Single-stage multi-port optical storage power generation system power distribution method based on repetitive control

Abstract

The invention discloses a single-stage multi-port optical storage power generation system power distribution method based on repetitive control. The method comprises the following steps: determining a power reference value of a direct current port through a series of steps of voltage and current acquisition, port power calculation and power management; generating a system original modulation signal through a network side control loop; a zero-sequence component is generated through a direct-current side control loop of the embedded repetitive controller; and superposing the original modulation signal and the zero-sequence component to form a final modulation signal, and comparing the modulation signal with a triangular carrier to generate a digital switching signal. According to the invention, the decoupling of the DC / AC control loop of the single-stage multi-port optical storage power generation system is realized, the power ripple of the DC port is effectively suppressed, and the operation performance of the single-stage multi-port optical storage power generation system is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of photovoltaic power generation. More specifically, it relates to a power distribution method for a single-stage multi-port photovoltaic energy storage power generation system based on repetitive control. Background Art

[0002] As an important form of renewable energy utilization, photovoltaic power generation has significant advantages in coping with the exhaustion of fossil energy and alleviating environmental problems, and has received extensive attention from the industry in recent years. However, due to the intermittent and fluctuating characteristics of photovoltaic energy, the reliability of traditional photovoltaic power generation systems is limited, it is difficult to achieve stable power supply, and it cannot meet the grid support requirements. Integrating energy storage devices is a solution to improve the reliability of photovoltaic power generation systems. By configuring energy storage devices as auxiliary regulation units, power fluctuations can be smoothed and power quality can be effectively improved. Such composite power generation systems are called photovoltaic energy storage power generation systems.

[0003] In a photovoltaic energy storage power generation system, the converter undertakes the electrical connection functions of the photovoltaic, energy storage, and grid sides, and its performance has a decisive impact on key indicators such as system deployment cost, conversion efficiency, and power density. Among various converter solutions, the single-stage multi-port converter has become an optimal solution for photovoltaic energy storage power generation systems due to its topological advantage of not requiring a DC conversion device and its single-stage power transmission characteristics. Therefore, a photovoltaic energy storage power generation system based on a single-stage multi-port converter also has significant advantages such as low system deployment cost, high conversion efficiency, and high power density. The system constructed based on this converter is called a single-stage multi-port photovoltaic energy storage power generation system.

[0004] In a single-stage multi-port photovoltaic energy storage power generation system, how to achieve power distribution between DC ports is a key technical challenge. Traditional methods use linear PI controllers to achieve power regulation of DC ports. However, due to the strong coupling and nonlinear characteristics of the system, the method based on PI controllers is difficult to meet the accurate power distribution requirements and has the performance defect of excessive port power ripple. Therefore, it is urgent to introduce advanced control methods to improve the operation performance of single-stage multi-port photovoltaic energy storage power generation systems. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a power distribution method for a single-stage multi-port photovoltaic energy storage power generation system based on repetitive control. By using the zero-sequence component as a controllable degree of freedom to adjust the power distribution between DC ports and designing a repetitive controller with a nonlinear in-period model, the technical problem of excessive port power ripple caused by the strong coupling and nonlinear characteristics of the system is solved, and the operation performance of the single-stage multi-port photovoltaic energy storage power generation system is significantly improved.

[0006] To achieve the above-mentioned invention purpose, a power distribution method for a single-stage multi-port photovoltaic energy storage power generation system based on repetitive control according to the present invention is characterized by including the following steps:

[0007] (1), Real - time collect the grid - side output voltage V of the single - stage multi - port photovoltaic - energy - storage power generation system x , output current i x and the inverter - side current where x = a, b, c represents the three phases of the power grid; then calculate the grid - side active power P through the port power calculation module g , the photovoltaic DC - port power P pv and the energy - storage DC - port power P bat ;

[0008] (2), The system power management module combines the grid - side active power P g and the real - time operating states of the photovoltaic and energy - storage systems to generate the power reference value P pv * of the photovoltaic DC - port;

[0009] (3), Use the grid - side output voltage reference value V ref , the grid - side output voltage V x and the inverter - side current together as the input signals of the grid - side control loop to generate the original modulation signal U x ;

[0010] (4), Use the photovoltaic DC - port power reference value P pv * and the actual sampled power P pv as the input signals of the DC - side control loop's repetitive controller to generate the zero - sequence component U0 for regulating the power distribution between the DC ports;

[0011] (5), Superimpose the original modulation signal U x and the zero - sequence component U0 to obtain the final modulation signal, and then compare the final modulation signal U x * with the triangular carrier wave to generate the digital switching signal for driving the single - stage multi - port photovoltaic - energy - storage power generation system.

