Multi-power-supply system broadband oscillation risk test and evaluation method

Abstract

The invention relates to the field of power systems, in particular to a multi-power-supply system broadband oscillation risk testing and evaluating method. The method comprises the following steps: accessing a new energy physical controller to a semi-physical simulation platform, injecting a sweep frequency voltage disturbance signal, and collecting the signal to generate a semi-physical three-dimensional impedance matrix; constructing a corresponding single-machine electromagnetic model in electromagnetic transient simulation software, and injecting sweep-frequency voltage disturbance to generate a single-machine impedance characteristic curve; comparing the two, and correcting electromagnetic model control parameters according to a deviation frequency band; and finally, combining the corrected models and the like, injecting a sweep frequency disturbance signal at a grid-connected point, obtaining impedance, and evaluating the oscillation risk according to a Nyquist stability criterion. According to the method, a semi-physical simulation platform and electromagnetic transient simulation software are combined, impedance scanning is carried out on a physical controller, comparison verification and parameter correction are carried out on the physical controller and an electromagnetic model, the problem of large difference between the model and an actual system is effectively solved, and the accuracy and reliability of broadband oscillation risk assessment are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of power systems, and more specifically to a method for testing and assessing broadband oscillation risks in multi-source systems. Background Technology

[0002] With the continuous construction of grid-connected projects for new energy and energy storage systems, new energy sources, energy storage, static var generators (SVG), and traditional thermal power have formed a complex multi-source system. The oscillation problems caused by the interaction of these systems are becoming increasingly prominent, especially wide-frequency oscillations covering low frequencies, sub-synchronous / super-synchronous, and medium-to-high frequencies. This novel oscillation phenomenon is unprecedented in traditional power systems based on synchronous machines. Its wide oscillation frequency range, unclear oscillation mechanism, and uncertainties in control methods have attracted significant attention from power grid operators.

[0003] While existing technologies include a patent (CN119864831A) that proposes a broadband oscillation grid simulation method for wind turbine grid connection, this method primarily targets wind turbine grid-connected systems and has limitations in assessing broadband oscillation risks in multi-source systems encompassing renewable energy, energy storage, SVG, and traditional thermal power. Furthermore, existing broadband oscillation risk assessment methods largely rely on single simulation models or theoretical analyses, lacking verification of the differences between the actual system and the model, resulting in insufficient accuracy and reliability of the assessment results. For example, although existing technologies propose broadband oscillation risk assessment methods based on impedance analysis, they fail to fully consider the impact of actual operating conditions and parameter variations of various components in multi-source systems on oscillation risk.

[0004] Therefore, there is an urgent need for a broadband oscillation risk testing and assessment method for multi-source systems that can comprehensively consider the actual operating conditions and parameter changes of each component in the multi-source system, verify the differences between the actual system and the model, and thus improve the accuracy and reliability of the assessment results. Summary of the Invention

[0005] The purpose of this invention is to provide a method for testing and evaluating the risk of broadband oscillations in multi-power supply systems, in order to solve the problem that the existing technology lacks verification of the differences between the actual system and the model, resulting in insufficient accuracy and reliability of the evaluation results.

[0006] To achieve the above objectives, the following technical solution is adopted.

[0007] A method for testing and assessing broadband oscillation risk in multi-power supply systems, including:

[0008] S1. Connect the physical controllers of new energy, energy storage and SVG to the hardware-in-the-loop simulation platform, inject the sweep frequency voltage disturbance signal into the controller port, collect the response voltage and current signals, and generate a hardware-in-the-loop three-dimensional impedance matrix.

[0009] S2. Construct single-unit electromagnetic models of thermal power, new energy, energy storage and SVG in electromagnetic transient simulation software. Inject frequency sweep voltage disturbances into the grid connection point of each single-unit model through the impedance scanning module to generate single-unit impedance characteristic curves.

[0010] S3. Compare the semi-physical impedance matrix from step S1 with the single-machine impedance curve from step S2, and correct the corresponding control parameters of the electromagnetic model according to the deviation frequency band.

[0011] The electromagnetic models of S4, combined thermal power, modified new energy / energy storage / SVG, main transformer and power grid are used to inject frequency sweep disturbance signals at the grid and multi-source system connection points to obtain grid-side impedance and multi-source system-side impedance, and assess oscillation risk based on Nyquist stability criterion.

[0012] Optionally, step S1 specifically includes:

[0013] The analog output interface of the hardware-in-the-loop simulation platform outputs control signals to the physical controller, and the digital input interface receives feedback signals from the controller.

[0014] The three-phase controlled harmonic voltage source outputs a sweep frequency voltage disturbance signal, with the frequency range covering the preset minimum to maximum values.

[0015] Acquire the three-phase voltage and current response signals at the controller port;

[0016] The three-dimensional impedance matrix is ​​calculated using an impedance extraction program, and the amplitude-frequency response curve and phase-frequency response curve are output.

[0017] The frequency sweep operation includes:

[0018] The combined operating conditions of active and reactive power in new energy power plants;

[0019] SVG's operating mode, reactive power type, and power output conditions;

[0020] The charging and discharging status and power output conditions of the energy storage power station.

[0021] Optionally, the impedance scan module operation in step S2 includes:

[0022] Construct a scanning system that includes a disturbance voltage source, a multiple operation module, a harmonic measurement module, and an impedance calculation module;

[0023] By setting the start frequency, end frequency, and scan step size through multiple operation modules, the disturbance voltage source is driven to output harmonic voltage signals of corresponding frequencies in sequence.

