Grid-connected method of DC voltage synchronous grid-connected converter based on active disturbance rejection control

Abstract

The present invention discloses a method for connecting a DC voltage synchronous grid-type converter to the grid based on self-disturbance rejection control, which belongs to the field of power grids and includes the following steps: S1, designing a second-order extended state observer; S2, calculating the vector orientation angle of the control coordinate system of the grid-connected converter; S3, converting the three-phase inductor current and the three-phase capacitor voltage into d-axis and q-axis DC components in the dq coordinate system; S4, calculating the d-axis voltage outer loop instruction and the q-axis voltage outer loop instruction; S5, obtaining the d-axis and q-axis inductor current inner loop instructions in the dq coordinate system; S6, generating a switch tube control signal for the grid-connected converter. The above-mentioned method for connecting a DC voltage synchronous grid-type converter to the grid based on self-disturbance rejection control is adopted, and the internal and external disturbances of the system are estimated and compensated online through the extended state observer, which does not rely on an accurate system model and has strong robustness.

Description

Technical Field

[0001] The present invention relates to the technical field of power grids, and in particular to a direct current voltage synchronous grid-connected converter grid-connected method based on active anti-disturbance control. Background Art

[0002] With the large-scale construction of new energy bases (especially in deserts, Gobi and wasteland areas) and long-distance access to the main power grid, these grid connection points usually present the characteristics of weak or extremely weak grids with low short-circuit ratios. In this environment, traditional grid connection control methods (such as grid-following control) are prone to power oscillation and frequency instability.

[0003] The emerging grid-based control technology has the following advantages by simulating the behavior of traditional synchronous generators:

[0004] 1. Enhance system stability: Grid-based control can simulate the characteristics of synchronous generators, improve system stability and dynamic response, and especially show better dynamic response under weak grid conditions;

[0005] 2. Inertia and frequency support: Due to the massive access of new energy sources, the power grid presents the characteristics of low inertia and weak damping, and the frequency stability gradually decreases. At this time, the grid-connected converter under grid-type control can provide inertia and frequency support to improve the frequency stability of the power grid;

[0006] 3. Improvement of power quality: The large-scale access of power electronic equipment increases the complexity of the power grid, which may lead to power quality problems such as background harmonics and voltage flicker. For this type of grid control, the power quality can be improved by actively adjusting the grid-connected power and voltage.

[0007] According to the control target of the grid-connected converter, grid-connected control can be divided into grid-connected control based on active power synchronization and grid-connected control based on DC voltage synchronization. Currently, the grid synchronization link in grid-connected control based on DC voltage synchronization mostly adopts proportional control, which has the following defects:

[0008] 1. Since PID control is used in the synchronization link of DC voltage grid control, it has a high dependence on the mathematical model of the controlled object, so accurate system model parameters are required to design the controller;

[0009] 2. Due to the existence of an integral link in the DC bus capacitor during DC voltage synchronization, a phase lag is introduced, which results in a decrease in the stability margin of the system. In order to improve the stability of the system, existing research has connected a lag-lead correction in series in the proportional link. However, there are many control parameters in the lag-lead correction link, and the parameter design is complex. Improper parameter design may introduce defects such as high-frequency noise amplification. Summary of the invention

[0010] The purpose of the present invention is to provide a method for connecting a DC voltage synchronous grid-connected converter to the grid based on active disturbance rejection control to solve the above technical problems.

[0011] To achieve the above object, the present invention provides a method for connecting a DC voltage synchronous grid-connected converter to the grid based on active disturbance rejection control, comprising the following steps:

[0012] S1. Design a second-order extended state observer for observing DC voltage, DC voltage differential term and disturbance term;

[0013] S2, calculating the vector orientation angle of the grid-connected converter control coordinate system based on the DC voltage, DC voltage differential term and disturbance term observed in step S1;

[0014] S3, converting the three-phase inductor current and the three-phase capacitor voltage into d-axis and q-axis DC components in a dq coordinate system;

[0015] S4, calculating the d-axis voltage outer loop instruction and the q-axis voltage outer loop instruction based on the output reactive power and the filter value of the grid-connected converter;

