A model construction method of a photovoltaic power generation unit
By constructing a basic and simplified model of a photovoltaic power generation unit and adding perturbations to the model, the problems of long simulation time and limited scale of photovoltaic power generation systems are solved, improving the simulation speed and accuracy, and making it suitable for large-scale simulation calculations.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- STATE GRID JIANGSU ELECTRIC POWER CO LTD
- Filing Date
- 2022-07-13
- Publication Date
- 2026-06-02
AI Technical Summary
Existing photovoltaic power generation system simulation models take too long to run, have limited simulation scale, require excessively high sampling rates for simulation output data, and employ a single simulation method.
A basic model and a simplified model are constructed, and perturbations are added to the model. The effect is adjusted through simulation model to select an appropriate model, including components such as photovoltaic power source, filter inductor, current transformer, and voltage transformer. The simulation is performed using PSCAD/EMTDC software.
It enables the selection of appropriate models under different needs, improves simulation speed and accuracy, and meets the efficiency requirements of large-scale simulation calculations.
Smart Images
Figure CN115270436B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of power systems, and more specifically, to a method for modeling a photovoltaic power generation unit. Background Technology
[0002] To address global climate change and ensure energy security in line with economic development, countries worldwide are vigorously promoting renewable energy. Among the many renewable energy sources, solar energy undoubtedly holds the greatest potential, characterized by its safety, cleanliness, widespread availability, and abundant resources. Developing solar energy is of great significance for meeting global energy demand and reducing dependence on traditional energy sources.
[0003] Photovoltaic power generation systems have been widely used in power system construction, providing a new energy access method for the power system. In order to ensure that this new energy source can be effectively integrated into the power grid, participate in various regulation processes of the power system, and achieve the overall stable operation of the power system, the modeling and simulation process of photovoltaic power generation system grid connection is essential.
[0004] Currently, photovoltaic (PV) power generation systems typically connect to the power grid using PV grid-connected inverters. These inverters usually employ an outer voltage loop and an inner current loop to control the energy exchange process, with the controlled device being the insulated-gate bipolar transistor (IGBT). To investigate the grid-connected characteristics of PV power generation systems, it is necessary to simulate PV grid-connected inverters and model their regulation capabilities under various network conditions. However, existing PV inverter simulation methods are relatively simplistic, the simulation models are time-consuming, the simulation scale is limited, and the required sampling rate for the simulation output data is too high.
[0005] To address the above problems, this invention provides a method for constructing a model of a photovoltaic power generation unit. Summary of the Invention
[0006] To address the shortcomings of existing technologies, the present invention aims to provide a model construction method for photovoltaic power generation units. By constructing a basic model and a simplified model, and adding various perturbations to the above models, the adjustment effect of the model can be collected, and different models can be selected based on the adjustment effect under different requirements.
[0007] The present invention adopts the following technical solution.
[0008] This invention relates to a method for constructing a model of a photovoltaic power generation unit, wherein the method includes the following steps:
[0009] Step 1: Perform model simulation on the grid-connected inverter of the photovoltaic power generation unit. The simulation model includes a basic model and a simplified model. The simplified model is used to simplify the half-bridge structure of the grid-connected inverter into a three-phase power supply during the simulation process. Step 2: Input the simulation model of the grid-connected inverter into the power system simulation software and add operating disturbances to the simulation model to obtain the adjustment effect of the simulation model on the operating disturbances. Step 3: Based on the adjustment effect of the simulation model and the scale of the network to be analyzed, select either the basic model or the simplified model.
[0010] Preferably, the basic model includes a photovoltaic power source, a DC input capacitor, control switches T1 to T6, a filter inductor, a current transformer, a voltage transformer, an equivalent resistor, a transformer, and a grid-side power source. Control switches T1 to T6 are connected in series to the two ends of the DC input capacitor and the photovoltaic power source, respectively. The connection points of the series-connected control switches provide three-phase current and are connected to the filter inductor. The other end of the filter inductor passes through the current transformer, the voltage transformer, the equivalent resistor, the transformer, and the grid-side power source before being grounded.
[0011] Preferably, the simplified model includes a three-phase power supply pvaref, pvbref, pvcref, a filter inductor, a current transformer, a voltage transformer, an equivalent resistance, a transformer, and a grid-side power supply; wherein, the three-phase power supply is connected in parallel and then connected to the filter inductor; the other end of the filter inductor passes through the current transformer, the voltage transformer, the equivalent resistance, the transformer, and the grid-side power supply in sequence before being grounded.