[0024] After the system enters steady state, the harmonic measurement module acquires the response voltage and current signals and performs Fourier transform;

[0025] The impedance calculation module calculates the impedance value by the ratio of the magnitude of the response voltage to the current and the phase angle difference;

[0026] Perform the above scanning operation on the stand-alone electromagnetic models of thermal power, new energy, energy storage, and SVG respectively.

[0027] Optionally, the single-machine electromagnetic model construction process includes:

[0028] The electromagnetic model of new energy includes photovoltaic arrays or wind turbines, DC / DC converters, DC / AC inverters, LCL filters and controllers;

[0029] The energy storage electromagnetic model includes an AC voltage source, a transformer, a converter, a DC voltage source, and a controller;

[0030] The SVG electromagnetic model includes an AC voltage source, a reactor, a controller, and a power measurement module;

[0031] The electromagnetic model of thermal power plants is constructed based on the parameters of the measured modeling report of the excitation system and speed control system, and includes the prime mover, speed governor, automatic voltage regulator and generator.

[0032] Optionally, the correction logic in step S3 includes:

[0033] Compare the impedance amplitude-frequency curves and phase-frequency curves of the semi-physical and stand-alone electromagnetic models;

[0034] When the amplitude deviation exceeds the preset amplitude threshold or the phase deviation exceeds the preset phase threshold, the control parameters are corrected according to the deviation frequency band:

[0035] Correct DC bus voltage control, active power control, or reactive power control parameters when there is a deviation in the low frequency band.

[0036] Correcting phase-locked loop control parameters when there is a deviation in the mid-frequency range;

[0037] Correct current inner loop control or filter parameters when there is high-frequency deviation;

[0038] Iteratively execute steps S2 to S3 until the deviation meets the threshold requirement.

[0039] Optionally, the whole site model combination in step S4 includes:

[0040] The electromagnetic model of thermal power, the modified electromagnetic model of new energy, the electromagnetic model of energy storage, the electromagnetic model of SVG, the main transformer model, the power grid equivalent model and the line model are combined into a multi-source system;

[0041] The parameters of the power grid equivalent model and line model are generated based on the PSD-BPA power system stability calculation software.

[0042] The main transformer model is connected to the grid connection point and the power grid according to the actual topology.

[0043] Optionally, the oscillation risk assessment in step S4 includes:

[0044] Calculate the ratio of the grid-side impedance Zg to the multi-source system-side impedance Zs;

[0045] In logarithmic coordinates, the following criteria are applied: when |Zg(s) / Zs(s)|=1, if the phase angle γ=|arg(Zg(s) / Zs(s))|<180°, the system is considered stable; if γ≥180°, there is a risk of oscillation.

[0046] Optionally, the harmonic measurement module is executed when: after injecting the disturbance voltage signal, it monitors the system's operating status until the amplitude fluctuation of the response signal is less than a preset threshold, at which point it determines that it has entered a steady state and collects the response signal.

[0047] Optionally, the multi-condition test in step S4 includes:

[0048] Set up a combination of operating conditions including thermal power output, new energy power, energy storage charging and discharging status, and SVG working mode;

[0049] A frequency sweep disturbance signal is injected at the grid connection point using an impedance scanning module;

[0050] Obtain impedance characteristic curves of the grid side and the multi-source system side under different combined operating conditions.

[0051] Optionally, the semi-physical platform signal transmission in step S1 includes:

[0052] Three-phase voltage analog signals are output to the physical controller via the analog output interface;

[0053] Receive the PWM wave digital signal output by the controller through the digital input interface;

[0054] The response current signal is converted into a voltage signal by a current sensor and then input to the hardware-in-the-loop data acquisition card.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] A method for testing and assessing broadband oscillation risks in multi-power systems is proposed. This method combines a hardware-in-the-loop (HIL) simulation platform and electromagnetic transient simulation software to perform impedance scanning on the physical controllers of new energy sources, energy storage, and SVG (Static Var Generator). The results are compared and verified with electromagnetic models, model parameters are corrected, and finally, oscillation risk is assessed based on the Nyquist stability criterion. This method effectively addresses the problem of significant discrepancies between models and actual systems in existing technologies, significantly improving the accuracy and reliability of broadband oscillation risk assessment. Directly connecting the physical controllers to the HIL simulation platform realistically simulates the actual operating environment, ensuring the credibility of the assessment results. Furthermore, by comparing the HIL impedance matrix with the single-unit impedance curves and correcting the control parameters of the electromagnetic model based on the deviation frequency band, the differences between models and actual systems in existing technologies are further compensated for. This provides grid dispatchers with more accurate system characteristic information, helping to promptly identify and eliminate operational risks and avoid serious accidents such as large-scale new energy grid disconnection and thermal power plant shutdown caused by broadband oscillations.

[0057] The specific operation process of semi-physical impedance scanning includes signal transmission methods, output of frequency sweep voltage disturbance signals, acquisition of response signals, and generation of a three-dimensional impedance matrix. Clarifying these details not only improves the accuracy of impedance scanning but also covers various actual operating conditions, such as the combined active and reactive power conditions of new energy power plants, the operating mode and power output conditions of SVG (Static Var Generator), and the charging and discharging states and power output conditions of energy storage power plants, thus ensuring the comprehensiveness of the assessment. The operation process of the impedance scanning module has been further optimized. Automatic frequency modification is achieved through multiple operating modules, improving scanning efficiency. The harmonic measurement module acquires response signals after the system enters steady state, ensuring the accuracy and reliability of data acquisition. Detailed descriptions and optimizations are provided for key aspects such as the construction of single-machine electromagnetic models, correction logic, overall station model combination, oscillation risk assessment methods, multi-condition testing, and signal transmission on the semi-physical platform. The introduction of these technical features not only improves the accuracy and reliability of the model but also enhances the adaptability and practicality of the assessment method. Through these optimization measures, the evaluation method of this invention can more comprehensively reflect the dynamic characteristics of multi-source systems, providing power grid operators with a more scientific and reliable tool for assessing broadband oscillation risks. Attached Figure Description

[0058] Figure 1 This is a schematic diagram of the controller semi-physical impedance scanning process in an embodiment of a method for testing and assessing the risk of wideband oscillation in a multi-power supply system according to the present invention.