[0016] S5, based on the d-axis and q-axis DC components obtained in step S3 and the d-axis voltage outer loop instruction and the q-axis voltage outer loop instruction obtained in step S4, obtaining the d-axis and q-axis inductor current inner loop instructions in the dq coordinate system;

[0017] S6. Considering the deviation between the d-axis inductor current inner loop command in the dq coordinate system and the d-axis DC component of the three-phase inductor current in the control coordinate system, the deviation between the q-axis inductor current inner loop command and the q-axis DC component of the three-phase inductor current in the control coordinate system, and the voltage feedforward amount, the switch tube control signal of the grid-connected converter is generated.

[0018] Preferably, the second-order extended state observer expression in step S1 is as follows:

[0019] (1);

[0020] In the formula, , , Represent the observed values ​​of DC voltage , Observed value of DC voltage differential term and the observed value of the disturbance term The derivative of , , Both represent the gain parameters of the second-order extended state observer; Indicates system parameters; Represents the output item of the controller; Indicates the DC bus voltage of the grid-connected converter; represents the output of the second-order extended state observer.

[0021] Preferably, the expression of the vector orientation angle of the grid-connected converter control coordinate system described in step S2 is as follows:

[0022] (2);

[0023] In the formula, Indicates the reference value of DC voltage, , All represent control parameters in the feedback control rate; Represents the vector orientation angle of the grid-connected converter control coordinate system; represents a complex frequency variable; Indicates the rated angular frequency of the power grid.

[0024] Preferably, in step S3, the three-phase inductor current of the grid-connected converter is collected , , With three-phase capacitor voltage , , Input the coordinate transformation formula to obtain the d-axis and q-axis DC components of the three-phase inductor current in the control coordinate system. , And the d-axis and q-axis DC components of the three-phase capacitor voltage in the control coordinate system , , where the coordinate transformation formula is as follows:

[0025] (3).

[0026] Preferably, step S4 specifically includes the following steps:

[0027] S41. Calculate the output reactive power of the grid-connected converter and filter value :

[0028] (4);

[0029] (5);

[0030] In the formula, represents the cutoff frequency of the filter;

[0031] S42, output reactive power and filter value Substituting into formula (6) we get the d-axis voltage outer loop command: and q-axis voltage outer loop command :

[0032] (6);

[0033] (7);

[0034] In the formula, and represent the proportional and integral parameters of the reactive power controller respectively; represents the initial voltage; Indicates the reference reactive power.

[0035] Preferably, in step S5, the grid-connected converter sets the d-axis voltage outer loop instruction The d-axis DC component of the three-phase capacitor voltage in the control coordinate system Deviation, q-axis voltage outer loop command The q-axis DC component of the three-phase capacitor voltage in the control coordinate system The deviations are input into the PI regulator of the voltage outer loop to obtain the d-axis inductor current inner loop command in the dq coordinate system. , q-axis inductor current inner loop command .

[0036] Preferably, step S6 specifically includes the following steps:

[0037] S61, calculate the d-axis inductor current inner loop instruction The d-axis DC component of the three-phase inductor current in the control coordinate system The deviation between the q-axis inductor current inner loop command The q-axis DC component of the three-phase inductor current in the control coordinate system The deviation between them is input into the PI regulator of the inductor current inner loop respectively;

[0038] S62, the PI regulator output of the inductor current inner loop is superimposed on the voltage feedforward of the grid-connected point, and the d-axis grid-connected converter command in the dq coordinate system is obtained. ,q-axis grid-connected converter instruction ;

[0039] S63, using SVPWM to convert the d-axis grid-connected converter command in the dq coordinate system ,q-axis grid-connected converter instruction Converted into switch control signal of grid-connected converter;

[0040] S64. Control the grid-connected converter based on the switch control signal generated in step S64.

[0041] Therefore, the present invention adopts the above-mentioned DC voltage synchronous grid-connected converter grid-connected method based on active disturbance rejection control, which has the following beneficial effects:

[0042] 1. The system's internal and external disturbances are estimated and compensated online through the second-order extended state observer, which does not rely on an accurate system model. Even if the system model is inaccurate or the external grid impedance changes, the anti-disturbance control can achieve closed-loop control of the DC voltage, and has strong robustness.

