Frequency damping-based parameter identification method for active power control of grid-forming type photovoltaic converter

Abstract

The invention discloses a frequency damping-based parameter identification method for active power control of a grid-forming photovoltaic converter, and the method comprises the steps: collecting the voltage and current of a grid-connected point, and obtaining a corresponding DC component after coordinate transformation; obtaining active power and reactive power output by the photovoltaic grid-connected converter and active power and reactive power after passing through a low-pass filter; outputting frequency and voltage amplitude through active power control and reactive-voltage droop control of frequency damping; and the voltage amplitude and the feedback deviation are sent to a voltage and current double closed loop, and a converter driving signal is generated through modulation. When parameter identification is carried out on an active power control equation based on frequency damping, an active power control model is discretized and then transformed into a difference equation; unknown parameters in the difference equation are identified, and active power control parameters are calculated. According to the method, frequency damping optimization enhancement in active power control of the grid-forming type photovoltaic converter can be realized, identification prediction of control parameters is realized, and the photovoltaic converter is enabled to operate more stably.

Description

Technical Field

[0001] The present invention relates to the field of new energy access and control technology, and more specifically, to a parameter identification method for active power control of a grid-connected photovoltaic converter based on frequency damping. Background Art

[0002] As my country's energy structure continues to optimize, the proportion of new energy sources has gradually increased, among which the penetration rate of photovoltaic power generation has continued to increase. As an important link in connecting photovoltaic components to the power grid, the control structure of the converter is crucial to the stable operation of the system. Different from the passive following of the grid-following control, the grid-building control can realize active support characteristics, which can improve the dynamic performance and stability of the photovoltaic converter control system. However, the common virtual synchronous grid-building control has poor active power dynamic response characteristics, slow system dynamic response process, and large overshoot. In existing studies, in order to improve the synchronization stability of the photovoltaic converter control system by adjusting the control parameters, a control method of adding auxiliary damping to the synchronization is proposed, which improves the synchronization stability and small signal stability of the control system. However, the conventional auxiliary damping control scheme has a weak improvement on the dynamic performance of active power.

[0003] At the same time, when identifying the relevant parameters of the active power response model under the current grid-type control, it is usually to establish a second-order model of the grid-connected inverter based on VSG control, determine the applicable range of the linearized model to impose power disturbances, and finally propose a VSG inertia and damping identification algorithm based on the least squares method. However, the influence of the voltage and current dual closed-loop control structure is not considered in this identification model. In the actual operation of the system, the voltage and current dual closed-loop will have a certain lag characteristic relative to the power control loop of the previous level, and present a negative damping effect in the dynamic response process of active power. Therefore, when modeling the active power closed-loop control and studying its power response characteristics, it is necessary to consider the influence of the voltage and current closed-loop in the next link. Summary of the invention

[0004] The present invention aims to solve the deficiencies of the above-mentioned prior art and proposes a parameter identification method for active power control of a grid-connected photovoltaic converter based on frequency damping, in order to improve the damping characteristics in the frequency response process, suppress overshoot in the active power dynamic response process and accelerate the dynamic response speed of the system, thereby optimizing the dynamic response characteristics of the active power and providing better support for the power grid.

[0005] In order to achieve the above-mentioned purpose, the present invention adopts the following technical scheme:

[0006] The parameter identification method of the active power control of a grid-type photovoltaic converter based on frequency damping of the present invention is characterized in that it includes:

[0007] Collect the a-phase, b-phase, and c-phase voltages at the grid-connected point of the grid-connected photovoltaic inverter , , and the inductor currents of phases a, b, and c , , After transformation, we can get the voltages of phase a, phase b, and phase c. , , DC components of d-axis and q-axis voltages in a synchronously rotating coordinate system , And the inductor current of phase a, phase b, and phase c , , The DC components of the d-axis and q-axis currents in the synchronously rotating coordinate system , ;

[0008] based on , as well as , , obtain the active power output of the grid-connected photovoltaic inverter And the reactive power output of the stator ;

[0009] based on and , respectively obtain the active power after passing through the low-pass filter and reactive power ;

