ:

Calculate the sum of the voltage vector phase angle γ and the reference phase θ as the voltage phase reference value. According to the voltage phase reference value and the voltage vector amplitude |V ^ref |, the coordinate transformation is performed by formula (15) to obtain the target AC voltage

Obtain the target AC voltage

Then, according to the target AC voltage

Three-phase AC voltage signal output from the inverter

The deviation between the voltage PR regulator generates a basic control signal; furthermore, according to the current control signal and the three-phase AC current signal output by the inverter

For the deviation between the two, the target control signal is generated by the current PR regulator, and the target control signal is transmitted to the modulation unit. The modulation unit accordingly generates a drive signal based on the target control signal, and uses the drive signal to control the on and off of each semiconductor switch in the inverter circuit to adjust the inverter output target AC voltage

In this way, the distributed power supply in the three-phase AC distributed power generation system is controlled by the realization process shown in Figure 8, and the influence of the transmission and distribution line impedance is suppressed by the equivalent series virtual impedance method, thereby improving the three-phase AC Control precision of reactive power current sharing in distributed power generation system. In addition, in order to ensure the accuracy of current sharing control while ensuring that the voltage does not fall sharply, this method further transforms the voltage control component generated by the series virtual impedance to the synchronous rotating coordinate system to realize the decoupling of active and reactive components. After the DC voltage drop obtained by decoupling is adjusted, the target AC voltage used to adjust the output voltage of the inverter is obtained through the synthesis calculation of the voltage vector, thereby realizing the compensation of the voltage drop caused by the equivalent series virtual impedance. While ensuring the current sharing control accuracy in the three-phase AC distributed power generation system, it also ensures the reliability of power supply in the three-phase AC distributed power generation system.

Method Example Three

Referring to FIG. 9, FIG. 9 is a schematic diagram of the implementation architecture of another current sharing control method applied to a three-phase AC distributed power generation system according to an embodiment of the application. Since the realization process shown in Fig. 9 is different from the realization process shown in Fig. 8 only in the processing of the current signal output by the inverter and the processing of the equivalent series virtual impedance, in order to avoid the content being too full, Therefore, the following embodiment only introduces the steps that are different from the embodiment shown in FIG. 8 in detail.

The inverter obtains the three-phase AC current signal output by its internal inverter circuit

with

(Hereinafter referred to as

After the superscript abc represents phase a, phase b and phase c), the obtained three-phase AC current signal

Transform to a two-phase stationary coordinate system to obtain a two-phase AC current signal

(Represented as abc/αβ in Figure 9), in specific implementation, the three-phase AC current signal can be

Transform to two-phase stationary coordinate system:

Based on the two-phase AC current signal

When equivalent series virtual impedance, calculate the two-phase AC current signal

Multiplying the product with the preset virtual impedance matrix to obtain the two-phase AC voltage drop ΔV ^αβ , the two-phase AC voltage drop ΔV ^αβ is the AC voltage drop described in method embodiment one; the preset virtual impedance matrix is 2*2 matrix. In specific implementation, the two-phase AC voltage drop ΔV ^αβ can be calculated by formula (17):

Among them, L _αα , L _αβ , L _βα and L _ββ are all parameters in the preset virtual impedance matrix. In practical applications, these parameters can be set according to the preset virtual impedance.

In a typical implementation manner, the above-mentioned preset virtual impedance matrix is a diagonal matrix, and the diagonal elements of the diagonal matrix are all determined according to the preset virtual impedance _Lv . For example, the diagonal elements can be equalized. Set to sL _v (s is the Laplacian operator); the preset virtual impedance L _{v is} greater than the impedance of the transmission and distribution line between any inverter access point and the PCC in the distributed power generation system. When the preset virtual impedance matrix is a diagonal matrix and the diagonal elements are all sL _v , the two-phase AC voltage drop ΔV ^αβ can be calculated by formula (18):

Furthermore, according to the reference phase θ determined based on the active power-frequency droop control curve, the two-phase AC voltage drop ΔV ^{αβ is} transformed into a synchronous rotating coordinate system to obtain the DC voltage drop ΔV ^dq ^{including the d-axis component ΔV d} and the q-axis component ΔV ^q ; In specific implementation, the two-phase AC voltage drop ΔV ^{αβ can be} transformed into a synchronous rotating coordinate system through equation (19):

The other steps in the implementation process shown in FIG. 9 are all the same as the corresponding steps in the implementation process shown in FIG. 8, and will not be repeated here in this embodiment.