[0012] The invention object of the present invention is achieved as follows:

[0013] The power distribution method of a single-stage multi-port photovoltaic and energy storage power generation system based on repetitive control determines the power reference value of the DC port through a series of steps including voltage and current acquisition, port power calculation, and power management; generates the original modulation signal of the system through the grid-side control loop; generates the zero-sequence component through the DC-side control loop embedded with a repetitive controller; superimposes the original modulation signal and the zero-sequence component to form the final modulation signal, and generates the digital switching signal through the comparison of the modulation signal and the triangular carrier wave. The present invention realizes the decoupling of the DC and AC control loops of the single-stage multi-port photovoltaic and energy storage power generation system, effectively suppresses the power ripple of the DC port, and improves the operation performance of the single-stage multi-port photovoltaic and energy storage power generation system.

[0014] Meanwhile, the power distribution method of a single-stage multi-port photovoltaic and energy storage power generation system based on repetitive control of the present invention also has the following beneficial effects:

[0015] (1) Adjust the power distribution between DC ports through the zero-sequence component to decouple the DC-side and AC-side control loops;

[0016] (2) Adopt a repetitive controller with a non-linear periodic internal model to track the power reference of the DC port, so that the power ripple of the DC port is effectively suppressed, ensuring the improvement of the operation performance of the single-stage multi-port photovoltaic and energy storage power generation system. Description of the Drawings

[0017] Figure 1 is the circuit topology diagram of the single-stage multi-port photovoltaic and energy storage power generation system;

[0018] Figure 2 is the schematic diagram of the control structure of the single-stage multi-port photovoltaic and energy storage power generation system;

[0019] Figure 3 is the flowchart of the power distribution method of the single-stage multi-port photovoltaic and energy storage power generation system based on repetitive control of the present invention;

[0020] Figure 4 is the operation condition diagram of the single-stage multi-port photovoltaic and energy storage power generation system under different port power distribution instructions;

[0021] Figure 5 is the comparison diagram of the operation conditions of the single-stage multi-port photovoltaic and energy storage power generation system implemented according to the method of the present invention and the traditional method respectively. Detailed Embodiments

[0022] The following describes the specific embodiments of the present invention in conjunction with the drawings, so that those skilled in the art can better understand the present invention. It should be particularly noted that in the following description, when the detailed description of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

[0023] Embodiment

[0024] In this embodiment, the topology of the single-stage multi-port photovoltaic and energy storage power generation system is as Figure 1 shown. Its hardware circuit part includes diode D, voltage stabilizing capacitors C1 and C2, an LC filter, and three-phase bridge arms and their switching tubes S x1 , S x2 , S x3 , S x4 , where x represents any one of the three phases a, b, and c. In terms of topological connection, the upper port of the system is defined as the photovoltaic DC port, and the lower port of the system is defined as the energy storage DC port. The control structure of this embodiment is as Figure 2 shown, mainly including a grid-side control loop, a DC-side control loop, and a modulation link. The grid-side control loop includes two modules: constant voltage and constant frequency control and current control; the DC-side control loop includes three modules: port power calculation, power management, and zero-sequence component regulation based on repetitive control; the modulation link includes a triangular carrier comparison module. This embodiment also includes necessary analog signal sampling modules and digital signal driving modules.

[0025] Next, in combination with Figure 3 , the detailed steps of the power distribution method for the single-stage multi-port photovoltaic and energy storage power generation system based on repetitive control of the present invention will be described in detail as follows:

[0026] S1. Real-time collect the grid-side output voltage V x , output current i x , and the inverter-side current x = a, b, c represents the three phases of the power grid; then calculate the grid-side active power P g , the photovoltaic DC port power P pv , and the energy storage DC port power P bat through the port power calculation module;

[0027] In this embodiment, the calculation formulas for the grid-side active power P g , the photovoltaic DC port power P pv , and the energy storage DC port power P bat are:

[0028]

[0029] Among them, d x1 , d x2 respectively represent the duty cycles of the first switching tube and the second switching tube S x1 , S x2 of the three-phase bridge arms of the single-stage multi-port photovoltaic and energy storage power generation system, and V pv , V bat respectively represent the voltages of the photovoltaic DC port and the energy storage DC port.