[0043] 2. Through the combination of control rate and observer, the dynamic fluctuation of DC voltage can be effectively suppressed and the dynamic response of DC voltage can be improved;

[0044] 3. The extended state observer estimates and compensates disturbances in real time, which can not only eliminate the impact of external disturbances, but also compensate for the internal uncertainty of the system (such as parameter changes, etc.), thereby improving the DC voltage immunity of the system.

[0045] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a flow chart of a method for connecting a DC voltage synchronous grid-connected converter to the grid based on active disturbance rejection control according to the present invention;

[0047] Figure 2 A control block diagram of a method for connecting a DC voltage synchronous grid-connected converter to the grid based on active disturbance rejection control according to the present invention;

[0048] Figure 3 The dynamic waveforms of the DC voltage output and the grid-connected current output when the DC side input power disturbance increases as described in the simulation experiment, where (a) is the output dynamic waveform of the DC voltage; (b) is the waveform of the grid-connected current of the a-phase of the grid-connected converter;

[0049] Figure 4 The dynamic waveform diagram of DC voltage output and grid-connected current output when the DC voltage reference value changes stepwise in the simulation experiment, where (a) is the DC voltage waveform diagram; (b) is the current waveform diagram. DETAILED DESCRIPTION

[0050] In the description of the present invention, it should be noted that the terms "upper", "lower", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the invented product is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In the description of the present invention, it should also be noted that, unless otherwise clearly specified and limited, the terms "setting", "installation", and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0051] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0052] like Figure 1 and Figure 2 As shown, a method for connecting a DC voltage synchronous grid-connected converter to the grid based on active disturbance rejection control comprises the following steps:

[0053] S1. Design a second-order extended state observer for observing DC voltage, DC voltage differential term and disturbance term;

[0054] The second-order extended state observer expression in step S1 is as follows:

[0055] (1);

[0056] In the formula, , , Represent the observed values ​​of DC voltage , Observed value of DC voltage differential term and the observed value of the disturbance term The derivative of , , Both represent the gain parameters of the second-order extended state observer; Indicates system parameters; Represents the output item of the controller; Indicates the DC bus voltage of the grid-connected converter; represents the output of the second-order extended state observer.

[0057] S2, calculating the vector orientation angle of the grid-connected converter control coordinate system based on the DC voltage, DC voltage differential term and disturbance term observed in step S1;

[0058] The expression of the vector orientation angle of the grid-connected converter control coordinate system described in step S2 is as follows:

[0059] (2);

[0060] In the formula, Indicates the reference value of DC voltage, , All represent control parameters in the feedback control rate; Represents the vector orientation angle of the grid-connected converter control coordinate system; represents a complex frequency variable; Indicates the rated angular frequency of the power grid.

[0061] S3, converting the three-phase inductor current and the three-phase capacitor voltage into d-axis and q-axis DC components in a dq coordinate system;

[0062] In step S3, the three-phase inductor current of the grid-connected converter is collected , , With three-phase capacitor voltage , , Input the coordinate transformation formula to obtain the d-axis and q-axis DC components of the three-phase inductor current in the control coordinate system. , And the d-axis and q-axis DC components of the three-phase capacitor voltage in the control coordinate system , , where the coordinate transformation formula is as follows:

[0063] (3).

[0064] S4, calculating the d-axis voltage outer loop instruction and the q-axis voltage outer loop instruction based on the output reactive power and the filter value of the grid-connected converter;

[0065] Step S4 specifically includes the following steps:

[0066] S41. Calculate the output reactive power of the grid-connected converter and filter value :

[0067] (4);

[0068] (5);

[0069] In the formula, represents the cutoff frequency of the filter;

[0070] S42, output reactive power and filter value Substituting into formula (6) we get the d-axis voltage outer loop command: and q-axis voltage outer loop command :

[0071] (6);

[0072] (7);

[0073] In the formula, and represent the proportional and integral parameters of the reactive power controller respectively; represents the initial voltage; Indicates the reference reactive power.

