CN-115589027-B - Method and device for controlling current inner loop decoupling of grid-structured modular multilevel converter

CN115589027BCN 115589027 BCN115589027 BCN 115589027BCN-115589027-B

Abstract

The embodiment of the invention discloses a method and a device for controlling current inner loop decoupling of a grid-structured modular multilevel converter, wherein the method comprises the steps of obtaining three-phase alternating voltage and current of a public connection point, and outputting active power and reactive power; the method comprises the steps of obtaining an output alternating current voltage and a phase angle reference value of a converter according to output active power and reactive power, obtaining a dq axis voltage component and a dq axis current component of a public connection point according to a three-phase alternating current voltage current and the phase angle reference value, obtaining a first reference value of the dq axis current through integral control, respectively obtaining a dq axis second reference current through a decoupling link of the first reference value of the dq axis, respectively obtaining a dq axis control signal according to the dq axis current component and the dq axis second reference current, and obtaining a control signal according to the dq axis control signal to control the input or the cutting of the converter. The invention can reduce the coupling problem of the output active power and reactive power of the converter when the converter is connected with the grid by using the grid-structured control, and improve the dynamic performance of the control.

Inventors

CAI XU
ZHANG CHEN
LI JIANHUA
CAO LU
YANG RENXIN
HUANG ZHIGUANG
CHEN HAO
SHI YANQIANG
HOU YONG

Assignees

上海交通大学
国家电网有限公司华东分部

Dates

Publication Date: 20260505
Application Date: 20221031

Claims (7)

1. A current inner loop decoupling control method of a grid-structured modular multilevel converter comprises the following steps: acquiring three-phase alternating voltage, three-phase alternating current and output active power and reactive power of a public connection point; calculating an output alternating voltage reference value and an output phase angle reference value of the grid-structured modular multilevel converter according to the obtained output active power and reactive power; The method comprises the steps of obtaining a d-axis voltage component and a q-axis voltage component of a public connection point according to three-phase alternating current and an output phase angle reference value, and obtaining a d-axis current component and a q-axis current component of the public connection point according to the three-phase alternating current and the output phase angle reference value; Obtaining a first reference value of d-axis current and q-axis current through an integral controller and a proportional-integral control according to a difference value of the d-axis voltage component and an output alternating voltage reference value of the grid-formed modular multilevel converter and the q-axis voltage component, respectively obtaining a second d-axis reference current and a second q-axis reference current through a decoupling link by the first reference value of d-axis current and the first reference value of q-axis current, and further comprising the steps of forming a column vector I rec1 by the first reference value of d-axis current and the first reference value of q-axis current, decoupling the first reference value of q-axis current by a decoupling matrix, obtaining a second d-axis reference current and a second q-axis reference current according to the decoupled column vector I rec2 , wherein the decoupling matrix is in the form of: where s is the Laplacian, A reference value for the output frequency of the grid-structured modular multilevel converter; obtaining a d-axis control signal according to the d-axis current component and a d-axis second reference current, and obtaining a q-axis control signal according to the q-axis current component and a q-axis second reference current; And obtaining a final control signal according to the d-axis control signal and the q-axis control signal to control the investment or the cutting of the grid-structured modular multilevel converter.
2. The method for controlling current inner loop decoupling of a grid-formed modular multilevel converter according to claim 1, wherein in the step of calculating the output ac voltage reference value and the output phase angle reference value of the grid-formed modular multilevel converter according to the obtained output active power and reactive power, the difference between the output reactive power of the common connection point and the set reactive power reference value is obtained, multiplied by a preset droop coefficient, and added to a rated voltage, thereby obtaining the output ac voltage reference value of the grid-formed modular multilevel converter.
3. The method for controlling current inner loop decoupling of a grid-formed modular multilevel converter according to claim 2, wherein in the step of calculating the output ac voltage reference value and the output phase angle reference value of the grid-formed modular multilevel converter according to the obtained output active power and reactive power, the difference between the output active power of the common connection point and the set active power reference value is obtained, multiplied by a preset droop coefficient, added with a rated frequency to obtain the reference value of the output frequency of the grid-formed modular multilevel converter, and finally the reference value of the output frequency is integrated to obtain the output phase angle reference value.
4. The method of current loop decoupling control for a grid-structured modular multilevel converter of claim 3, wherein the step of obtaining the d-axis voltage component and the q-axis voltage component of the common connection point based on the three-phase alternating voltage and the output phase reference value further comprises performing a park change on the three-phase alternating voltage at the output phase angle reference value to obtain the d-axis voltage component and the q-axis voltage component.
5. The method of current loop decoupling control for a grid-structured modular multilevel converter of claim 4, wherein obtaining the d-axis current component and the q-axis current component of the common connection point based on the three-phase alternating current and the output phase angle reference value comprises performing a park change on the three-phase alternating current at the output phase angle reference value to obtain the d-axis current component and the q-axis current component.
6. The method for controlling current internal loop decoupling of a grid-structured modular multilevel converter according to claim 1, wherein the step of obtaining a d-axis control signal from the d-axis current component and a d-axis second reference current and obtaining a q-axis control signal from a q-axis current component and a q-axis second reference current further comprises: passing the d-axis current component and a d-axis second reference current through a proportional-integral controller to obtain the d-axis control signal; the q-axis current component and q-axis second reference current are passed through a proportional-integral controller to obtain the q-axis control signal.
7. A current inner loop decoupling control device of a grid-structured modular multilevel converter, comprising: the parameter acquisition unit is used for acquiring three-phase alternating voltage and three-phase alternating current of the public connection point and outputting active power and reactive power; The output alternating voltage and phase angle reference value calculation unit is used for calculating an output alternating voltage reference value and an output phase angle reference value of the grid-structured modular multilevel converter according to the obtained output active power and reactive power; the d-axis and q-axis voltage and current component obtaining unit is used for obtaining a d-axis voltage component and a q-axis voltage component of the public connection point according to the three-phase alternating current and the output phase angle reference value and obtaining a d-axis current component and a q-axis current component of the public connection point according to the three-phase alternating current and the output phase angle reference value; The integration unit is used for obtaining a first reference value of d-axis current and q-axis current through an integration controller and a proportional-integral control according to the difference value between the d-axis voltage component and the output alternating voltage reference value of the grid-structured modular multilevel converter and the q-axis voltage component; The decoupling unit is used for respectively obtaining a d-axis second reference current and a q-axis second reference current from the first reference value of the d-axis current and the first reference value of the q-axis current through a decoupling link, wherein the step of respectively obtaining the d-axis second reference current and the q-axis second reference current from the first reference value of the d-axis current and the first reference value of the q-axis current through the decoupling link further comprises the steps of forming a column vector I rec1 from the first reference value of the d-axis current and the first reference value of the q-axis current, decoupling the column vector I rec2 by using a decoupling matrix, and obtaining the d-axis second reference current and the q-axis second reference current according to the decoupled column vector I rec2 , wherein the form of the decoupling matrix is as follows: where s is the Laplacian, A reference value for the output frequency of the grid-structured modular multilevel converter; a dq-axis control signal acquisition unit configured to obtain a d-axis control signal based on the d-axis current component and a d-axis second reference current, and to obtain a q-axis control signal based on the q-axis current component and the q-axis second reference current; and the control unit is used for obtaining a final control signal according to the d-axis control signal and the q-axis control signal so as to control the input or the cutting of the grid-structured modular multilevel converter.

