A converter adaptive network configuration control method, system and control device

Abstract

This invention discloses an adaptive grid-connected control method, system, and control device for converters, aiming to solve the technical problems of insufficient adaptability of existing converter control technologies across a wide short-circuit ratio range and difficulties in switching between grid-connected and off-grid operation. The invention includes: determining the total number of modes and defining mode boundaries based on the range of grid operating state changes; obtaining grid sampling information, identifying the grid operating state by detecting equivalent grid parameters, determining the grid's off-grid or on-grid state and short-circuit ratio, and determining the modes; determining the corresponding modes based on the identification results, and adaptively adjusting three sets of control parameters: voltage loop, current feedforward compensation, and current loop; finally generating modulation commands, and generating modulation signals to control the power switches based on the control commands. This invention, through a multi-mode adaptive control strategy, achieves stable operation of the converter under different operating conditions in off-grid, weak grid, and strong grid environments, effectively improving the reliability of new energy grid connection and grid stability.

Description

Technical Field

[0001] This invention relates to the field of converter control, and more specifically, to a converter adaptive grid control method, system, and control device. Background Technology

[0002] With the increasing penetration of new energy sources such as wind and solar power into the power grid, the control technology of power electronic converters faces new challenges. In existing technologies, traditional grid-connected converters have stability problems under weak grid conditions and are prone to oscillation and instability; while grid-connected converters, although having good stability under weak grid conditions, exhibit insufficient response under strong grid conditions.

[0003] To address the aforementioned technical bottlenecks, existing solutions suffer from the following shortcomings: While the control strategy of switching between grid-based and follow-grid-based approaches attempts to combine the advantages of both, it is prone to causing shocks during the switching process and faces difficulties in coordinated control; although applying compensation can improve some performance, it has limited coverage and may even degrade the dynamic response of the system in extreme operating scenarios; in addition, most existing parameter adjustment schemes only optimize a single parameter and fail to achieve coordinated control of the voltage loop and current loop. Summary of the Invention

[0004] This invention overcomes the shortcomings of existing solutions and provides a converter adaptive grid control method, system and control device, which can realize a wide range of adaptive control from off-grid operation to strong grid and weak grid, in order to maintain grid stability.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: An adaptive grid-based control method for converters includes the following steps: Based on the range of common power grid operating states, the total number of modes n is determined and the boundaries of each mode are defined. Obtain grid sampling information, identify the grid operating status by detecting the grid's equivalent parameters, determine the grid's off-grid or on-grid status using the equivalent parameters, and map the corresponding mode based on the short-circuit ratio obtained from the equivalent parameters; Based on the determined mode, adjust the three sets of control parameters for the voltage loop, current feedforward compensation, and current loop. Based on the power grid sampling information and the control parameters, a modulation command is generated, and a modulation signal for controlling the power switch is generated based on the control command. The modes include mode 0, which represents the off-grid operation mode, and modes 1 to n with short-circuit ratios ranging from low to high. Each mode corresponds to the corresponding voltage loop, current feedforward compensation, and current loop parameters.

[0006] Preferably, the process of identifying the operating state includes measuring the equivalent parameters of the power grid, calculating the short-circuit capacity, and calculating the short-circuit ratio. The equivalent parameter detection method of the power grid includes passive detection of the fundamental frequency and active injection detection of small disturbances in the interharmonic frequency. The algorithm is set to switch between the two identification methods. In the long-term steady-state operation scenario, passive detection of the fundamental frequency is selected, and in the system sudden change scenario, active injection detection of small disturbances in the interharmonic frequency is selected.

[0007] As a preferred method, the fundamental frequency passive detection solves for the equivalent parameters of the external circuit by treating the external power grid as an unknown parameter Thevenin circuit and processing the difference between redundant sampling points.

[0008] As a preferred method, the active injection detection of small perturbations at interharmonic frequencies actively sends small perturbation signals at interharmonic frequencies and identifies the equivalent parameters of the external circuit corresponding to the frequency based on the sampling.

[0009] Preferably, when the mode is equal to 0, the voltage loop uses zero-error control and the current loop uses differential control.

[0010] Preferably, when the mode is greater than or equal to 1, the voltage loop and the current loop are controlled by PI. The proportional and integral parameters of the voltage loop decrease as the mode increases, while the proportional and integral parameters of the current loop increase as the mode increases.

[0011] Preferably, when the mode is greater than or equal to 1, the current feedforward compensation parameter is... It increases with the increase of the mode; when the mode is equal to 0, the current feedforward compensation parameter... quit.

[0012] Preferably, the proportional parameter of the voltage loop is: The integral parameter is The proportional parameter of the current loop is The integral parameter is ,in, For short-circuit ratio, , The set value varies with the modal stepwise variation. , The adjustment coefficients are configured as piecewise linearized based on the rate of change of adjacent modes.

[0013] Preferably, it also includes an adaptive parameter update mechanism, which optimizes the setpoint, adjustment coefficient and current feedforward compensation parameters by setting a closed-loop parameter control-state record and using an optimization algorithm.

[0014] A converter adaptive grid configuration control system, comprising: The modal boundary determination module is used to determine the total number of modes n and divide the boundaries of each mode based on the range of common operating states of the power grid. The mode determination module is used to obtain grid sampling information, identify the grid operating status by detecting the grid's equivalent parameters, determine the grid's off-grid or on-grid status by the equivalent parameters, and map the corresponding mode based on the short-circuit ratio obtained from the equivalent parameters. The parameter control module is used to adjust three sets of control parameters for the voltage loop, current feedforward compensation, and current loop according to the determined mode. The modulation signal generation module generates modulation commands based on the power grid sampling information and the control parameters, and generates modulation signals to control the power switch based on the control commands; The modes include mode 0, which represents the off-grid operation mode, and modes 1 to n with short-circuit ratios ranging from low to high. Each mode corresponds to the corresponding voltage loop, current feedforward compensation, and current loop parameters.