[0012] Preferably, the three-phase power supply can be a three-phase current source or a three-phase voltage source; wherein, the magnitude of the three-phase power supply can be acquired from the three-phase input signal of the PWM control unit in the grid-connected inverter.
[0013] Preferably, the operation disturbance includes a first operation disturbance and a second operation disturbance; wherein, the first operation disturbance is used to increase the active power reference value of the photovoltaic power station when it is connected to the grid to 120% of the active power when the simulation model is in the initial stable operating state; the second operation disturbance is used to reduce the voltage of the grid-side power supply to 72% of the voltage when the simulation model is in stable operation, and last for 3 seconds.
[0014] Preferably, the adjustment effect includes: the simulation duration when the simulation model is running stably, the active power, reactive power, overshoot, and simulation duration of the simulation model after being subjected to the first operational disturbance; and the active power, reactive power, voltage transformer acquisition voltage, overshoot, and simulation duration of the simulation model after being subjected to the first operational disturbance.
[0015] Preferably, the power system simulation software is PSCAD / EMTDC software.
[0016] Preferably, the network size to be analyzed includes the number of grid-connected inverters.
[0017] Preferably, when the size of the network to be analyzed exceeds a set threshold, a simplified model is used for simulation.
[0018] Preferably, when the size of the network to be analyzed does not exceed the set threshold, the basic model is used for simulation.
[0019] The beneficial effects of this invention are that, compared with the prior art, the model construction method for a photovoltaic power generation unit in this invention, by constructing a basic model and a simplified model, and adding various perturbations to the above models, achieves the acquisition of model adjustment effects, and selects different models based on the adjustment effects under different requirements. The method of this invention is simple, and the improvement of the simulation model is accurate and effective, fully meeting the requirements of model computational efficiency under large-scale simulation. Attached Figure Description
[0020] Figure 1 This is a schematic diagram of the steps in a method for constructing a photovoltaic power generation unit according to the present invention;
[0021] Figure 2 This is a schematic diagram of the simulation circuit of a basic model of a photovoltaic power generation unit in this invention;
[0022] Figure 3 This is a simulation circuit diagram of a simplified model of a photovoltaic power generation unit in this invention;
[0023] Figure 4 This is a schematic diagram illustrating the change of active power on the grid side over time when the model is subjected to a first operational disturbance in a model construction method for a photovoltaic power generation unit according to the present invention.
[0024] Figure 5 This is a schematic diagram illustrating the change of reactive power on the grid side over time when the model is subjected to a first operational disturbance in a model construction method for a photovoltaic power generation unit according to the present invention.
[0025] Figure 6 This is a schematic diagram illustrating the change of active power on the grid side over time when the model is subjected to a second operational disturbance in a model construction method for a photovoltaic power generation unit according to the present invention.
[0026] Figure 7 This is a schematic diagram illustrating the change of reactive power on the grid side over time when the model is subjected to a second operational disturbance in a model construction method for a photovoltaic power generation unit according to the present invention.
[0027] Figure 8 This invention provides a schematic diagram illustrating the change in the voltage collected by the voltage transformer over time when the model is subjected to a second operational disturbance in a photovoltaic power generation unit model construction method. Detailed Implementation
[0028] The present application will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and should not be construed as limiting the scope of protection of the present application.
[0029] Figure 1 This is a schematic diagram illustrating the steps of a photovoltaic power generation unit model construction method according to the present invention. Figure 1 As shown, a method for constructing a model of a photovoltaic power generation unit includes steps 1 to 3.
[0030] Step 1: Perform model simulation on the grid-connected inverter of the photovoltaic power generation unit. The simulation model includes a basic model and a simplified model. The simplified model is used to simplify the half-bridge structure of the grid-connected inverter into a three-phase power supply during the simulation process.
[0031] It is understandable that this invention constructs a corresponding simulation model to simulate the effects of grid-connected photovoltaic power generation units. To simultaneously ensure the accuracy and speed of the simulation, this invention employs two different methods for modeling.
[0032] Preferably, the basic model includes an IBGT (Insulated Gate Bipolar Transistor) device Tch, a parasitic resistance of 0.1 ohms, a DC circuit breaker BRK_DC, an ideal voltage source, a DC input capacitor, control switches T1 to T6, a filter inductor, a current transformer, a voltage transformer, an equivalent resistance, a transformer, and a grid-side power supply. Control switches T1 to T6 are connected in series in pairs to the DC input capacitor and the two ends of the photovoltaic power supply. The connection points of the series-connected control switches provide three-phase current and are connected to the filter inductor. The other end of the filter inductor passes through a current transformer, a voltage transformer, and then sequentially through the equivalent resistance, the transformer, and the grid-side power supply before being grounded.
