Second-order LADRC-based grid-connected pre-synchronization control method and system for network-constructed converter

Abstract

The invention discloses a second-order LADRC-based grid-connected pre-synchronization control method and system for a network-constructed converter, and the method comprises the steps: deducing a controlled object according to an active ring of a VSG; laplace inverse transformation is carried out on the controlled object; designing a second-order LADRC, wherein the second-order LADRC comprises a linear expansion observer and a linear state error feedback controller; and the bandwidth # imgabs0 # of the linear expansion observer and the bandwidth # imgabs1 # of the linear state error feedback controller are used as regulation factors to perform control regulation so as to realize grid-connected pre-synchronization of the constructed network type current converter. The control strategy based on second-order LADRC pre-synchronization has the advantages of being high in synchronization speed, small in voltage and power overshoot and small in dependence on system parameters, and can meet functional requirements of different working scenes.

Description

Technical Field

[0001] The present invention belongs to the field of power grids, and relates to grid-connected pre-synchronization control of a grid-connected converter, and specifically to a grid-connected pre-synchronization control method and system for a grid-connected converter based on second-order LADRC. Background Art

[0002] As the interface for distributed microgrids to access the grid, the grid-connected control strategy of the grid-connected converter is directly related to the stable operation of the grid. At present, the grid-connected converter (GFM) mainly uses virtual synchronous machine control (VSG) to provide inertia and damping for the grid. However, if the distributed microgrid is directly connected to the grid, it will cause a large voltage shock to the grid. At present, the main pre-synchronization control methods include phase-locked loop pre-synchronization and coordinate transformation-based pre-synchronization control methods.

[0003] The phase-locked loop-based pre-synchronization control obtains the voltage difference and phase angle difference between the grid side and the converter outlet, and sends them to the active loop and reactive loop controllers of the VSG for secondary adjustment. However, it takes a certain amount of time for the phase-locked loop to start and achieve stability, which affects the pre-synchronization speed of the system.

[0004] The pre-synchronization control based on coordinate transformation realizes the error-free tracking of the grid voltage through the PI controller, which can avoid the adverse effects of the cumbersome operation of the phase-locked loop. However, it is highly dependent on the system parameters and has a large amount of calculation, which requires a high-performance digital processor to implement, increasing the hardware cost.

[0005] Therefore, in the existing pre-synchronization control of the converter, the two requirements of "low dependence on system parameters" and "fast synchronization speed" cannot be achieved at the same time.

[0006] Therefore, a new technical solution is needed to solve this problem. Summary of the invention

[0007] Purpose of the invention: In order to overcome the deficiencies in the prior art, a grid-connected pre-synchronization control method and system for a grid-connected converter based on a second-order LADRC are provided to solve the problems of the existing pre-synchronization control, namely, high dependence on system parameters and slow synchronization speed.

[0008] Technical solution: To achieve the above object, the present invention provides a grid-connected presynchronization control method of a grid-connected converter based on a second-order LADRC, comprising the following steps:

[0009] S1: Derivation of the controlled object based on the active loop of VSG;

[0010] S2: Perform inverse Laplace transformation on the controlled object;

[0011] S3: Design a second-order LADRC, including a linear dilation observer and a linear state error feedback controller;

[0012] The linear extended observer is used to observe the output and total disturbance of the controlled system and provide them to the linear state error feedback controller;

[0013] The linear state error feedback controller is used to control the input of the controlled system according to the system reference value and the observation data provided by the linear expansion observer, and feed back the error data to the linear expansion observer;

[0014] S4: Linearly expand the bandwidth of the observer and the bandwidth of the linear state error feedback controller As a regulating factor, control and adjustment are performed to achieve grid-connected pre-synchronization of the grid-connected converter.

[0015] Furthermore, the expression of the controlled object in step S1 is:

[0016]

[0017] in, Represents the current system angular frequency, is the difference between the current angular frequency and the reference angular frequency, is the rated angular frequency, represents the moment of inertia, represents the damping coefficient, E is the grid voltage, U is the converter outlet voltage, X is the impedance between the converter and the grid; s is the complex frequency component, obtained by Laplace transformation; K p is the active loop droop coefficient; For input Output The transfer function of is the variable value.

[0018] Furthermore, in step S2, the Laplace inverse transform is performed on the controlled object to obtain:

[0019]

[0020] Where t is time; thus, the s domain is converted into the time domain, which is proved to be suitable for second-order active disturbance rejection control.