[0015] A converter control device includes: at least one processor, and a memory and a communication module communicatively connected to the at least one processor, wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to cause the at least one processor to perform the aforementioned converter adaptive grid configuration control method.

[0016] Compared with the prior art, the beneficial effects of the present invention are: (1) By dividing the modal boundaries, we can distinguish between high short-circuit ratio scenarios and low short-circuit ratio scenarios, and determine the control parameters of voltage loop, current feedforward compensation and current loop. In the high short-circuit ratio scenario, we actively weaken the voltage loop response to avoid the risk of strong voltage coupling instability. In the low short-circuit ratio scenario, we enhance the voltage loop response and reduce the current loop bandwidth to improve the system damping ratio and reduce the risk of oscillation. (2) Two equivalent parameter detection methods are set up: passive detection of fundamental frequency and active injection detection of small disturbances in interharmonic frequency. Passive detection of fundamental frequency has high precision and high robustness, while active injection detection of small disturbances in interharmonic frequency has high detection efficiency. Based on the switching of the power grid under steady-state and sudden change scenarios, it provides a basis for the determination of subsequent control parameters. (3) Provide an adaptive parameter update mechanism. Through closed-loop parameter control and status recording, the set value of the control parameters, the adjustment coefficient and the current feedforward compensation parameters are optimized and adjusted by the optimization algorithm, so that the system can cope with operating condition drift, equipment aging and environmental changes, improve the stability of the system and reduce jumps and shocks. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the present invention; Figure 2 This is a schematic diagram of the identification stage of the present invention; Figure 3This is a timing diagram illustrating the use of fundamental frequency passive detection and interharmonic frequency small disturbance active injection detection in this invention; Figure 4 The control effect diagram of the modal-based adaptive parameter control method used in this application differs from traditional fixed-parameter control. Figure 5 This is a system schematic diagram of the present invention; Figure 6 This is a schematic diagram of the voltage and current acquisition module, operating status identification module, power calculation module, and power control puppet module of the present invention. Figure 7 This is a schematic diagram of the principle of the parameter adaptive adjustment voltage control module and the feedforward compensation module of the present invention; Figure 8 This is a schematic diagram of the principle of the parameter adaptive adjustment current control module of the present invention; Figure 9 This is a diagram illustrating the effect of using the present invention; Figure 10 This is a schematic diagram of the device of the present invention. Detailed Implementation

[0018] The present disclosure will be further described below with reference to the accompanying drawings and embodiments.

[0019] As the proportion of new energy sources such as wind and solar power in the power grid continues to increase, traditional grid-connected electronic converters suffer from oscillation and instability issues under weak grid conditions. Grid-connected converters have good stability under weak grid conditions, but they cannot effectively cope with strong grid conditions and suffer from insufficient response.

[0020] To address these issues, related technologies combine the advantages of both grid-connected and grid-following converters by switching between them. However, this approach faces challenges in coordination and is prone to surges during switching. Another approach involves applying compensation, but this suffers from insufficient coverage and can even degrade the system's dynamic response in extreme scenarios. Solutions address parameter adjustment, but existing solutions only regulate individual parameters and fail to address the coordination between voltage and current.

[0021] Therefore, there is an urgent need for an adaptive control method and system that can adapt to a wide range of short-circuit ratios and meet the requirements of both grid-connected and off-grid operation. By intelligently identifying the grid operating state, the system achieves coordinated optimization of voltage and current dual-loop control, ensuring that the converter maintains excellent dynamic performance and stability under different grid intensities. This allows the converter to adapt well to changes in grid operating conditions, covering off-grid, weak grid, and strong grid scenarios, and to selectively and collaboratively adjust the parameters of the current loop, current feedforward compensation, and voltage loop, thus better stabilizing the grid.

[0022] Example 1: like Figure 1 As shown, the method includes the following steps: Based on the range of common power grid operating states, the total number of modes n is determined and the boundaries of each mode are defined. Obtain grid sampling information, identify the grid operating status by detecting the grid's equivalent parameters, determine the grid's off-grid or on-grid status using the equivalent parameters, and map the corresponding mode based on the short-circuit ratio obtained from the equivalent parameters; Based on the determined mode, adjust the three sets of control parameters for the voltage loop, current feedforward compensation, and current loop. Generate a modulation signal to control the power switch; Based on the power grid sampling information and the control parameters, a modulation command is generated, and a modulation signal for controlling the power switch is generated based on the control command. This method specifically identifies different modes of the power grid and adaptively adjusts the parameters of each mode. By configuring the parameters of the voltage loop, current loop, and current feedforward compensation, coordinated control of different modes is achieved. Based on the common operating state variation range of the system, multi-level adaptive control modes 0~n are set. The value of n and the step size of adjacent modes are determined based on the experience of those skilled in the art. Since the control parameters corresponding to the modes are updated using an adaptive parameter update mechanism in some embodiments, larger modes are set to achieve finer-grained adjustments. In some embodiments, the width of the boundary between adjacent modes is fixed. In other embodiments, based on the experience of those skilled in the art, a shorter width is used for short-circuit ratio positions that are prone to jumps, thereby improving the adjustment capability of this method.