[0059] Figure 2 This is the controller semi-physical impedance scanning working environment of an embodiment of the method for testing and evaluating the risk of wideband oscillation in multi-power supply systems according to the present invention.

[0060] Figure 3This is a schematic diagram of a single-machine electromagnetic transient impedance scanning system, which is an embodiment of a method for testing and evaluating the risk of wideband oscillation in multi-power supply systems according to the present invention.

[0061] Figure 4 This is a schematic diagram of the electromagnetic transient frequency sweep time logic of an embodiment of a method for testing and evaluating the risk of wideband oscillation in a multi-power supply system according to the present invention.

[0062] Figure 5 This is a system topology diagram of an embodiment of a method for testing and assessing the risk of wideband oscillation in a multi-power supply system according to the present invention.

[0063] Figure 6 This is a photovoltaic impedance scanning circuit topology according to an embodiment of a method for testing and evaluating the risk of wideband oscillation in multi-power supply systems according to the present invention.

[0064] Figure 7 This is an impedance scanning electromagnetic transient model, which is an embodiment of the method for testing and evaluating the risk of broadband oscillations in multi-power supply systems according to the present invention.

[0065] Figure 8 This is a comparison chart of the photovoltaic 0.1pu active power and maximum inductive reactive power operating conditions in an embodiment of the method for testing and evaluating the risk of wideband oscillation in a multi-power system according to the present invention.

[0066] Figure 9 This is a comparison diagram of photovoltaic 0.1 pu active and 0 reactive power conditions in an embodiment of the method for testing and evaluating the risk of broadband oscillation in a multi-power system according to the present invention.

[0067] Figure 10 This is a comparison diagram of the SVG constant reactive mode inductive 0.9 pu operating condition under an embodiment of the method for testing and evaluating the risk of wideband oscillation in a multi-power system according to the present invention.

[0068] Figure 11 This is a comparison diagram of the SVG constant reactive mode capacitive 0.1 pu operating condition under an embodiment of the method for testing and evaluating the risk of wideband oscillation in a multi-power system according to the present invention.

[0069] Figure 12 This is a schematic diagram of a whole-site frequency sweep of an embodiment of a method for testing and assessing the risk of broadband oscillation in a multi-power supply system according to the present invention.

[0070] Figure 13 The results are impedance scans of thermal power at 50% output, SVG inductive full-load, and photovoltaic at 0.3 pu, according to an embodiment of the present invention's method for testing and assessing the risk of broadband oscillation in multi-power systems.

[0071] Figure 14 This is an embodiment of the method for testing and evaluating the risk of broadband oscillation in a multi-power system according to the present invention, showing the impedance scan results of thermal power at 100% output, SVG capacitive full power generation, and photovoltaic at 0.5 pu. Detailed Implementation

[0072] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0073] The following detailed description is exemplary and intended to provide further detailed explanation of the invention. Unless otherwise specified, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terminology used in this invention is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention.

[0074] Example 1

[0075] like Figure 1 As shown, step S1 involves a semi-physical impedance scan of the controller. In this invention, the physical controllers of new energy sources, energy storage, and SVG (Static Var Generator) first need to be connected to a semi-physical simulation platform. A semi-physical simulation platform is an experimental device capable of simulating actual operating environments. It allows the injection of sweep voltage disturbance signals into the controller ports and the acquisition of response voltage and current signals to generate a semi-physical three-dimensional impedance matrix. The specific operation is as follows:

[0076] Physical Controller Connection: Connect the physical controllers of new energy sources, energy storage systems, and SVGs to the hardware-in-the-loop (HIL) simulation platform via dedicated interfaces. These controllers typically include digital signal processors (DSPs), field-programmable gate arrays (FPGAs), or other microcontrollers, used to control the operation of new energy equipment, energy storage systems, and SVGs. During connection, ensure the correctness and stability of electrical connections to avoid affecting test results due to poor contact or short circuits.

[0077] Signal injection and acquisition:

[0078] Control signals are output to the physical controller through the analog output interface of the hardware-in-the-loop simulation platform. These signals can be voltage signals, current signals, or other analog signals, used to drive the input ports of the controller.

[0079] Feedback signals from the controller are received via a digital input interface. These feedback signals are typically pulse-width modulation (PWM) signals or other digital signals output by the controller, used to monitor the controller's operating status.

[0080] The system controls the output of a three-phase controlled harmonic voltage source to perform a frequency sweep voltage disturbance signal, with the frequency range covering a preset minimum to maximum value. For example, the frequency range can be set from 2Hz to 1000Hz, and the amplitude can be set from 1% to 5% of the rated voltage. The specific frequency range and amplitude can be adjusted according to the characteristics of the actual system.

[0081] After the disturbance signal is injected, the three-phase voltage and current response signals at the controller port are acquired. The acquisition equipment should have high precision and a high sampling rate to ensure that the acquired signals accurately reflect the dynamic characteristics of the system. For example, the sampling rate of the acquisition equipment can be set to 10kHz or higher to capture rapidly changing signals.