[0021] Furthermore, the linear expansion observer in step S3 includes , and Three observation points and , and Three gain factors, The output y of the observation system is The differential used to observe the output y, The total disturbance used to observe the system, , and The three gain coefficients are used to estimate and compensate for the uncertain dynamics of the system in real time.

[0022] Furthermore, the linear expansion observer in step S3 is expressed as follows:

[0023] Write the controlled object as ;Will It is defined as the total disturbance of the system, where u and y are the input and output of the system respectively, is the derivative of the output y, w represents the external disturbance, represents the damping characteristics of the control system to the rate of change of the output y, It reflects the recovery characteristics of the output y tending to the equilibrium state, b is the gain coefficient of the input and the influence on the system state, is its estimated value;

[0024] Define the following state variables:

[0025]

[0026] in, represents the output y, represents the derivative of the output y, represents the total disturbance of the system, represents the derivative of the total disturbance of the system;

[0027] The corresponding linear extended state observer is:

[0028]

[0029] in, is the combined input of LESO, is the observer error feedback gain matrix to be designed, , , ; z represents the observed value of x, represents the derivative with respect to z, Represents the observed value of the output y

[0030] Furthermore, in step S3, the linear state error feedback controller adopts TD control to observe the state differential signal, and the TD control law is:

[0031]

[0032] in, , are the proportional gain coefficient and differential gain coefficient of the linear state error feedback controller respectively, and v is the reference value given by the system.

[0033] Furthermore, the bandwidth of the linear state error feedback controller in step S4 is The design and operation of the

[0034] When the system is stable, ; Find the closed-loop transfer function of the input and output:

[0035]

[0036] in, Represents the output, Represents the value of the reference input r after Laplace transformation;

[0037] The pole placement of the linear state error feedback controller is designed by , Make a reasonable choice and select the appropriate pole configuration to make the system stable.

[0038] Furthermore, the bandwidth of the linear expansion observer in step S4 is The design and operation of the

[0039]

[0040] in, represents the characteristic polynomial of the above formula; I represents the identity matrix;

[0041] After parameterization, the poles of the linear expansion observer are configured at the bandwidth On, we have:

[0042]

[0043] Bandwidth of the linear state error feedback controller in the present invention and the bandwidth of the linear expansion observer The control and adjustment methods used as adjustment factors include:

[0044] One is by adjusting the bandwidth Make the system converge to the desired state quickly, avoid voltage overshoot, and improve system stability.

[0045] The second is through bandwidth Quickly capture system dynamic changes, track unknown disturbances in a timely manner, accelerate microgrid pre-synchronization speed, and reduce dependence on system parameters.

[0046] The third is real-time adjustment according to different working conditions. , , optimize control performance.

[0047] The present invention also provides a grid-connected pre-synchronization control system for a grid-connected converter based on a second-order LADRC, comprising:

[0048] The controlled object establishment module is used to derive the controlled object and perform Laplace inverse transformation;

[0049] LADRC design module, used to design second-order LADRC, including linear expansion observer and linear state error feedback controller;

[0050] The pre-synchronization module is used to linearly expand the bandwidth of the observer and the bandwidth of the linear state error feedback controller As a regulating factor, control and adjustment are performed to achieve grid-connected pre-synchronization of the grid-connected converter.

[0051] The control strategy based on second-order LADRC pre-synchronization proposed in the present invention has the advantages of fast synchronization speed, small voltage and power overshoot, and less dependence on system parameters, and can be adapted to the functional requirements of different working scenarios.

[0052] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0053] 1. The present invention estimates and compensates for unknown disturbances and uncertain dynamics of the system in real time by designing an extended state observer, which has higher robustness during operation.

[0054] 2. The method of the present invention can directly control the input and output of the controlled system without complicated parameter setting, thus reducing the deterioration of control performance caused by inaccurate parameters and enhancing the reliability of system operation.

[0055] 3. The present invention has a fast state observation and feedback mechanism, which can complete the distributed microgrid pre-synchronization process in a very short time.