[0010] Under the premise of considering the voltage outer loop, the frequency of the grid-connected photovoltaic converter is output by using the active power control equation based on frequency damping. ,angle ;

[0011] Calculate the voltage amplitude of reactive power-voltage droop control output ;

[0012] Calculate the synchronous rotating coordinate system The DC component of the d-axis voltage Deviation, zero value and The deviation is input into the PI regulator of the voltage outer loop for processing, thereby outputting the d-axis and q-axis current instructions. , ;

[0013] Calculate the synchronous rotation coordinate system and The deviation between and The deviation between them is input into the PI regulator of the current inner loop for processing, thereby outputting the d-axis and q-axis voltage instructions of PWM modulation. , ;

[0014] Will , After coordinate inverse transformation and SVPWM modulation, the switch control signal of the grid-connected photovoltaic converter is generated to realize active power control of the photovoltaic converter.

[0015] The parameter identification method for active power control of grid-connected photovoltaic converter based on frequency damping of the present invention is also characterized in that the voltages of phase a, phase b and phase c of the grid-connected point are obtained by using formula (1). , , DC components of d-axis and q-axis voltages in synchronously rotating coordinate systems , And the a-phase, b-phase, and c-phase inductor currents , , The DC components of the d-axis and q-axis currents in the synchronously rotating coordinate system , :

[0016] (1)

[0017] In formula (1), is the orientation angle of the coordinate transformation, , , Represents the AC components of voltage and current in the stationary coordinate system of phase a, phase b, and phase c, , Represents the d-axis and q-axis DC components of voltage and current in the synchronous rotating coordinate system;

[0018] Use formula (2) to obtain the active power output of the photovoltaic converter and output reactive power :

[0019] (2)

[0020] Use formula (3) to obtain the active power after passing through the low-pass filter and reactive power after low-pass filter ,include:

[0021] (3)

[0022] In formula (3), represents the cutoff frequency of the low-pass filter, represents the Laplace operator.

[0023] Furthermore, the active power control equation based on frequency damping is constructed using equation (4):

[0024] (4)

[0025] In formula (4), is the inertia constant; D d is the damping coefficient; is the rated frequency; are active power reference values, For customized parameters.

[0026] Furthermore, the voltage amplitude is obtained using formula (5): , and used as the d-axis voltage reference value:

[0027] (5)

[0028] In formula (5), is the voltage reference value, is the reactive power reference value, is the droop proportionality coefficient.

[0029] Furthermore, the d-axis and q-axis voltage instructions of PWM modulation are obtained using formula (6): , :

[0030] (6)

[0031] In formula (6), and are the proportional coefficient and integral coefficient of the PI regulator of the current inner loop, and are the proportional coefficient and integral coefficient of the PI regulator of the voltage outer loop, is the inductance value of the filter inductor, is the capacitance value of the filter capacitor.

[0032] Furthermore, the parameters of the active power control equation based on frequency damping are identified according to the following process:

[0033] Active power control equation based on frequency damping The active power control model based on frequency damping is constructed;

[0034] The active power control model is discretized by using bilinear transformation to obtain the discretized active power control model;

[0035] Construct the difference equation based on the discretized active power control model;

[0036] The damped recursive least squares method is used to identify the parameters in the difference equation, and then the inertia constant of the active power control equation based on frequency damping is calculated using the identified parameters. , damping coefficient D d As well as the proportional coefficient and integral coefficient of the PI regulator of the voltage outer loop.

[0037] Furthermore, the active power control model based on frequency damping is constructed using equation (7): :

[0038] (7)

[0039] In formula (7), represents the gain coefficient;

[0040] Using formula (8), we can get the discretized active power control model: :

[0041] (8)

[0042] In formula (8), , are the input change of power given value and the output change of power response in the power response process, respectively. , , , , , , There are 7 parameters to be identified. represents a complex frequency variable;

[0043] Use formula (9) to construct the difference equation:

[0044] (9)

[0045] In formula (9), , , , Respectively represent , No. , No. , No. The power response output change of the wheel, , , , Respectively represent , No. , No. , No. The input change of the power setpoint of the wheel;

[0046] The recursive relationship of the damped recursive least squares method is constructed using formula (10):

[0047] (10)

[0048] In formula (10), is the damping factor, , , are the parameter vectors to be identified In the , No. , No. The identification value of the wheel, when k=0, let , Indicates The criterion coefficient of the wheel, Indicates The inverse of the wheel criterion coefficient, For the The data vector of the round input, T represents the transpose, and there are:

[0049] (11)

[0050] (12)

[0051] The termination criterion is constructed using formula (13), so that when formula (13) is satisfied, the parameters after 7 parameter identification are obtained. , , , , , , :

[0052] (13)

[0053] In formula (13), Indicates The wheel identification value, is the threshold of error accuracy.