[0082] Impedance matrix calculation:

[0083] The impedance extraction program calculates the three-dimensional impedance matrix. Based on the acquired voltage and current signals, this program uses impedance analysis to calculate the system's impedance characteristics. Specific calculation methods can include Fourier transform, least squares method, or other numerical analysis methods. For example, the time-domain signal can be converted to a frequency-domain signal using Fourier transform, and then the amplitude ratio and phase difference of the voltage and current signals can be calculated to obtain the impedance value.

[0084] The impedance extraction program outputs amplitude-frequency response curves and phase-frequency response curves. These curves can intuitively reflect the dynamic characteristics of the system and help analysts identify potential oscillation risks.

[0085] Frequency sweep settings:

[0086] Configure active and reactive power combination operating conditions for renewable energy power plants. For example, for photovoltaic power plants, different light intensities and temperature conditions can be set to simulate different power generation; for wind farms, different wind speed conditions can be set to simulate different power generation. At the same time, it is also necessary to consider the adjustment range of reactive power, such as the full range from inductive reactive power to capacitive reactive power.

[0087] The SVG's operating mode (such as constant reactive power mode, constant voltage mode, constant power factor mode), reactive power type (inductive or capacitive), and power output conditions can be set. For example, in constant reactive power mode, different reactive power output values ​​can be set; in constant voltage mode, different voltage regulation ranges can be set.

[0088] Configure the charging and discharging states and power output conditions of the energy storage power station. For example, different charging and discharging powers and depths of charge and discharge can be set to simulate the impedance characteristics of the energy storage system under different operating conditions.

[0089] Step S2: Single-unit electromagnetic transient impedance scanning. Construct single-unit electromagnetic models for thermal power, new energy, energy storage, and SVG in the electromagnetic transient simulation software. These models should accurately reflect the operating characteristics of each power source. Specific operations are as follows:

[0090] New energy electromagnetic models include photovoltaic arrays or wind turbines, DC / DC converters, DC / AC inverters, LCL filters, and controllers. For example, the photovoltaic array model should consider the impact of environmental factors such as light intensity and temperature on power generation; the wind turbine model should consider the impact of environmental factors such as wind speed and direction on power generation. The models of DC / DC converters and DC / AC inverters should consider the impact of parameters such as conversion efficiency and switching frequency on the system's dynamic characteristics.

[0091] Energy storage electromagnetic model: includes AC voltage source, transformer, converter, DC voltage source and controller. For example, the AC voltage source model should consider the influence of parameters such as voltage amplitude and frequency on the dynamic characteristics of the system; the transformer model should consider the influence of parameters such as turns ratio and leakage inductance on the dynamic characteristics of the system.

[0092] SVG electromagnetic model: Includes an AC voltage source, reactor, controller, and power measurement module. For example, the AC voltage source model should consider the influence of parameters such as voltage amplitude and frequency on the system's dynamic characteristics; the reactor model should consider the influence of parameters such as inductance and resistance on the system's dynamic characteristics.

[0093] The electromagnetic model of the thermal power plant is constructed based on the parameters from the measured modeling report of the excitation system and speed control system, and includes the prime mover, governor, automatic voltage regulator, and generator. For example, the model of the prime mover should consider the influence of parameters such as mechanical power and speed on the dynamic characteristics of the system; the model of the governor should consider the influence of parameters such as regulation speed and regulation accuracy on the dynamic characteristics of the system.

[0094] Impedance scan module operation:

[0095] Construct a scanning system comprising a disturbance voltage source, a multiple operation module, a harmonic measurement module, and an impedance calculation module. The disturbance voltage source should have adjustable frequency and amplitude, capable of outputting harmonic voltage signals of different frequencies. The multiple operation module should have the ability to set the start frequency, end frequency, and scan step size, and be able to drive the disturbance voltage source to output harmonic voltage signals of corresponding frequencies sequentially.

[0096] The start frequency, end frequency, and scan step size can be set through multiple operation modules. For example, the start frequency can be set to 2Hz, the end frequency can be set to 1000Hz, and the scan step size can be set to 1 Hz, 5Hz, or 10 Hz. The specific step size can be adjusted according to the characteristics of the actual system.

[0097] After the system reaches steady state, the harmonic measurement module acquires the response voltage and current signals and performs Fourier transform. The steady-state criterion can be that the amplitude fluctuation of the response signal is less than a preset threshold, for example, less than 1%. The harmonic measurement module should have high precision and a high sampling rate to ensure that the acquired signals accurately reflect the dynamic characteristics of the system.

[0098] The impedance calculation module calculates the impedance value by using the amplitude ratio and phase angle difference of the response voltage and current. Specific calculation methods can include Fourier transform, least squares method, or other numerical analysis methods. For example, the time-domain signal can be converted to a frequency-domain signal using Fourier transform, and then the amplitude ratio and phase angle difference of the voltage and current signals can be calculated to obtain the impedance value.

[0099] The above scanning operation was performed on the individual electromagnetic models of thermal power, new energy, energy storage, and SVG to generate individual impedance characteristic curves. These curves can intuitively reflect the dynamic characteristics of each power supply device and help analysts identify potential oscillation risks.

[0100] Step S3: Model Correction. Compare the semi-physical impedance matrix generated in Step S1 with the single-machine impedance curve generated in Step S2, and correct the corresponding control parameters of the electromagnetic model according to the deviation frequency band. The specific operation is as follows:

[0101] Deviation comparison:

[0102] Compare the impedance amplitude-frequency curves of the semi-physical model and the stand-alone electromagnetic model. Calculate the amplitude deviation between the two curves at each frequency point to determine if it exceeds a preset amplitude threshold. For example, the preset amplitude threshold can be ±10dB.

[0103] Compare the impedance phase-frequency curves of the semi-physical model and the stand-alone electromagnetic model. Calculate the phase deviation between the two curves at each frequency point and determine if it exceeds a preset phase threshold. For example, the preset phase threshold can be ±10°.