For the distributed power generation system shown in Fig. 10, the inventors respectively applied the current sharing control method shown in Figs. 8 and 9 and the current sharing control method based on reactive power-voltage droop control in the related art to compare the current sharing control method shown in Fig. 10 The distributed power generation system shown in the figure performs current sharing control. The specific experimental results are shown in Fig. 11 and Fig. 12. The distributed power generation system is controlled based on the current-sharing control method shown in Fig. 8 or Fig. 9 within 0 to 0.2s, and the distributed power generation system is controlled within 0.2s to 0.4s. The reactive power-voltage droop control curve with a smaller droop coefficient performs current sharing control on the distributed power generation system. After 0.4s, the reactive power-voltage droop control curve with a larger droop coefficient is used to perform current sharing control on the distributed power generation system.

As shown in Fig. 11, the two waveforms respectively represent the corresponding output power of the power generating unit 1001 and the power generating unit 1002. Through comparison, it can be found that within 0 to 0.2s, when the current sharing control method shown in Figure 8 or Figure 9 is used to perform current sharing control on the distributed power generation system, the active power and reactive power generated by the power generation unit 1001 and the power generation unit 1002 are Both the power and the apparent power tend to be the same, achieving a better current sharing effect. Within 0.2s to 0.4s, when a reactive power-voltage droop control curve with a small droop coefficient is used to perform current sharing control on a distributed power generation system, the power generation unit 1001 is affected by the difference in impedance between the transmission and distribution lines. There is a significant deviation from the reactive power generated by the power generation unit 1002, and the overall current sharing effect of the distributed power generation system is poor. After 0.4s, when a reactive power-voltage droop control curve with a large droop coefficient is used to perform current sharing control on the distributed power generation system, the sensitivity of the distributed power generation to power changes increases, and the stability of the distributed power generation system is weakened , There is a situation of unstable oscillation.

As shown in Figure 12, through comparison, it can be found that within 0 to 0.2s, when the current sharing control method shown in Figure 8 or Figure 9 is used to perform current sharing control on the distributed power generation system, the power generation unit 1001, the power generation unit 1002, and the The voltage on the load 1003 side is relatively stable, there is no significant drop, and the overall power supply quality of the distributed power generation system is good. Within 0.2s to 0.4s, when a reactive power-voltage droop control curve with a small droop coefficient is used to perform current sharing control on the distributed power generation system, the voltages on the power generation unit 1001, the power generation unit 1002, and the load 1003 all appear obvious. With a sharp drop, the overall power supply quality of the distributed power generation system is poor. After 0.4s, when a reactive power-voltage droop control curve with a large droop coefficient is used to perform current sharing control on the distributed power generation system, it is obvious that the stability of the distributed power generation system cannot be guaranteed.

Device embodiment one

Regarding the current sharing control method described above, this application also provides an inverter, so that the above current sharing control method can be implemented in practical applications.