[0030] S2. The system power management module combines the grid-side active power P g and the real-time operating states of the photovoltaic and energy storage systems to generate the power reference value P pv * ;

[0031] In this embodiment, the system power management module divides the operating states of the single-stage multi-port photovoltaic and energy storage power generation system according to the grid-side active power P g and the real-time operating states of the photovoltaic and energy storage systems;

[0032] State 1: When the grid-side active power P g is less than the maximum power that the photovoltaic system can generate and the energy storage system is fully charged, the photovoltaic system operates independently to supply power;

[0033] State 2: When the grid-side active power P g is greater than the maximum power that the photovoltaic system can generate and the energy storage system is in a state where it can discharge, the photovoltaic system and the energy storage system operate together to supply power;

[0034] State 3: When the grid-side active power P g is less than the maximum power that the photovoltaic system can generate and the energy storage system is in a state where it can be charged, the photovoltaic system supplies power while the energy storage system feeds power;

[0035] State 4: When the photovoltaic system fails or has no power generation capacity and the energy storage system is in a state where it can discharge, the energy storage system operates independently to supply power;

[0036] According to the specific operating state of the single-stage multi-port photovoltaic and energy storage power generation system, the power reference value P pv * :

[0037]

[0038] where H hpf (·) represents a high-pass filtering link, and P ch represents the rated charging power of the energy storage system.

[0039] S3. The grid-side output voltage reference value V ref , the grid-side output voltage V x and the inverter-side current are jointly used as the input signals of the grid-side control loop to generate the original modulation signal U x ;

[0040] S3.1. In the grid-side control loop, the grid-side output voltage reference value V ref is subjected to dq transformation to obtain the dq-axis voltage reference vectors u ref,d , u ref,q ; the grid-side output voltage V xPerform dq transformation to obtain the dq-axis voltage vectors \(u_d\) and \(u_q\). d and \(u_q\) q ; Perform dq transformation on the inverter-side current \(i\) to obtain the dq-axis current vectors \(i_d\)

[0041] In this embodiment, the formula for dq transformation is as follows:

[0042]

[0043] where \(\theta\) represents the power angle, \(x_d\) abc refers to the quantity that needs to be subjected to dq transformation as described above, and \(x_q\) dq refers to the quantity after dq transformation;

[0044] S3.2: Input the dq-axis voltage reference vectors \(u_d^*\) ref,d and \(u_q^*\) ref,q along with the dq-axis voltage vectors \(u_d\) d and \(u_q\) q into the constant voltage and constant frequency control module to obtain the inverter-side current reference vectors \(i_d^*\) ref,d and \(i_q^*\) ref,q ;

[0045] S3.3: Input the inverter-side current reference vectors \(i_d^*\) ref,d and \(i_q^*\) ref,q along with the dq-axis current vectors \(i_d\) into the current control module to obtain the original modulation signal \(U_d\) in the dq coordinate system dq ;

[0046] S3.4: Perform inverse dq transformation on the original modulation signal \(U_d\) in the dq coordinate system dq to obtain the original modulation signal \(U_a\) in the three-phase coordinate system x ;

[0047]

[0048] where \(\theta\) represents the power angle.

[0049] S4: Use the photovoltaic DC port power reference value \(P_{ref}\) pv * and the actual sampled power \(P\) pv as the input signals of the DC-side control loop repetitive controller to generate the zero-sequence component \(U_0\) for regulating the power distribution between the DC ports;

[0050] S4.1: Input the photovoltaic DC port power reference value \(P_{ref}\) pv * and the actual power \(P\) pv into the zero-sequence component regulation module based on repetitive control to obtain the error \(E(z)\):

[0051] E(z) = P pv * -P pv

[0052] S4.2. Define the transfer function G rc (z) of the repetitive controller's nonlinear periodic internal model:

[0053]

[0054] where k rc is the repetitive controller gain; Q(z) is the low-pass filter; N is the number of sampling points of the repetitive controller in each fundamental period, f s is the sampling frequency, f0 is the fundamental frequency; n is the coefficient of the periodic internal model, and z represents the Z-domain;

[0055] S4.3. Based on the transfer function G rc (z), introduce a fractional-order compensation link to construct the complete transfer function of the repetitive controller as follows:

[0056]

[0057] where represents rounding down the elements in the parentheses, m is the order of the fractional-order compensation, and A q is the q-th order compensation coefficient;

[0058] S4.4. Input the error E(z) into the complete repetitive controller G rc (z) to obtain the zero-sequence component U0.