[0104] Correction logic:

[0105] Low-frequency deviation correction: When there is a deviation in the low-frequency range (e.g., 2Hz to 200Hz), the DC bus voltage control, active power control, or reactive power control parameters are corrected. For example, the reference value or control gain of the DC bus voltage is adjusted to reduce the amplitude deviation.

[0106] Mid-frequency deviation correction: When there is a deviation in the mid-frequency range (e.g., 200Hz to 400Hz), the phase-locked loop (PLL) control parameters are corrected. For example, the loop gain or filter parameters of the PLL are adjusted to reduce the phase deviation.

[0107] High-frequency deviation correction: When there is a deviation in the high-frequency range (e.g., 400Hz to 1000Hz), the parameters of the current inner loop control or filter are corrected. For example, the control gain of the current inner loop or the cutoff frequency of the filter is adjusted to reduce the amplitude deviation.

[0108] Iterative correction: Steps S2 to S3 are executed iteratively until the deviation meets the threshold requirement, thereby ensuring that the impedance characteristics of the model are consistent with those of the actual system.

[0109] Step S4: Station impedance scan and oscillation risk assessment.

[0110] The electromagnetic models of thermal power, modified new energy sources, energy storage, SVG, main transformers, and the power grid are combined into a multi-source system. A frequency sweep disturbance signal is injected at the grid connection point of the multi-source system to obtain the grid-side impedance and the multi-source system-side impedance. Oscillation risk is then assessed based on the Nyquist stability criterion. The specific operation is as follows:

[0111] The electromagnetic models of thermal power plants, modified new energy sources, energy storage, SVG, main transformers, power grid equivalent models, and line models are combined into a multi-source system. The parameters of the power grid equivalent model and line models are generated based on the PSD-BPA power system stability calculation software, and the main transformer model is connected to the grid at the actual topology.

[0112] The accuracy of the electromagnetic transient models was ensured by comparing and validating new energy, energy storage, and SVG electromagnetic transient models. The electromagnetic models of the power grid, lines, and main transformers were built based on parameters from the PSD-BPA power system stability calculation software, while the electromagnetic models of thermal power plants were built based on measured modeling reports of the excitation system and speed regulation system.

[0113] Oscillation Risk Assessment:

[0114] By connecting the impedance scanning module in parallel between the power grid model and the multi-source system, and changing the operating mode and output of thermal power, new energy, energy storage, and SVG, impedance scanning is performed on various operating conditions to obtain the impedance characteristics of the power grid and the multi-source system.

[0115] Calculate the ratio of the grid-side impedance Zg to the multi-source system-side impedance Zs. In logarithmic coordinates, determine the following: when |Zg(s) / Zs(s)|=1, if the phase angle γ=|arg(Zg(s) / Zs(s))|<180°, the system is considered stable; if γ≥180°, there is a risk of oscillation. This method allows for a direct assessment of whether the system carries a risk of broadband oscillation.

[0116] Multi-condition testing:

[0117] Multiple operating conditions can be configured, including combinations of thermal power output, renewable energy power, energy storage charging / discharging status, and SVG operating mode. For example, thermal power output can be set to 50% or 100%, renewable energy power can be set to different proportions of rated power, energy storage can be set to charging or discharging status, and SVG can be set to different reactive power output modes.

[0118] By injecting a frequency sweep disturbance signal at the grid connection point using an impedance scanning module, impedance characteristic curves of the grid side and multi-source system side under different combined operating conditions are obtained. These curves can provide grid operators with more comprehensive reference information, helping them to optimize system operation and control strategies.

[0119] Example 2

[0120] A method for testing and assessing broadband oscillation risk in multi-power systems is disclosed. The power sources include renewable energy power plants, thermal power plants, and energy storage power stations. Renewable energy power plants include wind farms and photovoltaic power stations, each containing a static var generator (SVG). Energy storage power stations include both the energy storage systems integrated within the renewable energy power plants and the power storage stations themselves. The thermal power plants, renewable energy sources, and energy storage subsystems constitute a unified system, connected to the power grid via 110 / 220 / 500kV. Broadband oscillation is a novel oscillation problem caused by the interaction between power electronic devices in various power supply equipment and between the system and the power grid, with an oscillation frequency bandwidth ranging from several Hz to several kHz. The testing method includes four steps: controller semi-physical impedance scanning, single-machine electromagnetic transient impedance scanning, single-machine and semi-physical comparison verification, and whole-system impedance scanning. Impedance scanning is achieved through impedance analysis. The assessment method uses the Nyquist criterion to evaluate the oscillation risk between systems.

[0121] By injecting a voltage / current harmonic source of a certain frequency into the object under test, measuring the current / voltage response components of the object under test at the corresponding frequency, and then calculating the impedance at the corresponding frequency point, the impedance value of the frequency band under test can be obtained by continuously modifying the injected frequency and repeating this process.

[0122] Furthermore, the specific steps are as follows: (1) Set the starting frequency f min and termination frequency f max Define the step size Δf (e.g., 10Hz).

[0123] (2) Inject a disturbance signal into the object under test: Δv(t) = A·sin(2πf k t), f∈[f min f max Where f k The current scanning frequency is A, and the amplitude is A (typically 1% to 5% of the rated voltage / current).

[0124] (3) For each frequency f k Inject Δv(t) and wait for the system to reach steady state.

[0125] (4) Acquire response signal Ai resp (t).

[0126] (5) Calculate the impedance at this frequency point.

[0127]

[0128] (6) Cycle: Repeat steps (2) to (6) until the entire frequency band is covered.