Description

Method and device for controlling current inner loop decoupling of grid-structured modular multilevel converter Technical Field The invention relates to the technical field of power grids, in particular to a current inner loop decoupling control method and device for a grid-structured modular multilevel converter. Background Unlike grid-connected control based on grid-connected point voltage phase detection, the frequency and phase of the grid-connected control are actively established by the converter, and the grid is embodied as a controlled voltage source. The network-structured control of the converter is originally originated in a micro-grid without a synchronous power supply or a weak synchronous power supply, and is used for solving the off-grid operation problem of the inverter in the micro-grid. With the rapid increase of the renewable energy source ratio, the problem of low inertia weak current network is remarkable, and the research on network construction control is gradually expanded to grid-connected converters such as wind power converters, photovoltaic inverters and energy storage inverters, and has some initial demonstration application. For grid-connected converters under grid-formation control, current limiting is a major technical difficulty. Current limiting schemes currently available include virtual impedance methods and current inner loop methods. The output current is limited by adding an adjustable virtual impedance in the control loop, the current limiting effect is influenced by the fault position of the power grid, and the current limiting precision is poor. The latter realizes current limiting by establishing a three-ring structure of an active synchronous outer ring-alternating voltage middle ring-alternating current inner ring, but the control structure is generally based on a converter design of a two-level topology, adopts an alternating current side filter capacitor thereof as an alternating voltage reference point, and realizes decoupling of active-reactive control. However, the ac side of the modular multilevel topology has no filter capacitor, which makes it difficult to provide this voltage reference point, resulting in poor control performance and coupling of the active and reactive control loops. Disclosure of Invention In order to overcome the defects in the prior art, the invention aims to provide a method and a device for controlling the current inner loop decoupling of a grid-structured modular multilevel converter, so that the coupling between active and reactive control loops can be reduced and the control performance of the multilevel converter can be improved under the condition that a filter capacitor is not arranged at an alternating current side. In order to achieve the above purpose, the present invention provides a current inner loop decoupling control method for a grid-structured modular multilevel converter, comprising the following steps: acquiring three-phase alternating voltage, three-phase alternating current and output active power and reactive power of a public connection point; calculating an output alternating voltage reference value and an output phase angle reference value of the grid-structured modular multilevel converter according to the obtained output active power and reactive power; The method comprises the steps of obtaining a d-axis voltage component and a q-axis voltage component of a public connection point according to three-phase alternating current and an output phase angle reference value, and obtaining a d-axis current component and a q-axis current component of the public connection point according to the three-phase alternating current and the output phase angle reference value; Obtaining a first reference value of d-axis current and q-axis current through integral control according to the difference value between the d-axis voltage component and the output alternating voltage reference value of the grid-structured modular multilevel converter and the q-axis voltage component; respectively obtaining a d-axis second reference current and a q-axis second reference current by a decoupling link of the first reference value of the d-axis current and the first reference value of the q-axis current; obtaining a d-axis control signal according to the d-axis current component and a d-axis second reference current, and obtaining a q-axis control signal according to the q-axis current component and a q-axis second reference current; And obtaining a final control signal according to the d-axis control signal and the q-axis control signal to control the investment or the cutting of the grid-structured modular multilevel converter. Optionally, in the step of calculating the output ac voltage reference value and the output phase angle reference value of the grid-type modular multilevel converter according to the obtained output active power and reactive power, a difference value between the output reactive power of the common connection poi