Refer to FIG. 13, which is a schematic structural diagram of an inverter provided by an embodiment of the application. It should be noted that in practical applications, the input end of the inverter provided in the embodiment of the present application is connected to the distributed power supply in the distributed power generation system, and the output end of the inverter is connected to the corresponding transmission and distribution line PCC in a distributed power generation system. As shown in Figure 13, the inverter includes:

The sampling unit 1301 is configured to obtain the voltage signal and the current signal output by the inverter;

The active current sharing control unit 1302 is configured to determine active power according to the voltage signal and the current signal, and determine a reference phase according to the active power based on the active-frequency droop control strategy;

The virtual impedance compensation unit 1303 is configured to determine an AC voltage drop according to the current signal and a preset virtual impedance;

The voltage vector adjustment unit 1304 is configured to transform the AC voltage drop to a synchronous rotating coordinate system according to the reference phase to obtain a DC voltage drop; adjust the DC voltage drop, and determine the voltage vector according to the adjusted DC voltage drop Amplitude and voltage vector phase angle;

The voltage vector synthesis unit 1305 is configured to determine a voltage phase reference value according to the reference phase and the voltage vector phase angle; transform to a stationary coordinate system according to the voltage vector amplitude and the voltage phase reference value to obtain a target AC voltage ；

The adjusting unit 1306 is configured to adjust the output voltage of the inverter according to the target AC voltage.

During specific implementation, the sampling unit 1301 is used to execute the method in step 701. For details, please refer to the related description of step 701 in the method embodiment shown in FIG. 7. The active current sharing control unit 1302 is configured to execute the method in step 702. For details, refer to the related description of step 702 in the method embodiment shown in FIG. 7. The virtual impedance compensation unit 1303 is configured to execute the method in step 703. For details, refer to the related description of step 703 in the method embodiment shown in FIG. 7. The voltage vector adjustment unit 1304 is configured to execute the method in step 704, and for details, refer to the related description of step 704 in the method embodiment shown in FIG. 7. The voltage vector synthesis unit 1305 is used to execute the method in step 705. For details, refer to the related description of step 705 in the method embodiment shown in FIG. 7. The adjustment unit 1306 is configured to execute the method in step 706, and for details, refer to the related description of step 706 in the method embodiment shown in FIG. 7.

Optionally, the DC voltage drop includes: a d-axis component and a q-axis component; then the voltage vector adjusting unit 1304 is specifically configured to:

During specific implementation, the adjustment strategy adopted by the above-mentioned voltage vector adjustment unit 1304 can refer to the description of step 704 in the method embodiment shown in FIG. 7, which will not be repeated here.

Optionally, when the distributed power generation system is a three-phase AC distributed power generation system, the voltage signal is a three-phase AC voltage signal, and the current signal is a three-phase AC current signal; then the virtual impedance compensation unit 1303 is specifically used for:

Then the voltage vector adjusting unit 1304 is specifically configured to:

During specific implementation, the operation modes of the aforementioned virtual impedance compensation unit 1303 and the voltage vector adjustment unit 1304 can be referred to the related description in the embodiment shown in FIG. 8, which will not be repeated here.

Then the voltage vector adjusting unit 1304 is specifically configured to:

In a specific implementation, the operation modes of the aforementioned virtual impedance compensation unit 1303 and the voltage vector adjustment unit 1304 can be referred to the related description in the embodiment shown in FIG. 9, which will not be repeated here.

Optionally, the preset virtual impedance matrix is a diagonal matrix, and diagonal elements of the preset virtual impedance matrix are determined according to the preset virtual impedance; the preset virtual impedance is greater than that of the distributed power generation system The impedance of the transmission and distribution line between the access point of the inverter and the public access point.

During specific implementation, the manner of setting the above-mentioned preset virtual impedance matrix can refer to the related descriptions in the embodiments shown in FIG. 8 and FIG. 9, which will not be repeated here.

Optionally, the active power current sharing control unit 1302 is specifically configured to:

During specific implementation, the implementation of the above-mentioned active current sharing control unit 1302 can refer to the related description of step 702 in the method embodiment shown in FIG. 7, which will not be repeated here.

Optionally, the adjustment unit 1306 includes:

For specific implementation, for the implementation of the foregoing adjustment unit 1306, reference may be made to the related description of step 706 in the method embodiment shown in FIG. 7, which will not be repeated here.

Optionally, the control signal generating subunit includes:

During specific implementation, the implementation of the upper control signal generation subunit can refer to the related description of step 706 in the method embodiment shown in FIG. 7, which will not be repeated here.