[0129] (7) If the impedance ratio Zg / Zs between the two systems satisfies the Nyquist criterion, that is, the Nyquist curve of the impedance ratio Zg / Zs does not revolve around the point (-1, 0), then the grid-connected inverter will operate stably. When transformed to the logarithmic impedance coordinate system, that is, when |Zg(s) / Zs(s)|=1, the system is stable and there is no risk of oscillation when the phase angle γ=|arg(Zg(s) / Zs(s))| is less than 180°. When γ is equal to 180°, the system is at critical stability, while when γ is greater than 180°, the system has the risk of oscillation.

[0130] The controller mentioned refers to the physical control box for new energy, energy storage, and SVG.

[0131] The controller's semi-physical impedance scanning process is shown in the attached figure. Figure 1 As shown, it mainly consists of the following steps:

[0132] (1) Based on a hardware-in-the-loop simulation platform, an impedance testing system was built by connecting a new energy / energy storage / SVG physical controller; the controller and the main circuit model are connected via AO / DI data lines to transmit digital and analog signals, see Appendix. Figure 2 ;

[0133] (2) Inject the voltage signal into the three-phase controlled harmonic voltage source to inject voltage disturbance within the frequency range to be measured into the impedance test system;

[0134] (3) Measure the three-phase port voltage and port current of the unit under test, and record the waveform;

[0135] (4) Using an impedance extraction program, the three-phase voltage and current of the unit under test are solved, and a two-dimensional impedance matrix of new energy / energy storage / SVG is obtained.

[0136] (5) Draw the amplitude and phase frequency curves of the semi-physical object to be tested.

[0137] Standalone electromagnetic transient impedance scanning refers to the impedance scanning of electromagnetic transient models of thermal power, new energy, SVG, and energy storage using an impedance scanning module in electromagnetic transient simulation software. The system architecture is attached. Figure 3 The electromagnetic transient models for thermal power, new energy, SVG, and energy storage should support the same simulation step size and compiler version.

[0138] Furthermore, the principle is to inject a controlled voltage source with controllable amplitude and variable frequency into the grid connection point of the object under test through an impedance scanning module, and to perform Fourier transform on the measured response voltage and response current on the side of the object under test to obtain the amplitude and phase angle of the voltage and current at different frequencies. Thus, by dividing the voltage and current amplitudes and subtracting the phase angles, the curves of impedance amplitude and phase angle changing with frequency are obtained.

[0139] The impedance scanning module, which is built in electromagnetic transient simulation software, includes a disturbance voltage source: if the amplitude of the injected harmonic voltage source is too large, it will disrupt the original stable operating state; if it is too small, it will not cause fluctuations. Generally, 3% of the rated voltage can be selected.

[0140] It includes multiple operating modules, which can: (1) record the positive and negative sequence impedance amplitude and phase angle at a certain time point; (2) automatically save the positive and negative sequence impedance amplitude and phase angle in a folder; (3) set the start and end of the frequency and the step size to realize the automatic change of frequency.

[0141] Harmonic Measurement and Extraction Module: By injecting voltage disturbances of different frequencies, the module calculates the impedance amplitude and phase angle by performing Fourier transforms on the response voltage and response current at the corresponding frequencies.

[0142] Impedance calculation module: It can divide the amplitude and subtract the phase angle of multidimensional voltage and current signals to obtain multidimensional impedance amplitude and phase angle, and only takes the impedance at the frequency f corresponding to the injected voltage disturbance.

[0143] The timing for measuring the positive and negative sequence impedance amplitudes and phase angles during impedance scanning should be selected after the injection of the disturbance voltage and when the device under test is running stably, as shown in the attached figure. Figure 3 , 4 As shown.

[0144] The electromagnetic transient models for thermal power, new energy, SVG, and energy storage are described above. The electromagnetic model for energy storage includes at least an AC voltage source, a transformer, a converter, and a DC voltage source, and the control includes at least an outer loop voltage control, an inner loop current control, and a phase-locked loop control.

[0145] The electromagnetic model of the SVG includes at least an AC voltage source, a reactor, a controller, and a power measurement module. The control includes at least an outer loop voltage control, an outer loop power control, an inner loop current control, and a phase-locked loop control.

[0146] The electromagnetic model of new energy sources should include at least photovoltaic arrays / wind turbines, DC-DC converters, DC-AC inverters, LCL filters, and transformers; the control system should include at least outer loop voltage control, inner loop current control, and phase-locked loop control.

[0147] The electromagnetic model of thermal power is built based on the measured parameters of thermal power, including prime mover model, actuator model, speed governor model, automatic voltage regulator model, power system stabilizer model, generator model. The control includes at least power factor control, active power control, reactive power control, and thermal power unit coordination control.

[0148] An impedance scanning module is inserted between the electromagnetic model of new energy sources and the power grid, as shown in the attached diagram. Figure 2As shown, different operating conditions are set, including active power and reactive power, and the impedance scanning module is controlled to emit voltages of different frequencies. The amplitude frequency and phase frequency data are obtained from the folder path saved by the impedance scanning module, and the amplitude frequency and phase frequency curves of the electromagnetic model of the object under test are plotted.

[0149] An impedance scanning module is inserted between the electromagnetic model of the SVG and the power grid, as shown in the attached diagram. Figure 2 As shown, different operating conditions are set, including working mode (constant reactive power mode / constant voltage mode / constant power factor mode), reactive power type (inductive / capacitive), and reactive power. The impedance scanning module is controlled to emit voltages of different frequencies, and the amplitude frequency and phase frequency data are obtained from the folder path saved by the impedance scanning module. The amplitude frequency and phase frequency curves of the electromagnetic model of the object under test are plotted.

