Model prediction control system of three-phase light storage power spring
By introducing photo storage systems and model prediction control into the power spring system, the grid voltage fluctuation caused by the grid connection of new energy distributed power generation is solved, and the precise control of key load voltages and the improvement of photovoltaic utilization is achieved.
Patent Information
- Application Number
- CN202411613769.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-13
- Publication Date
- 2025-03-07
AI Technical Summary
The distribution grid power quality and grid voltage fluctuations caused by the grid connection of new energy distributed power generation, especially in the case of high fluctuations in photovoltaic power generation, it is difficult to effectively control the voltage stability of key loads.
A three-phase optical power storage spring system based on model prediction control is proposed. By adding the optical storage system to the original power spring topology, photovoltaic power generation and energy storage technology can achieve accurate control of critical load voltages. The specific steps include: designing the topological structure of the optical storage power spring, generating a reference voltage through a phase-locked loop, and using a model prediction control algorithm to achieve voltage stability.
Under the dual fluctuations of light and grid voltage, the voltage of critical loads can be accurately controlled, the photovoltaic utilization rate can be improved, and the power quality of critical loads can be stable, and the voltage stability can be achieved without parameter adjustment.
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Figure CN119582229A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of power electronics, and in particular to a model prediction control system of a three-phase photovoltaic power storage spring. Background Art
[0002] Since renewable energy sources such as wind and solar energy have the characteristics of large volatility, large intermittent, instability, and unpredictability, their large-scale grid connection has also brought many impacts to the power system, such as voltage fluctuations and frequency fluctuations. If the power generation of renewable energy does not meet the requirements during the peak load period, the normal power consumption of the load will not be guaranteed, which will have a great impact on the power grid. Especially for loads with a relatively high degree of importance in the power system, namely critical loads, such as medical equipment, industrial facilities for the production of precision instruments, etc., the quality requirements for the power grid are more stringent, which makes the grid connection of new energy sources face severe challenges. In this case, power springs are proposed as a new method to solve the problem of low power quality on the user side, and transfer the voltage fluctuations suffered by critical loads to non-critical loads with relatively loose power quality requirements, so as to ensure that the power quality of critical loads is effectively maintained at a high level.
[0003] Electric Spring, referred to as ES, was originally used mainly in grid voltage and frequency stabilization. In subsequent research work, the use of ES has been extended to achieve more complex functions through different circuit structures. There are three main types of ES, namely the original ES (ES-1), ES with ideal voltage source (ES-2) and back-to-back ES (ES-B2B). ES-1 can directly compensate non-critical loads for reactive power and indirectly control the active power consumption of non-critical loads. ES-2 is built on the basis of ES-1, but includes batteries, which can provide bidirectional active power flow, thus greatly broadening the working range of ES. The back-to-back electric spring ES-B2B adopts both parallel (coupled with the grid) and series ES (connecting the grid and NC load). In this way, ES-B2B not only saves the cost of battery storage in ES-2, but also further expands the working range of ES. At present, the most studied is ES-1, which has good control effect due to its simple structure. Therefore, this paper mainly studies the topology of the first generation three-phase electric spring (Three-Phase Electric Spring-1) TPES-1. In order to improve the utilization rate of photovoltaics, photovoltaic power generation is introduced into the electric spring to provide it with an energy source. In order to avoid the fluctuation of photovoltaic power generation caused by factors such as light and temperature, it is equipped with an energy storage system to ensure the DC voltage stability of photovoltaic power generation. And thus a photovoltaic storage electric spring topology is proposed. The present invention will improve the main circuit in the single-phase electric spring and use photovoltaic storage power generation technology. The proposed photovoltaic storage three-phase electric spring may be affected by many disturbances such as the microgrid voltage, the light temperature affecting photovoltaic power generation, and the high precision of the critical load voltage regulation. Simple PI control cannot meet the requirements, and its regulation speed and stability are poor. Summary of the invention
[0004] In order to solve the power quality and grid voltage fluctuation problems of the distribution network caused by the grid connection of new energy distributed generation, and improve the photovoltaic utilization rate, the present invention provides a three-phase photovoltaic storage power spring system based on model predictive control, including: (1) Establish a new three-phase power spring topology structure - photovoltaic power spring, which changes the original energy source from ideal voltage source to photovoltaic energy storage; (2) To control the three-phase photovoltaic power spring to achieve the same function as the original three-phase power spring, first make the photovoltaic power spring system output a stable voltage; (3) In order to make the voltage reference value and the critical load voltage phase consistent, a phase-locked loop is used to generate the reference value. ; (4) The critical load voltage is controlled to stabilize to the reference value through the model predictive control model.