[0033] Figure 2 This is a schematic diagram of the simulation circuit for a basic model of a photovoltaic power generation unit in this invention. Figure 2 As shown, the method of this invention employs two different modeling methods for grid-connected inverters: a basic model and a simplified model. Figure 2 The basic model in the diagram combines a three-phase circuit into a single phase, and uses the filter inductor Lrs and equivalent resistance of 0.001 ohms to simulate the output circuit. The transformer has a transformation ratio of 1:5 on the photovoltaic power supply side and the grid side. Voltage and current transformers are installed at the grid connection point to collect voltage and current data from the circuit.
[0034] In the basic model, this invention does not simplify switches T1 to T6. Therefore, the simulation data will output the on or off state of the three-phase switches at each point in time in real time and accurately, so as to provide different real-time outputs for the power exchange of the transformer. As a result, the model can simulate the power exchange state of the inverter very accurately, and when a disturbance occurs, it can maximize the acquisition of the inverter's adjustment in response to the disturbance.
[0035] Preferably, the simplified model includes a three-phase power supply pvaref, pvbref, pvcref, a filter inductor, a current transformer, a voltage transformer, an equivalent resistance, a transformer, and a grid-side power supply; wherein, the three-phase power supply is connected in parallel and then connected to the filter inductor; the other end of the filter inductor passes through the current transformer, the voltage transformer, the equivalent resistance, the transformer, and the grid-side power supply in sequence before being grounded.
[0036] Figure 3 This is a schematic diagram of a simulation circuit for a simplified model of a photovoltaic power generation unit according to the present invention. It is understood that the simplified model in this invention further improves upon the basic model, simplifying the control switches, capacitors, power supplies, and other related parameters in the basic model into a three-phase reference power supply. When the inverter and the grid are stable, this three-phase reference power supply can remain essentially unchanged under DC conditions. Therefore, the simulation calculation of the instantaneous response of the model is largely eliminated, and the inverter is simulated using the average state of the inverter over a longer period.
[0037] This simulation method can accurately obtain the average regulation effect of the inverter over a long period of time without adding more simulation data or sampling time points, and is therefore very accurate. At the same time, it ensures that the amount of calculation is small, the calculation speed is fast, and the simulation scale is larger.
[0038] Preferably, the three-phase power supply can be a three-phase current source or a three-phase voltage source; wherein, the magnitude of the three-phase power supply can be acquired from the three-phase input signal of the PWM control unit in the grid-connected inverter.
[0039] It's understandable that a three-phase power supply can be either a three-phase current source or a three-phase voltage source. The choice of power source actually depends on the regulation method of the grid-connected inverter. If the grid-connected inverter regulates based on voltage, it can be simulated as a three-phase voltage source; if it regulates based on current, it can be simulated as a three-phase current source.
[0040] like Figure 3 As shown, it should be noted that the settings for the voltage and current sources can be determined by referring to the three-phase input current or three-phase input voltage of the PWM (Pulse Width Modulation) unit in the model itself.
[0041] Step 2: Input the simulation model of the grid-connected inverter into the power system simulation software, add operating disturbances to the simulation model to obtain the effect of the simulation model on the adjustment of operating disturbances.
[0042] After the model is constructed, the present invention can also input the simulation model into the corresponding simulation software to adjust the running disturbance.
[0043] Specifically, the first operational disturbance is used to increase the reference value of active power when the photovoltaic power station is connected to the grid to 120% of the active power when the simulation model is in its initial stable operating state; the second operational disturbance is used to reduce the voltage of the grid-side power supply to 72% of the voltage when the simulation model is in stable operating state, and this lasts for 3 seconds.
[0044] It is understandable that operational disturbances can be achieved by suddenly changing the parameters of one or more components in the model.
[0045] For example, in this invention, relevant parameters of the power grid can be modified. The relevant parameters of the power source on the grid side can be modified at a certain point after the model reaches steady-state operation. For example, the input and output voltages of the power source can be modified to achieve corresponding adjustments. Simultaneously, the phase angle of the power source can be adjusted to regulate active and reactive power. Regardless of the adjustment method used, the essence is to achieve the first and second operating disturbances in this invention.
[0046] Preferably, the adjustment effect includes: the simulation duration when the simulation model is running stably, the active power, reactive power, overshoot, and simulation duration of the simulation model after being subjected to the first operational disturbance; and the active power, reactive power, voltage transformer acquisition voltage, overshoot, and simulation duration of the simulation model after being subjected to the first operational disturbance.