[0054] Furthermore, the inertia constant is obtained using formula (14): , damping coefficient D d And the proportional coefficient of the PI regulator of the voltage outer loop and the integration coefficient K iu :

[0055] (14)

[0056] In formula (14), , , They represent the inertia transfer coefficient, damping transfer coefficient, and voltage transfer coefficient respectively. is the sampling time of the bilinear transform, and:

[0057] (15).

[0058] An electronic device of the present invention includes a memory and a processor, wherein the memory is used to store a program that supports the processor to execute the parameter identification method for active power control of a grid-connected photovoltaic inverter based on frequency damping, and the processor is configured to execute the program stored in the memory.

[0059] The present invention provides a computer-readable storage medium, and the computer-readable storage medium stores a computer program, wherein when the computer program is run by a processor, the steps of the parameter identification method for active power control of a grid-connected photovoltaic inverter based on frequency damping are executed.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] 1. In order to optimize the active power dynamic response characteristics of the grid-type photovoltaic inverter during grid-connected power generation and provide better support for the power grid, the present invention proposes a grid-type photovoltaic inverter active power response optimization strategy based on frequency damping. This strategy solves the problem of insufficient damping in the frequency response process, improves the damping characteristics in the frequency response process, effectively suppresses the overshoot of the active power dynamic response process, and accelerates the dynamic response speed of the system.

[0062] 2. The present invention fully considers the hysteresis characteristics of voltage loop control, overcomes the problem of inaccurate traditional active power modeling, establishes a complete active power response identification model considering voltage loop control, realizes the identification and prediction of active power control parameters, and finally realizes the efficient and stable operation of grid-connected photovoltaic inverters.

[0063] 3. The present invention proposes a relevant parameter identification scheme based on the damped recursive least squares method, which overcomes the problem of large amount of calculation and easy divergence in traditional least squares parameter identification, and realizes the predictive identification of active power control parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 This is a control structure diagram of a grid-type photovoltaic converter based on frequency damping in the present invention;

[0065] Figure 2 This is a structure diagram of active power VSG control based on frequency damping in the present invention;

[0066] Figure 3 It is a reactive power-voltage droop control structure diagram in the present invention;

[0067] Figure 4 This is a voltage and current double closed-loop control structure diagram in the present invention;

[0068] Figure 5 This is a structural diagram of the active power control model based on frequency damping in the present invention. DETAILED DESCRIPTION

[0069] The specific implementation modes of the present invention will be further described in detail below in conjunction with the accompanying drawings.

[0070] In this embodiment, a parameter identification method for active power control of a grid-type photovoltaic converter based on frequency damping has the function of suppressing overshoot of the active power dynamic response process and accelerating the dynamic response speed of the system, while considering the hysteresis characteristics of the voltage loop control, and identifying and predicting the active power control parameters. Specifically, reference Figure 1 , the method is carried out in the following steps:

[0071] Step 1: Collect the voltages of phase A, phase B, and phase C at the grid connection point of the grid-connected photovoltaic inverter , , and the inductor currents of phases a, b, and c , , And after transformation using formula (1), we get the voltages of phase a, phase b, and phase c: , , DC components of d-axis and q-axis voltages in a synchronously rotating coordinate system , And the inductor current of phase a, phase b, and phase c , , The DC components of the d-axis and q-axis currents in the synchronously rotating coordinate system , ;

[0072] (1)

[0073] In formula (1), is the orientation angle of the coordinate transformation, , , Represents the AC components of voltage and current in the stationary coordinate system of phase a, phase b, and phase c, , Represents the d-axis and q-axis DC components of voltage and current in the synchronous rotating coordinate system;

[0074] Step 2: Based on , as well as , , using formula (2) to obtain the active power output of the grid-connected photovoltaic inverter And the reactive power output of the stator ;

[0075] Get the active power output of the photovoltaic inverter and output reactive power :

[0076] (2)

[0077] Step 3: Based on and , use formula (3) to obtain the active power after passing through the low-pass filter and reactive power ;

[0078] (3)

[0079] In formula (3), represents the cutoff frequency of the low-pass filter, represents the Laplace operator.