[0005] Furthermore, the topological structure of the three-phase photovoltaic power spring designed in step (1) is designed as follows: adding a photovoltaic storage system, making full use of new energy, and improving the utilization rate of photovoltaic storage; The low-voltage and high-voltage sides of the bidirectional DC / DC converter of the energy storage part are connected to the energy storage battery pack and the power spring DC bus respectively. After control, a controllable voltage source can be provided to the power spring, so as to better stabilize the critical load at different reference voltages.
[0006] Furthermore, in step (2), in order to make the photovoltaic storage system output a stable voltage, the maximum power point tracking control (MPPT) of the PV unit is first performed, and then the DC / DC converter of the energy storage part is controlled: Controllable switch and The converter has two working modes: step-up and step-down. is open and When it is always off, the converter operates in (buck) mode. Connect ( =1), the energy is stored in the inductor through the DC bus middle, closure( =0), the energy from the inductor Stored in the battery, its circuit model can be expressed as: The same reason In the switch state and When it is always off, the converter works in boost mode, and its circuit model can be expressed as: in is the inductance of the energy storage part, is the current flowing through the inductor of its energy storage part, Capacitor for energy storage voltage.
[0007] When the PV power is unstable, the power at the DC bus can be adjusted by controlling the charge and discharge of the energy storage unit to achieve the purpose of stabilizing the bus voltage Vdc. The stable DC bus voltage can be used as the energy source of the power spring. The energy storage battery adopts voltage and current dual closed-loop control. The voltage outer loop PI controller is used to adjust the voltage error of the bus, give the inductor reference current, and then use the current inner loop controller to control the inductor current and generate a set of PWM control signals to control the working state of the converter. Furthermore, the method for generating the voltage reference value in step (3) is as follows: Figure 4As shown, it is used to ensure the stability of the voltage amplitude and phase of the critical load. When the photovoltaic power spring acts, the signal of vCi is first collected, and the phase of vCi is obtained through the phase-locked loop. After selecting channel 1 in the switch, the phase signal is integrated through the sin module and the booster m to generate the reference voltage of CL.
[0008] Furthermore, the model predictive control described in step (4) is established, which includes the prediction of the critical load voltage and the construction of the objective function.
[0009] (4.1) Prediction of critical load voltage: Applying Kirchhoff's current law (KCL) and Kirchhoff's voltage law (KVL) yields: In this equation, i represents any one of the three phases - A, B or C. vGi is the microgrid voltage of phase i, and vESi represents the photovoltaic / energy storage system (PV / BESS) TPES voltage of phase i. iLi represents the output filter inductor current of the photovoltaic / energy storage system (PV / BESS) TPES of phase i, and iL1i represents the input current from the grid side of phase i. In addition, vCi, iCi, vNCi and iNCi are the current and voltage of CL and NCL of phase i, respectively. L1i represents the equivalent inductance of the transmission line, R1i represents the equivalent resistance of the transmission line, Ci and Li represent the output filter capacitor and inductor of the photovoltaic / energy storage system (PV / BESS) TPES, respectively. RCi and RNCi represent the resistance of CL and NCL, respectively.
[0010] From the above analysis, we can get: Substituting equation 9 into equation 8, we can obtain: Then, using the first-order forward difference method, we can get , and Discretization expression of : in, Substituting 13 into 14 we get: in, Finally, substituting equations 13 and 17 into equation 10 gives the predicted critical load voltage for: (4.2) Construction of objective function The objective function is a key element of the predictive control of the photovoltaic power spring model, which is determined by the control target. The photovoltaic power spring in this paper aims to control the critical load voltage to approach its reference voltage, so the objective function is selected. for: When the full-bridge inverter circuit is in different switching states, the voltage of the critical load is different. Here, the switching functions of the full-bridge inverter are defined as SA, SB, and SC, which are expressed as: Then the output relative neutral point voltage viN of the full-bridge inverter is: Further, through the above control of the light storage power spring, the key load voltage at the next moment is calculated in the model prediction algorithm to obtain 8 objective functions, and the minimum objective function is selected. The corresponding switch state ensures Stay steady.
[0011] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention innovates the original electric spring topology and greatly improves the photovoltaic utilization rate by adding photovoltaic storage.
[0012] (2) The model predictive control used in the present invention can accurately control the voltage of critical loads under the dual fluctuations of light intensity and grid voltage.
[0013] (3) The bus voltage output by the photovoltaic storage system of the present invention can be adjusted by double closed-loop control according to the bus voltage required by the power spring.
[0014] (4) The control method adopted by the present invention can achieve accurate control of voltage stability under multiple fluctuations without the need for parameter adjustment. BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The present invention is further described below in conjunction with the accompanying drawings and embodiments.