[0074] S5, based on the d-axis and q-axis DC components obtained in step S3 and the d-axis voltage outer loop instruction and the q-axis voltage outer loop instruction obtained in step S4, obtaining the d-axis and q-axis inductor current inner loop instructions in the dq coordinate system;

[0075] In step S5, the grid-connected converter sets the d-axis voltage outer loop instruction The d-axis DC component of the three-phase capacitor voltage in the control coordinate system Deviation, q-axis voltage outer loop command The q-axis DC component of the three-phase capacitor voltage in the control coordinate system The deviations are input into the PI regulator of the voltage outer loop to obtain the d-axis inductor current inner loop command in the dq coordinate system. , q-axis inductor current inner loop command .

[0076] S6. Considering the deviation between the d-axis inductor current inner loop command in the dq coordinate system and the d-axis DC component of the three-phase inductor current in the control coordinate system, the deviation between the q-axis inductor current inner loop command and the q-axis DC component of the three-phase inductor current in the control coordinate system, and the voltage feedforward amount, the switch tube control signal of the grid-connected converter is generated.

[0077] Step S6 specifically includes the following steps:

[0078] S61, calculate the d-axis inductor current inner loop instruction The d-axis DC component of the three-phase inductor current in the control coordinate system The deviation between the q-axis inductor current inner loop command The q-axis DC component of the three-phase inductor current in the control coordinate system The deviation between them is input into the PI regulator of the inductor current inner loop respectively;

[0079] S62, the PI regulator output of the inductor current inner loop is superimposed on the voltage feedforward of the grid-connected point, and the d-axis grid-connected converter command in the dq coordinate system is obtained. ,q-axis grid-connected converter instruction ;

[0080] In this embodiment, two PI controllers of the inner loop of the inductor current are used to implement fast zero-static-error tracking control of the inductor current.

[0081] S63, using SVPWM to convert the d-axis grid-connected converter command in the dq coordinate system ,q-axis grid-connected converter instruction Converted into switch control signal of grid-connected converter;

[0082] S64. Control the grid-connected converter based on the switch control signal generated in step S64.