Optionally, the control signal generating subunit includes:

During the current sharing control process of the inverter provided in the embodiments of the present application, the influence caused by the impedance of the transmission and distribution line is suppressed by means of equivalent series virtual impedance, thereby improving the current sharing control accuracy for reactive power. In addition, in order to ensure the accuracy of current-sharing control while ensuring that the voltage does not fall sharply, the inverter provided in this application can transform the voltage control component generated by the series virtual impedance to a synchronous rotating coordinate system to realize active and reactive components. After adjusting the DC voltage drop obtained by decoupling, the target AC voltage used to adjust the output voltage of the inverter is obtained through the synthesis calculation of the voltage vector, thereby realizing the resistance to the voltage generated by the equivalent series virtual impedance. The reduced compensation ensures the power supply reliability of the distributed power generation system while ensuring the current sharing control accuracy of the distributed power generation system.

Those skilled in the art can clearly understand that, for the convenience and conciseness of the description, the specific working process of the above-described system, device, and unit can refer to the corresponding process in the foregoing method embodiment, which will not be repeated here.

In the several embodiments provided in this application, it should be understood that the disclosed system, device, and method may be implemented in other ways. For example, the device embodiments described above are merely illustrative, for example, the division of the units is only a logical function division, and there may be other divisions in actual implementation, for example, multiple units or components may be combined or It can be integrated into another system, or some features can be ignored or not implemented. In addition, the displayed or discussed mutual coupling or direct coupling or communication connection may be indirect coupling or communication connection through some interfaces, devices or units, and may be in electrical, mechanical or other forms.

The units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the objectives of the solutions of the embodiments.

In addition, the functional units in the various embodiments of the present application may be integrated into one processing unit, or each unit may exist alone physically, or two or more units may be integrated into one unit. The above-mentioned integrated unit can be implemented in the form of hardware or software functional unit.

If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer readable storage medium. Based on this understanding, the technical solution of the present application essentially or the part that contributes to the existing technology or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium , Including several instructions to make a computer device (which may be a personal computer, a server, or a network device, etc.) execute all or part of the steps of the methods described in the various embodiments of the present application. The aforementioned storage media include: U disk, mobile hard disk, read-only memory (English full name: Read-Only Memory, English abbreviation: ROM), random access memory (English full name: Random Access Memory, English abbreviation: RAM), magnetic Various media that can store program codes, such as discs or optical discs.

As mentioned above, the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: The technical solutions recorded in the embodiments are modified, or some of the technical features are equivalently replaced; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

A current-sharing control method, characterized in that it is applied to a distributed power generation system, the distributed power generation system comprising: a distributed power source and an inverter supporting the distributed power source, the inverter through its corresponding The transmission and distribution line is connected to the common connection point; the inverter performs current sharing control by the current sharing control method, and the method includes:

Acquiring a voltage signal and a current signal output by the inverter;

Determine active power according to the voltage signal and the current signal, determine a reference phase according to the active power based on an active-frequency droop control strategy; determine an AC voltage drop according to the current signal and a preset virtual impedance;

Transforming the AC voltage drop to a synchronous rotating coordinate system according to the reference phase to obtain a DC voltage drop; adjusting the DC voltage drop, and determining a voltage vector amplitude and a voltage vector phase angle according to the adjusted DC voltage drop;

Determining a voltage phase reference value according to the reference phase and the voltage vector phase angle; transforming to a stationary coordinate system according to the voltage vector amplitude and the voltage phase reference value to obtain a target AC voltage;

The output voltage of the inverter is adjusted according to the target AC voltage.
The method according to claim 1, wherein the DC voltage drop includes: a d-axis component and a q-axis component; then the DC voltage drop is adjusted, and the voltage vector is determined according to the adjusted DC voltage drop Amplitude and voltage vector phase angle, including:

The d-axis component and the q-axis component are adjusted separately, and the voltage vector amplitude is determined according to the preset reference voltage vector, the adjusted d-axis component, and the adjusted q-axis component; and according to the reference voltage The reactive component in the vector, the adjusted d-axis component, and the adjusted q-axis component determine the voltage vector phase angle.
The method according to claim 1, wherein when the distributed power generation system is a three-phase AC distributed power generation system, the voltage signal is a three-phase AC voltage signal, and the current signal is a three-phase AC current Signal; the determining the AC voltage drop according to the current signal and the preset virtual impedance includes:

Calculating the product of the current signal and a preset virtual impedance matrix to obtain a three-phase AC voltage drop as the AC voltage drop; the preset virtual impedance matrix is a 3*3 matrix;

Then, transforming the AC voltage drop to a synchronous rotating coordinate system according to the reference phase to obtain the DC voltage drop includes:

The three-phase AC voltage drop is transformed into a synchronous rotating coordinate system according to the reference phase to obtain the DC voltage drop.
The method according to claim 1, wherein when the distributed power generation system is a three-phase AC distributed power generation system, the voltage signal is a three-phase AC voltage signal, and the current signal is a three-phase AC current Signal; the determining the AC voltage drop according to the current signal and the preset virtual impedance includes:

Transforming the current signal to a two-phase stationary coordinate system to obtain a two-phase alternating current signal;

Calculating the product of the two-phase AC current signal and a preset virtual impedance matrix to obtain a two-phase AC voltage drop as the AC voltage drop; the preset virtual impedance matrix is a 2*2 matrix;

Then, transforming the AC voltage drop to a synchronous rotating coordinate system according to the reference phase to obtain the DC voltage drop includes:

The two-phase AC voltage drop is transformed into a synchronous rotating coordinate system according to the reference phase to obtain the DC voltage drop.
The method according to claim 3 or 4, wherein the preset virtual impedance matrix is a diagonal matrix, and diagonal elements of the preset virtual impedance matrix are determined according to the preset virtual impedance; The preset virtual impedance is greater than the impedance of the transmission and distribution line between the access point of the inverter and the public access point in the distributed power generation system.
The method according to any one of claims 1 to 5, wherein the active-frequency droop control strategy based on determining the reference phase according to the active power comprises:

The reference frequency corresponding to the active power is determined according to a preset active power-frequency droop curve; and the reference phase is obtained by integrating the reference frequency.
The method according to any one of claims 1 to 5, wherein the adjusting the output voltage of the inverter according to the target AC voltage comprises:

Generating a target control signal according to the deviation between the target AC voltage and the AC signal output by the inverter;

A drive signal is generated according to the target control signal, and the drive signal is used to control turning on and off of a semiconductor switch in the inverter, so that the inverter outputs the target AC voltage.
The method according to claim 7, wherein the generating a target control signal according to the deviation between the target AC voltage and the AC signal output by the inverter comprises:

According to the deviation between the target AC voltage and the voltage signal output by the inverter, the target control signal is generated based on a voltage proportional resonance control strategy.
The method according to claim 7, wherein the generating a target control signal according to the deviation between the target AC voltage and the AC signal output by the inverter comprises:

Generating a basic control signal based on a voltage proportional resonance control strategy according to the deviation between the target AC voltage and the voltage signal output by the inverter;

According to the deviation between the basic control signal and the current signal output by the inverter, the target control signal is generated based on a current proportional resonance control strategy.
An inverter, characterized in that the input end of the inverter is connected to a distributed power source in a distributed power generation system, and the output end of the inverter is connected to a common connection point through its corresponding transmission and distribution line ; The inverter includes:

A sampling unit for acquiring the voltage signal and current signal output by the inverter;

An active current sharing control unit, configured to determine active power according to the voltage signal and the current signal, and determine a reference phase according to the active power based on an active-frequency droop control strategy;

A virtual impedance compensation unit, configured to determine an AC voltage drop according to the current signal and a preset virtual impedance;