[0016] Figure 1 Structure diagram of three-phase photovoltaic power storage spring.
[0017] Figure 2 Control block diagram of three-phase photovoltaic power spring.
[0018] Figure 3 Voltage and current dual closed-loop control block diagram.
[0019] Figure 4 Reference voltage generation diagram.
[0020] Figure 5 Block diagram of predictive control of three-phase photovoltaic power storage spring model. DETAILED DESCRIPTION
[0021] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner, and therefore only show the components related to the present invention.
[0022] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying 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 addition, features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.
[0023] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" 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 indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.
[0024] The present invention provides a model predictive control based on a three-phase photovoltaic power storage spring. In order to solve the power quality of the distribution network and the voltage fluctuation of the power grid caused by the grid connection of new energy distributed power generation, and to improve the photovoltaic utilization rate, the present invention provides a photovoltaic power storage spring system based on model predictive control, comprising: (1) Establish a new three-phase power spring topology structure - photovoltaic power spring, which changes the original energy source from ideal voltage source to photovoltaic energy storage; (2) To control the three-phase photovoltaic power spring to achieve the same function as the original three-phase power spring, first make the photovoltaic power spring system output a stable voltage; (3) In order to make the voltage reference value and the critical load voltage have the same phase, a phase-locked loop is used to generate the reference value; (4) The critical load voltage is controlled to stabilize to the reference value through the model predictive control model.
[0025] Furthermore, the topological structure of the photovoltaic power spring designed in step (1) is designed with the following design idea: adding a photovoltaic power storage system, making full use of new energy, and improving the utilization rate of photovoltaic power storage.
[0026] Furthermore, the topological structure of the three-phase photovoltaic storage power spring designed in step (1) is designed with the following design idea: adding a photovoltaic storage system, making full use of new energy, and improving the utilization rate of photovoltaic storage.
[0027] Furthermore, its topology and main control method are designed as follows: Figure 1 .
[0028] The low-voltage and high-voltage sides of the bidirectional DC / DC converter of the energy storage part are connected to the energy storage battery pack and the power spring DC bus respectively. After control, a controllable voltage source can be provided to the power spring, so as to better stabilize the critical load at different reference voltages.
[0029] Furthermore, in step (2), in order to make the photovoltaic energy storage system output a stable voltage, the maximum power point tracking control (MPPT) is first performed on the PV unit, and then the DC / DC converter of the energy storage part is controlled.
[0030] Controllable switch and The converter has two working modes: step-up and step-down. is open and When it is always off, the converter operates in (buck) mode. Connect ( =1), the energy is stored in the inductor through the DC bus middle, closure( =0), the energy from the inductor Stored in the battery, its circuit model can be expressed as: The same reason In the switch state and When it is always off, the converter works in boost mode, and its circuit model can be expressed as: in is the inductance of the energy storage part, is the current flowing through the inductor of its energy storage part, Capacitor for energy storage voltage.
[0031] When the PV power is unstable, the bus voltage can be achieved by controlling the charging and discharging of the energy storage unit to adjust the power at the DC bus. For the purpose of stability, the stable DC bus voltage can be used as the energy source of the power spring. The energy storage battery adopts voltage and current double closed-loop control. The voltage outer loop PI controller is used to adjust the voltage error of the bus, give the inductor reference current, and then use the current inner loop controller to control the inductor current and generate a set of PWM control signals to control the working state of the converter. The control principle diagram is as follows: Figure 3 : Furthermore, the method for generating the voltage reference value in step (3) is as follows: Figure 4 As shown, it is used to ensure the stability of the voltage amplitude and phase of the critical load. When the photovoltaic power spring acts, the signal of vCi is first collected, and the phase of vCi is obtained through the phase-locked loop. After selecting channel 1 in the switch, the phase signal is integrated through the sin module and the booster m to generate the reference voltage of CL.
[0032] Furthermore, the model predictive control described in step (4) is established as follows Figure 5 As shown, this includes the prediction of critical load vCi and the construction of objective function.
[0033] (4.1) Prediction of critical load voltage: Applying Kirchhoff's current law (KCL), applying Kirchhoff's voltage law (KVL) yields: In the above formula, is the grid voltage, and The line impedance is The current injected into the grid, is the current through the non-critical load, For filter capacitor Capacitor voltage, is the filter inductor, is the current through the filter inductor, is the output relative neutral point voltage of the full-bridge inverter.