[0056] 4. The LADRC-based pre-synchronization control in the present invention relies on an adaptive parameter adjustment mechanism and does not require communication for data transmission, so that when the converter is connected to the grid, the output voltage and frequency are quickly synchronized with the grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 Schematic diagram of the pre-synchronization control strategy based on LADRC;

[0058] Figure 2 It is the control block diagram of the second-order LADRC;

[0059] Figure 3 It is a single distributed microgrid grid-connected simulation system;

[0060] Figure 4 The active power diagram of the converter with different control strategies under working condition 1;

[0061] Figure 5 The reactive power diagram of the converter with different control strategies under working condition 1;

[0062] Figure 6 The converter voltage data diagram of different control strategies under working condition 1;

[0063] Figure 7 The timing diagram of different strategies satisfying pre-synchronization control for working condition 1;

[0064] Figure 8 It is the active power diagram of different control strategies under working condition 2;

[0065] Fig. 9 It is the reactive power diagram of different control strategies under working condition 2;

[0066] Fig.10 The converter voltage data diagram of different control strategies under working condition 2;

[0067] Fig.11 This is the timing diagram of different strategies satisfying pre-synchronization control under working condition 2. DETAILED DESCRIPTION

[0068] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0069] Embodiment 1:

[0070] This embodiment provides a grid-connected pre-synchronization control method for a grid-connected converter based on a second-order LADRC, comprising the following steps:

[0071] S1: Reference Figure 1 According to the active loop of VSG, the controlled object can be derived according to the Mersenne formula, and its expression is:

[0072]

[0073] in, Represents the current system angular frequency, is the difference between the current angular frequency and the reference angular frequency, is the rated angular frequency, represents the moment of inertia, represents the damping coefficient, E is the grid voltage, U is the converter outlet voltage, X is the impedance between the converter and the grid; s is the complex frequency component, obtained by Laplace transformation; K p is the active loop droop coefficient; For input Output The transfer function of is the variable value; represents the integral, is the electromagnetic power of the converter, is the rated frequency, is the reference frequency, pi represents the pi parameter;

[0074] S2: Perform inverse Laplace transform on the controlled object to obtain:

[0075]

[0076] Where t is time; thus, the s domain is converted into the time domain, which is proved to be suitable for second-order active disturbance rejection control.

[0077] S3: Design a second-order LADRC, including a linear extended state observer (LESO) and a linear state error feedback controller (LSEF);

[0078] The linear extended observer is used to observe the output and total disturbance of the controlled system and provide them to the linear state error feedback controller;

[0079] The linear state error feedback controller is used to control the input of the controlled system according to the system reference value and the observation data provided by the linear expansion observer, and feed back the error data to the linear expansion observer;

[0080] like Figure 2 As shown, f represents external disturbance, G(s) represents transfer function; the linear expansion observer LESO includes , and Three observation points and , and Three gain factors, The output y of the observation system is The differential used to observe the output y, The total disturbance used to observe the system, , and The three gain coefficients are used to estimate and compensate for the uncertain dynamics of the system in real time;

[0081] The linear expansion observer is expressed as follows:

[0082] Write the controlled object as ;Will It is defined as the total disturbance of the system, where u and y are the input and output of the system respectively, is the derivative of the output y, w represents the external disturbance, represents the damping characteristics of the control system to the rate of change of the output y, It reflects the recovery characteristics of the output y tending to the equilibrium state, b is the gain coefficient of the input and the influence on the system state, is its estimated value.

[0083] Define the following state variables:

[0084]

[0085] in, represents the output y, represents the derivative of the output y, represents the total disturbance of the system, represents the derivative of the total disturbance of the system;

[0086]

[0087] in, , , , .

[0088] The corresponding linear extended state observer is:

[0089]

[0090] in, is the combined input of LESO, is the observer error feedback gain matrix to be designed, z represents the observed value of x, represents the derivative with respect to z, Represents the observed value of the output y.

[0091] The linear state error feedback controller uses TD control to observe the state differential signal. The TD control law is:

[0092]

[0093] in, , are the proportional gain coefficient and differential gain coefficient of the linear state error feedback controller respectively, and v is the reference value given by the system.

[0094] S4: Linearly expand the bandwidth of the observer and the bandwidth of the linear state error feedback controller As a regulating factor, control and adjustment are performed to achieve grid-connected pre-synchronization of the grid-connected converter.

[0095] Bandwidth of Linear State Error Feedback Controller The design and operation of the

[0096] When the system is stable, ; Find the closed-loop transfer function of the system input and output:

[0097]

[0098] in, Represents the output, Represents the value of the reference input r after Laplace transformation;

[0099] The pole placement of the linear state error feedback controller is designed by , Make a reasonable choice and select the appropriate pole configuration to make the system stable.