[0150] An impedance scanning module is inserted between the electromagnetic model of energy storage and the power grid, as shown in the attached diagram. Figure 2 As shown, different operating conditions are set, including charging and discharging states (charging / discharging), active power and reactive power. The impedance scanning module is controlled to emit voltages of different frequencies. The amplitude frequency and phase frequency data are obtained from the folder path saved by the impedance scanning module, and the amplitude frequency and phase frequency curves of the electromagnetic model of the object under test are plotted.

[0151] The comparison verification between the stand-alone unit and the semi-physical model involves comparing the amplitude-frequency and phase-frequency curves of the new energy, energy storage, and SVG semi-physical models with the amplitude-frequency and phase-frequency curves of the electromagnetic models of the new energy, energy storage, and SVG. If the comparison results meet the requirements of impedance amplitude deviation less than or equal to ±10dB and phase error less than or equal to ±10°, the impedance characteristics of the electromagnetic model are considered to be in good agreement with the actual model (the area around the fundamental frequency of 50Hz is not considered). If there are deviations in some frequency bands, the control parameters are modified according to Appendix 1 and the comparison is continued until the standard requirements are met.

[0152] The aforementioned whole-station impedance scan combines electromagnetic transient models of thermal power, new energy, energy storage, SVG, main transformer, power grid, and transmission lines. The electromagnetic transient models for new energy, energy storage, and SVG are verified through comparison. The electromagnetic models for the power grid, transmission lines, and main transformer are built based on parameters from the PSD-BPA power system stability calculation software. The electromagnetic model for thermal power is built based on the provided measured modeling reports for the excitation and speed control systems.

[0153] The impedance scanning module is connected in parallel between the power grid model and the multi-source system. By changing the operation mode and output of thermal power, new energy, energy storage, and SVG, impedance scanning is performed on various operating conditions to obtain the impedance characteristics of the power grid and the multi-source system. The Nyquist criterion is used to determine whether there is an oscillation risk between the multi-source system and the power grid.

[0154] Example 3

[0155] A method for testing and assessing the risk of broadband oscillations in multi-power supply systems. The circuit topology of the system to be analyzed is attached. Figure 5 As shown. The system includes a 600MW thermal power plant, a 6MW / 24MWh energy storage system, and a 60MW photovoltaic system, with a 20MVarSVG within the substation. The photovoltaic modules are collected by three 35kV collector lines to the 35kV side of the substation. After being stepped up by the main transformer, they are connected to the 220kV busbar via one 220kV cable, and then connected to the power grid via two outgoing lines. The technical solution adopted by this invention to solve its technical problem is as follows:

[0156] (1) Controller Hardware-in-the-loop Impedance Scan. The controllers for the photovoltaic (PV) and SVG (SVG) systems were connected to the hardware-in-the-loop simulation platform. Taking the PV system as an example, its impedance scan circuit topology is shown in the attached figure. Figure 6 As shown

[0157] Module 1 is the disturbance voltage input Δv(t), and module 2 is the impedance voltage and current measurement point.

[0158] Impedance tests were conducted on 15 photovoltaic and 11 SVG operating conditions, as shown in Appendix Tables 2-3. Frequency band settings are shown in Appendix Table 4.

[0159] (2) Single-machine electromagnetic transient impedance scanning. The electromagnetic transient model of the impedance scanning module is as follows: Figure 7 As shown. Among them,

[0160] 1- Disturbance voltage source; 2- Multiple operation module; 3- Harmonic measurement and extraction module; 4- Impedance calculation module.

[0161] Impedance scanning modules were interspersed between the electromagnetic models of photovoltaics and SVG and the power grid, respectively. Voltage disturbances were injected according to the operating conditions in Appendix 2 and Table 3 to obtain their impedance characteristic diagrams.

[0162] (3) Comparison and verification between stand-alone machine and semi-physical machine.

[0163] Some comparative verification images are attached. Figures 8-11 As shown, the impedance amplitude deviation is less than or equal to ±10 dB and the phase error is less than or equal to ±10°.

[0164] (4) Whole-site impedance scan. The whole-site model is shown in the attached figure. Figure 12 As shown

[0165] 1-Electromagnetic transient model of thermal power unit; 2-Electromagnetic transient model of photovoltaic power plant; 3-Electromagnetic transient model of SVG; 4-Equivalent model of power grid; 5-Electromagnetic transient model of power line; 6-Electromagnetic transient model of main transformer; 7-Impedance scanning module, some impedance scanning results are attached. Figure 13-14 As shown.

[0166] Appendix:

[0167] Appendix 1: Comparison Table of Control Parameters for Modified Electromagnetic Transient Model

[0168]

[0169]

[0170] Appendix 2 Operating Conditions of Photovoltaic Power Generation Units

[0171]

[0172] Appendix 3 SVG Operating Conditions

[0173]

[0174] Appendix 4: Frequency Bands

[0175]

[0176] As is known from common technical knowledge, this invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative in all respects and are not the only ones. All modifications within the scope of this invention or its equivalents are included in this invention.

Claims

1. A method for testing and assessing the risk of broadband oscillations in a multi-power supply system, characterized in that, include, S1. Connect the physical controllers of new energy, energy storage and SVG to the hardware-in-the-loop simulation platform, inject the sweep frequency voltage disturbance signal into the controller port, collect the response voltage and current signals, and generate a hardware-in-the-loop three-dimensional impedance matrix. S2. Construct single-unit electromagnetic models of thermal power, new energy, energy storage and SVG in electromagnetic transient simulation software, and inject sweep frequency voltage disturbances into the grid connection point of each single-unit model through the impedance scanning module to generate single-unit impedance characteristic curves. S3. Compare the semi-physical impedance matrix from step S1 with the single-machine impedance curve from step S2, and correct the corresponding control parameters of the electromagnetic model according to the deviation frequency band. S4, combined with the electromagnetic models of thermal power, modified new energy / energy storage / SVG, main transformer and power grid, injects frequency sweep disturbance signals at the grid and multi-source system connection points, obtains grid-side impedance and multi-source system-side impedance, and assesses oscillation risk based on Nyquist stability criterion.