[0023] The process of identifying different modes of the power grid is as follows: first, the operating status is identified to determine whether it is off-grid or connected to the grid. If it is connected to the grid, the mode is further determined based on the short-circuit ratio (SCR), and the specific mode is determined according to the aforementioned mode boundary. Figure 2 (a) illustrates the process of classifying the modes of power grid operation after identification.

[0024]

[0025] in This is the operating mode.

[0026] When the equivalent power supply voltage When the value is close to 0 or below a certain set threshold, the system is determined to be in an off-grid operation state; otherwise, the system is considered to be in a grid-connected operation state.

[0027] For grid-connected systems, the short-circuit capacity is further calculated, and the short-circuit ratio (SCR) is solved.

[0028] Figure 2(b) illustrates the specific process of obtaining the SCR value. The process of identifying the grid operating state is as follows: sampling is performed, the equivalent parameters of the external grid are obtained based on the sampling, the short-circuit capacity is calculated based on the equivalent parameters, the short-circuit ratio is calculated based on this, and the grid operating state is quantified through the short-circuit ratio. The measurement of equivalent parameters includes passive detection of the fundamental frequency and active injection detection of small disturbances at the interharmonic frequency. The sampled electrical signals include the three-phase voltage output from the converter. and three-phase current Passive fundamental frequency detection determines the operating status of the power grid by passively detecting the fundamental frequency.

[0029] Based on the short-circuit ratio calculation requirements, the Thevenin equivalent circuit of the external system circuit connected to the converter is performed to obtain the unknown equivalent resistance. Equivalent reactance and equivalent voltage Based on the circuit relationship, it is easy to obtain:

[0030] To determine , and Theoretically, complete amplitude and phase data of the converter output voltage E and current I at two sampling times are required; however, phase measurements usually have a certain deviation, and this deviation will significantly affect the analysis results. Therefore, the phase information is optimized by processing the difference between redundant sampling points as follows: Assuming grid voltage and equivalent impedance If the parameters do not change during the time period of parameter identification, then for the three measurement points T1, T2, and T3, we have:

[0031] Sorted as:

[0032] in,

[0033] Thus, based on data from every 3 sampling times, a relationship between Rg and Xg can be established. Based on two sets of parameters [A1, B1, C1] and [A2, B2, C2], Rg and Xg are solved as follows:

[0034] Based on the aforementioned voltage-current relationship, the equivalent grid voltage is determined. .

[0035] Furthermore, as can be seen from the above formula, when When smaller, and The accuracy of identification will decrease; a threshold χ should be set to reduce this. At the time, the current data was considered valid. However, during actual runtime, two sets of valid parameters... and At least The sampling time for a significant change in voltage and current may take longer in actual operation scenarios.

[0036] Therefore, the method, based on passive fundamental frequency detection, is combined with active interharmonic frequency perturbation injection detection. The acquired signal is decomposed into fundamental frequency and interharmonic frequencies using FFT. Active interharmonic frequency perturbation injection detection involves actively sending interharmonic frequency perturbation signals and identifying the equivalent impedance of the external circuit at the corresponding frequency based on the sampling. Its identification mechanism is consistent with the aforementioned passive fundamental frequency identification; the difference lies in the ability to preset interharmonic frequency perturbations with stepped amplitude variations, thereby generating signals that meet the requirements more quickly. The two sets of effective parameters under the conditions accelerate the detection speed and ultimately reduce the equivalent reactance of the interharmonic frequency. Convert back to fundamental frequency equivalent reactance To identify grid-connected and off-grid operating status and grid-connected short-circuit ratio.

[0037] It is worth noting that the small perturbation signal of the interharmonic frequency used for identification is a step-like change.

[0038] Based on this, a comprehensive decision-making algorithm is configured, which takes into account the high reliability of passive fundamental frequency identification and the controllability and speed of active interharmonic injection identification. In long-term steady-state operation scenarios, fundamental frequency detection is used to improve robustness; in system mutation scenarios, active interharmonic injection detection is used to improve the short-circuit ratio identification speed.

[0039] The comprehensive decision-making algorithm identifies system abrupt change scenarios and long-term steady-state operation scenarios by making judgments based on the statistical characteristics and changing trends of the sampled signals: In some possible embodiments, based on sampling information, a system abrupt change scenario is determined when any of the following conditions are detected: the instantaneous rate of change of voltage or current exceeds a set threshold; the power fluctuation amplitude exceeds a set percentage of the rated power within a short period of time; the frequency change rate exceeds a set threshold; or the continuous change of the short-circuit ratio calculation result exceeds a set range. Conversely, a long-term steady-state operation scenario is determined when all of the following conditions are met: the fluctuation range of parameters such as voltage, current, and power within a set time window is less than a set threshold; the short-circuit ratio calculation result remains relatively stable within a set time window; and the system operating parameters do not show a significant abrupt change trend.

[0040] According to the comprehensive decision-making algorithm, when the above conditions are detected to exceed the long-term steady-state operation scenario, the system immediately switches to active interharmonic injection detection. By injecting small perturbation signals of interharmonic frequencies, the system identifies the equivalent impedance of interharmonic frequencies based on sampling, taking advantage of its fast response characteristics.

[0041] In long-term steady-state operation scenarios, the transmission of small interharmonic frequency disturbance signals is stopped to maintain the high reliability of passive fundamental frequency detection. When the long-term steady-state operation scenario is exceeded, interharmonic frequencies are actively injected into the detection signal, and the equivalent impedance of the external circuit is obtained based on the sampling.