[0100] Bandwidth of the Linear Expansion Observer The design and operation of the

[0101] According to modern control theory, when the (A-LC) eigenvalue is less than 0, the system error will converge to 0 as time goes by.

[0102]

[0103] in, represents the characteristic polynomial of the above formula; I represents the identity matrix;

[0104] After parameterization, the poles of the linear expansion observer are configured at the bandwidth On, we have:

[0105]

[0106] Bandwidth of Linear State Error Feedback Controller and the bandwidth of the linear expansion observer The control and adjustment methods used as adjustment factors include:

[0107] One is by adjusting the bandwidth Make the system converge to the desired state quickly, avoid voltage overshoot, and improve system stability.

[0108] The second is to design a larger observer bandwidth Quickly capture system dynamic changes, track unknown disturbances in a timely manner, accelerate microgrid pre-synchronization speed, and reduce dependence on system parameters.

[0109] The third is real-time adjustment according to different working conditions. , , optimize control performance.

[0110] Embodiment 2:

[0111] Based on the pre-synchronization control method provided in Example 1, this embodiment provides a grid-connected pre-synchronization control system for a grid-connected converter based on a second-order LADRC, including:

[0112] The controlled object establishment module is used to derive the controlled object and perform Laplace inverse transformation;

[0113] LADRC design module, used to design second-order LADRC, including linear expansion observer and linear state error feedback controller;

[0114] The pre-synchronization module is used to linearly expand the bandwidth of the observer and the bandwidth of the linear state error feedback controller As a regulating factor, control and adjustment are performed to achieve grid-connected pre-synchronization of the grid-connected converter.

[0115] Embodiment 3:

[0116] In order to verify the effectiveness and effect of the solution of the present invention, the following simulation experiments are carried out:

[0117] like Figure 3 As shown in the figure, a single distributed microgrid grid-connected simulation system was built, in which: represents the impedance on the converter side, is the voltage at the common coupling point; Xv is the impedance between the converter and the grid side, P V is the active power transmitted to the grid by commutation, Qv is the reactive power transmitted to the grid by commutation, is the grid side voltage, is the grid side impedance, VSG stands for virtual synchronous generator; Grid stands for the grid; S g It is the grid-connected closing switch;

[0118] The parameter settings during the simulation are shown in Table 1, where: Represents the converter side capacitance.

[0119] Table 1 Simulation parameters

[0120]

[0121] Condition 1: When the distributed microgrid is operating in an island mode with a load of 5kW / 0.5kVar, the active reference value increases by 10kW and the reactive reference value increases by 1kVar at 0.2s. A pre-synchronous closing signal is given to the system at 0.5s. The simulation time of the entire system is 2s. The simulation waveform is as follows: Figure 4-Figure 7 shown.

[0122] pass Figure 4-Figure 6 It can be seen that within the 0.5s pre-synchronous closing transition time, the active, reactive and voltage outputs based on the second-order LADRC converter are significantly smoother than the pre-synchronous transition based on coordinate transformation, without a significant impact. Figure 7 It can be seen that the pre-synchronization speed based on the second-order LADRC is significantly faster than the pre-synchronization based on coordinate transformation.

[0123] Working condition 2: When the distributed microgrid is running in an isolated island for 0.2s, the load suddenly increases by 5kW. At 0.5s, the system is given a pre-synchronous closing signal. The active reference value is 10kW. The simulation time of the entire system is 2s. The simulation waveform is as follows: Figure 8-Figure 11 shown.

[0124] pass Figure 8-Figure 10 It can be seen that the active power deviation of the pre-synchronization output based on the second-order LADRC is only 0.1%, while the active power deviation of the pre-synchronization output based on the coordinate transformation is 2.37%, and the power and voltage transitions based on the second-order LADRC at the closing moment are relatively smooth. Fig.11 It can be seen that the pre-synchronization control based on the second-order LADRC can meet the pre-synchronization grid-connected requirements more quickly.

[0125] From the above analysis, it can be seen that the second-order LADRC pre-synchronization control strategy proposed in the present invention not only shortens the grid-connected closing time of the converter and reduces the voltage shock and power shock at the closing moment, but also greatly reduces the impact of external disturbances on the system operation stability and reduces the dependence on system parameters, thus providing a strong guarantee for the reliable grid connection of distributed microgrids.