2. The method for testing and assessing the broadband oscillation risk of a multi-power supply system according to claim 1, characterized in that, Step S1 specifically includes: The analog output interface of the hardware-in-the-loop simulation platform outputs control signals to the physical controller, and the digital input interface receives feedback signals from the controller. The three-phase controlled harmonic voltage source outputs a sweep frequency voltage disturbance signal, with the frequency range covering the preset minimum to maximum values. Acquire the three-phase voltage and current response signals at the controller port; The three-dimensional impedance matrix is ​​calculated using an impedance extraction program, and the amplitude-frequency response curve and phase-frequency response curve are output. The frequency sweep operation includes: The combined operating conditions of active and reactive power in new energy power plants; SVG's operating mode, reactive power type, and power output conditions; The charging and discharging status and power output conditions of the energy storage power station.

3. The method for testing and assessing the broadband oscillation risk of a multi-power supply system according to claim 1, characterized in that, The impedance scanning module operation in step S2 includes: Construct a scanning system that includes a disturbance voltage source, a multiple operation module, a harmonic measurement module, and an impedance calculation module; By setting the start frequency, end frequency, and scan step size through multiple operation modules, the disturbance voltage source is driven to output harmonic voltage signals of corresponding frequencies in sequence. After the system enters steady state, the harmonic measurement module acquires the response voltage and current signals and performs Fourier transform; The impedance calculation module calculates the impedance value by the ratio of the magnitude of the response voltage to the current and the phase angle difference; Perform the above scanning operation on the stand-alone electromagnetic models of thermal power, new energy, energy storage, and SVG respectively.

4. The method for testing and assessing the broadband oscillation risk of a multi-power supply system according to claim 3, characterized in that, The process of building a single-machine electromagnetic model includes: The electromagnetic model of new energy includes photovoltaic arrays or wind turbines, DC / DC converters, DC / AC inverters, LCL filters and controllers; The energy storage electromagnetic model includes an AC voltage source, a transformer, a converter, a DC voltage source, and a controller; The SVG electromagnetic model includes an AC voltage source, a reactor, a controller, and a power measurement module; The electromagnetic model of thermal power plants is constructed based on the parameters of the measured modeling report of the excitation system and speed control system, and includes the prime mover, speed governor, automatic voltage regulator and generator.

5. The method for testing and assessing the broadband oscillation risk of a multi-power supply system according to claim 1, characterized in that, The correction logic in step S3 includes: Compare the impedance amplitude-frequency curves and phase-frequency curves of the semi-physical and stand-alone electromagnetic models; When the amplitude deviation exceeds the preset amplitude threshold or the phase deviation exceeds the preset phase threshold, the control parameters are corrected according to the deviation frequency band: Correct DC bus voltage control, active power control, or reactive power control parameters when there is a deviation in the low frequency band. Correcting phase-locked loop control parameters when there is a deviation in the mid-frequency range; Correct current inner loop control or filter parameters when there is high-frequency deviation; Iteratively execute steps S2 to S3 until the deviation meets the threshold requirement.

6. The method for testing and assessing the broadband oscillation risk of a multi-power supply system according to claim 1, characterized in that, The complete site model assembly in step S4 includes: The electromagnetic model of thermal power, the modified electromagnetic model of new energy, the electromagnetic model of energy storage, the electromagnetic model of SVG, the main transformer model, the power grid equivalent model and the line model are combined into a multi-source system; The parameters of the power grid equivalent model and line model are generated based on the PSD-BPA power system stability calculation software. The main transformer model is connected to the grid connection point and the power grid according to the actual topology.

7. The method for testing and assessing the broadband oscillation risk of a multi-power supply system according to claim 1, characterized in that, The oscillation risk assessment in step S4 includes: Calculate the ratio of the grid-side impedance Zg to the multi-source system-side impedance Zs; In logarithmic coordinates, the following criteria are applied: when |Zg(s) / Zs(s)|=1, if the phase angle γ=|arg(Zg(s) / Zs(s))|<180°, the system is considered stable; if γ≥180°, there is a risk of oscillation.

8. The method for testing and assessing the broadband oscillation risk of a multi-power supply system according to claim 3, characterized in that, The harmonic measurement module is executed when: after injecting a disturbance voltage signal, it monitors the system's operating status until the amplitude fluctuation of the response signal is less than a preset threshold, at which point it determines that it has entered a steady state and collects the response signal.

9. The method for testing and assessing the broadband oscillation risk of a multi-power supply system according to claim 1, characterized in that, Step S4, the multi-condition test, includes: Set up a combination of operating conditions including thermal power output, new energy power, energy storage charging and discharging status, and SVG working mode; A frequency sweep disturbance signal is injected at the grid connection point using an impedance scanning module; Obtain impedance characteristic curves of the grid side and the multi-source system side under different combined operating conditions.

10. The method for testing and assessing the broadband oscillation risk of a multi-power supply system according to claim 1, characterized in that, The semi-physical platform signal transmission in step S1 includes: Three-phase voltage analog signals are output to the physical controller via the analog output interface; Receive the PWM wave digital signal output by the controller through the digital input interface; The response current signal is converted into a voltage signal by a current sensor and then input to the hardware-in-the-loop data acquisition card.

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