[0042] Simulations were conducted using an adaptive grid control system for a converter. Under a scenario of continuously varying short-circuit ratio, the short-circuit ratio increased from 1.8 to 3.9 at t1=14s and from 3.9 to 10.7 at t2=36s. The base frequency output voltage and current were set to change randomly every 2s. The identification results are as follows: Figure 3 As shown in (a), the fundamental frequency identification result is highly accurate, but takes a long time (4 cycles (8s) after the short-circuit ratio change). In actual systems, the interval between fundamental frequency voltage and current changes may be much higher than 2s, resulting in a longer identification time. Setting the interharmonic frequency to 175Hz and the step-like amplitude change period to 0.3s, we obtain... Figure 3 (b) and (c) Figure 3 Figures (b) and (c) are schematic diagrams of the simulation identification results of the active injection detection method for small perturbations at interharmonic frequencies, showing the identification time at times t1 and t2, respectively. Figure 3 The results for fundamental frequency identification (a) show that the interharmonic active injection identification time is significantly shorter (4 cycles (1.2s) after the change in short-circuit ratio), but the volatility is stronger. The results indicate that interharmonic active injection identification is more suitable for rapid detection, while fundamental frequency identification is more suitable for long-term reference.

[0043] The next step is to obtain the control parameters.

[0044] Given the known modes, the voltage loop, current feedforward compensation, and current loop control parameters are tuned based on mode i and the short-circuit ratio (SCR). Details are as follows: When the mode is greater than 1, the proportional parameter of the voltage loop is: The integral parameter is The proportional parameter of the current loop is The integral parameter is .

[0045] Specifically,

[0046] in, For short-circuit ratio, , The set value varies with the modal stepwise. , The adjustment coefficients are configured as piecewise linearized based on the rate of change of adjacent modes.

[0047] Specifically, and It decreases as the short-circuit ratio increases (corresponding to an increase in i). and With parameters and The rate of change of adjacent modes is piecewise linearized; the voltage loop is characterized as a weak voltage response in grid-connected operation scenarios with high short-circuit ratios and as a strong voltage response in grid-connected operation scenarios with low short-circuit ratios.

[0048] The compensation coefficient of the feedforward current compensation It is designed based on the following principles:

[0049] Compensation coefficient It increases with the short-circuit ratio; in grid-connected operation scenarios with high short-circuit ratios, a larger value is set. To improve the current reference regulation speed in weak voltage response mode; and to set a smaller current reference in low short-circuit ratio grid-connected operation scenarios. To avoid overshoot in high voltage response mode.

[0050] The proportional gain of the current loop With integral coefficient The following preset function relationships will be dynamically adjusted:

[0051] in, and These are the adjustment coefficients for the proportional and integral coefficients of the current loop in operating mode i, respectively. and These are the set values ​​for the proportional and integral coefficients of the current loop in operating mode i, respectively. The design is based on the following principles:

[0052] Overall, and It increases with the increase of the short-circuit ratio. and With parameters and The rate of change of adjacent modes is configured in a piecewise linearized manner; the current loop is characterized as a strong current response in grid-connected operation scenarios with high short-circuit ratios and as a weak current response in grid-connected operation scenarios with low short-circuit ratios.

[0053] When the system is operating in off-grid mode (i = 0), the voltage control loop uses a preset proportional coefficient. With integral coefficient A proportional-integral controller is used to achieve a steady-state error-free response to the voltage reference, ensuring voltage support for the off-grid system; the current loop operates in mode 0. The integral stage is locked out, and a pure proportional control mode is adopted. Meanwhile, the current feedforward compensation stage operates in mode 0. To avoid overshoot and oscillation.

[0054] It is worth noting that the above parameters , , , , , , , and All methods are pre-set and optimized based on stability analysis, multi-objective optimization, offline equipment testing, and actual operation data analysis. Furthermore, during the application of these methods, further optimization can be achieved based on recorded operational data.

[0055] Specifically, the parameters are optimized using an algorithm. This algorithm first establishes a state-space model of the converter system, including the dynamic characteristics of the voltage loop, current loop, and grid interaction. In each control cycle, the algorithm collects real-time system operating data, including voltage, current, power, and short-circuit ratio information. Based on the collected data, the algorithm constructs an objective function by weighting and summing stability, response speed, and overshoot suppression indices. Each of these indices is assigned a weighting coefficient. , , The weighting coefficient , , Manually configure as needed for the scenario. In scenarios where stability is paramount, increase... Weighting; in scenarios requiring rapid response, increase Weights.

[0056] The optimization process employs gradient descent combined with constrained optimization techniques to ensure parameter adjustments remain within a safe range. In some embodiments, the optimization algorithm may be a Bayesian algorithm, reinforcement learning algorithm, genetic algorithm, or other optimization algorithms. In some embodiments, a forgetting factor mechanism is also introduced to weight historical data, ensuring that the optimization results can adapt to slow changes in the power grid state. The optimized parameters are updated into the control system after online verification, achieving closed-loop adaptive parameter optimization.

[0057] After tuning the parameters for the voltage loop, current loop, and current feedforward compensation, network control is executed, specifically including: Based on the aforementioned sampling, three-phase voltages and three-phase currents were obtained. Through Park transformation, the values ​​in the dq coordinate system were obtained. , , and Next, calculate the corresponding active power P and reactive power Q, as shown in the following expressions:

[0058]

[0059] Based on a preset power reference and Given the current active power P and reactive power Q of the converter output, the d-axis voltage reference is obtained. and synchronization phase as follows:

[0060] Where s is the Laplace operator, J_s is the virtual inertia coefficient, and D is the virtual damping coefficient. This is the reactive power droop factor.