[0083] Simulation experiment

[0084] Based on Matlab / Simulink simulation platform, Figure 2 The control block diagram shown in the figure, where the grid strength is configured as an extremely weak grid, the grid short-circuit ratio is set to 1.1, and the resistance / reactance in the line impedance is set to 10. After the DC voltage synchronous grid-connected converter grid-connected method based on active disturbance rejection control of the present invention is adopted, when the DC side input power increases from zero to full load of the system, the output dynamic waveform of the DC voltage and the a-phase grid-connected current of the grid-connected converter are obtained as follows: Figure 3 As shown, it can be seen that during the whole process, the DC voltage remains at a relatively stable level. During the power change process, the DC voltage has some small fluctuations, but it can be restored to stability in a very short time. At the same time, it can be seen that with the increase of the DC side input power, the a-phase grid-connected current gradually increases. During the power change process, the current also has some fluctuations, but it gradually rises overall, and after the power reaches full load, the current tends to be stable. When the grid-connected converter is running at full power, the dynamic waveform of the DC voltage when the DC voltage command jumps up and down, the result is as follows Figure 4 As shown, it can be seen that the DC voltage remains at a stable level at the beginning, then rises at a certain time point (about 2 seconds), and remains stable thereafter; then, at another time point (about 6 seconds), it quickly drops back to the original level and continues to remain stable; at the same time, the current waveform remains relatively stable throughout the entire time period, without obvious mutations or abnormalities; thereby verifying the effectiveness of the present invention.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for connecting a DC voltage synchronous grid-connected converter to the grid based on active disturbance rejection control, characterized in that: The following steps are involved: S1. Design a second-order extended state observer for observing DC voltage, DC voltage differential term and disturbance term; S2, calculating the vector orientation angle of the grid-connected converter control coordinate system based on the DC voltage, DC voltage differential term and disturbance term observed in step S1; S3, converting the three-phase inductor current and the three-phase capacitor voltage into d-axis and q-axis DC components in a dq coordinate system; S4, calculating the d-axis voltage outer loop instruction and the q-axis voltage outer loop instruction based on the output reactive power and the filter value of the grid-connected converter; S5, based on the d-axis and q-axis DC components obtained in step S3 and the d-axis voltage outer loop instruction and the q-axis voltage outer loop instruction obtained in step S4, obtaining the d-axis and q-axis inductor current inner loop instructions in the dq coordinate system; In step S5, the grid-connected converter sets the d-axis voltage outer loop instruction The d-axis DC component of the three-phase capacitor voltage in the control coordinate system Deviation, q-axis voltage outer loop command The q-axis DC component of the three-phase capacitor voltage in the control coordinate system The deviations are input into the PI regulator of the voltage outer loop to obtain the d-axis inductor current inner loop command in the dq coordinate system. , q-axis inductor current inner loop command ; S6, considering the deviation between the d-axis inductor current inner loop command in the dq coordinate system and the d-axis DC component of the three-phase inductor current in the control coordinate system, the deviation between the q-axis inductor current inner loop command and the q-axis DC component of the three-phase inductor current in the control coordinate system, and the voltage feedforward amount, to generate a switch tube control signal of the grid-connected converter; Step S6 specifically includes the following steps: S61, calculate the d-axis inductor current inner loop instruction The d-axis DC component of the three-phase inductor current in the control coordinate system The deviation between the q-axis inductor current inner loop command The q-axis DC component of the three-phase inductor current in the control coordinate system The deviation between them is input into the PI regulator of the inductor current inner loop respectively; S62, the PI regulator output of the inductor current inner loop is superimposed on the voltage feedforward of the grid-connected point, and the d-axis grid-connected converter command in the dq coordinate system is obtained. ,q-axis grid-connected converter instruction ; S63, using SVPWM to convert the d-axis grid-connected converter command in the dq coordinate system ,q-axis grid-connected converter instruction Converted into switch control signal of grid-connected converter; S64. Control the grid-connected converter based on the switch control signal generated in step S64.

2. The method for connecting a DC voltage synchronous grid-connected converter to the grid based on active disturbance rejection control according to claim 1 is characterized in that: The second-order extended state observer expression in step S1 is as follows: （1）； In the formula, , , Represent the observed values ​​of DC voltage , Observed value of DC voltage differential term and the observed value of the disturbance term The derivative of , , Both represent the gain parameters of the second-order extended state observer; Indicates system parameters; Represents the output item of the controller; Indicates the DC bus voltage of the grid-connected converter; represents the output of the second-order extended state observer.

3. The method for connecting a DC voltage synchronous grid-connected converter to the grid based on active disturbance rejection control according to claim 2, characterized in that: The expression of the vector orientation angle of the grid-connected converter control coordinate system described in step S2 is as follows: （2）； In the formula, Indicates the reference value of DC voltage, , All represent control parameters in the feedback control rate; Represents the vector orientation angle of the grid-connected converter control coordinate system; represents a complex frequency variable; Indicates the rated angular frequency of the power grid.

4. The method for connecting a DC voltage synchronous grid-connected converter to the grid based on active disturbance rejection control according to claim 3 is characterized in that: In step S3, the three-phase inductor current of the grid-connected converter is collected , , With three-phase capacitor voltage , , Input the coordinate transformation formula to obtain the d-axis and q-axis DC components of the three-phase inductor current in the control coordinate system. , And the d-axis and q-axis DC components of the three-phase capacitor voltage in the control coordinate system , , where the coordinate transformation formula is as follows: （3）。 5. The method for connecting a DC voltage synchronous grid-connected converter to the grid based on active disturbance rejection control according to claim 4 is characterized in that: Step S4 The specific steps include: S41. Calculate the output reactive power of the grid-connected converter and filter value : （4）； （5）； In the formula, represents the cutoff frequency of the filter; S42, output reactive power and filter value Substituting into formula (6) we get the d-axis voltage outer loop command: and q-axis voltage outer loop command : （6）； （7）； In the formula, and represent the proportional and integral parameters of the reactive power controller respectively; represents the initial voltage; Indicates the reference reactive power.

Images