[0080] Step 4. Reference Figure 2 , the active power control equation based on frequency damping is constructed using equation (4), so that the frequency of the grid-type photovoltaic converter is output using the active power control equation based on frequency damping under the premise of considering the voltage outer loop. ,angle :

[0081] (4)

[0082] In formula (4), is the inertia constant; D d is the damping coefficient; is the rated frequency; are active power reference values, For customized parameters.

[0083] In the specific implementation, the parameters of the active power control equation based on frequency damping are identified according to the following process:

[0084] Step a: Reference Figure 5 , the active power control equation based on frequency damping, using formula (7) to construct the active power control model based on frequency damping ;

[0085] (7)

[0086] In formula (7), represents the gain coefficient;

[0087] Step b: Discretize the active power control model using the bilinear transformation shown in formula (8) to obtain the discretized active power control model ;

[0088] (8)

[0089] In formula (8), , are the input change of power given value and the output change of power response in the power response process, respectively. , , , , , , There are 7 parameters to be identified. represents a complex frequency variable;

[0090] Step c: Based on the discretized active power control model, a differential equation is constructed using formula (9);

[0091] (9)

[0092] In formula (9), , , , Respectively represent , , , The power response output change of the wheel, , , , Respectively represent , , , The input change of the power setting value of the wheel

[0093] Step d, using the damped recursive least squares method to identify the parameters in the differential equation to obtain the identified parameters: Step d1, using formula (10) to construct the recursive relationship of the damped recursive least squares method:

[0094] (10)

[0095] In formula (10), is the damping factor, , , are the parameter vectors to be identified , in , , The wheel identification value, Indicates Wheel criterion coefficient, Indicates The inverse of the wheel criterion coefficient, For the The input data vector is round, T represents transpose, specifically:

[0096] (11)

[0097] (12)

[0098] Step d2: Set the initial value of the parameter to be identified, and then use the damped recursive least squares method to iterate. For convenience, in actual application, the initial value is As the recursive process progresses, when the error reaches a certain accuracy When , the operation process terminates, and the termination criterion is:

[0099] (13)

[0100] in Indicates The wheel identification value.

[0101] Step d3: Use the damped recursive least squares method to obtain the actual values ​​of the seven parameters after identification. , , , , , , .

[0102] Step e: Using the identified parameters, calculate the inertia constant of the active power control equation based on frequency damping according to the following process: , damping coefficient D d As well as the proportional coefficient and integral coefficient of the PI regulator of the voltage outer loop.

[0103] Step e1: Combining equation (7) and equation (9), the relationship between the parameter to be identified and the active power control parameter can be obtained as shown in equation (14):

[0104] (14)

[0105] In formula (14), , , They represent the inertia transfer coefficient, damping transfer coefficient, and voltage transfer coefficient respectively. is the sampling time of the bilinear transformation. And:

[0106] (15)

[0107] Step e2: Substitute the actual values ​​of the 7 parameters after identification into equation (14) to obtain the control parameters of the active power control system: , D d And voltage outer loop control parameters , K iu The value of .

[0108] Step 5. Reference Figure 3 , use formula (5) to calculate the voltage amplitude of reactive power-voltage droop control output , and used as the d-axis voltage reference value;

[0109] (5)

[0110] In formula (5), is the voltage reference value, is the reactive power reference value, is the droop proportionality coefficient.