[0061] Next, based on the voltage reference command The voltage control loop proportional coefficient under the grid-connected control mode i (i=1,2,…,n) tuned in the aforementioned steps is adopted. With integral coefficient Output current reference and As shown below, the voltage deviation is used as input, and a current reference is generated through modal adaptive PI regulation. At the same time, current compensation is injected into the filter capacitor to achieve decoupling, and finally the d-axis and q-axis current commands for the inner current loop tracking are output.

[0062]

[0063] in, For power frequency, This is a filter capacitor.

[0064] In the current feedforward compensation stage, based on voltage, power signals, and current reference commands... and Based on the aforementioned current compensation coefficient Output current compensation reference and Based on the mode, compensation is performed or decompensation is stopped through current feedforward compensation. The formula is as follows:

[0065] Current loop, based on current reference command and and current compensation reference and The current control loop proportional coefficient under the aforementioned tuned grid-connected control mode i (i=1,2,…,n) is adopted. With integral coefficient Output modulation voltage reference and Similar to the voltage loop principle, it uses current deviation as input, generates a current reference through modal adaptive PI control, and simultaneously injects current compensation through a filter capacitor to achieve decoupling. The final output is the d-axis and q-axis current commands for tracking by the inner current loop. The current loop enters either PI or pure P control depending on the mode. The formula is as follows:

[0066] in, This is a filter inductor.

[0067] and The controller generates modulation commands and sends them to the power elements of the controlled converter, thus completing a comprehensive adaptive grid-connected control method for wide short-circuit ratio grid-connected and off-grid operation of the converter.

[0068] During the application of the method, key indicators, including stability and response speed, can be recorded in real time based on the running data. An adaptive parameter design algorithm update mechanism can be established, and parameter design algorithm optimization can be carried out based on data-driven approaches. This enables the dynamic evolution of parameter setting principles and improves the robustness and environmental adaptability of the method.

[0069] Continue Figure 3 The corresponding simulation model is compared with the traditional constant-parameter method. While maintaining the short-circuit ratio variation setting, to avoid the coupling effect of power fluctuations and short-circuit ratio variations, the converter output power remains constant during short-circuit ratio changes. Fundamental frequency detection is disabled, and only the interharmonic active injection identification results are used as the basis for operating mode switching. The comparison yields a result using only constant parameters. Figure 4 (a) The control method described in this application is applied at time t2. Figure 4 (b) and the full name adopt the method of this application. Figure 4 (c). It is evident that, after the method described in this application is applied, the instability problem of traditional fixed parameter control under high short-circuit ratio can be avoided, and the method has the capability to operate with a wide short-circuit ratio.

[0070] Reference Figures 5 to 8As shown, in order to implement the aforementioned converter adaptive grid-building control method, a converter adaptive grid-building control system is also disclosed, comprising: Voltage and current sampling module, used to collect sampled data from the converter output; The power calculation module calculates the power information output by the converter based on the sampled data. The power information includes active power and reactive power. The operating status and short-circuit ratio identification module identifies whether the converter is in grid-connected or off-grid status based on power information and sampled data, and quantifies the converter's short-circuit ratio. The power control module is used to simulate the external characteristics of a synchronous generator and establish frequency and voltage references for the converter. The parameter adaptive voltage control module, based on the voltage reference command and the mode corresponding to the short-circuit ratio, adaptively adjusts the PI parameters according to the operating mode and outputs the reference command for the inner current loop. The current feedforward compensation module calculates the theoretical current value and performs feedforward compensation based on voltage reference commands and modes; The parameter adaptive current control module receives the current reference output from the outer voltage loop and adaptively adjusts the PI parameters according to the operating mode, outputting a modulated voltage signal. The modulation module converts the modulated voltage signal output from the parameter adaptive current control module into switching commands for the power devices of the converter.

[0071] The voltage and current sampling module acquires the three-phase voltage output from the converter. and three-phase current .

[0072] The power calculation module, operating status, and short-circuit ratio identification module of the power grid obtain power information based on sampling. Based on this power information, they identify the power grid's operating status by detecting equivalent parameters, determining whether the grid is in an off-grid or on-grid state using these equivalent parameters, and mapping the corresponding mode based on the short-circuit ratio obtained from the equivalent parameters. The power control module, parameter adaptive voltage control module, current feedforward compensation module, and parameter adaptive current control module adjust three sets of control parameters—voltage loop, current feedforward compensation, and current loop—according to the determined mode.

[0073] The modulation module combines the grid sampling information with the control parameters to generate a modulation command, and generates a modulation signal to control the power switch based on the control command.

[0074] The system performs sampling and calculation. and The process involves sending modulation commands to the power elements of the controlled converter to achieve control.

[0075] The following embodiment will explain the functions of each module and the communication relationships between them one by one.

[0076] The voltage and current sampling module, as a system sensing module, is responsible for collecting the three-phase voltage output from the converter. and three-phase current The acquired analog quantities are converted from analog to digital, and then transformed into a rotating coordinate system using the Park transformation. Components under axis , , , Output The data is synchronously sent to the power calculation module, the operating status and short-circuit ratio identification module, the parameter adaptive voltage control module, the parameter adaptive current control module, and the current feedforward compensation module, serving as the input reference for each control link.

[0077] The power calculation module calculates the active and reactive power output of the converter in real time based on the sampled data.