[0034] From the above analysis, we can get: Substituting equation 9 into equation 8, we can obtain: Then, using the first-order forward difference method, we can get , and Discretization expression of : in, Substituting 13 into 14 we get: in, Finally, substituting equations 13 and 17 into equation 10 gives the predicted critical load voltage for: (4.2) Construction of objective function The objective function is a key element of the predictive control of the photovoltaic power spring model, which is determined by the control target. The photovoltaic power spring in this paper aims to control the critical load voltage to approach its reference voltage, so the objective function is selected. for: When the full-bridge inverter circuit is in different switching states, the voltage of the critical load is different. Here, the switching functions of the full-bridge inverter are defined as SA, SB, and SC, which are expressed as: Then the output relative neutral point voltage viN of the full-bridge inverter is: Further, through the above control of the light storage power spring, the key load voltage at the next moment is calculated in the model prediction algorithm to obtain 8 objective functions, and the minimum objective function is selected. The corresponding switch state ensures Stay steady.
[0035] The above description is based on the ideal embodiment of the present invention. Through the above description, relevant personnel can make various changes and modifications without departing from the technical concept of the present invention. The technical scope of the present invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.
Claims
1. A model predictive control system for a three-phase photovoltaic power spring, characterized in that: The following steps are involved: S1. Establish a three-phase power spring topology structure - a three-phase photovoltaic storage power spring, and adjust the inverter energy source from an ideal voltage source to photovoltaic storage energy; S2, in order to adjust the light storage system to make it output a stable voltage, so as to control the three-phase light storage power spring to achieve the same function as the original power spring; S3, using a phase-locked loop to generate a reference value so that the voltage reference value and the critical load voltage are in phase; S4. Stabilize the critical load voltage to the reference value through model predictive control.
2. The model predictive control system of the three-phase photovoltaic power spring according to claim 1 is characterized in that: In step S1, the energy source of the inverter is changed from an ideal DC source to a photovoltaic energy source as follows: Connect the low-voltage and high-voltage sides of the bidirectional DC / DC converter of the energy storage part to the energy storage battery pack and the power spring DC bus respectively; After control, a controllable voltage source can be provided to the power spring, so as to better stabilize the critical load at different reference voltages. The specific circuit model is shown as follows; The same reason In the switch state and When it is always off, the converter works in boost mode, and its circuit model can be expressed as: in is the inductance of the energy storage part, is the current flowing through the inductor of its energy storage part, Capacitor for energy storage Voltage , They are and time The derivation of .
3. The model predictive control system of the three-phase photovoltaic power spring according to claim 1 is characterized in that: In step S2, the voltage reference value is generated by the phase-locked loop in the following way: S2.1, when the light storage power spring acts, the collected signal; S2.2, after the phase is obtained through the phase-locked loop, channel 1 in the switch is selected and the phase signal is integrated through the sin module and the booster m to generate the reference voltage of CL.
4. The model predictive control system of the three-phase photovoltaic power spring according to claim 1 is characterized in that: The specific method of controlling the critical load voltage to stabilize to the reference value by using the model predictive control model is: S4.
1. Apply Kirchhoff's current law (KCL) and Kirchhoff's voltage law (KVL) to obtain: In this equation, i represents any one of the three phases - A, B or C, vGi is the microgrid voltage of phase i, vESi represents the photovoltaic / energy storage system (PV / BESS) TPES voltage of phase i, iLi represents the output filter inductor current of the photovoltaic / energy storage system (PV / BESS) TPES of phase i, and iL1i represents the input current from the grid side of phase i. In addition, vCi, iCi, vNCi and iNCi are the current and voltage of CL and NCL of phase i, respectively, L1i represents the equivalent inductance of the transmission line, R1i represents the equivalent resistance of the transmission line, Ci and Li represent the output filter capacitor and inductor of the photovoltaic / energy storage system (PV / BESS) TPES, respectively, and RCi and RNCi represent the resistance of CL and NCL, respectively; From the above analysis, we can get: Substituting equation 9 into equation 8, we can obtain: Then, using the first-order forward difference method, we can get , and Discretization expression of : in, Arrange formula 11 to get: in, Finally, substituting equations 11 and 14 into equation 10 gives the predicted critical load voltage for: S4.
2. Construction of objective function The objective function is a key element of the predictive control of the photovoltaic power spring model, which is determined by the control target. The photovoltaic power spring in this paper aims to control the critical load voltage to approach its reference voltage, so the objective function is selected. for: When the full-bridge inverter circuit is in different switching states, the voltage of the critical load is different. Here, the switching functions of the full-bridge inverter are defined as SA, SB, and SC, which are expressed as: Then the output relative neutral point voltage viN of the full-bridge inverter is: Further, through the above control of the light storage power spring, the key load voltage at the next moment is calculated in the model prediction algorithm to obtain 8 objective functions, and the minimum objective function is selected. The corresponding switch state ensures Stay steady.