[0111] Step 6: Calculate the synchronous rotating coordinate system The DC component of the d-axis voltage Deviation, zero value and The deviation is input into the PI regulator of the voltage outer loop for processing, thereby outputting the d-axis and q-axis current instructions. , ;

[0112] Step 7. Reference Figure 4 , using formula (6) to calculate the synchronous rotating coordinate system and The deviation between and The deviation between them is input into the PI regulator of the current inner loop for processing, thereby outputting the d-axis and q-axis voltage instructions of PWM modulation. , ;

[0113] (6)

[0114] In formula (6), and are the proportional coefficient and integral coefficient of the PI regulator of the current inner loop, and are the proportional coefficient and integral coefficient of the PI regulator of the voltage outer loop, is the inductance value of the filter inductor, is the capacitance value of the filter capacitor.

[0115] Step 8: , After coordinate inverse transformation and SVPWM modulation, the switch control signal of the grid-connected photovoltaic converter is generated to realize active power control of the photovoltaic converter.

[0116] In this embodiment, an electronic device includes a memory and a processor, wherein the memory is used to store a program that supports the processor to execute the above method, and the processor is configured to execute the program stored in the memory.

[0117] In this embodiment, a computer-readable storage medium stores a computer program on the computer-readable storage medium, and the computer program executes the steps of the above method when executed by a processor.

[0118] In summary, the present invention adds a control structure based on frequency damping to the traditional grid-type VSG active power control, improves the damping characteristics in the frequency response process, effectively suppresses the overshoot of the active power dynamic response process, and accelerates the dynamic response speed of the system. The active power control output based on frequency damping controls the angle of the system coordinate transformation, the reactive-voltage droop control outputs the reference value of the voltage outer loop, the voltage outer loop output is used as the current inner loop reference value, and finally the current inner loop output is PWM modulated to generate the switch tube control signal of the photovoltaic converter. At the same time, the present invention takes into account the hysteresis characteristics of the voltage loop control, establishes a complete active power response identification model considering the voltage loop control, proposes a related parameter identification scheme based on the damped recursive least squares method, and realizes the prediction and identification of active power control parameters.

Claims

1. A parameter identification method for active power control of a grid-connected photovoltaic converter based on frequency damping, characterized in that: include: Collect the a-phase, b-phase, and c-phase voltages at the grid-connected point of the grid-connected photovoltaic inverter , , and the inductor currents of phases a, b, and c , , After transformation, we can get the voltages of phase a, phase b, and phase c. , , DC components of d-axis and q-axis voltages in a synchronously rotating coordinate system , And the inductor current of phase a, phase b, and phase c , , The DC components of the d-axis and q-axis currents in the synchronously rotating coordinate system , ; based on , as well as , , obtain the active power output of the grid-connected photovoltaic inverter And the reactive power output of the stator ; based on and , respectively obtain the active power after passing through the low-pass filter and reactive power ; Under the premise of considering the voltage outer loop, the frequency of the grid-connected photovoltaic converter is output by using the active power control equation based on frequency damping. ,angle ; Calculate the voltage amplitude of reactive power-voltage droop control output ; Calculate the synchronous rotating coordinate system The DC component of the d-axis voltage Deviation, zero value and The deviation is input into the PI regulator of the voltage outer loop for processing, thereby outputting the d-axis and q-axis current instructions. , ; Calculate the synchronous rotation coordinate system and The deviation between and The deviation between them is input into the PI regulator of the current inner loop for processing, thereby outputting the d-axis and q-axis voltage instructions of PWM modulation. , ; Will , After coordinate inverse transformation and SVPWM modulation, the switch control signal of the grid-connected photovoltaic converter is generated to realize active power control of the photovoltaic converter.

2. The parameter identification method for active power control of a grid-connected photovoltaic converter based on frequency damping according to claim 1 is characterized in that: Use formula (1) to obtain the phase a, phase b, and phase c voltages of the grid connection point: , , DC components of d-axis and q-axis voltages in synchronously rotating coordinate systems , And the a-phase, b-phase, and c-phase inductor currents , , The DC components of the d-axis and q-axis currents in the synchronously rotating coordinate system , : (1) In formula (1), is the orientation angle of the coordinate transformation, , , Represents the AC components of voltage and current in the stationary coordinate system of phase a, phase b, and phase c, , Represents the d-axis and q-axis DC components of voltage and current in the synchronous rotating coordinate system; Use formula (2) to obtain the active power output of the photovoltaic converter and output reactive power : (2) Use formula (3) to obtain the active power after passing through the low-pass filter and reactive power after low-pass filter ,include: (3) In formula (3), represents the cutoff frequency of the low-pass filter, represents the Laplace operator.