[0078] Based on the data obtained from the voltage and current sampling module , , and Calculate active power and reactive power The expression is:

[0079]

[0080] Calculated power signal , The data is sent to the following modules respectively: the operating status and short-circuit ratio identification module, the power control module, and the current feedforward compensation module.

[0081] The operating status and short-circuit ratio identification module is responsible for determining whether the converter is currently in grid-connected or off-grid status, quantifying the grid strength (Short-circuit ratio SCR), and determining the mode based on a preset SCR range. The operating status and short-circuit ratio identification module has two identification methods, one fast and one slow. Specifically, the slow identification method is: passive base frequency detection, utilizing the natural fluctuations of base frequency voltage and current during normal operation, and solving the problem through redundant sampling point difference processing. , , One rapid identification method is: active injection detection of small interharmonic frequency disturbances. This involves actively sending an active detection signal for small interharmonic frequency disturbances to the modulation module, injecting non-characteristic subharmonic disturbances with stepped amplitudes to quickly trigger a system response. This identification method samples the power grid, equating the external power grid to a Thevenin circuit with unknown parameters: equivalent resistance... Equivalent reactance Equivalent voltage source Based on circuit relationships:

[0082] The impedance is converted to the external power grid impedance, and the corresponding short-circuit ratio is calculated.

[0083] The two identification methods switch according to the power grid status. When the power grid is in a stable state, the fundamental frequency passive detection is used; otherwise, the interharmonic frequency small disturbance active injection detection is used.

[0084] Based on a preset short-circuit ratio range, the converter state is set to modes 0-n, where mode 0 indicates the converter is in an off-grid state, and modes 1 and above indicate a grid-connected state. A higher mode number indicates a stronger grid. In specific judgments, if the equivalent power supply voltage... If the current is below the set threshold, the converter state is mode 0; otherwise, it is mode 1 or above.

[0085] After determining grid connection and off-grid status and quantizing the modes, mode information is input to the parameter adaptive voltage control module and the parameter adaptive current control module. To achieve active injection detection of small interharmonic frequency disturbances, communication with the modulation module is established to send active detection signals for small interharmonic frequency disturbances.

[0086] In some embodiments, for converters operating in a field station or cluster, the operating status and short-circuit ratio identification module can be deployed in the central controller, and each converter directly receives the identification results sent down, avoiding duplicate calculations.

[0087] The power control module is the core of the grid-type control system. It simulates the external characteristics of a synchronous generator and establishes frequency and voltage references for the converter. A virtual synchronous machine (VSM) control strategy is employed, including active-frequency and reactive-voltage loops. Virtual inertia coefficients are introduced by simulating the rotor motion equations. and virtual damping coefficient This achieves frequency support and power distribution; and also introduces a reactive power droop factor. This enables reactive power regulation and voltage support. The power control module outputs... Shaft voltage reference and synchronization phase .

[0088] Specifically, the active power P is compared with the reference value of active power using a subtractor. The net power is obtained by subtracting damping loss from the power deviation, and then converted through angular frequency transformation. The angular frequency change is obtained through the virtual rotor motion equation, and the angular frequency deviation is obtained by subtracting it from the power frequency, and then converted into phase angle. .

[0089] The reactive power is compared with the reference value of reactive power using a subtractor. The reactive power-voltage gain is converted into a voltage regulation quantity, which is then superimposed with the no-load voltage to generate a voltage reference. .

[0090] The parameter adaptive voltage control module, acting as the outer voltage loop, receives voltage reference commands from the power control module, outputs reference commands for the inner current loop, and adaptively adjusts the PI parameters according to the operating mode. Based on the mode, it retrieves the corresponding PI parameters using a lookup table, which serve as the control parameters for the outer voltage loop. According to the PI control method, it outputs the corresponding current adjustment reference. , .

[0091] Its expression is

[0092]

[0093] in , With increasing short-circuit ratio (modal) (Increases) and decreases; , Segmented linear configuration based on the rate of change of adjacent modes.

[0094] The above settings have different effects in different scenarios. Under strong power grid conditions with large modes and high short-circuit ratios, its proportional coefficient... Smaller, integral coefficient A relatively large proportional gain can prevent resonance caused by excessively rapid dynamic response under strong grid conditions and avoid overshoot. For weak grid conditions with small modes and small short-circuit ratios, its proportional gain is relatively large. Larger, integral coefficient The smaller voltage is used to improve response speed, enhance voltage support capability, and eliminate steady-state voltage deviation. When in the off-grid state of mode 0, error-free control is adopted, and PI is involved at the same time to ensure that the load voltage is error-free in steady state.

[0095] The parameter adaptive voltage control module communicates with the power control module and receives voltage regulation reference data from it. It communicates with the voltage and current sampling module and receives voltage feedback from it. , ; Communicates with the operating status and short-circuit ratio identification module, and receives operating status commands (modal) from it. It communicates with the current feedforward compensation module, sending it a current regulation reference. , To parameter adaptive adjustment current control module.

[0096] The current feedforward compensation module is used for dynamic performance optimization. It calculates the theoretical current value using a power reference and performs feedforward compensation to improve the adjustment speed of the current reference.

[0097] Based on power reference , Based on the current voltage sample value, the theoretical current reference is calculated, and then filtered (filter time constant). After eliminating transient impacts (with fixed parameters), the current is superimposed onto the current loop reference. Specifically, the ideal current is calculated based on power theory, compared with the voltage outer loop output, scaled according to the mode adaptive parameter gain, and then smoothed by fixed filtering. The final output current feedforward compensation is superimposed on the voltage loop command for the current inner loop to track, thereby improving the system's dynamic response speed.