[0059] S5. Add the original modulation signal U x and the zero-sequence component U0 to obtain the final modulation signal, and then compare the final modulation signal U x * with the triangular carrier wave to generate a digital switching signal for driving the single-stage multi-port photovoltaic energy storage power generation system;

[0060] S5.1. Perform amplitude limiting processing on the zero-sequence component U0 to make it satisfy the constraint relationship:

[0061]

[0062] S5.2. Add the zero-sequence component U0 to the original modulation signal U x to obtain the final modulation signal U x * ,

[0063] S5.3. Compare the final modulation signal U x *The triangular carrier comparison module input to the modulation link obtains a digital switching signal, and then the single-stage multi-port photovoltaic energy storage power generation system is operated through the digital signal driving module.

[0064] Example verification

[0065] The parameters of the single-stage multi-port photovoltaic energy storage power generation system are set as follows: the voltage of the photovoltaic DC port is V pv = 400V, the voltage of the energy storage DC port is V bat = 240V, the rated voltage of the grid side is V n * = 110V, the rated power of the grid side is P g * = 1000W.

[0066] Figure 4 The operating conditions of the single-stage multi-port photovoltaic energy storage power generation system under three power distribution modes are shown. Specifically: Figure 4 (a) The power reference value of the photovoltaic DC port is set to P pv * = 800W; Figure 4 (b) The power reference value of the photovoltaic DC port is set to P pv * = 1000W; Figure 4 (c) The power reference value of the photovoltaic DC port is set to P pv * = 1200W. It can be seen from observing the example verification results that the power of the photovoltaic DC port can be flexibly adjusted according to the reference value given by the power management module, and the grid side voltage and current still remain stable and sinusoidal without obvious distortion. The verification results show that the method proposed in the present invention can effectively realize the power distribution requirements between the DC ports of the single-stage multi-port photovoltaic energy storage power generation system.

[0067] Figure 5 The performance differences of different control methods are compared. Specifically: Figure 5 (a) The method adopted is the method proposed in the present invention; Figure 5 (b) The method adopted is the traditional method one; Figure 5 (c) The method adopted is the traditional method two. It can be seen from observing the power error of the DC port that the power ripple of the DC port of the method proposed in the present invention is smaller than that of the traditional method one and the traditional method two. The verification results show that the method proposed in the present invention has successfully realized the effective suppression of the port power ripple and effectively improved the operating performance of the single-stage multi-port photovoltaic energy storage power generation system.

[0068] Although the above-described illustrative embodiments of the present invention have been described to facilitate understanding of the present invention by those skilled in the art, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions made using the concept of the present invention are within the scope of protection.

Claims

1. A power allocation method for a single-stage multi-port photovoltaic power generation system based on repetitive control, characterized in that: The following steps are involved: (1) Real-time acquisition of the grid-side output voltage V of a single-stage multi-port photovoltaic power generation system x , output current i x and inverter side current Represents the three phases of the power grid; then the grid-side active power P is calculated through the port power calculation module g , PV DC port power P pv and the energy storage DC port power P bat ; (2) The system power management module combines the grid-side active power P g As well as the real-time operating status of photovoltaic and energy storage, generate the power reference value P of the photovoltaic DC port pv * ; (3) Set the grid-side output voltage reference value V ref , grid-side output voltage V x And the inverter side current Together they serve as the input signal of the grid-side control loop to generate the original modulation signal U x ; (4) Set the PV DC port power reference value P pv * The actual sampling power P pv As the input signal of the repetitive controller of the DC side control loop, it generates the zero sequence component U0 for adjusting the power distribution between DC ports; (5) The original modulated signal U x The final modulation signal is superimposed with the zero-sequence component U0, and then the final modulation signal U x * By comparing with the triangular carrier, a digital switching signal for driving a single-stage multi-port photovoltaic power generation system is generated.