3. The parameter identification method for active power control of a grid-connected photovoltaic converter based on frequency damping according to claim 2 is characterized in that: The active power control equation based on frequency damping is constructed using equation (4): (4) In formula (4), is the inertia constant; D d is the damping coefficient; is the rated frequency; They are active power reference value, For customized parameters.

4. The parameter identification method for active power control of a grid-connected photovoltaic converter based on frequency damping according to claim 3 is characterized in that: Using formula (5) to get the voltage amplitude , and used as the d-axis voltage reference value: (5) In formula (5), is the voltage reference value, is the reactive power reference value, is the droop proportionality coefficient.

5. The parameter identification method for active power control of a grid-connected photovoltaic converter based on frequency damping according to claim 4 is characterized in that: Using formula (6), we can get the d-axis and q-axis voltage instructions of PWM modulation: , : (6) In formula (6), and are the proportional coefficient and integral coefficient of the PI regulator of the current inner loop, and are the proportional coefficient and integral coefficient of the PI regulator of the voltage outer loop, is the inductance value of the filter inductor, is the capacitance value of the filter capacitor.

6. The parameter identification method for active power control of a grid-connected photovoltaic converter based on frequency damping according to claim 5 is characterized in that: The parameter identification of the active power control equation based on frequency damping is carried out according to the following process: Active power control equation based on frequency damping The active power control model based on frequency damping is constructed; The active power control model is discretized by using bilinear transformation to obtain the discretized active power control model; Construct the difference equation based on the discretized active power control model; The damped recursive least squares method is used to identify the parameters in the difference equation, and then the inertia constant of the active power control equation based on frequency damping is calculated using the identified parameters. , damping coefficient D d As well as the proportional coefficient and integral coefficient of the PI regulator of the voltage outer loop.

7. The parameter identification method for active power control of a grid-connected photovoltaic converter based on frequency damping according to claim 6 is characterized in that: Using formula (7) to construct the active power control model based on frequency damping : (7) In formula (7), represents the gain coefficient; Using formula (8), we can get the discretized active power control model: : (8) In formula (8), , are the input change of power given value and the output change of power response in the power response process, respectively. , , , , , , There are 7 parameters to be identified. represents a complex frequency variable; Use formula (9) to construct the difference equation: (9) In formula (9), , , , Respectively represent , No. , No. , No. The power response output change of the wheel, , , , Respectively represent , No. , No. , No. The input change of the power setpoint of the wheel; The recursive relationship of the damped recursive least squares method is constructed using formula (10): (10) In formula (10), is the damping factor, , , are the parameter vectors to be identified In the , No. , No. The identification value of the wheel, when k=0, let , Indicates The criterion coefficient of the wheel, Indicates The inverse of the wheel criterion coefficient, For the The data vector of the round input, T represents the transpose, and there are: (11) (12) The termination criterion is constructed using formula (13), so that when formula (13) is satisfied, the parameters after 7 parameter identification are obtained. , , , , , , : (13) In formula (13), Indicates The wheel identification value, is the threshold of error accuracy.

8. The parameter identification method for active power control of grid-connected photovoltaic converter based on frequency damping according to claim 7 is characterized in that the inertia constant is obtained by using formula (14): , damping coefficient D d And the proportional coefficient of the PI regulator of the voltage outer loop and the integral coefficient K iu : (14) In formula (14), , , They represent the inertia transfer coefficient, damping transfer coefficient, and voltage transfer coefficient respectively. is the sampling time of the bilinear transform, and: (15)。 9. An electronic device, comprising a memory and a processor, characterized in that: The memory is used to store a program that supports the processor to execute the parameter identification method for active power control of a grid-connected photovoltaic inverter based on frequency damping as described in any one of claims 1-8, and the processor is configured to execute the program stored in the memory.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the parameter identification method for active power control of a grid-connected photovoltaic converter based on frequency damping as recited in any one of claims 1 to 8 are executed.

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