Claims

1. A grid-connected presynchronization control method for a grid-connected converter based on a second-order LADRC, characterized in that: The steps include: S1: Derivation of the controlled object based on the active loop of VSG; S2: Perform inverse Laplace transformation on the controlled object; S3: Design a second-order LADRC, including a linear dilation observer and a linear state error feedback controller; The linear extended observer is used to observe the output and total disturbance of the controlled system and provide them to the linear state error feedback controller; The linear state error feedback controller is used to control the input of the controlled system according to the system reference value and the observation data provided by the linear expansion observer, and feed back the error data to the linear expansion observer; S4: Linearly expand the bandwidth of the observer and the bandwidth of the linear state error feedback controller As a regulating factor, control and adjustment are performed to achieve grid-connected pre-synchronization of the grid-connected converter.

2. A grid-connected presynchronization control method for a grid-connected converter based on a second-order LADRC according to claim 1, characterized in that: The expression of the controlled object in step S1 is: ； in, Represents the current system angular frequency, is the difference between the current angular frequency and the reference angular frequency, is the rated angular frequency, represents the moment of inertia, represents the damping coefficient, E is the grid voltage, U is the converter outlet voltage, X is the impedance between the converter and the grid; s is the complex frequency component; K p is the active loop droop coefficient; For input Output The transfer function of is the variable value.

3. A grid-connected pre-synchronization control method for a grid-connected converter based on a second-order LADRC according to claim 2, characterized in that: In step S2, the Laplace inverse transform is performed on the controlled object to obtain: ； Where t is time.

4. A grid-connected presynchronization control method for a grid-connected converter based on a second-order LADRC according to claim 3, characterized in that: The linear expansion observer in step S3 includes , and Three observation points and , and Three gain factors, The output y of the observation system is The differential used to observe the output y, The total disturbance used to observe the system, , and The three gain coefficients are used to estimate and compensate for the uncertain dynamics of the system in real time.

5. A grid-connected presynchronization control method for a grid-connected converter based on a second-order LADRC according to claim 4, characterized in that: The linear expansion observer in step S3 is expressed as follows: Write the controlled object as ;Will It is defined as the total disturbance of the system, where u and y are the input and output of the system respectively, is the derivative of the output y, w represents the external disturbance, represents the damping characteristics of the control system to the rate of change of the output y, It reflects the recovery characteristics of the output y tending to the equilibrium state, b is the gain coefficient of the input and the influence on the system state, is its estimated value; Define the following state variables: ； in, represents the output y, represents the derivative of the output y, represents the total disturbance of the system, represents the derivative of the total disturbance of the system; The corresponding linear extended state observer is: ； in, is the combined input of LESO, is the observer error feedback gain matrix to be designed, , , ; z represents the observed value of x, represents the derivative with respect to z, Represents the observed value of the output y.

6. A grid-connected presynchronization control method for a grid-connected converter based on second-order LADRC according to claim 5, characterized in that: In step S3, the linear state error feedback controller uses TD control to observe the state differential signal, and the TD control law is: ； in, , are the proportional gain coefficient and differential gain coefficient of the linear state error feedback controller respectively, and v is the reference value given by the system.

7. A grid-connected presynchronization control method for a grid-connected converter based on a second-order LADRC according to claim 6, characterized in that: The bandwidth of the linear state error feedback controller in step S4 is The design and operation of the When the system is stable, ; Find the closed-loop transfer function of the input and output: ； in, Represents the output, Represents the value of the reference input r after Laplace transformation; The pole placement of the linear state error feedback controller is designed by , Make a selection and choose the pole configuration to make the system stable.

8. A grid-connected presynchronization control method for a grid-connected converter based on a second-order LADRC according to claim 7, characterized in that: The bandwidth of the linear expansion observer in step S4 The design and operation of the ； in, represents the characteristic polynomial of the above formula; I represents the identity matrix; After parameterization, the poles of the linear expansion observer are configured at the bandwidth On, we have: 。 9. A grid-connected presynchronization control system for grid-connected converters based on second-order LADRC, characterized in that: include: The controlled object establishment module is used to derive the controlled object and perform Laplace inverse transformation; LADRC design module, used to design second-order LADRC, including linear expansion observer and linear state error feedback controller; The pre-synchronization module is used to linearly expand the bandwidth of the observer and the bandwidth of the linear state error feedback controller As a regulating factor, control and adjustment are performed to achieve grid-connected pre-synchronization of the grid-connected converter.

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