2. The power allocation method for a single-stage multi-port photovoltaic power generation system based on repetitive control according to claim 1 is characterized in that: The grid-side active power P g , PV DC port power P pv and the energy storage DC port power P bat The calculation method is: Among them, d x1 d x2 They represent the first switch tube and the second switch tube S of the three-phase bridge arm of the single-stage multi-port photovoltaic power generation system. x1 , S x2 The duty cycle, V pv 、V bat Represent the voltages of the PV DC port and the energy storage DC port respectively.

3. The power allocation method for a single-stage multi-port photovoltaic power generation system based on repetitive control according to claim 1 is characterized in that: The power reference value P of the photovoltaic DC port pv * The generation method is: (3.1) The system power management module divides the operating status of the single-stage multi-port photovoltaic power generation system; State 1: When the grid-side active power P g When the power is less than the maximum power that can be generated by photovoltaic power generation and the energy storage is in a fully charged state, photovoltaic power generation is operated alone; State 2: When the grid-side active power P g When the power is greater than the maximum power that can be generated by photovoltaics and the energy storage is in a dischargeable state, photovoltaics and energy storage will work together to supply power; State 3: When the grid-side active power is less than the maximum power generation of the photovoltaic power plant and the energy storage is in a chargeable state, the photovoltaic power supply / energy storage feed operation is in progress; State 4: When the photovoltaic fails or has no power generation capacity and the energy storage is in a dischargeable state, the energy storage is used to supply power alone; (3.2) According to the specific operating status of the single-stage multi-port photovoltaic storage power generation system, the power reference value P of the photovoltaic DC port is generated. pv * : Among them, H hpf (·) represents the high-pass filter link, P ch Indicates the rated charging power of the energy storage.

4. The power allocation method for a single-stage multi-port photovoltaic power generation system based on repetitive control according to claim 1 is characterized in that: The original modulated signal U x The specific generation process is: (4.1) In the grid-side control loop, the grid-side output voltage reference value V ref Perform dq transformation to obtain the dq axis voltage reference vector u ref,d 、u ref,q ; Grid-side output voltage V x Perform dq transformation to obtain the dq axis voltage vector u d 、u q ; The inverter side current Perform dq transformation to obtain the dq axis current vector (4.2), the dq axis voltage reference vector u ref,d 、u ref,q and dq axis voltage vector u d 、u q Input to the constant voltage and constant frequency control module to obtain the inverter side current reference vector i ref,d 、i ref,q ; ( 4.3) The inverter side current reference vector i ref,d 、i ref,q and dq axis current vector Input to the current control module to obtain the original modulation signal U in the dq coordinate system dq ; (4.4), the original modulated signal U in the dq coordinate system dq Perform inverse dq transformation to obtain the original modulation signal U in the three-phase coordinate system x ; Wherein, θ represents the power angle.

5. The power allocation method of a single-stage multi-port photovoltaic power generation system with repeated control according to claim 1 is characterized in that: The specific method for generating the zero-sequence component U0 is: (5.1), the PV DC port power reference value P pv * With actual power P pv Input the zero-sequence voltage regulation module based on repetitive control and get the error E(z): E(z)=P pv * -P pv (5.2), define the transfer function G of the nonlinear periodic internal model of the repetitive controller rc (z): Among them, k rc is the repetitive controller gain; Q(z) is the low-pass filter; N is the number of sampling points of the repetitive controller in each fundamental wave cycle, f s is the sampling frequency, f0 is the fundamental frequency; n is the periodic internal mode coefficient, z represents the Z domain; (5.3), in the transfer function G rc (z), the fractional-order compensation link is introduced to construct the complete repetitive controller transfer function as follows: in, Indicates that the elements in the brackets are rounded down, m is the fractional compensation order, A q is the qth order compensation coefficient; (5.4), the error E(z) is input into the complete repetitive controller G rc (z), the zero-sequence voltage U0 is obtained.

6. The power allocation method for a single-stage multi-port photovoltaic power generation system based on repeated control according to claim 1 is characterized in that: The method for generating the digital switch signal in step (5) is: (6.1) The zero-sequence component U0 is limited to satisfy the constraint relationship: (6.2) and superimpose the zero-sequence component U0 on the original modulated signal U x The final modulated signal U is obtained x * ; ( 6.3) The final modulated signal U x * The triangular carrier comparison module input to the modulation link obtains a digital switching signal, and then the digital signal driving module realizes the operation of the single-stage multi-port photovoltaic power generation system.

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