[0098] The expression for the compensation coefficient is modally adjusted.

[0099] When under strong power grid conditions with large modes and high short-circuit ratios, a larger setting is required. In weak voltage response mode, the current reference regulation speed is improved to compensate for the dynamic loss caused by the reduction in voltage loop bandwidth; when in a weak grid state with small modes and small short-circuit ratios, a smaller setting is used. In the high voltage response mode, it avoids current overshoot; in the off-grid state with mode 0, it completely exits feedforward compensation to prevent overshoot and oscillation under off-grid no-load or light-load conditions.

[0100] The current feedforward compensation module communicates with the parameter adaptive adjustment current control module to send current reference feedforward compensation. , .

[0101] The parameter-adaptive current control module, acting as the inner current loop, receives the current reference (including feedforward compensation) from the outer voltage loop, outputs a modulated voltage signal, and adaptively adjusts the PI parameters according to the operating mode. These correspond to... shaft current and shaft current Two sets of adjustable PI controller parameters.

[0102] The expression for the parameters of the PI controller with respect to the mode is as follows:

[0103]

[0104] in , It increases with the increase of the short-circuit ratio; , Segmented linear configuration based on the rate of change of adjacent modes.

[0105] Under the strong power grid conditions with high short-circuit ratios corresponding to large modes, its proportional gain Larger, integral coefficient A larger ratio increases the current loop bandwidth and accelerates current tracking speed (at the cost of reducing some damping ratio). For weak grid conditions with small modes and low short-circuit ratios, its proportional gain is... Smaller, integral coefficient The damping ratio is relatively small, reducing the current loop bandwidth and avoiding instability caused by phase lag in weak grids. When in the off-grid state of mode 0, differential control is adopted, and only proportional regulation is used to avoid overshoot and oscillation.

[0106] The parameter adaptive current control module communicates with the modulation module and sends voltage modulation signals to it. , .

[0107] The parameter adaptive adjustment current control module, current feedforward compensation module, and parameter adaptive adjustment voltage control module all possess an adaptive parameter design algorithm update mechanism. By setting a closed-loop parameter control-state record, the setpoints, adjustment coefficients, and current feedforward compensation parameters are optimized through an optimization algorithm. The optimization algorithm is based on runtime data recording, real-time recording of key indicators including stability and response speed during execution. This establishes an adaptive parameter design algorithm update mechanism, enabling data-driven optimization of the parameter design algorithm, achieving dynamic evolution of parameter setting principles, and improving the robustness and environmental adaptability of the method.

[0108] The modulation module is used to execute the output of the current control module. The shaft-modulated voltage reference is converted into switching commands for the power devices, and receives input from the parameter adaptive current control module. , Synchronization phase from the power control module It also performs the active detection signal transmission of small disturbances in the interharmonic frequency of the operating status and short-circuit ratio identification module. The modulation module generates PWM (pulse width modulation) commands and sends them to the power components (such as IGBTs and SiC MOSFETs) of the controlled converter.

[0109] This solution has a significant advantage: it requires only minor modifications to the existing power grid to achieve adaptive grid control for both wide short-circuit ratio grid-connected and off-grid operation. Specifically, it only adds an operating status sensing module and a current feedforward compensation module, and upgrades the traditional fixed-parameter voltage and current loops to an adaptive adjustable structure. This eliminates the need for complex compensation mechanisms such as virtual impedance, thus completing the modification. Therefore, this solution has significant engineering value.

[0110] When simulating the scenario described in this application, the changes in voltage, current, and voltage and current waveform details during the grid-connected-off-grid-connected operation are as follows: Figure 9 As shown ( Figure 9 (a) shows the power change graph during the switching process. Figure 9 (b) shows the voltage and current changes during the switching process. Figure 9 (c) shows the detailed ripple of voltage and current changes during the switching process. Figure 9 As shown, the system remains stable during initial grid-connected operation, switching to off-grid operation, and resuming grid-connected operation, indicating that the method has adaptive operation capabilities in both grid-connected and off-grid modes.

[0111] Example 2: A (virtual) converter adaptive grid-connection control system is also disclosed for implementing a converter adaptive grid-connection control method, including: The modal boundary determination module is used to determine the total number of modes n and divide the boundaries of each mode based on the range of common operating states of the power grid. The mode determination module is used to obtain grid sampling information, identify the grid operating status by detecting the grid's equivalent parameters, determine the grid's off-grid or on-grid status by the equivalent parameters, and map the corresponding mode based on the short-circuit ratio obtained from the equivalent parameters. The parameter control module is used to adjust three sets of control parameters for the voltage loop, current feedforward compensation, and current loop according to the determined mode. The modulation signal generation module generates modulation commands based on the power grid sampling information and the control parameters, and generates modulation signals to control the power switch based on the control commands; The modes include mode 0, which represents the off-grid operation mode, and modes 1 to n with short-circuit ratios ranging from low to high. Each mode corresponds to the corresponding voltage loop, current feedforward compensation, and current loop parameters.

[0112] Example 3: This invention provides a converter control device, such as... Figure 10 As shown, it includes: at least one communication interface 301, at least one communication bus 302, at least one memory 303, and at least one processor 304, such as a CPU (Central Processing Unit).

[0113] The communication interface 301 is used for data interaction with the sampling information and control commands of the external controller and the controlled converter, and may include a serial interface, Ethernet, wireless, or fiber optic.