[0047] Understandably, this invention can set the simulation time for both models to 10 seconds, and the simulation step size to 10 μs. The switching frequency of multiple control switches in the model is set to 1950 Hz. Furthermore, this invention can consider setting the reactive power reference value to 0 Mvar under ideal conditions. After a short simulation time, the system can reach a steady state, and after reaching steady state, two different perturbations are applied to the model.
[0048] Before the perturbation was implemented, the simulation and completion times of the two models were different. The basic model reached steady state after 0.86391s, while the improved simplified model only needed 0.60187s to reach steady state.
[0049] Furthermore, after the model reaches steady state, a first operational disturbance is applied to the model, and relevant parameters are collected throughout the entire process from the implementation of the first operational disturbance until the model reaches steady state again. In this invention, active power and reactive power are collected.
[0050] Figure 4 This is a schematic diagram illustrating the change of active power on the grid side over time when the model is subjected to a first operational disturbance in a photovoltaic power generation unit model construction method of the present invention. Figure 5 This is a schematic diagram illustrating the change of reactive power on the grid side over time when the model is subjected to a first operational disturbance in a photovoltaic power generation unit model construction method according to the present invention. Figure 4 and Figure 5 As shown, the changes in active power and reactive power exhibit a complementary relationship.
[0051] The basic model is better able to reflect the inverter's adjustment process during the brief moment of a disturbance, while the simplified model can only obtain the inverter's average operating state and therefore cannot obtain the instantaneous inverter adjustment process.
[0052] The overshoot described in this invention can be obtained by comparing the local peak states in the active and reactive power waveforms with the voltage difference and steady-state voltage after adjustment. For the basic model, after adding the first operating disturbance, the model reaches steady state after 0.82013s with an overshoot of 1.45%. For the improved simplified model, the model reaches steady state after 0.2402s, and only simulates an overshoot of 0.26%.
[0053] It is evident that, although the improved model is slightly inferior to the basic model in calculating overshoot, its simulation time has been significantly shortened, meeting the requirements of large-scale model simulation in this invention.
[0054] Figure 6 This is a schematic diagram illustrating the change of active power on the grid side over time when the model is subjected to a second operational disturbance in a photovoltaic power generation unit model construction method of the present invention. Figure 7 This is a schematic diagram illustrating the change of reactive power on the grid side over time when the model is subjected to a second operational disturbance in a photovoltaic power generation unit model construction method of the present invention. Figure 8 This invention provides a method for constructing a photovoltaic power generation unit model, illustrating the change in the voltage collected by the voltage transformer over time when the model is subjected to a second operational disturbance. (See diagram below.) Figure 6-8As shown, after the model reaches stability again, the present invention can introduce a second operational disturbance. In the second operational disturbance, the active and reactive power of the basic model reach steady state after 0.54838s, while the simplified model takes a relatively longer time to reach steady state, requiring 0.95704s. Furthermore, the overshoot of the active power in the basic model is 24.81%, while that in the simplified model is 14.79%. It should be noted that although the active power of the simplified model takes longer to recover under this disturbance, this is only because the actual instantaneous control of the control switch overcomes the disturbance more quickly, while the simulation is not as accurate. However, even with the extended time to reach steady state, the simulation speed is significantly improved when multiple grid-connected inverters are simulated simultaneously.
[0055] Of course, this improvement in simulation speed comes at the cost of reduced overshoot. However, in large-scale calculations, since multiple grid-connected inverters are unlikely to experience interference regulation at the same time, this reduction in overshoot will not affect the actual simulation results.
[0056] Similarly, in the basic model, the voltage transformer's acquisition voltage needs to stabilize after 0.32253s, while in the simplified model it takes 0.94624s. Furthermore, the acquisition voltage overshoot in the basic model reaches 30.15%, while in the simplified model it is 18.40%.
[0057] Preferably, the power system simulation software is PSCAD / EMTDC software.
[0058] Step 3: Based on the adjustment effect of the simulation model and the size of the network to be analyzed, select either the basic model or the simplified model.
[0059] Preferably, the network size to be analyzed includes the number of grid-connected inverters. When the network size to be analyzed exceeds a set threshold, a simplified model is used for simulation; when the network size to be analyzed does not exceed the set threshold, a basic model is used for simulation.
[0060] It is understood that a threshold value for the network scale can be pre-designed in this invention. The threshold can be set according to parameters such as the power conversion capacity of the network or the number of grid-connected inverters. When the scale is large, simulating the entire model requires a long time and a large amount of computation. In this case, a simplified model can be used to simulate the system exceeding the threshold value. In this case, the simulation does not focus on the voltage ride-through capability of a single grid-connected inverter, but rather needs to fully consider the coordinated control of the entire power grid.