The voltage vector adjustment unit is configured to transform the AC voltage drop to a synchronous rotating coordinate system according to the reference phase to obtain a DC voltage drop; adjust the DC voltage drop, and determine the voltage vector amplitude according to the adjusted DC voltage drop Value and voltage vector phase angle;

A voltage vector synthesis unit, configured to determine a voltage phase reference value according to the reference phase and the voltage vector phase angle; transform to a stationary coordinate system according to the voltage vector amplitude and the voltage phase reference value to obtain a target AC voltage;

The adjusting unit is configured to adjust the output voltage of the inverter according to the target AC voltage.
The inverter according to claim 10, wherein the DC voltage drop includes: a d-axis component and a q-axis component; then the voltage vector adjustment unit is specifically configured to:

The d-axis component and the q-axis component are adjusted separately, and the voltage vector amplitude is determined according to the preset reference voltage vector, the adjusted d-axis component, and the adjusted q-axis component; and according to the reference voltage The reactive component in the vector, the adjusted d-axis component, and the adjusted q-axis component determine the voltage vector phase angle.
The inverter according to claim 10, wherein when the distributed power generation system is a three-phase AC distributed power generation system, the voltage signal is a three-phase AC voltage signal, and the current signal is a three-phase AC voltage signal. AC current signal; the virtual impedance compensation unit is specifically used for:

Calculating the product of the current signal and a preset virtual impedance matrix to obtain a three-phase AC voltage drop as the AC voltage drop; the preset virtual impedance matrix is a 3*3 matrix;

Then the voltage vector adjustment unit is specifically used for:

The three-phase AC voltage drop is transformed into a synchronous rotating coordinate system according to the reference phase to obtain the DC voltage drop.
The inverter according to claim 10, wherein when the distributed power generation system is a three-phase AC distributed power generation system, the voltage signal is a three-phase AC voltage signal, and the current signal is a three-phase AC voltage signal. AC current signal; the virtual impedance compensation unit is specifically used for:

Transforming the current signal to a two-phase stationary coordinate system to obtain a two-phase alternating current signal;

Calculating the product of the two-phase AC current signal and a preset virtual impedance matrix to obtain a two-phase AC voltage drop as the AC voltage drop; the preset virtual impedance matrix is a 2*2 matrix;

Then the voltage vector adjustment unit is specifically used for:

The two-phase AC voltage drop is transformed into a synchronous rotating coordinate system according to the reference phase to obtain the DC voltage drop.
The inverter according to claim 12 or 13, wherein the preset virtual impedance matrix is a diagonal matrix, and the diagonal elements of the preset virtual impedance matrix are determined according to the preset virtual impedance. The preset virtual impedance is greater than the impedance of the transmission and distribution line between the access point of the inverter and the public access point in the distributed power generation system.
The inverter according to any one of claims 10 to 14, wherein the active current sharing control unit is specifically configured to:

The reference frequency corresponding to the active power is determined according to a preset active power-frequency droop curve; and the reference phase is obtained by integrating the reference frequency.
The inverter according to any one of claims 10 to 14, wherein the adjustment unit comprises:

A control signal generating subunit, configured to generate a target control signal according to the deviation between the target AC voltage and the AC signal output by the inverter;

The modulation subunit is configured to generate a drive signal according to the target control signal, and use the drive signal to control the on and off of the semiconductor switch in the inverter, so that the inverter outputs the target AC voltage.
The inverter according to claim 16, wherein the control signal generating subunit comprises:

The first voltage adjustment module is configured to generate the target control signal based on a voltage proportional resonance control strategy according to the deviation between the target AC voltage and the voltage signal output by the inverter.
The inverter according to claim 16, wherein the control signal generating subunit comprises:

The second voltage adjustment module is configured to generate a basic control signal based on a voltage proportional resonance control strategy according to the deviation between the target AC voltage and the voltage signal output by the inverter;

The current adjustment module is configured to generate the target control signal based on a current proportional resonance control strategy according to the deviation between the basic control signal and the current signal output by the inverter.