[0114] The communication bus 302 is used to realize the connection and communication between these components. It can be a peripheral component interconnect (PCI) bus or an extended industry standard architecture (EISA) bus, etc. The communication bus 302 can be divided into address bus, data bus, control bus, etc. For ease of representation, Figure 8 The symbol is represented by only one line, but this does not mean that there is only one bus or one type of bus.

[0115] The memory 303 is also used to store program instructions and runtime data. It may include volatile memory, such as random-access memory (RAM); the memory may also include non-volatile memory, such as flash memory, hard disk drive (HDD), or solid-state drive (SSD); the memory 303 may also include a combination of the above types of memory.

[0116] The processor 304 can execute the aforementioned converter adaptive network control method. The processor 301 may further include a hardware chip. This hardware chip can be an application-specific integrated circuit (ASIC), a programmable logic device (PLD), or a combination thereof. The PLD can be a complex programmable logic device (CPLD), a field-programmable gate array (FPGA), a generic array logic (GAL), or any combination thereof. A set of program code is stored in memory 404, and the processor 304 calls the program code stored in memory 303 to execute the aforementioned converter adaptive network control method.

[0117] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0118] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0119] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

[0120] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications may be made without departing from the technical solutions described in the claims.

Claims

1. A converter adaptive network control method, characterized in that, Includes the following steps: Based on the range of common power grid operating states, the total number of modes n is determined and the boundaries of each mode are defined. Obtain grid sampling information, identify the grid operating status by detecting the grid's equivalent parameters, determine the grid's off-grid or on-grid status using the equivalent parameters, and map the corresponding mode based on the short-circuit ratio obtained from the equivalent parameters; Based on the determined mode, adjust the three sets of control parameters for the voltage loop, current feedforward compensation, and current loop. Based on the power grid sampling information and the control parameters, a modulation command is generated, and a modulation signal for controlling the power switch is generated based on the control command. The modes include mode 0, which represents the off-grid operation mode, and modes 1 to n with short-circuit ratios ranging from low to high. Each mode corresponds to the corresponding voltage loop, current feedforward compensation, and current loop parameters.

2. The converter adaptive grid control method according to claim 1, characterized in that, The process of identifying the power grid operating status includes detecting the equivalent parameters of the power grid, calculating the short-circuit capacity, and calculating the short-circuit ratio. The methods for detecting the equivalent parameters of the power grid include passive detection of the fundamental frequency and active injection detection of small disturbances in the interharmonic frequency. The algorithm is set to switch between the two identification methods. In the long-term steady-state operation scenario, passive detection of the fundamental frequency is selected, and in the system sudden change scenario, active injection detection of small disturbances in the interharmonic frequency is selected.

3. The converter adaptive grid control method according to claim 2, characterized in that, Passive fundamental frequency detection solves for the equivalent parameters of the external circuit by treating the external power grid as an equivalent Thevenin circuit with unknown parameters and processing the difference between redundant sampling points.

4. The converter adaptive grid control method according to claim 2, characterized in that, The active injection detection of small perturbations at interharmonic frequencies actively sends out signals to detect small perturbations at interharmonic frequencies and identifies the equivalent parameters of the external circuit corresponding to the frequency based on the sampling.

5. The converter adaptive grid control method according to claim 1, characterized in that, When the mode is equal to 0, the voltage loop uses zero-error control and the current loop uses differential control; when the mode is greater than or equal to 1, the voltage loop and the current loop use PI control. The proportional and integral parameters of the voltage loop decrease as the mode increases, while the proportional and integral parameters of the current loop increase as the mode increases.

6. The converter adaptive grid control method according to claim 1, characterized in that, When the mode is greater than or equal to 1, the current feedforward compensation parameter It increases with the increase of the mode; when the mode is equal to 0, the current feedforward compensation parameter... quit.

7. The converter adaptive grid control method according to claim 5, characterized in that, The proportional parameter of the voltage loop is The integral parameter is The proportional parameter of the current loop is The integral parameter is ,in, For short-circuit ratio, , The set value varies with the modal stepwise variation. , The adjustment coefficients are configured as piecewise linearized based on the rate of change of adjacent modes.

8. The converter adaptive grid control method according to claim 7, characterized in that, It also includes an adaptive parameter update mechanism, sets up a closed-loop parameter control-state record, and optimizes the setpoint, adjustment coefficient, and current feedforward compensation parameters through optimization algorithms.

9. A converter adaptive grid-connected control system, characterized in that, include: The modal boundary determination module is used to determine the total number of modes n and divide the boundaries of each mode based on the range of common operating states of the power grid. The mode determination module is used to obtain grid sampling information, identify the grid operating status by detecting the grid's equivalent parameters, determine the grid's off-grid or on-grid status by the equivalent parameters, and map the corresponding mode based on the short-circuit ratio obtained from the equivalent parameters. The parameter control module is used to adjust three sets of control parameters for the voltage loop, current feedforward compensation, and current loop according to the determined mode. The modulation signal generation module generates modulation commands based on the power grid sampling information and the control parameters, and generates modulation signals to control the power switch based on the control commands; The modes include mode 0, which represents the off-grid operation mode, and modes 1 to n with short-circuit ratios ranging from low to high. Each mode corresponds to the corresponding voltage loop, current feedforward compensation, and current loop parameters.

10. A converter control device, characterized in that, include: At least one processor, and a memory and a communication module communicatively connected to the at least one processor, wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to cause the at least one processor to perform a converter adaptive grid control method according to any one of claims 1-8.

Images