[0061] Alternatively, if the scale is small, a basic model can be used. In this case, it is not necessary to reduce the simulation time of each grid-connected inverter to a very small extent; it is only necessary to study the accurate results of the simulation model in depth.
[0062] The beneficial effects of this invention are that, compared with the prior art, the model construction method for a photovoltaic power generation unit in this invention, by constructing a basic model and a simplified model, and adding various perturbations to the above models, achieves the acquisition of model adjustment effects, and selects different models based on the adjustment effects under different requirements. The method of this invention is simple, and the improvement of the simulation model is accurate and effective, fully meeting the requirements of model computational efficiency under large-scale simulation.
[0063] The applicant of this invention has provided a detailed description of the embodiments of the invention in conjunction with the accompanying drawings. However, those skilled in the art should understand that the above embodiments are merely preferred embodiments of the invention. The detailed description is only intended to help readers better understand the spirit of the invention and is not intended to limit the scope of protection of the invention. On the contrary, any improvements or modifications made based on the inventive spirit of the invention should fall within the scope of protection of the invention.
Claims
1. A method for constructing a model of a photovoltaic power generation unit, characterized in that, The method includes the following steps: Step 1: Perform model simulation on the grid-connected inverter of the photovoltaic power generation unit. The simulation model includes a basic model and a simplified model. The simplified model is used to simplify the half-bridge structure of the grid-connected inverter into a three-phase power supply during the simulation process. The simplified model includes a three-phase power supply pvaref, pvbref, pvcref, filter inductor, current transformer, voltage transformer, equivalent resistance, transformer, and grid-side power supply; The three-phase power supply is connected in parallel and then connected to the filter inductor respectively. The three-phase power supply can be a three-phase current source or a three-phase voltage source; The magnitude of the three-phase power supply can be acquired from the three-phase input signal of the PWM control unit in the grid-connected inverter; The other end of the filter inductor passes through the current transformer, the voltage transformer, and then through the equivalent resistance, the transformer, and the grid power supply before being grounded. When the inverter and the grid are stable, the three-phase power supply remains unchanged in DC mode; Step 2: Input the simulation model of the grid-connected inverter into the power system simulation software, and add operating disturbances to the simulation model to obtain the adjustment effect of the simulation model on the operating disturbances; The operational disturbance includes a first operational disturbance and a second operational disturbance; wherein, The first operational disturbance is used to increase the reference value of active power when the photovoltaic power station is connected to the grid to 120% of the active power when the simulation model is in its initial stable operating state; The second operational disturbance is used to reduce the voltage of the grid-side power supply to 72% of the voltage at which the simulation model is running stably, and to last for 3 seconds. Step 3: Based on the adjustment effect of the simulation model and the size of the network to be analyzed, select the basic model or the simplified model.
2. The method for constructing a model of a photovoltaic power generation unit according to claim 1, characterized in that: The basic model includes a photovoltaic power source, a DC input capacitor, control switches T1 to T6, a filter inductor, a current transformer, a voltage transformer, an equivalent resistor, a transformer, and a grid-side power source. Among them, the control switches T1 to T6 are connected in series in pairs to the two ends of the DC input capacitor and the photovoltaic power supply, and the connection points of the control switches connected in series in pairs respectively provide three-phase current and are connected to the filter inductor. The other end of the filter inductor passes through the current transformer, the voltage transformer, and then through the equivalent resistance, the transformer, and the grid power supply before being grounded.
3. The method for constructing a model of a photovoltaic power generation unit according to claim 2, characterized in that: The adjustment effects include: The simulation duration during which the simulation model is running stably. The simulation model is subjected to the first operational disturbance, including active power, reactive power, overshoot, and simulation duration. The simulation model is subjected to the first operational disturbance, which includes active power, reactive power, voltage collected by the voltage transformer, overshoot, and simulation duration.
4. The method for constructing a model of a photovoltaic power generation unit according to claim 3, characterized in that: The power system simulation software is PSCAD / EMTDC software.
5. The method for constructing a model of a photovoltaic power generation unit according to claim 4, characterized in that: The network size to be analyzed includes the number of grid-connected inverters.
6. The method for constructing a model of a photovoltaic power generation unit according to claim 5, characterized in that: When the size of the network to be analyzed exceeds a set threshold, the simplified model is used for simulation.
7. The method for constructing a model of a photovoltaic power generation unit according to claim 6, characterized in that: When the size of the network to be analyzed does not exceed the set threshold, the basic model is used for simulation.